KR102311779B1 - Control system of frequency and Method for controlling frequency - Google Patents

Abstract

A frequency control system according to an embodiment of the present invention includes a power storage system including a plurality of unit storage devices and connected to a grid; and receiving frequency value information of the grid and comparing it with a reference value to determine a power exchange direction between the grid and the power storage system, wherein the SOC of each unit storage device constituting the power storage device is a preset SOC upper limit value a control unit for charging each unit storage device to 100% SOC or discharging it to 0% SOC when it is out of a range between the lower limit value; includes

Description

Control system of frequency and Method for controlling frequency

The present invention relates to a frequency control system and a frequency control method using the same for limiting a change in frequency according to a change in power consumption appearing in a grid.

An energy storage system (ESS) can increase energy efficiency by storing electrical energy produced during light loads, such as late at night, and supplying electrical energy at times when electrical energy consumption is high, such as during daytime peak hours. Such an energy storage device may be used in various ways, such as frequency adjustment of a grid, peak reduction, and the like.

The amount of electrical energy consumed by the loads connected to the grid is not fixed, but may change continuously, and may also vary depending on the circumstances of the generator that produces and supplies the electrical energy. is not always fixed.

In order to limit the frequency fluctuations of the grid due to the fluctuations in the amount of generation that change every moment or the fluctuations in the electricity consumption of the load, there is a method of adjusting the frequency of the grid by adjusting the generation of the power plant according to the change in the amount of consumed electric energy. Although it is commonly used, there is a limit to this frequency control method alone.

That is, in the case of general power plants (ex: hydroelectric power plant, thermal power plant, etc.), the efficiency of the detector is different for each power plant, so there may be a problem that the power generation efficiency of the power plant is deteriorated when the output is adjusted, and a power plant that produces new and renewable energy In the case of (ex: wind power generation, a power plant using solar power/solar power generation), it may be difficult to control the amount of power generation in that the natural environment is not always provided under constant conditions.

Therefore, there is a need to develop a frequency control system capable of efficiently controlling the frequency of the grid without limitation due to the circumstances of the power plant.

The present invention has been devised in consideration of the above technical problem, and has an object to provide a frequency control system capable of efficiently controlling the frequency of a grid using an energy storage system, and in particular, configuring an energy storage system In the case where a portion of each unit storage device does not operate normally, an object of the present invention is to ensure that a reserve power storage amount of the energy storage system can be sufficiently secured.

However, the technical problems to be solved by the present invention are not limited to the above-described problems, and other problems not mentioned will be clearly understood by those skilled in the art from the description of the invention described below.

A frequency control system according to an embodiment of the present invention for solving the above-described technical problem includes a power storage system including a plurality of unit storage devices and connected to a grid; and receiving frequency value information of the grid and comparing it with a reference value to determine a power exchange direction between the grid and the power storage system, wherein the SOC of each unit storage device constituting the power storage device is a preset SOC upper limit value A frequency control system comprising a; when out of the range between the lower limit and the control unit to charge each unit storage device to 100% SOC or to discharge to 0% SOC;

The control unit causes the power storage system to supply power to the grid through discharging when the frequency value of the grid exceeds a reference value, and charges the power storage system when the frequency value of the grid does not meet the reference value power can be supplied from the grid.

The controller is configured to charge each unit storage device to 100% SOC when the SOC of each unit storage device exceeds the SOC upper limit value, and the SOC of each unit storage device is less than the SOC lower limit value , it is possible to discharge each unit storage device to 0% SOC.

The controller may change the SOC upper limit value and the SOC lower limit value according to a ratio of the unit storage devices in an online state among the unit storage devices.

When a unit storage device in an offline state is generated among the unit storage devices, the controller may decrease the upper limit value of the SOC and increase the lower limit of the SOC as the ratio of the unit storage devices that are offline increases.

The controller may change the SOC upper limit value and the SOC lower limit value in consideration of the degree of degradation of the unit storage devices.

The controller may decrease the upper limit value of the SOC and increase the lower limit of the SOC as the deterioration degree of the unit storage devices increases.

On the other hand, the frequency control method according to an embodiment of the present invention for solving the above technical problem, (S1) receiving the frequency value information of the grid; (S2) comparing the received frequency value information with a reference value; (S3) Determine the power exchange direction between the grid and the power storage system, but when the SOC of each unit storage device constituting the power storage system is out of the range between the preset SOC upper limit value and the lower limit value, each and controlling the unit storage device to be charged to 100% SOC or discharged to 0% SOC.

In the step (S3), when an offline unit storage device is generated among the unit storage devices, decreasing the SOC upper limit value and increasing the SOC lower limit value as the number of offline unit storage devices increases may include.

The step (S3) may include decreasing the upper limit value of the SOC and decreasing the lower limit of the SOC as the degree of degradation of the unit storage devices increases.

According to one aspect of the present invention, it is possible to more efficiently control the grid frequency regardless of the circumstances of the power plant or the load.

According to another aspect of the present invention, even if a portion of the unit storage device constituting the energy storage device cannot be operated normally, it is possible to stably control the frequency.

The following drawings attached to this specification illustrate preferred embodiments of the present invention, and serve to further understand the technical spirit of the present invention together with the detailed description of the present invention to be described later, so the present invention is described in such drawings should not be construed as being limited only to
1 is a diagram schematically showing the configuration of a frequency control system according to an embodiment of the present invention.
FIG. 2 is a graph schematically illustrating a change in SOC of a power storage system that appears in a grid frequency control process.
3 is a diagram illustrating a case in which some unit storage devices constituting the energy storage system applied to the present invention are dropped off.
4 is a graph illustrating adjustment of SOC upper and lower limits of a unit storage device when a part of the unit storage device is partially dropped.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, the terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor should properly understand the concept of the term in order to best describe his invention. Based on the principle that it can be defined, it should be interpreted as meaning and concept consistent with the technical idea of the present invention. Accordingly, the embodiments described in this specification and the configurations shown in the drawings are only some of the most preferred embodiments of the present invention and do not represent all the technical spirit of the present invention, so at the time of the present application, various It should be understood that there may be equivalents and variations.

With reference to FIG. 1, the overall configuration of the frequency control system according to an embodiment of the present invention will be described.

1 is a diagram schematically showing the configuration of a frequency control system according to an embodiment of the present invention.

Referring to FIG. 1 , the frequency control system according to an embodiment of the present invention is a power storage system 10 connected to a grid G to perform charging or discharging, and a grid G and power storage system 10 . It is connected between the control unit 20 for controlling the charging and discharging of the power storage system (10).

The grid G refers to a power grid that connects a power plant P that produces electric energy and a load R corresponding to various electric devices consuming electric power.

The power storage system 10 is capable of storing or discharging power through charging and discharging, and supplies insufficient power to the grid G through discharging in order to stabilize the frequency fluctuations generated according to the situation of the grid G. The surplus power remaining in the grid (G) is brought by supplying or charging.

Specifically, the frequency of the grid G has a statutory reference value (ex: 60Hz), and this frequency value increases when the power of the grid G is in a surplus state, and on the contrary decreases when the power is insufficient. will do

Accordingly, the power storage system 10 applied to the present invention stabilizes the frequency of the grid G so as not to deviate from the reference value by supplying power to the grid G, or by taking power from the grid G on the contrary.

The control unit 20 is connected between the grid G and the power storage system 10, and the power storage system 10 according to the frequency of the grid G and the state of charge (SOC) of the power storage system 10 . control the charging or discharging of

In order to perform this function, the control unit 20 may include a frequency measurement unit 21 and a charge/discharge determination unit 22 .

In this case, the frequency measuring unit 21 measures a frequency that varies from moment to moment according to a change in the power situation of the grid G, or a frequency transmitted from a separate measuring device included in the grid G to measure the frequency It receives the information and serves to transmit it to the charge/discharge determination unit 22 .

The charge/discharge determining unit 22 determines whether to perform charging or discharging of the power storage system 10 by comparing the obtained frequency information, ie, a frequency value, with a pre-stored reference value. That is, when the frequency of the grid G is higher than the reference value, the charge/discharge determining unit 22 charges the power storage system 10 to bring the surplus power of the grid G, and vice versa. When the frequency of is lower than the reference value, by discharging the power storage system 10 to supplement the insufficient power in the grid G, the frequency can be controlled.

On the other hand, in controlling the charging/discharging operation of the power storage device 10, the charge/discharge determining unit 22 determines whether to charge or discharge in response to a change in frequency within a predetermined SOC range, but outside the predetermined SOC range. In this case, the control is performed so that only the charging or discharging operation is continuously performed regardless of the frequency value.

Referring to FIG. 2 , it can be seen that charging and discharging patterns within a predetermined SOC range and outside the predetermined SOC range are different from each other.

Specifically, the charge/discharge determining unit 22 is charged or discharged in response to a frequency change of the grid G in a normal operation range in which the SOC of the power storage system 10 is maintained within a predetermined range. However, in an abnormal operation range in which the SOC of the power storage system 10 is out of a certain range, the grid G is continuously charged or discharged regardless of the change in frequency. Stabilize.

That is, when the SOC of the power storage system 10 exceeds the upper limit of the SOC, the charge/discharge determination unit 22 recognizes that the degree of power surplus of the grid G is large, and the SOC 100% regardless of the frequency The surplus power of the grid (G) is brought through continuous charging until it reaches The power storage system 10 is controlled to stabilize the grid G through continuous discharge until

In FIG. 2 of the present application, the case in which the SOC of the power storage system 10 is within the range of 40% to 60% is shown as a normal range, but this is only an example, and the upper limit value and the lower limit value may be determined differently if necessary. is of course

Referring to FIGS. 1 and 3 together, the control unit 20 applied to the frequency control system according to an embodiment of the present invention may further include a limit value adjusting unit 23, such a limit value adjusting unit 23 can make the normal operating range narrower in proportion to the number of unit storage devices 11 in an offline state among the individual unit storage devices 11 constituting the power storage system 10 . have.

That is, referring to FIG. 4 , the limit value adjusting unit 23 decreases the upper limit of the SOC of each unit storage device 11 as the number of the unit storage devices 11 in the offline state increases, and vice versa. By increasing the lower limit, the normal operating range becomes narrower.

For example, in the case where there are 10 unit storage devices 11 constituting the power storage system 10, one of the unit storage devices 11 goes offline due to a failure or diagnosis. Let's assume

In this case, in the abnormal operating range, the total amount of energy received or supplied through the 10 unit storage devices 11 and the total amount of energy to be received or supplied through the 9 unit storage devices 11 should be the same, so The upper limit of the SOC is made small in proportion to the number of the placed unit storage devices 11 , and the lower limit of the SOC is increased to narrow the normal operating range.

SOC upper limit and SOC lower limit according to the number of unit storage devices 11 in an online state among all unit storage devices 11 may be calculated according to the following equations:

(Equation 1):

Total Energyⅹ(on-line racks/total racks)ⅹ(1-high SOC limit/100)=required Powerⅹrequired backup time

(Equation 2):

Total Energyⅹ(on-line racks/total racks)ⅹLow SOC limit/100=required Powerⅹrequired backup time

- Total Energy means the total amount of energy of the power storage system 10 when all unit storage devices 11 are online and all are fully charged

- total rack means the total number of unit storage devices (11)

- On-line racks means the number of unit storage devices in a state in which charging or discharging is possible among all unit storage devices 11

- required powerⅹrequired backup time means the total amount of energy that the power storage system 10 must accept or supply through charging or discharging in an abnormal operating range (unit: MWh)

- High SOC limit means the SOC upper limit of the normal operating range (unit: %)

- Low SOC limit means the SOC lower limit of the normal operating range (unit: %)

In the power storage system having the specifications shown in Table 1 below, the SOC upper and lower limits calculated according to Equations 1 and 2 are shown in Table 2.

Item Value Unit Required Backup time (bidirectional) 0.5 hr Required Power One MW Total Energy 2 MWh No. of Total Rack 20 EA

No. of offline racks (EA) High SOC Limit(%) Low SOC Limit(%) 0 75 25 One 74 26 2 72 28 3 71 29 4 69 31 5 67 33 6 64 36 7 62 38 8 58 42 9 55 45 10 50 50

** SOC values correspond to approximations calculated by rounding to one decimal place

Referring to Table 2, when the number of unit storage devices 11 in the offline state reaches 10, the SOC upper limit value and the SOC lower limit value have the same value. Since it means that the normal operating range does not exist at all, in this case, it is necessary to check the entire system.

On the other hand, in the frequency control system according to an embodiment of the present invention, in addition to whether the unit storage device 11 in an offline state is generated, the SOC upper limit value and the SOC lower limit value may be additionally determined in consideration of the degree of degradation of the unit storage devices 11 . have.

As such, when the SOC upper limit value and the SOC lower limit value are determined in consideration of the degree of degradation of the unit storage device 11 in addition to whether the unit storage device 11 in the offline state is generated, the degradation degree of the unit storage device 11 is increased. Since the normal operating range should be set narrower the more, the limit value adjusting unit 23 decreases the upper limit of the SOC as the degree of degradation of the unit storage devices 11 increases, and on the contrary, the lower limit of the SOC increases as the degree of degradation increases.

Here, the degree of degradation can be defined in various ways, for example, it may mean an average value of the degree of degradation of all unit storage devices 11 . The degree of degradation may serve as a representative value.

In this way, when the normal operating range is determined in consideration of the ratio of the unit storage device 11 in the online state and the degree of degradation at the same time, more efficient and stable system operation is possible.

Next, a frequency adjustment method according to an embodiment of the present invention will be described.

A frequency adjustment method according to an embodiment of the present invention, as using the frequency adjustment system according to an embodiment of the present invention as described above, comprises the steps of: (S1) receiving frequency value information of a grid; (S2) comparing the received frequency value information with a preset reference value; (S3) Determine the power exchange direction between the grid and the power storage system according to the comparison result, but the SOC of each unit storage device constituting the power storage system is a range between the SOC upper limit value and the lower limit value, that is, the normal operating range and charging each unit storage device to 100% SOC or discharging to 0% SOC when it is out of the range.

On the other hand, in this frequency control method, in the step (S3), when an offline unit storage device is generated among the unit storage devices, the SOC upper value is reduced as the number of offline unit storage devices increases, and vice versa. The SOC lower limit may comprise increasing.

In addition, the step (S3) may further include reducing the upper limit of the SOC and lowering the lower limit of the SOC as the degree of degradation of the unit storage devices increases.

In the above, although the present invention has been described with reference to limited embodiments and drawings, the present invention is not limited thereto and will be described below with the technical idea of the present invention by those of ordinary skill in the art to which the present invention pertains. Of course, various modifications and variations are possible within the scope of equivalents of the claims.

P: power plant
G: grid
R: load
10: power storage system
11: Unit storage
20: control unit
21: frequency measurement unit
22: charge/discharge determining unit
23: limit value adjustment unit

Claims (10)

a power storage system including a plurality of unit storage devices and connected to a grid; and
a control unit for controlling charging and discharging of the power storage system;
includes,
The control unit is
Receive frequency value information of the grid and compare it with a reference value to determine a power exchange direction between the grid and the power storage system,
When the SOC of the power storage system is maintained within a preset range, it is determined as a normal operating range and determines whether to charge or discharge the power storage system in response to a change in the frequency of the grid,
When the SOC of each unit storage device constituting the power storage system is out of a preset range, it is determined as an abnormal operating range in which the degree of power surplus or power shortage of the grid is abnormal and is independent of the change in the frequency. A frequency control system for stabilizing the grid by continuously charging each unit storage device to 100% SOC or continuously discharging each unit storage device to 0% SOC regardless of the frequency change. According to claim 1,
The control unit is
When the frequency value of the grid exceeds the reference value, the power storage system is charged to bring surplus power from the grid, and when the frequency value of the grid does not reach the reference value, the power storage system is discharged to provide insufficient power to the grid. A frequency control system that allows you to replenish power. According to claim 1,
The control unit is
When the SOC of each unit storage device exceeds the SOC upper limit value, each unit storage device is charged up to 100% SOC, and when the SOC of each unit storage device appears less than the SOC lower limit value, the Frequency control system, characterized in that each unit storage device is discharged to 0% SOC. According to claim 1,
The control unit is
A frequency control system for changing the SOC upper limit value and the SOC lower limit value according to a ratio of the unit storage devices in an online state among the unit storage devices. 5. The method of claim 4,
The control unit is
A frequency control system for decreasing the upper limit value of the SOC and increasing the lower limit value of the SOC when a unit storage device in an offline state is generated among the unit storage devices, as the ratio of the offline unit storage devices increases. 6. The method of claim 5,
The control unit is
A frequency control system for changing the SOC upper limit value and the SOC lower limit value in consideration of the degree of degradation of the unit storage devices. 7. The method of claim 6,
The control unit is
A frequency control system for decreasing the upper limit value of the SOC and increasing the lower limit value of the SOC as the degree of degradation of the unit storage devices increases. A frequency control method for adjusting the frequency of a grid using the frequency control system according to any one of claims 1 to 7,
(S1) receiving frequency value information of the grid;
(S2) comparing the received frequency value information with a reference value;
(S3) determine the power exchange direction between the grid and the power storage system, but when the SOC of each unit storage device constituting the power storage system is out of the range between the preset SOC upper limit value and the lower limit value, each controlling the unit storage device to be charged to 100% SOC or discharged to 0% SOC;
A frequency control method comprising a. 9. The method of claim 8,
The step (S3) is,
and decreasing the SOC upper limit value and increasing the SOC lower limit value as the number of offline unit storage devices increases when an offline unit storage device is generated among the unit storage devices. 10. The method of claim 9,
The step (S3) is,
and decreasing the SOC upper limit and decreasing the SOC lower limit as the degradation degree of the unit storage devices increases.

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