| With the continuous upgrade of railway signal technology in China, in the interval, ZPW-2000 track circuit has been widely used in railway block system instead of other track circuit. The correct detection of ZPW-2000 shift-frequency signal is the premise to ensure the safety of train operation. But now, in the environment of electrification and high-speed railway, signal system as week current equipment by the interference of traction current increases with the number and volume of tracking train growing in the interval. More complex track circuit environment cause the traditional method of detection of shift-frequency signal interfered by strong noise in poor detection quality and results, and even lead to error signal display.This thesis put a detection method of good anti-noise performance to ensure that the shift-frequency signal detection is reliable in strong noise environment.Based on the chaos theory of Duffing oscillator has better anti-interference performance, sine and 2 binary system frequency shift key(2FSK) signal under the strong interference environment, the detection signal noise ratio(SNR) threshold can be as low as-66 dB. In this thesis, according to the characteristics of Duffing oscillator which sensitive to parameters and immune to noise, it is used in carrier frequency and low frequency detection of ZPW-2000 shift-frequency in low SNR environment. Duffing oscillator detection model is established by Matlab, to achieve the ZPW-2000 shift-frequency signal detection simulation.First of all, the working principle of ZPW-2000 automatic blocking system and the system constitution of ZPW-2000 shift-frequency track circuit are introduced in detail in this thesis, the characteristics of ZPW-2000 shift-frequency signal and the common detection methods of track circuit shift-frequency signal are analyzed. According to the analysis of the common interference of track circuit and the characteristics of ZPW-2000 shift-frequency signal, the detection process is divided into the carrier frequency detection and low frequency detection.Secondly, the dynamic characteristic of Duffing oscillator is analyzed and according to the variable scale method to improve the Duffing equation to meet all frequency signal detection requirements, and the detection principle of general 2FSK signal based on Duffing oscillator is analyzed. In addition, on the basis of elaborating several kinds of commonly used assessment method, summarize the advantages and disadvantages of various kinds of discriminant method.Finally, combining with the characteristics of Duffing oscillator is immune to noise, the Duffing oscillator detection step of ZPW-2000 shift-frequency signal is given, including the carrier frequency detection based on extremum variance method and the low frequency detection based on the adaptive step length intermittent chaos method. Using simulink establish Duffing oscillator detection model, and analysis the Duffing oscillator detection method of clear, traction current harmonic interference and white noise interference environment of ZPW-2000 shift-frequency signal, and comparing with the traditional detection methods are analyzed. Experiment results shown that the Duffing oscillator detection method can solve the detection weak ability problem of shift-frequency signal in low SNR condition, and has high accuracy and better anti-noise performance. |
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