Robust Feedback Control for Nonminimum Phase, Delayed, or Unstable Systems with Multiple Inputs

This paper presents a feedback control solution that achieves robust stability and disturbance rejection in systems with multiple manipulated inputs and a single measurable output. The uncertain plant models may exhibit either nonminimum phase, or delay, or unstable phenomena, which makes it not easy to take full advantage of the frequency response of each plant. In the framework of quantitative feedback theory (QFT), a methodology is proposed to decide the best control bandwidth distribution among inputs and to design the set of parallel controllers with as small as possible gain at each frequency. The temperature regulation in a continuous stirred-tank reactor (CSTR) illustrates the benefits of a quantitative frequency distribution of the dynamic controllability between the jacket flow and the feed flow. The main challenge is that the feed flow exhibits a higher temperature regulation capacity and also produces a temporary decrease in the reactor temperature (nonminimum phase behaviour).