LOAD REACTIVE POWER COMPENSATION BY USING SERIES INVERTER OF UPQC

Transcription

1 International Journal of Advances in Applied Science and Engineering (IJAEAS) ISSN (P): ; ISSN (E): X Vol-1, Iss.-3, JUNE 2014, IIST LOAD REACTIVE POWER COMPENSATION BY USING SERIES INVERTER OF UPQC B.MANTHRU NAIK 1 Associate Professor, Electronics & Electrical Engineering, Dr.Samuel George Ins. Of Technology,Markapur, India ABSTRACT:- In this paper presents a Design of a Unified Power Quality conditioner (UPQC) connected to three phase three wire system (3P3W). 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. In this simulation we observe the power quality problems such as unbalanced voltage and current, harmonics by connecting non linear load to 3P3W system with Unified Power Quality conditioner. A new control strategy such as unit vector template is used to design the series APF to balance the unbalanced current present in the load currents by expanding the concept of single phase P-Q theory. The P-Q theory applied for balanced three phase system. And also be used for each phase of unbalanced system independently. The MATLAB / Simulink based simulations are provided the functionality of the UPQC. KEYWORDS Reactive, power, UPQC, compensation, series inverter. I. INTRODUCTION The extensive use of nonlinear loads is further contributing to increased current and voltage harmonics issues. Furthermore, the penetration level of small/large-scale renewable energy systems based on wind energy, solar energy, fuel cell, etc., installed at distribution as well as transmission levels is increasing significantly. This integration of renewable energy sources in a power system is further imposing new challenges to the electrical power industry to accommodate these newly emerging distributed generation systems [3]. To maintain the controlled power quality regulations, some kind of compensation at all the power levels is becoming a common practice [5] [9]. At the distribution level, UPQC is a most attractive solution to compensate several major power quality problems [7] [9], [14] [28]. The general block diagram representation of a UPQCbased system is shown in Fig. 1. It basically consists of two voltage source inverters connected back to back using a common dc bus capacitor. This paper deals with a novel concept of optimal utilization of a UPQC. Figure 1: Unified power quality conditioner (UPQC) system configuration II. IMPLEMENTATION OF SERIES APF In series APF the Inverter injects a voltage in series with the line which feeds the polluting load through a transformer. The injected voltage will be mostly harmonic with a small amount of sinusoidal component which is in-phase with the current flowing in the line. The small sinusoidal in-phase (with line current ) component in the injected 220

2 voltage results in the right amount of active power flow into the Inverter to compensate for the losses within the Series APF and to maintain the D.C side capacitor voltage constant. Obviously the D.C voltage control loop will decide the amount of this in-phase component. Series active power filter compensate current system distortion caused by non-linear load by imposing a high impedance path to the harmonic current. The line diagram of series active power filter is shown in figure 2. Figure 2: Line diagram of series active power filter. 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 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 optimalvaload of the series inverter ofupqcespecially during voltage sag condition [25] [28]. 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 [15], 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 [26], [27] or particle swarm optimization technique [28]. 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. The proposed system is designed to meet a certain minimum active power demand (Preq) from the grid side. PV is the main source, which is continuously made to track the MPP, while feeding the required amount of power into the grid. 221

3 The FC source, with buckboost type dc dc converter, acts as a current source in parallel with the PV source. It is only used to supplement the PV source during low or zero insolation. Thus, FC supplies only the deficit power into the grid. On the other hand, any excess power generated by the PV source is conditioned and diverted to an auxiliary application such as electrolysis, to produce hydrogen, which can be stored for later use by the FC source. This results in an optimal utilization of the available sources, rendering a highly economical system [14]. III. IMPLEMENTATION OF SHUNT APF The active filter concept uses power electronics to produce harmonic current components that cancel the Harmonic current components that cancel the harmonic current components from the non- linear loads. The active filter uses Power electronic switching to generate harmonic currents that cancel the harmonic currents from a non-linear load. In this configuration, the filter is connected in parallel with the load being compensated.therefore the configuration is often referred to as an active parallel or shunt filter. Fig.3 illustrates the concept of the harmonic current cancellation so that the current being supplied from the source is sinusoidal. The voltage source inverter used in the active filter makes the harmonic control possible [13]. This inverter uses dc capacitors as the supply and can switch at a high frequency to generate a signal that will cancel the harmonics from the non-linear load. Figure 3: Shunt Active Power Filter The control algorithm for series APF is based on unit vector template generation scheme [8].Where as the control strategy for shunt APF is discussed in this section. Based on the load on the 3P4W system, the current drawn from the utility can be unbalanced. In this paper, the concept of single phase P-Q theory [9], [10]. According to this theory, a single phase system can be defined as a pseudo two-phase system by giving π/2 lead or π /2 lag that is each phase voltage and current of the original three phase systems. These resultant two phase systems can be represented in α-β coordinates, and thus P-Q theory applied for balanced three phase system [11] can also be used for each phase of unbalanced system independently. In order to eliminate these limitations, the reference load voltage signals extracted for series APF are used instead of actual load voltage. For phase a, the load voltage in α-β coordinates can be represented by π /2 lead as 222

4 Where Where represents the reference load voltage and VLm represents the desired load voltage magnitude. Similarly, for phase b, the load voltage in α-β coordinates can be represented by π/2 lead as Where and represent the dc components that are responsible for fundamental load active and reactive powers, whereas and represent the ac components that are responsible for harmonic powers. The fundamental instantaneous load active and reactive power components can be extracted from respectively, by using low pass filter (LPF). and In addition, for phase c, the load voltage in α-β coordinates can be represented by π/2 lead as Therefore, the instantaneous fundamental load active power for phase a is given by And the instantaneous fundamental load reactive power for phase a is given by The instantaneous fundamental load active and reactive power for phase b is given by By using the definition of three-phase system [11], the instantaneous power components can be represented as Instantaneous active power. Instantaneous reactive power The instantaneous fundamental load active and reactive power for phase c is given by Considering phase a, the phase- a instantaneous load active and instantaneous load reactive powers can be represented by 223

5 The aforementioned task can be achieved by summing instantaneous fundamental load active power demands of all the three phases and redistributing it again on each utility phase from above equations The performance of the proposed concept of UPQC-S is validated through experimental study. The pictorial view of the UPQC experimental circuit model in figure 4. Thus, the reference compensating currents are representing a perfectly balanced 3-phase system can be extracted by taking the inverse of In above equation, is the precise amount of per-phase active power that should be taken from the source in order to maintain the dc-link voltage at a constant level and to overcome the losses associated with UPQC. Therefore, the reference source current for phase a, b and c can be estimated as Figure 4: Proposed Circuit Model Figure 5: Source current, load current, shunt current 224

6 IV. RESULTS The simulation and experimental studies demonstrate the effectiveness of the proposed concept of simultaneous voltage sag/swell and load reactive power sharing feature of series part of UPQC-S. The significant advantages of UPQC- S over general UPQC applications are: 1) the multifunction ability of series inverter to compensate voltage variation (sag, swell, etc.) while supporting load reactive power; 2) better utilization of series inverter rating of UPQC; and 3) reduction in the shunt inverter rating due to the reactive power sharing by both the inverters. V. REFERENCES 1. Doncker, C. Meyer, R. W. De, W. L. Yun, and F. Blaabjerg, Optimized control strategy for a mediumvoltage DVR Theoretical investigations and experimental results, IEEE Trans. Power Electron., vol. 23, no. 6, pp , Nov C. N. Ho and H. S. Chung, Implementation and performance evaluation of a fast dynamic control scheme for capacitor-supported interline DVR, IEEE Trans. Power Electron., vol. 25, no. 8, pp , Aug 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 , Aug 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 S. Subramanian and M. K. Mishra, Interphase AC AC topology for voltage sag supporter, IEEE Trans. Power Electron., vol. 25, no. 2, pp , Feb H. Fujita and H. Akagi IEEE Trans. Power Electron., vol. 13, no. 2,pp , Mar 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 , Oct 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 , 1998, pp 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 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 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 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 , Jan 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 , Jul I. Axente, J. N. Ganesh, M. Basu, M. F. Conlon, and K. Gaughan, A 12-kVA DSP-controlled laboratory prototype UPQC capable of mitigating unbalance in source voltage and load current, IEEE Trans. Power Electron., vol. 25, no. 6, pp , Jun 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 ritical load point, IET Generat., Transmiss. Distrib., vol. 2, no. 3, pp , May AUTHOR S PROFILE B.MANTHRU NAIK is working as an associate professor in EEE Department. He received his P.G(M.TECH) in POWERSYSTEMS HIGH VOLTAGE domain. He is pursuing his Ph.D from Andhra University. 225