Using the Bode Plot of a system to use as a model in Simulink

Hi! I got the frequency response of a non linear system using lock in amplifier. Now My question is whether i can use this bode plot in Simulink or MATLAB as a plant model. Moreover, how can i use this frequency response to estimate the model of plant using built in functions.

Answer 1

[Samhitha]

Hi @Muneeb ur Rehman,

The Bode plot obtained with a lock-in amplifier represents the system's response to small-signal (linearized) excitation. If application involves small input amplitudes around the same operating point, use this frequency response as a linear plant model.

For larger signals or different operating points, the actual system may deviate from this response. Use any one of the following toolboxes

1. System Identification Toolbox

• Use idfrd to create a frequency response data object from measured data (frequency and complex response).
• Use tfest to estimate a transfer function model directly from the frequency response data.

2.Control System Toolbox

• Use invfreqs to fit a continuous-time transfer function to the frequency response data by specifying the number of poles and zeros.
• Use tf to create a transfer function object from the numerator and denominator coefficients obtained from invfreqs.

3.Simulink

• Use the Transfer Function block to implement and simulate the estimated transfer function model.
• Optionally, use the Frequency Response Data (FRD) block to simulate directly with the measured frequency response data.

For more details look into following documentation:

https://www.mathworks.com/help/ident/ref/idfrd.html

https://www.mathworks.com/help/signal/ref/invfreqs.html

Hope this helps!