Microprocessor Algorithm for the Control of SCR Motor Systems

Abstract

This chapter¹contains a new algorithm for the microprocessor control of three phase SCR controlled DC machines. Two look up tables provide the open loop nominal steady state SCR firing angle and steady state current as a function of the demanded speed. A feedback correction is made to the nominal SCR firing angle according to a linear combination of the sampled deviations of the current, the speed and the sum of the speed deviations from their expected steady state values. Nonuniform sampling is used and sampling occurs at the instant of firing each SCR. The nonlinear discrete-time equations are linearized for the sake of stability analysis in the event of small speed and current deviations. The linearization analysis and digital computer simulations of a three horsepower motor indicate that control can be achieved and constant disturbance torque inputs rejected using only two sets of feedback gains; one set each for the continuous and discontinuous conduction modes of motor operation. The compute delay phenomenon is included in both the analysis and the simulations.