A Fault-Tolerant Resonant DC-Link Inverter With Bidirectional Alternate Commutation

Contemporary resonant DC-link inverter (RDCLI) designs predominantly maintain soft-switching operation exclusively during unidirectional power flow from the DC source to the load. However, under reverse power transfer conditions where energy flows from the load back to the DC bus, the auxiliary circuits fail to enable zero-voltage or zero-current switching for the main power devices. This limitation results in conventional hard-switching operation during regenerative modes, consequently compromising the system's overall energy recovery efficiency. This paper proposes a novel RDCLI incorporating two structurally symmetrical auxiliary resonant circuits at the DC interface. These complementary circuits operate alternately according to the direction of power flow, enabling consistent soft-switching performance during bidirectional energy transfer. Furthermore, in the event of an open-circuit fault within either auxiliary set, the inverter maintains soft-switching capability along one power flow direction while experiencing performance degradation only in the opposite direction. This fault-tolerant characteristic prevents complete loss of soft-switching functionality across both power transfer directions during auxiliary device failures. This work presents a systematic analysis of the auxiliary network's operational mechanisms under bidirectional power flow conditions, coupled with the development of a complete parametric design framework. Experimental results verify that the auxiliary circuit maintains all theoretically derived operating modes during both power flow directions, with all semiconductor devices successfully achieving soft-switching transitions throughout the operational range. The measured peak efficiencies of 98.1% in forward operation and 96.7% in reverse operation at rated power establish the distinct advantage of the proposed bidirectional architecture over conventional unidirectional soft-switching alternatives. These findings validate the topology's considerable potential to advance the performance envelope and practical implementation of resonant DC-link solutions in high-frequency bidirectional power conversion systems.