Torque Control of PMSM Motor

Thread Starter

Minsaraganesh

Joined Mar 31, 2021
3
I saw an example file for torque control of matlab. In that, they used speed as the load to the motor but question is that we use torque as the load for motor then why they used speed as load?
Is it due to torque control? if yes then during torque control how speed becomes controlled?
 

Papabravo

Joined Feb 24, 2006
18,071
I think you must be very confused.

Speed and torque are not considered as loads for a motor. A load for a motor is Moment of Inertia or friction of a rotating shaft or pulley or gear train.
Torque is produced by current in the motor windings. So an increase in current leads to an increase in torque which leads to an increase in rotational speed. As the speed increases however the torque will decrease and so the is a limit to how fast a motor can rotate.
 

Papabravo

Joined Feb 24, 2006
18,071
Thank you dear friends Papabravo and Bordodynov. Can we control speed of pmsm when doing torque control?
At low speed you can do this, but torque is a limited resource. That is the available torque decreases as the speed increases. At some point you will run out of torque and when that happens you will no longer be able to control the speed. If this is OK you may do as you please.
 

Danko

Joined Nov 22, 2017
1,263
@Minsaraganesh,
You can control speed, by changing torque, in diapason
of speed from ωbase to ωmax.
Please, look at that:
2021.12.05 06-52-08.png
Typical characteristic curves of torque/power vs. speed of IPMSMs.
 
Last edited:

Papabravo

Joined Feb 24, 2006
18,071
@Minsaraganesh,
You can control speed by changing torque in diapason
from ωbase to ωmax.
Please, look at that:
View attachment 254199
Typical characteristic curves of torque/power vs. speed of IPMSMs.
Bravo! "diapason" is not a commonly used English word, and it is not often that I learn new words. I believe the usage is correct in that it means a range, as in a range of musical notes on a scale.
 

Thread Starter

Minsaraganesh

Joined Mar 31, 2021
3
@Minsaraganesh,
You can control speed, by changing torque, in diapason
of speed from ωbase to ωmax.
Please, look at that:
View attachment 254199
Typical characteristic curves of torque/power vs. speed of IPMSMs.
From the characteristic curve, Torque is constant and speed is variable below base speed then how controlling a constant torque would control speed? For example I have a rated torque 100Nm and rated speed 3000RPM then to achieve 2000 RPM what will be my torque in torque control method?
 

MisterBill2

Joined Jan 23, 2018
11,565
First it needs to be clarified what sort of motor is being controlled, because that matters a great deal, and also what sort of controller is being used, For applications with any old motor and a simple controller either speed or torque can be controlled.
BUT iif the motor is an electronic controlled permenent Magnet Brushless Servomotor then more capability for control is available. The speed can be set by using the electronic phase rotation to set the speed of rotation. That is quite simple to do if exact position control is not required. It can even be done open loop, without any tachometer feedback. In addition, the available torque can be set by controlling the current fed to the motor, since torque is proportional to current. So limiting the current can limit the available torque. Now it gets complicated because the load may be great enough to slow the motor by causing slip in following the magnetic rotation. So to provide a constant speed, more current to provide more torque is required.
So within a limited range it is possible to set both torque limit and speed.

I actually did this once in a production test machine for rotary compressors. The motor speed was determined by the drive frequency and the torque was set to stall the motor if excessive torque was required. An torque sensor detected the stall condition and so the operation was quite simple.
 
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