Research On The Control Method Of Three-phase AC/DC Converter In Hybrid Microgrid

AC/DC hybrid micro-grid can enable intermittent renewable energy connect to the grid flexibly and improve the utilization of renewable energy. In the meantime, its framework contains both AC bus and DC bus, reduceing the times of ac/dc power conversion, simplifying the topology of the distributed power microgrid, cutting down the power loss of the converter, has attracted many attentions of experts and scholars. Three-phase AC / DC converter, which connects the AC bus and DC link and can work in the state of rectification and inverter, has important significance in AC/DC hybrid micro-gridThe paper presents a three-phase AC / DC converter control system in hybrid micro grid. The proposed control strategy can makes the system achieve sinusoidal AC current in AC voltage unbalance, while maintaining the DC bus voltage constant and ensure the AC/DC hybrid microgrid can operate stablly with voltage unbalance. The specific contents are as follows:First, this paper introduces briefly the research status and the development of AC/DC hybrid microgrid and establishes the structure of the photovoltaic cells and storage system. Based on those, the output characteristics of photovoltaic cells are analyzed and the control strategy of boost converter in photovoltaic cells is designed to achieve the maximum power output. In the meanwhile, the operating principle of lithium battery and super capacitor is analysised, which is batter to design energy storage charge and discharge control strategy for bidirectional DC / DC converter.Second, based on analysis of structure and working principle in hybrid micro-grid, the mathematical modeling of the three-phase AC / DC converter in different coordinate systems getting the transfer function of the controller, and the control strategy is proposed. Finally, the simulation models in Matlab/Simulink are builed to prove the strategy of three-phase AC/DC converter feasibly.Third, the three-phase AC/DC converter is designed with considering the ubalanced voltage. When the three-phase AC/DC converter is connected to the voltage unbalance system, the AC current is not asymmetry and the DC bus voltage has two times frequency fluctuation, affecting the normal operation of the converter and deteriorating the power quality of hybrid microgrid. Based on that background, for this often appears, this paper presents control system based on super capacitor compensation of three-phase AC/DC converter. It can inhibited the negative sequence current of AC side to make the AC side current sinusoidal, symmetrical through the control of the three-phase AC/DC converter, and maintain the DC bus voltage stability, using super capacitor charging and discharging. Finally, the simulation models in Matlab/Simulink are builed to prove the strategy of three-phase AC/DC converter feasibly.Fourth, low-voltage experimental platform of the three-phase AC/DC converter is designed. And the results show that the three-phase AC/DC converter can maintain the balance of power system, guarantee the stability of the DC bus with the balanced voltage. And the proposed control system under unbalanced voltage can ensure improve the quality of operation of the DC hybrid microgrid and enhance the operational capacity of the hybrid microgrid.