The characteristics of power system transients seen today present a problem for the classical Fourier analysis technique because it fails to effectively and accurately localize and quantify power system effects. This paper looks into the application of the technique of multi-resolution analysis, based on the wavelet transforms, on voltage waveforms obtained from a pulse width modulation (PWM) induction motor drive during work on ASHRAE Research Project 770. The technique is introduced and applied to mathematically generated waveforms simulating the constant and transient speed operations of a PWM induction motor. It is then applied to waveforms obtained during constant speed operation of an actual induction motor.

A new power quality criterion based on the wavelet transform coefficients also is presented and compared to total harmonic distortion (THD). It is seen that since THD is based only on the root mean squared (RMS) value of the harmonics present in the waveforms, it fails to quantify the effects of phases of these harmonics. In addition, all harmonics are weighted equally when calculating the THD, which leads to loss of information regarding the individual harmonic number and magnitude. The new method presents a number that takes into account all the above mentioned effects.

Units: Dual