ROBUST CONTROLLER DESIGN USING INTERNAL MODEL CONTROL TECHNIQUE

Abstract

The fundamental concepts of control system have not changed significantly in the last few decades. The basic reasons for using control systems in contrast to open loop systems include the need to improve transient response times, reduce the steady state errors, and reduce the sensitivity to load parameters. Improving the transient response time generally means increasing the system bandwidth. Faster response times mean quicker settling allowing for higher machine throughput. Reducing the steady state errors relates to control system accuracy. Finally, reducing the sensitivity to load parameters means the control system can tolerate fluctuations in both input and output parameters. An example of an input parameter fluctuation is the incoming power line voltage and frequency. Examples of output parameter fluctuations include a real time change in load inertia or mass and unexpected shaft torque disturbances. Keeping all above stated factors, the.IMC technique proves to be one of the simple, generic, effective and advanced robust as well as optimal design and synthesis scheme. In this thesis, an attempt has been made to study the internal model control (IMC) technique in a comprehensive way. Evolution of IMC structure, its various forms and their design procedure is presented. A new IMC design scheme based on two-degree-of-freedom structure is proposed, which signifies the utility of model-order reduction technique and modified filter form. The simulation study for this scheme is conducted on single area isolated power system consisting single generator with non-reheated turbine. The results have been found to be efficient in terms of robustness and optimality. Next, to demonstrate the unique feature of IMC to tune PID-type controller through a single tuning parameter, simulation studies have been carried out for DC servomotor speed control. Modified IMC-PID scheme is suggested by striking off the lag term which is obtained while converting the conventional IMC controller into conventional feedback controller. This concept provides fast command tracking and disturbance rejection. Finally, advances and future prospects in the field of design and synthesis scheme pertaining to IMC theory are suggested for the contemporary research motivation.