Design of controllers for open-loop unstable multivariable system using inverse Nyquist array

The application of Rosenbrock's inverse-Nyquist-array design method to a multivariable system which is openloop unstable is illustrated. The original system description arises in state-space form, and has more outputs than inputs. However, the design specifications allow the problem to be recast as a regulator design, and the openloop system is analysed to determine the best choice of measurements. A simple controller using only proportional gains is determined using the inverse-Nyquist-array design method such that the system is stable. A satisfactory dynamic and static performance is obtained by the addition of classical single-loop compensators.