Design and control of a synchronous reluctance motor drive

It is the purpose of this research to examine the design considerations, performance features, and control strategies of synchronous reluctance motors as a possible alternative for ac drives. The synchronous reluctance machine is a singly salient machine in which only the rotor is constructed with salient poles while the stator inner surface is cylindrical and typically wound in an identical manner to an induction machine so as to produce a sinusoidal uniformly rotating air gap MMF. It is demonstrated that the rotor design of synchronous reluctance machines can be optimized in terms of a key geometric parameter, i.e., the ratio of the rotor insulation width to the rotor iron width so as to obtain maximum torque production. The equation which gives the maximum motor power factor in terms of the saliency ratio is derived and it is shown that the power factor of 0.8 is a realizable value with the optimal rotor design. An experimental motor has been fabricated where the rotor consists of punched rotor laminations and no connecting magnetic material exists between iron layers. It is shown that the motor has almost no cross coupling effects on both d- and q-axis magnetizing inductances. The results of measurements of the motor parameters prove the validity of the rotor design optimization. It is demonstrated that the synchronous reluctance motor can produce higher torque than an induction machine with same copper losses. Control strategies, practical implementation, limitation, and experimental performance of a field oriented control of synchronous reluctance motor is presented. Excellent control performance is obtained, which indicates that although there exists a limitation on the field weakening range, the synchronous reluctance motor can be suitably applied to high performance drive systems. A current sensorless field oriented control of synchronous reluctance motors is proposed and examined. A good control performance is obtained. A rotor position detection scheme based on current measurements is presented and implemented. A promising performance is obtained at low rotor speed. A combination of the proposed scheme with another scheme that is effective for high rotor speed is proposed as a future work.