Low-turnover planar transformer design in a rich-source, high-tuning LLC resonant converter

Nowadays, large-scale data center [1] has become a big trend. LLC resonant converter, as the core component of large-scale data center, has great theoretical and practical significance to support the construction of large-scale data center, solve the problem of high energy consumption, high carbon emission and green development of large-scale data center. For the currently used second-generation data center power supply system, the voltage ratio of the voltage regulator (VR, LLC resonant converter) is 48V:1V, and for the future third-generation data center and green Internet power supply system, the voltage ratio of the DC/DC converter part (using LLC resonant converter) will also be 400V:12 or 380V:12 [2]. LLC resonant converter belongs to the high voltage ratio structure in both the second-generation data center power supply system, which is widely used today, and the third-generation and green Internet power supply system that will be used in the future. In addition, to meet the development trend of blade servers, bulk components such as transformers and inductors of LLC converters must adopt low-height planar structures and planar magnetic integrated structures.

An existing method for achieving high transformation ratios in resonant LLC converters is to magnetically integrate several transformers with a smaller number of turns into a single-stage topology. ^[3]The total number of turns of conventional transformers reaches 40 turns or even more.^[4-5], and if printed circuit board (PCB) windings are used, this leads to an increase in the number of PCB winding layers, which not only complicates the winding design and reduces their reliability, but also significantly complicates the analysis of the proximity effect between the converter windings and winding losses. Furthermore, using a PCB winding structure with a large number of layers not only leads to high PCB manufacturing costs, but also creates large losses in the converter winding conductor when passing large currents. The heat generated by the losses is difficult to dissipate, leading to a high PCB temperature rise, reducing the reliability and service life of the converter, and also limits the current density in the conductor, making it difficult to pass large currents over a long period of time to meet the low-current power requirements of CPUs and GPUs. The current density in the conductor is very limited, making it difficult to pass large currents over a long period of time to meet the low-voltage and high-current power requirements of the converter for CPUs and GPUs.

To solve the existing problems, this paper proposes a low-ratio planar transformer, which can reduce the number of turns of the planar transformer winding while maintaining a high variable ratio of the LLC resonant converter, and reduce the number of core components and the overall volume, thereby improving the efficiency of the transformer.

First, the working principle and gain characteristics of the main circuit of the high-ratio LLC resonant converter are analyzed, the slot parameters of the resonant converter are calculated, then the core structure of the low-ratio planar transformer and its winding diagram on the printed circuit board are given, the parametric calculation of the transformer is carried out to calculate the losses and efficiency, a 3D model of the transformer is built and magnetic finite element modeling is carried out, which proves that this planar transformer is feasible and the efficiency of the planar transformer.