LabVIEW discrete transfer function

[aldosebastian]

I’m having trouble with the discrete transfer function implementation for a while now. So I discretized my PID controller with 100 us and Tustin method in MATLAB, and checked the response to a 1 Hz wave in discrete time using Simulink, with the discrete response as attached. Then I tried doing the same with Discrete transfer function VI in FPGA Labview, taking care to factorise the large numerator coefficients so that it respects the input limits of the VI, and then will multiply the coefficient later after the response of the VI. I also made sure the sampling time in the FPGA code is the same as the sampling time of the discrete controller. Despite this the response saturates to its minimum and doesn’t recover. I attach my LabView code and also the response I got (response before multiplying with the large numerator coefficient).

 

I also tried to do this with a simple integrator, and with this case it actually worked. I attach the results with integrator as well.

 

Could someone help please?

: Simulation results

: Discretized PID

: Response of PID in Labview

: Response of Integrator in Labview

discretetransferfunction.zip

Edited January 31, 2020 by aldosebastian

[Neville D]

Rounding error on the coefficients in FPGA?