Motor drive system and method capable of suppressing heat generation during low speed operation

Patent metadata

Field	Value
Publication number	US-11223317-B2
Application number	US-201916695571-A
Country	US
Kind code	B2
Filing date	Nov 26, 2019
Priority date	May 9, 2019
Publication date	Jan 11, 2022
Grant date	Jan 11, 2022

Abstract

A motor drive system capable of suppressing heat generation during a low speed operation may include: an inverter including a plurality of switching elements to convert direct current power to alternating current power having a plurality of phases; a motor driven with the alternating current power converted in the inverter; and a controller determines an operating point of the motor on the basis of a torque command of the motor and generates a d-axis current command and a q-axis current command corresponding to the operating point. In particular, when each of the switching elements is overheated, the controller changes the d-axis current command and the q-axis current command by changing the operating point to a different operating point corresponding to a torque of the same magnitude as the torque command.

First claim

What is claimed is:

1. A motor drive system capable of suppressing heat generation during a low speed operation, the motor drive system comprising:
an inverter including a plurality of switching elements to convert direct current power to alternating current power having a plurality of phases;
a motor driven with the alternating current power converted in the inverter; and
a controller configured to determine an operating point of the motor based on a torque command of the motor and generate a d-axis current command and a q-axis current command corresponding to the operating point,
wherein when a switching element of the plurality of switching elements is overheated, the controller is configured to change the d-axis current command and the q-axis current command by changing the operating point to a different operating point corresponding to a torque of the same magnitude as the torque command, and
wherein when the switching element is overheated, the controller is configured to:
convert three phase currents based on the d-axis current command and the q-axis current command by using the following Equations:

ρ
=

θ
+
270
-

β
x

,

⁢

I
U

=

Im
x

·
sin

⁢

⁢
ρ

,

⁢

I
V

=

Im
xx

·

sin
⁡

(

ρ
+

2
3

⁢
π

)

,
and

I
W

=

Im
x

·

sin
⁡

(

p
-

2
3

⁢
π

)

,

where, Im x is a peak value of each of the three phase currents, and β X is a phase angle of the d-axis current command and the q-axis current command, and
change the operating point of the motor by searching for the phase angle of the d-axis current command and the q-axis current command so as to change an angle section to which a variable ρ belongs in a plurality of angle sections divided at preset intervals.

2. The motor drive system of claim 1 , wherein a switching element to which a square of the three phase currents is maximally applied is designated in the plurality of angle sections, and
the controller is configured to change an angle section to which the variable p belongs to an adjacent angle section in which the switching element to which the maximum square of the three phase currents is applied is changeable.

3. The motor drive system of claim 2 , wherein the controller is configured to:
calculate the phase angle of the d-axis current command and the q-axis current command so as to change the angle section to which the variable ρ belongs to the adjacent angle section in which the switching element to which the maximum square of the three phase currents is applied is changeable, and
change the operating point of the motor to a point at which an equal torque line of the operating point at which the d-axis current command and the q-axis current command are determined by selecting an equal magnetic flux line corresponding to the phase angle and the selected equal magnetic flux line intersect with each other.

4. The motor drive system of claim 2 , wherein the controller is configured to:
calculate the phase angle of the d-axis current command and the q-axis current command so as to change the angle section to which the variable ρ belongs to the adjacent angle section in which the switching element to which the maximum square of the three phase currents is applied is changeable, and
alternately apply an operating point of the motor corresponding to a point at which an equal torque line of an operating point at which the d-axis current command and the q-axis current command are determined by selecting an equal magnetic flux line corresponding to the phase angle and the selected equal magnetic flux line intersect with each other and a prior operating point of the motor to the operating point of the motor.

5. The motor drive system of claim 2 , wherein the controller is configured to:
calculate the phase angle of the d-axis current command and the q-axis current command so as to change the angle section to which the variable ρ belongs to a border between the adjacent angle section in which the switching element to which the maximum square of the three phase currents is applied is changeable and the angle section to which a present variable ρ belongs, and
change the operating point of the motor to a point at which an equal torque line of the operating point at which the d-axis current command and the q-axis current command are determined by selecting an equal magnetic flux line corresponding to the phase angle and the selected equal magnetic flux line intersect with each other.

6. A motor drive method for a motor using a motor drive system capable of suppressing heat generation during a low speed operation, the motor drive method comprising:
determining, by a controller, whether a switching element is overheated; and
changing, by the controller, a d-axis current command and a q-axis current command by changing an operating point to a different operating point corresponding to a torque of the same magnitude as a torque command when it is determined that the switching element is overheated,
wherein changing the d-axis current command and the q-axis current command includes:
converting three phase currents based on the d-axis current command and the q-axis current command by using the following Equations:

Assignees

• Hyundai Motor Co Ltd
• Kia Motors Corp

Inventors

• Yoo Tae Il

Classifications

• H02P21/04 Primary

  specially adapted for very low speeds · CPC title

• H02P27/085

  wherein the PWM mode is adapted on the running conditions of the motor, e.g. the switching frequency · CPC title

• H02P23/14

  Estimation or adaptation of motor parameters, e.g. rotor time constant, flux, speed, current or voltage · CPC title

• H02P29/60

  Controlling or determining the temperature of the motor or of the drive (H02P29/02 takes precedence) · CPC title

• B60L2240/423

  Torque · CPC title