On-line measurement of an induction machine's rotor time constant by small signal d-axis current injection

A controller for controlling operation of an induction machine based on field oriented control, the controller including:

• means for controlling inputs to a stator of an induction machine based on commanded d-axis and q-axis current command signals, a calculated position associated with an electrical frequency, and monitored feedback regarding the present value of d-axis and q-axis currents in the induction machine;
• means for generating and injecting a small signal oscillation onto the d-axis current command signal, the small signal oscillation generated at a desired frequency;
• means for estimating d-axis rotor flux generated in the induction machine in response to the small signal oscillation injected onto the d-axis current command signal;
• means for updating an estimate of the rotor time constant based, in part, on the monitored d-axis rotor flux generated in response to the small signal oscillation;
• means for modifying the desired frequency of the small signal oscillation based on the present estimated value of the rotor time constant;
• and
• means for adjusting the calculated position associated with the electrical frequency used to generate the inputs provided to the stator of the induction machine based, in part, on the present estimated value of the rotor time constant.

A method of making on-line measurements of a rotor time constant associated with an induction machine, the method comprising:

• generating a small signal oscillation at a determined frequency;
• providing the small signal oscillation to the induction machine as an input;
• measuring rotor flux generated by the induction machine in response to the small signal oscillation;
• estimating a present value of the rotor time constant based on a position of the measured rotor flux generated in response to the input small signal oscillation;
• and
• modifying the determined frequency of the small signal oscillation based on the estimated rotor time constant.

A controller for controlling an induction machine, the controller comprising:

• means for interrogating the induction machine with a small signal oscillation generated at a frequency selected based on a most recent estimate of the rotor time constant;
• means for monitoring the response of the induction machine by measuring a rotor flux generated in response to the small signal oscillation;
• means for updating the most recent estimate of the rotor time constant and the frequency of the small signal oscillation based on the rotor flux generated in response to the small signal oscillation;
• and
• means for providing control instructions to the induction machine based, in part, on the most recent estimate of the rotor time constant.