Multi-construction-network type grid-connected system admittance model construction and frequency oscillation characteristic analysis method

Abstract

The invention provides an admittance model construction and frequency oscillation characteristic analysis method for a multi-construction-network type grid-connected system, and belongs to the technical field of construction-network type control, and the method comprises the steps: obtaining a small disturbance quantity of reference active power and a small disturbance quantity of a common AC bus frequency; based on the small disturbance quantity of the reference active power and the small disturbance quantity of the common AC bus frequency, constructing a single GFM output admittance model (a first type of output admittance model) under different GFM control strategies, or an output admittance model (a second type of output admittance model) of a multi-GFM grid-connected system; based on the first type of output admittance model or the second type of output admittance model, calculating to obtain the output angular frequency of the multi-GFM grid-connected system; and based on the output angular frequency of the multi-GFM grid-connected system, analyzing the frequency oscillation characteristics of the multi-GFM grid-connected system to obtain an analysis result. According to the scheme, the accuracy of frequency oscillation characteristic analysis of the multi-configuration grid-connected system can be improved.

Description

Technical Field

[0001] The present application relates to the field of grid-connected control technology, and in particular to a method for constructing a multi-grid-connected grid-connected system admittance model and analyzing frequency oscillation characteristics. Background Art

[0002] At present, the output admittance model in the prior art mainly includes the P / ω "admittance" model. This model has the following disadvantages: the model can only be used to analyze the stability and power response of the system under load disturbance, which limits its application in studying the power-frequency oscillation characteristics of multi-machine systems, and does not have the ability to study the dynamic response performance of active power and angular frequency.

[0003] In the prior art, the accuracy of frequency oscillation characteristic analysis of multi-grid type grid-connected systems is low. Therefore, how to improve the accuracy of frequency oscillation characteristic analysis of multi-grid type grid-connected systems has become a problem to be solved. Summary of the invention

[0004] The purpose of this application is to provide a method for constructing a multi-grid type grid-connected system admittance model and analyzing frequency oscillation characteristics, which can solve the problem of low accuracy in frequency oscillation characteristics analysis of multi-grid type grid-connected systems in the prior art.

[0005] In a first aspect, an embodiment of the present application provides a method for constructing a multi-grid type grid-connected system admittance model and analyzing frequency oscillation characteristics, the method comprising: Obtaining a small disturbance amount of reference active power and a small disturbance amount of public AC bus frequency; Based on the small disturbance of reference active power and the small disturbance of common AC bus frequency, a single GFM output admittance model under different GFM control strategies or an output admittance model of a multi-GFM grid-connected system is constructed; wherein the single GFM output admittance model is a first-type output admittance model, and the output admittance model of a multi-GFM grid-connected system is a second-type output admittance model; Based on the first type output admittance model or the second type output admittance model, the output angular frequency of the multi-GFM grid-connected system is calculated; Based on the output angular frequency of the multi-GFM grid-connected system, the frequency oscillation characteristics of the multi-GFM grid-connected system are analyzed and the analysis results are obtained.

[0006] In a possible implementation of the first aspect, the GFM control strategy includes: a conventional control strategy, a droop control strategy, and a control strategy with a damping correction link; the first type of output admittance model includes: a first output admittance model, a second output admittance model, and a third output admittance model; The first output admittance model is a single GFM output admittance model under the conventional control strategy. The specific expression is as follows:

[0007] in, represents a small perturbation of the angular frequency, represents the first admittance, represents the complex frequency variable in the Laplace transform of the transfer function, represents the second admittance, represents a small disturbance of the reference power, Represents the small disturbance of the common AC bus frequency; The second output admittance model is a single GFM output admittance model under the droop control strategy. The specific expression is as follows:

[0008] in, represents the angular frequency, represents the synchronization coefficient, represents the droop control coefficient; The third output admittance model is a single GFM output admittance model under the control strategy with a damping correction link. The specific expression is as follows:

[0009] in, Indicates energy, represents the moment of inertia, represents the damping coefficient, Indicates the reference angular frequency.

[0010] In a possible implementation manner of the first aspect, the expression of the second type of output admittance model is as follows:

[0011]

[0012] in, Indicates ordinal number, represents the number of GFMs, represents the equivalent admittance, represents the output admittance of the grid impedance, represents the intermediate variable, Indicates the small disturbance of the power grid frequency.

[0013] In a possible implementation manner of the first aspect, calculating the output angular frequency of the multi-GFM grid-connected system based on the first type output admittance model or the second type output admittance model includes: Based on the first output admittance model and the common coupling point frequency, the output angular frequency of the multi-GFM grid-connected system is calculated. The specific expression is as follows:

[0014] in, represents the output angular frequency of the multi-GFM grid-connected system, represents the ordinal number of GFM, represents the first angular frequency coefficient, represents the small disturbance of the mth reference frequency, t represents the ordinal number, represents the second angular frequency coefficient, represents the small disturbance of the tth reference frequency, represents the third angular frequency coefficient; The expression for the frequency of the common coupling point is as follows:

[0015] in, represents the frequency of the common coupling point, represents the i-th first output admittance, represents the i-th second output admittance.

[0016] In a possible implementation manner of the first aspect, the expression of the first angular frequency coefficient is as follows:

[0017]

[0018] in, represents the mth first output admittance, represents the mth second output admittance, Represents an intermediate variable.

[0019] In a possible implementation manner of the first aspect, the expression of the second angular frequency coefficient is as follows:

[0020] in, represents the tth first output admittance, represents the t-th second output admittance.

[0021] In a possible implementation manner of the first aspect, the expression of the third angular frequency coefficient is as follows: .

[0022] In a possible implementation manner of the first aspect, based on the first type of output admittance model or the second type of output admittance model, calculating and obtaining the output angular frequency of the multi-GFM grid-connected system further includes: Based on the second type output admittance model and the common coupling point frequency, the output angular frequency of the multi-GFM grid-connected system is calculated.

[0023] In a possible implementation manner of the first aspect, based on the output angular frequency of the multi-GFM grid-connected system, analyzing the frequency oscillation characteristics of the multi-GFM grid-connected system includes: Based on the influencing factors and changing rules of the first angular frequency coefficient, the second angular frequency coefficient and the third angular frequency coefficient, the frequency oscillation characteristics of the multi-GFM grid-connected system are analyzed.

[0024] In a second aspect, an embodiment of the present application provides a device for constructing a multi-grid type grid-connected system admittance model and analyzing frequency oscillation characteristics, the device comprising: An acquisition unit, used for acquiring a small disturbance amount of reference active power and a small disturbance amount of a common AC bus frequency; A construction unit is used to construct an output admittance model of a single GFM or an output admittance model of a multi-GFM grid-connected system under different GFM control strategies based on a small disturbance amount of reference active power and a small disturbance amount of a common AC bus frequency; wherein the output admittance model of a single GFM is a first-type output admittance model, and the output admittance model of a multi-GFM grid-connected system is a second-type output admittance model; A calculation unit, used for calculating the output angular frequency of the multi-GFM grid-connected system based on the first type output admittance model or the second type output admittance model; The analysis unit is used to analyze the frequency oscillation characteristics of the multi-GFM grid-connected system based on the output angular frequency of the multi-GFM grid-connected system to obtain an analysis result.

[0025] In a third aspect, an embodiment of the present application provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the method for constructing a multi-grid type grid-connected system admittance model and analyzing frequency oscillation characteristics of any one of the above-mentioned first aspects is implemented.

[0026] In a fourth aspect, an embodiment of the present application provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, it implements the method for constructing a multi-grid type grid-connected system admittance model and analyzing frequency oscillation characteristics of any one of the above-mentioned first aspects.

[0027] In a fifth aspect, an embodiment of the present application provides a computer program product. When the computer program product runs on an electronic device, the electronic device executes any one of the multi-grid type grid-connected system admittance model construction and frequency oscillation characteristic analysis methods of the first aspect.

[0028] The present application scheme first obtains the small disturbance of reference active power and the small disturbance of common AC bus frequency; secondly, based on the small disturbance of reference active power and the small disturbance of common AC bus frequency, constructs a single GFM output admittance model under different GFM control strategies, or an output admittance model of a multi-GFM grid-connected system; wherein the single GFM output admittance model is a first-type output admittance model, and the output admittance model of a multi-GFM grid-connected system is a second-type output admittance model; then, based on the first-type output admittance model or the second-type output admittance model, the output angular frequency of the multi-GFM grid-connected system is calculated; finally, based on the output angular frequency of the multi-GFM grid-connected system, the frequency oscillation characteristics of the multi-GFM grid-connected system are analyzed to obtain analysis results.

[0029] The application scheme can improve the accuracy of frequency oscillation characteristic analysis of multi-grid type grid-connected systems and has strong ease of use and practicality.

[0030] Other features and advantages of the present application will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0032] Figure 1 It is a schematic diagram of the GFM control strategy provided in the embodiment of the present application; Figure 2 It is a schematic diagram of the steps of the method for constructing the admittance model of a multi-grid type grid-connected system and analyzing the frequency oscillation characteristics provided in an embodiment of the present application; Figure 3 Schematic diagram of a power / frequency small signal model of the GFM of an embodiment of the present application; Figure 4 is a simplified block diagram of an active power control loop provided in an embodiment of the present application; Figure 5 is a block diagram of an inverter grid-connected system according to an embodiment of the present application; Figure 6 is a schematic diagram of an equivalent two-terminal network in an embodiment of the present application; Figure 7 is a schematic diagram of a small signal model of a vertical control strategy according to an embodiment of the present application; Figure 8 is a schematic diagram of an admittance model of a multi-GFM grid-connected system according to an embodiment of the present application; Fig. 9is a simplified output admittance model schematic diagram of a multi-GFM grid-connected system according to an embodiment of the present application; Fig.10 It is a structural schematic diagram of a device for constructing a multi-grid type grid-connected system admittance model and analyzing frequency oscillation characteristics provided in an embodiment of the present application; Fig.11 It is a schematic diagram of an electronic device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0033] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0034] It should be understood that when used in this specification and the appended claims, the term "comprising" indicates the presence of described features, integers, steps, operations, elements and / or photovoltaic components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, photovoltaic components and / or combinations thereof.

[0035] It should also be understood that the terms used in this application specification are only for the purpose of describing specific embodiments and are not intended to limit the application. As used in this application specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0036] It should be further understood that the term “and / or” used in the specification and appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0037] As used in this specification and the appended claims, the term "if" may be interpreted as "when" or "upon" or "in response to determining" or "in response to detecting," depending on the context. Similarly, the phrases "if it is determined" or "if [described condition or event] is detected" may be interpreted as meaning "upon determination" or "in response to determining" or "upon detection of [described condition or event]" or "in response to detecting [described condition or event]," depending on the context.

[0038] In addition, in the description of the present application, the terms "first", "second", "third", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0039] References to "one embodiment" or "some embodiments" etc. described in the specification of this application mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0040] At present, the output admittance model in the prior art mainly includes the P / ω "admittance" model. This model has the following disadvantages: the model can only be used to analyze the stability and power response of the system under load disturbance, which limits its application in studying the power-frequency oscillation characteristics of multi-machine systems, and does not have the ability to study the dynamic response performance of active power and angular frequency.

[0041] The time domain modeling method can not only describe each state variable in detail, but also obtain the complete dynamic performance of the system by establishing the state space model of the system. However, with the complexity of the control strategy and network structure, the size of the state space matrix will increase dramatically, making the model more complex.

[0042] The frequency domain modeling method depends on the transfer function of the system. According to different control bandwidths, the frequency domain modeling method can be used to model and analyze the voltage, current inner loop and power outer loop respectively. The impedance modeling method of the inverter inner loop has been widely studied and applied in the fields of harmonic resonance analysis and subsynchronous oscillation analysis of new energy grid connection.

[0043] However, when performing stability analysis in the low-frequency domain, the existing impedance modeling methods have frequency coupling effects, which will affect the accuracy of modeling. In addition, the dynamic response of active power and frequency in the low-frequency domain is more worthy of study and attention than voltage and current.

[0044] In the prior art, the accuracy of frequency oscillation characteristic analysis of multi-grid type grid-connected systems is low. Therefore, how to improve the accuracy of frequency oscillation characteristic analysis of multi-grid type grid-connected systems has become a problem to be solved.

[0045] In view of the above-mentioned defects, an embodiment of the present application provides a method for constructing an admittance model of a multi-grid-type grid-connected system and analyzing frequency oscillation characteristics. First, a small disturbance of reference active power and a small disturbance of common AC bus frequency are obtained; secondly, based on the small disturbance of reference active power and the small disturbance of common AC bus frequency, a single GFM output admittance model under different GFM (Grid-Formming, grid-forming) control strategies, or an output admittance model of a multi-GFM grid-connected system is constructed; wherein the single GFM output admittance model is a first-type output admittance model, and the output admittance model of a multi-GFM grid-connected system is a second-type output admittance model; then, based on the first-type output admittance model or the second-type output admittance model, the output angular frequency of the multi-GFM grid-connected system is calculated; finally, based on the output angular frequency of the multi-GFM grid-connected system, the frequency oscillation characteristics of the multi-GFM grid-connected system are analyzed to obtain an analysis result.

[0046] The application scheme can improve the accuracy of frequency oscillation characteristic analysis of multi-grid type grid-connected systems and has strong ease of use and practicality.

[0047] The specific process implemented by this application is introduced below through specific embodiments.

[0048] The core idea of ​​GFM is to use a power inverter to simulate the operating characteristics of a synchronous generator, thereby providing the system with rotational inertia and damping components, and enabling it to have the ability of primary frequency modulation and reactive voltage regulation. Usually, the main circuit of GFM consists of a DC power supply, a DC-DC conversion unit, a DC-AC inverter unit, and an isolation transformer. The DC side bus capacitor maintains the DC side voltage constant by storing or releasing energy.

[0049] Therefore, a constant voltage source is connected to the DC side of the micropower inverter to simulate the prime mover. The converter topology of the micropower inverter adopts a three-phase voltage PWM structure and is connected to the common coupling point (PCC) through an LC filter.

[0050] The topology and control strategy of GFM are as follows: Figure 1 As shown in the figure. The control part mainly includes power-frequency control loop, reactive power-voltage control loop, electromagnetic equation, current control loop, PR control loop and SVPWM modulation. In addition, power-frequency control simulates inertia and primary frequency modulation characteristics, while reactive power and voltage control loops simulate excitation and voltage regulation characteristics.

[0051] See also Figure 2 , Figure 2 Schematic diagram of the steps of constructing a multi-grid type grid-connected system admittance model and analyzing frequency oscillation characteristics provided by the embodiment of the present application. Figure 2 As shown, the method may include the following steps: S201, obtaining a small disturbance amount of reference active power and a small disturbance amount of a common AC bus frequency.

[0052] S202, based on the small disturbance of the reference active power and the small disturbance of the common AC bus frequency, construct an output admittance model of a single GFM under different GFM control strategies, or an output admittance model of a multi-GFM grid-connected system; wherein the output admittance model of a single GFM is a first-type output admittance model, and the output admittance model of a multi-GFM grid-connected system is a second-type output admittance model.

[0053] S203, based on the first type of output admittance model or the second type of output admittance model, calculate and obtain the output angular frequency of the multi-GFM grid-connected system.

[0054] S204, analyzing the frequency oscillation characteristics of the multi-GFM grid-connected system based on the output angular frequency of the multi-GFM grid-connected system to obtain an analysis result.

[0055] According to an embodiment of the present application, the GFM control strategy includes: a conventional control strategy, a droop control strategy, and a control strategy with a damping correction link; the first type of output admittance model includes: a first output admittance model, a second output admittance model, and a third output admittance model; The first output admittance model is a single GFM output admittance model under the conventional control strategy. The specific expression is as follows:

[0056] in, represents a small perturbation of the angular frequency, represents the first admittance, represents the complex frequency variable in the Laplace transform of the transfer function, represents the second admittance, represents a small disturbance of the reference power, Represents the small disturbance of the common AC bus frequency; The second output admittance model is a single GFM output admittance model under the droop control strategy. The specific expression is as follows:

[0057] in, represents the angular frequency, represents the synchronization coefficient, represents the droop control coefficient; The third output admittance model is a single GFM output admittance model under the control strategy with a damping correction link. The specific expression is as follows:

[0058] in, Indicates energy, represents the moment of inertia, represents the damping coefficient, Indicates the reference angular frequency.

[0059] According to one implementation of the present application, the expression of the second type of output admittance model is as follows:

[0060]

[0061] in, Indicates ordinal number, represents the number of GFMs, represents the equivalent admittance, represents the output admittance of the grid impedance, represents the intermediate variable, Indicates the small disturbance of the power grid frequency.

[0062] According to an implementation of the present application, based on the first type of output admittance model or the second type of output admittance model, the output angular frequency of the multi-GFM grid-connected system is calculated, including: Based on the first output admittance model and the common coupling point frequency, the output angular frequency of the multi-GFM grid-connected system is calculated. The specific expression is as follows:

[0063] in, represents the output angular frequency of the multi-GFM grid-connected system, represents the ordinal number of GFM, represents the first angular frequency coefficient, represents the small disturbance of the mth reference frequency, t represents the ordinal number, represents the second angular frequency coefficient, represents the small disturbance of the tth reference frequency, represents the third angular frequency coefficient; The expression for the frequency of the common coupling point is as follows:

[0064] in, represents the frequency of the common coupling point, represents the i-th first output admittance, represents the i-th second output admittance.

[0065] According to one embodiment of the present application, the expression of the first angular frequency coefficient is as follows:

[0066]

[0067] in, represents the mth first output admittance, represents the mth second output admittance, Represents an intermediate variable.

[0068] According to one embodiment of the present application, the expression of the second angular frequency coefficient is as follows:

[0069] in, represents the tth first output admittance, represents the t-th second output admittance.

[0070] According to one implementation of the present application, the expression of the third angular frequency coefficient is as follows: .

[0071] According to an implementation manner of the present application, based on the first type output admittance model or the second type output admittance model, the output angular frequency of the multi-GFM grid-connected system is calculated, and further includes: Based on the second type output admittance model and the common coupling point frequency, the output angular frequency of the multi-GFM grid-connected system is calculated.

[0072] According to an embodiment of the present application, based on the output angular frequency of the multi-GFM grid-connected system, the frequency oscillation characteristics of the multi-GFM grid-connected system are analyzed, including: Based on the influencing factors and changing rules of the first angular frequency coefficient, the second angular frequency coefficient and the third angular frequency coefficient, the frequency oscillation characteristics of the multi-GFM grid-connected system are analyzed.

[0073] In some embodiments, when modeling a single GFM, in order to simplify the model and focus on analyzing the frequency oscillation characteristics of the multi-VSG grid-connected system, the following assumptions are made: The coupling effect between active power and reactive power is ignored, so that the active power-frequency loop can be analyzed separately; the control bandwidth of the inverter double closed loop is much larger than the control bandwidth of the power loop; the system impedance of the inverter is small, which makes the voltage phase angle difference between the inverter and the public AC bus very small; the high-frequency instability caused by the LC filter and the switching action is not considered.

[0074] Based on the above assumptions, the power-frequency loop control of GFM can be analyzed separately, such as Figure 3 In the figure, J represents the moment of inertia. The inertia time constant H is usually used to measure the inertia of synchronous generators of different sizes and power levels. .

[0075] Among them, S n is the rated capacity of the synchronous generator, D P is the damping / droop coefficient, P ref is the power reference value, P is the output power, is the synchronization coefficient, is the output voltage amplitude of the grid-type converter, is the voltage amplitude at the grid connection point, Z is the transmission impedance of GFM, that is, the sum of the output impedance and the line impedance, represents the reference angular frequency, is a small disturbance in the common AC bus frequency.

[0076] According to the Mason formula, Figure 3 can be simplified to Figure 4 .in: and are the open-loop transfer functions of the power-frequency small signal model, respectively. Z x1 and Y x2 The specific expression of is shown in (1). In addition, Y x1 yes Z x1 The reciprocal of .

[0077] (1) from Figure 4 The active output power of the power loop can be derived from, as shown in formula (2).

[0078] (2) make , then let formula (2) equal to formula (3): (3) The inverter grid-connected system block diagram and its corresponding Norton equivalent circuit are as follows Figure 5 As shown. Figure 5 (b) It can be seen that the control current source Gi ref and the output admittance 1 / Y s Parallel connection, output current i The power grid is connected to the point of common coupling (PCC) and the following relationship is met: (4) Where i represents the grid-connected current, i ref is the current reference value, u p is the grid voltage, Y s is the output impedance admittance, which describes the relationship between the output current and the grid voltage. The circuit parameters include the main inductor L1, L2, and the filter capacitor C f, and the control-related gain K pwm (PWM modulation gain), K c (current control gain) and G cont (s) (current controller transfer function). In addition, G represents the closed-loop transfer function, which comprehensively reflects the dynamic characteristics of the system, and s is a complex frequency variable used for dynamic system analysis.

[0079] By comparing formula (3) and formula (4) by analogy, we can find that they have the same mathematical expression form. The consistency of this mathematical form reflects that they have some common laws in their physical nature. Therefore, Figure 4 It can be written as a Norton equivalent model, such as Figure 6 (a), and the specific analogy relationship is shown in Table 1.

[0080] Table 1

[0081] In addition, assuming that the active power and angular frequency They can be regarded as current and voltage respectively, and the relationship analysis method between voltage and current can be used to analyze the mechanism of angular frequency oscillation and its influencing factors.

[0082] From formula (2), we can see that the equivalent admittance , which satisfies the relationship of resistors in parallel. Therefore, the equivalent admittance Y p (s) It can be considered as admittance Y x1 and Y x2 Parallel combination. Y x1 is called the first admittance, Y x2 It is called the second admittance.

[0083] Based on the above analogy, Figure 6 As shown in (b), Figure 4 It can be converted into a more comprehensive two-terminal network form. This model can not only fully describe the GFM in the excitation source and Under disturbance and response, and satisfies the equivalent relationship in formula (5). In addition, the first admittance Y x1 and the second admittance Y x2It only depends on the operating point and parameters of the GFM itself and does not contain information about the power network, which means that the model can separate the GFM from the power network. This feature makes the model easily extendable to the modeling of multiple GFMs and more suitable for system analysis.

[0084] (5) In addition, the output admittance modeling method proposed in the embodiment of the present application is not only applicable to inverters adopting the GFM control strategy, but also applicable to inverters adopting the droop control strategy and other GFM control strategies.

[0085] Take the droop control strategy (Droop) as an example. Figure 7 According to the GFM modeling method, it can be written as Figure 6 In the two-terminal network form shown in (b), the output admittance model of these two control strategies can be expressed as follows: (6) In some embodiments, when multiple GFMs are connected to the grid for modeling, due to the influence of the grid impedance Lg, multiple Figure 6 The two-terminal network shown is connected in parallel to the grid to obtain the output admittance model of the multi-GFM grid-connected system, as shown in Figure 8 This model can fully describe the active power response and angular frequency response of each GFM in the multi-machine grid-connected system.

[0086] The output admittance of the grid impedance is ,in K g According to the synchronization coefficient K P The calculated result is ,in is the initial grid voltage, is the initial phase angle difference between the grid voltage and the grid connection point voltage.

[0087] according to Figure 6 (a) shows the Norton equivalent model. When only the stability of the system is concerned, Figure 8 can be simplified to Fig. 9 , and satisfies formula (8): (8) In some embodiments, when analyzing the frequency oscillation mechanism of a multi-GFM grid-connected system: like Figure 7 As shown, if only a single excitation source is considered (with P ref1 As an example), the frequency response mechanism of the multi-GFM grid-connected system can be described as follows: In the “current excitation” Pref1 Under the disturbance of Y x1 An "internal potential" changes ω 1, and output a "current" P 1. Then, the output current produces a potential change at the point of common coupling (PCC) ω c .

[0088] After that, other GFMs are at potential ω c The "internal potential" is generated under the action of ω m (m = 2, ..., n, n is the total number of GFMs). Therefore, it can be seen that GFM m Output angular frequency ω m Controlled not only by its own control strategy, but also by other GFMs connected in parallel s This shows that there is interaction between different GFMs, but this interaction makes the frequency oscillation characteristics of the multi-GFM grid-connected system more complicated.

[0089] According to Kirchhoff's law, the frequency of the point of common coupling (PCC) It can be expressed as: (9) By substituting formula (9) into formula (5), we can derive GFM m The specific expression of angular frequency is: (10) (11) (12) (13) (14) It can be seen from formula (10) that the grid-connected GFM m The output frequency is composed of three parts. m (s) is the response of GFM to its own active power command disturbance, T m,t (s) is the response of the interaction with other GFMs, S m (s) is the response of the grid frequency disturbance. It can be observed that there are different interactions in the GFM grid-connected system, which makes the frequency oscillation characteristics complicated.

[0090] Therefore, by analyzing the three coefficients R m (s), T m,t (s) and S mThe influencing factors and changing rules of (s) can verify and analyze the frequency oscillation characteristics of multi-GFM grid-connected connections.

[0091] The method for constructing an admittance model of a multi-grid-type grid-connected system and analyzing frequency oscillation characteristics provided in an embodiment of the present application first obtains a small disturbance amount of a reference active power and a small disturbance amount of a common AC bus frequency; secondly, based on the small disturbance amount of the reference active power and the small disturbance amount of the common AC bus frequency, constructs an output admittance model of a single GFM under different GFM control strategies, or an output admittance model of a multi-GFM grid-connected system; wherein the output admittance model of a single GFM is a first-type output admittance model, and the output admittance model of a multi-GFM grid-connected system is a second-type output admittance model; then, based on the first-type output admittance model or the second-type output admittance model, the output angular frequency of the multi-GFM grid-connected system is calculated; finally, based on the output angular frequency of the multi-GFM grid-connected system, the frequency oscillation characteristics of the multi-GFM grid-connected system are analyzed to obtain an analysis result.

[0092] The application scheme can improve the accuracy of frequency oscillation characteristic analysis of multi-grid type grid-connected systems and has strong ease of use and practicality.

[0093] The active power-frequency control loop output admittance model of a GFM grid-connected system provided by the present application not only fully describes the active power response and angular frequency response of each GFM under active power and load disturbances, but also explains the mechanism of frequency oscillation in a multi-GFM grid-connected system. The proposed modeling method is compared with the existing modeling methods (time domain modeling method and frequency domain modeling method). Through comparison, it is found that the model built by this modeling method is simple, can fully describe the dynamic response characteristics of the system and has good scalability.

[0094] This modeling method not only fully describes the active power response and angular frequency response of each GFM under load disturbance, but also can analyze the active power response and angular frequency response of GFM under active power disturbance scenario, and can explain the mechanism of frequency oscillation in multi-GFM grid-connected system.

[0095] The modeling method of the present application is not only easy to expand to multi-machine systems, but also applicable to droop control and GFM control with additional damping correction, and can give a specific expression of the angular frequency. When power coupling is ignored, the modeling method can also be used for transient analysis of reactive power and voltage control loops.

[0096] The modeling proposed in this proposal not only fully describes the active power response and angular frequency response of each GFM under active power and load disturbances, but also has a simple model that is easy to extend to multi-machine systems. In addition, based on the analogy method, the theory and method of analyzing the relationship between voltage and current in this proposal can be applied to explore the relationship between active power and angular frequency.

[0097] The active power-frequency control loop output admittance model of the multi-GFM grid-connected system of the present application solution can better meet the requirements of modern power systems for high efficiency and reliability.

[0098] The unified analysis method for frequency oscillation characteristics of virtual synchronous generator grid-connected system proposed in this application has the following advantages: (1) Compared with the traditional state-space modeling method, the modeling method proposed in the present application is easy to extend to a multi-machine system and can give a specific expression of the angular frequency response; (2) Based on the analogy method, the theory and method of analyzing the relationship between voltage and current can be applied to explore the relationship between active power and angular frequency; (3) It is also applicable to droop control, grid-connected control with additional damping correction and other control methods. In addition, this method has the advantages of simple model, wide application range and high accuracy. (4) When power coupling is ignored, this modeling method can also be used for transient analysis of reactive power and voltage control loops.

[0099] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0100] Corresponding to the method of the above embodiment, Fig.10 1 is a schematic diagram of the structure of the multi-grid type grid-connected system admittance model construction and frequency oscillation characteristic analysis device provided in the embodiment of the present application. For the convenience of explanation, only the parts related to the embodiment of the present application are shown.

[0101] Reference Fig.10 , the device comprises: An acquisition unit 101 is used to acquire a small disturbance amount of reference active power and a small disturbance amount of a common AC bus frequency; A construction unit 102 is used to construct a single GFM output admittance model or an output admittance model of a multi-GFM grid-connected system under different GFM control strategies based on a small disturbance amount of reference active power and a small disturbance amount of a common AC bus frequency; wherein the single GFM output admittance model is a first type of output admittance model, and the output admittance model of a multi-GFM grid-connected system is a second type of output admittance model; A calculation unit 103, configured to calculate an output angular frequency of the multi-GFM grid-connected system based on the first type of output admittance model or the second type of output admittance model; The analyzing unit 104 is used to analyze the frequency oscillation characteristics of the multi-GFM grid-connected system based on the output angular frequency of the multi-GFM grid-connected system to obtain an analysis result.

[0102] It should be noted that the information interaction, execution process, etc. between the above-mentioned devices / units are based on the same concept as the method embodiment of the present application. Their specific functions and technical effects can be found in the method embodiment part and will not be repeated here.

[0103] Those skilled in the art can clearly understand that for the convenience and simplicity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In actual applications, the above-mentioned functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of this application. The specific working process of the units and modules in the above-mentioned system can refer to the corresponding process in the aforementioned method embodiment, which will not be repeated here.

[0104] Fig.11 1 is a schematic diagram of the structure of the electronic device 11 provided in the embodiment of the present application. Fig.11 As shown, the electronic device 11 of this embodiment includes: at least one processor 111 ( Fig.11 Only one is shown in the figure), a memory 113, and a computer program 112 stored in the memory 113 and executable on at least one processor 111. When the processor 111 executes the computer program 112, the steps in the above method embodiment are implemented.

[0105] The electronic device 11 may be a computing device such as a desktop computer, a notebook, a PDA, or a mobile phone. The electronic device 11 may include, but is not limited to, a processor 111 and a memory 113. Those skilled in the art will appreciate that Fig.11 It is only an example of the electronic device 11 and does not constitute a limitation on the electronic device 11. It may include more or fewer components than shown in the figure, or a combination of certain components, or different components. For example, it may also include input and output devices, network access devices, etc.

[0106] The processor 111 may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware photovoltaic modules, etc. A general-purpose processor may be a microprocessor or any conventional processor, etc.

[0107] In some embodiments, the memory 113 may be an internal storage unit of the electronic device 11, such as a hard disk or memory of the electronic device 11. In other embodiments, the memory 113 may also be an external storage device of the electronic device 11, such as a plug-in hard disk, a smart memory card (Smart Media Card, SMC), a secure digital card (SecureDigital, SD), a flash card (Flash Card), etc. equipped on the electronic device 11. Further, the memory 113 may also include both an internal storage unit of the electronic device 11 and an external storage device. The memory 113 is used to store an operating system, an application program, a boot loader (Boot Loader), data, and other programs, such as program codes of computer programs, etc. The memory 113 may also be used to temporarily store data that has been output or is to be output.

[0108] If the above-mentioned integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, when the present application implements all or part of the processes in the above-mentioned embodiment method, it can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a computer-readable storage medium. When the computer program is executed by the processor, it can implement the steps applied to the above-mentioned method embodiment. Among them, the computer program includes computer program code, which can be in source code form, object code form, executable file or some intermediate form. The computer-readable storage medium may at least include: any entity or device that can carry the computer program code to the computing device / electronic device, recording medium, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electric carrier signal, telecommunication signal and software distribution medium, such as USB flash drive, mobile hard disk, disk or optical disk. In some jurisdictions, according to legislation and patent practice, computer-readable storage media cannot be electric carrier signals and telecommunication signals.

[0109] An embodiment of the present application further provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, the steps in the above-mentioned method embodiments are implemented.

[0110] An embodiment of the present application provides a computer program product. When the computer program product is run on an electronic device, the electronic device executes the steps in the above-mentioned method embodiments.

[0111] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0112] Those of ordinary skill in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0113] In the embodiments provided in the present application, it should be understood that the disclosed devices / electronic devices and methods can be implemented in other ways. The device / electronic device embodiments described above are merely schematic, and the division of the above modules or units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or photovoltaic components can be combined or integrated into another system, and some features can be ignored and not executed. Another point is that the indirect coupling, direct coupling or communication connection between each other shown or discussed can be an indirect coupling, direct coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0114] The units described above as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple 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.

[0115] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A method for constructing a multi-grid type grid-connected system admittance model and analyzing frequency oscillation characteristics, characterized in that: The method comprises: Obtaining a small disturbance amount of reference active power and a small disturbance amount of public AC bus frequency; Based on the small disturbance of reference active power and the small disturbance of common AC bus frequency, a single GFM output admittance model under different GFM control strategies or an output admittance model of a multi-GFM grid-connected system is constructed; wherein the single GFM output admittance model is a first-type output admittance model, and the output admittance model of a multi-GFM grid-connected system is a second-type output admittance model; Based on the first type of output admittance model or the second type of output admittance model, calculating the output angular frequency of the multi-GFM grid-connected system; Based on the output angular frequency of the multi-GFM grid-connected system, the frequency oscillation characteristics of the multi-GFM grid-connected system are analyzed and the analysis results are obtained.

2. The method for constructing a multi-grid type grid-connected system admittance model and analyzing frequency oscillation characteristics according to claim 1, characterized in that: The GFM control strategy includes: conventional control strategy, droop control strategy and control strategy with damping correction link; the first type of output admittance model includes: first output admittance model, second output admittance model and third output admittance model; The first output admittance model is a single GFM output admittance model under the conventional control strategy, and the specific expression is as follows: in, represents a small perturbation of the angular frequency, represents the first admittance, represents the complex frequency variable in the Laplace transform of the transfer function, represents the second admittance, represents a small disturbance of the reference power, Represents the small disturbance of the common AC bus frequency; The second output admittance model is a single GFM output admittance model under the droop control strategy, and the specific expression is as follows: in, represents the angular frequency, represents the synchronization coefficient, represents the droop control coefficient; The third output admittance model is a single GFM output admittance model under a control strategy with a damping correction link, and the specific expression is as follows: in, Indicates energy, represents the moment of inertia, represents the damping coefficient, Indicates the reference angular frequency.

3. The method for constructing a multi-grid type grid-connected system admittance model and analyzing frequency oscillation characteristics according to claim 2, characterized in that: The expression of the second type of output admittance model is as follows: in, Indicates ordinal number, represents the number of GFMs, represents the equivalent admittance, represents the output admittance of the grid impedance, represents the intermediate variable, Indicates the small disturbance of the power grid frequency.

4. The method for constructing a multi-grid type grid-connected system admittance model and analyzing frequency oscillation characteristics according to claim 3, characterized in that: Based on the first type of output admittance model or the second type of output admittance model, the output angular frequency of the multi-GFM grid-connected system is calculated, including: Based on the first output admittance model and the common coupling point frequency, the output angular frequency of the multi-GFM grid-connected system is calculated, and the specific expression is as follows: in, represents the output angular frequency of the multi-GFM grid-connected system, represents the ordinal number of GFM, represents the first angular frequency coefficient, Indicates m A small perturbation of the reference frequency, t Indicates ordinal number, represents the second angular frequency coefficient, Indicates t A small perturbation of the reference frequency, represents the third angular frequency coefficient; The expression for the frequency of the common coupling point is as follows: in, represents the frequency of the common coupling point, Indicates i The first output admittance, Indicates i A second output admittance.

5. The method for constructing a multi-grid type grid-connected system admittance model and analyzing frequency oscillation characteristics according to claim 4, characterized in that: The expression of the first angular frequency coefficient is as follows: in, Indicates m The first output admittance, Indicates m The second output admittance, Represents an intermediate variable.

6. The method for constructing a multi-grid type grid-connected system admittance model and analyzing frequency oscillation characteristics according to claim 5, characterized in that: The expression of the second angular frequency coefficient is as follows: in, Indicates t The first output admittance, Indicates t A second output admittance.

7. The method for constructing a multi-grid type grid-connected system admittance model and analyzing frequency oscillation characteristics according to claim 6, characterized in that: The expression of the third angular frequency coefficient is as follows: 。 8. The method for constructing a multi-grid type grid-connected system admittance model and analyzing frequency oscillation characteristics according to claim 4, characterized in that: Based on the first type of output admittance model or the second type of output admittance model, the output angular frequency of the multi-GFM grid-connected system is calculated, and further includes: Based on the second type of output admittance model and the common coupling point frequency, the output angular frequency of the multi-GFM grid-connected system is calculated.

9. The method for constructing a multi-grid type grid-connected system admittance model and analyzing frequency oscillation characteristics according to claim 7, characterized in that: Based on the output angular frequency of the multi-GFM grid-connected system, the frequency oscillation characteristics of the multi-GFM grid-connected system are analyzed, including: Based on the influencing factors and changing rules of the first angular frequency coefficient, the second angular frequency coefficient and the third angular frequency coefficient, the frequency oscillation characteristics of the multi-GFM grid-connected system are analyzed.

10. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the method for constructing an admittance model of a multi-grid type grid-connected system and analyzing frequency oscillation characteristics as described in any one of claims 1-9 is implemented.

11. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the method for constructing an admittance model of a multi-grid-type grid-connected system and analyzing frequency oscillation characteristics according to any one of claims 1 to 9 is implemented.

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