适用于功率突变的MTDC系统改进下垂控制

直流电压的稳定控制是多端柔性直流输电系统安全运行的关键,多端系统的安全运行需要满足N-1法则。在功率发生突变时,功率不平衡将导致直流电压发生偏移,严重时造成换流站脱网,且传统下垂控制的换流站受限于固定的下垂系数,难以适应功率突变。针对此问题,提出改进下垂控制,通过监测换流站直流电压和有功功率的偏差值,引入影响因子并设置电压滞环,自适应修正下垂系数,以抑制功率突变情况下直流电压的偏移。基于Matlab/Simulink搭建基于电压源型换流器的四端柔性直流输电系统仿真模型,构造主/从站退出运行、潮流反转3种工况,验证改进下垂控制策略在功率突变情况下,能够满足N-1法则,保障多端系统的安全运行。

Improved Droop Control Strategy for MTDC System Suitable for Changed Active Power

Reasonable control strategy for DC voltage is the key factor to ensure the stable operation of multiterminal direct current(MTDC)system. Moreover,MTDC system is required to satisfy the N-1 rule. When the active power changes suddenly,DC voltage will be offset due to the unbalanced active power. More seriously,the converter station may be disconnected from the grid. Traditional droop control strategy is limited by the fixed droop control coefficient which is difficult to adapt to complex working conditions. In order to solve this problem,the improved droop control strategy was proposed. By detecting the deviation value of DC voltage and active power,setting impact factor and voltage hysteresis,the droop coefficient would be automatically corrected. Based on Matlab/Simulink,a four-terminal VSC-MTDC transmission system simulation model was built. By constructing three working conditions:main/slave station exits and power flow reversal,it was proved that the improved droop control strategy can satisfy the N-1 rule and ensure the stable operation of power system,when the active power changes suddenly.