CN116882342A - Two-stage photovoltaic system sequence impedance modeling method, device, equipment and medium - Google Patents
Two-stage photovoltaic system sequence impedance modeling method, device, equipment and medium Download PDFInfo
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Classifications
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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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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F30/00—Computer-aided design [CAD]
- G06F30/30—Circuit design
- G06F30/36—Circuit design at the analogue level
- G06F30/367—Design verification, e.g. using simulation, simulation program with integrated circuit emphasis [SPICE], direct methods or relaxation methods
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
- H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
- H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F2113/00—Details relating to the application field
- G06F2113/04—Power grid distribution networks
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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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- 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
- H02J2300/22—The renewable source being solar energy
- H02J2300/24—The renewable source being solar energy of photovoltaic origin
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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
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
Abstract
The invention discloses a photovoltaic system sequence impedance modeling method, which relates to the technical field of power electronic converters and is used for solving the problem that the characteristic description of the existing impedance model is incomplete, and the method comprises the following steps: at the point of common coupling, positive and negative sequence perturbation voltages are assumed; according to a circuit structure of a two-stage photovoltaic system, coordinate transformation, a first-stage control link and a second-stage control link, calculating to obtain positive and negative sequence response currents, wherein the first-stage control link is a DC/DC link, and the second-stage control link is a DC/AC link; dividing the disturbance voltage and the response current to obtain an impedance model; and simulating the impedance model to verify the accuracy of the impedance model. The invention also discloses a photovoltaic system sequence impedance modeling device, electronic equipment and a computer storage medium. The invention further increases the accuracy of the model by modeling the combined impedance characteristics.
Description
Technical Field
The invention relates to the technical field of power electronic converters, in particular to a two-stage photovoltaic system sequential impedance modeling method, device, equipment and medium considering maximum power tracking control.
Background
Along with the rapid development of the power electronic technology, the construction cost of the new energy power generation system is reduced, so that the large-scale photovoltaic system is connected into a power grid, and the dependence of people on fossil energy is effectively relieved. However, the power electronic converter of the photovoltaic grid-connected system has the characteristics of nonlinearity and control coupling, so that the impedance characteristic at the alternating current port is different from the impedance characteristic of the linear equipment, the impedance interaction among multiple equipment can influence the stable operation of the power grid, the problem of mutual resonance/oscillation among the multiple equipment is caused when the power grid is light, the power quality of the power grid is deteriorated, the power grid instability is caused when the power grid is heavy, and serious power grid accidents are caused.
Currently, the hidden trouble of a photovoltaic system is mainly dealt with through sequential impedance modeling. However, part of researches are to equivalent a direct current side to a constant direct current voltage source, neglect the influence of voltage fluctuation of the direct current side on the impedance of an alternating current port, so that the built sequential impedance model is accurate only in a high frequency band, and the impedance characteristic of a photovoltaic system cannot be comprehensively represented. There are also studies to consider the dc side voltage fluctuation, equivalent a photovoltaic system as a form of parallel connection of a dc current source and a capacitor, and the model regards the output current of the photovoltaic panel as a constant value, and fails to sufficiently describe the influence of the dc side circuit structure and the controller parameters on the impedance characteristics. At present, a literature establishes a sequential impedance model of a single-stage photovoltaic system, and simultaneously researches the influence of a maximum power tracking (Maximum Power Point Tracking, MPPT) control parameter on the established model, wherein the model more comprehensively reflects the impedance characteristic of the photovoltaic system, but the model is not established by taking the two-stage photovoltaic system as a topology.
In summary, the existing sequential impedance model does not comprehensively describe the impedance characteristics of the two-stage photovoltaic power generation system, and does not combine a circuit structure, different control links and the like to design the impedance model.
Disclosure of Invention
In order to overcome the defects of the prior art, one of the purposes of the invention is to provide a two-stage photovoltaic system sequence impedance modeling method, which considers the influence of a direct current side circuit structure and a direct current side control module of a photovoltaic grid-connected converter on a sequence impedance model, and further provides a model foundation for two-stage photovoltaic system resonance and stability analysis.
One of the purposes of the invention is realized by adopting the following technical scheme:
a two-stage photovoltaic system sequence impedance modeling method comprises the following steps:
at the point of common coupling, positive and negative sequence perturbation voltages are assumed;
according to a circuit structure of a two-stage photovoltaic system, coordinate transformation, a first-stage control link and a second-stage control link, calculating to obtain positive and negative sequence response currents, wherein the first-stage control link is a DC/DC link, and the second-stage control link is a DC/AC link;
dividing the disturbance voltage and the response current to obtain an impedance model;
and simulating the impedance model to verify the accuracy of the impedance model.
Further, the DC/DC link uses Boost circuitry and the DC/AC link uses a two-level voltage source inverter.
Further, the calculation of the positive and negative sequence disturbance voltages and the positive and negative sequence disturbance currents includes:
constructing a circuit equation of a direct current side and an alternating current side under a three-phase static coordinate system;
expressing the output voltage and current at the public coupling point as a time domain expression of superposition of fundamental frequency, positive sequence disturbance frequency and negative sequence disturbance frequency, and converting the time domain expression into a frequency domain expression;
and according to the frequency domain expression, combining abc to dq coordinate transformation formulas to obtain d and q component frequency domain expressions of voltage and current under dq coordinates.
Further, the circuit equation satisfies:
further, the first-stage control link uses maximum power tracking as a control target, performs closed-loop control on the output current of the photovoltaic panel through the MPPT control link, performs maximum tracking of the output power through the PI link, and satisfies the transfer function:
further, the second stage control link uses the maintenance of the direct current voltage as the control target, the second stage control link includes PI control on the direct current voltage ring, the phase-locked loop and the current ring in sequence, and outputs the direct current voltage ring as the reference value of the d-axis current component of the current ring under the dq coordinate system, and the transfer function satisfies:
the PI control of the phase-locked loop further comprises: calculating a transfer function between the phase-locked loop output phase deviation amount and the input disturbance voltage, and meeting the following conditions:
T PLL (s)＝G PLL (s)/[1+G PLL (s)U 1 ]，
the PI control of the current loop converts the error between the current loop reference value and the current actual value into modulation voltage, transfer function, and meets the following requirements:
further, dividing the disturbance voltage by the response current to obtain an impedance model, and further including:
and combining the circuit equation, the phase-locked loop transfer function, the direct-current voltage loop transfer function, the current loop transfer function and the MPPT control link transfer function to obtain the relation between the output voltage and the current at the public coupling point, substituting the relation into a steady-state operation parameter, and dividing the disturbance voltage and the response current to obtain an impedance model.
The second objective of the present invention is to provide a photovoltaic system sequence impedance modeling device, which calculates positive and negative sequence disturbance voltages and currents to obtain an impedance model.
The second purpose of the invention is realized by adopting the following technical scheme:
a two-stage photovoltaic system sequence impedance modeling apparatus, comprising:
a calculation module for calculating positive and negative sequence disturbance voltages assuming a point of common coupling; according to the circuit structure of the two-stage photovoltaic system, coordinate transformation, a first-stage control link and a second-stage control link, positive and negative sequence response currents are calculated, wherein the first-stage control link is a DC/DC link, and the second-stage control link is a DC/AC link;
the modeling module is used for dividing the disturbance voltage and the response current to obtain an impedance model;
and the simulation module is used for simulating the impedance model and verifying the accuracy of the impedance model.
It is a third object of the present invention to provide an electronic device for performing one of the objects of the present invention, comprising a processor, a storage medium, and a computer program stored in the storage medium, which when executed by the processor, implements the above-mentioned photovoltaic system sequential impedance modeling method.
It is a fourth object of the present invention to provide a computer readable storage medium storing one of the objects of the present invention, having stored thereon a computer program which, when executed by a processor, implements the above-described method of modeling the impedance of a photovoltaic system.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides a two-stage photovoltaic system sequence impedance modeling method considering maximum power tracking control, which combines a circuit structure and coordinate transformation, and simultaneously considers the influence of an alternating current side structure, a direct current side structure and a control system of a photovoltaic system on the impedance characteristic of an alternating current port, so that the application frequency band of a sequence impedance model is enlarged, and more accurate analysis results are obtained in the aspects of grid-connected stability analysis, subsynchronous resonance analysis and multi-machine cross coupling analysis of the photovoltaic system.
Drawings
FIG. 1 is a topological structure diagram of a two-stage photovoltaic system of the present invention;
FIG. 2 is a flow chart of a two-stage photovoltaic system sequence impedance modeling method according to the first embodiment;
FIG. 3 is a control block diagram of a two-stage photovoltaic system according to the first embodiment;
FIG. 4 is the positive sequence impedance characteristic and the simulation experiment sweep result of the first embodiment;
FIG. 5 is a negative sequence impedance characteristic and a simulation experiment sweep result of the first embodiment;
FIG. 6 is a block diagram of a photovoltaic system sequence impedance modeling apparatus of embodiment two;
fig. 7 is a block diagram of the electronic device of the third embodiment.
Detailed Description
The invention will now be described in more detail with reference to the accompanying drawings, to which it should be noted that the description is given below by way of illustration only and not by way of limitation. Various embodiments may be combined with one another to form further embodiments not shown in the following description.
Example 1
The first embodiment provides a two-stage photovoltaic system sequence impedance modeling method, aims to perfect the defects of the current two-stage photovoltaic system sequence impedance modeling method, comprehensively considers the influence of a direct current side circuit structure and a direct current side control module of a photovoltaic grid-connected converter on a sequence impedance model, and provides a model foundation for two-stage photovoltaic system resonance and stability analysis.
In this embodiment, since the formulas are more involved, the meaning of each symbol in the formulas is illustrated and explained by table 1.
Table 1 symbol description
Referring to fig. 1, a topology structure diagram of a two-stage photovoltaic system is shown, the topology is composed of a photovoltaic panel, a photovoltaic output voltage stabilizing capacitor Cpv, a Boost circuit, a direct-current side voltage stabilizing capacitor Cdc, a three-phase inverter and an LCL filter, the system is operated in a grid-connected mode, wherein L1 and L2 are the inductances of the LCL filter, and the difference is that one is the inductance close to the inverter side, and the other is the inductance close to the grid side. The circuit equation satisfies:
on the basis of the two-stage photovoltaic system topology structure, the embodiment provides a photovoltaic system sequence impedance modeling method, as shown in fig. 2, which is characterized by comprising the following steps:
s1, assuming a public coupling point, calculating positive and negative sequence disturbance voltage;
the point of common coupling in S1 generally refers to a grid connection point where the photovoltaic system is connected to a power grid, and can be arbitrarily assumed in the impedance measurement process. The above expression "calculating positive and negative sequence disturbance voltages assuming a point of common coupling" means that a positive and negative sequence disturbance voltage of a suitable magnitude is assumed to be injected at the point of common coupling for subsequent obtaining of positive and negative sequence response currents.
The method described in this embodiment is most different from the prior art in that it is directed to a two-stage photovoltaic system and considers the effects of the two-stage pre-stage and post-stage circuits on the impedance characteristics of the ac port.
S2, calculating to obtain positive and negative sequence response currents according to a two-stage photovoltaic system circuit structure, coordinate transformation, a first-stage control link and a second-stage control link, wherein the first-stage control link is a DC/DC link, and the second-stage control link is a DC/AC link;
in S2, the DC/DC link uses Boost circuitry and the photovoltaic system uses a two-level voltage source inverter. The Boost circuit is used as a DC/DC conversion circuit and used for raising the output voltage of the photovoltaic panel to the voltage of the direct current side of the DC/AC link; the two-level voltage source type inverter is used for converting direct-current side direct-current voltage into alternating-current side three-phase voltage, during modeling, the direct-current side and the alternating-current side are separated for sequential impedance modeling, and then a complete two-stage photovoltaic system sequential impedance model is obtained through the relation between the alternating-current side and the direct-current side.
The calculation of the positive and negative sequence disturbance voltages and the positive and negative sequence disturbance currents comprises the following steps:
constructing a circuit equation of a direct current side and an alternating current side under a three-phase static coordinate system;
expressing the output voltage and current at the public coupling point as a time domain expression of superposition of fundamental frequency, positive sequence disturbance frequency and negative sequence disturbance frequency, and converting the time domain expression into a frequency domain expression;
and according to the frequency domain expression, combining abc to dq coordinate transformation formulas to obtain d and q component frequency domain expressions of voltage and current under dq coordinates.
It should be noted that, the voltage and the current obtained above are both voltage and current under a hypothetical state, and the current used is still an unknown quantity because the voltage and the current inevitably occur in the basic equation of the circuit. The subsequent step of deducing can obtain an expression between the current and the voltage, and the impedance model researched by the embodiment can be obtained by dividing the voltage in the expression and the current. The voltage and current obtained by coordinate transformation can be regarded as a hypothetical quantity, the voltage corresponds to the disturbance voltage, the current corresponds to the response current, the voltage can be a quantity determined by assumption, and the current is not a specific value.
Specifically, the circuit equations of the direct current side and the alternating current side are written in a three-phase static coordinate system, an output voltage Uabc (t) and a current Iabc (t) at the PCC are written into a time domain expression with superimposed fundamental frequency, positive sequence disturbance frequency and negative sequence disturbance frequency, the expression is converted into a frequency domain expression, frequency domain expressions of the output voltage Uabc [ f ] and the current Iabc [ f ] at the PCC are respectively obtained, the following modeling process is carried out in the frequency domain, and the frequency domain expressions of d and q components of the voltage and the current under the dq coordinate are respectively obtained according to the voltage, current expression and abc to dq coordinate transformation formulas: ud [ f ], uq [ f ], id [ f ], iq [ f ], note that there are multiple different frequency components in the frequency domain expression, and the method is applicable to positive/negative sequence disturbance voltages of any frequency.
Referring to fig. 3, a control block diagram of a two-stage photovoltaic system is shown, where the control block diagram includes a first-stage control link and a second-stage control link.
Specifically, the first stage control link is photovoltaic panel output maximum power tracking control, and the output of the photovoltaic panel output maximum power tracking control is used as a control signal of a Boost circuitThe mathematical expression of the MPPT controller can be written asThe second stage control link aims at stabilizing Vdc, wherein a direct-current voltage outer ring is used for obtaining a reference value of a d-axis current component, and the expression is +.>Wherein->The current loop controls d and q axis current components to obtain modulation voltages Md and Mq, and the expressions are as follows:
and->Wherein the method comprises the steps ofThe phase-locked loop obtains phase information theta PLL through PI module on the q-axis component of the voltage at PCC, the phase is influenced by the input disturbance voltage, the phase can be written into a form formed by superposing phase theta 1 at steady state and phase deviation delta theta after being influenced by disturbance, and thus obtaining> Wherein T is PLL (s)＝G PLL (s)/[1+G PLL (s)U 1 ]，/>
According to the circuit equation and the control link equation, the positive and negative sequence impedance of the two-stage photovoltaic system considering the maximum power tracking control can be obtained as follows:
wherein:
wherein P is 1 Is rated power at the alternating current side,Rated power factor of alternating current side, j is imaginary symbol, I 1 Is rated current on the alternating current side. Note that, the undelayed symbol in the above formula belongs to an intermediate variable that is convenient for calculation, and is not actually significant, so this embodiment is not defined.
Negative sequence impedance can be passed throughThe above is a complete sequence impedance model, and if MPPT and dc side voltage fluctuation are not considered, the corresponding module s1=0.
S3, dividing the disturbance voltage and the response current to obtain an impedance model;
specifically, a circuit equation, a phase-locked loop transfer function, a direct current voltage ring transfer function, a current ring transfer function and an MPPT control link transfer function of a two-stage photovoltaic system are combined to obtain a relation between output voltage and current at a PCC, and according to a harmonic linearization principle, in order to obtain a two-stage photovoltaic system sequence impedance model considering maximum power tracking control, a steady-state operating point of the system is required to be determined, so that steady-state operating parameters of the two-stage photovoltaic system are required to be obtained, wherein the steady-state operating parameters comprise system output active power, alternating-current side voltage, direct-current side photovoltaic panel output active power, direct-current side voltage and the like, and the obtained steady-state operating parameters are substituted into the model to obtain the two-stage photovoltaic system sequence impedance model.
S4, simulating the impedance model, and verifying the accuracy of the impedance model.
In order to ensure the accuracy of the model, the embodiment uses a MATLAB/Simulink simulation experiment platform to carry out sweep verification on the impedance model, and establishes a photovoltaic system sequence impedance model without considering a DC/DC link and maximum power tracking control, so as to respectively obtain positive and negative sequence impedance baud diagrams as shown in fig. 4 and 5;
in fig. 4, a solid line is a positive sequence impedance model of a two-stage photovoltaic system taking maximum power tracking control into consideration, a dotted line is a positive sequence impedance model of the photovoltaic system without taking a DC/DC link and maximum power tracking control into consideration, and a 'x' is a sweep result obtained by sweeping a positive sequence disturbance voltage injected into the two-stage photovoltaic system in a MATLAB/Simulink simulation experiment platform, which shows that the sweep result is basically consistent with the sequence impedance model established by the invention, meanwhile, the sequence impedance model established by the invention has a larger difference with a photovoltaic system sequence impedance model without taking a direct current side dynamic process into consideration in a middle-low frequency band, has a relatively consistent characteristic in a high frequency band, and further illustrates that the conventional sequence impedance model has errors in the description of the impedance characteristics of the middle-low frequency band of the system, so that the impedance characteristics of the whole frequency band of the system cannot be completely reflected;
in fig. 5, the solid line is a negative sequence impedance model of the two-stage photovoltaic system taking the maximum power tracking control into consideration, the dotted line is a negative sequence impedance model of the photovoltaic system taking no consideration of the DC/DC link and the maximum power tracking control, and the "x" is a sweep result obtained by sweeping the negative sequence disturbance voltage injected into the two-stage photovoltaic system in the MATLAB/Simulink simulation experiment platform, and the result shows that the sweep result is basically identical to the sequence impedance model established by the invention, so that the two-stage photovoltaic system sequence impedance modeling method taking the maximum power tracking control into consideration provided by the embodiment is applicable to the full frequency range.
In summary, the method considers the influence of the alternating current side and direct current side structures of the photovoltaic system and the control system on the impedance characteristic of the alternating current port, particularly accurately describes the influence of MPPT control and direct current voltage control on the impedance characteristic of the photovoltaic system in a middle-low frequency band, expands the applicable frequency band of a sequential impedance model, and is beneficial to obtaining more accurate analysis results in the aspects of grid-connected stability analysis, subsynchronous resonance analysis and multi-machine cross coupling analysis of the photovoltaic system.
Example two
A second embodiment discloses a device corresponding to the photovoltaic system sequential impedance modeling method of the above embodiment, which is a virtual device structure of the above embodiment, and referring to fig. 6, and includes:
a calculation module 210 for calculating positive and negative sequence disturbance voltages assuming a point of common coupling; according to the circuit structure of the two-stage photovoltaic system, coordinate transformation, a first-stage control link and a second-stage control link, positive and negative sequence response currents are calculated, wherein the first-stage control link is a DC/DC link, and the second-stage control link is a DC/AC link;
the modeling module 220 is configured to divide the disturbance voltage by the response current to obtain an impedance model;
and the simulation module 230 is used for simulating the impedance model and verifying the accuracy of the impedance model.
Example III
Fig. 7 is a schematic structural diagram of an electronic device according to a third embodiment of the present invention, as shown in fig. 7, the electronic device includes a processor 310, a memory 320, an input device 330 and an output device 340; the number of processors 310 in the computer device may be one or more, one processor 310 being taken as an example in fig. 7; the processor 310, the memory 320, the input device 330 and the output device 340 in the electronic device may be connected by a bus or other means, in fig. 7 by way of example.
The memory 320 is used as a computer readable storage medium for storing software programs, computer executable programs and modules, such as program instructions/modules corresponding to the photovoltaic system sequence impedance modeling method in the embodiment of the present invention. The processor 310 executes various functional applications of the electronic device and data processing by executing software programs, instructions and modules stored in the memory 320, i.e., implements the photovoltaic system sequential impedance modeling method of the first embodiment.
Memory 320 may include primarily a program storage area and a data storage area, wherein the program storage area may store an operating system, at least one application program required for functionality; the storage data area may store data created according to the use of the terminal, etc. In addition, memory 320 may include high-speed random access memory, and may also include non-volatile memory, such as at least one magnetic disk storage device, flash memory device, or other non-volatile solid-state storage device. In some examples, memory 320 may further include memory located remotely from processor 310, which may be connected to the electronic device via a network. Examples of such networks include, but are not limited to, the internet, intranets, local area networks, mobile communication networks, and combinations thereof.
The input device 330 may be used to receive input user identity information, system data, circuit data, and the like. The output device 340 may include a display device such as a display screen.
Example IV
A fourth embodiment of the present invention also provides a storage medium containing computer executable instructions, the storage medium being usable for a computer to perform a photovoltaic system sequential impedance modeling method, the method comprising:
assuming a public coupling point, calculating positive and negative sequence disturbance voltages;
according to a circuit structure of a two-stage photovoltaic system, coordinate transformation, a first-stage control link and a second-stage control link, calculating to obtain positive and negative sequence response currents, wherein the first-stage control link is a DC/DC link, and the second-stage control link is a DC/AC link;
dividing the disturbance voltage and the response current to obtain an impedance model;
and simulating the impedance model to verify the accuracy of the impedance model. Of course, the storage medium containing the computer executable instructions provided in the embodiments of the present invention is not limited to the method operations described above, and may also perform the related operations in the photovoltaic system order-based impedance modeling method provided in any embodiment of the present invention.
From the above description of embodiments, it will be clear to a person skilled in the art that the present invention may be implemented by means of software and necessary general purpose hardware, but of course also by means of hardware, although in many cases the former is a preferred embodiment. Based on such understanding, the technical solution of the present invention may be embodied essentially or in a part contributing to the prior art in the form of a software product, which may be stored in a computer readable storage medium, such as a floppy disk, a Read-Only Memory (ROM), a random access Memory (Random Access Memory, RAM), a FLASH Memory (FLASH), a hard disk or an optical disk of a computer, etc., and include several instructions for causing an electronic device (which may be a mobile phone, a personal computer, a server, or a network device, etc.) to execute the method according to the embodiments of the present invention.
It should be noted that, in the embodiment of the photovoltaic system sequence-based impedance modeling method apparatus, each unit and module included are only divided according to the functional logic, but are not limited to the above-mentioned division, so long as the corresponding functions can be implemented; in addition, the specific names of the functional units are also only for distinguishing from each other, and are not used to limit the protection scope of the present invention.
It will be apparent to those skilled in the art from this disclosure that various other changes and modifications can be made which are within the scope of the invention as defined in the appended claims.
Claims (10)
1. The two-stage photovoltaic system sequence impedance modeling method is characterized by comprising the following steps of:
at the point of common coupling, a positive and negative sequence perturbation voltage is assumed;
according to a circuit structure of a two-stage photovoltaic system, coordinate transformation, a first-stage control link and a second-stage control link, calculating to obtain positive and negative sequence response currents, wherein the first-stage control link is a DC/DC link, and the second-stage control link is a DC/AC link;
dividing the disturbance voltage and the response current to obtain an impedance model;
and simulating the impedance model to verify the accuracy of the impedance model.
2. The two-stage photovoltaic system sequence impedance modeling method of claim 1, wherein the DC/DC link uses Boost circuitry and the DC/AC link uses a two-level voltage source inverter.
3. The method of modeling the sequence impedance of a two-stage photovoltaic system according to claim 2, wherein the calculation of the positive and negative sequence disturbance voltages and the positive and negative sequence disturbance currents comprises:
constructing a circuit equation of a direct current side and an alternating current side under a three-phase static coordinate system;
expressing the output voltage and current at the public coupling point as a time domain expression of superposition of fundamental frequency, positive sequence disturbance frequency and negative sequence disturbance frequency, and converting the time domain expression into a frequency domain expression;
and according to the frequency domain expression, combining abc to dq coordinate transformation formulas to obtain d and q component frequency domain expressions of voltage and current under dq coordinates.
4. The two-stage photovoltaic system sequence impedance modeling method of claim 3, wherein the circuit equation satisfies:
wherein u is iabc Representing the AC side voltage of the inverter, L 1 、L 2 、C f 、R f Representing inductance, capacitance and resistance in LCL filter, G MPPT (s) represents MPPT transfer function, u abc Representing the voltage at the point of common coupling, U dc Represents the DC side voltage of the inverter, s represents the basic variable in the complex frequency domain, i iabc Representing the inverter output current, i abc Represents PCC point current, L dc 、I dc C (C) dc Indicating the inductance, current and capacitance of the DC side of the inverter, I LD Represents PV output current, Z D Representing the dc side output impedance.
5. The method for modeling the sequence impedance of the two-stage photovoltaic system according to claim 2, wherein the first-stage control link takes maximum power tracking as a control target, performs closed-loop control on the output current of the photovoltaic panel through the MPPT control link, performs maximum tracking on the output power through the PI link, and the transfer function satisfies the following conditions:
wherein G is MPPT (s) represents MPPT transfer function, K p_MPPT The proportion control coefficient K representing MPPT control link i_MPPT And the integral control coefficient of the MPPT control link is represented.
6. The method for modeling the sequence impedance of the two-stage photovoltaic system according to claim 2, wherein the second-stage control link takes maintenance of direct-current voltage stabilization as a control target, the second-stage control link comprises PI control of a direct-current voltage loop, a phase-locked loop and a current loop in sequence, and the output of the direct-current voltage loop is used as a reference value of a d-axis current component of the current loop in a dq coordinate system, and a transfer function is as follows:
wherein G is v (s) represents the voltage loop transfer function, K p_v K is as follows i_v Respectively representing the proportional and integral control coefficients of the DC voltage control link;
the PI control of the phase-locked loop further comprises: calculating a transfer function between the phase-locked loop output phase deviation amount and the input disturbance voltage, and meeting the following conditions:
T PLL (s)＝G PLL (s)/[1+G PLL (s)U 1 ]，T PLL (s) represents the phase-locked loop overall transfer function, G PLL (s) represents the transfer function, U, of the phase-locked loop internal proportional-integral control link 1 Representing the effective value of the alternating-current side phase voltage;
the PI control of the current loop converts the error between the current loop reference value and the current actual value into modulation voltage, transfer function, and meets the following requirements:
wherein G is i (s) represents the transfer function of the current loop, K p_ K i_i The representation represents the current loop ratio and integral control coefficient.
7. The method of modeling the sequence impedance of a two-stage photovoltaic system according to claim 5 or 6, wherein dividing the disturbance voltage by the response current to obtain an impedance model, further comprises:
and combining the circuit equation, the phase-locked loop transfer function, the direct-current voltage loop transfer function, the current loop transfer function and the MPPT control link transfer function to obtain the relation between the output voltage and the current at the public coupling point, substituting the relation into a steady-state operation parameter, and dividing the disturbance voltage and the response current to obtain an impedance model.
8. A two-stage photovoltaic system sequence impedance modeling apparatus, comprising:
a calculation module for calculating positive and negative sequence disturbance voltages assuming a point of common coupling; according to the circuit structure of the two-stage photovoltaic system, coordinate transformation, a first-stage control link and a second-stage control link, positive and negative sequence response currents are calculated, wherein the first-stage control link is a DC/DC link, and the second-stage control link is a DC/AC link;
the modeling module is used for dividing the disturbance voltage and the response current to obtain an impedance model;
and the simulation module is used for simulating the impedance model and verifying the accuracy of the impedance model.
9. An electronic device comprising a processor, a storage medium, and a computer program stored in the storage medium, characterized in that the computer program, when executed by the processor, implements the two-stage photovoltaic system sequential impedance modeling method of any of claims 1 to 7.
10. A computer readable storage medium having stored thereon a computer program, which when executed by a processor implements the two-stage photovoltaic system sequence impedance modeling method of any of claims 1 to 7.
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