Externally-fed auxiliary power supply of MMC converter cells

We designed an auxiliary power supply for medium voltage MMC-converters with system voltages up to 36 kV
rms
. The system supplies up to 250 W power and is based on a two-stage design. The first stage is an inductive power transfer system that isolates against the system voltage. It is connected to a low voltage DC-supply on ground potential, and shows DC-DC efficiency between 90–95%. Two distinct insulation concepts for the coupled coil design have been designed and passed partial discharge tests. The second stage supplies the various gate and control units of each MMC power cell. Its insulation requirement is given by the cell voltage. Functional and insulation tests as well as a sensitivity analysis are included. The full auxiliary power supply shows an efficiency of 86%.