I have a simple Simulink System which appears to be unstable for low sampling rates.
The model looks like this (.slx file was created in 2020a release and is attached to this thread)
- The model is simulated with fixed time steps (no continuous states)
- The sampling frequency is an integer multiple of audio sampling frequency, e.g. 44100 * 64
- The z-transfer-function Y(z)/U(z) in the middle is calculated depending on the sampling rate. It is a first-order system in the s-domain that is converted as follows:
clc; clear; close all;
s = tf('s');
fs_sim = 44100*64;
T = 1/(s*1.1e-9+0.0002288);
model = 'tustin';
[N4 D4] = tfdata(c2d(T, 1/fs_sim, model),'v')
Now I observe the following behaviour:
For high sampling rates, e.g.
the model does what it is supposed to do.
For low sampling rates, e.g.
the system becomes unstable.
Can someone explain why this happens?
Thanks for any advice!