KR20130066412A - Capacity estimation method of plural energy storage devices for grid connection of intermittent generation - Google Patents

Abstract

PURPOSE: A method for calculating the capacity of multiple energy storage devices is provided to calculate an optimal, stable, and economical energy capacity when connecting an intermittent power generation system to a power system. CONSTITUTION: An objective function for calculating the optimal capacity of multiple energy storage devices is defined(S21). The optimal capacity is calculated(S23) in order to satisfy the constraints on the sums of the output power and output energy(S22) by considering the limiting conditions of a ramp rate required in the power system connection. [Reference numerals] (S21) Define objective function for calculating the optimal capacity of multiple energy storage devices; (S22) Regulate limiting conditions; (S23) Calculate optimum capacity

Description

Capacity Estimation Method of Plural Energy Storage Devices for Grid Connection of Intermittent Generation

The present invention provides an optimal capacity of the plurality of energy storage devices in order to control the output to the system most economically and reliably when connecting an intermittent generation source combined with a plurality of energy storage devices including BESS and ELDC to the grid. It is about how to calculate.

As the cost of fossil fuels increases and the global supply of fossil fuels decreases, the importance of alternative energy sources becomes increasingly important. Non-fuel based renewable energy in the form provided by most renewable resources is efficient, readily available and environmentally friendly.

In addition, recently, the energy storage device of the hybrid power transmission system has a vehicle to grid connected to the grid (smart grid) such as an externally supplied electricity and a vehicle that can be charged with energy from an engine or regenerative breaking. ) Was introduced. V2G, for example, to charge the car during the night time when the demand for electricity is low, and to sell the electricity back during the daytime when the demand for electricity is high, so that consumers are supplied with electricity at a low time, to charge the electric car, It can be seen as a model to make a profit by reselling the surplus power in an expensive time.

However, because most non-fuel-based renewable energy sources, such as wind and solar power, or V2G resources are intermittent sources, they cannot always provide the grid with the amount of power they want. . In other words, even if more power / energy is desired, users cannot increase the intensity of sunlight or wind speed to generate power / energy. Therefore, when the user is using less power / energy than generated by the intermittent power generation as described above, it is desirable to store the extra power for later use.

In the case of the intermittent power generation as described above, a conventional energy storage device for storing excess power is generally used by a battery energy storage system (hereinafter referred to as “BESS”) such as a lithium ion battery. do. However, the BESS cannot charge large amounts of energy in a short time and must control from current source charging to voltage source charging by a charging algorithm. In addition, even in energy discharge, about 20% of short discharge lasts long life, and about 80% of deep discharge shortens its life. That is, energy storage devices such as BESS have a short life cycle and must be managed for a long time at all times, and have disadvantages in energy use efficiency and pollutant emission, in which 100% of the charge cannot be used.

Therefore, in recent years, Super Capacitor (Super Capacity) has been widely used as an alternative or bottled product for energy storage devices such as the above-described BESS. Unlike a battery using a chemical reaction, the supercapacitor uses a simple phenomenon of ions moving to an electrode and an electrolyte interface or a charging phenomenon by a surface chemical reaction. Accordingly, rapid charging and discharging, high charge and discharge efficiency and semi-permanent cycle life characteristics are attracting attention as a replacement battery or a battery replacement. In the 1980s, small electric double layer capacitors (hereinafter referred to as "EDLC") using high specific surface area of activated carbon materials were commercialized for memory backup of various electronic devices. Various applications include the starter power supply for automobiles, the auxiliary power source for exhaust gas catalytic heating, the regenerative power source for HEV, and the power source for replacing the motor driving battery for toys. However, for effective control of supercapacitors such as EDLC, each charge / discharge controller must be provided, and an energy design method circuit must be provided for efficient use of energy, and some compensation techniques must be used to control optimal operation. .

As such, since each energy storage device has its own problems when only one of the BESS and EDLC is used as the energy storage device, a power generation system including both the BESS and EDLC has recently been studied. When such power generation systems, especially intermittent power generation systems, are connected to the grid, there is a need for a method that can most efficiently and reliably calculate the optimal capacity of BESS and ELDC and efficiently control their active power. .

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an optimal power supply system for an intermittent power generation system including a plurality of energy storage devices including a BESS and an EDLC. It relates to a method for estimating the dose.

According to a preferred embodiment of the present invention for achieving the above object, in the method of calculating the optimal capacity of a plurality of energy storage devices coupled with the intermittent power generation source for grid connection of the intermittent power generation source, Defining an objective function for optimal dose estimation; And

Calculating an optimum capacity of the plurality of energy storage devices to satisfy the constraints on the sum of the output power and the output energy of the plurality of energy storage devices in consideration of the increase and decrease rate limit condition required for the grid connection; It is characterized by.

Here, the plurality of energy storage devices may include a battery energy storage system (BESS) and an electric double layer capacitor (EDLC).

In addition, the defining of the objective function may be to minimize the sum of energy costs of the BESS and the EDLC.

According to the present invention as described above, when connecting the intermittent power generation system including a plurality of energy storage devices including BESS and EDLC to the grid, the optimal energy capacity of the plurality of energy storage devices is most stably and economically achieved. There is an effect that can be estimated.

1 is a block diagram schematically illustrating an intermittent power generation system 10 coupled to a grid in combination with a plurality of energy storage devices including a BESS and an ELDC according to an embodiment of the present invention.
2 is a view for explaining in detail the method of calculating the optimal capacity of a plurality of energy storage devices when connecting the intermittent power generation system shown in FIG.
3 is a view for explaining an example of the constraint condition in consideration of the increase and decrease rate according to an embodiment of the present invention.

In order to fully understand the present invention, operational advantages of the present invention, and objects achieved by the practice of the present invention, reference should be made to the accompanying drawings and the accompanying drawings which illustrate preferred embodiments of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic block diagram of an intermittent power generation system 10 coupled to a grid in conjunction with a plurality of energy storage devices, including, for example, BESS and ELDC, according to one embodiment of the invention.

The intermittent generation source system 10 according to the present invention comprises an intermittent generation source 11, a BESS 12 as a first energy storage device and an EDLC 13 as a second energy storage device, and is installed in an isolated system. If connected to the customer load (not shown) alone, if connected to the power system is connected to the power system 15 through the associated transformer 14

The intermittent generation source 11 includes non-fuel-based renewable energy resources such as wind power generation and solar power generation, or V2G resources using electric vehicles. These resources do not always provide the system with the desired amount of power, so the redundant power is stored in the BESS 12 and EDLC 13 as an energy storage device, and with the intermittent generation source 11. Output power to (15).

FIG. 2 is a view for explaining in detail the method of calculating an optimum capacity for each of a plurality of energy storage devices when the intermittent power generation system shown in FIG. 1 is connected to a grid. Hereinafter, a case in which BESS and EDLC are included as a plurality of energy storage devices will be described as an example. However, the present invention is not limited thereto, and a case in which any energy storage device is included as a plurality of energy storage devices is provided. It will be appreciated that it may also apply.

Referring to FIG. 2, first, when the BESS and EDLC as the first and second energy storage devices are included, an objective function for calculating an optimum capacity of each of the BESS and EDLC is defined (step S21). Since the BESS and EDLC used as energy storage devices have different lifetimes and energy per kg, the capacity of each intermittent power generation system including these can be most cost-effectively calculated when connected to the grid. Should. Accordingly, the objective function in step S21 may be defined as a first function of energy capacities of BESS and EDLC, that is, a minimum value of the sum of energy costs, as shown in Equation 1 below.

[Equation 1]

Where w _ES and w _SC are the cost per unit energy of BESS and EDLC, respectively, and E _ES and E _SC indicate the energy capacities of BESS and EDLC, respectively.

For example, a lithium ion battery that can be used as a BESS (12) typically has a lifespan of about 5000 charges, but 200 Wh / kg of energy per kg, 3 kW / kg of output per kg and $ 2 per unit energy. / Wh, so the cost per unit output would be about 0.13 $ / W. In addition, the supercapacitor represented by EDCL 13 is generally known to have a million life cycles of charging (although the supercapacitor's life is more affected by time than a charge / discharge cycle), but the energy per kg is 5 Wh / kg. For example, the output per kg would be 10kW / kg and the cost per unit energy would be $ 20 / Wh, so the cost per unit power would be $ 0.01 / W.

After the objective function for calculating the optimum capacity of each of the plurality of energy storage devices is defined in step S21, various constraints must be defined in order to solve the objective function (step S22).

First, when connecting the intermittent power generation system 10 of FIG. 1 to the grid, it is necessary to most economically and stably adjust the output of the intermittent power generation system incorporated in the power grid in order to meet the changing power demand in real time.

Generally, grid connection regulations include ramp rate limiting, power curtailment, and power droop with frequency. In particular, frequency is the difference between power demand and generator output, and the control amount is distributed to the individual generators using the ramping up and down characteristic of the individual generators to reduce the deviation between the current frequency and the normal frequency (60 Hz). shall.

Here, the increase and decrease rate is a limit value in consideration of the system's ability to adjust the frequency, and may be defined differently according to each country's power system. For example, in China, in the case of wind power generation, if the installation capacity of wind power generation is less than 30MW, the 10-minute increase / decrease rate is 20MW / 10min, the 1-minute increase / decrease rate is 6MW / min, and if the installation capacity exceeds 150MW, it is increased by 10 minutes. The power generation rate is 100MW / 10min, and the one-minute increase and decrease rate is 30MW / min. Sometimes smaller systems limit to 1 MW / min. The regulation of increase / decrease rate may be differently set according to each country's electric power situation or policy.

In the present invention, the constraints in step S22 of FIG.

3 is a view for explaining a constraint considering the increase and decrease rate according to an embodiment of the present invention.

가 된다. 이는 증감발율이 1분 증감발율[즉 MW/min]을 고려한 것이다. 또한 증감발율 제한을 만족시키기 위한 단속적 발전원 시스템의 필요 에너지는 도 3에 도시된 삼각형의 넓이인

(MWh)이 될 것이다. Assuming that the maximum generated output power of the intermittent power generation source is P _{RE, MAX} and the increase / deceleration rate power limiting power of the installation region is P _{T, RR} (MW / min), as shown in FIG. If the output suddenly becomes zero, assuming that the required output power of the intermittent generation system to satisfy the increase / deceleration rate limit is P _{RE, MAX} (MW), the output time is

. This is because the increase and decrease rate takes into account the 1 minute increase and decrease rate [ie MW / min]. In addition, the required energy of the intermittent power generation system to satisfy the increase and decrease rate limit is the area of the triangle shown in FIG.

(MWh) will be.

As the constraint in step S22 of FIG. 2, when the output of the intermittent power generation source suddenly becomes 0 as described above, the sum of the output powers of the BESS and EDLC is greater than the increase / decrease rate limit value, and the output energy of the BESS and EDLC is increased or decreased. It can be considered that if it is larger than the required energy to satisfy the power limit, the system can be reliably supplied with power.

Constraints as described above may be defined by the following equations.

&Quot; (2) "

&Quot; (3) "

[Equation 4]

[Equation 5]

Where P _ES and P _SC are the output power of BESS and EDLC, E _ES and E _SC are the output energy of BESS and EDLC, respectively, and P _ES.kg and P _{SC, kg} are the output power of BESS and EDLC per _kg , respectively. E _{ES, kg} and E _{SC, kg} represent the output energy of BESS and EDLC per _kg , respectively. In addition, P _{RE, MAX} is the maximum generation output power of the intermittent generation source, P _{T, RR} represents the limit of the increase and decrease rate of the output power of the installation area of the intermittent generation system, which has a unit of MW per minute, that is, MW / min .

Subsequently, if a solution meeting the objective function of step S21 is obtained under the constraints of step S22, a solution regarding the optimal capacity of BESS and EDLC in the intermittent power generation system including BESS and EDLC can be obtained (step S23).

As described above, optimal embodiments have been disclosed in the drawings and the specification. Although specific terms have been employed herein, they are used for purposes of illustration only and are not intended to limit the scope of the invention as defined in the claims or the claims. Therefore, those skilled in the art will understand that various modifications and equivalent other embodiments are possible from this. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

10 intermittent power generation system
11 intermittent development
12 First Energy Storage Device (BESS)
13 Second Energy Storage Device (EDLC)

Claims (5)

In the method of calculating the optimal capacity of a plurality of energy storage devices combined with the intermittent power source for grid connection of the intermittent power source,
Defining an objective function for calculating an optimum capacity of the plurality of energy storage devices; And
Calculating an optimum capacity of the plurality of energy storage devices to satisfy the constraints on the sum of the output power and the output energy of the plurality of energy storage devices in consideration of the increase and decrease rate limit condition required for the grid connection; Method for calculating the optimal capacity of the plurality of energy storage device, characterized in that. The method of claim 1,
The plurality of energy storage devices includes a battery energy storage system (BESS) and Electric Double Layer Capacitor (EDLC), the method of calculating the optimal capacity of the plurality of energy storage devices. 3. The method of claim 2,
The defining of the objective function comprises minimizing a sum of energy costs of the BESS and the EDLC. The method of claim 3, wherein
The objective function is defined by Equation 1 below.
[Equation 1]

Where w _ES and w _SC are the cost per unit energy of the BESS and the EDLC, respectively, and E _ES and E _SC are the energy capacities of the BESS and the EDLC, respectively. Calculation method. The method of claim 3, wherein
The constraint is defined by the following equations 2) to 5),
&Quot; (2) "

&Quot; (3) "

&Quot; (4) "

&Quot; (5) "

Where P _ES and P _SC are the output power of the BESS and the EDLC, E _ES and E _SC are the output energy of the BESS and the EDLC, respectively, and P _{ES .kg} , P _{SC, kg} , E _{ES, kg} and E _{SC, kg} is the output power and output energy per _kg of the BESS and EDLC, respectively _, and P _{RE, MAX} is the maximum generation output power of the intermittent generation source _, and P _{T, RR} is the installation area of the intermittent generation source. A method of calculating the optimum capacity of a plurality of energy storage devices, characterized in that it represents the increase / decrease rate limit value of the output power.

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