Three-phase voltage sources are power electronic systems, which generate specific, highquality
voltage waveforms for many different applications. They are used in Power Hardware-inthe-
Loop (PHIL) systems for the emulation of electrical machines or grids as well as in test and
measurement systems for the characterization of passive components, transformers, magnetic
materials, etc. The proposed 3AC voltage source is realized by a Modular Multilevel Converter
(MMC), which generates voltage waveforms with small steps due to its series-connected cells.
The quality of the voltage is further improved by a small filter to eliminate harmonics in the
range of the switching frequency. Measurements are performed on a low voltage MMC prototype
to evaluate the precision of the voltage waveforms. A MMC in 1AC-3AC configuration,
which is coupled to a medium frequency transformer, is presented to meet the requirement of a
galvanically isolated power supply and to overcome the limitations at low frequency operation.