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Design Considerations of a Utility Interactive Fuel Cell Inverter

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Abstract and Figures

The concept of deregulated energy infrastructure is rapidly shaping the future of power generation and grid constitution. Control, communication and integration of various alternative energy resources within a Distributed Generation (DG) network have opened up areas of new challenges and opportunities. The power interface between a fuel cell system and the distribution grid is one such intriguing issue. With the advent of various grid-interactivity, safety, efficiency and power quality standards (such as, IEEE 1547), the design of a cost effective-high performance power electronic inverter for a fuel cell system is a challenge. In this paper, various design criteria, topologies and control aspects of a grid-tied fuel cell inverter are discussed. An overview of some fundamental design standards, and a systematic approach for topology selection is given. An outline of a possible DSP based hardware configuration, communication and control is also provided. Initial simulation of the proposed scheme along with considerations for practical implementations of fuel cell inverter are discussed.
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IEEE, NECEC 2004, October 12, St. John’s, NL
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Abstract—The concept of deregulated energy infrastructure is
rapidly shaping the future of power generation and grid
constitution. Control, communication and integration of various
alternative energy resources within a Distributed Generation
(DG) network have opened up areas of new challenges and
opportunities. The power interface between a fuel cell system and
the distribution grid is one such intriguing issue.
With the advent of various grid-interactivity, safety, efficiency
and power quality standards (such as, IEEE 1547), the design of
a cost effective-high performance power electronic inverter for a
fuel cell system is a challenge. In this paper, various design
criteria, topologies and control aspects of a grid-tied fuel cell
inverter are discussed. An overview of some fundamental design
standards, and a systematic approach for topology selection is
given. An outline of a possible DSP based hardware
configuration, communication and control is also provided.
Initial simulation of the proposed scheme along with
considerations for practical implementations of fuel cell inverter
are discussed.
Index Terms—Fuel cell, Distributed Generation, Single Phase
Inverter, Controller, Modeling and Simulation
I. INTRODUCTION
ITH increasing interest in alternative energy systems
wind, solar, micro-hydro, biomass and fuel cell based
power sources are being considered for domestic, commercial
and industrial installations in various parts of the world. Solar
and wind power based systems are forerunners in this
category. Bulk energy production from renewable sources for
commercialization through the main electricity grid has been
regarded as a success in many countries. However, connecting
smaller energy sources for injecting power into the grid is a
relatively novel concept. This idea of tying small-scale
alternate power sources to the distribution grid for commercial
purposes is termed as Distributed Generation (DG) [1,2]. It is
expected that, utilization of distributed energy resources
would be economical and beneficial to the overall power
scenario, in terms of power quality, reliability and energy
efficiency.
Power from almost all of these alternative systems is either
inherently variable or dependent on environmental conditions.
A power-conditioning unit is therefore required to extract
1*Graduate Student, Ph: 709 737 2049, Email: mjakhan@engr.mun.ca
2Assistant Professor, Ph: 709 737 8934, Email: tariq@engr.mun.ca
Faculty of Engineering and Applied Science, Memorial University of
Newfoundland, St. John’s, NL, Canada A1B 3X5.
* Corresponding Author
usable energy from these sources. There is a great research
need to provide directions and solutions in designing low-cost,
high-performance, efficient and reliable power converters for
such systems [1,3].
Fuel cells are electrochemical devices that convert energy in
the hydrogen fuel directly into electrical energy and water
vapor. This technology is potentially suited for a diverse field
of applications such as, automobile, residential houses, and
consumer electronics. Flexibility of fuel usage, scalability,
longevity and emission free operation make this a good
alternative for future power generation.
This paper focuses on various issues regarding
interconnection of fuel cells to the utility grid through a
power-conditioning unit. Various policy and regulatory issues
along with cost and performance conditions dominate the
design of such a power converter. These non-technical aspects
are discussed in Section II. A review of various available
power electronic solutions and inverter topologies are
discussed in Section III. Power electronic converter for fuel
cell systems and their controller design procedures are
discussed in Section IV. Based on these discussions, two
inverter systems are approached for further analysis, followed
by a computer-based modeling (using MATLAB-SimulinkTM
environment) in Section V. Simulation results and an outline
of DSP based implementation method are discussed in
Sections VI and VII, respectively.
II. SYSTEM REQUIREMENTS
Utility interactive inverter systems are defined as power
conditioning units that maintain sufficient flexibility and
robustness to interact with the power distribution grid.
Variations in grid voltage, frequency, and outage are some of
the aspects that an inverter should be capable of handling.
Power quality, safety, electromagnetic interference (EMI),
reliability, efficiency, cost, size, weight etc. are some of the
deciding factors that determine the practical usability of such
an inverter [3,5,6]. There exists a number of regulatory and
policy directions for interconnecting distributed energy
resources to the grid. IEEE standard 1547TM [6] is the most
recent and well-researched document for such systems.
Several issues outlined in this standard along with some
practical considerations [5] are highlighted below:
A. Grid Interactivity
The inverter system should be able to detect the grid
automatically and start delivering power upon a controlled
Design Considerations of a Utility Interactive
Fuel Cell Inverter
M. J. Khan1*, M. T. Iqbal2
W
IEEE, NECEC 2004, October 12, St. John’s, NL
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request. Whenever a grid outage occurs, the inverter should
disconnect itself immediately from the utility to avoid
islanding. The unit can also be designed for standalone when
needed. . An agreed list of tolerance level in voltage and
frequency is given in Table I [5,6].
B. Power Quality
The power should have a low harmonic distortion (typically
5% or better) and good peak power capability (typically 5:1)
(Table II).
C. Performance
The fuel cell based inverter system should have an overall
efficiency of 90% or above, with power level varying from 5%
to 100%. The input could be a variable DC source with wide
range of variation (for 1 kW system, DC input voltage may
vary from 30V to 60V). A modular design scheme run by
simple control mechanism should be followed to increase
reliability.
D. Safety and Other Issues
Galvanic isolation, lifetime, environmental conditions,
noise, EMI, protection, auxiliary storage device are also
significant factors in designing inverter systems. Therefore,
available industry standards need to be followed in the design
level.
III. SURVEY OF INVERTER TOPOLOGIES
Fuel cell output voltage is a variable DC, usually much
lower than the r.m.s. value of the grid voltage. Therefore a
boost stage is generally used in the converter. To protect the
power source, a galvanic isolation is required. Two
fundamental converter topologies are shown in Fig 1.
The topology in Fig .1(a) requires a low frequency
transformer at the second stage, which makes the system
heavy and costly. In most cases the second topology is chosen.
It gives a range of options in designing DC-DC converters and
using different switching and control schemes. This topology
could be further classified in two major categories: Voltage-
fed and current-fed (Fig 2) inverters.
The DC-DC boost stage in the voltage fed converter may
use a conventional-boost, forward, fly-back, or High-
frequency link converter. On the other hand the current fed
scheme may utilize a push-pull or full-bridge converter at the
DC-DC stage [7]. A further classification of these topologies
are given below:
A. PWM Inverter with Low Frequency Transformer
In this scheme, the low-level DC voltage of the fuel cell is
inverted by a Pulse Width Modulated (PWM) inverter and fed
to the grid through a line-frequency transformer (Fig. 3). This
structure is also robust, simple and provides proper boost and
isolation with minimum number of components.
On the contrary, the transformer size is comparatively large
in order to deliver sufficient power to the grid. The only
control available for the inverter is the PWM modulation of
the power switches. These limitations make the topology
practically unsuitable for most applications.
B. Boost Converter, PWM Inverter with Low-Frequency
Transformer
The switch mode boost converter increases the DC input
voltage to a higher level. For many cases, the amplification
cannot be done with only one boost stage. Therefore, the
inverted output of the PWM inverter is further stepped up with
the low-frequency transformer (Fig. 4).
Even though higher degree of control is available in this
TABLE I
VOLTAGE AND FREQUENCY VARIATIONS ACCEPTABLE LIMITS
Voltage
Tolerance
110V
Variation: +15% ~
-
20%
240V
Variation: +15% ~
-
20%
<50V
Clearance time: 0.16s
50<V<88
Clearance time: 2.0s
110<V<120
Clearance time: 1.00s
V>120V
Clearance time: 0.16s
Frequency
Tolerance
60 Hz
Variation: ± 2%
50 H
z
Variation: ± 2%
>60.5 Hz (<30 kW)
Clearance time: 0.16s
<59.3 Hz (<30 kW) Clearance time: 0.16s
<59.8-57.0 Hz (>30 kW) Clearance time: 0.16s ~ 300s
TABLE II
HARMONIC ORDER AND ACCEPTABLE RANGES
Individual Harmonic
Order,h (odd
Harmonics)
H <
11
11
H <
17
17
H <
23
23
H <
35
35
H
Total
Distortion
Percent (%) 4.0 2.0 1.5 0.6 0.3 5.0
Fig. 1. (a) Inverter with AC boost stage (b) DC boost stage with inverter
Fig. 2: (a) Voltage fed converter (b) Current fed converter
Fig. 3. PWM Inverter with Low Frequency Transformer
Fig. 4. Boost Converter, PWM Inverter and Low-Frequency Transformer
Fig. 7. Square Wave Transformer Feeding a PWM Inverter
IEEE, NECEC 2004, October 12, St. John’s, NL
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configuration, the need for transformer is still an obstacle. The
hard switching of the boost converter makes it less efficient
and requires higher heat dissipation mechanisms.
C. Forward Converter with PWM Inverter
The limitations of the previous topology could be overcome
by a forward converter acting as the only boost stage. The
output of the PWM inverter could then be directly connected
to the grid through filters (Fig. 5).
The disadvantage of this configuration is, a high ripple in
the input current requires a large input capacitor. The DC bus
contains high-voltage square wave signals, which creates
electromagnetic interference (EMI) problems.
D. Flyback Converter with PWM Inverter
The flyback converter boosts the DC voltage and the PWM
inverter generates an approximate sine wave. Even though
simplicity and low cost are advantages of such topology, it is
suitable for low power applications (Fig. 6).
High stress on the switch makes this circuit unsuitable for
higher kW range applications.
E. Square Wave Transformer Feeding a PWM Inverter
The H-bridge inverter feeds a square wave current to the
transformer, which boosts it up to a higher level after
rectification on the secondary side. The second inverter
converts this DC into AC for direct integration with the grid
(Fig. 7).
Assuming the transfer inductance of the transformer to be
high, the inductor in the high voltage DC bus could be
eliminated. This topology is more dependent on solid-state
switches than passive components and has gained more
applicability than the previous configurations [8].
F. High Frequency Resonant Inverter-Cycloconverter
The high-frequency-resonant-inverter (HFRI) converts the
variable DC output of the fuel cell into a higher-level AC
voltage. However, the frequency of the HFRI is much higher
compared to the grid. Therefore, a cycloconverter could be
could be used for adjusting the frequency (Fig. 8).
The response of the system is fast, power factor is good,
number of stages is limited to two, and line connectivity is
simple. However, realization of a cycloconverter and its
control circuitry is relatively complicated.
G. High Frequency Resonant Inverter-Rectifier-PWM VSI
The HFRI-rectifier-PWM Voltage Source Inverter (VSI) is
one of the most suitable topologies in terms of cost, size, and
efficiency. It has a fast response, good power factor, and
favorable overall performance (Fig. 9).
It requires a line filter for grid connection and suitable
control circuitry for driving the resonant inverter at the boost
stage and the voltage source inverter at the final stage.
H. High Frequency Resonant Inverter-Rectifier-LCI
In this scheme a high-frequency inverter, rectifier and Line
Commutated Inverter (LCI) are used. The inductor at the high
voltage DC bus makes the previous assemblies appear as a
current source to the PWM inverter.
The line-commutated inverter (LCI) operates at the
maximum firing angle. The utility line current approximates
square wave and hence proper harmonic filter is required. The
control operation is conducted by adjusting the frequency of
the HFRI inverter (Fig. 10).
IV. ANALYSIS OF GRID INTERACTIVE INVERTER
The grid-connected inverter is probably the most significant
component in the utility interfaced fuel cell system. Initially,
one inverter with a third order filter (LCL type) and its
necessary control methods are investigated (Fig. 11). In the
latter section, a simplification using a first order filter (L type)
is employed to analyze a complete fuel cell based utility
Fig. 5. Forward Converter and PWM Inverter
Fig. 6. Flyback Converter and PWM Inverter
High
Frequency
Resonant
Inverter
Input Filter
FC
HF
Transforemer
1-phase
Cycloconverter
Grid
Fig. 8. High Frequency Resonant Inverter
-
Cycloco
nverter
High
Frequency
Resonant
Inverter
Input Filter
FC
HF
Transforemer
Grid
HF
Bridge Rectifier Filter
Line Filter
PWM VSI
Fig. 9. High Frequency Resonant Inverter
-
Rectifier
-
WM VSI
Fig. 11. Analysis of Grid Interactive Inverter
IEEE, NECEC 2004, October 12, St. John’s, NL
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interactive system (Fig. 17).
A single-phase half-bridge voltage source inverter
connected to the grid through a third order (LCL type, Fig. 11)
filter is discussed in reference [11]. Dynamic small-signal
modeling, selection of control variables, and investigation of
control methods are investigated in the sections to follow.
A. Selection of Controller Variables
It is required that the injected current to the grid should in
phase with the grid voltage to have near-unity power factor.
Variations of the grid voltage and frequency should also be
encountered sufficiently. To reduce stress on the switches, the
switching frequency should be optimum. On the other hand,
switching frequency need to be high enough to allow use of
smaller filter. Proper control variables should be chosen to
maintain stability of operation. In a practical system, the grid
voltage and frequency could be sensed by a Phase Locked
Loop (PLL) device. The dynamics of a PLL should also be
taken into account for designing the controller.
A single phase half bridge voltage sources inverter with
LCL filter may have a number of parameters to be considered
for feedback control. The inverter output voltage, Vinv,
Inverter output current, Iinv, Capacitor voltage Vc, Capacitor
current Ic and Grid current, Igrid are such parameters (Fig. 12).
Since the grid voltage is determined by the utility, the injected
grid current, Igrid need to be controlled. At the first look it may
appear that, direct sensing and control of Igrid would be enough
to achieve the control goal. However, a root locus plot for
these parameters using the small-signal dynamic models [11]
shows several significant deviations.
A root-locus plot of these parameters using equation set (1)
yields that; Grid current Igrid has two of its poles on the right-
hand side of the S-plane, making it unsuitable for stable
operation (Fig. 13).
o1
2
2
3
ggg
2
gg
gg
g
1
dc
^
inv
^
c
^
c
^
grid
^
asasas
CL/1L/sRs
)L/Rs(s
)L/Rs(C/1
CL/1
L
V2
d
i
i
v
i
(1)
Where, 21,, aaaodepends on Ri, Li, Rg, Lg and C [11].
On the contrary, capacitor current Ic, and Inverter current
Iinv have their poles on the left-hand side of the S-plane for the
closed loop root-locus analysis (Fig. 14, 15). Capacitor voltage
Vc shows oscillating pattern along the imaginary axis (Fig.
16).
A multiple feedback loop indirect control method for
allowing the inverter to inject current to the grid at a specified
power factor and harmonic distortion level is used [11]. The
capacitor current, Ic is used as the inner-loop feedback variable
whereas the capacitor voltage, Vc is used in the outer loop.
For a demand grid current, Igrid (with a specific power
factor), the reference capacitor voltage, Vcref could be found by
back calculation using the LCL filter component values.
High
Frequency
Resonant
Inverter
Input Filter
FC
HF
Transforemer HF
Bridge Rectifier Filter
Line Filter
PWM CSI
Grid
Fig. 10. High Frequency Resonant Inverter
-
Rectifier
-
LCI
Fig. 12. Selection of control variables
Fig. 13. Root-locus of Grid current, Igrid
Fig. 14. Root-locus of Capacitor current, Ic
IEEE, NECEC 2004, October 12, St. John’s, NL
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gridLggridcref VXIV (2)
Where, XLg, is the inductive filter reactance at the grid side,
which is composed of the inductor Lg and parasitic resistance
Rg. For unity power factor operation,
gridggrid
grid
gcref
gridRgLgcref
VRI
dt
dI
LV
VVVV
(3)
Similarly, the reference capacitor current, Ic ref could be
generated using the Capacitor voltage Vcref and values of the
capacitive branch components.
ccrefccref RIVV (4)
Modifying further and solving the following sets of equations,
Icref is determined.
dt
dV
CI
dt
dV
CRVV
c
cref
c
cccref
(5)
Where, C and RC are the capacitor and parasitic resistor in the
capacitive branch. These reference signals are generated from
the demand grid current, Igrid and could be used for controlling
Vc and Ic towards fulfilling the control goal.
B. Fuel Cell Inverter
A complete system made up of a 1 kW fuel cell, a DC-DC
high frequency link boost converter, a dual-half bridge
inverter (for split phase supply, i.e., both 120V/60 Hz and
230V/50Hz) with line filter and control mechanism is
analyzed in the following sections. Use of a LCL type filter is
avoided in order to observe the performance of the complete
system within a reasonable simulation time.
The DC-DC boost stage uses a high frequency full-bridge
inverter, high frequency transformer, bridge rectifier and a
controller. Two half-bridge inverters were arranged with
proper PWM technique to provide multiple phase supply. A
set of simulation is done to indicate use of the dual phase grid
connection system.
Among various types of fuel cells, Proton Exchange
Membrane (PEM) fuel cells are the most suitable systems for
the application being considered. A single fuel cell may
deliver 933 mA/cm2 at a rated voltage of 0.5V. Therefore,
several cells need to be connected in series to form a stack that
could deliver power to a required level.
A 1 kW fuel cell stack is modeled with dynamic approach
as outlined in [12]. The stack consists of 72 cells (each with
30cm2 area) in series and rated current and voltages are 28 A,
36 V respectively. A separate controller is required to operate
the fuel cell system. However, investigation of a fuel cell
controller is beyond the scope of this analysis.
C. DC-DC Converter
The DC-DC converter consists of a full-bridge inverter, high
frequency transformer and a rectifier. To avoid the need for an
inductor at the output of the rectifier, Sinusoidal Pulse Width
Modulation (SPWM) technique is applied. This may impose
high stress on the switches. Use of several switches in series –
parallel combination may reduce this problem. MOSFETs are
typically suitable for the high frequency operation. In this
analysis, the switching frequency is taken as 50 kHZ.
Fig. 15. Root-locus of Inverter current, Iinv
Fig. 16. Root locus of Capacitor voltage, Vc
Fig. 17. Analysis of a 1 kW Fuel-
Cell Based Grid Interactive Power
Conditioner
IEEE, NECEC 2004, October 12, St. John’s, NL
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D. Dual Half-Bridge Inverter
Two single-phase half bridge inverters operated at PWM
signals with 180o phase difference are employed to allow
multiple output phases. The neutral terminal is realized with a
capacitive branch having two equal high value capacitors with
their connection node grounded (Fig. 17). The switching is
done at 10 kHz and IGBTs are used. One L type filter is used
to reduce the output harmonics.
The high voltage DC bus is maintained at a 400V level by
using one PI controller. This controller senses the bus voltage,
compares it with the reference 400V and modulates the sine
wave that generates PWM switching signals for the high
frequency inverter. A separate controller generates the split
phase inverter switching signals. It senses the grid current,
compares with the demand current and adjusts the PWM
modulation index accordingly. A phase locked loop (PLL)
senses the variations in grid frequency and adjusts the demand
grid current frequency (Fig. 17).
V. MODELING AND SIMULATION
A. Modeling of System 1 (Grid Interactive Inverter)
The utility interactive inverter described in Section IV(A) is
simulated to study the behavior of such a system (Fig. 18).
The half-bridge inverter is connected to a LCL type filter
arrangement. Each of these filter components are kept separate
to have access to capacitor voltage and current. The filter
parameters are: Li=5e-3, Ri=400e-3, Lg=0.650e-3, Rg=280e-3,
C=45e-6, and Rc=5e-3.
The inverter is modeled with a simple comparator and logic
arrangements in a subsystem named Subsys-HBI (Fig 18). The
controller unit consists of two controllers. The current
controller (inner loop) compares capacitor current with the
reference signal. The output is then combined with the outer
voltage loop that senses capacitor voltage and compares with
the voltage reference signal.
The reference signal generator takes grid current as the
command signal and also accommodates changes in grid
voltage and frequency variations (Subsys-RFG, Fig 18). This
produces reference signals for the capacitor current and
voltage according to the equations outlined in Section 4(A).
The Phase Locked Loop (PLL) used in the reference signal
generator block is modeled within the Subsys-RSG (fig. 18)
according to [13].
B. Modeling of System 2(Fuel-Cell Based Grid Interactive
Power Conditioner)
The complete fuel cell based inverter system is modeled and
simulated with a view to indicating success of control methods
and topology flexibility in Fig. 19.
Fig. 19 shows the MATLAB/SimulinkTM blocks where the
output is is connected to 120V/60Hz grid. The value of line
filter parameters are Lg = 10mH, Rg = 0.5W.
It is required to protect the fuel cell from taking in
electricity. Therefore a diode is placed between the fuel cell
and the power converter. The fuel cell block is reported in [12]
and the ‘fuel-cell-current-estimator block is a virtual model
that approximates the current drawn from it such that the stack
output voltage could be determined.
VI. RESULTS
Fig 19: Grid (120V-60Hz) connected fuel cell inverter system with controller
Fig. 20. Simulation results for the half
-
bridge grid interactive inverter
Fig. 18. Grid connected Half-bridge inverter with multiple feedback loop indirect current controller
IEEE, NECEC 2004, October 12, St. John’s, NL
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A. System 1
The half bridge inverter with 3rd order LCL type filter is
designed and modeled such that several key goals of grid
interfacing could be demonstrated. The scheme should be able
to sense grid voltage and frequency variations, generate
reference capacitor current and voltage from the demand
current (or power) and control the inverter accordingly.
After several trial and error attempts the controller
parameters are found as: Inner current controller Kp = 1.75, KI
=0.25 and Outer voltage controller Kp = 5.75, KI =1.75.
As seen in Fig.20 (c, e), with a demand current of 8.33A
(corresponding to 1 kW power injection) the reference signal
generator creates Capacitor reference current, Ic_ref and
voltage, Vc _ref , which are of sinusoidal shape. In Fig. 20 (d, f)
it could be seen that the actual values of these parameters
match closely with the reference. However, the capacitor
current contains high amount of harmonics. The injected grid
current is a sinusoidal ac with near unity power factor (0.98)
as seen in fig. 20(a, b). A step change in demand current from
8.33 A to 6.5 A at 0.03 sec causes some adjustments in
reference signals and the grid current reduces to the desired
level (Fig. 20 (b)) within one cycle.
B. System 2
The second system is more comprehensive and maintains
the ability of connecting in two different types of grids. The
controller parameters were found to be: DC-DC boost
converter: Kp = 0.025, KI =0.015 and Inverter controller: Kp =
1.15, KI =0.5.
As seen in Fig. 21(a, b), there is some start-up transients
due to the computer simulation itself. Moreover, the reference
signal, Iref appeared to have suffered harmonic distortion due
to the PLL’s lack of controllability. Except for these
limitations, overall performance of the system is acceptable.
The PLL circuit encounters the changes in grid frequency at
0.04 second. The injected grid current was capable of
following the reference signals after the initial transients. A
change in demand current (i.e., power) at 0.1 second
successfully reduces the actual injected current (Fig. 22). The
changes in grid voltage at 0.08 second had little affect on the
overall performance.
Fig. 21. 120V/60Hz operation
DSP Controller
Board
2 Stage Inverter + Filter
FC
Control
Signals
Feedback
Grid
Real Time
Programming
& Debugging
Interface
CAN/USB
Interface
Short/Long
Communication
Interface with CAN
compatibility
Control Center
Load #1
Source #2
Load #2
Source #3
Load #3
Source #4
Load #4
Source #1
Fig. 22. Conceptual Outline of a fuel-cell inverter system within a DG network
IEEE, NECEC 2004, October 12, St. John’s, NL
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VII. DSP BASED IMPLEMENTATION IN A DG NETWORK
Various Digital Signal Processing (DSP) systems are
becoming cheaper and user friendly, especially in the fields of
data acquisition and control. Texas Instrument’s
TMS320LF2407TM chip based systems are being widely used
for power electronic and drives applications [14]. This DSP
chip is inherited from TI’s 240X family, and bears good real
time processing capability, which is optimized and suited for
control applications being considered. In order to allow “real-
time” communication, programming and debugging a custom-
built parallel port interface between the DSP board and the PC
could be developed.
The fuel cell inverter system works as a source node in the
distributed generation network. The Controller Area Network
(CAN) is a potential solution for communicating within
various elements of the system [15]. In order to connect a
personal computer for monitoring the data flow from the
resource side, a USB interface with CAN compatibility could
be designed. The design should include modular hardware and
user-friendly software.
The methods and mediums of short/long distance
communication and inverter paralleling are also issues of
significant implications. A conceptual outline of a fuel cell
system integrated in the DG network is shown in Fig. 22.
VIII. CONCLUSION
A general discussion on utility interface system
requirements followed by a literature review of available
power electronic circuit topologies have been discussed. Key
issues regarding an inverter’s interaction with the utility grid
were investigated with a half-bridge 3rd order filter based
system. To demonstrate the overall performance of a fuel cell
based grid tied power converter, a complete system has been
modeled and simulated with some simplification against the
initial scheme. Controllers were designed and their range of
controllability has been shown. It has been found that, the
LCL filter based system requires more rigorous analysis in
designing the controller. However, the L filter based system
showed good controllability but had drawbacks in the PLL
model.
Further work may include integrating both of these systems
into one, designing better controllers and grid sensing
elements. Analysis of harmonic distortion, cost, efficiency,
and regulatory issues are also expected. Design and testing of
such inverter system along with operation within a Distributed
Generation network are expected in the later works.
ACKNOWLEDGMENT
Author would like to thank Atlantic Canada Opportunities
Agency (ACOA) for providing support for this research
through their Atlantic Innovations Funds (AIF). Suggestions
and comments by Dr. John Quaicoe, Faculty of Engineering &
Applied Science, MUN, St. John’s, NL is duly acknowledged.
Graduate student M. Ordonez is also thanked for his
cooperation during the course of this work.
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Resonant Inverter for Photovoltaic Array to Utility Interface
  • A K S Bhat
  • S B Dewan
A.K.S. Bhat, S.B.Dewan, Resonant Inverter for Photovoltaic Array to Utility Interface, International Telecommunications Energy Conference (INTELEC), 1986, pp 135-142.
Indirect current control scheme for a single-phase voltage-source utility interface inverter
  • N Abdel-Rahim
  • J E Quaicoe
Abdel-Rahim, N.; Quaicoe, J.E.; Indirect current control scheme for a single-phase voltage-source utility interface inverter, Canadian Conference on Electrical and Computer Engineering, 1993., Vol. 1, pp:305 -308
Inverter for Green Power Applications
  • Lars Tønnes Søren Jul Christiansen
  • Børge Jakobsen
  • Morten Poulsen
  • Bach Sørensen
Søren Jul Christiansen, Lars Tønnes Jakobsen, Børge Poulsen and Morten Bach Sørensen., Inverter for Green Power Applications, December 2002, URL: http://www.iet.aau.dk/~skk/