How to synchronize two different VFD's using Mitsubishi PLC?

[mitsubishi_user 0]

Hi! I am new here. I would like to ask help from you guys regarding synchronization of two different VFD's using Mitsubsihi PLC. The master VFD is Mitsubishi while the slave VFD is UNICO both with the same line encoders. I got analog reference signal from the master VFD and then sent to the slave VFD to synchronize but I noticed that the slave VFD has different response, causing the slave machine to lag. Maybe you can give me advice on how to correct this problem. Note: Each VFD drives paper printing machine, so every time they do not synchronize the paper loop is cut.

[trespaser5 0]

What Mitsubishi CPU are you using ?

[mitsubishi_user 0]

I am using FX3U together with FX3U-4AD and FX3U-4DA.

[trespaser5 0]

Isn't the FX3u-4DA setting the speed of the mitsi vfd ?

[Goody 5]

It probably depends on how critical the speed matching is. I had a nightmare job a few years ago with the same scenario. All equipment was mitsubish and try as I might I couldn't get them to sychronize perfectly. (and it was critical that they did) In the end we had to change to servo motors and drives.

[Inntele 60]

Syncronize VFDs by speed (but not by phase) is possible without encoders, comparing the current. The algorithm works realy and for two drivers can be realized succesfully even on ALPHA XL.

[mitsubishi_user 0]

Analog signal from Mitsubishi VFD is the master reference signal which is inputted to FX3U-4AD then I output analog signal to the UNICO VFD through FX3U-4DA. I used the two encoders for angle comparison if the other is leading or lagging by certain angle then I compensate the speed of slave VFD(UNICO).

[mitsubishi_user 0]

The speed matching is a bit critical because aside from the paper loop to be cut, the cutoff point is also affected. It is a newspaper printer machine, whenever there is a mismatch there is shift in printing also. We already tried to recommend to change the UNICO VFD into Mitsubishi since the Mitsubishi VFD has Positioning function so it's better to synchronize with the master, but the client insist to use the old VFD. Maybe you have other suggestions to make this work.

[mitsubishi_user 0]

I need to synchronize speed together with phase, it is critical for the output of the machine. Maybe you have more ideas, please kindly share it.

[Inntele 60]

For your requirements I have not progressive ideas. If you need to synchronize drives both by speed and phase, on my opinion it can be done with servodrives only, i.e. the way, described by Goody. The way to synchronize VFDs (described by you or another), is wrong initially and in any case may not be effective because of delay in processing. Mitsubishi Electric offers special servodrives for control asynchronous motors...

[Crossbow 294]

Sounds to me like the analog calibration in the two drives is different. I would have recommended 2 Mitsubishi VFDs on a network like CC-Link so they can both be sent a speed reference as a numeric value digitally over the network. That rules out any calibration of analog signals.

[mitsubishi_user 0]

Yes, there is a difference in response between the two drives. I already recommended before changing the other drive into Mitsubishi but I think they are still working out on the budget. Anyway, thank you so much for your time in sharing your ideas.

[mitsubishi_user 0]

I already tried recommending to change the other drive into Mitsubishi, but they are still working out on the budget. Anyway, I appreciate your kindness to share your ideas to me. Thank you so much.

[mitsubishi_user 0]

By the way, I would like also to ask if PID function is applicable into this kind of system?

[Crossbow 294]

You never said which drives, so not sure about PID in them. But the FX3U PLC does in fact have PID.

[mitsubishi_user 0]

Using FX3U plc can I use its built in PID function to control the UNICO vfd to make this system work?

[plcfreak 0]

Hi all In my opinion the best solution is to use 2 FR-A 700 Series Inverters with encoder feedback card. At the master Inverter you have to use the FR-A7AL card with pulse division output then connect the pulse output to the jog terminal of the slave FR-A700(Speed reference via pulse train input) . If you want even better performance use also a feedback card(FR-A7AP) at the slave drive in order to be closed loop. I Have done it many times so far and with excellent results.

[mitsubishi_user 0]

The master right now is using FR A500. Is it possible to synchronize it with FR a700 using those cards? By the way, is the master VFD necessarily in position control mode just to get the feedback pulse(pulse division output)?

[Inntele 60]

Keep in mind. The way, suggested by plcfreak, describes one kind of VFD syncronization by speed. And you wrote: "I need to synchronize speed together with phase, it is critical for the output of the machine." I contend, double syncronization is impossible to realize with VFDs, 'cause the rotation of asyncronous motor can not be controlled accurately due to its slip-effect. The delays, individual for each drive, make affect too.

[mitsubishi_user 0]

I suppose plcfreak is referring to Positioning mode of FR-A series and I think I'm going into that direction. You are right it is really impossible to synchronize 2 VFD's different brands with speed and phase. I tried before synchronizing 2 MR- J2S and 1 FR-A700 in positioning control mode and it worked. Right now I want to propose them changing UNICO drive to Mitsubishi since I'm not so familiar with their drives. The question right now, what is the best setup? The machine which runs FR-A500 is in CC link network while the other machine which runs UNICO uses only analog signal. I hope you can give me a better idea. Thanks!

[Inntele 60]

mitsubishi_user, As said already, I have not any ideas how to provide the syncronization of VFDs by speed and phase simultaneously, same as it is shown on this video for servodrives http://www.youtube.c...?v=m7oN5xkK6Jo. I consider it's just impossible for VFDs. We live on the Earth planet with its law of physics and by profession I have little faith in miracles. Perhaps there is another magician here...

[mitsubishi_user 0]

Inntele, I find this solution interesting. Please check it out. Thanks! A700-Electronic-Gearbox-Control.pdf

[Inntele 60]

Hi, mitsubishi_user Great, I've looked the document, but still not trust to ideas, outlined in it. Good, if the author got the synchronous work of both drives in the dynamic at various speed settings... The video, similar to the servo demo, could help to part with my opinion. Alas, sorry, to check out this in practice we can not, therefore if you trust in this solution, you will take risks independently. Good luck!!