Wavelet Based Diagnosis and Protection of Three-Phase Induction Motor Fed from Sinusoidal PWM Voltage Source Inverter

In this work, a novel wavelet packet transform based algorithm is developed for the on-line protection of three-phase induction motor fed from a sinusoidal pulse width modulated voltage source inverter (PWM-VSI). The algorithm is implemented in real-time using the DS1102 digital signal processor board. The criterion for the protection is the comparison of wavelet packet transform (WPT) coefficients of the second level high frequency sub-band of three-phase line currents using the selected mother wavelet `db3´ with a threshold determined experimentally during the healthy condition of the motor. The minimum description length and the Shannon entropy criteria are used for selecting the optimal mother wavelet and optimal number of levels of resolution, respectively. In all the tests carried out, the proposed algorithm identified the disturbances properly and initiated the trip signal almost at the instant or within one cycle of the fault occurrence.