High dimensional fuzzy controller for an UPS parallel system

Fuzzy logic as a basis for control method for nonlinear control systems is introduced. Multi-input/multi-output (MIMO) controllers are complex structures. Some of the main issues to be handled in a MIMO controller are practical limitations in memory space and processing time. In consequence, the design of a multivariable controller should consider aspects like the hierarchical controller structure, the input variables grouping, the existing cross coupling, or the composition method to be adopted. The paper describes two approaches, developed for a special configuration of the input variables, for designing a MIMO fuzzy controller. The parallel operation of uninterruptible power supplies (UPS) is described as a target application showing its MIMO characteristic, with high order transfer functions, high cross coupling, and containing parameters with some level of uncertainty. So, it is an appropriate system to validate the application of fuzzy logic theory as a basis for developing a nonlinear control method. Global simulation results, for real operating conditions and for both the designed controllers are presented. Comparative results state the relative performance of the two controllers. Experimental results for the two controller types, in the supervision of two UPSs in parallel operation, are presented and their relative complexity and performance are discussed