Limitations and Solutions of LLC Topology in High Power High Step-up Applications on Aircraft

In modern aircraft, there is a huge demand for high power high step-up (HPHS) DC-DC conversion from 28V to 270V or even higher voltage, such as Start Power Unit (SPU) and backup power supply systems. Due to high efficiency, high power density, low EMI, and soft-switching capability, LLC resonant topology are receiving special attention. However, when it comes to HPHS applications, original LLC resonant topology will encounter some limitations, resulting poor parameter controllability, low power density and low efficiency. This paper first analyzed the fundamental causes of these limitations. Then, solutions are given in terms of circuit topology and system architecture, respectively. A 5kW 2SV/222V prototype was designed, fabricated and tested. The feasibility of proposed solutions is validated.