METHOD AND SYSTEM FOR SENSORLESS CONTROL OF A PMSM MOTOR

Abstract

A method and system for adaptive sensorless determination of the position of a PMSM motor is described. The system and method include: determining the rotor position and the rotor polarity by means of discrete signal injection for the range between standstill up to low rotational speed; determining the rotor position by means of continuous signal injection at a rotational speed that is lower than a first changeover speed; determining the rotor position by means of back EMF at a rotational speed that is higher than the first changeover speed; wherein by means of a motor control system, depending on the rotational speed, a switch is made between rotor position determination by continuous signal injection and rotor position determination by back EMF; and wherein during movement of the rotor, the rotor polarity and/or the rotor position are/is monitored and optionally adjusted at a point in time using the rotor polarity and/or the rotor position at a previous point in time.

Claims

1. A method for adaptive sensorless determination of position of a permanent magnet synchronous machine (PMSM) motor, the method comprising: determining rotor position and rotor polarity by discrete signal injection for a range between standstill up to a predetermined rotational speed; switching, using a motor control unit and based on rotational speed, between: determining the rotor position using one of continuous signal injection at a rotational speed that is lower than a first changeover speed or back electromotive force (EMF) at a rotational speed that is higher than the first changeover speed; and thereafter determining the rotor position using another of the continuous signal injection at the rotational speed that is lower than the first changeover speed or the back EMF at the rotational speed that is higher than the first changeover speed.

2. The method of claim 1, wherein the rotor position is determined by the continuous signal injection at the rotational speed that is lower than the first changeover speed and thereafter by back EMF at the rotational speed that is higher than the first changeover speed.

3. The method of claim 1, wherein switching, based on rotational speed, between determinations of the rotor position is performed iteratively.

4. The method of claim 1, wherein controlling the at least one aspect of the motor based on the determined position comprises: monitoring, during movement of the rotor, at least one of the rotor polarity or the rotor position; and adjusting one or both of the rotor polarity or the rotor position at a point in time by using at least one of the rotor polarity or the rotor position.

5. The method of claim 1, further comprising, prior to determining the rotor position, performing a calibration step in which a calibration curve of a parameter depending on motor impedance is essentially independent of rotor magnetic field, and is generated as a function of angular position of a stator field of the motor, and in which a parameter curve determined during the position determination is compensated by the calibration curve.

6. The method of claim 5, wherein the calibration curve is stored in a lookup table in a nonvolatile data memory of the motor control unit.

7. The method of claim 5, wherein measured values determined in one or both of the rotor position and the rotor polarity, determined by one or both of the discrete signal injection and the continuous signal injection, are corrected using data from the calibration step; and wherein a difference is generated between the parameter curve and the calibration curve determined during the rotor position determination by one or both of the discrete signal injection and the continuous signal injection.

8. The method of claim 1, wherein determining rotor position by the continuous signal injection uses a sample period; wherein determining the rotor position is performed in each sample period; and wherein the determined rotor position is compared to the rotor position from a preceding sample period and corrected if necessary.

9. The method of claim 8, wherein a length of the sample period is selected such that rotor angle does not change by more than 90 during the sample period.

10. The method of claim 1, wherein the first changeover speed is less than 5% of a nominal speed of the motor.

11. The method of claim 1, wherein the first changeover speed is between 0.1% and 3% of a nominal speed of the motor.

12. The method of claim 1, wherein the first changeover speed is between 0.2% and 3% of a nominal speed of the motor.

13. The method of claim 1, wherein frequency of the continuous signal injection essentially corresponds to pulse width modulation frequency of the motor control unit.

14. The method of claim 1, wherein frequency of the continuous signal injection essentially corresponds to one-half pulse width modulation frequency of the motor control system.

15. The method of one of the beforementioned claims, further comprising controlling at least one aspect of the motor based on the determined position.

16. A permanent magnet synchronous machine (PMSM) motor system comprising: a motor; and a motor control unit in communication with the motor, the motor control unit comprising a processor and a memory and configured to: determine rotor position and rotor polarity by discrete signal injection for a range between standstill up to a predetermined rotational speed; switch, based on rotational speed, between: determining the rotor position using one of continuous signal injection at a rotational speed that is lower than a first changeover speed or back electromotive force (EMF) at a rotational speed that is higher than the first changeover speed; and thereafter determining the rotor position using another of the continuous signal injection at the rotational speed that is lower than the first changeover speed or the back EMF at the rotational speed that is higher than the first changeover speed.

17. The PMSM motor system of claim 16, wherein the motor control unit is configured to switch between rotor position determination by one or both of the discrete signal injection and the continuous signal injection the rotor position determination by the back EMF; and wherein the memory comprises a nonvolatile memory configured to store and read out one or both of the rotor position and rotor polarity data.

18. The PMSM motor system of claim 16, wherein the motor control unit is further configured, prior to determining the rotor position, perform a calibration step in which a calibration curve of a parameter depending on motor impedance is essentially independent of rotor magnetic field, and is generated as a function of angular position of a stator field of the motor, and in which a parameter curve determined during the position determination is compensated by the calibration curve.

19. The PMSM motor system of claim 18, wherein the memory comprises a nonvolatile memory; wherein the nonvolatile memory is further configured to store calibration data for forming the calibration curve; and wherein the motor control unit is further configured to generate a difference between a measured parameter curve and the calibration curve.

20. The PMSM motor of claim 16, wherein the motor has an ironless winding.

21. The PMSM motor of claim 16, wherein the motor is an S-PMSM motor having surface-mounted permanent magnets.

22. The PSMS motor system according to one of claims 16 to 21, wherein the motor control unit is further configured to control at least one aspect of the motor based on the determined position.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various aspects of the invention and together with the description, serve to explain its principles. Wherever convenient, the same reference numbers will be used throughout the drawings to refer to the same or like elements. The figures show the following:

[0037] FIG. 1 shows a schematic illustration of one exemplary implementation of the method;

[0038] FIG. 2 shows an illustration of a calibration curve and a measured parameter curve;

[0039] FIG. 3 shows an illustration of a difference curve; and

[0040] FIG. 4 shows a schematic illustration of a motor system according to an implementation.

DETAILED DESCRIPTION OF EMBODIMENTS

[0041] FIG. 1 shows a schematic illustration, in the form of a flow chart, of one exemplary implementation of the method according to the invention for determining the position of a PMSM motor. The system parameters are determined in a first initialization step at 102. In the exemplary implementation shown, the calibration curve is determined in the initialization step. The calibration curve is stored in a nonvolatile data memory of the motor or the motor control unit. When the motor is at a standstill, in a next step the initial rotor position and the initial rotor polarity are determined by discrete signal injection. This may be achieved by applying suitable test signals in various directions, for example using the INFORM method. At 104, the values determined by the discrete signal injection are processed, using the calibration curve stored in the nonvolatile data memory, and on this basis the rotor position and the rotor polarity are determined. The discrete signal injection may be used for standstill conditions and at very low rotational speeds, such as in a range of 0.1-1% of the nominal speed of the motor. If the initial rotor position and the rotor polarity are known, the discrete signal injection is discontinued and the position determination is carried out by continuous signal injection. At 106, the continuous signal injection may be carried out with a rotating space vector, for example. During the position determination, the instantaneous position is determined or adjusted, taking into account the position at the previous points in time. Sample periods may be introduced for this purpose, so that in a given sample period the position determination uses the values from the preceding sample period. The calibration curve may also be used for the continuous signal injection in order to process the values determined by the continuous signal injection, and based thereon determine the rotor position. In response to the rotational speed of the rotor reaches a first changeover speed (e.g., as soon as the rotational speed of the rotor reaches the first changeover speed), a switch is made to the position determination by back EMF at 108, wherein the first changeover speed is a rotational speed at which the signal of the back EMF is sufficient to ensure a signal-to-noise ratio that allows a reliable position determination. As indicated by the double arrows in FIG. 1 between 106 and 108, a switch may be made, for example as a function of the rotational speed, between the various position determination methods as required.

[0042] A calibration curve A is shown in FIG. 2. FIG. 2 also shows a measured parameter curve B. The parameter curve B may have been recorded, for example, during the discrete signal injection or during the continuous signal injection. The rotor position is unknown during measurement of the parameter curve B. Based on the two curves in FIG. 2, it is apparent that, in comparison to calibration curve A, parameter curve B shows a strong dependence on the rotor magnetic field between approximately 25 and approximately 95.

[0043] This is clarified by forming the difference d between the parameter curve B and the calibration curve A. The resulting difference curve is shown in FIG. 3. The dependence on the rotor magnetic field is greatest at an angle (see arrow C) at which the difference d is at a maximum. This angle is therefore the rotor angle, since the influence of the rotor magnetic field is strongest at this angle.

[0044] FIG. 4 shows a schematic illustration of a motor system 1 according to an implementation of the present invention. The motor system 1 is adapted for switching between rotor position determination by discrete and/or continuous signal injection and/or rotor position determination by back EMF for determining the orientation of a rotor 2 of an ironless PMSM motor 3 of the motor system 1. The motor system 1 further comprises a measuring device 4 and a control device 5. The measuring device 4 is adapted for measuring the current in the phases of the motor 3. The control device 5 comprises a processing unit 6 for digitally and/or analoguely generating a difference between the measured parameter curve and the calibration curve, a memory unit 7, such as a non-volatile memory, for storing and reading out rotor position and/or rotor polarity data, and/or calibration data for forming a calibration curve, and a switching unit 8 for digitally and/or analoguely switching between rotor position determination by discrete and/or continuous signal injection and/or rotor position determination by back EMF. FIG. 4 illustrates the separate elements of the processing unit 6, the memory unit 7, and the switching unit 8, with the processing unit 6 being in communication with memory unit 7 and switching unit 8. Alternatively, the functions performed by these units may be in a single element within control device 5.

[0045] The processing unit 6 is adapted for digitally and/or analoguely determining the position of the rotor 2 by discrete and/or continuous signal injection and/or rotor position determination by back EMF. The processing unit 6 may comprise a microprocessor or other type of processor, and a computer-readable medium that stores computer-readable program code (e.g., software or firmware) executable by the (micro)processor, logic gates, switches, an application specific integrated circuit (ASIC), a programmable logic controller, and an embedded microcontroller, for example. In particular, the processing unit 6 may be configured to perform the analysis (such as the calibration, determination, etc.) and the control aspects described herein. For example, the processing unit 6 may be in communication with memory unit 7 and switching unit 8. Further, the processing unit 6 may receive one or more inputs (such as one or more sensor inputs) in order to determine one or more aspects of the motor system 1 (e.g., the position of the rotor (such as by one or both of the discrete signal injection and continuous signal injection) and/or the rotor position determination (such as by back EMF). Further, the processing unit 6 may be configured to generate voltage pulses as well as discrete and continuous voltage signals to the phases of the motor 3. In addition, the processing unit 6 may be configured to generate one or more control signals as input to the switching unit 8, in order for the switching unit to switch between rotor position determination by discrete and/or continuous signal injection and/or rotor position determination by back EMF. In this regard, the processing unit 6 may comprise logic, such as computable executable instructions, which enable the determination of the one or more aspects of the motor system 1, the control of the motor, and the control of the switching unit 8.

[0046] Energy and/or data transmission lines 9 of the motor system 1 allow for transmitting electrical energy, data and/or measurement values between the motor 3, the measuring device 4 and the control device 5.

[0047] Thus, in a specific implementation, a method for adaptive sensorless determination of the position of a PMSM motor is disclosed. The method comprises: (a) determining the rotor position and the rotor polarity by means of discrete signal injection for the range between standstill up to low rotational speed; (b) determining the rotor position by means of continuous signal injection at a rotational speed that is lower than a first changeover speed; (c) determining the rotor position by means of back EMF at a rotational speed that is higher than the first changeover speed; wherein by means of a motor control system, dependent on the rotational speed, a switch is made between rotor position determination by continuous signal injection and rotor position determination by back EMF; and wherein during movement of the rotor, the rotor polarity and/or the rotor position are/is monitored and adjusted at a point in time by using the rotor polarity and/or the rotor position at a previous point in time.

[0048] Further, the method may be characterized in that prior to the rotor position determination, a calibration step is carried out in which a calibration curve of a parameter depending on the motor impedance is essentially independent of the rotor magnetic field, and is generated as a function of the angular position of the stator field, and in which a parameter curve determined during the position determination is compensated by the calibration curve. In addition, the method may be characterized in that the calibration curve is stored in a lookup table in a nonvolatile data memory, preferably a flash memory, of a motor control unit. Also, the method may be characterized in that the measured values determined in the rotor position and/or rotor polarity determination by discrete signal injection and/or continuous signal injection are corrected using the data from the calibration step, wherein the difference is generated between the parameter curve and the calibration curve determined during the rotor position determination by discrete and/or continuous signal injection.

[0049] In a further specific implementation, the method is characterized in that a sample period is used in the rotor position determination by continuous signal injection, wherein the rotor position determination is carried out in each sample period, and the determined rotor position is compared to the rotor position from the preceding sample period and corrected if necessary. Further, the method is characterized in that the length of the sample period is selected in such a way that the rotor angle does not change by more than 90 during the sample period. The first changeover speed may be less than 5%, preferably between 0.1% and 3%, particularly preferably between 0.2% and 3%, of the nominal speed of the motor. The frequency of the continuous signal injection may essentially correspond to the pulse width modulation frequency, or to one-half the pulse width modulation frequency, of the motor control system.

[0050] Likewise, a PMSM motor is disclosed that uses the method in the specific implementation. The PMSM motor comprises a motor control system for switching between rotor position determination by discrete and/or continuous signal injection and/or rotor position determination by back EMF; a nonvolatile memory for storing and reading out rotor position and/or rotor polarity data, and/or calibration data for forming a calibration curve; and a processing unit for generating a difference between the measured parameter curve and the calibration curve. The PMSM motor may be calibrated using a calibration step in which a calibration curve of a parameter depending on the motor impedance is essentially independent of the rotor magnetic field, and is generated as a function of the angular position of the stator field, and in which a parameter curve determined during the position determination is compensated by the calibration curve. As discussed above, the calibration curve is stored in a lookup table in a nonvolatile data memory, preferably a flash memory, of a motor control unit. Further, the measured values determined in the rotor position and/or rotor polarity determination by discrete signal injection and/or continuous signal injection may be corrected using the data from the calibration step, wherein the difference is generated between the parameter curve and the calibration curve determined during the rotor position determination by discrete and/or continuous signal injection.

[0051] It is intended that the foregoing detailed description be understood as an illustration of selected forms that the invention can take and not as a definition of the invention. It is only the following claims, including all equivalents, that are intended to define the scope of the claimed invention. Finally, it should be noted that any aspect of any of the preferred embodiments described herein can be used alone or in combination with one another.