Technical Field
[0001]
The present invention provides a power router that
asynchronously interconnects a plurality of power cells and performs
10 power interchange control of a plurality of routes. Further, the present
invention relates to a power network system formed by asynchronous
connection using this power router.
Background Art
[0002]
15 When a power supply system is constructed, in addition to a
further expansion of a power distribution grid in a more stable way, a
main issue has been providing such a system with a capability of
introducing a large amount of natural energy. A power network system
called Digital Grid (registered trademark) has been proposed as a new
20 power network (see Patent literature 1: Japanese Patent No. 4783453,
Non-patent literature 1: Website of Digital Grid Consortium,
http://www.digitalgrid.org/index.php/jp/).
Digital Grid (registered trademark) is a power network system in
which a power network is partitioned into small-sized cells and these
25 cells are asynchronously interconnected. Each power cell may be
small (e.g., a house, a building, or a commercial facility) or may be
large (e.g., a prefecture or a municipality). Each power cell naturally
includes a load, and may also include a power generation facility or a
power storage system. The power generation facility may be, as an
30 example, a power generation facility that uses natural energy generated
by, for example, photovoltaic power, wind power, and geothermal
power.
[0003]
In order to freely generate power inside each power cell and to
2
further smoothly interchange power among the power cells, the power
cells are asynchronously connected. (That is, even when the plurality
of power cells are interconnected, a frequency, a phase, and a voltage
of power used in each power cell is asynchronous with those used in
5 other power cells.)
Fig. 12 shows an example of a power network system 10. In Fig.
12, a utility grid 11 sends bulk power from a large-scale power plant
12. A plurality of power cells 21-24 are arranged. Each of the power
cells 21-24 includes a load such as a house 31 and a building 32, power
10 generation facilities 33 and 34, and a power storage system 35.
The power generation facility may include, as an example, a
solar panel 33 and a wind turbine 34. The power storage system is, for
example, a storage battery 34. In this specification, the power
generation facility and the power storage system may be collectively
15 called a distributed power supply.
[0004]
Further, the power cells 21-24 respectively include power
routers 41-44 which serve as connection ports to be connected to other
power cells or the utility grid 11. Each of the power routers 41-44
20 includes a plurality of legs (LEG). (Due -to space constraints, the
symbols for the legs are omitted in Fig. 10. It should be interpreted
that the white circles attached to the power routers 41-44 are
connection terminals of each leg.)
Now, each leg includes a connection terminal and a power
25 conversion unit, and an address is attached to each leg. The power
conversion by the leg means converting AC to DC or DC to AC and
changing the phase, the frequency, and the voltage of the power.
[0005]
All the power routers 41-44 are connected to a management
30 server 50 by a communication network 51, and operations of all the
power routers 41-44 are integrally controlled by the management
server 50. For example, the management server 50 instructs each of
the power routers 41-44 to transmit or receive power for each leg using
the address attached to each leg. Accordingly, power is interchanged
3
among power cells through the power routers 41-44.
[0006]
Since power interchange among the power cells is achieved, a
plurality of power cells can share, for example, one power generation
5 facility 33 or 34 or one power storage system 35. If an excessive
power can be interchanged among the power cells, a supply-demand
balance of power can be kept stable while greatly reducing the
equipment cost.
Citation List
10 Patent Literature
[0007]
Patent literature 1: Japanese Patent No. 4783453
Non Patent Literature
[0008]
15 Non-patent l i t e r a t u r e 1: Website of Digital Grid Consortium
( h t t p : / / w w w . d i g i t a l g r i d . o r g / i n d e x . p h p / j p /)
Summary of Invention
Technical Problem
20 [0009]
If the p l u r a l i t y of power cells can be asynchronously connected
by the power routers, the advantage caused by this asynchronous
connection would be extremely large. It is thus expected that the
power routers will be put into practical use at an early stage.
25 However, in order to put the power routers into practical use in
r e a l i t y , there is a specific problem that conventional power
transmission and d i s t r i b u t i o n f a c i l i t i e s do not have. Since a power
t r a n s m i s s i o n and d i s t r i b u t i o n facility which is the current mainstream
assumes a power system in which a voltage, a phase, and a frequency
30 are fully synchronized, power routers that connect power systems
having different voltages, phases, or frequencies raise the new
problem.
Solution to Problem
[0010]
4
A power router according to the present invention is a power
router to asynchronously connect a power cell to an external power
system, the power router including: a DC bus whose voltage is kept to
a predetermined rated voltage; a power conversion leg including one
5 connection end connected to the DC bus and another connection end
connected to an external connection partner as an external connection
terminal, the power conversion leg including a function of
bidirectionally converting power between the one connection end and
the other connection end; and a controller that controls an operation of
10 the power conversion leg, in which: a plurality of the power
conversion legs are provided, the power router is controlled according
to an instruction from a management server, the controller controls an
operation of the power conversion leg in an operation mode which is
one of a master mode and a designated power transmission/reception
15 mode, the power conversion leg operated in the master mode
supplements an insufficient power from the connection partner when
the voltage of the DC bus decreases from a rated voltage, and sends an
excessive power'to the connection partner when the voltage of the DC
bus increases from the rated voltage, the power conversion leg
20 operated in the designated power transmission/reception mode sends a
designated power to the connection partner or receives the designated
power from the connection partner according to a designation from the
management server, and the controller sets the operation mode of at
least one of the power conversion legs to the master mode during the
25 operation of the power router.
[0011]
A power network system according to the present invention
includes: one or a plurality of the power routers; and a power system
to which the power router is directly or indirectly connected, in which
30 the connection partner to which the power conversion leg operated in
the master mode is directly or indirectly connected is restricted to one
of a distributed power supply and a utility grid connected to a main
power plant.
[0012]
5
Further, a power network system according to the present
invention includes two or more of the power routers, and power is sent
between the power routers.
[0013]
5 A power interchange method according to the present invention
includes interchanging power by sending power between the power
routers using two or more of the power routers.
[0014]
An operation control program of a power router according to the
10 present invention is an operation control program of a power router
that includes: a DC bus whose voltage is kept to a predetermined rated
voltage; and a power conversion leg including one connection end
connected to the DC bus and another connection end connected to an
external connection partner as an external connection terminal, the
15 power conversion leg including a function of bidirectionally
converting power between the one connection end and the other
connection end, in which: a plurality of the power conversion legs are
provided, the power router is controlled according to an instruction
from a management server, the power router asynchronously connects a
20 power cell to an external power system, the power router is built into a
computer and the power router causes the computer to control an
operation of the power conversion leg in an operation mode which is
one of a master mode and a designated power transmission/reception
mode, the power conversion leg operated in the master mode
25 supplements an insufficient power from the connection partner when
the voltage of the DC bus decreases from a rated voltage, and sends an
excessive power to the connection partner when the voltage of the DC
bus increases from the rated voltage, the power conversion leg
operated in the designated power transmission/reception mode sends a
30 designated power to the connection partner or receives the designated
power from the connection partner according to a designation from the
management server, and the operation mode of at least one of the
power conversion legs is set to the master mode during the operation
of the power router.
A n o n - t r a n s i t o r y computer readable medium stores the operation
control program of the power router.
Advantageous Effects of Invention
5 [0015]
According to the present invention, it is possible to build a
power network system in which the power cells are asynchronously
i n t e r c o n n e c t e d .
10 Brief Description of Drawings
[0016]
Fig. 1 is a diagram showing a schematic configuration of a
power router;
Fig. 2 is a diagram showing the d e t a i l s of an internal
15 configuration of the power router;
Fig. 3 is a diagram showing one example in which the power
router is connected to a u t i l i t y grid, a load, and various d i s t r i b u t ed
power s u p p l i e s ; '
Fig. 4A is a diagram showing an example of a combination of
20 power routers whose connection is permitted;
Fig. 4B is a diagram showing an example of a combination of
power routers whose connection is permitted;
Fig. 5A is a diagram showing an example of a combination of
power routers whose connection is prohibited;
25 Fig. 5B is a diagram showing an example of a combination of
power routers whose connection is prohibited;
Fig. 5C is a diagram showing an example of a combination of
power routers whose connection is prohibited;
Fig. 5D is a diagram showing an example of a combination of
30 power routers whose connection is p r o h i b i t e d;
Fig. 6A is a diagram showing an example of a combination of
power routers whose connection is permitted when an AC-through leg
i s taken into consideration;
Fig. 6B is a diagram showing an example of a combination of
7
power routers whose connection is permitted when the AC-through leg
is taken into consideration;
Fig. 6C is a diagram showing an example of a combination of
power routers whose connection is permitted when the AC-through leg
5 is taken into consideration;
Fig. 6D is a diagram showing an example of a combination of
power routers whose connection is permitted when the AC-through leg
is taken into consideration;
Fig. 7 is a diagram showing a connection example in which AC--
10 through legs are used;
Fig. 8 is a diagram showing patterns of a combination of power
routers when the power routers are connected to each other;
Fig. 9 is a diagram of one example of a case in which four power
routers are interconnected;
15 Fig. 10 is a diagram showing one example of a state in which a
plurality of power routers are connected by a bus;
Fig. i 1 is a diagram showing one example of a connection form
in which a utility grid is provided between power routers; and
Fig. 12 is a diagram for describing the outline of a power
20 network system.
Description of Embodiments
[0017]
An exemplary embodiment of the present invention will be
described with reference to the drawings, in which elements are
25 denoted by symbols.
(First exemplary embodiment)
Fig. 1 is a diagram showing a schematic configuration of a
power router 100 according to a first exemplary embodiment. Fig. 2 is
a diagram showing the details of an internal configuration of the power
30 router 100.
The power router 100 typically includes a DC bus 101, a
plurality of legs 1 10-160, and a controller 190.
The controller 190 is a so-called computer and includes a CPU, a
ROM, and a RAM.
[0018]
The power router 100 includes the DC bus 101 to which the
plurality of legs 110-160 are connected in parallel. The DC bus 101 is
provided to enable DC power flow, and a voltage of the DC bus 101 is
5 controlled to be constant.
(How the voltage of the DC bus 101 is kept constant will be
described later.)
The power router 100 is connected to the outside through each of
the legs 110-160. All the power to be exchanged with the outside is
10 once converted into DC and the DC flows through the DC bus 101.
Since power is once converted into DC, it is possible to
asynchronously connect power cells without any consideration for the
differences in the phase, the voltage, or the frequency thereof. It is
assumed here that the DC bus 101 is, as shown in Fig. 2, a parallel
15 type including a smoothing capacitor 102. A voltage sensor 103 is
connected to the DC bus 101, and a voltage value of the DC bus 101
detected by the voltage sensor 103 is sent to the controller 190.
[0019]
Next, the plurality of legs 1 10-160 will be described. The
20 plurality of legs 110-160 are provided in parallel with the DC bus. In
Fig. 1, six legs 110-160 are shown. The six legs 110-160 are
represented, as shown in Fig. 1, as a first leg 110, a second leg 120,...,
and a sixth leg 160. In Fig. 1, due to space constraints, the first leg
110 is denoted by a leg 1 and the second leg 120 is denoted by a leg 2,
25 for example. Further, in Fig. 2, the third leg 130 and the fourth leg
1 40 are omitted.
[0020]
While the first leg 110 to the fifth leg 150 have the same
configuration, the sixth leg 160 is different from the first to fifth legs
30 110-150 in that the sixth leg 160 does not include a power conversion
unit. First, the configuration of the first leg 110 to the fifth leg 150
will be described. Since the first leg 110 to the fifth leg 150 have the
same configuration, just the configuration of the first leg 110 will be
described as an example.
9
The first leg 110 includes a power conversion unit 111, a current
sensor 112, a switch 113, a voltage sensor 114, and a connection
terminal 115. The power conversion unit 111 converts AC power to DC
power or DC power to AC power. Since DC power flows through the
5 DC bus 101, the power conversion unit 111 converts DC power flowing
through the DC bus 101 to AC power having a predetermined frequency
and voltage to allow the AC power to flow to the outside from the
connection terminal 115. Otherwise, the power conversion unit 111
converts AC power that flows from the connection terminal 115 into
10 DC power to allow the DC power to flow through the DC bus 101.
[0021]
The power conversion unit 1 1 1 has a configuration of an inverter
circuit in which anti-parallel circuits 11 IP formed of thyristors H IT
and feedback diodes 111D are three-phase bridge-connected.
15 (That is, six anti-parallel circuits 111P are provided for one
inverter circuit.)
While the power conversion unit 111 is a three-phase inverter
circuit since the three-phase AC is used in this example, a single-phase
inverter circuit may be used instead. A line that is drawn from a node
20 between two anti-parallel circuits 11 IP and connects the node and the
connection terminal is called a branch line BL. (Since the three-phase
AC is used, one leg includes three branch lines BL.)
[0022]
The direction of the power, the frequency of the AC power and
25 the like are controlled by the controller 190. That is, switching
operations of the thyristors H I T are controlled by the controller 190.
The operation control by the controller 190 will be described later.
[0023]
The switch 113 is provided between the power conversion unit
30 HI and the connection terminal 115. The branch line BL is opened or
closed by the operation of the switch 113, which means the connection
between the outside and the DC bus 101 is broken or established.
Further, the voltage of the branch line BL is detected by the voltage
sensor 1 14 and the current value of the current flowing through the
10
branch line BL is detected by the current sensor 112. The switching
operation of the switch 113 is controlled by the c o n t r o l l e r 190 and the
values detected by the voltage sensor 114 and the current sensor 112
are outputted to the controller 190.
5 [0024]
While the power conversion unit is the inverter circuit and the
connection partner of the leg uses AC as described above, the
connection partner of the leg may instead use DC and may be, for
example, a storage battery 35. (For example, in Fig. 1, the third leg
10 130 is connected to the storage b a t t e r y 35.)
The power conversion in this case is DC-DC conversion. While
not i l l u s t r a t e d in the drawings, a DC power supply ( e . g . , solar cells or
fuel cells) can be connected as well.
Accordingly, it is possible to provide an inverter circuit and a
15 converter circuit in parallel in the power conversion unit and
s e p a r a t e l y use the inverter circuit and the converter circuit depending
on whether the connection partner is AC or DC.
Otherwise, a leg dedicated for DC-DC conversion in which the
power conversion unit is a DC-DC conversion unit may be provided.
20 It will be often advantageous in terms of the size and the cost to
use a power router that includes both a leg dedicated for AC-DC
conversion and a leg dedicated for DC-DC conversion instead of
providing the inverter circuit and the converter circuit in parallel in
each leg.
25 [0025]
The first leg 110 to the fifth leg 150 have the same
configuration stated above.
[0026]
Next, the sixth leg 160 will be described. The sixth leg 160
30 does not include a power conversion unit, which means a connection
terminal 165 of the sixth leg 160 is not connected to the DC bus 101.
The sixth leg 160 is connected to the branch line BL of the fifth leg
150. An i n t e r n a l wire of the sixth leg 160 is also called a branch line
BL. The branch line BL of the sixth leg 160 is connected between the
11
connection terminal 155 and the switch 153 of the fifth leg 150.
[0027]
The sixth leg 160 includes a switch 163, a voltage sensor 164, a
current sensor 162, and a connection terminal 165. The branch line BL
5 of the sixth leg 160 is connected to the branch line BL of the fifth leg
150 through the switch 163. That is, the connection terminal 165 of
the sixth leg 160 is connected to the connection terminal 155 of the
fifth leg 150. Only the switch 163 is provided between the connection
terminal 165 of the sixth leg 160 and the connection terminal 155 of
10 the fifth leg 150 and the sixth leg 160 does not include a power
converter. Accordingly, power is conducted between the connection
terminal 165 of the sixth leg 160 and the connection terminal 155 of
the fifth leg 150 without being converted. A leg such as the sixth leg
160 that does not include a power converter may be called an AC-
15 through leg.
[0028]
The current sensor 162 and the voltage sensor 164 detect a
current value and a voltage value of the branch line BL to output the
current value and the voltage value to the controller 190. The
20 switching operation of the switch 163 is controlled by the controller
190.
[0029]
(Operation modes of legs)
The first leg 110 to the fifth leg 150 include power converters
25 111 = 15 1 and the switching operations of the thyristors in the power
converters are controlled by the controller 190, as already described
above.
The power router 100 is in the node of the power network 10,
and plays an important role of connecting the utility grid 11, the load
30 30, a distributed power supply, power cells and the like. At this time,
the connection terminals 115-165 of the respective legs 110-160 are
connected to the utility grid 11, the load 30, the distributed power
supply, and power routers of other power cells. The present inventors
have noticed that the legs 110-160 have different roles depending on
12
the connection partner and the power routers are not appropriately
operated unless each of the legs 1 10-160 is appropriately operated
according to each of their respective roles. While the legs have the
same configuration, the present inventors have changed the method of
5 operating the legs depending on the connection partner.
The method of operating the legs is called an operation mode.
The present inventors have prepared three types of operation
modes of the legs, and the modes are switched according to the
connection partner.
10 The operation modes of the legs include:
a master mode;
a stand-alone mode; and
a designated power transmission/reception mode.
In the following description, these operation modes will be
15 described in series.
[0030]
(Master mode)
The master mode is an operation mode when a leg is connected
to a stable power supply source such as an electrical grid, and is an
20 operation mode to keep the voltage of the DC bus 101. In Fig. 1, an
example in which the connection terminal 1 15 of the first leg 1 10 is
connected to the utility grid 1 1 is shown. In the case of Fig. 1, the
operation of the first leg 110 is controlled as a master mode, and plays
a role of keeping the voltage of the DC bus 101. While many other
25 legs 120-150 are connected to the DC bus 101, power may flow into the
DC bus 101 from the legs 120-150 or may flow out from the legs 12 0-
150. When the power flows out through the DC bus 101 and the
voltage of the DC bus 101 decreases from the rated voltage, the leg
110 which is in the master mode supplements an insufficient amount of
30 power due to the outflow from the connection partner (in this example,
the utility grid 11). On the other hand, when the power flows into the
DC bus 101 and the voltage of the DC bus 101 increases from the rated
voltage, the leg 110 which is in the master mode transfers an excessive
amount of power due to the inflow to the connection partner (in this
13
example, the u t i l i t y grid 11). The leg 110 which is in the master mode
i s therefore able to keep the voltage of the DC bus 101.
Accordingly, in one power router, at least one leg needs to be
operated in the master mode. Otherwise, the voltage of the DC bus 101
5 is not kept constant. In one power router, two or more legs may be
operated in the master mode. It is preferable, however, that only one
leg be operated in the master mode in one power router.
Further, the leg which is in the master mode may be DCconnected
to a DC power supply (e.g., fuel cell, storage battery)
10 having a stable output instead of being connected to the u t i l i ty grid.
Further, for example, the leg which is in the master mode may be ACconnected
to the d i s t r i b u t e d power supply (also including the storage
b a t t e r y ) on which a self-commutated inverter is mounted. It is
impossible, however, to connect the leg which is in the master mode
15 and the d i s t r i b u t e d power supply on which an e x t e r n a l ly commutated
i n v e r t e r is mounted.
[0031]
In the following d e s c r i p t i o n , the leg operated in the master mode
may be referred to as a master leg.
20 [0032]
The operation control of the master leg will be described.
The master leg is started as follows.
F i r s t , the switch 113 is set to the opened (broken) state. In t h is
s t a t e , the connection terminal 115 is connected to the connection
25 partner. In this embodiment, the connection partner is the u t i l i t y grid
i 1.
The voltage sensor 114 measures the voltage of the u t i l i ty grid
of the connection partner and obtains the phase, the frequency, and the
amplitude of the voltage of the u t i l i ty grid using a phase-locked loop
30 (PLL) or the like. After that, the output of the power conversion unit
1 1 1 is adjusted so that the voltage of the phase, the frequency, and the
amplitude that are obtained is outputted from the power conversion
unit 111. That is, the ON/OFF p a t t e r n s of the t h y r i s t o r s 1 1 IT are
determined. When this output is made stable, the switch 113 is turned
14
on and the power conversion unit 111 and the utility grid 11 are
connected. Since the output of the power conversion unit 11 1 and the
voltage of the utility grid 11 are synchronized at this point, the current
does not flow.
5 [0033]
The operation control when the master leg is operated will be
described.
The voltage of the DC bus 101 is measured by the voltage sensor
103. When the voltage of the DC bus 101 exceeds a predetermined
10 rated bus voltage, the power conversion unit 1 1 1 is controlled so that
power is sent from the master leg 110 to the utility grid. (At least
one of the phase and the amplitude of the voltage outputted from the
power conversion unit 1 1 1 is adjusted so that power is sent from the
DC bus 101 to the utility grid 11 through the master leg 110.) The
15 rated voltage of the DC bus 101 is predetermined.
[0034]
On the other hand, when the voltage of the DC bus 101 is below
the predetermined rated bus voltage, the power conversion unit 111 is
controlled so that the master leg 110 is able to receive power from the
20 utility grid 11. (At least one of the phase and the amplitude of the
voltage outputted from the power conversion unit 1 1 1 is adjusted so
that power is sent from the utility grid 11 to the DC bus 101 through
the master leg 110.) It will be understood that, according to the
operation of the master leg as described above, the voltage of the DC
25 bus 101 can be kept to the predetermined rated voltage.
[0035]
(Stand-alone mode)
The stand-alone mode is an operation mode in which a leg
generates a voltage of the amplitude and the frequency specified by the
30 management server 50 by itself, and sends power to and receives power
from the connection partner.
The stand-alone mode is, for example, an operation mode to
supply power to a device such as the load 30 that consumes power.
Alternatively, the stand-alone mode is an operation mode to directly
15
receive power sent from the connection partner.
Fig. 1 shows an example in which the connection terminal 125 of
the second leg 120 is connected to the load 30. The operation of the
second leg 120 is controlled as the stand-alone mode and power is
5 supplied to the load 30.
Further, when a leg is connected to another power router as in
the fourth leg 140 or the fifth leg 150, the fourth leg 140 or the fifth
leg 150 may be operated in the stand-alone mode as a mode to send
power required by the other power router.
10 Alternatively, when a leg is connected to another power router
as in the fourth leg 140 or the fifth leg 150, the fourth leg 140 or the
fifth leg 150 may be operated in the stand-alone mode as a mode to
receive power sent from the other power router.
While it is not i l l u s t r a t e d in the drawings, the second leg can be
15 operated in the stand-alone mode also in a case in which the second leg
is connected to a power generation f a c i l i ty in place of the load 30. In
t h i s case, however, an externally commutated inverter is i n s t a l l e d in
the power generation f a c i l i t y . '
The operation mode when the power routers are connected to
20 each other will be described later.
[0036]
The leg operated in the stand-alone mode is called a stand-alone
leg. In one power router, a p l u r a l i t y of stand-alone legs may be
provided.
25 [0037]
The operation control of the stand-alone leg will be described.
F i r s t , a switch 123 is opened (broken). The connection terminal
125 is connected to the load 30. The management server 50 notifies
the power router 100 of the amplitude and the frequency of the power
30 (voltage) that should be supplied to the load 30. The controller 190
causes the power (voltage) of the specified frequency and the specified
amplitude to be outputted from the power conversion unit 121 to the
load 30. (In short, the ON/OFF patterns of the t h y r i s t o r s 121T are
determined.) When this output becomes stable, the switch 123 is
16
turned on to connect the power conversion unit 121 and the load 30.
Lastly, when the power is consumed in the load 30, the power
corresponding to the consumed amount flows out to the load 30 from
the stand-alone leg 120.
5 [0038]
(Designated power t r a n s m i s s i o n / r e c e p t i o n mode)
A designated power t r a n s m i s s i o n / r e c e p t i o n mode is an operation
mode for t r a n s m i t t i n g or receiving a designated amount of power.
Specifically, the designated power t r a n s m i s s i o n / r e c e p t i o n mode
10 includes a case in which the designated power is transmitted to the
connection partner and a case in which the designated power is
received from the connection partner.
In Fig. 1, the fourth leg 140 and the fifth leg 150 are connected
to other power routers.
15 In such a case, a predetermined amount of power is fed from the
fourth leg 140 or the fifth leg 150 to the other power router or from
the other power router to the fourth leg 140 or the fifth leg 150.
A l t e r n a t i v e l y , the third leg 130 is connected to the storage
b a t t e r y 35.
20 In such a case, a predetermined amount of power is sent to the
storage battery 35 to charge the storage b a t t e r y 35.
Further, the designated power t r a n s m i s s i o n / r e c e p t i o n leg and the
d i s t r i b u t e d power supply (also including the storage battery) on which
a self-commutated inverter is mounted may be connected. However,
25 the designated power t r a n s m i s s i o n / r e c e p t i o n leg and the d i s t r i b u t ed
power supply on which an externally commutated inverter is mounted
cannot be connected.
[0039]
The leg operated in the designated power t r a n s m i s s i o n / r e c e p t i on
30 mode is called a designated power t r a n s m i s s i o n / r e c e p t i o n leg. In one
power router, a p l u r a l i t y of designated power t r a n s m i s s i o n / r e c e p t i on
legs may be provided.
[0040]
The operation control of the designated power
17
t r a n s m i s s i o n / r e c e p t i o n leg will be described. Since the control when
the designated power t r a n s m i s s i o n / r e c e p t i o n leg is started is basically
the same as that when the master leg is started, a description thereof
will be omitted.
5 [0041]
The operation control when the designated power
t r a n s m i s s i o n / r e c e p t i o n leg is operated will be described.
(In the following description, symbols attached to the
components of the fifth leg 150 will be used.)
10 A voltage sensor 154 measures the voltage of the e l e c t r i c a l grid
of the connection partner to obtain the phase and the frequency of the
voltage of the connection partner using a phase-locked loop (PLL) or
the like. The target value of the current that the power converter 151
receives or outputs is obtained based on an active power value and a
15 reactive power value specified by the management server 50 and the
phase and the frequency of the voltage of the connection partner. A
current sensor 152 measures the current value of the current. The
power converter 151 is adjusted so that the current corresponding to
the difference between the target value and the current value is
20 additionally output. (At least one of the phase and the amplitude of
the voltage outputted from the power conversion unit 151 is adjusted
so that a desired power flows between the designated power
t r a n s m i s s i o n / r e c e p t i o n leg and the connection p a r t n e r .)
[0042]
25 From the above description, it will be understood that the first
to fifth legs having the same configuration can play roles having three
different patterns according to the method of the operation control.
[0043]
(Connection r e s t r i c t i o n s)
30 Since the operations of the legs vary according to the difference
in the operation mode, there are respective r e s t r i c t i o n s regarding the
s e l e c t i o n of the connection partner and the selection of the operation
mode. That is, when the connection partner is determined, the
operation mode that can be selected is determined, and in contrast,
18
when the operation mode is determined, the connection partner that can
be selected is determined. (When the connection partner is changed,
the operation mode of the leg needs to be changed according to the
change of the connection partner.)
5 Patterns of p o s s i b l e combinations of connections will be
described below.
[0044]
In the following description, the expressions in the diagrams are
simplified as shown in Fig. 3.
10 Specifically, the master leg is denoted by M.
The stand-alone leg is denoted by S.
The designated power t r a n s m i s s i o n / r e c e p t i o n leg is denoted by
D.
The AC-through leg is denoted by AC.
15 Further, the legs may be differentiated from one another by
numbers such as " # 1 " attached to the top of the legs as necessary.
While systematized symbols are attached for each of Figs. 3-12,
the same elements are not necessarily denoted by the same reference
symbols throughout the drawings.
20 For example, the symbol 200 in Fig. 3 and the symbol 200 in
Fig. 4A do not i n d i c a t e the same component.
[0045]
All the combinations of the connections shown in Fig. 3 are
a v a i l a b l e . A first leg 210 is connected to the u t i l i t y grid 1 1 as a
25 master leg. This connection has already been described above.
A second leg 220 is connected to the load 30 as the stand-alone
leg. This connection has already been described above as well.
A third leg 230 and a fourth leg 240 are connected to the storage
b a t t e r y 35 as the designated power t r a n s m i s s i o n / r e c e p t i o n legs. This
30 connection has already been described above as well.
[0046]
A fifth leg 250 is an AC-through leg. The AC-through leg 250 is
connected to the designated power t r a n s m i s s i o n / r e c e p t i o n leg of
another power router 300 and the AC-through leg 250 is connected to
19
the storage battery 35 through a connection terminal 245 of the fourth
leg 240. Since the AC-through leg 250 does not include a power
conversion unit, this above connection r e l a t i o n is equivalent to the
s t a t e in which the designated power t r a n s m i s s i o n / r e c e p t i o n leg of the
5 other power router 300 is d i r e c t l y connected to the storage battery 35.
It is understood that such a connection is permitted.
[0047]
A sixth leg 260 is connected to the u t i l i t y grid 1 1 as the
designated power t r a n s m i s s i o n / r e c e p t i o n leg. If it is assumed that a
10 predetermined power is received from the u t i l i t y grid 11 through the
sixth leg 260, it is understood that such a connection is permitted.
Considering that the first leg 210 is the master leg, if the power
received by the sixth leg 260 is insufficient to keep the voltage of the
DC bus 201 to the rated voltage, the master leg 210 receives necessary
15 power from the u t i l i t y grid 11. In contrast, when the power received
by the sixth leg 260 exceeds the amount that is necessary to keep the
voltage of the DC bus 201 to the rated voltage, the master leg 210
t r a n s f e r s excessive power to the u t i l i t y grid 11.
[0048]
20 Next, a case in which the power routers are connected to each
other will be described. Connecting the power routers means
connecting a leg of one power router and a leg of another power router.
When the legs are connected to each other, the operation modes that
can be combined are r e s t r i c t e d.
25 [0049]
Both of the combinations of the connections shown in Figs. 4A
and 4B are available. In Fig. 4A, the master leg 1 10 of the first power
router 100 and the stand-alone leg 210 of the second power router 200
are connected. While the details of this connection will not be
30 described, the master leg 220 of the second power router 200 is
connected to the u t i l i t y grid 1 1, whereby the voltage of the DC bus 201
of the second power router 200 is kept to be the rated voltage.
[0050]
In Fig. 4A, when power is supplied to the load 30 from the first
20
power router 100, the voltage of the DC bus 101 decreases. The master
leg 110 obtains power from the connection partner so as to keep the
v o l t a g e of the DC bus 101. That is, the master leg 110 draws
insufficient power from the stand-alone leg 210 of the second power
5 router 200. The stand-alone leg 210 of the second power router 200
sends power required from the connection partner (in this example, the
master leg 110). While the voltage decreases by the amount of power
sent from the stand-alone leg 210 in the DC bus 201 of the second
power router 200, this is supplemented from the u t i l i t y grid 1 1 by the
10 master leg 220. In this way, the first power router 100 can obtain a
necessary amount of power from the second power router 200.
[0051]
As described above, even when the master leg 110 of the first
power router 100 and the stand-alone leg 210 of the second power
15 router 200 are connected, each of the master leg 110 and the standalone
leg 210 can each play a role. Therefore, no disadvantage occurs
in each of the operations in the master leg 110 and the stand-alone leg
210. Accordingly, the master leg and the stand-alone leg may be
connected as shown in Fig. 4A.
20 [0052]
In Fig. 4B, a designated power t r a n s m i s s i o n / r e c e p t i o n leg 310 of
the third power router 300 and a stand-alone leg 410 of the fourth
power router 400 are connected. While not described in d e t a i l , a
master leg 320 of the third power router 300 and a master leg 420 of
25 the fourth power router 400 are each connected to the u t i l i t y grid 11.
DC buses 301 and 401 of the third power router 300 and the fourth
power router 400 thus keep the rated voltage.
[0053]
I t is assumed that the designated power t r a n s m i s s i o n / r e c e p t i on
30 leg 310 of the third power router 300 is i n s t r u c t e d to receive a
designated power according to the i n s t r u c t i o n from the management
server 50. The designated power t r a n s m i s s i o n / r e c e p t i o n leg 310 draws
the designated power from the stand-alone leg 410 of the fourth power
router 400. The stand-alone leg 410 of the fourth power router 400
21
sends power required from the connection partner (in this example, the
designated power t r a n s m i s s i o n / r e c e p t i o n leg 310). While the voltage
of the DC bus 401 of the fourth power router 400 decreases by the
amount of power sent from the stand-alone leg 410, this is
5 supplemented from the u t i l i t y grid 1 1 by the master leg 420.
[0054]
As described above, even when the designated power
t r a n s m i s s i o n / r e c e p t i o n leg 310 of the third power router 300 and the
stand-alone leg 410 of the fourth power router 400 are connected, the
10 designated power t r a n s m i s s i o n / r e c e p t i o n leg 310 and the s t a n d - a l o ne
leg 410 can each play a role. Therefore, no disadvantage occurs in
each of the operations in the designated power t r a n s m i s s i o n / r e c e p t i on
leg 310 and the stand-alone leg 410. Accordingly, the designated
power t r a n s m i s s i o n / r e c e p t i o n leg and the stand-alone leg may be
15 connected as shown in Fig. 4B.
[0055]
While the case in which the third power router 300 obtains
power from the fourth power router 400 has been described above, it
should be understood that there is also no disadvantage in a case in
20 which the third power router 300 gives power to the fourth power
router 400.
[0056]
It is therefore possible to interchange the designated power
between the third power router 300 and the fourth power router 400.
25 [0057]
When the legs having the power conversion units are d i r e c t ly
connected to each other, only two connection patterns shown in Figs.
4A and 4B are permitted.
S p e c i f i c a l l y , only the case in which the master leg and the
30 stand-alone leg are connected and the case in which the designated
power t r a n s m i s s i o n / r e c e p t i o n leg and the stand-alone leg are connected
are permitted.
[0058]
Next, combinations of the legs that cannot be connected will be
22
described.
Figs. 5A to 5D are patterns in which legs should not be
connected.
As shown in Figs. 5A, 5B, and 5C, the legs that are in the same
5 operation mode must not be connected.
In the case of Fig. 5A, for example, the master legs are
connected.
The master leg first performs processing for generating power in
synchronization with the phase, the frequency, and the voltage of the
10 connection partner, as described above in the d e s c r i p t i o n of the
operation.
When the connection partner is also a master leg, each master
leg tries to be synchronized with the voltage and the frequency of the
other master leg. However, since the master leg does not establish the
15 voltage and the frequency in a stand-alone manner, the synchronous
processing stated above does not succeed.
Therefore, the master legs cannot be connected to each other.
' There are other reasons why the master legs cannot be connected
to each other as follows.
20 The master leg needs to draw power from the connection partner
in order to keep the voltage of the DC bus. (Otherwise excessive
power needs to be made to flow out to the connection partner in order
to keep the voltage of the DC bus.) When the master legs are
connected to each other, each master leg cannot meet the requirements
25 of the connection partner. (If the master legs are connected to each
other, neither of the power routers can keep the voltage of the DC bus.
This may cause a malfunction such as blackout in each power cell.) In
this way, if the master legs are connected to each other, the roles of
the master legs conflict with each other (do not match). The master
30 legs therefore must not be connected to each other.
[0059]
While the designated power t r a n s m i s s i o n / r e c e p t i o n legs are
connected to each other in Fig. 5B, it should be understood that this
connection is not available as well.
23
As described above in the description of the operation, similar
to the master leg, the designated power transmission/reception leg first
performs processing for generating power in synchronization with the
phase, the frequency, and the voltage of the connection partner.
5 When the connection partner is also a designated power
transmission/reception leg, each leg tries to be synchronized with the
voltage and the frequency of the other leg. However, since the
designated power transmission/reception leg does not establish the
voltage and frequency in a stand-alone manner, the synchronous
10 processing stated above does not succeed.
Therefore, the designated power transmission/reception legs
cannot be connected to each other.
There are other reasons why the above legs cannot be connected
to each other as follows.
15 Even if the designated transmitted power that should be sent by
one designated power transmission/reception leg 510 is made equal to
the designated received power that should be received by the other
designated power transmission/reception leg 610, such designated
power transmission/reception legs should not be connected to each
20 other. Assume a case, for example, in which one designated power
transmission/reception leg 510 adjusts the power conversion unit to
send the designated transmitted power. (For example, the output
voltage is made higher than that of the connection partner by a
predetermined value.) On the other hand, the other designated power
25 transmission/reception leg 610 adjusts the power conversion unit to
receive the designated received power. (For example, the output
voltage is made lower than that of the connection partner by a
predetermined value.) It will be understood that, when such an
adjustment operation is executed in both of the designated power
30 transmission/reception legs 510 and 610 at the same time, both of the
designated power transmission/reception legs 510 and 610 become
uncontrollable.
[0060]
While the stand-alone legs are connected in Fig. 5C, it should be
24
understood that such a connection is prohibited.
The stand-alone leg generates a voltage and a frequency by
itself.
If one of the voltage, the frequency, and the phase generated by
5 the two stand-alone legs is deviated from the other by even a slight
amount in a state in which the stand-alone legs are connected,
unintended power flows between the two stand-alone legs.
It is impossible to completely keep the voltage, the frequency,
and the phase generated by the two stand-alone legs to be equal.
10 Therefore, the stand-alone legs should not be connected.
[0061]
In Fig. 5D, the master leg and the designated power
t r a n s m i s s i o n / r e c e p t i o n leg are connected.
It should be understood from the above d e s c r i p t i o n that this
15 connection is not available as well. Even when the master leg 510
t r a n s m i t s power to or receives power from the connection partner to
keep the voltage of the DC bus 501, the designated power
t r a n s m i s s i o n / r e c e p t i o n leg 610 does not transmit or receive power
according to the request from the master leg 510. Accordingly, the
20 master leg 510 cannot keep the voltage of the DC bus 501. Further,
even when the designated power t r a n s m i s s i o n / r e c e p t i o n leg 610
t r a n s m i t s designated power to or receives it from the connection
p a r t n er (510), the master leg 510 does not transmit or r e c e i v e power
according to the request from the designated power
25 transmission/reception leg 610. Accordingly, the designated power
t r a n s m i s s i o n / r e c e p t i o n leg 610 cannot transmit the designated power to
or receive it from the connection partner (in this example, the master
leg 510).
[0062]
30 The case in which the legs including power conversion units are
connected has been stated above. When an AC-thr'ough leg is taken
into consideration, patterns shown in Figs. 6A to 6D are also available.
Since the AC-through leg does not include a power conversion unit, it
is a simple bypass. Accordingly, as shown in Figs. 6A and 6B, the
25
s i t u a t i o n in which the master leg 110 of the first power router 100 is
connected to the u t i l i t y grid 1 1 through the AC-through leg 250 of the
second power router 200 is s u b s t a n t i a l l y equal to the s i t u a t i o n in
which the master leg 110 is directly connected to the u t i l i t y grid 11.
5 In a similar way, as shown in Figs. 6C and 6D, the s i t u a t i o n in which
the designated power t r a n s m i s s i o n / r e c e p t i o n leg 110 of the first power
router 100 is connected to the u t i l i t y grid 11 through the AC-through
leg 250 of the second power router 200 is substantially equal to the
s i t u a t i o n in which the designated power t r a n s m i s s i o n / r e c e p t i o n leg 110
10 is directly connected to the u t i l i t y grid 11.
[0063]
S t i l l , it is convenient to provide the AC-through leg. There may
be a case, for example, in which the distance from the first power
router 100 to the u t i l i t y grid 1 1 is extremely long and some power
15 routers 200 and 300 need to be passed to connect the first power router
100 to the u t i l i ty grid 11, as shown in Fig. 7.
If it is assumed that the AC-through leg is not provided, as
shown in Fig. 4A, one or a p l u r a l i t y o'f stand-alone legs need to be
passed. When a leg including a power conversion unit is passed, it
20 requires conversion from AC power into DC power and conversion from
DC power into AC power. The power conversion causes an energy
loss, though the loss is low (several %). It is inefficient to r e q u i r e a
power conversion a p l u r a l i t y of times only to connect the power router
to the u t i l i t y grid.
25 It is therefore preferable that the AC-through leg which does not
include a power conversion unit is provided in the power router.
[0064]
Fig. 8 shows the combination of connections described above.
Fig. 9 shows one example in which the four power routers 100-
30 400 are interconnected.
Since all of the connection relations have been described above,
each connection partner will not be described in d e t a i l . It would be
understood, however, that all of the connection relations are permitted.
[0065]
26
Now, the connection line which connects the power router and
the connection partner will be a d d i t i o n a l l y described.
When the connection line that connects power routers is called a
p o w e r - t r a n s m i s s i o n line, the power-transmission line may be a part of
5 the u t i l i t y grid or may be separated from the u t i l i ty grid.
(In Fig. 9, the power-transmission line which is a part of the
u t i l i t y grid is denoted by the symbol 71A and the power-transmission
line separated from the u t i l i ty grid is denoted by the symbol 71B.)
In summary, a p l u r a l i t y of power routers may be connected to
10 the u t i l i t y grid. In this way, by connecting two or more power r o u t e rs
through the u t i l i t y grid, power interchange can be performed among the
p l u r a l i t y of power routers through the u t i l i t y grid, and the u t i l i t y grid
can adjust the excessive power or the insufficient power to be
interchanged. Alternatively, two or more power routers may be
15 connected to each other without the intervention of the u t i l i t y grid.
Further, when the connection line that connects the power router
and the load (or the distributed power supply) is called a d i s t r i b u t i on
line 72, the d i s t r i b u t i o n line 72 is separated from the u t i l i t y grid 11.
In summary, the d i s t r i b u t i o n line 72 that connects the power router and
20 the load (or d i s t r i b u t e d power supply) is not connected to the u t i l i ty
grid 11.
[0066]
Further, as shown in Fig. 10, the power routers 100-400 may be
connected like a bus connection.
25 While a description of the operation mode of each leg is
omitted, it is needless to say that the operation mode of each leg needs
to be appropriately selected in c o n s i d e r a t i o n of the direction of power
interchange and the connection r e s t r i c t i o n s described above.
As a matter of course, the u t i l i t y grid 1 1 may be replaced by a
30 distributed power supply such as a power generation f a c i l i t y or a
storage battery in Fig. 10. That is, the p l u r a l i t y of power routers may
be connected to the distributed power supply by a bus.
[0067]
Further, the example shown in Fig. 11 is an example of the
27
connection form in which the two power routers 100 and 200 are
connected to the utility grid 11.
In Fig. 11, the utility grid 11 may be replaced by a distributed
power supply.
5 [0068]
As described above, the connection partner of the power router
may be a utility grid, a distributed power supply including a storage
battery or a power generation facility, or another power router. In this
specification and claims, the above are collectively called a power
10 system.
[0069]
As described above, with the power router according to this
exemplary embodiment, the following effects can be achieved.
That is, with the power router according to this exemplary
15 embodiment, it is possible to build a power network system in which
the power cells are asynchronously interconnected. According to the
connection restrictions described in this exemplary embodiment, legs
can be connected to each other so that the roles of the legs do not'
conflict with each other. It is therefore possible to extend the power
20 network system and to operate the whole system in a stable manner.
[0070]
While the present invention has been described with reference to
the exemplary embodiment, the present invention is not limited to the
above exemplary embodiment. Various changes that can be understood
25 by those skilled in the art can be made on the configuration and the
details of the present invention within the scope of the present
invention.
The present invention may achieve any desired processing by
causing a central processing unit (CPU) to execute a computer
30 program. Further, the program can be stored and provided to a
computer using any type of non-transitory computer readable media.
Non-transitory computer readable media include any type of tangible
storage media. Examples of non-transitory computer readable media
include magnetic storage media (such as flexible disks, magnetic tapes,
28
hard disk drives, etc.), optical magnetic storage media (e.g. magnetooptical
disks), CD-ROM (Read Only Memory), CD-R, CD-R/W, and
semiconductor memories (such as mask ROM, PROM (Programmable
ROM), EPROM (Erasable PROM), flash ROM, RAM (Random Access
5 Memory), etc.). The program may be provided to a computer using any
type of transitory computer readable media. Examples of transitory
computer readable media include electric signals, optical signals, and
electromagnetic waves. Transitory computer readable media can
provide the program to a computer via a wired communication line
0 (e.g. electric wires, and optical fibers) or a wireless communication
line.
[0071]
This application is based upon and claims the benefit of priority
from Japanese Patent Application No. 2012-231590, filed on October
5 19, 2012, the disclosure of which is incorporated herein in its entirety
by reference.
Reference Signs List
[0072]
10 POWER NETWORK SYSTEM
0 11 UTILITY GRID
12 LARGE-SCALE POWER PLANT
21 POWER CELL
30 LOAD
31 HOUSE
5 32 BUILDING
33 SOLAR PANEL
34 WIND TURBINE
35 POWER STORAGE SYSTEM (STORAGE BATTERY)
41 POWER ROUTER
0 50 MANAGEMENT SERVER
51 COMMUNICATION NETWORK
100 POWER ROUTER
101 DC BUS
102 SMOOTHING CAPACITOR
103 VOLTAGE SENSOR
110 LEG
111 POWER CONVERSION UNIT
H I D FEEDBACK DIODE
H I P ANTI-PARALLEL CIRCUIT
H I T THYRISTOR
112 CURRENT SENSOR
113 SWITCH
114 VOLTAGE SENSOR
115 CONNECTION TERMINAL

CLAIMS
1. A power router to asynchronously connect a power cell to an
5 external power system, the power router comprising:
a DC bus whose voltage is kept to a predetermined rated voltage;
a power conversion leg including one connection end connected
to the DC bus and another connection end connected to an external
connection partner as an external connection terminal, the power
10 conversion leg including a function of bidirectionally converting
power between the one connection end and the other connection end;
and
a controller that controls an operation of the power conversion
leg, wherein:
15 a plurality of the power conversion legs are provided,
the power router is controlled according to an instruction from a
management server,
the controller controls an operation of the power conversion leg
in an operation mode which is one of a master mode and a designated
20 power transmission/reception mode,
the power conversion leg operated in the master mode
supplements an insufficient power from the connection partner when
the voltage of the DC bus decreases from a rated voltage, and sends an
excessive power to the connection partner when the voltage of the DC
25 bus increases from the rated voltage,
the power conversion leg operated in the designated power
transmission/reception mode sends a designated power to the
connection partner or receives the designated power from the
connection partner according to a designation from the management
30 server, and
the controller sets the operation mode of at least one of the
power conversion legs to the master mode during the operation of the
power router.
31
2. The power router according to Claim ls wherein:
the operation mode of the power conversion leg further includes
a stand-alone mode in addition to the master mode and the designated
power transmission/reception mode, and
5 the power conversion leg operated in the stand-alone mode
generates a voltage of an amplitude and a frequency specified by the
management server and sends and receives power to and from the
connection partner.
10 3. The power router according to Claim 1 or 2, further
comprising an AC-through leg including one connection end connected
to an external connection partner as an external connection terminal
and another connection end connected to an external connection
terminal of another leg by internal wiring, the AC-through leg
15 conducting one connection end and the other connection end without an
intervention of power conversion.
4. A power network system comprising:
one or a p l u r a l i t y of the power routers according to Claim 3; and
20 a power system to which the power router is d i r e c t l y or
i n d i r e c t l y connected, wherein the connection partner to which the
power conversion leg operated in the master mode is d i r e c t l y or
i n d i r e c t l y connected is r e s t r i c t e d to one of a d i s t r i b u t e d power supply
and a u t i l i t y grid connected to a main power plant.
25
5. The power network system according to Claim 4, wherein,
when the power conversion leg operated in the master mode is
indirectly connected to the utility grid or the distributed power supply,
only one of an AC-through leg and a power conversion leg operated in
30 a stand-alone mode is interposed between the power conversion leg and
the utility grid or the distributed power supply.
6. The power network system according to Claim 4 or 5,
wherein the connection partner to which the power conversion leg
32
operated in the designated power t r a n s m i s s i o n / r e c e p t i o n mode is
d i r e c t l y or i n d i r e c t l y connected is r e s t r i c t e d to any one of the u t i l i ty
grid, the d i s t r i b u t e d power supply, and the power conversion leg
operated in the stand-alone mode.
5
7. The power network system according to Claim 6, wherein,
when the power conversion leg operated in the designated power
t r a n s m i s s i o n / r e c e p t i o n mode is i n d i r e c t l y connected to one of the
u t i l i t y grid, the d i s t r i b u t e d power supply, and the power conversion leg
10 operated in the stand-alone mode, only an AC-through leg is i n t e r p o s ed
between the power conversion leg operated in the designated power
t r a n s m i s s i o n / r e c e p t i o n mode and one of the u t i l i t y grid, the d i s t r i b u t ed
power supply, and the power conversion leg operated in the standalone
mode.
15
8. A power network system comprising two or more of the
power routers according to any one of Claims 1 to 3, wherein power is
' sent between the power routers.
20 9. A power interchange method comprising interchanging power
by sending power between the power r o u t e r s using two or more of the
power routers according to any one of Claims I to 3.
10. An operation control program of a power router that
25 comprises:
a DC bus whose voltage is kept to a predetermined rated voltage;
and
a power conversion leg including one connection end connected
to the DC bus and another connection end connected to an external
30 connection p a r t n e r as an external connection terminal, the power
conversion leg including a function of b i d i r e c t i o n a l l y converting
power between the one connection end and the other connection end, in
which:
a p l u r a l i t y of the power conversion legs are provided,
'33
the power router is controlled according to an instruction from a
management server,
the power router asynchronously connects a power cell to an
external power system,
the power router is built into a computer and
the power router causes the computer to control an operation of
the power conversion leg in an operation mode, which is one of a
master mode and a designated power transmission/reception mode,
the power conversion leg operated in the master mode,
supplements an insufficient power from the connection partner when
the voltage of the DC bus decreases from a rated voyage, and sends anexcessive
power to the connection partner when the voltage of the DC
bus increases from the rated voltage,
the power conversion leg operated in the designated power
transmission/reception mode sends a designated power fo the
connection partner or receives-the designated power from the
connection partner according to a designation from the management
server, and *
the operation mode of at least one of the power conversion legs
is set to the master mode during the operation of the power router.