Optimal PI controller design for active power in grid-connected SOFC DG system

Abstract

This paper is concerned with optimal control of grid-connected solid oxide fuel cell (SOFC) stack based on a model developed and validated in the literature. Recent studies have shown that control of SOFC is challenging due to its slow dynamics and firm operating limits. For an SOFC, while the primary objective is to supply the demand active power, it is crucial to operate fuel cell within its safe operating constraints. In order to meet these requirements, a proper control strategy is developed in this study. This control strategy employs an optimal robust PI controller to control active power of the plant and at the same time satisfies physical and operating constraints via employing two proportional-gained controllers, of fuel utilization factor controller and anode–cathode pressure difference controller in such a way to maintain the fuel utilization factor at its optimal value of 85% and also keep pressure difference between anode and cathode within the safe bound of 0–0.08atm under transient conditions. A distributed generation (DG) system including an SOFC stack connected to the power grid through an IGBT inverter is implemented in MATLAB/SIMULINK™ environment. Moreover, dynamics of fuel processor are included. In addition, differential evolution (DE) algorithm evaluated by integral of time multiplied by absolute error (ITAE) criterion is used to search for optimal values of PI controller parameters. Dynamics of the DG system are analyzed for the cases of conventional and proposed PI controllers under different load changes and short circuit condition to verify the performance of proposed PI controller. Simulation results show that the proposed controller can provide satisfactory performance for load changes and short circuit condition at the cost of keeping the SOFC performance beyond its operating constraints.