风电机叶片回波模拟及其多普勒特性分析

Echo Simulation and Doppler Characterization of Wind Turbine Blades

准确模拟风电机叶片回波并分析其多普勒特性,是风电场杂波识别的关键问题。由于现有的散射点叠加模型无法体现出叶片复杂异形曲面上感应电流的连续性,为此,依据电磁散射理论,提出了基于散射电场的叶片回波模拟方法。根据雷达回波与散射电场的数学关系,发现目标的后向散射电场的复振幅矢量可转化为目标的回波信号回波基带信号,由此采用矩量法与物理光学法的混合算法,对散射电场进行求解,并采用短时傅里叶变换获取回波的时频域数据,通过与实测数据的对比,验证所提方法的正确性。最后,采用控制变量的方法分析了不同参数对多普勒频率的影响规律,即多普勒频率与叶片尺寸、电磁波发射频率以及叶片转速呈正相关,与方位角呈负相关,从而实现了叶片回波的多普勒特性分析,为风电机的回波识别及后续的杂波滤除工作提供了理论基础。

It is a key issue to accurately simulate wind turbine blade echo and analyze its Doppler characteristics in wind farm clutter recognition.The existing scattering point superposition model can not reflect the continuity of the induced current on the blade’s complex shaped surface,therefore,a blade echo simulation method based on the scattered electric field is proposed on the basis of the electromagnetic scattering theory.According to the mathematical relationship between the radar echo and the scattered electric field,it is found that the complex amplitude vector of the target backscattering electric field can be converted into the echo signal baseband signal of the target echo signal.Then,a hybrid algorithm containing the methods of moment and physical optics is used to solve the scattered electric field,the time-frequency domain data of the echo are obtained by the short-time Fourier transform,and the correctness of the proposed method is verified by comparison with the measured data.Finally,the influence of different parameters on the Doppler frequency is analyzed by the method of control variables,that is,the Doppler frequency is positively correlated with blade size,electromagnetic wave emission frequency and blade rotation speed,and negatively correlated with azimuth,so that the Doppler characteristics of blade echo are analyzed.The research results provide a theoretical basis for echo recognition and clutter filtering of wind turbines.