Modular multilevel converter（MMC） is widely used in the field of HVDC transmission

but its application in the medium voltage variable-speed motor driving system has the problem of the capacitor voltage fluctuations when the motor at low speed. Aiming at this problem

this paper designs a new hybrid MMC topology. Based on it

the medium voltage frequency converter can significantly reduce the capacitance voltage fluctuation

including the low speed condition. In addition

the new topology does not introduce common-mode voltage

so no insulation and bearing current problems

while the current stress in the entire speed range will remain within the limits

so the equipment is more efficient. Based on the working principle of the new hybrid topology

the related controller is designed. Finally

the prototype of the frequency converter is set up

and the test results verify the performance of the proposed new topology.