| Under the background of the national strategy of low-carbon environmental protection and the development of new energy vehicles,the demand for various vehicle sensors with better performance becomes more urgent,and the current range is increasing.However,when the range of current sensor increases,the measurement accuracy of weak current will be reduced.Therefore,the requirements of both a large current detection range and a high precision for small current should be considered.This thesis proposes the design of a dual-range,wide-bandwidth and high-precision current sensor.The fluxgate current detection technology is adopted to achieve innovative breakthroughs in the structure design and working principle of the sensing probe.Moreover,the system design and optimization are carried out in the aspects of signal extraction,signal analysis,noise suppression and zero-flux closed-loop feedback technology.Based on the research of domestic and foreign relevant literature,the development status and working principle of fluxgate technology are studied.The design scheme of dual-ring detection probes with higher signal-to-noise ratio is determined.In the aspect of signal processing,by analyzing the characteristics of time difference method,peak detection method and second harmonic method,the second harmonic method is determined to analyze the output signal of the detection probe.And the zero flux closed-loop design is adopted to further improve the detection range and linearity of the system.According to the requirement of dual-range design of fluxgate current sensor,a design method of dual-range current sensor system which integrates the small-range detection probe and the large-range detection probe is proposed.Based on theoretical calculation and simulation optimization,the relationship between the parameters of magnetic ring and magnetic induction intensity is studied.Furthermore,the influence of the size of magnetic ring,the winding method,as well as the number of winding,on the detection signal of current sensor and the feedback effect of zero-flux closed-loop is established.In addition,the detection probes of the two ranges share a part of the signal processing circuit.MCU can judge the range and automatically switch between two ranges according to the value of the measured current.In view of the wide-bandwidth design of fluxgate current sensor,considering the bandwidth limitation of fluxgate technology itself,a third magnetic core and corresponding induction coil are added as current transformer in the fluxgate probe,which is used to detect high frequency AC signal and could greatly improve the working bandwidth of the system.For the high-precision design requirement of fluxgate current sensor,both software and hardware are optimized.The induction coil adopts the form of differential output,and the instrument amplifier is used to extract the weak differential mode small signal from the common mode interference signal,which improves the signal-to-noise ratio.After that,Butterworth bandpass filter circuit with more stable passband is used to extract the second harmonic signal and attenuate the interference signal.In software programming,the algorithm of median averaging and zero bias calibration are carried out to realize the high precision data acquisition of the sensor.The fluxgate current sensor system is tested and analyzed on the self-built test platform in the laboratory.The test results demonstrate that the small-range current sensor shows good performance of a measuring range of 0～±10 A,a high resolution of 100 μA,a linearity of 0.133%,a repeatability of 0.171%,an accuracy of 0.304%.The large-range current sensor exhibits good performance of a measuring range of 0～±500 A,a resolution of 10 m A,a linearity of 0.339%,a repeatability of 0.265%,an accuracy of 0.604%.The working bandwidth of the current sensor system is DC～920 k Hz.The dual-range fluxgate current sensor designed in this thesis benifits many advantages of wide range and wide bandwidth,and can be widely applied in areas of new energy vehicles and electronic metering. |
PDF Full Text Request