Which sample time for simulating discrete Stepper Motor model (FOC Control)?

Is there an ideal sample time or rule of thumb for simulating discrete time motor models with field oriented control?

I've been working on a Motor Control Project, controlling a Stepper Motor with field oriented control. I oriented my model towards the motor control blockset. The Stepper Motor is a block build by myself (discrete time). My Current Control loop is working with 16kHz. My Motor is simulated every 160kHz, so 10 times faster, as the control loop (The factor of 10 is used in some motor control blockset examples). With the goal to get faster simulation results, i tried to reduce the sample time of my motor model. The strange thing is, that i've got different control behaviour. Here are some pictures of my motor speed response (speed is ramped) with different motor sample times.

Motor Sample Time: 160kHz (10 times faster than current control)

Motor Sample Time: 80kHz (5 times faster than current control)

Motor Sample Time: 32kHz (2 times faster than current control)

Answer 1

[Pratyush]

Hi Finn,

When simulating discrete-time motor models with field-oriented control (FOC), the sample time of the motor model significantly impacts accuracy and stability. Here are key points to consider:

General Guidelines

1. Nyquist Criterion: Sample frequency should be at least twice the highest frequency in the motor's dynamics.
2. Control Loop Frequency: Motor model sample time should be at least 5 to 10 times faster than the current control loop sample time.
3. Stability and Accuracy: Reducing sample time can lead to different control behavior due to numerical inaccuracies.

Recommendations

1. Maintain Higher Sampling Frequency: Preferably 5 to 10 times faster than the control loop.
2. Experiment with Intermediate Values: Balance between accuracy and simulation speed.
3. Frequency Analysis: Ensure sample time captures significant frequencies.
4. Validate with Hardware: Confirm simulation results with real hardware.

By following these guidelines, you can balance simulation speed and accuracy, ensuring reliable motor control performance.