Special Issue "Advances in High-Efficiency LLC Resonant Converters"

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "Electrical Power and Energy System".

Deadline for manuscript submissions: 30 November 2019.

Special Issue Editor

Prof. Dr. Jeehoon Jung
E-Mail Website
Guest Editor
School of Electrical and Computer Engineering, Ulsan National Institute of Science and Technology (UNIST), UNIST-gil 50, Ulsan 44919, Republic of Korea
Tel. +82-52-217-2140; Fax: +82-52-217-2109
Interests: High-frequency dc–dc converters and switched-mode power supplies using wide band-gap devices; bidirectional and resonant power converters for smart power transformers; digital control and signal processing algorithms for power management; wireless power transfer techniques for home appliances and EVs; power conversion for renewable energy; and real-time and power hardware-in-the-loop (HIL) simulations of smart power grids and dc microgrids

Special Issue Information

Dear colleagues,

LLC resonant converters have been widely used in industrial fields because of their high efficiency, simple structure, and cost effectiveness. Nowadays, many advanced technologies and approaches have been introduced and propose to improve their power conversion efficiency, dynamic performance, stability, reliability, etc., using enhanced devices such as wide band-gap power switches and high-speed controllers. In addition, new and advanced control algorithms have been applied to the LLC resonant converters.

The Guest Editor is inviting submissions for a Special Issue of Energies on the subject area of "Advances in High-Efficiency LLC Resonant converters". This Special Issue will focus on emerging power electronic topologies related to the LLC resonant converters and their design methodologies and control algorithms. Topics of interest for publication include, but are not limited to:

- LLC Resonant Topologies;

- Design Methodologies of Resonant Tanks for High Efficiency;

- Power Loss Analysis in LLC Resonant Converters;

- High-Frequency Magnetics in LLC Resonant Converters;

- Wide Band-gap Devices Applied to LLC Resonant Converters;

- Advanced Control Algorithms for LLC Resonant Converters

Prof. Dr. Jeehoon Jung
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • LLC Resonant Converters, High Efficiency
  • Power Loss
  • Resonant Tank Design
  • High-Frequency Magnetics
  • Wide Band-gap Devices
  • Control in Resonant Converters

Published Papers (8 papers)

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Research

Open AccessArticle
Circuit Topology and Small Signal Modeling of Variable Duty Cycle Controlled Three-Level LLC Converter
Energies 2019, 12(20), 3833; https://doi.org/10.3390/en12203833 - 10 Oct 2019
Abstract
With a view to regulate the output voltage with fixed frequency, without using any additional component or complex modulation technique, a topology of a variable duty controlled three-level LLC converter is proposed and an equivalent small signal model for Electric Vehicle (EV) charger [...] Read more.
With a view to regulate the output voltage with fixed frequency, without using any additional component or complex modulation technique, a topology of a variable duty controlled three-level LLC converter is proposed and an equivalent small signal model for Electric Vehicle (EV) charger applications is deduced in this paper. The steady state equations of each operating region are derived in time domain. Based on an Extended Describing Function (EDF) approach, a small signal equivalent circuit is modeled which includes both frequency and duty controlled terms. The equivalent circuit is further simplified to derive a transfer function of duty control to output voltage. The transfer function is verified through simulation software. Analyzing the transfer function, a voltage controller is designed and implemented with a PI compensator. The simulation results of the proposed control schemes are illustrated and discussed. The topology is compared to a conventional frequency control topology and the merits of the proposed topology are presented. Full article
(This article belongs to the Special Issue Advances in High-Efficiency LLC Resonant Converters)
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Open AccessArticle
Flux-Balance Control for LLC Resonant Converters with Center-Tapped Transformers
Energies 2019, 12(17), 3211; https://doi.org/10.3390/en12173211 - 21 Aug 2019
Abstract
LLC resonant converters with center-tapped transformers are widely used. However, these converters suffer from a flux walking issue, which causes a larger output ripple and possible transformer saturation. In this paper, a flux-balance control strategy is proposed for resolving the flux walking issue. [...] Read more.
LLC resonant converters with center-tapped transformers are widely used. However, these converters suffer from a flux walking issue, which causes a larger output ripple and possible transformer saturation. In this paper, a flux-balance control strategy is proposed for resolving the flux walking issue. First, the DC magnetizing current generated due to the mismatched secondary-side leakage inductances, and its effects on the voltage gain are analyzed. From the analysis, the flux-balance control strategy, which is based on the original output-voltage control loop, is proposed. Since the DC magnetizing current is not easily measured, a current sensing strategy with a current estimator is proposed, which only requires one current sensor and is easy to estimate the DC magnetizing current. Finally, a simulation scheme and a hardware prototype with rated output power 200 W, input voltage 380 V, and output voltage 20 V is constructed for verification. The simulation and experimental results show that the proposed control strategy effectively reduces the DC magnetizing current and output voltage ripple at mismatched condition. Full article
(This article belongs to the Special Issue Advances in High-Efficiency LLC Resonant Converters)
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Open AccessArticle
PV Micro-Inverter Topology Using LLC Resonant Converter
Energies 2019, 12(16), 3106; https://doi.org/10.3390/en12163106 - 13 Aug 2019
Abstract
In this paper, a DC–single-phase AC power converter with an LLC resonant converter is presented for a photovoltaic (PV) micro-inverter application. This application requires the leakage current suppression capability. Therefore, an isolated power converter is usually combined for DC/AC systems. The LLC resonant [...] Read more.
In this paper, a DC–single-phase AC power converter with an LLC resonant converter is presented for a photovoltaic (PV) micro-inverter application. This application requires the leakage current suppression capability. Therefore, an isolated power converter is usually combined for DC/AC systems. The LLC resonant converter is the one of the isolated power converter topologies, and it has good performance for conversion efficiency with easy control. On the other hand, a double-line frequency power ripple has to be compensated for in order to improve the performance of the maximum power point tracking (MPPT). Therefore, a bulky electrolytic capacitor is usually necessary for the power converter. However, the electrolytic capacitor may limit the lifetime of the micro-inverter. This paper introduces the PV micro-inverter with a LLC resonant converter. In addition, the active power decoupling circuit is applied in order to compensate the double-line frequency power ripple by the small capacitor in order to eliminate the electrolytic capacitor. Finally, the transformer design is considered in order to reduce the transformer losses. As a result, the conversion efficiency of the LLC converter is improved by 1% when the litz wire has many strands. Full article
(This article belongs to the Special Issue Advances in High-Efficiency LLC Resonant Converters)
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Open AccessArticle
Current Mode Control of a Series LC Converter Supporting Constant Current, Constant Voltage (CCCV)
Energies 2019, 12(14), 2793; https://doi.org/10.3390/en12142793 - 20 Jul 2019
Abstract
This paper introduces a control algorithm for soft-switching series LC converters. The conventional voltage-to-voltage controller is split into a master and a slave controller. The master controller implements constant current, constant voltage (CCCV) control, required for demanding applications, for example, lithium battery charging [...] Read more.
This paper introduces a control algorithm for soft-switching series LC converters. The conventional voltage-to-voltage controller is split into a master and a slave controller. The master controller implements constant current, constant voltage (CCCV) control, required for demanding applications, for example, lithium battery charging or laboratory power supplies. It defines the set-current for the open-loop current slave controller, which generates the pulse width modulation (PWM) parameters. The power supply achieves fast large-signal responses, e.g., from 5 V to 24 V , where 95% of the target value is reached in less than 400 s . The design is evaluated extensively in simulation and on a prototype. A match between simulation and measurement is achieved. Full article
(This article belongs to the Special Issue Advances in High-Efficiency LLC Resonant Converters)
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Open AccessArticle
Design Methodology of Tightly Regulated Dual-Output LLC Resonant Converter Using PFM-APWM Hybrid Control Method
Energies 2019, 12(11), 2146; https://doi.org/10.3390/en12112146 - 04 Jun 2019
Abstract
A dual-output LLC resonant converter using pulse frequency modulation (PFM) and asymmetrical pulse width modulation (APWM) can achieve tight output voltage regulation, high power density, and high cost-effectiveness. However, an improper resonant tank design cannot achieve tight cross regulation of the dual-output channels [...] Read more.
A dual-output LLC resonant converter using pulse frequency modulation (PFM) and asymmetrical pulse width modulation (APWM) can achieve tight output voltage regulation, high power density, and high cost-effectiveness. However, an improper resonant tank design cannot achieve tight cross regulation of the dual-output channels at the worst-case load conditions. In addition, proper magnetizing inductance is required to achieve zero voltage switching (ZVS) of the power MOSFETs in the LLC resonant converter. In this paper, voltage gain of modulation methods and steady state operations are analyzed to implement the hybrid control method. In addition, the operation of the hybrid control algorithm is analyzed to achieve tight cross regulation performance. From this analysis, the design methodology of the resonant tank and the magnetizing inductance are proposed to compensate the output error of both outputs and to achieve ZVS over the entire load range. The cross regulation performance is verified with simulation and experimental results using a 190 W prototype converter. Full article
(This article belongs to the Special Issue Advances in High-Efficiency LLC Resonant Converters)
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Open AccessArticle
ZVS Auxiliary Circuit for a 10 kW Unregulated LLC Full-Bridge Operating at Resonant Frequency for Aircraft Application
Energies 2019, 12(10), 1850; https://doi.org/10.3390/en12101850 - 15 May 2019
Abstract
In modern aircraft designs, following the More Electrical Aircraft (MEA) philosophy, there is a growing need for new high-power converters. In this context, innovative solutions to provide high efficiency and power density are required. This paper proposes an unregulated LLC full-bridge operating at [...] Read more.
In modern aircraft designs, following the More Electrical Aircraft (MEA) philosophy, there is a growing need for new high-power converters. In this context, innovative solutions to provide high efficiency and power density are required. This paper proposes an unregulated LLC full-bridge operating at resonant frequency to obtain a constant gain at all loads. The first harmonic approximation (FHA) model is not accurate enough to estimate the voltage gain in converters with high parasitic resistance. A modified FHA model is proposed for voltage gain analysis, and time-based models are used to calculate the instantaneous current required for the ZVS transition analysis. A method using charge instead of current is proposed and used for this ZVS analysis. Using this method, an auxiliary circuit is proposed to achieve complete ZVS within the whole load range, avoiding a gapped transformer design and increasing the efficiency and power density. A 28 Vdc output voltage prototype, with 10 kW peak output power, has been developed to validate the theoretical analysis and the proposed auxiliary circuit. The maximum efficiency (96.3%) is achieved at the nominal power of 5 kW. Full article
(This article belongs to the Special Issue Advances in High-Efficiency LLC Resonant Converters)
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Open AccessArticle
High-Frequency LLC Resonant Converter with GaN Devices and Integrated Magnetics
Energies 2019, 12(9), 1781; https://doi.org/10.3390/en12091781 - 10 May 2019
Cited by 1
Abstract
In this study, a light emitting diode (LED) driver containing an integrated transformer with adjustable leakage inductance in a high-frequency isolated LLC resonant converter was proposed as an LED lighting power converter. The primary- and secondary-side topological structures were analyzed from the perspectives [...] Read more.
In this study, a light emitting diode (LED) driver containing an integrated transformer with adjustable leakage inductance in a high-frequency isolated LLC resonant converter was proposed as an LED lighting power converter. The primary- and secondary-side topological structures were analyzed from the perspectives of component loss and component stress, and a full-bridge structure was selected for both the primary- and secondary-side circuit architecture of the LLC resonant converter. Additionally, to achieve high power density and high efficiency, adjustable leakage inductance was achieved through an additional reluctance length, and the added resonant inductor was replaced with the transformer leakage inductance without increasing the amount of loss caused by the proximity effect. To optimize the transformer, the number of primary- and secondary-side windings that resulted in the lowest core loss and copper loss was selected, and the feasibility of the new core design was verified using ANSYS Maxwell software. Finally, this paper proposes an integrated transformer without any additional resonant inductor in the LLC resonant converter. Transformer loss is optimized by adjusting parameters of the core structure and the winding arrangement. An LLC resonant converter with a 400 V input voltage, 300 V output voltage, 1 kW output power, and 500 kHz switching frequency was created, and a maximum efficiency of 97.03% was achieved. The component with the highest temperature was the transformer winding, which reached 78.6 °C at full load. Full article
(This article belongs to the Special Issue Advances in High-Efficiency LLC Resonant Converters)
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Open AccessArticle
Extension of Zero Voltage Switching Capability for CLLC Resonant Converter
Energies 2019, 12(5), 818; https://doi.org/10.3390/en12050818 - 01 Mar 2019
Abstract
TheCLLC resonant converter has been widely used to obtaina high power conversion efficiency with sinusoidal current waveforms and a soft switching capability. However, it has a limited voltage gain range according to the input voltage variation. The current-fed structure canbe one solution to [...] Read more.
TheCLLC resonant converter has been widely used to obtaina high power conversion efficiency with sinusoidal current waveforms and a soft switching capability. However, it has a limited voltage gain range according to the input voltage variation. The current-fed structure canbe one solution to extend the voltage gain range for the wide input voltage variation, butit has a limited zero voltage switching (ZVS) range. In this paper, the current-fed CLLC resonant converter with additional inductance is proposed to extend the ZVS range. The operational principle is analyzed to design the additional inductance for obtaining the extended ZVS range. The design methodology of the additional inductance is proposed to maximize the ZVS capability for the entire load range. The performance of the proposed method is verified with a 20 W prototype converter. Full article
(This article belongs to the Special Issue Advances in High-Efficiency LLC Resonant Converters)
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

1. Dr. Nikolay Hinov [email protected] Investigation of gallium nitride devices in high-frequency LLC resonant converters;

2. Dr. Young-Hoon Cho [email protected] Optimal Design Method Considering Transformer Parasitic Capacitance of LLC Resonant Converters;

3. Dr. Raed Mohsen [email protected] LLC resonant converter for electric vehicle battery chargers.

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