Patent ID: 8537578

Claim:
A method for controlling an inverter having three phase modules, with each phase module having an upper valve branch and a lower valve branch, and with each valve branch having at least three two-pole subsystems, which each comprise an energy store and are electrically connected in series, with the following method steps in the event of failure of at least one subsystem: a) identifying the valve branches in which at least one subsystem has failed, b) determining a number of failed subsystems in an identified valve branch, c) controlling each failed subsystem such that the terminal voltage of the at least one failed subsystem is permanently zero, d) identifying in each fault-free phase module a fault-free valve branch which corresponds to a faulty valve branch in a faulty phase module, e) controlling in each identified fault-free valve branch a number of subsystems equal to the number of failed subsystems such that their terminal voltages are permanently zero, f) increasing in each failed valve branch a voltage of each energy store in the fault-free subsystems with non-zero permanent terminal voltages such that a sum of the increased voltages of the energy stores in the fault-free subsystems in each failed valve branch is equal to a sum of the voltages of the energy stores of the subsystems in the fault-free valve branch which corresponds to the faulty valve branch in the faulty phase module, and g) controlling of the subsystems of the valve branches of the fault-free phase modules commensurate with a control of these subsystems before the failure of the at least one subsystem.