A control method and system for enhancing transient stability of grid-connected converter

Abstract

The present invention belongs to the field of renewable energy power generation, and provides a control method and system for enhancing the transient stability of a grid-type converter. The control method includes: using a VSM control strategy to control the phase of the grid-type converter to obtain the active angle of the grid-type converter and the power grid; making the difference between the current active angle and the active angle of the initial balance point under the regulation of the gain link, amplifying the influence, and acting on the voltage controller, so that the voltage value output by the grid-type converter increases with the increase of the active angle, so as to enhance the transient stability of the grid-type converter. Through the design of the control method, the present invention enables the system to automatically increase the voltage when subjected to a large disturbance, enhance the ability of the grid-type converter to resist large disturbances, and realize the enhancement of the transient stability of the grid-type converter.

Description

Technical Field

[0001] The present invention belongs to the field of renewable energy power generation, and in particular relates to a control method and system for enhancing the transient stability of a grid-connected converter. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] The penetration rate of new energy in the power grid continues to increase, and the proportion of synchronous power sources has decreased. At present, new energy units are mainly connected to the grid through grid-type converters, which do not have the ability to build a grid, have low inertia and small damping. The high proportion of grid-type converters leads to the fragility and reduced stability of the power system, and increases the risk of large-scale power outages. Therefore, in order to meet these challenges, the performance of the converter should be enhanced and the application of grid-type converters in the power grid should be promoted.

[0004] However, according to the inventors' understanding, grid-connected inverters face the problem of transient stability, there is little related research, and the research methods are cumbersome in calculation, the parameter adjustment is complex, and the implementation is difficult. Summary of the invention

[0005] In order to solve the technical problems existing in the above-mentioned background technology, the present invention provides a control method and system for enhancing the transient stability of a grid-type converter. A new grid-type converter control structure is designed based on a virtual synchronous machine (VSM) control strategy. Through the design of the control method, the system can automatically increase the voltage when subjected to a large disturbance, thereby enhancing the ability of the grid-type converter to resist large disturbances and achieving enhanced transient stability of the grid-type converter.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A first aspect of the present invention provides a control method for enhancing the transient stability of a grid-type converter.

[0008] A control method for enhancing transient stability of a grid-connected converter, comprising:

[0009] The VSM control strategy is used to control the phase of the grid-forming converter to obtain the active angle between the grid-forming converter and the power grid.

[0010] The difference between the current active angle and the active angle of the initial balance point is amplified under the control of the gain link and acts on the voltage controller, so that the voltage value output by the grid-type converter increases with the increase of the active angle, so as to enhance the transient stability of the grid-type converter.

[0011] A second aspect of the present invention provides a control system for enhancing the transient stability of a grid-type converter.

[0012] A control system for enhancing transient stability of a grid-type converter, comprising:

[0013] A VSM control module is configured to: use a VSM control strategy to control the phase of the grid-forming converter to obtain an active angle between the grid-forming converter and the power grid;

[0014] The enhanced stability module is configured to: amplify the influence of the difference between the current active angle and the active angle of the initial balance point under the regulation of the gain link, and act on the voltage controller, so that the voltage value output by the meshing type converter increases with the increase of the active angle, so as to enhance the transient stability of the meshing type converter.

[0015] A third aspect of the present invention provides a computer-readable storage medium.

[0016] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps in the control method for enhancing the transient stability of a grid-type converter as described in the first aspect above.

[0017] A fourth aspect of the present invention provides a computer device.

[0018] A computer device comprises a memory, a processor and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the steps in the control method for enhancing the transient stability of a grid-type converter as described in the first aspect above are implemented.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The control link proposed in the present invention can amplify the influence of the active angle and act on the voltage controller, so that the voltage increases with the increase of the active angle, thereby enhancing the transient stability of the grid-type converter.

[0021] The present invention enables the system to automatically increase voltage when subjected to a large disturbance through the design of the controller, thereby enhancing the ability of the grid-type converter to resist large disturbances.

[0022] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0024] Figure 1 is a basic structural diagram of a mesh converter shown in Embodiment 1 of the present invention;

[0025] Figure 2 It is a simplified model of a grid-forming converter and a grid shown in the first embodiment of the present invention;

[0026] Figure 3 is a VSM structure diagram shown in the first embodiment of the present invention;

[0027] Figure 4 is a schematic diagram showing the use of the equal area method to represent the acceleration area and the deceleration area in the power angle curve according to the first embodiment of the present invention;

[0028] Figure 5 is a logic diagram of a control method for enhancing transient stability of a grid-type converter shown in Embodiment 1 of the present invention;

[0029] Figure 6 is a comparison diagram of the power angle curve of the original system shown in the first embodiment of the present invention and the power angle curve of the present invention;

[0030] FIG. 7( a ) is a diagram showing a simulated converter voltage V under a stable condition (CCT = 0.321 s) when the method of the present invention is not used according to the first embodiment of the present invention. g , converter power P g and active angle δ g Waveform diagram of

[0031] FIG. 7( b ) is a diagram showing a simulated converter voltage V under an unstable condition (FCT>CCT, CCT=0.321s) when the method of the present invention is not used, as shown in the first embodiment of the present invention. g , converter power P g and active angle δ g Waveform diagram of

[0032] FIG. 7( c ) is a diagram showing a simulated converter voltage V under a stable condition (CCT = 0.347 s) when the gain K of the present invention is 1, as shown in the first embodiment of the present invention. g , converter power P g and active angle δ g Waveform diagram of

[0033] FIG. 7( d ) is a diagram showing a simulated converter voltage V under a stable condition (CCT = 0.394 s) when the gain K of the present invention is 3, as shown in the first embodiment of the present invention. g , converter power P g and active angle δ g Waveform diagram of . DETAILED DESCRIPTION

[0034] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0035] It should be noted that the following detailed descriptions are all illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0036] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0037] It should be noted that the flowcharts and block diagrams in the accompanying drawings illustrate the possible implementation architecture, functions and operations of the methods and systems according to various embodiments of the present disclosure. It should be noted that each box in the flowchart or block diagram can represent a module, a program segment, or a part of a code, and the module, program segment, or a part of a code may include one or more executable instructions for implementing the logical functions specified in each embodiment. It should also be noted that in some alternative implementations, the functions marked in the box can also occur in an order different from that marked in the accompanying drawings. For example, two boxes represented in succession can actually be executed substantially in parallel, or they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the flowchart and / or block diagram, and the combination of boxes in the flowchart and / or block diagram can be implemented using a dedicated hardware-based system that performs a specified function or operation, or can be implemented using a combination of dedicated hardware and computer instructions.

[0038] Embodiment 1

[0039] like Figure 1As shown, this embodiment provides a control method for enhancing the transient stability of a network-type converter. This embodiment uses the method applied to a server as an example. It can be understood that the method can also be applied to a terminal, and can also be applied to a system including a terminal and a server, and is implemented through the interaction between the terminal and the server. The server can be an independent physical server, or a server cluster or distributed system composed of multiple physical servers, or a cloud server that provides basic cloud computing services such as cloud services, cloud databases, cloud computing, cloud functions, cloud storage, network servers, cloud communications, middleware services, domain name services, security services CDN, and big data and artificial intelligence platforms. The terminal can be a smart phone, a tablet computer, a laptop computer, a desktop computer, a smart speaker, a smart watch, etc., but is not limited to this. The terminal and the server can be directly or indirectly connected via wired or wireless communication, which is not limited in this application. In this embodiment, the method includes the following steps:

[0040] The VSM control strategy is used to control the phase of the grid-forming converter to obtain the active angle between the grid-forming converter and the power grid.

[0041] The difference between the current active angle and the active angle of the initial balance point is amplified under the control of the gain link and acts on the voltage controller, so that the voltage value output by the grid-type converter increases with the increase of the active angle, so as to enhance the transient stability of the grid-type converter.

[0042] The specific solution of this embodiment can be implemented by referring to the following contents:

[0043] 1. Establish a simplified "grid-type converter-grid" model

[0044] Figure 1 The basic structure of the grid-type converter is shown. The grid-type converter is connected to the grid through an LCL filter. The capacitor voltage v is controlled by the internal voltage loop. gfabc control; suppress the LCL filter resonance through the internal current loop to increase damping; control the output frequency and phase of the grid-type converter through the external power loop.

[0045] Since the voltage control speed of the grid-type converter is fast and the accuracy is high, the grid-type converter can be regarded as a controllable AC voltage source. Generally, the power grid is simplified as an AC voltage source. In addition, the impedance on the transmission line is generally considered to be purely inductive, and is represented by X. gs Based on the above assumptions, a simplified model of two voltage sources of the grid-connected converter and the grid is established, as shown in Figure 2 As shown. Among them, V g Represents the voltage amplitude of the grid-type converter, V sRepresents the grid voltage amplitude. The phase of the converter is taken as zero radians as a reference, then the phase of the grid is -δ g δ g is the phase difference between the converter voltage and the grid voltage, also known as the active angle. The converter and grid voltages are represented by voltage vectors V g ∠0 and V s ∠-δ g .

[0046] The active power transferred from the converter to the grid can be expressed as:

[0047]

[0048] The power control adopts the VSM control strategy of simulating synchronous machine. VSM can provide inertia and damping for the converter. The swing equation of VSM is shown in equation (1), where H g is the inertia constant, D g is the damping coefficient; p g_ref_pu and p g_pu They represent the active reference value and the per-unit value of output power respectively; ω0 is the rated frequency, Δω pu It is the rated value of frequency variation.

[0049]

[0050] The control structure of VSM, such as Figure 3 shown.

[0051] 2. Study the transient stability improvement method by simplifying the model

[0052] Transient stability is the ability of a system to maintain stable operation when facing large disturbances. According to formula (1), the power angle curve can be drawn, such as Figure 4 As shown in the figure, curve I, curve II and curve III represent the power angle curves before, during and after the fault respectively. When the damping effect is ignored, the transient stability of the system can be described by the equal area method, that is, the transient stability is Figure 4 The acceleration area (S a ) and deceleration area (S d ), reducing the acceleration area and increasing the deceleration area are the fundamental methods to improve transient stability. Assuming that the active reference value P0 remains unchanged, Figure 4 By raising the power angle curve in the converter, the acceleration area can be reduced and the deceleration area can be increased. According to formula (1), increasing the output voltage V g , you can increase the power output and improve the height of the power angle curve.

[0053] 3. Design of automatic voltage regulation controller

[0054] like Figure 4As shown in the figure, when a fault occurs, the active angle goes from point a to point b, then increases, passes through points c and d, and finally returns to point e (when point e is on the left of point f); when point e coincides with point f, it is a critical stability situation; when point e crosses point f, the active angle will continue to increase, and the system will become unstable. It can be found that from point a to point e, the active angle continues to increase, that is, δ g -δ0≥0. Therefore, according to the increase of active angle during large disturbance, the coupling part of active loop and voltage loop is designed, such as Figure 5 K is the control link proposed in this embodiment, which is usually a proportional link, but can also be an integral, differential or other common control link. The proposed control link can amplify the influence of the active angle and act on the voltage controller, so that the voltage increases with the increase of the active angle, thereby enhancing the transient stability of the grid-type converter.

[0055] The K value is a fixed parameter and does not change. When K=0, the control link proposed in this embodiment does not work, that is, the voltage does not increase with the increase of the active angle; when K is small, the voltage increases slowly with the increase of the active angle; when K is large, the voltage increases rapidly with the increase of the active angle. The setting of the K value is determined according to the rated voltage and the maximum voltage limit of the system. The K value is set according to the voltage conversion range that the system can withstand; it is usually a proportional (P) link, but it can also be a proportional integral (PI) link, a proportional integral differential (PID) link or other common control links. Among them, P (proportional): K; PI (proportional integral): K+1 / (T i s); PID (proportional integral differential): K+1 / (T i s)+T d s.

[0056] After adopting the controller designed in this embodiment, the power angle curve will be as follows: Figure 6 The present invention achieves the following effects:

[0057] (1) After δ0, the power angle curve height increases, the acceleration area decreases, the deceleration area increases, and the transient stability improves.

[0058] (2) On the power angle curve, the part on the left side of the maximum power point is the stable area, and the part on the right side is the unstable area. Through the control structure proposed by the present invention, the maximum power point of the power angle curve is shifted to the right, the stable area of ​​the power angle curve is increased, and the static stability of the system is improved.

[0059] In particular, in addition to achieving a good stability improvement effect, this embodiment is easy to implement and apply.

[0060] 4. Simulation results

[0061] The critical clearing time (CCT) is usually used to evaluate the transient stability of the system. If the fault clearing time (FCT) is greater than the CCT, the system will crash. Therefore, the increase in CCT means the improvement of the transient stability of the system. The critical clearing time is the critical clearing time of the fault, that is, the maximum time allowed to clear the fault. If the fault is cleared within the critical clearing time, the system can remain stable, otherwise the system will crash.

[0062] The effect of this embodiment is verified by simulation. The parameters and values ​​involved in the simulation are shown in Table 1.

[0063] Table 1 Simulation parameters

[0064]

[0065]

[0066] Figure 7(a) and Figure 7(b) show the transient stability level of the original system when the method of this embodiment is not adopted. As shown in the simulation results, when the fault removal time FCT is greater than the limit removal time 0.321s, the system becomes unstable.

[0067] After using the control structure proposed in this embodiment, the simulation results are shown in Figure 7(c) and Figure 7(d). Figure 7(c) shows the effect when the coupling part gain K is 1, and Figure 7(d) shows the effect when the coupling part gain K is 3. It can be seen from the figure that when K=1, the voltage output by the converter increases when the active angle is greater than the initial value. When K=1, the limit removal time is increased from the original 0.321s to 0.347s; when K=3, the limit removal time is increased to 0.394s. Therefore, the method proposed in this embodiment buys more time for fault removal after a large disturbance and enhances the transient stability of the system.

[0068] Embodiment 2

[0069] This embodiment provides a control system for enhancing the transient stability of a grid-type converter.

[0070] A control system for enhancing transient stability of a grid-type converter, comprising:

[0071] A VSM control module is configured to: use a VSM control strategy to control the phase of the grid-forming converter to obtain an active angle between the grid-forming converter and the power grid;

[0072] The enhanced stability module is configured to: amplify the influence of the difference between the current active angle and the active angle of the initial balance point under the regulation of the gain link, and act on the voltage controller, so that the voltage value output by the meshing type converter increases with the increase of the active angle, so as to enhance the transient stability of the meshing type converter.

[0073] It should be noted that the examples and application scenarios implemented by the above-mentioned VSM control module and enhanced stability module are the same as those in the steps of Embodiment 1, but are not limited to the contents disclosed in the above-mentioned Embodiment 1. It should be noted that the above-mentioned modules as part of the system can be executed in a computer system such as a set of computer executable instructions.

[0074] Embodiment 3

[0075] This embodiment provides a computer-readable storage medium on which a computer program is stored. When the program is executed by a processor, the steps in the control method for enhancing the transient stability of a grid-type converter as described in the first embodiment above are implemented.

[0076] Embodiment 4

[0077] This embodiment provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, the steps in the control method for enhancing the transient stability of a grid-type converter as described in the first embodiment above are implemented.

[0078] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of hardware embodiments, software embodiments, or embodiments combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage and optical storage, etc.) containing computer-usable program code.

[0079] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks 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 produce 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.

[0080] 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.

[0081] 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.

[0082] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiments can be implemented by instructing the relevant hardware through a computer program, and the program can be stored in a computer-readable storage medium, and when the program is executed, it can include the processes of the embodiments of the above-mentioned methods. The storage medium can be a disk, an optical disk, a read-only memory (ROM) or a random access memory (RAM), etc.

[0083] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A control method for enhancing transient stability of a grid-connected converter, characterized in that: include: Establish a "grid-type converter-grid" model: The grid-type converter and the grid are connected through LCL The capacitor voltage is connected to the filter through the internal voltage loop v gfabc control; through the internal current loop to suppress LCL The filter resonates to increase damping; the output frequency and phase of the grid-type converter are controlled through an external power loop; The VSM control strategy is used to control the phase of the grid-forming converter to obtain the active angle between the grid-forming converter and the power grid; the VSM control strategy is: In the formula, δ g is the active angle; H g is the inertia constant, D g is the damping coefficient; p g_ref_pu and p g_pu Respectively represent the active reference value and the per unit value of output power; ω 0 is the rated frequency, Δ ω pu is the rated value of the frequency variation; The obtaining of the active angle between the grid-forming converter and the grid includes: obtaining the phase difference between the grid-forming converter voltage and the grid voltage, which is the active angle; The difference between the current active angle and the active angle of the initial balance point is amplified under the control of the gain link, and acts on the voltage controller, so that the voltage value output by the grid-forming converter increases with the increase of the active angle, so as to enhance the transient stability of the grid-forming converter; The gain link includes a proportional link, a proportional integral link and a proportional integral differential link; The transient stability is the ability of the system to maintain stable operation when facing large disturbances. Ignoring the damping effect, the transient stability of the system is described by the equal area method. The transient stability is related to the acceleration area and deceleration area in the power angle curve. Reducing the acceleration area and increasing the deceleration area are the fundamental methods to improve transient stability. According to the increase of active angle during large disturbance, the coupling part of active loop and voltage loop is designed, among which the control link K The value is a fixed parameter and does not change. The setting of K value is determined according to the rated voltage and maximum voltage limit of the system, and is set according to the voltage conversion range that the system can withstand.

2. A control system for enhancing transient stability of a grid-connected converter, characterized in that: A control method for enhancing transient stability of a grid-connected converter as claimed in claim 1, comprising: A VSM control module is configured to: use a VSM control strategy to control the phase of the grid-forming converter to obtain an active angle between the grid-forming converter and the power grid; The enhanced stability module is configured to: amplify the influence of the difference between the current active angle and the active angle of the initial balance point under the regulation of the gain link, and act on the voltage controller, so that the voltage value output by the meshing type converter increases with the increase of the active angle, so as to enhance the transient stability of the meshing type converter.

3. The control system for enhancing transient stability of a grid-connected converter according to claim 2, characterized in that: The stability of the control system is evaluated based on the relationship between the limit clearing time and the fault clearing time.

4. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the control method for enhancing transient stability of a grid-type converter as claimed in claim 1 are implemented.

5. A computer 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 program, the steps in the control method for enhancing transient stability of a grid-type converter as claimed in claim 1 are implemented.

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