Quasi-resonant multilevel converter for supercapacitor energy storage systems

There are several topologies that are used in multilevel converters. Most of them use hard-switching techniques to achieve the objective, particularly in modular multilevel converters. It is well known that hard-switching topologies are easier to control but has more switching power losses than soft-switching topologies. Usually, this is not a problem for multilevel converters attached with batteries, where the switching frequency can be kept at a low value. However, in converters for supercapacitors, a very high efficiency and compact design is needed. This is because, the supercapacitors have a very low voltage (∼2.7V) and a modular multilevel converter will use many modules to achieve the desired output voltage value. The use of soft-switching techniques allows the converter to work at a higher frequency by reducing the switching losses. The paper presents a quasi-resonant multilevel converter for supercapacitor storage systems. It analyses both power flow directions and simulations of a 62-supercapacitor converter were performed to validate the analysis.