BATTERY LESS UPS
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23-12-2010, 02:15 PM


Prepared by:Amiy Amritansh



Abstract
Here, new battery-less UPS system configuration powered by fuel cell is discussed. The proposed topology utilizes a standard standby UPS module and the battery is replaced by fuel cell and supercapacitor arrangement. Supercapacitor bank is sized as energy buffer and load transients, steady state power is supplied by the fuel cell.

What is a Battery less UPS ?

It is a fuel cell based UPS system uses a fuel cell instead of battery for the constant power supply.
This fuel cell uses an electrochemical process and converts without combustion hydrogen into electricity.
Supercapacitor bank in parallel to the fuel cell is used to provide power during the startup of the fuel cell and during peak power demands for fast startup and dynamics.
Fuel used
Mainly hydrogen
Other hydrogen containing fuels (such as natural gas or petrol) may be used after passing through a reformer, which convert them into a hydrogen rich gas.



A fuel cell consists of two electrodes, an anode and a cathode, with an electrolyte sandwiched in between.

Associated channels to deliver hydrogen and oxygen and to remove water and heat.


Oxygen passes over the cathode and hydrogen over the anode.
When the two gases try to interact, the presence of electrolyte splits the hydrogen atom into a proton and an electron.
The proton passes freely through the electrolyte.
The electron travels through the electrical circuit, creating an electric current before recombining with the hydrogen and oxygen, creating a molecule of water.


reactions,

(+)Anode Reactions: 2H2 => 4H+ + 4e-

(-)Cathode Reactions: O2 + 4H+ + 4e- => 2 H2O

Overall Cell Reactions: 2H2 + O2 => 2 H2O



MECHANISM OF BATTERY LESS UPS

1. Standard module offline ups system

2. Buck converter
A Buck converter consists of the
Power stage:- includes power switch and output filter. It converts a higher input voltage to a lower output voltage. and
Feedback control circuit:- The feedback control circuit regulates the output voltage.
Here it is used to match the supercapacitor and fuel cell voltage to UPS voltage.



3. Supercapacitors
Electrochemical double layer capacitors (EDLC).
Unusually high energy density when compared to common capacitors.
High power capability and long life.
Suited for short-term power backup requirements in the range from seconds to a few minutes.
An ideal device to connect in parallel with the fuel cell to form a hybrid source capable of satisfying both steady-state and peak power demand and work as energy buffer.


4. Fuel cell stack
5. Critical load
6. Supercapacitor charging circuit


WORKING PRINCIPLE OF BATTERY LESS UPS
When the utility power is available,
the supercapacitor bank charges through
the supercapacitor charging circuit.

Meanwhile, power is supplied to
the load through the ups system while
the fuel cell supplies for 10% of the power.

Supercapacitor bank to ramp up fuel cell from supplying 10% load to 100% load. Also for short term supply.

there might be some voltage and charge fluctuations in the bank. Hence, a buck converter is added between the supercapacitor bank and UPS to provide stable dc power.


 ADVANTAGES OVER BATTERY
Environmentally friendly and produces only green house gases as by-products
Require minimal maintenance
Easy reuse and replacement of fuel
Longer life span
Higher energy density
Cheaper


Other advantages
High efficiency.
Quality power.
Simple operation.
High energy density.
Highly scalable.
Environmentally friendly.
Safe.
Light weight.

DISADVANTAGES

long start-up time and slow dynamics.

limited by cold weather below 0oC

APPLICATIONS
Backup power supplies for computers, timers, security system and programmable controllers.
Inverters
Power supplies
Cameras
Power generators
Emergency power sources for aircraft
UPS systems

CONCLUSION
This system is reliable, high efficient, simple in operation, high energy density, highly scalable, environmentally friendly, safe and light weight.
Fuel cell based battery less UPS can be a better replacement of battery and other backup power systems for low and medium power applications.
BIBILOGRAPHY
W. Fuglevand and R.E. Grant, “Ultracapacitors and fuel cells make a perfect match for portable applications”, Portable Design,
Merlin Gerin UPS, “MGE UPS standards and topologies”,
A. F. Burke, “Batteries and ultracapacitors for electric, hybrid, and fuel cell vehicles”, Proceedings of the IEEE, vol. 95, April 2007.

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