A new three-level simplified sparce NPC topology for UHS PMSM motor applications

In ultra-high speed (UHS) motor applications, full SIC two-level (2L) inverters with high switching frequencies are generally used due to their lower cost. However, even with the usage of all WBG power devices, high-frequency hard-switched 2L inverters still do not achieve optimal efficiency characteristics. As a result, in order to simultaneously reduce the switching frequency and enhance overall efficiency, recently three-level (3L) topologies have emerged as a promising solution. Nevertheless, to fully meet the requirements of UHS applications, the switching frequency of 3L inverters should be increased beyond 30 kHz, which necessitates the usage of all SIC power devices. This, in turn, leads to a potential drawback where the cost of the drive system may become prohibitively high due to the requirement of all SIC switches. To address this issue and reduce the cost of a full SIC 3L inverter, a new 3L simplified sparse NPC (SSNPC) topology is proposed in this work. The operational principle of this topology, its distinctive control features, and the advantages it offers specifically for UHS applications are presented. Additionally, to further increase the efficiency and reduce the influence of dead time at low speeds, a new switching sequence is introduced. Finally, the overall performance and efficiency characteristics of the high-frequency SSNPC inverter were verified across all operational conditions of UHS motor drive system.