Decoupling of MIMO Systems Using Cascaded Control Architectures with Application for HVAC Systems

Coupling in control systems can create many difficulties for control engineers, especially when trying to use traditional control techniques. In this paper, the potential of cascaded control architectures utilizing standard PID control loops is explored as a means for decoupling highly coupled systems. A theoretical analysis of the decoupling effect is presented and is shown to completely separate input and output pairs under certain conditions. Criteria for selecting gains is determined and compared with previous work on linearization effects of the cascaded architecture. Finally a sample system based on multi-evaporator vapor compression system dynamics is presented to demonstrate key principles of the technique resulting in reduced coupling for specific ranges of inner loop gains.