用于分布式发电系统孤岛检测的偶次谐波电流扰动法

孤岛检测是分布式并网发电系统必须具备的能力,但频率或相位偏移等传统主动式孤岛检测方法在并网逆变器输出与本地负载功率平衡时难以有效检测出孤岛现象。针对已有孤岛保护方法的不足,本文分析了不同电流扰动信号对孤岛检测能力的影响,找到了适合多机并网系统快速孤岛检测的偶次谐波扰动信号,在此基础上结合过零点频率检测法,将电流谐波扰动的正反馈引入孤岛检测与保护中。并网逆变器的输出电流参考信号受到微弱扰动信号的影响,孤岛发生时,形成扰动信号的正反馈回路,并迅速累积使公共耦合点电压频率超出限定阈值,从而实现孤岛保护。该方法具有便于实现、对电网污染小、检测速度快及适合多机系统等优点。仿真和实验结果验证了该方法的有效性与可靠性。

Even Harmonic Current Disturbing Method for Islanding Detection in the Distributed Power Generation Systems

Islanding protection is necessary for the distributed generation(DG) systems,but it is difficult for some traditional methods such as frequency or phase variation methods to detect the islanding effect when the power generated by the DG systems matches with the demand power of the local load.The islanding detection capabilities about different disturbing signals are analyzed and even harmonic current disturbing signal suiting to multi-inverter DG system is available in this paper. Combining with a zero-crossing frequency detector,the positive feedback loop with even harmonic current disturbance is introduced to detect the islanding phenomenon.Output current reference in the grid-connected inverter is affected by a minute disturbance signal in general.Once the islanding occurs, the positive feedback of disturbance current makes the voltage frequency at the point of common coupling go beyond a preset threshold value.It is easy to design the software program,less to inject the current harmonics into the grid,quick to detect the islanding effect,equal to form the multi-inverter system.Simulation and experimental results verify that the method is effective and reliable.