Improved T-Type and ANPC Multilevel Converters by Means of GaN-Based T-Cell Branch and Bidirectional Device

By integrating standard power electronic modules like the half-bridge and bidirectional unit, it is possible to create a T-type circuit that is versatile for use in both DC-AC and AC-DC applications. Using these, various arrangements of bidirectional DC-AC converters, including mid-point-clamped-based multilevel inverters (MLIs), can be constructed. However, realization of such T-type circuit in mid point-clamped MLIs with limited voltage blocking capability of the available wide-band-gap devices is challenging as these MLIs suffer from half dc-link voltage utilization at the ac output. In this paper, new opportunities of bidirectional and T-cell branch in MLIs with Gallium Nitride-high electron mobility transistors (GaN-HEMTs) are outlined. Thanks to the contribution of a front-end T-cell branch, the half dc-link voltage utilization factor of the conventional mid point-clamped-based MLIs is enhanced, whilst more number of output voltage levels can be generated facilitating incorporation of standard commercially available 650 V GaN-HEMTs. This results in the creation of new MLIs that feature smaller grid-interfaced filters, reduced overall losses, and improved power density. Moreover, with additional bidirectional GaN-based cell, application of such converters can be further broadened within new inductor-less dual-mode MLIs topologies operating over a wide range of input dc voltage changes. Theoretical analysis with several simulation and experimental results extracted from a 3 kW, 99.2% efficiency, 1.92 kW/L GaN-based prototype are given to corroborate the effectiveness and feasibility of the proposed solution.