KR20180110513A - 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 with a grid; And determining a direction of power exchange between the grid and the power storage system by comparing the grid frequency with a reference value, wherein the SOC of each of the unit storage devices constituting the power storage device is set to a predetermined SOC upper limit value And to discharge the unit storage device to the 100% SOC or discharge to 0% SOC when the unit storage device is out of the range between the upper limit value and the lower limit value. .

Description

[0001] The present invention relates to a frequency control system and a frequency control method,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency control system for restricting a frequency change due to a variation in power consumption in a grid and a frequency control method using the same.

The energy storage system (ESS) can store energy generated by the light load such as late night, and it can increase the energy efficiency by supplying electric energy at a time when electric energy consumption such as the peak time is large. Such an energy storage device can be variously used for adjusting the frequency of the grid, reducing the peak, and the like.

Since the amount of electric energy consumed by the loads connected to the grid is not fixed but can be continuously varied and can also be varied depending on the situation of the generator side that generates and supplies electric energy, Is not always fixed.

In order to limit the fluctuation of the grid frequency due to fluctuations in the power generation amount varying from time to time or fluctuations in the power consumption of the load, a method of adjusting the grid frequency by adjusting the power generation amount of the power plant according to the change in the amount of consumed electric energy However, such a frequency adjustment method is limited.

In other words, in the case of general power plants (ex: hydroelectric power plants, thermal power plants, etc.), there may be a problem that the efficiency of the power plant is deteriorated when the power of the detector is different from each other, (eg, a power plant that uses wind power, solar power, or solar power), the natural environment may not always be provided under certain conditions, which may make it difficult to control the power generation.

Therefore, it is required to develop a frequency control system capable of efficiently controlling the frequency of the grid without being limited by the circumstances of the power plant.

It is an object of the present invention to provide a frequency control system capable of efficiently controlling the frequency of a grid using an energy storage system in consideration of the above technical problems, It is an object of the present invention that a reserve power storage amount of an energy storage system can be sufficiently secured in the case where a part of individual unit storage devices that do not operate normally can not be normally operated.

It is to be understood, however, that the technical subject matter of the present invention is not limited to the above-mentioned problems, and other matters not mentioned can be clearly understood by those skilled in the art from the description of the invention described below.

According to an aspect of the present invention, there is provided a frequency control system including: a power storage system including a plurality of unit storage devices and connected to a grid; And determining a direction of power exchange between the grid and the power storage system by comparing the grid frequency with a reference value, wherein the SOC of each of the unit storage devices constituting the power storage device is set to a predetermined SOC upper limit value And to discharge the unit storage device to the 100% SOC or discharge to 0% SOC when the unit storage device is out of the range between the upper limit value and the lower limit value.

Wherein the controller is configured to cause the power storage system to supply power to the grid through a discharge if the frequency value of the grid exceeds a reference value and if the frequency value of the grid falls below a reference value, To receive power from the grid.

Wherein the control unit causes each of the unit storage devices to be charged to 100% SOC when the SOC of each of the unit storage devices exceeds the SOC upper limit value, and if the SOC of each of the unit storage devices is less than the SOC lower limit value The respective unit storage devices may be discharged to 0% SOC.

The controller may change the SOC upper limit value and the SOC lower limit value according to the ratio of the unit storage devices that are in the on-line state among the unit storage devices.

The controller may decrease the SOC upper limit value and increase the SOC lower limit value when the offline storage unit is generated, when the offline storage unit is generated.

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

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

According to another aspect of the present invention, there is provided a frequency control method including: (S1) receiving frequency value information of a grid; (S2) comparing the received frequency value information with a reference value; (S3) determines the direction of power exchange between the grid and the power storage system, and if the SOC of each unit storage device constituting the power storage system deviates from a preset upper limit SOC and a lower limit value, And controlling the unit storage device to be charged to 100% SOC or discharged to 0% SOC.

The step (S3) may include decreasing the SOC upper limit value and increasing the SOC lower limit value as the number of offline unit storage devices is increased, when a unit storage device in an offline state is generated among the unit storage devices . ≪ / RTI >

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

According to an aspect of the present invention, the grid frequency can be controlled more efficiently regardless of the conditions of the power plant or the load.

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

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and, together with the description of the invention given below, serve to further the understanding of the technical idea of the invention. And should not be construed as limiting.
1 is a view schematically showing a configuration of a frequency control system according to an embodiment of the present invention.
FIG. 2 is a graph schematically showing changes in the SOC of the power storage system during the frequency control process of the grid.
3 is a view showing a case where some unit storage devices constituting an energy storage system applied to the present invention are dropped.
4 is a graph showing the adjustment of the SOC upper limit and the lower limit value of the unit storage device when some unit storage devices are partially removed.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor should appropriately interpret the concepts of the terms appropriately It should be interpreted in accordance with the meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined. Therefore, the embodiments described in the present 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 ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

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

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

1, a frequency control system according to an embodiment of the present invention includes a power storage system 10 connected to a grid G to perform charging or discharging, a grid G and a power storage system 10, And a control unit 20 connected between the power storage system 10 and the power storage system 10 to control charging and discharging of the power storage system 10.

The grid G refers to a power plant P for generating electrical energy and a power network for connecting a load R corresponding to various electric devices consuming power.

The power storage system 10 is capable of storing or discharging electric power through charging and discharging. In order to stabilize the fluctuation of the frequency generated according to the situation of the grid G, Or surplus power remaining on the grid (G) through charging.

Specifically, the frequency of the grid G is set to a reference value (ex: 60 Hz). The frequency value increases when the power of the grid G is surplus. On the contrary, when the power of the grid G is insufficient, .

Therefore, the power storage system 10 according 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 conversely bringing power from the grid G.

The control unit 20 is connected between the grid G and the power storage system 10 and controls the power storage system 10 according to the frequency of the grid G and the state of charge of the power storage system 10. [ Charge or discharge of the battery.

In order to perform such a 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 may measure the frequency varying in time according to the power situation change of the grid G, or may measure the frequency transmitted from the separate measuring apparatus included in the grid G, And transmits the information to the charge / discharge determination unit 22.

The charge / discharge determination unit 22 compares the obtained frequency information, that is, the frequency value, with a previously stored reference value, and determines whether charging or discharging of the power storage system 10 is to be performed. That is, when the frequency of the grid G is higher than the reference value, the charge / discharge determination unit 22 charges the power storage system 10 to bring the surplus power of the grid G, The power storage system 10 is discharged to supplement the insufficient power to the grid G, thereby making it possible to control the frequency.

The charge / discharge determination unit 22 determines whether charging or discharging is to be performed in response to a frequency variation within a predetermined SOC range in controlling the charge / discharge operation of the power storage device 10, , Only the charging or discharging operation is continuously performed irrespective of the frequency value.

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

Specifically, the charge / discharge determination unit 22 determines the charging / discharging state 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 frequency change, Stabilize.

That is, when the SOC of the power storage system 10 exceeds the SOC upper limit value, the charge / discharge determination unit 22 recognizes that the power surplus of the grid G is large, and thus the SOC 100% When the SOC falls below the lower limit value, it recognizes that the degree of the power shortage of the grid G is large, so that the SOC is 0% regardless of the frequency, And controls the power storage system 10 to stabilize the grid G through sustained discharge until the grid G is stabilized.

2, the case where 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 merely an example, and the upper limit value and the lower limit value can be determined as necessary Of course.

1 and 3, the control unit 20, which is applied to the frequency control system according to the embodiment of the present invention, may further include a threshold value adjustment unit 23. The threshold value adjustment unit 23, The normal operation range can be narrowed in proportion to the number of unit storage devices 11 in the off-line state among the individual unit storage devices 11 constituting the power storage system 10 have.

4, the threshold value adjuster 23 decreases the SOC upper limit value of each unit storage device 11 as the number of the unit storage devices 11 in the off-line state increases, while the SOC The lower limit value is increased to make the normal operating range narrower.

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

In this case, in the abnormal operating range, the total amount of energy received or supplied through the ten unit storage devices 11 and the total amount of energy to be received or supplied through the nine unit storage devices 11 should be the same, The SOC upper limit value should be decreased in proportion to the number of unit storage devices 11 placed, and conversely, the SOC lower limit value should be increased to set the normal operation range narrow.

The SOC upper limit value and the SOC lower limit value according to the number of the unit storage devices 11 that are in the on-line state among the entire unit storage devices 11 can be calculated according to the following equations, respectively:

(Formula 1):

Total Energy ⅹ (1-high SOC limit / 100) = required Powerⅹrequired backup time

(Formula 2):

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

- Total Energy means the total amount of energy that the power storage system 10 has when all of the unit storage devices 11 are on-line and all are fully charged.

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

- on-line racks refers to the number of unit storage devices in the state of being able to be charged or discharged among all unit storage devices (11)

- required power minrequired backup time is the total amount of energy that the power storage system 10 must accept or supply through charging or discharging in the unusual operating range (in MWh)

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

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

Table 2 shows the SOC upper and lower limit values calculated according to Equations 1 and 2 in the power storage system having the specifications as shown in Table 1 below.

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 off to the first decimal place

As shown in Table 2, when the number of the unit storage devices 11 in an off-line state reaches 10, the SOC upper limit value and the SOC lower limit value become equal to each other. This means that charging / discharging of the power storage system 10 is performed according to the frequency It means that there is no normal operating range at all, and in this case, it is considered that the whole system needs to be checked.

Meanwhile, the frequency control system according to an embodiment of the present invention may determine the SOC upper limit value and the SOC lower limit value in addition to the occurrence of the off-line unit storage device 11 in addition to the degradation degree of the unit storage devices 11 have.

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 or not the unit storage device 11 in an off-line state is generated, the degradation degree of the unit storage devices 11 increases The threshold value adjusting unit 23 decreases the SOC upper limit value as the degree of degradation of the unit storage devices 11 increases and conversely increases the SOC lower limit value as the degree of degradation increases.

Here, the degree of degradation may be variously defined, for example, may mean an average value of degrees of degradation of all unit storage devices 11, or may be different from that of the unit storage devices 11 having the highest degree of degradation The degree of degradation may serve as a representative value.

In this way, when the normal operating range is determined by simultaneously considering the rate and degradation degree of the unit storage device 11 in the on-line state, a more efficient and stable system operation becomes possible.

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

The frequency adjustment method according to an embodiment of the present invention uses the frequency adjustment system according to an embodiment of the present invention as described above, including: (S1) receiving frequency value information of a grid; (S2) comparing the received frequency value information with a preset reference value; (S3) The direction of power exchange between the grid and the power storage system is determined according to the result of the comparison. If the SOC of each unit storage device constituting the power storage system is within the range between the upper limit SOC and the lower limit value, The unit storage device is charged to 100% SOC, or discharged to 0% SOC.

Meanwhile, in the frequency control method, when the unit storage device is in the off-line state among the unit storage devices, the SOC value is decreased as the number of offline unit storage devices increases, And increasing the SOC lower limit value.

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

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not to be limited to the details thereof and that various changes and modifications will be apparent to those skilled in the art. And various modifications and variations are possible within the scope of the appended claims.

P: Power station
G: Grid
R: Load
10: Power storage system
11: Unit storage device
20:
21: Frequency measurement unit
22: charge / discharge determination unit
23:

Claims (10)

A power storage system including a plurality of unit storage devices and connected with a grid; And
And a controller for receiving the 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 set to a preset SOC upper limit value And to discharge the unit storage devices to the 100% SOC or to 0% SOC when the unit storage device is out of the range between the lower limit values.
. The method according to claim 1,
Wherein,
Wherein the power storage system is adapted to supply power to the grid through a discharge if the frequency value of the grid exceeds a reference value, and wherein when the frequency value of the grid falls below a reference value, A frequency control system for receiving power. The method according to claim 1,
Wherein,
Wherein when the SOC of each unit storage device exceeds the SOC upper limit value, the unit storage device is caused to be charged to 100% SOC, and if the SOC of each unit storage device is less than the SOC lower limit value, So that each unit storage device is discharged to 0% SOC. The method according to claim 1,
Wherein,
Wherein the SOC upper limit value and the SOC lower limit value are changed according to the ratio of the unit storage devices that are on-line among the unit storage devices. 5. The method of claim 4,
Wherein,
And decreasing the SOC upper limit value and increasing the SOC lower limit value as the proportion of the offline unit storage device increases when a unit storage device that is offline is generated among the unit storage devices. 6. The method of claim 5,
Wherein,
Wherein the SOC upper limit value and the SOC lower limit value are changed in consideration of the degradation degree of the unit storage devices. The method according to claim 6,
Wherein,
And decreasing the SOC upper limit value and increasing the SOC lower limit value as the degree of degradation of the unit storage devices increases. (S1) receiving frequency value information of the grid;
(S2) comparing the received frequency value information with a reference value;
(S3) determines the direction of power exchange between the grid and the power storage system, and if the SOC of each unit storage device constituting the power storage system deviates from a preset upper limit SOC and a lower limit value, Controlling the unit storage device to be charged to 100% SOC or to be discharged to 0% SOC;
/ RTI > 9. The method of claim 8,
The step (S3)
And decreasing the SOC upper limit value and increasing the SOC lower limit value as the number of the offline unit storage devices increases, when a unit storage device in an offline state is generated among the unit storage devices. 10. The method of claim 9,
The step (S3)
And decreasing the SOC upper limit value and decreasing the SOC lower limit value as the degree of degradation of the unit storage devices increases.

Images