Dynamic performance analysis in rapid acceleration and deceleration of a commutatorless DC motor.

Abstract

The commutatorless DC motor has been used in various fields as a variable speed motor since it can produce characteristics similar to those of a conventional DC motor without a mechanical commutator, and it is essentially important to know the dynamic performance of this variable-speed motor.In previous papers the author and his colleagues derived various transfer functions for this motor and a set of nonlinear equations valid for large-signal transient state, and analyzed in detail transient performance of the motor by using these functions and equations. They also investigated the stability and the dynamic responses of speed control systems containing this motor, and proposed control strategies to improve the dynamic performance of the systems.In this paper, the dynamic performance of the speed control system with air-gap flux and margin angle control loops as well as current control loop and a current limiter is analyzed in detail not only for the case of motoring but also for the case of regenerative braking operation. First, the dynamic responses of the system in the case of step-up change in speed reference is analyzed for two types of air-gap flux control circuits. It is clarified that when field current control loop is used for controlling the flux, the change in the margin angle of commutation during transients is reduced if the controller constants of the loop are selected so as to enlarge the increase in the field voltage in the transient state, and that satisfactory dynamic responses are obtained concerning the field voltage as well as the margin angle of commutation when the field voltage control loop is used as a flux loop. Second, the dynamic performance of the system in the case of regenerative braking operation is analyzed in detail and it is shown that the both types of air-gap flux control circuits in this operation are useful not only for a fast speed response but also for a safe commutation of the inverter, and that the transient increase in the field voltage for the case of the field current control is much larger than that for the field voltage control. Moreover, a guide for selecting controller constants for various moment of inertia is shown.