电抗器品质因数对TCSC特性的影响及阻抗特性的双解现象

EFFECTS OF THE REACTOR’S QUALITY FACTOR ON THE CHARACTERISTICS OF TCSC AND ITS DUAL IMPEDANCE SOLUTIONS

可控串联电容器(TCSC)装置的晶闸管控制支路电抗器(TCR)品质因数只能是有限值,该文通过时域数字仿真分析了这一参数对TCSC稳态阻抗特性的影响。仿真分析结果表明在电抗器品质因数有限的情况下,TCSC等效阻抗特性的谐振点相对理想情况会出现偏移;同时,在容性运行区间,对于同样的触发角指令,Q值越小,TCSC的等效基频电抗也越小,而在感性运行区间,情况则刚好相反。这种影响在感性和容性运行区间还因TCSC同步触发控制方式不同而存在较大的差异。当以电容电压过零点为同步触发参考时标时,触发角指令与等效阻抗之间是单值对应关系,而以线路电流为同步触发参考时标时,触发角指令与等效阻抗之间是双值对应关系,即所谓的双解阻抗特性。文章进一步研究了线电流同步方式下TCSC等效基频阻抗呈现双解的现象,指出产生该现象的根本原因是采用了不同的触发参考时标。TCSC等效基频阻抗特性的双解现象实际上是在以线路电流过零点为触发参考时标时TCSC表现出的一种特殊运行特性。它与以电容电压同步触发参考时标的阻抗特性之间具有确定的对应关系。在两种不同的触发时标下,通过详细时域仿真验证了上述结论。

Unlike the ideal reactor, the quality factor of the reactor (simply represented by Q) used in the implemented TCSC can only take limited value. This will affect the characteristics of the thyristor controlled series capacitor (TCSC) to some extent. This problem is further analyzed by time-domain digital simulation. Results show that with limited Q values, the resonant condition of the equivalent fundamental frequency impedance of the TCSC differs from that of the ideal case. It is found that for the same firing angle order in the capacitive operation condition, the equivalent reactance of the TCSC decreases with the decrease of Q,while that for the inductive operation condition will increase. Such effects may change due to the firing control mode used. With the capacitor voltage as the reference signal for firing control, the equivalent fundamental impedance of the TCSC is a monodromic function to the firing angle order. However, two equivalent fundamental impedances will exist when the line current is used as the reference signal. This is the so-called dual impedance solutions phenomenon of the TCSC. Further investigation shows that dual impedance solution phenomenon is a natural result of line current time scale used. The relationship between the dual impedance in the line current time scale and the monodromic impedance is found. The solutions above mentioned are verified by the time domain simulation.