Enhanced DAB for Efficiency Preservation Using Adjustable-Tap High-Frequency Transformer

Abstract

Efficient DC-DC power-conversion with wide-span voltage-regulation is crucial to a sustainable and robust power electronics system. Dual-active-bridge (DAB) offers straightforward regulation and its transformer enables voltage stepup/down required for many applications, such as battery chargers and bus converters for DC distribution systems. However, losing soft-switching at light loads or when operating at voltage gains far from the turns ratio severely degrades the efficiency of DAB, especially at high switching frequencies. In this work, we demonstrate an enhanced DAB (E-DAB) topology which employs an adjustable-tap transformer to extend the softswitching over wider voltage gains and increase the powertransfer capability. By a proper tap adjustment and with single phase-shift modulation, the proposed GaN-based converter achieved a peak efficiency of 97.4% with an overall efficiency greater than a conventional DAB for voltage gains of up to 2.8 times higher. Employing a quasi-planar matrix transformer with integrated leakage inductance at 300 kHz allowed for an extremely high power density of 10 kW/l (7.5 kW/l with cooling). The tapped transformer did not incur extra losses to the topology. The gain versus power-transfer characteristic for softswitching operation was derived for the E-DAB and its improvement in efficiency was experimentally verified over a wide power range.

Modeling of a DAB under phase-shift modulation for design and DM input current filter optimization

“…Applying Fourier series theory, the DM input current can be described in the frequency domain. The normalized coefficients are shown in (8), (9) and the reconstruction of the normalized input current, back to the time domain is then presented in (10). Notice that the frequency of the input current corresponds in theory to the double of the switching frequency as illustrated in Fig.…”

“…Giving the desired input voltage, output voltage and current ranges, the designer will be able to find an optimum design with respect to different parameters as well as to identify the critical regions and limitations found in a DAB. To overcome these natural limitations or to enhance its performance and keeping same or similar converter topology, different strategies can be implemented, such as different dual phase-shift modulation [8], variable-tap transformer [9], frequency modulation [10] or even a combination of phaseshift and frequency modulation [11].…”

A Low Complexity Algorithm for Efficiency Optimization of Dual Active Bridge Converters

“…Efficiency is influenced by a number of design and operation parameters. When considering modulation schemes, a couple of important issues are the high conduction loss, especially when operating at input-output voltage ratios different from the transformer turns ratio [13], [14], and the high switching loss in absence of zero voltage switching (ZVS) turn-on, as typically happens at light-load [15], [16]. Several modulation strategies have been presented in the literature to cope with these issues [17]- [19].…”

High-Accuracy Calibration-Free Calorimeter for the Measurement of Low Power Losses

“…HE emergence of high-performance wide-band-gap (WBG) technologies and high-quality passive components (e.g. high-frequency transformers and inductors) have enabled ultra-high efficiencies in high-frequency power conversion [1]- [6]. However, measuring high efficiencies using electrical methods is prone to large errors due to insufficient measurement accuracies [7], [8].…”