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In the typical Power over Ethernet (PoE) system, the conventional powered device (PD) with two-pair architecture can only provide power below 20 W to the distant loads, which greatly restricts its applications in many areas. An advanced type of four-pair architecture with an input current balance function for the PoE system is proposed in this paper to not only improve the power level, but also achieve the high conversion efficiency. The steady-state model of the four-pair architecture is built to explore the existing imbalance problem, which is mainly caused by the structure and impedance inconsistency. The proposed four-pair architecture consists of two main converter modules operated in parallel. An input current balance scheme is adopted to reduce the difference of both primary currents, which can increase the transmission power and improve the current sharing performance. Furthermore, the small-signal model of the paralleled converters with an input current balance control strategy is constructed to give a design guideline for the control loop. Finally, a 50-W prototype is built and tested to verify the effectiveness of the presented architecture and control strategy.
Date of Publication: May 2013