Patent ID: 8217605

Claim:
A motor controller for determining a position of a rotor of an AC motor, the motor controller comprising: a control input for receiving a control signal, an output for providing a power control signal for controlling power applied to a stator of the AC motor, the control input and output being coupled by a reference path; an input for receiving a feedback signal representative of the current in the stator, the input being coupled to the control input by a feedback path; a carrier signal injection element for injecting a high frequency carrier signal in the reference path at an injection node, the motor controller being arranged to generate the power control signal in dependence on the control signal, the feedback signal, and the high frequency carrier signal; a position determining element for generating a position signal representing the position of the rotor in dependence on the feedback signal which includes a carrier signal component comprising rotor position information; a filter block coupled between the control input and the injection node in the reference path for filtering signals in the reference path in a frequency range including the frequency of the high frequency carrier signal; and a load correction element for generating a correction value for the position of the rotor due to the response of the rotor to variations in load and a combining element for combining the correction value with the position signal to generate a corrected position signal.