A Hybrid Multilevel Converter Topology Based on NPC and CHB Series and Its Control Method

Aiming at the problems of the existing multilevel converters, such as the large number of devices, high loss, and low power density, a novel hybrid multilevel converter (HMC) topology is proposed in this paper. The HMC consists of a three-level neutral-point clamped (NPC) cell configured with Si GTO and a cascaded H-bridge (CHB) cell configured with a mixture of Si IGBT and SiC MOSFET. For this topology, a specific hybrid high-low frequency modulation is proposed to give full play to the advantages of low switching loss of SiC devices and low on-state loss of Si-based devices. In addition, in order to solve the problem of unbalanced capacitor voltage of the hybrid topology sub-modules, an alternate voltage balancing control (AVBC) strategy is proposed. Finally, the feasibility of the HMC topology and modulation is verified by simulation.