derivative block doesn't answer correctly.

i have an equation system noted down. my input "y1ref" and "y2ref" comes from a block and with the equations below, the "y1dot" and "y2dot" are calculated. (2 equations are separated and k11,k21,k22 are constant gains) using of derivative made may answers infinite numbers in some points. how can i prevent this from happening(for example how to turn equation to integrator?) i appreciate the help

the simulated sustem

[Birdman]

Can you share the model(Export to r2015a) and all necessary variables?

[Hamid Ghaedi]

yes of course. here is the model

Answer 1

[Yogananda Jeppu]

You require a set of integrator. Your input is ddot(Y2ref) and dot(Y1ref). Use integrator in series to get ddot(Y2ref)->dot(Y2ref)-> Y2ref and dot(Y1ref)->Y1ref. Construct the equation dot(y1) and ddot(y2). Use the integrator in series to get y1, dot(y2) and y2. Use these equations back on the ddot(y2) and dot(y1). This is better than differentiating.

[Hamid Ghaedi]

thanks Mr.jeppu but i think that's not correct. my inputs are y1 y2 y1ref and y2ref and the output are y1dot and y2ddot(second derivative) (my apologies because i gave the wrong input in my question.) now,based on these in/outputs how can i got outputs without any problem?

here is the model i'm working on. on>signal>FBC subsytem.

thanks for your help again.