Broadband Oscillation Suppression Method for Renewable Energy Grid-Connected System Based on Frequency-Selected Virtual Impedance Compensation Strategy of Power Conversion System

When renewable energy grid-connected system is connected to the weak grid, there will be the risk of broadband oscillation. In this paper, a frequency-selected virtual impedance (FSVI) compensation strategy based on power conversion system (PCS) is proposed to solve the broadband oscillation problem of renewable energy grid-connected system with PCS. The proposed control strategy can accurately locate the oscillation frequency segment and reconstruct the impedance output characteristics of the system in this frequency segment to avoid the occurrence of oscillation. Firstly, the sequence impedance model of parallel system between PCS and renewable energy generation device (REPGD) is established, and the output impedance characteristics of the parallel system are analyzed. In the frequency band that is prone to oscillation, the part of the impedance characteristic is capacitive and there is negative resistance, which is easy to interact with the inductive grid and cause oscillation problems. Secondly, for the frequency band prone to oscillation, the FSVI compensation strategy is introduced to reshape the output impedance characteristics of the frequency band, improve the stability margin of the renewable energy grid-connected system, and avoid the occurrence of broadband oscillation of the system to a certain extent. Finally, the effectiveness of the proposed method is verified by stability analysis and simulation examples.