Modified derivative decoupling control of nonlinear multivariable process

A method is developed for on-line noninteracting control of a nonlinear multivariable process to handle constraints on the control variables based on the derivative decoupling control approach. An extension of the proposed modified derivative decoupling control method to load changes (unknown disturbance) is also treated. This modified method is investigated for noninteracting control of laboratory-scale mixing tanks in series both by digital simulation and by experiment using an on-line microcomputer. Liquid levels and temperature in tanks mixing hot and cold water inflow streams are controlled. The results are compared with those obtained by instantaneously optimal control and by the inverse Nyquist array technique. Both simulated and experimental performances of the modified derivative decoupling controller are found to be better in comparison with those obtained by the controller based on the inverse Nyquist array. Further, experiments showed that the modified derivative decoupling controller can reduce interaction to a negligible level.