Dynamic behavior of closed grinding systems and effective PID parameterization

The object of the present study is to investigate the dynamic of closed circuit cement mills and based on that to tune robust PID controllers applied to three actual installations. The model that has been developed, consisting of integral part, time delay and a first order filter, is based exclusively on industrial data sets collected in a period more than one year. The model parameters uncertainty is also assessed varying from 28% to 36% as the gain is concerning and 34% to 42% as regards the time delay. As significant sources of model uncertainty are determined the grinding of various cement types in the same cement mill and the decrease of the ball charge during the time. The Internal Model Control (IMC) and M - Constrained Integral Gain Optimization (MIGO) methods are utilized to adjust the controller parameters. Specially by implementing the MIGO technique robust controllers are built deriving a daily average IAE 2.3-3% of the set point value. Due to the high flexibility and effectiveness of MIGO, the controllers can be parameterized by taking into account the cement type ground and the power absorbed. Subsequently the attenuation of main uncertainties leads to improvement of the regulation performance.

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