The variable frequency speed control system based on the modified two-degree-freedom internal model control and its robustness analysis

A conventional Internal Model Control (IMC) method cannot be applied to solve the contradiction of the output tracking and the load disturbance rejection performance. In order to overcome the shortcomings of it, two degree freedom (2DOF)-IMC is applied to solve the problem, but the normal 2DOF-IMC has a complex structure. This paper presents the modified 2DOF-IMC method that has a simple structure and control method. The modified 2DOF-IMC is applied in the speed control system of Asynchronous Machine (IM). Rotor flux & speed 2DOF controllers are designed, the robustness performance of the modified 2DOF-IMC is analysed. The performance of the modified 2DOF-IMC has been verified by computer simulation. Theoretical analyses and simulation results show that the output tracking and disturbance regulation characteristics of speed control system are regulated respectively by using controllers based on 2DOF-IMC, the proposed controllers provide very good dynamic response performance.