Implementering och utvärdering av en PID-regulator i simuleringsverktyget SUMO : En fallstudie av processtyrning vid Himmerfjärdsverket

Sammanfattning

Wastewater treatment plants are complex systems where effective process control is critical for plant performance. Since full-scale experiments are difficult to conduct, process models and simulations are commonly used to analyze and evaluate control strategies. For such analyses to be reliable, properly functioning controllers are required.In this work, the existing PID controller in the Sumo simulation tool is investigated. The results show deviations from established theory. In the proportional term, an unintended integral effect is introduced, while the integral term shows amplified integral action. The derivative term is calculated from initial values rather than differences between successive measurements, explaining the unexpected behavior observed during use.A PID controller consistent with theory was implemented and tested using several tuning methods. To support tuning, a script was created to estimate a FOPDT model from step-response data. The lambda method provided the most robust control, with the output converging toward the setpoint in the studied cases. It was also less sensitive to sampling time, enabling faster simulations. Overall, the lambda method was considered the most suitable approach.A process model of the new Himmerfjärdsverket plant was also developed in Sumo. The plant is under construction and not yet fully commissioned. The model showed good agreement with real data, but due to limited calibration it should mainly be used for qualitative evaluations or comparisons of control strategies. The model served as a case study for the implemented PID controller and tuning method. In the more complex and disturbance-prone system represented by the case study, additional tuning of the PID parameters was in several cases required to achieve desired performance.