【摘要】 交流系统故障引发换流器换相失败是直流系统中常见的故障。滤波换相换流器(FCC)作为一种新型的换流器电路拓扑结构,研究其在交流系统故障条件下的换相特性是十分必要的。本文分析计算了在三相对称和不对称故障条件下实际熄弧角,研究了换相电压变化ΔU与熄弧角、直流电流及换相电压过零点相位移之间的关系。基于FCC数学模型,详细分析了阀侧无功补偿度对直流系统的熄弧角、换相角、换流母线电压以及换相电抗等运行参数的影响。最后参考实验室背靠背直流输电系统参数,对FCC逆变器和电网换相换流器(LCC)逆变器在交流系统故障下的动态特性进行了仿真对比。结果表明:逆变器在交流系统单相故障条件下要比三相对称故障条件下更容易发生换相失败;FCC的换相电压中谐波含量更少,在相同熄弧角下,其能承受更大的电压暂降而不发生换相失败;FCC阀侧无功补偿度的大小直接影响到换相电压和换相电抗,选择时必须防止换相失败和换相电抗过大。更多还原

【Abstract】 The commutation failure of converters is a type of common faults in DC transmission system when faults of AC system occur.As filter commutated converter(FCC) is a new converter circuit topology structure,it’s necessary to research commutation characteristics of FCC under the conditions of AC system’s faults.Firstly,the actual extinction angle is calculated under the conditions of symmetrical and unsymmetrical AC three-phase faults;and the relationship between the commutation voltage reduction,the extinction angle,DC current and zero-crossing phase shift are researched.Further,based on the mathematical model of FCC,the influence of compensation factor at the valve side on the extinction angle,commutation angle,commutation voltage and commutated reactance is analyzed in detail.In the last,referring to the parameters of back-to-back DC transmission system in the lab,the simulating results are contrastively researched between FCC and LCC under the conditions of AC system faults,which indicated that the inverter is more inclined to occurring commutation failure under single phase fault than three phase symmetrical fault;for the harmonics in the commutation voltage of FCC is less than in the LCC,FCC can load more commutation voltage reduction,but when selecting the compensation factor at the valve side,the commutation failure and commutated reactance must both be taken into account.更多还原