A cascaded asymmetric multilevel inverter for aircraft ground power unit: design and implementation

Aircraft ground power units (GPUs) must supply regulated 115 V, 400 Hz power to aircraft systems during ground operations while satisfying strict power quality standards. Conventional GPU architectures commonly rely on two-level inverters with bulky output filters and transformers, increasing complexity and limiting harmonic performance at 400 Hz. This study proposes a single-phase cascaded asymmetric multilevel inverter topology specifically for aircraft ground power applications. The proposed inverter employs binary-scaled DC voltage modules combined with a conventional H-bridge to generate a high number of voltage levels using a reduced switching device. A deterministic switching strategy at low frequency enables staircase voltage synthesis without high-frequency pulse-width modulation. The feasibility of the proposed topology is verified through simulation and experimental studies on a 31-level laboratory prototype. Experimental results demonstrate that the inverter maintains stable voltage regulation under steady-state and dynamic load conditions while producing a high-quality output waveform with low total harmonic distortion. The multilevel voltage synthesis allows the inverter to satisfy aircraft requirements without bulky output filters. Additionally, comparative analysis shows that the proposed topology achieves higher voltage level density than several existing multilevel structures while avoiding flying-capacitors and clamping diodes.