A Hybrid PWM-Based DC-Link Voltage Balancing Algorithm for a Three-Level NPC DC/AC Traction Inverter Drive

This paper presents a hybrid pulsewidth modulation (H-PWM) technique, for a three-level neutral point clamped electric vehicle (EV) traction inverter drive. The proposed strategy depicts the advantages of both classic space-vector PWMs (SV-PWMs) as well as carrier-based PWM (CB-PWM). The duty cycles for the traction inverter switches are calculated by the CB-PWM, to reduce the computational time and to control the complexity of the system. The redundancies of the switching states are then used to balance the two dc-link capacitor voltages, similar to the SV-PWM-based strategy. The proposed scheme is capable of maintaining the difference between the two dc-link capacitor voltages for a wider range of machine speed-torque variations. Furthermore, a single carrier is used for PWM, instead of multiple carriers, which further reduces computational complexity. A detailed comparative study is carried out, to prove the performance difference between the low switching loss-based SV-PWM techniques, which is previously proposed by authors and the present proposed H-PWM strategy. In addition, total harmonic distortion of voltage and current (%THDv,i), duty cycles of the switches, total inverter power loss, as well as dc-link voltage balancing capabilities are also compared. The balancing ability of the proposed strategy by changing the neutral point potential control is also demonstrated. Detailed simulation and experimental studies are carried out to prove the performance of the proposed control strategy with a 6 kW, surface-mounted permanent magnet synchronous machine. Simulation and experimental test results prove the desired performance of the proposed scheme.