I. Introduction
Due to the development of renewable energy sources, there is an increasing demand for combining diverse sources, such as photovoltaic panels, wind turbines, fuel cells and batteries [1]–[4]. The integrated power supply system has higher flexibility, longer durability and improved effectiveness when compared with the conventional single-source power supply system. Therefore, the integrated power supply system is promising in many situations, such as energy harvesting of wireless sensor networks, electric vehicle applications, and future residential power supply systems [5]–[9].