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    • International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING & ISSN 0976 – 6553(Online) Volume 4, Issue 6, November - December (2013), © IAEME TECHNOLOGY (IJEET) ISSN 0976 – 6545(Print) ISSN 0976 – 6553(Online) Volume 4, Issue 6, November - December (2013), pp. 83-93 © IAEME: www.iaeme.com/ijeet.asp Journal Impact Factor (2013): 5.5028 (Calculated by GISI) IJEET ©IAEME www.jifactor.com LOAD REACTIVE POWER COMPENSATION USING UPQC WITH PAC - VDC CONTROL 1 SALOMIPUSHPARAJ, 1 2 Dr. D. MARY, Research Scholar, 2 Professor, 3 C. JEGADESWARREDDY 3 PG Scholar Arulmigu Meenakshi Amman College of Engineering, Sri Sapthagiri Institute of Technology ABSTRACT Power quality has become an important issue for several reasons e.g. modern society’s growing dependence on electricity and the fact that the poor power quality may generate significant economic losses in few moments. Probable power quality problems are harmonic, flicker, voltage dips and supply interruptions. The power quality may be improved by using filters and compensators. This thesis introduces a new concept of optimal utilization of a unified power quality conditioner (UPQC). The series inverter of UPQC is controlled to perform simultaneous 1) voltage sag/swell compensation and 2) load reactive power sharing with the shunt inverter. The active power control approach is used to compensate voltage sag/swell and is integrated with theory of power angle control (PAC) of UPQC to coordinate the load reactive power between the two inverters. Since the series inverter simultaneously delivers active and reactive powers, this concept is named as UPQC-S (S for complex power).Detailed mathematical analysis, to extend the PAC approach for UPQC-S, is presented in this thesis. In PAC to analyze the voltage sag and voltage swell conditions. Parameter estimation of series and shunt inverter also observed in voltage sag and swell conditions. Phase angle and magnitudes also calculated. MATLAB/SIMULINK-based simulation results are discussed to support the developed concept. Finally, the proposed concept is validated with a digital signal processor-based experimental study. Index Terms: Active Power Filter (APF), Power Angle Control(PAC), Power Quality, Reactive Power Compensation, Unified Power Quality Conditioner (UPQC), Voltage Sag And Swell Compensation. I. INTRODUCTION Power quality issues are becoming more and more significant in these days because of the increasing number of power electronic devices that behave as nonlinear loads. A wide diversity of 83
    • International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 6, November - December (2013), © IAEME solutions to power quality problems is available for both the distribution network operator and the end use. The power processing at source, load and for reactive and harmonic compensation by means of power electronic devices is becoming more prevalent due to the vast advantages offered by them. The shunt active power filter (APF) is usually connected across the loads to compensate for all current related problems such as the reactive power compensation, power factor improvement, current harmonic compensation and load unbalance compensation, whereas the series active power filter is connected in a series with a line through series transformer. It acts as controlled voltage source and can compensate all voltage related problems, such as voltage harmonics, voltage sag, voltage swell, flicker, etc. UPQC is a Custom Power Device and consists of combined series active power filter that compensates voltage harmonics, voltage unbalance, voltage flicker, voltage sag/swell and shunt active power filter that compensates current harmonics, current unbalance and reactive current Unified Power Quality Conditioner is also known as universal power quality conditioning system, the universal active power line conditioner and universal active filte. UPQC system can be divided into two sections: The control unit and the power circuit. Control unit includes disturbance detection, reference signal generation, gate signal generation and voltage/current measurements. Power circuit consists of two Voltage source converters, standby and system protection system, harmonic filters and injection transformers. Fig:1. Unified power quality conditioner (UPQC) system configuration The voltage sag/swell on the system is one of the most important power quality problems. The voltage sag/swell can be effectively compensated using a dynamic voltage restorer, series active filter, Unified power quality conditioner, etc., among the available power quality enhancement devices, the Unified power quality conditioner has better sag/swell compensation capability. Three significant control approaches for Unified power quality conditioner can be found to control the sag on the system: 1) active power control approach in which an in-phase voltage is injected through series inverter, popularly known as UPQC-P; 2) reactive power control approach in which a quadrature voltage is injected [4], [5], known as UPQC-Q; and 3) a minimum VA loading approach in which a series voltage is injected at a certain angle, in this paper called as UPQC-VAmin. Among the aforementioned three approaches, the quadrature voltage injection requires a maximum series injection voltage, whereas the in-phase voltage injection requires the minimum voltage injection magnitude. In a minimum VA loading approach, the series inverter voltage is injected at an optimal angle with respect to the source current. Besides the series inverter injection, the current drawn by 84
    • International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 6, November - December (2013), © IAEME the shunt inverter, to maintain the dc link voltage and the overall power balance in the network, plays an important role in determining the overall UPQC VA loading. The reported paper on UPQC-VAmin is concentrated on the optimal VA load of the series inverter of UPQC especially during voltage sag condition. Since an out of phase component is required to be injected for voltage swell compensation, the suggested VA loading in UPQC-VAmin determined on the basis of voltage sag, may not be at optimal value. A detailed investigation on VA loading in UPQC-VAmin considering both voltage sag and swell scenarios is essential. In the paper, the authors have proposed a concept of power angle control (PAC) of UPQC. The PAC concept suggests that with proper control of series inverter voltage the series inverter successfully supports part of the load reactive power demand, and thus reduces the required VA rating of the shunt inverter. Most importantly, this coordinated reactive power sharing feature is achieved during normal steady-state condition without affecting the resultant load voltage magnitude. The optimal angle of series voltage injection in UPQC-VAmin is computed using lookup table or particle swarm optimization technique. These iterative methods mostly rely on the online load power factor angle estimation, and thus may result into tedious and slower estimation of optimal angle. On the other hand, the PAC of UPQC concept determines the series injection angle by estimating the power angle δ. The angle δ is computed in adaptive way by computing the instantaneous load active/reactive power and thus, ensures fast and accurate estimation. II. UNIFIED POWER FLOW CONTROLLER The UPFC is a combination of a static compensator and static series compensation. It acts as a shunt compensating and a phase shifting device simultaneously. Fig: 2. Principle configuration of an UPFC The UPFC consists of a shunt and a series transformer, which are connected via two voltage source converters with a common DC-capacitor. The DC-circuit allows the active power exchange between shunt and series transformer to control the phase shift of the series voltage. This setup, as shown in Figure 4.13, provides the full controllability for voltage and power flow. The series converter needs to be protected with a Thyristor bridge. Due to the high efforts for the Voltage Source Converters and the protection, an UPFC is getting quite expensive, which limits the practical applications where the voltage and power flow control is required simultaneously. 85
    • International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 6, November - December (2013), © IAEME III. OPERATING PRINCIPLE OF UPFC The basic components of the UPFC 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. Fig :3. A basic UPFC functional scheme The series inverter is controlled to inject a symmetrical three phase voltage system (Vse), of controllable magnitude and phase 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 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 UPFC 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. The two VSI’s 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 low on the transmission line. The UPFC has many possible operating modes. In particular, the shunt inverter is operating in such a way to inject a controllable current, ish into the transmission line. The shunt inverter can be controlled in two different modes: 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. 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. For this mode of control, voltage feedback signals are obtained from the sending end bus feeding the shunt coupling transformer. 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. 86
    • International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 6, November - December (2013), © IAEME 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 P and Q to maintain on the transmission line despite system changes. III. SIMULATION RESULTS The performance of the proposed concept of simultaneous load reactive power and voltage sag/swell compensation has been evaluated by simulation. To analyse the performance of UPQC-S, the source is assumed to be pure sinusoidal. Furthermore, for better visualization of results the load is considered as highly inductive. The supply voltage which is available at UPQC terminal is considered as three phase, 60 Hz, 600 V (line to line) with the maximum load power demand of 15 kW + j 15 kVAR (load power factor angle of 0.707 lagging). The simulation results for the proposed UPQC-S approach under voltage sag and swell conditions are given Before time t1, the UPQC-S system is working under steady state condition, compensating the load reactive power using both the inverters. A power angle δ of 21◦ is maintained between the resultant load and actual source voltages. The series inverter shares 1.96 kVAR per phase (or 5.8 kVAR out of 15 kVAR) demanded by the load. Thus, the reactive power support from the shunt inverter is reduced from 15 to 9.2 kVAR by utilizing the concept of PAC. In other words, the shunt inverter rating is reduced by 25% of the total load kilovoltampere rating. At time t1 = 0.6 s, a sag of 20% is introduced on the system (sag last till time t = 0.7 s). Between the time period t = 0.7 s and t = 0.8 s, the system is again in the steady state. A swell of 20% is imposed on the system for a duration of t2 = 0.8–0.9 s. Fig: 4. Simulation Block Diagram 87
    • International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 6, November - December (2013), © IAEME DVR CIRCUIT: Fig:5. DVR sub circuit Voltage and power factor angle: Fig: 6. voltage and power factor angle sub circuit 88
    • International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 6, November - December (2013), © IAEME Simulation time period is 0.95secc. Fig: 7. Supply voltage In the above Supply Voltage The sag occurs in the time period of 0.6ssec to 0.7sec and 07.sec to 0.8sec stead state occurs. 0.8sec to 0.9sec the swell occurs. Here voltage decreases current increases. Fig:8. Load voltage In the above simulation of Load voltage is pure sinusoidal wave foram occurs because any faults occurs in the Load side the .UPQC compensate the faults. Fig:9. Self supporting dc bus voltage In the above dc bus voltage sag occurs 0.6sec to 0.7sec and swell occurs 0.8sec to 0.9sec. 89
    • International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 6, November - December (2013), © IAEME Fig: 10. Supply current In the supply current swell occurs 0.6sec to 0.7sec.here first swell occurs because voltage decreases and current increases. 0.8sec to 0.9sec swell occurs. Fig: 11. Shunt inverter injected current In shunt inverter injected current faults are Occurred.sag occurred in time period of 0.6sec to 0.7sec. swell occurred 0.8sec to 0.9sec. Fig: 12. Series inverter P and Q In series inverter active and reactive powers are increases in 0.6sec to 0.7sec due to increase of the load current. Active and reactive powers are decreased in time period 0.8 sec to 0.9 sec. 90
    • International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 6, November - December (2013), © IAEME Fig:13. Shunt Inverter P and Q In the above shunt inverter and active and reactive powers are shown. In shunt inverter reactive power is decreased at that time active power is increased. With vdc controller Simulation results: Fig:14. Self supporting dc bus voltage In self supporting dc bus voltage using dc regulater transient response is decreased and system dynamic performance increased. Fig:15. Series inverter P and Q using the dc regulater of series active and reactive powers are transient response is decreased. System starting period also decreased. 91
    • International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 6, November - December (2013), © IAEME Fig:16. Shunt inverter P and Q In shunt inverter active and reactive power are shunt reactive power is increased series active power decreased. System dynamic performance increases. REFERENCES [1] Y. Chen, C. Lin, J. Chen, and P. Cheng, “An inrush mitigation technique of load transformers for the series voltage sag compensator,” IEEE Trans. Power Electron., vol. 25, no. 8, pp. 2211–2221, Aug. 2010. [2] S. Subramanian and M. K. Mishra, “Interphase AC–AC topology for voltage sag supporter,” IEEE Trans. Power Electron., vol. 25, no. 2, pp. 514–518, Feb. 2010. [3] H. Fujita and H. Akagi IEEE Trans. Power Electron., vol. 13, no. 2, pp. 315–322, Mar. 1998. [4] V. Khadkikar and A. Chandra, “A new control philosophy for a unified power quality conditioner (UPQC) to coordinate load-reactive power demand between shunt and series inverters,” IEEE Trans. Power Del., vol. 23, no. 4, pp. 2522–2534, Oct. 2008. [5] M. Vilathgamuwa, Z. H. Zhang, and S. S. Choi, “Modeling, analysis and control of unified power quality conditioner,” in Proc. IEEE Harmon. Quality Power, Oct. 14–18, 1998, pp. 1035–1040. [6] D. Bala Gangi Reddy and M. Suryakalavathi, “Availability Transfer Capability Enhancement using Static Synchronous Series Compensator in Deregulated Power System”, International Journal of Electrical Engineering & Technology (IJEET), Volume 3, Issue 2, 2012, pp. 12 - 28, ISSN Print: 0976-6545, ISSN Online: 0976-6553. [7] M. Gon, H. Liu, H. Gu, and D. Xu, “Active voltage regulator based on novel synchronization method for unbalance and fluctuation compensation,” in Proc. IEEE Ind. Electron. Soc (IECON), Nov. 5–8,, 2002, pp. 1374–1379. [8] M. S. Khoor and M. Machmoum, “Simplified analogical control of a unified power quality conditioner,” in Proc. IEEE Power Electron. Spec. Conf. (PESC), Jun., 2005, pp. 2565–2570. [9] V. Khadkikar, A. Chandra, A. O. Barry, and T. D. Nguyen, “Analysis of power flow in UPQC during voltage sag and swell conditions for selection of device ratings,” in Proc. IEEE Electr. Computer Eng. (CCECE), May 2006, pp. 867–872. [10] Laith O. Maheemed and Prof. D.S. Bankar, “Harmonic Mitigation for Non-Linear Loads using Three-Phase Four Wire UPQC Control Strategy”, International Journal of Electrical Engineering & Technology (IJEET), Volume 3, Issue 1, 2012, pp. 247 - 260, ISSN Print: 0976-6545, ISSN Online: 0976-6553. [11] B. Han, B. Bae, H. Kim, and S. Baek, “Combined operation of unified power-quality conditioner with distributed generation,” IEEE Trans. Power Del., vol. 21, no. 1, pp. 330–338, Jan. 2006. 92
    • International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 6, November - December (2013), © IAEME [12] H. R. Mohammadi, A. Y. Varjani, and H. Mokhtari, “Multiconverter unified power-quality conditioning system:MC-UPQC,” IEEE Trans. Power Del., vol. 24, no. 3, pp. 1679–1686, Jul. 2009. [13] Satyendra Kumar, Dr.Upendra Prasad and Dr.Arbind Kumar Singh, “Reactive Power Management and Voltage Control using Facts Devices”, International Journal of Electrical Engineering & Technology (IJEET), Volume 4, Issue 1, 2013, pp. 184 - 189, ISSN Print: 0976-6545, ISSN Online: 0976-6553. [14] I. Axente, J. N. Ganesh, M. Basu, M. F. Conlon, and K. Gaughan, “A 12-kVA DSPcontrolled laboratory prototype UPQC capable of mitigating unbalance in source voltage and load current,” IEEE Trans. Power Electron., vol. 25, no. 6, pp. 1471–1479, Jun. 2010. [15] M. Basu, S. P. Das, and G. K. Dubey, “Investigation on the performance of UPQC-Q for voltage sag mitigation and power quality improvement at a critical load point,” IET Generat., Transmiss. Distrib., vol. 2, no. 3, pp. 414–423, May 2008. [16] K.Pounraj, Dr.V.Rajasekaran and S.Selvaperumal, “Fuzzy Co-Ordination of UPFC for Damping Power System Oscillation”, International Journal of Electrical Engineering & Technology (IJEET), Volume 3, Issue 1, 2012, pp. 226 - 234, ISSN Print: 0976-6545, ISSN Online: 0976-6553. [17] V. Khadkikar and A. Chandra, “A novel control approach for unified power quality conditioner Q without active power injection for voltage sag compensation,” in Proc. IEEE Int. Conf. Ind. Technol. (ICIT), Dec. 15–17, 2006, pp. 779–784. [18] M. Yun, W. Lee, I. Suh, and D. Hyun, “A new control scheme of unified power quality compensator-Q with minimum power injection,” in Proc. IEEE Ind. Electron. Soc. (IECON), Nov. 2–6,, 2004, pp. 51–56. [19] Y. Y. Kolhatkar and S. P. Das, “Experimental investigation of a singlephase UPQC with minimum VA loading,” IEEE Trans. Power Del., vol. 22, no. 1, pp. 373–380, Jan. 2007. 93