ANALYSIS OF STATE FEEDBACK CONTROL OF CHOPPER DRIVEN SEPARATELY EXCITED D.C. MOTOR

ABSTRACT

Armature voltage control of d.c. motor speed to a set point in the face of large step torque changes can be treated as a regulation problem in linear system theory. By proper pole assignment, one can have complete control over the dynamics of the closed loop system. The control input comes out as a function of the states, motor speed and armature current respectively, and integral of the output (speed error). The paper deals with separately exicited d.c. motors fed from a thyrister chopper circuit controlled by the state feed back signal. Discontinuous mode of current conduction in the chopper gives rise to unwanted swings in the dynamic response of the system. The proposed approach models the system taking discontinuous mode of current conduction into account, obtains the feed-back constants and predicts the oscillations that may come into picture at low shaft torques. Also a time varying model in proposed and this gives the designer an insight into the working of the system and guides him in his choice of the feedback coefficients. The proposed regulation method has been tested on a laboratory model d.c. motor, and the experimental and the theoritically predicted response curves are found to be in agreement