Network construction type converter impedance calculation method and system considering amplitude limiting link, and computer readable storage medium

Abstract

The invention discloses a network construction type converter impedance calculation method and system considering an amplitude limiting link and a computer readable storage medium. The method comprises the following steps: establishing an expression of voltage and current closed-loop control considering the amplitude limiting link; establishing an impedance model of a target network construction type converter system; carrying out nonlinear modeling based on a description function on an amplitude limiting link; setting an initial signal amplitude A and an initial frequency, and substituting the initial signal amplitude A into formulas (2)-(4) to obtain an impedance value of the nonlinear improved admittance model of the constructed network type converter under the initial frequency; and gradually increasing the frequency value, calculating the impedance value of the non-linear improved admittance model of the network-building converter under each frequency until the updated frequency reaches the target frequency band, and obtaining the impedance value under the target frequency band. The method makes up for the deficiency of a small signal impedance model in the aspect of analyzing a nonlinear link in converter modeling, and has the advantages of being scientific and reasonable, good in applicability, clear in mechanism and the like.

Description

Technical Field

[0001] The present invention relates to the field of power system stability analysis and control, and in particular to a method, system and computer-readable storage medium for calculating impedance of a grid-connected converter taking a limiting link into consideration. Background Art

[0002] The penetration rate of renewable energy such as wind power and photovoltaic power is increasing. By the end of 2023, China's installed capacity of solar power generation will be about 610 million kilowatts, a year-on-year increase of 55.2%; wind power installed capacity will be about 440 million kilowatts, a year-on-year increase of 20.7%, both ranking first in the world. However, with the grid connection of large-scale power electronic converters, a series of new stability challenges have been brought about. The grid-following converters currently used on a large scale in wind and solar power stations are prone to oscillation events when connected to weak power grids, which shortens the service life of the equipment and has an adverse impact on the stable operation of the power system.

[0003] Based on the characteristic that grid-type converters are more stable under weak power grids, grid-type converter equipment of major new energy bases are gradually being connected to the power grid, especially in the Shagohuang area. However, grid-type converters have nonlinear links such as saturation and limiting. When external disturbances trigger these strong nonlinear links, the characteristics of the impedance model of the system often change significantly, and the grid-type converter itself is prone to limiting. At this time, it is difficult to accurately describe the stability margin, oscillation frequency and other information of the grid-type converter when the limiting link is involved using the traditional small disturbance model. Therefore, it is necessary to propose an impedance model that takes the limiting link into account to accurately predict the impedance change of the system when oscillation occurs. Summary of the invention

[0004] In order to overcome the above-mentioned defects of the prior art, the present invention provides a method, system and computer-readable storage medium for calculating impedance of a grid-type converter taking into account a limiting link.

[0005] The technical solution of the present invention is as follows:

[0006] A method for calculating impedance of a grid-type converter considering a limiting link includes:

[0007] The expression of voltage and current closed-loop control considering the limiting link is established:

[0008]

[0009] Among them, N m is the limiting coefficient, L f is the inductance, G id and G iq are the transfer functions of the proportional-integral controller of the dq axis of the current loop, G vd and G vqare the transfer functions of the proportional-integral controller of the voltage loop dq axis, ω is the rated angular velocity, G t is the voltage feedforward filter, ΔE dref and ΔE qref are the dq axis voltage reference values ​​output by the current loop, ΔE m and ΔU q are the small signal quantities of the input voltage of the voltage loop dq axis, Δi d and Δi q are the small signal quantities of the current dq axis, Δu d and Δu q They are the small signal quantities of the voltage dq axis respectively.

[0010] Establish the impedance model of the target grid-connected converter system

[0011]

[0012] Among them, G idq is the transfer function of the current loop proportional-integral controller, G vdq is the transfer function of the voltage loop proportional-integral controller, F T is the transformation matrix of the virtual synchronization link, G H is the transfer function of the virtual synchronization link, I dq0 is the steady-state value of the converter output dq axis current, U dq0 is the steady-state value of the converter terminal voltage dq axis, Z Lf is the impedance matrix of the converter filter inductor.

[0013] The nonlinear modeling of the limiting link is based on the description function. Since the limiting link is easy to reach the unilateral upper limit, the limiting coefficient corresponding to formula (3) is obtained:

[0014]

[0015] Among them, A is the amplitude of the oscillation signal of the input limiting link, and a is the limiting threshold. When the oscillation diverges, A gradually increases, resulting in N M (A) By N M (A) = 1 becomes N M (A)<1, at this time, the limiter begins to affect the oscillation characteristics.

[0016] Set the initial signal amplitude A and the initial frequency, substitute the initial signal amplitude A into equations (2)-(4), and obtain the impedance value of the nonlinear improved admittance model of the grid-type converter at the initial frequency;

[0017] The frequency value is increased gradually, and the impedance value of the nonlinear improved admittance model of the grid-type converter at each frequency is calculated until the updated frequency reaches the target frequency band, the impedance value at the target frequency band is obtained, and the impedance value of the nonlinear improved impedance model of the grid-type converter at the initial signal amplitude is generated.

[0018] Furthermore, before solving the impedance model curve of the grid-type converter under the required frequency band, it is necessary to first construct the impedance model of the grid-type converter considering the limiting link. Specifically, the impedance model of the grid-type converter considering the nonlinearity of the limiting link is shown in formulas (5)-(6):

[0019] Z GFM (s)=[A GFM (F T G H Id 0 -E)]- 1 [Gidq+Z Lf -A GFM F T Uq 0 ] (5)

[0020] A GFM =G idq G vdq N M (6)

[0021] Among them, G idq is the transfer function of the current loop proportional-integral controller, G vdq is the transfer function of the voltage loop proportional-integral controller, F T is the transformation matrix of the virtual synchronization link, G H is the transfer function of the virtual synchronization link, I dq0 is the steady-state value of the converter output dq axis current, U dq0 is the steady-state value of the converter terminal voltage dq axis, Z Lf is the impedance matrix of the converter filter inductor.

[0022] Furthermore, to solve the impedance model of the grid-type converter considering the limiting link, it is necessary to obtain the limiting coefficient. Based on the describing function method, the nonlinear frequency domain modeling of the limiting link is performed, and its mathematical expression is:

[0023]

[0024] Where K is the slope of the linear link, and a is the threshold of the limit link. When the input amplitude x>a or x<-a, the limit link takes effect and the output is limited.

[0025] Since the limiting link is easy to reach the unilateral upper limit, the limiting coefficient corresponding to formula (7) is obtained:

[0026]

[0027] Among them, A is the amplitude of the oscillation signal of the input limiting link, and a is the limiting threshold. When the oscillation diverges, A gradually increases, resulting in N M (A) By N M (A) = 1 becomes N M (A)<1, at this time, the limiter begins to affect the oscillation characteristics.

[0028] Substituting the above-mentioned mathematical model of limiting nonlinearity into the small signal impedance model, a grid-type converter impedance model that can take into account the nonlinearity of the limiting link is obtained.

[0029] Furthermore, it also includes solving the impedance model curve of the grid-type converter under the required frequency band. First, an initial signal amplitude A and an initial frequency are set, and the obtained converter parameters, controller parameters and steady-state operating point parameters are substituted into the following formula:

[0030] Z GFM (s)=[A GFM (F T G H Id 0 -E)]- 1 [Gidq+Z Lf -A GFM F T Uq 0 ] (5)

[0031] A GFM =G idq G vdq N M (6)

[0032]

[0033] To solve the impedance value of the nonlinear impedance model of the grid-type converter under the initial signal amplitude and initial frequency disturbance; according to the preset target frequency change value, the initial frequency is gradually increased by the target frequency change value to obtain the updated frequency, and the impedance value of the nonlinear impedance model of the grid-type converter under the initial signal amplitude and updated frequency disturbance is re-solved. When the updated frequency is greater than the preset maximum frequency, the impedance value under the target frequency band is obtained to generate the nonlinear impedance model curve of the grid-type converter under the initial signal amplitude.

[0034] Technical effects and advantages of the present invention:

[0035] For a typical grid-controlled converter, the nonlinearity of its voltage loop limiting link is modeled by adopting the describing function method, and the mathematical model of limiting nonlinearity is merged into the traditional small-signal impedance model to obtain an improved impedance model of the grid-controlled converter that takes into account the limiting link. This makes up for the shortcomings of the traditional small-signal impedance model in analyzing the nonlinear link in converter modeling, and has the advantages of scientific rationality, good applicability, and clear mechanism. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0037] Figure 1 It is a structural diagram of a parallel system of a grid-following converter and a grid-forming converter;

[0038] Figure 2 This is a diagram of the steps for analyzing the interaction between the grid-following / grid-forming converters based on the torque coefficient;

[0039] Figure 3 It is a block diagram of virtual synchronous control of network-type converter;

[0040] Figure 4 It is a block diagram of the damping torque model of the grid / grid-connected converter parallel system. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] The present invention proposes a method for calculating the impedance of a grid-type converter considering the limiting link, which is used to describe the change of the converter impedance model when the limiting link in the grid-type converter control is actuated due to excessive external disturbance. The limiting link is mainly caused by the hard limiting link reaching the upper limit threshold of the limiting link. By analyzing the mathematical model of the limiting link, the nonlinearity of the limiting link is modeled based on the describing function method, and the expression of the limiting link is substituted into the traditional grid-type converter small signal impedance model, the grid-type converter impedance model considering the limiting link is obtained.

[0043] Embodiment 1

[0044] Figure 1 FIG. 1 is a flow chart of a method for calculating impedance of a grid-type current transformer taking into account a limiting link proposed in an embodiment of the present invention. Figure 1As shown, the impedance calculation method of the grid-type converter considering the limiting link may include the following steps:

[0045] Step 1: Obtain converter parameters, controller parameters and steady-state operating point parameters.

[0046] Among them, the converter parameters include: the converter filter inductance L f ; The controller parameters include: the transfer function G of the current loop proportional integral controller idq , the transfer function G of the voltage loop proportional-integral controller vdq , the transformation matrix F of the virtual synchronization link T , the transfer function of the virtual synchronization link G H ; Steady-state operating point parameters include: converter output dq axis current value I dq0 , the dq axis voltage value at the converter end is U dq0 .

[0047] Step 2: Given the initial amplitude and initial frequency of the signal, the impedance value at the current frequency is calculated according to the converter control parameters and the steady-state operating point parameters.

[0048] Step 3, gradually increase the frequency value to obtain the impedance value of the grid-type converter in the target frequency band.

[0049] On the basis of the initial frequency, the frequency value is gradually increased until the frequency reaches the maximum frequency of the required frequency band, at which time the impedance value of the grid-type converter under the target frequency band is obtained.

[0050] Before solving the impedance model curve of the grid-type converter in the required frequency band, it is necessary to first construct an impedance model of the grid-type converter that takes into account the limiting link.

[0051] First, according to Figure 2 and Figure 3 The impedance model of the grid-type converter considering the nonlinearity of the limiting link can be obtained as shown in formulas (5)-(6):

[0052] Z GFM (s)=[A GFM (F T G H Id 0 -E)]- 1 [Gidq+Z Lf -A GFM F T Uq 0 ] (5)

[0053] A GFM =G idq G vdq N M (6)

[0054] Among them, G idq is the transfer function of the current loop proportional-integral controller, G vdq is the transfer function of the voltage loop proportional-integral controller, F T is the transformation matrix of the virtual synchronization link, G H is the transfer function of the virtual synchronization link, I dq0 is the steady-state value of the converter output dq axis current, U dq0 is the steady-state value of the converter terminal voltage dq axis, Z Lf is the impedance matrix of the converter filter inductor.

[0055] In order to solve the impedance model of the grid-type converter considering the limiting link, the limiting coefficient is required. The nonlinear frequency domain modeling of the limiting link is performed based on the describing function method.

[0056] Figure 3 It is a schematic diagram of the limiting link in the power system, and its mathematical expression is

[0057]

[0058] Where K is the slope of the linear link, and a is the threshold of the limit link. When the input amplitude x>a or x<-a, the limit link takes effect and the output is limited.

[0059] Since the limiting link is easy to reach the unilateral upper limit, the limiting coefficient corresponding to formula (7) is obtained:

[0060]

[0061] Among them, A is the amplitude of the oscillation signal of the input limiting link, and a is the limiting threshold. When the oscillation diverges, A gradually increases, resulting in N M (A) By N M (A) = 1 becomes N M (A)<1, at this time, the limiter begins to affect the oscillation characteristics.

[0062] Substituting the above-mentioned mathematical model of limiting nonlinearity into the small signal impedance model, a grid-type converter impedance model that can take into account the nonlinearity of the limiting link is obtained.

[0063] In a possible implementation of the embodiment of the present invention, the impedance model curve of the grid-type converter considering the nonlinearity of the limiting link can be obtained by solving the following process:

[0064] First, set an initial signal amplitude A and an initial frequency, and substitute the obtained converter parameters, controller parameters and steady-state operation point parameters into the above formulas (5), (6) and (8) to solve the impedance value of the nonlinear impedance model of the grid-type converter under the initial signal amplitude and initial frequency disturbance; according to the preset target frequency change value, gradually increase the initial frequency by the target frequency change value to obtain the updated frequency, and re-solve the impedance value of the nonlinear impedance model of the grid-type converter under the initial signal amplitude and updated frequency disturbance. When the updated frequency is greater than the preset maximum frequency, obtain the impedance value under the target frequency band, and generate the nonlinear impedance model curve of the grid-type converter under the initial signal amplitude.

[0065] Embodiment 2

[0066] A grid-type converter impedance calculation system considering a limiting link comprises:

[0067] The expression establishment module of voltage and current closed-loop control is used to establish the expression of voltage and current closed-loop control considering the limiting link;

[0068] An impedance model building module is used to build an impedance model of a target grid-type converter system;

[0069] The nonlinear modeling module is used to perform nonlinear modeling of the limiting link based on the description function.

[0070] Furthermore, the expression establishment module of the voltage and current closed-loop control is used to establish the expression of the voltage and current closed-loop control considering the limiting link, specifically:

[0071]

[0072] Among them, N m is the limiting coefficient, L f is the inductance, G id and G iq are the transfer functions of the proportional-integral controller of the dq axis of the current loop, G vd and G vq are the transfer functions of the proportional-integral controller of the voltage loop dq axis, ω is the rated angular velocity, G t is the voltage feedforward filter, ΔE dref and ΔE qref are the dq axis voltage reference values ​​output by the current loop, ΔE m and ΔU q are the small signal quantities of the input voltage of the voltage loop dq axis, Δi d and Δi q are the small signal quantities of the current dq axis, Δu d and Δu qThey are the small signal quantities of the voltage dq axis respectively.

[0073] Furthermore, an impedance model of the target grid-connected converter system is established, specifically:

[0074] Z GFM (s)=[A GFM (F T G H Id 0 -E)]- 1 [Gidq+Z Lf -A GFM F T Uq 0 ] (2)

[0075] A GFM =G idq G vdq N M (3)

[0076] Among them, G idq is the transfer function of the current loop proportional-integral controller, G vdq is the transfer function of the voltage loop proportional-integral controller, F T is the transformation matrix of the virtual synchronization link, G H is the transfer function of the virtual synchronization link, I dq0 is the steady-state value of the converter output dq axis current, U dq0 is the steady-state value of the converter terminal voltage dq axis, Z Lf is the impedance matrix of the converter filter inductor.

[0077] Furthermore, the nonlinear modeling module is used to perform nonlinear modeling of the limiting link based on the description function, specifically: the limiting link is subjected to nonlinear modeling based on the description function. Since the limiting link is prone to reach a unilateral upper limit, the limiting coefficient corresponding to formula (3) is obtained:

[0078]

[0079] Among them, A is the amplitude of the oscillation signal of the input limiting link, and a is the limiting threshold; when the oscillation diverges, A gradually increases, resulting in N M (A) By N M (A) = 1 becomes N M (A)<1, at this time, the limiter begins to affect the oscillation characteristics.

[0080] Embodiment 3

[0081] A computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of any one of the methods in embodiment 1 are implemented.

[0082] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of complete hardware embodiments, complete software embodiments, or embodiments in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code. The scheme in the embodiments of the present application can be implemented in various computer languages, for example, object-oriented programming language Java and literal scripting language JavaScript, etc.

[0083] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0084] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0085] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0086] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0087] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A method for calculating impedance of a grid-type converter considering a limiting link, characterized in that: include: Establish the expression of voltage and current closed-loop control considering the limiting link; Establishing the impedance model of the target grid-connected converter system; The limiting link is modeled nonlinearly based on the describing function.

2. The impedance calculation method of a grid-type converter considering the limiting link according to claim 1 is characterized in that: The expression of voltage and current closed-loop control considering the limiting link is established, specifically: Among them, N m is the limiting coefficient, L f is the inductance, G id and G iq are the transfer functions of the proportional-integral controller of the dq axis of the current loop, G vd and G vq are the transfer functions of the proportional-integral controller of the voltage loop dq axis, ω is the rated angular velocity, G t is the voltage feedforward filter, ΔE dref and ΔE qref are the dq axis voltage reference values ​​output by the current loop, ΔE m and ΔU q are the small signal quantities of the input voltage of the voltage loop dq axis, Δi d and Δi q are the small signal quantities of the current dq axis, Δu d and Δu q They are the small signal quantities of the voltage dq axis respectively.

3. The impedance calculation method of a grid-type converter considering a limiting link according to claim 1 is characterized in that: The impedance model of the target grid-connected converter system is established as shown in formulas (2)-(3): A GFM =G idq G vdq N M (3) Among them, G idq is the transfer function of the current loop proportional-integral controller, G vdq is the transfer function of the voltage loop proportional-integral controller, F T is the transformation matrix of the virtual synchronization link, G H is the transfer function of the virtual synchronization link, I dq0 is the steady-state value of the converter output dq axis current, U dq0 is the steady-state value of the converter terminal voltage dq axis, Z Lf is the impedance matrix of the converter filter inductor.

4. The impedance calculation method of a grid-type converter considering the limiting link according to claim 3 is characterized in that: The nonlinear modeling of the limiting link is based on the description function. Since the limiting link is easy to reach the unilateral upper limit, the limiting coefficient corresponding to formula (3) is obtained: Among them, A is the amplitude of the oscillation signal of the input limiting link, and a is the limiting threshold. When the oscillation diverges, A gradually increases, resulting in N M (A) By N M (A) = 1 becomes N M (A)<1, at this time, the limiter begins to affect the oscillation characteristics.

5. The impedance calculation method of a grid-type current transformer considering a limiting link according to claim 1 is characterized in that: In establishing the impedance model of the target grid-type converter system, the nonlinear frequency domain modeling of the limiting link is carried out based on the describing function method, and its mathematical expression is: Where K is the slope of the linear link, and a is the threshold of the limiting link; when the input amplitude x>a or x<-a, the limiting link takes effect and the output is limited; Since the limiting link is easy to reach the unilateral upper limit, the limiting coefficient corresponding to formula (7) is obtained: Among them, A is the amplitude of the oscillation signal of the input limiting link, and a is the limiting threshold; when the oscillation diverges, A gradually increases, resulting in N M (A) By N M (A) = 1 becomes N M (A)<1, at this time, the limiter begins to affect the oscillation characteristics; Substituting the above-mentioned mathematical model of limiting nonlinearity into the small signal impedance model, a grid-type converter impedance model that can take into account the nonlinearity of the limiting link is obtained.

6. A grid-type converter impedance calculation system considering the limiting link, characterized in that: include: The expression establishment module of voltage and current closed-loop control is used to establish the expression of voltage and current closed-loop control considering the limiting link; An impedance model building module is used to build an impedance model of a target grid-type converter system; The nonlinear modeling module is used to perform nonlinear modeling of the limiting link based on the description function.

7. A grid-type converter impedance system considering the limiting link according to claim 6, characterized in that: The expression establishment module of voltage and current closed-loop control is used to establish the expression of voltage and current closed-loop control considering the limiting link, specifically: Among them, N m is the limiting coefficient, L f is the inductance, G id and G iq are the transfer functions of the proportional-integral controller of the dq axis of the current loop, G vd and G vq are the transfer functions of the proportional-integral controller of the voltage loop dq axis, ω is the rated angular velocity, G t is the voltage feedforward filter, ΔE dref and ΔE qref are the dq axis voltage reference values ​​output by the current loop, ΔE m and ΔU q are the small signal quantities of the input voltage of the voltage loop dq axis, Δi d and Δi q are the small signal quantities of the current dq axis, Δu d and Δu q They are the small signal quantities of the voltage dq axis respectively.

8. The impedance calculation system of a grid-type current transformer considering the limiting link according to claim 6, characterized in that: The impedance model of the target grid-connected converter system is established as follows: A GFM =G idq G vdq N M (3) Among them, G idq is the transfer function of the current loop proportional-integral controller, G vdq is the transfer function of the voltage loop proportional-integral controller, F T is the transformation matrix of the virtual synchronization link, G H is the transfer function of the virtual synchronization link, I dq0 is the steady-state value of the converter output dq axis current, U dq0 is the steady-state value of the converter terminal voltage dq axis, Z Lf is the impedance matrix of the converter filter inductor.

9. The impedance calculation system of a grid-type current transformer considering the limiting link according to claim 8, characterized in that: The nonlinear modeling module is used to perform nonlinear modeling of the limiting link based on the description function. Specifically, the limiting link is modeled based on the description function. Since the limiting link is easy to reach the unilateral upper limit, the limiting coefficient corresponding to formula (3) is obtained: Among them, A is the amplitude of the oscillation signal of the input limiting link, and a is the limiting threshold; when the oscillation diverges, A gradually increases, resulting in N M (A) By N M (A) = 1 becomes N M (A)<1, at this time, the limiter begins to affect the oscillation characteristics.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of any one of the methods of claims 1 to 5 are implemented.

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