I would like to build a cascaded multilevel converter. Each module should be supplied by an isolated power supply around 100VDC. Using available bench power supplies is not practical, because they could not be cascaded to build more than 240VDC. In addition, since the switching frequency of modules is around 100kHz, an earth leakage due to high-frequency operation could happen causing a damaging on gate drivers of modules. Any solution?
(1) If you want to suppy the cells via DC/DC converters, each one has to provide full insulation according to the DC link of the cascaded multilevel converter. Therefore, you have to get power supplies with the right insulation level.
(2) Alternatively, you could energize the DC link caps of the cells with a dedicated control scheme of the cascaded multilevel converter. This is not too difficult, see e.g.
Wim van der Merwe, Peter Hokayem, Lidia Stepanova, "Analysis of the 2-Cell Single Phase MMC Natural Balancing Mechanism", Emerging and Selected Topics in Power Electronics IEEE Journal of, vol. 2, no. 4, pp. 1149-1158, 2014.
(3) In industrial medium-voltage cascaded multilevel converter systems, they employ (1) with dedicated power supplies (emphasis on the high-frequency insulation transformers) or (2).