Method and apparatus for transducerless position and velocity estimation in drives for AC machines

A motor drive for providing drive power to polyphase AC motors of the type which have stator windings and a rotor which is constructed to provide impedance as seen by the stator windings which varies as a periodic function of the rotational position of the rotor, comprising:

• (a) an inverter bridge adapted to receive power and having a plurality of switching devices which can be switched to provide polyphase AC power at output supply lines of the inverter;
• (b) control means for controlling the switching of the switching devices of the inverter to provide AC power at the output terminals of the inverter which can be provided to stator windings of an AC motor, wherein the control means controls the switching of the switching devices of the inverter to provide output power which includes a polyphase component at a fundamental drive frequency for a motor and a balanced polyphase component at a substantially higher signal frequency;
• and
• (c) means for measuring the response of the stator windings at the output supply lines to the signal frequency power to determine the variation of the response as a function of time during operation of the motor whereby the angular position or the speed of the rotor or both can be determined.

A motor drive for providing drive power to polyphase AC motors such as motors of the type which have stator windings and a rotor which is constructed to provide impedance as seen by the stator windings which varies as a periodic function of the rotational position of the rotor, comprising:

• (a) drive means, having output supply lines which can be connected to the stator windings, for providing polyphase AC drive power at a fundamental drive frequency to a motor connected to the output supply lines to receive the AC drive power and for also providing balanced polyphase power to the output supply lines at a signal frequency which is substantially higher than the drive frequency;
• (b) sensors connected to the output supply lines sensing the response of the motor to the power provided by the drive means and providing output signals indicative of the response;
• and
• (c) a heterodyne demodulator connected to receive the signals from the sensors and mix a signal which is a function of the high signal frequency with the response signals from the sensors to provide a signal indicative of the rotational position of the rotor.

A method of determining the rotational position of an AC motor comprising the steps of:

• (a) providing a polyphase motor including a stator with a plurality of stator windings thereon, and a rotor mounted for rotation within the stator, the rotor constructed to provide impedance as seen by the stator windings which varies as a periodic function of the rotational position of the rotor;
• (b) providing balanced AC drive power to the stator windings at a fundamental drive frequency of the motor;
• (c) providing balanced AC power to the stator windings at a signal frequency which is substantially higher than the drive frequency;
• and
• (d) measuring the response of the stator windings to the signal frequency power to determine the variation of the response as a function of time during operation of the motor whereby the angular position of the rotor as a function of time or the speed of the rotor or both can be determined from the variation of the response during operation of the motor.

A motor drive system comprising:

• (a) a linear motor including a primary and a secondary, the primary and secondary movable linearly with respect to each other, the secondary magnetically coupled to the primary to provide impedance as seen by the primary which varies as a function of the relative position of the primary and secondary;
• (b) drive means, connected to the primary, for providing AC drive power to the primary at a fundamental drive frequency of the motor and for also providing power to the primary at a signal frequency which is substantially higher than the drive frequency;
• and
• (c) means for measuring the response of the primary to the signal frequency power to determine the variation of the response as a function of time during operation of the motor whereby the relative linear position of the primary and secondary can be determined.