As the proportion of new energy sources in microgrids grows, their intermittent nature poses challenges to the power balance operation of microgrid. The availability of energy storage units in microgrids can effectively address the power dynamic balance problem. The energy storage unit’s reasonable and simplified configuration has a direct impact on the system’s response time and operational stability. Based on the VSG equation under PV disturbance, this paper establishes a relationship equation between different damping ratios and the configuration of the energy storage unit, and proposes an energy storage unit configuration method based on the control parameters of the second-order oscillation equation. The variable features of the power of the energy storage unit caused by the damping ratio are next analyzed, taking frequency variation into account. Simultaneously, the microgrid power balance process is studied under various damping ratios, as well as the system’s stability in this situation, by limiting energy storage power. Finally, Simulink, a semi-physical platform based on HIL, is used to verify the accuracy of the findings presented in this study.