Hybrid cascaded H-bridge inverter with even power distribution and improved total harmonic distortion: analysis and experimental validation

For high-power applications, cascaded H-bridge (CHB) inverters are conventionally controlled by selective harmonic mitigation (SHM) strategy. This technique is applied to reduce the switching loss and the optimised switching angles are calculated to mitigate low-order harmonics at the output voltage. However, this strategy causes an uneven power distribution among the CHB cells. Also mitigating more harmonics needs more number of pulses and consequently higher switching frequency and dissipated power. This study proposes a new hybrid CHB inverter with optimised dc sources. Considering the optimisation of the CHB dc sources' values along with the optimised switching angles, significant improvements such as mitigating more low-order harmonics, even power distribution among the CHB cells and reducing the switching loss are achieved. Analysis and simulations are carried out on a five-level CHB inverter. Experimental verifications also validate the simulation results. The results demonstrate that the new hybrid CHB inverter considerably improves the performance of the conventional SHM strategy.