3-Bridge LLC resonant converter for achieving wide output voltage control range based on topology morphing
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ORIGINAL ARTICLE
3‑Bridge LLC resonant converter for achieving wide output voltage control range based on topology morphing Sang‑Jae Yoo1 · Min‑Ji Kim1 · Eun‑Soo Kim1 · Yong‑Seog Jeon1 Received: 21 June 2020 / Revised: 14 August 2020 / Accepted: 23 August 2020 © The Korean Institute of Power Electronics 2020
Abstract In this paper, a control method for a 3-bridge LLC resonant converter operating with a wide output voltage control range is described. Duty changes that stem from switching devices cause topology transitions that allow the converter to shift sequentially across four operating modes, where the primary resonant tank circuits and the secondary terminals can be connected in parallel or in series making it possible to achieve a wide controllable output voltage (7.5–120 VDC). During topology mode transitions, morphing control within narrow hysteresis bands, which is achieved by varying the switching frequency and duty of the switching devices, maintains a tight regulation without noticeable output voltage transients. To verify the performance of the proposed converter, a 5-kW 700 VDC input prototype with an output voltage ranging from 7.5 to 120 VDC is built and tested. Keywords DC–DC converter · LLC resonant converter · Battery charger · Topology morphing control · Wide ranges
1 Introduction Recently, the utilization of industrial devices such as battery-powered golf-carts and forklifts has rapidly increased. Therefore, there is an increasing demand for power charging converters that operate with wide outputs (VBATT: 12 VDC/24 VDC/48 VDC/96 VDC) to charge different types of lead-acid batteries. In addition, power converters that operate with a high efficiency and a high switching frequency are required to improve power density. LLC resonant converters with soft switching operation characteristics that operate with a wide input/output voltage gain are considered to be advantageous topologies for achieving high efficiency and high power density [1]. However, when an output voltage range is greater than twice the nominal output voltage, increases in the LLC gain characteristics under all load conditions require a significant reduction in the transformer magnetization inductance, which increases the conduction losses [2–4]. To solve the aforementioned problems, a two-stage DC–DC converter composed of a hard switching buck/boost * Eun‑Soo Kim [email protected] 1
Department of Electrical and Electronics Engineering, Jeonju University, Jeonju, Korea
converter for output voltage control and an unregulated LLC converter for electrical isolation has been used in various applications [5]. However, a major drawback of two-stage converters is the increased number of components, which increases the intricacy and cost of the circuit. Another approach to deal with a very wide output-voltage range is to employ a topology transition, i.e., a topology change (half bridge ↔ full bridge). By changing the topology, the gain of the converter is changed. The half-bridge (HB) LLC topology is used in the low output voltage
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