State-of-the-Art Review on Topology and Deductive Methods of LLC Resonant Converter

Li Yazhuo,Cheng Xu-Feng,Zhao Jiapeng,Zhao Qianqi,Li He,Zhang Yu,Hao Xin 대한전기학회 2024 Journal of Electrical Engineering & Technology Vol.19 No.4

The LLC resonant converter has many advantages, such as low operating loss, wide output range, small size, and simple structure. It is widely used in the fi elds of automobile charging, special power supply, and new energy power generation. Topology is a very important part of the LLC resonant converter. However, at present, the overview of LLC resonant converter topology only briefl y summarizes some traditional topologies, which cannot cover the emerging new topologies. In this paper, the topology and deductive methods of LLC resonant converter, which concerns the literatures in the past fi ve years, are reviewed. At the same time, for the integrity of this article, the modulation strategy of the LLC converter is introduced briefl y. This paper fi rstly introduces the basic working principle and characteristics of the LLC resonant converter, and then discusses the basic topology and modulation strategy of the LLC resonant converter. Classifi cation and deductive methods of related topologies are summarized in detail, and the related results help engineers analyze, select, and design LLC resonant converters. Finally, the future development trend of LLC resonant converter is predicted and discussed according to the status of industrial applications.

Digital Implementation of Optimal SR ON-time Control and Asymmetric Duty Control in LLC Resonant Converter

Cheol-O Yeon,Dong Kwan Kim,Jae-Bum Lee,Jong-Woo Kim,Cheon-Yong Lim,Gun-Woo Moon 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

In this paper, a half-bridge (HB) LLC resonant converter which has been used for server power supply, is controlled by digital controller. In order to increase the entire load efficiency of HB LLC converter, a synchronous rectifier (SR) should has a robust control at any condition such as PFC noise or the lack of current sensing. For these reason, digital controller with LLC SR control is preferred in server power supply market. In this paper, the optimal SR ON-time control which operates as a constant ON-time at below region, and the same ON-time of primary switch at above region, is implemented. However, the problems of optimal SR ON-time control still exist. Because of senseless operation, when the ON-time of SR is larger than the half period of LLC resonant tank, the current of converter flows reversely and it will make the big surge current which damage to active devices. From this result, the ON-time of SR should be shorter than the half period of LLC resonant tank. Moreover, in the case of current unbalance in center-tapped rectifier, the conducting time of rectifiers is different due to the parasitic components. Since the powering periods of two SR are different, the SR ON-time of HB LLC resonant converter should be determined by minimum conducting time of rectifiers. This result causes a large conduction loss of body diodes which makes the low efficiency or the reliability problem of LLC resonant converter. Therefore, HB LLC resonant converter with optimal SR ON-time control is implemented and the asymmetric duty control is proposed in this paper, which solves the current unbalance problem in center-tapped rectifier. Therefore, the LLC resonant converter which has wide input variation, can achieve the high efficiency with optimal SR ON-time control and eliminate the current unbalance problem with asymmetric duty control.

LLC 공진 컨버터에 적합한 자동화 권선 LLC 공진변압기 설계에 관한 연구

배준형,김종해 한국전기전자학회 2019 전기전자학회논문지 Vol.23 No.3

This paper presents the comprehensive transformer design methodology with the winding method of automatic typesuitable for LLC resonant converter. The problem with conventional LLC resonant transformer is that it is difficult toimplement the winding method of automatic type because all windings are wound in one bobbin. Therefore, the LLCresonant transformer, which is capable of the winding method of automatic type to multiple section bobbin withoutinsulation tape and barrier tape, is proposed in this paper and the design procedure of the proposed LLC resonanttransformer is also shown. Modeling and analysis of the proposed LLC resonant transformer using Maxwell 3Dsimulation tool are described in detail and a protype 150W LLC resonant converter using the proposed LLC resonanttransformer manufactured by 3D modelling is also verified through the experimental test. 본 논문은 LLC 공진 컨버터에 적합한 자동화 권선 변압기 설계에 대한 포괄적인 방법에 대해서 나타낸다. 기존의 LLC 공진 변압기는 하나의 보빈에 모든 권선이 감겨져 있기 때문에 자동화 권선 구현이 어렵다는 문제점이 있다. 따라서 본 논문에서는 절연 테이프와 배리어 테이프가 없이 다중 보빈으로 자동 권선이 가능한 LLC 공진 변압기를 제안하였으며 제안한 LLC공진 변압기의 설계 절차에 대해서도 나타내었다. Maxwell 3D 시뮬레이션 툴을 이용하여 제안한 LLC 공진 변압기의 해석및 모델링을 상세하게 기술되었으며 또한 3D 모델링에 의해 제작된 제안한 LLC 공진 변압기를 이용하여 프로타입 150WLLC 공진 컨버터를 실험을 통해 확인하였다.

Analysis of Backward Mode for LLC-based Bidirectional Batteries Charger

생차야,서정진,차한주 대한전기학회 2023 전기학회논문지 Vol.72 No.7

This paper proposes a bidirectional dc-dc converter for the energy storage systems (ESS) that operate in forward and backward mode power direction between the DC bus of the PV system and batteries. A bidirectional dc-dc converter with LLC resonant method has the advantage of simple structure and soft switching. In the forward direction, the LLC resonant converter can realize a normalized gain greater than one or less than one and can operate to reach soft switching zero voltage switching (ZVS), and zero current switching (ZCS) in light load and heavy load at the resonant point. However, in the backward direction only a normalized gain of less than one can be achieved. Since the operation modes of the LLC converter are different between forward and backward modes, the operated switching frequency is also different. Without changing the LLC resonant converter’s basic topology, the backward mode of the LLC converter can be achieving soft switching by operating in a specific switching frequency below the resonant. The backward mode of the LLC converter study in this paper is operated at 0.9 value of normalized switching frequency in order to achieve soft switching ZCS with an easy control method. The backward mode of the LLC resonant converter was analyzed in this paper and verified soft switching by simulation and experiment.

LLC Resonant Converter with asymmetric PWM for hold-up time

Bong-Chul Kim,Ki-Bum Park,Gun-Woo Moon 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

To narrow down the switching frequency variation range of an LLC resonant converter, asymmetric pulse-width modulation (APWM) of the hold-up time is proposed. During the hold-up time, the modulation method of an LLC resonant converter is changed from frequency modulation (FM) to APWM. Since the LLC resonant converter achieves a higher gain with APWM than it does with FM at the same switching frequency, the switching frequency variation range is reduced. Therefore, an optimal design of the magnetic components is possible, resulting in a high efficiency under normal operation and a high power density. The proposed control scheme is applied to an 85 W LLC resonant converter.

평면형 변압기를 사용한 병렬 LLC 공진형 컨버터의 간단한 교차제어기 설계 및 구현

김태완,정세교 전력전자학회 2023 전력전자학회 논문지 Vol.28 No.6

The design and implementation of a simple interleaved controller for LLC resonant converters with a planar transformer is presented. The interleaved operation of a power converter is used to reduce the size of the passive components. It is, however, difficult to achieve the interleaved control of the LLC resonant converter because the frequency control is generally applied to resonant-type converters. A digital control method using a digital signal processor (DSP) is mostly used for the interleaved control. However, it is still complex to implement because of the additional processing for the analog feedback signals. The size, cost and power consumption of a DSP and peripheral devices are also practical issues. This paper describes the design and implementation of the interleaved LLC resonant converter using a commercial analog resonant controller. The interleaved gate pulse generation and over current protection circuits are proposed using this controller. The analysis for the current unbalancing due to the parameter deviations of the resonant circuit components are also provided. The two-phase interleaved LLC resonant converter with a power rating of 1.5kW is implemented to verify the validity of the proposed controller.

LLT 변압기 적용 LLC 직렬공진컨버터 동작특성

이현관,김은수,허동영,이기식,정봉근,강성인 전력전자학회 2006 전력전자학회 논문지 Vol.11 No.5

Operating Characteristics of LLC Series resonant converter with a LLT(Inductor-Inductor-Transformer) transformer is presented. LLT transformer used to combine the inductor and transformer into one unit has the increased leakage inductance in the primary and secondary due to the winging method and the use of the gaped core. The increased leakage inductance in the primary and secondary of LLT transformer can be impacted on the DC voltage gain characteristics of LLC series resonant converter. In the paper, DC gain characteristics and the experimental results of the LLC series resonant converter with a LLT transformer are verified on the simulation based on the theoretical analysis and the 400W experimental prototype. LLT 변압기 적용 LLC 직렬공진컨버터의 동작특성에 대해 설명하였다. 본 논문에서는 1차측 권선과 2차측 권선을 분리하고, 변압기 중간에 공극(Air-Gap)을 삽입한 일체화된 LLT 변압기를 적용하였다. 이와 같이 적용된 LLT 변압기의 경우 1차측 누설인덕턴스만이 증가되는 것이 아니고 2차측 누설인덕턴스 또한 증가되게 된다. 이렇게 증가된 2차측 누설인덕턴스는 전압이득 특성곡선에 있어 LLC 직렬공진컨버터에 적용한 변압기를 사용한 경우보다 전체적으로 높은 전압이득 특성을 가지게 된다. 따라서 본 논문에서는 2차측 누설인덕턴스를 고려한 일체화된 LLT 변압기적용 LLC 직렬공진컨버터에 대해 이론적으로 해석하고 시뮬레이션 하였으며, 400W급 시제품을 제작하여 실험한 결과에 대해 서술하였다.

3-브리지 LLC-LC 공진컨버터 이득특성

김태란(Tae-Ran Kim),박경수(Kyung-Su Park),김은수(Eun-Soo Kim) 전력전자학회 2023 전력전자학회 논문지 Vol.28 No.5

In this paper, a LLC-LC resonant converter with wide output voltage gain characteristics and a control method thereof are presented. The proposed converter could operate in a narrower frequency control range by adding parallel resonant circuits to the previously proposed 3-bridge LLC resonant converter. And the converter is changed to four operation modes according to the switching pattern of the main switch for wide output voltage control. In each operation mode, frequency modulation was performed to control the output voltage, and the morphing control was used to control the stable output voltage in mode transition. We analysed the gain and impedance characteristics of the 3-bridge LLC-LC resonant.

Tightly Regulated Current-fed LLC Resonant Converter Employing Spread Spectrum Technique to Reduce Electromagnetic Interference

Mina Kim,Hwa-Pyeong Park,Sang Gyu Cheon,Chang Ui Lee,Jee-Hoon Jung 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

A spread spectrum technique (SST) can effectively reduce the conductive noise by spreading the operating frequency without additional components. However, the input-output voltage gain of the resonant converter is highly sensitive to the operating frequency, it is hard to apply the SST to the resonant converter. In this paper, the SST is employed to a current-fed LLC resonant converter with low output voltage ripple. The resonant network design is provided to obtain the insensitive voltage gain according to the operating frequency, which can reduce the output voltage ripple caused by the SST operation. The proposed current-fed LLC resonant converter with the SST is implemented to a 200-W prototype, and its performance is be evaluated in terms of the output voltage ripple and the EMI reduction by experiments.

A New Tightly-Regulated Dual-output LLC resonant converter

Yoon Choi,Sang-Ho Cho,Sung-Soo Hong,Kwang-Seung Cho,Dong-Sung Oh,Sang-Kyoo Han 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

A New Tightly-Regulated Dual output LLC resonant converter is proposed in this paper. The proposed converter can get tightly regulated dual-output voltages by both pulse frequency modulation (PFM) and pulse width modulation (PWM) using only one control IC compared with the conventional LLC resonant converter. Therefore, it features a simpler structure, less mass, and lower cost of production. Furthermore, since all power switches are turned on under zero-voltage switching (ZVS) condition, it has several favorable advantages such as a high-efficiency, low switching loss, improved electromagnetic interference (EMI), and reduced burden on the cooling system. This paper presents a dual-output LLC resonant converter applicable to the 40” LCD TV power supply.