A novel suppression strategy of frequency coupling oscillation for grid-connected VSI-based systems

Voltage source inverters (VSIs) are connected to the weak grid in parallel. The interaction between VSIs and the grid can result in frequency coupling oscillations, threatening the stable operation of the system. The conventional methods of oscillation suppression are unable to automatically adjust the parameters in response to changing systems, nor can they effectively adapt to multi-mode frequency coupling oscillations. This paper proposes a novel adaptive control strategy to suppress frequency coupling oscillations. The strategy in the suppression device enables automatic adjustment of the oscillation current's reference value, allowing it to adapt to diverse operational conditions of the grid-connected system. The strategy is not limited by the modeling precision and the steadiness of the controller structure. Furthermore, the self-stability and interactive stability are analyzed by using the generalized Nyquist criterion (GNC). It is found that the influence of the interactive current on the stability analysis cannot be ignored. Finally, considering the number of VSIs, load mutation, and existing suppression method, the suppression effect of the proposed adaptive control strategy is verified by experiments.