DC-Link Voltage Balancing for a Three-Level Electric Vehicle Traction Inverter Using an Innovative Switching Sequence Control Scheme

This paper presents an advanced switching sequence for space-vector pulsewidth modulation (SV-PWM)-based three level neutral-point clamped inverter. The developed scheme helps to reduce the number of converter switching sequences, compared with the conventional SV-PWM strategy, and keeps the voltage difference between the two dc-link capacitors at the desired voltage level. The developed test bench is utilized for a permanent magnet synchronous machine (PMSM) drive for electric vehicle applications. The proposed strategy is compared with the performance of a PI controller-based voltage balancing strategy. The proposed control strategy is based on the nearest three-vector (N3V) scheme, with a hysteresis control of the dc-link capacitor voltage difference. Conventional N3V scheme uses a higher number of switching sequences, which makes the switching losses higher. In addition, these switching sequences are not same for all subsectors. This makes the switching frequency to vary extensively. In the proposed control strategy, a reduced number of switching sequences are used, and they are same for all subsectors. This makes the system operate with constant switching frequency. Detailed simulation studies are performed to verify the performance of the proposed control strategy. The performance-based test results are then compared with those of a PI controller-based strategy. Experimental test results show significant improvement in the performance of the PMSM with respect to dc-link capacitor voltage variation as well as wide speed and torque range of machine operation.