Impact of Mixed Switching Frequency Scheme on Different Topologies of Multilevel Converters for Efficiency Improvement

Multilevel converter generally consists of more switching devices than the conventional two-level converter topology. The performance of these multilevel converters tends to increase by using high switching frequency which may also increase the switching loss that is the largest dominating loss of a power converter. This paper proposed a novel modulation strategy with a mixed switching frequency scheme that uses both high and low switching frequency to overcome this problem. Different multilevel converter topology such as Cascaded H- Bridge (CHB), Cascaded H5 (CH5), Neutral point Clamped (NPC), and Flying Capacitor Converter (FCC) topologies are presented for the validation of using proposed mixed switching frequency scheme. The level shifted modulation technique is used for CHB, CH5, NPC, and FCC except for CH5 topology which doesn’t allow level shifting operation. Moreover, it is observed that the zero-voltage state occurs for the CH5 topology during mixed switching condition which may result in reactive power flow from load/grid to the photovoltaic solar panel. Hence a new modified H5 topology is proposed to avoid the reactive power flow. H5 topology has never been implemented into the multilevel converter application. This research work emphasizes the efficiency improvement of different multilevel converter topologies. MATLAB SIMULINK is used for the simulation and the results are carried out clearly to demonstrate the effectiveness and efficient outcomes of the proposed switching scheme for grid- connected multilevel converters.