电容换相逆变器换相失败的研究

换相失败是直流输电系统的常见故障之一,研究逆变器的熄弧角对理解换相失败的本质及设计保护措施具有重要意义。详细描述传统逆变器熄弧角、电容换相逆变器的视在熄弧角和实际熄弧角的概念和数学模型,比较、分析三者之间的区别与联系。根据熄弧角的数学模型推导实际熄弧角的数学模型,分析影响电容换相逆变器换相失败的主要因素以及影响规律:电容换相逆变器在直流电流下降和交流母线电压升高时,实际熄弧角均减小,可能导致换相失败;换相电容设计值过大,静态换相裕度较小;交流系统不对称会恶化电容换相逆变器的换相性能,甚至导致换相失败。

Commutation failure of capacitor commutated inverter

Commutation failure is common in HVDC system and the study of inverter extinction angle is helpful to understand the essence of commutation failure and to design the countermeasures. The extinction angle of conventional inverter and the apparent and real extinction angles of CCI(Capacitor Commutated Inverter) as well as their mathematical equations are described,analyzed and compared. The mathematical equation of real extinction angle is deduced from the mathematical equations of extinction angle,which is used to analyze the main influencing factors of CCI commutation failure and their influence laws. The decrease of DC current or the increase of AC bus voltage may reduce the real extinction angle,resulting in commutation failure. When the commutation capacitor is too big,the commutation margin becomes smaller. The asymmetry of AC system may worsen commutation performance, resulting in commutation failure.