Methods and systems for emulating an induction motor utilizing an electronically commutated motor
View Patent ↗A method for emulating induction motor operation using an electronically commutated motor (ECM) is described herein. The method includes receiving, at the ECM, a desired operating torque, accessing induction motor operating characteristics stored within the ECM, and calculating a new torque demand if a speed associated with the desired operating torque is greater than a breakdown speed of the induction motor. The method also includes setting an output torque for the motor substantially equal to the torque demand for the motor if the speed associated with the desired operating torque is less than the breakdown speed of the induction motor, moving the output torque toward the demanded torque if not substantially equal, and operating the motor at the output torque.
1. A method for emulating induction motor operation using an electronically commutated motor (ECM), said method comprising:
receiving, at the ECM, a desired operating torque;
accessing induction motor operating characteristics stored within the ECM;
calculating a new torque demand if a speed associated with the desired operating torque is greater than a breakdown speed of the induction motor being emulated;
setting an output torque for the motor substantially equal to the torque demand for the motor if the speed associated with the desired operating torque is less than the breakdown speed of the induction motor being emulated;
moving the output torque toward the demanded torque if not substantially equal; and
operating the ECM at the output torque.
2. A method according to claim 1 wherein calculating a new torque demand comprises calculating a new torque demand based on the desired operating torque.
3. A method according to claim 2 wherein calculating a new torque demand comprises calculating a new torque demand as a function of at least one of desired operating torque, motor operating speed, induction motor breakdown speed, induction motor no load speed, and an exponential value.
4. A method according to claim 3 wherein calculating a new torque demand as a function comprises calculating a new torque demand according to:
Desired
operating
torque
×
[
1
-
(
i
.
m
.
operating
speed
-
i
.
m
.
breakdown
speed
)
n
(
i
.
m
.
noload
speed
-
i
.
m
.
breakdown
speed
)
n
]
.
5. A method according to claim 4 where n=2.5, motor noload speed is 1200 revolutions per minute (rpms), and motor breakdown speed is 1050rpms.
6. A method according to claim 4 where the induction motor (i.m.) breakdown speed is calculated according to:
i.m. noload speed−per unit torque demand×(i.m. noload speed−i.m. breakdown speed).
7. A method according to claim 1 wherein operating the motor at the output torque comprises operating the motor at the output torque if the output torque is substantially equal to the demanded torque.
8. A method according to claim 1 wherein moving the output torque toward the demanded torque comprises stepping the output torque toward the demanded torque.
9. A method according to claim 1 further comprising repeating the steps beginning at a next processing time slot.
10. An electronically commutated motor comprising:
a permanent magnet DC brushless motor comprising a plurality of external winding connections coupled to an external surface of said electronically commutated motor, at least one stator winding electrically coupled to said plurality of external winding connections;
an electronic commutator, said electronic commutator electrically coupled to said motor; and
a control circuit programmed with motor operating characteristics that cause said permanent magnet DC brushless motor to emulate operation of an induction motor, said control circuit comprising a processor and a memory, said processor programmed to;
access motor operating characteristics stored within said memory;
calculate a new torque demand if a speed associated with a desired operating torque is greater than a breakdown speed of the emulated motor;
set an output for said electronically commutated motor substantially equal to the torque demand if the speed associated with the desired operating torque is less than the breakdown speed of the emulated induction motor;
move the output torque toward the demanded torque if not substanially equal; and
cause said electronically commutated motor to operate at the output torque.
11. An electronically commutated motor according to claim 10 wherein said processor is programmed to calculate a new torque demand based on the desired operating torque.
12. An electronically commutated motor according to claim 11 wherein said processor is programmed to calculate a new torque demand as a function of at least one of desired operating torque, motor operating speed, induction motor breakdown speed, induction motor no load speed, and an exponential value.
13. An electronically commutated motor according to claim 12 wherein said processor is programmed to calculate a new torque demand according to:
Desired
operating
torque
×
[
1
-
(
i
.
m
.
operating
speed
-
i
.
m
.
breakdown
speed
)
n
(
i
.
m
.
noload
speed
-
i
.
m
.
breakdown
speed
)
n
]
.
14. An electronically commutated motor according to claim 13 wherein induction motor (i.m.) breakdown speed is calculated according to:
i.m. noload speed−per unit torque demand×(i.m. noload speed−i.m. breakdown speed).
15. An electronically commutated motor according to claim 10 wherein said processor is programmed to operate said electronically commutated motor at the output torque if the output torque is substantially equal to the demanded torque.
16. An electronically commutated motor according to claim 10 wherein to move the output torque toward the demanded torque, said processor is programmed to step the output torque toward the demanded torque.