On-line process identification and implementation of a proportional- integral-derivative controller in a full-scale wastewater treatment plant

In this article, a new on-line process identification method for the automatic tuning of the proportional-integral-derivative (PID) controller is proposed and applied to a full-scale wastewater treatment plant. The proposed method can identify general time-invariant linear systems with a frequency weighting, while retaining simplicity. The frequency weighting makes it possible to improve the robustness to underparameterization and uncertainties such as disturbances and noise. Under the proposed scheme, the high-order model is reduced to a lower order using a model reduction method to enable the tuning of the PID controller using the well-established tuning rules based on the first- or the second-order plus time delay model. Because the suggested process identification method uses only process input/output, it overcomes many of the disadvantages of previous identification methods; in particular, it does not require a special test signal generator such as a relay or a P controller. The properties of well-known signal generators are discussed, and guidelines are also outlined for choosing an appropriate signal generator. The proposed method showed better control performance in the simulation studies than previous methods, and was successfully applied to dissolved oxygen (DO) control in a full-scale wastewater treatment plant.