An Accurate Design Algorithm for LLC Resonant Converters—Part I

This paper proposes a circuit configuration of LLC converter a wide voltage range and high efficiency. The proposed LLC overcomes the narrow voltage gain range of conventional full-bridge (FB) LLC converters. Owing to the switching patterns of the primary side, two resonant tanks operate in half-bridge and FB modes. The two resonant tanks are designed with different parameters, and the proposed LLC has six operating modes. These modes enable a squeezed switching frequency span, which is close to the resonance frequency. The proposed control method achieves seamless transition between the operating modes and a wide voltage gain range. First, the operating principles and characteristics of the proposed converter are analyzed. The transitions between modes are determined based on the analyzed theory. In addition, the design guidelines for the two resonant tanks are describe. The parameters of the two resonant tanks are designed using the first harmonic approximation method, and each is determined to achieve a wide voltage range and high efficiency. A prototype rated to 1.0-kW is designed to convert the input of 360 V to an output of 100-420 V, and the proof of concept is validated. Experimental results confirm that the proposed circuit achieves a voltage gain of less than 0.5 to more than 2.0 under different load conditions. Furthermore, the proposed mode transition method achieves seamless transition between modes without complicated calculations. Experiments confirm a maximum efficiency of 96.5%.

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“…(4), which is 100 V from Eq. (11) and (12). On the other hand, the minimum voltage in mode2 is 166 V according to Eq.…”

Section: Output Voltage Range and Design Guidelinesmentioning

confidence: 99%

“…Furthermore, when f s is higher than f r , the primary switches of the FB-LLC converter suffer from a high turn-off current. In addition, it loses its main advantages such as low switching loss (12) (13) . As a result, it becomes less efficient.…”

Section: Introductionmentioning

confidence: 99%

Wide-Range Voltage Gain and High-Efficiency of Isolated LLC Converter using Six-Switch and Two Asymmetric Transformers

Kinoshita

Haga

2020

IEEJ Journal IA

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“…A way of designing the LLC converter is proposed in [ 45 ] and [ 46 ]. However, the leakage inductance and excitation inductance of transformer are hardly regulated.…”

Section: Design and Selection Of Parametersmentioning

confidence: 99%

An improved large signal model of full-bridge LLC converter

Yao

Liu

2018

PLoS ONE

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For the full-bridge LLC converter, it is necessary to establish a large signal model with low-complexity and high-precision when the current of filter inductor works under the continuous conduction mode (CCM) situation. In terms of low complexity, peak values of resonant state variables and average values of slow state variables are taken as the measured indexes between models and actual converter. Models based on the first harmonic approximation (FHA) are studied in depth because they have lower complexity than the existing models. From prospective of high precision, deficiencies of typical FHA model are explained in the light of harmonic generation mechanism of primary current and influence of Fourier series on the typical equivalent circuit. Therefore, transient process of each metallic oxide semiconductor field effect transistor (MOSFET) and its related fast recovery diode, transient process of Schottky rectifier diodes, piecewise equivalent circuit, appropriate selection of variables, and simplified modified dynamic equations are all considered. Furthermore, the unified proposed model is achieved according to the equivalent principle of indexes between aforementioned improved analyses and proposed model. Numerical results of typical FHA model and proposed model are given in accordance with the key indexes. Then, corresponding experimental results are also presented. Differences of indexes between the two models and the actual converter are compared respectively. Though complexity of proposed model is the same as that of typical FHA model, precision of proposed model is higher than that of typical FHA model.

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“…The derivation procedure is complicated and the accuracy improvement is not obvious. In the literature [11,12], time domain methods are used to find out all the possible parameters that can satisfy the required peak gain in PN and PON modes. However, the soft-switching condition of the converter will be lost and the switching losses will be increased.…”

Section: Introductionmentioning

confidence: 99%

Time Domain Simplified Equations and its Iterative Calculation Model for LLC Resonant Converter

et al. 2020

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LLC resonant converters can achieve soft switching and loss reduction. However, the analysis methods of wide frequency range LLC converters generally have problems with incomplete working condition analysis at non-resonant frequencies and there is always a tradeoff between the accuracy and the simplicity. These problems will affect the loss calculation, synchronous rectification and so on. The research objective of this paper focuses on the full-bridge LLC resonant converter. In this paper, three conditions are analyzed in time-domain including switching frequency lower than the resonant frequency at heavy load, switching frequency lower than the resonant frequency at light load, and switching frequency larger than the resonant frequency. Based on proper assumption and simplification, the approximate equivalent of the trigonometric function is used to simplify the complex time-domain equations. The simplified equations are obtained with the resonant capacitor voltage and resonant inductor current as the key variables. In order to make the simplified equations easy to use, an iterative calculation model is proposed with more simplicity than sophisticated software to solve nonlinear equations. The simplified equations and the model proposed in this paper are verified by comparison with the fundamental analysis methods, the simulation, and the experiments. By using the iterative calculation model, the voltage, current, time and other variables of switching points can be obtained with the relative error less than 3% to theoretic values, which can be used in loss calculation, synchronous rectification and so on. And the iterative calculation model can be realized on DSP or other processors in real-time.

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An Accurate Design Algorithm for LLC Resonant Converters—Part I

Cited by 90 publications

References 34 publications

Wide-Range Voltage Gain and High-Efficiency of Isolated LLC Converter using Six-Switch and Two Asymmetric Transformers

Wide-Range Voltage Gain and High-Efficiency of Isolated LLC Converter using Six-Switch and Two Asymmetric Transformers

An improved large signal model of full-bridge LLC converter

Time Domain Simplified Equations and its Iterative Calculation Model for LLC Resonant Converter

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