SISO Design tool in discrete time

I've been using the SISO Control system design tool to carry controller designs using auto tuning. Even though I specified PI, PID or PD controllers using robust response time, it gives controllers of the following form below

(1.499e004 z - 1.495e004), (2.527e004 z - 2.526e004), (7103 z - 7014), (1.803e004 z - 1.799e004)

These controllers seem improper and cant be implemented as they require future inputs, but matlab does not flag these as improper and the response time specifications I get meet my specifications. Is there a different interpretation of these results or does the SISO tool box produce incorrect results all together.

I'd like to know if there is something am doing wrong and if so how do I correct this or possibly is there a different interpretation of these results by matlab as it didnt flag the results and the responses meet specification.

I'd like suggestions and ideas on how to understand these results.

Thank you.

Answer 1

[Craig]

Hi Adeyemi,

In the SISO Design Tool there is an check box option on the PID tuning panel for "Design with first order derivative filter". This will add a filter that will make the PD or PID controllers proper.

For the PI case, if you are getting an improper controller can you please post the plant model and resulting controller so that I can further investigate.

Thanks,

-craig