can anybody help me in simulink? (fractional order PID)

I removed the following article its robust controller and used a fractional-order PID instead.

But there is a problem in the simulation that one of the control signals (u_3) becomes negative (figure below).

Can you help solve this problem?

The simulation program in MATLAB is come attach.

(article name: Control of malaria outbreak using a nonlinear robust strategy with adaptive gains)

The simulation uses the FOMCON Toolbox for MATLAB.