RECURSIVE STEP RESPONSE ESTIMATION

As discussed in the previous section, a standard relay experiment typically produces a limit cycle that is dominated by a single frequency. However, this information is not sufficient for the estimation of an accmate process step response model. This raises the issue of how to generate the appropriate information. One approach is to inject a dither signal while the process is under some sort of feedback control, either additively to the controller output or via the setpoint. However, this requires design of the dither signal, i.e. decisions must be made concerning its power spectrum. Another alternative is to make use of multiple relay experiments to generate frequency response information at several frequencies. 

Recursive Estimation from Relay Feedback Experiments 

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This chapter describes two new methods for obtaining frequency response and step response models from processes operating under relay feedback control. Both methods are based on the frequency sampling filter model structure and a recursive least squares estimator. 

Here, we study the performance of the proposed methodology for recursive estimation of the process step response using five examples, four of which have been selected from the test batch presented in Astrdm and Hagglund (1995). 

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