PID controller tuning, cannot linearize the plant and error.

Hi, hope your doing well

need to tune the PID controller but I am facing a lot of errors, like linearizing failors, and this error :

"The Simulink model DABClosedLoop could not be linearized when downsampling unstable poles with large magnitude with a sample time of 1e-07 to 0.0001. Try decreasing the target sampling time."

The Simulink model is attached.

Please help and thanks

Answer 1

[Zhao Wang]

The model would be linearized while lauhcing the PID Tuner from the PID Controller block's parameters dialog. The attached model, is a switching model with PWM signals driving the IGBT/Diodes. Because of the discontinuities in the model, linearization would error out or maybe linearize to zero. As a result, tuning the PID controller is not possible based on this default linearization result.

To workaround this issue, there are two possible approaches:

1. Use an average-value model to replace the switching circuit model using the same component parameters. This would allow linearization to obtain a meaningful result for controller tuning.
2. Keep the switching circuit and conduct frequency response estimation to obtain a linear plant model. The frequency response estimation result can then be loaded into the PID Tuner for controller tuning.

[Zhao Wang]

The sample times mentioned in the error message come from the model itself:

1. A sample time of 1e-07 is used in the powergui block for discrete-time simulation
2. A sample time of 0.0001 is used in the discrete time PID Controller block

The signals' sample times need to match each other in the linearization process.

[Hassan Iskandarani]

Thank you for your time and the answers Sir.