advantages for the instrumentist
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PCR takes benefit of control blocks where the PID is known to be poor :
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Significant time delay : in most cases the efficiency of the PID is limited to a time delay rather short compared to the time constant of the system. Using a model (including the time delay), PCR avoids the inconvenient.
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The tuning parameters are specifications having a clear physical meaning : desired closed loop time response (CLTR) and constraints on the actuator.
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Integrative system : level control by a PID is too much active (frequent and important moves of the actuator), although the level only requires to be kept within a range by smooth actions. Through the CLTR handling, PCR yields smooth actions when the level is inside the desired range.
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Split-range : applied with a PID controller, the split range principle assumes that the dynamics are similar for each action (heating and cooling). In fact, they are usually quite different (time constant and time delay) and this explains the poor and oscillating results. Relying on two different models, PCR handles correctly each actuator. Also, each action is computed with the knowledge of all the actions applied in the past.
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Feedforward : the effects of measured disturbances are taken into account in the prediction
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PCR is well design for chemical reactors and other thermal systems
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Availability of a CAD : easy tuning and testing on a simulator
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Simplified integration : the PCR is a library of modular control blocks in C language and Structured Text
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Technical assistance from Sherpa in case of necessity
- Really ADVANCED control technology (MBPC - Model Based Predictive Control)
