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CN-115211025-B - Method and device for controlling an electric machine

CN115211025BCN 115211025 BCN115211025 BCN 115211025BCN-115211025-B

Abstract

A method of controlling an inverter that powers a permanent magnet alternating current (PERMANENTMAGNETALTERNATING CURRENT, PMAC) motor having a plurality of phase windings is described. The method includes selecting a first phase winding of a PMAC motor, electrically connecting the first phase winding to a first DC terminal of a Direct Current (DC) link circuit at a first time, maintaining a connection between the first phase winding and the first DC terminal, determining a difference in magnetic flux between the first phase winding and a second phase winding of the PMAC motor, selecting a second time at which the second phase winding is electrically connected to the first DC terminal, electrically connecting the second phase winding to the first DC terminal at the second time, and maintaining a connection between the second phase winding and the first DC terminal. The second moment in time is selected based on the determined flux difference.

Inventors

  • KEN THOMPSON
  • Jolin Zhou
  • JACK DUNN

Assignees

  • 博格华纳盖茨黑德有限公司

Dates

Publication Date
20260508
Application Date
20201008
Priority Date
20191008

Claims (20)

  1. 1. A method of controlling an inverter that supplies power to a Permanent Magnet Alternating Current (PMAC) motor having a plurality of phase windings, the method comprising: selecting a first phase winding of the PMAC motor; Electrically connecting the first phase winding with a first Direct Current (DC) terminal of a DC link circuit at a first time and maintaining the connection between the first phase winding and the first DC terminal; determining a flux difference between the first phase winding and a second phase winding of the PMAC motor; selecting a second time instant for electrically connecting the second phase winding to the first DC terminal, the second time instant being different from the first time instant, wherein the second time instant is selected based on the determined difference in magnetic flux between the first phase winding and the second phase winding; At the second moment, electrically connecting the second phase winding with the first DC terminal and maintaining the connection between the second phase winding and the first DC terminal.
  2. 2. The method of claim 1, further comprising: the second phase winding is electrically connected to the second end of the DC link circuit during a time interval between the first time and the second time.
  3. 3. The method of claim 2, wherein the time interval between the first and second instants is selected based on the determined difference in magnetic flux between the first and second phase windings and a DC voltage of the second end of the DC link.
  4. 4. A method according to any of claims 2 or 3, wherein the second moment and/or the time interval is selected based on the time required for the flux difference between the first phase winding and the second phase winding of the PMAC motor to reach zero.
  5. 5. The method of claim 4, wherein selecting the second time instant and/or the time interval comprises: collecting motor data at a plurality of sampling moments, wherein a predetermined sampling time period is provided between successive sampling moments; calculating a corresponding plurality of time estimates, each of the time estimates being an estimate of the time required for the flux difference between the first phase winding and the second phase winding of the PMAC motor to reach zero based on the collected motor data at the sampling instant; Comparing each of the plurality of time estimates to the predetermined sampling time period, and Selecting a first time estimate less than or equal to the predetermined sampling time period; the second time instant is selected using the selected first time estimate.
  6. 6. The method of claim 5, wherein connecting the second phase winding to the first DC terminal at the second time comprises: A pulse of length selected for the first time estimate is applied to electrically connect the second phase winding with the first DC terminal at the second time instant.
  7. 7. The method of claim 5 or 6, wherein the inverter has a pulse width modulated time base equal to the sampling time period.
  8. 8. The method of claim 1, further comprising: Determining a flux difference between the first phase winding and a third phase winding of the PMAC motor; Selecting a third time instant to electrically connect the third phase winding with the first DC terminal, the third time instant being different from the first time instant and the second time instant, wherein the third time instant is selected based on the determined difference in magnetic flux between the first phase winding and the third phase winding of the PMAC motor; At the third moment, electrically connecting the third phase winding with the first DC terminal and maintaining the connection between the third phase winding and the first DC terminal.
  9. 9. The method of claim 1, wherein selecting the first phase winding of the PMAC motor comprises: determining a magnetic flux in each of the plurality of phase windings of the PMAC motor, and The phase winding having the highest magnetic flux value is selected as the first phase winding.
  10. 10. The method of claim 1, further comprising: Before the first time point of the time period, A plurality of switching elements in the inverter are switched to provide Alternating Current (AC) power to each phase winding.
  11. 11. The method of claim 10, further comprising: the magnetic flux in each of the plurality of phase windings of the PMAC motor is monitored while switching the switching element to provide the alternating current to each of the phase windings.
  12. 12. The method of claim 11, wherein a flux difference between the first and second phase windings and/or between the first and third phase windings of the PMAC motor is determined based on the magnetic flux in the first and second and/or third phase windings monitored at the first time.
  13. 13. The method of claim 8, wherein the second time is later than the first time and the third time is later than the first time.
  14. 14. The method of claim 13, wherein determining the flux difference between the first phase winding and the second phase winding of the PMAC motor comprises: determining a time-varying voltage across the first phase winding; determining a time-varying voltage across the second phase winding; calculating an integral of the voltage over the first phase winding over time; calculating an integral of said voltage over said second phase winding over time, and A difference between the integral of the voltage on the first phase winding and the integral of the voltage on the second phase winding is determined.
  15. 15. The method of claim 13, wherein determining the flux difference between the first phase winding and the second phase winding of the PMAC motor comprises: determining a time-varying voltage across the first phase winding; determining a time-varying voltage across the second phase winding; Determining a difference between said voltage over said first phase winding and said voltage over said second phase winding over time, and An integral of the difference between the voltage on the first phase winding and the voltage on the second phase winding over time is calculated.
  16. 16. The method of claim 14 or 15, wherein determining the voltage across the first phase winding and the voltage across the second phase winding comprises determining one or both of: the voltage on the DC link circuit, and Pulse width modulated outputs from the respective power outputs.
  17. 17. The method of claim 16, wherein determining the flux difference between the first phase winding and the second phase winding of the PMAC motor comprises: the current in the first phase winding and the second phase winding is determined by making measurements using hall effect sensors, sense resistors, or Giant Magneto Resistance (GMR) sensors.
  18. 18. The method of claim 17, wherein determining the flux difference between the first phase winding and the second phase winding further comprises: The rotor angle of the motor is determined.
  19. 19. The method of claim 18, wherein determining the flux difference between the first phase winding and the second phase winding further comprises: Based on the current and the rotor angle, a lookup table is used to identify the flux difference or the magnetic flux in the first phase winding and the second phase winding.
  20. 20. The method of claim 17 or 18, wherein determining the magnetic flux of the motor comprises using a model that relates magnetic flux to current.

Description

Method and device for controlling an electric machine Technical Field The present invention relates to controlling the power supply of an electric motor, in particular a multiphase electric motor. More specifically, the present invention provides an improved means for turning on an active short circuit mode in a multiphase motor that alleviates the problems of prior art systems. Background Motors are used in a variety of machines, primarily for vehicles such as automobiles, but also for other industrial and commercial devices such as fans, pumps, elevators, and refrigerators. Such motors typically have a controller for controlling the operation of the motor. Many of these motors are multi-phase (e.g., three-phase). Many of these motors are powered by a Direct Current (DC) voltage source (e.g., battery powered). An inverter may be provided to convert the DC voltage to an alternating current (ALTERNATING CURRENT, AC) voltage to drive each phase. Disclosure of Invention The invention is set forth in the independent claims. Preferred features are set out in the dependent claims. Described herein is a method of controlling an inverter that powers a permanent magnet alternating current (PERMANENT MAGNET ALTERNATING current, PMAC) motor having a plurality of phase windings, the method comprising selecting a first phase winding of the PMAC motor, electrically connecting the first phase winding to a first DC terminal of a DC link circuit at a first time and maintaining the connection of the first phase winding to the first DC terminal, determining a flux difference between the first phase winding and a second phase winding of the PMAC motor, selecting a second time to electrically connect the second phase winding to the first DC terminal, the second time being different from the first time, wherein the second time is selected based on the determined flux difference between the first phase winding and the second phase winding, electrically connecting the second phase winding to the first DC terminal at the second time, and maintaining the connection of the second phase winding to the first DC terminal. In some cases, such as in the event of a motor or power failure or accident (e.g., a vehicle crash), the motor must either drop fairly quickly to a zero torque condition (or safe state), or drop the motor power fairly quickly. For safety reasons and to prevent (further) damage to the equipment, it is often important that the motor stops relatively quickly. For example, in the event of an accident, it is desirable to stop the rotation of the wheels of the vehicle as soon as possible. Motor failure can result in unwanted braking torque, and failure of the motor and battery can cause the inverter to be damaged by high voltage. Particularly for permanent magnet motors, stopping the motor by disconnecting the battery may cause the DC link current to be high enough to damage the inverter if the back emf is high. Another way to quickly stop the motor is to turn off the switching devices of the motor, such as insulated gate bipolar transistors (insulated gate bipolar transistor, IGBTs) or metal-oxide-semiconductor FIELD EFFECT transistors (MOSFETs), but this can cause natural rectification back to the DC link power supply and strong motor braking. If the vehicle turns at high speed, higher braking torque may cause the wheels to lose traction and the vehicle may deviate from the road, for example. Thus, an active short circuit (active short circuit, ASC) mode may be applied to stop the motor while natural commutation does not occur and low braking torque is maintained. The DC link voltage will decrease in a safe manner. Active shorting (because active control is not required) is a fairly simple way to reduce these problems and to dissipate energy in the motor (and therefore no battery is needed). The use of ASC mode prevents a large back emf, thus preventing unwanted braking torque and/or may protect the inverter and motor from damage. In a multi-phase motor, the ASC mode involves shorting all phase windings in the motor, for example, by connecting all phase windings in the motor to a positive or negative connection point of the DC link. However, a rapid entry into the active short circuit mode in the motor may generate significant transient currents that may damage the inverter or the motor. Application of ASCs may also demagnetize rotor magnets in the motor and/or damage other components such as switches (e.g., IGBTs/MOSFETs) or capacitors. The methods and systems described herein attempt to alleviate these problems, particularly transient currents. By shorting the phase windings at different times based on the magnetic flux in each phase, an improved way of turning on the ASC mode in a multi-phase PMAC motor may be provided. Advantageously, by staggering the application of ASCs on each phase based on the flux difference between the phases, transient currents that occur in the motor when ASCs are applied can be reduced. The i