A New Current Source Converter Using AC-Type Flying-Capacitor Technique

Entering the new millennium, current source converters (CSCs) have drawn increasing attention not only for high-power but also some emerging low-power applications which prefer the inherent voltage boosting nature and low dv/dt on ac-side. However, the dc-link quality of CSC has not been well improved and is rarely discussed in literature. To fill this gap, a new type of CSC topology is proposed in this article through the isomorphic theory. It utilizes the ac-type flying capacitors in each phase leg and provides alternative commutation loops, which can reduce the dc-side dv/dt and improve the common-mode voltage simultaneously. Besides, this technique can increase the withstand voltage of the converter without series connections of switching devices. Different from the voltage-source converter type, the flying capacitor voltage in CSC should be maintained as ac voltage, thus, active voltage regulation is necessary. To deal with such a challenge, carrier-based pulsewidth modulation with flying capacitor voltage regulation is also developed in this work. Compared with the traditional device-series-connected CSC topologies, the numbers of active switches and the device blocking voltage can remain the same, while the ac-type flying capacitors are added in the proposed topology to gain all the above merits. Simulation and experiment results are obtained to verify the advantages of this new type of CSC topology.