What is mistake in the PWM generator for the Dual Active Bridge model I built?

I am building a PWM generator with dual phase shift control for Dual Active Bridge by Simulink(The model I built is in attachment).

Then I met the following question:

When the simulation time is very short, the output waveform is correct, as shown below.

But when the simulation time is set to three PWM cycles or longer, the output waveform will be wrong. The phase shift angle between S1S2 and S3S4 is lost, and angle between S1S2 and Q1Q2 decreases, as shown below.

Did I make any mistakes with the configurations?

Answer 1

[Sabin]

The problem is the Max step size computed by the model. The parameter ‘Max step size’ in the Model Settings/Solver is set to ‘auto’. When running the simulation for 0.002 seconds, the max step size is computed to 4e-5 which is small enough to capture the delay. However, when the simulation stop, time is increased to 0.004 seconds, the max step size computed in 8e-5 and the delay is not captured in the simulation. The solution is to change the parameter Max step size’ in the Model Settings/Solver to a small enough value that will capture the delay, for example setting it to ‘4e-5’.