CN110707749A - Wind-hydrogen coupling system and control method thereof - Google Patents

Wind-hydrogen coupling system and control method thereof Download PDF

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Publication number
CN110707749A
CN110707749A CN201911097268.0A CN201911097268A CN110707749A CN 110707749 A CN110707749 A CN 110707749A CN 201911097268 A CN201911097268 A CN 201911097268A CN 110707749 A CN110707749 A CN 110707749A
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wind
power
hydrogen
grid
direct
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韩俊飞
邢文珑
胡宏彬
任永峰
俞超宇
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Inner Mongolia Electric Power Research Institute of Inner Mongolia Power Group Co Ltd
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Inner Mongolia Electric Power Research Institute of Inner Mongolia Power Group Co Ltd
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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
    • 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
    • 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
    • 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
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E70/00—Other energy conversion or management systems reducing GHG emissions
    • Y02E70/30—Systems combining energy storage with energy generation of non-fossil origin

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Fuel Cell (AREA)
  • Control Of Eletrric Generators (AREA)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)

Abstract

The invention is suitable for the technical field of electric power, and provides a wind-hydrogen coupling system and a control method thereof, wherein the wind-hydrogen coupling system comprises the following steps: the direct-drive wind driven generator is used for converting captured wind energy into mechanical energy and converting the mechanical energy into electric energy; the machine side converter is used for converting alternating current output by the direct-drive wind driven generator into direct current; the grid-side converter is used for converting the direct current output by the rotor-side converter into alternating current, and feeding the alternating current into a regional power grid after filtering; the basic electrolytic cell and the proton exchange membrane fuel cell are respectively coupled to a direct current bus connecting the machine side converter and the grid side converter through a DC/DC converter and used for adjusting the balance of system power. The wind-hydrogen coupling system can effectively solve the problem of wind abandonment of distributed wind power, furthest consumes redundant power, supplements power difference when the output of the fan is insufficient, realizes peak clipping and valley filling, has relatively stable output power of each unit, and is favorable for friendly grid-connected operation of high permeability of the distributed wind power.

Description

Wind-hydrogen coupling system and control method thereof
Technical Field
The invention belongs to the technical field of electric power, and particularly relates to a wind-hydrogen coupling system and a control method thereof.
Background
Compared with a centralized wind power mode, the distributed wind power mode has a wide development prospect due to the advantages of high efficiency, flexibility, load center approaching and the like. However, the inherent intermittency and fluctuation of wind energy are great restrictions for preventing the distributed wind power grid connection, the serious wind abandon condition is still the problem which needs to be solved at present, and statistics shows that the national wind abandon quantity in 2018 reaches 277 hundred million kilowatt hours. The coordination of energy storage devices is one of means for solving the problem of complaints, and different from the traditional energy storage form, hydrogen energy is the cleanest and environment-friendly green energy at present, and the hydrogen energy has high energy density and can be stored for a long time. With the gradual development of the hydrogen production technology and the continuous breakthrough of the fuel cell technology, the hydrogen energy is used as an energy storage medium to balance the production and supply of wind power, and a new idea is provided for the system power regulation and the low voltage ride through capability of the distributed wind power in future.
At present, researches for improving the dispersive wind power absorption and low voltage ride through capability based on wind-hydrogen coupling at home and abroad are few, and no commercially operated wind power hydrogen production energy storage and fuel cell power generation system exists at home, so that the aspects of the operation economy, reliability, stability and the like of a hydrogen energy storage system need to be further deepened.
Disclosure of Invention
The embodiment of the invention aims to provide a wind-hydrogen coupling system and a control method thereof, aiming at filling the blank that no commercially operated wind-power hydrogen production energy storage and fuel cell power generation system exists in China.
The embodiment of the invention is realized in such a way that the wind-hydrogen coupling system comprises:
the direct-drive wind driven generator is used for converting captured wind energy into mechanical energy, converting the mechanical energy into electric energy and outputting low-frequency alternating current to the machine side converter;
the machine side converter is used for converting alternating current output by the direct-drive wind driven generator into direct current to be output to the grid side converter;
the grid-side converter is used for converting the direct current output by the rotor-side converter into alternating current, and feeding the alternating current into a regional power grid after filtering;
the basic electrolytic cell and the proton exchange membrane fuel cell are respectively coupled to a direct current bus connecting the machine side converter and the grid side converter through a DC/DC converter and used for adjusting the balance of system power.
Another objective of an embodiment of the present invention is to provide a control method of a wind-hydrogen coupling system, including:
establishing mathematical models of a direct-drive fan, an alkaline electrolytic cell and a proton exchange membrane fuel cell;
determining wind power output according to the mathematical model of the direct-drive fan;
when the wind power output is greater than the load requirement, controlling the residual power of the electrolytic cell water electrolysis hydrogen production absorption system according to the basic electrolytic cell mathematical model;
and when the wind power output is smaller than the load requirement, controlling the fuel cell to supplement the power difference according to the proton exchange membrane fuel cell mathematical model.
The wind-hydrogen coupling system provided by the embodiment of the invention comprises a direct-drive wind driven generator, a machine side converter, a grid-connected converter, an alkaline electrolysis cell and a proton exchange membrane fuel cell, wherein the alkaline electrolysis cell and the proton exchange membrane fuel cell are respectively coupled to a direct current bus connecting the machine side converter and the grid-connected converter through a DC/DC converter and are used for adjusting the balance of system power. The wind-hydrogen coupling system can effectively solve the problem of wind abandonment of distributed wind power, furthest consumes redundant power, supplements power difference when the output of the fan is insufficient, realizes peak clipping and valley filling, has relatively stable output power of each unit, and is favorable for friendly grid-connected operation of high permeability of the distributed wind power.
Drawings
Fig. 1 is a schematic structural diagram of a wind-hydrogen coupling system according to an embodiment of the present invention;
FIG. 2 is a flow chart illustrating the basic operation principle of the wind-hydrogen coupling system according to the embodiment of the present invention;
FIG. 3 is a block diagram of a coordinated control of the wind-hydrogen coupling system according to an embodiment of the present invention;
fig. 4 illustrates a failure phase EL-side converter control strategy according to an embodiment of the present invention;
fig. 5 is a flowchart illustrating an implementation of a control method of a wind-hydrogen coupling system according to an embodiment of the present invention;
FIG. 6 is a U-I characteristic curve diagram of an electrolytic cell according to an embodiment of the present invention;
FIG. 7 is a graph showing U-I and P-I characteristics of a fuel cell according to an embodiment of the present invention;
FIG. 8 is a graph of wind speed versus load demand provided by an embodiment of the present invention: (a) a wind speed curve; (b) a load demand;
fig. 9 is a simulation waveform diagram of the individual fan grid-connected system according to the embodiment of the present invention: (a) mechanical torque and electromagnetic torque; (b) the voltage and current of the grid side A phase; (c) the voltage and current of the A phase on the network side are locally amplified; (d) the output of the fan; (e) network side active power;
fig. 10 is a graph showing the unit curves of the hydrogen energy storage system according to the embodiment of the present invention under the normal operation condition: (a) the electrolytic cell absorbs power; (b) hydrogen flow rate by EL; (c) fuel cell output power; (d) a direct current bus voltage;
FIG. 11 is a graph illustrating changes in wind turbine output and grid-side active power provided by an embodiment of the present invention;
fig. 12 is a graph of a simulation result of adding hydrogen energy storage when three-phase voltage on the grid side drops symmetrically according to an embodiment of the present invention: (a) a grid side voltage; (b) a grid side current; (c) network side active power; (d) network side reactive power; (e) a direct current bus voltage; (f) the electrolytic cell absorbs power; (g) the pressure of the hydrogen storage tank.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The terminology used in the embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the examples of the invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.
It should be understood that although the terms first, second, etc. may be used to describe various information in embodiments of the present invention, the information should not be limited by these terms. These terms are only used to distinguish one type of information from another.
The wind-hydrogen coupling system provided by the embodiment of the invention comprises a direct-drive wind driven generator, a machine side converter, a grid-connected converter, an alkaline electrolysis cell and a proton exchange membrane fuel cell, wherein the alkaline electrolysis cell and the proton exchange membrane fuel cell are respectively coupled to a direct current bus connecting the machine side converter and the grid-connected converter through a DC/DC converter and are used for adjusting the balance of system power. The wind-hydrogen coupling system can effectively solve the problem of wind abandonment of distributed wind power, furthest consumes redundant power, supplements power difference when the output of the fan is insufficient, realizes peak clipping and valley filling, has relatively stable output power of each unit, and is favorable for friendly grid-connected operation of high permeability of the distributed wind power.
To further explain the technical means and effects of the present invention adopted to achieve the predetermined objects, the following detailed description of the embodiments, structures, features and effects according to the present invention will be given with reference to the accompanying drawings and preferred embodiments.
Fig. 1 shows a structural schematic diagram of a wind-hydrogen coupling system provided by an embodiment of the present invention, and for convenience of explanation, only the parts related to the embodiment of the present invention are stated, and the details are as follows:
the wind-hydrogen coupling system comprises a direct-drive wind power generator 101, a machine side converter 102, a grid side converter 103, an alkaline electrolysis cell 104 and a proton exchange membrane fuel cell 105.
Specifically, the wind-hydrogen coupling system consists of a direct-drive wind driven generator, 4 converters, an alkaline electrolysis cell and a proton exchange membrane fuel cell.
The direct-drive wind power generator 101 is used for converting captured wind energy into mechanical energy, converting the mechanical energy into electric energy, and outputting low-frequency alternating current to the machine side converter.
The machine side converter 102 is configured to convert the alternating current output by the direct-drive wind turbine generator into direct current to be output to the grid-side converter.
In the embodiment of the invention, the machine side converter adopts the conventional two-level SVPWM modulation technology to realize the control of the motor torque, and has the advantages of simple system structure, relatively mature control technology and the like.
In the embodiment of the invention, the convex motor parameters are adopted, so that the machine side converter adopts the maximum torque current ratio control and adopts a double closed loop structure of a rotating speed outer loop and a current inner loop. The rotating speed loop adjusts the rotating speed of the motor, and the rotating speed deviation outputs a direct-axis current reference value i according to the torque current relationship after passing through the rotating speed adjustersq *、isd *With actual q-axis and d-axis currents isq、isdAfter comparison, the voltage compensation term is added to obtain u through PI regulationsd、usqAnd obtaining a switch driving pulse by utilizing a two-level SVPWM technology after coordinate transformation, and realizing maximum power tracking by controlling the generator.
And the grid-side converter 103 is used for converting the direct current output by the rotor-side converter into alternating current, and feeding the alternating current into a regional power grid after filtering.
In the embodiment of the invention, the grid-side converter adopts a three-level SVPWM modulation technology, and compared with a two-level converter, the voltage stress of a switching tube is reduced, and the harmonic content is reduced, so that the quality of electric energy injected into a power grid is improved.
In the embodiment of the invention, the grid-side inverter is of a three-level diode clamping type, and a double closed-loop control structure of a voltage outer loop and a current inner loop is adopted. The q-axis current is usually referenced to a value igq *Set to 0, d-axis current reference value igd *Output by the voltage regulator, the result and the actual AC-DC axis current igq、igdAfter comparison, the voltage compensation term is added to obtain u through PI regulationgd、ugqAnd modulating a switch driving pulse by utilizing a three-level SVPWM technology after seat conversion so as to achieve the purposes of controlling the voltage of a direct-current bus to be stable and controlling a network-side inverter to operate in a unit power factor state.
The basic electrolytic cell 104 and the proton exchange membrane fuel cell 105 are respectively coupled to a direct current bus connecting the machine side converter and the grid side converter through a DC/DC converter, and are used for adjusting the balance of system power.
In the embodiment of the invention, the side of the basic electrolytic cell (EL) is a buck type DC/DC converter; the proton exchange membrane fuel cell (PEMFC/FC) side is a boost type DC/DC converter. The basic electrolytic cell takes KOH, NaOH aqueous solution as electrolyte, and electrolyzes water to generate hydrogen and oxygen under the action of direct current, the technology is mature at present, and detailed description is omitted; the proton exchange membrane has high energy conversion efficiency, long service life of the battery, good stability and zero emission, and is an excellent choice for the hydrogen-electric energy conversion device.
In the embodiment of the invention, the alkaline electrolytic cell is used for consuming the surplus power of the system under the action of direct current when the power of the direct-drive wind power generator is greater than the load requirement; the proton exchange membrane fuel cell is used for compensating the corresponding power shortage of a power grid when the power of the direct-drive wind power generator is smaller than the load requirement.
Specifically, the embodiment of the invention converts captured wind energy into mechanical energy through the fan blade, converts the mechanical energy into electric energy through the permanent magnet synchronous generator, converts the generated low-frequency alternating current into power-frequency alternating current through the full-power converter, and feeds the power-frequency alternating current into the regional power grid after filtering. The EL and the PEMFC are coupled to a direct current bus through a current transformer to realize power balance adjustment. When the power of the fan is larger than the load demand, the residual power is electrolyzed into hydrogen and oxygen by the water electrolysis device, and the hydrogen and the oxygen are stored in the hydrogen storage tank 201 so as to facilitate the use of the PEMFC and also can be transported to other nearby industries for use; when the power of the fan is smaller than the load demand, the PEMFC quickly supplements the corresponding power shortage to ensure the safe and stable operation of the power system. The working principle flow is shown in fig. 2.
When the fan output is greater than the load demand, the power reference value P which needs to be consumed by EL is generated by the upper energy management centerel *Terminal U of and ELelDividing to generate a current reference value Iel *，Iel *With real-time measured values IelThe obtained error value is compared with a triangular wave through a PI controller to generate a buck converter control signal Del。
When the output of the fan is smaller than the load requirement, the upper energy management center generates a reference power value P of FC to be compensatedfc *Terminal U with FCfcDividing to generate a current reference value Ifc *，Ifc *With real-time measured values IfcThe obtained error value is compared with a triangular wave through a PI controller to generate a boost converter control signal Dfc. The overall control block diagram of the system is shown in fig. 3.
The wind-hydrogen coupling system provided by the embodiment of the invention comprises a direct-drive wind driven generator, a machine side converter, a grid-connected converter, an alkaline electrolysis cell and a proton exchange membrane fuel cell, wherein the alkaline electrolysis cell and the proton exchange membrane fuel cell are respectively coupled to a direct current bus connecting the machine side converter and the grid-connected converter through a DC/DC converter and are used for adjusting the balance of system power. The wind-hydrogen coupling system can effectively solve the problem of wind abandonment of distributed wind power, furthest consumes redundant power, supplements power difference when the output of the fan is insufficient, realizes peak clipping and valley filling, has relatively stable output power of each unit, and is favorable for friendly grid-connected operation of high permeability of the distributed wind power.
As shown in fig. 1, another wind-hydrogen coupling system is provided in the embodiment of the present invention, and for convenience of description, only the parts related to the embodiment of the present invention are shown, which are similar to the above embodiment except that:
the alkaline type electrolytic cell 104 is also used for balancing system power when a short-circuit fault occurs on the power grid side so as to keep the direct-drive wind driven generator to run in an uninterrupted grid-connected mode.
In the embodiment of the invention, when the short-circuit fault occurs on the power grid side, the power of the EL balance system is started, and the uninterrupted grid-connected operation of the fan is kept.
Specifically, when a single-phase or three-phase short-circuit fault occurs in the grid-side voltage, the EL-side converter control switches to the fault mode, with FC in the shutdown state. The process adopts a direct current bus voltage outer ring and an electrolytic cell current inner ring double closed-loop control strategy, and the obtained difference value is subjected to PI regulation to generate a control signal Del0To keep the dc bus voltage stable and ensure that the wind turbine can be run in grid-connected mode during a fault, as shown in fig. 4. And after the fault is eliminated, switching to a normal working condition control strategy.
According to the wind-hydrogen coupling system provided by the embodiment of the invention, when a short-circuit fault occurs on the power grid side, the basic electrolytic cell is controlled to balance the system power so as to keep the direct-drive wind driven generator to run in a continuous grid-connected mode; under the fault state, the fan can well run without being disconnected from the network, and theoretical reference and test basis are provided for the actual transient fault ride-through technology of the unit.
As shown in fig. 1, the embodiment of the present invention further provides another wind-hydrogen coupling system, and for convenience of illustration, only the parts related to the embodiment of the present invention are shown, which is similar to the above-mentioned embodiment, except that the wind-hydrogen coupling system further includes a capacitor C;
and the capacitor C is respectively connected with the machine side converter and the network measurement converter and is used for providing direct-current voltage support for the machine side converter and the network measurement converter.
The wind-hydrogen coupling system provided by the embodiment of the invention can effectively solve the problem of wind abandon of distributed wind power, furthest consumes redundant power, supplements power difference when the output of the fan is insufficient, realizes peak clipping and valley filling, has relatively stable output power of each unit, and is favorable for high-permeability friendly grid-connected operation of the distributed wind power.
Fig. 5 shows an implementation flow of a control method of a wind-hydrogen coupling system provided by an embodiment of the present invention, and for convenience of description, only parts related to the embodiment of the present invention are shown, and detailed descriptions are as follows:
in step S501, mathematical models of the direct-drive fan, the basic electrolytic cell, and the proton exchange membrane fuel cell are established.
In an embodiment of the present invention, the mathematical model of the direct-drive Wind Turbine is a Wind Turbine and a permanent magnet synchronous generator model, wherein an aerodynamic model of a Wind Turbine (WT) is:
Figure BDA0002268714500000081
in the formula, PwOutputting power for the fan; s is the wind sweeping area of the blade; ρ is the air density; vwIs the wind speed; cpThe wind energy conversion efficiency coefficient of the blade; beta is the pitch angle; λ is the tip speed ratio.
In dq coordinate system, the stator voltage equation of the permanent magnet synchronous generator is as follows:
Figure BDA0002268714500000082
in the formula usd、usq、isd、isqVoltage and current of d and q axes of the stator respectively; rs、Ld、LqStator resistance and d and q axis inductance respectively; and L isd＝Lq；ωrIs the rotor speed; psifIs a permanent magnet flux linkage.
The PMSG rotor operational equation is:
in the formula, TeIs an electromagnetic torque; t iswIs a mechanical torque; b ismEquivalent moment of inertia; j. the design is a squareeqDamping viscosity coefficient.
The PMSG electromagnetic torque equation is:
Figure BDA0002268714500000092
in the embodiment of the invention, at any temperature, the U-I equation of the basic electrolytic cell is as follows:
Figure BDA0002268714500000093
in the formula of UcellFor cell voltage of the cell, UrevIs a reversible open circuit voltage; r is1、r2The ohmic resistance parameter of the electrolyte; t iselThe temperature of the electrolytic cell; a. thecellIs the electrode area; i iselIs an electrolytic current; sn、tnThe electrode overvoltage coefficient is n ═ 1,2, 3; n is a radical ofelThe number of the modules is the number of the serial connection modules of the electrolytic bath.
The hydrogen production rate of the electrolytic cell is as follows:
Figure BDA0002268714500000094
wherein z is a gas compression coefficient, F is a Faraday constant, etaFThe expression is as follows:
Figure BDA0002268714500000095
in the formula, anThe faraday efficiency coefficient is 1,2,3, 4, 5.
The U-I characteristic curve of the cell at different temperatures is shown in FIG. 6, in which the cell reversible open circuit voltage U isrev1.2282V, the voltage at the same current decreased with increasing electrolysis temperature.
In the embodiment of the invention, the stack voltage equation of the pem fuel cell is as follows:
Figure BDA0002268714500000101
in the formula of UcellIs the cell voltage; enernstIs a thermodynamic electromotive force; etaactTo activate the overvoltage; etaohmIs an ohmic overvoltage; etaconIs concentration overvoltage; n is a radical offcNumber of monocells, UcellIs the stack voltage.
EnernstThe expression is as follows:
Figure BDA0002268714500000102
wherein Δ G is a variation value of the free Gibbs energy; Δ S is a variation value of entropy; t isfcIs the battery temperature; t isrefIs a reference temperature; r is a gas constant;
Figure BDA0002268714500000106
is the partial pressure of hydrogen at the anode catalyst/gas interface;
Figure BDA0002268714500000105
is the partial pressure of hydrogen at the cathode catalyst/gas interface.
ηactThe expression is as follows:
Figure BDA0002268714500000107
in the formula, xi1、ξ2、ξ3、ξ4Is an empirical parameter;
Figure BDA0002268714500000108
the oxygen concentration of the cathode gas-liquid interface is obtained; i isfcIs the battery current.
ηohmThe expression is as follows:
Figure BDA0002268714500000103
in the formula, RmIs equivalent membrane resistance of proton exchange membrane; rcImpedance to impede passage of protons through the membrane; l is the proton exchange membrane thickness; a is the effective area of the membrane; r ismIs the proton exchange membrane resistivity.
ηconThe expression is as follows:
wherein B is the battery operating coefficient;j is the actual current density of the battery; j. the design is a squaremaxIs the maximum current density of the battery.
The U-I, P-I characteristic curve of the PEMFC at different temperatures is shown in FIG. 7, and when the pressure is constant, the stack voltage decreases with the increase of the current, but the overall power tends to increase.
In the embodiment of the invention, the invention also relates to a hydrogen storage model, wherein a physical hydrogen storage mode is adopted, and the pressure of the storage tank is calculated by using the hydrogen flow:
Figure BDA0002268714500000111
in the formula, pbTo the actual tank pressure, pbiFor initial tank pressure, R is the universal gas constant, TbIn order to be at the working temperature,
Figure BDA0002268714500000112
is H2Molar mass, VbIs the volume of the hydrogen storage tank. Auxiliary power equipment such as pumps, valves, compressors, etc. are not considered in this modeling process.
In step S502, the wind power output is determined according to the direct-drive fan mathematical model.
In the embodiment of the invention, the parameters of the convex motor are adopted, so that the machine side converter adopts the maximum torque current ratio control and adopts a double closed loop structure of a rotating speed outer loop and a current inner loop. The rotating speed loop adjusts the rotating speed of the motor, and the rotating speed deviation outputs a direct-axis current reference value i according to the torque current relationship after passing through the rotating speed adjustersq *、isd *With actual q-axis and d-axis currents isq、isdAfter comparison, the voltage compensation term is added to obtain u through PI regulationsd、usqAnd obtaining a switch driving pulse by utilizing a two-level SVPWM technology after coordinate transformation, and realizing maximum power tracking by controlling the generator.
The grid-side inverter is of a three-level diode clamping type and adopts a double closed-loop control structure of a voltage outer loop and a current inner loop. The q-axis current is usually referenced to a value igq *Set to 0, d-axis current reference valueigd *Output by the voltage regulator, the result and the actual AC-DC axis current igq、igdAfter comparison, the voltage compensation term is added to obtain u through PI regulationgd、ugqAnd modulating a switch driving pulse by utilizing a three-level SVPWM technology after seat conversion so as to achieve the purposes of controlling the voltage of a direct-current bus to be stable and controlling a network-side inverter to operate in a unit power factor state.
In step S503, determining whether the wind power output is greater than a load demand, if so, entering step S504; if not, the process proceeds to step S505.
In step S504, when the wind power output is greater than the load demand, the residual power of the electrolytic cell water electrolysis hydrogen production and consumption system is controlled according to the basic electrolytic cell mathematical model.
In the embodiment of the invention, when the fan output is greater than the load demand, the power reference value P which needs to be consumed by the EL is generated by the upper energy management centerel *Terminal U of and ELelDividing to generate a current reference value Iel *，Iel *With real-time measured values IelThe obtained error value is compared with a triangular wave through a PI controller to generate a buck converter control signal Del。
In step S505, when the wind power output is smaller than the load demand, the fuel cell is controlled to perform power difference compensation according to the mathematical model of the pem fuel cell.
In the embodiment of the invention, when the output of the fan is smaller than the load requirement, the reference power value P which needs to be compensated for FC is generated by the upper energy management centerfc *Terminal U with FCfcDividing to generate a current reference value Ifc *，Ifc *With real-time measured values IfcThe obtained error value is compared with a triangular wave through a PI controller to generate a boost converter control signal Dfc. The overall control block diagram of the system is shown in fig. 3.
According to the control method of the wind-hydrogen coupling system provided by the embodiment of the invention, when the wind power output is greater than the load requirement, the electrolytic cell electrolyzes water to produce hydrogen and consume the residual power of the system; when the wind power output is smaller than the load requirement, the fuel cell performs power difference supplement; the control method can effectively solve the problem of wind abandonment of the distributed wind power, furthest consumes redundant power, supplements power difference when the output of the fan is insufficient, realizes peak clipping and valley filling, has relatively stable output power of each unit, and is favorable for the friendly grid-connected operation of the distributed wind power with high permeability.
For convenience of description, only the parts related to the embodiments of the present invention are described, which are similar to the above embodiments, except that the method for controlling the wind-hydrogen coupling system further includes:
when the short circuit fault occurs on the network side, the system power is balanced by an electrolytic hydrogen production method so as to realize low voltage ride through.
In the embodiment of the present invention, when a short circuit fault occurs on the grid side, the power of the system is balanced by an electrolytic hydrogen production method to realize low voltage ride through, which specifically comprises: when the voltage on the network side has single-phase or three-phase short circuit fault, a double closed-loop control strategy of a direct current bus voltage outer ring and an electrolytic cell current inner ring is adopted, and the obtained difference value is subjected to PI regulation to generate a control signal so as to stabilize the direct current bus voltage.
In the embodiment of the invention, when a single-phase or three-phase short-circuit fault occurs in the grid-side voltage, the EL-side converter control is switched to a fault mode, and the FC is in a shutdown state. The process adopts a direct current bus voltage outer ring and an electrolytic cell current inner ring double closed-loop control strategy, and the obtained difference value is subjected to PI regulation to generate a control signal Del0To keep the dc bus voltage stable and ensure that the wind turbine can be run in grid-connected mode during a fault, as shown in fig. 4. And after the fault is eliminated, switching to a normal working condition control strategy.
According to the control method of the wind-hydrogen coupling system provided by the embodiment of the invention, when the short circuit fault occurs on the network side, the power of the system is balanced by an electrolytic hydrogen production method so as to realize low voltage ride through; under the fault state, the fan can well run without being disconnected from the network, and theoretical reference and test basis are provided for the actual transient fault ride-through technology of the unit.
The feasibility of the wind-hydrogen coupling system provided by the embodiment of the invention for improving wind power absorption and low voltage ride through capability is tested by a specific simulation experiment, and is detailed as follows:
simulation analysis under the normal operation condition of the system:
in order to test the feasibility of the wind-hydrogen coupling system for improving the wind power absorption and low voltage ride through capacity, a Simulink simulation model of the system is established in Matlab software. The simulation parameters are as follows: the rated wind speed is 13m/s, the rated power of a fan is 2MW, the electrolytic cell is 1.2MW, the fuel cell is 0.5MW, the load of a power grid is set to be 0.8MW required by 0-1s, 0.75MW required by 1-3s and 0.85MW required by 3-4s, the voltage rating of the direct current side of the grid-side converter is 1200V, and other related parameters are set in tables 1-3.
TABLE 1 wind turbine parameters
Figure BDA0002268714500000131
Figure BDA0002268714500000141
TABLE 2 cell parameters of the electrolyzer
Figure BDA0002268714500000142
TABLE 3 Fuel cell Unit parameters
Figure BDA0002268714500000151
When the wind turbine is independently connected to the grid, the system simulation result is shown in fig. 9, and it can be seen that the electromagnetic torque of the generator can well follow the mechanical torque, and the whole machine runs stably; the phase of the network side phase A current is opposite to that of the voltage, the working is in an inversion state, the expected effect of unit power factor power generation is met, the total harmonic distortion rate of the network side current is 2.09% in a steady state, the total voltage distortion rate is 0 and is close to a standard sine wave, and the fact that a fan can inject friendly clean electric energy into a power grid is proved; the active power output of the fan changes along with the wind speed and is respectively 1.22MW, 0.67MW and 1.22 MW; the active power of the network side well tracks the output of the fan. The simulation results verify the effectiveness of the topological structure of the adopted machine side two-level converter and the adopted network side three-level converter and the relevant control strategy.
As can be seen from comparison between fig. 8(b) and fig. 9(d), when the system is not added with the hydrogen energy storage device for grid connection, a serious wind abandoning condition exists in the interval of 0-1s and 3-4s, and the output power of the system is not matched with the load demand of the power grid, which causes serious waste of energy; the power output between 1s and 2s is insufficient, and the load requirement cannot be met.
After the hydrogen energy storage device is added, the contradiction of the complaints can be effectively solved. When the fan output is larger than the load demand, the converter 3 is controlled to rapidly put the electrolytic cell into operation, the excess power of the system is absorbed for 420kW within 0-1s and 370kW within 3-4s by electrolyzing water to produce hydrogen, and the produced hydrogen is conveyed to the hydrogen storage tank at the speed of 2.27mol/s for 0-1s and 1.9mol/s for 3-4 s. When the output of the fan is smaller than the load demand, the fuel cell is started to work by controlling the boost converter, and the system shortage power is supplemented by 120 kW. In this process, the dc bus voltage is generally maintained at about 1200V, as shown in fig. 10.
As can be seen from FIG. 11, the active power at the grid side tracks the dynamic change of the load well, the active power fluctuates momentarily during the power jump, the excess power is absorbed to the maximum extent during the periods of 0-1s and 1-3s, the wind energy is insufficient within 1-3s, the fuel cell burns hydrogen to generate electricity to provide power support, the dynamic process of the system is fast and stable, and the response is good.
Simulation analysis under the working condition of short-circuit fault of the power grid:
according to the technical regulation of wind power access to an electric power system, the wind speed is set to be 9m/s for 2s, the most serious three-phase short-circuit fault occurs at the moment of 1s, the voltage of a power grid drops by 80%, the fault duration is 625ms, and then the normal state is recovered. Because the input and output power at two sides of the direct current side is unbalanced during the fault, the current at the grid side can be increased rapidly, the voltage of a direct current bus is lifted rapidly, and the capacitor at the direct current side and power electronic devices of a converter face damage risks, so that the safety of the whole system is endangered without limitation. According to the relevant regulations of the wind turbine technology, at the moment, the wind turbine generator is considered to be safe, the protection action enables the wind turbine generator to be disconnected from the power grid, and fault ride-through operation cannot be achieved.
After the hydrogen energy storage unit is added, hydrogen is produced by utilizing electrolyzed water, the power difference between the wind driven generator and the power grid is absorbed, the rapid rise of the voltage of a direct current bus is avoided, and a direct current side capacitor and a power switch device in an inverter are protected, as shown in fig. 12. The grid side current, although rising during a fault, is generally below the nominal value of 1.5 times. Due to the adoption of unit power factor control, the reactive power of the network side is basically kept to be zero. The maximum value of the direct current bus voltage is 1240V, the minimum value is 1165V, the change is 6.25 percent compared with the normal value, and the amplitude is within a safety margin. The cell waveform shows a transient power increase at the point of failure occurrence, due to the cell opening current, which is within the safe range. The hydrogen tank pressure increases with the accumulation of hydrogen gas from an initial 1000pa to 2308 pa. When the power grid returns to normal, the grid-side converter operates in the unit power factor state again, and the maximum active power is guaranteed to be provided for the power grid. Therefore, the hydrogen energy storage system can well avoid overvoltage and overcurrent, keep the unit in grid-connected uninterrupted operation and realize low-voltage ride through.
In conclusion, the following conclusions can be obtained through simulation research:
(1) the wind-hydrogen coupling system provided by the embodiment of the invention can effectively solve the problem of wind abandon of distributed wind power, furthest consumes redundant power, supplements power difference when the output of a fan is insufficient, realizes peak clipping and valley filling, has relatively stable output power of each unit, and is favorable for high-permeability friendly grid-connected operation of the distributed wind power;
(2) the wind-hydrogen coupling system provided by the embodiment of the invention can well realize non-grid-disconnection operation of the fan in a fault state, and provides theoretical reference and test basis for the actual transient fault ride-through technology of the unit.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims (10)

1. A wind-hydrogen coupling system, characterized in that the wind-hydrogen coupling system comprises:
the direct-drive wind driven generator is used for converting captured wind energy into mechanical energy, converting the mechanical energy into electric energy and outputting low-frequency alternating current to the machine side converter;
the machine side converter is used for converting alternating current output by the direct-drive wind driven generator into direct current to be output to the grid side converter;
the grid-side converter is used for converting the direct current output by the rotor-side converter into alternating current, and feeding the alternating current into a regional power grid after filtering;
the basic electrolytic cell and the proton exchange membrane fuel cell are respectively coupled to a direct current bus connecting the machine side converter and the grid side converter through a DC/DC converter and used for adjusting the balance of system power.
2. The wind-hydrogen coupling system according to claim 1,
the alkaline electrolytic cell is used for consuming surplus power of the system under the action of direct current when the power of the direct-drive wind power generator is larger than the load requirement;
the proton exchange membrane fuel cell is used for compensating the corresponding power shortage of a power grid when the power of the direct-drive wind power generator is smaller than the load requirement.
3. The wind-hydrogen coupling system according to claim 2, wherein the manner of the alkali type electrolytic cell to absorb the surplus power of the system is as follows:
the basic electrolytic cell electrolyzes water to generate hydrogen and oxygen, and stores the hydrogen and oxygen in a hydrogen storage tank for the proton exchange membrane dye battery.
4. The wind-hydrogen coupling system according to claim 1, wherein the alkaline type electrolytic cell is further used for balancing system power to keep the direct-drive wind driven generator in uninterrupted grid-connected operation when a short-circuit fault occurs on the power grid side.
5. The coupling system of claim 1, wherein the machine-side converter is controlled by a maximum torque to current ratio using a double closed loop configuration of a speed outer loop and a current inner loop.
6. The wind-hydrogen coupling system according to claim 1, wherein the grid-side inverter is a three-level diode-clamped type, and adopts a double closed-loop control structure with a voltage outer loop and a current inner loop.
7. The wind-hydrogen coupling system according to claim 1, further comprising a capacitor;
and the capacitor is respectively connected with the machine side converter and the network side converter and is used for providing direct-current voltage support for the machine side converter and the network side converter.
8. A control method of a wind-hydrogen coupling system is characterized by comprising the following steps:
establishing mathematical models of a direct-drive fan, an alkaline electrolytic cell and a proton exchange membrane fuel cell;
determining wind power output according to the mathematical model of the direct-drive fan;
when the wind power output is greater than the load requirement, controlling the residual power of the electrolytic cell water electrolysis hydrogen production absorption system according to the basic electrolytic cell mathematical model;
and when the wind power output is smaller than the load requirement, controlling the fuel cell to supplement the power difference according to the proton exchange membrane fuel cell mathematical model.
9. The control method of the wind-hydrogen coupling system according to claim 8, further comprising:
when the short circuit fault occurs on the network side, the system power is balanced by an electrolytic hydrogen production method so as to realize low voltage ride through.
10. The control method of the wind-hydrogen coupling system according to claim 9, wherein when a short-circuit fault occurs on the grid side, the step of balancing the system power by means of electrolytic hydrogen production to realize low voltage ride through specifically comprises:
when the voltage on the network side has single-phase or three-phase short circuit fault, a double closed-loop control strategy of a direct current bus voltage outer ring and an electrolytic cell current inner ring is adopted, and the obtained difference value is subjected to PI regulation to generate a control signal so as to stabilize the direct current bus voltage.
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