Multi-level operation of triple two-level PWM converters

This paper presents a new connection method of triple two-level PWM converters to provide multi-level output waveform to a motor/transformer which has triple independent sets of three-phase winding. By simply changing the connection between the PWM converters and the windings of the motor/transformer, the level of winding voltage can be increased without any hardware modification. With triple 2-level converters, the level of the voltage of a phase winding can be increased up to 9 levels for delta-connected winding and 17 levels for wye-connected winding. The number of the voltage level of the proposed connection method is equivalent to that of 5-level converter. The equivalent circuits for the proposed connection are derived for both delta- and wye-connected winding cases. Through the equivalent circuit, the winding voltage has been expressed in terms of phase voltage of each PWM converter. The validity of the equivalent circuit and the proposed connection has been verified with experimental result.