Abstract: A method for controlling a back-to-back three-phase three-level converter having a grid-side AC/DC converter and a machine-side DC/AC converter connected by a split DC link which defines a DC link midpoint. The method includes controlling the grid-side converter to convert AC power from a grid into DC power of the DC link, controlling the machine-side converter to convert DC power from the DC link to AC power to feed a low frequency machine, and concurrently performing common mode voltage injection for the machine-side converter so as to at least partially compensate midpoint voltage ripple caused by the machine-side converter. The method further includes performing common mode voltage injection for the grid-side converter so as to at least partly further compensate the portion of the midpoint voltage ripple which remains uncompensated by controlling the machine-side converter. A control system implementing the control method and a power conversion system utilizing same.

Abstract: A method for controlling a back-to-back three-phase three-level converter having a grid-side AC/DC converter and a machine-side DC/AC converter connected by a split DC link which defines a DC link midpoint. The method includes controlling the grid-side converter to convert AC power from a grid into DC power of the DC link, controlling the machine-side converter to convert DC power from the DC link to AC power to feed a low frequency machine, and concurrently performing common mode voltage injection for the machine-side converter so as to at least partially compensate midpoint voltage ripple caused by the machine-side converter. The method further includes performing common mode voltage injection for the grid-side converter so as to at least partly further compensate the portion of the midpoint voltage ripple which remains uncompensated by controlling the machine-side converter. A control system implementing the control method and a power conversion system utilizing same.

Abstract: A method for operating an N-level K-phase electrical power converter, wherein N is greater than or equal to 3 and K is greater than or equal to 1. The method includes: providing a plurality of N connection points that each correspond to a definable potential, wherein a first connection point corresponds to a first potential, a second connection point corresponds to a second potential, and at least one further connection point corresponds to a further potential which is lower than the first and greater than the second potential; providing a plurality of K output connections that are each selectively connected to a respective one of the connection points via at least one switching device; and having at least one current flowing into the at least one further connection point.

Abstract: A method for operating an N-level K-phase electrical power converter, wherein N is greater than or equal to 3 and K is greater than or equal to 1. The method includes: providing a plurality of N connection points that each correspond to a definable potential, wherein a first connection point corresponds to a first potential, a second connection point corresponds to a second potential, and at least one further connection point corresponds to a further potential which is lower than the first and greater than the second potential; providing a plurality of K output connections that are each selectively connected to a respective one of the connection points via at least one switching device; and having at least one current flowing into the at least one further connection point.