Fuzzy control law based-on flatness property for a DC link stabilization for a fuel cell/supercapacitor hybrid power plant

This paper presents a fuzzy control law based on differential flatness approach for distributed dc generation (nonlinear system) supplied by a fuel cell (FC) (main source) and supercapacitor (auxiliary source). The main technical feeble point of FCs is slow dynamics because the power slope is limited to prevent fuel starvation problems, improve performance and increase lifetime. The very fast power response and high specific power of a supercapacitor complements the slower power output of the main source to produce the compatibility and performance characteristics needed in a load. The energy in the system is balanced by dc bus energy regulation (or indirect voltage regulation). A supercapacitor module functions by supplying energy to regulate the dc bus energy. The FC, as a slow dynamic source in this system, supplies energy to the supercapacitor module in order to keep it charged. Using the intelligent fuzzy control law based on the flatness property, we propose straightforward solutions to hybrid energy management, dynamic and stabilization problems. To validate the proposed method, a hardware system is realized with analog circuits, and digital estimation is accomplished with a dSPACE controller. Experimental results with small-scale power plant (a polymer electrolyte membrane FC of 1200 W, 46 A and a supercapacitor module of 100 F, 500 A, and 32 V) in a laboratory corroborate the excellent control scheme during a load cycle.