基于下垂特性锁相环的反孤岛性能分析

Analysis with Anti-Islanding Performance of Grid-Connected Inverters Based on Drooped PLL

基于下垂特性锁相环可以实现逆变器单位功率因数并网运行,当负载的谐振频率在电网的正常频率范围内,该锁相环不能有效检测出孤岛的发生,相对于现有的主动扰动检测方法的盲区要大。为减小该锁相环的孤岛检测盲区,提出了在电网正常工作频率范围以及其周围较小的频率范围内施加相位差扰动,并给出了改进下垂特性锁相环的参数选取原则。改进后的锁相环的孤岛检测盲区明显减小。仿真和实验结果表明,该方法在不影响正常并网电流波形质量的情况下,实现了孤岛检测盲区的减小。

The grid-connected inverter which employs phase lock loop （PLL） with drooped characteristic can obtain unity power factor. However, the islanding can＇t be detected when the resonant frequency of parallel RLC load is in the range of normal power grid frequency. Compared to other islanding detecting method, this zone is relatively larger. In order to decrease the NDZ, an improved PLL is proposed, which introduces a phase difference disturbance to the drooped PLL. The principle of parameters selecting is given and the NDZ of the improved PLL strategy is significant decreased. The simulation and experimental results verify that the proposed method is effective for islanding detection without affecting the quality of grid current.