The application of a multi-loop self-tuning digital controller to an electromechanical drive

This paper describes the development of a twin-loop, self-tuning digital controller for an electromechanical drive incorporating a separately-excited DC motor. Details of the controller structure and the design equations are presented together with an outline of the RLS estimator used to obtain estimates of the parameter values in the plant models used in the design of the controllers. Results are presented first for the open loop run-up of the drive (both with and without a series armature starting resistor) and for the digital fixed-gain armature current and speed controllers developed using the proposed design algorithm. The modification required to enable the estimator to produce simultaneous estimates of parameters for the two separate plant models required is described, and results are presented showing the run-up of the drive with self-tuning implementations of the current and speed controllers. The response is shown to compare favourably with that obtained using a fixed-gain controller, and the effects of sampling interval and controller and estimator initialisation are discussed and recommendations are made. It is shown that the twin-loop controller self-tunes successfully from an initial open loop configuration thereby eliminating the need for any prior detailed controller design. The effects of neglecting the armature time constant are also considered.