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

Nowadays, PWM excitation is one of the most common waveforms seen by magnetic components in power electronic converters. Core loss modeling approaches, such as improved Generalized Steinmetz equation (iGSE) or the loss map based on composite waveform hypothesis (CWH), process the pulse-based 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 modeled 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 modeling 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 modeling of core losses in PWM converters. This work enhances the fundamental understanding of the core loss process by advancing from the average model to the time-domain model.