Power system stabilization system, power storage device, and DC transmission system

Abstract

To provide a power system stabilization system, a power storage device, and a DC power transmission system that take into account differences in frequency fluctuations between generators and reduce the risk of power outages due to fall-off of the generators even when an accident such as a power failure or system separation occurs in a power system to which many renewable energy sources are connected.SOLUTION: A central processing unit 4 to which information from a power system 1, a plurality of generators 2A to 2C, and a power storage device 3 is input, and that controls the output of the power storage device on the basis of the information includes a power storage device command calculation unit. The power storage device command calculation unit includes a frequency change rate calculation unit that calculates frequency change rates at multiple points in the power system on the basis of the frequencies of the plurality of generators, a determination value calculation unit that determines which of the plurality of generators is to be stably operated by the control of the power storage device on the basis of the frequency change rates calculated by the frequency change rate calculation unit, the sensitivity of the frequency change rates, and operation information on the plurality of generators, and an active power control amount calculation unit that calculates the output of active power of the power storage device.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a power system stabilization system, a power storage device, and a DC transmission system, and more particularly to a power system stabilization system, a power storage device, and a DC transmission system suitable for those using renewable energy power sources such as solar power generation and wind power generation. [Background technology]

[0002] In recent years, with the expansion of renewable energy sources such as solar and wind power, the interconnected ratio of traditional power sources such as thermal and nuclear power plants has been declining.

[0003] Most of the generators used in conventional power systems, such as thermal and nuclear power plants, are synchronous generators that operate at a constant rotational speed. These synchronous generators have inertia that keeps the rotational speed constant, and also have a synchronizing force, which is the action by which multiple synchronous generators adjust to the same rotational speed through the power system.

[0004] On the other hand, many of the renewable energy sources, such as solar power and wind power, which have been increasingly introduced in recent years, are connected to the power grid via inverters that convert direct current (DC) to alternating current (AC), and therefore do not have the inertia or synchronizing power that traditional sources such as thermal and nuclear power have. As a result, in power grids with a high proportion of renewable energy sources, if an accident such as a power source tripping or system separation occurs, the accident is more likely to spread than in traditional power grids.

[0005] For example, if a power source trips and causes an imbalance in the supply and demand of a power grid, the fluctuations of the generators remaining in the power grid will be greater than before due to the reduction in inertia. As a result, the change in frequency per unit time, df / dt, will tend to increase.

[0006] In the following description, the frequency change per unit time df / dt is referred to as the time derivative of the frequency, and the magnitude of the frequency change per unit time |df / dt| is referred to as the rate of change of frequency (RoCoF).

[0007] In addition, Fault Ride Through requirements (hereinafter referred to as FRT requirements) are set for renewable energy power sources, and currently, they are required to continue operation for RoCoFs within ±2 [Hz / s].

[0008] If an accident such as a power source tripping or grid isolation causes fluctuations in synchronous power sources and the RoCoF is detected to exceed the FRT requirement, there is a risk that renewable energy sources will trip in a chain reaction, causing further frequency drops.

[0009] In the following, the case where a renewable energy source falls outside the RoCoF due to a grid accident is referred to as "cascading dropout."

[0010] To address these issues, it is effective to increase the inertia by installing a synchronous phase modifier or to increase the synchronizing force by strengthening the grid. However, because synchronous phase modifiers are rotating machines, they incur high maintenance costs, and strengthening the grid requires huge costs and time.

[0011] On the other hand, with the promotion of the introduction of renewable energy sources, it is expected that in the future, DC transmission will become more common for long-distance power transmission from suitable renewable energy locations to areas of demand. In particular, DC transmission systems using self-commutated converters are capable of independent, high-speed control of active and reactive power, and have a faster response than active power adjustment using a governor of a synchronous generator, making them highly effective as instantaneous adjustment capability.

[0012] Patent Document 1 describes a power system stabilization device that stabilizes the power system by suppressing fluctuations in the power system caused by accidents or the like.

[0013] Patent Document 1 describes how, in order to obtain a power system stabilization device capable of supplying and absorbing active power and reactive power, a system fault is detected immediately after the fault is detected by a system fault detection unit from information that suddenly changes in the event of a fault, such as bus voltage and line current, and the control target value is forcibly controlled to achieve the maximum absorption amount, thereby compensating for active power that has a high effect on stabilizing the power system. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] JP 2012-125019 A Summary of the Invention [Problem to be solved by the invention]

[0015] In the above-mentioned Patent Document 1, the bus frequency or the rotation speed of a specific generator is detected, and the target value of the active power control is calculated based on the calculated frequency fluctuation. However, in the case of a system with reduced inertia or synchronizing force, it is possible that the fluctuation of the generator differs depending on the area in the system.

[0016] For example, assume that there are two generators (generator A and generator B) in the same grid. If a grid fault causes generator A to accelerate and generator B to decelerate, active power control intended to suppress the acceleration of generator A may promote the deceleration of generator B. In this case, the RoCoF in area B of generator B may deviate from the FRT requirements, creating a risk of a chain reaction of renewable energy power sources.

[0017] The present invention has been made in consideration of the above-mentioned points, and an object of the present invention is to provide a power system stabilization system, a power storage device, and a DC transmission system that can take into account differences in frequency fluctuations between generators and reduce the risk of power outages due to generator tripping, even in the event of an accident such as a power source tripping or system isolation in a power system to which a large number of renewable energy power sources are connected. [Means for solving the problem]

[0018] In order to achieve the above object, the power system stabilization system of the present invention comprises a plurality of generators connected to a power system, devices connected to the power system via a power conversion circuit, and a central processing unit that receives information from the power system, the plurality of generators, and the devices connected to the power system via the power conversion circuit and controls outputs of the devices connected to the power system via the power conversion circuit based on the information, wherein the central processing unit comprises at least a device command calculation unit connected to the power system via the power conversion circuit, and the device command calculation unit connected to the power system via the power conversion circuit comprises: a frequency change rate calculation unit that calculates frequency change rates of a plurality of points in the power system based on frequencies of the plurality of generators; a judgment value calculation unit that determines which of the plurality of generators should be operated stably by controlling the devices connected to the power system via the power conversion circuit based on the frequency change rate calculated by the frequency change rate calculation unit, the sensitivity of the frequency change rate, and operation information of the plurality of generators; and an active power control amount calculation unit that calculates an active power output of the devices connected to the power system via the power conversion circuit.

[0019] In addition, in order to achieve the above-mentioned object, the power storage device of the present invention is a power storage device that is connected to a power system and has a storage device on the DC side, and is characterized in that the power storage device determines an active power output based on an active power command given from a power system stabilization system.

[0020] In order to achieve the above-mentioned object, the DC transmission system of the present invention is a DC transmission system that is connected to a power grid and has a DC system on the DC side, and is characterized in that the DC transmission system determines an active power output based on an active power command given from a power grid stabilization system. Effect of the Invention

[0021] According to the present invention, even if an accident such as a power source failure or system separation occurs in a power system to which a large number of renewable energy power sources are connected, the difference in frequency fluctuation between each generator can be taken into account, thereby reducing the risk of a power outage due to a generator failure. [Brief description of the drawings]

[0022] [Figure 1] 1 is a diagram showing a schematic configuration of a power system stabilization system according to a first embodiment of the present invention; [Diagram 2] FIG. 2 is a diagram showing a configuration of a central processing unit used in the power system stabilization system according to the first embodiment of the present invention. [Diagram 3] FIG. 3 is a diagram showing an example of assumed accident data input to a power storage device command calculation unit in the power system stabilization system according to the first embodiment of the present invention. [Figure 4(a)] FIG. 2 is an explanatory diagram of a first calculation method of sensitivity information dRoCoF / dPBESS in the power system stabilization system according to the first embodiment of the present invention, and is a diagram showing an output of a power storage device. [Figure 4(b)] FIG. 2 is an explanatory diagram of a first calculation method of sensitivity information dRoCoF / dPBESS in the power system stabilization system according to the first embodiment of the present invention, and is a diagram showing the frequency of a certain generator among a plurality of generators. [Figure 5(a)] FIG. 11 is an explanatory diagram of a second calculation method of the sensitivity information dRoCoF / dPBESS in the power system stabilization system according to the first embodiment of the present invention, illustrating a case where the output of the power storage device is changed. [Figure 5(b)] FIG. 5(b) is an explanatory diagram of a second calculation method of the sensitivity information dRoCoF / dPBESS in the power system stabilization system according to the first embodiment of the present invention, and is a diagram showing a change in the frequency of the generator in the case of FIG. 5(a). [Figure 6] FIG. 2 is a conceptual diagram showing behavior of the output and frequency of a generator in the power system stabilization system according to the first embodiment of the present invention. [Figure 7] FIG. 3 is a diagram showing a display example of an output command for a power storage device in the power system stabilization system according to the first embodiment of the present invention. [Figure 8]FIG. 1 is a diagram showing a configuration of a power storage device used in a first embodiment of a power system stabilization system according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, a power system stabilization system, a power storage device, and a DC power transmission system according to the present invention will be described based on the illustrated embodiments. In each drawing, the same reference numerals are used for the same components. EXAMPLES

[0024] FIG. 1 shows a schematic configuration of a power system stabilization system according to a first embodiment of the present invention.

[0025] As shown in FIG. 1 , the power system stabilization system of the present embodiment includes a power system 1, a plurality of generators (in this embodiment, a first generator 2A, a second generator 2B, and a third generator 2C) connected to the power system 1, a power storage device 3 that is connected to the power system 1 and has a power storage device on the DC side (for example, on the side of a solar power generation device or a wind power generation device) and is connected to the power system 1 via a power conversion circuit to balance the supply or demand of power in the power system 1, and a power storage device 3 that is connected to the power system 1 via a power conversion circuit and has a power storage device on the DC side (for example, on the side of a solar power generation device or a wind power generation device). The system is roughly composed of a central processing unit 4 which receives information from the third generator 2C and the power storage device 3 (information from the first generator 2A is indicated by dotted arrow G1, information from the second generator 2B is indicated by dotted arrow G2, information from the third generator 2C is indicated by dotted arrow G3, information from the power system 1 is indicated by dotted arrow R1, and information from the power storage device 3 is indicated by dotted arrow R2) and controls the output of the power storage device 3 based on that information, and a control terminal 5 which transmits the output from the central processing unit 4 to the power storage device 3.

[0026] FIG. 2 shows a detailed configuration of the central processing unit 4 described above.

[0027] As shown in FIG. 2, the central processing unit 4 of this embodiment is composed of a power storage device command calculation unit 9 to which power system data 6, assumed accident data 7, and sensitivity data 8 are input. This power storage device command calculation unit 9 is roughly composed of a frequency change rate calculation unit 9a that calculates frequency change rates at multiple points in the power system 1 based on the frequencies of the first generator 2A, the second generator 2B, and the third generator 2C, a judgment value calculation unit 9b that determines which generator out of the first generator 2A, the second generator 2B, and the third generator 2C should be operated stably by controlling the power storage device 3 based on the frequency change rate and the sensitivity of the frequency change rate calculated by the frequency change rate calculation unit 9a and the operation information of the first generator 2A, the second generator 2B, and the third generator 2C, and an active power control amount calculation unit 9c that calculates the active power output of the power storage device 3.

[0028] Then, the control content 10 , which is an output command for the power storage device 3 output from the power storage device command calculation unit 9 of the central processing unit 4 , is transmitted to the power storage device 3 via the control terminal 5 .

[0029] The power system data 6 input to the power storage device command calculation unit 9 described above is data related to the power system 1, and is information data such as specifications of the first generator 2A, the second generator 2B, and the third generator 2C and renewable energy, outputs of the first generator 2A, the second generator 2B, and the third generator 2C, configuration and impedance of the power transmission network, and magnitude of power demand.

[0030] The postulated accident data 7 input to the power storage device command calculation unit 9 is data on information on postulated accidents in the power system 1 to which the central processing unit 4 is connected. An example of this is shown in FIG.

[0031] The sensitivity data 8 input to the power storage device command calculation unit 9 is data obtained by calculating the sensitivity of the RoCoF of the generator to the amount of change ΔPBESS in the active power of the power storage device 3 to be controlled. In this embodiment, the sensitivity is defined as dRoCoF / dPBESS.

[0032] Next, a method for calculating dRoCoF / dPBESS will be described with reference to Figures 4(a) and 4(b) and Figures 5(a) and 5(b).

[0033] Figures 4(a) and 4(b) are explanatory diagrams of the first calculation method of the sensitivity information dRoCoF / dPBESS in this embodiment, where the waveform in Figure 4(a) shows the output of the power storage device 3, and the waveform in Figure 4(b) shows the frequency of a generator among multiple generators.

[0034] Figures 5(a) and 5(b) are explanatory diagrams of the second calculation method of the sensitivity information dRoCoF / dPBESS in this embodiment, and show a conceptual diagram of the change in generator frequency when the output of the power storage device 3 is changed in comparison with Figures 4(a) and 4(b).

[0035] For example, as shown in Figures 4(a) and 4(b), consider the case where, in the event of a hypothetical power supply accident, if the active power of the power storage device 3 is not changed, the RoCoF of the generator takes a maximum value of 2.3 [Hz / s].

[0036] In contrast, as shown in Fig. 5(a) and Fig. 5(b), when the power storage device 3 is controlled to ΔP=90 MW at time t_fip, the RoCoF at t_rmax is assumed to decrease to 1.7 [Hz / s]. In this case, the sensitivity |dRoCoF / dPBESS| is calculated as 90 / 0.6=150.

[0037] As described above, FIG. 3 shows an example of the configuration of information indicating postulated accidents in this embodiment, and includes items such as postulated accident case number, monitoring point, and type of postulated accident.

[0038] Next, the frequency change rate calculation unit 9a, the judgment value calculation unit 9b, and the active power control amount calculation unit 9c of the power storage device command calculation unit 9 will be described in accordance with an operation example in this embodiment. Note that, here, the case where the third generator 2C is disconnected from the power grid 1 will be described as an example.

[0039] FIG. 6 shows the behavior of the generator output and frequency in this embodiment.

[0040] As shown in Figure 6, in this embodiment, an example will be described in which, before the third generator 2C is disconnected, the output P1 of the first generator 2A is 250 [MW] and the output P2 of the second generator 2B is 500 [MW], and the RoCoF due to the disconnection of the third generator 2C is -2.3 [Hz / s] for the first generator 2A and +2.2 [Hz / s] for the second generator 2B.

[0041] First, the power storage device command calculation unit 9 and the frequency change rate calculation unit 9a calculate the frequency change rate of the area in which each generator and busbar is located from the rotation speed of the generator or the frequency of the busbar. Here, the RoCoF of the first generator 2A and the second generator 2B are calculated to be -2.3 [Hz / s] and +2.2 [Hz / s], respectively.

[0042] Next, the judgment value calculation unit 9b of the power storage device command calculation unit 9 calculates a judgment value for determining the output direction (power generation or power reception) of the power storage device 3 and determines the output direction of the power storage device 3. In this embodiment, the judgment is made using the product of the absolute value of the deviation width of the RoCoF of each generator from the reference value and the output of the generator before the third generator 2C is disconnected.

[0043] The judgment formula in this embodiment is based on the idea that by controlling the power storage device 3 so as not to disconnect a generator that has a large RoCoF, a high risk of tripping, and a large output, even if a chain of generator trips occurs, the change in supply and demand imbalance when the generator is disconnected is minimized.

[0044] If the RoCoF reference value is set to ±2.0 [Hz / s], the judgment value for the first generator 2A is calculated as |-2.3 + 2.0| x 250 = 75, and the judgment value for the second generator 2B is calculated as |2.2 - 2.0| x 500 = 100.

[0045] In this embodiment, since the judgment value of the second generator 2B is larger, the power storage device 3 is controlled so that the second generator 2B does not disconnect. That is, since the RoCoF of the second generator 2B is positive and the second generator 2B is accelerating, the output direction of the power storage device 3 is controlled to be in a direction that cancels the acceleration of the second generator 2B, that is, to receive power.

[0046] In addition, the active power control amount calculation unit 9c of the power storage device command calculation unit 9 determines the active power output value of the power storage device 3, and the method for determining the magnitude of the active power output value in the active power control amount calculation unit 9c is preferably proportional control in which the absolute value of the deviation range from the RoCoF reference value of the second generator 2B is multiplied by a control gain.

[0047] Furthermore, when there are two or more (plural) power storage devices 3, output commands may be distributed to the multiple power storage devices 3 for control.

[0048] That is, the judgment value calculation unit 9b of the power storage device command calculation unit 9 determines which of the multiple power storage devices 3 to give an output command to based on the sensitivity of the generator to the frequency change rate of the output of the multiple power storage devices 3 connected to the power system 1.

[0049] In this case, it is preferable to give an output command preferentially to a power storage device 3 having a high sensitivity using the sensitivity information dRoCoF / dPBESS. For example, it is possible to adjust the allocation amount of a plurality of power storage devices 3 by multiplying the absolute value of the deviation width from the RoCoF reference value of the second generator 2B by a control gain and then multiplying the result by a correction coefficient according to the sensitivity information dRoCoF / dPBESS.

[0050] In addition, since the positive or negative (direction) of the active power output value has already been determined by the judgment value calculation unit 9b of the power storage device command calculation unit 9, the magnitude of the active power output value multiplied by this positive or negative direction becomes the final output command value of the power storage device 3.

[0051] The above is an explanation of an example of the operation of the frequency change rate calculation unit 9a, the judgment value calculation unit 9b, and the active power control amount calculation unit 9c of the power storage device command calculation unit 9 in this embodiment.

[0052] FIG. 7 shows an example of a display of an output command for the power storage device 3 in this embodiment.

[0053] For example, FIG. 7 shows contingency faults and outputs of the power storage device 3 that have been detected as accidents from the most recent time in the control content table.

[0054] Next, the configuration of the power storage device 3 used in the above-described embodiment will be described with reference to FIG.

[0055] As shown in Fig. 8, the power storage device 3 used in this embodiment is composed of a power conversion device 3a and a power storage device 3b. In the power storage device 3, the voltage at its own end is detected by a voltage sensor 3c, a frequency calculation unit 3d and a RoCoF (rate of change of frequency) calculation unit 3e calculate a frequency and a RoCoF, and the value calculated by the RoCoF (rate of change of frequency) calculation unit 3e is transmitted to an active power command value calculation unit 3f, which controls the power conversion device 3a so that the active power command value transmitted from the control terminal 5 is satisfied, and outputs active power.

[0056] By adopting this embodiment, even if an accident such as a power source failure or system separation occurs in a power system 1 to which a large number of renewable energy power sources are connected, the difference in frequency fluctuation between each generator can be taken into consideration, and the risk of a power outage due to a generator failure can be reduced.

[0057] In this embodiment, the output of the generator before it is disconnected is used for the judgment in the judgment value calculation unit 9b of the power storage device command calculation unit 9. However, the effects of the present invention can be obtained even if the rated capacity of the generator is used instead.

[0058] This is because by controlling the power storage device 3 so that a power source having a large rated capacity generator is not disconnected, it is possible to minimize the decrease in inertia of the power system 1.

[0059] In addition, in this embodiment, the power storage device 3 has been described as an example of a device connected to the power system 1 via a power conversion circuit, but the effects of the present invention can be obtained even if a DC power transmission system having a DC system on the DC side is used instead of the power storage device 3. In this case, it goes without saying that a DC power transmission system command calculation unit is provided instead of the power storage device command calculation unit 9.

[0060] The present invention is not limited to the above-described embodiments, and includes various modified examples. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the configurations described. In addition, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. In addition, it is possible to add, delete, or replace a part of the configuration of each embodiment with another configuration. [Explanation of symbols]

[0061] Reference Signs List: 1...power system, 2A...first generator, 2B...second generator, 2C...third generator, 3...power storage device, 3a...power conversion device, 3b...energy storage device, 3c...voltage sensor, 3d...frequency calculation unit, 3e...RoCoF (rate of change of frequency) calculation unit, 3f...active power command value calculation unit, 4...central processing unit, 5...control terminal, 6...power system data, 7...assumed accident data, 8...sensitivity data, 9...power storage device command calculation unit, 9a...frequency change rate calculation unit, 9b...judgment value calculation unit, 9c...active power control amount calculation unit, 10...control content.

Claims

1. a plurality of generators connected to an electric power system; devices connected to the electric power system via a power conversion circuit; and a central processing unit that receives information from the electric power system, the plurality of generators, and the devices connected to the electric power system via the power conversion circuit, and controls an output of the devices connected to the electric power system via the power conversion circuit based on the information; the central processing unit comprises at least a device command calculation unit connected to the power system via a power conversion circuit, the device command calculation unit connected to the power system via the power conversion circuit comprising: a frequency change rate calculation unit that calculates a frequency change rate at a plurality of points in the power system based on the frequencies of the plurality of generators; a judgment value calculation unit that determines which of the plurality of generators should be operated stably by controlling a device connected to the power system via the power conversion circuit, based on the frequency change rate calculated by the frequency change rate calculation unit, a sensitivity of the frequency change rate, and operation information of the plurality of generators; and an active power control amount calculation unit that calculates an active power output of a device connected to the power system via the power conversion circuit.

2. 2. The power system stabilization system according to claim 1, 2. A power system stabilization system, further comprising a control terminal for transmitting an output from the central processing unit to a device connected to the power system via a power conversion circuit.

3. 3. The power system stabilization system according to claim 1 or 2, The power system stabilization system according to claim 1, wherein the frequency change rate calculation unit calculates the frequency change rate for each of the generators or busbars connected to the power system.

4. A power system stabilization system according to any one of claims 1 to 3, the judgment value calculation unit calculates a judgment value using the frequency change rate calculated in the frequency change rate calculation unit and a rated capacity of the generator connected to the power system or an output of the generator, and determines a direction of power generation or power reception of a device connected to the power system via a power conversion circuit.

5. A power system stabilization system according to any one of claims 1 to 3, a power system stabilization system including a plurality of devices connected to the power system via a power conversion circuit, and the judgment value calculation unit determines, based on sensitivity to the rate of change of frequency of the generator with respect to outputs of the devices connected to the plurality of power systems via a power conversion circuit, to which device connected to the power system via a power conversion circuit an output command should be given, among the devices connected to the plurality of power systems via the power conversion circuit.

6. A power system stabilization system according to any one of claims 1 to 5, The power system stabilization system according to claim 1, wherein the device connected to the power system via a power conversion circuit is a power storage device having a power storage device on a DC side, and the device command calculation unit connected to the power system via the power conversion circuit is a power storage device command calculation unit.

7. A power system stabilization system according to any one of claims 1 to 5, The power system stabilization system is characterized in that the device connected to the power system via a power conversion circuit is a DC power transmission system having a DC system on the DC side, and the device command calculation unit connected to the power system via the power conversion circuit is a DC power transmission system command calculation unit.

8. A power storage device connected to a power grid and equipped with a power storage device on a DC side, 7. The power storage device according to claim 6, wherein the power storage device determines an active power output based on an active power command given from the power system stabilization system according to claim 6.

9. The power storage device according to claim 8, The power storage device is characterized in that it determines an active power output value based on a rate of change of frequency of the generator connected to the power grid.

10. The power storage device according to claim 8 or 9, The power storage device is characterized in that it is composed of a power conversion device and a power storage device, detects the voltage at its own end with a voltage sensor, calculates the frequency and the frequency change rate in a frequency calculation unit and a frequency change rate calculation unit, and controls the power conversion device so that the effective power command value is equal to the effective power command value sent from a control terminal in an effective power command value calculation unit, thereby outputting effective power.

11. A DC transmission system connected to a power grid and having a DC system on a DC side, 8. The DC transmission system, wherein the DC transmission system determines an active power output based on an active power command given from the power system stabilization system according to claim 7.

12. 12. The DC power transmission system according to claim 11, The DC transmission system is characterized in that it determines an active power output value based on a frequency change rate of the generator connected to the power grid.

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