中文摘要：

随着海上风场规模的增大,全直流风场成为未来海上风电的发展趋势。模块化多电平变换器（modular multilevel converter,MMC）广泛应用在大功率、高电压的AC/DC电力变换领域,并且能够实现电能直接从低压交流到高压直流的转换,是一种适用于海上全直流风场的风力发电变流器拓扑。该文针对基于MMC的风力发电变流器的运行特性进行了分析,发现在低调制比的工况下MMC的子模块电容电压纹波会使交流输出电压产生畸变,通过对其机理的分析,提出一种改进的电流控制方法,改善受到电压畸变影响的电流动态控制性能。为了验证理论分析与控制方法,在RT-LAB中对一将6 k V永磁同步发电机连接到50 k V直流网的10 MW风力发电系统进行了建模和仿真,并在30k W的MMC实验平台上进行了实验验证。

英文摘要：

With the increasing scale of offshore wind farms, DC wind farms become the future development trend of offshore wind power. MMCs have been widely used for high-power high-voltage AC/DC applications, and they are able to convert power directly from a low voltage AC source to a high DC voltage source, which makes them a promising solution for wind power converters in offshore DC wind farms. The operation of MMC DC wind power converters was analyzed. It is found the voltage ripple of submodule capacitors will distort the output AC voltage in low- modulation-ratio operating conditions. By analyzing the mechanism of voltage distortion, a modified control scheme was proposed to enhance the dynamic performance which is affected by the distorted AC voltage. The detailed digital simulation on RT-LAB platform confirms the theoretical analysis and the control scheme on a 10 MW test system, which connects a 6 kV permanent magnetic synchronous generator to a 50 kV DC grid. To further test the proposed system, an experiment was carried out on a 30 kW MMC platform.