Multi-Stage Noninteracting PID Control by Precompensators with Series-Parallel Connection

In multivariable control systems, controlled variables interact each other in general. In this case one compensation for a control loop exerts harmful influence upon other control loop through the interaction. If we could take away this interaction by some ways for a complete one to one corresponds between the manipulated variable and the controlled variable, then the design of control systems results in the individual compensation of the single loop control. A cross controller was used for removing the interaction thus far mainly, but it was complicated and the controller was high-order. On the other hand, the precompensator by the Inverse Nyquist Array method was also used for noninteraction of the controlled variables. However it is difficult to remove the interaction of the controlled system, which has very strong interaction, when the precompensator is used only one. This paper proposes the series and/or parallel connection of the precompensators for a multi-stage noninteracting PID control, and the multi-stage precompensators are applied to the control of the fluid temperature and liquid level interacting plant to confirm the effectiveness.