hybrid regulation: parallel 1 & 3 stage controllers [RE-wrenches]

[Dan Duffield]

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We have a customer who has a 3 stage MPPT controller (Outback MX60) for PV 
and a diversion single stage controller for wind -Bergey XL.1, they want to 
use both in parallel on the same battery bank? Someone here started asking 
questions- and this made me wonder. I like MPPT and regulators that use 
temperature compensation. "All in one" wind regulators don't have these 
features.
	Problem is that our client has a sealed  AGM battery bank and when used 
with a wind type single stage PWM diversion regulator -  at the fixed float 
voltage of 27.0vdc (2.35vpc) - problem is - power is wasted.
	Where's the leak?
	What happens in this set-up, is that, the power from the pv source circuit 
is siphoned off to the dummy load in/to the diversion regulator once the 
batteries get above 27.0vdc. The wind unit can produce current for extended 
hours (sometimes days on end) and we can't set the wind regulator voltage 
any higher than is safe for these sealed batteries (float).
	During this diversion PWM "siphoning",  the MPPT circuit is looking at a 
combined impedance of the noisy battery bank and diversion load, in an 
attempt to find the sweet spot of the PV array- meanwhile - valuable amps 
are being dumped to the power resistor and effective battery charging is 
stopped from the MPPT above 27.0 volts - during the day -even if the wind 
is not blowing.
	This site is about 200 miles from our shop.
How can this be fixed when we really have only one battery bank?
	Has anyone tried this?  If i set the aux relay in the Outback MX-60 to 
activate at exactly 27.0vdc and turn off at 26.8vdc, this could supply the 
milli-amp current draw of a slave high current dc mercury contactor or 
relay. This relay would switch the "battery voltage seen" by the diversion 
regulator to a distinctly separate voltage source that we could supply. The 
relay would switch the output of the diversion regulator from the main 
battery bank to a fixed voltage source of 27.0vdc - a small dc power supply 
with some decent amount of capacitance added.
	When the actual battery volts rises above the fixed regulation set point 
of the single stage diversion regulator 27.0,  that same diversion 
regulator now only "sees" a new voltage source, namely a fixed 27.0vdc from 
a small DC power supply and the available power if any from the wind or 
hydro unit is dumped to the power resistor or auxiliary  24vdc load - "main 
battery not connected".
	  Now the MPPT tracker is free to correctly perform its function.
	Once the actual battery voltage falls below 26.8 vdc, the smart relay in 
the Outback would switch the diversion regulator's output back again to 
"see" the true battery voltage and regulate any excess power from the wind 
turbine in the normal manner.

I see 4 drawbacks with this system
a)  wind power can only charge the main battery bank in combination with 
sun (during daily insolation window) if the batteries are below27.0vdc, 
otherwise the wind unit is "lost" - purposely dumped.
b) and when the batteries are below 27.0vdc - both power sources producing 
- the MPPT controller may not work optimally- since it's switching 
frequency is around 30Khz and may conflict with the switching frequency of 
most diversion regulators that are lower (ripple/noise city), old NRMXR's 
400Hz. ,   XL.1's-2500Hz,   C-series-?hz,   Southwest Windpowers 
EZ-controller - ? hz.
c) the wind turbine power may not be available - till the main battery 
bank's voltage settles down after sundown and the switch-over occurs or a 
large battery load "happens" to depress voltage.
d) Since MPPT controllers do there optimal current boosting when the 
voltage difference is greatest between the array and battery bank - we have 
a threshold value of 27.0 that we might actually want to adjust this 
setpoint further down-  unless Outback or others; someday uses a pv source 
circuit actuated "timer" to actively change  the auxiliary relay setpoint 
value (lower), one for concurrent daytime solar charging and back up to 
27.0 after the PV voltage falls below 3.0vdc or something. A distinct 
second smart milliamp relay could be added for time independent supervision 
of a 24 hr hydro dump load, while I'm asking.


It we use a just a dummy load with a mercury contactor and the MX-60 smart 
relay,  we would have added benefit of temp comp for sun and diversion 
supervision - but the diversion would be all or nothing, not really 
"siphoning excess" voltage as found in true PWM shunt regulation.


  Other related issues:
Since the NEC still has no specific section pertaining to wind turbines, in 
the Index of the NEC, the closest they come is "WINDOWS"- what would one do 
( anything special) to be code compliant in spirit?
the redundancy requirement for diversion controllers specifies pv but does 
not say anything about wind, just a vague dc charging source.

Since people who buy large capital cost grid connected inverters like the 
idea of battery back-up, and the inverter manufacturers seem to be 
listening - this brings up the issue of the non-ideal characteristics of 
using wet-lead acid batteries in extended float service- that could 
persuade future system purchasers to once again face the charge limitations 
with sealed batteries mentioned above.

I live in the southwest and am blessed with lots of sun - but for 
independent power production to catch on in other geographic climes - 
people will and must turn to wind - and time will march on.

Maybe a AC line commutating wind inverter making up a micro-grid with a 
normal line commutating  battery based inverter  might be the better way to 
go (as has been discussed recently) - present code issues aside. This 
inherently seems likely to be overcomplicated - one inverter failure -whole 
system down even battery charging on dc side.

Anybody have an elegant or quick solution to this 55 gallon drum of worms ?

Hammer me with ideas, please

Dan Duffield

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