This thesis proposes a modified modulation method based on phase-shifted PWM (PS-PWM) method to improve reliability and output performance for cascaded H-bridge (CHB) multilevel inverter. In generally, the PS-PWM method is one of the popular modulation method because it has a high performance of output. However, this generates the higher switching loss than the other modulation method such as level-shifted PWM (LS-PWM) method. The switching loss leads to major failure mechanism about power semiconductor switch, therefore it should reduce for improving reliability of CHB multilevel inverter. The clamped scheme conducts different switching operation each leg of same cell for reducing switching loss. However, the clamped scheme distributes dwelling time of zero-voltage vector unevenly. This bring about increases THD of output current and decreases output performance of CHB multilevel inverter. To improve output performance, the proposed modulation method is distributed a dwelling time of zero-voltage vector evenly by modifying phase difference of triangular carrier waveforms. Finally, the proposed modulation method is applied the rotation method to distribute even lifetime through distributing power losses evenly. The validity of the proposed modulation method for CHB multilevel inverter is demonstrated by the simulation and experimental results.
