KR101277303B1 - Microgrid system - Google Patents

Abstract

PURPOSE: A microgrid system is provided to perform stable system operation by controlling a cooperation of first and second energy control devices. CONSTITUTION: A first energy storage device(10) is operated in an output control mode. A second energy storage device(20) is operated in the output control mode. The second energy storage device is connected between the first energy storage device and a load(30). The first energy storage device comprises a battery energy storage system (BESS). The second energy storage device comprises a super-capacitor. [Reference numerals] (40) First filter; (50) Second filter

Description

Microgrid System {MICROGRID SYSTEM}

The present invention relates to a microgrid system, and to a microgrid system that can increase the reliability and stability of the system while reducing the burden on the system by adjusting the cooperative control of the two energy storage devices according to the connection with the system. .

Microgrid is a small power system that can be separated from the main system in the event of serious accidents such as ground and short-circuit accidents, large-scale generator dropouts, and can maintain continuous power supply to the load by using only microgrid distributed power supply. Microgrid is composed of distributed power supply, energy storage device and load. Since renewable energy sources inside the microgrid are highly variable in output, a stable power supply strategy is required to operate the microgrid.

As a control method of the distributed power source, there are a frequency / voltage control mode, a constant power mode, and a droop control mode in the same principle as the control of conventional thermal power generation.

The frequency / voltage control mode is a method of controlling the output while keeping the set frequency and voltage constant. It is suitable when a single distributed power supply is operated in the system, and has the ability to meet the total demand of the microgrid internal load. do. The constant output mode is a method of controlling the output to a value commanded by the microgrid energy management system (μ-EMS) regardless of the frequency and voltage of the system.In a microgrid, a microgas turbine or fuel used for cogeneration power generation is used. It is a control method that the battery mainly adopts. The droop control mode is a method of controlling the same principle as the governor of the existing thermal power generation by giving a slope of the active power and the reactive power value to the frequency variation and the voltage variation.

In the droop control mode, when two or more controllable power supplies are connected, the load sharing ratio of each power supply can be automatically determined according to the droop slope for load fluctuations, thereby preventing the hunting effect and providing a stable distributed power supply. Operation is possible.

The droop control mode can be divided into a feeder flow control mode and a unit power control mode according to the control position. The tidal current control mode is a method of controlling the tidal current of the front line of the distributed power supply for the frequency variation and the voltage variation, and the output control mode is a method of controlling the output of the distributed power supply for the frequency variation and the voltage variation.

Renewable energy sources and active loads inside the microgrid are highly variable and feature large prediction errors. In addition, a stable operation plan is needed when linking with the system and converting to independent operation. In consideration of the characteristics of such a microgrid, as described in Application No. 2007-0094311 (name: control method of a microgrid including a plurality of distributed power sources and energy storage devices), the connection between the main grid and the microgrid is different. An energy storage device with faster output dynamics and charging and discharging than a distributed power source is installed, and the energy storage device participates in frequency adjustment and voltage adjustment through droop control.

In case of tidal current control mode at linkage point, the frequency is changed by droop coefficient when changing to independent operation, and if there is no separate frequency recovery function, it can be kept constant at the changed frequency regardless of load variation. This can improve power quality by minimizing frequency fluctuations against frequent load fluctuations of renewable energy. However, if the load fluctuation exceeds the maximum output of the energy storage device in the grid connection, there is a problem in the absence of a control source responsible for supply and demand balance. In addition, the output control mode at the connection point has a problem that the utilization of the energy storage device when the grid connection is less.

The present invention is to solve the above problems of the prior art, by adjusting the cooperative control between the two energy storage devices in accordance with the presence or absence of the system, by reducing the burden of the system microgrid that can improve the reliability of the system Provide a system.

As a technical means for achieving the above technical problem, the microgrid system according to an aspect of the present application, is connected between the first energy storage device and the first energy storage device and the load connected to the connection point with the grid Including a second energy storage device, the first energy storage device and the second energy storage device may be operated in an output control mode for outputting power in response to changes in the frequency and voltage of the tidal current.

According to the exemplary embodiment of the present invention, in the period in which the system and the linked operation is converted to the independent operation, the first energy storage device recovers the changed frequency and voltage to the commercial frequency and the commercial voltage when the frequency and voltage change. Frequency / voltage recovery control can be performed.

According to the exemplary embodiment of the present application, when the frequency and the voltage become the commercial frequency and the commercial voltage by the first energy storage device, the output of the second energy storage device may be zero.

According to an embodiment of the present disclosure, a first filter connected to the front end line of the first energy storage device and outputting a first algae filtering value that filters the tidal flow change amount of the front end line to the first energy storage device is provided. It may further include.

According to the exemplary embodiment of the present application, the first energy storage device may output power corresponding to the tidal current filtering value input from the first filter.

According to an embodiment of the present disclosure, a second filter connected to the front end line of the second energy storage device and outputting a second algae filtering value that filters the tidal current change amount of the front end line to the second energy storage device It may further include.

According to the exemplary embodiment of the present application, the second energy storage device may output power corresponding to the second tidal current filtering value input from the second filter.

According to one embodiment of the present application, the second energy storage device is characterized in that the dynamic characteristics are faster than the first energy storage device.

According to the exemplary embodiment of the present disclosure, the first energy storage device may be a battery energy storage system (BESS), and the second energy storage device may be a super capacitor.

According to the above-described problem solving means of the present application, in the embodiment of the present application by cooperatively controlling the first and second energy control device by reflecting the change amount of the tidal flow, it is possible to reduce the burden on the system due to frequent output fluctuations of renewable energy The microgrid system can be operated stably during the communication delay of the energy management system (μ-EMS).

In addition, the frequency and voltage recovery control is performed by the first energy storage device in the section Scenario2 and the independent operation section Scenario3 converted from the grid connection to the independent operation, so that the frequency and voltage are increased within the available time of the second energy storage device. Can be quickly recovered to the commercial frequency and commercial voltage.

1 is a block diagram of a microgrid system according to an embodiment of the present application.
2 is a diagram illustrating a droop characteristic curve of an energy storage device operated in an output control mode.
3 is a diagram illustrating a droop characteristic curve of an energy storage device operating in an output control mode and performing frequency / voltage recovery control.
4 is a diagram illustrating a droop characteristic curve of an energy storage device operated in an output control mode with reference to an amount of tidal current input from a filter connected to a preceding line.
5 is an exemplary diagram of a local controller of the energy storage device of FIG. 4.
FIG. 6 is a diagram illustrating droop characteristic curves of first and second energy storage devices in a system linkage section scenario1.
FIG. 7 is a diagram illustrating droop characteristic curves of the first and second energy storage devices in a section (scenario2) converted from the grid connection to the independent operation.
FIG. 8 is a diagram illustrating droop characteristic curves of the first and second energy storage devices in the independent operation section scenario3.
FIG. 9 illustrates a simulation result of a control method of a microgrid system when the first energy storage device does not perform frequency / voltage recovery control without the first and second filters in FIG. 1.
FIG. 10 illustrates a simulation result of a control method of the microgrid system of FIG. 1 when the first energy storage device performs frequency / voltage recovery control.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. It should be understood, however, that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In the drawings, the same reference numbers are used throughout the specification to refer to the same or like parts.

Throughout the specification, when a part is referred to as being "connected" to another part, it includes not only "directly connected" but also "electrically connected" with another part in between .

Throughout this specification, when a member is located "on" another member, this includes not only when one member is in contact with another member but also when another member exists between the two members.

Throughout this specification, when an element is referred to as "including " an element, it is understood that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise. The terms "about "," substantially ", etc. used to the extent that they are used throughout the specification are intended to be taken to mean the approximation of the manufacturing and material tolerances inherent in the stated sense, Accurate or absolute numbers are used to help prevent unauthorized exploitation by unauthorized intruders of the referenced disclosure. As used throughout this specification, the term "step to" or "step of" does not mean "step for."

Throughout this specification, the term “combination of these” included in the expression of the makushi form means one or more mixtures or combinations selected from the group consisting of the constituents described in the expression of the makushi form, wherein the constituents It means to include one or more selected from the group consisting of.

In the exemplary embodiment of the present invention, the time when the microgrid is connected to the grid and operated is referred to as "system linkage section (scenario1)", and the time when the microgrid is converted from the connection with the system to independent operation is converted from "system linkage to independent operation". "Scenario2", and the time when the microgrid independently operates is called "independent driving section (scenario3)". More specifically, the section (scenario2) converted to independent operation in the grid connection corresponds to the independent operation section (scenario3), but the microgrid system of the present invention is characterized in that the section (scenario2) converted to independent operation in the grid connection. Therefore, in order to explain this more clearly, embodiments of the present disclosure will be described by dividing the independent driving section into a section (scenario2) and an independent driving section (scenario3) converted from the grid connection to the independent operation.

1 is a block diagram of a microgrid system according to an embodiment of the present application.

As shown in FIG. 1, the microgrid system 100 is connected through a point of common coupling (PCC) with a grid, and the microgrid system 100 is connected with a grid (PCC) and a load ( A first filter connected to at least two energy storage devices 10 and 20 connected between the PLs 30 and a front line of the first energy storage device 10 to filter the amount of change of the algae PFL1. 40 and a second filter 50 connected to the front line of the second energy storage device 20 to filter the amount of change of the tidal current PFL2 and output the filtered amount to the second energy storage device 20.

At the connection point (PCC) between the grid and the microgrid, there is a switch (STS) that can cut off the accident in the event of a grid or microgrid.

The energy storage device has a limited energy density, fast output dynamics, output characteristics according to state of charge (SOC), and self discharge characteristics. In general, the energy storage system is operated to satisfy 100 ~ 20% of SOC range for stable operation. In the embodiment of the present invention, the second energy storage device 20 is characterized by a faster dynamic characteristics than the first energy storage device 10, the first energy storage device 10 may be a battery energy storage system (BESS), The second energy storage device 20 may be a super capacitor (SC).

These two energy storage devices 10 and 20 cooperatively control each other to improve the reliability and stability of the system.

First, the first energy storage device 10 and the second energy storage device 20 is an output control mode (Unit Power Control) for controlling the output in response to the fluctuation of the frequency and voltage of the tidal flow over the entire section (scenario 1 ~ scenario 3) mode), the first energy storage device 10 is the frequency of the tidal current within the available time of the second energy storage device 20 in the section (scenario2) and the independent operation section (scenario3) converted from the grid connection to the independent operation And frequency / voltage recovery control for restoring the voltage to the commercial frequency and the commercial voltage.

However, when the tidal current is input through the first filter 40, the first energy storage device 10 operates in an output control mode that outputs electric power based on the tidal current change amount, and the second energy storage device 20. When the flow rate of change of the tidal current is input through the second filter 50, the operation is performed in an output control mode for outputting power based on the flow rate of tidal flow.

Prior to describing the cooperative control of the first energy storage device and the second energy storage device according to an embodiment of the present application, a basic concept of the operation mode of the energy storage device will be described with reference to FIGS. 2 to 5.

FIG. 2 is a diagram illustrating a droop characteristic curve of an energy storage device operated in an output control mode, and a droop coefficient is represented by Equation 1. FIG.

Where f ₀ is a reference value of frequency, f is a measurement value of frequency, V ₀ is a reference value of voltage, V is a measurement value of voltage, P ₀ is a reference value of active power, and P is a measurement value of active power Q ₀ is the reference value of reactive power, Q is the measured value of reactive power, R _f is the droop coefficient of frequency, R _V is the droop coefficient of voltage, P _max is the maximum value of active power, Q _max Is the maximum value of reactive power, f _max is the maximum value of frequency, f _min is the minimum value of frequency, V _max is the maximum value of voltage, and V _min is the minimum value of voltage.

As shown in FIG. 2, since the frequency is fixed in the system linkage section (scenario1), the output P _ESSO of the energy storage device is fixed at 0 KW and the microgrid energy management system (μ-EMS, not shown). According to the instruction, the output of the energy storage system (P _ESSO ) can be changed.

When the frequency changes from point A to point B in the section (scenario2) and the independent operation section (scenario3) converted from the grid connection to the independent operation, the output of the energy storage device (P _ESSO ) changes from the A point to the B point. do.

3 is a diagram illustrating a droop characteristic curve of an energy storage device operating in an output control mode and performing frequency / voltage recovery control.

In the section (scenario2) and the independent operation section (scenario3) converted from the grid connection to the independent operation, the frequency / voltage recovery control function should be performed to restore the frequency of the microgrid to the commercial frequency.

In the output control mode of FIG. 3, when the frequency of the load changes from fo to f ′, the output P _ESSO of the energy storage device moves from point A to point B. Then, the droop curve is shifted to C through frequency recovery control, and the output of the energy storage device (P _ESSO ) moves from point B to point C, and the frequency returns to f _o, and the output reference value is P _ESSO to P ′ _ESSO. Fluctuates.

4 is a diagram illustrating a droop characteristic curve of an energy storage device operated in an output control mode with reference to a tidal flow change input from a filter connected to a front line, and FIG. 5 is an example of a local controller of the energy storage device of FIG. 4. It is also.

In order to increase the efficiency of the energy storage system, the grid connection section (scenario1) requires a controller that can change the output reference value regardless of the energy management system (μ-EMS) command and frequency variation. Therefore, the energy storage device receives the algae filtering value ΔP _ft from the filters 40 and 50 for filtering the algae change of the preceding line, and moves the droop curve from A to A 'as shown in FIG. 4. The output reference can be changed from P _ESS0 to P ' _ESS0 . That is, the energy storage device using the filter 40, 50 is responsible for the rapid output fluctuations of the tidal flow, it is possible to reduce the burden on the system due to the frequent output fluctuations of renewable energy.

The local controller of the energy storage device may be a controller in which the control value of the filtering value of the tidal current PFL of the front line is added as shown in FIG. 5. The energy storage device using the local generator of FIG. 5 controls the output fluctuation by using the filters 40 and 50 rather than the energy management system (μ-EMS), thereby reducing the microgrid during the communication delay of the energy management system (μ-EMS). Stable operation of the system is possible.

A control method of the microgrid system according to the exemplary embodiment of the present disclosure will be described with reference to FIGS. 6 to 8 based on the basic concept of the operation mode of the energy storage device.

6 to 8 are diagrams illustrating the droop characteristic curves of the first and second energy storage devices in the system linking section (scenario1), the section (scenario2) converted to independent operation in the grid connection, and the independent operation section (scenario3), respectively. .

In the exemplary embodiment of the present application, the first and second energy storage devices 10 and 20 are basically operated in the output control mode, and according to the tidal stream filtering value input through the first and second filters 10 and 20, And outputs of the second energy storage devices 10 and 20 may be changed.

In a section (scenario2) converted from the grid connection to independent operation, the first energy storage device 10 performs frequency / voltage recovery control for restoring the frequency and voltage of the tidal current to the commercial frequency and the commercial voltage.

As shown in FIG. 6, since there is no frequency fluctuation in the system linkage section scenario1, the system is responsible for the fluctuation of the load 30. The droop characteristic curve of the front tidal current of the first energy storage device 10 moves left and right according to the load variation value ΔP _L , and the system is responsible for the variation value of the load. Since the droop characteristic curves of the first and second energy storage devices 10 and 20 are not changed, the first and second energy storage devices 10 and 20 output the set initial values.

As shown in FIG. 7, the frequency varies from f _o to f ′ as the tidal current of the first stage of the first energy storage device 10 disappears in the section 2 converted from the grid connection to independent operation. In this case, the frequency variation value may be expressed as Δf.

The output of the first energy storage device 10, output P _BESSO (A point) changes in a P _BESS1 (B point) and the second energy storage device 20 according to the frequency variation value P _SCO (C point) Change to P _SC1 (point D) to achieve equilibrium point. Here, the fluctuating output P _BESS1 of the first energy storage device 10 may be _expressed as P _FL0 * R _{f _ SC} / (R _{f _ BESS} + R _{f _ SC} ), and the second energy storage device 20 The fluctuating output P _SC1 can be expressed as P _FL0 * R _{f _ BESS} / (R _{f _ BESS} + R _{f _ SC} ).

In addition, the first energy storage device 10 performs frequency / voltage recovery control to recover the frequency and the voltage to the commercial frequency and the commercial voltage in the section (scenario2) converted from the grid connection to the independent operation. When the first energy storage device 10 performs frequency / voltage recovery control and the frequency returns to the commercial frequency, the frequency variation value becomes 0, and the output power of the second energy storage device 20 may be 0 kW. In this case, the output power of the second energy storage device 20 may be a value commanded by the energy management system μ-EMS in addition to zero.

For this reason, in the exemplary embodiment of the present application, the frequency and the voltage may be restored to the commercial frequency and the commercial voltage within the available time of the second energy storage device 20.

As shown in FIG. 8, in the independent operation section scenario3, the first energy storage device 10 operates in an output control mode in which the output power is changed according to the change of the load 30.

6 and 8, the first filter 40 may include a first tidal stream filtering value for filtering tidal currents in a front line of the first energy storage unit 10. 10), the first energy storage device 10 quickly charges or discharges power corresponding to the first tidal stream filtering value. The second filter 50 inputs the second tidal stream filtering value, which filters the tidal flow change amount of the front line of the second energy storage unit 20, to the second energy storage unit 20, and the second energy storage unit 20. ) Rapidly charges or discharges power corresponding to the second tidal current filtering value.

As a result, in the embodiment of the present application, it is possible to reduce the burden on the system due to frequent output fluctuations of the renewable energy in the system linkage section (scenario1), and to stabilize the microgrid system during the communication delay of the energy management system (μ-EMS). Can operate.

In the above, the cooperative control operation method of the first and second energy storage devices 10 and 20 according to the embodiment of the present application described with reference to FIGS. 6 to 8 has been described, and the first and second energy storage devices ( In the cooperative control of 10, 20), the frequency fluctuation value, the load fluctuation value, and the flow change amount can be formulated as shown in Table 1 below.

ΔP _DG Birds
Change
(ΔP _FL ) Load
Change
(ΔP _L ) frequency
Change value (Δf) Primary energy storage device
(BESS) Second energy storage device
(SC) Output control mode
(UPC) Output control mode
(UPC) Scenario 1 0 0 ΔP _L ΔP _L 0 Scenario 2

-ΔP _FL0
0
Δf Scenario 3

0
ΔP _L
Δf

As described above, in the embodiment of the present application, by cooperatively controlling the first and second energy control devices by reflecting the change amount of the tidal current, the burden on the system due to frequent output fluctuations of renewable energy can be reduced, and the energy management system (μ-EMS) The microgrid system can be operated stably during the communication delay of.

In addition, since the first energy storage device performs the frequency / voltage recovery control in the section (scenario2) converted from the grid connection to the independent operation, the frequency and the voltage are rapidly changed to the commercial frequency and the commercial voltage within the available time of the second energy storage device. Can be recovered.

Hereinafter, a result of the simulation of the cooperative control method of the first and second energy storage devices 10 and 20 using the PSCAD / EMTDC program, which is a power system analysis program, will be described. Since the cooperative control method of the first and second energy storage devices 10 and 20 is a control method of the microgrid system according to an exemplary embodiment of the present application, the cooperative control method between the energy storage devices is referred to as a control method of the microgrid system. do.

FIG. 9 illustrates a simulation result of a control method of the microgrid system when the first energy storage device 10 does not perform the frequency / voltage recovery control without the first and second filters in FIG. 1.

Prior to the simulation results, the simulation conditions are as follows.

Rated power (maximum output) of the first and second energy storage devices 10, 20: 50 kW

_-Rated output of distributed power supply (P _DG0 ): 0kW

-Droop coefficient (R _{f _ BESS} ) of the first energy storage device 10: 0.01

Droop coefficient (R _{f - SC} ) of the second energy storage device 20: 0.015

As shown in FIG. 9, 0 to 3 seconds is a system linkage section (scenario1), 3 to 4 seconds is a section (scenario2) which is converted to independent operation in a grid connection, and 4 to 6 seconds is an independent operation section (scenario3). )to be.

First, since there is no frequency fluctuation in the grid linkage section scenario1, the grid P_Grid is responsible for the load fluctuation.

In the section (scenario2) converted from the grid connection to independent operation, the front tidal current (0.6pu) of the first energy storage device 10 disappears, and the frequency variation value by the droop coefficient is 0.01 * 0.36 = 0.015 * 0.24 = 0.36% The frequency is at equilibrium at 59.78 Hz.

 The output of the first energy storage device 10 is 0.6 * 0.015 / (0.01 + 0.015) = 0.36pu (18kW) by the droop control, and the second energy storage device 20 is 0.6 * 0.01 by the droop control. The output fluctuates as /(0.01+0.015)=0.24pu(12kW).

Since the first energy storage device 10 does not perform the frequency / voltage recovery control in the section (scenario2) converted from the grid connection to the independent operation, the output of the second energy storage device (20) in the independent operation section (scenario3) The output is varied in cooperation with the first energy storage device 10 according to the load of the load without decreasing.

FIG. 10 illustrates a simulation result of a control method of the microgrid system of FIG. 1 when the first energy storage device 10 performs frequency / voltage recovery control.

Prior to the simulation results, the simulation conditions are as follows.

Rated power (maximum output) of the first and second energy storage devices 10, 20: 50 kW

_-Rated output of distributed power supply (P _DG0 ): 0kW

-Droop coefficient (R _{f _ BESS} ) of the first energy storage device 10: 0.01

Droop coefficient (R _{f - SC} ) of the second energy storage device 20: 0.015

Gain of the first filter 40: 1

characteristic frequency (w _c ): 6Hz

damping ratio: 3.2

Gain of the second filter 50: 1

characteristic frequency (w _c ): 60 Hz

damping ratio: 3.2

As shown in FIG. 13, 0 to 3 seconds is a system linkage section (scenario1), 3 to 4 seconds is a section (scenario2) which is converted to independent operation in a grid connection, and 4 to 6 seconds is an independent operation section (scenario3). )to be.

First, since there is no frequency variation in the grid linkage section scenario1, the grid P_Grid is responsible for the load P_Load. In addition, the first and second energy storage devices 10 and 20 are in charge of the amount of change of the algae according to the load variation according to the first and second algae filtering values input through the first and second filters 40 and 50. This reduces the fluctuation of the system.

In the first half of the section (scenario2) converted from the grid connection to the independent operation, the output of the second energy storage device 20 is increased than the output of FIG. 9 while the frequency may drop below 59.78 Hz of FIG.

However, in a section (scenario2) that is converted to independent operation in the grid connection, as the first energy storage device 10 performs frequency / voltage recovery control, the frequency and voltage may be quickly restored to the commercial frequency and the commercial voltage.

Therefore, in the second half of the section (scenario2) that is converted to independent operation in the grid connection, the output of the second energy storage device 20 drops to 0 kW.

As the frequency and voltage are restored to the commercial frequency and the commercial voltage in the independent operation section (scenario3), the first energy storage device 10 is responsible for the load of the load 30.

It will be understood by those of ordinary skill in the art that the foregoing description of the embodiments is for illustrative purposes and that those skilled in the art can easily modify the invention without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

10: first energy storage device
20: second energy storage device
30: load
40: first filter
50: second filter

Claims (9)

In a microgrid system,
A first energy storage device connected to the link point with the grid and a second energy storage device connected between the first energy storage device and the load,
The first energy storage device and the second energy storage device are operated in an output control mode for outputting power in response to fluctuations in the frequency and voltage of the tidal current,
In a period in which the system and the link operation are converted to the independent operation, the first energy storage device performs frequency / voltage recovery control to recover the changed frequency and voltage to the commercial frequency and the commercial voltage when the frequency and voltage change. When the frequency and voltage are restored to the commercial frequency and commercial voltage by the first energy storage device, the output of the second energy storage device is reduced to a predetermined value.
The first energy storage device is a BESS (Battery Energy Storage System), the second energy storage device is a supercapacitor, the second energy storage device is a microgrid system having a faster dynamic characteristics than the first energy storage device. delete The method of claim 1,
And the output of the second energy storage device becomes zero when the frequency and voltage become the commercial frequency and the commercial voltage by the first energy storage device. The method of claim 1,
And a first filter connected to the front end line of the first energy storage device and outputting a first tidal current filtering value filtering the amount of tidal current change of the front end line to the first energy storage device. 5. The method of claim 4,
And the first energy storage device outputs power corresponding to the tidal current filter value input from the first filter. The method of claim 1,
And a second filter connected to the front end line of the second energy storage device and outputting a second tidal flow filtering value filtering the amount of tidal current change of the front end line to the second energy storage device. The method according to claim 6,
And the second energy storage device outputs power corresponding to a second tidal current filter value input from the second filter. delete delete

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