Jamoclements
1 µW
- Joined
- Jul 6, 2021
- Messages
- 2
Afternoon all,
I've been struggling to understand the exact working of field weakening in order to increase motor speed. My understanding is that to speed up the motor the AC voltage is increased, upto the base speed of the motor. At this point the rotor voltage and stator voltage is equal due to the BEMF equaling the max AC voltage the inverter can supply. To increase the speed further the control system using FOC control, must start reducing the Id current to counteract the BEMF voltage. Now that there is a difference between the stator and rotor voltage, the machine will speed up. Untill the rotor and stator voltage are equal again. Then the id current is reduced again, and this loop continues as the motor speeds up.
My question is, is the BEMF voltage reduced because it must be lower than the AC voltage inorder to prevent damage to the inverter and current flowing the wrong way? or is it simply reduced in order accelerate the motor?
My other question is as the Id current is reduced, is iq also reduced as they are linked? Or does iq stay the same, but the torque is reduced as the rotor field and stator field will gradually be going over 90degrees, with 90degrees being the optimum angle to produce torque?
I've been struggling to understand the exact working of field weakening in order to increase motor speed. My understanding is that to speed up the motor the AC voltage is increased, upto the base speed of the motor. At this point the rotor voltage and stator voltage is equal due to the BEMF equaling the max AC voltage the inverter can supply. To increase the speed further the control system using FOC control, must start reducing the Id current to counteract the BEMF voltage. Now that there is a difference between the stator and rotor voltage, the machine will speed up. Untill the rotor and stator voltage are equal again. Then the id current is reduced again, and this loop continues as the motor speeds up.
My question is, is the BEMF voltage reduced because it must be lower than the AC voltage inorder to prevent damage to the inverter and current flowing the wrong way? or is it simply reduced in order accelerate the motor?
My other question is as the Id current is reduced, is iq also reduced as they are linked? Or does iq stay the same, but the torque is reduced as the rotor field and stator field will gradually be going over 90degrees, with 90degrees being the optimum angle to produce torque?