A study of active power filters using quad-series voltage-source PWM converters for harmonic compensation

An active power filter using quad-series voltage-source PWM converters is used to suppress ac harmonics by injecting PWM modulated currents to the ac side. In this paper, the calculation circuits for the harmonic currents to be injected, the compensation characteristics, and the capacity of the dc capacitor are discussed. A new control circuit for the dc capacitor voltage is proposed. These discussions focus on transient states and are on the basis of the instantaneous reactive power theory. Finally, a passive LC filter is designed to remove the switching voltage and current ripples caused by the PWM converters at the ac side. Some experiments to illustrate the details of the study are shown.