Bridging unit

A bridging unit for shorting a first input and a second input of a converter cell of a modular converter, the bridging unit comprising:

• a bistable mechanical relay;
• a power-electronic switch;
• a drive for switching the relay and the power-electronic switch;
• and
• an energy store for supplying power to the mechanical relay, the power switch and the drive;
• wherein the bistable mechanical relay is configured to electrically connect the first input to the second input;
• wherein the power-electronic switch is configured to electrically connect the first input to the second input;
• wherein the drive comprises passive overvoltage detection configured to charge the energy store if the overvoltage is exceeded;
• wherein the drive has a further electronic switch, which is configured to be closed when a voltage on the energy store exceeds a predefined value, and the drive is configured to supply current from the energy store to at least one of the bistable relay and the power-electronic switch, and
• wherein the drive has hysteresis, such that, if the voltage on the energy store is undershot, at least one of the relay and the power-electronic switch is still supplied with current from the energy store.