Evolutionary parameter optimization of a fuzzy controller which is used to control a sewage treatment plant

摘要

In order to meet new environmental standards, sewage treatment plants may need to benredesigned or extended. Instead of reconstructing large parts of a sewage treatment plant,nwhich can be very costly, it is in many cases sufficient to install relatively inexpensive equipment,nwhich controls partscof the plant in a new way. Fuzzy controllers are often used for this task.nUse of these controllers often leads to an improved water quality. Such fuzzy controllers containna number of parameters which are determined by a human expert. With this contribution,na dedicated multi-objective evolutionary algorithm is developed to optimize these parameters.nThe evolutionary algorithm is based on the successful strength pareto evolutionary algorithm 2n(SPEA2). The fuzzy control parameters, which are optimized are continuous parameters.nTherefore, an evolution strategy was employed which uses the multi-objective ranking as used bynthe SPEA2 algorithm. Optimal parameters were first evolved on simulated sewage treatmentnplants. One set of parameters was also tested on an actual plant. Owing to the enormousncomputational demands of simulating a sewage treatment plant, it is only possible to work withnsmall population sizes. Nevertheless, it was possible to evolve parameters which were equallynwell as those found by a human expert indicating that the parameter tuning can be automized.