Control Method and Compensation Characteristics of the Active Filter System using a Current Source PWM Converter and a High-Pass-Filter

Abstract

Nonlinear loads using power semiconductor devices produce harmonic currents and reactive power in AC power lines. As they are popular in many fields, the elimination of harmonic currents and reactive power is one of the important research projects.
This paper describes a control method and compensation characteristics of the combined filter system of a current source active filter and a high-pass-filter. The system senses three signals, load currents, source currents and line voltages, to create the reference signals of the active filter. The goal of this paper is to solve the problems:
(1) A harmonic-enlarging effect due to the parallel resonance,
(2) Filtering of the harmonic currents produced by source-side harmonic voltages, and
(3) Drawbacks of analog control such as being sensitive to noises, etc.
The transfer function of the current source converter is identified, and is used for designing the control system of the active filter. Digital control based on a DSP is adopted to remove the drawbacks stemming from analog counterpart, but it is found that it introduces a new problem, a computational delay in the output, that results in serious deterioration of the fiter performance. It is shown that the addition of the source current feedback can solve not only the delay problem but ones due to the parallel resonance and source-side harmonic voltages.
Finally a small setup controlled by a DSP was built, and the validity of the proposed method was demonstrated by experimental results.