Schneider's New Conext SW inverters

[Vic]

Hi Ram,

Welcome to the Forum,

Am surprised that the XW Inverter is as BAD as 5% THD ...   this is not very good, IMO.

And,  you really want a Worst-Case THD number,  and this will depend on a number of variables,  so a simple snapshot will not show Worst-Case unless one is very lucky.

Really,  this number must come from Schneider,  and if they are not putting this important data in their specs,  but,  rather in a manual,  seems to me to me that Schneider is not willing to guarantee this spec.

Have been running Xantrex SW+ 5548s for a decade,  and under certain conditions,  the output sinewave from the inverters is completely flat-topping the waveform -- this is during EQ at about 63.5 - 64 V on the battery.  ad felt that this might well have been an AC output  voltage regulation strategy that these inverters employ when Vbatt is very high ...  just guessing.

Also,  it will be difficult to determine just what is the THD from one oscillogram.

Additionally,  IMO,  it is probably not THD that is causing flicker of lights.   Would guess that it has more to do with AC output voltage regulation,  and this is readily affected by battery voltage regulation,  and this often involves battery interconnections,  etc.

Just my opinions,  and guesses.    FWIW,   Good Luck,   Vic

[Ram]

Thanks for penning your thoughts, @Vic. You're right that THD alone does not cause light flicker, but I have experimented with a number of inverters and looked at waveforms, measured THDs, watched lights flickering etc and I have come to the conclusion that the THD and flicker factors are correlated; quite simply, the [in]ability of an inverter (which may be speced at 5% with resistive loads) to handle nonlinear loads like a laptop SMPS which draws several spikes of current per second, is related to its [in]ability to hold the output voltage and its shape steady. Its inability to do that in any measure manifests as flicker.

By way of an update - I got an email from Eric Bentsen at Schneider acknowledging that while they have not published their THD spec for the Conext SW, their technical champion says it is less than 3%. Puzzling that an SW should have a better spec than its big brother the XW, and more puzzling why they do not publish it if it is really as good as 3%! He also said THD testing is done with resistive loads which leaves that all important question of nonlinear loads hanging :-(.

[Ram]

Here is a detailed update I got on the Conext SW after chasing the matter further with Douglas Wicks, product manager for the battery inverter line.
best-Ram

...our product will probably NOT meet your requirements for audio equipment. For the IEC version, the THD is less than 5% with the normal input voltage range 44V-56V. When the input voltage range is 40V-44V, the THD is less than 8%. The tests are conducted under pure resistive load condition. (We are not sure where the <3% came from... )

I talked with our compliance team and they provided the following information.

For the CSW (IEC and UL models), the requirements for Vthd on OUTPUT of an inverter are summarized as follows.

    IEC 62109-1 = no requirement
    EN 50178 = no requirement
    IEC 60240-1:  (UPS safety) = no requirement
    IEC 60240-2: (UPS EMC) = no requirement
    IEC 60240-3 (UPS performance) =The effect on the output of the UPS by non-linear loads both in steady-state and dynamic is, in many cases, to cause deviation from the output characteristic specified by the manufacturer/supplier where these are quoted under linear load conditions. Due to the higher peak to r.m.s. steady-state current ratios, the output voltage total harmonic distortion may be increased beyond the manufacturer's stated limit. Compatibility with the load for higher levels of THD is a matter of agreement between the manufacturer and the purchaser.

    IEC60335-1 (household equipment) = no requirement
    CSA107.1 says 30% THD  (mark a warning if higher)
    UL1741 says same