Seamless Switching Method Between Grid-Following and Grid-Forming Control for Renewable Energy Conversion Systems

In alignment with decarbonization efforts, there has been widespread global interest in renewable energy sources such as wind and solar, which are connected to the grid via grid-connected inverters. The transition from traditional synchronous generator-based power systems to power-electronic-based power systems has introduced increased complexity due to the stochastic and intermittent nature of renewable energy outputs. Consequently, grid-connected inverters need to dynamically adapt their control strategies to cope with varying external grid conditions and ensure high reliability. However, such transitions can cause abrupt changes in the control loops (e.g., power loop or voltage loop), and lead to voltage and current distortions, potentially compromising safe operation. To address this issue, this paper proposes a smooth switching method between the grid-following (GFL) and grid-forming (GFM) control in grid-connected mode. This method can improve the control flexibility of the grid-connected converters and broaden the stability boundary of the power system. The proposed method is verified in a case study of a 15.8 kVA grid-connected converter. Time-domain simulations carried out in Matlab/Simulink and an established experimental prototype are applied to verify the effectiveness of the proposed control method. The results demonstrate that the proposed control method effectively mitigates voltage and current distortions during transitions, ensuring safer and more reliable operation.