Research on Modular LLC Converters for High-Voltage DC Power Supply Systems in More Electric Aircraft

With increasing load power capacity in more electric aircraft, voltage levels of high-voltage power supply systems are correspondingly elevated. To better adapt to this trend, aviation high-voltage DC converters can adopt multi-module series-parallel configurations to enhance system power rating and power density. Modular multilevel LLC resonant converters demonstrate promising development prospects, effectively resolving excessive voltage stress caused by high-voltage input environments while increasing system power through modular parallelization. However, limitations in current component manufacturing processes lead to deviations in resonant component parameters, significantly reducing system reliability and potentially causing system collapse. To address these issues, an adaptive algorithm based on the functional relationship between duty cycle and load current is established. Symmetrical phase-shift control compensates for uneven power distribution caused by parameter deviations while effectively reducing output current ripple. In parallel-connected converter systems, DC circulating currents can occur at the output, which leads to increased ripple in individual converters. To mitigate the impact of DC circulating currents, the system employs a method analogous to droop control by connecting small resistors in series to address the issue.