Variable structure systems are examined from both an adaptive and an optimal control point of view. A theoretical procedure is developed which allows the optimal switching curve for a class of bang-bang variable structure systems to be directly generated. It is shown that the optimal and adaptive control strategies are highly compatible in certain cases and that the advantages of both philosophies may be obtained by the application of a correctly chosen variable structure control law. The theoretical procedures developed are applied to the practical problem of the speed control of a 5 H.P. D.C. machine. The variable structure controller was realised in the form of a Motorola 6800 Microprocessor based system. The performance of the machine to step speed demands and to step loading was investigated with both a variable structure control law and a conventional linear control law. In both cases, the respective control law is applied after an initial period where the machine is accelerated at the maximum safe value. It is seen that substantial improvements in the dynamic performance and the consistency of performance over a range of operating conditions are obtained with the variable structure control law, when compared to the performance with the conventional linear control law.
|Date of Award||1981|