High Efficiency Traction Drive Operation with a Partial Load Three-Phase Triangular Current Mode Modulation Concept

Improving drive cycle efficiency in electrical vehicles is one of the key design criteria in traction drives, pushed by a need for lower total energy consumption and reduction of battery capacity costs. Additionally, in passenger cars the peak performance requirements also need to be respected for an adequate driving experience. This paper proposes an operating-point dependent inverter voltage modulation concept termed as Partial-Load Triangular Current Mode modulation, which operates either under Triangular Current Mode modulation or Space Vector modulation for low or high loads respectively, targeting higher cycle-efficiency without over-rating inverter components at full load operation. This work elaborates on the implementation of such a modulation scheme for a 300 kW, 800 V synchronous machine drive with Silicon Carbide switches. It then proposes subsequent modifications to the scheme with an optimal common mode voltage injection to achieve further efficiency gains. Finally, the loss validation is conducted in two steps. First the power module, filter inductor and capacitor are individually characterized and then the inverter and filter system losses are measured with triangular currents. This concept aims to save up to 23% drive losses (4.5% gain in driving range) in the WLTP drive cycle when compared with space vector modulation at a constant 10 kHz switching frequency, a saving comparable to gains made during the transition from Silicon to Silicon Carbide devices for traction inverters.