Research On The Flexible Dispatch Of VSC-MTDC Interconneted AC/DC Power System With High Share Of Renewable Energy Power

In recent years,with the large-scale development of renewable energy power generation,a high share of renewable energy grid-connection becomes an important feature of new-type power system in China.The characteristics of this kind of renewable energy change the intrinsic operation performances of the power system,bringing new challenges to the reliable and flexible operation of the system.At the same time,the renewable resource in China is concentrated and distributed in a few provinces,inversely with the main power-consumption provinces or districts,which makes it difficult for local consumption.Therefore,the nation constructed a series of renewable power transmission lines or projects,such as "West-to-East Power Transmission Project" and " North-South Mutual Supply",to promote the multi-area power grids for coordinated operation,at the same time,realize the goal of carbon peaking and carbon neutrality of China government.In this context,voltage source converter based-high voltage direct current transmission technology(VSC-HVDC),with flexible and fast power regulation capability and convenience to form a multiterminal grid topology,becomes a new form of large-scale renewable resource transmission and consumption,wide-area energy complementary operation,and multiarea power grids asynchronous interconnection.For this emerging VSC-HVDC interconnected AC/DC hybrid system,how to use the means of optimal dispatch to fully exert the power flexible control and regulation capability of VSC-HVDC,to improve the coordinated operation for multiple areas and cooperative dispatch for multiple power resources in a wide area while considering the multiple uncertainties of generation side,grid side and load side,is a new practical issue to be solved.In this paper,the flexible dispatch appoarches for VSC-HVDC interconnected AC/DC hybrid system with a high share of renewable energy power is chosen as the topic,mainly focus on two types of grid interconnection used by VSC-MTDC grid,the renewable power collection system,and multi-area interconnected power system.The main research contents are as follows:(1)An optimal pwer flow(OPF)model of VSC-MTDC collection system with renewable power stations is proposed.In view of the lack of optimal operation method considering the renewable outputs characteristics and the VSC-MTDC power flexible regulation characteristics,a multiple renewable outputs model used by Pair-copula combined with 2m+1 point estimation method is proposed to describe their uncertainty and spatial correlation.An OPF model of the collection system considering the VSCMTDC power transmission and droop regulation mode is proposed to promote the consumption of multiple renewable energy bases and multiple resource cooperative dispatch,by decentralized optimizing and setting operation parameters for each VSC station.By the case study of the collection system,the flexible regulation capabilities,and influencing factors in improving renewable power consumption,reducing system operation loss,and reducing DC voltage deviation are analyzed.Moreover,a flexible regulation domain under different capacity ratios between enewable power and storage system is formed,which can describe the role of power regulation performances of MTDC grid-side in the collection system.(2)A day-ahead flexible dispatch appoarch of VSC-MTDC collection system with renewable power stations is proposed.To fully excert the VSC station power regulation capability in system dispatch to cope with large fluctuations of renewable power and improve the system safe and reliable operation,a power margin tracking(PMT)power droop regulation mode of the VSC station is proposed.By introducing a power margin correction factor,each VSC station can dynamically track its power margin and selfadapt its operation status.On this basis,a day-ahead flexible dispatch model of the collection system considering the daily regulation-energy storage is proposed,for improving the flexible and safe comsuption of renewable power.The case study proves that the proposed model can improve the fluctuating power allocation between multiple VSC stations and the coordinated operation of the system,therefore promotes the DC voltage stability and renewable power consumption level in a day-ahead dispatch plan.(3)A flexible resource dispatch appoarch for VSC-HVDC interconnected crossarea systems is porposed.In view of the lack of cross-area power-reserve coordinated dispatch involving VSC stations,a cross-area decentralized optimization basedintraday flexible resource coordinated dispatch approach is proposed.A prediction scenario cooperative with flexible adjustment scenarios and VSC station-generator coordinated dispatch model is addressed to fully exert the intraday power regulation of VSC staions,ensuring the flexibility regulation demands caused by the intraday renewable power fluctuations and random prediction errors.An ATC techeque baseddistributed optimization method is addressed to adapt to intraday coordinate interaction and power regulation of two areas.The case study proves that the proposed VSC station-generator cooperative regulation moel and cross-area power-reserve sharing mode can promote the mutual economical dispatch of flexible resources and the coordinated operation of the interconnected system.(4)A decentralized coordinated dispatch hierarchy and approach for multi-area VSC-MTDC interconnected system is proposed.The existing method cannot meet the coordinated interaction demands for MTDC-interconnected multiple areas in China hierarchical and regional dispatch orginazations,also cannot exert autonomous control and operation of multiple VSC stations.According to the general form of multi-area systems,a hierarchical and decentralized coordinated dispatch hierarchy and approach is proposed.The whole system is divided into three dispatch layers,ACgrid,VSC station and DC grid.In low layer,a stochastic chance constraints-based generationreserve joint dispatch model is proposed,where a modified system reserve demand decision method is addressed to consider the grid-side power uncertainty by VSC random locks.In the middle layer and the high layer,the OPF model of the VSC station and DC grid are proposed respectively,where the power droop regulation mode is adopted for each VSC station.The case study proves that the proposed appoarch can optimize the management responsibilities and benefits for AC grids,fully exerting the flexible and autonomous regulation of VSC stations,promoting the system coordinated operation and the economical dispatch for multiple resources.