Mitsubishi A700 VFD torque control by RSV (Load Sharing)

[isengineer]

Hi All, 

I was wondering if any of you guys could help me about improving my load sharing application. At the moment it's very unstable and i can't see what i am doing wrong! Thanks. 

Details:

I am trying to run a industrial chain conveyor using Torque control by Real sensorless vector control function of A700 Mitsubishi VFD. I have been following "Technical Note" which is provided by mitsubishi (see attached PDF). 

As described on technical note, i am trying to control 5 motors ( 1 X 2.2kW, 4 X 1.1kW) to share the load on this chain conveyor. Torque command (SV) and Motor Torque (PV) read from Master VFD and PID output (MV) of Q03UDE transferred to Slave VFDs over CC-link.

i would appreciate any information and help you can provide,

Many Thanks. 

Application_Technical_Note_Load_Sharing.pdf

[Mitsm83]

Not positive I can help but can take a look. I have a little experience with this. 

Are you able to post your projects PLC and VFD?

More details on the problem you are experiencing as well. 

[isengineer]

Hi All, 

If you are interested to have a go, you may find my programs below. Thanks. 

K-line torque control(mr PLC).zip

K_-Line 310517.zip

[Mitsm83]

So, I am not able to find a problem here. Hopefully someone else can help.

isengineer, if you see this and do not mind doing so post the symptoms you had sent to me that may give a better idea of where to look for others. 

Good luck

[isengineer]

Symptoms are,

• On run signal all drives accelerating up to set frequency (30Hz) fine (i believe during acceleration and deceleration, torque control not exercised)  
• Then master drive runs at 30Hz and slave drives continues to increase their speed. I know that this is happening because MV (which is my torque command for slave drives) is quite large. Maybe i need to adjust my PID parameters to make it less responsive!
• But what i don't understand, all 4 slave drives not running at same speed, even though same MV value driving them all! Because of this some section of the chain conveyor stretches and some sections bunched up. 
• Ideally i need all drives to run at same speed ( apart from Sinew drive, because this one has a larger diameter drive wheel and it needs to run 0.96 times slower than the others) so i can keep line tension same on everywhere on the line but i need all 5 drives to share the load.

Thanks.

[kaare_t]

A bit late.

I must admit I haven't tried the load-sharing function before, but I've ran torque controls. Do you also set the maximum speed limit for all drives (e.g. speed should never exceed master drive + e.g. 2%)? Unless you set a maximum speed limit, all drives will continue to increase speed "unlimited" until their torque is applied correctly.