A new direct torque control method for switched reluctance motor with high torque/ampere

Switched reluctance motor (SRM) has gained attention due to simple construction, ruggedness, high reliability, low cost, minimum maintenance and advancement in power electronics technology. However, SRM has some inherent disadvantages such as torque ripple, acoustic noise, requirement of rotor position information and control difficulties due to nonlinearities. It is reported in literature that smooth torque in SRM is achieved using the philosophy of direct torque control (DTC) of ac machines. In this paper, a comparative study of DTC with other torque control methods for 3-phase SRM is performed. It is observed that in case of DTC, high phase rms current is required to maintain constant flux linkage at all rotor positions of SRM thereby reducing the torque/ampere. It is also observed that in this scheme, different flux linkage references are required at different speeds to produce same torque for optimum torque/ampere. A new DTC scheme which addresses these limitations is proposed in this paper. In this scheme, the voltage vectors are selected judiciously to increase torque/ampere. The flux linkage is maintained constant only during phase commutation to avoid the need for rotor position information.