Analysis of a Three-Phase Buck-Boost AC Chopper Controlled in Two Phases

We propose a three-phase buck-boost AC chopper controlled by two phases. Characteristics of the circuit are analyzed by the simulation considering the dissipation of semiconductor devices and inductors. Ripple and total harmonic distortion (THD) of an input current and an output voltage increase when inductive components increase in the load. Variations appear in each phase in buck-boost ratio. The resonance frequency is changed due to the inductive components in the load. The pi-connected output filter is analyzed, and it operates as the second reverse L-connected output filter. THDs in the output voltages are improved when the capacitance in the output filter is changed to adjust the resonance frequency of the output circuit. The three-phase four-wire system is analyzed, and the circuit is compared with the two phases control method. Then, the cause of unbalance at each phase for the three-wire systems is proved to be the two phase control method.