High-frequency Power Converters Research Articles

Performance Improvement of Wireless Power Transfer System for Sustainable EV Charging Using Dead-Time Integrated Pulse Density Modulation Approach

The recent developments in electric vehicle (EV) necessities the requirement of a human intervention free charging system for safe and reliable operation. Wireless power transfer (WPT) technology shows promising options to automate the charging process with user convenience. However, the operation of the WPT system is designed to operate at a high-frequency (HF) range, which requires proper control and modulation technique to improve the performance of power electronic modules. This paper proposes a dead-time (DT) integrated Pulse Density Modulation (PDM) technique to provide better control with minimal voltage and current ripples at the switches. The proposed technique is investigated using a LCC-LCL compensated WPT system, which predominantly affects the high-frequency voltage and current ripples. The performance analysis is studied at different density conditions to explore the impact of the integrated PDM approach. Moreover, the PDM technique gives better control over the power transfer at different levels of load requirement. The simulation and experimental analysis was performed for a 3.7 kW WPT prototype test system under different modes of operation of the high-frequency power converters. Both the simulated and experimental results demonstrate that the proposed PDM technique effectively enhances the efficiency of the HF inverter while significantly reducing output current ripples, power dissipation and improving the overall WPT system efficiency to 92%, and leading to a reduction in the power loss in the range of 10% to 20%. This leads to improved overall system control and performance.

Contactless Current Sensing With Bandwidth Enhancement for High-Frequency Power Converters

Contactless Current Sensing With Bandwidth Enhancement for High-Frequency Power Converters

Input-parallel output-series Si-SiC hybrid inverter with fractional harmonic elimination

This paper proposes an input-parallel output-series (IPOS) Si-SiC hybrid inverter with dual-frequency harmonic elimination modulation strategy. The proposed topology composed of two power conversion cells and a three-phase five-column medium-frequency step-down transformer, the low-frequency power conversion cell (LFPC-C, 1 kHz) leverages strong current-carrying capacity of silicon-based devices for dealing with the system main power, and the high-frequency power conversion cell (HFPC-C, 30 kHz) based on wide-bandgap semiconductor SiC devices is used to addressing the fractional harmonics compensation power. This topology combines the strong current carrying capability of Si devices with the low switching loss of SiC devices at high frequency and achieves high quality power conversion at low cost and low loss. Compared to existing “IPOP” Si-SiC hybrid inverters, this topology adopts a coupling step-down transformer on the output side of both LFPC-C and HFPC-C, which can effectively reduce current stress of HFPC-C SiC devices. Additionally, a dual-frequency harmonic elimination modulation strategy based on the topology is proposed to solve the fractional harmonics caused by the LFPC-C. The paper establishes a mathematical model according to the harmonic distribution characteristics of the LFPC-C and HFPC-C, and designs the system control schedules. Building upon the derivation of the voltage ripple model and the design of hardware parameters, Si IGBT and SiC MOSFET were selected for constructing a 7.5 kW prototype for testing, and the experimental results validate the feasibility of this topology and the accuracy of theoretical analysis.

Wet chemistry-synthesized Fe/mixed ferrite soft magnetic composites for high-frequency power conversion

State-of-the-art soft magnetic (SM) alloy systems such as electrical steels and permalloys exhibit large eddy current losses at high-frequency (kHz range and above), limiting their application in fast switching devices. Eddy current losses can be reduced for metallic alloys through a decrease in characteristic length scale or embedding them in an insulation layer. This work proposes the development of fine-scale core materials consisting of metallic SM nano/microparticles with magnetic, inorganic insulation layers, and their synthesis using a wet chemistry-based, scalable method for high frequency and high-power applications. More specifically, a magnetic ferrite coating (Ni0.5-xMnxZn0.5Fe2O4, x = 0.0–0.5) was applied via deposition of ferrite powder produced using a “wet chemistry-based” co-precipitation method; the ferrite was distributed through the Fe micropowder via either ball milling or ultrasonic mixing. Powder cores were prepared by compaction of the synthesized composites. Relative magnetic permeability and core loss were measured at excitation frequencies to 200 kHz. A core loss of 127 kW/m3 was measured at excitation frequency of 100 kHz and magnetization of 0.02 T. This value improves on the 199.3 kW/m3 reported in literature at identical excitation conditions for a compact formed from a composite comprising Fe microparticles coated with low-permeability Ni0.5Zn0.5Fe2O4. Ultrasonic mixing resulted in slightly lower core loss than ball milling, possibly because ball milling causes loss-increasing deformation of the Fe micropowder. XRD and SEM were used to observe composite composition and core cross-section microstructure.

Multirate Modeling and Predictive Control for WBG-Device-Based High-Switching-Frequency Power Converters

With the growth of wide bandgap devices, it is necessary to exploit the high switching frequency benefits to improve the power converter's performance, thus requiring a higher sampling/interrupt frequency in digital signal processors. However, such a short interrupt time duration imposes big computational difficulty in the execution of programming code, especially using the model predictive control (MPC). Thus, most of the existing MPCs are applied with switching frequencies below 20 kilohertz, which cannot exploit the full potential of the wide bandgap device-based power converters. To solve this challenge, this article proposes a multi-rate MPC scheme, where the trigger of interrupt and switching device transition can be performed at different rates. Compared to conventional MPCs, the main uniqueness of the proposed multi-rate MPC is that the high-dimension control sequence is solved and applied within each interrupt interval. Therefore, the increased switching frequency objective can be easily achieved with a low sampling/interrupt frequency configuration, which also significantly relieves the digital execution of the heavy interrupt tasks. The proposed method shows a more optimized control input and higher computational efficiency over the multi-rate finite-control-set MPC counterpart. A silicon carbide inverter-fed AC motor drive system is used to verify the proposed multi-rate MPC. The results show the improved system performance with the combined advantages of both the high switching frequency and MPC strategy.

A Monolithic GaN Power Stage with Common-Mode Transient Immunity and Negative Voltage Operation Design for High Frequency Power Converters

A Monolithic GaN Power Stage with Common-Mode Transient Immunity and Negative Voltage Operation Design for High Frequency Power Converters

수배전반용 배터리 충전기의 최적 설계 방안에 관한 연구

This paper proposes a method for the optimal design of a battery charger for a distribution system using a high-frequency PWM power converter to solve the problems of the conventional rectifier-based battery charger for supplying power to the distribution system during a power outage. The proposed battery charger for the distribution system is designed by reviewing the charging time and current according to the battery capacity, thereby reducing the cost of the battery charger system during manufacture and improving charging efficiency owing to the conduction loss of the battery charger during operation. In addition, the proposed battery charger system for the distribution system utilizes a high-frequency power conversion device to minimize the size and volume of the charger system compared with the conventional rectifier-based battery chargers.
 Therefore, in this paper, we propose an optimal design method for the proposed battery charger for the distribution system and verify its feasibility through simulation results.

The TSM-net: a new strategy for insulated bearings intelligent faults diagnosis

With the development of power semiconductor devices, pulse width modulation technology is widely used in high-power frequency conversion control motors, which significantly improves the dynamic performance of variable-speed drive system equipment. However, the high-frequency shaft voltage generated during the drive process acts on the bearing to generate high-frequency current. The damage caused by the shaft current sharply shortens the fatigue wear process of the bearing, which in turn leads to premature failure of the bearing. A high insulating ceramic coating is prepared on the outer surface and side face of the inner and outer rings of the bearing by plasma spraying. That is, an insulating protective film is formed on the outer surface of the bearing, which can effectively isolate or reduce the bearing current, prevent the occurrence of electric erosion, and prolong the service life of the variable speed drive system equipment. However, the vibration excitation generated by the variable-speed drive system equipment will cause cracks or fatigue damage to the insulating bearing, resulting in a very complex fault mechanism of the vibration signal. The fault signal characterization lacks a professional signal analysis method, especially the high-reliability, high-precision and long-life high-performance insulating bearing. There is no qualitative formula or characteristic index to explain its failure. To fill this research gap, a new strategy for optimizing the temporal information fusion model and introducing the self-attention mechanism is innovatively developed, and it is named TSM-Net model, and the first attempt is made to realize intelligent identification of insulated bearing faults. Specifically, a multi-channel insulated bearing time information fusion diagnostic model is designed, and the coarse-grained characteristics with timing law are extracted from the measured insulated bearing fault data. Then, the self-attention mechanism is introduced into the designed insulated bearing time information fusion diagnostic model to optimize, and the weight coefficient is continuously updated to calculate the correlation weight between the insulated bearing fault data and the data, so that the final decision of the TSM-Net model is more focused, so as to improve the diagnostic accuracy. Finally, comparing the proposed TSM-Net model with the current five advanced methods, it is found that the proposed TSM-Net model has good diagnostic accuracy for rail transit motor insulated bearing faults, which verifies the effectiveness and superiority of the strategy, and provides a new way for the fault diagnosis of insulated bearings of high-power inverter control motors.

High frequency isolated bidirectional dual active bridge DC-DC converters and its application to distributed energy systems: an overview

Among the DC-DC converters, an isolated bidirectional dual active bridge converter is a core circuit for high-frequency power converters in distributed energy system applications. These high-frequency power conversion systems attract academia and industry due to various advantages, such as high-power density, less weight, reduced noise, high efficiency, low cost and high reliability. First, the importance of power electronic converters in modern-day life is introduced. Second, a topological overview of voltage-fed and current-fed isolated bidirectional dual active bridge converters is presented with their importance in integrating hybrid power sources. Third, switching modes of isolated bidirectional DC-DC converters are also presented with a degree of freedom of control. Forth, performance evaluation of voltage-fed and current-fed isolated bidirectional converters has been presented with an example. Their suitability in integrating fuel cells and photovoltaics with energy storage systems in low to medium-power applications is presented.

A Simple Switching-Event Dependent High-Frequency Sampling Method for Power Conversion System

Precise current and voltage sensing are challenging for digital control in high-frequency power conversion systems. Given that the power electronics circuitry is triggered repetitively by power device switching events, a switching-time dependent sampling method is proposed to realize an equivalent high-frequency signal sampling with a low-speed Analog Digital Converter (ADC) and digital controller. Two sampling modes are developed in the proposed methods in terms of sampling rates lower and higher than the digital controller clock frequency, respectively. A fast and simple signal reconstruction method is designed to ensure the feasibility in a low-cost processor. A series-resonant dual-active-bridge (SR-DAB) is taken as an example for the theoretical analysis and experimental verification. The resonant current and Miller plateau voltage in the topology are sampled to verify the potential of the proposed method for online parameter recognition of DC-DC converters and device behavior monitoring of power devices.

Investigation of Current Collapse Mechanism on AlGaN/GaN Power Diodes

In this paper, a methodology is proposed for studying the current collapse effects of Gallium Nitride (GaN) power diodes and the consequences on the dynamic on-resistance (RON). Indeed, the growing interest of GaN based, high frequency power conversion requires an accurate characterization and a deep understanding of the device’s behaviour before any development of power converters. This study can ultimately be used to model observed trap effects and, thus, improve the equivalent electrical model. Using an in-house circuit and a specific experimental setup, a current-collapse phenomenon inherent to gallium nitride semiconductor is studied on planar 650 V—6 A GaN diodes by applying high voltage stresses over a wide range of temperatures. With this method, useful data on activation energy and capture cross section of electrical defects linked to dynamic RON are extracted. Finally, the origins of such defects are discussed and attributed to carbon-related defects.

High Pulsed Voltage Alkaline Electrolysis for Water Splitting.

Pulsed electrolysis has become a promising research topic in recent decades due to advances in solid-state semiconductor devices. These technologies have enabled the design and construction of simpler, more efficient, and less costly high-voltage and high-frequency power converters. In this paper, we study high-voltage pulsed electrolysis considering variations in both power converter parameters and cell configuration. Experimental results are obtained for frequency variations ranging from 10 Hz to 1 MHz, voltage changes from 2 V to 500 V, and electrode separations from 0.1 to 2 mm. The results demonstrate that pulsed plasmolysis is a promising method for decomposing water for hydrogen production.

Multiconstraint Design of Single-Switch Resonant Converters Based on Extended Impedance Method

The single-switch resonant converter is attractive for low-cost high-frequency power conversion applications. However, the exiting design method needs complicated derivations to meet various practical demands, and it would become impossible as the circuit order increases. This article incorporates the extended impedance method to evaluate the potential designs. The practical demands can be mathematically represented by the inequality constraints. Given the design variables, the proposed design is able to improve the steady-state performance (like the system robustness, voltage gain, load insensitivity, efficiency, current stress, and voltage stress) for the existing resonant converters. A family of Class E inverters is designed to justify the generality and validity of the proposed design. The first case is a classical Class E inverter. The EIM-based design is able to improve the system robustness under 6% parameter variation. The second case is a Class E inverter with resonant input inductor. The EIM-based design is able to offer a wider voltage gain compared to the benchmark method. The last case is a Class E inverter using <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> network. Compared to the previous design approach, the proposed method is able to find a better design point, whose light-load efficiency is improved by 5%.

High-frequency magnetic response of superparamagnetic composites of spherical Fe65Co35 nanoparticles

The response of composites of magnetic nanoparticles (MNPs) with randomly-oriented magnetocrystalline anisotropy axes to a linearly-polarized ac field or a rotating field is studied with regard to the concept of using superparamagnetic nanocomposites as core materials for high (sub-GHz and GHz) frequency power conversion devices. We perform micromagnetic simulations of systems of spherical 5nm-diameter nanoparticles of Fe65Co35 with two different concentrations arranged periodically within a dielectric matrix, including thermal fluctuations of the magnetization within the stochastic thermal field. Because the particles are closely packed, the effect of surface anisotropy is neglected. The dependence of the amplitude of the magnetic response function on temperature is determined. We show the inapplicability of Brown’s classic theory of thermal excitations in single-domain magnetic particles for given material parameters even in the absence of the magnetostatic field. Magnetostatic interactions of MNPs are found to be necessary for stabilizing the dynamical magnetic response in the high temperature (low-energy-barrier) range. They allow for driving magnetization oscillations at room temperature with amplitude comparable to the zero-temperature case. Dynamical (hysteretic and residual) losses are discussed.

Application of Tunnel Magnetoresistance for PCB Tracks Current Sensing in High-Frequency Power Converters

Application of Tunnel Magnetoresistance for PCB Tracks Current Sensing in High-Frequency Power Converters

Buck Converter Current Measurement Using Differential Amplifier

The accuracy of the measured current is a preeminent parameter for Current Control based Power Converter applications to ensure genuine operation of the designed converter. The current measurement accuracy can be affected by several parameters which includes the type of technology used, components used for the selected technology, aging, usage, operating and environmental conditions. The effect of gain resistors and their manufacturing tolerances on differential amplifier-based buck converter current measurement is investigated in this work. The analysis mainly focused on the output voltage variation and its accuracy with respect to the change in gain resistance tolerances. The gain resistors with 5%, 1%, 0.5% and 0.1% manufacturing tolerances taken for the worst-case analysis and the calculated performance results are compared and verified with the simulation results. The Operational amplifiers (Op-Amp) for high frequency power converter applications must operate in a high frequency noise environment and the intended current measuring system must manage common mode noise disturbances paired with the signal to be measured. Based on the Common Mode Rejection Ratio (CMRR) the common mode voltages and noise signals will effectively get filtered out. Lesser CMRR results in lower common mode signal rejection, resulting in poor precision and noise rejection. In differential amplifiers, the CMRR predominantly depends on gain resistors. So, the variations in Common Mode Rejection Ratio due to gain resistor tolerances also analyzed and compared with the output voltage variations. Besides the effects of resistor tolerances, this paper also examines the effect of Op-Amp offset voltage on output accuracy specifically for low magnitude input currents. The obtained results from this analysis clearly shows that the gain resistors with 0.1% tolerance gives maximum accuracy with improved CMRR and accuracy at low magnitude input currents will get well improved by using Op-Amps with Low Offset voltage specifications.

Modeling and Minimization of the Parasitic Capacitances of Single-Layer Toroidal Inductors

High-frequency power converters need electromagnetic interferences filters using common and differential mode chokes with low parasitic capacitance to comply with the electromagnetic compatibility standards. This article proposes a modeling method of this capacitance and ways to minimize it. The studied components are ring core inductors with magnetic materials considered as perfect conductors or with high permittivity, such as nanocrystalline material and most Mn-Zn ferrite materials. In comparison to other work in the literature, the proposed approach takes into account the curvature of the turn, in addition to the coating of the core and the insulation layer of the wire. The hypotheses, used in this article to simplify the real geometry, are compatible with two-dimensional (2-D) approaches to compute the parasitic interturns and turn–core capacitances. These capacitances are evaluated thanks to the 2-D finite element method. The obtained model allows accurate evaluation of the effect of turn–core space on the parasitic capacitance, and enables to reduce its value with a limited impact on the volume of the magnetic component.

Methods for the Accurate Real-Time Simulation of High-Frequency Power Converters

This article presents general modeling approaches to achieve an accurate real-time simulation (RTS) of high switching frequency converters.The proposed methods are based on the direct mapped method (DMM) and make use of decoupling techniques when appropriate. The DMM links state variables to diode statuses and provides an exact and noniterative solution to network equations. An electric vehicle battery charger test case comprised of a full-bridge rectifier, an interleaved boost, and a three-phase <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> is used to demonstrate the high accuracy achieved by the proposed methods compared to a conventional approach. Field-programmable gate array (FPGA) implementations are proposed and shown to achieve from 75- to 175-ns RTS time steps for this test case circuit, allowing its accurate simulation while switched at 200 kHz. To further validate the effectiveness of the FPGA-based simulator, a resonant boost converter is also implemented and simulated in real time.

Opportunities in magnetic materials for high-frequency power conversion

Opportunities in magnetic materials for high-frequency power conversion

Research and Application of Capacitive Power Transfer System: A Review

Capacitive power transfer (CPT) uses an electric field as the transfer medium to achieve wireless power transfer (WPT). Benefitting from the low eddy current loss, simple system structure and strong plasticity of the coupling coupler, the CPT system has recently gained much attention. The CPT system has significantly improved transfer power, system efficiency, and transfer distance due to continuous research and discussion worldwide. This review briefly presents the basic working principle of the CPT system and summarizes the theoretical research in four aspects, including coupling coupler and high-frequency power converter. Following this, the review focuses on research in six key directions, including system modelling and efficiency optimization. The application of CPT technology in five fields, including medical devices and transportation, is also discussed. This review introduces the progress of CPT research in recent years, hoping to serve as a reference for researchers, to promote the further research and application of the CPT system.