Torque Production in Permanent-Magnet Synchronous Motor Drives with Rectangular Current Excitation

Special features of torque production in self-controlled permanent-magnet (PM) synchronous motor drives with rectangular current excitation have been investigated. Addressed issues include the generation of undesired torque pulsations at low speeds and system operating locus limits imposed at high speeds by saturation of the current regulator. Attention is limited to motors in which sources of reluctance torque are suppressed by surface-mounting of the rotor magnets and skewing of the stator slots. Results from the low-speed investigation indicate that the pulsating torque can be minimized by a combination of steps including proper adjustment of the rotor magnet pole atc and effective use of rotor speed feedback compensation. High-speed saturated-regulator performance is significantly influenced by the 120 electrical degree inverter switch conduction intervals inherent with rectangular current excitation. The system torque-speed operating envelope can be expanded by several means, including on-line adjustment of the converter excitation phase angle a, but resulting performance trade-offs require careful scrutiny. A 15-kW prototype PM synchronous motor drive system has been used to confirm key analytical results.