Method for balancing voltages in a DC grid and balancing unit for a DC grid

A balancing circuit for a DC grid with a first DC conductor and a second DC conductor, wherein at least one DC load and an electrical energy store and/or a DC source are connected between the first DC conductor and the second DC conductor, comprising:

• a first semiconductor switch and a second semiconductor switch, which are connected in series between the first DC conductor and the second DC conductor, and
• a connection to ground potential arranged between the first semiconductor switch and the second semiconductor switch,
• wherein the balancing circuit is configured to operate at least one of the first and second semiconductor switches such that, in a presence of an asymmetry in voltages of the first DC conductor and the second DC conductor to ground potential, a compensation current flows between at least one of the first DC conductor and the second DC conductor and the ground potential via the at least one semiconductor switch, wherein the asymmetry in the voltages of the first DC conductor and the second DC conductor to ground potential is reduced and/or the voltages with respect to ground potential are balanced by the compensation current,
• wherein the compensation current is generated via the first or second semiconductor switch when the asymmetry in the voltages exceeds a predefinable first threshold value,
• a control circuit configured to monitor the asymmetry in the voltages,
• wherein the control circuit is configured to monitor a size of the compensation current and generate a switch-off signal and output the switch-off signal when a predefinable second threshold value is exceeded.

A DC grid with a balancing circuit for the DC grid with a first DC conductor and a second DC conductor, wherein at least one DC load and an electrical energy store and/or a DC source are connected between the first DC conductor and the second DC conductor, wherein the balancing circuit comprises:

• a first semiconductor switch and a second semiconductor switch, which are connected in series between the first DC conductor and the second DC conductor, and
• a connection to ground potential arranged between the first semiconductor switch and the second semiconductor switch,
• wherein the balancing circuit is configured to operate the at least one of the first and second semiconductor switches such that, in a presence of an asymmetry in voltages of the first DC conductor and the second DC conductor to ground potential, a compensation current flows between at least one of the first DC conductor and the second DC conductor and the ground potential via the at least one semiconductor switch, wherein the asymmetry in the voltages of the first DC conductor and the second DC conductor to ground potential is reduced and/or the voltages with respect to ground potential are balanced by the compensation current,
• wherein the compensation current is generated via the first or second semiconductor switch when the asymmetry in the voltages exceeds a predefinable first threshold value,
• a control circuit configured to monitor the asymmetry in the voltages,
• wherein the control circuit is configured to monitor a size of the compensation current and generate a switch-off signal and output the switch-off signal when a predefinable second threshold value is exceeded.

A method for operating a DC grid comprising a first DC conductor and a second DC conductor, wherein at least one DC load and an electrical energy store and/or a DC source are connected between the first DC conductor and the second DC conductor, wherein the method comprises:

• balancing voltages on the first DC conductor and the second DC conductor using a balancing circuit comprising a series connection of a first semiconductor switch and a second semiconductor switch arranged between the first DC conductor and the second DC conductor and a connection to a ground potential arranged between the first semiconductor switch and the second semiconductor switch,
• determining an asymmetry in the voltages of the first DC conductor to ground potential and of the second DC conductor to ground potential using a control circuit,
• generating a compensation current between at least one of the first DC conductor and the second DC conductor and ground potential via at least one of the first and second semiconductor switches when the asymmetry in the voltages exceeds a predefinable first threshold value,
• wherein the asymmetry in the voltages of the first DC conductor and the second DC conductor to ground potential is reduced and/or the voltages of the first DC conductor and the second DC conductor to ground potential are balanced by the compensation current;
• and
• monitoring a size of the compensation current by the control circuit and generating a switch-off signal and outputting the switch-off signal when a predefinable second threshold value is exceeded.