Application of three-degree-freedom Internal Model Control and mechanism analysis of IMC system robustness

In the conventional two-degree-freedom (2DOF) internal model control (IMC) method, input controller is applied to regulate the output tracking, forwardback controller to regulate both load disturbance rejection performance and robustness performance. In order to regulate respectively them, this paper presents the three-degree-freedom(3DOF) IMC method, the additional feedback controller is used to regulate the robustness of the system. First the principle of 3DOF-IMC is analyzed, and the relation between robustness and feedback controller is searched. Then the 3DOF-IMC method is applied to the speed adjusting drive system of DC machine. The performances of system, based on 3DOF-IMC, have been verified by computer simulation. Simulation results show that the output tracking, the load disturbance rejection and robustness performance of system are regulated respectively by using the 3DOF-IMC method, the proposed 3DOF-IMC methods provide very good dynamic response performances.