Development of Ultra-High Efficiency, High-Density 3kW Single-Phase AC-DC Converter
The project aims to develop a high-efficiency and high-density AC-DC power supply with 48V output for telecom and data center applications. Due to the limit of Si devices, it is hard to further improve the performances of the commercial rectifier products. With the implementation of wide band gap (wbg) devices and soft-switching techniques, the power supply can operate with high frequency and lower power loss, thus leading to higher power density and power efficiency simultaneously. The proposed rectifier can achieve 98% peak efficiency with small size and weight, which is regarded as the next generation medium rectifier for telecom and data center applications.
Prototype and testing waveforms of the two-stage 3kW GaN-based rectifier
The project aims to develop a next generation of rectifier power supply with 98% peak efficiency and high density based on new wide band gap devices. To achieve this, approaches in several aspects are conducted:
- System architecture: Single-stage architecture consisting of 277 Vac â€“ 480 Vdc totem-pole power factor correction (PFC) converter, and 480 Vdc â€“ 48 Vdc isolated LLC DC-DC converter is designed and implemented.
- Power semiconductor devices: to enhance the switching frequency and reduce the power loss, gallium-nitride (GaN) devices are implemented with high-voltage (HV) GaN FETs on the primary side, and low-voltage (LV) GaN FETs on the secondary side. Further, advanced packaging and layout techniques are conducted to improve parasitics and associated switching losses.
- Control Strategies: for the PFC stage, full-line-cycle zero-voltage-switching (ZVS) is achieved with critical conduction mode operation and variable on-time control. For the isolated DC-DC stage, LLC converter is designed at resonant point to achieve theoretically highest efficiency with ZVS in all primary devices and zero-current switching (ZCS) in all secondary devices.
- Passive components: Innovative magnetic devices are designed to fully utilize the superior switching performance of WBG devices. Also, the achieved higher switching frequency enables smaller magnetics. Modern magnetic materials such as nanocrystalline and powder cores are used to minimize passive losses and size
- Power quality and EMI filter design: circuit noise sources are analyzed and input filter is designed to meet the conducted EMI, THD and power quality requirements. Also, the filter loss and thermal performance will be measured and optimized.
How WBG Can Help
HV and LV GaN FETs are used in the project due to the superior characteristics including lower on-resistance, higher temperature capability, faster switching speed, etc. With the GaN devices, both the PFC and the isolated DC-DC converter can achieve lower conduction loss with the low on resistance, and minimized switching loss by adopting soft switching technique. Also, GaN devices allow the converter to operate at very high switching frequency, which reduces the size and weight of passive components like inductor, transformer, and EMI filter significantly. In addition, higher temperature capability enables thermal design to realize higher requirement.
 Huang, Qingyun, and Alex Q. Huang. "Review of GaN totem-pole bridgeless PFC." CPSS Transactions on Power Electronics and Applications 2.3 (2017): 187-196.
 Zhang, Weimin, "Energy-efficient and power-dense DC-DC converters in data center and electric vehicle applications using wide bandgap devices." PhD diss., University of Tennessee, 2015.
 Sun, Jingjing, et al. "Inductor design and ZVS control for a GaN-based high efficiency CRM totem-pole PFC converter." IEEE Applied Power Electronics Conference and Exposition (APEC). IEEE, 2019.
 Strain, Nathan N., et al. "ZVS analysis of a GaN-based series-parallel dual Transformer LLC resonant converter." IEEE 7th Workshop on Wide Bandgap Power Devices and Applications (WiPDA). IEEE, 2019.