Research on Adaptive Control Strategy of Microgrid Inverter based on Virtual Synchronous Generator

The adaptive control of virtual synchronous generator (VSG) is studied in off-grid and grid-connected mode of microgrid inverter. In the mode of islanding micro-grid, the traditional control of VSG can only realize the primary frequency regulation, but cannot solve the frequency deviation caused by load fluctuation. Although the control strategy of conventional secondary frequency regulation can realize the frequency deviation-free adjustment, but there are problems such as slow adjustment speed and low control accuracy, so the frequency can not be effectively controlled. The control structure of virtual governor is adjusted according to the power frequency characteristic of VSG, and a VSG control strategy of adaptive droop coefficient is proposed, which can ensure that the micro-grid always maintain rated frequency under the condition of meeting the power demand, and implements no-deviation frequency control smoothly and quickly. When the microgrid inverter is connected to the grid, the output mutation of the distributed power supply and the disturbance of the microgrid system may cause frequency fluctuation and power fluctuation of the grid. Based on the characteristics of flexible and adjustable VSG parameters, proposes an exponential type of coordinated adaptive control strategy of rotational inertia and damping coefficient. Compared with the traditional control method, this strategy can adjust the virtual inertia and damping coefficient online when the VSG angular velocity change rate and deviation are large. It can reduce the system overshoot during the transient process, shorten the adjustment time, and optimize the dynamic adjustment of VSG inertia and damping characteristic.Further improve the active power and frequency response characteristics. The VSG control model was built base on the simulation software of MATLAB, and the effectiveness and feasibility of the proposed control strategy were verified.