Inverter with identification of neutral connection

1. A method for determining a connection configuration of an inverter to an AC voltage grid, the inverter having a terminal with four conductor connectors for connection of the inverter to three outer conductors and to a neutral conductor of the AC voltage grid, comprising:

actuating switching elements of a bridge circuit of the inverter to generate a zero-phase sequence system having a zero-phase sequence system current;

measuring and evaluating output currents of the inverter with respect to the zero-phase sequence system current;

identifying a presence of a connection of the neutral conductor to a conductor connector provided for connection to the neutral conductor when the zero-phase sequence system current exceeds a prescribed threshold value and identifying that the neutral conductor is not connected to the conductor connector provided for connection to the neutral conductor otherwise; and

using a control structure to actuate the switching elements of the bridge circuit of the inverter, in which the control structure compares a setpoint value for the zero-phase sequence system current with an actual value of the zero-phase sequence system current.

2. The method as claimed in claim 1 , further comprising:

selecting a first operational management procedure adjusted to four-conductor operation with connected neutral conductor when it has been identified that there is a connection of the neutral conductor to the conductor connector provided for connection to the neutral conductor; and

selecting a second operational management procedure adjusted to three-conductor operation without connected neutral conductor otherwise, wherein the second operational management procedure is different from the first operational management procedure.

3. The method as claimed in claim 2 , further comprising using a preset value stored in the inverter to prescribe whether the inverter is to be operated in a feed-in mode on the basis of the first operational management procedure or on the basis of the second operational management procedure.

4. The method as claimed in claim 3 , further comprising generating a warning message in the event of a discrepancy between the operational management procedure prescribed by the preset value and the operational management procedure to be selected on account of the determining act, wherein the warning message is stored in the inverter and/or communicated to an operator of the inverter.

5. The method as claimed in claim 3 , wherein in the event of a discrepancy between the operational management procedure prescribed by the preset value and the operational management procedure selected on account of the determining act, preventing the inverter from feeding electrical power into the AC voltage grid.

6. The method as claimed in claim 2 , further comprising operating the inverter on the basis of the operational management procedure selected on account of the determining act.

7. The method as claimed in claim 6 , wherein the inverter feeds electrical power into the AC voltage grid.

8. The method as claimed in claim 7 , wherein the first operational management procedure comprises asymmetrical in-feeding of the output currents to the AC voltage grid.

9. The method as claimed in claim 1 , wherein the determining act is executed as part of an activation and/or during a start-up process of the inverter.

10. The method as claimed in claim 1 , wherein as part of the determining act, actuating the switching elements of the bridge circuit of the inverter to generate a zero-phase sequence system at a frequency above a grid frequency.

11. The method as claimed in claim 10 , wherein the frequency of the zero-phase sequence system has a non-integer multiple of the grid frequency.

12. An inverter for converting electrical power from direct current to alternating current and in-feeding the converted electrical power to an AC voltage grid, wherein the inverter has a terminal with four conductor connectors for connection of the inverter to three outer conductors and to a neutral conductor of an AC voltage grid, wherein the inverter comprises a control unit configured to determine a connection configuration of the inverter to the AC voltage grid by:

actuating switching elements of a bridge circuit of the inverter to generate a zero-phase sequence system having a zero-phase sequence system current;

measuring and evaluating output currents of the inverter with respect to the zero-phase sequence system current;

identifying a presence of a connection of the neutral conductor to a conductor connector provided for connection to the neutral conductor when the zero-phase sequence system current exceeds a prescribed threshold value and identifying that the neutral conductor is not connected to the conductor connector provided for connection to the neutral conductor otherwise; and

using a control structure to actuate the switching elements of the bridge circuit of the inverter, in which the control structure compares a setpoint value for the zero-phase sequence system current with an actual value of the zero-phase sequence system current.

13. The inverter as claimed in claim 12 , wherein the conductor connector provided for the connection of the neutral conductor is connected to a center point of a DC link circuit.

14. The inverter as claimed in claim 13 , wherein the conductor connector provided for the connection of the neutral conductor is connected by means of a switching element to the center point of the DC-side DC link circuit.