多端柔性直流输电系统交流故障穿越仿真研究

Simulation Research on AC Fault Ride -through of MMC -MTDC Transmission System

摘要:

针对多端柔性直流输电系统交流侧发生故障,直流系统与电网公共连接点电压也随之跌落的问题，文中提出了一种交流故障穿越技术来维持公共连接点电压稳定。根据公共连接点电压跌落程度增发相应的无功功率从而维持公共连接点的电压稳定,保证系统的有功功率传输。当公共连接点电压跌落程度较大时,增发的无功功率导致交流系统过电流,提出通过降低故障端的有功功率参考值，从而减小交流侧电流幅值,避免过电流的产生。同时,针对有功功率的减小将使系统的不平衡功率进一步增大导致直流电压发生较大波动的现象,通过定直流电压换流站根据直流电压的变化来消纳系统的不平衡功率，从而达到维持多端柔性直流输电系统直流电压稳定的目的。

Abstract:

Aiming at the problem that when failures occur in AC side of MMC -MTDC system, the voltage at the point of common coupling (PCC) between DC system and power grid also drops, an AC fault ride -through technology is proposed to maintain voltage stability of PCC. According to the voltage sag degree of PCC, the corresponding reactive power is increased to maintain the voltage stability of PCC and ensure the active power transmission of the system. When the voltage sag of PCC is large, the additional reactive power will cause the overcurrent of AC system. So it is proposed to reduce the reference value of active power at the fault end, thus reducing the current amplitude in AC side and avoiding the generation of overcurrent. At the same time, in view of the phenomenon that the reduction of active power will further increase the unbalanced power of the system, resulting in large fluctuations in DC voltage, the unbalanced power of the system is absorbed by the constant DC voltage converter station based on the change of DC voltage, thereby to achieve the purpose of maintaining DC voltage stability of multi -terminal flexible DC transmission system.