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

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

Department of Control and Instrumentation Engineering, Korea National University of Transportation, Chungju (KS001) 27469, Korea
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Energies 2019, 12(20), 3833; https://doi.org/10.3390/en12203833
Received: 26 August 2019 / Revised: 21 September 2019 / Accepted: 27 September 2019 / Published: 10 October 2019
(This article belongs to the Special Issue Advances in High-Efficiency LLC Resonant Converters)
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. View Full-Text
Keywords: LLC Converter; Duty Control; Extended Describing Function; Small Signal Modeling LLC Converter; Duty Control; Extended Describing Function; Small Signal Modeling
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Humaira, H.; Baek, S.-W.; Kim, H.-W.; Cho, K.-Y. Circuit Topology and Small Signal Modeling of Variable Duty Cycle Controlled Three-Level LLC Converter. Energies 2019, 12, 3833.

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