A Practical Approach for Core Loss Estimation of a High-Current Gapped Inductor in PWM Converters With a User-Friendly Loss Map

Abstract

Core loss estimation of filter inductors is critical for modelling and optimising high-frequency, highefficiency and high-density Pulse Width Modulation (PWM) power electronics converters. However, data provided by inductor core manufacturers is insufficient for core loss estimation in PWM converters, particularly in the case of customized gapped inductors. This paper presents a whole process of characterising and estimating the core loss of a customised high-current gapped inductor for PWM converters. To excite the inductor for the B-H loop measurement, a test circuit formed by a half-bridge structure is proposed, which has the ability to compensate the asymmetric rectangular voltage on the inductor caused by the device voltage drops. To overcome the other challenges raised by high excitation current, a discontinuous test procedure, Triple Pulse Test (TPT), is applied to reduce the requirements of the high-current test setup (thermal stress, current-time stress for current probes, capacity of dc sources, etc.). For practical purposes, a user-friendly loss map approach is proposed involving only time-domain and electrical variables to replace magnetic variables to enable straightforward loss mapping process and core loss calculations. Presented experimental results show consistency between the estimated inductor loss and measured values. Overall, the proposed testing approach can be easily implemented on the user's side to develop a loss map of a given inductor. The established core loss map enables the users to accurately and rapidly estimate the core loss of a tested inductor for given PWM waveforms.

An Efficient Analytical Inductor Core Loss Calculation Method for Two-level and Three-level PWM Converters based on a User-friendly Loss Map

“…To characterize the core loss of an inductor, B-H loop measurement is widely used in previous studies [3], [5], [7]. As the most important feature of this approach, only the core loss is measured out from the total inductor losses.…”

“…To drive the excitation current into the inductor-under-test, a power converter is required. According to [7], a half-bridge structure with the DC-link formed by two adjustable power supplies in series is preferred for the power converter stage. This configuration allows the excitation current to flow in both directions and enables the compensation of asymmetric inductor voltage caused by the voltage drops on power devices.…”

“…For an individual inductor, the loss map in magnetic/time domain can be converted into electrical/time domain following equations (5)- (7), assuming UL1/UL2 = N1/N2.…”

“…Since the core loss profile varies from inductor to inductor ( [7], [17]), this study focuses on one specific inductor that has been built and tested. A Triple Pulse Test (TPT) procedure [7] is applied to build up the loss map in this study. The tested inductor is a customized, high-current inductor with gapped CoFe EE cores.…”

“…While the copper loss can be accurately estimated by analytical models (e.g. [2]), the core loss is more difficult to predict in PWM converters [3]- [7]. The particular difficulties in the case of inductor core loss in PWM converters are caused by PWM operations, which involves dcbias (pre-magnetization) [5], varying pulse widths and squarewave excitation.…”