Year

1998

Degree Name

Doctor of Philosophy

Department

University of Wollongong.School of Electrical, Computer and Telecommunications Engineering

Abstract

This thesis describes the development of a novel form of single and three-phase Active Power Filter (APF) which require less components than normal. This is achieved by making use of energy storage components which are already present inthe system and at the load. The implementation of a single-phase APF, which requires just one bidirectional switch across the nonlinear load, is described. A simple control strategy is presented to reduce the current distortion to an acceptable level. Simulation and experimental results for a low power prototype circuit are included showing that current harmonic filtering using this APF circuit is effective.

To achieve current harmonic filtering and compensate the negative and zero sequence current in three-phase four-wire systems, a new APF is presented. The proposed APF consists of four bidirectional switches connected in star at the AC terminals of the nonlinear load. A new control algorithm based on three-dimensional vector switch control is derived and implemented on a digital signal processor (DSP) to control the APF. Results from simulation and a 2.5 kVA experimental set-up show the suitability of the proposed approach for the removal of current harmonics and for the compensation of fundamental unbalance currents and reactive power consumed by the load.

It is proposed to use the new circuit in a commercial building installation, although there are a number of practical problems to be solved before this can become feasible.These practical problems are investigated in the thesis. The effect of the APF switching on power diodes in the nonlinear load is investigated. A simple model for reverse recovery in a power diode is used to predict the switching losses of the power diodes, and tested by experimental results. The other problem to be investigated is overvoltage across switches because of downstream line inductance between the APFlocation and the nonlinear load. It is shown that this problem can be solved by installing the APF across the biggest nonlinear load.

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