Instantaneous Core Loss -- Cycle-by-cycle Modeling of Power Magnetics in PWM DC-AC Converters

TL;DR

This paper introduces the concept of instantaneous core loss in power magnetic components under PWM excitation, enabling cycle-by-cycle modeling of core losses in PWM DC-AC converters, which was previously unachievable.

Contribution

It proposes a novel method to measure and model instantaneous core loss as a function of time, capturing the fundamental-frequency effects on core loss.

Findings

Discovered higher core loss during discharging stages.

Developed a time-domain model for major loop core loss.

Enabled cycle-by-cycle core loss prediction in PWM converters.

Abstract

Nowadays, PWM excitation is one of the most common waveforms seen by magnetic components in power electronic converters. Core loss modelling approaches such as improved Generalized Steinmetz equation (iGSE) or the loss map based on composite waveform hypothesis (CWH) process the PWM excitation piecewisely, which is proven to be effective for DC DC converters. As the additional challenge in PWM DC AC converters, the fundamental-frequency sinewave component induces the "major loop loss" on top of the piecewise high-frequency segments, which however cannot be modelled on a switching cycle basis by any existing methods. To address this gap, this paper proposes a novel fundamental concept, instantaneous core loss, which is the time-domain core loss observed experimentally for the first time in history. Extending the reactive voltage cancellation concept, this work presents a method to measure the instantaneous core loss, which only contains real power loss, as a function of time. Based on measurements in evaluated soft magnetic components, it was discovered that the discharging stage exhibits higher core loss than the charging stage. A modelling approach is then proposed to break down the major loop core loss, typically an average value in the literature, into the time domain to enable cycle-by-cycle modelling of core losses in PWM converters. This work enhances the fundamental understanding of the core loss process by moving from the average model to the time-domain model.