背靠背换流器控制策略的比较与分析

Comparison and Analysis on Control Strategies for Back to Back Converters

结合直流工程的实际设计和运行经验,对背靠背换流站工程中逆变器的3种控制策略进行了分析研究。背靠背换流站工程中逆变器的控制策略有3种:第1种为定阀侧空载直流电压控制,即阀侧空载直流电压恒定,通过调换流变压器分接开关,由熄弧角控制直流电压;第2种为定熄弧角控制,即熄弧角恒定,通过调阀侧空载直流电压控制直流电压;第3种为熄弧角带宽控制,即使熄弧角在17°～19.5°范围内变化,直流电压恒定,当熄弧角超出该范围时,通过调节换流变压器分接开关改变阀侧空载直流电压,使熄弧角回到17°～19.5°范围内。从换流变压器阀侧空载直流电压、换流变压器参数、换流站无功功率损耗以及系统运行参数4个方面进行比较,指出定阀侧空载直流电压控制在减少换流变压器分接开关档位、降低分接开关动作次数和提升紧急功率方面具有一定的优势,这一结果对选择背靠背直流系统控制策略具有借鉴意义。

Based on the experience in the design and operation of DC power transmission projects, the control strategies for converters in back-to-back converter station are analyzed. There are three kinds of control strategies： the first one is the constant no-load DC voltage control at valve side, that is, through switching-over tap-changer of converter transformer the DC voltage is controlled by extinction angle; the second one is the constant extinction angle control, that is, keeping the extinction angle constant and by means of regulating no-load voltage at valve side to control DC voltage; the third one is the bandwidth control of extinction angle, that is, the DC voltage keeps constant while the extinction angle varies within the range from 17° to 19.5°, when the variation of extinction angle is out of above-mentioned range, by means of adjusting the tap-changer of converter transformer the no-load DC voltage at valve side is varied to make the variation range of extinction angle returning to the above-mentioned range. These control strategies are compared in four aspects, i.e., the no-load DC voltage at converter transformer side, the parameters of converter transformer, reactive power loss of converter station and system operation parameters, and the conclusion is that the control strategy of keeping constant no-load DC voltage at valve side possesses such superiorities in decreasing the total numbers of converter transformer’s tap-changer, reducing the action times of the tap-changer, and emergency power ascension. This conclusion can be referred in choosing the control strategy for back-to-back DC system.