Looking for best way of communication between power converters.  - Page 1
Forum section: electronics / projects

author: Miyuki
author_rank: Frequent Contributor
timestamp: September 09, 2019, 06:07:16 am
content: Hi folks.I want to ask if you have some experience with some IOT/power modules communicationI am looking for best way of communication between power optimizers, inverters and batteries.So everything is connected with DC busI prefer data over power solution, but all look expensive, sub GHz 802.15.4 wireless look cheaperI want some standardized protocol with possibility to change hardware and keep compatibility in future.And interface shall be cheap up to 6$ or soWhat to choose ?

author: Psi
author_rank: Super Contributor
timestamp: September 09, 2019, 10:02:32 am
content: Do you really want a standardized protocol? i.e. do you actually need to connect with systems other people create?Standardized protocols can be great but a lot of the time they are extremely complicated compared to what you need.Data over power is cheap and easy if you only need slow speed comms, normal serial baudrate kind of levels.You can implement your own protocol and have any features or future provisions that you want.Making the system yourself allows you do get all the features you need and implement them in the way that works best for your application.Just make sure you design the V1 protocol to have feature extension blocks for V2,3,4,5 data which V1 knows how to handle 10 years from now when it receivers a data stream from a V5 device.It's easy to paint yourself into a corner with protocol versions.You can change the protocol spec in next version but you cannot easily change how old devices handle the new protocol version.

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 09, 2019, 12:57:36 pm
content: RS485 is one popular standard to consider.

author: Miyuki
author_rank: Frequent Contributor
timestamp: September 10, 2019, 07:28:33 am
content: I dont need big speed, I can easy live with 4800BPS from chips like ST7540But I want to push price little lower, just ST7540 alone is about 7-8$ + plus some support stuffAnd other alternatives I found are even more expensiveI would like something at half of this price

author: Psi
author_rank: Super Contributor
timestamp: September 10, 2019, 08:23:05 am
content: You don't really need a dedicated IC for 4800baud over power rail.You could do it with the main MCU and some decoupling caps to read/write digital data onto the power rail.I would recommend using manchester coding. It gets around the issue when a long string of 0 or 1 can get lost because the frequency is so low. With manchester coded data the frequency is very narrow and easy to filter

author: Siwastaja
author_rank: Super Contributor
timestamp: September 10, 2019, 08:39:21 am
content: Note that for a stiff low-impedance DC link, it may be harder to inject and detect than on an AC power line.Devices running on AC power line naturally need rectification and EMC filtering components, which also provide a separation for communication injection and detection.With a well bypassed, low-impedance DC bus, you don't necessarily have that. I'm not 100% sure you can do it very easily, without adding cost to every device, think about extra DC bus filter components.A one-wire or two-wire communication, even bog standard CAN bus, might be lower in cost, including extra wire installation work, especially if you work for the total development cost, unless you are going to produce thousands of installations with hundreds of meters of DC bus per installation. But if you were to do that, why wouldn't you simplify the problem for that specific case, reducing modularity?As a general note, such modular systems are not going to be cost-optimized anyway, so I wouldn't try to save on communication wiring.Instead, for ultimate cost reduction, look for maximizing integration, so that you minimize the amount of DC bus wiring altogether - and solve the communication problem at the same time. In essence, this means, whatever "power optimizer" means, it could be a feature on your inverter or battery charger instead of a separate product - done on a single MCU, no communication needed.

author: Psi
author_rank: Super Contributor
timestamp: September 10, 2019, 08:50:53 am
content: good points

author: ddavidebor
author_rank: Super Contributor
timestamp: September 10, 2019, 09:04:27 am
content: I think the CAN bus standard will be perfect for your need as long as:* you can wire a couple extra small wires* you have at least two fixed components in your system you can wire at the start and end of the bus to terminate it (there are workaround if you do not have this luxury)this meet also your price requirementsI would stay away from wireless comunication as in proximity with switching circuit you might have reliability issues and shielding everything correctly is not trivial.If you want to go with the DC bus route to have the simplest installation possible, there seems to be solutions available already:https://en.wikipedia.org/wiki/DC-BUSBut I think it will be extremely hard to approach that company if they're used to work in the automotive sector.Also, consider this was not designed for switching applications, you're going to have much much more noise.I would stick with CAN.

author: Miyuki
author_rank: Frequent Contributor
timestamp: September 11, 2019, 10:40:32 am
content: I bassicaly want some more modern alternative to ancient LM1893 or TDA5051As more cabling is pain what I want to avoidAnd push frequency little higher than plain manchester for simpler filtering

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 11, 2019, 11:05:10 am
content: Quote from: Miyuki on September 11, 2019, 10:40:32 amNeither of which are relevant because they are for communication over *AC mains* which can be (mostly) relied upon to have a high impedance to high frequency AC; you want to communicate over a DC bus will have a diminishing impedance with frequency due to the obligatory filter/decoupling capacitors in each device. Now, if you were to insert a choke in front of the capacitor in each device you could then use the DC link as a communication bus, but that choke is likely going to cost a whole lot more than a CAN bus transceiver IC and some twisted pair cabling. The exception would be if the devices are current-fed (e.g. - are a boost-derived converter) so already have a choke in series with the DC input, otherwise, just suck it up and go with CAN, as has been repeatedly suggested.

author: Miyuki
author_rank: Frequent Contributor
timestamp: September 11, 2019, 11:42:26 am
content: For reasonable impedance at 100s kHz is choke miniature just few uH is enough it is not an expensive solution even for higher currents

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 11, 2019, 12:05:42 pm
content: Quote from: Miyuki on September 11, 2019, 11:42:26 amInjecting a signal at 100's of kHz onto your DC bus? I guess you aren't planning on passing any EMC tests, eh?

author: Miyuki
author_rank: Frequent Contributor
timestamp: September 12, 2019, 09:04:59 am
content: Quote from: MagicSmoker on September 11, 2019, 12:05:42 pmI dont need to pass proper EMC testBut I dont want something silly, just if impedance at 132kHz will be too low, then just double the frequency to get little more roomAnd direct emission from two wire cable shouldn't bee so big deal