JP7494971B2 - Power Control Device - Google Patents

Description

The present invention relates to a power control device.

In recent years, plug-in hybrid vehicles (PHEVs) and electric vehicles (EVs) have begun to increase. In particular, electric vehicles require a large amount of charging power because they run only on electricity. In many cases, charging is performed in the parking lot of the user's home by attaching a connector at the end of a charging cable connected to indoor wiring to the electric vehicle (see, for example, Patent Document 1).
Regarding charging of electric vehicles, it has been considered to set a certain charging power in consideration of various conditions and charge the vehicle (for example, see Patent Document 2).

JP 2014-128180 A JP 2008-136291 A

Electricity consumers, such as ordinary households, often have contracts with electric power companies for a single-phase, three-wire system, for example, around 6 kVA. The main breaker in the distribution board has a current rating that matches the contracted power. If the consumer's power consumption increases and exceeds the current rating, the main breaker trips according to a specified time-limit characteristic. When a consumer is operating a large number of relatively high-power household appliances, such as air conditioners, and an electric vehicle, which consumes a certain amount of power, is being charged, the main breaker may trip.

In addition, as electric vehicles become more widespread, there is a possibility that many electric vehicles will be charged simultaneously in a nearby area. In this case, the voltage in the power distribution system will drop due to voltage drops caused by line impedance. On the other hand, if the charging power for electric vehicles is limited to a low, fixed value, electricity that could have been used will not be used, and electric vehicles may not be fully charged.

In view of these issues, the present invention aims to charge electric vehicles without tripping the main breaker and by effectively utilizing available power.

This disclosure includes the following inventions, however, the invention is defined by the claims.

The energy storage system according to one embodiment of the present invention is an energy storage system that electrically connects an electric vehicle equipped with a storage battery to a consumer via a charging cable, and includes a power measurement unit that measures the current flowing at the consumer's power receiving point and the power based on the voltage applied to the power receiving point to obtain a power measurement value, and transmits information on the power measurement value and a predetermined receiving power target value, a power control unit that receives the information from the power measurement unit and sequentially updates the charging power target value of the storage battery based on the received power measurement value and the receiving power target value, and an AC/DC conversion circuit that charges the storage battery in accordance with the control of the power control unit.

In addition, a method for charging a storage battery according to one embodiment of the present invention is a method for charging a storage battery when a power storage system is present, the power storage system being made up of an electric vehicle equipped with a storage battery and a consumer, the consumer and the electric vehicle are electrically connected to each other using a charging cable, a current flowing at a power receiving point of the consumer and a power based on a voltage applied to the power receiving point are measured to obtain a power measurement value, information on the power measurement value and a predetermined target value for received power is transmitted, a charging power target value for the storage battery is successively updated based on the received power measurement value and the target value for received power, and the storage battery is charged according to the target value for charging power.

This invention makes it possible to prevent excessive incoming power from tripping the main breaker, and to effectively use available power to charge the storage battery with appropriate charging power.

FIG. 1 is a diagram showing an example of an outline of equipment on the consumer side (residential side) of a power storage system. FIG. 2 is a diagram showing an example of an outline of equipment on the electric vehicle side of the power storage system. FIG. 3 is a circuit diagram showing a commonly used AC/DC conversion circuit as a reference example. FIG. 4 is a diagram showing an example of an AC voltage (dotted line) and a current (solid line) when leading-phase reactive power is injected into the AC/DC conversion circuit of FIG. FIG. 5 is a circuit diagram showing the AC/DC conversion circuit of this embodiment. FIG. 6 is a diagram showing an example of an AC voltage (dotted line) and a current (solid line) when leading-phase reactive power is injected into the AC/DC conversion circuit of FIG.

[Summary of the embodiment]
The gist of the embodiments of the present invention includes at least the following.

(1) The present disclosure relates to an energy storage system that electrically connects an electric vehicle equipped with a storage battery to a consumer via a charging cable, and includes a power measurement unit that measures the current flowing to the consumer's power receiving point and the power based on the voltage applied to the power receiving point to obtain a power measurement value, and transmits information on the power measurement value and a predetermined receiving power target value, a power control unit that receives the information from the power measurement unit, and successively updates the charging power target value of the storage battery based on the received power measurement value and the receiving power target value, and an AC/DC conversion circuit that charges the storage battery in accordance with the control of the power control unit.

In the energy storage system configured as described above, the power control unit sequentially updates the charging power target value of the storage battery based on the received power measurement value and the received power target value. Therefore, the charging power target value is not always constant, but may change based on the current power measurement value and the received power target value. In this way, it is possible to prevent the received power from becoming excessive and causing the main breaker to trip, and to charge the storage battery with appropriate charging power by effectively using available power.

(2) In the power storage system of (1), the received power target value may be a fixed value or a variable value that changes depending on the time.
If the target value is a variable value, for example, when the electricity rate varies depending on the time of day due to a contract with the power company, the electricity rate can be reduced by changing the target received power value accordingly.

(3) In the power storage system according to (1) or (2) above, the power control unit may set the charging power target value within a range from 0 to a charging power upper limit value.
In this case, it is possible to prevent the storage battery from being discharged and overcharged.

(4) In any of the energy storage systems (1) to (3) above, it is preferable that the acquisition of the power measurement value, the transmission of the information, and the update of the charging power target value are performed at intervals equal to or less than the period of the AC fundamental wave at the power receiving point.
In this case, the charging power can be reduced before the main breaker trips in response to an overcurrent, thereby preventing tripping.

(5) In any one of the energy storage systems (1) to (4) above, for example, the power measurement unit is installed at the consumer, and the power control unit and the AC/DC conversion circuit are mounted on the electric vehicle.
In this case, the necessary information is provided by the consumer side, and the power control unit can charge the vehicle according to the provided information. Therefore, the electric vehicle can be charged by other equipment that is compatible with the same system as the consumer side, and even if the electric vehicle is replaced, it can be charged at the same consumer side.

(6) In any one of the power storage systems (1) to (5) above, the power measurement unit may have a display unit that displays the current power measurement value.
In this case, for example, the power measurement value and the target value of received power can be displayed on the display unit to alert the resident of the consumer's house. For example, if the resident sees the display unit and saves power on unimportant loads, it becomes possible to obtain more charging power.

(7) In any of the energy storage systems (1) to (6) above, the AC/DC conversion circuit may be a full bridge circuit configured with switching elements, and the power control unit may control the AC/DC conversion circuit so that a leading-phase reactive current flows from the consumer to the AC/DC conversion circuit.
In this case, when the AC voltage of the consumer is reduced due to charging of the storage battery, the reduction in the AC voltage can be suppressed.

(8) In any one of the power storage systems (1) to (7) above, for example, communication between the power measurement unit and the power control unit is performed via the charging cable.
In this case, by attaching the charging cable to the electric vehicle, it is possible to connect a power line for charging and a communication line at the same time.

(9) In any one of the power storage systems (1) to (8) above, the power control unit may be configured to operate the AC/DC conversion circuit so as to discharge the storage battery.
In this case, not only can the consumer provide charging power to the battery of the electric vehicle, but the battery can also supply power to the consumer. For example, if the battery is charged at a low cost in a location other than the consumer's house and discharged when it returns to the consumer's house, it can save electricity bills and mitigate the duck curve phenomenon.

(10) On the other hand, this is a method for charging a storage battery when there is a power storage system consisting of an electric vehicle equipped with a storage battery and a consumer, in which the consumer and the electric vehicle are electrically connected to each other using a charging cable, the current flowing at the consumer's power receiving point and the power based on the voltage applied to the power receiving point are measured to obtain a power measurement value, and information on the power measurement value and a predetermined receiving power target value is transmitted, the charging power target value of the storage battery is successively updated based on the received power measurement value and the receiving power target value, and the storage battery is charged according to the charging power target value.

According to the above-described method for charging a storage battery, the target charging power value of the storage battery is successively updated based on the received power measurement value and the target receiving power value. Therefore, the target charging power value is not always constant, but may change based on the current measured power value and the target receiving power value. In this way, it is possible to prevent the received power from becoming excessive and causing the main breaker to trip, and to charge the storage battery with appropriate charging power by effectively utilizing available power.

[Details of the embodiment]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a power storage system and a method for charging a storage battery according to an embodiment of the present invention will be described with reference to the drawings.

Example of a power storage system configuration
1 is a diagram showing an example of an overview of equipment on the consumer side (residential side) of a power storage system 100. For ease of explanation, a commercial power system 1 to a distribution board 6 are shown as double-line diagrams, but the rest are shown as single-line diagrams.

In FIG. 1, a power meter 3 is connected to a single-phase three-wire service line 2 from a commercial power system 1. The equipment from the commercial power system 1 to the power meter 3 is owned by the power company. If the starting point from the power meter 3 on the consumer 4 side is called the power receiving point 5, the electrical wiring from the power receiving point 5 to the consumer 4 side is equipment owned by the consumer 4. The power meter 3 has a bidirectional metering function for buying and selling electricity.

The receiving point 5 and the distribution board 6 in the consumer 4 are connected to each other by two electric circuits 7u and 7w, which are voltage lines, and a neutral electric circuit 7o. The electric circuits 7u, 7o, and 7w are provided with a current detection unit 8. The current detection unit 8 is composed of a current sensor (CT) 8u and a current sensor 8w, which are provided on the electric circuits 7u and 7w, respectively. The electric circuits 7u, 7o, and 7w drawn into the distribution board 6 are branched from the primary side of the main breaker and drawn out as voltage measurement lines 9u, 9o, and 9w. The voltage measurement lines 9u, 9o, and 9w are input to the power measurement unit 12. The current detection unit 8 can detect the current flowing through the receiving point 5. The detection output of the current detection unit 8 is sent to the power measurement unit 12. The power measurement unit 12 measures the power of the receiving point 5 based on the detection output of the current detection unit 8 and the voltage directly taken in through the voltage measurement lines 9u, 9o, and 9w. The power measurement unit 12 includes a display unit 12d for displaying measurement data, etc. The display unit 12d may be a separate monitor capable of communicating with the main body of the power measurement unit 12.

The consumer 4 is provided with, for example, a solar power generation panel 10. The power output of the solar power generation panel 10 is converted into AC power by a power conditioner 11. The AC power output from the power conditioner 11 is sent to a distribution board 6. Note that the solar power generation panel 10 is a typical example of a distributed power source, but other distributed power sources such as fuel cells may also be used.

Although not shown in the figure, the distribution board 6 is provided with a main breaker and a number of breakers under it, and indoor and outdoor wiring is laid out within the customer premises 4 via each breaker.

The parking lot of this consumer 4 is provided with a charging stand 13 for charging electric vehicles. The charging stand 13 receives a voltage supply of, for example, 200 V from a power line 14p drawn from the distribution board 6. The charging stand 13 is provided with a charging cable 15. The tip of the charging cable 15 is provided with a connector 15c that can be attached to and detached from the electric vehicle.

The power measurement unit 12 measures the current flowing through the power receiving point 5 and the power based on the voltage applied to the power receiving point 5 to obtain a power measurement value. A predetermined receiving power target value is set and stored in the power measurement unit 12. The power measurement unit 12 is connected to the charging stand 13 via the communication line 14c. The charging cable 15 is a single cable that contains the extensions of the power line 14p and the communication line 14c. The power measurement unit 12 can send information on the measured power measurement value and the receiving power target value to the electric vehicle 20 (Figure 2) via the communication line 14c.

The power measurement unit 12 can be configured with only hardware, but may also include a computer. When it includes a computer, the computer executes software (computer programs) to realize the necessary control functions. The software is stored in a storage device (not shown) of the power measurement unit 12.

Figure 2 is a diagram showing an example of an overview of the equipment on the electric vehicle side of the energy storage system 100. In the figure, an electric vehicle 20 is equipped with a large-capacity storage battery 21 for driving. An AC/DC conversion circuit 22 capable of converting AC to DC and vice versa is connected to the storage battery 21. The AC/DC conversion circuit 22 is controlled by a power control unit 23. The power control unit 23 includes, for example, a computer, and the computer executes software (computer programs) to realize the necessary control functions. The software is stored in a storage device (not shown) of the power control unit 23.

When the connector 15c of the charging cable 15 is attached to the electric vehicle 20, the power line 24p connected to the AC/DC conversion circuit 22 is connected to the power line 14p on the consumer 4 side. In addition, the communication line 24c connected to the power control unit 23 is connected to the communication line 14c on the consumer 4 side.

<Charging power control>
In the above-described energy storage system 100, the current detection unit 8 is disposed closer to the grid than the position on the electric path where the output of the photovoltaic power generation panel 10 enters the distribution board 6. Therefore, the power that can be consumed by the consumer 4, including the charging power for the electric vehicle 20, can be increased to the total value obtained by adding the power generated by the photovoltaic power generation panel 10 to the upper limit of the power received from the commercial power grid 1.

The power measurement unit 12 calculates the power (active power) p _r at the power receiving point 5. In the following description, the sign of the power p _r is assumed to be positive in the direction of power reception from the commercial power system 1 and negative in the direction of reverse power flow. The power measurement unit 12 obtains and updates the power measurement value at the fundamental wave period (50 or 60 Hz) of the commercial power system 1. The power measurement unit 12 transmits the power measurement value obtained by measurement to the power control unit 23.

The power control unit 23 compares the measured power value p _r with a receiving power target value p ^* _r set to be equal to or lower than the upper limit of the receiving power, and updates the charging power target value p ^* _c of the AC/DC conversion circuit 22 based on the following formula (1) or formula (2). Here, K _p is a proportional gain, and K _i is an integral gain. When formula (1) is used, the third term on the right side (integral term) may be omitted. Note that differences in character fonts in the following formulas (1) and (2), as well as in formulas (3) and (4) described below, are meaningless. The same characters represent the same physical quantity regardless of the character font.

... (1)

... (2)

The received power target value p ^* _r may be a fixed value. However, when power is supplied from the commercial power system 1 under a time-of-day contract, it is possible to save on the electricity bill for charging the electric vehicle 20 by combining with time information and setting p ^* _r small during time periods when the electricity rate is high and setting p ^* _r large during time periods when the electricity rate is low.

The power control unit 23 further compares the charging power target value p ^* _c once updated by the formula (1) or (2) with the charging power upper limit value pc _-max , and rewrites p ^* _c [n+1] by the formula (3). If p ^* _c [n+1] is negative, the power control unit 23 treats it as 0 and stops charging. Furthermore, if p ^* _c [n+1] is equal to or greater than pc _-max , the power control unit 23 rewrites p ^* _c [n+1] to _pc-max . The charging power upper limit value pc _-max may be the maximum allowable power value of the AC/DC conversion circuit 22, or may be an optimal value calculated from the charging state of the storage battery 21, the target charging state, and the time required for charging.

...(3)

When the power measurement value p _r exceeds the upper limit of the received power, the main breaker of the distribution board 6 reacts and trips, for example, in a few seconds, cutting off the current. Therefore, it is desirable for the power control unit 23 to throttle the charging power and control the received power within an allowable range before the current is cut off. To this end, it is desirable for the power measurement value p _r transmitted from the power measurement unit 12 to the power control unit 23 to be updated at a period equal to or shorter than the AC fundamental wave period.

As shown in FIG. 2, the power control unit 23 and the AC/DC conversion circuit 22 may be mounted on the electric vehicle 20, or may be incorporated in the charging station 13, for example. In the former case, the necessary information is provided by the consumer 4, and the power control unit 23 can charge the vehicle according to the provided information. Therefore, the electric vehicle 20 can be charged by other equipment that is compatible with the same system as the consumer 4, and even if the electric vehicle 20 is replaced, it can be charged at the same consumer 4.

Furthermore, for example, if the current value of the power measurement value p _r and the target received power value p ^* _r are displayed on the display unit 12d of the power measurement unit 12, it is possible to alert the residents of the consumer premises 4. For example, if the residents look at the display on the display unit 12d and save power on unimportant loads, it becomes possible to obtain more charging power and perform rapid charging.

Summary so far:
What is disclosed is a power storage system 100 that electrically connects an electric vehicle 20 equipped with a storage battery 21 to a consumer 4 via a charging cable 15, and is equipped with a power measurement unit 12 that measures the current flowing to the consumer 4's power receiving point 5 and the power based on the voltage applied to the power receiving point to obtain a power measurement value p _r and transmits information on the power measurement value and a predetermined received power target value p ^* _r , a power control unit 23 that receives information from the power measurement unit 12 and sequentially updates the charging power target value p ^* _c of the storage battery 21 based on the received power measurement value and received power target value, and an AC/DC conversion circuit 22 that charges the storage battery 21 in accordance with the control of the power control unit 23.

In the energy storage system 100 configured as described above, the power control unit 23 sequentially updates the charging power target value p ^* _c of the storage battery 21 based on the received power measurement value p _r and the received power target value p ^* _r . Therefore, the charging power target value p ^* _c is not always constant, but may change based on the current power measurement value p _r and the received power target value p ^* _r . In this way, it is possible to prevent the received power from becoming excessive and causing the main breaker to trip, and to charge the storage battery 21 with appropriate charging power by effectively using available power.

Also disclosed is a method for charging a storage battery in a case where a power storage system 100 is configured by an electric vehicle equipped with a storage battery 21 and a consumer 4, comprising:
(a) A consumer 4 and an electric vehicle 20 are electrically connected to each other using a charging cable 15;
(b) measuring the current flowing through the power receiving point 5 of the consumer 4 and the power based on the voltage applied to the power receiving point 5 to obtain a power measurement value p _r , and transmitting information on the power measurement value p _r and a predetermined receiving power target value p ^* _r ;
(c) sequentially updating the charging power target value p ^* _c of the storage battery 21 based on the received power measurement value p _r and the receiving power target value p ^* _r ;
(d) This is a method of charging the storage battery, in which the storage battery 21 is charged in accordance with a charging power target value p ^* _c .

According to the above-described method for charging a storage battery, the target charging power value of the storage battery is successively updated based on the received power measurement value and the target receiving power value. Therefore, the target charging power value is not always constant, but may change based on the current measured power value and the target receiving power value. In this way, it is possible to prevent the received power from becoming excessive and causing the main breaker to trip, and to charge the storage battery with appropriate charging power by effectively utilizing available power.

<Mitigating system voltage drops caused by concentrated load consumption>
When load consumption in each house and charging of electric vehicles are concentrated in a neighborhood, the voltage of the power distribution system drops. In this case, the power control unit 23 can reduce the set value of p _c-max to suppress the charging power and mitigate the voltage drop. In order to suppress the voltage drop while maintaining the charging power, the charging current (the direction flowing from the commercial power system 1 to the consumer 4 is positive) can be advanced relative to the system voltage and leading-phase reactive power can be injected. The leading-phase reactive power increases the system voltage, and therefore the voltage drop can be mitigated.

A suitable example of the AC/DC conversion circuit in this case will be described.
3 is a circuit diagram showing, as a reference example, a commonly used AC/DC conversion circuit 220. In the figure, the AC/DC conversion circuit 220 is located between a commercial power system 1 and a storage battery 21. The AC/DC conversion circuit 220 includes a diode bridge 227, a power factor correction circuit (PFC) 228, and a DC/DC converter 229.

Figure 4 is a diagram showing an example of AC voltage (dotted line) and current (solid line) when leading-phase reactive power is injected into the AC/DC conversion circuit 220 in Figure 3. When reactive power is injected into the AC/DC conversion circuit 220 shown in Figure 3, distortion occurs near the zero crossing of the current, as shown in Figure 4.

In contrast, FIG. 5 is a circuit diagram showing the AC/DC conversion circuit 22 of this embodiment. In the figure, the AC/DC conversion circuit 22 is located between the commercial power system 1 and the storage battery 21. The AC/DC conversion circuit 22 includes a filter circuit 221, a full bridge circuit 222 configured with switching elements capable of gate control, a smoothing capacitor Cd, and a DC/DC converter 223. The filter circuit 221 includes a capacitor Ca and an AC reactor L. The full bridge circuit 222 includes switching elements S1, S2, S3, and S4, which are, for example, IGBTs (Insulated Gate Bipolar Transistors). The switching elements S1 to S4 and the DC/DC converter 223 are controlled by the power control unit 23.

Figure 6 is a diagram showing an example of AC voltage (dotted line) and current (solid line) when leading-phase reactive power is injected into the AC/DC conversion circuit 220 of Figure 5. When reactive power is injected into the AC/DC conversion circuit 22 shown in Figure 5, as shown in Figure 6, a distortion-free sine wave current can be maintained even when reactive power is injected.

<<Peak power shift and voltage drop mitigation through discharge from electric vehicles>>
By using the AC/DC conversion circuit 22 of FIG. 5 instead of the AC/DC conversion circuit 22 of FIG. 2, the energy stored in the storage battery 21 mounted on the electric vehicle 20 can be used for load consumption on the consumer 4 side. At this time, the charging power target value p ^* _c [n+1] obtained by the above-mentioned formula (1) or formula (2) is reset by the following formula (4) instead of formula (3). As a result, when the charging current target value p ^* _c [n+1] is a negative value, it is possible to perform discharging within the discharge power lower limit value _pc-min (negative value, maximum discharge power). If the receiving power target value p ^* _r is set to a smaller value equal to or greater than 0, it is possible to increase the amount of discharge from the electric vehicle while preventing reverse power flow from the consumer to the grid.

...(4)

If the electric vehicle discharges electricity when the grid voltage measured by the power measurement unit 12 is low, the drop in grid voltage can be mitigated.
According to this circuit and control, the electric vehicle 20 is charged with power during a time period when surplus power is generated by a distributed power source or the like installed in the consumer 4, and the power is discharged during a time period when there is a power shortage, and can be used for load consumption. Furthermore, as described above, when the power control unit 23 and the AC/DC conversion circuit 22 are mounted on the electric vehicle 20, the electric vehicle 20 can discharge the power at a location different from where it is charged. For example, by using the electric vehicle 20 for commuting to work, and absorbing surplus power from a solar power generation system installed at the workplace during the day, and using this power in accordance with the power peak after returning home, it is possible to contribute to stabilizing the entire power system.

"others"
In the above embodiment, the power storage system 100 is described as including the electric vehicle 20. However, the power storage system can be configured similarly for other electric vehicles such as electric motorcycles and electric industrial vehicles.
In the above embodiment, the communication from the power measurement unit 12 to the power control unit 23 is wired communication, but may be wireless communication instead.

《Addendum》
The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, and it is intended to include all modifications within the scope and meaning equivalent to the claims.

REFERENCE SIGNS LIST 1 Commercial power system 2 Inlet line 3 Power meter 4 Consumer 5 Receiving point 6 Distribution board 7u, 7o, 7w Circuit 8 Current detection unit 8u Current sensor 8w Current sensor 9u Voltmeter side line 9o Voltage measurement line 9w Voltage measurement line 10 Photovoltaic power generation panel 11 Power conditioner 12 Power measurement unit 12d Display unit 13 Charging stand 14p Power line 14c Communication line 15 Charging cable 15c Connector 20 Electric vehicle 21 Storage battery 22 AC/DC conversion circuit 23 Power control unit 24p Power line 24c Communication line 100 Storage system 220 AC/DC conversion circuit 221 Filter circuit 222 Full bridge circuit 223 DC/DC converter 227 Diode bridge 228 Power factor correction circuit 229 DC/DC converter Ca Capacitor Cd Smoothing capacitor L AC reactor S1, S2, S3, S4 Switching element

Claims (7)

A power control device used in a power storage system that electrically connects an electric vehicle equipped with a storage battery to a consumer via a charging cable,
a receiving unit that receives information from a power measuring unit that transmits information on a power measurement value obtained by measuring a current flowing at a power receiving point of the consumer and power based on a voltage applied to the power receiving point and a predetermined receiving power target value;
an update unit that sequentially updates a charging power target value of the storage battery based on the received power measurement value and the received power target value;
Equipped with
Power control device. The receiving power target value is a fixed value or a variable value whose value changes depending on the time.
The power control device according to claim 1 . The charging power target value is set within a range from 0 to a charging power upper limit value.
The power control device according to claim 1 or 2. The power measurement unit is installed in the consumer facility,
The power control device is mounted on the electric vehicle.
The power control device according to any one of claims 1 to 3. The power measurement unit and the power control device are each installed in the consumer.
The power control device according to any one of claims 1 to 3. The power control device controls an AC/DC conversion circuit that charges the storage battery,
the AC/DC conversion circuit is a full bridge circuit configured with switching elements,
The power control device controls the AC/DC conversion circuit so that a leading-phase reactive current flows from the consumer to the AC/DC conversion circuit.
The power control device according to any one of claims 1 to 5. The power control device controls an AC/DC conversion circuit that charges the storage battery,
The power control device may operate the AC/DC conversion circuit to discharge the storage battery.
The power control device according to any one of claims 1 to 6.

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