Inverter Nominal DC Voltage

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pmanson
Inverter Nominal DC Voltage

I'm entering the specs for an inverter data sheet. The data sheet specifies an MPPT Voltage Range, which I enter as min and max MPPT DC voltage, but it doesn't specify Nominal DC Voltage. Is this number used in the energy model? If it is, can it be calculated from other specs?

Paul Gilman

Hello,

The inverter model uses the nominal DC voltage to calculate internal parameters. What inverter are you modeling? Can you provide me with a link to the data sheet, or attach a copy to your original post above? It might be possible to determine a value from other information on the data sheet.

Best regards,
Paul.

pmanson

I'm looking at the Canadian Solar inverters. They have datasheets for the 23 & 28 kW inverters and for the 36 kW inverter. For the 60 kW inverter, I only found the specs in their string sizing spreadsheet. I was going to attach a screenshot of the specs but I can't see how to attach to a forum post.

Thanks!

Paul Gilman

Based on my comparison of the specs for the 23 and 28 kW inverters on the data sheet and in the SAM library (which originated from the CEC), I would say that averaging the minimum and maximum operating input voltages is a reasonable estimate for the nominal input voltages.

For example, for the CSI-28KTL inverter, the spec sheet range is 300 - 900 VDC, and the nominal voltage in the SAM library is 722 VDC. The average of 300 and 900 is 750, which is reasonably close to 722. You might experiment with different values to see how much of an effect it has on the results.

Best regards,
Paul.

pmanson

I set it to the average of the min and max as you suggested, but the value doesn't affect the energy output at all, so I guess it doesn't matter. Even values like 1V or 10000V don't affect energy output.

Paul Gilman

One more note on this: For the Inverter Datasheet option, SAM sets the C coefficients of the Sandia inverter model to zero, which effectively removes Vdco from the simulation equations. That is why you don't see a difference in the results over the range of Vdco values you tried.

The C coefficients are small empirical adjustments to the Sandia inverter equations. To learn more about them, see King (2007) listed under "Inverter Models" on the Performance Model documentation page of this website:

https://sam.nrel.gov/performance

Best regards,
Paul.

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