Performance of unified power quality conditioner using pi and fuzzy logic controllers - Free Essay Example

Sample details Pages: 31 Words: 9154 Downloads: 6 Date added: 2017/06/26 Category Statistics Essay Did you like this example? ABSTRACT Power electronics is playing an important role in transmission and utilization of electrical power due to its capability of processing electric power in most efficient and cost-effective way. However, the nonlinear characteristics of power electronic devices give rise to two important limitations; they generate harmonics and draw lagging current from the utility. In recent years unified power quality conditioner (UPQC) is being used as a universal active power conditioning device to compensate both harmonics as well as reactive power. Don’t waste time! Our writers will create an original "Performance of unified power quality conditioner using pi and fuzzy logic controllers" essay for you Create order UPQC is an advanced version of unified power flow controller (UPFC). The performance of UPQC mainly depends upon how quickly and accurately compensation signals are derived. The UPQC mitigates harmonics and provides reactive power to the power systems network so as to improve the power factor close to unity. The UPQC is a combination of shunt active and series active power filters connected through a dc bus. The shunt active filter of UPQC acts as a current source for injecting compensating current through a shunt transformer, whereas, the series active filter acts as a voltage source for feeding compensating voltage through a series transformer. The aim of the dissertation work is to study the control strategies of UPQC based on PI controller and fuzzy logic controller in detail. In the case of PI controller, the dc link voltage is sensed at regular intervals and is compared with a reference value. The error signal thus derived is processed in a PI controller. A limit is put on the output of the controller to ensure that the shunt active power filter supplies active power of the load through the series active power filter. The fuzzy logic controller is basically nonlinear and adaptive in nature. This gives a robust performance in the cases where the effects of parameter variation of controller are also taken into consideration. It is a well established fact that the fuzzy logic controller yields results that are superior to those obtained as compare to those obtained through conventional controllers such as PI and PID because of the fact that it is based on linguistic variable set theory and does not require a mathematical model. Generally, the input variables are error and rate of change of error. If the error if coarse, the fuzzy controller provide coarse tuning to the output variable and if the error is fine it provides fine tuning of the output variable. The present thesis investigates PI controller and fuzzy logic controller as concerned to UPQC application for power quality improvement. The UPQC is studied and its advantages over conventional APFs and UPFC are discussed in detail. The relevant mathematical models and equations to explain the working of UPFC are derived for both the cases (PI controller and fuzzy logic controller).The relevant simulations are carried out using MATLAB/Simulink. The result obtained reveals that the fuzzy logic controller gives better dynamic performance than the PI controller for power quality improvement. Chapter 1 INTRODUCTION 1.1 Theory The electrical power system consisting of generation, transmission and distribution system are based on alternative voltage and currents. When linear load consisting of inductances, capacitances and resistances are connected to the power system the sine wave is preserved and the system components are said to be linear. Traditionally, linear loads consume major part of electrical power. However situation has changed now as more and more electrical power are being developed using power electronic devices due to their energy efficiency and control. Power electronic devices possess inherent non linear characteristics. The nonlinear characteristics of this devices results in two important limitations, drawing of large reactive volt-amperes and injection of harmonics into the utility. Large reactive volt-amperes drawn from the utility leads to increase voltage drops at various buses. The harmonics increase the losses in transformers, generators, motors, capacitors, conductors, etc. some o f the control devices interfaced with the utility starts malfunctioning due to excessive harmonic currents. As the non linear load consists of the major portion of the total load for the last two three decades, reactive power compensation and harmonic filtering have received a great deal of attention. To restrict the consumers against excessive loading VARs and harmonics, stricter standards has been laid down by the utilities. Most popular among them is standard 519-1992 [1]. Static VAR compensators using thyristor switched capacitors (TSC) and thyristor control inductors (TCI) [2], [3] have been traditionally used for reactive power compensation. As the VAR generated in these schemes are directly proportional to the energy storage capability of capacitors and inductors, there is considerable increase in the size of these elements when the VARs to be compensated are large. Moreover TSC and TCI produce additional current harmonics. Therefore shunt passive filters require filtering them out. Active power filter (APF) using voltage or current source inverter can be used for reactive power compensation and harmonic filtering together. The major advantage of using voltage source or current source inverter is that the size of the energy storing element is drastically reduced as compare to TSC or TCI. The shunt APF is the most commonly used APF. The power circuit of shunt APF is shown in Fig. 1.1. In shunt APF, a reactive volt ampere calculation estimates the real component of the load current, Ipland then determines the resistive component of the load current by subtracting Ipl from IL(Iql= IL-Ipl). If nonlinearity present in the load current, it is present in Iql as well. Since compensation current Icomp is made to follow Iql, load harmonics also get eliminated. Apart from shunt APF various other APF topologies such as series active filter, hybrid series active filter and power line conditioner have been proposed in the literature. The series active filter as shown in Fig. 1.2 is connected in series with supply mains using a matching transformer. Its limitation is that the presence of active impedance in series with source produces voltage harmonics. IL = Ipl +Iql Source Icomp = Iql Source Source side Series transformer Load side Shunt transformer DC Link Capacitor Converter 1 converter 2 Using combine series APF and shunt APF unified power flow controller (UPFC) realized, which performs active power compensation, reactive power compensation and phase angle regulation. UPFC believed to be the most complete power conditioning device. But as the time changes, problem also changes. Now days electrical engineers facing problem regarding harmonic compensation, voltage sag and voltage flickering and UPFC is not able to overcome these problems. So a new concept based on UPFC derived called unified power quality conditioner (UPQC) as shown in Fig. 1.3, which performs all the basic functions of UPFC in addition it also compensate for current /voltage harmonics with constant voltage maintenance at load terminals. 1.2 Unified Power Quality Conditioner The UPQC is the most versatile and complex of the FACTS devices, combining the features of the STATCOM and the SSSC. The UPQC can provide simultaneous control of all basic power system parameters, transmission voltage harmonic compensation, impedance and phase angle. It is recognized as the most sophisticated power flow controller currently, and probably the most expensive one. The basic components of the UPQC are two voltage source inverters (VSIs) sharing a common dc storage capacitor, and connected to the power system through coupling transformers. One VSI is connected to in shunt to the transmission system via a shunt transformer, while the other one is connected in series through a series transformer. A basic UPQC functional scheme is shown in Fig.1.3. The series inverter is controlled to inject a symmetrical three phase voltage system of controllable magnitude and phase angle in series with the line to control active and reactive power flows on the transmission line. So, this i nverter will exchange active and reactive power with the line. The reactive power is electronically provided by the series inverter, and the active power is transmitted to the dc terminals. The shunt inverter is operated in such a way as to demand this dc terminal power (positive or negative) from the line keeping the voltage across the storage capacitor Vdc constant. So, the net real power absorbed from the line by the UPQC is equal only to the losses of the inverters and their transformers. The remaining capacity of the shunt inverter can be used to exchange reactive power with the line so to provide a voltage regulation at the connection point [8]-[11]. A conventional UPQC topology is comprised of the integration of two active power filters connected back to back to a common dc link bus. A simple block diagram of a typical UPQC is shown in Fig. 1.4. The first active filter connected in series through an injection transformer is commonly termed as series filters (SF). It acts as a controlled voltage generator. It has capability of voltage imbalance compensation, voltage regulation and harmonic compensation at the utility-consumer PCC. In addition to this, it provides harmonic isolation between a sub-transmission system and a distribution system. A UPQC consists of combination of shunt active filter and series active filter with a common dc link as shown in Fig. 1.4. The dc link capacitor allows the active power generated by the shunt active filter and active power drawn by the series filter to be same. Further dc link capacitor increases or decreases with respect to rated voltage which depends upon power generated and absorbed by both active filter can be choosen independently which gives flexibility to the power outlet. The performance of these active filters is based on three basic design criteria. They are: Design of power inverter (semiconductor switches, inductances, capacitors, dc voltage); PWM control method (hysteresis, triangular carrier, periodical sampling); Method used to obtain the current reference or the control strategy used to generate the reference template. Both series voltage control and shunt current control involve use of voltage source converters. Both these inverters each consisting of six IGBTs with anti parallel diode connected with each IGBT are operated in current control mode employing PWM control technique. Capacitor is used as an interface between the two back to back connected inverters and the voltage across it acts as the dc voltage source driving the inverters The two VSIs can work independently of each other by separating the dc side. So in that case, the shunt inverter is operating as a STATCOM that generates or absorbs reactive power to regulate the voltage magnitude at the connection point. Instead, the series inverter is operating as SSSC that generates or absorbs reactive power to regulate the current flow, and hence the power flows on the transmission line. The UPQC has many possible operating modes. In particular, the shunt inverter is operating in such a way to inject a controllable current into the transmission line. The shunt inverter can be controlled in two different modes: (1) VAR Control Mode:The reference input is an inductive or capacitive VAR request. The shunt inverter control translates the VAR reference into a corresponding shunt current request and adjusts gating of the inverter to establish the desired current. For this mode of control a feedback signal representing the dc bus voltage, Vdc, is also required. (2)Automatic Voltage Control Mode:The shunt inverter reactive current is automatically regulated to maintain the transmission line voltage at the point of connection to a reference value.. The series inverter controls the magnitude and angle of the voltage injected in series with the line to influence the power flow on the line. The actual value of the injected voltage can be obtained in several ways: Direct Voltage Injection Mode:The reference inputs are directly the magnitude and phase angle of the series voltage. Phase Angle Shifter Emulation mode: The reference input is phase displacement between the sending end voltage and the receiving end voltage. Line Impedance Emulation mode: The reference input is an impedance value to insert in series with the line impedance. Automatic Power Flow Control Mode:The reference inputs are values of active and reactive power to maintain the transmission line despite system changes. A UPQC control strategy should preferably have following attributes: (1) Shunt converter Reactive power control by shunt current injection Real power regulation through dc link capacitor DC capacitor voltage regulation Harmonic compensation (2) Series converter Real reactive power control by series voltage injection Voltage control Phase angle regulation Power factor correction 1.3 Characteristics of UPQC Basic characteristics of UPQC are same as UPFC but UPQC in addition, performs active filtering. The operation of UPQC from the standpoint of conventional power transmission based on reactive shunt compensation, series compensation and phase angle regulation, the UPQC fulfill these functions there by meet multiple control objectives by adding injected voltage with appropriate magnitude and phase angle to the terminal voltage. Using phasor representation, basic UPQC control functions explained: (1)Terminal Voltage Regulation The change in voltage shown in Fig.1.5 is injected in phase or anti phase. UPQC with its series voltage control detects and calculates the required terminal voltage vo to be injected in series with the line to compensate both the dip and swell in the supply voltage. vo + vo vo (2) Series Capacitive Compensation Here, vpq = vc where vcis injected capacitive voltage in quadrature to the line current functionally it is similar to series capacitive and inductive line compensation attained by SSSC as shown in Fig. 1.6. Series inverter in combination with the insertion transformer produces the series injected voltage as calculated to mitigate the effects of the fluctuations of supply voltage by drawing the required power from the dc link. vc vo vo + vc Fig. 1.6 Series capacitive compensation (3) Transmission Angle Regulation Here, vpq = v () is injected with an angular relationship with respect to the voltage that achieves desire phase shift without any change in the magnitude as shown in Fig. 1.7. At any given transmission angle , the transmitted real power demand P and reactive power demand at transmission line sending end Qs and receiving end Qr can be freely controlled by UPQC Vc vd vo vo + v (4) Multifunction Power Flow Control This property is executed by simultaneous terminal voltage regulation, series capacitive line compensation and phase shifting as shown in Fig.1.8. This function makes UPQC unique device that performs all power quality improvement functions. vc vv vpq vo + v + vc + v (e) Active Filtering The compensating shunt currents generated contain harmonic content of the load current but with opposite polarity such that when they are injected at the point of common coupling the harmonic content of supply current is effectively reduced. As discussed earlier in this chapter. 1.4 Aim of Work This work deals with UPQC, which aims at the integration of series-active and shunt-active power filters. Fig. 1.3 shows the basic system configuration of such a UPQC. In this system, the power supply is assumed to be a three-phase, three-wire system. The two active power filters are composed of two 3-leg voltage source (VSI). The main purpose of the series-APF is harmonic isolation between a sub transmission system and a distribution system. In addition, the series-APF has the capability of voltage imbalance compensation as well as voltage regulation and harmonic compensation at the utility-consumer point of common coupling (PCC). Atthe same time, the main purpose of the shunt- APF is to absorb current harmonics, compensate for active power and reactive power injected by the load. Also, the voltage of the DC link capacitor is controlled to a desired value by the shunt-APF. The aim of the dissertation is to design different control strategies for (UPQC), which is one of the major custom power solutions capable of mitigating the effect of supply voltage sag, swell, flicker and spikes at the load end or at the Point of Common Coupling (PCC). It also prevents load current harmonics from entering the utility and corrects the input power factor of the load. Further, the main aim of the dissertation is to implement a control strategy for UPQC, modeling of UPQC using simulink and to analyze the control strategy to use the series voltage injection and shunt current injection for UPQC control The control strategies used here are based on PI controller, fuzzy controller. The relative performance of the two controls is also studied. The present work discusses the compensation principle and different control strategies (PI, Fuzzy) of the UPQC in detail [12]-[15]. The control strategies are modeled using MATLAB/Simulink. The performance of UPQC is examined by considering, a diode rectifier feeding an RL load (non linear load) that acts as a source of harmonics, to the system of concern. The performance is also observed by switching the extra RL load. The simulation results are listed in comparison of different control strategies and for the verification of result [16]-[18]. 1.5 Organization of the Report The report of the work done is organized as follows: Chapter 2 gives brief overview of control strategy of UPQC. In this chapter introduction to dq theory, compensation strategy, basic control function and modeling of UPQC using PI controller discussed with results. Chapter 3 discusses about fuzzy logic controller and implementation in UPQC. Membership functions, rule base table and surface viewer also discussed in this chapter. Chapter 4 gives comparison studied between fuzzy logic controller and PI controller. Simulation results of both are discussed in detail with the help of table and graphs. The last chapter 5 presents important conclusions and future work. Adequate references provided at the end of the chapter. Chapter 2 CONTROL STRATAGEY FOR UNIFIED POWER QUALITY CONDITIONER 2.1 Introduction Control strategy plays vital role in overall performance of power conditioner. Control strategy includes features like rapid detection of harmonic signals by maintaining higher accuracy, fast processing, and faster dynamic response of the controller. The control strategy can be realized using discrete analog and digital devices or advanced programmable devices, such as single chip micro computers, DSPs etc[10]. The control strategy determined by the appropriate switching pattern or signal obtained by compensating gate signal compared obtained by comparing with its reference value. Since derivation of reference signal plays an important role in control strategy, many theories and techniques were proposed in recent years. There are number of control strategies were proposed among them dq method is used in the present work and discussed below: 2.2 dq Transformation It is established that the active filter flows from leading voltage to lagging voltage and reactive power flows from higher voltage to lower voltage. Therefore both active and reactive power can be controlled by controlling the phase and the magnitude of the fundamental component of the converter voltage with respect to line voltage. dq theory provides an independent control of active reactive power by controlling phase and the magnitude of the fundamental component with respect to converter voltage According to the dq control theory three-phase line voltages and line currents are converted in to its equivalent two-phase system called stationary reference frame. These quantities further transformed into reference frame called synchronous reference frame. In synchronous reference frame, the components of current corresponding to active and reactive power are controlled in an independent manner. This three-phase dq transformation and dq to three-phase transformation are discussed in detail in this chapter. The outer loop controls the dc bus voltage and the inner loop controls the line currents. The instantaneous real power at any point on line can be defined by: p =vRIR + vBIb + vCIc (2.1) And we can define instantaneous reactive voltage conceptually as a part of three phase voltage set that could be eliminated at any instant without altering p. Reference frame theory based d-q model of shunt active filter is presented in this section. While dealing with instantaneous voltages and currents in three phase circuits mathematically, it is adequate to express their quantities as the instantaneous space vectors [10]. Vector representation of instantaneous three phase quantities R, Y and B which are displaced by an angle 2/3 from each other is shown in Fig.2.1 [17]. B 90o R 120o Y The instantaneous current and voltage space vectors are expressed in terms of instantaneous voltages and currents as: v= [vRvYvB] I = [IR IY IB] (2.2) Instantaneous voltages and currents on the RYB co ordinates can be transformed into the quadrature , coordinates by Clarke Transformation as follows: vvv0.=TvRvYvB. (2.3) III0.=TIRIYIB. (2.4) Where Transformation matrix T=2/31-1/2-1/203/2-3/21/21/21/2 (2.5) Since in a balanced three-phase three-wire system neutral current is zero, the zero sequence current does not exist and zero sequence current can also be eliminated using star delta transformer. These voltages in - reference frame can further be transformed into rotating d- q reference frame as Fig. 2.2. d Y R B q T1=cosr-sinrsinrcosr (2.7) Where r is the angular velocity of the d- q reference frame as shown in Fig. 2.2. The current components in the d- q reference frame can be similarly obtained using the - to d-q transformation matrix T1. The unit vector required for this transformation is generated using the grid voltage 2.3 Compensation Strategy vc iL ic VL vs As shown in Fig. 2.3,vs is the supply voltage. vc, Ic are the series compensation voltage, shunt compensation current and vL, iL are the load voltage and current respectively. The source voltage may contain negative, zero as well as harmonic components. The per phase voltage of the system can be expressed as: va=v1pm+sintsin+valn+k=2Vaksin kt + ka (2.8) Where v1pa is the fundamental frequency positive sequence components, v1naand v10a are negative and zero sequence components respectively. The last term of equation represents the harmonic content in the voltage. In order for the load voltage to be perfectly sinusoidal and balanced, the series filter should produce a voltage of: vah=v1an+v10a+ k=2vka sin kt + ka 2.9 In the latter section, it will be shown how the series-APF can be designed to operate as a controlled voltage source whose output voltage would be automatically controlled according to the above equation. The functions of the shunt active filter is to provide compensation of the load harmonic current, load reactive power demand and also to maintain dc link current constant. To provide load reactive power demand and compensation of the load harmonic and negative sequence currents, the shunt-APF acts as a controlled current source and its output components should include harmonic, reactive and negative-sequence components in order to compensate these quantities in the load current [6]. The per phase load current of shunt active filter is expressed as: Ial=I1pmcos t 1 + Taln+k=2Ialk (2.10) =I1pmcost cos1 + I1pmsin t sin 1 k=2Ialk (2.11) In order to compensate harmonic current and reactive power demand the shunt active filter should produce a current of: Iah=I1pm+sin t sin 1 +Ialn+k=2Iak (2.12) Then the harmonic, reactive and negative-sequence current will not flow into power source. Hence, the current from the source terminal will be: Ias=Ial-Iah=Ipmcos t 1 + Taln+k=2Ialk (2.13) This is a perfect harmonic free sinusoidal current in phase with voltage. 2.4 Basic Control Function It is evident from above discussion that UPQC should separate out the fundamental frequency positive sequence components first from the other components. Then it is required to control both series and shunt active filter to give output as shown in equations (2.9) and (2.18) respectively. The control strategy uses a PLL based unit vector template for extraction of reference signal from the distorted input supply. The block diagram of extraction of unit vector template is as given in Fig. 2.4. vm va,vb,vc vLa,vLb,vLc The input source voltage at point of common coupling contains fundamental and distorted component. To get unit vector templates of voltage, the input voltage is sensed and multiplied by gain equal to 1/vm, where vm is peak amplitude of fundamental input voltage. These unit vector templates are then passed through a PLL for synchronization of signals. The unit vector templates for different phases are obtained as follows: va=sin t vb=sin (t-1200) (2.14) vc=sin (t+1200) 2.5 Shunt Converter Control The unit vector template of voltage is used to generate the reference signal for shunt APF. The control block diagram of shunt active filter is given in Fig. 2.5. As indicated earlier, the shunt APF compensates current harmonics in addition to maintaining the dc link current at a constant level. To achieve this, dc link current of the UPQC is compared with a constant reference current of magnitude equal to peak of harmonic current [10.]. The error between measured dc link current and reference current is processed in a PI controller. Gatting Signals Ia Ib I vavbvc Iar Ibr Icr dc link Pdc Ploss Idc ref The output of PI controller is added to real power loss component to derive reference source current given as: vv = 1/2 -1/2-1/203/2 -3/2 vavbvc (2.15) II =1/2 -1/2-1/203/2 -3/2IaIbIc (2.16) pt=vtIt+vtIt qt=-vtIt+vtIt (2.17) In matrix form it is given as: pq = vv-vv II (2.18) From equation 2.18 the values of p and q can be expressed in terms of dc components plus the ac components as follows: p=p+p q=q+q (2.19) Where p is the dc component of the instantaneous power p, and is related to the fundamental active current. p is the ac component of the imaginary power p, and is related to the harmonic current caused by the ac component of the instantaneous real power q is the dc component of the imaginary instantaneous power q, and is related to the reactive power generated by the fundamental components of voltage and current qis the ac component of the instantaneous imaginary power q, and is related to the harmonic current caused by the ac component of instantaneous reactive power. To compute harmonic free unity power factor, three-phase currents, compensating powers pc and qc are selected as: pc = pldc + ploss (2.20) qc = 0 Where, plossis the instantaneous active power corresponding to the switching loss and resistive loss of UPQC. The total instantaneous active power is calculated by adding real power loss due to switching as shown in Fig.2.5. The orthogonal components of the fundamental current are obtained as follows: II = vv-vv pcqc (2.21) The a-b-c components of fundamental reference current are obtained as follows: i*sai*sbi*sc =2/30-1/31/3-1/31/3II (2.22) The reference currents are then; compared with actual source current in a hystresis controller band to derive the switching signals to shunt inverter. 2.6 Series Converter Control In order for the load voltage to be perfectly sinusoidal and balanced, the series filter should produce a voltage equal to equation (2.9). The reference load voltages are obtained by multiplying the unit vector templates with a constant equal to peak amplitude of fundamental input voltage. The compensation signals for series filter are thus obtained by comparing these reference load voltages with actual source voltage using equation (2.23). v*fa=vsa-vmva v*fa=vsb-vmvb v*fa=vsc-vmvc (2.23) The control of the series-active power filter is given in Fig. 2.6. The series-APF should behave as a controlled voltage source and its output should follow the pattern of voltage given in equation (2.9). This compensating voltage signal can be obtained by comparing the actual load terminal voltage with the desired value. These compensation signals are compared with actual signals at the terminals of series filter and the error is taken to hystresis controller to generate the required gating signal for series filter as shown in Fig. 2.6. vla v v*fa Gatting va signal v*fb vb v*fa vlb vfa vfb vfc Fig. 2.6 Control block diagram of series-APF 2.7 Modeling of UPQC The three-phase system shown in Fig. 2.7 is considered for verifying the performance of UPQC. Three-phase source feeding this system at one end. For the best performance, UPQC is placed at the midpoint of the system as shown in Fig. 2.7. UPQC is placed between two sections B1and B2 of the transmission line. The complete system parameters are given in Table 2.1. The STATCOM model in UPQC is connected in shunt with transmission line using step down transformer. the voltage can be regulated to improve the voltage stability of the power system. Thus the main function of the STATCOM is to regulate key bus voltage magnitude by dynamically absorbing or generating power to the ac transmission line. The SSSC which is connected by series transformer with transmission line generates three-phase voltage of controllable magnitude and phase angle. This voltage injection in series with the transmission line is almost in quadrature with the line current and hence emulates an equivalent inductive or capacitive reactance in series with the transmission line. A small part of this injected voltage is in phase with the transmission line current supplying the required losses in the Inverter Bridge and transformer. Three-phase AC source Rated voltage 11 kV Frequency 50 Hz SC level 200 MVA Base voltage 11 KV X/R 8 Transmission line parameters Resistance of the line 0.01273 /km Inductive reactance of the line 0.09337 mH/km Capacitive reactance of the line 12.74 nF/km DC link Capacitance of DC link Capacitor 2500 F DC link voltage 700 V Shunt transformer Nominal power 50 MVA Frequency 50 Hz Primary voltage 11 kV Secondary voltage 440 V Magnetization resistance 50 p.u. Magnetization reactance 50 p.u. Series transformer Nominal power 50 MVA Frequency 50 Hz Primary voltage 440 V Secondary voltage 230 V Magnetization resistance 20 p.u. Magnetization reactance 20 p.u. Table 2.1 Power system parameter 2.8 abc to dq Conversion in MATLAB As shown in Fig. 2.8 (a), a discrete 3-Phase Programmable Source block is used to generate 1pu, 1200 degrees positive sequence voltage. At t = 0.1s an unbalance is introduced by adding a 0.3 p.u. negative sequence component with a phase shift of -300. The Phase Locked Loop block measures the system frequency and provides the phase synchronous angle (more precisely [sin (), cos ()]) for the dq Transformations block. In steady state, sin () is in phase with the fundamental (positive sequence) of the component. Fig. 2.8 (b) shows the main conversion block used for conversion, the first block is three phase sequence analyzer; its function is to do Fourier analysis over one cycle of the specified frequency is first applied on the three input signals to find phasor va, vb and vcat fundamental or harmonic frequency. Then, transformation is applied to obtain the positive-sequence v1, negative-sequence v2 and zero-sequence v0. This block can be used in a control system to measure a positive sequence voltage or current. The abc_to_dq0 Transformation block computes the direct axis, quadratic axis, and zero sequence quantities in a two-axis rotating reference frame for a three-phase sinusoidal signal. The following transformation is used: vd= 2/3 (vasin (t)+ vb sin (t-2/3)+vc sin (t+2/3)) vq= 2/3 (vacos (t)+ vb cos (t-2/3)+vc cos (t+2/3)) (2.24) vo=1/3(va+vb+vc) Where = rotation speed (rad/s) of the rotating frame. This block can be used to measure the positive-sequence component of a set of three-phase voltages or currents. The vd and Vq(or Id and Iq) then represent the rectangular coordinates of the positive-sequence component. Math Function and Trigonometric Function blocks are used to evaluate the magnitude and phase of the positive sequence from the d and q components, using the Math Function block and the Trigonometric Function block the modulus and angle of voltage is obtained as : Modulus: | v| = [(vd)2 +(vq)2 ]1/2(2.25) Angle: v = atan2 (vq / vd) The Math Function block shown performs numerous common mathematical functions, hypot indicates Square root of sum squares. The Trigonometric Function block performs common trigonometric functions. The name of the function appears on the block. Here, atan2 function is selected the block displays two inputs. In the Fig. 2.8 (b) first input is the y-axis or complex part of the function argument. The second input is the x-axis or real part of the function argument. There is another block for dq to abc conversion. The dq0_to_abc Transformation block performs the reverse Park transformation, which is commonly used in three-phase electric machine models. It transforms three quantities (direct axis, quadratic axis, and zero-sequence components) expressed in a two-axis reference frame back to phase quantities. The following transformation is used: va= ( vd sin (t)+vqcos(t)+vo ) vb= ( vd sin (t-2/3)+vqcos(t-2/3)+vo ) (2.26) vc = ( Vd sin (t+2/3)+vqcos(t+2/3)+vo) Where = rotation speed (rad/s) of the rotating frame. 2.9 Simulated Results As shown in Fig.2.9 phase abc and synchronous reference frame quantity dq shown. As shown, unbalance created at 0.1s by adding 0.3 p.u. negative sequence component with phase shift of 300 hence significant changes in the magnitude of phase voltage and dq quantity occurs. 2.10 Shunt Controller/STATCOMin MATLAB The controller shown in Fig. 2.10 is an integral part of the converter present in STATCOM to operate voltage control mode. Its function is to operate the rectifier power switches so as to maintain a fixed dc voltage in the dc link and to generate a fundamental output voltage waveform with demanded magnitude and phase angle in synchronism with the sinusoidal system which forces the reactive power exchange required for compensation. The STATCOM controller has the capability of independently controlling the shunt real and reactive power components. In the automatic voltage control mode, the shunt converter reactive current is automatically regulated to maintain the transmission line voltage to a reference value at the point of connection. However, the shunt real power control is dictated by the dc voltage controller as shown in Fig. 2.11, which acts to maintain a preset voltage level on the dc link, thereby providing the real power supply or sink needed for the support of the series voltage injection. In other words, this dc voltage controller ensures the real power balance between the shunt and series converters. In the scheme shown in Fig. 2.8 (a) and Fig. 2.8 (b) the three-phase voltage and current are sensed and transformed into two-phase quantities using Parks transformation, which gives d-q-axis current and voltage for the controller. The dc voltage controller calculates the reference value for the d-axis inner current controller. As shown in Fig. 2.12, inner current controller is considered particularly suitable for current source rectifier due to its safety, stability performance and fast response. Typically the inner current control loop is at least ten times faster than the outer loop controlling the dc voltage. The Idrefobtained from the voltage controller is compared with the actual d-axis current and stabilized through PI controller to get the equivalent d-axis reference voltage vd. Similarly the actual q-axis current is compared with Iqrefand the error so obtained is stabilized through PI controller to get the equivalent q-axis reference voltage vq. The parameters of these PI controllers are tuned and fine adjustment is carried out by trial and error procedure to minimize the performance indices, namely the integral square error and integral time absolute error so as to give the best response. The reference voltages vdand vqare compared with actual vdand vqto obtain the equivalent vdav, and vqav. Then these two-phase quantities are converted into three-phase quantities using dq-abc transformation. These three-phase voltages are fed as control signals to the PWM modulator for developing the switching pulses to the current source rectifier switches. 2.11 SeriesConverter/SSSC Modelin MATLAB A SSSC is a solid-state voltage source inverter, which generates a controllable AC voltage source, and connected in series to power transmission lines in a power system. The injected voltage (vq) is in quadrature with the line current I, and emulates an inductive or a capacitive reactance so as to influence the power flow in the transmission lines. The compensation level can be controlled dynamically by changing the magnitude and polarity of vq and the device can be operated both in capacitive and inductive mode. The MATLAB modeling of control system of SSSC is shown in Fig. 2.13. The control system consists of: A phase-locked loop (PLL) which synchronizes measured positive-sequence component of the current with self generated current. The output of the PLL ( =t) is used to compute the direct-axis and quadrature-axis components of the AC three-phase voltages and currents. Sequence of voltages v1 and v2 (V1q and v2q) as well as the dc voltage vdc. AC and DC voltage regulators which compute the two components of the converter voltage (vdcnv and vqcnv) required obtaining the desired dc voltage (vdcref) and the injected voltage (vqref). The variation of injected voltage is performed by means of a Voltage-sourced converter (VSC) connected on the secondary side of a coupling transformer. The VSC uses forced-commutated power electronic devices (e.g. GTOs, IGBTs or IGCTs) to synthesize a voltage vcnv from a dc voltage source. A capacitor connected on the dc side of the VSC acts as a dc voltage source. In the control system block diagram vdcnv and vqcnv designate the components of converter voltage vcnv which are respectively in phase and in quadrature with line current I. VSC using IGBT-based PWM inverters is used in the present study. Harmonics are cancelled by connecting filters at the AC side of the VSC. This type of VSC uses a fixed dc voltage vdc. The converter voltage vcnv is varied by changing the modulation index of the PWM modulator. 2.12 Simulation Results of UPQCUsing PI Controller An ideal three-phase sinusoidal supply voltage of 11kV, 50Hz is applied to the non-linear load (diode rectifier feeding an RL load) injecting current harmonics into the system. Fig. 2.14 (b) shows supply current in three phase before compensation from 0s to 0.1s, and after compensation from 0.1s to 0.4s. Shunt inverter is able to reduce the harmonics from entering into the system. The Total Harmonic Distortion (THD), which was 20.02% (Fig.2.20a) before compensation was effectively reduced to 4.04 % (Fig. 2.20b) after compensation using PI controller. It is clearly shown in Fig. 2.18 which shows single phase-phase b compensation. THD of all the waveforms discussed in detail in chapter 3. The compensating shunt currents generated contain harmonic content of the load current Fig. 2.14 (a) but with opposite polarity such that when they are injected at the point of common coupling the harmonic content of supply current is effectively reduced. Reduced value is held constant using PI controller. Fig. 2.14 (d) shows the source voltage with THD of 2.72%. Fig. 2.14 (c) and Fig. 2.14 (d) shows the load voltage and load currents respectively. The distortion due to non linear RL load. THD response of the line current and line voltage in the STATCOM side are found to be very low. Fig. 2.14 (c) shows load voltage. Fig. 2.23 shows the bus voltage and current in the STATCOM side, which are found to be in phase with each other. This shows that the UPQC takes the role of phase angle compensation by absorbing or supplying the reactive power with the transmission line for any load variations. Fig. 2.26 shows dc capacitor voltage at 0.1s UPQC turned on and capacitor starts charging. Because of use of PI controller, capacitor charging takes some time and capacitor voltage also shows more oscillations in comparison to use of fuzzy logic controller. Here simulation is performed on 11kV line and the capacitor value used is 2500F which is much lesser compare to actual requirement, hence dc capacitor shows more fluctuations. When the transmission line is without UPQC, the real and reactive power flow cannot be controlled. Fig. 2.19 (a) shows the active power and Fig. 2.19 (b) shows reactive power through the line without UPQC from 0s to 0.1s after that with UPQC connected. The active power flow through line which is controlled by UPQC. Transmission capability of the existing transmission line is highly improved with the presence of UPQC. The difference between the sending-end real power and receiving end real power is high in the transmission line without UPQC. This is due to the increase in transmission losses, which are minimized with the help of UPQC as shown in Fig. Fig. 2.19 (c).It also helps in improving power factor of the transmission line. As shown in Fig. 2.19 (d), without UPQC, power factor of the transmission line is 0.93 but as UPQC switched, the power factor increases to 0.99. The reactive Power flow through the transmission line with and without UPQC is shown in Fig. 2.19 (b). The raise i n the transmission capability is noticed from the simulation results. The power transfer capability of long transmission lines is usually limited by their thermal capability. Utilizing the existing transmission line at its maximum thermal capability is possible with UPQC. The series inverter injects voltage of variable magnitude and phase into the transmission line at the point of its connection, there by controlling real and reactive power flow through the line. The active power through the line is supplied by SSSC active power. This real power obtained from the dc source connected to its dc terminals. The shunt inverter provides the required power to the series inverter through the dc link. For unbalanced condition extra RL load at dc side of the capacitor is connected at 0.4s. The response of active power, reactive power and terminal voltage is shown in Fig. 19 (a)- Fig.19 (d) .Unbalance is created by switching RL load on the ac side of the diode rectifier on phase a and at 0.5s and 0.6s another RL load at phase b and phase c connected respectively as shown in Fig. 2.7. It is obvious from the Fig.19 (a) Fig. 19(d) that in unbalanced load condition, UPQC performs active, reactive compensation, phase angle regulation and harmonic filtering. Hence UPQC performance tasted under normal as well as unbalanced condition. Fig 2.21 (a) and Fig. 2.21 (b) shows the behavior of the PI controller when extra RL load is connected after 0.4s.With the use of PI controller, load current THD is reduced to 3.52% while THD of the source current is 1.89%. Fig. 2.20 shows the voltage across dc link capacitor under various conditions. UPQC is switched at 0.1s, at the same instant dc capacitor starts charging and obtained certain voltage which cause active power transfer to series APF, after switching load at dc terminals of load diode rectifier, fluctuation in dc capacitor increases this is due to use of PI controller. When unbalance condition created by switching load to all three-phase one by one as explained earlier, dc capacitor voltage still maintained. This proves that UPQC is able to transfer active power through dc link capacitor in all the conditions. Where Ps= Sending end active power, Pr =Receiving end active power, Ps= Sending end active power, Pr =Receiving end active power Vs =Sending end voltage, Vr =Receiving end voltag 2.13 Conclusion This chapter presents control and performance of UPQC intended for installation on a transmission line with the help of PI controller. A control system is simulated in switching and unbalanced condition with shunt inverter and series inverter in open loop phase angle control mode. Simulation results show the effectiveness of UPQC in active filtering and controlling real and reactive power through the line.AC voltage regulation and power factor of the transmission line also improved. This chapter presents an improvement in the real and reactive power flow through the transmission line with UPQC using PI controller when compared to the system without UPQC. Chapter 3 MODELING OF UPFC USING FUZZY LOGIC CONTROLLER 3.1 Introduction Fuzzy Logic is a new control approach with a great potential for real-time application. Fuzzy logic controller is a rule based controller where a set of rules represents a control decision mechanism to correct the effect of certain causes coming from power systems [13]. In fuzzy logic, the linguistic variables are expressed by fuzzy sets defined on their respective universes. Error (input) can be selected as current, voltage or impedance, according to selected control type. The output of the fuzzy logic controller is the angle signal and the pulse generator provides firing pulses to thyristors.The fuzzy control is basically a nonlinear and adaptive in nature, giving the robust performance in the cases where in the effects of parameter variation of controller is present. It is claimed that the fuzzy logic controller yields the results which are superior to those obtained with the conventional controllers such as PI, PID etc. In the fuzzy controller, the simplicity of a PI controller is combined with the intelligent and adaptive ness of the fuzzy logic based control system [14]-[15]. Inputs to the fuzzy controller are categorized as various linguistic variables with their corresponding membership values as shown in the Table3.1. Depending upon the range (very large, large, medium, small and Zero) and the sign (positive or negative) of the error signals E1 and E2 , the FPI searches the corresponding output from the linguistic codes given in the Table 3.1. The simulation results using fuzzy controller are discussed in chapter 4. 3.2 Fuzzy Logic Implementation in UPQC Controller As shown in Fig. 3.1 fuzzy logic controller block implemented instead of traditional PI controller in shunt controller Fig. 3.1, dc voltage regulating circuit Fig. 3.2 and series controller as shown in Fig.3.3.In order to achieve the desired response the PI controllers present in the control scheme are replaced by a fuzzy logic controller (FLC) whose membership functions are given in Fig. 3.4a, Fig 3.4b and Fig. 3.4c. The corresponding rule sets are given in Table 3.1. In order to observe the performance of self regulated dc bus, the voltage across the capacitor is sensed at regular intervals and controlled by employing a suitable closed loop control. The dc link voltage, vdc is sensed at a regular interval and is compared with its reference counterpart vdc*. The error signal is processed in a fuzzy controller. A limit is put on the output of controller this ensures that the source supplies active power of the load and dc bus of the UPQC Fig. 3.2. Part of active power supplied by source is used to provide a self supported dc link of the UPQC. Thus, the dc bus voltage of the UPQC is maintained to have a proper current control Table 3.1 Set of Fuzzy Rule Representation for FPI E2 E1 PL PM PS Z NS NM NL NL PL PL PL PM PM PS Z NM PL PL PM PM PS Z ZS NS PL PM PS Z NS NM NL Z PL PM PS Z NS NM NL PS PM PS Z NS NM NL NL PM PS Z NS NM NM NL NL PL Z NS NM NM NL NL NL As shown in Fig. 3.5, The surface viewer can generate a three-dimensional output surface where any two of the inputs vary, but two of the inputs must be held constant because computer monitors cannot display a five-dimensional shape. In such a case, the input is a two-dimensional vector with NaNs holding the place of the varying inputs while numerical values indicates those values that remain fixed. Because this curve represents a two-input one-output case, one can see the entire mapping in one plot [15]. 3.3 Simulation Results and Discussion Fig. 3.6a and Fig. 3.6b shows the source current and source voltage respectively. As shown in Fig. 3.6a, after switching of UPQC, source current becomes sinusoidal and from Fig. 3.7a the THD of compensated source current is 3.81% which is lesser compare to PI controller. The source voltage THD is 2.23% as shown in Fig. 3.7b. Fig. 3.6c is the dc link voltage (voltage across the dc capacitor) that feeds both the shunt and series inverters. The capacitor is effectively charged to the reference voltage, vdc drawing the charging current from the supply. Once it is charged to required value, it is held constant using fuzzy controller. There is no drop in the capacitor voltage when it feeds shunt inverter, because shunt inverter draws only reactive power to compensate the load current harmonics. When extra RL load is switched, the source current THD reduces to 3.26% as per Fig. 3.8a and source voltage THD is reduced to 1.26% as per Fig. 3.8b. 3.4 Conclusion This chapter gives overview of fuzzy logic controller and its implementation in UPQC under switching and unbalanced conditionr. Triangular membership function with rule table is implemented using two input one output. Surface viewer is shown to evaluate the output response compare to two inputs. Fuzzy controller with use of the power flow as controlling input is designed in order to improve systems transient stability. Chapter 4 COMPARISON OF PI CONTROLLER AND FUZZY CONTROLLER 4.1 Introduction The simulation results of UPQC obtained using PI controller (obtained in chapter 2) and simulation results obtained using fuzzy logic controller (obtained in chapter 3)are compared in this chapter 4.2SimulationResults and Discussions Table 4.1 shows simulated performance parameters of PI controller and fuzzy logic controller. It is clearly evident from the Table 4.1 that fuzzy logic control having an edge over PI controller. Results shown in Table 4.1 are verified one by one. Table 4.1 Simulation Results Obtained Factor PI Controller Fuzzy Controller 1 Source current THD 4.04% 3.81% 2 Dynamic response Slow ( 0.20s) Fast ( 0.10s) 4 Capacitor charging Slower Faster 5 Capacitor voltage balance under unbalanced load condition Less stable More stable 6 Source current THD with switching RL load 3.52% 3.26% (1) Source current THD As shown in Fig. 4.1, before compensation when UPQC not connected, source current THD is 20.02%, due to non linear RL load. The dominant harmonic is 5th harmonic and its magnitude is 18% of fundamental component. As shown in Fig. 2.15 in chapter 2, there is passive filter LC connected on shunt side which is tuned to 5th harmonic. Fig. 2.15b in chapter 2 shows source current THD after compensation when UPQC connected at 0.1s and PI controller used, source current THD is reduced to 4.04% and the magnitude of the 5th harmonic also reduces to 1% of fundamental component. But when PI controller replaced by the fuzzy logic controller, source current THD reduces to 3.81% as shown in Fig. 3.6a and Fig. 3.7a in chapter 3. And the magnitude of the 5th harmonic also reduces to 0.5% of fundamental component. So in the 1st, 3rd factor of Table 4.1, fuzzy controller proves to be more a advantageous. (2) Dynamic response This parameter is the measurement of how quickly controllers respond to the situation, in table 4.1 dynamic response (2) shows the time taken by the controller to reduce THD from 20.02% to 4.5%. as shown, time taken by PI controller is 0.20s and time taken by the fuzzy controller is 0.15s. Hence it is proved that dynamic response of th PI controller is faster than the fuzzy logic controller. (3) DC capacitor voltage regulation Fig. 2.20 in chapter 2 and Fig. 3.6c in chapter 3 is the dc link voltage that feeds both the shunt and series inverters. The capacitor is effectively charged to the reference voltage, vdc drawing the charging current from the supply. Once it is charged to required value, it is held constant using PI and fuzzy controller. There is no drop in the capacitor voltage. Fig. 2.20 shows the dc link voltage which reflects more the disturbance in the supply voltage because use of PI controller. But when fuzzy controller replaced, as shown in Fig. 3.6c, it shows less fluctuation and hence smoother exchange of real power between STATCOM and SSSC. From both fig. 2.20 and Fig. 3.6c, it can be seen that when UPQC switched at 0.1s, dc capacitor voltage using fuzzy controller quickly attains reference value compared to PI controller. In another condition, when extra RL load switched at 0.4s, fuzzy controller shows better response compare to the PI controller. This shows that capacitor voltage chargi ng is faster in case of fuzzy controller. So the operating band of dc voltage limited to narrow range which is one of the salient nature of fuzzy logic controller. So in the 4th, 5th factor of Table 4.1, fuzzy controller proves to be more a advantageous. (4) Source current THD with switching RL load Fig. 2.21a and Fig. 2.21b in chapter 2 shows the source current THD after switching extra RL load in non linear diode rectifier. Fig. 2.21a shows Source current THD using PI controller and its value is 3.52%. While Fig. 3.7a in chapter 3 shows Source current THD using Fuzzy controller and its value is 3.26%. Fig. 2.21b and Fig. 3.7b shows the source voltage THD after switching extra RL load in non linear diode rectifier. Fig. 2.21b shows Source current THD using PI controller and its value is 1.89%. While Fig. 3.7b shows Source current THD using fuzzy controller and its value is 1.27%. So it is obvious that under switching condition, fuzzy controller gives better performance then PI controller. So in the 6th, 7th factor of Table 4.1, fuzzy controller proves to be more a advantageous under switching condition. 4.3 CONCLUSION Simulated results of two control strategy of UPQC are discussed in detail with the help of comparison table. Comparison studies show that fuzzy logic controller is more advantageous in terms of compensation, dynamic response and capacitor voltage balancing. Simulated results are already discussed in detail. Chapter 5 CONCLUSION AND FUTURE WORK 5.1 Conclusion VAR compensation and harmonic filtering technique has gain tremendous interest over the years. Various topologies and control techniques have been reported in the literature. In this work various aspects of reactive power compensation and harmonic filtering is studied chronologically. UPQC which combines the series and shunt active filter has been selected for further study in this work. Different control strategy of UPQC has been studied and one of the control strategies (dq method) has been studied in detail. The relevant simulations studies of UPQC have been carried out using MATLAB under various conditions. One of the disadvantages of the dq theory is that it requires a PI controller minimizing the error between the sensed quantity and reference quantity. However, the tuning of the PI controller is cumbersome and time consuming job. In the present work fuzzy logic controller has been proposed in place of conventional PI controller. Fuzzy logic controller is non linear and adaptive in nature which gives the best performance under varying condition. Further no frequent tuning required so it is less time consuming and it is more accurate method then PI controller. Results obtained from the simulation shows better performance of UPQC when fuzzy logic controller used then that of PI controller in terms of harmonic compensation and dc capacitor voltage balancing at load terminals in switching as well as unbalanced conditions. Under this conditions the dynamic response of fuzzy logic controller proved to be faster than PI controller. Hence it is proved that fuzzy logic controller is superior then PI controller. UPQC and its method of control are the new area of concern. Present work focuses on two different control strategies PI control and fuzzy logic control. This work proves the advantages of the fuzzy logic control over traditional PI controller; fuzzy logic control of UPQC is the most recent area of concern. This work contributes towards fuzzy implementation in UPQC and the results discuss improvement of UPQC characteristics using fuzzy logic control. So performance of UPQC is evaluated using MATLAB/Simulink with 11kV transmission line. In this scheme the fuzzy controller provides better results than traditional PI controller in both switching and varying load condition. 5.2 Scope Future Work New fuzzy PI control strategy can be implemented using both fuzzy and PI controller simultaneously To test the system with different membership function apart from triangular. To develop new membership function and rule base table and implement in UPQC

Similarities Of The Mayan Civilization - 1102 Words

Despite bearing some minor similarities the difference between Mayan artwork like the Cylindrical vessel with ritual ballgame scene and Pablo Picasso’s Les Demoiselles d’ Avignon are pronounced. The best way to understand the Mayan is to have some historical information about them. The Maya civilization was a Mesoamerican civilization from around 2000 BCE to 1500 CE. This civilization developed in areas like Guatemala, Belize, Mexico, Yucatà ¡n Peninsula, western El Salvador and Honduras. Ritual, religion, and Cosmology are essential components of Mayan life, (Ca.A.D. 1200-1513) and Colonial (A.D. 1513-1830) periods of indigenous migrations and Spanish Conquest. Many of their actions were based on ceremonies and rituals. Ritual also†¦show more content†¦His artwork was intertwined with his life; he used the word â€Å"diary† in reference to his work. Later the family moves to Barcelona where Pablo is enrolled in â€Å"La Lonja† in advanced art classes. At the age of 49 his painting is exhibited at the Paris exposition Universelle. Picasso discovered what had been implied in the theme of blindness during his Blue Period. In summer of 1907 he discover s African sculptures at the ethnographic museum at Palais du Trocadero. In 1908 Cubism is born, Pablo gives a banquet at the Bateau-Lavoir in honor of Douanier Rousseau. Nine years later he works on costumes and dà ©cor of ballet costumes for the Paris Parade at Theatre du Chatelet. He meets ballerina Olga Khokhlova. The following year, Olga and Picasso marry and move to rue La Boetie. In 1921 Picasso’s son is born he continues to work for Diaghilev and works with mother and child subjects. In 1934 Pablo takes a trip back to his home town with his wife and son, where he does drawings, paintings, and engraving, of bullfights. After the birth of his daughter Maia, he returns to watercolors, painting, and drawing. The republican government appoints Pablo director of the Prado Museum. Forty years of his life were displayed at the Museum of Modern Art in New, York. â€Å"Picasso is anShow MoreRelatedSimilarities Between Civilizations And Civilizations958 Words   |  4 Pages Throughout history there have been similarities between civilizations, some of which were on separate parts of the world. Many scholars and historians have been baffled by the discoveries of these similarities due to the fact that these cultures were not only hundreds of miles apart but also were separated by hundreds of years. The ancient Egyptian civilization located in northern Africa around 3,100 B.C. is considered to be one of the cradles of civilization and also a major contributor to theRead MoreMayans, Aztecs, And Incas Essay1540 Words   |  7 PagesThe Aztecs, Mayans, and Incas were civilizations that settled in Central and South America thousands of years ago. There are vastly similar to each other, but also very different. They each had their own ways of growing their civilizations into what they needed to be successful. They had their own cultures and ways of life, but the ideas of each of them similarly came together in one way or another. The Mayan civilization was located in Central America on the Yucatan peninsula and down into theRead MoreThe Cultural Similarities Differences Between the Inca and Mayan Empires619 Words   |  3 PagesThough the Inca and Mayan empires existed at different times in history, they have a few things in common. Like other societies throughout history though, they have many things that set them apart from each other. The biggest similarity they share is that they both had control of massive empires that eventually ceased to exist. To start off with, the Mayans existed earlier in history than the Incas. The Mayans existed from 1000 BC to AD 1697 and no one is quite certain what wiped out their ancientRead MoreThe Ancient Civilization1622 Words   |  7 PagesThe Mayans has always existed through the telling of their ritualistic practices or their calendar, but the fall of such an advanced civilization is perhaps the most intriguing story of all.To understand what causes great civilizations, it is vital to note the process of collapse in other civilizations, such as the great Roman Empire. Differences in time period, geographical landscapes, and other circumstances mean no direct correlations are possible, but the outstanding point of similarity is thatRead MoreEssay on Popol Vuh vs. Gilgamesh861 Words   |  4 Pagesmany similarities, themes characters ect. I personally would not call the two texts similar. In my opinion for two texts to be similar they must poses similar general themes that apply to the e ntire text, not small themes that only apply to portions of the text. In other words I believe that two texts can have similar events, yet have completely different meanings. Popol Vuh and Gilgamesh actually had more similarities than dissimilarities, but it is the significance of those similarities, notRead MoreThe Origins Of The Ancient Civilization1308 Words   |  6 PagesThat is what happened to the Mayans. In a time span of only one hundred years, the whole Maya population was wiped out. There are several theories about the cause of their decline. Due to their disappearance the great Mayan inventions were lost in time until modern day anthropologists discovered that they made their own calendar and language along with many other things. What anthropologists do know for sure is that the Mayans were an ancient Mesoamerican civilization dating back to 250 B.C â€Å"madeRead MoreHow Did The History Of Meroe Reflect Interaction With Neighboring Civilizations?1707 Words   |  7 PagesMeroe 1) How did the history of Meroe reflect interaction with neighboring civilizations? The way the history of Meroe reflected interaction with neighboring civilizations is they traded more often with their neighbors. That is how they received their fortune and power. 2) How was the decline of Meroe connected to the changing patterns of long-distance trade? The decline of Meroe was caused by deforestation because wood was needed to make charcoal for iron. The deforestation made Egypt’s trade goRead MoreHistory: Spanish Colonization of the Americas and Spanish Conquest1021 Words   |  5 PagesCaribbean and Yucatan by European, Resulted in significant cultural, biological environmental changes to both regions Maggie Jim Professor Ancient History [Date] 1. Briefly discuss (but in detail) the similarities/differences between the initial Spanish colonization of the Caribbean and the Yucatan. In your discussion include the initial reaction of the Taino and Maya to the presence of the Spanish and the rational for the Spanish conquest. The SpanishRead MoreThe Mayan Civilization : An Advanced Society, Rich And Full Extraordinary Architecture1597 Words   |  7 PagesThe Mayan civilization was an advanced society, rich and full extraordinary architecture with a prodigious complexity of patterns and variety of expressions, that flourished in Mesoamerica. They were skilled architects and engineers, building phenomenal cities out of primarily limestone that still remains standing a thousand years after their civilization. Greatness and Magnificence was the signature of all Mayan cities, from their inception period and continued until the desertion of all the cityRead MoreHistory: Spanish Colonization of the Americas and Spanish Conquest1021 Words   |  5 PagesCaribbean and Yucatan by European, Resulted in significant cultural, biological environmental changes to both regions Maggie Jim Professor Ancient History [Date] 1. Briefly discuss (but in detail) the similarities/differences between the initial Spanish colonization of the Caribbean and the Yucatan. In your discussion include the initial reaction of the Taino and Maya to the presence of the Spanish and the rational for the Spanish conquest. The Spanish

Human Resource Information Systems Free Essays

INTRODUCTION Office automation has become a reality. Stand-alone personal computers are universally used for word processing, and spread sheets have become the workhorses of office life. As a result, electronic records are being created virtually everywhere in the world. We will write a custom essay sample on Human Resource Information Systems or any similar topic only for you Order Now Wherever computers are used to carry out a function records are being generated. Records provide the primary evidence of how the functions of public administration are carried out. They are the building blocks of accountability. In a growing number of organizations human resources are now viewed as a source of competitive advantage. There is greater recognition that distinctive competencies are obtained through highly developed employee skills, distinctive organizational cultures, management processes, and systems. Increasingly, it is being recognized that competitive advantage can be obtained with a high quality work force that enables organizations to compete on the basis of market responsiveness, product and service quality, differentiated products, and technological innovation. The effective management of human resources in a firm to gain a competitive advantage in the marketplace requires timely and accurate information on current employees and potential employees in the labour market. With the evolution of computer technology, meeting this information requirement has been greatly enhanced through the creation of HRIS. A basic assumption is that the effective management of employee information for decision makers will be the critical process that helps. A HRIS is concerned with activities related to employees and potential employees of the organization. Because the human resources function relates to all other functional areas in the business, the HRIS plays a valuable role in ensuring organizational success. Some of the activities performed by the HRIS are workforce analysis and planning, hiring, training, job and task assignment and many other personnel related issues (Stair R,2006,241). THE EVOLUTION OF HRIS In the 1980s, office automation began to appear on the landscape, and HRIS were developed as a special category of office automation systems (OAS). At first it seemed the emphasis was on developing systems as cheaply as possible. The replacement of people with software was seen as the main advantage. Rather than have HR managers maintain extensive employee records, data-entry technicians would enter data once into a system and update records as necessary. Today, however, HRIS would be more accurately viewed as a hybrid of several classical types of information systems. Along with OAS capabilities, current HRIS include features of transaction processing systems (TPS), decision support systems (DSS) and communication systems. HRIS may comprise stand-alone software for any of the primary areas of use for information systems in HR management. These areas include employee record management, compensation and benefits, recruitment and retention, training and development, performance appraisal, and promotion and succession planning. It became evident as HRIS took hold in the corporate culture that a quality HRIS could provide valuable information to the organization in managing one of its most valuable assets: the organization’s human resources. As top management began to put pressure on HR managers to use HRIS, it was becoming clear that by collecting and processing more and more information in a timely manner, the value added was in the use of the data in decision making and not in the actual system used for collection and storage. This evolution has resulted in firms being able to leverage HRIS for administrative and strategic competitive advantage. WHY THE NEED FOR HRIS IN HUMAN RESOURCE MANAGEMENT Using HRIS gives firms several benefits. They include the following: †¢Providing a comprehensive information picture as a single, integrated database; this enables organizations to provide structural connectivity across units and activities and to increase the speed of information transactions. Increasing competitiveness by improving HR operations and management processes †¢Collecting appropriate data and converting them to information and knowledge for improved timeliness and quality of decision making †¢Producing a greater number and variety of accurate and real-time HR-related reports †¢Streamlining and enhancing the efficiency and effectiveness of HR administrative functions †¢Shifting the focus of HR from the processing of transactions to strategic HRM †¢Reengineering HR processes and functions Improving employee satisfaction by delivering HR services more quickly and accurately TYPES OF HUMAN RESOURCES INFORMATION SYSTEMS Although there are multiple classifications of computer-based systems, these the most basic types of systems that are most readily applied to the HR context and for use within an HRIS Transaction Processing Systems: Managers need systems that keep track of the elementary activities and transactions of the organization such as payroll, sales, receipts, cash deposits and the flow of material in an organization. Transaction processing system provides this kind of information. This is a computerized system that performs and records the daily routine transactions necessary to conduct business such as employee record keeping and payroll. This type of system is used as operational level and at this level tasks, resources and goals are predefined and highly structured (Laudon K, 2012,76). When using a transaction processing system for payroll processing, a payroll system keeps track of money paid to employees. An employees’ time sheet with their number of hours worked per week is an example of a single transaction. The system also supplies data to the business on employee payment history for insurance, pension and other benefit calculations to the firms human resources function. The overall aim of this system is to improve transaction speed and accuracy, improve efficiency in the processing of daily business transactions, automate routine transactions and reduce transaction costs Management Information System: This type of system serves the level of middle management and provides managers with reports on the organizations current performance. This information can be used to monitor and control the business and predict future performance. This system summarizes and reports on the company’s basic operations using data from the transaction processing systems. The basic transaction data is compressed and usually presented in the form of reports that are produced on a regular schedule and many of these reports can today be found online. Management information systems serve managers primarily interested in weekly, monthly and yearly results. These systems are also used to answer routine questions that have been specified in advance and have a predefined procedure for answering them as opposed to sophisticated mathematical models or statistical techniques (Laudon K, 2012,77-78). The main focus of this system is to provides key data to managers, supports regular and on-going decisions as well as provides defined and ad-hoc reporting. Decision support systems: In contrast to management information systems this system supports more non- routine decision making. They focus on problems that are unique and rapidly changing. For which the procedure for arriving at a solution may not be fully predefined in advance. Although this system uses internal information from both the above systems they often bring in data from external sources such as prices of competitors (Laudon K, 2012, 78) These systems use a variety of models to analyse the data and are designed so that users can work with them directly. The systems main concern is to provide interactive managerial decision making, support forecasting and â€Å"what-if† analysis and support business simulations. It can be used to assess staffing needs, analyse the labour market and assess employee skills Executive support systems: Helps senior managers address questions like what will the employment level be in five years? They deal with non-routine decisions requiring judgement, evaluation and insight because there is no agreed procedure for arriving at a solution. This system presents graphs and data from many sources through an interface that is easy for senior managers to use. These systems are designed to incorporate data about external events such as new tax laws or competitors but they also use summarized information from internal management information systems and decision support systems (Laudon K, 2012, 80). The primary focus of this system is to provide aggregate high-level data, to helps managers with long term planning and support strategic direction and decisions. It can be used to assist HR managers with succession planning which means having a systematic process where managers identify, assess and develop their staff to make sure they are ready to assume key roles within the company. Enterprise resource planning systems: are used to integrate business processes in human resources as well as manufacturing and production, finance and accounting and sales and marketing into a single system. Information that was previously separated into many different systems is stored into a single comprehensive system where it can be used in many different parts of the business. Managers are able to use firm-wide information to make more precise and timely decisions about daily operations and long term planning as well as share data across functional boundaries (Laudon K, 2012, 81). ADVANTAGES AND DISADVANTAGES OF HRIS SYSTEMS Widespread Access Traditionally, records and archives have been created and maintained in paper form as physical objects. Their physical state limits access to a specific time and place: only one person can use a record at one time and only in one physical location. Producing multiple copies is expensive and time consuming, requiring access to photocopiers or printers. Duplication also leads to confusion about which of many versions of a document is the official record. Electronic records, on the other hand, can be shared widely and they can be accessed and used by several people at the same time, even if they are in different places. In environments where resources are scarce or distances are great, the ability to provide access to information without the boundaries of time or space can dramatically improve service, increase information sharing and enhance operations. In some countries, for example, the ability to share an electronic record among government offices in different parts of the country saves money and time. Copying and mailing or faxing documents across thousands of miles can become prohibitively expensive and can slow down operations and delay decisions and actions. But even in some less developed countries, governments today are installing computers in community outposts in rural, underdeveloped areas so that people in the area can keep abreast of government activities and world events. Flexibility HRIS enhance flexibility in the creation, storage, use and management of information and records. In a paper environment, records are created, received and filed in one office, and they accumulate in one place. Electronic records can be stored remotely or on CD’s or flash discs, allowing people to share records and use their information resources more dynamically. Because so many people in an organisation can have access to electronically stored records at the same time, they can carry out their duties without being hindered by a lack of information. They also have better access to more up-to-date information, since they can access data such as electronic records on employees or databases directly. Efficiency and Effectiveness The use of information technologies improves information handling and allows for the speedy retrieval of records and information through electronic search facilities. As a result, policy makers can make informed decisions quickly and efficiently, contributing to the effectiveness of the organisation. Further, when the retrieval of records and information happens swiftly and decisions are made on time, the image of the organisation improves as it is seen to be reliable, capable and responsive to the needs of its clients or the public. Certainly, if someone knows where records are stored, whether in paper or electronic form, he or she can retrieve them in good time, but too often knowledge about where manual records can be found maybe held by only one person in the organisation, and if he or she is not available then access to records is delayed. And once the volume of records reaches a certain point, no one person can ‘remember’ where everything is. Well-designed HRIS will facilitate easy retrieval of electronic information, improving the speed and quality of service. Economic Benefits In the paper environment where records are physical objects, their accumulation requires ever-increasing amounts of space, including office space, shelves, filing cabinets and storage boxes. Several staff members may be needed to carry out routine procedural work such as filing documents and retrieving boxes. Through the use of new technologies, organisations are able to economise in terms of storage space, as HRIS can store large volumes of data and records in a small physical space. Database management systems, electronic mail systems, web and multimedia software programs are all good examples of information technologies that can store far more information than traditional paper records storage systems. In a well-managed organisation, it is also possible to manage staff resources more effectively. Much of the day-to-day work of filing and retrieval will be done by officers throughout the organisation as part of their daily routine, leaving time for other staff to participate more actively in activities such as appraisal. General Business Opportunities The professional image of an organisation can be enhanced by improved information flow, and the organisation may be able to take on more complex work because it is more efficient and cost-effective. HRIS can improve communications, reduce the loss of essential information, speed up the completion of projects and increase public awareness of the organisation. The use of technologies also exposes organisations to communities outside of their normal client base, locally, regionally, nationally and internationally. Auditing Capabilities Well-designed records and document management systems also allow an organisation to regulate and oversee actions and decisions. Many HRIS include mechanisms to maintain audit trails, encouraging more accountable record keeping and promote compliance across the organisation. HRIS Disadvantages An HRIS also can be a problematic for small businesses in which some employees must wear many hats. If your company isn’t big enough to have a dedicated human resources technology specialist, consider outsourcing. Some of the disadvantages of an HRIS involve human error during information input, costly technology to update your system and malfunctions or insufficient applications to support your human resources needs. There is a demand for computer and technology specialists with general information technology knowledge, and finding a qualified specialist with human resources functional area knowledge can be difficult. With such a demand, your cost to hire an HRIS specialist may be far above the average salary for a computer technology specialist. The cost per-hire for another employee in a specialized field may be a stretch for some small businesses. CONCLUSION It is obvious as we move into the 21st century that data will drive an increasing number of business decisions and strategies. HRIS is an excellent example of an area where businesses can capitalize not only on administrative cost savings, but also on leveraging a strategic advantage through information gathering, processing, and sharing. Despite certain potential pitfalls, it appears that HRIS are now today’s cutting-edge software for effective human resources management. We are only now beginning to realize the potential not only within the HR function, but organization-wide. What was once a future vision is reality and HR managers should jump aboard immediately. If they do not, the train is about to pick up speed rapidly, and they will be left behind. | How to cite Human Resource Information Systems, Papers

A novel structured on the theme of morality, the Adventures of Huckleberry Finn by Mark Twain Essay Example For Students

A novel structured on the theme of morality, the Adventures of Huckleberry Finn by Mark Twain Essay A novel structured on the theme of morality, the Adventures of Huckleberry Finn by Mark Twain focuses on Huck Finns multifaceted growing up process. Huck, through his escapades and misfortunes is obliged to endure the agonizing process from childhood to adulthood where he attains self-knowledge and discovers his own identity. Throughout the journey down the Mississippi River, Jim, Ms. Watsons runaway slave, accompanies Huck, and is later joined by two con men. It is during this journey that a great moral crisis in Hucks life occurs where he must make a painful decision as to whether he is going to give Jim up to the slave hunters or notify Ms. Watson about Jims whereabouts and assist him to remain a free man. This is the turning point in his character where through deep introspection, he learned to think and reason morally for himself. He comes to his own conclusions, unaffected by the accepted, and often hypocritical, perceptions of Southern culture. Huck also deciphers the truth in the face of lies held by the antagonistic society with its evil nature. From the very introduction of Huckleberry Finn in the Adventures of Tom Sawyer, Huck was known for his mastery of playing tricks on those gullible to his antics. In this novel, he played two tricks on Jim, enough to never make him do such a thing again. The first time as a joke, Huck puts a dead rattlesnake near Jims sleeping place, and its mate comes and bites Jim. He learned for his own sake never to do that because it could have been him bitten by the snake. However, the second prank Huck pulls on Jim unbeknownst to him does not seem to be as funny as he thought it would be when he pretended that the whole fog incident was a figment of Jims imagination. Jim was hurt by Huck and calls him trash, the exact turning point of Hucks morality; he even had the decency to apologize, showing acceptance to a black man. As I quote from pages 83-84 What do dey stan for? Ise gwyne to tell you. When I got all wore out wid work, en wid de callin for you, en went to sleep, my heart wuz mos broke bekase you wuz los, en I didn kyer no mo what become er me en de raf. En when I wake up en fine you back agin, all safe en soun, de tears come, en I could a got down on my knees en kiss yo foot, Is so thankful. En all you wuz thinkin bout wuz how you could make a fool uv ole Jim wid a lie. Dat truck dah is TRASH; en trash is what people is dat puts dirt on de head er dey frens en makes em ashamed. Then he got up slow and walked to the wigwam, and went in there without saying anything but that. But that was enough. It made me feel so mean I could almost kissed HIS foot to get him to take it back. It was fifteen minutes before I could work myself up to go and humble myself to a nigger; but I done it, and I warnt ever sorry for it afterwards, neither. I didnt do him no more mean tricks, and I wouldnt done that one if Id a knowed it would make him feel that way. As a reader, you can noticeably see the number of lies Huck tells, even conning a few people. However, you can understand the importance of his white lies that led to the protection of Jim against slave-hunters by telling them his father was ill with the smallpox. Huck is also burdened with the fact that Jim considers him his best and only friend in the whole wide world, making him consciensously aware that he must now keep Jim protected under whatever circumstance. Pages 87-88 quotes Hucks attempt at keeping the slave-hunters away from the raft. à ¢Ã¢â€š ¬Ã‚ ¦Only one, sir. .ua85bb40c46207ec8f41a4ac1cb45f497 , .ua85bb40c46207ec8f41a4ac1cb45f497 .postImageUrl , .ua85bb40c46207ec8f41a4ac1cb45f497 .centered-text-area { min-height: 80px; position: relative; } .ua85bb40c46207ec8f41a4ac1cb45f497 , .ua85bb40c46207ec8f41a4ac1cb45f497:hover , .ua85bb40c46207ec8f41a4ac1cb45f497:visited , .ua85bb40c46207ec8f41a4ac1cb45f497:active { border:0!important; } .ua85bb40c46207ec8f41a4ac1cb45f497 .clearfix:after { content: ""; display: table; clear: both; } .ua85bb40c46207ec8f41a4ac1cb45f497 { display: block; transition: background-color 250ms; webkit-transition: background-color 250ms; width: 100%; opacity: 1; transition: opacity 250ms; webkit-transition: opacity 250ms; background-color: #95A5A6; } .ua85bb40c46207ec8f41a4ac1cb45f497:active , .ua85bb40c46207ec8f41a4ac1cb45f497:hover { opacity: 1; transition: opacity 250ms; webkit-transition: opacity 250ms; background-color: #2C3E50; } .ua85bb40c46207ec8f41a4ac1cb45f497 .centered-text-area { width: 100%; position: relative ; } .ua85bb40c46207ec8f41a4ac1cb45f497 .ctaText { border-bottom: 0 solid #fff; color: #2980B9; font-size: 16px; font-weight: bold; margin: 0; padding: 0; text-decoration: underline; } .ua85bb40c46207ec8f41a4ac1cb45f497 .postTitle { color: #FFFFFF; font-size: 16px; font-weight: 600; margin: 0; padding: 0; width: 100%; } .ua85bb40c46207ec8f41a4ac1cb45f497 .ctaButton { background-color: #7F8C8D!important; color: #2980B9; border: none; border-radius: 3px; box-shadow: none; font-size: 14px; font-weight: bold; line-height: 26px; moz-border-radius: 3px; text-align: center; text-decoration: none; text-shadow: none; width: 80px; min-height: 80px; background: url(https://artscolumbia.org/wp-content/plugins/intelly-related-posts/assets/images/simple-arrow.png)no-repeat; position: absolute; right: 0; top: 0; } .ua85bb40c46207ec8f41a4ac1cb45f497:hover .ctaButton { background-color: #34495E!important; } .ua85bb40c46207ec8f41a4ac1cb45f497 .centered-text { display: table; height: 80px; padding-left : 18px; top: 0; } .ua85bb40c46207ec8f41a4ac1cb45f497 .ua85bb40c46207ec8f41a4ac1cb45f497-content { display: table-cell; margin: 0; padding: 0; padding-right: 108px; position: relative; vertical-align: middle; width: 100%; } .ua85bb40c46207ec8f41a4ac1cb45f497:after { content: ""; display: block; clear: both; } READ: The Tempest Epilogue AnalysisWell, theres five niggers run off to-night up , above the head of the bend. Is your man white or black? à ¢Ã¢â€š ¬Ã‚ ¦ Hes white. I reckon well go and see for ourselves. I wish you would, says I, because its pap thats there, and maybe youd help me tow the raft ashore where the light is. Hes sickà ¢Ã¢â€š ¬Ã¢â‚¬ and so is mam and Mary Ann. à ¢Ã¢â€š ¬Ã‚ ¦ Set her back, John, set her back! says one. They backed water. Keep away, boyà ¢Ã¢â€š ¬Ã¢â‚¬ keep to looard. Confound it, I just expect the wind has blowed it to us. Your paps got the small-pox, and you know it precious well. Why didnt you come out and say so? Do you want to spread it a ll over? Not only does he realize Jim is a human, but he also learns that telling a lie can actually do good deeds, depending on the purpose. Much of the novel consists of Huck lying to folks because conscientiously, he feels the need to help those in turmoil such as the robbers on the sinking boat, the daughters of dead Peter Wilks, and such. This insight is part of Hucks learning process as he finds that some of the things the he has been taught contradict what seems to be right. The last and final straw that revealed Hucks maturation was when he was contemplating whether or not he should write to Ms. Watson to notify that Jim was enslaved at the Phelps. Page 206 It was a close place. I took it up, and held it in my hand. I was a-trembling, because Id got to, forever, betwixt two things, and I knowed it. I studied a minute, sort of holding my breath, and then says to myself: All right, then, Ill GO to hellà ¢Ã¢â€š ¬Ã¢â‚¬ and tore it up. It was awful thoughts and awful words, but they was said. And I let them stay said; and never thought no more about reforming. I shoved the whole thing out of my head, and said I would take up wickedness again, which was in my line, being brung up to it, and the other warnt. And for a starter I would go to work and steal Jim out of slavery again; and if I could think up anything worse, I would do that, too; as long as I was in, and in for good, I might as well go the whole hog. The social consequences of his actions had at one point been contemplated, rather than the lessons he learned about equality of men. He was also burdened with the thought that Ms. Watson had never done anything wrong to him and here he was helping her escaped slave. He decides to go to hell for helping a slave escape instead of following societys cruel principles because he had already decided then he was not going to re-enter the civilized world. Although Jim is a slave, Huck has already learned to recognize Jim as a real human being with emotions and deep consideration for his family. Because of these conclusions, he will do anything to fight for his friends rightful freedom. By the middle of the novel, anyone could believe that Huck Finn learned a great lesson of equality and made a complete 360 in becoming a new person. However, this is not so because from the time that Tom Sawyer, Hucks friend from St. Petersburg, returns to the picture, Huck goes back to his indecent ways and disregards Jim as what he once believed him to be, an equal. They both toy around with Jim as they plan his escape from the Phelps. In conclusion, his hard work to fight against the hypocritical ideals of society at the time came right back and sucked him into their beliefs, all to impress his friend. Once he comes back to living in their society, he would no longer feel like he would have a say in his way of life and ideals especially the fact that Aunt Sally was going to civilize him. This idea of being captivated and made to be civilized does not suit Huck, he plans to run away to the west to escape all that burdens him in this society.