how to solve linearization errror

I have an model with PSIM and two chart which trigger for different time interval ,when i perform auto tune of the model in a closed loop ,obtained following error " linearization failed: The plant model in the PID loop linearizes to zero, and therefore cannot be used in PID controller design. This problem occurs when one or more blocks in the PID loop have zero gain or the feedback loop is not physically closed. Click "Continue" to launch the PID Tuner and obtain a new plant model in the "Obtain plant model" dialog. Click "Cancel" to return to the PID Controller block dialog." i tried with frequency estimation of PID and obtained error for command "frestimate" because model contain function and trigger.how can i solve it?