Modified carrier-based over-modulation technique for improved switching performance of multilevel converters

A modified over-modulation (OVM) scheme with phase disposed carriers to improve switching performance of cascaded H-bridge multilevel converter is depicted in this article. With the regular OVM techniques, pulse dropping region has higher conduction loss, greater signal distortion and voltage gain. In the proposed OVM method, the switching and conduction loss scenario is improved with lower harmonic distortion. Also, the voltage gain can be increased up to limited range. Four types of reference signals, such as pure sinusoidal signal, sinusoidal 60° bus clamped signal, third harmonic injected signal and third harmonic injected 60° bus clamped signal are used to investigate the overall performance with the proposed OVM method. The OVM technique is applied to a 3.0 kV, 120 kW, 5-level cascaded H-bridge converter and simulated in MATLAB/Simulink environment. The results demonstrate reduced output harmonic distortion, increased voltage gain, lower switching and conduction loss as well as improved efficiency on the whole.