Coordinating Systematic Grid-Forming Control of Hybrid Photovoltaic Plants in Weak Grids

With the anticipated integration of numerous hybrid photovoltaic (PV) plants into subtransmission and distribution grids, managing a mix of inverter-based energy resources such as PV systems and battery energy storage systems (BESS) becomes crucial. These resources are required to effectively coordinate for primary frequency (f) and voltage (V) control and participate in power sharing, particularly in weaker grids. Currently, inverter-based energy resources are predominantly coordinated by droop-based control, which proves inadequate for hybrid PV plants in more resistive subtransmission and distribution grids due to the tightly coupled active power (P) and reactive power (Q). To overcome this challenge, this paper proposes an innovative coordinating systematic primary control strategy for grid-forming inverters in hybrid PV plants based on the multiple-input and multiple-output (MIMO) decoupling control. This method adaptively decouples the connected subtransmission or distribution grids during operation, with the aim of achieving effective, coordinated, and independent primary f and V regulation and accurate power sharing. For verification, comparative case studies are conducted in Simulink between the proposed control strategy and a conventional droop control scheme. The findings indicate that our proposed control method facilitates autonomous and independent primary f and V control, along with precise power sharing without relying on communication links. This results in markedly enhanced steady-state and dynamic performance. The decentralized primary controller offers simplicity, robustness, and cost-effectiveness, contributing to the stability and resilience of utility grids.