Three-level DC-DC Converters versus Half-bridge Voltage Balancers for Bipolar DC Microgrids - An Efficiency Comparison

This paper compares the efficiency of a buck three-level DC-DC converter with respect to a two-level and a three-level half-bridge voltage balancer. These converters serve to balance the positive and negative pole-to-neutral voltages in bipolar DC microgrids in the presence of unbalanced loading conditions. In contrast to well-known half-bridge voltage balancers, buck three-level DC-DC converters can interface battery storage and photovoltaic systems with bipolar DC microgrids and balance the pole-to-neutral voltages at the same time. To this end, it asymmetrically injects power in the positive and the negative pole, depending on the demand. This paper starts by revisiting the causes and consequences of voltage balancing. Subsequently, the paper classifies voltage balancing converters in direct and indirect voltage balancing converter types. Furthermore, the paper defines the balanced and unbalanced conversion efficiency, which the authors recommend to include in balancing converter datasheets. Finally, a comparative case study evaluates the conversion losses in unbalanced bipolar DC microgrids with different balancing converter arrangements.