The invention discloses an 
aviation direct-current converter online fault combined prediction method based on fractional order 
wavelet transformation. The method includes: (1) monitoring and collecting output 
voltage signals of the 
aviation direct-current converter in real time, calculating output 
voltage change rate of different moments, and using the output 
voltage change rate as converter performance degradation parameters; (2) conducting abnormal value rejection and 
missing data filling on performance degradation data by using a 3 sigma method and an interpolation method; (3) conducting fractional order 
wavelet transformation on the performance degradation data, the performance degradation data is decomposed into subcomponents with different scales, and determining 
noise components and removing the 
noise components by calculating a combination entropy between high-frequency components and environment data; (4) building a predication model of the high-frequency components in 
decomposition data by using a 
wavelet neural network, building a prediction model of low-frequency components by using a gray neural network, and conducting 
time sequence prediction; and (5) stacking predication values of the high-frequency components and the lower-frequency components to obtain a final predication value, conducting performance evaluation and fault predication on the 
aviation direct-current converter by combining fault threshold values. The aviation direct-current converter online fault combined prediction method removes disturbances caused by environment factor fluctuation in performance degradation data, restores real performance degradation data, simultaneously decomposes the performance degradation data into different frequency subcomponents with strong regularity, predicts the subcomponents by using a combined prediction model, enables prediction risks to be dispersed, and improves online fault prediction 
correctness.