Search

In the field of high‐frequency transformers, winding losses and core losses constrain the improvement of the power density of planar transformers. Reducing losses on the AC resistor and losses on the core is the key to improving the energy transfer efficiency of planar transformers. Aiming at the half‐bridge LLC resonant converter, this paper proposes a novel structure of a four‐pillar magnetically integrated fractional‐turn planar transformer. In terms of the core structure, according to the principle of magnetic integration, integrate four discrete magnetic cores into a single core, effectively reducing the core volume, so reduces core losses. In the winding, the secondary winding for half‐turn structure, compared with the traditional planar transformer, the primary winding and the secondary winding turns ratio from n:1 to 0.5n:0.5, the primary winding and secondary winding loss reduced to the original 1 of 2. The secondary side windings are combined with the windings of the same current direction by suitable arrangement. By increasing the current path, effectively reduces the problem of uneven distribution of current density in the winding and reduces the AC losses on the winding. © 2024 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Planar magnetic components have been widely used in high-density power converters and are suitable for various topologies. The application of planar inductors in LLC resonant converters can lead to parasitic capacitance, which causes current ringing and results in EMI issues. To mitigate the impact of current ringing, the parasitic capacitance of the planar inductor needs to be reduced. This paper proposes a new six-turn interleaved winding design. Compared to the previous four-turn interleaved winding design, it maintains low parasitic capacitance while positioning both the input and output terminals of the inductor on the outer turn, further enhancing the integration of high-density power converters. The parasitic capacitance was calculated using theoretical methods and verified through finite element simulations. Experimental validation was conducted using an LLC resonant converter test platform. Compared to the previous four-turn interleaved winding design, the new six-turn interleaved winding design satisfies both the input and output terminals, using an outer turn configuration. Additionally, the new design exhibits reduced parasitic capacitance and is suitable for use in LLC resonant converters, where it also minimizes current ringing. [ABSTRACT FROM AUTHOR]

In this paper, partial energy processing is applied to the current sharing technique for multiphase LLC resonant converters. The proposed circuit consists of an LLC resonant converter and a flyback converter, where the flyback converter is only used for partial energy processing. The input voltage of the LLC resonant converter is fine-tuned by the flyback converter to solve the problem of a voltage gain difference between the two phases of the LLC resonant converter caused by the error of the resonant tank components, which prevents the output current from being nonequalized. Since the compensation power is much smaller than the output power, and only one phase will be during circuit operation, the impact on the overall efficiency is minimal. Due to the low dependence between the LLC resonant converter and the flyback converter, they are operated at different switching frequencies. In addition, due to the low dependence between each phase, the circuit can be expanded using odd and even phases. [ABSTRACT FROM AUTHOR]

Objective High-efficiency LLC (logic link control of) topology high-voltage direct current power supplies are widely used in the field of rail transit. However, due to the variable frequency control characteristics of LLC circuits, achieving full digitalization is challenging, and research on domestication lags behind. Thus it is necessary to carry out relevant research. Method Based on the HPM6300 series of full digital control LLC high-voltage power supply circuits from Shanghai Xianji Semiconductor Technology Co., Ltd. (hereinafter referred to as 'Xianji'), an analysis is conducted using the primary harmonic approximation method to establish a circuit model. The control flow of the circuit system program is analyzed. Experimental verification is performed by constructing a prototype with a power of 1.5 kW. Result & Conclusion The experimental results confirm that using the domestic Xianji embedded control chip HPM6300 MCU to build an LLC test prototype, and through PFM+PWM hybrid control, wide-range input can be achieved, and voltage output can be quickly stabilized. Different control methods can be adopted in the future, to achieve wide-range input with structural changes.

In this study, a current-equalization technology utilizing a variable-capacitance technique for a multiphase inductor–inductor–capacitor (LLC) converter is studied. Accordingly, the proposed method involves adjusting the resonant capacitance of the LLC resonant converter to balance the currents between phases. This is achieved primarily by biasing ferroelectric multilayer ceramic capacitors (MLCCs) through a step-down circuit and a common-mode bias structure. These ferroelectric MLCCs serve as the resonant elements, allowing for variable capacitance by leveraging capacitance sensitivity to their trans voltages. This approach provides additional control flexibility to the resonant circuit. Furthermore, since each phase operates independently, the circuit can be scaled to accommodate any number of phases. Moreover, all switches in the circuit have zero-voltage switching (ZVS) turn-on, minimizing switching losses. This study initially analyzes and evaluates the proposed common-mode bias variable capacitance technique and the corresponding operational principles. Subsequently, a two-phase LLC experimental circuit based on a field-programmable gate array (FPGA) digital controller is utilized to assess current equalization and efficiency. That is to say, this experimentation aims to validate the effectiveness of the current-equalization variable-capacitance technique in an LLC resonant converter. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The reliability of high-voltage power converters, which play a key role in driving electric vehicles, is becoming increasingly important owing to the rapid popularization of electric vehicles. In particular, the DC-DC converter, which plays the most basic role among the components of the power conversion system of an electric vehicle, uses a high-voltage battery as a source to properly control and provide the voltage specifications required by each electronic device, which significantly affects the electrical efficiency and performance of the vehicle. In this electrical interaction process, reliability problems such as electromagnetic waves between electronic devices and driver safety problems are crucial owing to the use of large batteries. High-voltage DC-DC converters applied to electric vehicles can be designed using various topologies. The LLC resonant topology, which can be implemented with ZVS and ZCS to minimize electrical losses in high-speed switching environments, is often used. Therefore, this study analyzes the characteristics of electromagnetic EMI-conducted emission noise under the ZVS switching operation conditions of LLC converters and presents critical factors related to the optimal design of noise reduction. [ABSTRACT FROM AUTHOR]

This paper accentuates the study of LLC resonant converter by a comparative analysis of the properties of LLC resonant and pulse width modulation direct current-direct current converters. Lately, LLC resonant converters have become more appealing and desirable in many applications than other pulse width modulation converters (e.g., Buck, Boost, Cuk) for their soft-switching techniques like zero voltage switching, zero current switching as well as low electromagnetic interference. This paper presents an analysis of efficiency variation, output voltage's ripple, and various transient performances like percentage overshoot, and the settling time with the variation of load current in a comparative way between LLC resonant converter's buck, boost operation, and conventional pulse width modulation converter's buck, boost operation. Feedback prop ortio nal-i ntegr al-d eriva tive duty cycle controller is used in all converter topologies for some specific analysis. A fixed input voltage of 100 V is selected for simulation and an output voltage of 24 V for buck operation and 120 V for boost operation are chosen. For simulation purposes, MATLAB/SIMULINK software is used. [ABSTRACT FROM AUTHOR]

Static waste heat recovery, by means of thermoelectric generator (TEG) modules, constitutes a fast-growing energy harvesting technology on the way towards greener transportation. Many commercial solutions are already available for small internal combustion engine (ICE) vehicles, whereas further development and cost reductions of TEG devices expand their applicability at higher-power transportation means (i.e., ships and aircrafts). In this light, the integration of waste heat recovery based on TEG modules in a shipboard distribution network is studied in this work. Several voltage step-up techniques are considered, whereas the most suitable ones are assessed via the LTspice simulation platform. The design procedure of the selected LLC resonant converter is presented and analyzed in detail. Furthermore, a flexible control strategy is proposed, capable of either output voltage regulation (constant voltage) or maximum power point tracking (MPPT), according to the application demands. Finally, both simulations and experiments (on a suitable laboratory testbench) are performed. The obtained measurements indicate the high efficiency that can be achieved with the LLC converter for a wide operating area as well as the functionality and adequate performance of the control scheme in both operating conditions. [ABSTRACT FROM AUTHOR]

A spacecraft power processing unit (PPU) is utilized to convert power from solar arrays or electric batteries to the payload, including electric propulsion, communication equipment, and scientific instruments. Currently, a high-voltage converter is widely applied to the spacecraft PPU to improve power density and save launch weight. However, the high voltage level poses challenges such as high step-down ratios and high power losses. To achieve less conduction loss, a SiC-based T-type three-level (TL) L L C resonant converter is proposed. To further broaden the gain range and achieve high step-down ratios, a variable frequency and adjustable phase-shift (VFAPS) modulation scheme is proposed. Meanwhile, the steady-state time-domain model is established to elaborate the operation principles and boundary conditions for soft switching. Furthermore, the optimal resonant element design considerations have been elaborated to achieve wider gain range and facilitate easier soft switching. Furthermore, the numerical solutions for switching frequency and phase shift (PS) angle under each specific input could be figured out. Finally, the effectiveness of this theoretical analysis is demonstrated via a 500-W experimental prototype with 650∼950-V input and constant output of 48-V/11-A. [ABSTRACT FROM AUTHOR]

Copyright of Urban Mass Transit is the property of Urban Mass Transit Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The LLC resonant converter, which is extensively utilized across various industrial fields, significantly depends on its parameters for performance optimization. This paper establishes a time-domain analytical model for the LLC resonant converter under Pulse Frequency Modulation (PFM) and proposes a multi-objective parameter optimization design method with stepwise constraints. The proposed method limits the resonant capacitor voltage while ensuring that the converter meets the voltage gain requirement and realizes Zero-Voltage Switching (ZVS). The converter's performance is then optimized with the objective of minimizing the switching frequency range, the resonant inductor current, and the RMS value of the switching current on the secondary side. Compared with the existing methods, the proposed method has the advantages of comprehensive consideration and wide application scenarios. Finally, a 1200 W experimental prototype was fabricated, with experimental results verifying the feasibility of the proposed optimization design method and demonstrating that the prototype's maximum efficiency reaches 96.54%. [ABSTRACT FROM AUTHOR]

To enhance the power density of LLC resonant converters, multilayer planar inductors are required. However, multilayer planar inductors have high parasitic capacitance, which may cause inductor current ringing in LLC resonant converters, leading to EMI problems. In this paper, it is found that by using interleaved winding inductors, compared with traditional winding inductors, the parasitic capacitance of multilayer planar inductors is reduced, which can reduce current ringing, without sacrificing power density and increasing manufacturing complexity. The method used to analyze current ringing is to establish an impedance model, and the parasitic capacitance of the interleaved winding inductors is verified by FEM simulations. The analysis is validated in an LLC resonant converter prototype. [ABSTRACT FROM AUTHOR]

In this paper, a hybrid control method with adaptive phase-shifting modulation (PSM) and pulse-frequency modulation (PFM) is proposed to optimize the steady-state performance of an LLC resonant converter in wide voltage-gain range application. For the primary-side switches under the hybrid control method, zero-voltage switching (ZVS) performance is maintained over wide voltage-gain range and the turn-off loss is reduced; therefore, the converter reconciles wide voltage-gain range and high efficiency. Mode characteristics under different phase-shifting-angle-θ and switching-frequency-fs combinations is analyzed, and then the soft-switching characteristic is revealed. By introducing time domain analysis, the turn-on current of the primary-side switches is calculated, and thus the ZVS boundary of different θ and fs combinations is inferred. In addition, to acquire the optimum steady-state operation of the converter, the turn-off current is calculated; by making the converter work near to the minimum turn-off current operating point, the turn-off loss can be reduced greatly. With the principles of achieving ZVS performance and minimizing turn-off current, the phase-shifting angle θ of PSM is designed to be adaptive to the reference output voltage, no additional circuits are needed, and the two control degrees (θ and fs) are simplified to one (fs). The simulation and experiment are developed to verify the feasibility and effectiveness of the hybrid control method; the results show that ZVS performance is maintained at wide voltage-gain range and the turn-off current of the hybrid control method is reduced to that of the single PFM, and thus the turn-off loss is reduced. The efficiency comparison validates the fact that the hybrid control method has less power loss than single PSM and single PFM. [ABSTRACT FROM AUTHOR]

Single-phase solid-state transformers (SSTs) have the advantages of a compact structure, higher reliability, and multiple functions, and have been widely studied. However, bulky energy storage elements and inherent ripple power with double-grid frequency issues are the main disadvantages of conventional single-phase SSTs. This paper presents a single-phase matrix-type AC-AC SST eliminating ripple power with double-grid frequency. The presented SST consists of a line-frequency-commutated rectifier without bulky DC-link capacitors, an LLC resonant converter, a buck converter, and a line-frequency-commutated inverter. The LLC operates efficiently with a fixed voltage gain, and the buck converter provides a voltage regulation function. As a result, high conversion efficiency, high power density, and potentially high reliability are achieved. A 1 kW SST prototype is developed and tested to validate the feasibility and functionality of the proposed methods. [ABSTRACT FROM AUTHOR]

The LLC resonant converter used in high-power situations suffers from the problems of high conduction loss and current stress, which can be solved using input-parallel output-parallel (IPOP)-connected converter modules. However, this leads to a multiple increase in the number of magnetic components, which reduces power density. Magnetic integration technology is an effective way to reduce the volume of converters. Currently, the magnetic integrated transformer based on EE-type cores is widely used to realize miniaturization, and it uses leakage inductance instead of resonant inductance to improve power density. However, leakage inductance is difficult to control, and the external radiated magnetic field will produce serious eddy current loss and electromagnetic interference. This article proposes a novel double B-type magnetic integrated transformer, which can integrate the magnetic components of two LLC resonant converters simultaneously and where the resonant inductances are wound independently. The structure contains four low reluctance branches, which are used as the cores of the transformer and the resonant inductance. The decoupling integration method, which integrates the four components into a single core, has been used to increase core utilization and improve power density. On this basis, the transformer's high- and low-voltage windings are cross-arranged to reduce the magnetic field intensity in space, further decreasing the loss and electromagnetic interference. Compared with the EE-type magnetic integrated transformer, the volume of the proposed structure is reduced by 5.9%. A 400W experimental prototype is built, and the results verify the validity of the design. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Chongqing University of Technology (Natural Science) is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Underwater wireless power transfer (UWPT) systems are appropriate for battery charging of compact, submerged devices without a complicated and expensive sealing structure or human contact because the power source and load are not physically connected. For the shore-based power supply situation, the underwater power conversion and junction technology should be required to drop down shore-based voltage to the target voltage for the underwater energy supply of the UWPT system. This paper proposes a lightweight, high efficiency and power density underwater power conversion connector system for the UWPT system, in which the LLC resonant converter is constructed with SiC transistors. The full load range zero-voltage switching (ZVS) and load adaptive characteristics have been achieved. The optimized RC level shift driver is adopted to highly reduce the switching loss of SiC transistors. Shore-based voltage of 1000 V was converted to the target voltage of 375 V for the UWPT system. The highest measured efficiency is over 98% at a load power level of 1500 W underwater conditions. [ABSTRACT FROM AUTHOR]

Input-Series-Output-Parallel (ISOP) LLC converters have the capability to leverage lower voltage semiconductor devices, thereby enabling applications with higher voltage requirements. The primary advantages lie in enhanced efficiency and power density attributed to improved device performance. Given the utilization of multiple modular LLC converters, the potential impact of component parameter mismatch becomes a significant concern. Specifically, issues related to input voltage sharing (IVS) and device zero voltage switching (ZVS) are critical considerations. This paper develops a precise mathematical model during deadtime to determine ZVS boundaries, taking into account parameter mismatches. Within the developed boundaries, all LLC sub-modules are assured of ZVS operation. To assess IVS performance, a mathematical model is formulated using the first harmonic approximation (FHA) equivalent circuit. To validate the proposed modeling and analysis, a 3 kW 1 MHz GaN-based ISOP LLC is constructed, comprising four modular 750W-LLC units. Experimental results showcase successful ZVS operations and natural voltage balancing of the ISOP LLC converter across a broad range of parameter mismatches.

The LLC resonant converter is a widely utilized power electronics converter, due to its numerous industrial and domestic applications. This converter offers some advantages such as soft-switching operation of all switches, high efficiency, high power density, low voltage stress, minimal electromagnetic interference (EMI) noise, input/output isolation, wide input/output voltage range, and reliable and good performance under the wide load variation ranges, as well as good light-load operation. However, this converter has certain limitations, which can be addressed to enhance its operation and efficiency. This paper provides an in-depth review and comparison of various LLC-based resonant converter configurations, focusing on their operational principles, mathematical analysis, control methods, and some practical applications including electric vehicle chargers, TV power supplies, LED drivers, photovoltaic cells, HVDC production, fuel cells, and wireless power transfer applications. By examining the strengths and weaknesses of the different LLC resonant converter designs, this study aims to contribute to the ongoing research efforts in improving the performance and efficiency of this important power electronics converter.

The high charging efficiency of LLC resonant converters over a very wide range of load conditions in electric vehicle charging systems has long been a research hotspot. In this paper, a hybrid control method is proposed for LLC resonant converter by combining pulse width modulation (PWM) and burst control to address the issues of small excitation current and limited output voltage range under the light load condition. The resonant current energy in the burst-on period is used to supplement the missing excitation current energy from PWM control zero voltage switching to realize PWM-Burst control. Therefore, a hybrid control of PFM and PWM-Burst is employed for LLC resonant converters under full load conditions. The proposed hybrid control method focuses on steady-state operation, and its operating principles are introduced and analyzed. Finally, simulation and experiments were conducted through Matlab-Simulink to verify the feasibility of the proposed method, and a 1-kW laboratory prototype was constructed to validate the effectiveness and advantages of the proposed method.

A novel center-tapped rectifier with current-balancing and voltage-clamped (CBVC) capability for the LLC resonant converter is proposed. A secondary capacitor is inserted between the contact points of the rectifier diode and the secondary winding of the transformer. The amount of the current flowing through each primary switches and rectifier diodes become almost the same by adopting the CBVC center-tapped rectifier. Equal distribution of the current improves the reliability and lifetime of the primary switches and rectifier diodes. In addition, the voltage across the rectifier diodes in the CBVC center-tapped rectifier is clamped by two times the output voltage. The conduction loss of the rectifier diodes is decreased since the diodes with low forward voltage drop can be used. Moreover, half of the output capacitor is utilized as a secondary side capacitor, which means no additional components. The validity of the proposed converter is verified through experiments on a prototype for 400 VDC input to 45–70 V/4 A output application.

The LLC resonant converter used in high-power situations suffers from the problems of high conduction loss and current stress, which can be solved using input-parallel output-parallel (IPOP)-connected converter modules. However, this leads to a multiple increase in the number of magnetic components, which reduces power density. Magnetic integration technology is an effective way to reduce the volume of converters. Currently, the magnetic integrated transformer based on EE-type cores is widely used to realize miniaturization, and it uses leakage inductance instead of resonant inductance to improve power density. However, leakage inductance is difficult to control, and the external radiated magnetic field will produce serious eddy current loss and electromagnetic interference. This article proposes a novel double B-type magnetic integrated transformer, which can integrate the magnetic components of two LLC resonant converters simultaneously and where the resonant inductances are wound independently. The structure contains four low reluctance branches, which are used as the cores of the transformer and the resonant inductance. The decoupling integration method, which integrates the four components into a single core, has been used to increase core utilization and improve power density. On this basis, the transformer's high- and low-voltage windings are cross-arranged to reduce the magnetic field intensity in space, further decreasing the loss and electromagnetic interference. Compared with the EE-type magnetic integrated transformer, the volume of the proposed structure is reduced by 5.9%. A 400W experimental prototype is built, and the results verify the validity of the design. [ABSTRACT FROM AUTHOR]

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The LLC resonant converter design is a very challenging design problem for electric vehicle charging applications, since Lm, Lr, Cr and the quality factor are complex functions of voltage gain and it is very hard to find a choice of switching frequency range that can provide Zero Voltage Switching (ZVS) serving the voltage gains depending on the application. This study presents a new nature-inspired mathematical method-based design methodology that can evaluate multiple design components and constraints together for air gap magnetic components. The proposed method selects the most convenient design among numerous cores in the created core database by using the Particle Swarm Algorithm. Unlike the traditional design algorithms, the proposed novel algorithm determines the optimal magnetic flux density by minimizing an objective function that includes the loss, cost, and volume of magnetic components. The presented method was tested for a 3700W, 48V LLC resonant converter installed in a lightweight EV charger. In the algorithm, a design study was carried out considering the multi-core structures in which serial and parallel multi-couplings are applied in the primary and secondary windings, respectively. The designed magnetic components were validated in the common simulation environment of Ansys Electronic Desktop and Simplorer, and the most convenient core structures were selected from the core database. It was shown that the proposed method can be used as part of a system-level optimization algorithm where multiple combinations can be evaluated together and rapidly to find the most suitable LLC resonant converter design. [ABSTRACT FROM AUTHOR]

The LLC resonant converter is a widely used DC/DC converter that offers the benefit of enabling soft switching compared to classical DC/DC converters. However, traditional PI control strategy based on a linear model has drawbacks such as slow dynamic response and poor anti-interference performance. To overcome the shortage, a passivitybased control strategy based on the Euler-Lagrange (EL) model is proposed in this paper to improve the dynamic performance of the half-bridge LLC resonant converter. In addition, the stability of the system based on the proposed strategy is analyzed and verified. Further, the effectiveness and performance of the proposed strategy is verified in the simulation by comparing with the traditional PI controller. Finally, a prototype was built to verify the dynamic performance of the LLC resonant converter based on the proposed control strategy. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Polytechnic is the property of Journal of Polytechnic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, partial energy processing is applied to the current sharing technique for multiphase LLC resonant converters. The proposed circuit consists of an LLC resonant converter and a flyback converter, where the flyback converter is only used for partial energy processing. The input voltage of the LLC resonant converter is fine-tuned by the flyback converter to solve the problem of a voltage gain difference between the two phases of the LLC resonant converter caused by the error of the resonant tank components, which prevents the output current from being nonequalized. Since the compensation power is much smaller than the output power, and only one phase will be during circuit operation, the impact on the overall efficiency is minimal. Due to the low dependence between the LLC resonant converter and the flyback converter, they are operated at different switching frequencies. In addition, due to the low dependence between each phase, the circuit can be expanded using odd and even phases.

LLC resonant converters are prone to generating a large inrush current during the start-up process, which will cause damage to the resonant elements and threaten the safe operation of the circuit. In this study, we investigate the soft-start method to suppress the inrush current of an LLC resonant converter. Based on the traditional frequency-decreasing method, we integrate PWM control to broaden the output voltage gain range during the start-up. Additionally, to ensure the smooth establishment of the output voltage, the controller performs the closed-loop control of the duty cycle and frequency in sequence based on the rate of output voltage rise. A prototype experiment based on STM32F334C8T6 is established to experimentally validate the presented soft start-up method. The experiment results indicate that the soft start-up method improves the start-up performance, reduces the maximum inrush current by 47.5% compared with that of the frequency-decreasing method, and builds up the output voltage quickly. The start-up process is smooth, which improves the reliability of the LLC resonant converter. [ABSTRACT FROM AUTHOR]

Summary: The expected depletion of fossil fuels has brought in an increased demand for electric vehicles with better performance in terms of easiness of control and reliability of operation and hence is a fertile area of research. In the present scenario, motoring, regenerative braking, and charging operations are performed in electric vehicles by separate converters. In this paper, an integrated scheme is developed, wherein the same voltage source inverter is employed to obtain all the three modes of operation, which in turn reduces the number of switching devices. Further, a sensorless control used in the proposed scheme improves the operational reliability. This novel approach adopts a simple switching scheme for voltage source inverter to operate as a dual‐boost DC‐DC converter during the regenerative braking period. This switching scheme enables reconfiguring voltage source inverter to a dual‐boost rectifier in conjunction with a LLC resonant converter in the charging mode. A comparison is also provided between the performance of single switch boost and dual‐boost converters used for braking operation. The performance of a prototype brushless DC (BLDC) motor drive with Li‐ion battery pack is evaluated in motoring, regenerative braking, and battery charging modes. This paper presents a detailed design of the scheme, the simulation of which is done on a MATLAB/SIMULINK platform and validated experimentally. [ABSTRACT FROM AUTHOR]

The marine DC power supply system is the key to a ship's power supply, which needs to convert the energy from storage batteries or distributed power generation units into stable DC voltage for electric propulsion or the ship's electronics. The LLC resonant converter can be used as the key power conversion link in the marine DC power supply system due to its ability to realize electrical isolation in a high-power environment and soft switching within a wide load range. Aiming at the problem of sudden changes in voltage gain at a high switching frequency under light load conditions and the problem of insufficient voltage gain under heavy load conditions due to the parasitic parameters of power devices (mainly referring to the junction capacitor), this paper first proposes a full operating range performance optimization design method. By adding an auxiliary circuit that can be opened according to the operating conditions and a multi-objective particle swarm parameter optimization method that considers the converter loss and voltage gain under heavy load conditions, the performance of the LLC resonant converter can be improved in a full range of operating conditions. Finally, the effectiveness of the proposed method is verified by an experimental prototype and compared with the conventional methods and existing solutions to highlight the superiority of the proposed method in this paper. [ABSTRACT FROM AUTHOR]

The power supply of many applications running off the power line is made up of an isolated dc-dc converter powered by a front-end power factor corrector (PFC) stage. The PFC stage ensures compliance with the electromagnetic compatibility regulations but does not usually provide safety isolation since it is typically implemented with a boost converter. Lately, the increase in multi-output power supplies, especially in lighting and USB Power Delivery applications, has raised the need for an isolated PFC at power levels where currently there is not an industry standard solution. This isolated PFC is intended to power one or more non-isolated post-regulators to enable a substantial simplification of the overall architecture and a cost reduction. The usage of an LLC resonant converter as an isolated PFC has been considered and demonstrated only quite recently, raising the industry's attention due to the favorable converter's characteristics that have led to its success as a dc-dc converter. This paper provides two significant contributions. Firstly, it provides a quantitative assessment of the difference in the results obtained by designing an LLC-based PFC converter based on the first harmonic approximation analysis or the time-domain analysis by applying them to the design of the same converter. Secondly, it demonstrates that designing an LLC-based PFC converter to work also in the above-resonance region optimizes its performance by reducing the (magnetizing) reactive current in the resonant tank and, therefore, the rms currents on both the input and the output side and the related power loss. [ABSTRACT FROM AUTHOR]

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The LLC resonant converter is a widely used DC/DC converter that offers the benefit of enabling soft switching compared to classical DC/DC converters. However, traditional PI control strategy based on a linear model has drawbacks such as slow dynamic response and poor anti-interference performance. To overcome the shortage, a passivitybased control strategy based on the Euler–Lagrange (EL) model is proposed in this paper to improve the dynamic performance of the half-bridge LLC resonant converter. In addition, the stability of the system based on the proposed strategy is analyzed and verified. Further, the effectiveness and performance of the proposed strategy is verified in the simulation by comparing with the traditional PI controller. Finally, a prototype was built to verify the dynamic performance of the LLC resonant converter based on the proposed control strategy.

In this study, a current-equalization technology utilizing a variable-capacitance technique for a multiphase inductor–inductor–capacitor (LLC) converter is studied. Accordingly, the proposed method involves adjusting the resonant capacitance of the LLC resonant converter to balance the currents between phases. This is achieved primarily by biasing ferroelectric multilayer ceramic capacitors (MLCCs) through a step-down circuit and a common-mode bias structure. These ferroelectric MLCCs serve as the resonant elements, allowing for variable capacitance by leveraging capacitance sensitivity to their trans voltages. This approach provides additional control flexibility to the resonant circuit. Furthermore, since each phase operates independently, the circuit can be scaled to accommodate any number of phases. Moreover, all switches in the circuit have zero-voltage switching (ZVS) turn-on, minimizing switching losses. This study initially analyzes and evaluates the proposed common-mode bias variable capacitance technique and the corresponding operational principles. Subsequently, a two-phase LLC experimental circuit based on a field-programmable gate array (FPGA) digital controller is utilized to assess current equalization and efficiency. That is to say, this experimentation aims to validate the effectiveness of the current-equalization variable-capacitance technique in an LLC resonant converter.

Static waste heat recovery, by means of thermoelectric generator (TEG) modules, constitutes a fast-growing energy harvesting technology on the way towards greener transportation. Many commercial solutions are already available for small internal combustion engine (ICE) vehicles, whereas further development and cost reductions of TEG devices expand their applicability at higher-power transportation means (i.e., ships and aircrafts). In this light, the integration of waste heat recovery based on TEG modules in a shipboard distribution network is studied in this work. Several voltage step-up techniques are considered, whereas the most suitable ones are assessed via the LTspice simulation platform. The design procedure of the selected LLC resonant converter is presented and analyzed in detail. Furthermore, a flexible control strategy is proposed, capable of either output voltage regulation (constant voltage) or maximum power point tracking (MPPT), according to the application demands. Finally, both simulations and experiments (on a suitable laboratory testbench) are performed. The obtained measurements indicate the high efficiency that can be achieved with the LLC converter for a wide operating area as well as the functionality and adequate performance of the control scheme in both operating conditions.

A spacecraft power processing unit (PPU) is utilized to convert power from solar arrays or electric batteries to the payload, including electric propulsion, communication equipment, and scientific instruments. Currently, a high-voltage converter is widely applied to the spacecraft PPU to improve power density and save launch weight. However, the high voltage level poses challenges such as high step-down ratios and high power losses. To achieve less conduction loss, a SiC-based T-type three-level (TL) LLC resonant converter is proposed. To further broaden the gain range and achieve high step-down ratios, a variable frequency and adjustable phase-shift (VFAPS) modulation scheme is proposed. Meanwhile, the steady-state time-domain model is established to elaborate the operation principles and boundary conditions for soft switching. Furthermore, the optimal resonant element design considerations have been elaborated to achieve wider gain range and facilitate easier soft switching. Furthermore, the numerical solutions for switching frequency and phase shift (PS) angle under each specific input could be figured out. Finally, the effectiveness of this theoretical analysis is demonstrated via a 500-W experimental prototype with 650∼950-V input and constant output of 48-V/11-A.

The LLC resonant converter, which is extensively utilized across various industrial fields, significantly depends on its parameters for performance optimization. This paper establishes a time-domain analytical model for the LLC resonant converter under Pulse Frequency Modulation (PFM) and proposes a multi-objective parameter optimization design method with stepwise constraints. The proposed method limits the resonant capacitor voltage while ensuring that the converter meets the voltage gain requirement and realizes Zero-Voltage Switching (ZVS). The converter’s performance is then optimized with the objective of minimizing the switching frequency range, the resonant inductor current, and the RMS value of the switching current on the secondary side. Compared with the existing methods, the proposed method has the advantages of comprehensive consideration and wide application scenarios. Finally, a 1200 W experimental prototype was fabricated, with experimental results verifying the feasibility of the proposed optimization design method and demonstrating that the prototype’s maximum efficiency reaches 96.54%.

This article presents a planar transformer design and optimization method for high power density on-board chargers (OBCs) utilized in electric vehicles (EVs). Owing to considerations of electrical safety, OBCs require an isolated converter, leading to a substantial increase in volume due to the inclusion of a transformer. To address this issue and achieve high power density, a planar transformer is used, and an optimized design method is proposed for pattern arrangement, width, and core shape. The feasibility of the design is verified through the development of a 3.3 kW OBC prototype. Consequently, when compared to conventional transformers, the design method in this article results in a 27% reduction in the transformer's height and a 20% reduction in its overall volume. This reduction is advantageous for meeting the requirements of high power density OBCs. [ABSTRACT FROM AUTHOR]

This paper proposes a bidirectional low-voltage DC-to-DC converter for advanced fuel-cell electric vehicles (FCEVs). The proposed converter consists of two parallel-operated power converters driving the low-voltage output stage to reduce the size of the filter. Two power converters are internally connected in series with an isolated LLC resonant converter and a non-isolated buck/boost converter to achieve high efficiency in both directions while ensuring very wide input and output voltage ranges. The LLC resonant converter generates an input from a 12 V low-voltage battery to a non-isolated converter when starting an FCEV. Once the fuel-cell stack is activated, the power flow reverses, and the non-isolated buck/boost converter regulates the input voltage for the LLC resonant converter from the power generated in the fuel-cell stack. To validate the performance of the proposed converter, a prototype converter is designed, built, and tested with 2.0 kW in the forward powering mode, 4.5 kW in the reverse powering mode, a 260–430 VDC input, and a 10–15 VDC output. Experimental results demonstrate that the proposed converter achieves a power conversion efficiency of over 95.5% in both the forward and reverse powering modes, while ensuring stable bidirectional operation and much lower current and voltage ripples. [ABSTRACT FROM AUTHOR]

Planar transformers have been widely used in isolated power supplies. However, with a large current density, the parallel windings usually cannot share the current evenly. This uneven current-sharing may cause additional winding losses, and damage the performance of the power converter. In this paper, a novel central-tapped planar transformer structure is proposed. Regardless of whether it is in the first half cycle or the second half cycle, the proposed twelve-layer transformer can be simplified as four three-layer transformers connected in parallel. Moreover, there is a "shielding layer" between adjacent three-layer transformers. In addition, the proposed transformer structure is optimized with a symmetrical layer arrangement, and the skin effect and proximity effect can be further reduced. Simulation and experimental tests indicate that the optimized planar transformer can stably provide 476.1 W of output power at a frequency of 1.25 MHz. The peak efficiency of the optimized transformer is up to 99.2%, and there is no obvious hot spot on the PCB board. It is noteworthy that the temperature difference in the secondary windings is less than 5 °C, which means the current-sharing in the secondary windings works well. [ABSTRACT FROM AUTHOR]

Summary: A bidirectional half‐bridge (BHB) LLC resonant converter with automatic current sharing characteristics is proposed in this paper for high‐power bidirectional energy storage applications. With the help of magnetizing inductance of transformer, all MOSFETs on the primary and secondary sides can realize zero‐voltage switching. By grouping the secondary windings of the transformer, excellent current sharing can be achieved in both forward and backward operation modes even if there is a 10% error of the resonant parameters. Due to the half bridge structure in both primary and secondary sides, the number of switches is reduced. And the resonant capacitance is small, which is conducive to integrate into the isolation transformer. Thus, the power density and overall efficiency of the proposed converter can be improved. Whether the converter is in forward or backward operation mode, the PWM control strategy is consistent, and it is not required to control the power flow by regulating the phase shift angle of primary and secondary sides, which makes the control strategy of the proposed converter easier. Finally, an 850 W experimental prototype is established to verify the superiority of the proposed circuit. Under the full load condition, the measured peak efficiency is 98.11% and 97.11% in the forward and backward operating modes, respectively. [ABSTRACT FROM AUTHOR]

For low-power applications, this paper presents the development and design of a compact and ultra-highly efficient half-bridge LLC resonant converter. By using Galium Nitride (GaN) devices and high-efficient magnetics, the efficiency and power density of resonant converters can be improved. Compared to Silicon MOSFETs, GaN high-electron-mobility transistors (GaN HEMT) have a lower output capacitance and gate charge, resulting in lower driving loss and shorter dead times. Consequently, the proposed LLC converter based on GaN devices has excellent performance characteristics such as ultra-high efficiency, low switching losses, compact size, high voltage endurance, high operating temperature and high operating frequency. Furthermore, the proposed resonant converter features soft switching properties that ensure that the switches and diodes on the primary side are always switched at zero voltage and current. By doing so, LLC resonant converter switching losses are significantly reduced by up to 3.1%, and an overall efficiency of 98.5% is achieved. The LLC resonant converter design with GaN HEMT has great advantages over Si MOSFET solution regarding efficiency, overall losses, switching loose and power factor correction. A 240 W, 240 V to 60 V half-bridge GaN HEMT LLC resonant converter is simulated with a switching frequency of 75 KHz, along with the comparative analysis of the Si metal oxide semiconductor field effect transistor (MOSFET) solution. Moreover, the design and analysis of highly efficient magnetics with a power factor of 0.99 at full load is presented. A 240-Watt single stage LED driver with power factor correction is also designed to verify and compare the performance of proposed LLC resonant converter. [ABSTRACT FROM AUTHOR]