A Slack Bus Grid-forming Inverter Based on Symmetric Sliding Mode Control Against Power Sharing Imbalances Among Microgenerators

The new generation power system formed by many inverter-based resources (IBRs) faces challenges like low-inertial and poor-damping problems. Furthermore, due to the developing power system portfolios and intermittent nature of the resource of wind and solar etc., the grid dynamics can change significantly. At first, this article analyzes power sharing between microgenerators. Based on the mechanism of imbalance power sharing when relatively slow dynamic devices are used to support grid, this paper illustrates that a robust and fast dynamic slack bus grid-forming inverter (GFI) is able to mitigate synchronizing problems. Then, a symmetric sliding mode control (SSMC) method is proposed to meet the robustness and fast tracking performance. Finally, simulation results verify the low tracking error characteristic of the symmetric sliding mode approach and high robustness against variable grid strength in case study I, using comparison with internal voltage generator (IVG), fuzzy sliding mode control (FSMC), discrete repetitive sliding mode control (DRSMC). In case study II, it demonstrates imbalance power sharing phenomenon and effectiveness of the proposed slack bus GFI against it.