Signal Demodulation Algorithm based on Hilbert Transform and its applicaTion in Aircraft Power Supply System Characteristic Parameters Testing

The working state of aircraft power supply system, which can be evaluated by its characteristic parameters, greatly affects the flight safety. In the test of aircraft power supply system's characteristic parameters, voltage modulation amplitude, frequency modulation amplitude and distortion spectrum are important parameters. These parameters should be tested in high sampling rate and resolution according to relevant aircraft standards. A digital signal demodulation algorithm for aircraft power supply system testing is proposed. This algorithm uses Hilbert transform to separate the modulation waveform from the original signal. The amplitude and frequency of the modulation waveform then can be identified. Both amplitude modulation and frequency modulation signal can be demodulated by this algorithm. The modulation waveform can be a sine wave or a triangle wave. A testing system for characteristic parameters of aircraft power supply system is built based on this algorithm. This system uses a voltage divider and a unit gain buffer amplifier for signal conditioning. A high-speed digitizer is applied to sample the conditioned signal, which will be further processed by the demodulation algorithm. To evaluate the accuracy of this testing system, an experiment was performed with an arbitrary signal generator, which can simulate the modulated output of the aircraft power supply system. The experiment results indicate that the relative error of amplitude demodulation is less than 0.07% and the relative error of frequency demodulation is less than 0.02%, which can satisfy the related standards for aircraft power supply system testing.