Multivariable control of two‐input and two‐output system using relay autotuning method: An experimental analysis

Abstract In this paper, the improved decentralized controllers for a MIMO system are designed using the sequential and simultaneous relay autotuning method. Conventionally, the decentralized controllers are designed without including the effect of higher‐order harmonics. Few papers in the literature, discuss the design of controllers with the consideration of higher‐order harmonics using simultaneous relay autotuning for different levels of interactive processes. The selection of the relay autotuning method based on the level of interaction has not been revealed in the literature so far. In this paper, the controllers are designed for the TITO system using the improved method of sequential and simultaneous relay autotuning by considering the effect of higher‐order harmonics, and also the interaction is analyzed. The relay feedback test using sequential and simultaneous loop tuning methods is performed. The effect of higher‐order harmonics from the initial dynamics of the sustained relay oscillation is analyzed for the Wood and Berry Distillation Column. The decentralized controllers are designed with the relay response data and the improved amplitude values are estimated by incorporating the higher‐order harmonics. To verify the usefulness of the proposed method, the improved method of sequential and simultaneous relay autotuning method is demonstrated in a real‐time laboratory experimental setup. From the qualitative and quantitative analysis, it is inferred that the improved method of simultaneous autotuning provides good setpoint tracking and disturbance rejection. It also gives better robustness and effect of measurement noise than the sequential autotuning method.