Suboptimal Control of a Static Scherbius Induction Motor System Using a Microprocessor

A theoretical and experimental application of modern control theory and the microprocessor to the speed control of a static Scherbius induction motor system are described. When the microprocessor is used as a controller for such a system, and where motion is fast, the processing time of the microprocessor cannot be neglected since it may well be comparable to a tenth of the time constant of the induction motor. This processing time should be taken into account as an input dead-time for the controlled object. Moreover, the range of variation of the controlling angle of the cycloconverter must be limited to within a certain value to maintain normal commutation of the thyristors. This represents an input variable constraint. In order to consider these physical restrictions and at the same time keep almost zero steady-state errors under various operating conditions, a suboptimal control design method which has been obtained by improving the original optimal regulator theory is used. Using an Intel 8080A microprocessor system, several experiments have been conducted and satisfactory results were obtained.