A High Efficiency Non-Isolated Three-Phase Unfolding Based Electric Vehicle Powertrain

Three-phase unfolding based converters offer a radically different approach to two-stage dc to three-phase ac conversion, with potential benefits for electric vehicle (EV) powertrains. However, current research on non-isolated three-phase unfolding, particularly for EV powertrains, is limited. This paper presents a non-isolated bidirectional buck-boost three-phase unfolding system for EV drivetrains. The proposed converter incorporates a non-inverting buck-boost converter and a voltage balancer circuit in the dc-dc stage. Unlike existing unfolding systems in the literature that require two dc-dc converters capable of handling full system power, the balancer in the proposed system only handles a fraction of the total power, resulting in reduced size and improved efficiency of the converter when compared to a conventional two-stage EV powertrain. The paper provides detailed design guidelines and presents a straightforward control strategy for the proposed converter. To evaluate its performance, a 5 kW prototype is constructed and tested with an induction motor. The experimental results demonstrate peak efficiencies exceeding 98%.