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Summary: The four‐level hybrid clamp converter (4L‐HCC) is one of the next‐generation multilevel topologies due to its simplified structure and excellent performance. However, it consists of several DC‐link and flying capacitors, which must be precharged to the rated voltage before the normal operation. Without proper control, those internal capacitors could easily induce inrush currents and cause system fatal failure due to the unsymmetrical circuit structure. This paper proposes soft start‐up control methods for both single‐phase and three‐phase HCCs. The precharging mathematical models of DC‐link and flying capacitors are established. A straightforward algorithm using the selected switching states and rotating regions is developed to build precharging circuits properly. A full‐scale simulation model and a downscale laboratory prototype of the 4L‐HCC are established to validate the superiority of the proposed method. Results demonstrate that the proposed approach is effective in charging all capacitors through internal elements rapidly with suppressed and controllable charging currents. [ABSTRACT FROM AUTHOR]

The four-level hybrid-clamped converter (HCC) is a new high-efficiency dc–ac converter. However, its dc-link capacitors face challenging voltage fluctuation issues at low frequencies, resulting in the distorted ac current and oversize converter volume. This letter presents a simple and effective control method of the HCC using open-loop common-mode voltage (CMV) injection. The mathematical model of the CMV and the capacitor voltage fluctuations is derived. The optimal CMV algorithm with the maximum suppression effect of capacitor voltage fluctuations is proposed as well as the implementation method. The microlevel mechanism of the proposed method in suppressing voltage fluctuation is clarified. The capability of the proposed method in improving dc voltage utilization is explored. Compared with existing methods, the proposed one reduces dc-link voltage sensors and computation complexity and mitigates CMVs at the load side. The optimal CMV is approximately 25% of the output voltage magnitude, and enhances the dc-bus voltage utilization by 12%. Results demonstrate that voltage fluctuations of HCC capacitors are reduced by over 60%. The proposed method has a solid dynamic balancing capability and works well for the wide-range frequency and modulation index. [ABSTRACT FROM AUTHOR]