Analysis of DC Grid Prospects in China

Extended Summary正文参见pp.7-12Analysis of DC Grid Prospects in ChinaWEN Jialiang, WU Rui, Peng Chang, Wang Yu(China Electric Power Research Institute)KEY WORDS: renewable energy; DC grid; voltage source converter high voltage direct current (VSC-HVDC); DC circuit breaker;network frameworkRecently China has paid more and more attention toHVDC lines may connect with VSC-HVDCthe construction of smart grid and the development ofsystems in the near future, and will form a national DC .renewable energy. As the renewable energy generation isgrid system, which is shown in Fig.1.intermittent and unstable， power grid systems willFar. easten enery base in Russiabecome unstable when renewable power plants areSiberian energy base in Russiaintegrating in a large scale. In order to solve thisMongolia encryproblem, one of the promising methods is establishing awide-area DC grid.The fosil fuels are mainly located in northwestFuel lecrte plantChina, while the electric load center is in east and southChina. Thus there is a great amount of power which needsSolar power plantto be transmitted in a long distance. Traditional highWind power plen GCeo-thermalvoltage direct current (HVDC) transmission systems candeliver high-capacity power without frequency oscillation,Fig. 1 Blueprint of DC grid development in Chinawhich is a severe problem in AC power systems. MoreWith the development of electric vehicle, lightand more HVDC lines will be developed in China andemitting diode (LED) lighting, information technologyused to connect energy bases in foreign countries, suchand power electronic equipment, DC supply in theas Russia, Mongolia and central Asia countries. HVDCdistribution network has become increasingly important.lines can also be used to connect fuel electric plants inIt is difficult to use AC lines or cables to transmit bulkthe northwest and hydro electric plants in the southwestpower in big cities, because of space and capacityto the electric load center in east China.The renewable energy generations (e.g. solarlimitations. DC grid has several advantages: 1)power, wind power, ocean power) may cause voltage andconnecting DC electric loads and dispersed generationsfrequency instability when connected to power systemsdirectly without ACDC converters; 2) transmitting moredirectly. It is a good choice to use voltage sourcepower over longer distance by avoiding reactive power;converter high voltage direct current (VSC-HVDC),3) saving cost by only using two DC cables. It is highlysince it can control active and reactive powerrecommended to use DC distribution network in bigcities.independently, and realize power flow inversion. WithVSC-HVDC, solar power plants in the north, wind plantsThere are some key technologies to be studied inin the north and the southeast, geo-thermal plants inthe near future: 1) topologies of DC grid; 2) steady-stateTibet can be connected into a large-scale DC grid.and transi中国煤化工equipment, e.g DCBesides, distribution networks in big cities, such asbreakers,:YHCNMHGVSC-HVDCandBeijing, Shanghai and Guangzhou, may use VSC-HVDChigh-voltage DC cables; 4) power analysis, controlto form a DC network, as a part of DC grids.methods, protection; 5) related standards.S2 .