Hierarchy and decoupling in multivariable fuzzy controllers for a class of power electronics systems

Multi-input/multi-output fuzzy logic based controllers allow the inclusion of different types of knowledge about the controlled process. The application of multivariable fuzzy controllers in a real process is difficult due to practical limitations. After revising the available methods, the paper describes two approaches to the implementation of a MIMO fuzzy controller in a real process. Introducing a loop structure for the fuzzy controller, the first approach is based on the decomposition method and the second on a mixed decomposition and hierarchical structure. The approach allows an important reduction in a global fuzzy relation needed to control the process under consideration - the parallel operation of uninterruptible power supplies. The process multivariable and nonlinear characteristics makes it an appropriate one to test the presented methods. Simulation results are presented based on the two controller types and they are characterised in absolute terms and in relation to each other.