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

Wed Feb 11 19:20:38 PST 2004

Dan,

If it's one of the Bergey's with the second generation controllers, I would
recommend removing the dump load from the wind part of the system. The newer
controller works better, IMHO, without the dump. The dump circuitry appears
to be the weak link. The controller basically shuts the turbine down during
high winds and high voltages.

You'll need to contact Bergey to make sure the voltage setpoints are what
you want.

Then you can use Chris' idea to provide an "emergency" dump load from the
batteries, rather than from the wind turbine.

Jeff
Jeffery D. Wolfe, P.E.
NABCEP Certified Solar PV InstallerT
Global Resource Options, LLP, Solar  Wind  Energy Solutions
A Woman-Owned Limited Liability Partnership
601 Old River Road, Suite 3, White River Junction, VT 05001-9030
800-374-4494 x107 Toll Free     802-295-4415 x107 Phone      802-295-4417
Fax
Jeff at GlobalResourceOptions.com <mailto:Jeff at GlobalResourceOptions.com> ,
www.GlobalResourceOptions.com

Distributor for:
BP Solar - photovoltaic panels
SMA - Inverters
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Other fine products for renewable energy

-----Original Message-----
From: Dan Duffield [mailto:dand at directpower.com] 
Sent: Tuesday, February 10, 2004 11:07 PM
To: RE-wrenches at topica.com
Subject: hybrid regulation: parallel 1 & 3 stage controllers [RE-wrenches]

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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