Analysis and validation of cascade H-bridge five-level converter operating condition

Taking two power cells cascaded per phase as an example, the topology of cascaded H-bridge multilevel converter and carrier phase-shifted SPWM (CPS-SPWM) modulation strategy are introduced. The operation principle of the converter under the SPWM modulation is described in detail through the analysis of operating condition The power devices switching, output voltage, current circulation and balance voltage are analyzed. According to the analysis, the feasibility, reliability and convenience of the PWM strategy for the cascaded converter are proved, the theoretical basis for the modulation optimization and topology improvement is also provided. Operating mode of five-level converter is described in detail in the paper. Mathematical model of five-level converter is deduced and validated by computer simulation. Cascade H-bridge five-level converter pulse generator is implemented by DSP and FPGA, which has the feature of simplifying circuit-design, guaranteeing reliability of system and concurrent triggering of power devices. Cascade multilevel converter based on carrier phase shifted PWM can achieve high equivalent switching frequency at low switching frequency devices, which is of perfect prospect in high voltage and power industry application.