Method and apparatus for transducerless flux estimation in drives for induction machines

A motor drive for providing drive power to polyphase AC induction motors of the type which have a stator with stator windings and a uniform 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 at a level sufficient to provide magnetic saturation in the stator 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 magnetic flux vector or both can be determined.

A motor drive for providing drive power to polyphase AC induction motors of the type which have a stator with stator windings and a uniform 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 an AC induction motor connected to the output supply lines to receive the AC drive power at a level sufficient to provide magnetic saturation in the stator 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 magnetic flux vector.

A method of determining the rotational position of the magnetic flux vector in an AC induction 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 being uniform such that the impedance as seen by the stator windings does not substantially vary as a 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 at a level sufficient to provide magnetic saturation in the stator;
• (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 magnetic flux vector as a function of time or the speed of the flux vector or both can be determined from the variation of the response during operation of the motor.

A motor drive system comprising:

• (a) a linear induction 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, the secondary being uniform such that the impedance as seen by the primary does not vary 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 which is at a level sufficient to provide magnetic saturation in the primary 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 magnetic flux vector with respect to the primary can be determined.