An Approach to Discretization in Simultaneous Design of Structure and Control Systems
Tatsuto Ichiya, March 1998 (in Japanese)

A control system is an interconnection of plants and controllers. Since the performance of the control system is determined by plants as well as controllers, we have to design not only controllers but also structure parameters of plants in order to achieve desired performance. In ordinary control system synthesis, we first design structure parameters, and design controllers afterwards. In this approach, it is difficult to choose structure parameters taking account of the performance of the total control system. Therefore, we should design structure parameters and controllers simultaneously.

The simultaneous design of continuous-time control systems with continuous-time controllers has been investigated by several researchers. The controller is, however, discrete-time in actual control systems, which makes the total closed loop is a sampled-data system. In these sampled-data systems, not only plants and controllers but also sample/hold periods influence the performance of the control systems. A structure parameter has different influences on the performance for different periods. When we design sampled-data control systems, we should pay attention to sample/hold periods in addition to characteristics of plants and controllers. In this point, sampled-data simultaneous design is different from continuous-time one considerably.

This paper focuses on simultaneous design of structure parameters and controllers in sampled-data control systems. In the case of simultaneous design in continuous-time system, all design parameters are continuous-time. But in sampled-data systems, structure parameters are continuous-time, and controllers are discrete-time. The simultaneous design of sampled-data systems are different from the design of continuous-time ones in this point as well. Therefore, we cannot apply ordinary methods of continuous-time or discrete-time controller synthesis to simultaneous design of sampled-data systems. The author proposes an approach to simultaneous design of structure parameters and discrete-time controllers. An example is presented to illustrate the effectiveness of the proposed method.