Planning And Control Technology Of VSC-HVDC Applied To 220kV Partition Interconnection Of Urban Power Grid

In order to limit the short-circuit current and avoid the operation risk of electromagnetic loop network,large-scale urban power gird has formed a power supply pattern with 500kV substation as the center and multiple 220kV partitions.However,the partition operation mode has some problems such as insufficient power supply capability,low safety and reliability,and poor flexible regulation ability.VSC-HVDC has the advantages of active and reactive power flexible control,easy to form multi-terminal DC system,improve system safety and stability,etc.Applying it to the urban grid 220kV partition interconnection can enhance the power flow flexible control capability and improve the power supply capacity without increasing the short-circuit current,and has great technical and economic advantages.This paper studies the application of VSC-HVDC to urban grid partition interconnection planning and control technology,including the following contents:Firstly,the power flow calculation method of AC/DC hybrid power grid with VSC-HVDC is studied.The steady-state model of VSC-HVDC interconnection device is derived.The alternating solution method is used to realize the power flow calculation program of AC/DC hybrid power network.The effectiveness of the algorithm is verified through Zhoushan five-terminal DC example,which lays the foundation for subsequent research.Then,according to the characteristics of urban power grid partition interconnection and VSC-HVDC function orientation,the optimum selection method of VSC-HVDC rated capacity and configuration location is proposed,which meets actual demands of the power grid and is easy to implement.Specifically,it includes five steps:partition power supply capability assessment,sending and receiving partition grid selection,VSC-HVDC rated capacity determination,configuration location selection,safety and stability verification.The VSC-HVDC optimization control technology supporting partition interconnection of urban power grid is studied,the optimal control objectives under steady and transient conditions are proposed.In order to achieve the optimal operation target under steady-state conditions,a comprehensive evaluation index considering load balancing and network loss is established.The information entropy method is used to calculate the index weight,and the optimal power of VSC-HVDC is obtained by successive approximation method.For the component overload problem under transient fault conditions,an adaptive droop control strategy based on the power margin of the converter station is proposed.The droop coefficient can be adjusted adaptively according to the power margin of the converter station,and this control strategy is applied to the multi-terminal DC emergency power support of urban power grid,therefore,the power support among partitions can be realized to eliminate component overload.The proposed control strategy can reasonably allocate power support amount,avoid overload of converter station and maintain safe and stable operation of power grid.Finally,taking Zhengzhou urban power grid as an example,PSD-BPA software is used to verify the VSC-HVDC locating and sizing and optimization control method.The results show that the proposed method can achieve the established goals and has good engineering applicability,which can provide a theoretical basis for VSC-HVDC applied to urban power grid partition interconnection.