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The role of data centers has become significant in the era of information technology, and their operation consumes a substantial amount of energy. Therefore, the point-of-load (POL) converter or voltage regulation module (VRM) used in data centers must have high efficiency and power density to deliver a large current to specific servers. A common bus voltage 48V at the rack stage needs to be stepped down to intermediate bus voltage, which is 6-5V in this case. To achieve this, a new pentacentra transformer was developed for a 4-phase LLC converter. A centra bar serving as the 5th leg of the core is added to the conventional 4-leg matrix transformer. The interleaving and integration of windings in the proposed pentacentra transformer enabled balanced current sharing and reduced conduction loss by 45% compared to the traditional winding layout. The experimental prototype of the converter was designed to achieve 800 W power output at a switching frequency of 500 kHz and 48V-40V/6V-5V voltage conversion. The peak efficiency achieves 98.1% along with the power density of 240 W/in3 with the experimental result. Without the heatsink, the whole converter is operating at rated power within a safe temperature lower than 86 °. The excellent thermal performance ensures the reliable operation of the converter and promises a larger power delivery capability.

This paper presents an optimization of a 6.78-MHz inductive power transfer (IPT) system for unmanned aerial vehicles (UAVs). Firstly, in order to mitigate the impact of the misalignment between the transmitting coil and the receiving coil on the output power and system efficiency, a homogeneous-flux transmitting coil was developed. The optimal allocation of turns of the transmitting coil for generating a homogeneous magnetic field was obtained using a built magnetic field and mutual inductance model combined with an optimization algorithm. In addition, an analytical eddy-current loss model of the air-core inductors was developed. Through the iterative processes for proximity-effect loss, the resistance modeling of the spiral and helical coils is improved, with errors of 7.1% and 4.9%, respectively. Then, the parameters of all the air-core inductors used in the study were optimized using the built loss model and optimization algorithm with various design considerations. Finally, a 6.78-MHz 200-W IPT system with a homogeneous-flux transmitting coil was demonstrated. The proposed system exhibited high-misalignment-tolerance and high-efficiency characteristics, maintaining an output power of approximate 200W and an efficiency of 89% with a 25-mm lateral misalignment.

This paper aims to study the core losses behavior at high frequency (MHz range) with superimposed DC bias in ferrite. Inductive compensation method is employed in the measurement circuit to reduce sensitivity to phase errors. An addition to the circuit is proposed in this work to make easier DC bias generation. Furthermore, a detailed measurement accuracy consideration is also discussed. The tested MnZn ferrite has a nominal relative permeability of 1500 and 800, which was tested at frequency from 500 kHz to 3 MHz. The measurement results are explained thoroughly with three controlling parameters: excitation frequency, peak AC flux density, and DC bias. There are several important findings. First, a higher DC bias creates higher losses at the same frequency and AC flux density. Secondly, at the same DC bias and AC flux density, higher frequency generates a lower relative losses increase. This second point has not been seen in previous literature and is elaborated more in Section III.B. Thirdly, the measurement result shows how DC bias increases the hysteresis loop area and coercivity. The first and third findings confirm the the existing literature findings. As a final step, an improved Steinmetz Premagnetization Graph and Artificial Neural Network are used to create core loss prediction model. The measurement data and the built model can be accessed online for use by other magnetics designer.

Future generations of power converters must be miniaturized to power future electronic devices that are getting smaller and smarter. Monolithic integration is an ideal approach toward compact, efficient, and low-cost converters. This letter addresses two technology gaps in packaging technology and integrated inductor technology using the so-called power interposer technology (PIT). We implemented a step-down power converter to demonstrate PIT. The converter uses two GaN FETs, capacitors, and a gate driver stacked on a 0.28-mm-thick silicon die that hosts a 3D substrate-embedded toroidal microinductor. The converter switches 22 MHz in zero-voltage-switching mode achieving a peak efficiency of 83% at the full load of 1 W. PIT has shown unique technology advantages for future generations of integrated power converters, including high power density, low profile, superior thermal performance, scalability, and heterogeneous integration. Furthermore, PIT holds great commercial potential for high-power-density integrated power converters.

Internet-of-thing (IoT) is an assembly of devices that collect and share data with other devices and communicate via the internet. This massive network of devices, generates and communicates data and is the key to the value in IoT, allowing access to raw information, gaining insight, and making an intelligent decisions. Today, there are billions of IoT devices such as sensors and actuators deployed. Many of these applications are easy to connect, but those tucked away in hard-to-access spots will need to harvest ambient energy. Therefore, the aim is to create devices that are self-report in real-time. Efforts are underway to install a self-powered unit in IoT devices that can generate sufficient power from environmental conditions such as light, vibration, and heat. In this review paper, we discuss the recent progress made in materials and device development in power- and, storage units, and power management relevant for IoT applications. This review paper will give a comprehensive overview for new researchers entering the field of IoT and a collection of challenges as well as perspectives for people already working in this field.

An integrated inductor for a highly compact embedded battery charger is designed in this article. A zero-voltage switching (ZVS) buck converter is the selected topology to achieve high power density. ZVS is achieved by sizing the inductor based on energy balance and introducing the $k$ factor. A novel four-leg magnetic core structure is proposed as the integrated inductor. By introducing a modified parameter $\alpha _{\mathrm{eff}}$ to the improved generalized Steinmetz equation method, the optimal switching frequency for core losses can be found. From the constructed inductor model and semiconductor loss calculation, the design tradeoff and optimization is analyzed. The optimal $f_{\mathrm{sw}}$ is found to be around 2 MHz, which is when the performance factor for the core material peaks. As a proof of concept, a highly compact prototype, featuring stacked printed circuit board solution, with 16.2 × 19.2 × 6 mm$^{3}$ dimension is built. The input voltage ranges from 6 to 12 V, and the converter is capable of delivering up to 10 A at the 4-Voutput. Converter peak efficiency of 96% is achieved, and the inductor design has a power density of 113.6 W/cm$^{3}$. This shows improvement over several state-of-the-art designs. This article is accompanied by a video demonstrating the flux distribution in the magnetic core over the switching period.

This article investigates the modeling and implementation of the load-independent operation for the push–pull Class E topology with coupled inductors. The analytical modeling is first presented and provides a new design methodology, which distantly improves the soft-switching performance, load regulation, and efficiency compared with the conventional inductor-coupled Class E topology. An LCC-S resonant Class E$ ^2$ converter, which combines the load-independent inductor-coupled inverter and active rectifier, is proposed for MHz-wireless power transfer (MHz-WPT) applications. The active inductor-coupled Class E rectifier maintains soft switching, constant voltage gain, and zero-phase-angle input at various loads. A three-winding magnetic structure is also proposed to improve the coupled inductors by enhanced self-inductance, which features more effective harmonic suppression with lower magnetic losses and volumes. By the proposed methodology and the improved magnetic structure, the converter features negligible harmonic contents and maintains soft switching with a constant voltage conversion ratio over the entire load range. A 6.78-MHz WPT prototype was built to verify the proposed methodology with detailed parameter design and hardware implementation. The prototype realizes load-independent zero-voltage switching and maintains an approximately constant voltage gain with +5/$-$4% variance from no-load to 320-W output power. The measured dc–dc efficiency reaches 89.3% at 210 W.

Bond wires aging is one of the most common failure modes of insulated gate bipolar transistor (IGBT) module. Real-time monitoring of bond wires status is an important guarantee for the stable operation of power electronics system. In this paper, a method of monitoring the aging state of bond wires in IGBT module based on the spectrum characteristics of electromagnetic radiation (EMR) signature is proposed. Firstly, the turn-off process of IGBT module is analyzed, and the behavior model of IGBT module in the stage of rapid current change is established, which shows that EMR interference in buck converter mainly occurs during the turn-off process of IGBT module. Secondly, the relationship between the aging degree of bond wires and differential mode (DM) interference signal is deduced. Thirdly, the IGBT module is equivalent to a magnetic dipole, which proves that the change of DM interference signal will cause the change of EMR signal, thus demonstrating the feasibility of using EMR signal to monitor bond wires aging. Finally, a buck converter composed of IGBT module is used as the equipment to be tested. The EMR signal is extracted by the near-field probe, and the EMR signal spectrum is used to monitor the aging degree of the bond wires. The experimental results show that with the deepening of the aging degree of bond wires, the spectrum amplitude of EMR signal increases.

The momentum to achieve high efficiency, high frequency, and high power density in power supplies limits the use of conventional wire-wound transformers, but widely employs planar transformers. Planar transformers intrinsically benefit from low profile, predictable parasitic components, ease of manufacture, and excellent repeatability of construction, which are generally applied to high frequency and high current applications, such as data centers and telecoms. Reducing the current density through parallel connections is becoming common practice in planar transformers. However, the current on every parallel conductor is usually unbalanced and hard to be predicted. Start from the motivation to predict parallel current distribution, a phenomenon is discovered in this article that the parallel current distribution is constant from medium frequency (MF) and follows the same pattern in higher frequency range. Besides, this article points out that the insulation thickness also affects the current distribution. Furthermore, the phenomenon that the magnetic flux in the space between two parallel conductors approaches zero when parallel currents are frequency independent is proved theoretically and demonstrated experimentally. Together with Ampere's circuital law, which links the current to the magnetic field, the current distribution can be derived. No complex mathematical calculation or simulation tool is required. Any applications using planar transformers with parallel conductors at MF or higher frequency can adopt this method to predict the parallel current distribution for design optimization.