Modeling, Control and Modulation Strategy of a Three-phase Four-switch PWM Voltage-source Rectifier Based on Novel Non-orthogonal Coordinate

Modeling and controller design principles for six switch PWM voltage-source rectifiers have been covered thoroughly in recent studies. In contrast, the control strategies for four-switch PWM VSRs are rarely reported. In order to achieve a high performance control, this paper develops a control oriented dual single-input-single-output model for 4-switch PWM VSRs in a novel non-orthogonal frame. Using given DSISO model, the controller design becomes much easier than ever before, and basic guidelines are provided in this paper. To suppress the DC voltage offset inherited in 4-switch PWM VSRs, a split capacitor voltage balancing method is analyzed in details. Then, a very simple modulation strategy is proposed based on the non-orthogonal coordinate system, which exhibit the merits of less computation and higher accuracy compared with traditional methods. The resultant zero voltage vector of 4-switch PWM VSRs is synthesized by a pair of opposite vectors, thus two switching sequences derived from alternative selection of zero vector synthesis schemes are introduced in this paper. For lower harmonic distortion injected to the grid currents, performances of two applied switching sequences are fully evaluated when the RMS value of current ripple is chosen as the standard. Experimental results are presented to demonstrate the feasibility and validity of the proposed methods.