Fuzzy Polar Dynamic Voltage Restorer as Voltage Sag Restorer and Active Filter Without Zero Sequence Blocking

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1 Fuzzy Polar Dynamic Voltage Restorer as Voltage Sag Restorer an Active Filter Without Zero Sequence Blocking Margo P, M Hery P, M Ashari, Zaenal P *),Takashi Hiyama **) *) Dept. of Electrical Eng, Sepuluh Nopember Institute of Technology, Inonesia **) Dept of Electrical Eng an Computer Science, Kumamoto University, Japan margo@ee.its.ac.i, margo_pujiantara@yahoo.com Abstract: Dynamic Voltage Restorer (DVR) is a power electronic evice to protect sensitive loas from voltage sag. Commonly, sensitive loas are electronic-base evices which generate harmonics. Typical DVR works in stanby moe when no fault occurs. This paper presents fuzzy polar base DVR as voltage sag restorer an also voltage istortion compensator cause by harmonics. In a system with groune neutral, voltage sag is extremely affecte by zero sequence component. To avoi the effect of zero sequence component, typically DVR employs zero blocking metho using eltaconnecte blocking transformer installe between the supply an the booster transformer. Research present in this paper uses -q-0 axis metho consiering the value of neutral axis, because the metho works very well if the neutral axis value is zero. Result shows that this metho can compensate voltage sag with a compensation error of 0.99%. Using this metho, DVR may reuce voltage THD from 0.22% to 0.66%. Keywors: voltage sag harmonics DVR - fuzzy polar. Introuction Two of the main problems in the fiel of power quality are voltage sag an instantaneous power loss. Two main parameters concerning voltage sag are magnitue an uration. Typically, DVR voltage injection metho is use to compensate the ifference between voltage when sag occurs an when before sag occurs, using AC voltage in series [Arora, 998]. Another metho is to inject voltage in phase with supply voltage when sag occurs [Abi, 996]. The avantage of both methos is that it uses economical energy storage, yet it has isavantage of the occurrence of phase shift. Voltage sag cause by symmetrical phase fault can be overcome by DVR employing backpropagation neural network control [Margo, 2005]. This metho compensate very well, but it neee a relatively long time. Conventional fuzzy logic controller [Jurano, 200] can reuce the time neee; however this controller neee many membership functions. Some

2 researches have been one to ecrease the number of membership functions, for example by the use of fuzzy polar controller. Fuzzy polar metho coul ecrease the number of conventional fuzzy logic membership functions [Margo, 2007]. Many previous researchers were using zero sequence blocking system, by installing wye-elta transformer to block zero current or voltage so that the sensitive loa will not be affecte. This was one because of the ifficulty to eliminate zero sequence. Using the blocking transformer will make it easier to eliminate zero sequence effect, but this solution is relatively expensive. By this reason, another solution without blocking transformer is evelope. This paper presente DVR with fuzzy polar controller which concerns zero sequence current compensation to compensate voltage sag an harmonics in low voltage istribution system by employing zero sequence unblocking system. Simulation result showe that this controller coul compensate voltage sag an harmonics very well uner conition of symmetrical an unsymmetrical fault without using zero sequence blocking. 2. Dynamic Voltage Restorer (DVR) DVR is power electronic evice installe in series with istribution system line as can be seen in Figure. DVR uses semiconuctor evice to maintain voltage of sensitive loa by injecting voltage whose magnitue, phase, an frequency can be controlle. How a DVR works to compensate harmonics is shown in Figure 2. From Figure an Figure 2 it can be seen that DVR Figure. DVR topology as voltage sag compensator DVR Figure 2. DVR topology as harmonics compensator the topology of DVR as voltage sag compensator is similar to that of as harmonics compensator. Therefore, the DVR can compensate both voltage sag an voltage istortion cause by harmonics. Zero sequence unblocking system use for simulation is epicte in Figure. It can be seen that the sensitive loa is irectly connecte to istribution system. Instea of the elta transformer as zero sequence isolation, DVR is installe in between. Sensitive loa is represente by non linear loa (6-pulse-rectifier) an installe in bus C.

3 Sensitive loa Figure. DVR using zero sequence unblocking Voltage is injecte to bus C through a booster transformer when sag occurs ue to fault in bus A or when voltage istortion cause by harmonics exists. Therefore, the sensitive loa is protecte from sag. At the other sie, voltage harmonics generate by sensitive loa will not propagate to the source.. DVR Control.. DVR as sag restorer Fuzzy polar application metho is applie to replace the conventional PI compensator. In this research, fuzzy polar is use as control for DVR. Fuzzy polar metho has been evelope for control application in power system [Hiyama, 994]. Fuzzy polar consists of basic parameters: erivative multiplier (A s ), the angle membership function (, an raius membership function (Dr). Operation values of polar coorinate are shown in equations to. p(k) [Z s(k) As Za(k)] () 2 2 D( k ) Z ( k ) ( A.Z ( k )) (2) s ( k ) tan As.Za( k )/ Zs( k )) () Given the input signal Z s, the controller nees the signal erivative to get Z a. Point p(k) is represente by input Z s as x axis an Z a as y axis. To be use for fuzzy polar controller, input form p(k) in rectangular form shoul be converte to polar form, D(k) as magnitue an (k) is the angle. The polar form of fuzzy polar is shown in Figure 4. Three other factors which is also neee in this control system is maximum control signal Umax, sampling time T, an elay time DT. These parameters are often explaine by external criteria. Defuzzification rule for the control system is shown in equation 4 [Hiyama, 994]. s a

4 U ( k) G( D( k))[ N( ( k)) P( ( k))]. Umax (4) Switching Line /2 /2 Sector B O As. Za(k) 45 D(k) p(k) (k) Figure 4. Polar Form Sector A Zs(k) Umax shows the maximum allowable control signal. G(D(k)) shows the membership value of magnitue D(k), while N((k)) an P((k)) show membership value of the angle (k). Membership function of fuzzy polar is shown in Figure 5. grae grae N( ) α 90 P( ) Degree 0.0 D ( k ) G( D ( k)) Magnitue 5 80 Figure 5. Fuzzy Polar Membership Function The moel in Figure 6 is the simple moel of fuzzy polar with input an output. In reality, there is only one input, Zs. But it nees erivative signal Z a so that it can be converte to polar coorinate as shown in figure 4. Fuzzy polar Output (U) is explaine in equation 4. Input Signal t Za Zs Rule Fuzzy Polar Figure 6. Fuzzy polar control iagram Conversion of a-b-c axis to -q-0 makes it easier for the control system to work, because time-varying parameters are converte to constant parameters. Consequently, it gives goo result in sag compensating. Conversion of a-b-c axis to -q-0 can be seen in equation 5. v v v q 2 sin cos sin cos 2 2 sin 2 cos 2. U v a v b v c Figure 7 shows simulation moel of sag compensator (in fig ) iagram block. Voltage sag restorer metho employe is the comparison between real time voltage an voltage in a-b-c axis converte to -q-0 axis, using -q-0 reference voltage. Reference voltages are taken of Vref=, Vqref=0 an V0ref=0. The ifference is the error signal which shows the value of voltage rop. It is clear that not only -q voltage is being compensate as many researches i, but also, q, an 0, so that the asymmetrical voltage sag (consisting of zero sequence component) can be restore. Error signal (5)

5 Vabc abc to q0 V ref Vq ref V0 ref Error (V) Error q (Vq) Error 0(V0) t t V' Vq' t V0' To Polar Coorinate Fuzzy Polar Rule Fuzzy Polar Controller V Vq V0 q0 to abc SPWM Energy Storage Inverter Injection Tegangan Voltage Injeksi Figure 7. Voltage regulator block iagram V, V, Vq, Vq, V0, an V0 are then converte to polar -q-0 form using polar block, q polar block, an 0 polar block in Figure 4, applying eqs., 2, an. The result becomes the input of fuzzy polar control. Result of error compensation from fuzzy polar control is control signal which shows the value of the voltage will be injecte to the system by the inverter..2. DVR as voltage harmonics compensator DVR control as voltage harmonics compensator is similar to that of as sag compensator, with a ifference in voltage feeback sie. In sag compensator, the feeback voltage use is the measure voltage before the booster, while in harmonics compensator (active filter), the feeback voltage the voltage in the loa sie. So, by using this metho, all istortion signal cause by harmonics will be compensate. The value of harmonics voltages injection to the system is shown in equations 6, 7, 8. V h = V act - V f (6) V qh = V qact - V qf (7) V 0h = V 0act V 0f (8) The values of harmonics voltages V h, V qh, V 0h are obtaine by comparing measure voltages V act, V qact, V 0act with funamental voltages (50 hz) V f, V qf, V 0f. The value of funamental voltage V f =, V qf = 0, an V 0f = Simulation an Result Simulation is performe using Matlab SimPowerSystem. Simulation uration is 4 cycles, an the simulation results of the conition with an without fuzzy polar DVR are compare. Parameters of fuzzy polar are shown in table an table 2. Table, Fuzzy Polar Parameters for Sag Compensator Fuzzy Polar Parameter No Direct input Quarature input q Zero input 0. As Dr. α 90º 90º 90º 4. Umax It is simulate that a short circuit fault occurs in bus A for 2 cycles, which causes voltage sag. Sensitive loa (non linear loa) in bus C will generate harmonics in bus C. DVR installation in bus C (sensitive

6 loa bus) is intene to restore the voltage which is istorte by sag an harmonics. Table 2. Fuzzy Polar Parameters for Harmonics Compensator Fuzzy Polar Parameter No Direct input Quarature input q Zero input 0. As Dr α 90º 90º 90º 4. Umax Normal conition (without sag) Figure 8 shows voltage profile at bus C which is istorte by harmonics. Figure 9 shows voltage profile at bus C after fuzzy polar DVR installation. Figure 0. Iniviual harmonics before DVR Figure. Iniviual harmonics after DVR t (secon) Figure 8. Distorte voltage at bus C Uner Sag Conition To see the DVR performance as sag restorer, sags of 0%, 50%, an 70% in bus C will be simulate. Figure 2 shows voltage profile at bus C when 50 % sag occurs, cause by -phase fault in bus A.. Figure shows voltage profile after DVR installation. t (secon) Figure 9. Voltage at bus C after DVR Voltage profile in Figure 8, has THD of 0.22%. After voltage restoration using fuzzy polar DVR, THD ecreases to 0.66%. Figure 0 an show iniviual harmonics before an after DVR installation. t (secon) Figure 2. 50% sag at bus C cause by - phase fault. t (secon) Figure. 50% sag voltage at bus C restore by DVR

7 From Figure, it can be seen that the DVR can restore the voltage up to % an voltage THD becomes.5%. 50% voltage sag cause by phase-phase-groun fault an the compensate voltage are shown in Figure 4 an Figure 5, while in Figure 6 it is shown the value of zero sequence voltage in bus C which is cause by phase-phase-groun in bus A. Figure 7 shows the value of zero sequence voltage at bus C after installation of unblocking DVR. Using this zero sequence compensation metho, the asymmetrical voltage sag can be restore without zero blocking transformer. t (secon) Figure 4. 50% sag at bus C cause by phase-phase-groun fault. t (secon) Figure 5. 50% sag at bus C (cause by phase-phase-groun fault) restore by DVR. t (secon) Figure 6. Zero sequence voltage at bus C cause by phase-phase-groun. Figure 7. Zero sequence voltage at bus C cause by phase-phase-groun after DVR Fuzzy polar DVR can restore the voltage up to % as seen in Figure 5. Voltage THD at the faulte phase ecreases to.55%. From Figure 6 an Figure 7 we can see that the value of zero sequence voltage ecreases from 0. pu to 0.04 pu after the installation of the DVR. Figure 8 shows voltage profile at bus C when groun fault occurs. t (secon) t (secon) Figure 8. 70% sag at bus C cause by groun fault. t (secon) Figure 9. 50% sag at bus C (cause by phase-phase-groun fault) restore by DVR In Figure 9, DVR can restore voltage sag up to 98.94%, an voltage THD at the faulte phase ecreases to 2.48%. Several types of fault have been simulate an the result can be seen in table. The table shows that DVR can

8 restore voltage sag as well as compensate the voltage istortion cause by harmonics. Sags cause by both symmetrical an asymmetrical fault can be restore well. Table, Voltage sag an harmonics restoration Voltage Fuzzy Polar DVR Sag Restoration (%) Error (%) THD (%) 0 % GF % GF % GF % 2F % 2F % 2F % 2FG % 2FG % 2FG % F % F % F GF : groun fault. 2F : phase-phase fault 2FG : phase-phase-groun fault F : -phase-fault Simulation results show that fuzzy polar DVR can restore both symmetrical an asymmetrical voltage sag very well, without zero blocking transformer. An it can compensate the voltage harmonics as well. 5. Summary Simulation results show that DVR can restore both the voltage sag an voltage harmonics. Uner normal conition, DVR is able to ecrease voltage THD from 0.22 % to 0.66%. An using the propose metho, DVR can restore asymmetrical voltage sag without zero blocking transformer. The average error of DVR voltage sag compensation is 0.99%. 6. References Abi-Samra, N., an Sunaram, A., 996, The istribution system ynamic loas, Westinghouse Electric Corporation, Technical Report. Arora, A., Chan, K., Jauch, T., Kara, A., an Wirth, E., 998, Innovative system solutions for power quality enhancement, ABB Review. Fransisco Jurao, manuel Valvere, May 200, Voltage Correction By Dynamic Voltage Restorer Base on Fuzzy Logic Controller IEEE Transaction on Inutrial Electronics. Margo P, M Hery P, M Ashari, Imana, 2005, Dynamic Voltage Restorer Using Y connecte Boost Transformer Controlle by Backpropagation Neural Network SMELDA, Malang. Margo P, M Hery P, M Ashari, T Hiyama, September 2007, Balance Voltage Sag Correction using Dynamic Voltage Restorer Base on Fuzzy Polar Controller, ICICIC 2007 Conference Proceeings, Kumamoto Japan. Hiyama, T., 994, Robustness of Fuzzy Logic Power System Stabilizers Applie to Multimachine Power Systems, IEEE Trans. on Energy Conversion, Vol. 9, No., pp