A Hybrid Renewable Sources Implementation for a DC Microgrid with Flatness-Nonlinear Control to Achieve Efficient Energy Management Strategy

Abstract

The significance of energy management using sustainable energy sources and the merits of DC in AC microgrids are due to less complexity, smaller size, and fewer conversion stages. In this paper, we propose a standard-islanded DC microgrid with photovoltaic (PV) and fuel cell (FC) primary sources and a supercapacitor (SC) storage unit. The proposed system provides high-quality energy supplied to the DC load under different levels of solar irradiation and changing loading situations. Taking into account the slow dynamic response of the FC, the SC provides transient periods under various conditions to maintain stability of the system. Because of the nonlinear system's behavior, differential flatness-based control has been applied mainly in nonlinear systems where the number of variables to the outputs is reduced with a robust control system established through inherited parameter reductions and equality constraints due to the system trajectories (x, u) is straightforwardly estimated from flat output trajectories y and their derivatives without any differential equation integration. The PI control is executed when the SC adjusts the DC bus voltage variation. Therefore, the objective is to provide management that ensures stable DC bus voltage and arranges power sharing between variable sources and power balance with a load. Flatness PI has been investigated and has proven effective in offering faster response without overshoot and greater robustness.