Water level control of sewage wells : PID-tuning and optimal selection of active pumps

Sammanfattning

Huge amounts of energy is used every day to pump wastewater from one point to anotherleading to a demand for optimization strategies of pump systems. A typical pump systemconsists of one of more pumps submerged in a basin with varying inflow, pumping water to ahigher level. PID-control is utilized to match the pump speed to the inflow and keep the waterlevel in the basin somewhat even. At certain speed thresholds extra pumps are added orremoved. This paper investigates strategies to tune the PID-controller and to define the speedthresholds to minimize the energy usage of the pumps. This is done by creating a model of apump system, trying different strategies and evaluating which strategies require the smallestenergy output by comparing how well the estimated results compare to the true best results,and then measure the energy usage over a 24-hour period of a made-up system. The resultsshow that tuning the PID-parameters has a low impact on energy usage. Furthermore, when thepumps installed are of a model that well suits the system, using default thresholds values is agood idea because the best practice is in that case to add extra pumps only when the speed isclose to 100%. In cases when the pump installed is stronger than necessary a method to findthe optimal speed thresholds has been constructed and can be used to get lower energyconsumption