Reactive Power Control Strategy for Isolated Single-Stage Three-Phase SWISS AC-DC Converter Based on Dual Active Bridge Converters

This paper proposes a reactive power control strategy for a three-phase single-stage isolated SWISS AC-DC converter based on the dual active bridge (DAB). By analyzing the conduction states of the SWISS converter, the relationship between the input currents of the two DAB converters and the grid current in different voltage sectors is examined. A triple phase shift (TPS) control strategy is applied to ensure the DAB converter works in the globally optimal working modes, thereby achieving zero-voltage switching (ZVS) of the high-frequency switching devices and effectively reducing conduction losses. Based on TPS control, an analytical expression relating the phase shift angle and the input current of the DAB converter is derived, with the sign of the phase shift angle determined according to the polarity of the grid current in each sector, thereby enabling precise control over both the magnitude and direction of the input current. A dual-loop control strategy is proposed to achieve reactive power control on the grid side and output regulation on the load side, thereby improving the power quality of the system. The variations in the working modes and control variables under the reactive power control strategy at different load powers are analyzed, demonstrating the strategy's adaptability to a wide range of loads. In addition, the design method for the series inductor is analyzed to achieve reactive power control while meeting the load power requirements. Finally, the proposed control strategy is applied to a 1.4 kW three-phase single-stage SWISS converter based on DAB with 200V/50Hz input line voltage and 200V output voltage. The experimental results validate the feasibility and effectiveness of the proposed control strategy.