Apparatus for quasi-sensorless adaptive control of switched reluct ange motor drives

Abstract

A method and apparatus for quasi-sensorless adaptive control of a high rotor pole switched-reluctance motor (HRSRM). The method comprises the steps of: applying a voltage pulse to an inactive phase winding and measuring current response in each inactive winding. Motor index pulses are used for speed calculation and to establish a time base. Slope of the current is continuously monitored which allows the shaft speed to be updated multiple times and to track any change in speed and fix the dwell angle based on the shaft speed. The apparatus for quasi-sensorless control of a high rotor pole switched-reluctance motor (HRSRM) comprises a switched-reluctance motor having a stator and a rotor, a three-phase inverter controlled by a processor connected to the switched-reluctance motor, a load and a converter.

Claims

1. A method for controlling a high rotor pole switched-reluctance motor (HRSRM), the method comprising steps of: a) providing an HRSRM with a rotor; b) applying current to an active phase winding to rotate the rotor; c) establishing a time base for a software control module on a magnetic sensor; d) updating the time base by generating a motor index pulse from the magnetic sensor; e) calculating a shaft speed of the motor; f) canceling out a switching threshold of the magnetic sensor; g) monitoring a slope of a current waveform in the active phase to fine-tune a firing angle based on said shaft speed; h) adjusting a pulse time t.sub.on based on an estimated time base; i) monitoring the shaft speed to track any change in the shaft speed; and j) adjusting a dwell angle based on the shaft speed and the current.

2. The method of claim 1 further comprising: a. applying a voltage pulse to an inactive phase winding of the HRSRM; b. measuring current response in the inactive phase of the HRSRM; c. applying multiple diagnostic pulses to the inactive phase of the HRSRM.

3. The method of claim 2 wherein after ten rotations the software control module establishes the time base and the inactive phase is not necessary to maintain operation.

4. The method of claim 1 wherein at least three signals are generated per rotor pole and the shaft speed of the motor is calibrated.

5. The method of claim 1 wherein the time base is established to avoid slip in calculated value of speed.

6. The method of claim 1 wherein the dwell angle is reduced if the commanded current is below a lower band.

7. The method of claim 1 wherein the dwell angle is increased if the commanded current is above an upper band.

8. A method for quasi-sensorless adaptive control of a high rotor pole switched-reluctance motor (HRSRM), the method comprising steps of: a) providing an HRSRM with a rotor; b) aligning the rotor with respect to an initial position to start with a known phase and to rotate in a direction; c) applying current to an active phase winding to rotate the motor; d) establishing a time base for a software control module on a magnetic sensor; e) calculating a speed and updating the time base by generating a motor index pulses from the magnetic sensor; f) calibrating a shaft speed of the motor and calibrating a software encoder to operate on the time base; g) canceling out a switching threshold of the magnetic sensor; h) monitoring the slope of the current waveform in the active phase to fine-tune a firing angle from an encoder software; i) adjusting a pulse time t.sub.on based on an estimated time base; and j) monitoring the shaft speed to track any change in speed and fixing a dwell angle based on the shaft speed.

9. The method of claim 8 wherein the rotor produces an inductance profile in each of the stator poles as each of the rotor poles comes into and out of alignment with the stator poles when the rotor is rotated.

10. The method of claim 8 wherein the active phase winding is the phase that has a rotor pole close to the aligned position.

11. The method of claim 8 wherein a pulse of voltage is applied to the phase winding to measure the current response.

12. The method of claim 8 further comprising a. estimating position using a diagnostic pulse on an inactive phase winding during an initial rotation by estimating the inductance profile; b. applying a voltage pulse to the inactive phase winding and measuring current response in each inactive phase; c. applying multiple diagnostic pulses to the inactive phase to identify the next phase; d. wherein the multiple diagnostic pulses are applied for at least ten rotations to establish the time base for the software control module.

13. The method of claim 12 wherein after ten rotations the software control module establishes the time base and the inactive phase is not necessary to maintain operation.

14. The method of claim 8 wherein at least three signals are generated per rotor pole and the shaft speed of the motor is calibrated.

15. The method of claim 8 wherein the dwell angle is reduced if the commanded current is below a lower band.

16. The method of claim 8 wherein the dwell angle is increased if the commanded current is above an upper band.

17. An apparatus for quasi-sensorless control of a high rotor pole switched-reluctance motor (HRSRM) comprising: a switched-reluctance motor having a stator and a rotor, the rotor having a plurality of circumferentially spaced rotor poles, the rotor rotationally related to a motor shaft having a magnetic sensor; a three-phase inverter controlled by a processor connected to an input of the switched-reluctance motor, the three-phase inverter adaptable to provide a power supply the switched-reluctance motor, the processor having a software control module and a software encoder; a load connected to an output of the switched-reluctance motor via an inline torque meter; a converter connected to the load; and a software control module at the processor, the software control module comprising: a rotor position estimation module to determine an initial position of the rotor utilizing a sequence of relation between phase inductances of the HRSRM, to estimate rotor position and to establish a firm time base for the software control module; a time base module to calculate a shaft speed; a slope monitoring module to monitor slope of a current waveform in an active phase; a pulse time module to adjust pulse time based on an estimated time base; and a dwell control module to fix a dwell angle and to establish a current band for controlling a dwell angle thereby operating the SRM at a saturation level.

18. The apparatus of claim 17 wherein a time base is established in the magnetic sensor utilizing an inactive phase.

19. The apparatus of claim 17 wherein the time base is established to avoid slip in calculated value of speed.

20. The apparatus of claim 17 wherein at least three signals are generated per rotor pole and the shaft speed is calibrated.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to enhance their clarity and improve understanding of these various elements and embodiments of the invention, elements in the figures have not necessarily been drawn to scale. Furthermore, elements that are known to be common and well understood to those in the industry are not depicted in order to provide a clear view of the various embodiments of the invention, thus the drawings are generalized in form in the interest of clarity and conciseness.

(2) FIG. 1 illustrates a flow chart of a method for controlling a high rotor pole switched-reluctance motor (HRSRM) in accordance with the present invention;

(3) FIG. 2 is a graph illustrating an inductance profile according to the phase changes of a three phase SRM in accordance with the present invention;

(4) FIG. 3 illustrates a block diagram of an apparatus for controlling the high rotor pole switched-reluctance motor (HRSRM) in accordance with the present invention;

(5) FIG. 4A is a graph illustrating a current waveform of a three-phase SRM at a particular load in accordance with the present invention;

(6) FIG. 4B is a graph illustrating the current waveform of the three-phase SRM at another load in accordance with the present invention; and

(7) FIG. 4C is a graph illustrating the current waveform of the three-phase SRM at yet another load in accordance with the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(8) In the following discussion that addresses a number of embodiments and applications of the present invention, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and changes may be made without departing from the scope of the present invention.

(9) Various inventive features are described below that can each be used independently of one another or in combination with other features. However, any single inventive feature may not address any of the problems discussed above or only address one of the problems discussed above. Further, one or more of the problems discussed above may not be fully addressed by any of the features described below.

(10) As used herein, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. “And” as used herein is interchangeably used with “or” unless expressly stated otherwise. As used herein, the term ‘about” means +/−5% of the recited parameter. All embodiments of any aspect of the invention can be used in combination, unless the context clearly dictates otherwise.

(11) Unless the context clearly requires otherwise, throughout the description and the claims, the words ‘comprise’, ‘comprising’, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”. Words using the singular or plural number also include the plural and singular number, respectively. Additionally, the words “herein,” “wherein”, “whereas”, “above,” and “below” and words of similar import, when used in this application, shall refer to this application as a whole and not to any particular portions of the application.

(12) The description of embodiments of the disclosure is not intended to be exhaustive or to limit the disclosure to the precise form disclosed. While the specific embodiments of, and examples for, the disclosure are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the disclosure, as those skilled in the relevant art will recognize.

(13) Referring to FIGS. 1-2, a flow chart of a method for controlling a high rotor pole switched-reluctance motor (HRSRM) 100 in accordance with present invention is illustrated in FIG. 1. The method 100 described in the present embodiment enhances the accuracy of estimating the rotor position and also allows positioning of at least one phase of the SRM at the fully aligned position from either rotating in a clockwise or counterclockwise direction. The method 100 allows quasi-sensorless control of speed in the switched reluctance motor and creates a control algorithm that naturally calibrates with the inductance profile of the SRM. For the proper switching operation of the SRM, it is important to synchronize the stator phase excitation with the rotor position.

(14) The method 100 comprises the steps of: estimating an initial position of the rotor of the HRSRM using a unique sequence of relation between the phase inductances of the HRSRM as indicated at block 102.

(15) The rotor produces an inductance profile in each of the stator poles as each of the rotor poles comes into and out of alignment with the stator poles when the rotor is rotated. The inductance profile of a three phase SRM is illustrated in FIG. 2. For example, to estimate the initial rotor position, six startup regions are defined in the inductance profile as illustrated in FIG. 2 where the values of the phase inductances have a fixed relationship. Let L.sub.a, L.sub.b and L.sub.c be the inductances of phases A, B and C respectively. From the inductance relationship, which phase or phases needs to be excited to drive the motor to a fully aligned position can be identified. The initial position is determined by applying a voltage pulse to each phase winding in turn and measuring the time it takes for the resulting phase current to reach a preset limit.

(16) To determine the initial position, a voltage pulse is applied to each phase winding in turn and the time it takes for the resulting phase current to reach a preset limit is measured. The current ramp time is a function of the phase inductance and voltage pulse amplitude and is given by the following equation:
E=L*di/dt
where E is the applied voltage reference amplitude, L is the phase inductance and i is the phase current.

(17) The time for the current to rise to the reference limit is longer the greater the value of the inductance. For an initial phase current of zero and a reference current of Iref, the time Tp to reference is given by;
Tp=L*Iref/E
Initial position is identified from the measured current ramp time.

(18) Based on the initial position, hard alignment is set so as to start with a known phase and to rotate in the correct direction as indicated at block 104. Current is applied to an active phase winding to rotate the motor as indicated at block 106. The active phase is essentially the phase that has a rotor pole nearest the closest aligned position. During the initial rotation, position is estimated by applying a diagnostic pulse on an inactive phase winding and by estimating the inductance profile as indicated at block 108. The inductance profile of SRM indicates that inductance is at a maximum when the rotor is in an aligned position and minimum inductance occurs when the rotor is in an unaligned position. The next step is the application of a voltage pulse to the inactive phase winding and measurement of current response in each inactive phase as indicated at block 110. Multiple diagnostic pulses are applied to the inactive phase to identify when the next phase must be fired as indicated at block 112 and establishing a firm time base for a software control module on a magnetic sensor as indicated at block 114. The magnetic sensor generates index pulses from the magnetic sensor (20 edges per revolution) to calculate speed and continuously update the time base. Multiple diagnostic pulses can be applied for 10 rotations to establish a firm time base for the software control module to fire the next phase. After 10 rotations, the software timing takes over and the inactive phase is no longer necessary to maintain operation. The motor speed is calculated and the time base is updated by generating motor index pulses from the magnetic sensor as indicated at block 116. Three signals are generated per rotor pole. In other words, shaft speed for the motor is calibrated 30 times for a motor with 10 rotor poles. This step is repeated for 10 (or more, for higher accuracy) revolutions and is used to calibrate a software encoder to operate on this time base. As indicated at block 118, the shaft speed of the motor is calibrated and the software encoder is calibrated to operate on the time base. The time base is established to avoid any slip in the calculated value of speed. The method of the present invention also cancels out the switching threshold of the magnetic sensor as indicated at block 120. This ensures that the time-base is firmly established in the control algorithm to avoid any slip in calculated values. The slope of the current waveform in the active phase is monitored to fine-tune a firing angle from the encoder software as indicated at block 122. The slope of current is evaluated for a fixed duration of time to fine-tune the firing angle from encoder software. The calculated shaft speed is updated 30 times in one cycle to continuously track any change in speed.

(19) Based on the estimated time base, the pulse time t.sub.on is individually adjusted for each phase as indicated at block 124. By this step, pulse t.sub.on is individually adjusted for each phase, equaling thirty corrections per mechanical revolution. The method then monitors the shaft speed to track any change in speed and fix the dwell angle based on the shaft speed as indicated at block 126. The speed can be very tightly monitored, in one instance with as many updates as 30 per revolution, thereby providing better resolution than several sensorless approaches currently in use.

(20) Dwell is fixed based on speed. A current band is established that reduces dwell if the command current is below the lower band and increases dwell if the commanded current is above the upper band. If the commanded current is below a lower band, the dwell angle is reduced and if the commanded current is above an upper band, the dwell angle is increased. This has the effect of increasing the phase current at lower power levels thereby operating the SRM at a higher saturation level. For a given power output, decreasing dwell will command a lower phase current.

(21) FIG. 3 represents an apparatus 200 for quasi-sensorless control of the high rotor pole switched-reluctance motor (HRSRM) comprising a switched-reluctance motor 202 having a stator and a rotor. The rotor comprises a plurality of circumferentially spaced rotor poles and is rotationally related to a motor shaft, the motor shaft having a magnetic sensor. The HRSRM further comprises a Programmable brushless direct current load 204 connected to an output of the switched-reluctance motor 202 via an inline torque meter 206 and a converter 208 connected to the load. A software encoder is positioned in the control processor 210, the software encoder establishing a firm time base on the magnetic sensor. The rotor produces an inductance profile in each of the stator poles as each of the rotor poles comes into and out of alignment with the stator poles when the rotor is rotated. At least three signals are generated per rotor pole so that the shaft speed of the motor is calibrated. A three-phase inverter 212 controlled by the control processor 210 is connected to the switched-reluctance motor 202. The inverter 212 is adaptable to act as a power supply for the switched-reluctance motor 202, the control processor 210 has a software control module and the software encoder.

(22) The quasi-sensorless control of the high rotor pole switched-reluctance motor (HRSRM) 202 naturally calibrates the control algorithm to the inductance profile of the switched-reluctance motor 202 that is being tested. The switched-reluctance motor 202 is scalable to all power levels and the creation of a control algorithm does not have to be calibrated for all motor specifications and power ratings. The switched-reluctance motor 202 can automatically accommodate for motor-to-motor or process variations.

(23) In one embodiment, the system comprises a method for controlling a high rotor pole switched-reluctance motor (HRSRM), the method comprising the steps of: estimating an initial position of the rotor of the HRSRM using a unique sequence of relation between the phase inductances of the HRSRM; applying current to an active phase winding to rotate the motor; applying a voltage pulse to an inactive phase winding; measuring current response in the inactive phase; applying multiple diagnostic pulses to the inactive phase to identify the next phase; establishing a firm time base for a software control module on a magnetic sensor; updating the time base by generating a motor index pulse from the magnetic sensor; calculating a shaft speed of the motor and calibrating a software encoder to operate on the time base; canceling out a switching threshold of the magnetic sensor; monitoring a slope of the current waveform in the active phase to fine-tune a firing angle from the encoder software; adjusting the pulse time t.sub.on based on the estimated time base; monitoring the shaft speed to track any change in the speed; and adjusting the dwell angle based on the shaft speed and the current.

(24) Referring to FIGS. 4A-4C, the current waveforms of the three-phase SRM at different loads in accordance with the present invention are illustrated. A current waveform of the three-phase SRM at a light load with a speed of 900 RPM and 1 Nm is illustrated in FIG. 4A and the current waveform of the three-phase SRM at a partial load having a speed of 1200 RPM and 6 Nm is illustrated in FIG. 4B. FIG. 4C illustrates the current waveform of the three-phase SRM at full load having a speed of 1800 RPM and 6 Nm. The method of the present invention monitors the slope of the current waveform to fine-tune the firing angle from the encoder software. FIGS. 4A-4C illustrate the variation of dwell angle in accordance with load variations. The processor with the software control module advances or retards the timing of the current waveform in response to load or commanded current changes. The amount of advance or retard is chosen to maintain the current slope to a constant reference value.

(25) The foregoing description of the preferred embodiment of the present invention has been presented for the purpose of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teachings. It is intended that the scope of the present invention not be limited by this detailed description, but by the claims and the equivalents to the claims appended hereto.