A two-degree-of-freedom ratio control scheme

A two-degree-of-freedom ratio control scheme is proposed in this paper. The ratio control system includes two control loops, both of which have two-degree-of-freedom control structure so that the setpoint response could be decoupled from the disturbance response. In order to achieve perfect ratio control both at the steady states and during the transients caused by setpoint and load disturbance changes, the ratio controllers for setpoint and load disturbance changes are introduced between the two loops, respectively. For ease of implementation in industrial practice, the analytical design formulas for the controllers are all provided. Meanwhile, quantitative performance and robust stability of the system are discussed. Simulation tests are included to demonstrate the effectiveness of the proposed method.