High Frequency Power Electronics Research Articles

Machine learning based feedforward voltage control for buck converters in envelope tracking applications

Tracking the voltage envelope of 5G base station power supplies poses a significant long-term challenge. To achieve fast and accurate envelope tracking, an efficient and high-frequency power electronics circuit and an excellent voltage controller are essential. This paper presents a novel machine learning (ML) based feedforward control method for precise voltage reference tracking. The method is exemplified using a standard buck converter in both continuous conduction mode (CCM) and discontinuous conduction mode (DCM). A feedforward neural network (FNN) is trained to capture non-ideal and non-linear effects in real circuits. An automated data collection system, developed with MATLAB and Simulink, facilitates data acquisition and model training process. The trained FNN predicts the duty cycle for the buck converter to generate the targeted output voltage and output power. A simulation model is built to validate the effectiveness of the FNN controller in envelope tracking applications.

Recent Advanced Ultra‐Wide Bandgap β‐Ga2O3 Material and Device Technologies

AbstractGallium oxide (Ga2O3) is an emerging ultra‐wide bandgap (UWBG) semiconductor material that has gained significant attention in the field of high voltage and high frequency power electronics. Its noteworthy attributes include a large bandgap (Eg) of 4.8 eV, high theoretical critical breakdown field strength (EC) of 8 MV cm−1, and saturation velocity (νs) of 2 × 107 cm s−1, as well as high Baliga figures of merit (BFOM) of 3000. In addition, Ga2O3 has the advantages of large‐size substrates that can be achieved by low‐cost melt‐grown techniques. This review provides a partial overview of pivotal milestones and recent advancements in the Ga2O3 material growth and device performance. It begins with a discussion of the fundamental material properties of Ga2O3, followed by a description of substrate growth and epitaxial techniques for Ga2O3. Subsequently, the contact technologies between Ga2O3 and other materials are fully elucidated. Moreover, this article also culminates with a detailed analysis of Ga2O3‐based high voltage and high frequency power devices. Some challenges and solutions, such as the lack of p‐type doping, low thermal conductivity, and low mobility are also presented and investigated in this review.

Contribution of Magnetization Mechanisms in MnZn Ferrites with Different Grain Sizes and Sintering Densification

This study investigates the magnetization mechanisms in MnZn ferrites, which are key materials in high-frequency power electronics, to understand their behavior under various sintering conditions. Employing X-ray diffraction and scanning electron microscopy, we analyzed the microstructure and phase purity of ferrites sintered at different temperatures. Our findings confirm consistent spinel structures and highlight significant grain-growth and densification variabilities. Magnetic properties, particularly the saturation magnetization (Ms) and initial permeability (μi), were explored, revealing their direct correlation with the sintering process. The decomposition of magnetic spectra into domain-wall-motion and spin-rotation components offered insights into the dominant magnetization mechanisms, with the domain wall movement becoming increasingly significant at higher sintering temperatures. The samples sintered at 1310 °C showcased superior permeability and the least loss in our investigations. This research underscores the impact of sintering conditions on the magnetic behavior of MnZn ferrites, providing valuable guidelines for optimizing their magnetic performance in advanced electronic applications and contributing to the material science field’s understanding of the interplay between sintering, microstructures, and magnetic properties.

Grain refinement and high-frequency properties of spark plasma sintered MnZn ferrite

MnZn soft magnetic ferrites are essential materials for energy conversion in power electronics. The rapid development of miniaturized and energy-saving electronics has put forth an urgent need for high-frequency MnZn ferrites. However, the current MnZn ferrites suffer from a rapid decline of permeability and a drastic increase in power loss at frequencies above 5 MHz, which severely limits their use in high-frequency power electronics. In this study, the Spark Plasma Sintering (SPS) technology was used to prepare high-frequency MnZn ferrites. Compared to samples prepared by traditional solid-state sintering, SPS ferrite exhibits superior high-frequency properties with cut-off frequency of 57 MHz, and a power loss of 169.6 kW/m3 at 20 MHz. The improved high-frequency performance is due to the monodomain structure which is induced by grain refinement via spark plasma sintering. This study presents an effective method for manufacturing high-frequency soft magnetic ferrite and will promote the development of high-performance power electronics.

Measurement and Calculation Techniques of Complex Permeability Applied to Mn-Zn Ferrites Based on Iterative Approximation Curve Fitting and Modified Equivalent Inductor Model

In many cases, power inductors are responsible for most of the power loss, volume, and cost if applied to high-frequency power electronics applications. It is desirable to optimize their design by the proper calculation of winding and core loss. It allows faster and cheaper commercial product release, which is the key to being successful in a highly competitive market. This is only possible if existing calculation techniques and technical data given by, e.g., core manufacturers, are verified and correct; otherwise, the inductor optimization process is less precise and requires several iterations to achieve good convergence. This paper addresses existing and proposes improved measurement and calculation techniques with regard to complex permeability, one of the key quantities that define inductor behavior in the frequency domain. This is done through impedance measurement and improved definition of the equivalent inductor model. Moreover, the proposed calculation techniques fulfill the need for the simple, accurate analytical methods required in commercial designs.

Mega-Hertz High-Voltage EMAT Pulser Based on LCC Resonant Inverter Using SiC MOSFETs

Pulse power supply is an important field of high-frequency power electronics. In advanced applications, such as ultrasonic sensors, Lidar waves and laser generators, the voltage supply with high amplitude and high frequency is required to achieve sufficient technical performance. Meanwhile, the high power quality is pursued in some sensor applications to obtain better performance. This paper develops a ±1000 V/1.5 MHz LCC resonant pulse inverter for Electro-Magnetic Acoustic Transducer. First, the LCC filter is optimized to achieve the goals of low THD, small gain variation and ZVS soft-switching in a wide load range. The design guideline of LCC filter for non-resistive load conditions is proposed, and the design considerations for burst mode converters are summarized. Second, the start-up and ending transients occur repetitively, which is a common problem for burst mode converters. The proposed pre-charging and damping strategy solves this transient problem. Moreover, by analyzing the circuit state equations, this strategy provides a general method for eliminating transients of resonant converters. Next, the signal receiving circuit uses depletion mode MOSFETs to attenuate the high transmitting load voltage while amplifying microvolt receiving signals. Finally, the experimental results under four worst-case conditions validate the LCC filter design. A control experiment with or without the proposed transient mitigation method has been conducted to verify the effectiveness of the proposed strategy.

Resonant driving scheme for p-doped gallium nitride high electron mobility transistor to reduce driving power loss

In high-frequency power electronics applications, gallium nitride high electron mobility transistors (GaN HEMTs) can switch at frequencies of several megahertz. In this case, the driving loss of transistors becomes one of the important reasons that affect the entire conversion efficiency of the system. p-doped GaN (p-GaN) as a new GaN HEMT structure has achieved commercial success in recent years, but due to its special structure, traditional resonant driving schemes designed for Si-MOSFETs have poor applicability to p-GaN HEMTs. Therefore, according to the structure characteristics and the driving requirements of p-GaN HEMTs, an improved resonant driving scheme is proposed. In the proposed driving scheme, the gate charge energy is recycled to the resonant capacitor when the p-GaN HEMT is turned off, and released when it is turned on, thus reducing the driving power loss. The working principle of the driving circuit and the design method of component parameters are given in this paper. The experimental results show that for high-frequency applications with switching frequencies exceeding several megahertz, the power loss of the proposed resonant driving scheme is significantly lower than that of non-resonant driving scheme, which verifies the effectiveness and feasibility of the proposed scheme.

Practical Study of Mixed-Core High Frequency Power Transformer

The design of medium- to high-frequency power electronics transformer aims not only to minimize the power loss in the windings and the core, but its heat removal features should also allow optimal use of both core and copper. The heat removal feature (e.g., thermal conduction) of a transformer is complex because there exist multiple loss centers. The bulk of total power loss is concentrated around a small segment of the core assembly where windings are overlaid. The primary winding is most constrained thermally. For superior use of core and copper, the temperature rise in different segments of the transformer should be well below their respective safe operating limits. In practice, cores of same soft-magnetic materials are traditionally used. To achieve superior temperature profile and for better long-term performance, this article proposes to use the mixed-core configuration. The new core(s) would replace the parent ones from the segment where windings are laid. The characteristic features of new cores would share increased burden of heat removal from the transformer. To obtain the qualitative insight of magnetic and thermal performance, the proposed mixed-core transformer would be thoroughly validated practically in two different high-power applications. In the first case, the core is always energized to its rated value, and in the second one, windings are always energized at respective rated current capacity.

Event-Driven Approach With Time-Scale Hierarchical Automaton for Switching Transient Simulation of SiC-Based High-Frequency Converter

On the emerging development of SiC MOSFET, the switching frequency of power converters has been pushed to the order of hundreds of kilohertz or even megahertz to improve power density. However, the state-of-the-art simulations for such high-frequency power electronics circuits are usually time-consuming, blocking the studies of long dynamics such as several seconds. What’s worse, adopting physical models to simulate the turn-on and turn-off transients leads to high stiffness and therefore convergence problems. In this paper, an event-driven approach is proposed to improve the solving speed and simulation stability of SiC based high-frequency converters. A time-scale hierarchical automaton is proposed to model the system, where piecewise analytical transient model for SiC MOSFET is established as the second layer in the automaton to simulate the switching transients with improved numerical stability. Simulation of the system is driven by discrete events in the automaton. A 3.3 kW 79.1 kHz wireless power transfer system for the wireless charging of electric vehicle is studied. Compared with ideal switch model in Simulink and physical switch model in LTspice, 60-fold and 400-fold increases in terms of simulation speed with same level of accuracy are achieved respectively. The simulated results are also attested to by experimental verifications.

High-frequency magnetic characteristics and operating thermal stability of industrialized Fe76Si13B8Nb2Cu1 nanocrystalline alloy

Increasing the saturation magnetic induction (Bs) while maintaining excellent high-frequency magnetic characteristics of nanocrystalline alloys is still a challenge. Herein, Fe76Si13B8Nb2Cu1 alloy ribbons with completely amorphous precursor were industrially prepared with industrial raw materials. This industrialized nanocrystalline alloy with Bs of 1.39 T has a low core loss of 179 kW/m3 at 0.2 T and 100 kHz, which is slightly higher than that of the commercially applied Fe73.5Si13.5B9Nb3Cu1 alloy with low Bs of ∼ 1.24 T but lower than that of other current alloys. Besides, the real part of complex permeability (μ') of the alloy reaches 24,500 at 100 kHz under an applied filed of 0.06 A/m, which is comparable to that of Fe73.5Si13.5B9Nb3Cu1 alloys. Furthermore, the μ' in the operating temperature of 130 °C increase below 9% at 100 kHz and 2% at 200 kHz with respect to μ' at room temperature. Hence, the industrialized alloy with good castability, high-frequency magnetic performance and operating thermal stability has a good application prospect in high-frequency power electronics.

Isolated Ultrafast Gate Driver with Variable Duty Cycle for Pulse and VHF Power Electronics

Ultrafast and isolated gate drivers advance the development of pulse and very high frequency power electronics for applications that include LiDAR, space systems, miniaturized hardware, and testing of emerging ultrafast devices. The isolated ultrafast gate driver in this letter achieves a gate voltage slew rate above 12 GV/s with rise and fall times below 260 ps with the proper choice of components. Magnetic isolation provides transient immunity and positive feedback enables dynamic dc restoration to allow arbitrarily long on - and off -times and preserve variable duty cycles. With the isolated ultrafast gate driver, an EPC 2038 GaN FET achieves a drain voltage slew rate of over 37 GV/s when hard-switching and improves total efficiency by 8% (including gating loss) with a careful choice of logic inverters in a symmetric 100 MHz current-mode class D (CMCD) wireless power transfer system. The ultrafast gate driver with isolation and positive feedback was implemented with a commercial radio frequency signal transformer and discrete logic inverters and validated in a hard-switching double pulse test, a narrow pulse test repeating at 165 MHz, and a 100 MHz soft-switching CMCD resonant converter.

FPGA-based real-time simulation for EV station with multiple high-frequency chargers based on C-EMTP algorithm

The electric vehicle (EV) charging station is a critical part of the infrastructure for the wide adoption of EVs. Real-time simulation of an EV station plays an essential role in testing its operation under different operating modes. However, the large numbers of high-frequency power electronic switches contained in EV chargers pose great challenges for real-time simulation. This paper proposes a compact electromagnetic transient program (C-EMTP) algorithm for FPGA-based real-time simulation of an EV station with multiple high-frequency chargers. The C-EMTP algorithm transforms the traditional EMTP algorithm into two parallel sub-tasks only consisting of simple matrix operations, to fully utilize the high parallelism of FPGA. The simulation time step can be greatly reduced compared with that of the traditional EMTP algorithm, and so the simulation accuracy for high-frequency power electronics is improved. The EV chargers can be decoupled with each other and simulated in parallel. A CPU-FPGA-based real-time simulation platform is developed and the proposed simulation of the EV station is implemented. The control strategy is simulated in a CPU with 100 μs time-step, while the EV station circuit topology is simulated in a single FPGA with a 250 ns time-step. In the case studies, the EV station consists of a two-level rectifier and five dual-active bridge (DAB) EV chargers. It is tested under different scenarios, and the real-time simulation results are validated using PSCAD/EMTDC.

High-Frequency Power Electronics at the Grid Edge: A Bottom-Up Approach Toward the Smart Grid

Currently, Solar Energy Systems are supplying 2% of U.S. electricity generation and their use is rapidly growing. Data centers make up 2% of the U.S. total energy consumption. By 2030, 40% of the overall worldwide energy consumption is expected to be in the form of electricity. The future development of transportation electrification and smart grids requires grid-scale energy storage. These emerging and high-impact applications locate in the distribution grid. They represent exciting opportunities in developing fundamentally new principles for high-performance power electronics that are smaller, smarter, more efficient, and capable of performing new functions (Figure 1).

Vertical GaN power rectifiers: interface effects and switching performance

The emergence of free-standing GaN substrates enables the development of vertical GaN-on-GaN devices with high-power ratings and high frequencies. The Schottky interface plays an important role in determining the current transport mechanisms and the forward/reverse electrical performance of the vertical GaN Schottky barrier diodes. Moreover, given its direct bandgap and ultrashort minority carrier lifetime, it is of particular interest and importance to evaluate the fast switching performance of the vertical GaN power rectifiers. In this paper, we discuss the technology, physical mechanisms and characterizations of vertical GaN power rectifiers with high-quality interfaces and fast switching performances, including: (a) accurate characterization and carrier transport mechanisms of the Schottky interface; (b) Schottky interface engineering with optimized post-metallization annealing and a tunneling-enhancement layer; (c) fast reverse recovery performance that is characterized by high-speed board-level tests. The investigations and analysis on the interface effects and switching performance of the vertical GaN power rectifiers are valuable for high-efficiency and high-frequency power electronics applications.

Evaluation and Analysis of Temperature-Dependent Dynamic $R_{{{\mathrm{DS}}},{{\mathrm{ON}}}}$ of GaN Power Devices Considering High-Frequency Operation

Commercial enhancement-mode gallium nitride (GaN) HEMTs device is a superior candidate for high-frequency power electronics applications. However, GaN power devices have a unique dynamic ${R}_{{\mathrm{\scriptscriptstyle DS},\mathrm{\scriptscriptstyle ON}}}$ problem which increases the conduction loss of the converter during operation. In this article, the temperature-dependent dynamic ${R}_{{\mathrm{\scriptscriptstyle DS},\mathrm{\scriptscriptstyle ON}}}$ at high frequency is evaluated experimentally for the first time using the double-pulse test (DPT) and multiple-pulse test (MPT) techniques. Different temperature-dependent dynamic ${R}_{{\mathrm{\scriptscriptstyle DS},\mathrm{\scriptscriptstyle ON}}}$ characteristics between the DPT and the MPT at high temperatures are investigated. The significance of the dynamic ${R}_{{\mathrm{\scriptscriptstyle DS},\mathrm{\scriptscriptstyle ON}}}$ ’s temperature dependence is important since GaN devices are typically operating at elevated temperatures. The results suggest that the traditional wafer-level test method using one pulse or two pulses and the MPT without heating consideration or at lower pulse frequency may not be sufficient to evaluate the dynamic ${R}_{\mathrm{\scriptscriptstyle DS},\mathrm{\scriptscriptstyle ON}}$ effect. Combined with high-frequency, high-voltage, and high-current stress, high operating temperatures result in severe ${R}_{\mathrm{\scriptscriptstyle DS},\mathrm{\scriptscriptstyle ON}}$ degradation; hence, there is a diminished return on operating the devices at high temperatures.

Construction of a power electronic source for cold plasma generation

This paper presents the development of a high voltage and high-frequency power electronics source, for plasma generation, at atmospheric pressure and vacuum, using helium and air as working gases. The source design consists of an inductive (L) full bridge series resonant inverter at high frequency, where the control implemented allows varying duty cycle and frequency. Plasma generation is made by high voltage with the power signal applied on two electrodes, which provides a strong electric field that excites, and thus, ionize helium particles or air particles. The power electronic source operation was tested in different plasma reactor configurations (dielectric barrier discharge, double dielectric barrier discharge, and jet type discharge). The developed power electronics source shows a correct performance and generate a strong electric field to achieve the plasma discharges desired.

Integrate Method to alleviate the High Frequency PWM Pulse Voltage on SMES Magnet

The SMES system generally adopts the power conditioning system (PCS), which is made of high frequency power electronics switching devices. The superconducting magnet withstands high frequency PWM pulse voltage, which will induce insulation deterioration, even induce the insulation breakdown. This paper proposes the integrate method to alleviate the PWM pulse voltage. Based on the voltage distribution characteristic of SMES magnet, the influence factors of the pulse overvoltage on SMES magnet are analyzed. Then, considering the interaction between different components of SMES, the factors including PCS control, power cable parameters, filter type, and magnet parameters are designed comprehensively. Finally, the proposed method is implemented in a SMES model to evaluate its effectiveness.

Soft magnetic materials for a sustainable and electrified world.

Soft magnetic materials are key to the efficient operation of the next generation of power electronics and electrical machines (motors and generators). Many new materials have been introduced since Michael Faraday's discovery of magnetic induction, when iron was the only option. However, as wide bandgap semiconductor devices become more common in both power electronics and motor controllers, there is an urgent need to further improve soft magnetic materials. These improvements will be necessary to realize the full potential in efficiency, size, weight, and power of high-frequency power electronics and high-rotational speed electrical machines. Here we provide an introduction to the field of soft magnetic materials and their implementation in power electronics and electrical machines. Additionally, we review the most promising choices available today and describe emerging approaches to create even better soft magnetic materials.

Pseudo-differential CMOS analog front-end circuit for wide-bandwidth optical probe current sensor

In this paper, we present a pseudo-differential analog front-end (AFE) circuit for a novel optical probe current sensor (OPCS) aimed for high-frequency power electronics. It employs a regulated cascode transimpedance amplifier (RGC-TIA) to achieve a high gain and a large bandwidth without using an extremely high performance operational amplifier. The AFE circuit is designed in a 0.18 µm standard CMOS technology achieving a high transimpedance gain of 120 dB Ω and high cut off frequency of 16 MHz. The measured slew rate is 70 V/µs and the input referred current noise is 1.02 pA/. The magnetic resolution and bandwidth of OPCS are estimated to be 1.29 mTrms and 16 MHz, respectively; the bandwidth is higher than that of the reported Hall effect current sensor.

Electrical Trees and Their Growth in Silicone Rubber at Various Voltage Frequencies

The insulation property at high voltage frequencies has become a tough challenge with the rapid development of high-voltage and high-frequency power electronics. In this paper, the electrical treeing behavior of silicone rubber (SIR) is examined and determined at various voltage frequencies, ranging from 50 Hz to 130 kHz. The results show that the initiation voltage of electrical trees decreased by 27.9% monotonically, and they became denser when the voltage frequency increased. A bubble-shaped deterioration phenomenon was observed when the voltage frequency exceeded 100 kHz. We analyze the typical treeing growth pattern at 50 Hz (including pine-like treeing growth and bush-like treeing growth) and the bubble-growing pattern at 130 kHz. Bubbles grew exponentially within several seconds. Moreover, bubble cavities were detected in electrical tree channels at 50 Hz. Combined with the bubble-growing characteristics at 130 kHz, a potential growing model for electrical trees and bubbles in SIR is proposed to explain the growing patterns at various voltage frequencies.