A BLDC motor, has a first sub-motor and a second sub-motor. The first and second sub-motors have independent input terminals and a common rotor, including a common output shaft. In a normal operating mode the two sub-motors operate together as one motor to output a normal operating power of the motor. In an emergency operating mode, when one sub-motor has become faulty and generates a braking torque, the normal sub-motor is operated to generate a torque to compensate for the braking torque produced by the faulty sub-motor.
1. A BLDC motor, comprising:
a first sub-motor and a second sub-motor,
wherein the first sub-motor and the second sub-motor have independent input terminals and a common output shaft, a normal operating mode and an emergency operating mode are set for the first sub-motor and the second sub-motor;
in the normal operating mode, the two sub-motors operate together as one motor to output a normal operating power of the brushless DC motor; and
a normal sub-motor starts operating in the emergency operating mode when one of the two sub-motors becomes faulty and generates a braking torque, and a phase current waveform of the normal sub-motor in the emergency operating mode is different from a phase current waveform of the normal sub-motor in the normal operating mode.
2. The motor of claim 1 , wherein a torque output from the normal sub-motor in the emergency operating mode compensates for the braking torque generated by the faulty sub-motor, and a positive and smooth resultant torque is obtained.
3. The motor of claim 2 , wherein a phase current i q of the normal sub-motor is obtained according to the formula i q =−T/K t , wherein T is a torque output from the faulty sub-motor, and K t is a torque constant of the normal sub-motor.
4. The motor of claim 3 , wherein the first sub-motor and the second sub-motor are three-phase motors, and the fault is a fault in which two phase windings are shorted.
5. The motor of claim 4 , wherein the torque T output from the faulty sub-motor is obtained according to the following formula:
{
(
L
a
+
L
b
)
d
i
d
t
+
(
R
a
+
R
b
)
i
=
e
b
-
e
a
T
=
e
a
i
a
+
e
b
i
b
+
e
c
i
c
ω
=
e
a
-
e
b
ω
i
.
6. The motor of claim 3 , wherein the first sub-motor and the second sub-motor are three-phase motors, and the fault is a fault in which three phase windings are shorted.
7. The motor of claim 6 , wherein the torque T output from the faulty sub-motor is obtained according to the following formula:
{
(
L
a
+
L
b
)
d
i
1
d
t
+
(
R
a
+
R
b
)
i
1
=
e
b
-
e
a
(
L
c
+
L
b
)
d
i
2
d
t
+
(
R
c
+
R
b
)
i
2
=
e
b
-
e
c
(
L
a
+
L
c
)
d
i
3
d
t
+
(
R
a
+
R
c
)
i
3
=
e
c
-
e
a
T
=
e
a
i
a
+
e
b
i
b
+
e
c
i
c
ω
=
e
a
(
i
1
+
i
3
)
-
e
b
(
i
1
+
i
2
)
+
e
c
(
i
3
-
i
2
)
ω
.
8. The motor of claim 3 , further comprising: at least one controller, wherein the controller is connected to input terminals of the first sub-motor and the second sub-motor via switching elements, and the fault is a fault in which at least one of the switching elements is shorted.
9. The motor of claim 8 , wherein the torque T output from the faulty sub-motor is obtained according to the following formula:
T
=
e
a
i
a
+
e
b
i
b
+
e
c
i
c
ω
=
-
e
a
(
i
1
+
i
2
)
+
e
b
i
1
+
e
c
i
2
ω
,
wherein
{
if
(
e
a
>
e
b
)
,
(
L
a
+
L
b
)
d
i
1
d
t
+
(
R
a
+
R
b
)
i
1
=
e
a
-
e
b
;
else
,
i
1
=
0
if
(
e
a
>
e
c
)
,
(
L
a
+
L
c
)
d
i
2
d
t
+
(
R
a
+
R
c
)
i
2
=
e
a
-
e
c
;
else
,
i
2
=
0
.
10. The motor of claim 1 , wherein the first sub-motor and the second sub-motor each comprise several teeth and windings, and the teeth of the first sub-motor and the teeth of the second sub-motor are staggered in a circumferential direction.
11. The motor of claim 10 , wherein the teeth of the first sub-motor and the teeth of the second sub-motor are uniformly staggered in a circumferential direction.
12. The motor of claim 10 , wherein the number of stator slots of the brushless DC motor is twelve, the first sub-motor and the second sub-motor each comprise six teeth, the six teeth comprises two U phase teeth, two V phase teeth and two W phase teeth, and two teeth in the same phase are symmetrically distributed by 180 degrees.
13. The motor of claim 1 , wherein the first sub-motor and the second sub-motor each comprise several teeth and windings, and the teeth of the first sub-motor and the teeth of the second sub-motor are arranged in parallel in an axial direction.
14. An electric power steering system, comprising: a steering wheel, a steering column fixedly connected to the steering wheel, a steering gear fixedly connected to the steering column, and a motor drivingly connected to the steering gear, wherein the motor is the BLDC motor of claim 1 .
15. A method of controlling a BLDC motor, wherein the BLDC motor comprises a first sub-motor and a second sub-motor, the first sub-motor and the second sub-motor have independent input terminals and a common output shaft, the method comprises the steps of:
setting the first sub-motor and the second sub-motor to be capable of operating together as one motor, or operating independently;
setting a normal operating mode for the first sub-motor and the second sub-motor, wherein the two sub-motors operate together as one motor to output a normal operation torque of the brushless DC motor in the normal operating mode; and
setting an emergency operating mode for the first sub-motor and the second sub-motor, wherein a normal sub-motor starts operating in the emergency operating mode when one of the two sub-motors becomes faulty and generates a braking torque, a phase current waveform of the normal sub-motor in the emergency operating mode is different from a phase current waveform of the normal sub-motor in the normal operating mode, and a torque output from the normal sub-motor in the emergency operating mode compensates for the braking torque generated by the faulty sub-motor.
16. The method of claim 15 , wherein a positive and smooth torque waveform is generated from the torque output from the normal sub-motor and the torque output from the faulty sub-motor.
17. The method of claim 15 , wherein a phase current i q of the normal sub-motor is obtained according to the formula i q =−T/K t , wherein T is a torque output from the faulty sub-motor, and K t is a torque constant of the normal sub-motor.
18. The method of claim 17 , wherein the first sub-motor and the second sub-motor are three-phase motors, and the fault is a fault in which two phase windings of the faulty sub-motor are shorted, and the torque T output from the faulty sub-motor is obtained according to the following formula:
{
(
L
a
+
L
b
)
d
i
d
t
+
(
R
a
+
R
b
)
i
=
e
b
-
e
a
T
=
e
a
i
a
+
e
b
i
b
+
e
c
i
c
ω
=
e
a
-
e
b
ω
i
.
19. The method of claim 17 , wherein the first sub-motor and the second sub-motor are three-phase motors, and the fault is a fault in which the three phase windings of the faulty sub-motor are shorted, and the torque T output from the faulty sub-motor is obtained according to the following formula:
{
(
L
a
+
L
b
)
d
i
1
d
t
+
(
R
a
+
R
b
)
i
1
=
e
b
-
e
a
(
L
c
+
L
b
)
d
i
2
d
t
+
(
R
c
+
R
b
)
i
2
=
e
b
-
e
c
(
L
a
+
L
c
)
d
i
3
d
t
+
(
R
a
+
R
c
)
i
3
=
e
c
-
e
a
T
=
e
a
i
a
+
e
b
i
b
+
e
c
i
c
ω
=
e
a
(
i
1
+
i
3
)
-
e
b
(
i
1
+
i
2
)
+
e
c
(
i
3
-
i
2
)
ω
.
20. The method of claim 17 , wherein at least one controller is provided, and the at least one controller is connected to input terminals of the first sub-motor and the second sub-motor via switching elements, the fault is a fault in which at least one of the switching elements is shorted, and the torque T output from the faulty sub-motor is obtained according to the following formula:
T
=
e
a
i
a
+
e
b
i
b
+
e
c
i
c
ω
=
-
e
a
(
i
1
+
i
2
)
+
e
b
i
1
+
e
c
i
2
ω
,
wherein
{
if
(
e
a
>
e
b
)
,
(
L
a
+
L
b
)
d
i
1
d
t
+
(
R
a
+
R
b
)
i
1
=
e
a
-
e
b
;
else
,
i
1
=
0
if
(
e
a
>
e
c
)
,
(
L
a
+
L
c
)
d
i
2
d
t
+
(
R
a
+
R
c
)
i
2
=
e
a
-
e
c
;
else
,
i
2
=
0
.