A Novel Direct Torque Control Strategy for Interior Permanent Magnet Synchronous Motors Driven by a Three-level Simplified Neutral Point Clamped Inverter

Compared to the three-level neutral point clamped (3L-NPC) inverter, its simplified version, the 3L-SNPC, uses fewer switching devices to achieve a multi-level output. However, it offers fewer voltage vector selections, limiting its usefulness for motor drive applications. This issue is overcome through a proposed direct torque control (DTC) strategy utilizing the concept of virtual voltage vectors to increase the number of voltage vector selections available. In addition, a DTC based switching table employing at least one voltage vector within each sampling period is proposed to reduce the torque ripple. Further, the issue of neutral point capacitor voltage unbalance is addressed. The strategy is modelled for an Interior Permanent Magnet Synchronous Motor driven by a 3L-SNPC, and simulation results prove its feasibility. To the knowledge of the authors, the proposed strategy has not previously been reported.