Average power control of DC bus voltages of cascaded H-bridge multilevel converters

This paper presents an average power balancing control technique for the modular multilevel cascaded converter (MMCC) based on single-star bridge cells (SSBC) in the static synchronous compensator (STATCOM) applications. Detailed power flow analyses of the MMCC-SSBC converter, from the bottoem level of individual H-bridge modules, then the middle level of per-phase circuit, to the top level of the three-phase circuit, are performed. By utilizing the outcome of such power flow analyses, the proposed method can precisely control all the DC bus voltages of the MMCC-SSBC while performing the reactive power compensation, even under extreme conditions like voltage sags, thus enhance the low voltage ride through functionalities of the STATCOM, which is very critical for renewable energy deployment. The proposed control algorithm is verified by a MMCC-SSBC test bench in the laboratory under normal and fault grid conditions.