THVD8000: PLC communication for Solar application

Hi Brian,

I am so sorry for the delay!

1. There is a chance there could be - we haven't really seen many requirements from nation/government organizations that customers have explicitly expressed to us. It will need to conform to local emissions standards and there could be additional requirements. The THVD8000 itself has ratings for IEC 61000-4-2 and 61000-4-4 directly. 

I have seen customers require a system rating for IEC 61000-4-6 - but we don't directly test that standard (common noise immunity) so I don't have data on that - but it shouldn't disqualify the device without the rating - you may just need to test for it if any specific locality requires it.

2. So there is a limit - but it's based on multiple factors:

a) Modulation frequency - in general the lower the modulation frequency the longer the effective max bus length is - we don't have a direct number however due to the addition of the THS6222 which is going to be able to increase current output. If you have a standard 54 Ohm load then at a 125KHz modulation frequency you would typically have about a max effective bus length of ~610 meters - but with the THS6222 you have a stronger output - but the lower load will also impact max bus length - so you could run into issues at 400 meters even at lower bus lengths.

b) Loading - the loading is going to impact how long the bus can be. You will have losses due to cable (DC from attenuation and AC from capacitance) so the cable chosen matters as well. Then you also need to consider the output impedance of the driver (typically around 0.03 Ohms for THS6222) as well as the effective load. We have tested this system down to 1 Ohm loading - however the caveat there is that you burn a lot of power through the THS6222 at that low of a loading condition. 

I am assuming the system is in parallel - if not please let me know -  if they are in parallel you are looking at less than 1 Ohm effective loading (around 0.6 Ohms) which is beyond what we have tested for - so I'd be a bit concerned  on the loading due to the effective impedance of each panel (350kW / 1.5kV -> 233.3A ; 1.5kV/233.3A -> ~6.4 Ohms ; 6.4 Ohms/10 -= 0.64) - so there is an elevated risk in that case. Also if our system can handle that low of a load - which I am not sure of - the output impedance of the THS6222 will most likely exceed its typical value due to self heating of high current (it would be > 1A) so it could become much closer to the effective load - or possibly exceeding it which would greatly reduce effective bus length + if you add cable losses it could  become significant. If they are in series - which usually I don't think they - the situation is not really concerning as the effective load is higher than a standard RS-485 load- so distance really would be about cable properties + modulation frequency.

c) while mostly a combination of factors a and b - the impedance matching of the system becomes somewhat important and long bus lengths - as reflections can be problematic for longer bus lengths. Essentially the higher the modulation frequency the  quicker transmission line effects become noticeable - however at 400 meters I don't think you will be able to avoid transmission line effects and would need to consider that when looking at the cabling and effective "load" of the transformer on the line. 

Please let me know if you have any more questions and I will see what I can do!

Best,

Parker Dodson