Simplified Model and Closed-Loop Control of a Commutatorless DC Motor

A simplified dynamic model of a current-fed, self-commutated synchronous motor, operating with a constant angle between the motor counter electromotive force (CEMF) and the input current. The model, which is justified experimentally, includes only two time constants, associated with the rotor inertia and the dc link inductance. This permits the design of the current and speed controlling loops along the same principles used for classical armature-controlled dc motor drives. In this way, the experience which is widely available in industry can be applied, at least with a good approximation, to design of the commutatorless dc motor drives. Various control configurations are discussed. Control loops are designed and closed around the basic motor-inverter block. An experimental result is obtained for each control configuration, thus validating the proposed model.