A new switching strategy for transformer-less back-to-back cascaded H-bridge multilevel converter

In this study, a new switching strategy is introduced for transformer-less back-to-back cascaded H-bridge (CHB) converters. The main purpose of this novel switching algorithm is to eliminate the need for an isolation stage between the line side and the load side H-bridge cells. In other words, using this strategy, the CHB rectifier and the CHB inverter can be connected directly to each other in a back-to-back structure. The CHB rectifier regulates the intermediate DC bus voltages to the reference value, whereas the CHB inverter generates a controllable AC voltage from the intermediate DC links. The low-frequency selective harmonic elimination technique is applied to eliminate specific harmonics from the output voltage and to minimise the switching loss. The validity and effectiveness of the proposed method are verified by simulations and experiments on a five-level back-to-back converter.