Calibration of current sensors in parallel power converters

A power supply unit suitable for operation in parallel with one or more power supply units to supply a total electric current to a load, said power supply unit comprising:

• at least one current sensor for measuring a current supplied by the unit;
• and
• a feedback controller for using the measured current during said parallel operation and for controlling the unit to maintain a desired condition of supply, wherein said controller is further arranged to perform a current calibration procedure performed prior to said parallel operation by:
• (a) operating the power supply unit as a secondary supply in parallel connection with a primary power supply external to the power supply unit, while both are disconnected from said load;
• (b) operating said current sensor in the power supply unit to measure current flowing in said secondary supply;
• (c) receiving information of current flowing in said primary supply measured by a primary current sensor outside the power supply unit;
• and
• (d) calibrating the current measured in the power supply unit against the primary current sensor, on the basis that said current in the primary supply is equal and opposite to the current flowing in the secondary supply.