A Hybrid GaN + Si based Cascaded H-bridge Multi-Level Inverter and PWM scheme for Improved Efficiency

This paper proposes a hybrid Gallium Nitride (GaN) and Silicon (Si) multilevel converter and a PWM method for its operation, for reduced switching losses without significant increase in the system cost. Multi-level converters with high frequency converter have become popular due to high efficiency, low harmonics and small size compared to line traditional frequency transformers. The multi-level output voltage enables direct connection of renewables to medium/high voltage level collection grids. The hybrid power-circuit architecture described in this paper, which is well-suited for renewable integration, has a single primary side inverter and several series connected sub-modules on the secondary-side. Each sub-module consists of a high-frequency transformer, a diode bridge rectifier and H-bridge. In the proposed hybrid scheme, only one sub-module (SM) per phase employs GaN devices, and switches at high frequency to produce pulse-width modulated output voltage. All other sub-modules consist of conventional Si devices switching at near-fundamental frequency. Such a combination reduces the overall converter cost while also yielding high efficiency. The paper presents simulation and experimental results verifying the topology and the proposed PWM scheme on a nine-level H-Bridge multi-level converter hardware. Detailed topology analysis and and a brief loss budget is also included.