EP-4742526-A2 - PULSED ELECTRIC MACHINE CONTROL

EP4742526A2EP 4742526 A2EP4742526 A2EP 4742526A2EP-4742526-A2

Abstract

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 machine's energy conversion efficiency. Under selected operating conditions, the electric machine is intermittently driven (pulsed). The pulsed operation 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 output levels are selected such that at least one of the electric machine and a system that includes the electric machine has a higher energy conversion efficiency during the pulsed operation than the electric machine would have when operated at a third output level that would be required to drive the electric machine in a continuous manner to deliver the desired output. In some embodiments, the second output level is zero torque.

Inventors

TRIPATHI, ADYA S.

Assignees

TULA eTechnology Inc.

Dates

Publication Date: 20260513
Application Date: 20190314

Claims (14)

An electric machine system comprising: an electric machine; a power converter; and a controller 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 output of the electric machine alternates between a first output level and a second output level that is lower than the first output level, wherein the first output level varies as a function of an operating speed of the electric machine and the first and second output levels are selected such that an energy conversion efficiency of the electric machine system including at least the electric machine and the power converter is optimized during the pulsed operation of the electric machine considering at least an energy conversion efficiency of the power converter and an energy conversion efficiency of the electric machine.
The electric machine system as recited in claim 13 further comprising a battery that supplies power to the power converter and receives power from the power converter, and wherein the first and second output levels are selected for optimal energy conversion efficiency of the electric machine system taking into further consideration losses associated with transferring electrical power between the battery and the power converter.
The electric machine system as recited in claim 13 wherein the second output level is substantially zero torque.
The electric machine system as recited in claim 15 wherein the electric machine is turned off during at least portions of the times that the electric machine outputs substantially zero torque.
The electric machine system as recited in claim 16 wherein the electric machine is permanent magnet type electric machine.
The electric machine system as recited in claim 17 wherein the controller turns the power converter off each time the electric machine is pulsed off; and the controller is configured to cause the electric machine to be pulsed at a frequency of at least 100 times per second such that the power converter is turned off at least 100 times per second.
The electric machine system as recited in claim 15 wherein the power converter controls the electric machine to output substantially zero torque during at least a first portion of the time that the electric machine outputs substantially zero torque.
The electric machine as recited in claim 19 wherein the electric motor is an induction machine or a synchronous AC electric machine that does not include permanent magnet.
The electric machine system as recited in claim 19 wherein the power converter controls the electric machine to output substantially zero torque during at least a second portion of the time that the electric machine outputs substantially zero torque.
The electric machine system as recited in claim 13 wherein a period between beginnings of sequential first output level pulses is a pulse cycle duration, and the pulse cycle duration varies during operation of the electric machine.
The electric machine system as recited in claim 22 wherein the pulse cycle duration varies as a function of a rotational speed of the electric machine.
The electric machine system as recited in claim 13 wherein the electric machine is a motor and the power converter includes an inverter.
The electric machine system as recited in claim 13 wherein the electric machine is a generator and the power converter includes a rectifier.
The electric machine system as recited in claim 13 wherein the electric machine is configured to operate as a motor/generator.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority of U.S. Provisional Patent Application Nos.: 62/644,912, filed on March 19, 2018; 62/658,739, filed on April 17, 2018; and 62/810,861 filed on February 26, 2019, each of which is incorporated herein by reference in their entirety. 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. 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 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 output levels are selected such that at least one of the electric machine and a system that includes the electric machine has a higher energy conversion efficiency during the pulsed operation than th