Power Balance Strategy of Diode Clamped H-Bridge Cascade Multilevel Inverter

In the cascaded neutral point clamped (NPC) H-bridge multilevel inverter system, power balance between modules has attracted more and more attention. This paper proposes a hybrid modulation strategy based on analyzing the quantitative relationship between output power and RMS of the output voltage of the module under conventional carrier level-shifted PWM modulation strategy. The strategy combines the carrier disposition modulation strategy and phase shift modulation strategy, which not only guarantees the balance of output power of each module, but also improves the equivalent switching frequency of output voltage, as a result, both the size and the cost of the output filter are reduced. The simulation waveforms and comparative analysis under different modulation strategies and modulation indexes are given. Finally, a 1kW experimental prototype is built, and the experimental results verifies that the proposed modulation strategy can effectively solve the power balance problem between different modules in cascade system.