Dynamic Performance of a Field-Weakening Speed Control System for a Self-Controlled Synchronous Motor.

Abstract

The dynamic performances of a field-weakening speed control system for a self-controlled synchronous motor are analyzed in detail. The effects of controller constants of the system on the mechanical and electrical dynamic responses are first explored for the case of a small change in speed reference. It is shown that the responses tend to be oscillatory if the controller gains in the system are small. The dynamic performances of the system for larger changes in the speed reference are then discussed. It is clarified that if the parameters of the margin angle control loop of the system are constant, commutation failure occurs even when step-up change in the speed reference is not so large. To enable safe commutation for larger changes in the speed reference, one way of changing such parameters depending on the change in the speed reference is proposed, and it is shown that the method introduced here is very effective. The dynamic responses for various values of inertia constant are also examined, and it is shown that good speed responses with relatively small changes in margin angle of commutation can be obtained for a considerable range of inertia constant.