High Light-Load Efficiency Power Conversion Scheme Using Integrated Bidirectional Buck Converter for Paralleled Server Power Supplies
Abstract
This paper proposes a new power conversion scheme for paralleled server power supplies. The snubber capacitor voltage is utilized for the secondary voltage source, from which bidirectional buck converter provides output power to the load under a very light-load condition. To increase the energy of the secondary voltage source, an additional voltage bus is connected between the snubber capacitors from each power supply. The main advantage of the proposed scheme is that high efficiency can be achieved especially under a very light-load condition because of the lowswitching and core loss achieved by using the buck converter instead of the conventional structure composed of a primary inverter, an isolation transformer, and a secondary rectifier. Furthermore, the buck converter is integrated into the secondary rectifier circuits, so additional components are minimized. The validity of the proposed converter is confirmed by the experimental results from two 12-V/750-W prototype modules.
PROPOSED SYSTEM:
In this paper, a new power conversion scheme considering paralleled modules is proposed. Under a light-load condition, the redundant power supply enters standby mode as in the CR concept. However, under a very light-load condition, only a nonisolated buck converter in the secondary side of the remaining power supply provides the output power, which is different from the CR concept. Thus, the operating components and the related power losses are more minimized. Also, to achieve high power density, the buck converter is integrated with the rectifier circuits in the secondary side of the PSFB converter. Furthermore, in the proposed concept, the voltage source in the buck converter is maximized by using an additional voltage bus connecting between the snubber capacitors of each module.
EXISTING SYSTEM:
To improve the light-load efficiency in a PSFB converter, various researches has been presented. Discontinuous conduction mode operation reduces the operating duty ratio, which results in low core and switching losses. Also, the conduction loss in the body diode of the synchronous rectifiers (SRs) is reduced by using AND-gated signals for SRs. the gate driving voltage of power MOSFETs and the operating voltage of controller ICs are controlled according to the load condition. Below a certain load condition, the gate driving voltage is decreased so the gate driving loss and controller driving loss are decreased. A maximum duty point tracking method is applied. The link voltage is adjusted to keep the maximum duty ratio based on the link and output voltage, which reduce the circulating and switching losses. a three-level converter was studied. The switches in that converter must conduct about twice the current as those in a two-level converter, but it has low switch voltage stress that is half the input voltage. Thus, a three-level converter has low switching loss which means higher light-load efficiency, but higher conduction loss which means lower heavy-load efficiency. The power converter operates according to the load power with maximum efficiency by changing the dc-link voltage and the switching method. According to the load condition, the switching mode of the PSFB converter is changed into the pulse width modulation and burst modes. Thus, the light-load efficiency is increased by minimizing the switching and circulating conduction losses. Another approach is to consider paralleled modules, not limited to a single module. The cold-redundant (CR) concept is proposed. Under a certain light-load condition, the dc/dc converter in the redundant power supply is turned off and enters standby mode, so the remaining modules provide the total output power, which eliminates the switching, core, and control losses in the dc/dc converter of the redundant power supply.
CONCLUSION
A new power conversion scheme was presented using paralleled modules. The proposed converter has high efficiency, especially under a very light-load condition, achieved by using an integrated bidirectional buck converter. The buck converter was integrated easily by using switches instead of snubber diodes. Also, by connecting the snubber voltage from each module and by using it as additional voltage bus, an auxiliary voltage source was effectively obtained for the buck converter. The circuit operation and design considerations were illustrated in this paper. The validity of the basic operational principles was confirmed by the experiment with two 12-V/750-W prototype modules. The experimental results demonstrate that the proposed converter has higher light-load efficiency than the conventional converter.
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