N X 18-PULSE AUTOTRANSFORMER RECTIFIER UNIT (ATRU) SYSTEM WITH CONTROLLED ADJUSTABLE BALANCING RESISTOR

An auto-transformer rectifier system comprising an 18-pulse (or multiple of 18-pulse) autotransformer rectifier unit ATRU having three, or a multiple of three, diode bridge rectifiers (5a, 5b, 5c) and a balancing resistor (40) to balance the power flow through the diode bridge rectifiers, wherein the balancing resistor has a variable resistance, and further comprising a controller (80) configured to identify imbalances between power flows of the respective diode bridge rectifiers and to adjust the resistance of the balancing resistor in response to the detected imbalance.