nano-grid: small scale dc microgrid for residential houses...

Nano-grid: Small scale DC Microgrid for Residential Houses with Cogeneration System in Each House

Main author Toshinari Momose Osaka Gas Co. Ltd.

Japan [email protected]

Co-author

Hideki Hayakawa Hiroshi Fujimoto

Osaka Gas Co. Ltd. Japan

Hiroaki Kakigano

Yushi Miura Toshifumi Ise

Osaka University

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© Copyright © 2008 IGRC2008

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 "Nano-

grid". 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.

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C O N T E N T S

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

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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 "Nano-

grid". 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).

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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.

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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

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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.

3. REFERENCES

[1] 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. LIST OF FIGURES

Fig.1. The concept of the proposal “nano-grid” Fig.2. Advantage of "nano-grid" with SOFC (Estimated). Fig.3. The concept of the proposal “nano-grid” dc microgrid. Fig.4. Configuration of the experimental system. Fig.5. Experimental setup dc microgrid. Fig.6. Bulk power system supply to the Nano-gird system had shortage of power Fig.7. Power from bulk power system was turnd off Fig.8. All of the cogeneration system started to supply power

nano-grid: small scale dc microgrid for residential houses...

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