Method for reducing a circulating current in a power converter with two power converter units arranged in parallel

A power converter comprising:

• a first power converter unit and a second power converter unit arranged in parallel between a positive voltage rail and a negative voltage rail of a direct current (DC) power bus, wherein each power converter unit comprises at least one commutation cell with a top switching unit and a bottom switching unit connected as a half bridge circuit and configured to receive a DC input voltage and provide a single phase current;
• gate drivers, wherein each gate driver is associated with a power converter unit of the first and second power converter units, wherein each gate driver is configured to provide a pulsed output signal for controlling switching of the switching units of the respective power converter unit, wherein the pulsed output signal comprises a switching frequency, wherein each phase current provided by the power converter is a sum of a respective first phase current of a commutation cell of the first power converter unit and a respective second phase current of a commutation cell of the second power converter unit;
• a delay compensating circuit configured to:
• determine, for each phase current, a characteristic frequency in the respective phase current, wherein the characteristic frequency is a switching frequency or related to the switching frequency;
• determine a magnitude of the characteristic frequency;
• and
• compare the magnitude of the characteristic frequency with a predetermined magnitude and determine whether the magnitude is larger than the predetermined magnitude;
• and
• a single controller configured to:
• provide pulsed control signals to the gate drivers, wherein the gate drivers provide pulsed output signals to the switching units of the respective commutation cell based on the pulsed control signals received from the single controller;
• receive information when the magnitude of the characteristic frequency is larger than the predetermined magnitude;
• and
• (i) shut down operation of at least one gate driver of the gate drivers when the magnitude of the characteristic frequency is larger than the predetermined magnitude;
• or (ii) add or reduce in steps a switching delay to the pulsed control signals provided to the gate driver of that commutation cell of the first power converter unit that is involved with providing the first phase current for the respective phase current when the magnitude of the characteristic frequency is larger than the predetermined magnitude.