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

Claims

What is claimed is:

1. A motor drive system comprising:

(a) an induction motor including a stator with a plurality of stator windings thereon, and a rotor mounted for rotation within the stator, the rotor including means for providing impedance as seen by the stator windings which varies as a function of the rotational position of the rotor;

(b) drive means, connected to the stator windings, for providing AC drive power to the stator windings at a fundamental drive frequency of the motor and for also providing power to the stator windings at a signal frequency which is substantially higher than the drive frequency; and

(c) means for 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 or the speed of the rotor or both can be determined.

2. The motor drive system of claim 1 wherein the rotor is constructed to have a leakage inductance which varies as a function of the rotational position of the rotor at the signal frequency to provide impedance as seen by the stator windings which varies with rotor position.

3. The motor drive system of claim 2 wherein the leakage inductance of the rotor varies as a periodic function of the rotational position of the rotor and has a period of 180 electrical degrees.

4. The motor drive system of claim 1 wherein the drive means includes an inverter having a plurality of switching devices connected in a bridge configuration and control means for controlling the switching of the switching devices to provide AC power to the stator windings, wherein the control means controls the switching of the switching devices of the inverter in a pulse width modulated manner at a high switching frequency to provide pulse width modulated output power which includes a component at the fundamental drive frequency and a component at the high signal frequency.

5. The motor drive system of claim 1 wherein the means for measuring the response of the stator to signal frequency power includes a heterodyne demodulator mixing a signal which is a function of the high signal frequency with the response from the stator windings to provide a signal indicative of the rotational position of the rotor.

6. The motor drive system of claim 1 wherein the induction motor is a three phase motor having three input lines, wherein the means for measuring includes means for detecting the currents in the input lines to the motor, means for transforming the detected currents to equivalent q-axis and d-axis current signals i.sup.s.sub.qsi.sup.s and i.sub.dsi, respectively, means for heterodyning the current signals to provide a mixed signal .di-elect cons. which is a function in accordance with the expression:

.di-elect cons.=i.sub.qsi.sup.s cos(2 .theta..sub.r -.omega..sub.i t)-i.sub.dsi.sup.s sin(2 .theta..sub.r -.omega..sub.i t),

where .theta..sub.r is an existing estimate of the rotor position and .omega..sub.i is the signal frequency,

and including a low pass filter filtering the signal .di-elect cons. to provide a filtered signal .epsilon..sub.f which is a function in accordance with the expression

.di-elect cons..sub.f =I.sub.il sin[2(.theta..sub.r - .theta..sub.r)]

where I.sub.il is a current amplitude and .theta..sub.r is the actual rotor position.

7. The motor drive system of claim 6 wherein the measuring means further includes an observer controller receiving the filtered signal .di-elect cons..sub.f, and a model of the mechanical system of the motor, the observer controller providing a selectively weighted and conditioned version of the signal to the mechanical system model, the mechanical system model also receiving a torque input signal and providing output signals which are estimates of rotor speed .omega..sub.r and position .theta..sub.r, the position estimate .theta..sub.r being fed back to the means for heterodyning.

8. The motor drive system of claim 1 wherein the drive means includes a current regulated inverter and the means for measuring provides a signal indicative of the rotational position of the rotor, and including controller means for controlling the power applied by the inverter to the motor to control its speed and torque, the controller means receiving input signals indicating the desired speed and torque of the motor, and also receiving the signal indicative of the rotational position of the rotor from the means for measuring, and for providing output signals to the current regulated inverter which indicate the desired output currents.

9. The motor drive system of claim 1 wherein the drive means comprises an inverter connected to the stator windings to provide the AC drive power on supply lines to the stator windings at the fundamental frequency and signal generators coupled to the supply lines to provide power to the stator windings at the signal frequency.

10. The motor drive system of claim 1 wherein the motor is a three phase motor and the drive means provides balanced power at the drive frequency and the signal frequency to the three phase stator windings.

11. 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.

12. The motor drive of claim 11 wherein the means for measuring the response of the stator windings to the signal frequency power includes a heterodyne demodulator mixing a signal which is a function of the high signal frequency with the response from the stator windings to provide a signal indicative of the rotational position of the rotor.

13. The motor drive of claim 11 wherein the inverter is a current regulated inverter.

14. The motor drive of claim 13 wherein the means for measuring provides a signal indicative of the rotational position of the rotor, and including controller means for controlling the power applied by the inverter to the motor to control its speed and torque, the controller means receiving input signals indicating the desired speed and torque of the motor, and also receiving the signal indicative of the rotational position of the rotor from the means for measuring, and for providing output signals to the current regulated inverter which indicate the desired output currents.

15. The motor drive of claim 11 wherein the induction motor is a three phase motor having three input lines, wherein the means for measuring includes means for detecting the currents in the input lines to the motor, means for transforming the detected currents to equivalent q-axis and d-axis current signals i.sup.s.sub.qsi.sup.s and i.sub.dsi, respectively, means for heterodyning the current signals to provide a mixed signal .di-elect cons. which is a function in accordance with the expression:

.di-elect cons.=i.sub.qsi.sup.s cos(2 .theta..sub.r -.omega..sub.i t)-i.sub.dsi.sup.s sin(2 .theta..sub.r -.omega..sub.i t),

where .theta..sub.r is an existing estimate of the rotor position and .omega..sub.i is the signal frequency,

and including a low pass filter filtering the signal .di-elect cons. to provide a filtered signal .di-elect cons..sub.f which is a function in accordance with the expression

.di-elect cons..sub.f =I.sub.il sin[2(.theta..sub.r - .theta..sub.r)]

where I.sub.il is a current amplitude level and .theta..sub.r is the actual rotor position.

16. The motor drive of claim 15 wherein the measuring means further includes an observer controller receiving the filtered signal .di-elect cons..sub.f, and a model of the mechanical system of the motor, the observer controller providing a selectively weighted and conditioned version of the signal .di-elect cons..sub.f to the mechanical system model, the mechanical system model also receiving a torque input signal and providing output signals which are estimates of rotor speed .omega..sub.r and position .theta..sub.r, the position estimate .theta..sub.r being fed back to the means for heterodyning.

17. 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.

18. The motor drive of claim 17 further including a transform circuit means for receiving the signals from the sensors and providing equivalent q-axis and d-axis current signals, and wherein the heterodyne demodulator mixes signals at the high signal frequency with the q-axis and d-axis signals from the transform circuit means to provide a mixed signal to provide the signal indicative of the rotational position of the rotor.

19. The motor drive of claim 17 wherein the drive means includes a current regulated inverter connected to provide power to a motor.

20. The motor drive of claim 19 including controller means for controlling the power applied by the inverter to a motor to control its speed and torque, the controller means receiving input signals indicating the desired speed and torque of the motor, and also receiving the signal indicative of the rotational position of the rotor, and for providing output signals to the current regulated inverter which indicate the desired output currents.

21. The motor drive of claim 18 wherein the drive means comprises an inverter connected to the stator windings to provide the AC drive power on supply lines to the stator windings at the fundamental frequency and signal generators coupled to the supply lines to provide power to the stator windings at the signal frequency.

22. The motor drive of claim 18 wherein the motor is a three phase motor having three input lines, wherein the transform circuit means for transforming the detected currents to equivalent q-axis and d-axis currents provides signals i.sup.s.sub.qsi.sup.s and i.sub.dsi, respectively, and the heterodyne demodulator demodulates the current signals to provide a mixed signal .di-elect cons. which is a function in accordance with the expression:

.di-elect cons.=i.sub.qsi.sup.s cos(2 .theta..sub.r -.omega..sub.i t)-i.sub.dsi.sup.s sin(2 .theta..sub.r -.omega..sub.i t),

where .theta..sub.r is an existing estimate of the rotor position and .omega..sub.i is the signal frequency,

and a low pass filter which filters the signal e to provide a filtered signal .di-elect cons..sub.f which is a function in accordance with the expression

.di-elect cons..sub.f =I.sub.il sin[2(.theta..sub.r - .theta..sub.r)]

where I.sub.il is an equivalent current level and .theta..sub.r is the actual rotor position.

23. The motor drive of claim 22 wherein the measuring means further includes an observer controller receiving the filtered signal .di-elect cons..sub.f, and a model of the mechanical system of the motor, the observer controller providing a selectively weighted and conditioned version of the signal .di-elect cons..sub.f to the mechanical system model, the mechanical system model also receiving a torque input signal and providing output signals which are estimates of rotor speed .omega..sub.r and position .theta..sub.r, the position estimate .theta..sub.r being fed back to the means for heterodyning.

24. 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.

25. The method of claim 24 wherein the step of measuring the response of the stator windings includes the steps of mixing a signal which is a function of the high signal frequency with the current from the stator windings and low pass filtering the mixed signal to provide a signal indicative of the rotational position of the rotor.

26. The method of claim 24 wherein the motor is a three phase motor having three input lines, wherein the step of measuring the response includes the steps of detecting the currents in the input lines to the motor, transforming the detected currents to equivalent q-axis and d-axis current signals i.sup.s.sub.qsi and i.sup.s.sub.dsi, respectively, heterodyning the current signals to provide a mixed signal .di-elect cons. which is a function in accordance with the expression:

.di-elect cons.=i.sub.qsi.sup.s cos(2 .theta..sub.r -.omega..sub.i t)-i.sub.dsi.sup.s sin(2 .theta..sub.r -.omega..sub.i t),

where .theta..sub.r is an existing estimate of the rotor position and .omega..sub.i is the signal frequency,

and low pass filtering the signal .di-elect cons. to provide a filtered signal .di-elect cons..sub.f which is a function in accordance with the expression

.di-elect cons..sub.f =I.sub.il sin[2(.theta..sub.r - .theta..sub.r)]

where I.sub.il is a current amplitude and .theta..sub.r is the actual rotor position.

27. The method of claim 26 including the step of providing a selectively weighted and conditioned version of the signal .di-elect cons..sub.f to a mechanical system model for the motor and also providing a torque input signal to the mechanical system model, and providing output signals from the model which are estimates of rotor speed .omega..sub.r and position .theta..sub.r, and feeding back the position estimate .theta..sub.r to the step of heterodyning.

28. 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.

29. The motor drive system of claim 28 wherein the secondary is constructed to have a leakage inductance which varies as a function of the relative position of the secondary and primary at the signal frequency to provide impedance as seen by the primary which varies with relative position.

30. The motor drive system of claim 28 wherein the drive means includes an inverter having a plurality of switching devices connected in a bridge configuration and control means for controlling the switching of the switching devices to provide AC power to the primary, wherein the control means controls the switching of the switching devices of the inverter in a pulse width modulated manner at a high switching frequency to provide pulse width modulated output power which includes a component at the fundamental drive frequency and a component at the high signal frequency.

31. The motor drive system of claim 28 wherein the means for measuring the response of the primary to signal frequency power includes a heterodyne demodulator mixing a signal which is a function of the high signal frequency with the response from the primary to provide a signal indicative of the relative position of the primary and secondary.

FIELD OF THE INVENTION

This invention pertains generally to the field of motor drive and control systems and to the determination of rotor speed and position in AC machines.

BACKGROUND OF THE INVENTION

A variety of drive systems for AC machines utilizing electronic switching to control the power applied to the machines are presently available commercially. These AC machine drives allow the speed and/or torque of the machine to be controlled to meet various requirements. Such machine drives typically require mechanical shaft transducers to provide feedback of shaft position and/or velocity. Feedback is required both for torque control (i.e., field orientation or vector control) and trajectory tracking. However, shaft transducers and the associated wiring to provide the signals from the shaft transducers to the electronic drive add significantly to the cost and rate of failure of the system, and also add to the total volume and mass of the machine at the work site. Because induction machines are generally lower in cost and more rugged than other machine types, to a large extent the advantages of induction machines are the most compromised by the addition of such transducers.

Consequently, the desirability of eliminating position or velocity transducers in motor motion control applications has long been recognized. Several approaches have been proposed to allow estimation of the rotor position or velocity. Some success, although limited, has been obtained with techniques for determining the rotor position in synchronous and reluctance machines, which are considerably less complex than induction machines and have inherent spatially dependent rotor properties that can be easily tracked. Estimation of rotor position and velocity in the induction machine, which is by far the most common machine type and thus has the most significant commercial potential, is complicated because of its smooth symmetric rotor and symmetric induced rotor currents and slip. Nonetheless, accurate and parameter insensitive position and velocity measurement in induction machines can only be obtained by tracking spatial phenomena within the machine.

SUMMARY OF THE INVENTION

In accordance with the present invention, a drive system for polyphase AC machines provides power to the stator windings of the machine which includes a component at the fundamental drive frequency and a superimposed signal component which is at a higher frequency and lower power than the drive power--preferably a frequency high enough and a power low enough that the signal component does not substantially affect the motion of the rotor. The rotor of the machine has saliencies which change the rotor impedance and affect the response of the stator windings to the excitation signal at the signal frequency as a function of rotor rotational position. Preferably, the rotor leakage inductance in inductance machines, and the synchronous inductances in synchronous machines, as seen by the stator windings changes as a periodic function of rotor rotational position. The stator response at the signal frequency may then be detected and measured to provide a correlation between the magnitude of the response at the signal frequency and the rotor position. The information on rotor position as a function of time (and, thus, also information on the velocity of the rotor) can be utilized in a controller to provide appropriate fundamental frequency drive power to the motor to drive it at a desired speed or torque, or to a desired position.

The present invention can be carried out utilizing machines having inherent rotor saliency, such as some permanent magnet synchronous machines and all synchronous reluctance machines. However, it is a particular advantage of the present invention that it may be utilized with induction machines by introducing saliencies in the rotor which primarily have effect only at the relatively high frequency of the additional excitation signal. For example, the rotor may be constructed to have a variation in the effective leakage inductance of the rotor, and hence impedance as seen by the stator windings, as a function of the position of the rotor with respect to the stator at the signal frequency, but may have a substantially uniform and symmetrical impedance characteristic at the fundamental drive and slip frequencies with torque controlled operation. At low slip frequencies corresponding to field oriented operation and at normal fundamental drive frequencies, the impedance tends to be dominated by the effective rotor resistance and not leakage inductance. Thus, even if the inductance varies somewhat, at these low frequencies the effect on impedance and motor operation is small. Such asymmetries or saliencies in the induction machine rotor can be introduced in various ways, including but not limited to variations in rotor slot width and depth around the periphery of the rotor, variations in the cross-section or geometry of the conductive bars around the rotor, and by opening up selected rotor slots, with other rotor slots between them being closed. Existing squirrel cage induction motors can be modified to carry out the present invention by, for example, selectively cutting slots in the rotor over selected rotor bars or cutting slots of varying width over the bars.

The detection of the response to the high frequency signal at the stator windings is preferably carried out utilizing heterodyne detection by mixing a polyphase signal which is a function of the injected signal frequency with the polyphase response signal, and filtering the mixed signal to isolate the modulation of the response to the signal frequency, which is correlated with the angular position of the rotor.

The drive system may include an inverter which can be controlled in a space vector, pulse width modulated manner to provide output voltage to the stator windings at both the fundamental drive frequency and at the signal frequency. The inverter may also be controlled to provide only the fundamental drive frequency power to the stator, and a separate signal generator may be connected to inject the high frequency signal into the stator windings.

The invention may also be embodied in a linear motor. One of the windings of the linear motor acts as a primary (as do the stator windings) inductively coupled to a relatively movable secondary winding (corresponding to the rotor conductors). The impedance seen by the primary varies as a function of the relative position of the secondary.

Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic diagram of an exemplary transducerless torque controlled AC machine drive system in accordance with the invention which uses a direct field oriented controller based upon a rotor flux observer and a position and velocity observer.

FIG. 2 is a schematic diagram of a transducerless AC machine drive motion control system in accordance with the invention which uses an observer based direct or indirect field oriented controller and a position and velocity observer in accordance with the invention.

FIG. 3 is a schematic diagram of a torque controlled transducerless AC machine drive system in accordance with the invention which uses an indirect field oriented controller and a position and velocity observer in accordance with the invention.

FIG. 4A is a schematic diagram of an inverter system which may be utilized in the invention which has a pulse-width-modulated voltage source inverter to provide the low frequency drive and high frequency signal components.

FIG. 4B is a simplified schematic diagram of an inverter system similar to that of FIG. 4A but with current injection utilizing a current regulated voltage source inverter.

FIG. 5 is a schematic diagram of a closed loop position and velocity observer in accordance with the invention.

FIG. 6 is a schematic diagram of a closed loop position and velocity observer in accordance with the invention which has reduced sensitivity to unbalanced voltage sources.

FIG. 7 is a schematic diagram of a closed loop position and velocity observer in accordance with the invention which has reduced sensitivity to both unbalanced and weak high frequency voltage sources.

FIG. 8A is an equivalent circuit schematic diagram for a conventional induction machine in the steady state.

FIG. 8B is the effective equivalent circuit of FIG. 8A as seen by the high frequency excitation signal.

FIGS. 9A and 9B are simplified views through a portion of an induction machine rotor and stator showing simplified flux paths for magnetic flux at the fundamental drive frequency.

FIGS. 10A and 10B are simplified views through a portion of an induction machine rotor and stator illustrating simplified flux paths for magnetic flux at the frequency of the high frequency excitation signal over one slot pitch.

FIG. 11 is a view of an illustrative four-pole squirrel cage induction motor in accordance with the invention which incorporates spatially variant rotor leakage inductance created by variation of the width of rotor slot openings.

FIG. 12 is a simplified partial view through an induction machine of the type shown in FIG. 11 illustrating instantaneous flux paths for high frequency injected signal excitation over one machine pole pitch, with the rotor position relative to excitation corresponding to the low rotor leakage inductance position.

FIGS. 13A and 13B are illustrative views through a portion of an induction machine rotor illustrating rotor slot opening dimensions and the corresponding current and leakage flux components for a deep rotor slot.

FIG. 14 is an illustrative view through a portion of an induction machine rotor illustrating the rotor current and leakage flux for a shallow depth slot.

FIG. 15 is an illustrative view of a portion of an induction machine rotor similar to that of FIG. 14 but with a filled slot to provide low leakage flux.

FIGS. 16A and 16B are views through a portion of an induction machine rotor illustrating the current and leakage flux at the fundamental and at the injected signal frequency, respectively, for a filled deep rotor slot.

FIG. 17 is a simplified view through a four-pole squirrel cage induction motor having spatially variant rotor leakage inductance created by opening selected rotor slots while leaving other rotor slots closed.

FIG. 18 is a simplified view through a four-pole squirrel cage induction motor having spatially variant rotor leakage inductance created by variation in the rotor conductor bar depth and slot depth around the periphery of the rotor.

FIG. 19 is a simplified view of a two-pole squirrel-cage induction motor with spatially variant rotor leakage inductance created by variation in the rotor bar depth and slot depth.

FIG. 20 is a simplified view through a four-pole inset mounted permanent magnet synchronous machine having inherent rotor magnetic saliency.

FIG. 21 is a simplified view through a four-pole embedded (buried) permanent magnet synchronous machine with inherent rotor magnetic saliency.