Dynamometer absorber PID setup and tuning

The Dyno2 software uses advanced PID controller that is used to set dynamometer absorber torque according to target dyno speed and actual speed.
Following parameters of the controller are adjustable:

  • kP – proportional term of PID
  • kI – integral term of PID
  • kD – derivative term o PID
  • kD filter frequency – low pass filter cutoff frequency of derivative PID section
  • Integrator reset threshold – target percent range in which the integral section of PID is active. Outside of this range error accumulator is reset.
  • Target change ramp limit – when a step target change is issued it will be converted to ramp target change. Lowering this value will increase response time to step target change and reduce mechanical stress on dynamometer and vehicle drivetrain.
  • Max roller speed slip – this option is used to synchronize dyno roller speeds. It defines how big can roller speed difference be. If set to 100%, there is no restriction. If set to 1%, the slower roller target can be 99% of faster roller current speed. Reducing this value from some point will increase response time to step speed target reduction.

PID coefficient setup is required to enable dyno absorption unit control. Lots of information about the setup can be found on relevant Wikipedia page: https://en.wikipedia.org/wiki/PID_controller

It is possible to use automatic PID tuning algorithm built in the dyno software. It is accessible by clicking right mouse button on Brake Controller Mode in the RUN tab.

Keep in mind that automatic PID tuning uses Relay method which puts a lot of stress on mechanical components of dynamometer and the car. You are using this tool at your own risk!

To tune the PID controller:

  • Secure a car on the dyno.
  • Accelerate the engine to run in the middle of its speed range.
  • Enter target frequency roughly equal to current frequency.
  • Press gas pedal fully and click Get model parameters.
  • The controller will be tuned with relay method and the engine speed will oscillate for a few cycles. Model parameters and suggested coefficients for the controller will be calculated.
  • If the system have not oscillated with constant amplitude and period, the tool will not be able to suggest PID coefficients. Manual tuning will be required.
  • Load preferred coefficient set with▼button.
  • Verify the coefficients and fine tune them manually if needed.
  • If the controller works fine, save the PID coefficients with Save button. Reset button restores coefficients present at the start of the tuning tool. Closing the window, without clicking Save button, will abandon all changes.