Denoising using wavelets on electric drive applications

One common problem in drives applications is the presence of noise that corrupts the useful information in measurements such as of current, due to sensor imperfections. Digital low pass filters are a solution to the problem but they cannot cope when the useful information has time varying high frequency characteristics. In this paper, wavelet analysis, seldom used as yet in electric drives, is analysed and compared to classical methods. The key points of wavelet analysis are presented in a way that is appropriate for drives. Application of this new method to a typical practical current signal demonstrates the advantages and limitations of these methods over more conventional techniques. The true power of the wavelet transform is revealed when it is applied to a speed estimation problem where the rotor speed of a permanent magnet machine is modulated and coupled with high frequency components.