考虑直流电流上升及交流电压下降速度的换相失败分析

针对目前换相失败研究仅考虑电压降低以及考虑直流电流变化理论研究的不足,在经典关断角表达式的基础上,考虑整流侧、逆变侧以及直流线路运行参数,建立了完整的换相失败分析数学模型。该模型计及了交流电压下降对直流电流上升的影响,将交流电压和直流电流解耦,得到关断角与换流母线电压的单一关系表达式,并在此基础上推导了导致换相失败的临界换相电压值和临界电压下降速度。同时,对故障后电压下降速度与故障严重程度和无功补偿容量之间的关系进行了理论推导,电压下降速度随故障严重程度呈非线性加速下降趋势,在前几个换相过程中电压下降幅值越大,换相失败发生的可能性越高。PSCAD/EMTDC算例仿真结果验证了所提方法的准确性。

Commutation Failure Analysis Considering DC Current Rise and AC Voltage Drop Speed

In view of the inadequacy of the present research on commutation failure merely focusing on voltage drop without considering the rise of DC current, a complete commutation failure analysis model with the operating parameters of rectifier side, inverter side, and DC transmission lines taken into account is developed based on the classical turn-off angle expression. According to the influence of AC voltage drop on the DC current rise, the model can decouple AC voltage and DC current to obtain a single relational expression between the turn-off angle and the commutation bus voltage. Then the critical commutation voltage value and the critical voltage drop speed causing commutation failure are derived based on the above model. The theoretical derivation of relations between the voltage drop speed and fault severity and reactive power compensation capacity is also carried out. It is found that the voltage nonlinearly drops faster with the fault severity. In some earlier commutation processes, the larger the voltage drop amplitude is, the more likely the commutation failure will be. The PSCAD/EMTDC simulation results prove the proposed method.