a method and apparatus for converting three phase ac voltages on first , second and third input lines to dc voltage across positive and negative dc buses , the apparatus comprising a rectifier including first , second and third rectifier legs , each leg including a switch and a diode wherein the switch is linked between the positive dc bus and an cathode of the diode , an anode of the diode is linked to the negative dc rail and the first , second and third diode cathodes are linked to the first , second and third input lines , respectively , a dc bus voltage sensor linked to the positive dc bus and measuring the dc bus voltage to generate a measured dc bus voltage and a rectifier controller that receives the measured dc bus voltage , a reference voltage value and the three phase ac voltages wherein , when the measured dc bus voltage is at least equal to the reference voltage value , the controller turns on the switches in the first , second and third rectifier legs when the voltages on the first , second and third input lines are positive , respectively .