New hybrid control technique to improve light load efficiency while meeting the hold-up time requirement for two-stage server power

The main theme of this paper is to propose a new hybrid control technique to improve the light load efficiency and meet hold-up time requirement of the server power without additional sensors or auxiliary circuits. The server power consists of PFC and phase-shift full-bridge converter. The proposed hybrid control technique on-line controls the DC-link bus voltage of power factor corrector (PFC) to retain the maximum duty operation of phase-shift full-bridge converter. Therefore the efficiency under light load condition can be improved which is contributed by the reduction of circulating loss and switching losses of the converter. To meet the hold-up time requirement, the DC-link bus voltage is controlled to be its nominal value under heavy load conditions. The specifications of the server power supply include: AC input voltage = 110/220 V, DC output voltage = 12 V and output power = 480 W. Experimental results show that the efficiency can be improved up to 3% under light load conditions and meet the hold-up time requirement under whole load conditions. These results confirm the effectiveness of the proposed hybrid control technique.