| With the continuous construction and rapid development of high-power and long-distance high voltage direct current(HVDC)transmission systems,large-scale AC/DC interconnected power grids are gradually forming in China,and asynchronous interconnection is one of the typical interconnection modes.The asynchronous power system is a grid that the sending-end and receiving-end AC systems are interconnected only through HVDC channels.Compared with traditional AC power grid,its structural form and operating characteristic are extremly changed.If a large blackout occurs in the asynchronous grid,the deep involvement of HVDC will cause profound changes in restoration control of power system.As a new topic in the security defense field,it is of great practical significance to study the restoration strategy of asynchronous interconnection power system with participation of the HVDC,which meets the development requirements of the new generation power grids.Based on the traditional AC system restoration theory,this thesis studies the restoration strategy of asynchronous interconnection system with participation of the HVDC.This thesis mainly studies the participation problem of the line commutated converter based high voltage direct current(LCC-HVDC),and preliminarily studies the participation problem of the voltage source converter based high voltage direct current(VSC-HVDC).The interaction mechanism between LCC-HVDC restoration and AC system restoration,the source characteristic of LCC-HVDC,the source-grid coordinated restoration optimization,the partition restoration of multi-HVDC feeding power grid,the parallel coordinated restoration of asynchronous power grid and the black-start optimization based on VSC-HVDC are deeply studied.The main work of this thesis includes:(1)Research on the interactive influence mechanism of LCC-HVDC start-up and AC system restoration.The optimal control strategy for LCC-HVDC start-up and the support capability of the AC system represented by system strength are analyzed.Based on the electrical network theory,the restoring operations which mainly affects the strength of the system are analyzed,and the quantitative relationship between the restoration process of the AC system and the system strength is studied,then the restoration mechanism of AC system with participation of LCC-HVDC is clarified.In order to verify the correctness of this strategy,and to support HVDC start-up,an optimization method of rapid local reconstruction for AC power system is presented.The proposed AC system restoration strategy with participation of LCC-HVDC can provide theoretical support for subsequent research in this thesis.(2)Research on source-grid coordinated restoration optimization with LCC-HVDC support.Based on the requirements of system strength in LCC-HVDC start-up stage and operation stage,the influence of source-grid restoration on HVDC support capability is studied,the output characteristic function of LCC-HVDC is obtained,and the concept of "non-tree restoration network" is proposed.The path restoration is used to represent source-grid coordinated restoration,and an optimization model is established.A feasible restoration scheme generation method suitable for both tree and non-tree restoration networks is proposed.The optimal restoration scheme is obtained by using multi-population genetic algorithm.The proposed LCC-HVDC output characteristic function and generation method of non-tree restoration network are two important problems in system restoration research with LCC-HVDC participation,which can lay foundations for subsequent research in this thesis.(3)Research on partition restoration method of multi-HVDC feeding power grid.Considering the community structure characteristic of power grid and the interaction mechanism of AC and DC system restoration,based on system strength and interaction between multiple HVDCs,new partitioning principles and constraints are proposed.Then a partitioning model suitable for multi-HVDC feeding power grid is established.The improved GN splitting algorithm is used to obtain the reasonable partition scheme,and the source-grid coordination restoration optimization method is used to analyze the partition restoration process.The proposed partition method has some guiding significance and reference value for dispatchers to make partition decision and restoration plan for multi-HVDC feeding power grid.(4)Research on optimization method for parallel coordinated restoration of sending-end and receiving-end in asynchronous power grid.This method adopts the serial and parallel strategy in AC grids at each end,and realizes the parallel coordinated restoration of sending-end and receiving-end grids through LCC-HVDC.The role orientation principle of each sending-end or receiving-end AC subnet is proposed,and the power or load characteristics of each converter station are deduced according to the LCC-HVDC output characteristic.Based on this,an optimization model for parallel coordinated restoration of sending-end and receiving-end grids is established,and an optimization method is proposed,which can determine the timing of LCC-HVDC start-up and coordinate the restoration of LCC-HVDC,sending-end and receiving-end grids.The proposed method has reference value for the research of asynchronous power grid restoration.(5)Preliminary research on black-start optimization of VSC-HVDC participating in power grid restoration.Taking VSC-HVDC as black-start source,the extended black-start optimization of blackout power grid is studied.This thesis analyses the best control strategy of VSC-HVDC as black-start source,studies the source characteristic of VSC-HVDC during black-start process,and proposes an optimization method of extended black-start based on VSC-HVDC.PSCAD/EMTDC software is used to verify the feasibility and effectiveness of the optimal extended black-start scheme.The results show that VSC-HVDC is an ideal black-start source,which has a good ability to absorb reactive power and suppress overvoltage during the black-start process. |
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