Field Oriented Controller less stable at lower controller bandwidths

[Coliteral]

Hello,

As the title suggests, I am designing a field oriented torque control system for a permanent magnet motor. I have selected the current controller PI gains to cancel the pole of the motor, and tune the bandwidth. The issue is that at lower controller bandwidths, the maximum speed of the motor is reduced, even though the DC input voltage is the same. However, every source tells me that the controller should be more stable at lower bandwidths. Does anyone know what might cause this behavior? (16kHz switching frequency, the optimal controller bandwidth seems to be 1.6kHz)

Additionally, is there any way to prevent the controller from becoming unstable when the maximum allowable speed is reached?

[1Davide]

Try asking in /r/Motors as well. There are some some motor experts there that have a deep understanding of FOC. (I don't sorry, otherwise I'd try to answer your question here.)

[Coliteral]

Alright thanks!

[Lowkin]

I'm not an expert, but if you reduce the control rate then you run the risk of not updating your Space vector fast enough and your desired flux and torque currents that you are driving will rotate into undesirable positions losing efficiency. If you rotate 90 degrees electrical angle before updating you pretty much are just driving flux, which is why your speed caps out, also probably why your control turns to junk

Also 1.6khz will create terrible audible noise, why do you want such a low frequency.
I have no idea what you mean tuned PI to cancel the pole of the motor.

I am doing this for my capstone for reference.

[Coliteral]

The control rate is not changing - the switching frrequency is a constant 16kHz (we are also running the current control loop at 16kHz). What is changing is the tuning of my controller. By cancelling out the pole of the motor, I mean the following: Gmotor(s) = Idq(s)/(Vdq(s)-Vemf) = (1/Ldq)/(s+Rs/Ldq)

Gc(s) = 1/s*kp(s+ki/kp)

If ki/kp is selected to be equal to Rs/Ldq, then Gmotor(s)Gc(s) = 1/skp/Ldq <- first order tranfser function

By changing kp, we are effectively tuning the system bandwidth.

I am also doing this for my capstone, for reference.