Feed-forward control strategy

In this short initial communication we wish to describe a general purpose continuous-flow stirred-tank reactor (CSTR) system which incorporates a digital computer for supervisory control purposes and which has been constructed for use with radical and other polymerization processes. The performance of the system has been tested by attempting to control the MWD of the product from free-radically initiated solution polymerizations of methyl methacrylate (MMA) using oscillatory feed-forward control strategies for the reagent feeds. This reaction has been selected for study because of the ease of experimentation which it affords and because the theoretical aspects of the control of MWD in radical polymerizations has attracted much attention in the scientific literature. 

The major limitations of the feed forward control strategy presented here are that (i) it is only as good as the fundamental data which are used in the models and (ii) it can only be used for systems which conform to the conventionally accepted mode of behaviour of free radical chain polymerisation in solution. However, the same approach can be used with the appropriate models for any copolymerisation process. The range of application can be increased by making an arbitary assessment of the parameters necessary for the control models and/or by introducing a feedback loop which incorporates some state measurement device, e.g., an in-line gas chromatograph for measurement of residual monomers concentrations. Such a scheme is shown in Figure 21. 

A mathematical model with which the dryer and process parameters can be studied is of extreme utility to the industry. A reliable model often will prevent or minimize costly mistakes in prototype development. The model also can be utilized for the control of process, specifically in adaptive and feed-forward control strategies. With the proliferation of low cost and powerful computers, the simulation models are useful. In this chapter, the emphasis is on the presentation of formulas and equations rather than the conventional charts and graphs in drying calculations. 

Thus, with this feed-forward control strategy and with F linearly dependent on h together with the assumption that all loop delays are neglected, then h remains at all the time. 

An alternative scheme to pure feed-forward control is to use a combination of feedback and feed-forward control strategies. This is illustrated in Figure E21.4rcl and discussed below. 

Chapter 6 develops model predictive control concepts. This structure allows for the inclusion of predictive feed-forward control into the optimal control problem. We consider design strategies for completely measurable disturbances as well as systems with both measurable and unmeasurable disturbances. 

MBC-Tool an environment facilitating the testing of conventional and advanced model based control strategies within Matlab. It includes feed-forward control, cascade control, delay compensation, IMC control as well as decoupling control techniques. It can be used for both single-input single output and multi input multiple output processes and allows the computation of different robustness measures to compare alternative designs. 

Consider the feed section of the toluene process given in Figure 1.5. The flow of fresh toluene. Stream 1, is regulated by monitoring the level in the toluene storage tank, V-101. If the level is seen to drop, then the valve on Stream 1 opens and vice versa. This is an exanple of a feedback material balance control loop. For this system, inplement a feed-forward control scheme in which the flow of the recycle. Stream 11, is measured and used to control the flow of Stream 1. Do you foresee any potential problems with this control strategy ... 

Feedback control can never be perfect as it only reacts to the disturbances which are already measured in the system output. The feed-forward method tries to eliminate this drawback by an alternative approach. Instead of using the process output, the measured variable is taken as the measured inlet disturbances and its effect on the process is anticipated via the use of a model. The action is taken on the manipulated variable using the model to relate the measured variable at the inlet, the manipulated variable and the process output. The success of this control strategy depends largely on the accuracy of the model prediction, which is often imperfect as models can rarely predict the... 

The dynamic model was validated both in steady and unsteady-state conditions, which is quite interesting in case that a control based on feed-forward strategy is applied. The prediction of the final concentration of Orange II from the initial data would allow the system control to modify the flow rate of MnP, Orange II or H2O2, in order to adapt the conditions to the desired final value. 

The strategy of distillation control is open to many creative approaches because there are five or six main variables to manipulate and many possibilities for cascade, feed-forward ratios, and model-based computer control as well as conventional feedback control. 

Figure 20(b) illustrates a case where, at low NaOH addition, the concentration of carboxylate surfactants is near-zero and when the sulfonate surfactant concentration reaches Css, a first primary recovery maximum is observed. For the same oil sand processed at a moderately high NaOH addition level, the carboxylate snrfactant concentration has increased and reaches Ccs, which condition a second primary recovery maximum is observed. This two-peak processibdity curve is not an artifact, as it has been reproduced in mnltiple laboratory studies and also in continuous pilot-scale testing [104], This particular kind of oil sand (a type of channel margin origin) first gained notice when a so-called problem ore in a commercial extraction plant was encountered, for which traditional feed-forward fines-content process control strategies failed. 

There are many strategies used to control process variables in an operating plant. For more details, see Anderson [1] and Shinskey [2]. In this section, we consider only feedback, feed-forward, and cascade systems. 

Describe which form of control strategy (feed-forward, feedback, cascade, or a combination of y these) best describes how a responsible person drives an automobile. 

Rgab, O., D. L. Yu and J. B. Gomm. Polymer electrolyte membrane fuel cell control with feed-forward and feedback strategy. International Journal of Engineering, Science and Technology 2(10) 56-66, 2010. 

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