Download performant power converters for fuel cells applications

Z-SOURCE INVERTER FOR FUEL CELL
VEHICLES
Adriana FLORESCU, Alexandru VASILE, Constantin RADOI, Dan Alexandru STOICHESCU
University POLITEHNICA of Bucharest
Faculty of Electronics, Telecommunications and Information Technology
Department of Applied Electronics and Information Engineering
Topic: C
Presentation: P
Abstract - DC-DC converters for fuel cell power system are usualy bi-directional and have
complicated circuits, needing many devices and switching configurations. This article presents the
most advanced and new converter suitable for many applications (including FCHEVs applications),
including both the DC/DC converter and DC/AC inverter. It proves that high efficiences, low costs
and future developments in fuel cell power systems can and will be achieved with simple, ingenious,
widespread converters.
Keywords – Fuel cell (FC), PWM inverter, boosted PWM inverter, Z-source inverter, hibrid
electrical vehicle (HEV).
Motivation
Fuel cells are usually classified by the electrolyte employed in the cell. An exception to this
classification is the DMFC (Direct Methanol Fuel Cell) that is a fuel cell in which methanol is
directly fed to the anode. A second grouping is by their operating temperature: there are low
temperature fuel cells – the Alkaline Fuel Cell (AFC), the Polymer Electrolyte Fuel Cell (PEMFC –
that presents today the most interest of all types of fuell cells), the Direct Methanol Fuel Cell
(DMFC), the Phosphoric Acid Fuel Cell (PAFC) - and high-temperature fuel cells that operates at
600-1000°C – the Molten Carbonate Fuel Cell (MCFC) and the Solid Oxide Fuel Cell (SOFC – also
used in many applications).
Fig. 1 shows the basic fuel cell power systems for all the main applications that include the
fuel cell - who needs to be controlled in flow rate, pressure, humidity, temperature etc -,
the power converters (DC-DC converters and/or DC-AC converters) that adapt the fuel cell to the
load and the energy storage, such as a baterry or an supercapacitor, required by fuel cell’s dynamic
limitations.
Fig. 2 represents the block diagram of a fuel cell power system for mobile applications such as
hybrid vehicular applications. Besides the DC/DC converter and the traction inverter, the secondary
battery guarantees the load leveling, assuring braking energy recovery and good performances in the
transient operations. It also supplies with energy the air compressor, the hydrogen circulation pump
and the cooling pump for inverter/motor etc. Fig.6 represents the block diagram of a fuel cell power
system for portable applications such as laptops, cell phones or PDAs. It is similar to the block diagram in
fig.4 excepting the inverter that is missing, taking account of the DC load. Isolation may be or may be not
needed.
Fig.1. Basic fuel cell power
systems
Fig.2. Block diagram of fuel cell
power system for mobile
applications
Fig.3. Fuel cell power system
with Z-source inverter supplied
by a bidirectional DC/DC
converter
Results
By replacing one of the capacitors in the Z-source network (LC) with a battery as shown in
Fig. 1, the Z-source inverter can be used in FCHEVs. Traditional PWM inverter always requires an
extra DC/DC converter to interface the battery in FCHEVs. The Z-source inverter eliminates the
DC/DC converter and utilizes instead an exclusive Z-source (LC) network to link the main inverter
circuit to the FC (or any dc power source).
The comparison effiency results in fig.4 [7] shows that the Z-source inverter has lower
average switching device power in low boost ratio range (1–2) in which most fuel cells reside. In
cases when a low voltage fuel cell is used and a boost ratio much higher than 2 is needed, the dc–dc
boosted PWM inverter is the best configuration. Z-source inverter also provides higher efficiencies
in most operation ranges. From the above comparison, the Z-source inverter provides the highest
efficiency in most regions of the power range of the inverter itself.
Fig. 4. Calculated efficiency of inverters
Fig. 5. Inverter efficiency calculated using
Mitsubishi average loss simulation software
References
[1] V. C. Regep, E. Mamut, “Stand For The Experimental Study Of Pem Fuel Cells”, Rom. Journ. Phys.,
Vol. 51, Nos. 1–2, P. 41–48, Bucharest, 2006
[2] C. Liu, A. Ridenour, J.S. Lai, “Modeling and Control of a Novel Six-Leg Three-Phase High-Power
Converter for Low Voltage Fuel Cell Applications”, IEEE Transactions on Power Electronics, Vol. 21, No.
5, pp. 1292-1300, Sept. 2006