Controller Design of Two-Mass Resonant System by Coefficient Diagram Method

Abstract

In the controller design of position or velocity control, the flexibility of the mechanical system is always the limiting factor to the higher performance. In this paper, the speed control of a two-mass resonant system, where the speed sensor is located only on the drive motor side, is investigated. Such a system is typically found in steel mill drives. The controller design is made successfully in practical sense using various design techniques, such as classical control, resonance ratio control with disturbance observer, and H∞ control. However, a unified theoretical approach is needed to understand the real nature of the problem. For this purpose, a new controller design approach, called “Coefficient Diagram Method”, is introduced. The result shows that the optimum controller, in normalized form, is the sole function of the ratio of motor inertia to the total inertia. As the ratio increases, the controller type needed varies from PI control to PI control with lag, and finally to PID control with lag where D control is week positive feedback. The typical controller designed in the past have been compared with this design.