High-frequency Power Converters Research Articles

Conceptual Design and Characteristic Analysis of a Rotary-Type Superconducting Wireless Power Transfer System Using ReBCO Primary at 50 Hz

This paper presents the conceptual design and characteristic analysis of a sliding-type superconducting wireless power transfer (SWPT) system prior to practical device development. Structural designs of sliding transformer, copper secondary, and high temperature superconducting primary are presented. A single-pancake racetrack coil assembly wound by ReBCO tapes is used as the primary winding. 12-mm-width ReBCO tapes with 700 A class critical current are introduced to wind the ReBCO primary operated at 50 Hz. The relations among the transfer power, transfer efficiency, air-gap distance, primary current, secondary load and primary turn number are investigated to clarify the SWPT behaviors under different operating conditions. Benefited from high critical current and nearly zero loss of ReBCO primary and elimination of high-frequency power conversion devices, the sliding-type SWPT scheme could be well expected to combine the advantages of high power, high efficiency, and compact device structure.

Conceptual Design and Characteristic Analysis of a Sliding-Type Superconducting Wireless Power Transfer System Using ReBCO Primary at 50 Hz

This paper presents the conceptual design and characteristic analysis of a sliding-type superconducting wireless power transfer (SWPT) system prior to practical device development. Structural designs of sliding transformer, copper secondary, and high temperature superconducting primary are presented. A single-pancake racetrack coil assembly wound by ReBCO tapes is used as the primary winding. 12-mm-width ReBCO tapes with 700 A class critical current are introduced to wind the ReBCO primary operated at 50 Hz. The relations among the transfer power, transfer efficiency, air-gap distance, primary current, secondary load and primary turn number are investigated to clarify the SWPT behaviors under different operating conditions. Benefited from high critical current and nearly zero loss of ReBCO primary and elimination of high-frequency power conversion devices, the sliding-type SWPT scheme could be well expected to combine the advantages of high power, high efficiency, and compact device structure.

A Survey on Switching Oscillations in Power Converters

High-frequency power converters enabled by wide bandgap (WBG) and silicon semiconductor devices offer distinct advantages in power density and dynamic performance. However, switching oscillations are commonly observed in these circuits with undesirable consequences. This paper reviews the impacts, root causes, and mitigation techniques of switching oscillations through literature survey, modeling analysis, and experimental investigation. We categorize the following root causes for oscillations during switching transients: 1) damped oscillation triggered by high di/dt and/or dv/dt coupled with parasitic elements; 2) undamped oscillation of WBG devices as part of a negative resistance oscillator; and 3) semiconductor device physical mechanisms such as the negative capacitance phenomenon due to conductivity modulation in insulated gate bipolar transistors or impact ionization in MOSFETs, the plasma extraction transit-time effect in bipolar power devices, and the reverse conduction property of GaN HEMTs. Furthermore, this paper discusses various circuit techniques to suppress switching oscillations, and techniques of extracting parasitic inductances of power devices.

Dynamic on-State Resistance Test and Evaluation of GaN Power Devices Under Hard- and Soft-Switching Conditions by Double and Multiple Pulses

The dynamic on -state resistance ( R DSON) behavior of commercial GaN devices is very important for a GaN-based converter. Since the zero-voltage switching techniques are popular in high-frequency power conversion, a dynamic R DSON test board integrating both hard- and soft-switching test circuits is built in this study. Two types of commercial GaN devices are tested and compared under hard- and soft-switching conditions by double-pulse and multipulse test modes, respectively. It has been found that their dynamic R DSON exhibit different behaviors depending on the off -state voltage and frequency under hard- and soft-switching conditions due to different device technologies, which should be taken fully into account for GaN-based converter design and loss estimation. In order to simulate the R DSON behavior in a steady-state operating converter, a multipulse measurement has been implemented, the results of which are compared with that of double-pulse test. Furthermore, the primary trapping mechanisms responsible for dynamic R DSON increase under different switching conditions are identified and verified by the numerical device simulation using Silvaco TCAD tool.

Recent Topics of Low Loss Technologies of Magnetic Components for High Frequency Power Converters

Recent Topics of Low Loss Technologies of Magnetic Components for High Frequency Power Converters

Aluminum Electrolytic Capacitor Suitable for High-frequency Power Converters

Aluminum Electrolytic Capacitor Suitable for High-frequency Power Converters

Computer-Aided Design of Digital Compensators for DC/DC Power Converters

Digital control of high-frequency power converters has been used extensively in recent years, providing flexibility, enhancing integration, and allowing for smart control strategies. The core of standard digital control is the discrete linear compensator, which can be calculated in the frequency domain using well-known methods based on the frequency response requirements (crossover frequency, fc, and phase margin, PM). However, for a given compensator topology, it is not possible to fulfill all combinations of crossover frequency and phase margin, due to the frequency response of the controlled plant and the limitations of the compensator. This paper studies the performance space (fc, PM) that includes the set of achievable crossover frequencies and phase margin requirements for a combination of converter topology, compensator topology, and sensors, taking into account the effects of digital implementation, such as delays and limit cycling. Regarding limit cycling, two different conditions have been considered, which are related to the design of the digital compensator: a limited compensator integral gain, and a minimum gain margin. This approach can be easily implemented by a computer to speed up the calculations. The performance space provides significant insight into the control design, and can be used to compare compensator designs, select the simplest compensator topology to achieve a given requirement, determine the dynamic limitations of a given configuration, and analyze the effects of delays in the performance of the control loop. Moreover, a figure of merit is proposed to compare the dynamic performance of the different designs. The main goal is to provide a tool that identifies the most suitable compensator design in terms of the dynamic performance, the complexity of the implementation, and the computational resources. The proposed procedure to design the compensator has been validated in the laboratory using an actual DC/DC converter and a digital hardware controller. The tests also validate the theoretical performance space and the most suitable compensator design for a given dynamic specification.

Effect of CaCO3 and V2O5 Composite Additives on the Microstructure and Magnetic Property of MnZn Ferrites

Manganese-zinc (MnZn) ferrites have important application in convertors and switching mode power supplies. The core losses ( $\text{P}_{L}$ ) of MnZn ferrites have serious influence on the performance of power conversion devices. It is worth emphasizing that reducing the core losses at high frequency is of great significance for the miniaturization and integration of power conversion devices. Here in this paper, MnZn ferrites have been fabricated by the method of solid-state reaction, and the effect of CaCO3 and V2O5 co-additives on the microstructure and magnetic property has been investigated. This paper illustrated the competition mechanism of grain growth, which originated from the hindrance effect of CaCO3 and acceleration effect of V2O5, as well as the effect of CaCO3 and V2O5 on core losses by means of loss separation method. In addition, as for the MnZn ferrite sample with 0.1 wt% CaCO3 and 0.01 wt% V2O5 co-additives, core losses were suppressed to 46 and 664 kW/m3 corresponding to 3 MHz 10 mT and 3 MHz 30 mT at 25 °C, respectively. The state-of-the-art MnZn ferrites with ultralow core losses own potential application for high-frequency power conversion devices.

A Miniature 300-MHz Resonant DC–DC Converter With GaN and CMOS Integrated in IPD Technology

A 300-MHz class-E dc–dc converter using the resonant gate driving technique is proposed. The gate driver utilizes the harmonic shaping network and RC feedback to enhance the output swing voltage, and the class-E power converter can minimize the voltage–current overlap to improve efficiency. With the $0.\text{25-}{\mu} {\text{m}}$ GaN high-electron-mobility transistor and $\text{0.18-}{\mu} {\text{m}}$ CMOS for the switching power device and the gate driver, respectively, a complete dc–dc converter operating at 300 MHz is demonstrated including all the passive components microfabricated by integrated passive device (IPD) technology on the high-resistivity silicon substrate. The overall chip area is smaller than 1 cm × 1 cm and the volume is only 0.115 cm3. The measured results show a maximum output power of 4.16 W with 47.3% efficiency. An excellent power density of 36.2 W/cm3 can be achieved. The flip-chip assembled converter on the IPD substrate demonstrates the potential of heterogeneous integration for high-frequency power conversion applications.

A High-Bandwidth Integrated Current Measurement for Detecting Switching Current of Fast GaN Devices

Gallium nitride (GaN) devices are suitable for high-frequency power converters due to their excellent switching performance. To maximize the performance of GaN devices, it is necessary to study the switching characteristics, which requires measuring the switching current. However, GaN devices have a fast switching speed and are sensitive to parasitic parameters, so the current measurement should have a high bandwidth and should not introduce excessive parasitic inductance into the power converters. Traditional current measurements are difficult to meet these requirements, especially for fast GaN devices. This paper presents a high-bandwidth integrated current measurement for detecting the switching current of fast GaN devices. By effectively utilizing the parasitic inductance in the circuit, a single-turn coil is embedded in the printed circuit board. This coil could pick up a sufficiently strong voltage signal, which is then processed to reconstruct the switching current. Moreover, corrections are carried out to further improve the accuracy. The current measurement has a small insertion impedance and a high bandwidth with a small influence on the parasitic inductance of the converter. The accuracy of the current measurement is experimentally verified by a 40 V GaN-based double pulse test circuit with a load current up to 25 A.

Loss Optimization Method Based on the Main Circuit of T-type SVPWM

To reduce the switching loss of power devices and improve the efficiency, an effective method is to reduce the switching loss by optimizing the modulation strategy of the control algorithm. Traditionally, the amount of on-off times is used to qualitatively estimate the amount of switching losses, but the estimation error is large. In this paper, based on a T-type three-level topology, the 7-segment and 5-segment SVPWM strategies were analyzed theoretically, the calculation methods were set, and an experiment is carried out on a high-power frequency conversion system. It is proved that the reduction amount of switching losses of power devices is not only determined by the reduction amount of switching times under different modulation strategies.

Microfabricated Air-Core Toroidal Inductor in Very High-Frequency Power Converters

Miniaturization of power supplies is required for future intelligent electronic systems, e.g., Internet-of-Things devices. Inductors play an essential role, and they are by far the most bulky and expensive components in power supplies. This paper presents a miniaturized microelectromechanical system (MEMS) inductor and its performance in a very highfrequency (VHF) power converter. The MEMS inductor is a silicon-embedded air-core toroidal inductor, and it is constructed with through-silicon vias, suspended copper windings, silicon fixtures, and a silicon support die. The air-core inductors outperform the silicon-core inductors with higher quality factor at higher frequency. This is verified by small-signal measurements. A 20-turn air-core inductor achieved an inductance of 44.6 nH and a quality factor of 13.3 at 33 MHz, while a siliconcore inductor with the same geometry has a quality factor of 9 at 20 MHz. A dc-dc class-E boost converter is designed and implemented using the fabricated MEMS air-core inductor and a high-performance 65-V gallium nitride field-effect transistor. The VHF converter achieved a peak efficiency of 78% at an input voltage of 6.5 VDC. The MEMS inductor can carry 1-A root-mean-square ac current at 33 MHz and delivers 10.5 W to the output.

Highly Efficient Secondary-Resonant Active Clamp Flyback Converter

Both high switching frequency and high efficiency are critical in reducing power adapter size. The active clamp flyback (ACF) topology allows zero voltage soft switching (ZVS) under all line and load conditions, eliminates leakage inductance and snubber losses, and enables high frequency and high power density power conversion. Traditional ACF ZVS operation relies on the resonance between leakage inductance and a small primary-side clamping capacitor, which leads to increased rms current and high conduction loss. This also causes oscillatory output rectifier current and impedes the implementation of synchronous rectification. This paper proposes a secondary-side resonance scheme to shape the primary current waveform in a way that significantly improves synchronous rectifier operation and reduces primary rms current. The concept is verified with a ${\mathbf{25}}\hbox{--}{\text{W/in}}^{3}$ high-density 45-W adapter prototype using a monolithic gallium nitride power IC. Over 93% full-load efficiency was demonstrated at the worst case 90-V ac input and maximum full-load efficiency was 94.5%.

Thermal modeling of wide bandgap semiconductor devices for high frequency power converters

The emergence of wide bandgap semiconductors has led to development of new generation semiconductor switches that are highly efficient and scalable. To exploit the advantages of GaNFETs in power converters, in terms of reduction in the size of heat sinks and filters, a thorough understanding of the thermal behavior of the device is essential. This paper aims to establish a thermal model for wideband gap semiconductor GaNFETs commercially available, which will enable power electronic designers to obtain the thermal characteristics of the device more effectively. The model parameters is obtained from the manufacturer’s data sheet by adopting an exponential curve fitting technique and the thermal model is validated using PSPICE simulations. The model was developed based on the parametric equivalence that exists between the thermal and electrical components, such that it responds for transient thermal stresses. A suitable power profile has been generated to evaluate the GaNFET model under different power dissipation scenarios. The results were compared with a Silicon MOSFETs to further highlight the advantages of the GaN devices. The proposed modeling approach can be extended for other GaN devices and can provide a platform for the thermal study and heat sink optimization.

大電力高速パルス生成器によるオシロスコープのスキュー補正

Switching frequency of a power converter has increased because of recent development of power semiconductor devices. For measurements of switching waveforms in high-frequency power converters, it is important to precisely calibrate skew for an oscilloscope. In order to conduct skew calibration, we fabricate a high-power and high-speed pulse generator using a SiC power MOSFET. The skew of oscilloscope probes is discussed.

Taking a Look at Capacitive Power Conversion [White Hot

Recently, I wrote about the workshops and presentations at APEC 2017 that talked about the challenges of magnetics in high-frequency power conversion. Those challenges include losses at high frequency, a lack of good data and models on losses in magnetic materials and devices, and lack of standardization of data from manufacturers. But there were also two other presentations that got me thinking in an entirely different direction: capacitive power conversion. By capacitive power conversion, I generally mean the use of “charge pump” techniques. For example, I am sure many of us have used the charge pump in RS-232 serial line driver ICs to convert +12 Vdc to –12 Vdc. Or maybe we have used a simple charge pump to create a +12 V or +15 Vdc from a +5 Vdc rail to power some small amount of analog circuitry.

15-kV/40-A FREEDM Supercascode: A Cost-Effective SiC High-Voltage and High-Frequency Power Switch

High-voltage wide bandgap semiconductor devices such as the 15 kV SiC mosfet have attracted great attention because of their potential applications in high-voltage and high-frequency power converters. However, these devices are not commercially available at the moment, and their high cost due to expensive material growth and fabrication may limit their widespread adoption in the future. In this paper, a 15-kV 40-A SiC three-terminal power switch, the Future Renewable Electric Energy Delivery and Management (FREEDM) supercascode, is reported for the first time, which is based on a series connection of 1.2-kV SiC power devices. Compared with the monolithic 15-kV SiC mosfet , the FREEDM supercascode demonstrates obvious advantages in cost and thermal conductivity. The design and voltage-balancing mechanism of the FREEDM supercascode are introduced, and the performance including the voltage balancing, conduction characteristics over a wide range of temperatures, and dynamic switching performance, is analyzed. The FREEDM supercascode's low cost and excellent thermal dissipation capability will facilitate early applications of SiC in very high voltage and high frequency power converters.

Analysis and Design of Closed-Loop Control of Electrolytic Capacitor-Less Six-Pulse DC Link Three-Phase Inverter

Three-phase inverters in uninterrupted power supply, electric vehicles, and hybrid electric vehicles use an intermediate dc-link electrolytic capacitor, which has reliability issues and is one prominent cause of inverter failure and limited life. The large volume of an electrolytic capacitor increases the size and cost of the system. Recent research on electrolytic capacitorless inverters using six-pulse modulation technique along with high-frequency power conversion has attempted to address this issue. However, closed-loop operation and control has some issues due to capacitorless dc-link. In this paper, closed-loop operation, design, and implementation of an electrolytic capacitorless inverter is presented. A proof-of-concept 1-kW hardware prototype has been built and tested in a laboratory under different loading conditions. In total, 98% rated efficiency of the inverter is obtained with total harmonic distortion within 2%. Transient results during start-up and load change are smooth, demonstrating safe operation of the inverter.

(Invited) The Current Status and Future Prospects of SiC Devices

Although silicon power devices have served well as the key technology for power electronics for several decades, silicon-based technology is reaching its physical limits, in terms of power handling and switching frequency capabilities. Thanks to its superior material properties, SiC is the most promising post-silicon alternative for high voltage, high frequency, and high temperature power conversion applications. Since the advent of the first SiC Schottky Barrier Diode (SBD) in the 1990’s, numerous research groups have devoted their efforts to commercialize SiC devices such as MOSFETs, JFETs, and Thyristors. In this talk, issues regarding current SiC devices and processing technology will be identified and future research directions will be discussed.

Ruhrpumpen invests in new manufacturing plant in India

Fracturing equipment is the core device in shale gas reservoir stimulation. As domestic shale gas exploration and development steps into deep layers, the development of fracturing technology puts forward higher requirements for relevant equipment. Electric drive is an important development direction of fracturing equipment technology. In this paper, the technical progress of electric drive fracturing equipment in China and abroad was investigated. It is shown that a high-power frequency conversion system is the key technology to determine the performance of electric drive fracturing equipment. After the adaptability of the high-power frequency conversion technology to electric drive fracturing equipment was analyzed, based on the fracturing operation of Model 2500 electric drive fracturing trucks in the Weiyuan Block of the Sichuan Basin for shale gas reservoir stimulation, electric drive and diesel-driven fracturing equipment were comparatively analyzed from the aspects of economic and technical indicators. And the following research results were obtained. First, compared with a diesel-driven fracturing truck of the same power, an electric drive fracturing truck can realize a full power coverage and a continuous adjustment of output displacement, and can better meet the operation requirements of fracturing process for a precise control of the pumping displacement, while reducing the power cost by 68% and the equipment purchase cost by 10–20%. Second, compared with the skid mounted equipment, an electric drive fracturing truck has a better transport performance, being suitable for the fracturing well sites with poor road conditions, such as loess gullies, hills and mountains. It is suggested that the following development direction of the electric drive fracturing equipment should focus on the improvement of single machine power density. In addition, it is recommended to enhance the basic studies on high-pressure and high-power semiconductor devices and make a good plan for the power demand of shale gas platform construction in advance, so as to give a better play to the operating cost advantage of electric drive fracturing equipment.