If you look at an un-shaded PV array and note its Voc voltage and its MPP voltage that the normal MPPT tracking
algorithm finds, it will be somewhere around 75% to around 83% of that Voc. The Classic, in this mode, opens up
the array voltage to find the Voc voltage once every sweep interval (3 minutes default). Then, the Classic drops
its input voltage (and thereby the PV voltage) down to that percentage of the Voc it saw when it opened up.
It's just another way is all.. I first did this with the Outback MX60 but it was called "U-Pick" I had to call
it something different here. The REASON that I put that mode in there was two-fold. One, because
I could, and it can have some usefulness. Two, to prove a point. Rick at then RV-Power Products
had a patent on his wonderful MPPT controller at the end of the 1990s. One thing it mentioned was to open up
its input, measure the Voc and then operate the PV array at a constant "OFFSET" voltage below Voc.
This is not really what he does I don't think, but that's what his patent mentioned. We learned about him
from his attorney who sent us a letter to warn us that we might be infringing on his patent and should
license his patent. We told him this i NOT what we were doing but FINALLY found out that it wasn't the
tracking technique they were warning us about but instead, the fact that it was an MPPT controller
with constant voltage charge cycle (Absorb). Well, we know of prior art from the 1990s from a small
company in Australia that had been doing this so I got a letter from Dennis, the owner of that company
and he had a great response. This pretty much made RVPP go away, BUT they still told us that it would
be good to license their technology! Yeah, right ! All this was before the MX60 was even on the market !
During this time, I had found a paper from the late 1970s that spilled the beans (it was published) that
talked about running a charge controller at a percentage of the open circuit Voc of the array and I placed
a reference to that paper in the MX60 manual. The two techniques, percentage or offset are about
the same thing except that %-Voc should work even better than offset. Inside the RVPP controller was
a trim-pot you had to adjust instead of changing it in an LCD menu. That method does NOT work
for PV arrays with partial shading issues. You NEED to track the PV array in that case. I think that the
RVPP unit did percentage of Voc as well but I didn't look at it that closely.
There are SO many bogus patents out there and especially in our field. I have very little faith in the
US patent system but once in a while there are good patents drawn up.