High-frequency Power Converters Research Articles

Aspects on SIC Switches for Soft-Switching Converters in an Industrial Application

The paper presents an anlysis of the impact of power module parasitic inductances on the operation of a specific high frequency power converter for an industrial application which uses SIC Power switches. It is shown that in the analysed circuit the parasitic inductances limit the operational frequency.

GaN Power Transistor Modeling for High-Speed Converter Circuit Design

A circuit simulator has been developed to design power losses of high-frequency power converters using GaN-based heterojunction field-effect transistors (GaN-HFETs). The simulator is based on a high-accuracy equivalent model of GaN-HFETs with peculiar device physics and high-speed loss calculation methods. The simulated power losses were consistent with measured results in dc-dc converters constructed by a GaN-HFET and a SiC Schottky diode with more than 93% accuracy. By utilizing the developed simulator, key requirements in heat-dissipation technologies, circuit parasitic inductances, and gate-drive technologies for next-generation converters are discussed.

A High Temperature, Fast Switching SiC Multi-chip Power Module (MCPM) for High Frequency (> 500 kHz) Power Conversion Applications

In high frequency power conversion applications, the dominant mechanism attributed to power loss is the turn-on and -off transition times. To this end, a full-bridge silicon carbide (SiC) multi-chip power module (MCPM) was designed to minimize parasitics in order to reduce over-voltage/current spikes as well as resistance in the power path. The MCPM was designed and packaged using high temperature (> 200 °C) materials and processes. Using these advanced packaging materials and devices, the SiC MCPM was designed to exhibit low thermal resistance which was modeled using three-dimensional finite-element analysis and experimentally verified to be 0.18 °C/W. A good agreement between the model and experiment was achieved. MCPMs were assembled and the gate leakage, drain leakage, on-state characteristics, and on-resistance were measured over temperature. To verify low parasitic design, the SiC MCPM was inserted into a boost converter configuration and the switching characteristics were investigated. Extremely low rise and fall times of 16.1 and 7.5 ns were observed, respectively. The boost converter demonstrated an efficiency of > 98.6% at 4.8 kW operating at a switching frequency of 250 kHz. In addition, a peak efficiency of 96.5% was achieved for a switching frequency of 1.2 MHz and output power of 3 kW.

A State-Space Modeling Approach for the FPGA-Based Real-Time Simulation of High Switching Frequency Power Converters

A comprehensive approach to the real-time simulation of power converters using a state-space representation is covered in this paper. Systematic formulations of state-space equations as well as a new switch model are presented. The proposed switch model exhibits a natural switching behavior, which is a valuable characteristic for the real-time simulation of power converters, thereby allowing individual treatment of switching devices irrespective of the converter topology. Successful implementations of the proposed switch model on a field programmable gate array (FPGA) device are reported, with two alternative approaches: 1) precomputing network equations for all switch state combinations and 2) solving network equations on-chip using the Gauss-Seidel iterative method. A two-level three-phase voltage source converter is implemented using the first approach, with a time step of 80 ns and a switching frequency of 200 kHz. Ideal and nonideal boost converters are also implemented on FPGA using the second approach, with a time step of 75 ns and a switching frequency of 20 kHz. Comparison with SPICE models shows that the proposed switch model offers very satisfactory accuracy and precision.

Hybrid Modeling of a DC-DC Series Resonant Converter: Direct Piecewise Affine Approach

A dc-dc resonant converter has the advantage of overcoming switching losses and electromagnetic interference which are the main limitations of high frequency power converters. Nevertheless, the modeling and stability analysis of dc-dc resonant converters are considerably more complex than pulsewidth modulation counterparts. The conventional averaged linearized model of the resonant converter has limitations due to averaging and linearization. First of all, the linearized model has large modeling error in presence of large variations of reference voltage and input voltage. Furthermore, Converging area for stabilizing controllers is smaller in the averaged model. In order to overcome these limitations, this paper presents a novel framework for modeling of dc-dc resonant converters. As dc-dc resonant converters are naturally switched systems with affine subsystems, a piecewise affine model is derived directly from the converter model. The new model is based on analysis of the resonant converter on state plane trajectories. It is also suitable for precise simulation and high performance controller design of resonant converters. In addition, a stability analysis theorem is provided for the proposed model. The simulation and experimental results on a dc-dc series resonant converter show the effectiveness of this modeling approach.

Influence of Layer Thickness on the Performance of Stacked Thick-Film Copper Air-Core Power Inductors

This paper presents the fabrication and characterization of air-core power inductors that leverage vertically-stacked, thick copper spiral windings to deliver high inductance densities >; 100 nH/mm2 and quality factors >; 10 on silicon substrates. The inductors are designed for on-chip or in-package integration with high-frequency power converter circuits to enable chip-scale power management in size-constrained applications. A process for realizing the inductors through multilevel, three-dimensional molding of electroplated copper structures has been enhanced with capabilities for four independent copper layers in thicknesses of up to 30 μm each. The impact of increasing the thickness of the stacked copper traces is specifically explored and compared to similar inductors with 10-μm-thick stacked windings. Impedance characterization revealed a drastic decrease in the series resistance in the thicker inductors as desired but also revealed undesired eddy current and magnetic coupling effects.

Inductor Design Methods With Low-Permeability RF Core Materials

This paper presents a design procedure for inductors based on low-permeability magnetic materials, for use in very high frequency power conversion. The proposed procedure offers an easy and fast way to compare different magnetic materials based on Steinmetz parameters and quickly select the best among them, to estimate the achievable inductor quality factor and size, and to design the inductor. Approximations used in the proposed methods are discussed. Geometry optimization of magnetic-core inductors is also investigated. The proposed design procedure and methods are verified by experiments.

Integrated High-Frequency Power Converters Based on GaAs pHEMT: Technology Characterization and Design Examples

The potential of GaAs pHEMT technology for high-frequency power-switching applications is discussed within the context of integrated power supplies for portable wireless systems. Various technology considerations are presented, including the optimization of the power-switching transistor and passives integration. Two design examples for integrated dc-dc converters are implemented in a 0.5-μm GaAs E/D pHEMT process. The first uses coupled inductors to reduce the current ripple and enhance the dynamic performance of the converter. The two-phase, 0.5 A/phase converter occupies 2 mm × 2.1 mm without the output network. An 8.7-nH filter coupled inductor is implemented in 65-μm-thick top copper metal layer, and flip-chip bonded to the dc-dc converter board. The presented converter converts 4.5-V input to 3.3-V output at 150-MHz switching frequency with a measured power efficiency of 84%, which is one of the highest efficiencies reported to date for similar current/voltage ratings. The second example is a hysteric controlled, 100-MHz switching frequency single-phase GaAs pHEMT buck converter designed to drive power amplifier loads. The design can deliver up to 37-dB·m output power and has a peak efficiency of 88% and a 3-dB bandwidth of 14.5 MHz.

Mode-locked Yb:YAG thin-disk oscillator with 41 µJ pulse energy at 145 W average infrared power and high power frequency conversion

We demonstrate the generation of 1.1 ps pulses containing more than 41 µJ of energy directly out of an Yb:YAG thin-disk without any additional amplification stages. The laser oscillator operates in ambient atmosphere with a 3.5 MHz repetition rate and 145 W of average output power at a fundamental wavelength of 1030 nm. An average output power of 91.5 W at 515 nm was obtained by frequency doubling with a conversion efficiency exceeding 65%. Third harmonic generation resulted in 34 W at 343 nm at 34% efficiency.

Thermal aberrations and high power frequency conversion in a barium nitrate Raman laser

Raman frequency conversion of high average power pulsed Nd:YAG laser radiation into the near IR spectral region in a barium nitrate Raman laser was studied with the emphasis on thermal effects inside the Raman-active medium. The probe-beam technique together with numerical reconstruction, done by integrating the transient heat conduction and paraxial wave equations, revealed dynamics of the induced distortions featuring high-order optical aberrations. By utilizing the Zernike expansion of the reconstructed phase profile and implementing a special focusing geometry of the pump beam, partial compensation of the distortions was realized in a stable configuration of the Raman cavity. Generation of the first-, second-, and third-order Stokes radiation with output power of 17, 9.5, and 5.5 W corresponding to a quantum conversion efficiency of 32, 21, and 13% is reported.

Generalized Self-Driven AC–DC Synchronous Rectification Techniques for Single- and Multiphase Systems

This paper extends the single-phase self-driven synchronous rectification (SDSR) technique to multiphase ac-dc systems. Power MOSFETs with either voltage- or current-sensing self-driven gate drives are used to replace the diodes in the rectifier circuits. The generalized methodology allows multiphase SDSRs to be designed to replace the multiphase diode rectifiers. Unlike the traditional SR that is designed for high-frequency power converters, the SDSR proposed here can be a direct replacement of the power diode bridges for both low- and high-frequency operations. The SDSR utilizes its output dc voltage to supply power to its control circuit. No start-up control is needed because the body diodes of the power MOSFETs provide the diode rectifier for the initial start-up stage. The generalized method is demonstrated in 2-kW one-phase and three-phase SDSRs for inductive, capacitive, and resistive loads. Power loss reduction in the range of 50%-69% has been achieved for the resistive load.

High-Frequency Soft-Switching AC Conversion Circuit With Dual-Mode PWM/PDM Control Strategy for High-Power IH Applications

This paper presents a novel high-frequency soft-switching power conversion circuit for high-power induction heating (IH) applications such as the following: (1) heat treatment of metals; (2) hot water; and (3) superheated steam producers. This high-frequency power conversion circuit can operate from single-phase or three-phase systems to produce high current for high-power IH applications under the principles of soft-switching operation. It can regulate its ac output power from the rated value to a low power level. A dual-mode control scheme based on high-frequency pulse width modulation (PWM), in synchronization with the utility frequency positive and negative half-cycles, and pulse density modulation (PDM) is proposed to extend the soft-switching operating range for wide-output power regulation. A dual-pack heat exchanger assembly is designed to be used in consumer and industrial fluid pipeline systems and it is proved to be suitable for hot water, steam, and superheated steam producers. Experimental and simulation results are given to verify the operating principles of the proposed power conversion circuit and to evaluate its power regulation and conversion efficiency.

Comparison of 10 kV 4H-SiC Power MOSFETs and IGBTs for High Frequency Power Conversion

For the first time, large area 10 kV SiC power devices are being produced capable of yielding power modules for high-frequency megawatt power conversion. To this end, the switching performance and power dissipation of silicon carbide (SiC) n-channel IGBTs and MOSFETs are evaluated using numerical simulations software over an extended current range to determine the best device suitable for 10 kV applications. Each device is also optimized for minimal forward voltage drop in the on-state.

Equivalent circuit model of electromagnetic behaviour of wire objects by the matrix pencil method

The electromagnetic behaviour of thin-wire objects is an important engineering problem. A general analysis of such objects is done according to the moment method approach within an antenna-based electromagnetic model. This paper concerns possible extraction of parameters that would enable determination of an equivalent circuit model of such wire-structure objects. As an example, the authors focused on the electromagnetic behaviour of high frequency power converters and grounding conductors.

Loss Characterization and Calculation of Nanocrystalline Cores for High-Frequency Magnetics Applications

The loss density of the nanocrystalline magnetic material is experimentally characterized up to 500 kHz and above 1 Tesla in this paper. B-H hysteresis magnetization curves and loss density of the material under various operating temperatures up to 150degC are measured and presented. The core preparing effect on magnetic loss density is also identified by experiments, which provides information necessary to practical magnetic designs. A new empirical core loss calculation method, flux-wave-form-coefficient Steinmetz equation, is proposed and verified for the nanocrystalline material under resonant operations, which are often employed in high-frequency power converter applications. The proposed approach is either more accurate or easier to use than the previous methods.

A Practical, Accurate and Very General Core Loss Model for Nonsinusoidal Waveforms

Nonsinusoidal voltage waveforms are quite common in high frequency power conversion magnetics. Low frequency nonsinusoidal waveforms are also common in ac motor applications with waveforms such as pulsewidth modulation and six-step. Previous attempts to model these losses, based on the Steinmetz equation, can work only in a limited range of frequencies, flux density excitations, and waveforms. In this paper, we present a very practical, yet very general and accurate model, for core loss calculations in case of nonsinusoidal voltage waveforms. We show the model is equally applicable to low and high frequencies, metallic as well as nonmetallic (e.g., ferrites) core materials, by comparing the model prediction with measured data for various waveforms, frequencies, and flux densities. The model can be used for the design of high frequency transformers and inductors for use in switched mode power supplies. The model can also be used for ac motors where it is hard to estimate derating factor and to avoid uncontrolled temperature rise

High-Power and High-Repetition Frequency Conversion LD-YAG Laser for Industrial Applications

We report on the recent developments of laser-diode pumped frequency conversion solid-state lasers in our section. A 150W TEM00 mode, linearly polarized 1064nm beam was generated with a MOPA system. The system was applied for high-power frequency conversion. 30W 355nm and 5.6W 213nm output power was generated at a repetition rate of more than 10kHz. Frequency-tripling-efficiency of CBO (CsB3O5) crystal was compared with LBO (LiB3O5) crystal experimentally. We also introduce an industrial 200W 532nm laser, developed for TFT annealing process.

Novel Current-Source Multi-Level Inverter Driven by Single Gate Drive Power Supply

This paper proposes a novel current-source multi-level inverter, which is based on a current-source half bridge topology. Multi-level inverters are effective to reduce harmonic distortion of the output voltage and the output current. However, the multi-level inverters require many gate drive power supplies to drive switching devices. The gate drive circuits using a bootstrap circuit and a pulse transformer can reduce the number of the gate drive power supplies, but a pulse width of the output PWM waveform is limited. Furthermore, high-speed power switching devices are indispensable to compose a high-frequency power converter but various problems of high frequency noise arise due to high dv/dt rate, especially in high-side switching devices.The proposed current-source multi-level inverter is composed with a common emitter topology of all switching devices. Therefore, it is possible to operate with a single power supply of gate drive circuit, which allows stabilizing a potential level of all the drive circuits.In this paper, effectiveness of the proposed circuit is verified with experimental results.

Modeling of solenoidal transformer for the calculation of leakage inductance using eddy-current reaction field

The design of high-frequency power converter is very difficult because the leakage inductance of the transformer affects the performance. With consideration of the high-frequency eddy current, the flux linkage due to the eddy-current reaction field using a proposed summation calculation method is computed. The leakage inductance of a high-frequency transformer is therefore characterized. An optimum design method of the transformer can be obtained. Experimental results confirm the affectivity of the calculation method.

High-frequency flyback-type soft-switching PWM DC-DC power converter with energy recovery transformer and auxiliary passive lossless snubbers

A two-switch high-frequency flyback-type zero voltage soft-switching PWM DC-DC power converter for use in auxilary power supplies is proposed. Its basic building block is composed of two active power switches and a flyback high frequency transformer. In addition, two passive lossless snubbers with power regeneration loops for energy recovery that consist of a three-turn auxiliary high frequency transformer, auxiliary capacitors and diodes, are introduced to achieve zero voltage soft switching in the full range of light to full load conditions. The power converter has the advantages of a low cost circuit configuration, a simple control scheme and a high efficiency.The converter's operating principle is described and to in order determine circuit parameters, some practical design considerations are discussed. The effectiveness of the proposed power converter is evaluated and is compared to a hard-switching PWM DC-DC converter. The comparative electromagnetic conductive noise characteristics of both DC-DC power converter circuits are also investigated.