Hierarchical fuzzy controller and its industrial application

To reduce the difficulties involved in choosing an appropriate fuzzy knowledge base, i.e. scaling factors, membership functions, rules, etc., of a fuzzy PI controller that is capable of control in most industrial environments, a kind of fuzzy controller with a hierarchical structure is proposed which takes accumulated control as an input in addition to the error and change of error. The new fuzzy controller is divided into several subcontrollers which can be designed separately. Each subcontroller can be designed easily and can perform well in a certain running state. When all the subcontrollers perform well, the hierarchical fuzzy controller can obtain a good performance. A general strategy for dividing up the whole controller is defined. Simulation results show that both the transitory performance and the steady-state performance are better than that of conventional fuzzy PI controllers. The proposed hierarchical fuzzy controller is applied to a 10 tonne/hour coal-burning grate boiler and some real-time running results are given.