Topology And Control Of Wind/PV Interfaces For DC-Based Microgrid

With the growing energy crisis and environmental problems, many countries around the world are concerned about the development of renewable energy.The distributed energy, such as wind energy and solar energy, has become a hotspot both in academic and industrial areas.However, due to the extensiveness and randomness of distributed generation in space and time, when the penetration of distributed generation increases, the existing power system faces great challenges. To solve this problem, some American researchers proposed the concept of microgrid at the beginning of this century. In recent years, the research for microgrid has become one of the hottest topics in Electrical Engineering community. The major research of this paper forcuses on the topology and control of Wind/PV interfaces for DC Microgrid.1. In wind power generation, Back-EMF algorithm based on state observer is used to realize the sensorless FOC for PMSG. On this basis, the inherent MPPT strategy is utilized to achieve the maximum energy capture and power management. Meanwhile, the stability of this strategy over the entire operating range is proved by the first theorem of Lyapunov. Finally, a5kW platform is built and the effectiveness of the control strategy is validated.2. In PV generation, taking advantage of the existing high step-up converters, a single phase high step-up converter with improved multiplier cell is proposed. The coupled inductor voltage doubler cell is introduced and provides another control freedom to achieve large voltage conversion ratio. Besides, leakage inductance of coupled inductor is used to achieve ZVS soft switching of all the switches. This converter realizes the conversion of low PV voltage to high bus voltage which is required by the grid-connected inverter. In laboratory, a prototype is built and the effectiveness of this novle converter in photovoltaic applications is verified.3. According to the requirements of DC microgrid, this paper selects the hierarchical control schemes for the system. Furthermore, converter control level, bus regulation level and scheduling management level are proposed in this paper. In the converter control level, all the converters can be represented as a controllable current source. In the bus regulation level, all the converters have their own control algorithms. According to the variation in bus voltage, each module in DC microgrid can work in three different modes to ensure the stable operation of the system. Finally, a set of DC microgrid platform is built and a set of experimental results verify the feasibility of the theoretical analysis.