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Enhanced Floating Capacitor Voltage Balancing Schemes for Single-Source Seven-Level Inverters With Capacitor Fed H-Bridge Units

Two novel floating capacitor voltage balancing schemes are proposed in this article, which enhance the linear modulation range of single-source seven-level inverters having floating capacitor fed H-bridge units. Extreme pole voltage levels associated with cascaded H-bridge units can be used for enhancing dc bus utilization. But, these pole voltage levels lack redundant switching states, which limits the linear modulation range for which floating capacitor voltages remain balanced. In recent times, a few literature have addressed the issue of balancing these capacitor voltages by employing appropriate modulation schemes, which enhances the modulation range of a inverter to a certain extent. The proposed balancing schemes further extend the linear modulation range by adding a suitable common-mode offset to reference signals. The addition of a predefined low-frequency offset and an online calculated dynamic offset is proposed here that helps in extending the modulation ranges to 0.84 and 0.85. Under these schemes, the dc bus utilization can reach up to 0.637Vdc at unity power factor, where Vdc is the input voltage of the single-source inverters. Three well-established optimized seven-level inverters are used to analyze these schemes and their effectiveness is demonstrated using simulation and experimental results at different modulation and load conditions.