Multivariable control of unstable systems by goal attainment method

Goal attainment method is used to design (i) decentralized PI controllers for a 3×3 stable multivariable transfer function matrix and (ii) decentralized and centralized PI controllers for an unstable 2×2 transfer function matrix. The performance of the closed loop system of 3×3 stable multivariable system is compared with that of the biggest log modulus (BLT) method, sequential tuning method, and the method of inequality. For unstable systems, the performance of the present method is compared with the method proposed by Govindhakannan and Chidambaram. The present method gives the improved performances.