Closed loop flux weakening for permanent magnet synchronous motors
View Patent ↗A closed loop flux weakening method and apparatus are provided. The closed loop flux weakening apparatus may include a difference circuit that obtains a difference between a q-axis reference voltage and a q-axis voltage, a controller that converts the difference between the q-axis reference voltage and the q-axis voltage into a d-axis current of a stator of the motor, and a summation circuit that obtains a d-axis reference current by adding the d-axis current of the stator of the motor and a feed forward d-axis current of the stator of the motor.
1. An apparatus for generating a d-axis reference current used for controlling a motor, the apparatus comprising:
a difference circuit that obtains a difference between a q-axis reference voltage and a q-axis voltage;
a controller that converts the difference between the q-axis reference voltage and the q-axis voltage into a corrective d-axis current of a stator of the motor; and
a summation circuit that obtains the d-axis reference current by adding the corrective d-axis current of the stator of the motor and a feed forward d-axis current of the stator of the motor;
wherein the q-axis reference voltage, V qref , is determined based on the following equation: V qref =√{square root over (V max 2 −V d 2 )};
wherein V max 2 is the square of a maximum voltage that can be applied to the motor; and
wherein V d 2 is the square of a d-axis voltage of the motor; and
wherein the d-axis reference current is used to control the motor.
2. The apparatus of claim 1 , wherein the feed forward d-axis current of the stator of the motor, I ds _ feedfw , is determined based on the following equation:
I
ds_feedfw
=
V
q
ref
-
(
r
s
×
i
q
ref
+
L
qs
×
di
q
ref
dt
+
E
)
ω
×
L
ds
wherein, r s is a stator resistance of the motor;
wherein, i q ref is a q-axis reference current;
wherein, L qs is a q-axis inductance of the stator of the motor;
wherein,
di
q
ref
dt
is a derivative of the q-axis reference current with respect to time;
wherein, E is the back electromotive force of the motor;
wherein, ω is the electrical speed of the motor; and
wherein, L ds is the d-axis inductance of the stator of the motor.
3. The apparatus of claim 1 , wherein the difference circuit receives the q-axis reference voltage at a positive input of the difference circuit and receives the q-axis voltage at a negative input of the difference circuit.
4. An apparatus for generating a d-axis reference current used for controlling a motor, the apparatus comprising:
a difference circuit that obtains a difference between a q-axis reference voltage and a q-axis voltage;
a controller that converts the difference between the q-axis reference voltage and the q-axis voltage into a corrective q-axis voltage of a stator of the motor;
a gate that converts the corrective q-axis voltage of the stator of the motor into a d-axis current of a stator of the motor; and
a summation circuit that obtains the reference current by adding the d-axis current of the stator of the motor and a feed forward d-axis current of the stator of the motor;
wherein the q-axis reference voltage, V qref , is determined based on the following equation: V qref =√{square root over (V max 2 −V d 2 )};
wherein V max 2 is the square of a maximum voltage of the motor;
wherein V d 2 is the square of a d-axis voltage of the motor; and
wherein the d-axis reference current is used to control the motor.
5. The apparatus of claim 4 , wherein the feed forward d-axis current of the stator of the motor, I ds _ feedfw , is determined based on the following equation:
I
ds_feedfw
=
V
q
ref
-
(
r
s
×
i
q
ref
+
L
qs
×
di
q
ref
dt
+
E
)
ω
×
L
ds
wherein, r s is a stator resistance of the motor;
wherein, i q ref is a q-axis reference current;
wherein, L qs is a q-axis inductance of the stator of the motor;
wherein,
di
q
ref
dt
is a derivative of the q-axis reference current with respect to time;
wherein, E is the back electromotive force of the motor;
wherein, ω is the electrical speed of the motor; and
wherein, L ds is the d-axis inductance of the stator of the motor.
6. The apparatus of claim 4 , wherein the difference circuit receives the q-axis reference voltage at a negative input of the difference circuit and receives the q-axis voltage at a positive input of the difference circuit.
7. The apparatus of claim 4 , wherein the gate converts the q-axis voltage of the stator of the motor into a d-axis current of a stator of the motor by dividing the q-axis voltage of the stator of the motor by the product of an electrical speed of the motor and a d-axis inductance of the stator of the motor.
8. A method for generating a d-axis reference current used for controlling a motor, the method comprising:
obtaining, by a difference circuit, a difference between a q-axis reference voltage and a q-axis voltage of the motor;
converting, by a controller, the difference between the q-axis reference voltage and the q-axis voltage into a d-axis corrective current of a stator of the motor;
determining, by a summation circuit, the d-axis reference current by adding the d-axis corrective current of the stator of the motor and a feed forward d-axis current of the stator of the motor; and
wherein determining the q-axis reference voltage, V qref , is based on the following equation: V qref =√{square root over (V max 2 −V d 2 )};
wherein V max 2 is the square of a maximum voltage of the motor and V d 2 is the square of a d-axis voltage of the motor; and
wherein the d-axis reference current is use to control the motor.
9. The method of claim 8 , wherein the converting the difference between the q-axis reference voltage and the q-axis voltage into a d-axis current of a stator of the motor comprises:
converting the difference between the q-axis reference voltage and the q-axis voltage into a q-axis voltage of the stator of the motor; and
converting the q-axis voltage of a stator of the motor into a d-axis current of the stator of the motor.
10. The method of claim 8 , further comprising determining the feed forward d-axis current of the stator of the motor, I ds _ feedfw , based on the following equation:
I
ds_feedfw
=
V
q
ref
-
(
r
s
×
i
q
ref
+
L
qs
×
di
q
ref
dt
+
E
)
ω
×
L
ds
wherein, r s is a stator resistance of the motor;
wherein, i q ref is a q-axis reference current;
wherein, L qs is a q-axis inductance of the stator of the motor;
wherein,
di
q
ref
dt
is a derivative of the q-axis reference current with respect to time;
wherein, E is the back electromotive force of the motor;
wherein, ω is the electrical speed of the motor; and
wherein, L ds is the d-axis inductance of the stator of the motor.