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14 pages, 7980 KiB

Open AccessArticle

Design Considerations of Series-Connected Devices Based LLC Converter

by Dongkwan Yoon, Sungmin Lee and Younghoon Cho

Energies 2020, 13(1), 264; https://doi.org/10.3390/en13010264 - 5 Jan 2020

Cited by 4 | Viewed by 3448

This paper describes the design of a Series-Connected Device based on a fixed–frequency LLC resonant converter (SCDLLC). Isolation of the dc-dc converter like the LLC resonant converter is used for the stability of the high voltage system such as a solid-state-transformer (SST). The [...] Read more.

This paper describes the design of a Series-Connected Device based on a fixed–frequency LLC resonant converter (SCDLLC). Isolation of the dc-dc converter like the LLC resonant converter is used for the stability of the high voltage system such as a solid-state-transformer (SST). The series-connected devices driving method is one of the methods applicable to a high voltage system. When driving series-connected devices, an auxiliary circuit for voltage balancing between series-connected devices is required, which can be simply implemented using a passive element. In this paper, LLC converter design with balancing circuits configured in parallel with a device is provided, and both the simulations and experiments were performed. Full article

(This article belongs to the Special Issue Advances in High-Efficiency LLC Resonant Converters)

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21 pages, 7335 KiB

Open AccessArticle

Circuit Topology and Small Signal Modeling of Variable Duty Cycle Controlled Three-Level LLC Converter

by Hussain Humaira, Seung-Woo Baek, Hag-Wone Kim and Kwan-Yuhl Cho

Energies 2019, 12(20), 3833; https://doi.org/10.3390/en12203833 - 10 Oct 2019

Cited by 3 | Viewed by 4944

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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18 pages, 12840 KiB

Open AccessArticle

Flux-Balance Control for LLC Resonant Converters with Center-Tapped Transformers

by Yuan-Chih Lin, Ding-Tang Chen and Ching-Jan Chen

Energies 2019, 12(17), 3211; https://doi.org/10.3390/en12173211 - 21 Aug 2019

Cited by 4 | Viewed by 4576

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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11 pages, 2541 KiB

Open AccessArticle

PV Micro-Inverter Topology Using LLC Resonant Converter

by Hiroki Watanabe, Jun-ichi Itoh, Naoki Koike and Shinichiro Nagai

Energies 2019, 12(16), 3106; https://doi.org/10.3390/en12163106 - 13 Aug 2019

Cited by 14 | Viewed by 3553

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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18 pages, 2221 KiB

Open AccessArticle

Current Mode Control of a Series LC Converter Supporting Constant Current, Constant Voltage (CCCV)

by Michael Heidinger, Qihao Xia, Christoph Simon, Fabian Denk, Santiago Eizaguirre, Rainer Kling and Wolfgang Heering

Energies 2019, 12(14), 2793; https://doi.org/10.3390/en12142793 - 20 Jul 2019

Viewed by 3922

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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20 pages, 6141 KiB

Open AccessArticle

Design Methodology of Tightly Regulated Dual-Output LLC Resonant Converter Using PFM-APWM Hybrid Control Method

by HwaPyeong Park, Mina Kim, HakSun Kim and JeeHoon Jung

Energies 2019, 12(11), 2146; https://doi.org/10.3390/en12112146 - 4 Jun 2019

Cited by 3 | Viewed by 3624

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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20 pages, 14978 KiB

Open AccessArticle

ZVS Auxiliary Circuit for a 10 kW Unregulated LLC Full-Bridge Operating at Resonant Frequency for Aircraft Application

by Yann E. Bouvier, Diego Serrano, Uroš Borović, Gonzalo Moreno, Miroslav Vasić, Jesús A. Oliver, Pedro Alou, José A. Cobos and Jorge Carmena

Energies 2019, 12(10), 1850; https://doi.org/10.3390/en12101850 - 15 May 2019

Cited by 9 | Viewed by 5509

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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19 pages, 6529 KiB

Open AccessArticle

High-Frequency LLC Resonant Converter with GaN Devices and Integrated Magnetics

by Yu-Chen Liu, Chen Chen, Kai-De Chen, Yong-Long Syu and Meng-Chi Tsai

Energies 2019, 12(9), 1781; https://doi.org/10.3390/en12091781 - 10 May 2019

Cited by 25 | Viewed by 6020

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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14 pages, 7608 KiB

Open AccessArticle

Extension of Zero Voltage Switching Capability for CLLC Resonant Converter

by HwaPyeong Park, DoKyoung Kim, SeungHo Baek and JeeHoon Jung

Energies 2019, 12(5), 818; https://doi.org/10.3390/en12050818 - 1 Mar 2019

Cited by 1 | Viewed by 5156

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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