| With the rapid development of the information technology industry,the market demand for offline power supplies is also increasing,especially for computers,LED display power supplies,electric vehicles,communications,computer servers,and data centers.On the one hand,in order to meet the AC input voltage of 85-265 Vac worldwide,the pre-stage PFC circuit part of the commonly used offline power supply usually takes 400 V as the DC output voltage.On the other hand,in the data center,the 400 V high-voltage DC power supply architecture can significantly reduce the line loss on the bus due to fewer power conversion times and lower DC bus current,which is one of the trends of the future data center power supply architecture.It can be seen that the DC bus voltage of 400 V is not only the transition bus voltage output by the pre-stage PFC in the commonly used offline power supply,but also the trend of the bus voltage in the future data center power supply architecture.However,most IT equipment requires isolated low-voltage,high-current output,such as high-power LED display power supply requires 4V/160 A output.Therefore,it is of great academic significance and industrial value to study the high-efficiency realization technology of 400 V input high-step-down ratio low-voltage high-current output DC transformers.However,the current DC/DC converter under the background of 400 V DC bus voltage has the following problems:(1)The power and efficiency of the isolated DC/DC converter with high step-down ratio are low,and it is difficult to meet the increasing power and efficiency requirements;(2)The multi-level conversion DC transformer in the data center restricts the improvement of its overall efficiency.Therefore,combined with the project requirements,this paper takes the high-power LED display power supply(400V to 4V/160A)application as traction,taking into account the requirements of the data center 400 V high-voltage DC power supply architecture for conversion efficiency and power density,using Ga N HEMT as the primary side switch tube,combined with planar matrix transformers and magnetic integration technology,to carry out research on high-step-down ratio low-voltage high-current output DC transformers.First,compared with other soft-switching converter topologies,LLC resonant converters use the resonant elements in the converter to make the voltage or current cycle zero-cross,and can achieve zero-voltage turn-on on the primary side and zero-current turn-off on the secondary side within the full load range,so it has higher conversion efficiency and power density.In this paper,combined with the characteristics of high voltage input,low voltage and high current output of high step-down ratio DC transformer,in order to achieve high efficiency and high power density,the half-bridge LLC resonant converter is determined as the main circuit topology,and its working principle is analyzed in detail.Then,combined with the project requirements,a preliminary design and optimization of the high step-down ratio DC transformer with 4V/160 A output was made,focusing on the design of the transformer part,aiming at the problems of large AC terminal loss,large leakage inductance,low power density and limited layout of secondary synchronous rectifier tubes in traditional wound transformers,the design and optimization of planar matrix transformers are studied.First of all,a quad-split planar transformer with the primary side of the transformer in series and the secondary side rectified in parallel is used to evenly disperse the large current of the secondary side into each sub-transformer,effectively reducing the AC terminal loss of the secondary winding and the leakage inductance of the transformer,and improving the efficiency and power density of LLC resonant converters.Then,based on the four-split planar transformer,the magnetic integration and synchronous rectifier integration technology are used to further optimize the leakage inductance,AC terminal loss and power density.The traditional wound single transformer prototype,the four-split planar transformer prototype and the magnetic integrated four-split transformer prototype were designed in a step-by-step optimization manner.The experiments proved the effectiveness and advancement of the proposed scheme.Finally,combined with the above research results,in order to meet the project efficiency index,a magnetic integrated six-split transformer scheme is designed,which optimizes the magnetomotive force between the primary winding and the secondary winding,and greatly reduces the conduction loss of the primary winding,secondary winding and synchronous rectifier,as well as the AC terminal loss of the secondary winding of the transformer.The laboratory built an optimized design prototype of a 400 V to 4V/160 A magnetic integrated six-split transformer,which achieved 96.84% peak efficiency and 96.22% full load efficiency,meeting the project efficiency index of high-power LED display power supply with 4V/160 A output.Compared with the current two-stage high step-down ratio solution for data centers by well-known teams at home and abroad,the full-load efficiency of this solution is improved by at least 2 percentage points.Therefore,the research results can also provide a new feasible reference scheme for high step-down ratio DC transformers in data centers. |
