Highly Efficient Three Level Sparse NPC Inverter for Ultra-High-Speed PMSM

One of the promising applications of ultra-high-speed (UHS) motors is the fuel cell’s turbo compressor. In fuel cell systems high efficiency at all operating conditions is one of the main requirements. Most commercial high-speed drives use two-level (2L) inverters due to the simple structure, reliability, and low cost. However, better performance characteristics at a slightly higher cost can be achieved with the three-level (3L) topologies. In this work, a comparative analysis of different 3L topologies for the usage in UHS drives is conducted. Based on the comparison results 3L Sparse-NPC (SNPC) topology is chosen for the performance evaluation. The switching losses are analyzed for each switching transition. Based on this analysis, the modified switching sequence considering the application in UHD drive is proposed. It has the inherent zero-voltage switching (ZVS) capability for the 2L stage and thus can further reduce the switching losses. Finally, a complete sensorless drive system based on the SNPC inverter and the UHS motor is simulated in MATLAB/Simulink. The simulation results demonstrate that this topology is able to efficiently control the UHS motor at the whole operating range. The results also demonstrate that relatively good voltage balancing capabilities can be achieved with the ZVS-based switching sequence.