Sensorless Electric Drive for Permanent Magnet Synchronous Motors

The development and availability of very high energy permanent magnet materials has contributed to an increased use of the permanent magnet synchronous motor PMSM in high performance underwater applications. The PMSM offers advantages such as increased efficiency, superior torque to volume and power to volume ratios, and quiet operation. These advantages have resulted in the Navy considering a switch from its present induction motor technology to the PMSM. In order to individually control stator current and angle and thus fully exploit the characteristics of the PMSM, high resolution rotor angle information is required. An encoder or resolver attached to the shaft of the motor normally provides this rotor position information. Such devices add length, size, and inertia to the machine, raise system cost, and present reliability issues in harsh underwater environments. The drawbacks of the rotor position sensor have led to an intense interest in rotor position sensorless operation of the PMSM. This study develops a sensorless electric drive strategy suitable to the PMSM. The proposed sensorless strategy is implemented in hardware and tested on several permanent magnet machine types. The implementation of the sensorless drive is discussed, and the performance of the developed system is evaluated. Experimental results show that the rotor position estimation strategy performs well under various steady state and transient conditions.