A Capacitor Inertia Based VSG and the Stability Analysis

The traditional virtual synchronous generator strategy usually completely relies on the DC side battery to stabilize the DC-link voltage. Therefore, all the power support provided to the grid must be supplied by the battery when the grid power fluctuates, which leads to frequent and deep charge and discharge of the battery. As a result, the battery heat is increased and its life is reduced. To lower the current shock of DC power supply, a virtual synchronous generator control strategy based on the inertia support of DC-link capacitor is proposed. It uses the DC capacitor to simulate the rotor to provide the inertial support for the power grid by establishing a proportional relationship between the output frequency deviation and the DC voltage difference in the DC/AC converter. At the same time, the battery only provides the power for the frequency droop regulation by setting up the droop relationship between the battery current and the DC-link voltage in the DC/DC converter. In addition, the small signal model of the proposed strategy is established, based on which the correlation of state variables and eigenvalues is analyzed by the sensitivity calculation. Finally, the influence of control parameter changes on system eigenvalues is obtained, which is useful for the parameter design. Simulation results show the superiority of the proposed strategy and the correctness of the model analysis.