I am getting the following error messages which is weird.

The language feature differentiation of function abs is not supported. Suggested workaround: no suggestion
Error: Derivative of expression abs(-CV.Outlet.w) is non-existent

I guess the error is for the following snippet of code

der(po) = wi - wo;
  po - pi + g * L + k * wi * abs(wi) = 0;
  A * der(H) + wi * B * H + E * H = A * der(po) * V - D * T + D * Tw + M * hIN;