A hybrid-PWM based DC-link voltage balancing algorithm for a 3-level neutral-point-clamped (NPC) DC/AC traction inverter drive

This paper presents a hybrid pulse-width modulation (PWM) technique, for a 3-level neutral point clamped (NPC) electric vehicle (EV) traction inverter drive. In this strategy both the advantages from the SV-PWM and carrier-based PWM strategies are introduced. The duty cycles for the switches are calculated using carrier based PWM, to reduce the computational time and complexity. The redundancies of the switching states are used to balance the two DC-link capacitor voltages, as in the SV-PWM based strategies.

The proposed scheme is capable of maintaining the difference between the two DC-link capacitor voltages stable for a wider range of machine speed-torque variations. Moreover, a single carrier is used instead of multiple carriers, which also reduces the computational complexities. A detailed simulation studies are carried out in MATLAB/SIMULINK® platform to verify the controllability of the proposed control scheme. Experimental studies are carried out with a 6.0 kW surface permanent magnet synchronous machine (SPMSM). The simulation and experimental results show the desired performance of the proposed scheme.