idnlgrey model - solver computing other values than ode45

Hi all,

I'm trying to do an parameter estimation of a model with three ODEs and six parameters with System Identification Toolbox. I'm using a nonlinear grey-box-model. I'm getting a fit of about 77%, but my state variables take complete unrealistic values. When solving the system with ode45 and my initial values computed per hand, the solution is complete different (but about how I expect). So the model should work.

When trying to find initial states with findstates(), MATLAB computes totally wrong values.

Any suggestions what I could do?

The equations are:

    function [dx, y] = muehle2(t, x, u, k_c, k_pf, k_pc, k_ppf, k_mil, k_ppa, varargin)  % Output equations.

 %Outputs  
y = x(3);       %Druckverlust                        

   %Stoffwerte etc.
   %CM=0.04;                                             %Feuchte der Kohle
   %T_amb=30;                                            %Umgebungstemperatur °C
   %C_pc=1.3;                                            %spez. Wärmekapazität Kohle kJ/kg*K
   %C_pa=1.005;                                          %spez. Wärmekapazität Luft kJ/kg*K
   %H_evap=2257;                                         %Verdampfungsenthalpie Wasser bei 100°C kJ/kg
   %T_cin=20;                                            %Temperatur Rohkohle °C

   %Dichteberechnung
   %rho=u(6)/(287.058*u(2));
   %rho=1.5;

   %Zustandsgleichungen
   dx =[ u(1) * 1000/3600 - k_c * x(1);                             %Massenbilanz Rohkohle in Mühle
       k_c * x(1) - k_pf * u(3) * x(2);                      %Massenbilanz gemahlene Kohle in Mühle
       k_pc * x(1) + k_ppf * x(2) - k_mil * x(3) + k_ppa * u(3)];      %Druckverlust über Mühle

Thanks.