A High Efficiency and High Power Density DC Transformer Topology With Output Regulation Capability

LLC based dc transformer (DCX) with fixed voltage ratio is a suitable candidate for telecommunication equipment and data center for its high efficiency. Traditionally, a pulsewidth modulation (PWM) regulator are employed to achieve voltage regulation capability. However, the two-stage structure makes sacrifice in efficiency. Hence, this article proposes a novel partial regulated DCX with fixed switching frequency. The input power issplit into two parts in the proposed converter. Most power is delivered by the main DCX and only a small part is converted by an auxiliary DCX cascading with a PWM converter. The output voltage of DCX can be regulated by the PWM converter. Therefore, the efficiency sacrifice is minimized and high efficiency can be obtained. The operating principle and design consideration are analyzed to achieve an optimal global efficiency. The source-impedance-equivalent method is also proposed to simplify the small-signal modeling process. Based on the proposed topology, a prototype with 360–440V input and 12V/500-W output is demonstrated. A peak efficiency of 96.3% and a power density of 148 W/in ³ are achieved on the prototype. A total 2% efficiency improvement and 55% power density improvement can be obtained compared with the conventional two-stage structure.