JP2021005985A - Dc power network - Google Patents

Abstract

To provide a DC power network having a plurality of power networks in which electric power may be supplied to a power network from another power network at any timing even when no power shortage occurs at the power network.SOLUTION: The DC power network includes at least one first power network for supplying electric power and at least one second power network for supplying electric power, and increases a reference voltage of the first power network or decreases a reference voltage of the second power network when supplying electric power from the first power network to the second power network.SELECTED DRAWING: Figure 1

Description

The present invention relates to a DC power network having a plurality of power networks, in which power can be supplied to a certain power network from another power network at an arbitrary timing.

Conventionally, in a DC power network (DC microgrid) having a plurality of power networks, the voltage of all DC lines is controlled to be constant.
The power supply of the conventional DC power grid will be described with reference to FIG. 7.
The DC power grid 100'has a first power grid 10 and a second power grid 20. The first power grid 10 and the second power grid 20 are connected by a DC line.
The first power grid 10 is, for example, a power grid of a large-scale factory, and has the highest power consumption in the DC power grid 100'. The first electric power network 10 is connected to a commercial electric power system and purchases electric power from an electric power company. The first power grid 10 has an AC load a, a photovoltaic power generation system (PVa), and a storage battery a. The AC load a is connected to the DC line via AC / DC, and the PVa and the storage battery a are connected to the DC line via DC / DC, respectively.
The second power grid 20 is, for example, a power grid for a large-scale residential land or a commercial facility. The second power grid 20 has an AC load b, a photovoltaic power generation system (PVb), and a storage battery b, similarly to the first power grid 10. However, since the second power grid 20 is not connected to the commercial power system, the PVb and the storage battery b are normally used to cover the total power consumption of the AC load b, and the second power grid 20 lacks power. Is generated, power is supplied from the first power grid 10.
As described above, in the DC power network 100', the voltage of all the DC lines is controlled to be constant. Therefore, normally, the reference voltage Va of the first power network 10 is the reference voltage Va of the second power network 20. Equal to the reference voltage Vb (Va = Vb).

As shown in (1), normally, PVb is used to supply electric power to the AC load b.
When the power consumption of the AC load b is larger than the generated power of the PVb, as shown in (2), the storage battery b is used to supply the insufficient power to the AC load b.
When the power supply from the storage battery b is stopped (when the charge amount of the storage battery b becomes zero) or when the power supply from the storage battery b becomes smaller than the insufficient power, the reference voltage Vb of the second power network 20 drops. As a result, the reference voltage Vb of the second power network 20 becomes lower than the reference voltage Va of the first power network 10 (Vb <Va), and as shown in (3), the first power network 10 to the second power network Power is supplied to 20.
In the prior art, the reference voltage Vb is maintained constant from the relationship between the line impedance between the AC load b and the storage battery b and the line impedance between the AC load b and the first power network 10. The power is preferentially supplied from the storage battery b closest to the AC load b, and the power is supplied from the first power network 10 only when the power supply from the storage battery b is insufficient.
Therefore, even if surplus power is generated in the first power grid 10, this surplus power cannot be supplied to the first power grid 10. Further, when power is supplied from the first power network 10, the maximum value of the insufficient power is supplied. Therefore, a DC line (power cable) that links the first power network 10 and the second power network 20. It is necessary to use one having a large allowable current.

Further, Patent Document 1 describes that a power supply control device for distributing electric power to a plurality of energy components controls a method of adjusting a DC bus, but a specific method of controlling a DC bus voltage. Is not described.

Special Table 2002-510957A

In view of the above-mentioned problems, the present invention has a DC power network having a plurality of power networks, and even if there is no power shortage in the power network for a certain power network, the present invention can be performed at an arbitrary timing from another power network. It is an object of the present invention to provide a DC power grid capable of supplying electric power.

The DC power grid of the present invention has at least one first power grid to supply power and at least one second power network to be supplied with power.
When power is supplied from the first power grid to the second power grid, the reference voltage of the first power grid is raised or the reference voltage of the second power grid is lowered.

In the DC power network of the present invention, the reference voltage of the first power network or the reference voltage of the second power network is determined based on the line loss of the DC line that links the first power network and the second power network. It is preferable to be done.

In the DC power network of the present invention, it is preferable that the DC line that links the first power network and the second power network forms a loop shape.

In the DC power grid of the present invention, it is preferable that the storage battery of the first power network and the storage battery of the second power network are directly connected to the DC line.

In the DC power grid of the present invention, the reference voltage of the first power grid is preferably determined in consideration of the voltage rise due to the charging resistance of the storage battery of the first power grid.

It is a block diagram of the DC power grid which concerns on 1st Embodiment of this invention, and the system for controlling this DC power grid. It is a graph which shows the electric power pattern in the 2nd electric power grid on a weekday. It is a graph which shows the electric power pattern in the 2nd electric power grid of a holiday. It is a block diagram of the DC power grid which concerns on 2nd Embodiment of this invention, and the system for controlling this DC power grid. It is a block diagram of the DC power grid which concerns on 3rd Embodiment of this invention, and the system for controlling this DC power grid. It is a block diagram of the DC power grid which concerns on 4th Embodiment of this invention, and the system for controlling this DC power grid. It is a block diagram of the DC power grid of the prior art.

FIG. 1 is a block diagram of a DC power network according to the first embodiment of the present invention and a system for controlling the DC power network.
The DC power grid 100 according to the first embodiment has a first power grid 10 and a second power grid 20. The first power grid 10 and the second power grid 20 are connected by a DC line. Since the components of the first power network 10 and the second power network 20 are the same as the components of the conventional DC power network 100'shown in FIG. 7, the description thereof will be omitted.

The systems for controlling the DC power network 100 include a first energy management system (EMSa) for controlling the first power network 10 and a second energy management system (EMSb) for controlling the second power network 20. ), And a centralized energy management system (supervised EMS) for controlling the first and second energy management systems (EMSa, EMSb).
Each EMS measures the power consumption of the AC loads a and b, controls the charging and discharging of the storage batteries a and b, monitors the generated power of the PVa and PVb, and connects the first power grid 10 and the second power grid 20. Determine the power supplied to each other.
Each EMS is a computer such as a personal computer, a server, and a workstation, and has a CPU, a memory, a communication I / F, an input / output device, and the like as a hardware configuration. The CPU reads and executes the program stored in the memory. Programs, data, etc. are stored in the memory. EMSs communicate with each other via the communication I / F.
Communication between EMS and communication between each EMS and each device (DC / DC, etc.) can be performed not only by wire but also by wireless (including optical multi-hop and 5G line).

Consider a case where power is supplied from the first power grid 10 to the second power grid 20. Normally, the reference voltage Va of the first power grid 10 is equal to the reference voltage Vb of the second power grid 20 (Va = Vb).
When the general EMS determines that power should be supplied from the first power grid 10 to the second power grid 20 based on the information from EMSa and EMSb, it is used for the storage battery of the first power grid 10 via EMSa. The reference voltage Va is increased by + α from the normal V for the DC / DC converter, the DC / DC converter for PV, and the AC / DC converter. The value of α is determined based on the line loss (line impedance) of the DC line that links the first power network 10 and the second power network 20.
As a result, the reference voltage Va of the first power grid 10 becomes higher than the reference voltage Vb of the second power grid 20, and the voltage difference (Va-Vb) causes the power from the first power grid 10 to the second power network 20. Is supplied.
The information from EMSa is, for example, information that surplus power is generated in the first power network 10, SOC (charge rate) of the storage battery a, and the like, and the information from EMSb is, for example, alternating current from EMSb. Information that the power consumption of the load b is larger than the generated power of the PVb, the SOC (charging rate) of the storage battery b, future demand forecast, and the like.
As described above, in the present invention, not only when the power shortage has already occurred in the second power grid 20, but also when the power shortage is likely to occur in the future, or when the power shortage has occurred in the second power network 20. Even if it is not present, power can be supplied from the first power grid 10 to the second power grid 20 at an arbitrary timing, such as when surplus power is generated in the first power grid 10, so that a DC line is allowed. The power of the DC power grid 100 can be efficiently operated without exceeding the current.
The electric power supplied from the first electric power network 10 to the second electric power network 20 may be consumed by the AC load b or may be charged to the storage battery b.

2 and 3 are graphs showing the power pattern of the second power grid of the DC power grid according to the first embodiment of the present invention.
FIG. 2 is a graph showing a power pattern in the second power grid on weekdays.
As shown by the wide bar graph, the power consumption in the second power grid 20 increases from the 6 o'clock level, is maintained high (about 0.9 MW) during the daytime hours, and decreases after the 17:00 level. As shown in the line graph, PV power generation increases with sunrise, peaks during the day, and reaches zero after sunset. In the storage battery charge / discharge graph shown as a narrow bar graph, a plus indicates charge and a minus indicates discharge.
Since the relationship of power consumption <PV power generation is established between 9:00 and 16:00, all the power consumption required in the second power network 20 can be supplied by PV power generation, and surplus power (PV power generation- Power consumption) can be charged to the storage battery b. For example, at around 12 o'clock, the storage battery b can be charged with the surplus electric power indicated by the double-headed arrow p.
Since the relationship of PV power generation <power consumption is established between 0:00 to 7:00 and 17:00 to 23:00, the insufficient power is supplied by discharging the storage battery b.
As described above, in the second power grid 20 on weekdays, the self-sufficiency of power is achieved without the need for power supply from other power grids.

FIG. 3 is a graph showing a power pattern in the second power grid on a holiday, FIG. 3A shows a case where there is no power supply from the first power grid (conventional), and FIG. 3B shows a first. The case where there is power supply from the power grid of (the present invention) is shown.
As shown in the wide bar graph, the power consumption in the second power grid 20 increased from the 6 o'clock level, remained high (1.2 MW to 1.3 MW) during the daytime hours, and decreased after the 17:00 level. To do.
Since the power consumption on holidays is higher than the power consumption on weekdays in FIG. 2, as shown in FIG. 3A, when there is no power supply from the first power grid 10, the storage battery b is charged at 6 o'clock. Since the amount is used up and PV power generation has not started, a power shortage occurs from the latter half of 6 o'clock to 8 o'clock. The insufficient power is a total of 1.4 MW in the bar graph shown by the diagonal line in FIG. 3 (a). As described above, since the power consumption of the second power grid 20 is larger on holidays than on weekdays, a power shortage occurs especially in the time zone before sunrise.
Therefore, in order to cover this shortage of power, as shown in FIG. 3B, the reference voltage Va of the first power grid 10 is increased by + α from the normal V between 0 o'clock and 7 o'clock. As a result, a total of 1.4 MW (200 kW x 7 hours) of electric power is supplied from the first electric power network 10 to the second electric power network 20. As a result, the amount of discharge of the storage battery b decreases between 0 o'clock and 5 o'clock as compared with the case of FIG. 3A, and the amount is discharged from 6 o'clock to 8 o'clock. , The power consumption of the second power grid 20 can be covered.
In the past, power was supplied from the first power grid 10 after the charge amount of the storage battery b was used up. Therefore, as shown in FIG. 3A, it is necessary to supply a maximum of 700 kWh of power at 7 o'clock. is there. On the other hand, in the present invention, as shown in FIG. 3B, since 200 kWh of electric power is supplied, the electric power flowing through the DC line can be reduced to 1/3 or less, and the allowable current of the DC line can be reduced. Can be done.

In FIG. 3B, the second power grid 20 is supplied with 200 kW of power from the first power grid 10 in 7 hours, but 100 kW of power is supplied in 14 hours. Is possible. In this way, by leveling (dividing) and supplying the insufficient power in a certain period of time, the power flowing through the DC line can be reduced, and the DC line having a low allowable current can be used. Further, when the power supplied from the first power network 10 is purchased from the commercial power system and leveled, the power is reduced from 700 kW to 200 kW, so that the peak of the purchased power can be suppressed.

FIG. 4 is a block diagram of a DC power network according to a second embodiment of the present invention and a system for controlling the DC power network.
The DC power network 200 according to the second embodiment has a third power network 30, except that the DC lines linking the first power network 10 and the second power network 20 form a loop shape. This is the same as the DC power grid 100 according to the above.
The components of the third power grid 30 are similar to the components of the first power grid 10 and the second power grid 20.
Consider a case where power is supplied from the first power grid 10 to the second power grid 20. Here, the third power grid 30 supplies power from the first power grid 10 to the second power grid 20 without supplying power to the other power grid or from the other power grid. Just let it pass.
When the general EMS determines that power should be supplied from the first power grid 10 to the second power grid 20 based on the information from EMSa and EMSb, the reference voltage of the first power grid 10 is determined via EMSa. Ra raises Va from normal V by + α.
As a result, the reference voltage Va of the first power grid 10 becomes higher than the reference voltage Vb of the second power grid 20, and the voltage difference (Va-Vb) causes the power from the first power grid 10 to the second power network 20. Is supplied. Electric power is supplied directly from the first power grid 10 to the second power grid 20 (via the DC line X on the right side in the figure), and also passes through the first power grid 10 to the third power grid 30 to the second. Is supplied to the power grid 20 (via the DC lines Y and Z on the left side of the figure).
The amount of power directly supplied from the first power grid 10 to the second power grid 20 and the amount of power supplied from the first power grid 10 through the third power grid 30 to the second power grid 20 are direct currents. It is determined by the ratio of the line loss of the line X and the line loss of the DC lines Y and Z.
In this embodiment, the DC line that links the first power network 10 and the second power network 20 forms a loop shape, so that a backup system can be configured without using a switch.

FIG. 5 is a block diagram of a DC power network according to a third embodiment of the present invention and a system for controlling the DC power network.
The DC power grid 300 according to the third embodiment has two first power grids 10 and 10c, and power is supplied from the two first power grids 10 and 10c to the second power grid 20.
Further, the system for controlling the DC power grid 300 has a first energy management system (EMSc) for controlling the first power grid 10c in addition to EMSa and EMSb, and the integrated EMS is EMSa and EMSb. And control EMSc.
When the general EMS determines that power should be supplied from the first power grids 10 and 10c to the second power grid 20 based on the information from EMSa, EMSb, and EMSc, the general EMS passes through the EMSa to the first power grid. The reference voltage Va of 10 is increased by + α from the normal V, and the reference voltage Vc of the first power grid 10c is increased by + β from the normal V via EMSc. The values of α and β are the amount of power supplied from the first power grids 10 and 10c to the second power grid 20, the line loss of the DC line X linking the first power grid 10 and the second power grid 20, and the first. It is determined based on the line loss of the DC line Z that links the power network 10c of 1 and the power network 20 of the second.
As a result, the reference voltages Va and Vc of the first power grids 10 and 10c become higher than the reference voltages Vb of the second power grid 20, and due to the respective voltage differences (Va-Vb) and (Vc-Vb), the first Power is supplied from the power grids 10 and 10c of the first to the second power grid 20.

FIG. 6 is a block diagram of a DC power network according to a fourth embodiment of the present invention and a system for controlling the DC power network.
The DC power network 400 according to the fourth embodiment is not provided with a DC / DC converter for a storage battery, that is, the DC power network according to the first embodiment except that the storage battery a and the storage battery b are directly connected to the DC line. It is the same as 100.
When the general EMS determines that power should be supplied from the first power grid 10 to the second power grid 20 based on the information from EMSa and EMSb, the reference voltage of the first power grid 10 is determined via EMSa. Ra raises Va from normal V by + α. The value of α is determined as α ≦ Zbatt × I based on the internal impedance Zbatt of the storage battery a and the allowable charging current value I. As a result, it is possible to prevent the electric power to be supplied from the first power grid 10 to the second power grid 20 to be filled in the storage battery a of the first power grid 10 (in the figure, the arrow toward the storage battery a). X is shown in).
However, in the above-mentioned voltage value (Va = V + α = V + Zbatt × I) from the line loss of the DC line linking the first power network 10 and the second power network 20 and the voltage drop due to the internal impedance, the first power network 10 When it is not possible to supply power to the second power grid 20, the value of α can be set to a value capable of supplying power, and an EV (not shown) can be instructed to charge to prevent overcharging of the storage battery a. it can.
In this embodiment, since the storage batteries a and b are directly connected to the DC line without going through the DC / DC converter, the conversion loss and the component cost can be reduced.
Further, the reference voltage Va is determined in consideration of the voltage rise due to the charging resistance of the storage battery a, so that the storage battery a can be prevented from being excessively charged.

The present invention is not limited to the above-described embodiment, and various modifications can be made.
In the above-described embodiment, power is supplied from the first power grid 10 to the second power grid 20 by increasing the reference voltage Va of the first power grid 10, but the reference voltage Vb of the second power grid 20 is lowered. By doing so, power can be supplied from the first power grid 10 to the second power grid 20.
In the above-described embodiment, power is supplied from the first power grid 10 to the second power grid 20, but power is supplied from the first power grid 10 to the second power grid 20 on holidays, while the first power grid 20 is supplied on weekdays. Electricity can also be supplied to each other between the power grids, such as supplying power from the second power grid 20 to the first power grid 10. In this case, it is preferable that the first power grid 10 has high weekday power consumption and low holiday power consumption, while the second power grid 20 has low weekday power consumption and high holiday power consumption. That is, the power consumption curve of the first power grid and the power consumption curve of the second power grid are different on weekdays and holidays, and are preferably complementary.
Further, the reference voltage Va can be finely adjusted by charging / discharging the DC-connected quick charger and EV.

10, 10c 1st power grid 20 2nd power grid 30 3rd power grid 100, 100', 200, 300, 400 DC power grid

Claims (5)

A DC power grid having at least one first power grid to supply power and at least one second power grid to be powered.
When supplying power from the first power grid to the second power grid, the reference voltage of the first power grid is raised or the reference voltage of the second power grid is lowered.
A DC power grid characterized by this. The reference voltage of the first power grid or the reference voltage of the second power grid is determined based on the line loss of the DC line that links the first power grid and the second power grid.
The DC power grid according to claim 1. The DC line that links the first power network and the second power network forms a loop shape.
The DC power grid according to claim 1 or 2. The storage battery of the first power grid and the storage battery of the second power grid are directly connected to the DC line.
The DC power grid according to any one of claims 1 to 3. The reference voltage of the first power grid is determined in consideration of the voltage rise due to the charging resistance of the storage battery of the first power grid.
The DC power grid according to claim 4.

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