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As a key factor in the design of a voltage-adjustable LLC resonant converter, frequency regulation range is very important to the optimization of magnetic components and efficiency improvement. This paper presents a novel optimal design method for LLC resonant converters, which can narrow the frequency variation range and ensure high efficiency under the premise of a required gain achievement. A simplified gain model was utilized to simplify the calculation and the expected efficiency was initially set as 96.5%. The restricted area of parameter optimization design can be obtained by taking the intersection of the gain requirement, the efficiency requirement, and three restrictions of ZVS (Zero Voltage Switch). The proposed method was verified by simulation and experiments of a 150 W prototype. The results show that the proposed method can achieve ZVS from full-load to no-load conditions and can reach 1.6 times the normalized voltage gain in the frequency variation range of 18 kHz with a peak efficiency of up to 96.3%. Moreover, the expected efficiency is adjustable, which means a converter with a higher efficiency can be designed. The proposed method can also be used for the design of large-power LLC resonant converters to obtain a wide output voltage range and higher efficiency.
Junhao Luo; Junhua Wang; Zhijian Fang; Jianwei Shao; Jiangui Li. Optimal Design of a High Efficiency LLC Resonant Converter with a Narrow Frequency Range for Voltage Regulation. Energies 2018, 11, 1124 .
AMA StyleJunhao Luo, Junhua Wang, Zhijian Fang, Jianwei Shao, Jiangui Li. Optimal Design of a High Efficiency LLC Resonant Converter with a Narrow Frequency Range for Voltage Regulation. Energies. 2018; 11 (5):1124.
Chicago/Turabian StyleJunhao Luo; Junhua Wang; Zhijian Fang; Jianwei Shao; Jiangui Li. 2018. "Optimal Design of a High Efficiency LLC Resonant Converter with a Narrow Frequency Range for Voltage Regulation." Energies 11, no. 5: 1124.
The gain of a LLC resonant converter can vary with the loads that can be used to improve the efficiency and power density for some special applications, where the maximum gain does not apply at the heaviest loads. However, nonlinear gain characteristics can make the converters unstable during a major disturbance. In this paper, the stability of an LLC resonant converter during a major disturbance is studied and a trigger control scheme is proposed to improve the converter’s stability by extending the converter’s operational range. Through in-depth analysis of the gain curve of the LLC resonant converter, we find that the switching frequency range is one of the key factors determining the system’s stability performance. The same result is also obtained from a mathematical point of view by utilizing the mixed potential function method. Then a trigger control method is proposed to make the LLC resonant converter stable even during a major disturbance, which can be used to extend the converter’s operational range. Finally, experimental results are given to verify the analysis and proposed control scheme.
Zhijian Fang; Junhua Wang; Shanxu Duan; Jianwei Shao; Guozheng Hu. Stability Analysis and Trigger Control of LLC Resonant Converter for a Wide Operational Range. Energies 2017, 10, 1448 .
AMA StyleZhijian Fang, Junhua Wang, Shanxu Duan, Jianwei Shao, Guozheng Hu. Stability Analysis and Trigger Control of LLC Resonant Converter for a Wide Operational Range. Energies. 2017; 10 (10):1448.
Chicago/Turabian StyleZhijian Fang; Junhua Wang; Shanxu Duan; Jianwei Shao; Guozheng Hu. 2017. "Stability Analysis and Trigger Control of LLC Resonant Converter for a Wide Operational Range." Energies 10, no. 10: 1448.
Three kinds of fiber reinforced plastic (FRP) composites, including modified polyurethane resin (LGD), epoxy resin (E44) and modified unsaturated polyester resin (D33) glass-fiber reinforced plastics, were subjected to a 5000 h multi-factor accelerated aging test according to the power industry standard. To examine aging resistance and thermal stability of transmission towers made by these three composites, relevant bending properties, thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG), activation energy, as well as microscopic morphology were revealed. The results showed that for these composites, bending modulus retention rates were higher than 94% under the aging test and that of the LGD was highest. Additionally, the onset degradation temperature, temperature at maximum rate of weight loss and T5% reduced at 5000 h, with D33 having highest value and lowest decline rate. The activation energy was calculated with the Bagchi, Coats-Redfern and Broido method, respectively. Although the activation energy of all composites decreased after test, the D33, LGD materials had the highest activation energy which enjoys slight decline. Analysis of the whole experimental results suggested that D33 and LGD composites have good aging resistance, whose basic performance could still perform well after 5000 h aging test, so they can be used to composite towers and applied to engineering practice.
Jianwei Shao; Junhua Wang; Mengjiao Long; Jiangui Li; Yayun Ma. 5000 h Multi-Factor Accelerated Aging Test of FRP Made Transmission Tower: Characterization, Thermal Decomposition and Reaction Kinetics Study. Polymers 2017, 9, 170 .
AMA StyleJianwei Shao, Junhua Wang, Mengjiao Long, Jiangui Li, Yayun Ma. 5000 h Multi-Factor Accelerated Aging Test of FRP Made Transmission Tower: Characterization, Thermal Decomposition and Reaction Kinetics Study. Polymers. 2017; 9 (12):170.
Chicago/Turabian StyleJianwei Shao; Junhua Wang; Mengjiao Long; Jiangui Li; Yayun Ma. 2017. "5000 h Multi-Factor Accelerated Aging Test of FRP Made Transmission Tower: Characterization, Thermal Decomposition and Reaction Kinetics Study." Polymers 9, no. 12: 170.