CN114865669A - Wind storage system power control method and system considering charge-discharge imbalance - Google Patents

Wind storage system power control method and system considering charge-discharge imbalance Download PDF

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CN114865669A
CN114865669A CN202210282539.5A CN202210282539A CN114865669A CN 114865669 A CN114865669 A CN 114865669A CN 202210282539 A CN202210282539 A CN 202210282539A CN 114865669 A CN114865669 A CN 114865669A
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battery pack
charge
wind
batteries
wind power
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钱仲豪
王小栋
茅雷
张刘冬
雷震
张骏
吕晓祥
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Nantong Power Supply Co Of State Grid Jiangsu Electric Power Co
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Nantong Power Supply Co Of State Grid Jiangsu Electric Power Co
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/28—Arrangements for balancing of the load in a network by storage of energy
    • H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/0013—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries acting upon several batteries simultaneously or sequentially
    • H02J7/0014—Circuits for equalisation of charge between batteries
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/0047—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries with monitoring or indicating devices or circuits
    • H02J7/0048—Detection of remaining charge capacity or state of charge [SOC]
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/28—The renewable source being wind energy
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E70/00—Other energy conversion or management systems reducing GHG emissions
    • Y02E70/30—Systems combining energy storage with energy generation of non-fossil origin

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  • Power Engineering (AREA)
  • Charge And Discharge Circuits For Batteries Or The Like (AREA)

Abstract

A wind power storage system power control method and system considering charge-discharge imbalance comprises the following steps: the grid-connected target power of the wind power plant is output by adopting a first-order low-pass filtering algorithm, the filtering time constant is corrected in real time according to the unbalance index and the charge state of the battery pack, the batteries are controlled in groups, one group of the batteries is responsible for charging, the other group of the batteries is responsible for discharging, if any one group of the batteries reaches the upper limit value or the lower limit value of the charge state, the two groups of the batteries immediately switch the charging and discharging states, the original wind power is absorbed or compensated by the mode, the final output power of the wind power plant reaches the grid-connected target power, and the grid-connected active power fluctuation index of the wind power plant in national standard is met. The wind power smoothing method provided by the invention considers the problem of unbalanced charge and discharge of the battery pack, and avoids the problem of insufficient charge or discharge capacity possibly occurring in the work of the battery pack; the effect is very good in improving the attenuation degree of the battery pack and prolonging the service life of the battery pack.

Description

Wind storage system power control method and system considering charge-discharge imbalance
Technical Field
The invention belongs to the technical field of wind power smoothing, and particularly relates to a wind storage system power control method and system considering charge-discharge imbalance.
Background
Wind power generation is a green, clean and friendly renewable energy source, and by the end of 2020, the installed capacity of wind power integration in China exceeds 282GW, the wind power construction scale and the installed capacity in China will continue to be enlarged in the future and become the most common power generation form of relay power and hydropower, however, the characteristics of intermittence and volatility of wind power also bring huge challenges to the aspects of power grid stability and safe operation, and how to smooth severe fluctuation of wind power becomes the current research hotspot.
The technology of smoothing the wind power by adopting a single battery pack is mature, but frequent charging and discharging are caused by uncertainty of the wind power, so that the charging and discharging depth is shallow, the utilization efficiency of the battery is low, and the service life loss of the battery is large. The charging and discharging are carried out by adopting the battery grouping control, and the charging and discharging states are switched when the charge state of any battery pack reaches the upper limit value and the lower limit value, so that the problem that the charging and discharging capacity is insufficient due to unbalanced charging and discharging when the battery groups run is avoided.
In summary, in order to solve the above mentioned problems, a new control method is provided based on the battery grouping control, so as to improve the unbalance degree and the life attenuation of the battery pack and ensure the stable operation of the power system.
Disclosure of Invention
In order to solve the defects in the prior art, the invention aims to provide a wind storage system power control method and system considering charge-discharge imbalance.
The invention adopts the following technical scheme:
a wind power storage system power control method considering charge-discharge imbalance comprises the following steps:
step 1: collecting the output of the wind power plant and the power generated by the two groups of energy storage batteries in real time;
step 2: filtering the original wind power, namely the output of the wind power plant, by adopting a first-order low-pass filter to obtain the grid-connected target power of the wind power plant;
and step 3: and (3) calculating the charge states and the unbalance of the two groups of energy storage batteries, calculating the time constant T of the first-order low-pass filter at the next moment based on the charge states and the unbalance, and returning to the step 1.
In step 2, the transfer function of the first order low pass filter is:
Figure BDA0003558395460000021
t is a time constant and s is time.
The time constant T (k Δ T) of the first order low pass filter is calculated as follows:
T(kΔt)＝T 0 +α(kΔt)·ΔT
wherein, T 0 Taking the time constant as a basic time constant, wherein alpha (T) and delta T are filter time constant correction terms, alpha (T) is a filter correction coefficient, delta T is an adjusting step length, and delta T is a sampling period;
the filter time constant correction term satisfies the following relation:
Figure BDA0003558395460000022
in the formula, S soc ((k-1) Δ t) is the state of charge at the previous time, f ch,disch And f A To distinguish the flag variables of the 4 modes, f ch,disch,ne And f A,ne Are respectively f ch,disch And f A To get the inverseNumber, e.g. f ch,disch When taking 1, then f ch,disch,ne Take 0. f. of ch,disch Indicating that the battery pack needs to be charged or discharged for smooth wind power, f A Representing the current state of a (k Δ t). If f ch,disch 1, indicating that the battery pack is being charged, f ch,disch 0, indicating that the battery pack is discharging; if f A 1 denotes the degree of unbalance A>0，f A 0 denotes the degree of unbalance A<0。
In step 4, when the unbalance degree of the energy storage battery pack is larger than zero and the energy storage battery pack executes a charging task, the time constant is reduced.
In step 4, when the unbalance degree of the energy storage battery pack is larger than zero and the energy storage battery pack executes a discharging task, the time is increased.
In step 4, when the unbalance degree of the energy storage battery pack is less than or equal to zero and the energy storage battery pack performs a charging task, the time constant is increased.
In step 4, when the unbalance degree of the energy storage battery pack is less than or equal to zero and the energy storage battery pack performs a discharging task, the time constant is reduced.
The method for calculating the charge states of the two groups of energy storage batteries comprises the following steps:
Figure BDA0003558395460000031
in the formula, S soc1 (k.DELTA.t) and S soc2 (k Δ t) is the SOC values of the battery pack 1 and the battery pack 2 at the present time, μ 1 、μ 2 Respectively marking the charging role and the discharging role of the battery pack; mu.s 1 Indicates the charge and discharge state of the battery pack 1, μ 2 Indicates the charge-discharge state of the battery pack 2; when the battery is being charged, mu 1 、μ 2 The value of (A) is 1; when the battery is discharging, mu 1 、μ 2 The value of (A) is 0; p ch (kΔt)、P disch (k delta t) is respectively the charging power and the discharging power required by the wind power plant at the current moment, and the P is assigned according to the roles of the two groups of batteries b1 (k.DELTA.t) and P b2 (kΔt)；E 1 ((k-1) Δ t) and E 2 (k-1) Δ t is the remaining power of the two battery packs at the previous moment, Δ t is the sampling period, η ch And η disch Efficiency of charging and discharging, respectively, of the battery pack, E 1 、E 2 The rated capacities of the battery pack 1 and the battery pack 2, respectively.
The unbalance degrees of the two groups of batteries satisfy the following relational expression:
A(kΔt)＝(S soc1 (kΔt)+S soc2 (kΔt))-(S socmax +S socmin )
wherein, the closer A (k delta t) is to 0, the higher the balance degree of the two groups of batteries is, and when the capacities of the two groups of batteries are the same, the chargeable quantity is approximately equal to the dischargeable quantity; when A (k delta t) is less than 0, the chargeable quantity in the two groups of batteries is larger than the dischargeable quantity, and conversely, when A (k delta t) is larger than 0, the dischargeable quantity is larger than the chargeable quantity; the absolute value | A (k Δ t) | of A (k Δ t) is used for representing the absolute unbalance degree of the two groups of batteries, and the larger the value | A (k Δ t) | is, the higher the unbalance degree of the two groups of batteries is; s socmax And S socmin Respectively the set upper and lower limits of the state of charge of the battery pack.
The upper and lower limits of the charge state of the battery pack satisfy the following relational expression:
Figure BDA0003558395460000032
wherein, Delta S socb The standard charging and discharging depth is the charging and discharging depth corresponding to the maximum value of the throughput energy in the service life cycle of the battery, represents the lowest service life attenuation degree, and is an optimal operation state.
The used energy storage battery pack is an energy storage lithium battery pack.
The invention also discloses a wind storage system power control system based on the wind storage system power control method considering charge-discharge imbalance, which comprises a wind power plant, a lithium battery pack, an energy control system, a DC/AC converter and an alternating current power grid;
the lithium battery packs are two groups;
the two groups of lithium battery packs are respectively connected with the wind power plant in parallel through different DC/AC converters;
the energy control system calculates grid-connected target power according to the original wind power and outputs the grid-connected target power to the alternating current power grid, and adjusts the charging and discharging state of the lithium battery pack.
The energy control system filters the original wind power through a first-order low-pass filter to obtain the grid-connected target power of the wind power plant.
The invention has the beneficial effects that:
(1) compared with the prior art, the output of the battery pack is controlled according to the grid-connected target power output by the low-pass filtering algorithm, and the severe fluctuation of the output power of the wind power plant is effectively inhibited;
(2) according to the invention, the filtering time constant is corrected in real time according to the unbalance index and the state of charge of the battery pack, so that the balance state of the battery pack is maintained, and the service life of the battery is prolonged;
(3) the invention has obvious effect on smoothing wind power and has obvious advantages on improving the unbalance degree and the charging and discharging depth of the battery pack and prolonging the service life of the battery.
Drawings
FIG. 1 is a wind-storage combined system topology structure of the present invention;
FIG. 2 is a flow chart of the operation of the method of the present invention;
FIG. 3 is a graph of wind farm output power before and after smoothing by the method of the present invention, the conventional method, and the fuzzy control method;
FIG. 4 shows the maximum output power fluctuation within 1min from the original wind power after smoothing by the method of the present invention;
FIG. 5 is a state of charge of a battery pack using a conventional method;
FIG. 6 is a state of charge of a battery pack when a fuzzy control method is employed;
FIG. 7 is a battery pack state of charge when the method of the present invention is employed;
FIG. 8 is a graph of absolute unbalance of a battery pack when operating using the method of the present invention, the conventional method, and the fuzzy control method;
fig. 9 is a life decay index of a battery pack when operating by the method of the present invention, the conventional method, and the fuzzy control method.
Detailed Description
The present application is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present application is not limited thereby.
A wind storage system power control method considering charge-discharge imbalance is disclosed, as shown in figure 1, a wind storage combined system model adopts a form that a wind power plant and two groups of energy storage lithium batteries are connected in parallel, and the output of the wind power plant at the moment t is P w (t), the two groups of lithium battery packs are respectively connected with the wind power plant in parallel through a converter, and the power generated at the moment t is P b1 (t) and P b2 (t)，P g And (t) the total output power of the wind power plant and the energy storage device is finally converged into an alternating current power grid. When P is present b1 (t) or P b2 When the (t) is a positive value, the battery pack sends out power, otherwise, the battery pack absorbs power, and according to the principle of energy conservation, the relationship among the powers is as follows:
P w (t)+P b1 (t)+P b2 (t)＝P g (t)。
as shown in fig. 2, a method for controlling power of a wind storage system in consideration of charge-discharge imbalance includes the following steps:
step 1: collecting the output of the wind power plant and the power generated by the two groups of energy storage batteries in real time;
step 2: filtering the original wind power, namely the output of the wind power plant, by adopting a first-order low-pass filter to obtain the grid-connected target power of the wind power plant;
calculating the time constant T in the first-order low-pass filtering algorithm:
T(kΔt)＝T 0 +α(kΔt)·ΔT
wherein, T 0 As basic time constant, alpha (T) · delta T is filter time constant correction term, alpha (T) is correction coefficient, delta T is regulation step length; Δ t represents a sampling period;
the formula for calculating the filter time constant correction term is as follows:
Figure BDA0003558395460000051
in the formula, S soc ((k-1) Δ t) is the state of charge at the previous time, f ch,disch And f A To distinguish the flag variables of the 4 modes, f ch,disch,ne And f A,ne Are respectively f ch,disch And f A By inverting, e.g. f ch,disch When taking 1, then f ch,disch,ne Take 0. f. of ch,disch Indicating that the battery pack needs to be charged or discharged for smooth wind power, f A Representing the current state of a (k Δ t). If f ch,disch 1, indicating that the battery pack is being charged, f ch,disch 0, indicating that the battery pack is discharging; if f A 1, represents the degree of unbalance a (k Δ t)>0，f A 0 denotes the degree of unbalance a (k Δ t)<0；
Filtering the original wind power through a first-order low-pass filter to obtain the grid-connected target power P of the wind power plant g_ref (k Δ t), the transfer function of the first order low pass filter is:
Figure BDA0003558395460000061
the skilled person can select the transfer function of the first-order low-pass filter according to the actual situation, and the transfer function of the first-order low-pass filter provided by the present invention is only a preferred embodiment and cannot be a necessary limitation of the present invention;
when the difference value between the output of the wind power plant at the time t and the grid-connected target power of the wind power plant is a positive number, charging the battery pack; when the difference value between the output of the wind power plant at the moment t and the grid-connected target power of the wind power plant is negative, discharging the battery pack;
a person skilled in the art can determine a battery pack charging and discharging power model according to actual conditions, and the method provided by the invention is only a preferred embodiment and cannot be necessarily limited by the invention;
specifically, P is judged w (t)-P g_ref Positive or negative of (k Δ t), if P w (kΔt)-P g_ref (k delta t) >0, namely the output of the wind power plant is greater than the target power at the moment, the battery pack is required to absorb the surplus wind power, the battery pack is charged, and the charging and discharging power of the battery at the moment is respectively as follows:
Figure BDA0003558395460000062
if P w (kΔt)-P g_ref (k delta t) <0, the output of the wind power plant is less than the target power at the moment, the deficient wind power needs to be compensated by the battery pack, the battery pack discharges, and the charging and discharging power of the battery at the moment is as follows:
Figure BDA0003558395460000063
respectively calculating the state of charge S of the two groups of batteries soc1 (kΔt)、S soc2 (k Δ t) and an unbalance a (k Δ t);
the state of charge of the two groups of batteries is as follows:
Figure BDA0003558395460000064
in the formula, S soc1 (k.DELTA.t) and S soc2 (k Δ t) is the SOC values, μ, of the battery pack 1 and the battery pack 2, respectively, at the present time 1 、μ 2 Respectively marking the charging role and the discharging role of the battery pack; mu.s 1 Represents the charge and discharge state of the battery pack 1, μ 2 Indicates the charge-discharge state of the battery pack 2; when the battery is being charged, mu 1 、μ 2 The value of (A) is 1; when the battery is discharging, mu 1 、μ 2 The value of (A) is 0; p is ch (kΔt)、P disch (k delta t) is respectively the charging power and the discharging power required by the wind power plant at the current moment, and the P is assigned according to the roles of the two groups of batteries b1 (k.DELTA.t) and P b2 (k Δ t). It is noted that P is required ch And (k deltat) takes a negative value and is assigned to the battery pack for performing the charging task. E 1 ((k-1) Δ t) and E 2 (k-1) Δ t) are the previous time, respectivelyResidual electric quantity of two battery packs at the moment, delta t is a sampling period, eta ch And η disch Efficiency of charging and discharging, respectively, of the battery pack, E 1 、E 2 The rated capacities of the battery pack 1 and the battery pack 2, respectively.
For example, when the battery 1 assumes the charging task and the battery 2 assumes the discharging task, μ 1 ＝1，μ 2 ＝0，P b1 (kΔt)＝-P ch (kΔt)，P b2 (kΔt)＝P disch (k Δ t); conversely, when the battery 1 is discharged and the battery 2 is charged, μ 1 ＝0，μ 2 ＝1，P b1 (kΔt)＝P disch (kΔt)，P b2 (kΔt)＝-P ch (kΔt)；
The unbalance of the battery pack is:
A(kΔt)＝(S soc1 (kΔt)+S soc2 (kΔt))-(S socmax +S socmin )
for the unbalance degree of the battery pack obtained by the formula, the closer A (k delta t) is to 0, the higher the balance degree of the two groups of batteries is, and when the capacities of the two groups of batteries are the same, the chargeable quantity is approximately equal to the dischargeable quantity; when A (k delta t) is less than 0, the chargeable quantity in the two groups of batteries is larger than the dischargeable quantity, and conversely, when A (k delta t) is larger than 0, the dischargeable quantity is larger than the chargeable quantity; and the absolute value | A (k Δ t) | of A (k Δ t) is used for representing the absolute unbalance degree of the two groups of batteries, and the larger the value of | A (k Δ t) | is, the higher the unbalance degree of the two groups of batteries is. S socmax Represents the maximum value of SOC of the two groups of batteries, S socmin Represents the minimum value of the SOC of both sets of batteries.
During charging and discharging of a battery, in order to avoid great loss of battery life, an upper limit and a lower limit are usually set for the state of charge of the battery, and a calculation formula is as follows:
Figure BDA0003558395460000071
wherein S is socmax And S socmin Respectively, the upper and lower limits of the set state of charge, Δ S socb Is called standard charge-discharge depth and is the maximum value of endocytosis and spitting energy in the life cycle of the batteryThe corresponding charge and discharge depth represents the lowest life attenuation degree, and is an optimal operation state.
The used energy storage battery pack is an energy storage lithium battery pack.
And step 3: and (3) calculating the charge states and the unbalance of the two groups of energy storage batteries, calculating the time constant T of the first-order low-pass filter at the next moment based on the charge states and the unbalance, and returning to the step 1.
When the unbalance degree of the battery pack is greater than 0 and the battery pack executes a charging task, or when the unbalance degree of the battery pack is less than 0 and the battery pack executes a discharging task, reducing the filtering time constant T; when the unbalance degree of the battery pack is greater than 0 and the battery pack executes a discharging task, or when the unbalance degree of the battery pack is less than 0 and the battery pack executes a charging task, increasing a filtering time constant T;
the time constant is adjusted by the following 4 modes:
g1, A (k delta T) >0, and when the battery pack executes the charging task, the SOC of the two groups of batteries is close to the upper limit at the moment, the dischargeable quantity is larger than the chargeable quantity, the battery pack executing the charging task should reduce the charging power, the rising amplitude of the SOC of the battery pack in the charging state can be reduced by properly reducing the filtering time constant T, and the larger the SOC represents that the chargeable quantity of the battery pack is less, the T should be continuously reduced;
g2, A (k delta T) >0, and when the battery pack executes a discharging task, T is increased appropriately, so that the discharging power of the battery is improved, the discharging battery pack SOC drop is accelerated, and the larger the SOC is, the larger the dischargeable quantity of the battery is, the larger T is;
g3, A (k delta T) <0, and when the battery pack executes the charging task, the SOC of the two groups of batteries is close to the lower limit, the chargeable quantity is larger than the dischargeable quantity, and the charging quantity of the rechargeable batteries can be improved by increasing the filtering time constant T. The smaller the SOC is, the more the chargeable quantity of the rechargeable battery is, the larger the value of T is, so as to achieve the purpose of accelerating the increase of the SOC;
g4, A (k delta T) <0, and the battery pack performs the discharging task, at this time, T should be reduced appropriately to reduce the discharging power and delay the SOC drop. And the smaller the discharging battery SOC, the smaller T should be.
The steps of the method are according to the control flow shown in the attached figure 2, and the service life of the battery pack is prolonged by improving the service life attenuation of the battery pack while the electric power fluctuation meets the grid-connected condition through battery grouping control.
The invention also discloses a wind storage system power control system considering charge-discharge imbalance based on the wind storage system power control method considering charge-discharge imbalance, which comprises a wind power plant, a lithium battery pack, an energy control system, a DC/AC converter and an alternating current power grid;
specifically, the lithium batteries are two groups;
the two groups of lithium battery packs are respectively connected with the wind power plant in parallel through different DC/AC converters;
the energy control system calculates grid-connected target power according to the original wind power and outputs the grid-connected target power to an alternating current power grid, and adjusts the charging and discharging state of the lithium battery pack;
specifically, the energy control system filters the original wind power through a first-order low-pass filter to obtain grid-connected target power of a wind power plant;
the transfer function of the first order low pass filter is:
Figure BDA0003558395460000091
t is the calculated time constant and s is time;
the method for adjusting the charge-discharge state of the lithium battery pack comprises the following steps:
when the difference value between the output of the wind power plant at the time t and the grid-connected target power of the wind power plant is a positive number, charging the battery pack; when the difference value between the output of the wind power plant at the time t and the grid-connected target power of the wind power plant is negative, discharging the battery pack;
a specific example is provided below to further illustrate the control effect of the present invention.
In this embodiment, the energy storage system is divided into two groups of batteries of the same rated capacity. The initial SOC of the battery pack 1 and the initial SOC of the battery pack 2 are 0.9 and 0.1, respectively, the initial task of the battery pack is allocated to the charging of the battery pack 1 and the charging of the battery pack 2. The conventional control strategy employs battery grouping control with a constant filter time constant, which is 240 s. The specific simulation parameters used are shown in the table below.
Figure BDA0003558395460000092
As shown in fig. 3, for an actually measured wind speed of 2 days, a traditional method, a fuzzy control method and the method of the present invention are respectively adopted, a wind power waveform is obtained after grid connection is obtained through simulation, wind power can be effectively smoothed through 3 smoothing methods, for example, a local enlarged image of 24-26 h, and a relatively flat power curve can be obtained after the original wind power is smoothed.
As shown in FIG. 4, aiming at the method of the invention, the maximum fluctuation of the wind power respectively within 1min and 10min before and after smoothing is obtained through simulation, the maximum fluctuation power value within 10min completely accords with the national standard, the power difference value within 1min is shown in the figure, the power before smoothing obviously exceeds the 3MW maximum limit value specified by the national standard in partial time period, and is very close to the maximum limit value in more time periods, the wind power difference value after smoothing by the strategy is reduced to be below 1.5MW, and accords with the national technical specification, thereby verifying the effectiveness of the strategy on the wind power smoothing.
As shown in fig. 5, 6 and 7, in the conventional method, the charging and discharging depths of the two groups of batteries are generally shallow, especially 12h to 18h, at this time, the fluctuation of wind power is severe, and the power to be absorbed or compensated by the battery pack is large, so that the SOC of the two groups of batteries is extremely unbalanced; the unbalanced state of the two groups of batteries under the fuzzy control method is better than that of the traditional strategy, but the unbalanced state occurs in 12-18 h; compared with the two strategies, the method disclosed by the invention has the advantages that the unbalance state of the battery pack is well improved, and particularly, the unbalance condition of two groups of batteries is obviously relieved within 12-18 h. Due to the improvement of the charging and discharging depth, the method reduces the times of charging and discharging switching of the battery, compared with the traditional method of switching 9 times to 7 times, avoids the frequent switching of the charging and discharging states of two groups of batteries, and improves the service life of the battery to a certain extent.
As shown in fig. 8, the inventive method has a smaller | a |. Compared with the traditional method and the fuzzy control method, the absolute unbalance degree of the two groups of batteries is smaller under the method, and the | A | fluctuation is smaller even in the 12-18 h period with violent wind power fluctuation, which indicates that the two groups of batteries under the method disclosed by the invention are maintained in a charge-discharge balance state as far as possible.
As shown in fig. 9, the inventive method has a smaller β. Under the traditional control strategy and the fuzzy control strategy, the beta values of the two groups of batteries are rapidly deteriorated at the moment of 12-18 h with larger wind power fluctuation, and the deviation degree of the beta value is large on the whole.
The method can fully utilize the capacity of the battery pack and delay the charge-discharge switching time. As can be seen from fig. 8, the last charge-discharge switching of this method occurs at about 48h, while the other two methods occur at about 42 h. By adopting the method, the charging and discharging switching time is delayed relative to the traditional strategy every time, which shows that the charging and discharging depth is optimized, so that more electric quantity can be taken and sent in each charging and discharging stage, and the service life of the charging and discharging system is prolonged.
The present applicant has described and illustrated embodiments of the present invention in detail with reference to the accompanying drawings, but it should be understood by those skilled in the art that the above embodiments are merely preferred embodiments of the present invention, and the detailed description is only for the purpose of helping the reader to better understand the spirit of the present invention, and not for limiting the scope of the present invention, and on the contrary, any improvement or modification made based on the spirit of the present invention should fall within the scope of the present invention.

Claims (12)

1. A wind storage system power control method considering charge-discharge imbalance is characterized in that a wind storage system adopts a form that a wind power plant and two groups of energy storage batteries are connected in parallel; the method is characterized by comprising the following steps of:
step 1: collecting the output of the wind power plant and the power generated by the two groups of energy storage batteries in real time;
step 2: filtering the original wind power, namely the output of the wind power plant, by adopting a first-order low-pass filter to obtain the grid-connected target power of the wind power plant;
and step 3: and (3) calculating the charge states and the unbalance of the two groups of energy storage batteries, calculating the time constant T of the first-order low-pass filter at the next moment based on the charge states and the unbalance, and returning to the step 1.
2. The wind storage system power control method considering charge-discharge imbalance according to claim 1, is characterized in that:
in step 2, the transfer function of the first order low pass filter is:
Figure FDA0003558395450000011
t is a time constant and s is time.
3. The wind storage system power control method considering charge-discharge imbalance according to claim 2, is characterized in that:
the time constant T (k Δ T) of the first order low pass filter is calculated as follows:
T(kΔt)＝T 0 +α(kΔt)·ΔT
wherein, T 0 Taking the time constant as a basic time constant, wherein alpha (T) and delta T are filter time constant correction terms, alpha (T) is a filter correction coefficient, delta T is an adjusting step length, and delta T is a sampling period;
the filter time constant correction term satisfies the following relation:
Figure FDA0003558395450000012
in the formula, S soc ((k-1) Δ t) is the state of charge at the previous time, f ch,disch And f A To distinguish the flag variables of the 4 modes, f ch,disch,ne And f A,ne Are respectively f ch,disch And f A Is gotInverse numbers, e.g. f ch,disch When taking 1, then f ch,disch,ne Take 0. f. of ch,disch Indicating that the battery pack needs to be charged or discharged for smooth wind power, f A Representing the current state of a (k Δ t). If f ch,disch 1, indicating that the battery pack is being charged, f ch,disch 0, indicating that the battery pack is discharging; if f A 1 denotes the degree of unbalance A>0，f A 0 denotes the degree of unbalance A<0。
4. The wind storage system power control method considering charge-discharge imbalance according to claim 1 or 3,
in step 4, when the unbalance degree of the energy storage battery pack is larger than zero and the energy storage battery pack executes a charging task, the time constant is reduced.
5. The wind storage system power control method considering charge-discharge imbalance according to claim 1 or 3, wherein:
in step 4, when the unbalance degree of the energy storage battery pack is larger than zero and the energy storage battery pack executes a discharging task, the time is increased.
6. The wind storage system power control method considering charge-discharge imbalance according to claim 1 or 3, wherein:
in step 4, when the unbalance degree of the energy storage battery pack is less than or equal to zero and the energy storage battery pack performs a charging task, the time constant is increased.
7. The wind storage system power control method considering charge-discharge imbalance according to claim 1 or 3, wherein:
in step 4, when the unbalance degree of the energy storage battery pack is less than or equal to zero and the energy storage battery pack performs a discharging task, the time constant is reduced.
8. The wind storage system power control method considering charge-discharge imbalance according to claim 1, is characterized in that:
the method for calculating the charge states of the two groups of energy storage batteries comprises the following steps:
Figure FDA0003558395450000021
in the formula, S soc1 (k.DELTA.t) and S soc2 (k Δ t) is the SOC values of the battery pack 1 and the battery pack 2 at the present time, μ 1 、μ 2 Respectively marking the charging role and the discharging role of the battery pack; mu.s 1 Indicates the charge and discharge state of the battery pack 1, μ 2 Indicates the charge-discharge state of the battery pack 2; when the battery is being charged, mu 1 、μ 2 The value of (A) is 1; when the battery is discharging, mu 1 、μ 2 The value of (A) is 0; p is ch (kΔt)、P disch (k delta t) is respectively the charging power and the discharging power required by the wind power plant at the current moment, and the P is assigned according to the roles of the two groups of batteries b1 (k.DELTA.t) and P b2 (kΔt)；E 1 ((k-1) Δ t) and E 2 (k-1) Δ t is the residual electric quantity of the two battery packs at the previous moment, Δ t is the sampling period, η ch And η disch Efficiency of charging and discharging, respectively, of the battery pack, E 1 、E 2 The rated capacities of the battery pack 1 and the battery pack 2, respectively.
9. The wind storage system power control method considering charge-discharge imbalance according to claim 1 or 8,
the unbalance degrees of the two groups of batteries meet the following relational expression:
A(kΔt)＝(S soc1 (kΔt)+S soc2 (kΔt))-(S socmax +S socmin )
wherein, the closer A (k delta t) is to 0, the higher the balance degree of the two groups of batteries is, and when the capacities of the two groups of batteries are the same, the chargeable quantity is approximately equal to the dischargeable quantity; when A (k delta t) is less than 0, the chargeable quantity in the two groups of batteries is larger than the dischargeable quantity, and conversely, when A (k delta t) is larger than 0, the dischargeable quantity is larger than the chargeable quantity; the absolute value | A (k Δ t) | of A (k Δ t) represents the absolute unevenness of the two groups of batteriesThe larger the value of the A (k delta t) is, the higher the unbalance degree of the two groups of batteries is; s socmax And S socmin Respectively the set upper and lower limits of the state of charge of the battery pack.
10. The wind storage system power control method considering charge-discharge imbalance according to claim 9,
the upper and lower limits of the state of charge of the battery pack satisfy the following relational expression:
Figure FDA0003558395450000031
wherein, Delta S socb The standard charging and discharging depth is the charging and discharging depth corresponding to the maximum value of the throughput energy in the service life cycle of the battery, represents the lowest service life attenuation degree, and is an optimal operation state.
11. The wind storage system power control method considering charge-discharge imbalance according to claim 1,
the energy storage battery pack is an energy storage lithium battery pack.
12. The wind power storage system power control system of the wind power storage system power control method considering charge-discharge imbalance according to any one of claims 1 to 11,
the wind storage system power control system comprises a wind power plant, a lithium battery pack, an energy control system, a DC/AC converter and an alternating current power grid;
the lithium battery packs are two groups;
the two groups of lithium battery packs are respectively connected with the wind power plant in parallel through different DC/AC converters;
the energy control system calculates grid-connected target power according to the original wind power and outputs the grid-connected target power to an alternating current power grid, and adjusts the charging and discharging state of the lithium battery pack.
The energy control system filters the original wind power through a first-order low-pass filter to obtain the grid-connected target power of the wind power plant.
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