永磁直驱式风机采用混合直流并网的控制策略

A Control Strategy for Integration of Permanent Magnet Direct-driven Wind Turbines Through a Hybrid HVDC System

提出一种永磁直驱式风机经混合直流系统并网的拓扑,直流系统整流侧采用模块化多电平换流器(modular multilevel converter,MMC),逆变侧采用电网换相换流器(line commutated converter,LCC)。该系统结合了MMC和LCC各自的优点,既可以为风电场无源系统提供电压支撑,又可以降低投资成本和运行损耗。MMC可以通过子模块投切瞬间改变直流侧级联子模块输出的总电压。基于此项特性,提出整流侧MMC控制直流电流的方法,将MMC的控制维度从交流侧拓展至直流侧。仿真结果表明,在逆变侧主网发生远区故障时,整流侧MMC可以抑制直流电流增长,降低换相失败发生的机会;在逆变侧发生换相失败后,可以帮助系统平稳地恢复直流功率,实现故障穿越功能。

This paper proposed a topology for integration of permanent magnet direct-driven wind turbines through a hybrid HVDC system. The HVDC system, adopting a modular multilevel converter（MMC） on the rectifier side and a line commutated converter（LCC） on the inverter side, combines the advantages of both MMC and LCC. MMC can transmit power from the passive networks of wind farms without an external commutation voltage; LCC can reduce the investment cost and power losses. By changing the number of the switched-on sub-modules, MMC can change its DC side voltage instantaneously. Based on this characteristic, this paper proposed a method to control the DC current of MMC, extending MMC control dimensions from AC side to DC side. The results of simulations show that MMC DC current control can reduce the possibility of LCC commutation failures and improve the power recovery performance after a commutation failure, achieving the goal of fault ride-through.