Patent ID: 8687391

Claim:
A converter system for the switching of least three voltage levels, the converter system comprising: a converter unit having a DC side and an AC side, the DC side of the converter unit being connected to a DC circuit having a voltage zero point, and the AC side of the converter unit is connected to a shorting circuit having a plurality of thyristors and at least two shorting resistors, wherein the converter unit is configured to monitor current carried by the converter unit in relation to a threshold value and, when the threshold value is exceeded, to actuate the thyristors by the application of a closing signal, such that the AC side of the converter unit is connected to the at least two shorting resistors; and a voltage-limiting device connected to the DC circuit and to the at least two shorting resistors, the voltage-limiting device being configured to restrict any overvoltage on the DC circuit and to turn-off the thyristors, wherein when the threshold value is no longer exceeded, the converter unit is configured to switch the AC side of the converter unit to the voltage zero point of the DC circuit and terminate application of the closing signal, and wherein the voltage-limiting device is configured to connect the at least two shorting resistors to the DC circuit for a configurable time interval, whereafter the converter unit is configured to isolate the AC side of the converter unit from the voltage zero point of the DC circuit once more.