KR20160107877A - A method for smoothing wind power fluctuation based on battery energy storage system for wind farm - Google Patents

Abstract

A method of smoothening wind generation fluctuations based on a battery energy storage system in a wind plant according to an embodiment of the present invention is a method of smoothening wind generation output power fluctuations in a wind plant having a plurality of wind turbines into which a battery energy storage system (BESS) is integrated, comprising the steps of: receiving reference power from a power system operator in the wind plant; measuring output power for the wind turbines from a point of common coupling (PCC), wherein the wind turbines are commonly connected to the PCC such that the wind plant is connected with a power system; controlling charging and discharging of the BESS; and controlling output power of the wind turbines. The method of smoothening wind generation fluctuation based on a battery energy storage system in a wind plant according to the present invention uses wind turbines, into which the BESS is integrated, to rapidly cope with fluctuations in a power generation amount and follow reference power of a power network by charging and discharging a battery in the BESS. Therefore, fluctuations in output power to the power network in the wind plant due to wind power variations can be reduced, which maintains a balance between a power station and the power network. Also, the power system can be operated stably.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a method of smoothing wind power generation based on a battery energy storage system in a wind power generation plant,

The present invention relates to a method for smoothing wind power fluctuations based on a battery energy storage system in a wind farm. And more particularly to a wind turbine having a battery energy storage system to quickly respond to fluctuations in the amount of wind power generated by the battery charge / discharge of the battery energy storage system and to follow the reference power of the power network, To a method of smoothing the fluctuation of wind power generation that can smooth the output power fluctuation to the power network of the power generation complex. Thus, the present invention relates to a method for supplying stable power to a power grid.

Wind power generation has recently attracted a great deal of attention as a renewable energy that can overcome the harmful effects of energy caused by conventional fossil fuels. However, the intermittent nature of wind power causes problems in terms of stability of wind power generation in utilizing such renewable energy. Therefore, efforts have been made to secure the stability of such wind power generation.

On the other hand, the energy storage system is emerging as a solution to the stability problem of wind power generation. The energy storage system can store electricity when the amount of wind power is large, while it can discharge when the amount of wind power is low, and can provide electricity when necessary. Therefore, a method of stably operating a wind power generation plant using such an energy storage system may be useful.

As a conventional method for stabilizing the wind turbine, there is a method of smoothing fluctuation of the wind power generation amount by controlling the pitch angle. However, this conventional method has a problem in that the pitch angle does not respond quickly when the output power of the wind farm requires rapid adjustment. Therefore, the wind power generation complex can not quickly follow the reference power. Meanwhile, a method of stabilizing a wind turbine using an energy storage system has been proposed. However, when the wind speed is variable, the energy storage system can smooth the output power of the wind turbine, There is a problem that can not be done.

In order to solve the above problems, the present invention uses a wind turbine incorporating a battery energy storage system, which quickly responds to fluctuations in wind power generation through battery charge / discharge of a battery energy storage system, It is possible to smooth the fluctuation of the output power to the power grid of the wind power generation complex due to the wind power fluctuation and thereby to maintain the balance between the power plant and the power grid and to realize a stable operation of the power system, It is an object of the present invention to provide a method for smoothing the wind power fluctuation based on an energy storage system.

According to an aspect of the present invention, there is provided a method of smoothing a wind power generation variation based on a battery energy storage system in a wind power generation complex including a plurality of wind turbines incorporating a battery energy storage system (BESS) A method for smoothing wind power generation output fluctuations in a wind farm, the method comprising the steps of: receiving a reference power from a power grid operator in the wind farm; connecting the plurality of wind turbines Measuring output power by the plurality of wind turbines from a commonly connected point of common coupling (PCC), controlling charging and discharging of the battery energy storage system, and controlling the output power of the wind turbine .

Controlling charging and discharging of the battery energy storage system comprises comparing the output power of the plurality of wind turbines being measured with the reference power and charging the battery energy storage system according to a result of the comparison Or discharging.

Wherein when the reference power value is smaller than the output power of the plurality of wind turbines, the battery energy storage system is charged to store extra energy, and when the reference power value is greater than the output power of the plurality of wind turbines , And discharges the battery energy storage system to provide energy.

Wherein controlling the output power of the wind turbine comprises: controlling the output power of the wind turbine while charging the battery energy storage system; and controlling the output power of the wind turbine during discharging the battery energy storage system .

Controlling the output power of the wind turbine while charging the battery energy storage system limits the battery state of charge (SOC) to prevent overcharge of the battery energy storage system.

Controlling the wind turbine with a maximum power point tracking (MPPT) control strategy when the SOC is less than an upper limit value of the SOC,

If the SOC is greater than or equal to the upper limit of the SOC, charging of the battery energy storage system is stopped and the wind turbine is controlled using an absolute power production control strategy.

Controlling the output power of the wind turbine while discharging the battery energy storage system controls the wind turbine with a maximum power point tracking (MPPT) control strategy.

The maximum power point tracking (MPPT) control strategy is a strategy for controlling the output power of the wind turbine to follow the maximum power coefficient when the wind speed is less than the rated wind speed, Limiting the power to the rated power of the wind turbine.

The absolute power production control strategy limits the power production of the wind turbine to a maximum power point so that the output power of the measured wind turbine follows the reference power.

The technique disclosed in the present invention can have the following effects. It is to be understood, however, that the scope of the disclosed technology is not to be construed as limited thereby, as it is not meant to imply that a particular embodiment should include all of the following effects or only the following effects.

The method of smoothing the fluctuation of wind power generation based on the battery energy storage system in the wind power generation complex according to the present invention uses a wind turbine incorporating a battery energy storage system. The fluctuation of the wind power generation amount It is possible to smooth the fluctuation of the output power to the power network of the wind power generation plant due to the wind power fluctuation and thereby to maintain the balance between the power plant and the power network, It is possible to achieve stable operation.

1 shows the construction of a wind turbine.
Figure 2 shows that BESS is used to compensate for the intermittent output power of a wind turbine.
3 shows a network arrangement of a wind turbine constructed of a plurality of wind turbines.
4 shows a control flow chart of a wind turbine coupled with BESS.
Fig. 5 shows a wind turbine equipped with three wind turbines used in the simulation.
6 shows a simulation structure of a wind turbine.
7 shows simulation results of a four-component synthetic wind speed model of a wind power plant.
Fig. 8 shows the output power of the wind power generation network without BESS.
Fig. 9 shows the output power at the wind power generation network side with the BESS.
10 shows the power change of BESS.
11 shows the voltage of the DC bus.
12 shows the three-phase voltage of the power network converter.

For the embodiments of the invention disclosed herein, specific structural and functional descriptions are set forth for the purpose of describing an embodiment of the invention only, and it is to be understood that the embodiments of the invention may be practiced in various forms, The present invention should not be construed as limited to the embodiments described in Figs.

The present invention is capable of various modifications and various forms, and specific embodiments are illustrated in the drawings and described in detail in the text. It is to be understood, however, that the invention is not intended to be limited to the particular forms disclosed, but on the contrary, is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms may be used for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, . On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between. Other expressions that describe the relationship between components, such as "between" and "between" or "neighboring to" and "directly adjacent to" should be interpreted as well.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprise", "having", and the like are intended to specify the presence of stated features, integers, steps, operations, elements, components, or combinations thereof, , Steps, operations, components, parts, or combinations thereof, as a matter of principle.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be construed as meaning consistent with meaning in the context of the relevant art and are not to be construed as ideal or overly formal in meaning unless expressly defined in the present application .

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The same reference numerals are used for the same constituent elements in the drawings and redundant explanations for the same constituent elements are omitted.

Currently, weibull distribution model, 4-component composite wind speed model, and equivalent wind speed model are used to generate wind speed in wind power system. There are various models such as. In the present invention, a wind speed is generated using a four-component synthetic wind speed model.

The four-component synthetic wind speed V _wt can be expressed by the following equation (1).

Where V _wb is the base wind, V _wg is the blast, V _wc is the wind that gradually changes, and V _wr is the stochastic wind.

A wind turbine is a device that converts kinetic energy from the wind into mechanical energy. It consists of a wind turbine rotary wing, a gear box, a double fed induction generator (DFIG), and a converter. Fig. 1 shows the construction of such a wind turbine.

The wind turbine conversion power P can be expressed by the following equation (2).

Where ρ is the air density, R is the rotor radius, V _wt is the wind speed, C _p is the power efficiency coefficient, λ is the tip speed ratio, and β is the blade pitch angle.

Energy storage systems include, for example, a battery energy storage system (BESS), a pumped hydro-system (PHS), a flywheel energy storage system, a superconducting magnetic energy storage system (Superconducting Magnetic Energy Storage System (SMESS), Compressed Air Energy Storage (CAES), and the like.

PHS, CAES, FESS, etc. require a complex balance of large-scale facilities and power plants, but the battery has advantages such as being highly efficient, containerable and easily applicable to distributed and centralized systems. In addition, the BESS technology is already at a mature stage, and the life span is greatly improved. Thus, the present invention relates to a method for smoothing wind energy with large fluctuations in a wind farm using BESS.

Battery models can usually be divided into experimental models, electrochemical models, and equivalent circuit models, among which the equivalent circuit model is best suited for dynamic simulation.

The voltage source E controlled in the dynamic simulation can be expressed by the following equation (3).

Where E is the no-load voltage, E ₀ is the constant voltage of the battery, K is the polarization voltage, Q is the battery capacity (Ah), A is the exponential amplitude (V) (Ah ^-1 ).

The intermittent nature of the wind is the biggest problem associated with wind power generation, and thus the present invention uses a battery energy storage system (BESS) to reduce power fluctuations. Figure 2 shows that BESS is used to compensate for the intermittent output power of a wind turbine.

2, the DFIG is driven by a wind turbine and a gearbox, and the output of the mechanical power of the wind turbine, which is a function of the wind speed and the pitch angle of the rotary vane, is shown . The BESS is connected to the wind turbine between the DC / AC converter and the AC / DC converter. Also, the BESS can be charged / discharged to smooth out the output power.

BESS capacity configuration is very important. If the BESS capacity configuration is not sufficient, the effect of stable output power can not be guaranteed. Conversely, if the BESS capacity configuration is too large, the output power is relatively stable but the economic cost is increased. Therefore, it is necessary to appropriately configure the BESS capacity.

After deriving wind speed and wind speed-power characteristic curves for the wind turbine, the BESS capacity is calculated as described below.

After deriving the wind speed and wind speed-power characteristic curve by the wind speed model and the wind turbine model, the one-hour predicted power E of the wind turbine is calculated by the following equation (4).

In this case, E is the estimated wind power of the wind turbine, P (ν) is the wind speed-power curve of the wind turbine, q (ν) is the probability distribution of the wind speed, ν _cut-in is the cut- ν _rated is the rated wind speed, and ν _cut-out is the cut-out wind speed.

The capacity S of the BESS is calculated by the following equation (5).

Where H is the time for the wind turbine to maintain a stable output power.

The following describes the layout of wind farms.

The wind farm is composed of a plurality of wind turbines, and the network arrangement is as shown in Fig. The wind farm operates like a centralized unit, which receives input requests from the system operator and measures the output from a point of common coupling (PCC). Depending on the actual network situation, the system operator requires specific operation of the wind farm, ie normal production or absolute production.

4 shows a control flow chart of a wind turbine coupled with BESS. Referring to FIG. 4, the control method according to the present invention can be divided into two parts, that is, charge / discharge control of the BESS and control of the wind turbine.

First, charge / discharge control of the BESS will be described below. A major challenge for wind energy resources is to smooth out intermittent power output. Therefore, a method of charging or discharging BESS is problematic in order to smooth such intermittent power output. Also, the charging limit state of the BESS should be considered. For this purpose, in the present invention, the difference between the measured power of the wind turbine and the reference power is used to control charging or discharging of the BESS. The state of the BESS can be divided into a charging step and a discharging step as follows.

The charging step is called the power peak, and if the reference power is less than the measured power of the wind turbine, the battery stores extra energy. This can be expressed by the following equation (6).

The discharging step is called a power valley, and when the reference power is greater than the measured power of the wind turbine, the battery provides energy. This can be expressed by the following equation (7).

In Equations (6) and (7), P _wt is the measured power of the wind turbine, P _ref is the reference power of the wind turbine, and P _com is the power command of BESS.

The following describes the control of the wind turbine. In order to smooth the fluctuation of the output power and protect the BESS, the present invention divides the control of the wind turbine into two parts. The first is that the wind turbine is controlled during the battery charging phase, and the second is that the wind turbine is controlled during the battery discharging phase. And, the state of charge (SOC) of the battery has an important influence on the smoothing control of the wind force. The battery SOC is defined as a percentage of the capacity Q, and is calculated by the following equation (8).

Where E _m is the initial capacity of the battery, E _h is the rated capacity of the battery, U _h is the voltage of the battery, and I _h is the current of the battery.

First, in the battery charging step, the battery storage system stores extra energy. In this battery charging step, the SOC is limited to prevent overcharging of the BESS. Therefore, the battery charging step in consideration of the SOC is divided into the following two steps.

The first is the SOC ≤ SOC _max step, which uses the maximum power point tracking (MPPT) control strategy of the wind turbine when the SOC is less than the SOC _{max, which} is the upper percentage of the battery capacity. The second is SOC ≥ SOC _{max. In} order to prevent overcharging of the battery, if the SOC is greater than SOC _max , the charging is stopped and therefore, at this stage the wind turbine is controlled using the absolute power production control strategy.

Next, in the battery discharge step, an MPPT control strategy is used to maximize the use of wind energy.

Maximum power point tracking (MPPT) and power absolute production control strategies are described below.

The MPPT control strategy consists of a power optimization strategy (below the rated wind speed) in which energy capture is maximized by following the maximum power coefficient and a strategy of limiting power to the rated power of the power limited to the turbine's rated power ).

The absolute power production control strategy limits the power production to the set maximum power point. Then, the measured output power will follow the reference power. In the present invention, the output power is limited by using the wind turbine pitch angle.

The wind farm consists of a plurality of wind turbines with BESS integrated into the wind turbine to smooth out the output power. The reference power of the wind farm is distributed to each wind turbine by the operator. Then, each wind turbine follows the reference power of each wind turbine by BESS.

The simulation results using Matlab / Simulink to verify the effectiveness of BESS are described below. The wind farm is connected to the end of the transmission line by a common connection point. The network arrangement of the wind power generation complex is as shown in Fig. The three wind turbines WT1, WT2 and WT3 are connected to the respective terminals and the connection of the wind farm to the power plant and the power plant itself are modeled by actual physical elements (transformer, line, bus bar, etc.). The BESS is connected via a DC bus to the back-to-back converter of each wind turbine. Therefore, the BESS can compensate the output power fluctuation of each wind turbine.

The wind farm is connected to a 25kV distribution system that delivers power to a 120kV network via a 30km 25kV feeder. Wind turbines use DFIG. The stator windings are connected directly to the common connection point (PCC) and the rotor is driven by a variable pitch controlled wind turbine. The simulation structure of the wind power generation complex is shown in Fig.

Wind speeds are generated by a four-component synthetic wind speed model. In the four-component synthetic wind model, the basic wind is set at 9 m / s, the blast and gradually changing wind are set at 0 second to 1 second, and 1 second to 2.5 seconds. The maximum hard wind is assumed to be 1.7 seconds at 1 second, and the variable hard wind at 1.7 seconds to 2.5 seconds. Probabilistic winds are set from 0 to 5 seconds. The simulation results of the four-component synthetic wind speed model of the wind power plant are as shown in Fig.

Fig. 8 shows the output power at the wind farm site without the BESS. From Fig. 8, it can be seen that the output power fluctuation of the wind farm is caused by the fluctuation of the wind speed. In the wind power plant without BESS, there is a large variation in the output power of the wind power plant, and the output power of the wind power plant can not follow the reference power of the wind power plant. As a result, unstable power output will have a significant impact on the power grid.

FIG. 9 shows the output power of the wind power plant with BESS, from which the power fluctuation of the wind farm can be quickly smoothed, and extra power is absorbed or insufficient power is compensated by BESS. If P _com ≥ 0, BESS absorbs extra power, and if P _com <0, BESS provides power to the power network to follow the reference power.

10 shows the power change of BESS. Also, in consideration of the battery life in the control, SOC _max = 90% is set. If the output power of the wind farm is greater than the reference power of the wind farm, the BESS stores the extra power. Conversely, if the output power of the wind farm is less than the reference power of the wind farm, the BESS provides power.

Fig. 11 shows the voltage of the DC bus, showing that the DC link voltage of each wind turbine can be maintained near 1150 V through voltage closed loop control of the generator side converter.

12 shows the three-phase voltage of the power network side converter, showing the three-phase voltage of each wind turbine, and the DC link voltage is converted by the power network side converter.

As described above, the method of smoothing the fluctuation of the wind power generation based on the battery energy storage system in the wind power generation complex according to the present invention uses the wind turbine incorporating the battery energy storage system, It is possible to smooth the fluctuation of the output power to the power network of the wind power generation plant due to the wind power fluctuation and thereby to balance the power plant and the power grid So that it is possible to achieve stable operation of the power system.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

Claims (10)

CLAIMS 1. A method for smoothing wind power output power fluctuations in a wind farm comprising a plurality of wind turbines incorporating a battery energy storage system (BESS)
Receiving reference power from a power system operator in the wind farm;
Measuring output power by the plurality of wind turbines from a point of common coupling (PCC) in which the plurality of wind turbines are commonly connected to connect the wind farm to the power system;
Controlling charging and discharging of the battery energy storage system; And
And controlling the output power of the wind turbine. The method according to claim 1,
Wherein the step of controlling charging and discharging of the battery energy storage system comprises:
Comparing the measured output power of the plurality of wind turbines with the reference power; And
And charging or discharging the battery energy storage system according to a result of the comparison. 3. The method of claim 2,
Wherein when the reference power value is smaller than the output power of the plurality of wind turbines, the battery energy storage system is charged to store extra energy,
Wherein the battery energy storage system discharges and provides energy when the reference power value is greater than the output power by the plurality of wind turbines. The method according to claim 1,
Wherein controlling the output power of the wind turbine comprises:
Controlling the output power of the wind turbine while charging the battery energy storage system; And
And controlling the output power of the wind turbine during discharging the battery energy storage system. 5. The method of claim 4,
Wherein controlling the output power of the wind turbine while charging the battery energy storage system comprises: limiting the battery state of charge (SOC) to prevent overcharge of the battery energy storage system, Smoothing method. 6. The method of claim 5,
Controlling the wind turbine with a maximum power point tracking (MPPT) control strategy when the SOC is less than an upper limit value of the SOC,
And stopping charging the battery energy storage system and controlling the wind turbine using an absolute power production control strategy when the SOC is equal to or greater than an upper limit value of the SOC. The method according to claim 6,
The maximum power point tracking (MPPT)
When the wind speed is less than the rated wind speed, the output power of the wind turbine follows the maximum power coefficient,
Wherein the output power of the wind turbine is limited to the rated power of the wind turbine when the wind speed is equal to or higher than the rated wind speed. The method according to claim 6,
The power absolute production control strategy includes:
Wherein the power generation of the wind turbine is limited to a maximum power point so that the output power of the measured wind turbine follows the reference power. 5. The method of claim 4,
Wherein controlling the output power of the wind turbine while discharging the battery energy storage system controls the wind turbine with a maximum power point tracking (MPPT) control strategy. 10. The method of claim 9,
The maximum power point tracking (MPPT)
When the wind speed is less than the rated wind speed, the output power of the wind turbine follows the maximum power coefficient,
Wherein the output power of the wind turbine is limited to the rated power of the wind turbine when the wind speed is equal to or higher than the rated wind speed.

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