A study on the effects of the neutral inductor on the modeling and performance of a four-wire three-phase/switch/level fixed-frequency rectifier

This paper presents a performance evaluation of three-phase, three-switch, three-level, fixed-frequency pulse-width-modulated (PWM) rectifier, when an inductive connection is added between the DC-side capacitive mid-point and the AC-side source neutral. A new continuous-mode model that takes into account the presence of the added zero-sequence inductor is developed using the state-state averaging technique in the synchronous frame. The stability and the performance of the converter in terms of input current Total Harmonic Distortion (THD), power factor and DC voltage regulation are investigated, even for operation under unbalanced DC loads. The converter characteristics are evaluated for different values of the zero-sequence inductor in an attempt to derive useful optimized criteria for the design of the converter. The proposed study is supported by numerical simulations that are carried out a switching-functions-based model of the converter.