question

cydrox avatar image
cydrox asked

using MPPT solar inverter DC input with an AC generator

Hello,

I have a question regarding the possibility of using an AC generator with an MPPT solar inverter.

So basically I have a wind power turbine, the generator is a 3 phases permanent magnet synchrone generator.

In order to have a DC voltage, I will use a diode bridge with a DC/DC converter to meet the requirement of DC input of the inverter.

Lets say I will use the Victron EasySolar-II GX (who handle a DC input between 38V - 66V) without battery, and I'm able with the diode bridge and the DC/DC converter to convert the voltage of the AC generator to a DC voltage that oscillate between 38V - 66V. Will the inverter be able to generate power and behave normally ?

I want to know too how the MPPT will work under those circumstances. Feel free to correct me if I'm mistaken, from what I understood, the MPPT algorithme changes the value of the voltage on the DC input in order to find and drag maximum power. In the system that I explained above, the source imposes the voltage I believe, how the MPPT algorithm will be able to find the maximum power point?

Feel free to ask more questions if I misexplain something.

Thanks in advance

Regards



MPPT ControllersPhoenix Invertersolardc systemac
2 comments
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solarbone avatar image solarbone commented ·
As i have seen commented in another respect, the MPPT is not designed to work without battery.
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cydrox avatar image cydrox solarbone commented ·
@solarbone

Thank you for your comment, I dont think so, as I've found on the net some wind turbine inverters that have the MPPT option, but dont have a DC input ( only AC for wind turbine generator). So basicaly you cannot put batery with such inverters and they have the MPPT option.

You can correct me if I have mis understood something

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1 Answer
marekp avatar image
marekp answered ·

@cydrox

If you connect your wind gen to MPPT input of MP inverter, you will get DC-ripple error and that will be the end of the experiment.

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cydrox avatar image cydrox commented ·

@MarekP Thank you for your answers.


I thaught that there is only input voltage that matter, and if my input voltage is in the inverter's input voltage range it should works. Thank you for clarifying things.


Although, I cannot find the DC ripple limit on the datasheet. I imagine there is a limit that we should not exceed. Do you have any idea, documents datasheets of the DC ripple limit for the inverter in question (Victron EasySolar-II GX ) or any other MPPT solar inverter ?


I imagine that knowing the DC ripple limit, we can calculate the proper value of a capacitor to put after the diode bridge, in order to have a stable DC voltage.

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marekp avatar image marekp cydrox commented ·

@cydrox

screen-shot-2022-10-28-at-25052-pm.png

Can you clarify to what input you want to connect your wind gen?

The 38-66V range is for battery input but you keep asking about MPPT.

MPPT, inside ES-II, is for PV panels and here voltage can be between "battery volts + 5V" as a minimum and "250V" (hard limit) at maximum.

Neither of those inputs can be used for wind gen output.

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cydrox avatar image cydrox marekp commented ·

@MarekP Thank you for your answer.


Perhaps I have not explain well.

Basicaly, I have a wind generator ( who is a 3 phases synchronous generator). I am well aware that you cannot use it with a solar inverter since the solar inverter has 2 DC inputs : one for the solar pannels and one for the battery.

What do I want to know is that if I take the solar inverter, and in the DC solar input, instead of putting solar pannels, I will take the 3 phases of the generator, connect them with a diode bridge to convert the 3 phases AC into a DC, add a capacitor to reduce the voltage ripple, as shown bellow:

1666962940651.png

For sake of argument, lets say that the generator has a rotation speed that is generating a voltage that, after rectifying it and filter it with the capacitor, is in the input range of the "solar DC input" and has a good voltage ripple. Will the inverter be capable of generate power from that power source ? and how the MPPT algorithme will behave since its a DC voltage comming from a source other than solar pannel ?


In your first answer, you talked about a ripple voltage error, were you talking about a ripple coming from battery DC voltage or solar DC voltage ?



in the data sheet :

1666963383384.png

the input voltage highlighted in yellow, is it the DC battery input voltage or the DC solar voltage input ?


If there is still something badly explained, please dont hesitate to ask me again.


Thank you for your time

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1666962940651.png (8.4 KiB)
1666963383384.png (139.1 KiB)
marekp avatar image marekp cydrox commented ·

@cydrox

DC ripple is measured on the battery terminals.

Input voltage range is for battery.

Solar panel DC input:

screen-shot-2022-10-28-at-35045-pm.png

You cannot use the SmartSolar Charge Controller for Wind Turbine generator because it those not have a brake function. Even after you make its output a DC.

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cydrox avatar image cydrox marekp commented ·

@MarekP thank you for your answer.


For me, the brake function is a security thing. If I'm pretty sure that the generator will not exceed the maximum speed rotation or I have something else to stop the generator (actual brakes for example), I don't find any reason why I cannot use a solar inverter, right ?


I'm reading again your second response, you said in your response that the "DC solar range" is from battery +5V to roughly 250 V , is that means that the solar inverter cannot work without battery ?


Also, now when you talked about voltage ripple, is there a limit on voltage ripple on the "DC solar input" too? lets say that I have a DC voltage that has a curve as shown bellow ( red curve)


and the minimum value is 100V and the maximum is 140V

As you can say, the Dc voltage is above the minimum value and bellow the maximum value, but there is a voltage ripple that is not negligible. (40V). Will the inverter have a DC ripple voltage ?

The reason I'm asking is because that there is apparently a ripple voltage limitation on "DC battery input", but I cannot find in the datasheet if there is a DC ripple limit on "DC solar input"


Thank you again for your time.

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marekp avatar image marekp cydrox commented ·

@cydrox

There is no ripple limitation on PV input.

DC-ripple is measured on the battery input.

As the name imply the SmartSolar Charger Controller is for charging battery.

ES-II needs battery to work.

BTW

The ripple in your drawing is for single phase.

You said your turbine is 3-phase.

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cydrox avatar image cydrox marekp commented ·

@MarekP


Sorry I think I've misexplain,

The ripple that I've drawn is the ripple after rectifying the 3 phases:

1666968413324.png


Thank you for the clarifications. So basically you cannot use the inverter in question without battery. Is there an alternative ? i.e, a solar inverter that could be used without the need of using battery ?


Thank you again for your time


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1666968413324.png (23.3 KiB)
marekp avatar image marekp cydrox commented ·

@cydrox

3 phase rectifier would look like this:

screen-shot-2022-10-28-at-60653-pm.png

As you can see the "ripple" is smaller then from 1 phase.

Victron is not making inverters for wind turbine.

I never worked with wind turbine so I do not know what is available.

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cydrox avatar image cydrox marekp commented ·
@MarekP


Thank you sir for your responses and your time, you were helpful.

Have a good day !!

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