Real-Time Testing of WPT-Based Protection of Three-Phase VS PWM Inverter-Fed Motors

This paper presents an experimental testing of a wavelet packet transform (WPT)-based technique for protecting and controlling three-phase voltage-source (VS) pulse-width modulated (PWM) inverters under extreme load conditions. The proposed technique is based on a two-level multiresolution analysis (MRA) applied on output currents of a 3Phi VS PWM inverter. The MRA aims to extract certain signatures, which are the second level highest frequency subband coefficients. These coefficients take a nonzero value for any signal that is short-duration, nonperiodic and nonstationary with impulse-super imposed high frequencies. Such a signal perfectly matches a current arising from any typical fault occurring in either the inverter legs or on the load side. The proposed technique is realized using a -code hosted and executed by a dSPACE ds1102 controller board. The tested inverter supplies loads that include a 3Phi Y -connected R - L load, a 3Phi squirrel-cage induction motor and a 3Phi synchronous reluctance motor. The extreme load conditions include inverter open-leg, motor starting currents and different faults in motor stator windings. The experimental test results show accurate, fast, and effective response to all disturbances including fault currents by the proposed WPT-based technique.