Minimum Loss Operation and Optimal Design of High-Frequency Inductors for Defined Core and Litz Wire

Abstract

This paper studies the loss-optimal design of a power inductor employed in a 2 kW, 400 V input DC-DC converter. The design of an inductor is subject to a large number of design parameters and the implications of the different design parameters on the losses are often not clearly traceable in a full optimization, e.g., different current ripple amplitudes can lead to designs with similar losses, as larger ripple amplitudes lead to increased AC core and winding losses but lower DC losses in the winding due to lower inductance values and/or numbers of turns. In an effort to achieve a comprehensible description of the implications of the key design parameters (switching frequency, current ripple, number of turns) on the losses, the remaining parameters, e.g., core (E55/28/21 N87) and type of conductor (litz wire), are considered to be given. In a first step, the investigation is based on a simplified analytical model, which is refined in a step-by-step manner, e.g., to consider core saturation. In a second step, the implications of further critical aspects on the losses, e.g., temperatures of core and coil, are examined using a comprehensive semi-numerical model. Surprisingly, the evaluation of the losses calculated in the fr domain reveals that nearly minimum inductor losses are obtained for a current ripple that is inversely proportional to the frequency, i.e., for a constant inductance, within a wide frequency range, from 200 kHz to 1 MHz. Furthermore, the investigation reveals a decrease of the losses for increasing frequencies up to 375 kHz, e.g., from 4.32 W at 80 kHz (r = 110 %) to 2.37 W at 375 kHz (r = 18 %). The detailed analysis related to these results enables the compilation of a simple two-equations guide for the design of an inductor that achieves close to minimum losses. In a next step, interesting trade-offs are identified based on a study of the design space diversity, e.g., with respect to low cost and increased partial-load efficiency. The findings of this work are experimentally verified, i.e., the losses of three different inductors are measured with an accurate calorimetric method and at four different frequencies, ranging from 150 kHz to 700 kHz.

Modular SEPIC-Based Isolated dc–dc Converter with Reduced Voltage Stresses across the Semiconductors

“…With an optimized design methodology in the output inductors, the leakage inductance could be lower, which would decrease the losses in the switches and also in the snubber cells. The theoretical losses are calculated based on the methodology from [45][46][47].…”

Spectral Steady-State Analysis of Inverters With Temperature-Dependent Losses Using Harmonic Balance

“…Next to thermal design of the inverter, the obtained temperature cycles can serve as input for life-time estimations [22]. State-of-the-art calculation methods for inductor and capacitor losses could be added to optimize the complete system [23], [24]. Beyond design of inverters, a possible application of harmonic balance could be over-temperature protection.…”

dv/dt filter design incorporating machine impedance and voltage slew rate for WBG-based electric drives

“…The main losses in an inductor are the core losses P core and winding losses P wind which can be calculated analytically for a given core material and geometry. The winding losses can be calculated using the equation set in (8) where the skin and proximity losses are accounted based on the strand diameter d r and skin depth δ for the operating switching frequency f sw [16].…”