基于无功-频率下垂特性的无功扰动法在孤岛检测中的应用

Application of reactive power disturbance based on Q-f droop curves on islanding detection of grid-connected inverter system

孤岛检测是光伏并网研究的难点,特别在光伏并网逆变器输出与负载功率平衡时难以有效检测出孤岛,为此提出一种基于无功-频率下垂特性的无功扰动孤岛检测方法。该方法通过引入一个与负载无功-频率特性相关的线性函数作为无功扰动的输入量,打破功率平衡情况下发生孤岛时所存在的孤岛稳定运行点。再将实时检测到公共耦合点频率的偏差,引入到无功扰动的函数中形成正反馈回路,加速频率的偏移,使并网逆变器输出电压频率超出限定阈值,从而实现孤岛检测。仿真结果表明,该方法具有无检测盲区、响应快速、对电能质量影响小的特点。

It is difficult to detect islanding in photovoltaic grid-connected generation, especially in the condition of power balance between the output of inverter and the load power. A method of reactive power disturbance islanding detection based on Q-f droop curves is proposed. Once an islanding condition occurs, this new method forces the photovoltaic grid-connected generation to lose its stable operation by drawing into a linear function relying on a Q-f droop curve between load reactive and frequency. Then it detects the system frequency deviation by real time, and draws into the function of reactive disturbance to form a positive feedback effect, so the frequency drifting is accelerated and the frequency of the output voltage of the photovoltaic grid-connected inverter exceeds a preset threshold value, and then the islanding will be detected. Simulation shows that the proposed method has no detection dead zone and it is fast and has little influence on power quality.