Control method for redundant use in the event of a fault in a polyphase converter with distributed energy stores

A method for controlling a converter having at least two phase modules, each phase module having a first and a second valve branch wherein each of the first and second valve branches has at least three series-connected two-pole subsystems, in the event of a failure of at least one subsystem of a valve branch, the method comprising the steps of:

• identifying a failed valve branch of a phase module having at least one failed subsystem, said at least one failed subsystem located in a first valve branch of a phase module,
• controlling at least one subsystem in a corresponding first valve branch of each of the others of the at least two phase modules so as to cause a terminal voltage of the at least one subsystem in the corresponding first valve branch of the other phase modules to be zero,
• controlling at least one subsystem in each of the second valve branches so as to cause a terminal voltage of the subsystems in each of the second valve branches to be equal to a capacitor voltage of the subsystem sequentially controlling the two-pole subsystems of a valve branch of a phase module with control signals having a mutual time offset so as to change an output voltage of the valve branch.