Near-optimal productivity control of a continuous bioreactor by a conventional proportional-integral controller poses stability problems, and certain nonlinear controllers yield excessive variation of the manipulated variable. A nonlinear controller based on the Hammerstein model is proposed to overcome such problems. The performance of the proposed nonlinear control is compared with that of the nonlinear controllers proposed by Henson and Seborg.

Manickam Chidambaram

Bioreactors

Control equipment

Mathematical models

Nonlinear control systems

Two term control systems

CONTINUOUS BIOREACTOR

HAMMERSTEIN MODEL

NEAR OPTIMAL PRODUCTIVITY CONTROL

Optimal control systems

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IIT Madras

IEE Proceedings: Control Theory and Applications

A steady-state nonlinear feedforward controller (FFC) for measurable disturbances is designed for a continuous bioreactor, which is represented by Hammerstein type nonlinear model wherein the nonlinearity is a polynomial with input multiplicities. The manipulated variable is the feed substrate concentration (Sf) and the disturbance variable is the dilution rate (D). The productivity (Q=DP) is considered as the controlled variable. The desired value of Q=3.73 gives two values of feed substrate concentration. The nonlinearity in the gain is considered for relating output to the manipulated variable and separately for the relation between output to disturbance variable. The FFC is also designed for the overall linearized system. The performance of the FFC is evaluated on the nonlinear differential equation model. The FFC is also designed for the model based on a single nonlinear steady-state equation containing both D and Sf. This nonlinear FFC gives the best performance. The nonlinear FFC is also designed by using only linear gain for the disturbance and nonlinear gain for the manipulated variable. Similarly, nonlinear FFC is also designed by using linear gain for the manipulated variable and the nonlinear gain for the disturbance variable. The performances of these FFC schemes are compared.

Bioprocess and Biosystems Engineering

Nonlinear feedforward control of bioreactors with input multiplicities

A closed loop identification method of Hammerstein model for continuous bioreactor with input multiplicity is proposed. Hammerstein model consists of nonlinear steady-state gain followed by a unity gain linear system. The method consists of first getting local first order plus time delay (FOPTD) models around the two input multiplicity values of the substrate feed concentration. The model parameters of the FOPTD is identified by a least square optimization method. The initial guess for the model parameters are obtained from the settling time, the initial delay in the closed loop servo response and using a simple proportional controller formula. From the local process gain values obtained for the several step changes around the two operating conditions, the nonlinear gain portion of the Hammerstein is then obtained. The actual nonlinear gain and the identified nonlinear gain is compared.

Bioprocess Engineering

Identification of hammerstein model for bioreactors with input multiplicities

Control of bioreactors exhibiting two input multiplicities, i.e., steady-state gains having opposite sign, is theoretically analyzed. The nonlinear system is represented by a unity gain linear system cascaded with a nonlinear gain. A conventional PI controller designed for the linear portion of the system followed by the solution of the nonlinear gain equation gives a nonlinear controller. The performance of the nonlinear controller is compared with that of the linear PI controller designed for the overall linear system. The nonlinear PI controller performance is superior to that of the linear PI controller. © 1994 Springer-Verlag.

Nonlinear control of bioreactors with input multiplicities

Chemical Engineering Science

Nonlinear control strategies for continuous fermenters

Journal of Process Control

Critique of exact linearization strategies for process control

The control of a semibatch reactor is treated as a multivariable setpoint trajectory tracking problem. Global input/output linearization is used to obtain a decoupled linear system that is placed under internal model control. A coordination strategy is proposed for the operation of the two loops. Adaptive features are incorporated in the strategy to account for uncertain kinetics. The control system has a number of tuning parameters that can be used to obtain performance tradeoff. © 1991, American Chemical Society. All rights reserved.

Industrial and Engineering Chemistry Research

Multivariable Global Input/Output Linearized Internal Model Control of a Semibatch Reactor

Industrial & Engineering Chemistry Research

Adaptive control of the hydrogen concentration in anaerobic digestion

Near-optimal productivity control of a continuous bioreactor

Journal	IEE Proceedings: Control Theory and Applications
Publisher	IEE, Stevenage, United Kingdom
ISSN	13502379
Open Access	No