适用于频率偏移情况下同步相量测量的DFT算法研究

Study of DFT Algorithm for Synchrophasor Measurement Under Frequency Offset

在频率偏移情况下,传统的离散傅里叶变换(discrete Fourier transform,DFT)法在同步相量计算过程中会产生固定误差和动态误差,严重降低了计算精度。为此,提出一种基于对称平移1/12采样窗的自适应DFT相量算法。该算法通过对称平移采样窗,构建与当前相量偏差±p/6的2个虚拟相量,利用相量间的平衡关系,在理论上可完全削减动态误差。实际应用中,由于采样频率固定,相量之间的相角差无法准确达到p/6。为此将可变窗长与平移采样窗相结合,以减小采样窗平移误差,并使采样窗最大程度地接近待测信号的一个周期。仿真结果表明,该算法在保证响应快速性的同时,对频率偏移下的相量计算误差修正效果明显,能够满足智能电网同步相量测量的计算精度和实时性要求。

When power signal frequency offset occurs,synchrophasor accuracy will be reduced because discrete Fourier transform（DFT） has computation error including fixed and dynamic.For this reason,adaptive DFT based on one-twelfth sampling window symmetric translation is proposed.Two virtual ±π/6 deviation phasors can be constructed with sampling window symmetrical translation.Theoretically,dynamic error can be eliminated completely with equilibrium relationship between the phasors.In practice because of fixed sampling frequency,phase angle difference between phasors cannot be accurately achieved to π/6,calculation error will occur.So variable window length and translational sampling window are combined to reduce sampling window translation error.Sampling window length shall be as close as possible to a signal period.Simulation results show that,correction effect of calculation error of the proposed algorithm is obvious in frequency offset and response speed is fast.The proposed algorithm also meets requirements of accuracy and real-time of synchronized phasor measurement of smart grid.