A big challenge in construction of a power supply system is to more stably expand a power transmission network. In recent years, the system is further facing a big challenge of affording introduction of a large amount of natural energy. To overcome such challenges, PTL 1 and NPL 1 suggest a power network system called Digital Grid (registered trademark) as a new power network.
Digital Grid (registered trademark) is a power network system in which a power network is subdivided to cells (also called as power cells) that are mutually connected in an asynchronous manner. Small-scale power cells may include, for example, an ordinary house, a building, and a commercial facility. Large-scale power cells may include, for example, a collection of such facilities and the like in a prefecture or municipality unit.
Each power cell includes equipment that functions as a power load (or, simply, a load). Further, each power cell may include power generation equipment, power storage equipment, and the like. The power generation equipment may be, for example, power generation equipment that utilizes natural energy, such as solar power generation, wind power generation, and geothermal power generation.
The power cells are connected in an asynchronous manner so that the equipment inside each power cell can freely generate power and the power cells can smoothly interchange power with one another. That is, even if a plurality of power cells are mutually connected, the voltage, phase, and frequency of power used in each power cell are asynchronous with other power cells.
FIG. 7 is an explanatory diagram illustrating an example of a power network system 10. In the example illustrated in FIG. 7, the trunk transmission power system 11 transmits trunk power that is supplied from a large-scale power plant 12. In addition, a plurality of power cells 21 to 24 are disposed. The power cells 21 to 24 each have loads, such as a house 31 and a building 32, power generation equipment 33, 34, power storage equipment 35, or the like. FIG. 7 exemplifies a solar power generation panel 33, a wind power generator 34, and the like as power generation equipment. The power storage equipment is, for example, a storage battery 35 or the like. It should be noted that the power generation equipment and power storage equipment may be collectively referred to as a dispersion type power source.
Further, the power cells 21 to 24 are respectively equipped with power routers 41 to 44 as connection hubs (connection ports) for connecting to other power cells and the trunk transmission power system 11. The power routers 41 to 44 are equipped with a plurality of legs. It should be noted that, in FIG. 7, the joining terminal of each leg is indicated by an open circle on the edge of each of powers router 41 to 44. In this example, each leg is assigned an address. Then, each leg has a joining terminal and a power converter. It should be noted that power conversion by a leg is conversion from alternating current to direct current or conversion from direct current to alternating current, or a change in the voltage, frequency, phase of power, and the like.
All the power routers 41 to 44 are connected to a management server 50 via a communication network 51, and the management server 50 integrally controls the operation of all the power routers 41 to 44. For example, the management server 50 uses the addresses assigned to the respective legs to instruct the power routers 41 to 44 equipped with the legs to transmit or receive power. In this way, the power routers 41 to 44 mediate interchange of power among the power cells.
As power interchange among power cells is enabled, for example, a plurality of power cells can share power generation equipment 33, 34 and power storage equipment 35. Interchanging surplus power among power cells makes it possible to largely decrease equipment costs, while maintaining a stable balance between power supply and demand.