A fixed switching frequency adaptive sliding mode controller for shunt active power filter system

The theory, design and simulation of a fixed frequency pulse width modulation (PWM) based adaptive sliding mode current control for single phase shunt active power filter (APF) to improve power quality is presented in this article. Artificial neural network (ANN) based modified control strategy is being used to control the DC capacitor voltage as well as to generate reference source current. The application of ANN enhances the convergence rate of APF and also makes it adaptive under variable load conditions. The instantaneous phase of the source voltage is extracted by a phase locked loop (PLL). The same phase is used by ANN for calculating the reference source current. That is why the proposed APF is applicable under both nominal and distorted voltage source. The complete non-linear system is analyzed and simulated using MATLAB/Simulink software. Simulation results are presented to validate the theory.

I. Introduction

The extensive use of nonlinear load (computers, TVs, refrigerators, printers, fax machines, etc) causes harmonic distortion. Harmonics increase the conduction losses, eddy current losses and also have bad impacts on other loads connected to the same voltage source. Passive filters can be used to improve the power quality, but these are expensive and bulky solutions. These problems can be overcome by use of active power filter (APF). Two types of APFs exist; shunt APFs and series APFs. Shunt APFs are used to compensate current harmonics, while series APFs are used to compensate the voltage harmonics caused by nonlinear loads. In this article a single phase shunt APF is presented. Different control strategies have been applied to control single phase shunt APFs in the literatures [1]– [8]. However sliding mode (SM) control is well known due to its ease of implementation and robustness. SM controllers have a property of operating at infinite and varying switching frequency such that the state variables of the system follow the required trajectory. However high and varying switching frequency causes losses and even damage of the system.