Severe oscillations during downward motion – BLDC 24V with FOC + Hall sensors – PID tuning help needed

[Christophe65]

Hi,
I’m controlling a 4-pole BLDC motor (24V) for a tilting door using STM32F303, configured via MC Workbench and monitored with ST Motor Pilot.
Control method is FOC with Hall sensors and 3-shunt current sensing. PWM frequency is 25kHz.

:wrench: Motor specs:

• Rs = 0.83Ω, Ls = 0.97mH
• BEMF = 8.75 Vrms/Krpm
• Inertia = 55.53 µN·m·s², Friction = 38.94 µN·m·s
• Max speed = 1000 rpm

🧠 Control parameters:

• Hall sensors: Displacement = 120°, Electrical angle = 60°
• FIFO = 16, Input capture filter = 4 µs
• Regulation time = 80 µs (2 PWM), T-rise = 1500 ns, T-noise = 2000 ns
• Angle interpolation enabled
• Speed control mode with Feed Forward enabled
• Torque & Flux cutoff frequency = 6000 rad/s
• Execution rate = 5 ms

:chart_decreasing: Issue:
Upward motion is relatively clean (minor oscillation), but downward motion shows strong oscillations. The torque required for closing is higher than for opening, and I can’t find PID values that stabilize the system.

:backhand_index_pointing_right: Questions:

• Could the electrical angle setting be incorrect?
• Should I disable angle interpolation?
• Is asymmetric PID tuning recommended for up/down motion?
• Any other parameters that could cause this instability?

Thanks in advance for your help!

[GMA]

Hello @Christophe65,

Did you use the MC Profiler tool to profile the Hall sensor as presented here?
Do you observe the same asymmetrical behavior with no load?
Using the MC Pilot tool, you can open the "Advanced settings" interface and dynamically tune the PID speed by increasing the Speed KP to decrease oscillation.

[GMA]

Hello @Christophe65,

For Hall sensor use case oscillations, could you run a test with the following Hall sensor speed sensing configuration?

[federico.rodighiero87]

• Could the electrical angle setting be incorrect? Yes
• Should I disable angle interpolation? No
• Is asymmetric PID tuning recommended for up/down motion? not needed in my experience
• Any other parameters that could cause this instability? Is the current loop running correctly ?

[Christophe65]

Hello, my problem was due to a bad current loop. I had a lot of noise, so I increased the filter capacitor to solve the issue. Thank you for your cooperation.