Implementation and Analysis of Direct Torque Control on High-Speed PMSMs: A Comparative Study of Commercial and Laboratory-Developed Motors

This paper analyzes the Direct Torque Control (DTC) algorithm applied to ultra-high-speed (UHS) Permanent Magnet Synchronous Motors (PMSMs) for applications up to 500,000 RPM. A sensor-less DTC algorithm is formulated and implemented using MATLAB-based automatic code generation, incorporating optimized speed, torque, and flux control loops for enhanced dynamic performance and computational efficiency. To ensure stable and precise speed transitions, an adaptive transition control mechanism is incorporated, which considers thermal and electrical constraints such as motor winding temperature, inverter limitations, and phase current regulation. This mechanism assists in managing acceleration profiles while maintaining system integrity at high speeds. Simulations have been conducted for two motors up to 500,000 RPM. Experimentally, the commercial motor operated at 110,000 RPM, and the lab-built---A Mechanically Based Antenna (AMEBA)---PMSM motor operated at 70,000 RPM with closed-loop operation. With modulation index regulation, AMEBA motor was also operated up to 150,000 RPM in open-loop operation. AMEBA has been developed for communications with submarines, underground mines, and underwater facilities. The study also compared DTC with Field-Oriented Control (FOC), under ultra-high-speed conditions. Furthermore, the effects of current sensor delays are analyzed, and a phase-advancing method is employed to mitigate their impact. Future work will involve operating both motors across their full speed range and addressing additional delays through hardware testing.