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Thread: PF penalty of Solar building

  1. #21
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    A little off the main thread.

    Back in the mid-1990's when Trace Engineering introduced the SW series inverters that were capable of interactive operation with the utility I installed one for a customer in a rural area and the utility was getting it's first experience with these. The utility brought out power quality equipment and could display and quantify the current and voltage waveforms. We observed remarkable differences with the inverter on and off. With the inverter off the voltage waveform was was distorted while the current waveform (residential service) was reasonably clean. When the inverter was on-line things changed, the voltage waveform became clean while the current waveform was highly distorted. This puzzled the utility technician and he was initially not going to approve the connection because of the current distortion. I called the utilities' interconnect manager and he traveled to the site to also observe. The manager approved the installation since he determined that the inverter operation was producing harmonics that offset and corrected the existing situation. The SW inverters are not voltage followers, but rather standalone inverters that synchronize with the grid voltage, phase and frequency, then connect.

    I do not know if the same effect is produced by the modern transformer-less inverters. One local utility, SRP, is now deploying special versions of inverters that offer VAR control. No public results yet. Utility scale inverters in Europe have had this capability for a few years.

  2. #22
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    Quote Originally Posted by Carultch View Post
    Maybe "provide" isn't the best term here.

    What such an inverter does, is it intentionally adjusts the current timing relative to the voltage cycles such that it has a non-unity power factor, to correct for the prevailing imbalance of premises loads.
    so it can detect and supply an inductive phase shift to cancel the lighting out?

    i've clamped on a meter and looked at what the waveforms look like coming off
    LED's and lighting controls. that's a sine wave? really? how can you tell?
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  3. #23
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    Quote Originally Posted by Fulthrotl View Post
    so it can detect and supply an inductive phase shift to cancel the lighting out?

    i've clamped on a meter and looked at what the waveforms look like coming off
    LED's and lighting controls. that's a sine wave? really? how can you tell?
    A grid tie inverter can be considered a programmable current source, able to supply the intended instantaneous current at any instantaneous voltage. As such, it will either follow the connected grid voltage waveform with proportional current OR deliver different amounts of current at each point in the voltage waveform.
    It is easy to program it supply current as an out of phase sine wave, or it is possible to program it to supply even more than proportional current at the voltage peak to offset the flat topping current drain of a capacitor input filter. But to do the latter you would need to tell it what to do rather than have it somehow deduce that information from the observed voltage waveform.
    I do not know of any GTIs that do anything other than allow a phase offset in the current.

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