The 4-level nested neutral point-clamped converter (4L-NNPC) is a novel multilevel converter characterized by a simple topology

the absence of series power devices

and a common DC bus

making it highly suitable for applications requiring a 10 kV DC link and high power density. The balance control of the floating capacitor with low common mode voltage in the whole frequency range is studied in this paper. First

the construction method of H-bridge 4L-NNPC virtual level is proposed. On this basis

a single-phase space virtual vector modulation is introduced

which realizes the floating capacitor voltage balance on both sides of the H-bridge in the whole frequency range. Secondly

the selection of vector and the responding action sequence is reasonably arranged to offset the instantaneous amplitude of the common-mode voltage

so that the common-mode voltage of the three-phase four-level NNPC H-bridge inverter is suppressed to below 2Vdc/9

and leaves the floating capacitor voltage control unchanged. Finally

corresponding stimulation model and prototype of three phase 4L-NNPC H-bridge inverters are constructed. The fluctuation of 4L-NNPC floating capacitors voltage is below 5% and the common-mode voltage is under 2Vdc/9 in the whole frequency range. The feasibility and correctness of the proposed modulation algorithm are verified by simulation and experiment.