Analysis of DC-Link Voltage Fluctuations in CHB Inverter With Supercapacitor and DC–DC Stage Under Hybrid Modulation Strategy

The hybrid modulation strategy (HMS) offers the advantages of simple voltage balancing and low current harmonic distortion, rendering it suitable for the cascaded H-bridge (CHB) inverter with supercapacitor (SC) and dc–dc stage. The rounding function is essential in the HMS-based voltage balancing method, as it determines the number of the inserted submodules (SMs) within each control cycle. However, the voltage fluctuations in the dc-link among the SMs may either increases or decreases, affected by the rounding function employed. To explore this, three common rounding functions are considered, including fix(x), round(x), and ceil(x). Among these dc-link voltage fluctuations under the three functions, fix(x) yields the lowest, followed by round(x), and ceil(x) results in the highest fluctuation. Simulation and experimental results demonstrates the correctness of the theoretical analysis in this paper.