Method for operating an inverter with reactive power capability having a polarity reverser, and inverter with reactive power capability having a polarity reverser

A method for operating an inverter with reactive power capability comprising a bidirectional DC/DC converter, a voltage link circuit, and an unfolding bridge, wherein the bidirectional DC/DC converter comprises at least one storage inductor device, wherein one terminal of the storage inductor device is configured to be connected to one pole of a DC input via a switch, another terminal of the storage inductor device is connected to one pole of the voltage link circuit, and the one terminal of the storage inductor device, or a further terminal of the storage inductor device connected to the same winding of the storage inductor device as the other terminal, is configured to be connected to the other pole of the voltage link circuit via a switching element, wherein poles of the voltage link circuit are configured to be connected to terminals of an AC output in different configurations by means of the unfolding bridge, in order to change a polarity of the AC output relative to the voltage link circuit, and wherein the method comprises:

• in the case of a phase shift between an AC current (I) and an AC voltage (U) at the AC output, reversing the direction of a current flowing via the voltage link circuit, when the polarity of the AC output relative to the voltage link circuit is changed by the unfolding bridge between the half-cycles of the AC voltage;
• reversing the direction of the current flowing via the voltage link circuit in the case of the AC current (I) lagging behind the AC voltage (U) at the AC output, wherein the reversing comprises:
• charging the voltage link circuit with the current flowing through the storage inductor device, and
• discharging the voltage link circuit via the storage inductor device or via a further storage inductor device.

An inverter with reactive power capability, comprising:

• a bidirectional DC/DC converter,
• a voltage link circuit coupled to the bidirectional DC/DC converter,
• an unfolding bridge, and
• an operation controller,
• wherein the unfolding bridge is connected between poles of the voltage link circuit and terminals of an AC output, and
• wherein the operation controller is operably coupled to the unfolding bridge and is configured to operate the inverter according to a method comprising:
• in the case of a phase shift between an AC current (I) and an AC voltage (U) at the AC output, reversing the direction of a current flowing via the voltage link circuit, wherein reversing the direction of the current flowing via the voltage link circuit comprises:
• disconnecting the AC output from the voltage link circuit,
• providing a freewheeling path between the terminals of the AC output, while the AC output is disconnected from the voltage link circuit, and
• reconnecting the AC output to the voltage link circuit with the polarity of the AC output relative to the voltage link circuit being changed by the unfolding bridge.