Elimination of common-mode voltage in three-phase sinusoidal power converters

This paper presents an active solution to a common-mode voltage created by typical three-phase inverters. It is shown that the addition of a fourth leg to the bridge of a three-phase inverter eliminates the common-mode voltage to ground created by the modulation of the inverter. An appropriate four-phase LC filter is inserted between the inverter and the load in order to create sinusoidal output line-to-line voltage. A simple modification of the modulation strategy is implemented for the four-phase inverter to achieve a three-phase wye-output neutral-to-ground voltage which is equal to zero at all times for an ideal inverter. The modulation strategy thereby completely eliminates the common-mode potential produced by traditional modulation techniques with traditional three-phase inverter topologies.