Sma Solar Technology Ag

Wilfried Vogt

Burkard Mueller

Klaus Rigbers

A method for operating a transformerless inverter includes operating first and second half-bridges of the inverter using a unipolar clocking method as a first clocking method, determining a value of a grid-frequency stray current at the DC terminals of the inverter during the unipolar clocking method, and when a limit value is exceeded by the stray current value, operating the first and second half-bridges of the inverter using a stray-current-reducing clocking method as a second clocking method in which the first half-bridge provides an AC voltage at the first AC output, wherein an amplitude of the AC voltage is less than 50% of the amplitude of a voltage amplitude of the grid, and the second half-bridge provides a difference voltage between the grid voltage and the voltage provided by the first half-bridge at the first AC output.

Hybrid clocking method for single-phase transformer-free network inverters

For defining an electric potential of input lines of an inverter with respect to ground, in all current-carrying output lines of the inverter capacitors are arranged and charged to a DC voltage in order to shift the electric potential of the input lines with respect to a reference potential present at the current-carrying output lines of the inverter by this DC voltage.

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Kassel, Germany

Wilfried Vogt