Operation Simulation And Small Signal Stability Analysis Of Microgrid Based On Droop Control

In recent years, large area power failures have occurred so frequently that fully exposed the malpractice of traditional grid. In the grim situation of increasing energy crisis and environmental pollution, people start to pay attention to distributed generation technologies based on renewable clean energy. Distributed generation has many advantages, but the adverse effects that the connection of a large number of distributed sources brings to the grid restrict its development, micro-grid is a good solution to this problem. Micro-grid combines distributed sources, loads, energy storage units and control devices into a single manageable system, which can both operate in grid-connected mode and islanding mode. Good operational control is the premise of micro-grid to achieve its advantages. The small inertia of micro-grid makes it vulnerable to disturbance and easily to oscillate, so it’s essential to study on its stability.Micro-grid based on droop control can achieve automatic adjustment of voltage and frequency without resorting to communication when operating in islanding mode, so it can improve reliability of the micro-grid system, and can easily implement the plug-and-play of micro-sources and loads, moreover, micro-grid can change its operation mode without changing the control method of micro-sources, so that it can achieve seamless switching of operation mode.Firstly, based on the analysis of output power transmission characteristics of micro-sources and droop control theory, droop controller is designed. For the line impedance is resistive in the low voltage micro-grid, the transfer function of the voltage and current double loop control is analyzed using frequency domain method, and the equivalent output impedance of inverter sources is made inductive though design of PI control parameters, thus it can meet P-f, Q-U droop characteristics.Secondly, simulation model of the droop controller is built in Matlab/Simulink software and verified by a designed simulation example, based on this, a micro-grid simulation model using peer-to-peer control strategy is established, then simulation research on operating characteristics of islanding mode, grid-connected mode and operation mode switching is conducted to verify the effectiveness of droop control method and the control effect of peer-to-peer control strategy.Finally, complete small-signal state-space model of micro-grid in islanding operation mode is established, then the influence of different parameters’changing on micro-grid stability is concluded by analyzing the state matrix of micro-grid small-signal model though eigenvalue method:the increase of droop characteristic coefficient will reduce the stability of micro-grid system, and the micro-grid system will easily lose stability when the line impedance parameters become small. The conclusions of micro-grid small-signal stability analysis are demonstrated to be correct by simulation result.