光伏并网系统送出线路不对称故障的差动保护灵敏度研究

针对光伏并网发电系统的故障特性，分析了在并网送出线路发生不对称跌落时，比率制动特性差动保护在光伏逆变器有无无功补偿条件下的灵敏度。结果表明，在无功补偿状态下，光伏并网发电系统送出线部分的传统比率制动特性差动保护灵敏度下降。通过比较传统比率制动特性曲线的整定方式，不过原点的特性曲线在灵敏度的方面具有更大优势。在此基础上，考虑到不对称故障中零序电流受故障电阻和负荷电流影响小及低电压穿越(LVRT)期间以电网电压正序分量定向的逆变器控制策略，零序电流作为保护判据的传统比率制动式差动保护，由于不受无功补偿电流的影响且保护动作整定值较小，具有更高的灵敏度，作为光伏送出线路的保护效果更佳。通过Simulink搭建光伏并网发电系统仿真模型验证了这一结论。

Sensitivity studies on differential protection during the output line of grid-connected photovoltaic systems occur asymmetrical faults

For fault characteristic of grid-connected photovoltaic (PV) systems, the sensitivity of ratio-restraining characteristic differential protection on the condition of PV inverter reactive/active power compensation is studied when the output line of grid-connected PV systems occur asymmetrical failures. The results show that sensitivity of differential protection of ratio-restraining characteristic will decrease in the state of reactive power compensation. The characteristic curve without passing through the origin has a greater advantage in terms of sensitivity, after comparing the tuning mode of traditional ratio-restraining characteristic curve. On this basis, taking into account the zero-sequence current which is less affected by fault resistance and load current in asymmetrical fault, and inverter control strategy oriented by grid voltage positive sequence component during LVRT, traditional ratio-restraining differential protection which takes zero-sequence current as protection criterion possesses a higher sensitivity, for it is not affected by reactive current and has a small protection action setting value, it is better for the protection of output lines of photovoltaic power station. This conclusion is verified by simulation model of grid-connected photovoltaic system built on Simulink.