Power management device, power management method, and computer program

Abstract

To provide a power management device with which, irrespective of the magnitude of a power factor, it is possible to more accurately calculate a power value at a prescribed power management point located closer to a power grid side than a connecting point of a distributed energy resource and an electric wire in a grid-linked system.SOLUTION: The power management device comprises: a current detector and a voltage detector for detecting a current and a voltage at a connecting point of a distributed power supply and an electric wire; a storage unit for storing an electric resistance value of an electric wire between the connecting point and a prescribed power management point closer to a power system side than the connecting point; and an arithmetic unit. The arithmetic unit calculates an active power at the connecting point, a reactive power at the connecting point, and an effective voltage value at the connecting point on the basis of the current and the voltage detected by the current detector and the voltage detector, and calculates power at the power management point on the basis of the calculated active power at the connecting point, the reactive power at the connecting point, and the effective voltage value at the connecting point, and the electric resistance value stored by the storage unit.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a power management device, a power management method, and a computer program. [Background technology]

[0002] Distributed power supply systems that interconnect distributed energy resources (DES), such as solar power generation systems and large-capacity storage batteries mounted on electric vehicles, have become widespread as emergency power sources during long-term power outages caused by disasters and as systems to compensate for power supply shortages during peak power periods in summer and winter (see, for example, Patent Document 1).

[0003] Distributed energy resources are connected to the power grid by electric wires. The connection point between the distributed energy resources and the electric wires is called PoC (Point of Connection), and the point where power is received from the grid is called PCC (Point of Common Coupling).

[0004] Distributed energy resources can directly measure the voltage and power values ​​at the connection point PoC, but if a resistance component exists between the power receiving point PCC and the connection point PoC, the voltage and power values ​​at the connection point PoC and the power receiving point PCC will differ.

[0005] When operation is regulated based on the power and voltage at the power receiving point PCC, such as in the grid interconnection standard IEEE1547, it is necessary to control the value at the power receiving point PCC and estimate the value at the power receiving point PCC. In fact, the UL1741 standard describes a method of calculating the PCC voltage from the PoC voltage with the resistance component as a known value as dynamic calibration. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2017-189041 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, if the power is corrected based on the above-described voltage correction, the power error becomes large under conditions where the power factor is low.

[0008] An object of the present invention is to provide a power management device, a power management method, and a computer program that can more accurately calculate the power of a specified power management point that is located on the power grid side of the connection point between a distributed energy resource and an electric wire in a grid interconnection system, regardless of the magnitude of the power factor. [Means for solving the problem]

[0009] A power management device according to one aspect of the present disclosure is a power management device that manages power supplied from a distributed power source through an electric wire to a power grid, and includes a current detector that detects a current at a connection point between the distributed power source and the electric wire, a voltage detector that detects a voltage at the connection point between the distributed power source and the electric wire, a memory unit that stores an electrical resistance value of the electric wire between the connection point and a predetermined power management point on the power grid side of the connection point, and a calculation unit that calculates the power at the power management point, wherein the calculation unit calculates an active power at the connection point, a reactive power at the connection point, and an effective voltage value or effective current value at the connection point based on the current and voltage detected by the current detector and the voltage detector, and calculates the power at the power management point based on the calculated active power at the connection point, the reactive power at the connection point, the effective voltage value or effective current value at the connection point, and the electrical resistance value stored in the memory unit.

[0010] A power management method according to one aspect of the present disclosure is a power management method for managing power supplied from a distributed power source to a power grid through an electric wire, comprising the steps of: detecting a current and voltage at a connection point between the distributed power source and the electric wire; reading out the electrical resistance value of the wire between the connection point and a power management point on the power grid side of the connection point from a memory unit that stores the electrical resistance value of the wire; calculating an active power at the connection point, a reactive power at the connection point, and an effective voltage value or an effective current value at the connection point based on the detected current and voltage; and calculating the power at the power management point based on the calculated active power at the connection point, the reactive power at the connection point, the effective voltage value or the effective current value at the connection point, and the electrical resistance value stored in the memory unit.

[0011] A computer program according to one aspect of the present disclosure is a computer program that causes a computer to execute a process of managing power supplied from a distributed power source through an electric wire to a power grid, the computer program detecting a current and voltage at a connection point between the distributed power source and the electric wire, reading out the electrical resistance value of the wire between the connection point and a power management point on the power grid side of the connection point from a memory unit that stores the electrical resistance value of the wire, calculating an active power at the connection point, a reactive power at the connection point, and an effective voltage value or an effective current value at the connection point based on the detected current and voltage, and calculating the power at the power management point based on the calculated active power at the connection point, the reactive power at the connection point, the effective voltage value or the effective current value at the connection point, and the electrical resistance value stored in the memory unit. Effect of the Invention

[0012] According to the above, regardless of the magnitude of the power factor, it is possible to more accurately calculate the power of a predetermined power management point that is located on the power grid side of the connection point between the distributed energy resource and the power line in the grid interconnection system. [Brief description of the drawings]

[0013] [Figure 1]1 is a block diagram showing a configuration example of a grid interconnection system according to a first embodiment of the present invention. [Diagram 2] 2 is a block diagram showing an example of a hardware configuration of a power management apparatus. [Diagram 3] 4 is a flowchart showing a power calculation process according to the first embodiment. [Figure 4] 1 is a graph showing the relationship between the relative error of the active power calculated by the conventional technique and the power factor. [Diagram 5] 4 is a graph showing the relationship between the relative error of the active power calculated by the method according to the first embodiment and the power factor. [Figure 6] 10 is a flowchart showing a power calculation process according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] A power management device, a power management method, and a computer program according to an embodiment of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0015] (Embodiment 1) 1 is a block diagram showing a configuration example of a grid interconnection system 1 according to the present embodiment 1. The grid interconnection system 1 includes a power grid 2, a distributed energy resource 3 interconnected with the power grid 2, an electric wire 4 connecting the power grid 2, a power management device 5, a current detector 6, and a voltage detector 7.

[0016] The distributed energy resource 3 includes a distributed power source that outputs DC power, such as a solar power generator, a wind power generator, a fuel cell, a cogeneration system, or a storage battery. The distributed energy resource 3 includes a storage battery and a generator mounted on a vehicle.

[0017] The current detector 6 is a current sensor that detects the AC current value output from the distributed energy resource 3 and outputs current value data indicating the detected current value to the power management device 5. The voltage detector 7 is a voltage sensor that detects the AC voltage value output from the distributed energy resource 3 and outputs voltage value data indicating the detected voltage value to the power management device 5. The power management device 5 and the current detector 6 detect the current and voltage at a connection point 4a between one end of the electric wire 4 having a resistive component and the distributed power source. The connection point 4a is called a Poc (Point of Connection).

[0018] 2 is a block diagram showing an example of a hardware configuration of the power management device 5. The power management device 5 is a computer including a calculation unit 51, a storage unit 52, and a communication unit 53, and calculates the power at a predetermined power management point 4b located closer to the power grid than the connection point 4a, and manages the power supplied from the distributed energy resource 3 to the power grid 2. The power management point 4b is, for example, a power receiving point PCC (Point of Common Coupling).

[0019] The memory unit 52 has, for example, a main memory unit and an auxiliary memory unit. The main memory unit is a temporary storage area such as a static random access memory (SRAM), a dynamic random access memory (DRAM), or a flash memory, and temporarily stores data required for the calculation unit 51 to execute calculation processing. The auxiliary memory unit is a storage device such as an electrically erasable programmable ROM (EEPROM). The auxiliary memory unit stores a computer program 81 executed by the calculation unit 51, an electrical resistance value between the connection point 4a of the electric wire 4 and the power management point 4b, and various other data required for processing. For example, the electrical resistance value between the connection point 4a of the electric wire 4 and the power management point 4b may be calculated based on the voltage drop when a predetermined current, for example, 20 [Arms], is passed through the electric wire 4, and the electrical resistance value may be stored in the memory unit 52 of the power management device 5.

[0020] The computer program 81 may be written into the auxiliary storage unit during the manufacturing stage of the power management device 5, or may be distributed by an external computer and acquired by the power management device 5 via communication and stored in the auxiliary storage unit. The computer program 81 may be recorded in a readable manner on a recording medium 8 such as a magnetic disk, optical disk, or semiconductor memory, or may be read from the recording medium 8 by a reading device and stored in the auxiliary storage unit.

[0021] The communication unit 53 is a communication circuit that is connected to and communicates with the distributed energy resources 3, the current detector 6, and the voltage detector 7. The communication unit 53 communicates with the distributed energy resources 3 and manages the power supplied to the power system 2. The communication unit 53 also receives current value data and voltage value data output from the current detector 6 and the voltage detector 7, respectively. The calculation unit 51 acquires the current value data and voltage value data via the communication unit 53 at a predetermined monitoring timing, and stores each acquired data in the memory unit 52.

[0022] 3 is a flowchart showing a power calculation process procedure according to the present embodiment 1. The calculation unit 51 of the power management device 5 detects the voltage and current at the connection point 4a using the current detector 6 and the voltage detector 7 (step S111). Specifically, the calculation unit 51 acquires the current value data and voltage value data transmitted from the current detector 6 and the voltage detector 7 using the communication unit 53.

[0023] Next, the calculation unit 51 calculates the active power, reactive power, and effective voltage value at the connection point 4a based on the acquired current value data and voltage value data (step S112). The calculation unit 51 calculates the loss due to the wire resistance between the connection point 4a and the power management point 4b (the right term in the following formula (1)) based on the following formulas (1) and (2) (step S113), and calculates the power at the power management point 4b (step S114). The details of the following formula (1) will be described later. The calculation unit 51 manages the power in the grid interconnection system 1 based on the calculated power value (step S115). For example, the calculation unit 51 controls the output of the distributed energy resource 3.

[0024]

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[0025] 4 is a graph showing the relationship between the relative error of the active power calculated by the conventional technology and the power factor. The horizontal axis shows the power factor, and the vertical axis shows the relative error between the calculated active power value at the power control point 4b and the true active power value.

[0026] The dashed line indicates the active power value at power control point 4b measured and calculated under predetermined conditions (apparent power S=6600 [VA], electrical resistance value R of wire 4=100 [Ω]) without correction taking into account the influence of wire resistance. In other words, the dashed line indicates the active power value measured and calculated at connection point 4a.

[0027] The solid line indicates the power value at power control point 4b corrected by conventional dynamic calibration. Dynamic calibration is a method of calculating the voltage value at power control point 4b based on the output effective current value I and the voltage value at connection point 4a, assuming that the electrical resistance value R between connection point 4a and power control point 4b (between PoC and PCC) is known, as shown in the following formula (3).

[0028]

number

[0029] At this time, the current flowing through the connection point 4a and the power management point 4b is the same, so the active power at the power management point 4b is expressed by the following formula (4).

[0030]

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[0031] As shown in Figure 4, dynamic calibration can correct the power factor without any problems when the power factor is 1, but the smaller the power factor is, the larger the error becomes due to the phase shift caused by the reactive current. This raises concerns that the required accuracy may not be met.

[0032] Therefore, in this embodiment 1, we consider compensating for the loss due to the wire resistance by using complex power. When complex power and complex current are used, the complex current can be expressed by the following formula (5), and the loss due to the wire resistance between the connection point 4a and the power management point 4b can be expressed by the following formula (6). The complex power at the power management point 4b is expressed by the following formulas (7) to (9).

[0033]

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[0034] Therefore, it can be seen that the active power at the power management point 4b can be calculated by subtracting the loss represented by the above formula (6) from the active power at the connection point 4a. Therefore, the active power at the power management point 4b can be expressed by the above formula (1). The loss expressed by the above formula (6) does not have an imaginary component. In other words, there is no reactive power loss due to the resistance component of the electric wire 4. Therefore, the active power at the power control point 4b and the active power at the connection point 4a have the same value, and the reactive power at the power control point 4b is expressed by the above formula (2).

[0035] 5 is a graph showing the relationship between the power factor and the relative error of the power calculated by the method according to the embodiment 1. The horizontal axis shows the power factor, and the vertical axis shows the relative error between the calculated effective power value and the true power value at the power management point 4b.

[0036] The thick solid line indicates the power value at the power control point 4b corrected by the method according to the embodiment 1. The thin solid line indicates the power value at the power control point 4b corrected by the conventional dynamic calibration.

[0037] As can be seen from FIG. 5, according to the method according to the first embodiment, the power value can be corrected regardless of the power factor value.

[0038] As described above, according to the first embodiment, regardless of the magnitude of the power factor, it is possible to more accurately calculate the power value at a predetermined power management point 4b located closer to the power grid than the connection point 4a between the distributed energy resource 3 and the power line 4 in the grid interconnection system 1. The power management device 5 can manage the power of the grid interconnection system 1 based on the accurately calculated current value.

[0039] (Embodiment 2) The grid interconnection system 1 according to the second embodiment differs from the grid interconnection system 1 according to the first embodiment in the method of calculating active power. Other configurations of the grid interconnection system 1 are similar to those of the grid interconnection system 1 according to the first embodiment, so the same reference numerals are used for the same parts and detailed descriptions are omitted.

[0040] 6 is a flowchart showing the procedure of the power calculation process according to the embodiment 2. The calculation unit 51 of the power management device 5 detects the voltage and current at the connection point 4a using the current detector 6 and the voltage detector 7 (step S211).

[0041] Next, the calculation unit 51 calculates the active power, reactive power, and effective current value at the connection point 4a based on the acquired current value data and voltage value data (step S212). The calculation unit 51 calculates the loss due to the wire resistance between the connection point 4a and the power management point 4b (the right term in the following formula (10)) based on the following formulas (10) and (11) (step S213), and calculates the power at the power management point 4b (step S214). The calculation unit 51 manages the power in the grid interconnection system 1 based on the calculated power value (step S215).

[0042]

number

[0043] Thus, according to the second embodiment, similarly to the first embodiment, regardless of the magnitude of the power factor, it is possible to more accurately calculate the power value at a predetermined power management point 4b located closer to the power grid than the connection point 4a between the distributed energy resource 3 and the power line 4 in the grid interconnection system 1. The power management device 5 can manage the power of the grid interconnection system 1 based on the accurately calculated current value.

[0044] The embodiments disclosed herein are illustrative in all respects and should not be considered as limiting. The scope of the present invention is indicated by the claims, not by the above meaning, and is intended to include all modifications within the meaning and scope of the claims. In other words, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention. [Explanation of symbols]

[0045] 1: Grid-connected system 2: Power system 3: Distributed energy resources 4: Electric wire 4a: Connection point 4b: Power management point 5: Power management device 6: Current detector 7: Voltage detector 8: Recording media 51: Arithmetic section 52: Storage section 53: Communications Department 81: Computer Programs

Claims

1. A power management device that manages power supplied from a distributed power source through an electric power line to a power grid, a current detector that detects a current at a connection point between the distributed power source and the electric wire; a voltage detector that detects a voltage at the connection point between the distributed power source and the electric wire; a storage unit that stores an electrical resistance value of the electric wire between the connection point and a predetermined power control point on the power grid side of the connection point; A calculation unit for calculating power at the power management point; Equipped with The calculation unit is calculating an active power at the connection point, a reactive power at the connection point, and an effective voltage value or an effective current value at the connection point based on the current and voltage detected by the current detector and the voltage detector; Calculating power at the power management point based on the calculated active power at the connection point, the reactive power at the connection point, the effective voltage value or the effective current value at the connection point, and the electrical resistance value stored in the storage unit. Power management device.

2. The calculation unit is The power at the power management point is calculated based on the following formulas (1) and (2). The power management apparatus of claim 1 . [0010]

3. The calculation unit is The power at the power management point is calculated based on the following formulas (3) and (4). The power management apparatus of claim 1 . [0025]

4. A power management method for managing power supplied from a distributed power source through a power line to a power grid, comprising: Detecting a current and a voltage at a connection point between the distributed generation and the electric wire; reading out an electrical resistance value of the electric wire between the connection point and a power management point on the power grid side of the connection point from a storage unit that stores the electrical resistance value; Calculating an active power at the connection point, a reactive power at the connection point, and an effective voltage value or an effective current value at the connection point based on the detected current and voltage; Calculating power at the power management point based on the calculated active power at the connection point, the reactive power at the connection point, the effective voltage value or the effective current value at the connection point, and the electrical resistance value stored in the storage unit. Power management methods.

5. A computer program for causing a computer to execute a process for managing power supplied from a distributed power source through an electric power line to a power grid, Detecting a current and a voltage at a connection point between the distributed generation and the electric wire; reading out an electrical resistance value of the electric wire between the connection point and a power management point on the power grid side of the connection point from a storage unit that stores the electrical resistance value; Calculating an active power at the connection point, a reactive power at the connection point, and an effective voltage value or an effective current value at the connection point based on the detected current and voltage; Calculating power at the power management point based on the calculated active power at the connection point, the reactive power at the connection point, the effective voltage value or the effective current value at the connection point, and the electrical resistance value stored in the storage unit. A computer program that causes the computer to execute a process.

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