Single-stage LLC AC/DC converter with wide input range and low bus voltage
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ORIGINAL ARTICLE
Single‑stage LLC AC/DC converter with wide input range and low bus voltage Jingxiang Gao1,2 · Junhong Zhang1 · Zhongni Zhu3 · Qingguo Song3 Received: 26 May 2020 / Revised: 28 August 2020 / Accepted: 31 August 2020 © The Korean Institute of Power Electronics 2020
Abstract The traditional single-stage boost LLC resonant AC/DC converter has been widely studied due to advantages such as few power stages, high power factor, and soft switching. However, it also has several disadvantages, such as a low and narrow input voltage, a DC bus voltage that is much higher than the input voltage, and high stress of the switching devices. Therefore, it is generally used in power grids under 110 V. In order to overcome the above problems, this paper proposed a buck-boost LLC resonant AC/DC converter for both 110 V and 220 V power grids. In addition to its traditional structure, the proposed converter has the advantages of a wide input voltage range and a low bus voltage. The proposed converter adopts the PFM–PWM hybrid control strategy. In this paper, the working principle of the proposed converter is analyzed in detail, the realization of the power factor correction mechanism and the soft switching are described, and the design methods of the key parameters are given. Finally, an experimental prototype with a 110 V-250 V input and a 48 V/100 W output is built. Experimental results verify the correctness of the theoretical analysis of the converter and its applicability to power grids. Keywords Single-stage converter · Buck-boost · LLC · PFC · Wide input range · Low bus voltage
1 Introduction DC converters based on LLC resonance [1–3] have been widely used in electric vehicle charging, LED driving, solar photovoltaic panels, household appliances, consumer electronics, etc. [4–8]. Due to advantages such as soft switching, high efficiency, and electromagnetic isolation [9, 10], the LLC resonant circuit has been further studied in single-stage AC/DC converters. The traditional single-stage boost LLC resonant AC/ DC converter was proposed and studied in Refs. [11–13]. It eliminates large capacity electrolytic capacitors after the bridge rectifier. In order to realize power correction, an inductor is inserted after the bridge rectifier, and the inductor current works in the discontinuous current mode (DCM). To realize the DCM, the falling slope of the current must be * Jingxiang Gao [email protected] 1
School of Electrical Engineering, Naval University of Engineering, Wuhan, China
2
Air Force Early Warning Academy, Wuhan, China
3
Wuchang Shouyi University, Wuhan, China
greater than the rising slope. That is, the DC bus voltage is greater than 2 times the input voltage peak value, and the front part of the circuit operates in the boost mode. The disadvantage of this scheme is that the input voltage of the converter is low and narrow, usually only 80–130 V. When applied to a 220 V power grid, the DC bus voltage is close to or more than 900 V. This results in high requirements for the voltage stress
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