How to implement the closed-loop control for an induction motor with vector control method

[Duy]

Dear all,

I need to implement the closed-loop control for an induction motor with vector control method as the following diagram:

In this diagram, we need to implement two controls on speed and current through the speed controller and the current controller. With the current controller, we will need the PWM generation function to control the induction motor. And PI Controller is for the speed controller. So, can Ni's Motion Controller card resolve this problem ? Can you suggest to me which cards ? As well as how to do this ?

Thank you very much for your helps and supports.

Best regards,

Duy

[Jochen]

Hi Duy,

NI motion control devices like the NI 7340 close the position loop (PID). As position feedback they accept quadrature encoder signals (proportional analog feedback is also available, but this is only used in special cases). As an output signal these devices generate a DC signal (+/- 10 V). You need an external power drive that accepts a +/- 10 V command input signal. The current control is done in the drive.

The general setup looks like that:

NI also offers some drives, but not for 3 phase induction motors, so a 3rd party drive is required for you setup. If you need more fexibility, you also could think of a LabVIEW FPGA based solution.

If you need a more detailed advise, please provide some more information about your application (motor datasheet, types of motion, real-time requirements,...).

Kind regards,

Jochen Klier

National Instruments

[Duy]

Dear Jochen,

Thank you very much for your reply.

I can describe more details about my project as follows:

Actually, there will be two closed-loop in my project.

Firstly, it is for controlling current with the current controller. As the diagram, we will use 6 analog signals (ia*, ib*, ic*, ia, ib, and ic)

where:

ia*, ib*, and ic* are the signals which will be calculated from an algorithm which is described as the diagram

ia, ib, and ic are the signals which will be measured from machine.

These 6 signals will be used to generate 6 PWM digital signals which can trigger 6 IGBTs of an inverter of the drive system. When the inverter works, it will create three analog voltage signals which will be supplied for the machine. This is a basic principle of the closed-loop for the current control.

So, I want to ask that:

-Is there a PWM signal generation function in LabVIEW with Motion control card ?

Secondly, it is for controlling speed. We are using an encoder for measuring the machine speed.

Is there a speed measuring function of a machine in LabVIEW with Motion control card ? 

With the measured speed and the reference speed, we use a PI controller for controlling speed. That is a basic principle of the speed control.

So, is there a PI controller in LabVIEW with Motion control card ?

Those are necessary functions for my project. So, can you suggest to me Motion control cards which can satisfy for me ?

Thanks so much for your helps and supports.

Best regards,

Duy

[Jochen]

Hi Duy,

thank you for the comprehensive reply. I think for this type of a scenario the best solution would be an FPGA based solution like a CompactRIO system. cRIO can be scaled from a modular prototyping platform all the way down to an inexpensive OEM solution. LabVIEW FPGA provides optimized control algorithms for motion control (position/velocity), that can be configured as P, PI, PD or PID controller. There are also examples for the underlying current control and PWM generation, so all your requirements should be covered.

The NI-SoftMotion module provides an easy to use high level API for FPGA based motion control systems, extended example code and an overall good framework for motion control applications (e. g. multi-axes synchronization, gearing, camming,...). For your application (velocity control) the NI SoftMotion module provides some benefits, but it's not mandatory.

For a more detailed consulting I recommend that you contact your local NI branch. May I ask in which country you are living? Then I could help you to find a competent contact person there.

Kind regards,

Jochen

[Duy]

Dear Jochen,

Thank you very much for your consulting opinions.

You meant that we can use CompactRIO system along with NI-SoftMotion module for our application. Is that right ? Do you think that how much are they all ?   

I am living and working in Edinburgh, UK.

Once again, thanks so much for your helps.

Best regards,

Duy 

[Jochen]

Duy,

the complete system price depends on many factors (e. g. do you have already a LV license or not? Do you need one or more systems? Is a single board RIO solution an option? What are your additional requirements? and so on) and I think it's going too far to discuss these details on the forums. That's why we have a great team of local engineering resources that can help you with your decission. Here you can find the contact information for the UK.

To give you an idea, the hardware cost for a system that meets your needs could be in the range of about € 2000 (cRIO integrated backplane + digital output module + analog input module). With sbRIO cost's could be lower.

Best regards,

Jochen

[Duy]

Dear Jochen,

Thank you very much for your information.

Another option, if I have the Multifunction PCI 6251 card, BNC 2110, and LabVIEW 8.5 software. So, do you think we can implement closed-loop controls with those available elements ? I mean that we can use PCI 6251 for generating PWM signals as well as signals for controlling the machine speed. Basically, in my opinion, this PCI 6251 is enough I/O analog and digital for our application. I do not have so much experience about software and hardware of LabVIEW. Please help me advices for this option.

Thanks so much for your helps.

Best regards,

Duy

[Jochen]

Hi Duy,

motion control applications require hard real-time behavior (deterministic timing for I/O operations and calculations). You need at least a real-time operating system to get deterministic control behavior with a DAQ board like the PCI-6251, but this will still be not sufficient for your application and here are some reasons:

• The 6251 is a multiplexed board, but you probably need to acquire the current values simultaneously.
• The position control loop should run with at least 4 to 10 kHz and the current control loop should run at least at the same pace. The PWM generation needs to be synchronized to the current control loop and it probably needs to run even faster (e. g. 20 kHz).

As all operations can't be run in a buffered I/O mode (latency!), but need to be run in single-point I/O mode, it will be very hard or even impossible to meet these requirements with a PCI based solution.

But again, it's a bit hard to take everything into account in a forum thread and I strongly recommend to discuss your application face to face with one of our local engineers in the UK.

Best regards,

Jochen

[Duy]

Dear Jochen,

Thanks so much for your helps.

Best regards,

Duy