| With the proposal of dual carbon goals,the proportion of new energy sources in China’s power grid is increasing.Because the new energy resources and load centers in China are inversely distributed,large-scale long-distance transmission has become an inevitable trend of power transmission in China.HVDC transmission technology can overcome the limitations of traditional long-distance and large-capacity AC transmission,and realize the flexible use and optimal allocation of resources nationwide.Hybrid High Voltage Direct Current(Hybrid-HVDC)technology has the advantages of superior control performance of Voltage sourced converter High Voltage Direct Current(VSC-HVDC)technology and long transmission distance and large transmission capacity of line commutated converter High Voltage Direct Current(LCC-HVDC)technology,which reduces the risk of commutation failure and avoids the shortcomings of line commutated converter(LCC)and voltage source converter(VSC)converter stations to the maximum extent.In recent years,more and more Hybrid Multi-Terminal High Voltage Direct Current(Hybrid-MTDC)projects have been put into operation,and the transmission capacity is also increasing.The interaction between AC and DC systems is becoming more and more serious,which is bound to bring severe challenges to the static voltage stability evaluation of AC and DC systems with Hybrid-MTDC,and it is difficult for deterministic analysis methods to effectively consider the impact of load and new energy output uncertainty on the voltage stability of AC and DC systems.Therefore,it is urgent to propose a fast and accurate construction method of Static Voltage Stability Region(SVSR)for large-scale AC/DC systems with Hybrid-MTDC.This paper mainly completed the following research work:Firstly,the basic definition,topological properties and fast search principle of SVSR boundary(SVSRB)of AC system are briefly introduced.Furthermore,the topological properties of SVSRB of AC/DC system are analyzed.Based on the basic principle of finding the Saddle Node Bifurcation(SNB)point of AC/DC system by Continuation Power Flow(CPF)method,CPF method with Hybrid-MTDC is adopted to search for SVSRB of AC/DC system..Then,the LCC converter station and VSC converter station with different control strategies are respectively equivalent to different types of nodes,and the power flow solution models of AC and DC systems are respectively constructed,and an alternating iterative power flow solution method for AC and DC systems with Hybrid-MTDC is proposed.Taking IEEE-5 and IEEE-118 node test systems with Hybrid-MTDC as examples,the effectiveness and universality of the proposed power flow calculation method are verified.Finally,a fast search prediction-correction method for SVSRB of AC/DC power system with Hybrid-MTDC is proposed.Considering the influence of control strategies of various converter stations on voltage stability,an AC-DC CPF model with Hybrid-MTDC is constructed to search the first critical point on SVSRB.Then,according to the topological characteristics of the AC/DC power system SVSRB with Hybrid-MTDC,a fast search model of the AC/DC SVSRB with Hybrid-MTDC is constructed,and the adjacent critical point information of the AC/DC system SVSRB with Hybrid-MTDC is quickly and accurately obtained by the proposed prediction-correction method,taking into account the switching characteristics of control strategies of various types of converter stations and the cooperative mechanism of inter-station control strategies,and then the SVSRB of the AC/DC system with Hybrid-MTDC is searched.Then,taking IEEE-5 and IEEE-118 bus test systems with Hybrid-MTDC as examples,the validity and accuracy of the proposed method are verified.Through the verification of an example,it can be concluded that the proposed method can quickly and accurately construct an AC/DC power system SVSR with Hybrid-MTDC,which provides a powerful tool for the static voltage stability analysis and evaluation of power system operation controllers. |
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