Methods and systems for determining rotor position offset of an electric motor

Abstract

A method for calibrating a motor to determine an angular offset between a position indicated by a motor sensor and the actual rotor position includes the steps of: supplying current to the stator windings; identifying the quadrant of the rotor in which the rotor poles are located; approximating a line between a torque value measured at the lower angular boundary of the identified quadrant and a torque value measured at the upper angular boundary of the identified quadrant; and determining the angular offset by locating an angular position in which the torque applied by the rotor is zero.

Description

Technical Field

[0001] This application relates to electric motors, and more particularly, to determining rotor position offsets of rotors included in a machine. Background Technology

[0002] An electric motor (also known as an electric motor) comprises a stator having multiple windings and a rotor that is angularly displaced relative to the stator in response to the application of current to the windings via induction. Electric motors can exist in a wide variety of different designs or configurations. In some applications, motor sensors can monitor the angular position of the rotor and / or the angular position of the motor shaft coupled to the rotor to determine the precise angular position of the rotor / motor shaft relative to the stator. However, motor sensors can also indicate the angular position of the rotor / motor shaft relative to the stator, which is offset from the actual relative angular position of the rotor / motor shaft relative to the stator. Summary of the Invention

[0003] In one implementation, a method for calibrating a motor to determine the angular offset between the position indicated by a motor sensor and the actual rotor position includes: supplying current to the stator windings; identifying the quadrant of the rotor in which the rotor poles are located; approximating a line between a torque value measured at the lower angular boundary of the identified quadrant and a torque value measured at the upper angular boundary of the identified quadrant; and determining the angular offset by locating an angular position in which the torque applied by the rotor is zero.

[0004] In another implementation, the method for calibrating the motor to determine the angular offset between the position indicated by the motor sensor and the actual rotor position includes: supplying current to the stator windings; identifying the quadrant of the rotor in which the rotor poles are located; approximating a line between a torque value measured at the lower corner boundary of the identified quadrant and a torque value measured at the upper corner boundary of the identified quadrant; performing a bi-section search to determine the angular offset by locating an angular position along the approximated line where the torque applied by the rotor is zero; determining an initial angular offset position by approximating a line between a torque value measured at the lower corner boundary of the identified quadrant and a torque value measured at the upper corner boundary of the identified quadrant; performing a bi-section search to determine a final angular offset by locating an angular position along the approximated line where the torque applied by the rotor is zero to refine the initial angular offset position; and storing the angular offset in the control system.

[0005] In another implementation, the system is configured to calibrate the motor to determine the angular offset between the position indicated by the motor sensor and the actual rotor position, and includes: a controller, wherein the controller includes non-volatile memory and is programmed to: supply current to the stator windings; identify the quadrant of the rotor in which the rotor poles are located; approximate a line between a torque value measured at the lower angular boundary of the identified quadrant and a torque value measured at the upper angular boundary of the identified quadrant to determine an initial offset position value; and determine the final angular offset position by locating an angular position along the approximate line in which the torque applied by the rotor is zero. Attached Figure Description

[0006] Figure 1 It is a diagram depicting how a system using an electric motor is implemented;

[0007] Figure 2 It is a diagram depicting how a calibration system capable of calibrating a motor is implemented;

[0008] Figure 3 This is a flowchart depicting the implementation of a method for calibrating a motor;

[0009] Figure 4 This is a flowchart depicting part of the implementation of a method for calibrating a motor;

[0010] Figure 5 This is a flowchart depicting part of the implementation of a method for calibrating a motor;

[0011] Figure 6 This is a table describing part of the implementation of the method for calibrating the motor; and

[0012] Figure 7 This is a flowchart depicting part of the implementation of a method for calibrating a motor. Detailed Implementation

[0013] The motor includes a stator with multiple stator windings and a rotor that shifts angularly relative to the stator in response to the application of current to the stator windings. The system is able to determine the angular offset between the rotor angular position indicated by the motor sensor and the actual rotor angular position. That is, the rotor's magnetic poles may be at angular positions different from the angular position indicated by the motor sensor, and the angular difference can be referred to as angular offset.

[0014] The determination of angular offset can be achieved as part of motor calibration, which applies current to the stator windings at a known or fixed current level, thereby causing the rotor to rotate relative to the stator at a known or fixed angular velocity ratio. When the stator windings are supplied with a fixed current level, a first torque value can be measured at a first angular position of the motor shaft or rotor. When the stator windings are supplied with a fixed current level, a second torque value can be measured at a second angular position of the rotor. The quadrant of the actual rotor pole angle position can be selected based on the first and second torque values. After selecting the quadrant, an approximate line can be established on the measured torque values ​​measured between the quadrant angles defining the selected quadrant. Convergence at the actual rotor pole angle position can be determined using any of many techniques (such as half-search) to locate the point along the approximate line where the measured torque of the motor shaft is zero when current is supplied to the stator windings.

[0015] This calibration identifies the actual angular position of the rotor relative to the stator and compares this actual angular position with the indicated angular position of the rotor relative to the stator to determine the angular offset. This angular offset can be stored in the non-volatile memory of the microcontroller or other power electronics controlling the motor. The microcontroller receives signals indicating the angular position of the rotor relative to the stator from motor sensors, retrieves the angular offset from memory, and adds / subtracts this offset to the indicated angular position of the rotor to improve measurement accuracy. This calibration can be performed without any existing knowledge of the motor and can identify the actual angular position of the rotor much faster than previous calibration methods.

[0016] An electric motor (also known as an electric motor) can be used as part or solely the propulsion source of a vehicle, and in this implementation, the motor is implemented as a permanent magnet synchronous machine. However, the calibration process described herein can be used with other implementations of the motor and in other systems. Although in one possible implementation the motor is shown as part of the system, calibration can be performed before installation in the system when the motor can be removably coupled to a force gauge that supplies a known current level to the stator windings and rotates the rotor at a predefined angular velocity. When the force gauge supplies a known or predefined current level to the stator windings, the force gauge can measure the torque at the motor shaft. The force gauge can use one or more microprocessors to perform the process (described in more detail below) to execute the calibration method.

[0017] Go to Figure 1 The diagram illustrates an implementation of an electrical system 10, which includes a motor capable of being calibrated as described herein. System 10 includes a power grid 12 and an electric vehicle (EV) 14 capable of receiving electrical power from the power grid 12.

[0018] Power grid 12 may include any of a number of power generators and electrical transmission mechanisms. A generator (not shown) (such as a nuclear-powered device that converts energy from nuclear fission, water flowing through a dam, or wind power from a turbine, a hydraulically powered device, or a wind-powered device) generates AC power, which can then be transmitted over considerable distances away from the generator for residential and commercial use. The generator can be coupled to power grid 12, which transmits the AC power from the generator to end users, such as residences or businesses. When the AC power is supplied to power grid 12, it can be present at a relatively high voltage, allowing it to be transmitted over relatively long distances. Once the power reaches the location where it is intended to be used, a power transformer (not shown) can be used to reduce the voltage level before it is finally supplied to the residence or business. In one implementation, the voltage level of the AC power received by the residence or business is 240 volts (V). However, this voltage can be a different value.

[0019] EV 14 includes one or more motors 16 (also referred to as electric motors), said one or more motors 16 including a stator having stator windings and a rotor (not shown) capable of angular displacement relative to the stator. In one implementation, the motor is a permanent magnet synchronous motor, which includes a rotor having a plurality of angularly spaced permanent magnets. The permanent magnets can be made of any of a number of different materials, an example of which is neodymium alloy or other rare earth elements. As noted above, the stator windings are capable of receiving current, the supply of which can be controlled by a control system 18, which causes angular displacement of the rotor relative to the stator. The control system 18 may include an array of power control electronics that facilitate the operation of the motor 16. These electronics may include an inverter 18a implemented using a plurality of MOSFETs (in Figure 2 (As shown in the diagram), the plurality of MOSFETs are switched on and off according to a sequence and timing arranged in the direction of the motor controller 18b to cause rotor angular movement. The motor controller 18b can be implemented as one or more microprocessors having inputs / outputs and non-volatile memory in which data can be stored and accessed. In one implementation, the angular offset can be stored in non-volatile data. In addition to the inverter 18a, the control system 18 may also include a DC-DC converter (not shown) for regulating the voltage level of the electrical power supplied to the motor 16.

[0020] EV service equipment 20 (also referred to as an EV charging station) is capable of receiving AC power from the power grid 12 and supplying power to EV 14. EV service equipment 20 may include input terminals that receive AC power from the power grid 12 and transfer the AC power to an on-board vehicle battery charger included on EV 14. The on-board vehicle battery charger may include an AC / DC inverter, enabling the AC power received from the power grid 12 to be supplied to vehicle battery 26. Cable 24 is detachably connected to a receptacle on EV 14 and electrically links the EV charging station to EV 14, allowing AC power to be transferred between the charging station and EV 14. The EV charging station can be classified as a "Level 2" EV service equipment that receives 240VAC from the power grid 12 and supplies 240VAC to EV 14. In other implementations, the levels of AC power input to the charging station and / or output from the charging station may be different.

[0021] The term "electric vehicle" or "EV" can refer to a vehicle that is wholly or partially propelled by an electric motor or electric motor. EVs can refer to electric vehicles, plug-in electric vehicles, hybrid electric vehicles, and battery-powered vehicles. The vehicle battery 26 is capable of supplying DC power, converted from AC power, to one or more motors 16 that propel the EV. As noted above, the control system 18 is capable of converting DC power back to AC power to cause angular movement of the rotor relative to the stator. One or more vehicle batteries 26 are rechargeable and, to name just a few, may include lead-acid batteries, nickel-cadmium (NiCd), nickel-metal hydride, lithium-ion, and lithium-polymer batteries. Typical vehicle battery voltages can vary from 200 to 800V DC power (VDC).

[0022] Figure 2The implementation of a calibration system 50 capable of performing a calibration process is described. The calibration system 50 may include a force gauge 52, which receives power from the motor 16 for the purpose of calibrating the machine 16 to find the angular misalignment of the rotor. The force gauge 52 may include a torque unit 56, which is releasably coupled to the motor shaft 54 ​​of the motor 16 to measure the amount and direction of the torque applied by the motor shaft 54. The force gauge 52 may also include a force gauge controller 58 that receives data and generates control signals. The force gauge controller 58 may be implemented using one or more microprocessors having inputs / outputs and non-volatile memory in which data can be stored and accessed. The force gauge controller 58 is capable of receiving a data signal generated by the torque unit 56 indicating the amount of torque applied by the motor shaft 54. The force gauge controller 58 is also capable of generating a current command that can be transmitted via a data link 60 that directs the motor to flow a defined amount of current through the stator conductors. Additionally, the force gauge controller 58 can calculate the angular offset using the calibration process described herein, transmit the angular offset via a data link, and the control system 18 can store the angular offset in non-volatile memory. The force gauge capable of performing the calibration process should be able to operate in four quadrants, operate at both positive and negative angular velocities, and supply power to and recover power from the motor under test.

[0023] Go to Figures 3-5 This illustrates a process 100 for calibrating a motor 16 to determine the angular offset between the angular position of the rotor indicated by a motor sensor and the actual angular position of the rotor. Process 100 identifies the actual angular position of the rotor relative to the stator, compares this actual angular position with the indicated angular position of the rotor relative to the stator, and determines the angular offset. This angular offset can be stored in the non-volatile memory of a control system 18. The control system 18 can receive a signal indicating the angular position of the rotor relative to the stator from the motor sensor, access the angular offset from the memory, and add / subtract the angular offset to the indicated angular position to improve the accuracy of the microprocessor. Process 100 begins at step 102 by supplying current to the stator windings at a known or fixed current level, thereby causing the rotor to rotate relative to the stator at a known or fixed angular velocity ratio. In one implementation, a force gauge can supply 150 amperes to the stator windings. A force gauge controller 58 can rotate the rotor at a known angular velocity. In one implementation, this is 1000 revolutions per minute (RPM). The force gauge controller 58 can then send a known or fixed stator current command and a known or fixed rotor offset angle to the calibration system 50. The control system 50 can adjust the stator current level in the electric motor 16 to the commanded value. Method 100 proceeds to step 104.

[0024] In step 104, the rotor quadrant can be determined. Determining the rotor quadrant can begin in sub-step 104a by measuring a first torque value at a first angular offset value while a fixed current level is supplied to the stator windings. In one implementation, the force gauge 52 can apply a current of 150 amperes to cause the rotor to rotate at 1000 revolutions per minute (RPM), thereby causing the motor shaft to rotate at 1000 RPM. This step 104a can be performed by the force gauge 52, which has a controller 58 that commands the calibration system 50 via data link 60 to control the stator current supply to a known or fixed value and a known or fixed first angular offset position. The first torque value can be measured using a torque unit 56. During this process, the force gauge 52 can monitor the signal output received from the motor sensors, indicating the angular position of the rotor relative to the stator. In substep 104b, following the measurement of the first torque value at the first angular offset position, when the stator winding is supplied with a fixed current level, the force gauge is able to measure the second torque value at the second angular offset position. One implementation of those measurements is as follows: Figure 7 The diagram shows the torque value measured at the motor shaft of motor 16 when the rotor angular offset position is angularly shifted relative to the stator, while a known or fixed stator winding current is commanded.

[0025] In step 104c, the quadrant of the actual rotor pole position can be selected based on a first torque value measured at the first angular offset position and a second torque value measured at the second angular offset position. In this implementation, the first angular offset position can be 90 degrees, and the second angular offset position can be 180 degrees. The force gauge 52 can select one of the four quadrants by comparing the first torque value measured at the first angular offset position and the second torque value measured at the second angular offset position with the contents of a lookup table accessible by one or more microprocessors of the force gauge. The lookup table can be stored in non-volatile memory at the force gauge controller 58 or accessible from an external memory device. Figure 6 The explanation of the lookup table is shown below.

[0026] For example, the first torque value measured at the first angular offset position and the second torque value measured at the second angular offset position can be determined to be negative or positive. If the torque value measured at the first angular offset position is negative, and the torque value measured at the second angular offset position is also negative, then the force gauge 52 can select the first quadrant. As defined on a conventional unit circle with an angular range of 2π or 360 degrees and moving counterclockwise, the first quadrant can have a lower angular boundary of 0 degrees and an upper angular boundary of 95 degrees. If the torque value measured at the first angular offset position is negative, and the torque value measured at the second angular offset position is positive, then the force gauge 52 can select the second quadrant. The second quadrant can have a lower angular boundary of 90 degrees and an upper angular boundary of 185 degrees. If the torque value measured at the first angular offset position is positive, and the torque value measured at the second angular offset position is negative, then the force gauge 52 can select the third quadrant. The third quadrant can have a lower angular boundary of 180 degrees and an upper angular boundary of 275 degrees. If the torque value measured at the first corner position is negative, and the torque value measured at the second corner position does not meet the criteria for selecting the first, second, or third quadrant, then the force gauge 52 can select the fourth quadrant. The fourth quadrant can have a lower corner boundary of 270 degrees and an upper corner boundary of 365 degrees (or 5 degrees).

[0027] exist Figure 7 An example is shown, illustrating the measured torque value of motor 16 when the torque value of motor 16 is measured within an angular rotor position extending from 0-360 degrees, as indicated by the motor sensor indicating the rotor or motor shaft position. In this example, the torque measured at 90 degrees and 180 degrees does not meet the criteria in the lookup table required to select one of the first, second, or third quadrants; therefore, in this implementation, the force gauge 52 can select quadrant four. The lower corner boundary can be set to 270 degrees, and the upper corner boundary can be set to 365 degrees. The force gauge 52 can set the torque measurement value associated with the lower corner boundary and the torque measurement value associated with the upper corner boundary. Method 100 proceeds to step 106.

[0028] In step 106, an approximate line is obtained between the torque value measured at the lower corner boundary of the quadrant and the torque value measured at the upper corner boundary of the quadrant. (Reference) Figure 7 In the example shown, the lower corner boundary can be 270 degrees and the torque measurement can be 7 Newtons per meter (N / m), while the upper corner boundary can be 365 degrees and the torque measurement can be -3 N / m. The force gauge 52 can approximate the line between these two torque measurements using the line approximation shown. Given the torque measurement at the lower corner boundary and the torque measurement at the upper corner boundary, the midpoint torque can be determined by adding the lower corner boundary to the upper corner boundary and dividing by two to determine the midpoint. The torque measured at the midpoint can be used to approximate the line. For example,

[0029] θ = θ1 degrees, measure the lower corner boundary torque T1

[0030] θ = θ² degrees, measure the upper angle boundary torque T².

[0031] θ = (θ1 + θ2) / 2 degrees, measure the midpoint torque T m

[0032] If the lower corner boundary torque T1 is multiplied by the midpoint torque T m If it is greater than zero, then θ1 becomes θ m And T1 becomes T m Furthermore, if the lower corner boundary torque T1 is multiplied by the midpoint torque T... m If it is not greater than zero, then θ2 becomes θ m And T2 becomes T m The fitted line can be obtained from θ. a to θ b The angular range between them extends, θ a to θ b The angular range between them can be determined using the following:

[0033] θ x = (θ2-θ1) / (T2-T1)×-T1+θ1

[0034] θ a =max(θ) x -θ ∈ ,θ1)

[0035] θ b =min(θ) x +θ ∈ ,θ2)

[0036] + / -θ ∈ This can be achieved when the rotor magnetic poles are very close to θ1 or θ2, by adding θ. a and θ b Additional margin. In one implementation, the value θ ∈ It can be set to + / - 5 degrees. Method 100 proceeds to step 108.

[0037] In step 108, the position of the rotor's magnetic poles is determined, and thereby the rotor offset, indicating the difference between the rotor's position relative to the stator as indicated by the motor sensor and the actual rotor position relative to the stator, is determined. The force gauge 52 is capable of determining when the torque measured on the motor shaft is equal to zero. This can be determined in any of a variety of ways. In one implementation, the force gauge 52 is capable of locating zero torque on the approximate line using a half-search. This is shown as... Figure 5The subroutine begins with step 108a. In step 108a, the number of iterations can be set to zero and the following assumptions can be made:

[0038] N = number of iterations

[0039] N max = Maximum number of iterations. For example, N max = 20 iterations

[0040] Δθ ∈ = Rotor angular tolerance. For example, Δθ ∈ =0.01e degrees

[0041] T ∈ = Torque tolerance. For example, T ∈ =0.05Nm.

[0042] In one implementation, N max =20 iterations, Δθ ∈ = 0.01e degrees, T ∈ =0.05Nm. Method 100 proceeds to step 108b, where the iteration count is incremented by one. Then, in step 108c, (θ) is determined. a +θ b ) / 2. In step 108d, the force gauge 52 is able to measure the torque T at the motor shaft. n Then, in step 108e, the force gauge 52 is able to determine T. n Is it greater than zero? If yes, then in step 108f, θ can be... a Set to θ n Otherwise, in step 108g, θ b Will be set to θ n Method 100 proceeds to step 108h.

[0043] In step 108h, a comparison can be made. If θ b -θ a The absolute value < Δθ ∈ or the absolute value of Tn <T ∈ Or N>N max In step 108i, the force gauge 52 can measure θ n The offset angle value is stored as the difference between the actual relative position of the rotor relative to the stator and the indicated relative position of the rotor relative to the stator. The force gauge 52 can store the offset angle value in non-volatile memory at the control system 18, and this value can be accessed later and used to compensate for errors. Then, method 100 will end. Otherwise, method 100 returns to step 108b.

[0044] It should be understood that the foregoing description describes one or more embodiments of the invention. The invention is not limited to the specific embodiments disclosed herein, but is defined solely by the claims below. Furthermore, except where terms or phrases are expressly defined above, statements included in the foregoing description relate to specific embodiments and should not be construed as limiting the scope of the invention or the definitions of the terms used in the claims. Various other embodiments and various changes and modifications to the disclosed embodiments will become apparent to those skilled in the art. All such other embodiments, changes, and modifications are intended to fall within the scope of the appended claims.

[0045] As used in this specification and claims, when used in conjunction with a list of one or more components or other items, the terms “for example,” “for instance,” “like,” “such as,” and “similar,” as well as the verbs “comprising,” “having,” “including,” and their other verb forms, shall each be interpreted as open-ended, meaning that the list shall not be construed as excluding other additional components or items. Other terms shall be interpreted using their broadest reasonable meaning unless used in a context that requires a different interpretation.

Claims

1. A method for calibrating a motor to determine the angular offset between the position indicated by a motor sensor and the actual rotor position, comprising the following steps: (a) Supplying current to the stator windings; (b) Identify the quadrant of the rotor in which the rotor poles are located; (c) An approximate line between the torque value measured at the lower corner boundary of the identified quadrant and the torque value measured at the upper corner boundary of the identified quadrant; and (d) Determine the angular offset by locating an angular position where the torque applied by the rotor is zero.

2. The method for calibrating a motor according to claim 1, wherein, The current supplied to the stator winding is a constant.

3. The method for calibrating a motor according to claim 1, wherein, Steps (a)-(d) are performed by a force gauge.

4. The method for calibrating a motor according to claim 1, wherein, Step (b) also includes measuring a first torque value at the first angular offset position and measuring a second torque value at the second angular position.

5. The method for calibrating a motor according to claim 4, wherein, The first angle offset position is located at 90 degrees, and the second angle position is located at 180 degrees.

6. The method for calibrating a motor according to claim 1, further comprising the step of storing the angular offset in a control system.

7. A method for calibrating a motor to determine the angular offset between the position indicated by a motor sensor and the actual rotor position, comprising the following steps: (a) Supplying current to the stator windings; (b) Identify the quadrant of the rotor in which the rotor poles are located; (c) The initial angular offset position is determined by approximating a line between the torque value measured at the lower corner boundary of the identified quadrant and the torque value measured at the upper corner boundary of the identified quadrant; and (d) Perform a half-search to determine the final angular offset by locating the angular position where the torque applied by the rotor is zero along the approximate line to improve the initial angular offset position; (e) Store the angular offset in the control system.

8. The method for calibrating a motor according to claim 7, wherein, The current supplied to the stator winding is a constant.

9. The method for calibrating a motor according to claim 7, wherein, Steps (a)-(d) are performed by a force gauge.

10. The method for calibrating a motor according to claim 7, wherein, Step (b) also includes measuring a first torque value at a first angular position and measuring a second torque value at a second angular position.

11. The method for calibrating a motor according to claim 10, wherein, The first angle is located at 90 degrees, and the second angle is located at 180 degrees.

12. A system configured to calibrate a motor to determine an angular offset between a position indicated by a motor sensor and an actual rotor position, comprising: A controller, wherein the controller includes a non-volatile memory and is programmed to supply current to the stator windings; The quadrant of the rotor in which the rotor's magnetic poles are located; An approximate line is drawn between the torque value measured at the lower corner boundary of the identified quadrant and the torque value measured at the upper corner boundary of the identified quadrant to determine the initial offset position value; and the final angular offset position is determined by locating the angular position where the torque applied by the rotor is zero along the approximate line.

13. The system according to claim 12, wherein, The system includes a force gauge.

14. The system according to claim 12, wherein, The controller is a force gauge controller.

15. The system of claim 12, further comprising a control system for controlling the motor.

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