Quad active-bridge single-stage bidirectional three-phase AC-DC converter with isolation: introduction and optimized modulation

This paper introduces the quad active-bridge (QAB) ac-dc converter, which provides isolation and bidirectional power flow in a single-stage topology. While Matrix-based topologies commonly use bipolar voltage switches, the proposed solution allows the use of unipolar voltage switches. Compared to a six-switch PFC, the average voltage stress is reduced by a factor two. A modulation scheme is derived for this converter, that is analytically optimized towards minimum conduction losses to improve the conversion efficiency. The modulation scheme consists of closed-form algebraic solutions such that no lookup tables are required for implementation. Considerations for converter design and the main component selection procedures are given. The proposed topology and modulation strategy is implemented in a 20 kW prototype. Measurements are conducted and show that the methods operate as expected. Experimental results show that the load step is stable, the power factor is close to unity, and the phase current THD is than 5%. Lastly, it is shown that the circulating current can be controlled independent of the output power. The methods and tools provided can be used for the design and analysis of ac-dc power converters based on the QAB-topology.