Analysis and Design of Speed Controller for Permanent Magnet Synchronous Motor

Abstract

Stabilization is a process which controls the linear time invariant system under certain performance indices either in time domain or in frequency domain. In classical control system, the stabilization of linear time invariant system is achieved by state variable feedback technique or selection of proportional-plus-integral (PID) controller or compensator. The design of controllers and compensators for higher order system involves computationally difficult and cumbersome tasks. Hence there is a need for the design of a higher order system through suitable reduced order models. The controller designed on the basis of reduced order models should effectively control the original higher order system. Permanent magnets to replace electromagnets, which have windings and require an external electric energy source, resulted in compact dc machines. The synchronous machine, with its conventional field excitation in the rotor, is replaced by the PM excitation; the slip rings and brush assembly are dispensed with. In the presence of a d axis stator current, the d and q current channels are cross-coupled and the model is non-linear, as a result of the torque term. Under the assumption that the d axis current being zero, then the system becomes linear and resembles that of a separately-excited dc motor with constant excitation. From then on, the block-diagram derivation, current loop approximation, speed-loop approximation and derivation of the speed controller by using symmetric optimum are identical to those for a dc motor drive speed controller design. The model order reduction method proposed in this work gives better approximated reduced order model for the given PMSM drive system. Because of this we get the reduced order system performance as close as possible to the higher order system response. This will result in reduction in design cost and system complexity. This study focuses on the reduction of models it minimizes the complexity in direct design of controller. A PID controller is sufficient for many industrial applications; hence, it is considered in this work. The approximate values for PID controller are calculated from the reduced order model and suitably tuned to meet the required performance specifications involved in direct design of controller. The approximate values for PID Controller parameters are calculated from the pole zero cancellation method and suitably v tuned to meet the required performance specifications. The tuned values of these controller parameters are attached with the original system and its closed loop response for a unit step input is found to be in good accord with the response of reduced order model. The step response of the original plant with reduced order controller is almost similar to original plant with original controller.