This paper proposes an isolated ultra-flat DC-DC converter architecture capable of directly converting high-voltage distribution rails (15-150 V) into regulated sub-1 V outputs with extremely high voltage conversion ratio. The solution is based on a resonant single-transformer structure specifically designed to enable large step-down operation while minimizing conduction path complexity. A 12:1 turns ratio with a single-turn secondary and reduced primary turns allows high gain realization using only one magnetic component and a minimized number of series devices along the main current path. The complete hardware implementation achieves a total height of 3.5 mm, making it compatible with Surface Power Delivery and Direct-to-Chip integration constraints. An improved version incorporating a secondary-side active clamp is introduced to enhance controllability and transient behavior without increasing magnetic complexity. Both implementations are experimentally validated and quantitatively compared under equivalent operating conditions. The results demonstrate the feasibility of achieving extreme gain, wide gain variation, and ultra-low-profile integration using a single-magnetic isolated architecture suitable for future high-performance computing and AI processors.

This article introduces a 48V-1V high-current single-stage power converter for high performance applications. A hardware prototype is designed and built by stacking four 12:1V modules, with the primary stacks connected in series and the secondary side in parallel. This configuration provides voltage balance in the primary stacks and intrinsic current sharing between the secondary cells. The Segmented Winding Transformer is designed to achieve a 5mm height; a Planar Matrix Transformer with custom magnetic cores is implemented on a standard 3oz PCB, ensuring repeatability and simplifying manufacturing. A significant characteristic of this power converter is the high efficiency achieved, exceeding 90% for currents from 200A to 2000A, with a peak efficiency of 93.6% at 500A, including driving losses. By modifying the primary side, the power converter offers fast dynamic response and output voltage regulation, achieved through low leakage inductance and high voltage in the transformer. With a current slope exceeding 3000A/mu s and interleaved phases, the power converter can handle a 440A load step with minimal output voltage deviation.

The 48V-1V Low-Profile Direct Power Converter, described in this paper, is a single-stage converter for high-current applications with height limitation. Based on the DPx converter, this 5mm-height power converter takes steps forwards by using standard PCB and a Planar Matrix Transformer with commercial cores. This Low-Profile converter becomes a so-called electric center, worsening the conversion performance but improving the manufacturability. A non-optimized prototype was built and tested up to 350A output current, reaching a peak efficiency of 94% and a full-load efficiency of 85% with 412 W/in 3 power density. The 5mm height power converter presented in this article enables a power-supply-in-package for applications where the height dimension becomes highly restrictive.

This article presents a high gain (24:1 V) high current (500A) dc-dc converter. One major advantage is the high efficiency measured, higher than 90% for 500A, higher than 95% for 200A, with a peak efficiency of 97.1%. Another major advantage is that the transformer is built using standard 3oz PCB, which facilitates manufacturability and repeatability at a reduced cost. The prototype is built stacking two 12:1V modules, connecting primary sides in series and output sides in parallel with intrinsic voltage balance in the primary stack and intrinsic current sharing in the output capacitors. Stacking four modules to implement 48:1V is straight forward, maintaining the same efficiency.

This paper introduces an isolated and regulated Ultra-Flat DC-DC power converter designed to address the energy supply challenges posed by the increasing demand for High Performance Computing (HPC) and AI computation. The converter is engineered to accommodate an extremely wide input voltage range of 15V to 150V with significant gain to low output voltage (1V). To achieve this, the converter utilizes a Direct Power Converter topology with an added active clamp to the primary side switch. The key advantage of this design lies in the reduction of the number of switches in the current paths, which enhances its efficiency.The converter features three ports that can function as either input or output, with one port optionally serving as intermediate storage. The Segmented Winding Transformer is employed for internal current path reduction, and the low-profile (3.5mm height) packaging further enhances its compactness. The study validates the converter's performance in both open-loop and closed-loop configurations.

This paper presents a 12-1V fixed gain Multi-Phase Direct Power Converter, a one-stage converter for high current applications. Based on the Direct Power Converter and it’s operation principles, it enables duty cycles up to 85 to 90% for all the power switches, reducing drastically the rms current in the power devices, zero voltage switching (ZVS) in both primary and secondary side and zero current switching (ZCS) in secondary side. Due to the expected high output current, Segmented Winding Transformer (SWT) was also implemented to reduce secondary side losses. A prototype with four phases parallel connected is designed and build to split the high output current into multiple parallel current paths, allowing to reduce the output voltage ripple and the overall capacitance as the phases can be shifted. The prototype was tested up to 550A, achieving a peak efficiency of 97% at 200A and 95% efficiency at full load (500A) with a switching frequency of 150kHz, which allows to parallelize power switches without increasing driving losses dramatically.

The energy demand of future computing gives rise to new challenges in high current voltage regulator modules (VRMs). This paper reviews the recent development in architecture and magnetics for 48-V VRMs, with a focus on achieving high efficiency, high power density, high control bandwidth, and compact system packaging. The strengths and weaknesses of many representative solutions are compared. We highlight the key opportunities and challenges and present comprehensive co-design guidelines for 48-V VRM architecture and magnetics.

A multi-level boost topology based on a flying capacitor is compared in this work with the hybrid, multi-level, partial power processing topology already presented in the literature for use as a highly efficient and compact dc/dc stage in 1500-V, two-stage, grid-connected PV systems. Different variations of the resonant stage of the hybrid topology are analyzed and compared in terms of losses, volume and complexity. Full multivariable optimization is conducted for the multi-level boost topology with different number of levels and for all the analyzed variations of the resonant stage of the hybrid topology. Appropriately rated new classes of 650-V and 900-V WBG devices are included in the optimization algorithm. It is concluded that due to the dominant conduction losses and gap in the voltage rating of the commercially available WBG devices between 650V and 200V, increase of the number of levels over 4 leads to the deteriorated loss and volume performances. All the analysis related to the resonant stage of the hybrid topology is confirmed by detailed and comprehensive measurements of two prototypes of 4kW of nominal and 7kW of maximal power. Additionally, all the loss models applied in the optimization algorithms presented in this paper are confirmed by detailed measurements, thermal calibration and finite element thermal simulations of the wide bandgap devices and inductor designs employed in this work.

The design and optimization of coils for Inductive Power Transfer (IPT) systems is an iterative process conducted in Finite Element (FE) tools that takes a lot of time and computational resources. In order to overcome such limitations in the design process, new empirical equations for the evaluation of the self-inductance and mutual inductance values are proposed in this work. By means of a multi-objective genetic programming algorithm, the self-inductance, the mutual inductance and the coupling factor values obtained from FE simulations of IPT link are accounted by analytical equations, based on the geometric parameters defining the IPT link. The behavioral modeling results are compared with both FE-based and experimental results, showing a good accuracy.

This article reviews and classifies the representative types of “differential power processing (DPP)” architectures, focusing on the aspect of how the processed power is reduced with DPP. Comparing with existing review works on this topic, this article provides new viewpoints from three perspectives. First, the differential power ${P}_{{\text {diff}}}$ at both architecture level and converter level is discussed. For the calculation of the total processed power in a power architecture, instead of summing up the output power ${P}_{{\text {out}}}$ delivered by the DPP converters, we account for ${P}_{{\text {diff}}}$ inside the DPP converters because direct power exists not only at the architecture level but also at the converter level, and thus, the power processed in a converter may be lower than ${P}_{{\text {out}}}$ . Second, the VA area modeling is applied to the DPP architectures to illustrate and visualize the processed power in the power architectures and converters, thus analyzing and comparing them at high level. Finally, the processed power of different DPP architectures is compared quantitatively with statistical analysis for varied operating situations.

Only one transformer and two power switches are needed to implement a DPx dc-dc converter with constant gain (DCx). Both primary and secondary switches are ON and OFF simultaneously, connecting input and output through the transformer. At turn on, the leakage inductance limits the current transition to its steady state within the switching cycle, where it stays for a duty cycle higher than 50% featuring low rms current in the power switches. During the OFF time the transformer is reset, by a resonance between magnetizing inductance and the capacitance (parasitic and added) in parallel with the switches. It features 1-cycle dynamics and no-load operation. Bi-directional power flow and multiple outputs are straightforward. Excellent performance is obtained for 48 to 4V and 12 to IV dc-dc converters to supply high performance processors which may be extended to other gains as 48 to IV, just changing the transformer turns ratio

Generally, in non-isolated power converters, the highest temperature is reached in inductors and switching devices due to power losses. Extracting heat is always challenging, requiring a careful three dimensional (3-D) design and bulky heatsinks. For inductors, this challenge can also be addressed using custom magnetics; the shape of inductors could be designed aiming to decrease the reached temperature. In this work, a detailed study of new 3-D coils termed "Box inductors" has been carried out. The advantage of this new structure is that it has a large surface area for a given volume, which allows a better heat transfer and, thus, a decrease in temperature. This "Box inductor" is used in a single-phase single-stage transformerless inverter integrating the intermediate energy storage. Three Box inductor designs with the same PLT-3C95 core, but with different types of geometries are compared, which are also compared with a conventional RM14/I-N87 coil to establish which one leads to lower losses and temperature. Matlab and Maxwell are used to accurately estimate the losses. Prototypes of the three designs are built and tested, and the results of inductance value, losses, and temperature are compared.

This article presents a control linearization technique for a single-phase single-stage inverter with multiple modulation strategies. The power topology is based on an flying capacitor multi-level (FCML) inverter, and the control is based on the plant inversion. The proposed technique allows decoupling the control of the input current and the output voltage, which simplifies the control in two ways: first, the control of both variables is independent and second, the controllers are independent of the modulation applied, thanks to the plant inversion. This control is implemented in an field-programmable gate array. Since the converter operates at variable frequency, two different data acquisition alternatives are explored: sampling at variable frequency (once per switching cycle) or sampling at constant frequency (higher than the switching frequency).The proposed control is validated by simulation and experimental results with a 1-kVA prototype.

This article presents a hybrid converter combining soft-charged switched capacitors and an autotransformer with dc current in the windings, optimized for 4:1 fixed voltage gain conversion (DCX) for high output current. By adding an additional output inductor, it can also regulate the output voltage to lower than ¼ of the input voltage by changing the duty cycle. The switched capacitors voltage and the two winding currents in the transformer are auto-balanced. Nonresonant operation of the circuit enables dc current in the windings and simplifies both transformer and circuit design. Experimental results for 48 V–12 V DCX operation achieve 98% peak efficiency and 97.7% full load (250W) efficiency. Regulation by using the output inductor is verified experimentally up to 48–6V (8:1) voltage step down.

The analytical calculation of winding loss in gapped magnetic components is complex, and numerical analysis tools, such as finite elements analysis (FEA) tools, are commonly needed to characterize the windings. As FEA tools are used, the required design time of these types of components increases greatly when many simulations are needed to select the appropriate component for a given application, and simple analytical models become necessary to reduce the design time. In this paper, some analytical approaches for winding loss calculation in gapped magnetic components are reviewed and a general two-dimensional equivalent method, which aims to consider the frequency effects in conductors in a simplified manner, is proposed afterward. Due to its simplicity, it can be integrated into design and optimization tools in order to evaluate the influence of the air gap over the winding loss even at the early stages of the design process. The presented model shows good agreement with FEA simulations and measurements.

Hybrid converters are becoming popular in recent years for their high power density and high efficiency. This paper reviews and classifies hybrid converters from the perspective of the power processed by their components. The power processed by reactive components and transformer is calculated to illustrate how the power is processed "hybridly" by different components, which can help us to understand the operation principles. Component level parameters of example circuits are also provided to illustrate how hardware is affected by the amount of processed power, which explains why hybrid converters can achieve better performance.

In this article, analysis and design of a 3.3-kW isolated single-stage three-phase buck-type rectifier for aircraft applications is presented. The operating principle and modulation method of the proposed rectifier are introduced. The advantageous zero-voltage switching (ZVS) feature in all of the switching transitions is analyzed. A comparison with the VIENNA Rectifier III is done, being different both in the phase-leg implementation and the modulation sequence. A detailed rectifier design guideline is discussed and losses estimations are provided aiming at reaching 93.7% overall efficiency, including the EMI (electromagnetic interference) filter. Simulation waveforms are presented. Finally, experimental results obtained with the designed 3.3-kW hardware demonstrator are provided. The results verify achievement of ZVS in all of the switching transitions from full load down to 50% of nominal load, while exhibiting 1.9% THD$_I$ (total harmonic distortion) and 0.9996 PF (power factor) at nominal power, ultimately showing very good agreement to the simulation results. This article is accompanied by a video demonstrating experimental operation of the proposed rectifier at nominal input voltage, output voltage, and output power.

In industrial applications, such as modern piezoelectric inkjet printers or automated device testers, arbitrary voltage waveforms need to be reproduced onto a different type of loads, providing four-quadrant operation with excellent linearity, preserving high signal-to-noise ratio with acceptable stability margin and high EMI immunity. These stringent requirements can be easily addressed if linear power amplifiers (LPAs) are employed. Nevertheless, their power density is limited by the large heat-sinks due to dissipative behavior of the Class A/AB/B output stage. In order to improve the performance of LPAs, hybrid PAs (HPA) are utilized, which involve highly efficient switched-mode power converters, called tracking power supplies (TPSs). In this article, the concept of HPAs based on only one TPS which modulates both supply rails is elaborated and exploited in two design examples, for different requirements regarding the output voltage dynamics. The first design is applicable in cases with a very fast output voltage dynamics (slew-rates up to 45 V/μs) and capacitive loads (piezoelectric nozzles), while the second design provides an optimized, very compact GaN-based solution in case when alleviated requirements regarding the output voltage dynamics (slew-rates up to 1 V/μs) have to be met for all types of passive loads (four-quadrant operation).

The European XFEL is a hard X-ray free-electron laser (FEL) based on a high-electron-energy superconducting linear accelerator. The superconducting technology allows for the acceleration of many electron bunches within one radio-frequency pulse of the accelerating voltage and, in turn, for the generation of a large number of hard X-ray pulses. We report on the performance of the European XFEL accelerator with up to 5,000 electron bunches per second and demonstrating a full energy of 17.5 GeV. Feedback mechanisms enable stabilization of the electron beam delivery at the FEL undulator in space and time. The measured FEL gain curve at 9.3 keV is in good agreement with predictions for saturated FEL radiation. Hard X-ray lasing was achieved between 7 keV and 14 keV with pulse energies of up to 2.0 mJ. Using the high repetition rate, an FEL beam with 6 W average power was created. The first operation of the European X-ray free-electron laser facility accelerator based on superconducting technology is reported. The maximum electron energy is 17.5 GeV. A laser average power of 6 W is achieved at a photon energy of 9.3 keV.