Modbus TCP control of VSDs - What do you think (2)...

Hello all,

I don't know if this is considered rude but I'm re-posting this
because I'd really like to get some feedback. I got no
feedback the last time I posted this but that might be due to
the holidays. If re-posting this way is rude then I sincerely
apologize.

Anyway...

I've got an application where my customer is insisting on controlling his VSDs over ModbusTCP. The application doesn't
require blinding update times and the VSD network will be completely independent from the SCADA network. Some synchronization is required but it is not particularly tight.
The application initially calls for about 70 VSDs and should grow to a maximum of about 110 VSDs.

While I've got my own opinion I would really appreciate any comments on such an application. I am purposely being vague to allow people to give their feedback on the major PLC and VSD brands using similar configurations.

Thanks!

(8{)} .)
(Yosi)

Yosi,

I have done this with twelve Yaskawa V1000 VFDs, but I used MODBUS RTU with a Red Lion operator interface acting as the MODBUS master and comms bridge to a GE RX3i PLC. This way, I could do all of the speed logic in the PLC. The only issue that I have with the system is that when I download the Red Lion program, the OIT momentarily loses communications with the drives, which means that the drive speed references are set to zero and the drives stop. It is only a small inconvenience for this system and I just make sure that everything is stopped before I download to the Red Lion.

Best regards

I have done many projects using ModbusTCP network controlling vsds. In fact this is by far my preferred method, and given the choice I would always choose Schneider M340/Quantum/Premium and Altivar drives. With the Schneider gear the following services are provided.
- IO scanning - simply fill out a table in the plc and all the comms is setup for you and they are basically ready to go. eg polling rate, timeout, message lengths, data destinations are all done for you. In fact in Unity v5 there is a new feature to automatically find devices on a network and build the table for you (yet to try this)
- dhcp server in the plc - just set a name in the drive
- fdr - faulty device replacement - all the drive parameters are saved in the plc and automatically restored if a new drive (after setting its name) is detected.
- built in web pages - diagnostics, parameter setting and drive status can all be done using a standard web browser
- network tuning - if the io scanning table is used the estimated bandwidth usage can be displayed allowing simple adjustment and tuning.

Thanks Guys,

I'm a very small fan of Modbus RTU for control primarily because of timeout issues. Modbus RTU isn't integrated as part of the I/O network so I've got to somehow handle all communications stuff that and I/O network normally would handle in PLC code.

Back to ModbusTCP...

I can see using ModbusTCP for systems that don't have a large amount of inter-axis integration. In fact, I've yet to find such an application on the internet and this makes me leery. Finally, a system with 20 VSDs on the network is far less formidable than a system with more than 100 VSDs. The number of units on the network frightens me because, since I haven't done this with ModbusTCP, I don't know what I/O mapping limitations (max registers for example) there are with PLC. All I am being told by the distributor is that the system is the most wonderful solution in the world. That and 15 bux buys me a cup of coffee at Starbucks.

Thanks again,

(8{)} .)
(Yosi)

with regard to your concerns about number of device and registers see the following
http://www.schneider-electric.ae/su...nt&country=AE&lang=EN&locale=en_US&id=FA12116
To get an idea of register usage Altivar drives allow you to set up a read and a write io scanning table. Both are normally set to 10 registers
As far as multiaxis goes you should be able to scan critical drives at a much higher rate eg 10ms, and have the other drives at a more conservative 50 or 60ms

Hmmm...

10 Registers each way that means 20 bytes each way. That's far more than the Premium allows with Profibus.

As I said, I can't find any evidence on the internet that someone has
done an application with a high degree of integration between the motors based on ModbusTCP. I'm not saying it won't work I'm just afraid to be the first one to do it.

(8{)} .)
(Yosi)

I can assure you, you are not the first to do the level of integration with this many drives.
Modbus/TCP is more than capable of the task.
If you are unsure of the Schneider setup then ABB also has Modbus/TCP functionality as a native capability of its drives and PLCs.

Hi Yosi

I am not big fan of modbus.in fact I just replace 20 Vacon VFDs which work on Modbus and replace with AB E/IP.
I don't think system with 110 VFDs would not work with Modbus TCP.
ABB had good service over here and they had Modbus TCP adapters (about 750 NIS etch for ACS800).
I would stay with your preferred PLC and use Red Lion G3 adapter to control the Modbus communication.
If one adapter would not be enough you can divide your network for 2 adapters.
I just running now big line of Glass wool in Kiriat Gat.
with many of communication option.
You more then welcome to come and see.
The G3 have driver for E/IP.and account as 1 connection.Under the G3 you can put many as you want devices.
In the near future I have to make application like that with ABB.You can join me and get your self imprison.

feel free to call me on Sunday if you want more information.