Improved Modulation Strategy for Singe-Phase Cascaded H-Bridge Multilevel Inverter

In this letter, two new improved pulsewidth modulation (PWM) techniques are proposed for single-phase cascaded H-bridge inverter. Compared with the conventional modulation methods, including phase-shifted PWM (PS-PWM), level-shifted PWM (LS-PWM), discontinuous modulation (D-PWM), only PS-PWM can ensure the output quality and maintain the power balance between each module. That is why it is widely used. However, the switch with PS-PWM always operates in a high-frequency mode, resulting in the high switching losses and low efficiency. In order to solve the problem, two improved cascaded H-bridge multilevel PWM methods are proposed in this letter. With the proposed PWM methods, the power can be evenly distributed among modules, the utilization rate of switching devices is the same, while the switching times are reduced, which improves the system efficiency. Finally, the experimental tests are carried out on a digital-control single-phase cascaded H-bridge seven-level inverter. And the experimental results verify the effectiveness of the proposed solution.