电网不平衡下星形级联STATCOM负序电压控制

Negative Sequence Voltage Control Under Unbalanced Grid for Star-connected Cascaded STATCOM

电网电压不平衡下,星形级联H桥静止同步补偿器(STATCOM)三相有功功率分配不相等,造成三相相间直流电压不均衡,影响系统稳定工作。基于负序电压注入的相间直流电压均衡控制具有功率调节能力强的优点,可使系统在电网电压严重不平衡的情况下正常工作。为提高电网不平衡下相间直流电压的动态性能,通常采用基于负序电压注入的前馈控制。传统前馈控制算法建立在三相静止a,b,c坐标系上,引入了大量的反三角函数和开根号运算,极其复杂。不仅如此,忽略了正序电流控制环与负序电压的关系,致使前馈控制输出的负序电压不够精确。这里提出一种新的前馈控制算法,该算法建立在两相旋转d,q坐标系上,由直流形式表示。同时,还考虑正序电流控制环与负序电压的关系,故所提前馈控制算法准确且简单易行。最后,搭建400 V/±5 kvar的星形级联H桥STATCOM样机验证所提方法的可行性与有效性。

Under unbalanced grid voltage,the active power among three cluster is distributed unequally for the starconnected cascaded H-bridge static synchronous compensator(STATCOM),which will result in three unbalanced cluster voltages and affect the safety operation.Negative sequence voltage based cluster voltage balancing control has a large capability in regulating active power,which makes this scheme more suitable for the unbalanced grid.To improve the dynamic response of cluster voltages under unbalanced grid conditions,cluster voltage balancing feedforward control is usually introduced.The negative sequence voltage in the conventional feedforward control is derived in three phase static a,b,c frame,which introduces many inverse tangent and square root operations and makes the calculation very complex.In addition,the relation between the positive sequence current control and the negative sequence voltage is neglected,which makes the negative sequence from the feedforward control is inaccurate.A novel feedforward control algorithm is proposed using the direct current form representation in two phase rotation d,q frame and taking the relation between the positive sequence current control and the negative sequence voltage into consideration.Hence,the proposed feedforward control is more simple and accurate.Finally,the feasibility and effectiveness of the proposed control scheme is verified by a 400 V/±5 kvar star-connected cascaded H-bridge STATCOM prototype.