A Soft Switching Inverter Minimizing Bearing Currents in 800V Electric Vehicle Drives

Bearing currents and shaft voltages, generated by the switching of the traction inverter, are a major point of failure for electric drives. Mitigating these issues is an area of active research, where the focus is primarily on improved filtering and common mode voltage attenuation through topological modifications. This paper proposes a motor drive inverter topology that can control the common mode voltage at the motor terminals by adding an LC filter per phase with the filter’s neutral point connected to the DC negative. By controlling the common mode voltage, the leakage current, bearing current and shaft voltage can be attenuated. Critical soft switching is leveraged to keep the LC filter’s size small and to maintain high efficiency. Experiments demonstrate a 90% reduction in peak-to-peak and RMS leakage currents and shaft voltages with the proposed topology.