Pulse modulated control with field weakening for improved motor efficiency

Patent metadata

Field	Value
Publication number	US-2021323415-A1
Application number	US-202117204269-A
Country	US
Kind code	A1
Filing date	Mar 17, 2021
Priority date	Apr 21, 2020
Publication date	Oct 21, 2021
Grant date	—

Abstract

Modulated pulse control of electric machines to deliver a desired output in a more energy efficient manner by either (a) operating the electric machine in a continuous mode when a requested torque demand is greater than the peak efficiency torque of the electric machine or (b) in a pulsed modulation mode when the requested torque demand is less than the peak efficiency torque of the electric machine. When operating in the pulsed modulation mode, the inverter may be deactivated to further improve the system efficiency when field weakening is not required to mitigate or eliminate generation of a retarding torque in situations when Back Electromagnetic Force (BEMF) exceeds a supply voltage for the inverter of the machine.

First claim

1 . A method comprising:
receiving a torque demand; operating a motor in a continuous mode if the received torque demand exceeds a threshold; operating the motor in a pulsed mode if the received torque demand is less than the threshold, the pulsed mode comprising a series of “on” and “off” time durations periods; while operating in the pulsed mode, determining if back electromagnetic force (BEMF) of the motor is more than a supply voltage applied to a power inverter used to excite the motor and during periods of time between “on” time durations periods when operating in the pulsed mode: (a) maintaining the power inverter activated, but demanding no torque, when the BEMF is more than the supply voltage applied to the power inverter, and applying field weakening to the motor; and (b) deactivating the power inverter when no field weakening is applied.

2 . The method of claim 1 , further comprising applying no field weakening to the motor when the BEMF of the motor is less than the supply voltage applied to the power inverter during the continuous mode and the pulsed mode.

3 . The method of claim 1 , further comprising ascertaining a duty cycle for pulses when operating the motor in the pulsed mode, the duty cycle for the pulses sufficient to meet the received torque demand.

4 . The method of claim 3 , further comprising using a sigma-delta modulation to modulate pulses when operating the motor in the pulsed mode.

5 . The method of claim 1 , further comprising preventing or mitigating the motor from generating a retarding torque when the field weakening is applied to the motor.

6 . The method of claim 1 , wherein operating the motor in the pulsed mode further comprises interspersing pulses in which the motor is generating torque at or above the threshold the periods of time between the pulses within which the motor is generating no toque, wherein the pulses in which the motor is operating have a duty cycle and a magnitude sufficient for an average torque output of the motor during the pulses to meet the received torque demand.

7 . The method of claim 1 , further comprising ascertaining if the received torque demand exceeds the threshold of the motor for a given motor speed by accessing an efficiency torque map for the motor,
wherein the efficiency torque map is derived from loss maps for one or more operational parameters of the motor selected from the group including a hysteresis loss map, an eddy current loss map, a copper loss map, an inverter loss map or a motor shaft loss map.

8 . The method of claim 1 , further comprising ascertaining if the BEMF of the motor is less than the supply voltage and deactivating the power inverter during the periods between pulses in the pulsed mode when the BEMF of the motor is less than the supply voltage.

9 . The method of claim 1 , wherein the threshold is dependent on a current speed of the motor and is the same as or is derived from a peak efficiency torque for the motor.

10 . A motor assembly arranged to:
apply field weakening during a pulsed mode operation of a motor of the assembly when back electromagnetic force (BEMF) of the motor exceeds a supply voltage provided to an inverter that is used to excite the motor; maintain the inverter activated during periods of time between pulses when field weakening is applied, but with zero demanded torque; and maintain the inverter in a deactivated state during periods of time between pulses when field weakening is not applied.

11 . The motor configuration of claim 10 , further comprising a torque modulation decision module configured to:
receive a torque demand for the motor; operate the motor in a continuous mode if the received torque demand exceeds a threshold torque; and operate the motor in the pulsed mode if the received torque demand is less than the threshold torque.

12 . The motor assembly of claim 10 , wherein the torque modulation decision module is further configured to provide a waveform to the inverter indicative of either continuous operation of the motor in the continuous mode or pulsed operation in the pulsed mode depending on if the received torque demand exceeds or is less than the threshold torque of the motor respectively.

13 . The motor assembly of claim 12 , wherein the waveform is indicative of a duty cycle for the pulses when operating the motor in the pulsed mode.

14 . The motor assembly of claim 10 , wherein the inverter further includes a field weakening module to either (a) apply the field weakening when the BEMF of the motor exceeds the supply voltage provided to the inverter or (b) not apply the field weakening when the BEMF is less than the supply voltage provided to the inverter.

15 . The motor assembly of claim 10 , further comprising a sigma-delta torque modulation module configured to use sigma delta modulation to generate a modulated waveform for the inverter to control pulsing of the motor during the pulsed operation.

16 . The motor assembly of claim 10 , wherein the motor is selected from the group including the following types of motors:
internal permanent magnet motors; surface permanent magnet motors, induction motors, synchronous reluctance motors, permanent assisted synchronous reluctance motors, separately excited induction motors, flux switching motors, and switch reluctance motors.

17 . The motor assembly of claim 10 , further arranged to also apply field weakening during continuous operation of the motor when the BEMF of the motor exceeds a supply voltage provided to the inverter that is used to excite the motor.

18 . The motor assembly of claim 10 , wherein the motor is capable of reducing the BEMF in response to the field weakening by weakening a magnetic field associated with the motor.

19 . The motor assembly of claim 10 , wherein the motor is an electric machine capable of operating as a generator.

20 . The motor assembly of claim 10 , wherein the inverter is deactivated during the pulsed operation when field weakening is not required for mitigating or eliminating generation of a retarding motor torque in situations when BEMF does not exceeds the supply voltage.

21 . The motor assembly of claim 10 , wherein the threshold torque is dependent on a speed of the motor and is the same or is derived from a peak efficiency torque for the motor.

22 . A motor assembly arranged to operate in at least three modes, the three modes including:
(a) a continuous mode when a torque demand requested for the motor exceeds a threshold; (b) a first pulsed mode wherein an inverter used to excite the motor is deactivated during periods between pulses when (i) the torque demand is less than a threshold torque and (ii) back electromagnetic force (BEMF) of the motor is less than a supply voltage provided to the inverter; and (c) a second pulsed mode with the inverter turned activated, but no torque is demanded during periods between pulses when (i) the torque demand is less than a threshold torque and (ii) back electromagnetic force BEMF of the motor is more than the supply voltage provided to the inverter.

23 . The motor assembly of claim 22 , further configured to apply field weakening to the motor whenever the BEMF of the motor is more than the supply voltage provided to the inverter, the field weakening acting to prevent or mitigate the motor from generating a retarding torque.

24 . The motor assembly of claim 22 , wherein the motor is selected from the group including

Assignees

• Tula Technology Inc

Inventors

• Carvell Paul
• Tripathi Adya S

Classifications

• Y02T10/64

  Electric machine technologies in electromobility · CPC title

• B60L15/08 Primary

  using pulses · CPC title

• B60L2240/421

  Speed · CPC title

• B60L2240/423

  Torque · CPC title

• B60L15/2045

  for optimising the use of energy · CPC title