Abstract
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.
Highlights
LLC resonant converters are widely used for their advantages of high efficiency, high power density, easy implementation of magnetic integration, no need for a filter inductor for the output side, and low EMI [1,2,3,4,5]
There is a problem of a wide frequency regulating range [6] for the design of a voltage-adjustable converter, which will lead to increased transformer size and conduction losses [7,8] and is not conducive to the optimization of magnetic components and efficiency improvement [9]
In the optimal design of an LLC resonant converter, the frequency variation range should be reduced and high efficiency needs to be ensured under the premise of satisfying the required gain
Summary
LLC resonant converters are widely used for their advantages of high efficiency, high power density, easy implementation of magnetic integration, no need for a filter inductor for the output side, and low EMI [1,2,3,4,5]. A method [17] based on full mode time-domain analysis was proposed to achieve different output voltage ranges by combinations of different modes with high accuracy It works in various combinations of modes, which is not conducive to performance optimization of the converter, with an increased complexity of the design process. The method can reach 1.455 times the normalized voltage gain in the frequency variation range of about 56 kHz. Reference [20] presented a design method for a high efficiency LLC resonant converter with a wide output voltage. The method can reach 1.41 times the normalized voltage gain in the frequency variation range of about 38 kHz. This paper proposes an optimal design method for LLC resonant converters that can narrow the frequency range and ensure high efficiency under the premise of obtaining the required gain.
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