Frequency Problems

[stephendv]

Billi, much smaller frequency changes on the grid, I think a grid inverter by default works within 49.x - 50.x hertz.  Nowhere near the 5Hz difference russ is seeing.

[billi]

Hi again    ... naughty Billi here ...


Russ , if you can hear me , i have a question ,

How often is the sunny boy  is not feeding PV into your house , while your backup generator is running ?

i never thought of it before , since i have a Grid tie inverter and tried the AC coupling route , but while my diesel generator is running my Grid tied inverter does have problems to synchronise  , so does not feed my network  ,

Have you  same problems , or had you have a look at your Sunny boy  , how he/she behaves when Diesel Generator is  running .....

I hope for SMA   that they are  prepared for that "up and down " of a  Generator  ,  and still allow  the PV via the Sunny boy to produce



Regards Billi

[camillitech]

Good point Billi,

something that I'll look into myself, but a couple of things, firstly decent generators with multi cylinders and heavy flywheels don't go 'up down', secondly it may be worth using the 'quiet time' function of the inverter to only run the genny between dusk and dawn, and thirdly, does it really matter  You should be running the 'full cycle' to charge them anyway, or have I missed something  . The frequency on my Trace (which is by now very old technology) never budges more than .5 Hz no matter whats running/loaded.

My 'Windy boy' arrived two weeks ago and I've not even had time to remove it from the box 

Cheers, Paul

[stephendv]

As I understand it, the Sunny Island is designed to prevent sunny boys from operating at the same time as a generator.  The SI will first increase the frequency to knock the sunny boys offline, before starting the generator.  From the manual:

"If the battery is fully charged, the frequency limits the power output of the AC feed-in generators (Sunny Boy). If the generator is now manually started, for example, the frequency would be lowered, if required, as the Sunny Island synchronizes with the generator. The AC feeding-in generators (Sunny Boys) would then feed additional energy into the system and possibly overload the batteries. In order to prevent this, in this case the stand-alone grid frequency is temporarily increased, in line with the synchronization, until the AC feed-in generators (Sunny Boy) are disconnected from the stand- alone grid system as a result of the grid limits being exceeded."

[rogeriko]

The problem with sunny boys and generators is well documented and SMA themselves will tell you not to connect a sunny boy to a generator. Imagine your generator is running charging the batteries and running the house, suddenly the sun comes out, where is that extra 2/3 kilwatt going to go?  Straight back into your generator, blue smoke! When the inverter is running the house it changes frequency to control the sunny boy but when the generator is connected, the generator becomes the prime source with no frequency shifting, in other words sunny boy is on full power all the time. Thats why the sunny boy senses 50 cycle power but it will not connect because it is the wrong impedance for mains and its not from an inverter so it shows an error. SMA equipment is very complex I am installing now the Bi-Directional Inverters SI4500 you should try getting your head around their programming.

[rogeriko]

Billi I think you will find your little chinese grid tie inverter will connect to the generator easily because it dosn't have the sophisticated software of the sunny boy. Supposing we could only run our generators at night when its not windy.

[billi]

Typical .....

When the inverter is running the house it changes frequency to control the sunny boy but when the generator is connected, the generator becomes the prime source with no frequency shifting, in other words sunny boy is on full power all the time. Thats why the sunny boy senses 50 cycle power but it will not connect because it is the wrong impedance for mains and its not from an inverter so it shows an error.

Roger i know that , same here in my system  ..... Thats why i love DC charging  and DC Generators

So it means   for example , the  that the generator is started from the programmed inverter  like Sunny Islands or my Victron for example  at lunchtime ,
cause we want to bake bread and  the load in the house is bigger than 1000 watt ( programming setpoint)  and while my bread is baking , the sun can not help a lot or nothing , even its shining , cause switched of 

Or in absorption charge   , when the generator has to run for hours to get the battery full .....


Paul sure   we know your Harry  "Mr Lister" has the biggest     .... flywheel  , but beside that my , Diesel generator was just running fine and smooth , steady volts , hertz  .... but GTI refused to connect

So i just thought i have to mention this , before others  get fooled as well 

Billi

[russ_fae_fyvie]

Hi Billi, yup I hear you !

Right, as you know I am not an electrician so I will try and expalin, in laymans terms, how I am told the system works.

The Sunny Boy actually feeds AC directly into the MCB in the house, if the house doens't need it all then the surplus is sent back to the Sunny Island and into the batteries.

At the beginning we did have problems when the generator was running and the frequency fluctuated (that was the old genny which has since been replaced) and what happened was that the Sunny Boy shut down, this was because (apparantly) it was not set to the OFF GRID mode and sensed the frequency changes, once it was changed to OFF GRID (via software), and we also got the new SDMO Generator online (where the frequency is pretty stable) we haven't had the problem.

I am not sure what happens if the generator is running and there is still surplus from the PV going back to the SI, it seems to not make too much difference and there is certainly not obvious problems.

The only time the Sunny Boy shuts down now is when the batteries are full (during a genny charge) and the Wind Turbine is charging, the frequency from the SI then increases to tell the SB to slow down and eventually stop producing. At this point the Dump Loads kick in to take the charge from the Turbine.

The only time it all clashes (just the once so far) is when the SI starts the genny, then towards the end of the charge the Wind tries to add plus its a Sunny day as well !

Its annoying to see the SB shut down and the dump loads also working, can't win really !

However it doesn't happen very often.

Over the last few weeks everything seems to have been working okay, the frequency seems fairly settled, even during the genny charge. We still need the UPS for the Boiler because although, generally, the frequency is +/- 2Hz, that is still too much for the Boiler (its limits are +/- 0.5HJz) so with the UPS set to a max of +/- 0.1Hz it stops any more problems with that.

Hope that makes sense !

[billi]

Nice one ,  that does not sound bad then , so the Sunny boy seems to stay on-line  while Generator is working , would be interesting to find out if Power from PV goes down while  Generator is on

you see i try hard to find the  needle 

[camillitech]

Typical .....

When the inverter is running the house it changes frequency to control the sunny boy but when the generator is connected, the generator becomes the prime source with no frequency shifting, in other words sunny boy is on full power all the time. Thats why the sunny boy senses 50 cycle power but it will not connect because it is the wrong impedance for mains and its not from an inverter so it shows an error.

Roger i know that , same here in my system  ..... Thats why i love DC charging  and DC Generators

So it means   for example , the  that the generator is started from the programmed inverter  like Sunny Islands or my Victron for example  at lunchtime ,
cause we want to bake bread and  the load in the house is bigger than 1000 watt ( programming setpoint)  and while my bread is baking , the sun can not help a lot or nothing , even its shining , cause switched of 

Or in absorption charge   , when the generator has to run for hours to get the battery full .....


Paul sure   we know your Harry  "Mr Lister" has the biggest     .... flywheel  , but beside that my , Diesel generator was just running fine and smooth , steady volts , hertz  .... but GTI refused to connect

So i just thought i have to mention this , before others  get fooled as well 

Billi

I see your dilemma Billi but does it actually happen very often ?? We do have a similar problem, that I've learned to live with over the years.
 As my dumps are all AC, if it's pishing with rain, blowing a gale and the wife wants to bake and wash then the inverter sometimes starts the generator to 'load share'. All I do is switch it off, then put it back to 'auto' once the storm has passed.

In practice this only ever happens when someone is home and switching appliances on and off so it's never been a problem. Again, if a gale of wind is forecast and Mr Lister looks like he's about to start up or has started I'll switch him off.

Good to be aware of it but you soon get a feel for your battery bank/generator/renewables with a good meter in the kitchen or somewhere obvious.

Like you say, much to be said for DC charging 

Cheers, Paul

[rogeriko]

There is a little known way of connecting the inverter with the sunny boy using the data cable so the inverter still controls the sunny boy even when it cannot shift the frequency because the generator is providing the frequency. I have never done this but I have read about it, I think on the american SMA forum.

[russ_fae_fyvie]

Thats something I asked these guys at the beginning of the problems last year.

I couldn't see why the SI had to alter the frequency to the whole house just because it wanted to tell the SB to cut back on its output.

Ats the time, the increase to 55Hz to stop PV production (then compensating later by dropping to 47) was causing many problems so I asked that exact question, could the SI send a signal to the SB to reduce output by a seperate cable (or even wirelessly in this whiz bang age of computers!) without having to alter the frequency.

It seems a much better solution to me , but then I'm a simple Structural Engineer who likes simple solutions !

[stephendv]

There is a little known way of connecting the inverter with the sunny boy using the data cable so the inverter still controls the sunny boy even when it cannot shift the frequency because the generator is providing the frequency. I have never done this but I have read about it, I think on the american SMA forum.

The chap who mentioned this on the wind-sun site was misinformed - you can't do this with the data cable.  In the american setup you can configure the SB and SI to act as grid feeding devices when the grid is up but then change to an off-grid mode when the grid goes down.  The data comms link between the SI and SB in this configuration is used to change the SB from grid feeding mode to off-grid mode - but it can't be used to regulate the output of the SB.

Explained on page 144 in the US manual: http://files.sma.de/dl/7995/SI5048U-TUS101331.pdf   (yes it's a slow day today  )