A Battery-Based Auxiliary Power System for an All-Electric Aircraft: A Novel Converter Configuration

In all-electric airctaft, the Auxiliary Power Units (APU) based on fossil fuels are replaced by energy storage systems equipped with batteries or fuel cells. This paper proposes a novel 115V(rms), 400 Hz DC/AC converter for a 5 kW APU of a lightweight all-electric aircraft. The proposed DC/AC converter employs a Five-Level Cascaded H-Bridge (5-LCHB) supplied by a Triple-Active Bridge (TAB). The TAB allows the independent control of its two output ports while connected to a single electrochemical battery pack. The three-winding high-frequency transformer provides galvanic isolation, endowing reliability to the conversion system. The inherent decoupling condition established between the TAB output ports is modelled, and the proposed DC/AC converter design is assessed with a co-simulation study on PLECS and Matlab/Simulink. The proposed system has been experimentally validated on a scaled converter prototype. The results show that the TAB inherent decoupling condition is reached between the output ports achieving the proper implementation of the Selectvie Harmonic Elimination Pulse Active Width Modulation (SHE-PWM) in the 5-LCHB. Moreover, the control system exhibits good performance dynamics even under output step-load variations.