Without more information, perhaps the simulink diagram, the question will be difficult to answer.
In general, PID controllers will produce high outputs if:
1) P coefficient > 0 and the input value is high
2) D coefficient > 0 and the input signal has steep slopes
3) I coefficient > 0 and the average control error does not approach zero over time; i.e. the integrator just keeps integrating up the error.
3) can be remedied by anti-integrator-windup measures (there are several approaches with different complexities and side effects. I believe the Simulink PID controller block does offer this as a built-in feature.