Hysteresis Control for Shunt Active Power Filter under Unbalanced Three-Phase Load Conditions

Hindawi Publishing Corporation Journal of Electrical and Computer Engineering Volume 2015, Article ID 391040, 9 pages http://dx.doi.org/10.1155/2015/391040 Research Article Hysteresis Control for Shunt Active Power Filter under Unbalanced Three-Phase Load Conditions Z. Chelli,1,2 R. Toufouti,1 A. Omeiri,2 and S. Saad3 1 Department of Electrical Engineering, University of Mohamed-Cherif Messaadia of Souk Ahras, P.O. Box 1553, 41000 Souk Ahras, Algeria 2 Department of Electrical Engineering, University of Badji Mokhtar of Annaba, P.O. Box 12, 23000 Annaba, Algeria 3 Department of Electromechanical Engineering, University of Badji Mokhtar of Annaba, P.O. Box 12, 23000 Annaba, Algeria Correspondence should be addressed to Z. Chelli; Received 8 November 2014; Accepted 10 March 2015 Academic Editor: Muhammad Taher Abuelma’atti Copyright © 2015 Z. Chelli et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper focuses on a four-wire shunt active power filter (APF) control scheme proposed to improve the performance of the APF. This filter is used to compensate harmonic distortion in three-phase four-wire systems. Several harmonic suppression techniques have been widely proposed and applied to minimize harmonic effects. The proposed control scheme can compensate harmonics and reactive power of the nonlinear loads simultaneously. This approach is compared to the conventional shunt APF reference compensation strategy. The developed algorithm is validated by simulation tests using MATLAB Simulink. The obtained results have demonstrated the effectiveness of the proposed scheme and confirmed the theoretical developments for balanced and unbalanced nonlinear loads. 1. Introduction Power electronic equipments are largely used in modern electrical systems leading to an increase of the harmonics pollution in the AC main supplies. Thus, harmonic currents generated by static converter mainly rectifiers have become a great issue in the field of electrical engineering due to the adverse effects on all electrical equipments [1]. The intensive use of nonlinear equipments has increased the demand for harmonics suppression and reactive power compensation. It has been proved by many reported work that these nonlinear loads are the main cause of poor power factor and high harmonic distortion [2]. The presence of harmonics in the power system results in numerous drawbacks such as high power loss in distribution network, electromagnetic interference in communication systems, and failures of power protection devices and electrical and electronic equipments. These drawbacks can greatly affect the industrial process and commercial activities because they can lead to a decrease in the productivity and can also affect the quality of the products [3]. The harmonics generated by these nonlinear load cause voltage distortion affecting other loads connected at the same point of common coupling. The APF was deeply studied and applied as an efficient solution to the problem of harmonics pollution and their effects [4]. This type of filters is proved as an appropriate technique to suppress harmonic voltage and current disturbances [5, 6]. The APF injects harmonic current (for shunt active filter) or voltage (for serie active filter) into the power source but in opposite direction. Different harmonic current identification and extraction techniques were studied and used [7–10] such as synchronous reference (d-q-0) theory, instantaneous real-reactive power (p-q) theory, modified instantaneous p-q theory, flux-based controller, notch filter, and neural network techniques [10]. Though p-q theory has good transient response time and steady-state accuracy [6], it is found to be not suitable for estimating reference current under nonideal source voltage conditions [6, 11]. This paper presents an analysis and simulation of shunt active filter under unbalanced nonlinear load. In order to identify shunt APF reference current a novel p-q theory is used based on PLL for unbalanced main voltages to control shunt APF. 2 Journal of Electrical and Computer Engineering Source is il Ls Vsabc Unbalanced nonlinear loads Pcc isabc ifa Active P s_average power source Vsa Active power filter Lf Vsb Vdc/2 Vsc × ... u 2 u2 u2 2 Vsa 2 Vsb ÷ + Vsc2 × i∗ + × sb ÷ + Vdc/2 × ... ∗ i + × sc ÷ Figure 1: Shunt active filter under unbalanced nonlinear load. Hysteresis controllers are employed to generate switching signals of the voltage source inverter. The proposed active filter can compensate both harmonic currents and reactive power (correcting power factor to the unity) simultaneously. To validate and confirm the developed algorithms for the proposed scheme, simulation tests are conducted to show the effectiveness of this approach. 2. Shunt Active Filter Basic Principle The shunt active power filter operating principle is to inject into the power supply network the same harmonics current as that generated by the nonlinear load but in the opposite direction. Figure 1 illustrates a typical structure of the shunt APF connected to a main source [12]. Supposing that linear and nonlinear loads are connected at common coupling point (CCP) [11], under this condition the supply current (𝑖𝑠 ) flowing through the transmission line will be the load current (𝑖𝑙 ) which is nonsinusoidal. The designed active power filter is a three-phase PWM (pulse with modulation) voltage source inverter (VSI), connected in parallel with the AC source through the common coupling point of (CCP) [12]; the current source equation can be expressed as 𝑖𝑠 = 𝑖𝑙 − 𝑖𝑓 . (1) The performance of active power filter depends mainly on the technique used to identify and extract the reference current (harmonic current) and the inverter control strategy [9, 13]. This inverter uses DC voltage capacitor as a supply and can be switched at high frequency to generate the current that will eliminate the harmonic current from the main source. The current waveform used to suppress harmonics is obtained by VSI in the current controlled mode and the interface filter [14]. 3. Proposed Control Scheme The block diagram of the proposed shunt APF control scheme is illustrated in Figure 2. In addition, hysteresis controller is used to generate switching signals to control SAPF switches to force the desired current into the system. The compensating currents of active filter are calculated by sensing the load currents, peak voltage, and current of AC source. ∗ ifa i∗ + × sa + − ila ∗ ifb − ilb ∗ ifc − ilc Figure 2: Block diagram of the proposed control strategy. The switching signals based on hysteresis control are obtained in two stages. Firstly, by subtracting the real load currents (𝑖𝑙𝑎 , 𝑖𝑙𝑏 , and ∗ ∗ ∗ , 𝑖𝑠𝑏 , and 𝑖𝑠𝑐 ), 𝑖𝑙𝑐 ) from the reference current template (𝑖𝑠𝑎 ∗ , henc (...truncated)