Improved Multi-Carrier Modulation Strategy Suitable for Cascade H-Bridge Photovoltaic Inverters

Grid-connected photovoltaic systems often prefer transformer-less inverters because of their high efficiency, low cost, and lightweight design. However, without electrical isolation, leakage currents may flow through the system, resulting in increased losses, electromagnetic interference, harmonic distortion, and potential safety hazards. This study addresses this issue. Firstly, the common mode equivalent model of single-phase five-level cascaded H-bridge PV grid-connected inverter was established and the main factors affecting the leakage current were analyzed. Subsequent suppression of leakage current is achieved by reducing the rate of change of the sum of parasitic capacitor voltages during the switching state, and the strategy is simple to implement. Finally, the effectiveness of the proposed modulation strategy is verified by simulation analysis.