CN117578582A - Synchronization stability analysis method and system for grid-connected converter - Google Patents
Synchronization stability analysis method and system for grid-connected converter Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
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- H—ELECTRICITY
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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Abstract
The invention discloses a synchronization stability analysis method and a synchronization stability analysis system for a grid-connected converter, which are used for constructing an angle switching dynamic model based on a current limiting inequality; establishing segmented transient energy function expressions under different angle ranges based on the angle switching dynamic model; and determining a critical value condition for stability analysis based on the transient energy function, and judging that the system is stable when the transient energy function value of the system after the alternating current fault is smaller than the critical value. The method has the advantages of simple analysis method and high value for analyzing the stability of the converter under the condition of current limitation and starting, and is close to the practical engineering.
Description
Technical Field
The invention belongs to the technical field of electric power, and particularly relates to a synchronization stability analysis method and system of a grid-connected converter.
Background
Currently, inertia and frequency in low inertia power systems can be rapidly supported, and Grid Formation (GFM) converters are receiving more attention than Grid Following (GFL) converters. However, GFM converters may lose synchronization in severe ac faults, and recently, studies have been conducted to enhance the stability control of the dynamic system. Inverter limitations such as CLC may be activated during large disturbances and the system becomes a switched dynamic system. Stability analysis of such systems is urgent and necessary, and furthermore CLC has an important influence on the transient stability of GFM based converters.
On the one hand, existing studies rely on a current switching model, i.e. switching to CLC mode by determining whether the converter current exceeds its limit, which is not applicable to the system under study described by the state variables. On the other hand, existing stability analysis methods, such as Lyapunov method, equal area rule (Equal Area Criteria, EAC) and TEF, are well applied to autonomous systems. However, analytical analysis of switching power supply systems with CLCs has not been well studied before.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a synchronous stability analysis method and a synchronous stability analysis system for a grid-connected converter, which are used for solving the technical problem of stability analysis of the converter under the condition that a low inertia system (new energy access) is limited by a controller, such as Current Limiting Control (CLC) is activated.
The invention adopts the following technical scheme:
a synchronization stability analysis method of a grid-connected converter comprises the following steps:
s1, constructing an angle switching dynamic model based on a current limiting inequality;
s2, establishing segmented transient energy function expressions under different angle ranges based on the angle switching dynamic model obtained in the step S1;
s3, determining a critical value condition for stability analysis based on the transient energy function obtained in the step S2, and judging that the system is stable when the transient energy function value of the system after the alternating current fault is smaller than the critical value.
Preferably, in step S1, using a current switching rule, the angle switching dynamic model based on the current limiting inequality is specifically:
wherein P is c For the output electromagnetic power of the virtual synchronous generator control,is output power under constant voltage control, delta is virtual synchronous generator phase angle, delta sw For switching lines +.>Is output power under constant current control.
More preferably, the dynamic model of the virtual synchronous generator is:
wherein ω, ω c ，ω s For relative angular velocity, virtual rotor angular velocity, and reference angular velocity, T J And D is virtual inertia and damping of virtual synchronous generator control, P 0 Is the output power reference value of the virtual synchronous generator control.
More preferably, the conditions under which the virtual synchronous generator operates under constant voltage control are as follows:
wherein U is p For PCC point voltage reference, U s Is infinite bus voltage, I max X is the current limit of the converter l D is a reference variable for transmission line reactance.
Preferably, in step S2, the transient energy function expression of the segment is as follows:
wherein V (omega, delta) is the transient energy function of the system, T J The virtual inertia, ω being the relative angular velocity,for output power under constant voltage control, +.>For output power under constant current control, P 0 For virtual synchronous generator control of output power reference value, delta s To stabilize the equilibrium point, delta sw For switching lines, delta uep Is an unstable equilibrium point.
More preferably, the stability balance point delta s The method comprises the following steps:
δ s ＝sin -1 (P 0 X l /U p U s )
wherein X is l For transmission line reactance, U p For PCC point voltage reference, U s Is an infinite bus voltage.
More preferably, the unstable equilibrium point delta uep The method comprises the following steps:
δ uep ＝cos -1 [P 0 /(U s I max )]
wherein I is max For the current limit of the converter, U s Is an infinite bus voltage.
Still more preferably, when f' (x (0) )>0,g′(x (0) )>0 is established, the obtained balance point is a stable balance point, otherwise, the obtained balance point is an unstable balance point, and the method is solved as follows:
wherein f (x) and g (x) are algebraic terms generated in the process of deducing differential algebraic equations of different subsystem systems of VSC connected to infinite buses, U p For PCC point voltage reference, U s Is infinite bus voltage, T J For virtual synchronous generator inertia coefficient, ω s To fix the angular velocity of the system, L l For transmission line inductance, x is a system state variable, θ c(0) Is a stable value of a state variable of the system, I max For the current limit of the converter, phi is the phase of the ac term.
Preferably, in step S3, the critical energy function of the stability analysis is specifically as follows:
wherein,for output power under constant voltage control, P 0 For inverter output power reference,/->For output power under constant current control, delta sw For switching lines, delta uep is the point of unstable equilibrium, delta s To stabilize the equilibrium point.
In a second aspect, an embodiment of the present invention provides a synchronization stability analysis system for a grid-connected inverter, including:
the construction module is used for constructing an angle switching dynamic model based on the current limiting inequality;
the function module is used for establishing a segmented transient energy function expression based on the angle switching dynamic model obtained by the construction module;
and the analysis module is used for determining a critical value condition for stability analysis based on the transient energy function obtained by the function module, and judging that the system is stable when the transient energy function value of the system after the alternating current fault is smaller than the critical value.
Compared with the prior art, the invention has at least the following beneficial effects:
a synchronous stability analysis method of a grid-connected converter further establishes segmented transient energy function expressions under different angle ranges by constructing an angle switching dynamic model based on a current limiting inequality, and then determines a critical value condition for stability analysis based on the transient energy function, thereby providing theoretical support for stability analysis after the system is greatly disturbed.
Further, the setting of the angle switching dynamic model based on the current limiting inequality can give the output power of the converter under different running states.
Further, the setting of the dynamic model of the virtual synchronous generator gives the external characteristics of the converter.
Further, the setting of the operating conditions under constant voltage control gives a range of converter output power angles while maintaining constant voltage mode.
Further, the segmented transient energy function expression sets up criteria for system stability analysis in the unused operating range.
Furthermore, the derivative criterion simplifies the calculation step of stability judgment in a stand-alone infinite system.
Further, the critical energy function of the stability analysis gives a critical value for judging the stability of the system, i.e. the energy function of the system needs to be smaller than this value.
It will be appreciated that the advantages of the second aspect may be found in the relevant description of the first aspect, and will not be described in detail herein.
In conclusion, the method has the advantages of simple analysis method and close to engineering practice, and has high value for analyzing the stability of the converter under the condition of current limitation.
The technical scheme of the invention is further described in detail through the drawings and the embodiments.
Drawings
FIG. 1 is a flow chart of the present invention;
FIG. 2 is a schematic diagram of a segment constant area criterion at different initial angles;
FIG. 3 is a schematic diagram of the dynamic behavior of the system at various initial times;
fig. 4 is a schematic diagram of a computer device according to an embodiment of the invention.
Fig. 5 is a block diagram of a chip according to an embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are some, but not all embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In the description of the present invention, it will be understood that the terms "comprises" and "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It is also to be understood that the terminology used in the description 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 this specification 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 be further understood that the term "and/or" as used in the present specification and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes such combinations, e.g., a and/or B, may represent: a exists alone, A and B exist together, and B exists alone. In the present invention, the character "/" generally indicates that the front and rear related objects are an or relationship.
It should be understood that although the terms first, second, third, etc. may be used to describe the preset ranges, etc. in the embodiments of the present invention, these preset ranges should not be limited to these terms. These terms are only used to distinguish one preset range from another. For example, a first preset range may also be referred to as a second preset range, and similarly, a second preset range may also be referred to as a first preset range without departing from the scope of embodiments of the present invention.
Depending on the context, the word "if" as used herein may be interpreted as "at … …" or "at … …" or "in response to a determination" or "in response to detection". Similarly, the phrase "if determined" or "if detected (stated condition or event)" may be interpreted as "when determined" or "in response to determination" or "when detected (stated condition or event)" or "in response to detection (stated condition or event), depending on the context.
Various structural schematic diagrams according to the disclosed embodiments of the present invention are shown in the accompanying drawings. The figures are not drawn to scale, wherein certain details are exaggerated for clarity of presentation and may have been omitted. The shapes of the various regions, layers and their relative sizes, positional relationships shown in the drawings are merely exemplary, may in practice deviate due to manufacturing tolerances or technical limitations, and one skilled in the art may additionally design regions/layers having different shapes, sizes, relative positions as actually required.
The invention provides a synchronous stability analysis method of a grid-connected converter, which firstly provides an angle switching dynamic model based on a current limiting inequality, and the model can be directly used for analyzing stability; in addition, a segment-based TEF was also established for stability analysis of grid-tie VSGs with CLCs; the stability is easily judged by comparing the TEF value at the last switching instant with a defined critical energy; finally, in terms of stability analysis, it has been demonstrated that the two methods of the proposed TEF and Segmentation Equal Area Criterion (SEAC) are equivalent; the method can provide a useful guide for the design of the controller and can be easily expanded into the analysis of a multi-VSG embedded power system.
Referring to fig. 1, in the synchronous stability analysis method of the grid-connected converter, an angle switching dynamic model based on a current limiting inequality is established, and then a Transient Energy Function (TEF) expression based on segmentation is provided. And thereby also a threshold value for stability analysis; finally, the equivalence of the two methods of the proposed TEF and the Segmentation Equal Area Criterion (SEAC) is proved, and the synchronization stability analysis method of the grid-connected converter of the proposed segmentation transient energy function and the derivation of the related expression are proved to be reasonable; the method comprises the following specific steps:
s1, constructing an angle switching dynamic model based on a current limiting inequality;
an angle switching dynamic model based on a current limiting inequality is established, and only the model of the generator itself is considered in the process. The doubly-fed wind driven generator can be regarded as a wound rotor induction motor, a stator and a rotor loop are electrified, and stator and rotor windings are all involved in electromechanical energy conversion. Thus, the model of the doubly-fed wind generator is essentially the same as the model of the induction motor, except that the rotor voltage is provided by the power supply, i.e. the rotor-side converter. This configuration allows the fan to operate over a wide range of rotational speeds.
The output of the inverter is expressed as:
an angle switching model for stability analysis is proposed by a current clipping inequality; the virtual synchronous generator (Virtual Synchronous Generator, VSG) will operate in constant voltage control (Constant Voltage Control, CVC) mode if the following current limiting inequality is met.
Rearranging (3) to obtain
Wherein delta sw ＝cos -1 (d)，δ＝-δ sw And δ=δ sw Is the two switching thresholds for the VSG to switch between modes of CVC and CLC.
Based on (3) and (4), the power output of the converters of current switching rules (1) and (2) is converted to the following angle switching rules:
P c ＝P c CVC ,δ∈[-δ sw ,δ sw ] (5)
s2, establishing segmented Transient Energy Function (TEF) expressions under different angle ranges based on the angle switching dynamic model obtained in the step S1;
consider the following piecewise function:
δ s ＝sin -1 (P 0 X l /U p U s ) (8)
wherein delta s Is the stable equilibrium point (Stable equilibrium point, SEP), delta uep Is the unstable equilibrium point (Unstable equilibrium point, UEP) of the dynamic system under investigation, calculated as follows:
δ uep ＝cos -1 [P 0 /(U s I max )] (9)
the equilibrium point of the system is solved as follows:
wherein f (x) and g (x) are algebraic terms generated in the process of deducing differential algebraic equations of different subsystem systems of VSC connected to infinite buses, U p For PCC point voltage reference, U s Is infinite bus voltage, T J For virtual synchronous generator inertia coefficient, ω s To fix the angular velocity of the system, L l For transmission line inductance, x is a system state variable, θ c(0) Is a stable value of a state variable of the system, I max For the current limit of the converter, phi is the phase of the AC term, theta c(0) For a stable value of one state variable of the system, phi is the phase of some AC term, if f' (x (0) )>0,g′(x (0) )>And if 0 is true, the obtained balance point is a stable balance point, otherwise, the balance point is an unstable balance point.
In normal operation of grid connected VSG delta uep >δ sw >δ s . Based on the definition of (7), the function of the construct is continuous and the derivative with respect to time becomes in the range:
the results show that the derivative of the defined energy function along any system trajectory is non-positive. Furthermore, the system trace x (t) has a finite value like the V (x) format, meaning that x (t) is also bounded and the function is the desired TEF for the system under study.
S3, establishing a segment-based TEF, and providing a condition for analyzing a critical value of stability, wherein when the TEF of the system after the alternating current fault is smaller than the critical value, the stability of the system is ensured.
Based on TEF theory, critical energy of the system is represented by ω=0, δ=δ uep The value of V (ω, δ) is determined as follows:
for the dynamic system under investigation, if the TEF value after an ac fault is less than the value determined in (11), the stability of the system is ensured by the relative stability.
In still another embodiment of the present invention, a synchronous stability analysis system for a grid-connected inverter is provided, where the system can be used to implement the synchronous stability analysis method for a grid-connected inverter, and specifically, the synchronous stability analysis system for a grid-connected inverter includes a construction module, a function module, and an analysis module.
The angle switching dynamic model based on the current limiting inequality is built by the building module;
the function module is used for establishing a segmented transient energy function expression based on the angle switching dynamic model obtained by the construction module;
and the analysis module is used for determining a critical value condition for stability analysis based on the transient energy function obtained by the function module, and judging that the system is stable when the transient energy function value of the system after the alternating current fault is smaller than the critical value.
In yet another embodiment of the present invention, a terminal device is provided, the terminal device including a processor and a memory, the memory for storing a computer program, the computer program including program instructions, the processor for executing the program instructions stored by the computer storage medium. The processor may be a central processing unit (Central Processing Unit, CPU), but may also be other general purpose processor, digital signal processor (Digital Signal Processor, DSP), application specific integrated circuit (Application Specific Integrated Circuit, ASIC), off-the-shelf programmable gate array (Field-Programmable Gate Array, FPGA) or other programmable logic device, discrete gate or transistor logic device, discrete hardware components, etc., which are the computational core and control core of the terminal adapted to implement one or more instructions, in particular to load and execute one or more instructions to implement the corresponding method flow or corresponding functions; the processor of the embodiment of the invention can be used for the operation of the synchronization stability analysis method of the grid-connected converter, and comprises the following steps:
constructing an angle switching dynamic model based on a current limiting inequality; establishing segmented transient energy function expressions under different angle ranges based on the angle switching dynamic model; and determining a critical value condition for stability analysis based on the transient energy function, and judging that the system is stable when the transient energy function value of the system after the alternating current fault is smaller than the critical value.
Referring to fig. 4, the terminal device is a computer device, and the computer device 60 of this embodiment includes: a processor 61, a memory 62, and a computer program 63 stored in the memory 62 and executable on the processor 61, the computer program 63 when executed by the processor 61 implements the reservoir inversion wellbore fluid composition calculation method of the embodiment, and is not described in detail herein to avoid repetition. Alternatively, the computer program 63, when executed by the processor 61, performs the functions of each model/unit in the synchronous stability analysis system of the grid-connected inverter according to the embodiment, and is not described herein in detail for avoiding repetition.
The computer device 60 may be a desktop computer, a notebook computer, a palm top computer, a cloud server, or the like. Computer device 60 may include, but is not limited to, a processor 61, a memory 62. It will be appreciated by those skilled in the art that fig. 4 is merely an example of a computer device 60 and is not intended to limit the computer device 60, and may include more or fewer components than shown, or may combine certain components, or different components, e.g., a computer device may also include an input-output device, a network access device, a bus, etc.
The processor 61 may be a central processing unit (Central Processing Unit, CPU), but may also be other general purpose processors, digital signal processors (Digital Signal Processor, DSP), application specific integrated circuits (Application Specific Integrated Circuit, ASIC), field programmable gate arrays (Field-Programmable Gate Array, FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, or the like. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like.
The memory 62 may be an internal storage unit of the computer device 60, such as a hard disk or memory of the computer device 60. The memory 62 may also be an external storage device of the computer device 60, such as a plug-in hard disk provided on the computer device 60, a Smart Media Card (SMC), a Secure Digital (SD) Card, a Flash memory Card (Flash Card), or the like.
Further, the memory 62 may also include both internal storage units and external storage devices of the computer device 60. The memory 62 is used to store computer programs and other programs and data required by the computer device. The memory 62 may also be used to temporarily store data that has been output or is to be output.
Referring to fig. 5, the terminal device is a chip, and the chip 600 of this embodiment includes a processor 622, which may be one or more in number, and a memory 632 for storing a computer program executable by the processor 622. The computer program stored in memory 632 may include one or more modules each corresponding to a set of instructions. Further, the processor 622 may be configured to execute the computer program to perform the grid-tied inverter synchronization stability analysis method described above.
In addition, chip 600 may further include a power supply component 626 and a communication component 650, where power supply component 626 may be configured to perform power management of chip 600, and communication component 650 may be configured to enable communication of chip 600, e.g., wired or wireless communication. In addition, the chip 600 may also include an input/output (I/O) interface 658. Chip 600 may operate based on an operating system stored in memory 632.
In a further embodiment of the present invention, the present invention also provides a storage medium, in particular, a computer readable storage medium (Memory), which is a Memory device in a terminal device, for storing programs and data. It will be appreciated that the computer readable storage medium herein may include both a built-in storage medium in the terminal device and an extended storage medium supported by the terminal device. The computer-readable storage medium provides a storage space storing an operating system of the terminal. Also stored in the memory space are one or more instructions, which may be one or more computer programs (including program code), adapted to be loaded and executed by the processor. The computer readable storage medium may be a high-speed RAM Memory or a Non-Volatile Memory (Non-Volatile Memory), such as at least one magnetic disk Memory.
One or more instructions stored in a computer-readable storage medium may be loaded and executed by a processor to implement the respective steps of the method for synchronous stability analysis of a parallel network transformer in the above embodiments; one or more instructions in a computer-readable storage medium are loaded by a processor and perform the steps of:
constructing an angle switching dynamic model based on a current limiting inequality; establishing segmented transient energy function expressions under different angle ranges based on the angle switching dynamic model; and determining a critical value condition for stability analysis based on the transient energy function, and judging that the system is stable when the transient energy function value of the system after the alternating current fault is smaller than the critical value.
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the invention, as presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The equivalency of the TEF and SEAC methods was verified.
Please refer to the piecewise equal area criterion at different initial angles of fig. 2 to prove the correctness of the above derivation, if neglecting damping (d=0), the system stability can be judged by the piecewise equal area criterion SEAC, at the fault clearance instant δ 0 The region delta epsilon (delta) s ,δ sw ) In the inner, the acceleration area is equal to the deceleration area marked in the shadow area.
Wherein delta end Is omega end At 0, the furthest angle the inverter output can reach. Based on the proposed TEF method, when damping is ignored, the system is a conservative system, the system trajectory moves along the iso-energy plane, and the energy function is a constant value. In other words the energy at any point of the system trajectory remains the same.
Wherein is the furthest angle of the VSG reached at the output of the converter under ac fault. Based on the proposed TEF method, when damping is ignored, the system is a conservative system, the system trajectory moves along the iso-energy plane, and the energy function is a constant value.
The energy at any point of the system trajectory remains the same, as follows:
the energy of the points of interest is the same based on the proposed TEF method, as follows:
the results show that (14) and (15) are also equal and demonstrate that the SEAC method and the TEF method are identical for transient analysis of grid-tied VSG. However, the TEF method stands out by providing energy boundaries for the dynamic system under investigation, which is very beneficial for the design of the controller. More importantly, the TEF method is easier to extend to transient stability analysis of multi-VSG embedded power systems.
Table 1 parameter table
Please refer to the dynamic behavior of the system at different initial times of fig. 3 to prove the correctness of the above conclusion, and a grid-connected VSG is utilized to verify the correctness of the proposed analysis method. The relevant parameters are shown in table 1. The voltage of the bus bar set to infinity drops to 0.01pu at 10 milliseconds and returns to nominal after a few seconds.
Figure 3 shows the dynamic behaviour of the system under investigation in different situations. As shown in fig. 3 (a), the system stability can be maintained at 33 and 38 ms, respectively. Based on the proposed TEF method, TEF values at the fault clearing instants associated with points a and G are calculated as 0.2304 and 0.3413, respectively. As shown in Table I, they are all less than a defined threshold value (V cr ) 0.3639. The stability analysis results shown in table I verify well the correctness of the proposed method. Further, points B, C, D and F are the system trace and the switching line (δ=δ sw ) Is a cross point of (c). As is clear from fig. 3 (a), the system trajectory at these points is not smooth, which indicates that the active power of the VSG is discontinuous at the time of the switching event. As shown in fig. 3 (b), the value of TEF versus time well verifies the monotonically decreasing nature of the defined TEF. Further, the system trace covers the angle of UEP when increasing to 43 milliseconds. The proposed method also predicts instability, since the TEF value at point H is 0.4506, greater than the defined threshold.
In summary, the method and the system for analyzing the synchronous stability of the grid-connected converter are strict in theory, simple and visual in theory by providing the method for analyzing the synchronous stability of the grid-connected converter based on the piecewise transient energy function, and the method for analyzing the synchronous stability of the grid-connected converter has the advantage that an angle switching dynamic model based on a current limiting inequality is provided for the first time, and the model can be directly used for analyzing the stability. Furthermore, a segment-based TEF was also established for stability analysis of grid-tie VSGs with CLCs. Stability can be readily determined by comparing the TEF value at the last switching instant of the system with a defined threshold energy. Finally, in terms of stability analysis, the two methods of the proposed TEF and SEAC proved to be equivalent. The method provides a useful guide for the design of the controller and can be easily extended to the analysis of multi-VSG embedded power systems.
It will be apparent to those skilled in the art that, for convenience and brevity of description, only the above-described division of the functional units and modules is illustrated, and in practical application, the above-described functional distribution may be performed by different functional units and modules according to needs, i.e. the internal structure of the apparatus is divided into different functional units or modules to perform all or part of the above-described functions. The functional units and modules in the embodiment may be integrated in one processing unit, or each unit may exist alone physically, or two or more units may be integrated in one unit, where the integrated units may be implemented in a form of hardware or a form of a software functional unit. In addition, specific names of the functional units and modules are only for convenience of distinguishing from each other, and are not used for limiting the protection scope of the present application. The specific working process of the units and modules in the above system may refer to the corresponding process in the foregoing method embodiment, which is not described herein again.
In the foregoing embodiments, the descriptions of the embodiments are emphasized, and in part, not described or illustrated in any particular embodiment, reference is made to the related descriptions of other embodiments.
Those of ordinary skill in the art will appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, or combinations of computer software and electronic hardware. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the solution. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
In the embodiments provided in the present invention, it should be understood that the disclosed apparatus/terminal and method may be implemented in other manners. For example, the apparatus/terminal embodiments described above are merely illustrative, e.g., the division of the modules or units is merely a logical function division, and there may be additional divisions when actually implemented, e.g., multiple units or components may be combined or integrated into another system, or some features may be omitted or not performed. Alternatively, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection via interfaces, devices or units, which may be in electrical, mechanical or other forms.
The units described as separate units may or may not be physically separate, and units shown as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.
In addition, each functional unit in the embodiments of the present invention may be integrated in one processing unit, or each unit may exist alone physically, or two or more units may be integrated in one unit. The integrated units may be implemented in hardware or in software functional units.
The integrated modules/units, if implemented in the form of software functional units and sold or used as stand-alone products, may be stored in a computer readable storage medium. Based on such understanding, the present invention may implement all or part of the flow of the method of the above embodiment, or may be implemented by a computer program to instruct related hardware, where the computer program may be stored in a computer readable storage medium, and when the computer program is executed by a processor, the computer program may implement the steps of each of the method embodiments described above. Wherein the computer program comprises computer program code which may be in source code form, object code form, executable file or some intermediate form etc. The computer readable medium may include: any entity or device capable of carrying the computer program code, a recording medium, a usb disk, a removable hard disk, a magnetic disk, an optical disk, a computer Memory, a Read-Only Memory (ROM), a Random-Access Memory (RAM), an electrical carrier wave signal, a telecommunications signal, a software distribution medium, etc., it should be noted that the content of the computer readable medium may be appropriately increased or decreased according to the requirements of legislation and patent practice in jurisdictions, such as in some jurisdictions, according to the legislation and patent practice, the computer readable medium does not include electrical carrier wave signals and telecommunications signals.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The above is only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited by this, and any modification made on the basis of the technical scheme according to the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (10)
1. The synchronization stability analysis method of the grid-connected converter is characterized by comprising the following steps of:
s1, constructing an angle switching dynamic model based on a current limiting inequality;
s2, establishing segmented transient energy function expressions under different angle ranges based on the angle switching dynamic model obtained in the step S1;
s3, determining a critical value condition for stability analysis based on the transient energy function obtained in the step S2, and judging that the system is stable when the transient energy function value of the system after the alternating current fault is smaller than the critical value.
2. The method for analyzing the synchronous stability of the grid-connected inverter according to claim 1, wherein in the step S1, using a current switching rule, the angle switching dynamic model based on the current limiting inequality is specifically:
wherein P is c For the output electromagnetic power of the virtual synchronous generator control,is output power under constant voltage control, delta is virtual synchronous generator phase angle, delta sw For switching lines +.>Is output power under constant current control.
3. The method for analyzing synchronization stability of a grid-connected inverter according to claim 2, wherein the dynamic model of the virtual synchronous generator is:
wherein ω, ω c ，ω s For relative angular velocity, virtual rotor angular velocity, and reference angular velocity, T J And D is virtual inertia and damping of virtual synchronous generator control, P 0 Is the output power reference value of the virtual synchronous generator control.
4. The method for analyzing the synchronous stability of the grid-connected converter according to claim 2, wherein the virtual synchronous generator operates under the constant voltage control condition as follows:
wherein U is p For PCC point voltage reference, U s Is infinite bus voltage, I max X is the current limit of the converter l D is a reference variable for transmission line reactance.
5. The method for analyzing synchronization stability of grid-connected converters according to claim 1, wherein in step S2, the segmented transient energy function expression is as follows:
wherein V (omega, delta) is the transient energy function of the system, T J The virtual inertia, ω being the relative angular velocity,for output power under constant voltage control, +.>For output power under constant current control, P 0 For virtual synchronous generator control of output power reference value, delta s To stabilize the equilibrium point, delta sw For switching lines, delta uep Is an unstable equilibrium point.
6. The method for analyzing synchronous stability of grid-connected inverter according to claim 5, wherein the stable equilibrium point δ s The method comprises the following steps:
δ s ＝sin -1 (P 0 X l /U p U s )
wherein X is l For transmission line reactance, U p For PCC point voltage reference, U s Is an infinite bus voltage.
7.The method for analyzing synchronous stability of grid-connected inverter according to claim 5, wherein the unstable equilibrium point delta uep The method comprises the following steps:
δ uep ＝cos -1 [P 0 /(U s I max )]
wherein I is max For the current limit of the converter, U s Is an infinite bus voltage.
8. The method for analyzing synchronization stability of grid-connected inverter according to claim 6 or 7, wherein when f' (x) (0) )>0,g′(x (0) )>0 is established, the obtained balance point is a stable balance point, otherwise, the obtained balance point is an unstable balance point, and the method is solved as follows:
wherein f (x) and g (x) are algebraic terms generated in the process of deducing differential algebraic equations of different subsystem systems of VSC connected to infinite buses, U p For PCC point voltage reference, U s Is infinite bus voltage, T J For virtual synchronous generator inertia coefficient, ω s To fix the angular velocity of the system, L l For transmission line inductance, x is a system state variable, θ c(0) Is a stable value of a state variable of the system, I max For the current limit of the converter, phi is the phase of the ac term.
9. The method for analyzing the synchronous stability of the grid-connected inverter according to claim 1, wherein in the step S3, the critical energy function of the stability analysis is specifically as follows:
wherein,for output power under constant voltage control, P 0 For inverter output power reference,/->For output power under constant current control, delta sw For switching lines, delta uep Delta as an unstable equilibrium point s To stabilize the equilibrium point.
10. A grid-tied inverter synchronous stability analysis system, comprising:
the construction module is used for constructing an angle switching dynamic model based on the current limiting inequality;
the function module is used for establishing a segmented transient energy function expression based on the angle switching dynamic model obtained by the construction module;
and the analysis module is used for determining a critical value condition for stability analysis based on the transient energy function obtained by the function module, and judging that the system is stable when the transient energy function value of the system after the alternating current fault is smaller than the critical value.
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