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EP-3852265-B1 - PULSED ELECTRIC MACHINE CONTROL

EP3852265B1EP 3852265 B1EP3852265 B1EP 3852265B1EP-3852265-B1

Inventors

  • TRIPATHI, ADYA S.

Dates

Publication Date
20260506
Application Date
20190314

Claims (14)

  1. An electric machine system comprising: an electric machine (160); a power converter (140); a controller (310) arranged to direct the power converter to cause pulsed operation of the electric machine to deliver a net average of a desired output, wherein during the pulsed operation of the electric machine, the controller is configured to cause the output of the electric machine to alternate on and off and turn the power converter off during at least portions of the times that the electric machine is pulsed off, and characterised in that the electric machine system comprises a transient control circuitry (343) including a resonant capacitor, a boost converter or a buck/boost converter for reducing power rise and fall times between on and off states of the electric machine.
  2. The electric machine system as recited in claim 1 wherein the controller is configured to turn the power converter off each time the electric machine is pulsed off.
  3. The electric machine system as recited in claim 2 wherein the controller is configured to pulse the electric machine on and off at a frequency of at least ten times per second such that the power converter is turned off at least 10 times per second.
  4. The electric machine system as recited in any one of the above claims wherein the electric machine is configured to output at a first output level that is higher than the desired output level during at least portions of the time that the electric machine is turned on and the first output level is selected such that the electric machine system has an overall higher energy conversion efficiency during the pulsed operation of the electric machine system than the electric machine system would have when the electric machine is driven continuous manner at a third output level to deliver the desired output.
  5. The electric machine system as recited in claim 4 wherein the controller is configured to vary the first output level in accordance with variations in an operating speed of the electric machine.
  6. The electric machine system as recited in claim 5 wherein the first output level for a given operational speed is chosen to optimize the electric machine system's energy conversion efficiency the given operational speed.
  7. The electric machine system as recited in any one of claims 4 to 6, wherein the first output level corresponds to an electric machine output level that has substantially a highest system or electric machine energy conversion efficiency at a current operating speed of the electric machine.
  8. The electric machine system as recited in any one of claims 4 to 7 wherein a period between beginnings of sequential first output level pulses is a pulse cycle duration, and the controller is configured to direct the pulse cycle duration to vary during operation of the electric machine.
  9. The electric machine system as recited in claim 8 wherein the pulse cycle duration varies as a function of a rotational speed of the electric machine.
  10. A method of operating an electric machine system, the method comprising directing a power converter (140) to cause pulsed operation of the electric machine (160) to deliver a net average of a desired output, wherein during the pulsed operation of the electric machine, a controller (310) causes the output of the electric machine to alternate on and off and turns the power converter off during at least portions of the times that the electric machine is pulsed off, the method being characterised by reducing by a transient control circuitry (343), including a resonant capacitor, a boost converter or a buck/boost converter, the power rise and fall times between on and off states of the electric machine.
  11. The method as recited in claim 101 wherein the power converter is turned off each time the electric machine is pulsed off.
  12. The method as recited in claim 10 or 11 wherein the electric machine is pulsed on and off at a frequency of at least ten times per second such that the power converter is turned off at least 10 times per second.
  13. The method as recited in any one of claims 10 to 12 wherein the electric machine outputs at a first output level that is higher than the desired output level during at least a portion of the time that the electric machine is turned on and the first output level is selected such that the electric machine system has an overall higher energy conversion efficiency during the pulsed operation of the electric machine system than the electric machine system would have when the electric machine is driven continuous manner at a third output level to deliver the desired output.
  14. The method as recited in claim 13 wherein the first output level corresponds to an electric machine output level that has substantially a highest system or electric machine energy conversion efficiency at a current operating speed of the electric machine.

Description

BACKGROUND The present application relates generally to electric machine control. More specifically, control schemes and controller designs are described that pulse the operation of an electric machine during selected operating conditions to facilitate operating the electric machine in a more energy efficient manner. The phrase "electric machine" as used herein is intended to be broadly construed to mean both electric motors and generators. Electric motors and generators are structurally very similar. When an electric machine is operating as motor, it converts electrical energy into mechanical energy. When operating as a generator, the electric machine converts mechanical energy into electrical energy. Electric motors and generators are used in a very wide variety of applications and under a wide variety of operating conditions. In general, many modern electric machines have relatively high energy conversion efficiencies. However, the energy conversion efficiency of most electric machines can vary considerably based on their operational load. Many applications require that the electric machine operate under a wide variety of different operating load conditions, which means that the electric machine often doesn't operate as efficiently as it is capable of. The nature of this problem is illustrated in Fig. 1, which is a motor efficiency map 10 that diagrammatically shows the efficiency of a representative motor under different operating conditions. More specifically, the figure plots the energy conversion efficiency of the motor as a function of motor speed (the X-axis) and torque generated (the Y-axis). As can be seen in Fig. 1, the illustrated motor is generally most efficient when it is operating within a particular speed range and generating torque within a defined range. For the particular motor shown, the most efficient region of its operating range is the operating region labeled 14 which is generally in the range of 4500-6000 RPM with a torque output in the range of about 40-70 Nm where its energy conversion efficiency is approximately 96%. The region 14 is sometimes referred to herein as the "sweet spot", which is simply the motor's most efficient operating region. As can be seen in Fig. 1, at any particular motor speed, there will be a corresponding most efficient output torque which is diagrammatically illustrated by maximum efficiency curve 16. For any given motor speed, the motor's efficiency tends to drop off somewhat when the motor's load is higher or lower than the most efficient load. In some regions the motor's efficiency tends to drop relatively quickly, as for example when the torque output falls below about 30 Nm in the illustrated motor. If the operating conditions could be controlled so that the motor is almost always operated at or near its sweet spot, the energy conversion efficiency of the motor would be quite good. However, many applications require that the motor operate over a wide variety of load conditions with widely varying torque requirements and widely varying motor speeds. One such application that is easy to visualize is automotive and other vehicle or mobility applications where the motor speed may vary between zero when the vehicle is stopped to a relatively high RPM when cruising at highway speeds. The torque requirements may also vary widely at any of those speeds based on factors such as whether the vehicle is accelerating or decelerating, going uphill, downhill, going on relatively flat terrain, etc., the weight of the vehicle and many other factors. Of course, motors used in other applications may be subjected to a wide variety of operating conditions as well. US 2009/146615 A1 relates to a method for controlling the operation of a motor vehicle with a hybrid drive unit, which includes an internal combustion engine and in addition at least one electric machine which can be selectively switched to a motor or a generator mode. EP 2 605 398 A1 relates to a motor drive system that is provided with an inverter for driving a motor and a control unit. Although the energy conversion efficiency of conventional electric machines is generally good, there are continuing efforts to further improve energy conversion efficiencies over broader ranges of operating conditions. SUMMARY The invention is as defined in claims 1 and 10. Exemplary embodiments are defined in their dependent claims. A variety of methods, controllers and electric machine systems are described that facilitate pulsed control of electric machines (e.g., electric motors and generators) to improve the energy conversion efficiency of the electric machine when operating conditions warrant. More specifically, under selected operating conditions, an electric machine is intermittently driven (pulsed). The pulsed operation of the electric machine causes the output of the electric machine to alternate between a first output level and a second output level that is lower than the first output level. The first and second ou