Research Of Electric Energy Metering System For Locomotive

With the rapid development of electrified railway, large amounts ofharmonic current produced by electric locomotive are injected into the grid，which may seriously affect the security and stability of the power system. Theexisting power meter which is applied to locomotive can not detect theharmonic order and measure different order harmonic, and it is difficult toaccurately measure the power value of non-stationary signal, the accuratemeasurement of different order harmonic THD can provide reliable basis forpower energy charging and harmonic management.Fast Fourier Transform (FFT) or Wavelet Packet Transform (WPT) isseparately applied to measure power energy; the precisions of steady state andnon steady state are not satisfied at the same time. This paper studies theelectric locomotive harmonic characteristics and builds the simulation modelto produce locomotive harmonic signals by Matlab/Simulink software.Through comparing theory value and experimental value comparison whichcomputed by the FFT and WPT, this paper proposes an algorithm forlocomotive electric energy measurement methods based on WPT and FFT.Firstly, the sampling signal is analyzed by FFT and the dynamic measurementof power spectrum maximum envelope is calculated to detect main frequencypoint. Secondly, locate bandwidth which in the band of main frequency pointsignal are detected the steady-state by WPT, and the method of power energymeasurement is determined. if it is a steady-state signal, FFT will be used tocalculate electrical energy value, otherwise, the WPT will be used to calculateelectrical energy value; Finally, the measurement results are accumulated anddifferent order harmonic power energy value are displayed. The simulationresults show that the proposed algorithm can not only measure fundamentalwave power effectively, but also calculate harmonic content in the signalaccurately.This paper designs a scheme about locomotive harmonic power energymeasurement system which includes hardware and software, data acquisition,man-machine interface and data communication module are built by thehardware based on TMS320F2812. The software system includes dataacquisition and data processing module, the data processing mainly realizes power measurement algorithm which is put forward in the combination of FFTand WPT.Power energy measurement algorithm and system have strong theoreticaland engineering value, which provides some useful reference for measuringthe harmonics, interharmonics and unsteady signal power accurately.