Control of a multi-terminal HVDC system for the exchange of primary reserve power across AC grids

为了将北海和波罗的海规划或建设中的海上风电场的电力远距离传输到德国南部和西部的城市地区，目前正在讨论在现有交流电网的基础上实现高压直流（HVDC）电网。与此同时，还在讨论在北海建造高压直流输电网，将邻国相互连接起来，并连接到风力发电场。该研究项目的重点是开发一种用于HVDC换流器的控制结构，该换流器将多个远程位置的DC电网与一个或多个AC电网连接。一方面，控制结构应能够分散地控制DC电压，使得大型DC电网也是可行的。另一方面，根据AC电网中已知的控制过程，应提供处理DC功率流的特殊装置。除了海上产生的功率的纯分配之外，这样的DC电网还允许灵活的功率传输服务。这尤其适用于不同AC电网之间的备用功率交换和储能电站的使用。控制器应能够根据实际需求自动管理该备用功率传输。

For the transmission of electricity from offshore wind farms that are planned or in construction in North- and Baltic Sea over large distances to the urban areas in south- and west-Germany, the realization of a high-voltage-direct-current (HVDC) grid in addition to the existing AC-grid is currently in discussion. At the same time the construction of an HVDC grid in the North Sea for the connection of the neighbouring countries to each other and to the wind farms is also in discussion. This research project focuses on the development of a control structure for the HVDC converters, which connect the dc grid at multiple, remote locations with one or several AC-grids. The control structure shall on the one hand be able to control the DC-voltage decentrally, so that also large DC-grids are feasible. On the other hand, according to the known control processes in AC-grids, special means to handle the dc power flow shall be provided.Besides the pure distribution of the offshore generated power, such a dc grid also allows flexible power transmission services. This especially goes for the exchange of reserve power between the different AC-grids and the usage of storage power plants. The control shall be able to manage this reserve power transfer automatically and according to the actual demand.