Reseach And Design Of Droop Controller Based On Operation And Control In Low Voltage Micro-Grid

With the expansion of grid, centralized power supply of traditional power system can no longer meet the variety needs of users, prompting development of distributed generation technologies. Because distributed generation is random and uncontrollable, the use and supply efficiency of distributed generation is limited. As an effective using form of distributed generation, micro-grid can not only make full advantages of distributed generation, but also coordinate the conflict between distributed generation and grid. Control strategy determines micro-grid operation in islanding and grid-connecting mode, and affects smoothness of mode transition. Therefore, determining a appropriate control strategy is the key to achieve stable operation of micro-grid.Firstly, droop control principles and characteristics, a mathematical model of a three-phase voltage source inverter and parameters design standards of LC filter are analyzed, thus a droop controller of inverter is introduced, consisited of a power calculation module, a droop characteristic control module and a voltage and current closed-loop control module, and application of droop controller in the low voltage micro-grid is also introduced. Secondly, a operation and control strategy in low voltage micro-grid is proposed based on operation modes of peer-peer control. In islanded operation mode, aiming at situation that inverters parallel system has poor reactive power sharing and voltage instability problems caused by changing loads under different connecting impedances, a self-adjusting modified droop controller is proposed to improve accuracy of reactive power sharing and voltage stability; when micro-grid changes operating mode, a synchronization droop controller is designed, ensuring a smooth transition between the islanded and grid-connected modes in micro-grid, the voltage magnitude difference, frequency difference and phase angle difference between micro-grid and grid should meet grid-connecting requirements by adjusting their output voltage.Finally, a micro-grid simulation system is built under Matlab/Simulink environment. Experiments in both islaned mode and mode transition are simulated, and analysis of the simulation results verify the effectiveness of the proposed control strategy in low voltage micro-grid, self-adjusting modified droop controller and grid-connecting synchronization droop controller.