Analysis on Key Influence Factors of Ratio of Grid-forming and Grid-following Converters in Hybrid Parallel Grid-connected System
The grid-following converters have the risk of sub-synchronous oscillation(SSO)instability in the weak grid.The grid-forming converters can improve the stability of the hybrid parallel system in the sub-synchronous frequency range in the weak grid.The proper configuration of grid-forming units in renewable energy stations can enhance the system stability.Therefore,the ratio of grid-forming and grid-following converters is a key factor influencing the system stability.Aiming at the small-signal stability issue in the hybrid parallel grid-connected system with grid-forming and grid-following converters,this paper studies the influence of converter control system characteristics on the boundary conditions for the ratio of the grid-forming converter.First,the state space model of the hybrid parallel grid-connected system of grid-forming and grid-following converters is established.On this basis,this paper analyzes the influence of key parameters of grid-following/grid-forming control systems and the voltage loop control structures of grid-forming converter on the system stability.From the perspective of maintaining the small-signal stability of the system in the sub-synchronous frequency range,this paper analyzes the key influence factors for the lower limit of the ratio of grid-forming converters in the hybrid parallel system.The stability boundary under the constraint of each influence factor is obtained.In addition,the frequency-domain impedance method is used to explain the influence mechanism of each influence factor.Finally,the accuracy of the theoretical analysis is verified based on the RT-LAB semi-physical platform.
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维普
