the output of the integrator does not correspond the input

I bulid a modle which include a integrator in the loop, shown as fig.1

but the output of the integratoe is so weird, shown as fig.2

the yellow line is the input signal of the integrator and the blue line is the output signal of the integratoe.

I cannot figure out why. looking for help!

Answer 1

[DAWEI GAO]

I found the reason finally! It's due to the worng selection of solver. Select the proper step and solver and the result will be alright.