IMPROVEMENTS IN OR RELATING TO ROTOR POSITION DETECTION

摘要

Three windings (12) of a permanent magnet synchronousmotor10are connected from a common point (22) to respective feed points (24) and driven as a different phase of the motor 10by pwm excitation voltages from as witching circuit (28) under the control of a control circuit (38). Eight possible excitations state combinations exist for the circuit in Fig. 2 depending on whether the output of the circuit (28) is at supply voltage or ground for each of the three phases. Measurements are made of ratios of the voltage at the common point (22) as a proportion of the supply voltage, during various excitation states,and a comparison of these ratio values is used to derive position information for the rotor16of the motor (10).