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Operation Modes Analysis and Limitation for DiodeAssisted Buck–Boost Voltage Source Inverter With Small
Voltage Vector
Abstract:
Diode-assisted buck-boost voltage source inverter (VSI) boosts the dc source voltage by
introducing diode-assisted capacitor network. With parallel capacitive charging and series
capacitive discharging, the new topology extends voltage regulation range and avoids extreme
duty ratio of switching devices in the front boost circuit. As for the unique structure, various
novel pulse-width modulation strategies are provided to obtain the linear voltage gain with
regard to the chopped intermediate dc-link voltage of the inverter bridge in one switching time
period. It provides a competitive solution for high voltage gain applications. However, when the
inverter supplies inductive or capacitive load with extreme low load power factor, the
unidirectional current flow of the diode may limit the application of the converter utilizing small
voltage vectors for ac output voltage extension. As a result, diode-assisted buck-boost VSI
exhibits new operation mode that has not been discussed before. This paper makes a detailed
circuit analysis of the relationship between the undesired operation condition and load power
factor. Then, a simple approach to totally eliminate the undesired limitation by replacing the
diodes with controlled switching devices is provided. Finally, the related simulations and
experiments are implemented to verify all the theoretical findings and solutions.