Dual-Bridge LLC Resonant Converter With Fixed-Frequency PWM Control for Wide Input
Abstract
This paper proposes a dual-bridge (DB) LLC resonant converter for wide input applications. The topology is anintegration of a half-bridge (HB) LLC circuit and a full-bridge(FB) LLC circuit. The fixed-frequency PWM control is employed and a range of twice the minimum input voltage can be covered. Compared with the traditional pulse frequency modulation(PFM) controlled HB/FB LLC resonant converter, the voltagegain range is independent of the quality factor and themagnetizing inductor has little influence on the voltage gain,which can simplify the parameter selection process and benefit thedesign of magnetic components as well. Over the full load range,zero voltage switching (ZVS) and zero current switching (ZCS)can be achieved for primary switches and secondary rectifierdiodes, respectively. Detailed analysis on the modulation scheduleand operating principle of the proposed converter is presentedalong with the converter performance. Finally, all theoreticalanalysis and characteristics are verified by experimental resultsfrom a 120V-240V input 24V/20A output converter prototype.
EXISTING SYSTEM:
LLC resonant converter, which is capable of realizing soft-switching from zero to full loads and achieving high efficiency and high power density, has become a research hotspot in recent year. Normally, conventional half-and full-bridge LLC converters work with variable frequency control. The operating frequency range has to be extended or the inductor ratio has to be decreased in order to obtain a wide input voltage range which is very challenging to design and optimize magnetic components . This may cause many undesired problems such as low power density andhigh conduction losses. Therefore, the conventional LLCconverter is not suitable for wide input applications. Combining the three-level circuit with an LLC resonant tank,many types of three-level LLC (TL LLC) resonant converterscapable of achieving a wide input range have been proposed. A simple TL LLC resonant dc/dc converter with onlyone magnetic component is proposed in, which canachieve a wide input/output range within a narrow frequencyrange because of the two-stage resonance. Different from theTL LLC resonant converters with one resonant tank, thetopology discussed is a TL LLC resonant converterconsisting of two half-bridge (HB) LLC series resonantconverters in series, but sharing the same resonant inductor andtransformer. As an extension of, another TL LLC converter with one resonant tank is proposed in , where theresonant frequency is twice as high as the switching frequency,decreasing the size of resonant components and increasing thepower density. However, the frequency variations of theseaforementioned converters are still relatively large, e.g., 88-150kHz in , which is challenging for the optimization ofmagnetic components. By using the new modulation strategies,a TL isolated full-bridge (FB) LLC converter that can operate atfixed-frequency is presented in [19], which can operate inentire two-level or three-level modes depending on the voltagerange. However, a number of switches have to be employed andthe structure is complex. Jin et al proposed a hybrid FB TLLLC converter capable of operating under both three-level andtwo-level modes.
PROPOSED SYSTEM:
This paper proposes a fixed-frequency DB LLC resonantconverter for wide input voltage range applications. Thetopology can be seen as a combination of the HB LLCconverter and the FB LLC converter. The output voltage isregulated by controlling the percentage of operating time of theFB and HB during a switching circle. This converter employsthe fixed-frequency PWM control, and the switching frequencyequals to the resonant frequency, which facilitates the design ofmagnetic elements. Unlike traditional PFM controlled LLCresonant converters, the voltage gain range is independent ofthe quality factor Q. Moreover, the magnetizing inductor haslittle influence on the voltage gain, which means that theparameter design process can be simplified, and themagnetizing inductor can be designed as large as possible toreduce the conduction loss. In addition, all main switches andrectifier diodes are softly switched over the full load range,which significantly decreases the switching loss and the reverserecovery loss.
CONCLUSION
A fixed-frequency controlled DB LLC resonant converter with a wide input range has been proposed in this paper. In theproposed DB LLC resonant converter, two operating modes(HB and FB modes) are identified and utilized to regulate theoutput voltage within a wide input voltage range. Themodulation strategy, operating principle and characteristics areinvestigated in depth. Compared with conventionalPFM-controlled LLC converter, the proposed DB LLCresonant converter adopts the fixed frequency PWM control.The voltage gain range is independent of the quality factor Qand the magnetizing inductance has little impact on the dc voltage gain characteristics. Thus the process of parameterdesign can be simplified and also a larger inductor ratio can bechosen to reduce the conduction loss. The structure and controlstrategy of the DB LLC resonant converter are simplercompared with conventional fixed-frequency TL LLC resonantconverters. The performance of the proposed DB LLC resonantconverter is experimentally verified on a 120V-240V input24V/20A output converter prototype. All primary-side switchesoperate with ZVS and secondary-side diodes turn off with ZCSwithin wide input voltage and full load ranges. Also, gooddynamic performance with respect to input variations and loadchanges can be achieved under the closed-loop control.Therefore, the DB LLC resonant converter is a good candidatefor wide input voltage applications.
REFERENCES
[1] M. M. Jovanovic and B. T. Irving, “On-the-Fly Topology-MorphingControl-Efficiency Optimization Method for LLC Resonant ConvertersOperating in Wide Input- and/or Output-Voltage Range,” IEEE Trans.Power Electron., vol. 31, no. 3, pp. 2596–2608, Mar. 2016.
[2] J. Deng, C. C. Mi, R. Ma and S. Li, “Design of LLC Resonant ConvertersBased on Operation-Mode Analysis for Level Two PHEV Battery Chargers,” IEEE Trans. Mechatronics., vol. 20, no. 4, pp. 1595–1606,Aug. 2015.
[3] D. Moon, J. Park and S. Choi, “New Interleaved Current-Fed ResonantConverter With Significantly Reduced High Current Side Output Filterfor EV and HEV Applications,” IEEE Trans. Power Electron., vol. 30,no. 8, pp. 4264–4271, Jun. 2015.
[4] F. Musavi, M. Craciun, D. S. Gautam and W. Eberle, “Control Strategies forWide Output Voltage Range LLC Resonant DC-DC Converters inBattery Chargers,” IEEE Trans. Vehicular Technology., vol. 63, no. 3,pp. 1117–1125, Jun. 2014.
[5] C. W. Tsang, M. P. Foster, D. A. Stone, and D. T. Gladwin, “Analysis anddesign of LLC Resonant Converters with Capacitor-Diode ClampCurrent Limiting,” IEEE Trans. Power Electron., vol. 30, no. 3, pp.1345–1355, Mar. 2015.
[6] B. Yang, F. C. Lee, A. J. Zhang, and G. Huang, “LLC resonant converter forfront end DC/DC conversion,” in Proc. IEEE APEC Expo., 2002, vol. 2,pp. 1108-1112.
[7] H. Wang, S. Dusmez, and A. Khaligh, “Maximum Efficiency PointTracking Technique for LLC-Based PEV Chargers Through Variable DC Link Control,” IEEE Trans. Ind. Electron., vol. 61, no. 11, pp.6041–6049, Nov. 2014.
[8] Z. Hu, Y. Qiu, Y. F. Liu, and P. C. Sen, “A Control Strategy and Design Method for Interleaved LLC Converters Operating at Variable SwitchingFrequency,” IEEE Trans. Power Electron., vol. 29, no. 8, pp.4426–4437, Aug. 2014.
[9] K. H. Yi, and G. W. Moon, “Novel two-phase interleaved LLCseries-resonant converter using a phase of the resonant capacitor,” IEEETrans. Ind. Electron., vol. 56, no. 5, pp. 1815–1819, May. 2009.
[10] W. Feng, F. C. Lee, and P. Mattavelli, “Simplified optimal trajectorycontrol (SOTC) for LLC resonant converters,” IEEE Trans. PowerElectron., vol. 28, no. 5, pp. 2415–2426, May. 2013.