Patent ID: 8076898

Claim:
A method of controlling a three phase motor wherein each phase of the motor is driven from first and second power terminals by a respective switch arrangement comprising: a first switch and a first reverse diode connected in parallel between the first power terminal and a motor phase and a second switch and a second reverse diode connected in parallel between the second power terminal and the motor phase, the method comprising: operating the first switch so as to disconnect the motor phase from the first power terminal while the motor phase is disconnected from the second power terminal; determining a first time when a back-EMF of the motor phase crosses a non-zero reference back-EMF voltage level, which first time is earlier than a second time when the back-EMF next crosses a zero voltage level; using the first time to determine a third time later than the first time; and operating the second switch so as to connect the motor phase to the second power terminal at the third time.