Transcript 29th Annual Conference of the IEEE Industrial Electronics

Nordic Workshop on Power and Industrial
Electronics
NORPIE 2004 Trondheim, 14-16 June
Dimensioning of a Current Source
Inverter for the Feed-in of Electrical
Energy from Fuel Cells to the Mains
M. Mohr
F.W. Fuchs
CSI for fuel cells
Malte Mohr, Friedrich W. Fuchs
Chair for Power Electronics and Electrical Drives
Christian-Albrechts-Universität zu Kiel, Germany
Outline
1. Introduction
2. Fuel cell
3. Demands on the inverter
3.1 Current source inverter (CSI)
3.2 Dimensioning/optimisation
3.3 Laboratory test setup
4. Conclusion
M. Mohr
F.W. Fuchs
CSI for fuel cells
1. Introduction
• Fuel cells convert chemical energy directly into
electrical energy.
• Fuel cells have a high electrical efficiency.
• Application in decentral power generation.
• Fuel cells deliver dc-current.
• Power electronics converts it into ac-current.
• A current source inverter fulfils the
requirements for operation at fuel cells.
M. Mohr
F.W. Fuchs
CSI for fuel cells
2. Fuel cell
V [V]
M. Mohr
F.W. Fuchs
CSI for fuel cells
J [A/cm2]
2. Fuel cell
V-I characteristic curve of a single fuel cell:
• voltage depends significantly on current
V[V]
M. Mohr
F.W. Fuchs
CSI for fuel cells
J[A/cm2]
2. Fuel cell
V-I characteristic curve of a single fuel cell:
• voltage depends significantly on current
• maximum current depends on supplied fuel
V[V]
characteristic curve at
full fuel supply
M. Mohr
F.W. Fuchs
CSI for fuel cells
J[A/cm2]
2. Fuel cell
V-I characteristic curve of a single fuel cell:
• voltage depends significantly on current
• maximum current depends on supplied fuel
V[V]
M. Mohr
F.W. Fuchs
CSI for fuel cells
characteristic curve at
partial fuel supply
J[A/cm2]
2. Fuel cell
V-I characteristic curve of a single fuel cell:
• voltage depends significantly on current
• maximum current depends on supplied fuel
• operation in the linear part of the characteristic
curve
V[V]
M. Mohr
F.W. Fuchs
CSI for fuel cells
J[A/cm2]
2. Fuel cell
V-I characteristic curve of a single fuel cell:
• voltage depends significantly on current
• maximum current depends on supplied fuel
• operation in the linear part of the characteristic
curve
V[V]
operating point at partial load
operating point
at full load
M. Mohr
F.W. Fuchs
CSI for fuel cells
J[A/cm2]
3. Demands on the inverter
The inverter has to
• draw well smoothed dc-current from the fuel cell
to prevent damages of the cell,
• have low harmonics in the mains current,
• adapt the varying fuel cell voltage to the mains
voltage,
• feed in active power,
• be efficient,
• be economical.
M. Mohr
F.W. Fuchs
CSI for fuel cells
3.1 Current source inverter (CSI)
Current source inverter (CSI):
• meets the demands
• increases the voltage towards the mains
M. Mohr
F.W. Fuchs
CSI for fuel cells
3.1 Current source inverter (CSI)
• Losses of the current source inverter depend
on the current Id
 higher efficiency of the inverter system at
higher dc input voltages
• input voltage is limited: Vdc < Vline , depending
on ac-filter values
 load range is limited if the system is optimised
for high input voltages
M. Mohr
F.W. Fuchs
CSI for fuel cells
3.2 Dimensioning/optimisation
Efficiency dependend on input dc voltage:
stack with higher
system voltage
stack with lower
system voltage
maximum
inverter
input voltage
maximum
inverter current
M. Mohr
F.W. Fuchs
CSI for fuel cells
3.2 Dimensioning/optimisation
Efficiency dependend on input dc voltage:
maximum
inverter
input voltage
transmitted power at high system voltage
M. Mohr
F.W. Fuchs
CSI for fuel cells
transmitted power at moderate system voltage maximum
inverter current
transmitted power at low system voltage
3.2 Dimensioning/optimisation
Load range dependend on input dc voltage:
full load range
 lower input voltage
 low efficiency
moderate load range
 moderate input
voltage
 better efficiency
no load range
 high input voltage
 best efficiency
M. Mohr
F.W. Fuchs
CSI for fuel cells
3.2 Dimensioning/optimisation
• rated inverter power increases proportional to
the input dc current
maximum
transmitted power
Pmax at inverter
input voltage
Vd, max
0,8 · Vd, max
0,66 · Vd, max
installed
power range,
power / max. based on Pmax
transmitted
power Pmax
100 %
0%
125 %
45 %
150 %
90 %
 reducing the power range yields to better
efficiency and less rated inverter power
M. Mohr
F.W. Fuchs
CSI for fuel cells
3.2 Dimensioning/optimisation
Simulation of the current source inverter with
Simplorer®
100
A, V
Idd**
v
Id
Vlineline
Id
50
0
Id*, Id,
Vline/5, iline
-50
I, V
line
iiline
-100
0
12.5
25
67.5
ms
t
t
• rise time < ¼ periode of the mains
M. Mohr
F.W. Fuchs
CSI for fuel cells
• inverter much faster than fuel cell
50
3.3 Laboratory setup
circuit diagram of the laboratory setup:
M. Mohr
F.W. Fuchs
CSI for fuel cells
3.3 Laboratory setup
power circuit with low leakage
inductance
measuring and
M. Mohr
control devices
F.W. Fuchs
CSI for fuel cells
overvoltage protection
3.3 Laboratory setup
input dc-current, output ac-current and output ac-voltage;
M. Mohr
at ohmic-inductive load, open-loop controlled
F.W. inverter
Fuchs
CSI for fuel cells
4. Conclusion
The current source inverter
• is suitable to convert electrical energy from fuel
cells to feed in the mains,
• has poor utilisation and poor efficiency at low
dc-input voltages.
• Limitation of power range enhances efficiency
and inverter utilisation.
• In principle the CSI is suited for higher system
voltages and therefore higher power ratings.
M. Mohr
F.W. Fuchs
CSI for fuel cells
Nordic Workshop on Power and Industrial
Electronics
NORPIE 2004, 14-16 June
Dimensioning of a Current Source
Inverter for the Feed-in of Electrical
Energy from Fuel Cells to the Mains
M. Mohr
F.W. Fuchs
CSI for fuel cells
Malte Mohr, Friedrich W. Fuchs
Chair for Power Electronics and Electrical Drives
Christian-Albrechts-Universität zu Kiel, Germany