谐波畸变电网下的单相同步旋转坐标系锁相环

Single-phase Synchronous Reference Frame Phase-locked Loop Under Harmonic Distorted Power Grid Condition

锁相环技术是并网变流器的核心技术之一。针对传统单相同步旋转坐标系锁相环在畸变电网下锁相精度差的问题,提出一种基于离散傅里叶变换(DFT)的高精度锁相环技术。基于DFT的锁相技术的核心问题是如何准确获取电网频率,将DFT和单相同步旋转坐标系锁相环相结合,利用DFT的优异选择性滤波性能和相角变换性质,从畸变电网信号中准确提取基波和生成虚拟正交信号,在同步旋转坐标系提取电网频率,实现DFT的频率自适应,最终无静差、高精度跟踪电网相位。仿真和实验结果表明,所提出的锁相环对电网电压的畸变谐波、直流偏置误差和电网频率脉动等有很好的适应性,在各种电网条件下,均能准确地跟踪电网电压相位,验证了该锁相方法的有效性和优越性。

The phase-locked loop （PLL） is a key aspect of grid-tied converters. A new PLL technique based on discrete Fourier transform （DFT） is proposed to improve the performances of conventional synchronous reference frame PLLs under distorted power grid conditions. The major challenge of the category of DFT based synchronization methods is how to accurately obtain the grid frequency. For this problem, this paper combines the DFT with the single-phase synchronous reference frame PLL. It utilizes the selective filtering and phase shifting properties of DFT to accurately extract the fundamental and generate its virtual orthogonal signals from the distorted grid. Then by transforming to the synchronous reference frame and properly control the q-component, accurate synchronization with zero steady state errors is achieved. Besides, grid frequency variations are incorporated by adjusting the sampling period of DFT according to the estimated frequency. Simulation and experimental results show that the proposed DFT-based PLL offers high harmonics immunity and DC component rejection capacity, while accurate phase locking is achieved under various power grid conditions, thus validating the effectiveness and advantages of the proposed method.