Three-phase Four-Leg High Frequency Link Matrix Rectifier and Its Modulation Strategy

The three-phase four-leg PWM rectifier can be decomposed into three independent single-phase fullbridge rectifiers, and its structure has the advantages of high reliability and strong fault tolerance. In order to improve the applicability of the three-phase high frequency link matrix rectifier under the unbalanced grid, a three-phase four-leg high frequency link matrix rectifier topology is proposed in this paper. Based on the voltage source three-phase three-leg high-frequency link matrix rectifier, the fourth leg is introduced to provide a zero-sequence current path for unbalanced input current, thereby the working performance under unbalanced conditions of the power grid is improved. In this paper, the structure of the proposed topology is analyzed firstly, and then for this topology a de-re-coupling Saddle Pulse Width Modulation(SAPWM) method is proposed. Through this modulation strategy, a stable DC voltage can be output under the condition of unbalanced input power, at the same time, the DC bus voltage utilization rate is improved, and the input current harmonic content is low. The feasibility of the proposed topology and its de-re-coupling SAPWM method is verified by simulation.