Comparison of Two and Three-Level DC-AC Converters for a 100 kW Battery Energy Storage System

This paper discusses a qualitative comparison between Two and Three-Level Voltage Source Converter (VSC) topologies for battery energy storage applications. Three-Level Neutral Point Clamped (NPC) and T-Type circuit topologies are benchmarked versus the state-of-art Two-Level VSC in terms of efficiency and power density considering a 100 kW system. Analytical equations for determining the power losses in the semiconductor modules are given, and the procedure for designing the output LCL filter and the DC-link capacitors is described. The analysis, based on off-the-shelf circuit components, shows that the Three-Level topologies perform better than the Two-Level one in both considered metrics, mainly due to their lower switching losses that allow operating at higher switching frequency without significantly degrading the system efficiency, and, at the same time, increasing the system power density. Additionally, it is found that the T-Type topology shows better performances than the NPC topology at full and high partial loads, being then more suitable for applications that require most of the operation at maximum power.