考虑直流电流变化及交流故障发生时刻影响的HVDC换相失败分析方法

Research on Method to Analyze Commutation Failure in HVDC Power Transmission System Considering the Impact of DC Current Variation and Occurrence Moment of AC Fault

研究了交流系统三相对称故障造成的直流电流变化及故障时刻对HVDC换相失败的影响,由关断角减小到换相失败临界值,推出换相电压值的计算方法。该方法在经典计算方法的基础上,考虑了故障后直流电流的变化,推导了换相电压值与关断角的关系式;在此基础上进一步研究了故障时刻对临界换相电压值的影响,推导了故障时刻与临界换相电压值的关系式。对双极直流系统算例进行了相应的计算分析,并通过时域仿真验证了该分析结果的正确性。研究得出,计算临界换相电压值在计及故障造成的直流电流的变化和故障时刻的影响是不同的,该方法可有效提高理论分析临界换相电压值的计算精度,进一步说明故障后是否发生换相失败,与是否有足够的关断角或相应的反向换相电压时间面积相关。

The DC current variation in HVDC transmission system caused by three-phase symmetric fault in AC system and the impact of the occurrence moment of three-phase symmetric fault in AC system on commutation failure of HVDC transmission system are researched. Based on the decrease of the turn-off angle and the critical value of commutation failure, a method to calculate the commutation voltage value is derived. Based on classical calaulation method and considering the post-fault DC current variation, the derived method deduces the relational expression between commutation voltage value and turn-off angle; on this basis, the impact of occurrence moment of AC fault on critical commutation votlage is further analyzed and the relational expression between critical commutation voltage and the occurrent moment of AC fault is derived. Corresponding calulaton and analysis on the calculation example of a hi-polar HVDC transmission system are carried out, and the correctness of analysis results is validated by time-domain simulaiton. Research results show that the critical commutation voltage calculated under the DC current variation caused by AC fault is different from the critical commutation voltage considering the impact of the occurence moment of AC fault. The proposed method can effectively improve the calculation accuracy of critical commutation voltage for theoretical analysis and it is further explained that whether the post-AC fault commutation failure occurs or not depends on whether there is enough value of the turn-off angle or corresponding area of reversed commutation voltage vs. time.