CN115360738B - Electric automobile primary frequency modulation control method considering controllable domain constraint - Google Patents
Electric automobile primary frequency modulation control method considering controllable domain constraint Download PDFInfo
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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
- H02J3/322—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means the battery being on-board an electric or hybrid vehicle, e.g. vehicle to grid arrangements [V2G], power aggregation, use of the battery for network load balancing, coordinated or cooperative battery charging
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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
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
- H02J3/241—The oscillation concerning frequency
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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
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/0029—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries with safety or protection devices or circuits
- H02J7/00306—Overdischarge protection
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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
- 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]
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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
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/007—Regulation of charging or discharging current or voltage
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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
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/60—Other road transportation technologies with climate change mitigation effect
- Y02T10/70—Energy storage systems for electromobility, e.g. batteries
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Abstract
The invention discloses an electric vehicle primary frequency modulation control method considering controllable domain constraint, which comprises the steps of establishing an electric vehicle charging behavior characteristic model, a controllable domain model for providing primary frequency modulation service for an electric vehicle and an electric vehicle primary frequency modulation control power output model under the controllable domain constraint; and under the constraint of a controllable domain determined by the user requirements and behavior characteristics, performing primary frequency modulation optimization control on the electric automobile cluster. The controllable domain provided by the invention fully considers the behavior characteristics and the charging requirements of the electric automobile, and the primary frequency modulation control method provided on the basis can provide sufficient and sustainable frequency support for the power grid while meeting the charging requirements of users, so that the optimal utilization of the electric automobile regulation resources is realized, and the frequency stability of the large-scale electric automobile connected to the power grid is improved.
Description
Technical Field
The invention relates to the technical field of power interaction between an electric automobile and a power grid, in particular to an electric automobile primary frequency modulation control method considering controllable domain constraint.
Background
With the exhaustion of fossil fuels and the gradual worsening of atmospheric pollution conditions in the global world, the development of new renewable energy sources is gradually increasing. Electric vehicles are regarded as a representative of the field of new energy vehicles, and are regarded as important factors for changing the structure of the field of energy and improving environmental problems. The development of a vehicle-to-grid (V2G) technology is promoted on a large scale by the electric vehicle, the flexible power interaction characteristic of the electric vehicle and a power grid enables the electric vehicle to serve as a flexible energy storage system of the power grid to provide or consume power of the power grid when the electric vehicle is idle, and a large number of electric vehicle grid connection can provide effective active support for the power system, wherein the frequency is one of main support requirements of the power grid.
The unbalance of power supply and demand when the power system is disturbed can lead to the reduction of the frequency of the power grid, and if the reduction of the frequency of the system cannot be effectively restrained, serious consequences can be caused, and even the stability and the safety of the power system are affected. Because the charging and discharging of the electric automobile are electromagnetic and chemical processes rather than mechanical processes, compared with a power plant, the electric automobile has the advantages that the electric automobile reacts more rapidly, and the starting cost and the closing cost are not needed, so that the electric automobile is more suitable for participating in primary frequency modulation of a power grid with higher response speed. Different from wind power plants or fixed energy storage systems, the electric automobile is required to provide the frequency modulation service of the power system by considering the user behavior and the charging requirement, and the electric automobile batteries of different types, different charging and discharging characteristics and the random charging behaviors of the user can influence the primary frequency modulation service provided by the electric automobile. Therefore, by balancing the user demand and the grid primary frequency modulation demand, it is important to make the electric vehicle stabilize the output power to provide the primary frequency modulation service while guaranteeing the user charging demand.
The prior art scheme and the defects thereof are that:
(1) Measure 1: the primary frequency modulation control method considering the output characteristics of the electric automobile under a long time scale is proposed, and the following references can be referred to:
[ reference 1]Deng X,Zhang Q,Li Y,et al.Hierarchical Distributed Frequency Regulation Strategy of Electric Vehicle Cluster Considering Demand Charging Load Optimization[C ]//2020 IEEE Student Conference on Electric Machines and Systems (SCEMS) & IEEE,2020.
The electric automobile output characteristics of short time scale are not considered in the measures, and the electric automobile can influence battery charging due to participation in frequency control of an electric power system, so that traveling of an automobile owner is influenced.
(2) Measure 2: considering the state of charge of the batteries of an electric vehicle and the number of participating in the power system frequency control optimization strategy, reference may be made to the following references:
[ reference 2]Iqbal S,Xin A,Jan M U,et al.Aggregation of EVs for Primary Frequency Control of an Industrial Microgrid by Implementing Grid Regulation&Charger Controller[J ]. IEEE Access 2020,8:141977-141989.
The method sets the SOC (State-of-Charge) range of the electric automobile capable of participating in the frequency control of the electric power system to be conservative, and the adjustable frequency capacity of the electric automobile is not fully utilized, so that the utilization rate of the electric automobile adjusting resources is limited.
(3) Measure 3: the method for scheduling the priority of the electric automobile and the method for controlling the frequency by taking the charging time allowance and the SOC real-time state as constraints can be referred to the following references:
[ reference 3]Wang M,Mu Y,Li F,et al.State Space Model of Aggregated Electric Vehicles for Frequency Regulation[J ]. IEEE Transactions on Smart Grid,2020,11 (2): 981-994.
[ reference 4]Wang M,Mu Y,Shi Q,et al.Electric Vehicle Aggregator Modeling and Control for Frequency Regulation Considering Progressive State Recovery[J ]. IEEE Transactions on Smart Grid,2020,11 (5): 4176-4189.
The influence of the SOC and the residual charging time change of the electric automobile on the frequency supporting capacity of the electric automobile in the process of providing primary frequency modulation service cannot be fully considered in the measure, the electric automobile output power strategy designed according to the method has no adaptability, and the electric automobile cluster output power is unstable due to the fact that the running point reaches the controllable domain boundary and is forcedly converted into a charging state in the frequency modulation process. In addition, the measure does not consider the difference of charging requirements and behavior characteristics of different types of electric vehicles
Disclosure of Invention
Aiming at the problems, the invention aims to provide the primary frequency modulation control method of the electric automobile, which considers the constraint of the controllable domain, so as to reduce the influence of primary frequency modulation service of the electric automobile on the charging and the traveling of a user, fully utilize the primary frequency modulation capability of the electric automobile on the premise of meeting the charging requirement, enable the electric automobile to provide stable and sustainable power support for a power grid in the primary frequency modulation process, and improve the frequency stability. The technical proposal is as follows:
an electric automobile primary frequency modulation control method considering controllable domain constraint comprises the following steps:
step 1: establishing an electric vehicle charging behavior characteristic model: according to actual running data of the electric automobile, a distribution model of charging starting time, charging ending time and average daily driving mileage of the electric automobile is obtained;
step 2: establishing a controllable domain model of the electric automobile for providing primary frequency modulation service:
step 2.1: the relationship between the charging power and the state of charge is determined as follows:
wherein P is char Representing the charging power of the electric automobile, P con Representing the charging power of the electric automobile in a constant power charging state; SOC is a real-time state of charge value of the battery of the electric automobile; SOC (State of Charge) max Overcharging the battery with a threshold value; SOC (State of Charge) exp Is a state of charge expected value;
step 2.2: taking a real-time state of charge (SOC) value and residual charging time of an electric vehicle battery as constraint conditions, and establishing an electric vehicle primary frequency modulation controllable domain model:
taking a real-time state of charge (SOC) value of an electric vehicle battery as an ordinate and charging time as an abscissa;
the point A is used for representing the point of starting charging of the electric automobile, and the ordinate corresponds to the initial value SOC of the state of charge start The abscissa corresponds to the charge start time t sart ；
The point B is used for representing that the electric automobile is charged from the point A to the SOC at constant charging power exp The ordinate corresponds to the state of charge expected value SOC exp ；
C point is used for indicating that the state of charge of the electric automobile reaches SOC when charging is finished exp The ordinate corresponds to the state of charge expected value SOC exp The abscissa corresponds to the charge end time t end ；
The D point is used for representing the over-discharge critical value SOC of the electric automobile in the charge state min The forced charge point at the time and the ordinate correspond to the charge state overdischarge critical value SOC min The abscissa corresponds to the forced charging time t F ；
E point represents that the electric automobile discharges from A point to SOC at maximum discharge power min The ordinate corresponds to the state of charge over-discharge threshold SOC min ；
The slope of line AB represents constant charge power, and the slope of line AE represents maximum discharge power;
the upper boundary of the controllable domain, namely line segment BC, is SOC exp The electric automobile is charged to the SOC exp Then enters an idle state; the lower boundary of the operating region, line segment ED, is SOC min When the state of charge of the battery of the electric automobile is smaller than the SOC min When the battery is in an overdischarge state;
step 2.3: setting margin value for forced charging time, and enabling the state of charge of the battery of the electric automobile to be equal to SOC min Time of forced charging t F Determined by the following formula:
wherein eta c For charging efficiency, t mar To force the charge time margin, Q d The battery capacity of the electric automobile;
step 3: establishing an electric automobile primary frequency modulation control power output model under the constraint of a controllable domain:
step 3.1: considering state of charge, when the real-time state of charge value is smaller than SOC min In order to protect the battery, the battery is not allowed to discharge; when the real-time state of charge value is in SOC min And SOC (System on chip) exp In between, a discharge control strategy of two sections of parabolas is adopted, namely
Wherein P is dchar For discharging power, P max Maximum discharge power, SOC mid Is a battery state of charge midpoint, the value of which is determined by equation (4):
step 3.2: considering the remaining charging time of the electric automobile, so that the output power of the electric automobile in different remaining charging time and charge state is different when primary frequency modulation service is provided, namely, the closer the electric automobile is to the forced charging boundary, the smaller the discharging power is, until the discharging power is reduced to zero when the electric automobile reaches the forced charging boundary, the electric automobile forcedly enters the charge state; the modified electric automobile discharge power is
Wherein P is dchar_t The electric automobile discharge power considering the influence of the residual charging time; t is the initial frequency modulation time;
step 4: the primary frequency modulation optimization control method of the electric automobile cluster is provided.
Further, the step 4 specifically includes:
step 4.1: in order to enable the electric vehicles to respond to the power grid interference with different magnitudes in a self-adaptive way, multiplying the electric vehicle discharge power in the cluster by the same power output coefficient determined by the unbalanced amplitude of the power grid power; thus obtaining the total discharge power of the electric automobile cluster as follows
Wherein P is total The total discharge power of the electric automobile clusters is n, the number of the electric automobiles is n, and k is the self-adaptive coefficient of the electric automobiles for processing different power grid interferences; p (P) dchar_ti The electric automobile discharge power of the ith electric automobile considering the influence of the residual charging time;
step 4.2: setting a sustainability index of power output to judge time t of electric vehicle cluster providing primary frequency modulation service f_dur Whether the output power can be stabilized or not; the sustainability index of the power output is:
S sus ＝[(P end -P start )/P start ]*100％ (7)
wherein S is sus Is a sustainability index, P start The total output power of the electric automobile cluster at the starting moment of providing primary frequency modulation service, P end The total output power of the electric automobile cluster at the end time of providing the primary frequency modulation service;
step 4.3: when the power grid is interfered and the electric vehicles are required to provide primary frequency modulation service, the electric vehicle clusters collect the behavior parameters of each electric vehicle; grid power deficiency P caused by interference s Maximum total discharge power with electric automobile cluster, namely P total_max Comparing to determine how the electric automobile provides primary frequency modulation service; for different power grid interference, the output power of the electric automobile clusters is different, namely
Step 4.4: evaluating the sustainability of output power when the electric automobile provides primary frequency modulation service according to a formula (7);
when the electric automobile cluster cannot meet the requirement of the sustainability index, the electric automobile cluster controller stops power output of electric automobiles which reach a charging boundary in the process of providing primary frequency modulation service in the cluster according to the collected single electric automobile parameters in sequence from low output power to high output power, and then outputs P s And P total_max Comparing until a sustainable index is reached;
when the electric automobile cluster meets the requirement of the sustainability index, the electric automobile cluster controller sends a power adjusting signal to the electric automobile cluster, and the electric automobiles in the controllable domain start to provide primary frequency modulation service; setting a step length m to judge whether a single electric automobile under the cluster starts from an initial frequency modulation time t and reaches a forced charging boundary in the initial frequency modulation time; if the electric automobile reaches the forced charging boundary, the electric automobile is switched from a discharging state to a charging state; if not, continuing discharging according to the primary frequency modulation optimization control method, and then continuing judging in the next step length t+m; until the time reaches t f_dur The electric automobile clusters stop discharging.
The beneficial effects of the invention are as follows: the invention provides a primary frequency modulation optimization control method of an electric automobile cluster under the constraint of a controllable domain determined by user requirements and behavior characteristics. Firstly, an electric automobile primary frequency modulation controllable domain model is constructed according to the behavior characteristics and the charging requirements of the electric automobile, and an electric automobile primary frequency modulation control method capable of providing sustainable frequency support for a power grid while meeting the charging requirements of users is provided on the basis, so that the optimal utilization of electric automobile adjustment resources is realized, and the frequency stability of large-scale electric automobile access to the power grid is improved.
Drawings
Fig. 1 is a diagram of a controllable domain model of an electric vehicle providing primary frequency modulation service to a power grid.
FIG. 2 is a graph of electric vehicle output power for a 13:00 generator producing a 25kW power deficit
FIG. 3 is a graph of the change in grid frequency at 13:00 when the generator is generating a 25kW power deficit.
Detailed Description
The invention will now be described in further detail with reference to the drawings and to specific examples.
The control strategy provided by the invention is mainly applied to the situation that the electric automobile provides primary frequency modulation service for the power grid under the condition of high power loss of the power grid. Through deep analysis of the behavior characteristics and the charging requirements of the electric automobile, a more reasonable controllable domain and a forced charging boundary are determined, and a control method which fully considers the charging requirements and the primary frequency modulation requirements of the power grid is provided on the basis. The specific process is as follows:
1. establishing an electric automobile charging behavior characteristic model
According to the actual running data, a distribution model (such as normal distribution) of data such as the charging starting time, the charging ending time and the average day driving mileage of the electric automobile can be obtained.
2. Establishing controllable domain model for providing primary frequency modulation service for electric automobile
When an electric automobile owner charges an electric automobile, the electric automobile owner needs to preset the charging time and the expected value of the SOC (SOC) exp ) When the electric automobile is charged to the SOC exp When the charging is stopped, the electric automobile starts to be connected with the power grid but does not exchange power in an idle state, and the charging follows the following rule:
(1) When the SOC is less than the battery overcharge threshold value (SOC max ) When in use, constant power charging is carried out;
(2) When SOC is greater than SOC max At this time, trickle charging is performed, and the charging power is gradually reduced as the SOC increases.
(3) When the SOC reaches the SOC exp And when the charging is stopped, the electric automobile starts to be in an idle state. And due to different acceptance degree of users on charging cost, SOC exp Any value between the initial SOC and 1 may be taken.
The relationship between the charging power and the SOC is that
Wherein P is char Representing the charging power of the electric automobile, P con Representing the charging power of the electric automobile in a constant power charging state.
Therefore, the real-time SOC value and the residual charging time of the electric vehicle battery are used as constraint conditions, and the primary frequency modulation controllable domain model of the electric vehicle is built.
The controllable domain model of the electric automobile for providing primary frequency modulation service is shown in fig. 1. In fig. 1, a is a point at which an electric vehicle starts charging, and B is a point at which the electric vehicle is charged from a point a to SOC with a constant charging power exp C is the point that the SOC reaches the SOC when the electric automobile finishes charging exp D is the point that the electric automobile is at the SOC overdischarge critical value SOC min The forced charging point E is that the electric automobile discharges from the point A to the SOC with the maximum discharging power min Is a point of (2). The slope of line AB represents constant charge power, and the slope of line AE represents maximum discharge power.
In order to reduce the charging cost of the user as much as possible, the electric automobile is charged to the SOC exp And then enters an idle state. Therefore, the upper boundary of the controllable domain, segment BC, is SOC exp . When the SOC of the battery of the electric automobile is smaller than the SOC min At this time, the battery is in an overdischarged state. At this time, the electric vehicle should be prevented from providing primary frequency modulation service, so that the lower boundary of the running area, namely line segment ED, is SOC min 。FDP(t 0 ,SOC 0 ) Is the frequency scrambling point.
The forced charging time exists in the charging process of the electric automobile, namely the electric automobile can be ensured to charge the battery SOC to the SOC at the charging end time under the constant charging power exp Is the shortest time of (2). In this case, when the electric vehicle reaches the forced charging time, the electric vehicle will be forced into a charged state. In order to reduce the influences of state monitoring errors, charging losses and the like, corresponding margin values are set for the forced charging time.
SOC of electric automobile battery equals SOC min Time of forced charging t F Can be determined by the following formula
Wherein eta c For charging efficiency, t mar To force the charge time margin. Q (Q) d The battery capacity of the electric automobile.
3. Establishing an electric automobile primary frequency modulation control power output model under the constraint of a controllable domain
And constructing an electric automobile primary frequency modulation control power output model under the constraint of the controllable domain according to the established controllable domain model. First consider the SOC state when SOC is less than SOC min When the SOC is at the SOC, the battery is not allowed to discharge in order to protect the battery min And SOC (System on chip) exp In between, a discharge control strategy of two sections of parabolas is adopted, namely
Wherein P is dchar For discharging power, P max Maximum discharge power, SOC mid Is the battery SOC midpoint, the value of which is determined by equation (4).
The remaining charging time of the electric automobile is considered, so that the output power of the electric automobile in different remaining charging time and SOC states is different when primary frequency modulation service is provided, namely, the closer the electric automobile is to the forced charging boundary, the smaller the discharging power is, the discharging power is reduced to zero until the electric automobile reaches the forced charging boundary, and the electric automobile forcedly enters the charging state. The modified electric automobile discharge power is
Wherein P is dchar_t The electric vehicle discharge power is considered to influence the residual charging time.
4. Primary frequency modulation optimization control method for electric automobile cluster
In order to enable the electric vehicles to respond to the power grid interference with different magnitudes in a self-adaptive mode, the electric vehicle discharging power in the cluster is multiplied by the same power output coefficient determined by the unbalanced amplitude of the power grid power. Thus obtaining the total discharge power of the electric automobile cluster as follows
Wherein P is total The total discharge power of the electric automobile clusters is n, the number of the electric automobiles is n, and k is the self-adaptive coefficient of the electric automobiles for processing different power grid interferences; p (P) dchar_ti The electric automobile discharge power of the ith electric automobile considering the influence of the residual charging time.
Setting a sustainability index of power output to judge time t of electric vehicle cluster providing primary frequency modulation service f_dur Whether or not the output power can be stabilized. The sustainability index of the power output is
S sus ＝[(P end -P start )/P start ]*100％ (7)
Wherein S is sus Is a sustainability index, P start The total output power of the electric automobile cluster at the starting moment of providing primary frequency modulation service, P end The total output power of the electric automobile cluster at the end time of providing the primary frequency modulation service.
When the power grid is interfered and the electric vehicles are required to provide primary frequency modulation service, the electric vehicle cluster collects the behavior parameters (i.e. t 0 ,SOC 0 ,t end ,SOC exp ,t f_dur Etc.). The parameters are calculated according to the primary frequency modulation optimization control method of the electric automobile cluster under the control domain constraint. Grid power deficiency P caused by interference s Maximum total discharge power with electric automobile cluster, namely P total_max Comparing to determine how the electric vehicle provides primary frequency modulationAnd (5) serving. For different power grid interference, the output power of the electric automobile clusters is different, namely
Then, the sustainability of the output power when the electric vehicle provides the primary frequency modulation service is evaluated according to formula (7). If the electric automobile cluster cannot meet the sustainability index, the electric automobile cluster controller sequentially stops power output of electric automobiles which can reach a charging boundary in the process of providing primary frequency modulation service in the cluster from low output power to high output power according to the collected single electric automobile parameters, and then sequentially outputs P s And P total_max The comparison is performed until a sustainable indicator is reached.
When the electric automobile cluster meets the sustainability requirement, the electric automobile cluster controller sends a power adjusting signal to the electric automobile cluster, and the electric automobiles in the controllable domain start to provide primary frequency modulation service. The step length m is set to judge whether the single electric automobile under the cluster reaches the forced charging boundary within the initial frequency modulation time t from the initial frequency modulation time t. If the electric automobile reaches the forced charging boundary, the electric automobile is switched from a discharging state to a charging state; if not, the discharge is continued according to the primary frequency modulation optimization control method, and then the judgment in the next step length t+m is continued. Until the time reaches t f_dur The electric automobile clusters stop discharging.
Examples:
the invention is simulated on MATLAB/Simulink as an embodiment. In the simulation system, the alternating current system is represented by a generator with rated power of 487.5kW, and an IEEEG1 steam turbine model and a mechanical hydraulic control speed regulator are respectively adopted in the generator and the speed regulator. An electric vehicle is represented by a battery pack.
The battery capacity of the electric automobile is set to be 35kW, primary frequency modulation service is provided according to the control strategy provided by the invention, and the initial charging time and the final charging time of the electric automobile are given. Meanwhile, as the daily driving mileage of the electric automobile has uncertainty, the daily mileage and the battery power consumption rate of the electric automobile are given, and thus the initial SOC value of the electric automobile is obtained.
And (3) enabling 13: and when the power generator generates 25kW power shortage, observing the power grid frequency fluctuation characteristic of the electric automobile cluster primary frequency modulation optimization control method (hereinafter referred to as an optimization control method) under the constraint of the controllable domain determined by the user demand and the behavior characteristic, wherein the average power primary frequency modulation control method (hereinafter referred to as an average control method) is used for carrying out power output on the electric automobile in the controllable domain when the electric automobile cluster does not provide primary frequency modulation service. The electric automobile cluster controller refreshes the output power of the electric automobile once at intervals of 1s, the primary frequency modulation time is set to be 50s (which can be modified according to the actual power grid requirement), and the power of the electric automobile which can be continuously output to the power grid within 50s is considered. The output power curves of the electric vehicle average control method and the optimization control method are shown in fig. 2.
In fig. 2, the dashed line represents the average control method proposed by the present invention, and the solid line represents the optimal control method. Considering the sustainability index provided by the invention, S sus Should be less than 2%. Through calculation, the optimal control method is S in the primary frequency modulation time range sus =1.865%, reaching the output power stability index; the average control method does not consider the influence of the charging requirement of the electric automobile on the primary frequency modulation service, so that the output power is relatively unstable, S sus ＝6.312％。
The grid frequency variation when the 13:00 generator produces a 25kW power deficit is shown in figure 3.
As can be seen from fig. 3, 13: the power generator generates 25kW power shortage in 00 hours, if no electric automobile provides primary frequency modulation service for the power grid, the power grid frequency is reduced to 49.54Hz at the lowest frequency point within 2.67s after disturbance occurs, and then the stable value reaches 49.85Hz within 16.60 s; when an electric automobile cluster which outputs power to a power grid by an average control method is added, the frequency reaches the lowest point of 49.74Hz after disturbance occurs, but in order to enable the electric automobile to charge electric quantity to an expected value of an automobile owner in the preset charging time of the automobile owner, part of electric automobiles are forcedly changed in a charging and discharging state in the frequency modulation process, so that the system frequency is respectively suddenly reduced in the 3s, 8s, 19s and 35s after disturbance occurs and is finally stabilized at 49.89Hz, and compared with the average control method, the optimized control method provided by the invention is more stable in providing primary frequency modulation service and the frequency is stabilized at 49.92Hz in 13.85 s. Therefore, compared with the condition that no electric automobile provides primary frequency modulation service for the power grid, the frequency deviation in a new steady state is reduced by 46.7% by the optimized control method, and compared with the average control method, the frequency deviation is reduced by 27.3%. The optimization control method provided by the invention is high in feasibility and practicability.
Claims (2)
1. The electric automobile primary frequency modulation control method considering the controllable domain constraint is characterized by comprising the following steps of:
step 1: establishing an electric vehicle charging behavior characteristic model: according to actual running data of the electric automobile, a distribution model of charging starting time, charging ending time and average daily driving mileage of the electric automobile is obtained;
step 2: establishing a controllable domain model of the electric automobile for providing primary frequency modulation service:
step 2.1: the relationship between the charging power and the state of charge is determined as follows:
wherein P is char Representing the charging power of the electric automobile, P con Representing the charging power of the electric automobile in a constant power charging state; SOC is a real-time state of charge value of the battery of the electric automobile; SOC (State of Charge) max Overcharging the battery with a threshold value; SOC (State of Charge) exp Is a state of charge expected value;
step 2.2: taking a real-time state of charge (SOC) value and residual charging time of an electric vehicle battery as constraint conditions, and establishing an electric vehicle primary frequency modulation controllable domain model:
taking a real-time state of charge (SOC) value of an electric vehicle battery as an ordinate and charging time as an abscissa;
the point A is used for representing the point of starting charging of the electric automobile, and the ordinate corresponds to the initial value SOC of the state of charge start The abscissa corresponds to the charge start time t sart ；
The point B is used for representing that the electric automobile is charged from the point A to the SOC at constant charging power exp The ordinate corresponds to the state of charge expected value SOC exp ；
C point is used for indicating that the state of charge of the electric automobile reaches SOC when charging is finished exp The ordinate corresponds to the state of charge expected value SOC exp The abscissa corresponds to the charge end time t end ；
The D point is used for representing the over-discharge critical value SOC of the electric automobile in the charge state min The forced charge point at the time and the ordinate correspond to the charge state overdischarge critical value SOC min The abscissa corresponds to the forced charging time t F ；
E point represents that the electric automobile discharges from A point to SOC at maximum discharge power min The ordinate corresponds to the state of charge over-discharge threshold SOC min ；
The slope of line AB represents constant charge power, and the slope of line AE represents maximum discharge power;
the upper boundary of the controllable domain, namely line segment BC, is SOC exp The electric automobile is charged to the SOC exp Then enters an idle state; the lower boundary of the operating region, line segment ED, is SOC min When the state of charge of the battery of the electric automobile is smaller than the SOC min When the battery is in an overdischarge state;
step 2.3: setting margin value for forced charging time, and enabling the state of charge of the battery of the electric automobile to be equal to SOC min Time of forced charging t F Determined by the following formula:
wherein eta c For charging efficiency, t mar To force the charge time margin, Q d The battery capacity of the electric automobile;
step 3: establishing an electric automobile primary frequency modulation control power output model under the constraint of a controllable domain:
step 3.1: considering state of charge, when the real-time state of charge value is smaller than SOC min In order to protect the battery, the battery is not allowed to discharge; when the real-time state of charge value is in SOC min And SOC (System on chip) exp In between, a discharge control strategy of two sections of parabolas is adopted, namely
Wherein P is dchar For discharging power, P max Maximum discharge power, SOC mid Is a battery state of charge midpoint, the value of which is determined by equation (4):
step 3.2: considering the remaining charging time of the electric automobile, so that the output power of the electric automobile in different remaining charging time and charge state is different when primary frequency modulation service is provided, namely, the closer the electric automobile is to the forced charging boundary, the smaller the discharging power is, until the discharging power is reduced to zero when the electric automobile reaches the forced charging boundary, the electric automobile forcedly enters the charge state; the modified electric automobile discharge power is
Wherein P is dchar_t The electric automobile discharge power considering the influence of the residual charging time; t is the initial frequency modulation time;
step 4: the primary frequency modulation optimization control method of the electric automobile cluster is provided, and the sustainability index of output power when the electric automobile provides primary frequency modulation service is evaluated:
when the electric vehicle cluster fails to meet the sustainability index requirement,the electric automobile cluster controller stops power output in sequence from low output power to high output power of electric automobiles which can reach charging boundary in the process of providing primary frequency modulation service in the cluster according to the collected single electric automobile parameters, and then power shortage P of a power grid caused by interference is caused s Maximum total discharge power P with electric automobile cluster total_max Comparing;
when the electric automobile cluster meets the requirement of the sustainability index, the electric automobile cluster controller sends a power adjusting signal to the electric automobile cluster, and the electric automobiles in the controllable domain start to provide primary frequency modulation service; setting a step length m to judge whether a single electric automobile under the cluster reaches a forced charging boundary in the frequency modulation time from an initial frequency modulation time t; if the electric automobile reaches the forced charging boundary, the electric automobile is switched from a discharging state to a charging state; if not, continuing discharging according to the primary frequency modulation optimization control method, and then continuing judging in the next step length t+m; until the time reaches the time t when the electric vehicle cluster provides primary frequency modulation service f_dur The electric automobile clusters stop discharging.
2. The electric vehicle primary frequency modulation control method considering the controllable domain constraint according to claim 1, wherein the step 4 specifically includes:
step 4.1: in order to enable the electric vehicles to respond to the power grid interference with different magnitudes in a self-adaptive way, multiplying the electric vehicle discharge power in the cluster by the same power output coefficient determined by the unbalanced amplitude of the power grid power; thus obtaining the total discharge power of the electric automobile cluster as follows
Wherein P is total The total discharge power of the electric automobile clusters is n, the number of the electric automobiles is n, and k is the self-adaptive coefficient of the electric automobiles for processing different power grid interferences; p (P) dchar_ti The electric automobile discharge power of the ith electric automobile considering the influence of the residual charging time;
step 4.2: setting a sustainability index of power output to judge time t of electric vehicle cluster providing primary frequency modulation service f_dur Whether the output power can be stabilized or not; the sustainability index of the power output is:
S sus ＝[(P end -P start )/P start ]*100％ (7)
wherein S is sus Is a sustainability index, P start The total output power of the electric automobile cluster at the starting moment of providing primary frequency modulation service, P end The total output power of the electric automobile cluster at the end time of providing the primary frequency modulation service;
step 4.3: when the power grid is interfered and the electric vehicles are required to provide primary frequency modulation service, the electric vehicle clusters collect the behavior parameters of each electric vehicle; grid power deficiency P caused by interference s Maximum total discharge power with electric automobile cluster, namely P total_max Comparing to determine how the electric automobile provides primary frequency modulation service; for different power grid interference, the output power of the electric automobile clusters is different, namely
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