Virtual Space Vector Modulation for Three-Level Neutral-Point-Clamped Inverters Driving Three-Phase Series-End Winding Motors

Three-level (3L) inverters have seen widespread adoption in medium-to-high-voltage high-power drives compared to their two-level (2L) counterparts, owing to advantages such as reduced voltage stress on power devices and improved output waveform quality. Neutral-point voltage (NPV) balancing remains a critical issue in neutral-point-clamped (NPC) topologies, particularly in series-end winding (SEW) motor drives, which enhance DC-bus utilization but lack dedicated modulation strategies for NPV balance. To bridge this gap, this article introduces a virtual space vector modulation (VSVM) scheme. First, the effects of different voltage vectors on NPV in a 3L-SEW topology are analyzed. Then, virtual vectors that maintain NPV balance in both the α–β plane and the zero-sequence (ZS) axis are designed. Based on this, a straightforward lookup-table-based modulation scheme is developed. Furthermore, to enhance the operational range, an overmodulation strategy is introduced, with a clear motivation to extend the linear modulation region and ensure stable control at higher modulation indices. Comprehensive experimental results validate the effectiveness of the proposed modulation scheme for 3L-NPC inverters driving a SEW motor. © 2026 IEEE.