基于主动限流的混合直流输电换相失败抑制策略

Commutation failure suppression strategy of hybrid DC transmission based on active current limiting

针对混合直流输电系统换相失败时冲击电流较大的问题,文中首先推导冲击电流幅值与电压源型换流器(VSC)的关系,明确换相失败时VSC投入的子模块数量是决定冲击电流的关键参数。然后,研究影响电网换相换流器(LCC)换相能力的主要因素,提出基于主动限流的换相失败抑制策略,在VSC调制波中加入直流扰动量和交流扰动系数,从而改变子模块投切方式,抑制换相失败冲击电流的峰值和上升速度。最后,在Matlab/Simulink中搭建两端混合直流输电系统仿真模型,对所提策略在逆变站交流侧不同程度电压下降故障时的有效性进行验证,结果表明,所提策略不仅能限制冲击电流,减小桥臂电流应力,还可有效避免连续换相失败的发生。

Aiming at the problem of large inrush current when the commutation fails in the hybrid direct current(DC)transmission system,the relationship between the inrush current amplitude and the voltage source converter(VSC)is firstly derived.The number of submodule invested by VSC is a key parameter to determine the inrush current when the commutation fails.Then,the main factors affecting the commutation capability of the line commutated converter(LCC)are studied,and a commutation failure suppression strategy based on active current limiting is proposed.The DC disturbance amount and the accurate current(AC)disturbance coefficient are added to the VSC modulation wave,thereby changing the switching mode of the submodule and suppressing the peak value and rising speed of the commutation failure impulse current.Finally,the simulation model of the hybrid DC transmission system at both ends is built in Matlab/Simulink to verify the effectiveness of the proposed strategy in the event of different degrees of voltage drop faults on the AC side of the inverter station.The results show that the proposed strategy limits the inrush current and reduces the current stress of the bridge arm,thus effectively preventing continuous commutation failure.