CN112186786B - Energy storage auxiliary frequency modulation capacity configuration method based on virtual synchronous generator - Google Patents
Energy storage auxiliary frequency modulation capacity configuration method based on virtual synchronous generator Download PDFInfo
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- 238000004146 energy storage Methods 0.000 title claims abstract description 93
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- 238000000034 method Methods 0.000 title claims abstract description 7
- 239000002131 composite material Substances 0.000 claims abstract description 68
- 238000004364 calculation method Methods 0.000 claims abstract description 17
- 230000000694 effects Effects 0.000 claims abstract description 14
- 229910052720 vanadium Inorganic materials 0.000 claims description 37
- 239000003990 capacitor Substances 0.000 claims description 31
- 238000012423 maintenance Methods 0.000 claims description 15
- 238000005457 optimization Methods 0.000 claims description 12
- 230000005611 electricity Effects 0.000 claims description 11
- 238000013178 mathematical model Methods 0.000 claims description 10
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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
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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
- H02J3/008—Circuit arrangements for ac mains or ac distribution networks involving trading of energy or energy transmission rights
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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
- 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
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
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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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Abstract
The invention discloses an energy storage auxiliary frequency modulation capacity configuration method based on a virtual synchronous generator. Firstly, an improved equivalent circuit model suitable for energy storage to participate in frequency modulation static research is designed, and an energy storage access mode, a converter and a voltage type filter are selected and a parameter calculation method is provided. And secondly, controlling the grid-connected converter by using a virtual synchronous machine technology, and performing energy storage frequency modulation. Finally, aiming at the capacity configuration problem of large-scale composite energy storage participating in clean energy power grid frequency modulation, an objective function is established for two indexes of frequency modulation effect and comprehensive economy to obtain an optimal composite energy storage capacity configuration scheme.
Description
Technical Field
The invention belongs to the field of frequency modulation capacity configuration of a composite energy storage system and a clean energy power grid, and particularly relates to an energy storage auxiliary frequency modulation capacity configuration method based on a virtual synchronous generator.
Background
At present, under the pressure of fossil energy crisis and severe environmental protection, clean energy power grid construction has become a mainstream trend of research in the power grid direction of various countries. Because of the randomness and uncertainty of most clean energy sources, the influence on the frequency index of the electric power system is serious, and workers in the electric power industry and related scientific researchers are always plagued.
Disclosure of Invention
The invention aims at the problems and provides an energy storage auxiliary frequency modulation capacity configuration method based on a virtual synchronous generator.
In order to achieve the above purpose, the invention adopts the following technical scheme that the invention comprises the following steps:
and step 1, decoupling the virtual synchronous generator.
Step 1-1, constructing a second-order mathematical model of the virtual synchronous machine, wherein a stator equation is as follows
U in the formula abc Representing terminal voltage, i abc Representing the current of the virtual synchronous machine, R representing the resistance on the stator winding of the virtual synchronous machine, L S Representing the inductance of the stator winding of the virtual synchronous machine, e abc Representing the internal potential of the virtual synchronous machine.
Step 1-2, a virtual synchronous machine rotor equation:
wherein J represents the moment of inertia of the virtual synchronous motor, ω is the mechanical angular velocity thereof, T m Is mechanical torque, T e For electromagnetic torque, K D For damping coefficient omega n Representing the rated angular velocity, P, of a virtual synchronous machine m For virtual synchronous machine mechanical power, P e Representing output electromagnetic power derived from an energy storage converter。
Step 2, introducing a mathematical model equation of the synchronous machine into the virtual synchronous machine, wherein the mechanical power P of the virtual synchronous machine m The expression is
Wherein 1/D P Representing the active sag coefficient, P ref Reference power (omega) representing virtual synchronous machine calibration ref -ω pcc )/D P Refers to a power offset feedback command. The power of the virtual synchronous machine can be adjusted, so that the power grid frequency can be adjusted.
Step 3, in order to supplement the active deficiency of the power grid, the power P of the composite energy storage system H (t) is
P H (t)＝P SC (t)+P VRB (t) (4)
Wherein P is SC (t) and P VRB And (t) respectively outputting active power of the super capacitor and the vanadium redox flow battery.
When the system frequency in the power grid fluctuates, the missing power is as follows
P N (t)＝P O (t)-P L (t) (5)
Wherein P is N (t) represents the missing power when the grid fluctuates, P O (t) is the unit output power in the power grid, P L And (t) represents the total required response power of the load in the frequency modulation regional power grid. When a frequency modulation period instruction is given, a start time t is set 0 And end time t 1 The rated output power of the stored energy is
Wherein P is HR (t) represents the rated output power of the stored energy, eta 0 For DC/DC efficiency, η 1 For DC/AC efficiency, η SC_Q Represents the discharge efficiency, eta of the super capacitor VBR_Q Discharging all vanadium redox flow batteryEfficiency, P N (t) _max Is the maximum value of the frequency modulation required power of the regional power grid at a certain moment.
Considering the working efficiency of the energy storage system in actual working and the charging and discharging efficiencies of the power batteries, the real-time power P of the composite energy storage system NH (t) is expressed as
Wherein eta SC_C Represents the charging efficiency eta of the super capacitor VRB_C And the charging efficiency of the all-vanadium redox flow battery is shown.
Step 4, optimally designing the capacity of the composite energy storage system based on the frequency modulation effect, wherein the charge state Q of the super capacitor in energy storage SOC_SC And state of charge Q of all-vanadium redox flow battery SOC_VRB Respectively denoted as
Wherein Q is SOC_SC_0 Representing the initial charge state of the super capacitor, P SC_0 (t) represents the real-time power of the super capacitor, E SC Representing the capacity of the super capacitor, Q SOC_VRB_0 Representing the initial charge state of the all-vanadium redox flow battery, P VRB_0 Represents real-time power of all-vanadium redox flow battery, E VRB Representing the capacity of the vanadium redox flow battery.
Integral state of charge Q of composite energy storage system SOC Represented as
Wherein Q is SOC_0 Is the initial charge state of the super capacitor, P SC_0 Representing real-time power of super capacitor E SC Representing the capacity of the supercapacitor. In order to meet the frequency modulation requirement of the power grid, a function C is established by taking the optimal frequency modulation effect of the composite energy storage system as a target 1 The expression is
In order to reduce cost, extend life, and reduce battery consumption, it is desirable to satisfy the following constraints
Wherein Q is SOC_SC_max Represents that the charge state of the super capacitor is set to be maximum value, Q SOC_SC_min Representing the supercapacitor state of charge setting minimum. Q (Q) SOC_VRB_max Represents the maximum value of the allowable charge state of the all-vanadium redox flow battery, Q SOC_VRB_min Representing the minimum state of charge allowed for the all-vanadium redox flow battery.
And step 5, designing the capacity of the composite energy storage system by taking the best economic benefit as a target. The composite energy storage cost comprises the cost generated by one-time development and the daily operation and maintenance cost of the system, and the total cost expression is
C T ＝C E +C M (12)
Wherein C is T C is the total operation cost of the composite energy storage system M C is maintenance cost generated during the conventional operation of the composite energy storage system E The cost is input for the composite energy storage system once a year. One-time input cost of composite energy storage system
C E ＝C EVBR +C ESC (13)
Wherein C is EVBR One-time input cost for all-vanadium redox flow battery, C ESC And one-time investment cost is required for the super capacitor. The calculation formula of the one-time input cost of the all-vanadium redox flow battery and the supercapacitor is as follows
Wherein C is P_VRB Representing VRB unit powerCost, P VRB For its rated power, C E_VRB Representing VRB cost per unit volume, E VRB For its rated capacity. C (C) P_SC For SC unit power cost, P SC For its rated power, C E_SC Cost per unit capacity per unit time of SC, E SC For its rated capacity. Therefore, the operation and maintenance cost calculation formula of the composite energy storage system is as follows
C M ＝(C M_VRB E VRB +C M_SC E SC )×T (15)
Wherein C is M Representing the overall maintenance and operation cost of the composite energy storage system, C M_VRB Maintaining the running cost for the unit capacity of the all-vanadium redox flow battery, C M_SC Maintenance cost per capacity of supercapacitor, T represents the number of cycles.
The comprehensive economic benefit calculation formula of the composite energy storage system is as follows
I＝I 1 +I 2 (16)
Wherein I is the total economic benefit, I 1 Is the direct economic benefit of the composite energy storage system, I 2 Is an indirect benefit of the composite energy storage system.
Step 5-1, the direct income calculation formula is
I 1 ＝(λ T +β)Q T (17)
Wherein lambda is T Represents the frequency modulation electricity price, beta represents the price of the compensation electricity fee of auxiliary frequency modulation facilities formulated by government and power grid companies, omega T Representing the amount of frequency modulated electricity.
Step 5-2, indirect benefit mainly refers to that the loss cost generated by wind and light discarding after the composite energy storage system participates in grid frequency modulation is reduced, and the calculation formula is as follows
I 2 ＝U S Q S (18)
Wherein U is S To lose the cost per degree of electricity, Q S To lose power. Q (Q) S The solution formula of (2) is
Wherein P is L Power is lost for average wind and light rejection. From the above, the comprehensive economic benefit optimal mathematical model of the composite energy storage system participating in the frequency modulation of the power grid is as follows
M 2 ＝max{I-C T } (20)
Step 6, multi-objective optimization, namely selecting the optimal frequency modulation effect and the maximum economic benefit as an optimization objective when researching the optimal configuration of the frequency modulation capacity of the composite energy storage participated power grid, and optimizing the composite energy storage participated power grid according to an improved particle swarm algorithm, wherein the improved objective function is as follows
M＝max{K 1 M 1 +K 2 M 2 } (21)
Wherein K is 1 And K 2 And (3) representing the weight coefficient and meeting the constraint condition of the formula (11).
The invention has the beneficial effects that.
The invention is suitable for an improved equivalent circuit model of energy storage participating in frequency modulation static research, and provides a parameter calculation method for energy storage access modes, converters and voltage type filters. And secondly, controlling the grid-connected converter by using a virtual synchronous machine technology, and performing energy storage frequency modulation. Finally, aiming at the capacity configuration problem of large-scale composite energy storage participating in clean energy power grid frequency modulation, an objective function is established for two indexes of frequency modulation effect and comprehensive economy to obtain an optimal composite energy storage capacity configuration scheme.
When the regional power grid is regulated and controlled, the factors of the composite energy storage frequency modulation effect and the comprehensive economy are considered, and the capacity optimization model of the large-scale energy storage system is completed under the condition of meeting the frequency modulation requirement of the power system.
Drawings
The invention is further described below with reference to the drawings and the detailed description. The scope of the present invention is not limited to the following description.
Fig. 1 is a flow chart of auxiliary energy storage frequency modulation capacity configuration based on a virtual synchronous generator.
Fig. 2 is a schematic diagram of a virtual synchronous machine composite energy storage frequency modulation scheme.
Fig. 3 is a modified particle swarm algorithm flow.
Detailed Description
The invention provides a capacity configuration method of an energy storage auxiliary system based on a virtual synchronous generator, as shown in figure 1, firstly, a mathematical model of the virtual synchronous generator is constructed, comprising a stator equation and a rotor equation thereof. Then, the power P of the composite energy storage system needs to be given H (t) it contains the output active power of the supercapacitor and the all-vanadium redox flow battery. Through the missing power P N (t) and set start and end times to obtain the energy storage rated output power P HR And composite energy storage system real-time power P considering working efficiency of system and battery in real work NH (t) then using a multi-objective optimization function m=max { K based on an improved particle swarm algorithm 1 M 1 +K 2 M 2 And respectively designing schemes which are optimal based on the frequency modulation effect and optimal based on the economic benefit, and finally performing multi-objective optimization on the schemes to obtain an optimal solution.
And step 1, decoupling the virtual synchronous generator.
Step 1-1, constructing a second-order mathematical model of the virtual synchronous machine, wherein a stator equation is as follows
U in the formula abc Representing terminal voltage, i abc Representing the current of the virtual synchronous machine, R is the resistance of a stator winding of the virtual synchronous machine, L S Representing the inductance of the stator winding of the virtual synchronous machine, e abc Representing the internal potential of the virtual synchronous machine.
Step 1-2, a virtual synchronous machine rotor equation:
wherein J represents the rotational inertia of the synchronous motor, ω represents the mechanical angular velocity of the virtual synchronous motor, T m Representing the mechanical torque, T e For electromagnetic rotationMoment, K D Represents the damping coefficient omega n Representing rated angular velocity of virtual synchronous machine, P m For virtual synchronous machine mechanical power, P e Representing the output electromagnetic power derived from the energy storage converter.
Step 2, introducing a mathematical model equation of the synchronous machine into the virtual synchronous machine, wherein the mechanical power P of the virtual synchronous machine m The expression is
Wherein 1/D P Representing the active sag coefficient, P ref Reference power (omega) representing virtual synchronous machine calibration ref -ω pcc )/D P Refers to a power offset feedback command. The power of the virtual synchronous machine can be adjusted, so that the power grid frequency can be adjusted.
Step 3, in order to supplement the active deficiency of the power grid, the power P of the composite energy storage system H (t) is
P H (t)＝P SC (t)+P VRB (t) (4)
Wherein P is SC (t) and P VRB And (t) respectively outputting active power of the super capacitor and the vanadium redox flow battery.
When the system frequency in the power grid fluctuates, the missing power is as follows
P N (t)＝P O (t)-P L (t) (5)
Wherein P is N (t) represents the missing power when the grid fluctuates, P O (t) is the unit output power in the power grid, P L And (t) represents the total required response power of the load in the frequency modulation regional power grid. When a frequency modulation period instruction is given, a start time t is set 0 And end time t 1 The rated output power of the stored energy is
Wherein P is HR (t) represents the rated output power of the stored energy, eta 0 For DC/DC efficiency, η 1 For DC/AC efficiency, η SC_Q Represents the discharge efficiency, eta of the super capacitor VBR_Q Is the discharge efficiency of the all-vanadium redox flow battery, P N (t) _max Is the maximum value of the frequency modulation required power of the regional power grid at a certain moment.
Considering the working efficiency of the energy storage system in actual working and the charging and discharging efficiencies of the power batteries, the composite energy storage system has real-time power P NH (t) can be expressed as
Wherein eta SC_C Represents the charging efficiency eta of the super capacitor VRB_C And the charging efficiency of the all-vanadium redox flow battery is shown. Step 4, optimally designing the capacity of the composite energy storage system based on the frequency modulation effect, wherein the charge state Q of the super capacitor in energy storage SOC_SC And state of charge Q of all-vanadium redox flow battery SOC_VRB Respectively denoted as
Wherein Q is SOC_SC_0 For the initial charge state of the super capacitor, P SC_0 (t) is the real-time power of the super capacitor, E SC Representing the capacity of the super capacitor, Q SOC_VRB_0 Representing the initial charge state of the all-vanadium redox flow battery, P VRB_0 Represents real-time power of all-vanadium redox flow battery, E VRB Representing the capacity of the vanadium redox flow battery.
Integral state of charge Q of composite energy storage system SOC Represented as
Wherein Q is SOC_0 Is the initial charge state of the super capacitor, P SC_0 Representing the reality of a supercapacitorTime power, E SC Representing the supercapacitor capacity. In order to meet the frequency modulation requirement of the power grid, a function C is established by taking the optimal frequency modulation effect of the composite energy storage system as a target 1 The expression is
In order to reduce cost, extend life, and reduce battery consumption, it is desirable to satisfy the following constraints
Wherein Q is SOC_SC_max Represents that the charge state of the super capacitor is set to be maximum value, Q SOC_SC_min Representing the supercapacitor state of charge setting minimum. Q (Q) SOC_VRB_max Represents the maximum value of the allowable charge state of the all-vanadium redox flow battery, Q SOC_VRB_min Representing the minimum state of charge allowed for the all-vanadium redox flow battery.
And step 5, designing the capacity of the composite energy storage system by taking the best economic benefit as a target. The composite energy storage cost comprises the cost generated by one-time development and the daily operation and maintenance cost of the system, and the total cost expression is
C T ＝C E +C M (12)
Wherein C is T C is the total operation cost of the composite energy storage system M C is maintenance cost generated during the conventional operation of the composite energy storage system E Representing the annual average input cost of the composite energy storage system. The primary input cost of the composite energy storage system can be expressed as
C E ＝C EVBR +C ESC (13)
Wherein C is EVBR One-time input cost for all-vanadium redox flow battery, C ESC And one-time investment cost is required for the super capacitor. The calculation formula of the one-time input cost of the all-vanadium redox flow battery and the supercapacitor is as follows
Wherein C is P_VRB Representing VRB unit power cost, P VRB For its rated power, C E_VRB Representing VRB cost per unit volume, E VRB For its rated capacity. C (C) P_SC For SC unit power cost, P SC For its rated power, C E_SC Cost per unit capacity per unit time of SC, E SC For its rated capacity. Therefore, the operation and maintenance cost calculation formula of the composite energy storage system is as follows
C M ＝(C M_VRB E VRB +C M_SC E SC )×T (15)
Wherein C is M Representing the overall maintenance and operation cost of the composite energy storage system, C M_VRB Maintaining the running cost for the unit capacity of the all-vanadium redox flow battery, C M_SC Maintenance cost per capacity of supercapacitor, T represents the number of cycles.
The comprehensive economic benefit calculation formula of the composite energy storage system is as follows
I＝I 1 +I 2 (16)
Wherein I is the total economic benefit, I 1 Is the direct economic benefit of the composite energy storage system, I 2 Is an indirect benefit of the composite energy storage system.
Step 5-1, the direct income calculation formula is
I 1 ＝(λ T +β)Q T (17)
Wherein lambda is T Represents the frequency modulation electricity price, beta represents the price of the compensation electricity fee of auxiliary frequency modulation facilities formulated by government and power grid companies, omega T Representing the amount of frequency modulated electricity.
Step 5-2, indirect benefit mainly refers to that the loss cost generated by wind and light discarding after the composite energy storage system participates in grid frequency modulation is reduced, and the calculation formula is as follows
I 2 ＝U S Q S (18)
Wherein U is S To lose the cost per degree of electricity, Q S To lose power. Q (Q) S The solution formula of (2) is
Wherein P is L Power is lost for average wind and light rejection. From the above, the comprehensive economic benefit optimal mathematical model of the composite energy storage system participating in the frequency modulation of the power grid is as follows
M 2 ＝max{I-C T } (20)
Step 6, multi-objective optimization, namely selecting the optimal frequency modulation effect and the maximum economic benefit as an optimization objective when researching the optimal configuration of the frequency modulation capacity of the composite energy storage participated power grid, and performing multi-objective optimization on the two according to an improved particle swarm algorithm, wherein the optimization objective function is as follows
M＝max{K 1 M 1 +K 2 M 2 } (21)
Wherein K is 1 And K 2 The weight coefficient is expressed, and the constraint condition satisfied by the weight coefficient is formula (11).
It should be understood that the foregoing detailed description of the present invention is provided for illustration only and is not limited to the technical solutions described in the embodiments of the present invention, and those skilled in the art should understand that the present invention may be modified or substituted for the same technical effects; as long as the use requirement is met, the invention is within the protection scope of the invention.
Claims (1)
1. The energy storage auxiliary frequency modulation capacity configuration method based on the virtual synchronous generator is characterized by comprising the following steps of:
step 1, decoupling a virtual synchronous generator;
step 1-1, constructing a second-order mathematical model of the virtual synchronous machine, wherein a stator equation is as follows
U in the formula abc Representing terminal voltage, i abc Representing deficiencyQuasi-synchronous machine current, R represents virtual synchronous machine stator winding resistance, L S Representing the inductance of the stator winding of the virtual synchronous machine, e abc Representing the internal potential of the virtual synchronous machine;
step 1-2, a virtual synchronous machine rotor equation:
wherein J is the rotational inertia of the virtual synchronous motor, omega is the mechanical angular velocity, T m And T e The tables represent the mechanical torque and the electromagnetic torque, K, respectively D For damping coefficient omega n Represents the rated angular velocity, P e Representing the output electromagnetic power obtained from the energy storage converter, P m Representing the mechanical power of the virtual synchronous machine;
step 2, introducing a mathematical model equation of the synchronous machine into the virtual synchronous machine, wherein the mechanical power P of the virtual synchronous machine m The expression is
Wherein 1/D P Representing the active sag coefficient, P ref Reference power (omega) representing virtual synchronous machine calibration ref -ω pcc )/D P Refers to a power offset feedback command; the power of the virtual synchronous machine can be adjusted to realize the adjustment of the frequency of the power grid;
step 3, in order to supplement the active deficiency of the power grid, the power P of the composite energy storage system H (t) is
P H (t)＝P SC (t)+P VRB (t) (4)
Wherein P is SC (t) and P VRB (t) the output active power of the supercapacitor and the vanadium redox flow battery respectively;
when the system frequency in the power grid fluctuates, the missing power is as follows
P N (t)＝P O (t)-P L (t) (5)
Wherein P is N (t) represents the missing power when the grid fluctuates, P O (t) is the unit output power in the power grid, P L (t) represents the total demand response power of the load in the grid in the frequency modulated region; when a frequency modulation period instruction is given, a start time t is set 0 And end time t 1 The rated output power of the stored energy is
Wherein P is HR (t) represents the rated output power of the stored energy, eta 0 For DC/DC efficiency, η 1 For DC/AC efficiency, η SC_Q Represents the discharge efficiency, eta of the super capacitor VBR_Q Is the discharge efficiency of the all-vanadium redox flow battery, P N (t) _max Is the maximum value of the frequency modulation required power of the regional power grid at a certain moment;
considering the working efficiency of the energy storage system in actual working and the charging and discharging efficiencies of the power batteries, the real-time power P of the composite energy storage system NH (t) can be expressed as
Wherein eta SC_C Represents the charging efficiency eta of the super capacitor VRB_C Representing the charging efficiency of the vanadium redox flow battery; step 4, optimally designing the capacity of the composite energy storage system based on the frequency modulation effect, wherein the charge state Q of the super capacitor in energy storage SOC_SC And state of charge Q of all-vanadium redox flow battery SOC_VRB Respectively denoted as
Wherein Q is SOC_SC_0 Is the initial charge state of the super capacitor, P SC_0 (t) represents a super capacitorReal-time power of device E SC Representing the capacity of the super capacitor, Q SOC_VRB_0 Representing the initial charge state of the all-vanadium redox flow battery, P VRB_0 Represents real-time power of all-vanadium redox flow battery, E VRB Representing the capacity of the vanadium redox flow battery;
integral state of charge Q of composite energy storage system SOC Represented as
Wherein Q is SOC_0 Is the initial charge state of the super capacitor, P SC_0 Representing real-time power of super capacitor E SC Representing the capacity of the supercapacitor; in order to meet the frequency modulation requirement of the power grid, a function M is established by taking the optimal frequency modulation effect of the composite energy storage system as the objective 1 The expression is
In order to reduce cost, extend life, and reduce battery consumption, it is desirable to satisfy the following constraints
Wherein Q is SOC_SC_max Represents that the charge state of the super capacitor is set to be maximum value, Q SOC_SC_min Representing the state of charge of the supercapacitor to set a minimum value; q (Q) SOC_VRB_max Represents the maximum value of the allowable charge state of the all-vanadium redox flow battery, Q SOC_VRB_min Representing the minimum allowable state of charge of the all-vanadium redox flow battery;
step 5, designing the capacity of the composite energy storage system by taking the best economic benefit as a target; the composite energy storage cost comprises the cost generated by one-time development and the daily operation and maintenance cost of the system, and the total cost expression is
C T ＝C E +C M (12)
Wherein C is T C is the total operation cost of the composite energy storage system M C is maintenance cost generated during the conventional operation of the composite energy storage system E The cost is input for the composite energy storage system once a year; wherein the primary input cost of the composite energy storage system
C E ＝C EVBR +C ESC (13)
Wherein C is EVBR One-time input cost for all-vanadium redox flow battery, C ESC One-time investment cost is used for the super capacitor; the calculation formula of the one-time input cost of the all-vanadium redox flow battery and the supercapacitor is as follows
Wherein C is P_VRB Representing VRB unit power cost, P VRB For its rated power, C E_VRB Representing VRB cost per unit volume, E VRB For its rated capacity; c (C) P_SC For SC unit power cost, P SC For its rated power, C E_SC Cost per unit capacity per unit time of SC, E SC For its rated capacity; therefore, the operation and maintenance cost calculation formula of the composite energy storage system is as follows
C M ＝(C M_VRB E VRB +C M_SC E SC )×T(15)
Wherein C is M Representing the overall maintenance and operation cost of the composite energy storage system, C M_VRB Maintaining the running cost for the unit capacity of the all-vanadium redox flow battery, C M_SC Maintenance cost for the unit capacity of the super capacitor, wherein T represents the number of times of circulation;
the comprehensive economic benefit calculation formula of the composite energy storage system is as follows
I＝I 1 +I 2 (16)
Wherein I is the total economic benefit, I 1 Is the direct economic benefit of the composite energy storage system, I 2 Indirect benefit of the composite energy storage system;
step 5-1, the direct income calculation formula is
I 1 ＝(λ T +β)Q T (17)
Wherein lambda is T Represents the frequency modulation electricity price, beta represents the price of the compensation electricity charge of auxiliary frequency modulation facilities formulated by government and power grid companies, and Q T Representing the frequency modulation electric quantity;
step 5-2, indirect benefit mainly refers to that the loss cost generated by wind and light discarding after the composite energy storage system participates in grid frequency modulation is reduced, and the calculation formula is as follows
I 2 ＝U S Q S (18)
Wherein U is S To lose the cost per degree of electricity, Q S To lose electric quantity; q (Q) S The solution formula of (2) is
Wherein P is L Power is lost for average wind and light discarding; from the above, the comprehensive economic benefit optimal mathematical model of the composite energy storage system participating in the frequency modulation of the power grid is as follows
M 2 ＝max{I-C T } (20)
Step 6, multi-objective optimization, namely selecting the optimal frequency modulation effect and the maximum economic benefit as an optimization objective when researching the optimal configuration of the frequency modulation capacity of the composite energy storage participated power grid, and performing multi-objective optimization on the composite energy storage participated power grid according to an improved particle swarm algorithm, wherein an improved objective function is as follows
M＝max{K 1 M 1 +K 2 M 2 } (21)
Wherein K is 1 And K 2 The weight coefficient is expressed, and the constraint condition satisfied is formula (11).
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