Nano-grid: Small scale DC Microgrid for Residential Houses
with Cogeneration System in Each House
Main author
Toshinari Momose
Osaka Gas Co. Ltd.
Japan
IGRC2008@gasunie.nl
Co-author
Hideki Hayakawa
Hiroshi Fujimoto
Osaka Gas Co. Ltd.
Japan
Hiroaki Kakigano
Yushi Miura
Toshifumi Ise
Osaka University
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1.
ABSTRACT
In recent years, various energy systems to share heat or electric power have been proposed to
improve the energy efficiency and operation ratio of cogeneration systems. Some systems use
hydrogen from outside shared reformers as fuel for cogeneration systems.
So, the microgrid systems are researched all over the world as the sharing method of
electronic power and heat. The microgrid system is a district energy network of distributed
generators, such as cogeneration systems and renewable energy (wind turbines, photovoltaic
cells, etc.). They are suitable for large scale applications.
On the other hands, we propose a small scale microgrid system for apartments, called "Nanogrid". Each houses of apartment have small cogeneration systems and electrical power from
them can be shared among houses. So, Nano-grid can improve the energy efficiency and
operation ratio of cogeneration systems.
If it uses a DC system instead of a general AC system, it can reduce energy loss of inverter
because each generator don't need an inverter. Further more, it can continue to provide a
power supply when blackout occurs in the bulk power system.
© Copyright © 2008 IGRC2008
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CONTENTS
1.
Abstract ................................................................................................. 2
2.
Body of Paper......................................................................................... 4
2.1
Intoroduction. ................................................................................................ 4
2.2
Experimental System and Result. ................................................................... 5
2.3
CONCLUSIONS................................................................................................ 7
3.
References ............................................................................................. 8
4.
List Tables.............................................................................................. 8
5.
List Of Figures ........................................................................................ 8
© Copyright © 2008 IGRC2008
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2.
BODY OF PAPER
2.1.
Intoroduction
In recent years, various energy systems to share heat or electric power have been proposed to
improve the energy efficiency and operation ratio of cogeneration systems. Some systems use
hydrogen from outside shared reformers as fuel for cogeneration systems.
So, the microgrid systems are researched all over the world as the sharing method of
electronic power and heat. The microgrid system is a district energy network of distributed
generators, such as cogeneration systems and renewable energy (wind turbines, photovoltaic
cells, etc.). They are suitable for large scale applications.
On the other hands, we propose a small scale microgrid system for apartments, called "Nanogrid". Figure 1 shows a concept of the system.
Fig.1. The concept of the proposal “nano-grid”
In the "Nano-grid", there are around 50-100 houses, and the each house has a gas engine or a
fuel cell cogeneration. The outputs of all distributed generations are connected to the
distribution line, and the electrical power can be borrowed and lent among houses through the
line. Therefore, it can be expected that the operation chances of cogeneration become
increased, and it leads to higher utilization level of the cogeneration. To keep the high
efficiency, those distributed generations should not be operated by a partial load condition, but
operated by a start/stop control. The hot water is used in each house.
Estimated improvement effect for CO2-emmision and Gas seles Volume is shown in case of
using SOFC (Figure 2).
Fig.2. Advantage of "nano-grid" with SOFC (Estimated).
© Copyright © 2008 IGRC2008
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If the Nano-grid uses a DC system instead of a general AC system, it can reduce the energy
loss of the inverter because each generator doesn't need an inverter. Further more, it can
continue to provide a power supply when blackout occurs in the bulk power system. We built a
small scale model using residential gas engine cogeneration systems, and demonstrated that
the system was able to supply power to the loads even during a simulated blackout.
2.2.
Experimental System and Result
Figure 3 shows a the proposal l "DC-nano-grid"system. In this system, bulk power was
conected through a rectifier at one point, and various forms of electrical power like single phase
100 V, 3-phase 200 V, DC 100 V, etc. can be obtained by converters placed near loads. These
converters do not need transformers, therefore it contributes to the downsizing and high
efficiency.
Fig.3. The concept of the proposal “nano-grid” dc microgrid.
Secondary batteries and EDLC can be connected to the dc distribution line through dc/dc
converters. If a blackout occurs in the bulk power system, the dc microgrid is able to disconnect
it rapidly, and the power supply will be continued without any dc voltage sags at the load,
resulting in the intentional islanding mode.
The configuration of the experimental system is shown in Figure 4. The experimental setup and
the gas engine cogeneration system are shown in Figure 5.
Fig.4. Configuration of the experimental system.
© Copyright © 2008 IGRC2008
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Fig.5. Experimental setup dc microgrid.
By using the experimental system, we verified the fundamental characteristics: the electric
power sharing by the dc power line among the houses, the behavior at the accident in the bulk
power system or the dc microgrid, and the power quality to the loads.The 3-phase AC 200 V of
the bulk power system is converted to DC ±170 V by the rectifier, and the power is supplied to
each house through the dc distribution line. This system applied the bi-pole 3-wire system (two
±170 V lines and one neutral line) to the dc distribution. It is assumed that there are three
households in the experimental system, and each house has a gas engine cogeneration. In this
research, one of them is a real gas engine cogeneration, and other two houses use dc power
supplies as gas engine cogenerations. The dc/dc converters are connected between distributed
generations and dc lines. At the load side, the dc power is converted into the single phase 100V
with the inverter at one house, and other two houses are supplied the dc power directly. A
variable resistor and an electric load device are used as a load of each house.
By using this small scale model of the Nano-gird system, we simulated a bulk power system
blackout. At first, bulk power system supplies a shortage of power to the Nano-gird system.
The EDLC(Electric Double Layer Capacitor) was fully charged(Figure 6). Secondary, power from
the bulk power system was turnd off, EDLC started to supply power, and the gas-cogeneration
system in Nano-grid system started warm-up(Figure 7). Finally.two of the cogeneration system
started to supply power, then EDLC absorbed excess power (Figure 8).
Fig.6. Bulk power system supply to the Nano-gird system had shortage of power
© Copyright © 2008 IGRC2008
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Fig.7. Power from bulk power system was turnd off
Fig.8. Two of the cogeneration system started to supply power
2.3.
Conclusion
In this paper, we proposed the concept of the small-scale dc microgrid for residential houses
where each house has a cogeneration system such as a gas engine, and shares the power
among the houses by the dc distribution line.
To examine the fundamental characteristics of the system, a laboratory scale dc microgrid was
constructed. The experimental results by a small scale model demonstrated that the system was
able to continue supply power to the loads continue even during a simulated blackout.
© Copyright © 2008 IGRC2008
3.
[1]
REFERENCES
H. Kakigano, Y. Miura, T. Ise, T. Momose and H. Hayakawa, “Fundamental Characteristic
of DC Microgrd for Residential Houses with Cogeneration System in Each House,”
IEEE Power & Energy Society 2008 General Meeting , No.08GM0500
4.
LIST TABLES
None.
5.
Fig.1.
Fig.2.
Fig.3.
Fig.4.
Fig.5.
Fig.6.
Fig.7.
Fig.8.
LIST OF FIGURES
The concept of the proposal “nano-grid”
Advantage of "nano-grid" with SOFC (Estimated).
The concept of the proposal “nano-grid” dc microgrid.
Configuration of the experimental system.
Experimental setup dc microgrid.
Bulk power system supply to the Nano-gird system had shortage of power
Power from bulk power system was turnd off
All of the cogeneration system started to supply power