Diode-assisted buck-boost voltage source inverters

This paper proposes buck-boost voltage source inverters with a unique X-shape diode-capacitor network inserted between inverter circuitry and dc source for producing a large voltage boost gain. Comparing with other voltage buck-boost techniques, the presented topologies with only a little more passive components can significantly enhance voltage boost capability for dc-ac inversion. With different front-end circuitries, the diode-assisted buck-boost inverters can show different operational principle and voltage boost ratio. Carefully analyzing the operational principle for the inherent energy charging and discharging processes of passive components reveals that the dc-link voltage can alternate between two levels, which therefore demonstrate the phenomena that the specified modulation schemes should note. A modulation scheme that can achieve optimized harmonic switching is first designed with symmetrical state placement in each switching sequence to avoid unnecessary voltage stress across both passive and active components. To reduce the total commutation count, the designed modulation scheme is then modified without increasing voltage stress. All theoretical findings were verified experimentally using a number of scale-down laboratory prototypes.