G.P. Reddy and A.N. Raju (India)
Input multiplicities, NIMC, pseudo dynamic model, bioreactor, washout and stable
Input multiplicities mean more than one value of input variable produces the same value of output variable in a single input and single output (SISO) process. For a process with Input multiplicities, the value of steady state gain of the process changes as the input variable changes and after certain value of the input, the sign of the gain also changes. Proportional Integral (PI) controller for such nonlinear process with Input multiplicities may give unstable, less economical or oscillatory responses. Model based nonlinear controller controllers are reported to give superior performance for process with Input multiplicities. In the present work, the nonlinear internal model controller based on pseudo dynamic model is designed to a continuous bioreactor which exhibits input multiplicities in dilution rate on productivity i.e., two values of dilution rate will give the same value of productivity. As the NIMC provides always two values of dilution rate for control action and by selecting the value nearer to the operating point, it is found to give stable and better performance than the linear PI controller. Whereas, linear PI controller results in washout condition when linear PI designed for lower dilution rate is used for higher dilution rate. Thus, NIMC is found to overcome the control problems of PI controller due to the input multiplicities.
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