Mechanism analysis and suppression of bus voltage low fre-quency oscillation of multi-VSC connected substation
Large new energy stations are located in remote areas and integrate into boost substation,which is transmit-ted to load center through long-distance AC lines.This results in weak electrical connections between boost substation busbar and load center,and causes low-frequency oscillation instability.To reveal the mechanism of low-frequency os-cillation,a universal model for low-frequency dynamic analysis of multi-VSC system was established.Focusing on low-frequency dynamics,each VSC and AC power grid were independently established,which is applicable to differ-ent quantities of grid-tied VSC with various control strategies.Based on the proposed model,the impact mechanism of various factors such as power grid strength,VSC operating point,and coupling interaction of various VSC's dy-namic loops on low-frequency stability of multi-VSC system were revealed by state space analysis.Based on the analysis results,a virtual point of common coupling control strategy was proposed,which takes the voltage of substa-tion busbar as the unified control objective of each VSC.This strategy can effectively suppress the low-frequency os-cillations caused by dynamic interaction of different VSC,and a parameter self-tuning function was designed to elimi-nate errors caused by variation of line parameters.Finally,the correctness of the impact of various elements on low-frequency dynamics is verified through PSCAD/EMTDC simulation based on proposed model,as well as the effec-tiveness of proposed control strategy for low-frequency oscillation suppression.
multi-VSC systemuniversal analysis modelinteraction of dynamic loopsimproving control strategylow frequency oscillation suppression
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