风力发电系统中电网同步改进型锁相环设计

Design of Improved Phase Locked Loop for Grid Synchronization in Wind Power Generation Systems

针对风力发电系统中电力电子变流器同步信号检测中所存在的问题,提出了一种结合单相锁相环(MPLL)、正序电压计算单元和同步参考坐标变换锁相环(SRF PLL)的改进型锁相环设计方法。该方法采用2个MPLL来检测电网电压的α和β分量及其移相90°的电压信号,采用正序电压计算单元来检测正序电压分量,经SRF PLL锁定正序电压的相位,从而消除电压不平衡对检测结果的影响。且MPLL和SRF PLL的2次滤波对谐波有较强的抑制作用。此外,根据改进型锁相环的结构模型导出了正序电压分量检测的运算关系,进行了SRF PLL锁相环的控制器参数设计,给出了MPLL参数的系统化设计方法。仿真和实验结果表明,在电压不平衡、电压畸变、频率突变和单相接地情况下,所设计的锁相环均能够快速准确地锁定正序电压基波分量的相位,为风力发电系统控制提供可靠基准。

In order to solve the problem in synchronization signal detection of power electronics converters in wind power generation systems, we put forward a design method of improved phase locked loop which integrates the single-phase magnitude-phase locked loop（MPLL）, the computational unit of positive sequence voltage, and the phase locked loop based on synchronous reference frame（SRF PLL）. The method uses two MPLLs to detect the α and β components of voltage and their 90-degree phase-shifted versions, utilizes the computational unit of positive sequence voltage to detect positive-sequence voltage, and hence eliminates the influence of unbalanced voltage through locking the phase of positive-sequence voltage by SRF PLL. Moreover, the method can effectively suppress harmonics due to the two stages of filtering by the MPLL and the SRF PLL. In addition, on the basis of the structure of improved phase locked loop, we derived the formulas for detecting positive-sequence voltage, designed the parameters of SRF PLL＇s controller, and proposed a systematic design method of MPLL＇s parameters. Further simulation and experiment showed that, the proposed phase locked loop can lock the phase of the fundamental component of positive-sequence voltage quickly and accurately, under various conditions including unbalance and distortion of voltage, sudden change of voltage frequency, and single-phase grounding faults; it provides a reliable base for the control of wind power generation systems.