Phase Shift Controlled DC-DC Converters For DC-Based Microgrid

The energy crisis and environmental problems have affected the human being’s living and development. It is imminent to search for the energies that are renewable and clean. Nowadays, the microgrid is proposed to utilize the new energies, such as wind power, sorlar energy and fuel cells. Compared with the AC-microgrid, DC-microgrid is provided with more advantages. For example, stages of conversion will be reduced in the DC-microgrid, and the frequency and phase synchronization will never be taken into account. Therefore, the DC-microgrid has a wide developmental foreground.1. A phase shift controlled non-isolated bidirectional DC-DC converter is designed in this paper, to connect the DC bus and the energy storage components in the DC-microgrid. The topology is obtained by intergrating the resonant capacitor circuit and the conventional bidirectional Buck-Boost converter. The series half bridge structure in the high voltage side achieves the goal of reducing the voltage stress of the power swithes to half of the high voltage. By regulating the duty cycle, the high voltage and the low voltage of the converter can be matched, and the voltage auto-balance function at the high voltage side is realized at the same time. Phase shift control scheme is adopted to determine the energy flow. In addition, all of the power switches achieve zero-voltage-switching (ZVS), to depress the switching losses. The effectiveness of the topology is verified by the simulation and experiments.2. For the application of connecting the DC bus with the DC roads, a modular multilevel DC-DC converter is designed to sustain the high step-down and high power, by integrating the full-bridge converters and the three-level flying-capacitor circuit. The high switch voltage stress in the primary side is effectively reduced by the full-bridge modules in series. Therefore, the low-voltage rated power devices can be employed to obtain the benefits of low conduction losses. More importantly, the voltage auto-balance ability among the cascaded modules is achieved by the inherent flying capacitor. In addition, ZVS performance for all the active switches can be provided, which can reduce the switching losses. Finally, the performance of the presented converter is verified by the simulation and experiments.