International Journal of Smart Electrical Engineering, Vol.6, No.1,Winter 2017 ISSN: 2251-9246 EISSN: 2345-6221 27 A Hybrid Control Method for Stable Operation of Active Power Filters in Three-Phase Four-Wire Networks S. Sajjad Seyedalipour* 1 , Habib Allah Aalami 2 , Amin Barzegar 3 1 Faculty of Electrical Engineering, K. N. Toosi University of Technology, Tehran, Iran, sseyedalipour@gmail.com 2 Department of Electrical Engineering, Eyvanekey University, Tehran, Iran, h.aalami41@eyc.ac.ir 3 Department of Electrical Engineering, Imam Hossein University, Tehran, Iran, abarzegar@ihu.ac.ir Abstract The main goal of this study is the use of Lyapunov’s stability theory to a three-phase four-wire shunt active power filter (SAPF), since this method has been applied effectively to other areas of converter. The dynamic model of the SAPF is first established, after that, a combination of fuzzy tracking control and Lyapunov function is suggested in order to impose a desired transient waveform on the considered three-phase four-wire distribution grid, providing robustness and insensitivity to parameter changes. Furthermore, the suggested control technique guarantees appropriate tracking of the reference current components and simplifies the global control design. The feasibility of the suggested control method is validated using comprehensive simulation studies on a four-wire SAPF in order to compensate for nonlinear and unbalanced grid-connected loads in an electrical power distribution network. Keywords: Shunt active power filter (SAPF); Lyapunov function; fuzzy tracking control; three-phase four-wire distribution grid. Article history: Received 12- May-2017; Revised 19-May-2017; Accepted 03-Jun-2017. © 2017 IAUCTB-IJSEE Science. All rights reserved 1. Introduction The extreme application of power-electronic devices, that represent nonlinear loads, in an electrical power distribution grid has led to many disturbances in the power quality such as unbalanced currents, pollutions of harmonic currents, and reactive power drawbacks [1]. Consequently, low power factor, weakening efficiency, overheating of transformers and motors, breakdown of sensitive equipments are encountered. Thus, it is essential to improve the power quality in the electrical grids. Currently, it is well known that harmonic cancelation by means of a shunt active power filter (SAPF) provides superior and more flexible performance in comparison with a passive filter. As a result, the SAPF will be considered in order to enhance the power quality in the paper. The most significant step for designing the control approach of active filters is the current loop. There are a number of control approaches suggested in the literature for current control of power- electronic converters with SAPF capability namely, proportional-integral (PI) control [2], [3], Lyapunov function control [4], [5], sliding mode control (SMC) [6], feedback linearization control [7] and hysteresis control [8]. Utilizing the repetitive control technique is an usual scheme for SAPF control, that is generally according to single repetitive control (SRC). By means of the internal model principle [9], SRC has been found to be zero-error controller for the following or cancelation of harmonic currents for pulse width modulated (PWM) converters [10]-[12] and active power filters [13]. Reference [14] has improved the control of SAPFs by the use of feedback linearization method through utilizing power balance in grid side and SAPF sides. In [15], a nonlinear control method for a three-phase three- wire SAPF has been proposed and implemented on an experimental prototype of an SAPF. In [16], different techniques have been compared in order to extract the reference current components for SAPF in four-wire systems. A fuzzy sliding mode control for robot manipulator has reported in [17]. In the proposed research, a hybrid approach for stable operation of an SAPF in three-phase four-wire electrical power distribution networks has been pp. 27:33