Requirements of DC-DC Converters to facilitate large DC Grids
Requirements of DC-DC Converters to facilitate large DC Grids
复制标题
DOI：
--
复制
发表时间：
2012
期刊：
影响因子：
--
通讯作者：
C. Barker;C. Davidson;D. Trainer;R. Whitehouse
中科院分区：
文献类型：
--
作者：
C. Barker;C. Davidson;D. Trainer;R. Whitehouse
概述两个直流电网可以独立构建。由于这些直流电网是独立开发的，运行的直流电压、运行策略甚至直流拓扑都可能不同，因此，这两个直流电网不能直接连接。正如在不同电压下运行的交流系统需要变压器来交换电力一样，直流电网也需要DCDC变流器来在网络之间交换电力。一组海上风电场可以使用高压直流、多端、大容量电力传输方案将电力传输到陆上交流系统。在未来阶段，可以在距离现有方案或大陆足够远的地方建造一个新的海上风电场，以适合直流输电连接；但额定电压比现有方案低。因此，一种经济的互联方法可能是在风电场使用AC-DC转换器，并在现有的海上转换器本地使用DC-DC转换器，以便利用现有的直流电网将电力输送到陆地上。许多涡轮机实际上通过AC-DC-AC转换器产生交流输出。通过去除风力涡轮机内的DC-AC级，中压DC集线器母线可用作多个风力涡轮机的DC输出之间的公共电力互连。然后，可以使用DC-DC转换器将DC电压提高到更高的电压，以便传输到陆上DC-AC转换器。多年来，利用高压直流输电为分散在大范围内的多个小负荷供电的可能性一直存在。由于每个负载的功率可能相对较低，三相DC-AC高压转换器的成本可能很高；但可以使用低成本的DC-DC转换器来降低每个负载中心的DC母线电压。目前，有许多现有的LCC高压直流输电方案在运行。通过使用DC-DC换流器，可以将这些现有的直流方案与新的VSC高压直流换流器多端电网互连，从而提高现有电网的利用率。
SUMMARY Two DC grids may be constructed independently. As these DC grids are independently developed, the operating DC voltage, the operating strategy or even the DC topology may be different and hence, these two DC grids cannot be directly connected. Just as AC systems operating at different voltages require transformers to exchange power, DC grids require DCDC converters to exchange power between networks. A group of offshore windfarms may use a high voltage DC, multi-terminal, bulk power transfer scheme to transfer the power to the onshore AC system. At a future stage a new offshore windfarm may be constructed sufficiently remote from the existing scheme or the mainland to merit a DC transmission connection; but at a lower voltage rating than the existing scheme. An economic method of interconnection may, therefore, be the use of an AC-DC converter at the windfarm and a DC-DC converter local to the existing offshore converter in order to use the existing DC grid to bring the power onshore. Many turbines actually generate an AC output from an AC-DC-AC converter. By removing the DC-AC stage within the wind turbine a medium voltage DC collector bus could be used as a common power interconnection between the DC outputs from multiple wind turbines. A DC-DC converter could then be used to raise the DC voltage to a higher voltage for transmission to an onshore DC to AC converter. For many years the possibility has existed of utilising HVDC to supply multiple small loads dispersed over a large geographical area. As each load may only be at a relatively low power the cost of a 3-phase DC-AC high voltage converter may be prohibitive; but a low cost DC-DC converter could be used to reduce the DC bus voltage at each load centre. There are, today, many existing Line Commutated Converter (LCC) HVDC transmission schemes in operation. By using DC to DC converters it may be possible to interconnect these existing DC schemes with new VSC HVDC converter multi-terminal grids increasing the utilisation of existing grids.