19-05-2012, 05:02 PM
A Low-Cost Inverter for Domestic Fuel Cell Applications
61.A Low-Cost Inverter for Domestic Fuel Cell Applications.pdf (Size: 438.67 KB / Downloads: 72)
INTRODUCTION
IN the future, many local energy sources, such as photovoltaic
units, fuel cells, small turbines, small hydroelectric
plants, and other dispersed sources will become a
larger fraction of our electrical supply.” This quote is taken
from the 2001 Future Energy Challenge [1], a national US
student competition sponsored and set up by the Department
of Energy and the IEEE, which spanned Fall 2000 through
Summer 2001.
THE 2001 FUTURE ENERGY CHALLENGE
The Challenge sought to “. . . dramatically improve the design
and reduce the cost of dc-ac inverters and interface systems
for use in distributed generation systems . . . with the
goal of making these interface systems practical and cost effective.
The objectives are to design elegant, manufacturable
systems that would reduce the costs of commercial interface
systems by at least 50% to below $50 per kilowatt and,
thereby, accelerate the deployment of distributed generation
systems in homes and buildings.”
H-Bridge Driven 60 Hz Transformer—A First Attempt
The first topology considered was the H-bridge driven
60 Hz transformer topology shown in Fig. 2. This has much
promise since it is simple and robust, and provides the required
voltage boosting and isolation with a minimum of
components. However, research showed that this design was
not appropriate for the competition since the average 10 kW
60 Hz transformer weighs at least 170 pounds. This exceeds
the 70 pound weight limit of the entire inverter. Also these
transformers house a significant amount of copper and iron
causing prices to be well above $250.
Input Filter
The particular fuel cell used required the input current to
stay within certain bounds; bounds dependent on the fuel
flow. Furthermore, the input current ripple must remain
within limits or damage could result; the maximum ripple
specification is shown in Fig. 6. To keep the current ripple
within the required bounds two steps were taken. Firstly,
the 120 Hz power ripple was removed by using input current
control—see Section IV-E. Secondly, the dc/dc converter
switching ripple was filtered using an LC input filter. The
selected filter values were 150 μF and 6 μH. The filter inductor’s
cost was substantial, due to its 230 A average current
rating.