Time-Frequency Analysis of Complex Space Phasor in Power Electronics

This paper considers applying nonparametric and parametric methods for the calculation of the time-frequency representation of nonstationary signals in power electronics. A space phasor is proposed as a complex representation of a three-phase signal to calculate the spectrum of positive-and negative-sequence components. The developed methods are tested with nonstationary multiple-component signals occurring during the fault operation of inverter-fed drives. First, the main differences between parametric and nonparametric methods are underlined. Then, some aspects of additional kernel functions are introduced on the basis of Wigner and Choi-Williams distributions. An additional comparison of uncertainty of measurements using the described methods, as well as a widely used Fourier technique, can be useful for practitioners. The proposed methods allow tracking instantaneous frequency as well as magnitude that can lead to applications in the diagnosis and power quality areas.