Low-turn-ratio planar transformer design in a rich-source, high-tuning ratio LLC resonant converter
At present, large data center [1] has become a big trend.LLC resonant converter as the core component of large data center has great theoretical and practical significance to support the construction of large data center, solve the problem of high energy consumption, high carbon emission and green development large 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 is ( using an LLC resonant converter) will also be 400 V:12 or 380 V:12 [2]. LLC resonant converter refers to the high voltage ratio structure in both the second generation power supply system for data centers, which is widely used today, and the third generation power supply system and Internet green energy, which will be used in the future. In addition, to meet the development trend of blade servers, bulk components such as transformers and LLC inductors must have low-height planar structures and planar magnetic integral structures.
The current method for achieving high transformation ratios in resonant LLC converters is to magnetically integrate multiple transformers with fewer 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 PCB windings are used, this leads to an increase in the number of layers of PCB windings, which not only complicates the winding design and reduces its reliability, but also makes it much more difficult to analyze the effect of proximity between the converter windings and winding losses. In addition, using a PCB winding structure with a large number of layers not only results in high PCB manufacturing cost, but also creates large losses in the converter winding conductor when passing a large current, and the heat generated by losses is difficult to dissipate, resulting in high PCB temperature, reduces converter reliability and life, and limits the current density in the conductor, making it difficult to carry large currents over long periods of time to meet the low-current demands of CPU and GPU servers. The current density in the conductor is very limited, making it difficult to carry large currents over long periods of time to meet the low-voltage, high-current converter power requirements for CPUs and GPUs.
To solve the existing problems, this article proposes a low-ratio planar transformer, which can reduce the number of winding turns of a planar transformer while ensuring a high variable ratio of the resonant LLC converter, and also reduce the number of core components and the overall volume, which increases the efficiency of the transformer.
First, the operating principle and amplification characteristics of the main circuit of a resonant LLC converter with a high transformation ratio are analyzed, the parameters of the groove of the resonant converter are calculated, then the structure of the core of a planar transformer with a low transformation ratio and its winding circuit on a printed circuit board are given, a parametric calculation of the transformer is carried out to calculate 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.