A Submodule Implementation for Parallel Connection of Capacitors in Modular Multilevel Converters
2015 (English)In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 30, no 7, 3518-3527 p.Article in journal (Refereed) Published
In modular multilevel converters there is a trade-off between the switching frequency and the voltage ripple in the submodule capacitors. The reason for this is that it becomes increasingly difficult to balance the capacitor voltages when the switching frequency is reduced. This paper presents a new submodule circuit which improves the balancing of the capacitor voltages at low switching frequencies. The proposed submodule circuit consists of two capacitors and eight switches, forming a three-level submodule. Ideally, the voltage and current ratings of the switches can be chosen such that the combined power rating of the semiconductors is the same as for the equivalent solution with conventional half-bridge submodules. The proposed submodule circuit provides the possibility of connecting the two capacitors in parallel when the intermediate voltage level is used. This will reduce the capacitor voltage ripple, especially at low switching frequencies and thus allow for a reduction of the size, weight, and cost of the submodule capacitors. The proposed submodule circuit is validated by both simulations and experimental results. It is found that the parallel connection of the submodule capacitors will, in fact, significantly improve the balancing of the capacitor voltages.
Place, publisher, year, edition, pages
2015. Vol. 30, no 7, 3518-3527 p.
Capacitor voltages, modular multilevel converter (MMC), switching losses
Other Electrical Engineering, Electronic Engineering, Information Engineering
IdentifiersURN: urn:nbn:se:kth:diva-153757DOI: 10.1109/TPEL.2014.2345460ISI: 000353126300007ScopusID: 2-s2.0-84923933547OAI: oai:DiVA.org:kth-153757DiVA: diva2:753567
QC 201506222014-10-082014-10-082015-08-05Bibliographically approved