Simulation of Interline Dynamic Voltage Restorer for Sag/Swell Compensation and Power factor Improvement in Hybrid Electric System

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1 Simulation of Interline Dynamic Voltage Restorer for Sag/Swell Compensation and Power factor Improvement in Hybrid Electric System Mr.A.Mohammad Ovaiz Assistant Professor DR.RR, DR.SR Engineering college Chennai Kanaka Divya. V DR.RR, DR.SR Engineering College Chennai. Kankadivya48@gmail.c om Abstract This paper has highly beneficial in application oriented and mainly deals with improving the power quality on the distribution side in remote areas using an interline dynamic voltage restorer (IDVR).This IDVR is made up of several DVRs with a common dc link. When the voltage sags/ swells the active power from one feeder is transferred to other and this sag or swell for long durations can be mitigated and the Displacement Factor (DF) is very low depending upon the additional burden to the electrical supply side. This will affects the system voltage regulation and utilization of power in system is low. To overcome this limitations, in this paper the DF value is tuned using the power control and voltage control modes. Here the IDVR injects the voltage using PQ sharing which adjusts the DF value and thus the power quality as well as real and reactive power is improved. The performance of the proposed topology is verified by simulating using Mat lab/simulink. Keywords Back-to-Back voltage source Inverter, DVR, Interline Dynamic Voltage Restorer (IDVR), Displacement factor, Common DC link capacitor, power quality I. INTRODUCTION NOWADAYS, a lot of people exertions need aid accomplished for control personal satisfaction change. The voltage sag may be a standout amongst those significant power quality challenges for touchy loads [1]. Depending upon the duration and magnitude of the voltage sag/swell the damages on the consumers will be different. [2], [3]. The secondary costs about these ISSN: Girija. R DR.RR DR.SR Engineering College Chennai. giri30laxmi12@gmai l.com Christina.A Dr.RR,DR.SR Engineering college Chennai harms defend the expanding interest towards voltage sag mitigation techniques. Dynamic voltage restorers (DVRs) is a power electronic device used for compensating the voltage sag mitigation in the distribution side of power system [4]. Voltage sag can be compensated using the DVR by purely injecting a reactive power or combination of active and reactive power, but some amount of voltage drop is only compensated by injecting the reactive power attained. The compensation capacity is mainly depend upon the greatest achievable inverter voltage, the energy stored in the dc link, duration of voltage sag [5]-[8]. The compensation capability with the least energy is limited when the voltage sag exceeds some certain value, which is a function of load power factor [5]. Even though this method reduces energy consumption, the long term and deeper voltage sag cannot be completely compensated by injecting the reactive power. Therefore to have a complete compensation, it is necessary to inject both active and reactive power in distribution side. An interline DVR (IDVR) has been proposed in [9].The IDVR consist of several DVRs with a common DC link. It protects the touchy loads against voltage sags, by locating each DVR in an independent feeder. Therefore one of the DVRs in IDVR starts to compensate the voltage sag,other DVRs replenish the common dc-link voltage. In [10], the capability of DVR is extended to mitigate deeper voltage sags. In this shunt reactance is parallel 8 1

2 connected with the load to decrease the load power factor during the voltage sag condition. Using demonstrated phasor diagram in Fig. 2(a), (1) can be written as, In [11], the capacity of IDVR in compensating the sag at high power factor is improved by two 7-level cascaded H-bridge converters with common dc link. But due to the 24 switches used in the two 7-level cascaded H-bridge (multilevel inverter) the harmonics in each switches are high therefore the loss will be more, efficiency will be reduced and power factor will be less. PDVR1=VL1IL1Cos(ɸ1)-VS1IL1Cos(ɸ1-α) To overcome this limitation, a topology is proposed in this paper which reduces the total harmonics and which not only improves the capacity and ability of compensator to mitigate very deep sags at high and moderate factors and also displacement factor is improved by PQ sharing.in this paper, voltage sag is compensated by using an IDVR which employs two voltage source inverters (12 switches) with a common DC link in a three phase mode as in Fig1. Finally, the validity of the proposed configuration and its effectiveness is verified by simulation and experimental results. (2) Where it is obvious that load current IL1 is equal to source current IS1 due to series connection of DVR1 with load1. When minimum energy method is adopted for sag compensation, (2) is modified as, ME PDVR 1 ifvs 1 VL 1Cos( 1 ) 0 VL 1 I L 1 ( Cos( 1 ) VS 1 / VL 1 ) ifv V Cos( ) S1 L1 1 (3) Moreover, active power which is drown by DVR2 from feeder2 can be derived from Fig. 2(b) as follows, PDVR2 =VL2IL2(Cos(ɸ2-β) -Cos (ɸ2) ) (4) where injected voltage by DVR2 during sag period leads to a phase difference between V L2 and VS2 which is defined as According to (4), the maximum transferable active power is achieved when β is equal to φ2(phase of load2). In this condition, and (4) can be written as max PDVR 2 VL 2 I L 2 (1 Cos( 2 )) (5) Assuming that SL1=ρSL2 and VL1=IL1=1 p.u.,β can be derived from (3) and (4) as 0 Vsag 1 Cos( 1 ) 1 2 Cos ( Cos( 1 ) Cos( 2 ) (Vsag 1)) V sag 1 Cos( 1 ) (6) Fig.1. Schematic diagram of an IDVR with two feeder system II. OPERATING PRINCIPLES OF IDVR Interline Dynamic Voltage Restorer is a power electronic converter based device compensator that can protect touchy loads from disturbances of supply side other than outages. Interline dynamic voltage restorer (IDVR) plays a most important role in mitigating deeper voltage sag in distribution system. The IDVR system consists of several DVRs connected to different feeders with a common dc link, where these two independent feeders can be of the same or different voltage magnitude level. When one of the DVRs compensates for voltage sag, then the other DVR in IDVR system used to replenish the common dc link. Assuming P S1 and PL1 to be source 1 and load 1 active power, then the injected active power by DVR1 would be PDVR1=PL1-PS1 ISSN: (1) Fig.2.Phasor diagram of IDVR during voltage sag compensation (a) DVR1 injecting voltage (b) DVR2 injecting voltage 9 2

3 From (6), it is seen that for sag depth less than 1 Cos (ɸ1) p.u., DVR2 is not involved to power exchange and just DVR1 compensates the sag. But, for sag values greater than 1 Cos (ɸ1) p.u., DVR2 starts to exchange active power from feeder2 to feeder1 and participates in the compensation. In this case, the maximum value of β is φ2and the maximum voltage sag that can be compensated is obtained by ME max max PDVR 1 PDVR 2 Vsag 1 1 (Cos ( 1 ) Cos ( 2 )) (7) In other words, for voltage sags greater than Vsagmaxp.u., IDVR is not capable to compensate it completely. III. MODEL SYSTEM The maximum power at DVR2 depends on the load power factor and at Cos(φ2),(i.e.,) the injection of active power is limited at high power factors and due to the more no of switches used in multilevel inverter the switching losses and harmonic distortions are high. To overcome this limitations and to improve the performance of IDVR, the load power factor has to decrease during the sag period. To overcome this issues, the two three phase voltage source inverter based IDVR is used and the fixed inductance with reactive power is connected paralleled to each load. To determine the real and reactive power for improving the displacement factor by PQ sharing the fixed inductance is paralleled to each load. subtracted for phase angle(φ).for real power, both magnitude and angle is multiplied by cosine and for reactive power both magnitude and angle is multiplied by sine. IV. VSI BASED IDVR The two three phase voltage source inverter is used instead of using single Z source inverter and Cascaded H-Bridge multilevel inverter. The Z source inverter is connected commonly for two feeder lines, whereas in this the three phase voltage source inverter is connected separately for each feeder line. So that if the voltage sag occurs in each line can be compensated completely. In cascaded H-bridge multilevel inverter consist of 24 switches so that switching losses will be high and harmonics also be high whereas in this proposed scheme totally 12 switches are used. Therefore switching losses is less and total harmonic distortion is also. In this two 3 phase voltage source inverter, VSI 1 is connected to feeder line 1 and VSI 2 is connected to feeder line2. If voltage sag is occurred in feeder 1 then VSI1 is used to compensate and VSI2 is used to replenish the common dc link. Similarly if voltage sag is occurred in feeder 2 then VSI2 is used to compensate the voltage sag and VSI1 is used to replenish the common dc link. The switching operation: there are six combinations of conducting switches during an will be shown later the fundamental component of the three output cycle:(sw5, Sw6, Sw1), (Sw6, Sw1, Sw2), (Sw1, Sw2, Sw3), (Sw2, Sw3, Sw4), (Sw3, Sw4, Sw5), (Sw4, Sw5, Sw6). The output from this inverter is to be fed to a 3-phase balanced load Fig.3. Block diagram of proposed system As shown in above fig (3), the voltage and current from the inductance of each feeder line is carried out. By using Fast Fourier Transform the magnitude and phase shift of voltage and current are determined. Then magnitude of both voltage and current are multiplied and phase shift of current and voltage are ISSN: 10 3

4 Fig.4.schematic diagram of 3 phase VSI Fig.6.Grid Voltage at Condition in Distribution Line1 Here this inverter is used to inject the real power into the series transformer which is connected in feeder line when the voltage sag is occurred in the line. When the voltage swell occurs the voltage will be stored in the capacitor which is connected with common dc link voltage (130v). This DC link capacitor is replenished by one of the DVR in the IDVR system. V. Parameters of under experiment system Parameters Modulation Switching frequency PFs of the loads DC-link capacitor Value Phase shifted PWM 1KHz µF Total DC-link voltage Rated voltage (rms) 130v 415v Inductance value 1mH V. SIMULATION RESULT The detailed investigate of IDVR system consists of different feeder with parameter to be carried out using MATLAB/SIMULINK. Simulation has been carried out in IDVR system consisting of two line of 200v voltage. The restoration capability and performance of IDVR was tested by simulation using MATLAB/SIMULINK. Initially the IDVR system was subjected to voltage sag 50%. The transient performance of voltage sag front and recovery using simulation were observed also the performance was evaluated when the dc voltage drop during sag. It shows that IDVR using VSI, storage energy in common DC link can be utilized during the voltage compensation with use of boost property of the inverter. ISSN: 11 4

5 Fig.7.Grid Voltage at Condition after injection IDVR in Line 1 Fig.8.Grid Current at Condition in Distribution Line 1 Fig.10.Grid Voltage at Condition in Distribution Line 2 Fig.12.Grid Current at Condition in Distribution Line 2 ISSN: Fig.14.Real & Reactive power at condition before injection IDVR in Line 1 Fig.9Grid Current at Condition after injection IDVR in Line1 Fig11..Grid Voltage at Condition after injection IDVR in Line 2 Fig.13.Grid Current at Condition after injection IDVR in Line1 125

6 Fig.15. Real & Reactive power at condition after injection IDVR in Line1 Fig.16. Real & Reactive power at condition before injection in Line2 VI. CONCLUSION This paper proposes the concept of IDVR, which is an economical approach to improve power quality. In this mode, the DF feeder is improved via active and reactive power exchange (PQ sharing) between feeders through the common dc link. The main conclusion of this work can be summarized as follow: 1. In this mode, IDVR connected parallel to the impedance instead of reactance, the current will be tuned, real power and reactive power are also compensated thus increase the Displacement Factor (DF) When applying the proposed concept, DF of source feeder will have a notable improvement 2. using of minimum switches in inverter in this proposed IDVR, the switching losses is reduced and THD also reduced the harmonics. 3. The proposed mode is highly beneficial in application oriented, here we are using two sources in which one is DC source (solar) which is converted into AC and another one is of direct AC source like diesel power plant/wind mill. While utilize the stored energy (common DC link) with the used of boost convertor capability of the VSI using PI controller. The simulation shows that in IDVR system can mitigate about the deep voltage sag with long duration. The proposed concept has been supported with simulation and experimental result. VII. REFERENCES [1]P.F. Comesana, D.F. Freijedo, J.D. Gandoy, O. Lopez, A.G. Yepes, J. Malvar, "Mitigation of voltage sags, imbalances and harmonics in sensitive industrial loads by means of a series power line conditioner" Electric Power systems Research 84 (2012) [2] A. Felce, S. A. C. A. Inelectra, G. Matas, and Y. ISSN: Da Silva, Voltage Sag Analysis and Solution for an Industrial Plant with Embedded Induction Motors, In Industry Applications Conference, th IAS Annual meeting, conference record of 2004 IEEE, vol. 4, pp Fig17. Real & Reactive power at condition after injection IDVR in Distribution Line2 [3] A. Sannino, M. G. Miller, and M. H. J. Bollen, "Overview of voltage sag mitigation", Proc. IEEE Power Eng. Soc. Winter Meeting, vol. 4, pp [4] E. Babaei, M. F. Kangarlu, and M. Sabahi, Mitigation of voltage disturbances using dynamic voltage restorer based on direct converters, IEEE Trans. Power Del., vol. 25, no. 4, pp , Oct [5] D. M. Vilathgamuwa, A. A. D. R. Perera and S. S. Choi "Voltage sag compensation with energy optimized dynamic voltage restorer", IEEE Trans. Power Del., vol. 18, no. 3, pp [6] N. A. Samra, C. Neft, A. Sundaram, and W. Malcolm, The distribution system dynamic voltage restorer and its applications at industrial facilities with sensitive loads, in Proc. Power Conversion Intell. Mo-tion Power Quality, Long Beach, CA, Sept [7] S. S. Choi, B. H. Li, and D. M. Vilathgamuwa, Dynamic voltage restoration with minimum energy injection, IEEE Trans. Power System, vol. 15, pp , Feb [8] J. G. Nielsen and F. Blaabjerg, "A detailed comparison of system topologies for dynamic voltage restorers", IEEE Trans. Ind. Appl., vol. 41, no. 5, pp [9] D. Vilathgamuwa, H. Wijekoon and S. Choi "A novel technique to compensate voltage sags in multiline distribution system The interline dynamic voltage restorer", IEEE Trans. Ind. Electron., vol. 53, no. 5, pp [10] M. Moradlou and H. R. Karshenas "Design strategy for optimum rating selection of interline DVR", IEEE Trans. Power Del., vol. 26, no. 1, 13 6

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