Patent ID: 7015664
Filing Date: 2006-03-21
Classification: H02P

Abstract:
1. A drive system for a multi-phase brushless electric motor comprising a plurality of phases, the system comprising: a drive circuit including at least one switch arranged to vary the phase voltage applied across each of the phases, and; a controller arranged to control the at least one switch so as to provide PWM control of the phase voltages to produce PWM voltage patterns thereby to control a mechanical output of the motor, wherein the controller is further arranged to control the PWM voltage patterns so as to include a test period, to measure a rate of change of current in at least one of the phases during the test period and to determine therefrom an inductance of at least one of the phases thereby to determine a rotational position of the motor wherein the controller is arranged to define at least one pair of test periods such that the phase voltages in one of the pair of test periods are opposite to those in the other of the pair of test periods and the controller is arranged to determine from currents measured in the pair of test periods the inductance of one of the phases wherein the pair of test periods are both provided in the same PWM period.