Hi Nico,
The following changes in the model would resolve the issue.
Change 1: In the model, the output from ‘App’ port is an acceleration command. Whereas a speed command is expected as input at the ‘Spd’ port of the ‘strategy’ subsystem. Use an integrator block to convert the acceleration command into speed command as shown in the figure below.
Change 2: Disconnect the ‘ref_spd’ ‘goto’ block from ‘App’ signal and connect it to the ‘Drive cycle’ ‘RefSpd’ input signal.
Change 3: Open the subsystem containing the control logic (indicated with ‘Change 3’ in the above figure). Double-click on the ‘APP’ saturation block. We can observe that the lower limit is zero. Update the lower limit to -inf.
Run the simulation. The vehicle speed now closely tracks the drive cycle reference speed. I have attached the updated model 'Updated_SeriesHybridModel2021_TA.slx' for reference.