Performance Enhancement of Active Power Filter using Robust Control Strategies

Abstract

The prime focus of this thesis is to report control strategies to improve the performance of single phase shunt Active Power Filter (APF). Basically, Sliding Mode (SM) control strategy and Feedback Linearization based control strategy have been applied considering their ease of implementation and robustness under external disturbances. An low cost analog SM controller is presented to reduce the steady state current error. In this method a band pass filter is used for calculating the reference source current which makes source current Total Harmonic Distortion (THD) independent of source voltage THD. Multisim based simulation method and results are presented to report the method of low cost analog implementation. To overcome the drawbacks caused by varying switching frequency, a fixed switching frequency SM controller is presented, in which Artificial Neural Network (ANN) is used to generate the reference source current. In this control strategy, a proper combination of fixed frequency sliding mode current control, ANN based fundamental source current extraction circuit and unipolar PWM increases the dynamic response of APF system and makes it adaptive under variable load and source conditions. As feedback linearization based controller improves the performance of the power electronic systems by analysing stability of the complete system, a straight forward Partial Feedback Linearization (PFL) based control strategy is presented to reduce the source current THD of single phase shunt APF. The nonlinear system dynamics of the APF has been partially feedback linearized using its average dynamic model. New control input to the linearized system is obtained considering the stability of the complete APF system. After that, control input to APF is derived by nonlinear transformation. Stability of the internal dynamics of the system is analysed considering zero dynamics of the system. A prototype of the APF system is built and the proposed controller is implemented using dSPACE 1104. Both experimental and simulation results of the PFL based control strategy are compared with exact feedback linearization of APF via SM control for validation of performance improvement. Finally the application of PFL based control strategy is extended to three phase APF by considering it as Multiple Input Multiple Output (MIMO) system and MATLAB/Simulink based simulation results are presented to validate the theory.