CN112736989A - Frequency modulation method, system and device with battery energy storage participation and readable storage medium - Google Patents
Frequency modulation method, system and device with battery energy storage participation and readable storage medium 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
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/48—Controlling the sharing of the in-phase component
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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
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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
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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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
- 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
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- 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
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/70—Wind energy
- Y02E10/76—Power conversion electric or electronic aspects
Abstract
The invention provides a frequency modulation method, a system, a device and a readable storage medium for battery energy storage participation, which comprise the following steps: the system comprises a fan, a synchronous machine frequency modulation device and a battery energy storage device; the fan power generation assembly and the battery energy storage device are respectively merged into the output power of the power grid; the synchronous machine frequency modulation device is used for tracking the output power of the fan power generation assembly merged into the power grid in real time; when disturbance occurs in the system, the fan power generation assembly generates power drop, and the battery energy storage device is controlled to be connected into a power grid, so that the battery energy storage device and the fan power generation assembly run in parallel; the generated power makes up for the power shortage generated by the reduction of the output power of the fan power generation assembly. And controlling the battery energy storage system to participate in frequency modulation by adopting a variable droop coefficient control mode, wherein the droop coefficient takes different values due to different disturbance and different square wave frequency modulation stages where the fan is positioned. In a power grid system, a wind turbine generator can participate in frequency modulation to improve the lowest point of frequency by releasing kinetic energy of a rotor, and the disturbance coping capability of the system is greatly improved.
Description
Technical Field
The invention relates to the technical field of power grid frequency modulation, in particular to a frequency modulation method, a frequency modulation system, a frequency modulation device and a readable storage medium for battery energy storage participation.
Background
In recent years, the scale of grid-connected generation of new energy represented by wind energy is continuously enlarged, the installation occupation ratio is continuously increased, and synchronous machines are gradually replaced. The direct coupling between the rotating speed of the rotor of the conventional synchronous generator and the system frequency presents certain inertia to the system and can respond to the change of the system frequency. The wind turbine generator is connected with a power grid through a frequency converter, the kinetic energy and the frequency of a rotor are completely decoupled, and the inertia contribution of the wind turbine generator to the power grid is almost zero from the system perspective. With the improvement of the wind energy permeability, the inertia of the system is gradually reduced, the capability of bearing active impact and inhibiting frequency fluctuation is weakened, and the safe and stable operation of the power grid is challenged.
In order to meet the requirements of the system, the wind turbine generator can release the kinetic energy of the rotor through square wave control so as to participate in frequency regulation of the power system. During square wave frequency modulation, the system frequency drop problem caused by disturbance can be improved, and the buffer capacity of the system to the disturbance is improved. But the kinetic energy of the rotor of the fan can not be released infinitely, and when the release amount reaches an allowable value, the fan instantly reduces the output force and exits frequency modulation. The instantaneous drop of the output of the fan is equivalent to a new disturbance for a system, and secondary drop of frequency is caused, so that the safe operation of a power grid is threatened.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides a frequency modulation system with battery energy storage participation, which can further improve the disturbance handling capability of the system and can effectively eliminate the problem of frequency secondary drop caused by the fact that a fan exits frequency modulation.
The method comprises the following steps:
tracking the output power of the fan power generation assembly merged into the power grid in real time;
when disturbance occurs in the system, acquiring a power increasing value delta P of the fan power generation assembly entering a sudden power increasing stage1；
When the preset frequency modulation time is reached, the delta P generated by the wind turbine power generation assembly is collecteddropAnd the fan output power is lower than the value of the normal operating point;
a battery energy storage device controlled by a PWM controller is connected to enable the battery energy storage device and the fan power generation assembly to run in parallel;
and controlling the power emitted by the battery energy storage device, so that the emitted power makes up the power shortage generated by the reduction of the output power of the fan power generation assembly.
It should be further noted that, under normal operation, the output power of the fan is Pwe0；
When disturbance occurs in the system, the fan enters sudden power increaseRate staging and maintaining constant power increase Δ P1；
When the preset frequency modulation time is reached, the fan quits frequency modulation to generate delta PdropThe output power is lower than the value of the normal operating point;
obtaining the sudden power delta P in the square wave frequency modulation modeWTThe expression of (a) is:
wherein ,t0For the moment of disturbance occurrence, toffFor the moment when the fan exits the square wave frequency modulation, omegaoffThe rotor speed at the moment of exit can be determined from equation (3), Pwm(ωoff) The mechanical power corresponding to the exit time can be obtained by the formula (4);
in the formula ,ω0The rotor speed at the normal working point, H is the inertia time constant of the fan, rho is the air density, A is the area swept by the wind wheel blade, vwIs the wind speed, CpIs the wind energy utilization coefficient, the pitch angle beta and the rotor speed omegarIt is related.
It should be further noted that when the square wave frequency modulation is in the phase of increasing the transmission power, the droop coefficient k takes the value k1The battery energy storage device plays a role in auxiliary frequency modulation;
when the fan exits square wave frequency modulation, the droop coefficient k is increased to k2So that the battery energy storage device can send more power to make up for the power shortage caused by the fan quitting;
k2according to k1Calculating the square wave frequency modulation parameter value of the fan;
the expression of the frequency deviation (7) based on the equations (5) and (6) is:
wherein ΔPLIs a load disturbance value;
at the sudden power increase stage of square wave frequency modulation, the variable droop control coefficient k is k1In the exit phase, k is k2Substituting the equations (2) and (3) into (7) to obtain the frequency fluctuation delta f caused by the disturbance1And frequency fluctuation delta f in secondary falling2The relational expression of (1) is:
Δf1(t)＝F(k1,ΔPL,ΔP1,t) (7)
Δf2(t)＝f(k2,ΔPL,ΔP1,t0,toff,t) (8)
Δf1the variation with time t is influenced by k1、ΔPL、ΔP1Influence of values, F represents the mapping relation between the values; Δ f2The variation with time t is influenced by k2、ΔPL、ΔP1、t0、toffAnd f represents the mapping relation between the values.
It is further noted that, in order to ensure the system frequency is within the safety range Δ flimInternal fluctuation, then the equations (8) and (9) are satisfied
|Δf1(t)|max＝C1(k1,ΔPL,ΔP1)<Δflim (9)
|Δf2(t)|max＝C2(k2,ΔPL,ΔP1,t0,toff)<Δflim (10)
wherein ,|Δf1(t)|maxIs the maximum value of frequency fluctuation caused by disturbance, and k1、ΔPL、ΔP1Correlation, C1Representing the mapping relation between them;
|Δf2(t)|maxthe maximum value of frequency fluctuation when the fan quits to cause the secondary frequency drop, and k2、ΔPL、ΔP1、t0、toffCorrelation, C2Representing a mapping relationship.
It is further noted that, in order to reduce or even eliminate the secondary drop, the sum of the output of the fan and the output of the battery energy storage device is kept within a preset threshold range, that is, the sum of the output of the fan and the output of the battery energy storage device is kept within the preset threshold range
ΔPdrop＝-k2Δf1(toff)+k1Δf1(toff) (11)
wherein ,ΔPdropCan be calculated from the equation (13),
ΔPdrop＝Pwe0+ΔP1-Pwm(ωoff)＝C3(ΔP1,t0,toff) (12)
to obtain delta PdropValue of and Δ P1、t0、toffIs related by C3Representing the mapping relation between them;
substituting the formulas (8) and (13) into the formula (12) to eliminate the frequency secondary drop, k1、k2The limiting conditions to be met are:
C3(ΔP1,t0,toff)＝(k1-k2)·F(k1,ΔPL,ΔP1,toff) (13)
when the load disturbance in the system is of magnitude Δ PLAnd the occurrence time t0When determined, the equations (10) and (14) can be given as:
C1(k1,ΔP1)<Δflim (14)
C3(ΔP1,toff)＝(k1-k2)·F(k1,ΔP1,toff) (15)
equations (15) and (16) are relational equations which need to be satisfied between the control coefficient for eliminating the secondary drop of the frequency and the variable droop of the battery energy storage device and the square wave frequency modulation control parameter of the fan under the condition of disturbance.
The invention also provides a frequency modulation system with battery energy storage participation, which comprises: the system comprises a fan, a synchronous machine frequency modulation device and a battery energy storage device;
the fan power generation assembly and the battery energy storage device are respectively merged into the output power of the power grid;
the synchronous machine frequency modulation device is used for tracking the output power of the fan power generation assembly merged into the power grid in real time;
when disturbance occurs in the system, the synchronous machine frequency modulation device obtains the power increasing value delta P of the fan power generation assembly entering the sudden power increasing stage1；
When the preset frequency modulation time is reached, the synchronous machine frequency modulation device collects delta P generated by the fan power generation assemblydropAnd the fan output power is lower than the value of the normal operating point;
the synchronous machine frequency modulation device controls a battery energy storage device controlled by a PWM controller to be connected to a power grid, so that the battery energy storage device and the fan power generation assembly run in parallel;
and controlling the power emitted by the battery energy storage device, so that the emitted power makes up the power shortage generated by the reduction of the output power of the fan power generation assembly.
The invention also provides a synchronous machine frequency modulation device for realizing the frequency modulation method for the battery energy storage participation, which comprises the following steps:
the storage is used for storing a computer program and a frequency modulation method in which the battery energy storage participates;
and the processor is used for executing the computer program and the frequency modulation method in which the battery energy storage participates so as to realize the steps of the frequency modulation method in which the battery energy storage participates.
The invention also provides a readable storage medium with a frequency modulation method involving battery energy storage, on which a computer program is stored, the computer program being executed by a processor to implement the steps of the frequency modulation method involving battery energy storage.
According to the technical scheme, the invention has the following advantages:
the power generated by the battery energy storage system is used for making up the power shortage generated by the fan exiting, wherein the battery energy storage system is controlled to participate in frequency modulation by adopting a variable droop coefficient control mode, and the droop coefficient takes different values due to different disturbances and different square wave frequency modulation stages where the fan is located. In a power grid system containing high-proportion wind power, a wind turbine generator can participate in frequency modulation to improve the lowest point of frequency by releasing kinetic energy of a rotor, and the capacity of the system for coping with disturbance is greatly improved.
In a power grid system containing high-proportion wind power, the wind turbine generator can participate in frequency modulation to improve the lowest point of frequency by releasing kinetic energy of a rotor, so that the disturbance coping capability of the system is greatly improved. However, the existing fan inertia frequency modulation control mode represented by square wave frequency modulation has negative influence on the system frequency. When the fan exits frequency modulation, the system has secondary frequency drop and even frequency collapse, and the stability of the system is threatened. The battery energy storage system controlled by the variable droop coefficient control mode can further improve the disturbance handling capacity of the system and can effectively eliminate the problem of frequency secondary drop caused by the fact that the fan exits frequency modulation. When different disturbances occur, in order to solve the problem of frequency secondary falling, the relation required to be met between the variable droop control coefficient of the battery energy storage system and the control parameter of the square wave frequency modulation of the fan is obtained by theoretical derivation, and finally the accuracy and the effectiveness of the method are verified by the simulation result in the DIGSILENT/Power Factory platform.
Drawings
In order to more clearly illustrate the technical solution of the present invention, the drawings used in the description will be briefly introduced, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained based on these drawings without creative efforts.
FIG. 1 is a flow chart of a frequency modulation method involving battery energy storage;
FIG. 2 is a square wave frequency modulation control curve diagram according to the present invention;
FIG. 3 is a square wave frequency modulation control curve diagram according to the present invention;
FIG. 4 is a frequency response model diagram of the battery-containing energy storage system and fan frequency modulation of the present invention;
FIG. 5 is a power grid topology diagram according to an embodiment of the present invention;
FIG. 6 is a graph of the frequency variation of the system of the present invention;
fig. 7 is a graph of the output power of the battery energy storage system under droop coefficient control in the system of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a frequency modulation method and system for battery energy storage participation, which can further improve the disturbance handling capability of the system and effectively eliminate the problem of frequency secondary drop caused by the fact that a fan exits frequency modulation.
The invention relates to a frequency modulation system with participation of battery energy storage, which comprises: the system comprises a fan, a synchronous machine frequency modulation device and a battery energy storage device;
the fan power generation assembly and the battery energy storage device are respectively merged into the output power of the power grid;
the synchronous machine frequency modulation device is used for tracking the output power of the fan power generation assembly merged into the power grid in real time;
when disturbance occurs in the system, the synchronous machine frequency modulation device obtains the power increasing value delta P of the fan power generation assembly entering the sudden power increasing stage1；
When the preset frequency modulation time is reached, the synchronous machine frequency modulation device collects delta P generated by the fan power generation assemblydropPower drop of, and fan output powerA value below the normal operating point;
the synchronous machine frequency modulation device controls a battery energy storage device controlled by a PWM controller to be connected to a power grid, so that the battery energy storage device and the fan power generation assembly run in parallel;
and controlling the power emitted by the battery energy storage device, so that the emitted power makes up the power shortage generated by the reduction of the output power of the fan power generation assembly.
That is, the sum of the output of the fan and the output of the battery energy storage device needs to be kept within the preset threshold range in any case, that is, the increment of the output power of the battery energy storage device needs to be equal to the reduction of the output of the fan.
In order to weaken the secondary dropping of frequency and improve the buffering capacity of a system for responding disturbance, the invention provides a control strategy for configuring the battery energy storage auxiliary frequency modulation controlled by the variable droop coefficient at the side of a Power grid, analyzes the selection principle of the droop coefficient, and verifies the effectiveness of the provided strategy through DIGSILENT/Power factor simulation.
The units and algorithm steps of each example described in the embodiments disclosed in the embodiments of the method and system for frequency modulation involving battery energy storage provided by the present invention can be implemented by electronic hardware, computer software, or a combination of both, and in the above description, the components and steps of each example have been generally described in terms of functions in order to clearly illustrate the interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
The system, the device and the method for frequency modulation with participation of battery energy storage can be realized in other modes. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of the units is only one logical division, and other divisions may be realized in practice, for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or units, and may also be an electric, mechanical or other form of connection.
The synchronizer frequency modulation device may include a display unit, a communication unit, an audio/video input unit, a user input unit, a sensing unit, an output unit, a memory, an interface unit, a controller, a power supply unit, and the like. It is to be understood that not all illustrated components are required to be implemented. More or fewer components may alternatively be implemented. Elements of the mobile terminal will be described in detail below.
As an embodiment of the method provided by the present invention, as shown in fig. 1, the method includes:
s11, tracking the output power of the wind turbine power generation assembly merged into the power grid in real time;
when disturbance occurs in the system, acquiring a power increasing value delta P of the fan power generation assembly entering a sudden power increasing stage1；
S12, collecting delta P generated by the fan power generation assembly when the preset frequency modulation time is reacheddropAnd the fan output power is lower than the value of the normal operating point;
s13, connecting a battery energy storage device controlled by a PWM controller, and enabling the battery energy storage device and the fan power generation assembly to run in parallel;
and S14, controlling the power emitted by the battery energy storage device, and making the emitted power compensate the power shortage generated by the reduction of the output power of the fan power generation assembly.
The power generated by the battery energy storage device is used for making up the power shortage generated by the exit of the fan power generation assembly, wherein the battery energy storage device is controlled to participate in frequency modulation by adopting a variable droop coefficient control mode, and the droop coefficient takes different values according to different disturbances and different square wave frequency modulation stages where the fan is located.
Under the normal condition of the system, the fan works at the maximum power tracking point, and at the moment, the output electromagnetic power of the fan is as follows:
wherein koptAs coefficient of MPPT curve, omegarIs the rotor speed. Square wave frequency modulation has two important parameters: sudden increase power Δ PWTAnd exit time toff. And after the disturbance occurs, the fan controls to release the kinetic energy of the rotor through square waves to keep constant sudden power increase, and when the rotating speed of the rotor reaches the lower limit value of 0.7p.u. or the frequency modulation time reaches a preset value, the fan quits frequency modulation and switches the output power to an MPPT curve or a mechanical power curve. When the output power is switched to the MPPT curve, the rotating speed of the rotor is gradually recovered to the rated rotating speed because the mechanical power captured by the fan is greater than the electromagnetic power; if the output power is switched to the mechanical power curve, the electromagnetic power is equal to the mechanical power, and the fan is stabilized at the exit point. The invention relates to a fan power generation assembly which comprises a fan and related equipment.
The power shortage caused by the difference of the switching output power to the target curve at the exit moment of the fan is different, and the influence on frequency fluctuation in the frequency modulation period is different. Considering that the power shortage of the fan when the fan exits the MPPT curve is larger than that of the fan when the fan exits the MPPT curve and the recovery process of the rotating speed needs more energy, a control mode that the fan exits the MPPT curve is selected for research. Fig. 2 and fig. 3 show the relationship between the output power of the fan and the rotating speed and the variation of the output power of the fan with time during the square wave frequency modulation, respectively.
Under the normal operating point, the output power of the fan is Pwe0When disturbance occurs in the system, the fan enters a sudden power increase stage and keeps a constant power increase value delta P1When the preset frequency modulation time is reached, the fan quits frequency modulation to generate delta PdropThe output power is maintained at a value lower than the normal operating point. Easily obtaining burst power delta P in square wave frequency modulation modeWTThe expression of (a) is:
wherein ,t0For the moment of disturbance occurrence, toffFor the moment when the fan exits the square wave frequency modulation, omegaoffThe rotor speed at the moment of exit can be determined from equation (3), Pwm(ωoff) The mechanical power corresponding to the exit time can be obtained by equation (4).
in the formula ,ω0The rotor speed at the normal working point, H is the inertia time constant of the fan, rho is the air density, A is the area swept by the wind wheel blade, vwIs the wind speed, CpIs the wind energy utilization coefficient, the pitch angle beta and the rotor speed omegarIt is related.
According to the frequency modulation method involving battery energy storage, after disturbance occurs, the square wave frequency modulation control mode of the fan slows down the system frequency drop to a certain extent, but the rotor kinetic energy of the fan cannot be released infinitely, when the preset frequency modulation time is reached, the fan needs to quit frequency modulation, a large power drop is generated at the moment, the system is a new disturbance, and the frequency drops for a second time.
In order to reduce secondary falling, a battery energy storage device controlled by a PWM controller can be directly connected into a power grid to enable the battery energy storage device to run in parallel with a fan system, and power generated by a battery can make up for power shortage generated by the fan exiting as far as possible.
If the battery energy storage device adopts a constant droop coefficient control mode, the lowest point of frequency generated by disturbance and the lowest point of frequency secondary drop caused by fan exit can be obviously improved, the capacity of the system for coping with the disturbance is also improved, but the frequency secondary drop still exists.
Therefore, the participation of the battery energy storage device is controlled by adopting a variable droop coefficient control modeAnd frequency modulation and droop coefficients take different values due to different disturbance and different square wave frequency modulation stages where the fan is located. When the square wave frequency modulation is in the phase of increasing the power, the droop coefficient k can take a smaller value k1The battery energy storage device has a slight auxiliary frequency modulation effect, and the kinetic energy of the fan rotor and the synchronizer speed regulator have a main frequency modulation effect; when the fan exits square wave frequency modulation, the droop coefficient k is increased to k2So that the battery energy storage device can send more power to make up the power shortage caused by the exit of the fan, k2Can be according to k1And calculating the square wave frequency modulation parameter value of the fan. A frequency control system block diagram is shown in fig. 4.
In the figure, the position of the upper end of the main shaft,
wherein the meaning of each physical quantity is shown in table 1.
The expression of the frequency deviation obtained by fig. 4 and equations (5) and (6) is:
wherein ΔPLIs a load disturbance value. The droop control coefficient k is changed to k without being arranged at the sudden power increase stage of square wave frequency modulation1In the exit phase, k is k2Substituting equations (2) and (3) into equation (7) can obtain frequency fluctuation Δ f caused by disturbance1And frequency fluctuation delta f in secondary falling2The relational expression of (1) is:
Δf1(t)＝F(k1,ΔPL,ΔP1,t) (23)
Δf2(t)＝f(k2,ΔPL,ΔP1,t0,toff,t) (24)
Δf1the variation with time t is influenced by k1、ΔPL、ΔP1Influence of values, F represents the mapping relation between the values; Δ f2The variation with time t is influenced by k2、ΔPL、ΔP1、t0、toffAnd f represents the mapping relation between the values. To ensure that the system frequency is within a safe range deltaflimInternal fluctuation, then the equations (8) and (9) are satisfied
|Δf1(t)|max＝C1(k1,ΔPL,ΔP1)<Δflim (25)
|Δf2(t)|max＝C2(k2,ΔPL,ΔP1,t0,toff)<Δflim (26)
wherein ,|Δf1(t)|maxIs the maximum value of frequency fluctuation caused by disturbance, and k1、ΔPL、ΔP1Correlation, C1Representing the mapping relation between them; | Δ f2(t)|maxThe maximum value of frequency fluctuation when the fan quits to cause the secondary frequency drop, and k2、ΔPL、ΔP1、t0、toffCorrelation, C2Representing the mapping relationship between them. The frequency fluctuation of the two stages is required to be smaller than the maximum allowable fluctuation value of the frequency.
The secondary drop of the frequency is caused by the fan exiting from the frequency modulation, so that in order to reduce or even eliminate the secondary drop, the sum of the output of the fan and the output of the battery energy storage device needs to be kept at a constant value under any condition, namely the increment of the output power of the battery energy storage device needs to be equal to the reduction of the output of the fan, namely
ΔPdrop＝-k2Δf1(toff)+k1Δf1(toff) (27)
wherein ,ΔPdropCan be calculated from the equation (13),
ΔPdrop＝Pwe0+ΔP1-Pwm(ωoff)＝C3(ΔP1,t0,toff) (28)
easily obtain Δ PdropValue of and Δ P1、t0、toffIs related to the value of (C) is not adopted3Representing the mapping relationship between them.
Substitution of formulae (8), (13) for formula (12) can eliminate the frequency dip, k1、k2The limiting conditions to be met are:
C3(ΔP1,t0,toff)＝(k1-k2)·F(k1,ΔPL,ΔP1,toff) (29)
when the load disturbance in the system is of magnitude Δ PLAnd the occurrence time t0When determined, equations (10) and (14) may be rewritten as:
C1(k1,ΔP1)<Δflim (30)
C3(ΔP1,toff)＝(k1-k2)·F(k1,ΔP1,toff) (31)
equations (15) and (16) are relational equations which need to be satisfied between the variable droop control coefficient of the battery energy storage device and the square wave frequency modulation control parameter of the fan for eliminating the frequency secondary drop under the specific disturbance occurrence.
In a practical system, the sudden increase power delta P of the fan1Square wave frequency modulation duration (t)off-t0) Maximum deviation Δ f allowed by system frequencylimIs a given value. After disturbance occurs, the system acquires unbalanced delta P of active powerLAnd the disturbance occurrence time t0The specific expressions of equations (15) and (16) can be determined, t being given by the square-wave frequency modulation durationoffObtaining; will be delta P1K can be obtained by substituting formula (15)1The allowed value range; will be delta P1、toffSubstituting into formula (16) to obtain k1、k2Restricted form of value, in combination with k1Allowable value rangeSelect the k meeting the condition1、k2The value is obtained.
In order to verify the effectiveness of the method, a single-machine Power grid model as shown in FIG. 5 is built in an DIGSILENT/Power Factory simulation platform. In the system, the rated capacity of the synchronous machine is 330MW, the rated capacity of the fan is 220MW, and the rated capacity of the battery energy storage device is 50 MW. A load disturbance of 55MW is set at 10s of system operation, and if the fan and the battery energy storage device do not participate in frequency modulation, the frequency variation curve will be as shown in fig. 4k1＝0.5、k2The lowest point of the frequency is 49.416Hz, as shown by the 2.2 curve, which is lower than the safe range value of the frequency fluctuation of 49.5 Hz. Too low a frequency will cause instability in the operation of the system. Setting square wave frequency modulation sudden increase power delta P of fan10.1p.u., and exits the frequency modulation at 15s, at which point the lowest point of the frequency is as in FIG. 6k1＝1、k2The curve 3 shows that the system is obviously improved, but the frequency drops secondarily, and the exit of the frequency modulation of the fan is a new impact to the system. Therefore, the battery energy storage device also participates in the frequency modulation. The droop control coefficient k is set under the condition of satisfying the formula (15)1When 1, then k2It can be calculated by equation (16) to be about 3.
Under the participation of the frequency modulation of the battery energy storage device, the frequency lowest point is further improved, the secondary drop of the frequency is obviously reduced or even almost eliminated, and the simulation result is shown in fig. 4k1＝1.5、k2The curve is 3.7. In this process, the output power of the battery energy storage device is shown in fig. 7.
According to the analysis formulas (13) and (16), when the size and the occurrence time of the disturbance and the control parameter of the square wave frequency modulation of the fan are determined, k is1The larger the k is, the more the k is required to eliminate the frequency secondary droop2The larger the system frequency will fluctuate with k1、k2Is increased and decreased. Therefore, k can be increased as much as possible within the allowable range1、k2To obtain a better frequency modulation effect.
The battery energy storage device in the invention has limited energy, and the battery energy storage device cannot release energy indefinitely to help frequency modulation, and the simulation verification results are all in the condition of only considering one frequency modulation. Because the primary frequency modulation is a poor regulation, the frequency deviation Δ f will exist all the time, and the battery energy storage device adopting the droop control will output the battery power continuously to help the system frequency to keep stable. When the system is operating around 30s, the secondary frequency modulation pulls the frequency back to 50Hz, during which the output of the battery energy storage device gradually decreases to 0. The cooperation of the battery energy storage device and the fan frequency modulation in the primary frequency modulation process is only considered, so that the exit process of the battery energy storage device can be omitted.
In a power grid system containing high-proportion wind power, the wind turbine generator can participate in frequency modulation to improve the lowest point of frequency by releasing kinetic energy of a rotor, so that the disturbance coping capability of the system is greatly improved. However, the existing fan inertia frequency modulation control mode represented by square wave frequency modulation has negative influence on the system frequency. When the fan exits frequency modulation, the system has secondary frequency drop and even frequency collapse, and the stability of the system is threatened. The battery energy storage system controlled by the variable droop coefficient control mode can further improve the disturbance handling capacity of the system and can effectively eliminate the problem of frequency secondary drop caused by the fact that the fan exits from frequency modulation. When different disturbances occur, in order to solve the problem of frequency secondary falling, the relation required to be met between the variable droop control coefficient of the battery energy storage system and the control parameter of the square wave frequency modulation of the fan is obtained by theoretical derivation, and finally the accuracy and the effectiveness of the method are verified by the simulation result in the DIGSILENT/Power Factory platform.
Based on the system and the method, the invention also provides a synchronous machine frequency modulation device of the frequency modulation method for realizing the participation of battery energy storage, which comprises the following steps: the storage is used for storing a computer program and a frequency modulation method in which the battery energy storage participates; and the processor is used for executing the computer program and the frequency modulation method in which the battery energy storage participates so as to realize the steps of the frequency modulation method in which the battery energy storage participates.
Based on the above system and method, the present invention further provides a readable storage medium having a frequency modulation method with battery energy storage participation, where the readable storage medium has a computer program stored thereon, and the computer program is executed by a processor to implement the steps of the frequency modulation method with battery energy storage participation.
The synchronous machine frequency modulation device implementing the frequency modulation method involving battery energy storage is the unit and algorithm steps of the examples described in connection with the embodiments disclosed herein, and can be implemented in electronic hardware, computer software, or a combination of both, and the components and steps of the examples have been generally described in terms of functions in the foregoing description for clarity of illustrating interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (8)
1. A frequency modulation method with participation of battery energy storage is characterized by comprising the following steps:
tracking the output power of the fan power generation assembly merged into the power grid in real time;
when disturbance occurs in the system, acquiring a power increasing value delta P of the fan power generation assembly entering a sudden power increasing stage1；
When the preset frequency modulation time is reached, the delta P generated by the wind turbine power generation assembly is collecteddropAnd the fan output power is lower than the value of the normal operating point;
a battery energy storage device controlled by a PWM controller is connected to enable the battery energy storage device and the fan power generation assembly to run in parallel;
and controlling the power emitted by the battery energy storage device, so that the emitted power makes up the power shortage generated by the reduction of the output power of the fan power generation assembly.
2. A method for frequency modulation involving battery energy storage according to claim 1,
under normal operation, the output power of the fan is Pwe0；
When disturbance occurs in the system, the fan enters a sudden power increase stage and keeps a constant power increase value delta P1；
When the preset frequency modulation time is reached, the fan quits frequency modulation to generate delta PdropThe output power is lower than the value of the normal operating point;
obtaining the sudden power delta P in the square wave frequency modulation modeWTThe expression of (a) is:
wherein ,t0For the moment of disturbance occurrence, toffFor the moment when the fan exits the square wave frequency modulation, omegaoffThe rotor speed at the moment of exit can be determined from equation (3), Pwm(ωoff) The mechanical power corresponding to the exit time can be obtained by the formula (4);
in the formula ,ω0The rotor speed at the normal working point, H is the inertia time constant of the fan, rho is the air density, A is the area swept by the wind wheel blade, vwIs the wind speed, CpIs the wind energy utilization coefficient, the pitch angle beta and the rotor speed omegarIt is related.
3. A method of frequency modulation involving battery energy storage according to claim 2,
when the square wave frequency modulation is in the stage of increasing the power, the droop coefficient k takes the value k1The battery energy storage device plays a role in auxiliary frequency modulation;
when the fan exits square wave frequency modulation, the droop coefficient k is increased to k2So that the battery energy storage device can send more power to make up for the power shortage caused by the fan quitting;
k2according to k1Calculating the square wave frequency modulation parameter value of the fan;
the expression of the frequency deviation (7) based on the equations (5) and (6) is:
wherein ΔPLIs a load disturbance value;
at the sudden power increase stage of square wave frequency modulation, the variable droop control coefficient k is k1In the exit phase, k is k2Substituting the equations (2) and (3) into (7) to obtain the frequency fluctuation delta f caused by the disturbance1And frequency fluctuation delta f in secondary falling2The relational expression of (1) is:
Δf1(t)＝F(k1,ΔPL,ΔP1,t) (38)
Δf2(t)＝f(k2,ΔPL,ΔP1,t0,toff,t) (39)
Δf1the variation with time t is influenced by k1、ΔPL、ΔP1Influence of valueAnd F represents the mapping relation between the two; Δ f2The variation with time t is influenced by k2、ΔPL、ΔP1、t0、toffAnd f represents the mapping relation between the values.
4. A method of frequency modulation in which battery energy storage participates as claimed in claim 3,
to ensure that the system frequency is within a safe range deltaflimInternal fluctuation, then the equations (8) and (9) are satisfied
|Δf1(t)|max＝C1(k1,ΔPL,ΔP1)<Δflim (40)
|Δf2(t)|max＝C2(k2,ΔPL,ΔP1,t0,toff)<Δflim (41)
wherein ,|Δf1(t)|maxIs the maximum value of frequency fluctuation caused by disturbance, and k1、ΔPL、ΔP1Correlation, C1Representing the mapping relation between them;
|Δf2(t)|maxthe maximum value of frequency fluctuation when the fan quits to cause the secondary frequency drop, and k2、ΔPL、ΔP1、t0、toffCorrelation, C2Representing a mapping relationship.
5. A method of frequency modulation in which battery energy storage participates as claimed in claim 3,
in order to reduce or even eliminate the secondary drop, the sum of the output of the fan and the output of the battery energy storage device is kept within a preset threshold range, namely
ΔPdrop＝-k2Δf1(toff)+k1Δf1(toff) (42)
wherein ,ΔPdropCan be calculated from the equation (13),
ΔPdrop＝Pwe0+ΔP1-Pwm(ωoff)＝C3(ΔP1,t0,toff) (43)
to obtain delta PdropValue of and Δ P1、t0、toffIs related by C3Representing the mapping relation between them;
substituting the formulas (8) and (13) into the formula (12) to eliminate the frequency secondary drop, k1、k2The limiting conditions to be met are:
C3(ΔP1,t0,toff)＝(k1-k2)·F(k1,ΔPL,ΔP1,toff) (44)
when the load disturbance in the system is of magnitude Δ PLAnd the occurrence time t0When determined, the equations (10) and (14) can be given as:
C1(k1,ΔP1)<Δflim (45)
C3(ΔP1,toff)＝(k1-k2)·F(k1,ΔP1,toff) (46)
equations (15) and (16) are relational equations which need to be satisfied between the control coefficient for eliminating the secondary drop of the frequency and the variable droop of the battery energy storage device and the square wave frequency modulation control parameter of the fan under the condition of disturbance.
6. A frequency modulation system with participation of battery energy storage, comprising: the system comprises a fan, a synchronous machine frequency modulation device and a battery energy storage device;
the fan power generation assembly and the battery energy storage device are respectively merged into the output power of the power grid;
the synchronous machine frequency modulation device is used for tracking the output power of the fan power generation assembly merged into the power grid in real time;
when disturbance occurs in the system, the synchronous machine frequency modulation device obtains the power increasing value delta P of the fan power generation assembly entering the sudden power increasing stage1；
When the preset frequency modulation time is reached, the synchronous machine frequency modulation device collects delta P generated by the fan power generation assemblydropAnd the fan output power is lower than the value of the normal operating point;
the synchronous machine frequency modulation device controls a battery energy storage device controlled by a PWM controller to be connected to a power grid, so that the battery energy storage device and the fan power generation assembly run in parallel;
and controlling the power emitted by the battery energy storage device, so that the emitted power makes up the power shortage generated by the reduction of the output power of the fan power generation assembly.
7. A synchronous machine frequency modulation device for realizing a frequency modulation method with battery energy storage participation is characterized by comprising the following steps:
the storage is used for storing a computer program and a frequency modulation method in which the battery energy storage participates;
a processor for executing the computer program and the frequency modulation method with battery energy storage participation to realize the steps of the frequency modulation method with battery energy storage participation according to any one of claims 1 to 5.
8. A readable storage medium having a method for frequency modulation with participation in battery energy storage, characterized in that the readable storage medium has stored thereon a computer program which is executed by a processor to carry out the steps of the method for frequency modulation with participation in battery energy storage according to any one of claims 1 to 5.
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