Enhanced Torque Estimation in Variable Leakage Flux PMSM Combining High and Low Frequency Signal Injection

Torque measurement/estimation in Variable Leakage Flux Permanent Magnet Synchronous Motors (VLF-PMSMs) is preferred for accurate control. Torque measurement systems are expensive, require extra room, add weight, can introduce resonances into the system and can be sensitive to electromagnetic interference. Alternatively, torque can be estimated, accurate knowledge of machine parameters being often required in this case, which for the case of VLF-PMSMs can be a serious drawback due to the large variation of machine parameters with the operating condition. This paper proposes a torque estimation method for VLF-PMSMs based on stator flux linkage estimation. Machine parameters involved in stator flux linkage estimation are obtained from the response of the machine to a pulsating high frequency current signal and a low-frequency and small-magnitude, square-wave current signal. Both signals are injected on top of the fundamental excitation without interfering with the normal operation of the machine.