PI controller with PCI 6251

[Duy]

Hi all,

I am using DAQ PCI6251. Can I use this card for creating PI controller ?

Basically, I think that we can analyze a PI controller into two phases, including the proportional and integral phases. I could do this easily with Labview library. But I am facing a difficulty how to build the saturation block for PI controller ?

Pls give me the solution.

Thanks so much for your helps and supports.

Best regards,

Duy

[Jochen]

Duy,

before we go deeper into your question, please let me ask a very important question first:

Are you using a real-time operating system (LabVIEW RealTime) or are you running your application on Windows?

If you are not running your application on a real-time OS, it's important to know, how fast you control loop needs to run and how critical your control process is. Windows is not a deterministic operating system, so loops typically run with a significant amount of jitter. Stable loop timing is at least as important as the tunining parameters of your PI controller, so if your loop needs to run at higher rates (~100 Hz or higher) the usage of a non-deterministic operating system is highly discouraged.

Kind regards,

Jochen Klier

National Instruments

[Duy]

Dear Jochen,

Thank you very much for your reply.

I can describe what I am doing as follows:

I would like to control the induction motor drive system with vector control approach.

The equipments in my system include the induction motor drive system, inverter, PCI 6251 Labview card, block connector BNC2110. I am using Labview 7.1.

I will gather the stator currents and voltages from the induction motor under analog signals. Then I will make some calculations on Labview with available Labview library. After that I will output two analog signals. PCI 6251 has two analog signals. I will use two analog signals from PCI6251 Labview card as input signals for PWM generating board which I could bulid. This PWM generating board will create signals to trigger IGBTs of inverter. And the inverter will create signals to control the induction motor drive system.

In this drive system, we need to use two PI controller as the requirement of vector control approach.

I hope that my description is clear.

The expected sample rate is 10 kHz.

I am using XP Window OS.

I attach the diagram what I need to do as well.  

Thanks so much for your great ideas.

Best regards,

Duy

[Jochen]

Duy,

I'm sorry to say that, but there is absolutely no way to run an application with these real-time requirements on a Windows PC. You will either have to use LabVIEW RealTime. Here you can get an overview of available realtime targets.You even can convert a standard desktop PC into a LabVIEW realtime target as long as it meets some specific requirements, but I doubt, that the performance is sufficient (10 kHz control loop rate is kind of a limit for such a system)

For your application the ideal target is either an R-Series board with a programmable FPGA or a cRIO system. These targets offer the best realtime behavior and enough performance headroom.

I'm sorry, that this might not be the answer that your were looking for, but I think it's much better to switch to a better fitting system at an early project phase instead of wasting a lot of time on an approach with very little chances for success.

Kind regards,

Jochen

[Duy]

Dear Jochen,

Thanks for your opinions.

Best regards,

Duy