obtaining BLDC motor transfer function from measured step response

[fg45]

hello,
I have managed to obtain a measured step response (speed in revs/sec vs time)of a BLDC motor system (motor, driver circuit) and now need to obtain a transfer function in order to design a controller in matlab. Does anybody know how to work out a systems transfer function from a step response?

I have worked out the mathematical model of the motor using the motor parameters and got a transfer function, but i would like to get one for the whole real system.

Any help much appreciated!

 

[xnuke]

Since you plan to use MATLAB to design the controller algorithm, I figure you have access to it. The System Identification Toolbox for MATLAB fits your need. The process of system identification uses measured input/output data to determine mathematical models for systems that are too complicated to model from first principles. Step response data can be used with that toolbox.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[BrianE22]

You'll also need the drive signal to get a transfer function.