Fault Tolerant Sensorless Permanent Magnet Synchronous Motor Drives

High cost and complexity of fault tolerant motor drives has relegated them to mission critical, no-compromise applications. Heeding to this target application, past research efforts have been mainly focused on developing highly redundant, multiphase fault-tolerant solutions able to assure a very high fault tolerance level. However, many other applications would benefit from the availability of solutions ensuring an acceptable level of fault tolerance. The present work shows that, if tolerance is limited to few common faults and a reasonable performance penalty after a fault is accepted, a three-phase, voltage source inverter-fed, sensorless motor drive can be made fault tolerant by acting mainly on the control strategy, thus keeping to a minimum the required hardware modifications and additions. After an initial classification of the possible faults which may affect three-phase VSI-fed drives, a fault detection and identification technique for converter faults is analyzed, able to ensure reduced response times. Therefore, modifications to a sensorless rotor position estimation technique are proposed in order to make a sensorless drive as fault tolerant as their sensored counterparts. Succesively, considering a PMSM motor with star center accessibility, two-phase sensorless operation is extensively studied and a new model is introduced maintaining the same control performance of a standard qd reference frame model. The new model is used for vector control of the machine either in sensored and sensorless conditions to confirm that advanced control of two-phase sensorless operation is the only post-fault strategy allowing the elimination of any redundant hardware.