Alternative topology for three-phase four-wire PWM converters applied to a shunt active power filter

This paper presents an alternative three-phase four-wire converter for active power filter applications. The topology of this converter consists of four switch-legs, and it uses a "split-capacitor" in the dc-bus. In this converter, three legs are destined to control the injected currents in utility lines, while the fourth leg assures a balanced voltage sharing in the dc-bus capacitors. This converter solves the problem of dc-bus voltage imbalance in the three-leg split-capacitor converter. Moreover, this topology allows each leg to be controlled independently, so injected current control is simpler than in the four-leg full-bridge conventional converter, which utilizes a single capacitor on the dc-bus side. In this sense, a simple constant-frequency current control technique is proposed. In this paper, an analytical study and a verification by simulation are conducted.