Development Of Continuous Wave Coherent Laser Detection System For Turbine Control

Wind,as a renewable energy,is vigorously developed and utilized worldwide for the advantages of large reserves,wide distribution,environmental protection and cleanliness.Wind turbine is a key device for energy conversion,and should adjust the attitude of the wind wheel based on the information of the windward precisely and realtime.Therefore,accurate measurement of wind field in front of the wind turbine is particularly critical for improving the utilization of wind energy,stabilizing the output power of the unit,and reducing the load on the wind turbine.The continuous wave coherent detection system is simple structure and low cost,and has been proved to be a suitable sensor for wind observation in short range.This paper studies the coherent detection theory and introduces the development process of a CW(continuous wave)coherent detection system with all-fiber structure for turbine control applications.The main researches of the paper can be summarized as the following four contents:(1)For the yaw control of wind turbines,the performance indicators of the wind measurement system are formulated.Based on CW coherent detection technology,an experimental platform of 1.55 ?m all-fiber lidar has been constructed.The telescope of the system is coaxial transmission structure with 80 m focusing distance.The A/D card,where a FPGA chip on,processes the massive data,which improves the accuracy and real-time performance of the system.A compact prototype of the CW coherent laser detection system has been developed based on the experimental platform.(2)The hard target speed calibration and the atmospheric echo signal test were performed using the constructed experimental platform.The results show that the system has high accuracy of speed measurement,strong adaptability to different weather,and good availability and reliability.Through the noise test,the distribution characteristics of relative intensity noise in the system are analyzed.The reasons for the formation of the blind zone of this type of lidar are explained.(3)The performance of the CW coherent laser detection system is optimized.The improved spectral centroid algorithm is applied to estimate the center frequency of the Doppler signal,which reduces the radial wind measurement error caused by the spectral deformation(multiple Doppler frequency shift information).The concept of Rayleigh criterion in optics is introduced into signal processing.In order to defines the blind zone of the system accurately,the resolution limit of the Doppler signal and relative intensity noise in the frequency domain is obtained based on the generalized Rayleigh criterion,and the lower bound of speed measurement is calculatied as 0.72 m/s.At last,the scanning mode is studied,and the scanning parameters of the detection system are optimized.(4)A long-term radial wind measurement was performed,and a calibrated pulsed wind lidar was compared as a refence.The results verified the effectiveness and correctness of the improved spectral centroid algorithm,and reflecting the lower bound of the speed measurement which was consistent with the theoretical calculations.The field experiments were conducted in Hefei and Shenzhen.The good results were obtained compared with the wind measurement data from the anemometers on the meteorological observation gradient tower.