Methods and apparatus for controlling power converters in parallel connection

摘要

An uninterruptible power supply (UPS) system (100) comprises a plurality of UPS units (UPS-1, UPS-2) connected in parallel. Each UPS unit comprises a power converter (124) for supplying a share (i load l, i_load_2) of a total load current (i_tot). The total load is shared automatically between UPS units of power ratings, in a proportionate manner. A controller 130 of each converter is arranged to establish real-time feedback control of a current supplied by the power converter. An exchange current (i_exch) for each converter represents an imbalance between an output current of the converter in question and output currents of the parallel converters. Exchange current sensing circuits of the parallel-connected UPS units are connected together. The controller steers the exchange current of each converter toward a value (i_ exc_c) that is a non-zero proportion of a current (i_mut) sensed within the converter. Said non-zero proportion is calculated such that the exchange current will be steered towards a positive value in the case of a converter with higher than average nominal power rating and toward a negative value in the case of a converter with lower than average power rating.