Improved pulse-width modulation strategies for diode-assisted buck-boost voltage source inverter

The recently proposed diode-assisted buck-boost voltage source inverter (VSI) enhances the voltage boost capability greatly without extreme large boost duty ratio, which is more suitable for wide range voltage regulation in dc/ac power conversion. This paper mainly explores pulse-width modulation (PWM) strategies for diode-assisted buck-boost VSI and their relationship of voltage gain versus voltage boost duty ratio. In view of variable intermediate dc-link voltage, two kinds of improved PWM strategies with high dc-link voltage utilization are presented to obtain the maximum linear voltage gain in theory, as well as to minimize the voltage stress of switching devices. The operation principle, and the relationship of voltage gain versus voltage boost duty ratio and switching device voltage stress versus voltage gain are analyzed in detail. The related simulation and experiments are implemented to verify the theoretical analysis. Compared with existing counterparts, diode-assisted buck-boost VSI with improved PWM strategies demonstrates good performances: less switching device requirement and higher efficiency at high voltage gain. Owing to improved performance, diode-assisted buck-boost VSI is more promising and competitive topology for wide range dc/ac power conversion in a renewable energy application. Furthermore, the idea of improved modulation strategies can also be extended to the control of diode-assisted buck-boost current source inverter.