Cascaded Multilevel Inverter(CMLI)which consists of several H-bridge inverter modules for medium-voltage high-power DC micro grid is widely applied on the power electronic devices including energy router,intelligent energy hub and static transformer.The traditional CMLI has the same DC bus voltage for each H-bridge inverter modules,which reduces the number of voltage levels of the output.By applying voltage ratio of the DC bus voltage from 1∶1∶1 to 20∶21∶22 for a traditional 7-level 3H-bridge inverter,the proposed inverter operates with 15-level resolution.By applying staircase control and the modified nearest level modulation,the switching frequency,the switching power loss and the total harmonics distortion of output voltage to the proposed hybrid cascaded inverter are reduced effectively.The theoretical analysis and calculation on the working principle,staircase control and output voltage harmonics for the proposed hybrid cascaded 15-level inverter are presented,and a laboratory prototype of a 15-level IGBT-based CMLI is designed and implemented for the verification.
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