Tuning of Multivariable PI Controllers by BLT Method for TITO Systems

The design of decentralized proportional integral (PI) controller based on biggest log modulus tuning (BLT) tuning method is extended to design centralized PI controllers for two-input–two-output (TITO) systems. The multivariable PI control structure proposed by Tanttu and Lieslehto (1991 Tanttu, J. T., and Lieslehto, J. (1991). A comparative study of some multivariable PI controller tuning methods, in: Devanathan, R. (ed.), Intelligent Tuning and Adaptive Control, IFAC, Singapore, pp. 357–362.[Crossref] , [Google Scholar]) is considered. The single detuning parameter (F) is selected in order to get the biggest log modulus as 4 dB. Decentralized PI controllers are also designed using the IMC to get the biggest log modulus as 4 dB. The centralized PI controllers give improved main responses and decreased interactions. This improvement is shown particularly for TITO systems having the relative gain element, λij < 1. The robustness of these controllers is evaluated by the inverse maximum singular value versus frequency plot for both the input and output multiplicative uncertainties. Simulation results are given for two TITO examples. The present controllers give better performances over that of the original Tanttu and Lieslehto (TL) method. The present decentralized PI controllers give improved performances over the decentralized PI controllers proposed by Xiong and Cai (2006 Xiong, Q., and Cai, W.-J. (2006). Effective transfer function method for decentralized control system design of multi-input multi-output processes, J. Process Control, 16(8), 773–784.[Crossref], [Web of Science ®] , [Google Scholar]).