High precision torque control of reluctance motors

A method for the high-precision torque control of a reluctance motor for servo applications is presented. The prototype is a three-phase, eight-pole reluctance motor driven by a MOSFET inverter. The current control as well as the speed control is performed by the software of a digital signal processor. The motor is supplied with sinusoidal current, and two current control methods are proposed. One is based on the vector control principle to achieve linearity between current and torque, and another is developed to obtain the maximum torque/current ratio. Due to the saliency, the instantaneous torque contains a large ripple component. In the case of the test motor, the ripple torque was as much as 26% of the rated torque under the sinusoidal current drive. Experimental results show that the ripple component could be reduced to 6% by superimposing the compensation current component on the current reference.<>