A Five-Phase Six-Leg Inverter Under Unbalanced Loads for EV Applications: Topology Investigation and Control Design

Abstract

Compared to conventional three-phase permanent magnet synchronous motors (PMSMs) in electric vehicle (EV) applications, five-phase PMSMs driven by five-phase inverters exhibit enhanced fault tolerance. However, these systems may operate under unbalanced load conditions due to cabling asymmetry, operational faults, or winding ageing, leading to unbalanced phase voltages and disordered power distribution. To address this issue, this work proposes a dual-loop controlled five-phase six-leg inverter system capable of operating under both balanced and unbalanced loads. Using instantaneous voltage analysis, phase voltage equilibrium conditions for unbalanced loads are derived, and the topology-enabled zero-sequence compensation capability of the six-leg inverter is analytically validated through an averaged switching model. Then, a dual-loop control method for variable load conditions based on the generalised Park transformation dual-loop control scheme is proposed. Meanwhile, the generalised Park transformation can be applied to n-phase inverter systems, transforming the natural coordinates to the dq-axis coordinates. Finally, hardware in the loop (HIL) experiments in the real-time digital simulator (RTDS) platform are implemented. The experimental results show that, compared to a dual-loop controlled five-phase five-leg inverter, the proposed five-phase six-leg inverter can achieve balanced phase voltages and the required power distributions for each phase under unbalanced load conditions.