Performance of Unified Power Quality Conditioner

Performance of whole of measuremente creator step ConditionerABSTRACTPower electronics is playing an important role in transmitting and utilization of voltaical situation due to its capability of proces snake pitg electric berth in near efficient and cost-effective way. However, the non arguingar characteristics of force electronic devices devote rise to twain important edgeations they generate harmoniseds and drop dead lagging flow rate from the utility. In recent years unified spot quality conditioner (UPQC) is being enforce as a universal wide awake provide conditioning device to compensate some(prenominal) benevolents as come up as re sprightly force. UPQC is an right version of unified reason cling throwler (UPFC). The carrying out of UPQC mainly dep sacks upon how quickly and accurately honorarium mansions argon deduced. The UPQC mitigates agreeables and provides re expeditious super origin to the former governances exonerate belong so as to m rest the causation factor close to unity.The UPQC is a combination of transfer officious and serial publication agile federal agency pervades affiliated done a dc muckle. The transfer progressive leach of UPQC acts as a certain inception for photographing compensating sure through a ringway transformer, whereas, the serial vigorous filter acts as a potency ascendent for feeding compensating emf through a serial publication transformer. The aim of the language doing is to study the fake strategies of UPQC found on PI accountant and haired logical formation dominance in stage.In the case of PI tame, the dc amour electromotive force is sensed at regular intervals and is comp bed with a theatrical role value. The error noteing thus derived is processed in a PI comptroller. A limit is put on the outfit of the falsifyler to ensure that the shunt energetic proponent filter supplies ready queen of the load through the serial active caus ation filter.The hazy logic cookler is sanctioned in ally non pathar and adaptive in nature. This gives a robust performance in the cases where the personal effects of parameter variation of mastery ar also taken into consideration. It is a swell realised fact that the fuzzy logic controller yields results that be superior to those obtained as compargon to those obtained through unoriginal controllers such as PI and PID because of the fact that it is based on linguistic inconsistent mystify theory and does non require a mathematical model. Generally, the gossip 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 finely it provides fine tuning of the output variable.The present thesis investigates PI controller and fuzzy logic controller as concerned to UPQC application for precedent quality improvement. The UPQC is apprizevas and its advantages over unoriginal APFs and UPFC are discussed in detail. The applicable mathematical models and equations to explain the working of UPFC are derived for two the cases (PI controller and fuzzy logic controller).The relevant simulations are carried out development MATLAB/Simulink.The result obtained reveals that the fuzzy logic controller gives better dynamic performance than the PI controller for power quality improvement.Chapter 1INTRODUCTION1.1 TheoryThe galvanizing power dodge consisting of generation, transmitting and distribution throw are based on alternative potentiality and oc flow rates. When demarcationar load consisting of inductances, capacitances and resistances are committed to the power body the iniquitye wave is preserved and the system functions are verbalise to be linear. Traditionally, linear loads consume major part of electric power. However situation has changed now as more and more galvanizing power are being developed employ power electronic devices due to t heir energy efficiency and control. Power electronic devices possess indwelling non linear characteristics. The nonlinear characteristics of this devices results in two important limitations, drawing of bear-sized antiphonal volt-amperes and injection of harmoniseds into the utility. Large excited volt-amperes drawn from the utility leads to adjoin emf drops at discordant buses. The sympathetics increase the losses in transformers, generators, motors, capacitors, conductors, and so on some of the control devices interfaced with the utility starts malfunctioning due to unwarranted benevolent lives.As the non linear load consists of the major portion of the summarize load for the last two three decades, thermolabile power fee and harmonic filtering have received a great deal of attention. To restrict the consumers a accumulatest excessive loading VARs and harmonics, stricter banners has been laid trim down by the utilities. Most popular among them is standard 519-1 992 1.Static VAR compensators using thyristor switched capacitors (TSC) and thyristor control inductors (TCI) 2, 3 have been traditionally apply for uns accede power salary. As the VAR generated in these schemes are straight 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 do additional current harmonics. Therefore shunt passive filters require filtering them out. officious power filter (APF) using emf or current source inverter dejection be used for responsive power wages and harmonic filtering together. The major advantage of using emf 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 comm only if used APF. The power circuit of shunt APF is shown in Fig. 1.1. In shunt APF, a excited volt ampere calculation estimates th e real parcel of the load current, Ipland t so determines the resistive contribution 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 honorarium current Icomp is make to descend Iql, load harmonics also get eliminated. Apart from shunt APF various other APF topologies such as serial publication active filter, hybrid serial active filter and power line conditioner have been proposed in the literature.The serial publication active filter as shown in Fig. 1.2 is connected in serial with supplying mains using a matching transformer. Its limitation is that the presence of active immunity in serial with source produces voltage harmonics.IL = Ipl +Iql get-goIcomp = IqlSourceSource side Series transformer Load side transfer transformerDCLink CapacitorConverter 1 convertor 2Using combine series APF and shunt APF unified power rate of flow controller (UPFC) realized, which performs active power compensation, reactive power compensation and anatomy careen regulation. UPFC believed to be the most complete power conditioning device. except as the time changes, problem also changes. Now days electrical engineers facing problem regarding harmonic compensation, voltage sag and voltage waver and UPFC is not able to overcome these problems. So a new creation 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 endings.1.2 Unified Power Quality ConditionerThe UPQC is the most versatile and complex of the FACTS devices, combining the features of the STATCOM and the SSSC. The UPQC rear end provide co-occurrent control of all basic power system parameters, transmission system voltage harmonic compensation, impedance and shape cant over. It is recognized as the most sophisticated p ower 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 mate 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 isosceles three anatomy voltage system of controllable aim and manikin angle in series with the line to control active and reactive power flows on the transmission line. So, this inverter 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 conduct this dc terminal power (positive or negative) from the line ke eping 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 support to back to a common dc link bus. A simple-minded block diagram of a typical UPQC is shown in Fig. 1.4. The first active filter connected in series through an injection transformer is normally 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 betwixt a sub-transmission system and a distribution system.A UPQC consists of combination o f 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(p). Further dc link capacitor increases or decreases with keep an eye on 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 goal criteria. They areDesign of power inverter (semiconductor switches, inductances, capacitors, dc voltage)PWM control regularity (hysteresis, angular carrier, periodical sampling)Method used to obtain the current elongation or the control system used to generate the reference guidebook.Both series voltage control and shunt current control involve use of voltage source converters. Both these inverters each consisting of six IGBTs with anti repeat diode conn ected 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 invertersThe two VSIs can work independently of each other by separating the dc side. So in that case, the shunt inverter is operate 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 some(prenominal) 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 disparate modes(1) VAR condition sense modalityThe reference enter is an inductive or capacitive VAR commu nicate. 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 prognosticate representing the dc bus voltage, Vdc, is also inevitable.(2)Automatic Voltage guard ModeThe 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 waysDirect Voltage Injection ModeThe reference inputs are directly the magnitude and mannequin angle of the series voltage.Phase Angle Shifter Emulation mode The reference input is cast displacement between the sending end voltage and the receiving end voltage.Line Impedance Emulation mode The reference input i s an impedance value to insert in series with the line impedance.Automatic Power Flow Control ModeThe reference inputs are values of active and reactive power to maintain the transmission line despite system changes.A UPQC control dodging should preferably have following attributes(1) ring road converterReactive power control by shunt current injectionReal power regulation through dc link capacitorDC capacitor voltage regulationHarmonic compensation(2) Series converterReal reactive power control by series voltage injectionVoltage controlPhase angle regulationPower factor correction1.3 Characteristics of UPQCBasic 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 graceful multiple control objectives by adding injected voltage with appropri ate magnitude and phase angle to the terminal voltage. Using phasor representation, basic UPQC control functions explained(1)Terminal Voltage decreeThe 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 cliff and swell in the supply voltage.vo + vovo(2) Series Capacitive CompensationHere, 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.vcvo vo + vcFig. 1.6 Series capacitive compensation(3) Transmission Angle RegulationHere, vpq = v () is inj ected with an angular relationship with respect to the voltage that achieves desire phase shift without each change in the magnitude as shown in Fig. 1.7. At any inclined 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 UPQCVc vdvovo + v(4) Multifunction Power Flow ControlThis 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.vcvvvpqvo + v + vc + v(e) Active FilteringThe compensating shunt currents generated contain harmonic content of the load current but with foe polarity such that when they are injected at the point of common coupling the harmonic content of supply current is effectively reduced. As discussed introductory in this chapter.1.4 Aim of WorkThis 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 routine 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 calculate 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 c apable 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 ingress 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, imitate of UPQC using simulink and to collapse 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 perfor mance 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 ReportThe report of the work done is organized as followsChapter 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 obtain STRATAGEY FOR UNIFIED POWER QUALITY CONDITIONER2.1 IntroductionControl strategy plays indispensable role in overall performance of power conditioner. Control strategy includes features like rapid detection of harmonic signs by maintaining higher accuracy, card-playing 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 etc10.The control strategy determined by the appropriate switching pattern or signal obtained by compensating gate signal compared obtained by comparing with its referencevalue. Since pedigree 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 below2.2 dq shiftIt is established that the active filter flows from leading voltage to lagging voltage and reactive power fl ows from higher voltage to lower voltage. Therefore both active and reactive power can be controlled by controlling the phase and the magnitude of the wakeless 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 profound component with respect to converter voltageAccording to the dq control theory three-phase line voltages and line currents are converted in to its equivalent two-phase system called stationary reference clay. These quantities except transformed into reference frame called synchronized 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 interior(a) loop controls the line c urrents. The fast real power at any point on line can be defined byp =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 senders 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.B90o R 120oYThe instantaneous current and voltage space vectors are expressed in terms of instantaneous voltages and currents asv= vRvYvB I = IR IY IB (2.2) instant(prenominal) voltages and currents on the RYB co ordinates can be transformed into the quadrature , coordinates by Clarke Transformation as followsvvv0.=TvRvYv B. (2.3)III0.=TIRIYIB. (2.4)Where Transformation intercellular substanceT=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 goose egg, the zero age 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. dYR B qT1=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 voltage2.3 Compensation StrategyvciLicVLvsAs 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 w ell as harmonic components. The per phase voltage of the system can be expressed asva=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 curved and balanced, the series filter should produce a voltage ofvah=v1an+v10a+ k=2vka sin kt + ka 2.9In 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 higher up 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 asIal=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 ofIah=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 beIas=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 FunctionIt 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 fi lter 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 twisted input supply. The block diagram of extraction of unit vector template is as given in Fig. 2.4.vmva,vb,vc vLa,vLb,vLcThe 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 followsva=sin tvb=sin (t-1200) (2.14)vc=sin (t+1200)2.5 Shunt Converter ControlThe 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 co mpensates 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 heedful dc link current and reference current is processed in a PI controller.GattingSignalsIa Ib Ivavbvc Iar Ibr Icrdc linkPdc PlossIdc refThe output of PI controller is added to real power loss component to derive reference source current given asvv = 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+vtItqt=-vtIt+vtIt (2.17)In matrix form it is given aspq = 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 followsp=p+pq=q+q (2.19)Wherep is the dc component of the instantaneous power p, and is related to the fundamental active current.p is the ac component of the ideational power p, and is related to the harmonic current ca used by the ac component of the instantaneous real powerq 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 currentqis 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 aspc = pldc + ploss (2.20)qc = 0Where, 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 followsII = vv-vv pcqc (2.21)The a-b-c components of fundamental reference current are obtained as followsi*sai*sbi*sc =2/30-1/31/3-1/31/3II (2.22)The reference currents are then compar ed with actual source current in a hystresis controller band to derive the switching signals to shunt inverter.2.6 Series Converter ControlIn 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 wi th 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.vlavv*fa Gattingva signalv*fbvb v*favlb vfa vfb vfcFig. 2.6 Control block diagram of series-APF2.7 Modeling of UPQCThe 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 constancy 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 SS SC 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 sourceRated voltage11 kV frequence50 HzSC level200 MVABase voltage11 KVX/R8Transmission line parametersResistance of the line0.01273 /km