Using different size inverters to increase yeild

[Paul Camilli]

Hi Chaps,

it's been a while since I visited, mainly because everything is running so sweetly and we've been getting by on PV and hydro. However, winter is on the way and I'd like to start using the 6kW wind turbine I erected in April https://lifeattheendoftheroad.wordpress.com/2017/04/14/shes-flying-at-last/ The inverter I'll be using is an SMA WB6000 basically because that's what came with it. Trouble is these inverters (unlike the Auroras) have a ridiculously high start up voltage (230V) so what I'd like to do is use another inverter with it. I have also got an SMA WB1200 which starts up at 100V so what I plan to do is stack them and program the curves appropriately. The WB1200 coming online from 100V and the WB6000 at 230V. I know it's possible to do so as I have read of at least two people doing it. The programming I can do, what I'm not sure of is the wiring, any ideas Guys?

Cheers, Paul

[Rob Beckers]

Paul, do the WindyBoy inverters have an isolation transformer build-in, or are these 'transformerless' inverters? That is the main thing when stacking. If they have a build-in transformer it'll be as easy as connecting their outputs in parallel, for a transformerless inverter you will need to provide an isolation transformer for at least one of the two inverters (possibly both, as these things mess with the build-in GFI algorithm).

I've never worked with the WB inverters, but have been involved in many Power-One stacking projects.

-RoB-

[Paul Camilli]

Paul, do the WindyBoy inverters have an isolation transformer build-in, or are these 'transformerless' inverters? That is the main thing when stacking. If they have a build-in transformer it'll be as easy as connecting their outputs in parallel, for a transformerless inverter you will need to provide an isolation transformer for at least one of the two inverters (possibly both, as these things mess with the build-in GFI algorithm).

I've never worked with the WB inverters, but have been involved in many Power-One stacking projects.

-RoB-

Hi RoB,

good to talk again, yes, I should have mentioned, they are both transformer type inverters so no need for an isolation transformer. Having done a little more research it does seem quite simple to connect them in parallel. I think my problem will be protecting the WB1200 from overvoltage. The WB6000 is good for 600V but the WB1200 is only good for 400V. Have you any experience of altering the settings in the 7200 interface as per the ABB doc 'Wind Interface Diversion Load Activation Threshold' of 2010? My turbine produces Max power at 320-360V so if I could make the protection come on earlier all would be 'peachy'. The PDF is 'protected' so I can't 'cut and paste' but if you have not seen it I could email it to you.

Cheers, Paul

[Rob Beckers]

Hi RoB,

good to talk again, yes, I should have mentioned, they are both transformer type inverters so no need for an isolation transformer. Having done a little more research it does seem quite simple to connect them in parallel. I think my problem will be protecting the WB1200 from overvoltage. The WB6000 is good for 600V but the WB1200 is only good for 400V. Have you any experience of altering the settings in the 7200 interface as per the ABB doc 'Wind Interface Diversion Load Activation Threshold' of 2010? My turbine produces Max power at 320-360V so if I could make the protection come on earlier all would be 'peachy'. The PDF is 'protected' so I can't 'cut and paste' but if you have not seen it I could email it to you.

Cheers, Paul

Paul, trying to change the dump Voltage of the PVI-7200 is unfortunately a dead-end: It's default (if I recall right) is 530V DC, and you can change that with a few DIP switches, upwards! Unless you want to change components on the board there's no way to lower the dump Voltage.

There's another issue with these boxes. The dump load comes on in parallel with the inverter, and the bridge rectifier is both undersized in Amperage, as well as poorly cooled. Using the dump load feature is a recipe for a blow rectifier.

I've published a circuit to prevent over-Voltage that with a little adaptation may work for you (or a similar approach could do the trick). See https://www.solacity.com/docs/Wind%20Turbine%20Overvoltage%20Protection.pdf

-RoB-

[Paul Camilli]

Hi again RoB,

altering the voltages aside do you think the Interface is useable with your circuit set at a slightly higher voltage as 'belt and braces'? Would the box benifit from a bigger rectifier, leaving the lid off or some form of active cooling like a small fan?

Cheers, Paul

[Rob Beckers]

Hi Paul,

Power-One's box provides dump load control and rectification (if you can change the brake Voltage), that's nice. A bigger rectifier would certainly help, but won't fit in place. It also requires a larger heat-sink (the rectifier that's in there now could use a bigger one too).

You don't need Power-One's wind box, a simple 3-phase bridge works fine. This is one that I've recommended to many and I've yet to hear of any issues with it. Given the Voltage and current range it falls in the 'nearly indestructible' category: https://www.digikey.com/product-detail/en/M50100TB1200/CC1660-ND/752634

The inverters don't need capacitors to clean up the waveform coming from the rectifier, they already have some input capacitors and that seems to be enough.

That doesn't give you dump load control though. For that you'd either have to use the PVI-7200, or build something like my schematic.

-RoB-

[Joke Evers]

Hi,

I've a totally unrelated question regarding a transformerless inverter (SMA Sunnyboy 5kw) and a wind turbine...

My setup is:
3x5 kw solar panels and 3x5 SMA
a pitch controlled wind turbine used for direct water heating (DC/PWM)

The question is:
what would happen -to the inverters- if I feed the pulsed DC from the water heater into the 3 SMA's
(assume the solar input is neglectable and the DC voltage is below 700VDC)

E.g using the SMA's as alternative for a dump load heater
(in case the boilers are full or any other reason to dump )

Needless to say I've not yet tried anything...

Joke Evers

[Joke Evers]

Well, just for the record...
I'v tried it and the inverter will not start.
It keeps trying to connect to the mains (and does not go up in smoke either)
The slightest 'disturbance' on the DC input will cause trouble.
However once in SMA sunnyboy is started (e.g connects to the mains) it will accept a lot of noise on the DC input. (don't know to what extend)
It seems the algorithm for starting is trusted to do a one time "security" check.

joke

[Cor van Houtum]

Hello Joke

Nothing will happen

When your water system is also on DC power and the voltage complies to the inverter
this will work

When I understand well then you have a wind turbine that provides power to a heat water system.
when the water has reached the temperature then the power is disconnected by the controller and dumploaded or even the turbine is stopped by the controller

and now you want to use the wind turbine to power the inverter that is also in use by your solar panels for the time the water does not demand power.

First to know is what level dc voltage is coming from the water controller .
What is the voltage from the turbine when it is floating

When these voltages are in the mppt range of the solar inverter and NEVER exceed the maximum allowed input you can connect the dc power to the solar inverter.
But to try this DISCONNECT first the solar panels on the mppt channel you want to use.

If the turbine gives enough voltage to drive the mppt then the inverter will work.
But it is possible that the inverter will pull so much power from the turbine that is stalls
and comes to a almost standstill
that depends on the turbine voltage and power and the mppt setting of the the inverter.

So if you get reasonable power is yet not to say.

To make sure that the DC from the turbine cannot back feed I suggest to put a IN-LINE
Big diode into the + lead towards the inverter.

I have tried to hook up a wind turbine to a solar inverter several times and this works.
no problem.
It is not ideal because you cannot program the curve but it works.

But now you want to parallel your solar panels to the same mppt and there happens next,

Even when solar panels have almost no power the voltage will be high
and if this voltage is higher then the voltage coming from the turbine it will not work.
the highest input voltage will rule.

a about the same as putting a string of 3 panels and a string of 4 panels in parallel
with a diversion diode.
the string of 3 will do nothing because the higher voltage of the 4 string.
the voltage of the 4 string is simply higher and overrules the lower voltage.

But when the solar panels have no power (allmost) then the mppt tracker will not ask for more.

It all depends on voltages if it will work

when this are two separate floating systems and you put for safety a diode in line of the dc from turbine then
nothing will turn to smoke.

Kind regards

Cor

[Joke Evers]

Thanks for the information !

Joke