A multi-reactive source coordinated control method

Abstract

The present invention discloses a multi-reactive source coordinated control method. This control method proposes a VRPI index to characterize the ability of each reactive source to participate in voltage regulation based on variables such as the total reactive power deficit, reactive surplus output, and transient response time of each reactive source in the event of a multi-reactive source AC system fault. Based on this index, a multi-reactive source coordinated control method is proposed. When applied to a short-circuit fault on the AC side of a large-scale AC / DC system, the method can quantify the impact of reactive sources on the system fault response, ensuring that wind turbines can smoothly pass through the fault while effectively suppressing transient overvoltages and preventing wind turbine tripping. The application of the VRPI index in the present invention provides theoretical guidance for the planning and operation of AC / DC transmission systems and the configuration of reactive compensation devices under the grid connection of new energy sources.

Description

Technical Field

[0001] The present invention relates to the field of ultra-high voltage direct current (UHVDC) power transmission, and in particular to a multi-reactive source coordinated control method. Background Art

[0002] With the drastic depletion of traditional energy sources, renewable energy is increasingly becoming the primary energy source. According to the 2022 Global Wind Power Report, the 93.6 GW of new wind power capacity installed in 2021 will bring the global cumulative wind power capacity to 837 GW, a 12% year-on-year increase. However, this large installed capacity of wind power also poses voltage stability challenges for power grids. Voltage fluctuations on receiving grids can easily cause wind turbines to trip, leading to a series of cascading failures and ultimately system collapse. Power system failures can occur very quickly, and if not promptly adjusted or eliminated, they can quickly impact the entire system.

[0003] When a system fault occurs, the voltage drop can cause grid equipment to disconnect from the grid, seriously affecting the system's power quality (voltage, frequency). Large-scale wind turbine disconnections mainly come from two aspects: first, from the power grid. When a serious fault occurs during operation, the power grid will disconnect the entire fault network and all equipment connected to this network, including some wind power equipment. Second, from the wind turbines. Because when a grid disturbance or transient fault is disconnected, the grid voltage is low. If the wind turbine does not have low voltage ride-through function, it will cause the wind turbine to disconnect from the grid. When the proportion of wind turbines installed is large, wind turbine tripping will have a significant impact on the stability of grid voltage and frequency. Therefore, it is necessary to improve the low voltage ride-through capability of wind turbines to avoid large-scale wind turbine disconnections.

[0004] To improve voltage stability, various reactive power compensation devices, such as SVGs and synchronous capacitors, are typically installed in the sending grid. However, in the event of a three-phase short-circuit fault in the sending grid, the coordinated operation of multiple reactive power sources can easily lead to residual reactive power during fault recovery, potentially causing wind turbines to trip from the grid. Therefore, it is necessary to study the coordinated control of multiple reactive power sources. Summary of the Invention

[0005] The purpose of the present invention is to provide a multi-reactive source collaborative control method. According to variables such as the total reactive power shortage, reactive surplus output and transient response time of each reactive source in the case of a multi-reactive source AC system fault, a VRPI index is proposed to characterize the ability of each reactive source to participate in voltage regulation, and based on this index, a multi-reactive source collaborative control method is proposed. When it is applied to a short-circuit fault on the AC side of a large-scale AC / DC system, the impact of the reactive source on the system fault response can be quantified, which not only improves the reliability of low-voltage ride-through of wind turbines under AC system faults, but also effectively suppresses transient overvoltages, avoids wind turbine tripping, and provides theoretical guidance for the capacity configuration of reactive compensation devices.

[0006] The purpose of the present invention can be achieved through the following technical solutions.

[0007] A multi-reactive source coordinated control method, the control method comprising the following steps:

[0008] Step 1: Obtain the AC side voltage of the grid.

[0009] Step 2: Obtain the maximum remaining output reactive power of each reactive source.

[0010] Step 3: Determine whether the wind turbine is at risk of disconnection based on the grid AC voltage and calculate the VRPI value of each reactive power source.

[0011] Step 4: Allocate reactive power output tasks in proportion to the VRPI value of each reactive power source.

[0012] Step 5: Determine whether the reactive power output by the reactive source exceeds the limit. If so, the excess will be redistributed according to the VRPI value of other reactive sources. If not, the process ends.

[0013] Furthermore, the method for calculating the VRPI value of each reactive source includes:

[0014]

[0015] Where ΣQ is the maximum remaining reactive power output value of the reactive power source, ΔQ is the system reactive power loss under grid fault, Δt is the time required for the reactive power source to output ΣQ, K is the compensation coefficient, and f() satisfies the expression:

[0016]

[0017] Furthermore, the method for judging whether a wind turbine has a risk of disconnection based on the AC voltage of the power grid and calculating the VRPI value of each reactive source is as follows:

[0018] Monitor the AC side voltage of the power grid in real time and calculate the remaining maximum output reactive power of each reactive source. When the AC side grid voltage drops below 0.9pu, calculate the VRPI value of each reactive power source. Otherwise, re-monitor the AC voltage of the power grid.

[0019] Furthermore, the method for performing reactive power source coordinated control according to the VRPI value in step 4 is as follows:

[0020] The VRPI values ​​of each reactive source obtained in step 2 are used to proportionally distribute the reactive power output of each reactive source. Reactive sources with larger VRPI values ​​participate in voltage regulation and output more reactive power, while reactive sources with smaller VRPI values ​​participate in voltage regulation and output less reactive power. When the reactive power output of a reactive source exceeds the limit, there is a risk that the new energy unit will be tripped after a fault. The system will reconfigure the capacity of the reactive compensation device, and at this time, the excess will be redistributed according to the VRPI values ​​of other reactive sources. When the reactive power output of a reactive source does not exceed the limit, there is no risk that the new energy unit will be tripped after a fault, and there is no need to reconfigure the reactive compensation capacity.

[0021] The application of the above control method in the risk assessment of fan disconnection in the sending-end AC system.

[0022] A computer-readable storage medium storing one or more programs, the one or more programs comprising instructions that, when executed by a computing device, cause the computing device to perform any of the methods described.

[0023] A computing device comprising:

[0024] One or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include instructions for executing any of the methods.

[0025] Beneficial effects of the present invention:

[0026] 1. Compared with existing reactive power output evaluation indicators, the multi-reactive power coordinated control method of the present invention proposes a VRPI indicator to characterize the ability of each reactive power source to participate in voltage regulation based on the total reactive power shortage, reactive power surplus output, and transient response time of each reactive power source in the event of a multi-reactive power AC system fault.

[0027] 2. The multi-reactive source collaborative control method of the present invention can quantify the impact of reactive sources on system fault response by applying the VRPI indicator to short-circuit faults on the AC side of large-scale AC / DC systems. This not only improves the reliability of low-voltage ride-through of wind turbines under AC system faults, but also effectively suppresses transient overvoltages and avoids wind turbine tripping. It provides theoretical guidance for the planning and operation of AC / DC hybrid systems under the grid connection of new energy and the capacity configuration of reactive compensation devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be further described below with reference to the accompanying drawings.

[0029] Figure 1 This is a flow chart of the multi-reactive source coordinated control method of the present invention;

[0030] Figure 2It is a topological structure diagram of the simulation system of the present invention;

[0031] Figure 3 This is a diagram showing the AC voltage change when a three-phase short circuit fault occurs at the sending end of the present invention and the voltage drops by 30%;

[0032] Figure 4 This is a graph showing the reactive output change of a synchronous condenser when a three-phase short circuit fault occurs at the sending end of the present invention and the voltage drops by 30%.

[0033] Figure 5 This is the SVG reactive output change diagram when a three-phase short circuit fault occurs at the sending end and the voltage drops by 30%;

[0034] Figure 6 This is the reactive output change diagram of the DFIG unit and PMSG unit when a three-phase short circuit fault occurs at the sending end and the voltage drops by 30%;

[0035] Figure 7 This is a diagram showing the AC voltage change when a three-phase short circuit fault occurs at the sending end of the present invention and the voltage drops by 55%;

[0036] Figure 8 This is a graph showing the reactive output change of the synchronous condenser when a three-phase short circuit fault occurs at the sending end of the present invention and the voltage drops by 55%.

[0037] Figure 9 This is a graph showing the reactive output change of the SVG when a three-phase short circuit fault occurs at the sending end of the present invention and the voltage drops by 55%.

[0038] Figure 10 This is a diagram showing the reactive output changes of the DFIG unit and the PMSG unit when a three-phase short circuit fault occurs at the sending end of the present invention and the voltage drops by 55%. DETAILED DESCRIPTION

[0039] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making any creative efforts shall fall within the scope of protection of the present invention.

[0040] A multi-reactive source coordinated control method, such as Figure 1 As shown in the figure, the control method proposes a VRPI (voltage regulation participation index) to characterize the ability of each reactive source to participate in voltage regulation based on the total reactive power shortage, reactive surplus output, and transient response time of each reactive source in the case of a multi-reactive source AC system fault. VRPI is used to evaluate the ability of reactive sources to participate in voltage regulation during a fault. The control method specifically includes the following steps:

[0041] Step 1: Obtain the AC side voltage of the power grid;

[0042] Step 2: Obtain the maximum remaining output reactive power of each reactive source;

[0043] Step 3: Determine whether the wind turbine is at risk of disconnection based on the AC voltage of the grid and calculate the VRPI value of each reactive power source

[0044] Real-time monitoring of the AC voltage on the grid and calculation of the maximum remaining reactive power output of each reactive power source are performed simultaneously. According to the low-voltage ride-through standard for new energy generators, when the voltage at the wind farm's grid connection point drops to 20% of the nominal voltage, the wind turbines within the wind farm must remain connected and operate continuously for 625ms. Furthermore, if the voltage at the wind farm's grid connection point recovers to 90% of the nominal voltage within 2 seconds after the drop, the wind turbines must remain connected and operate continuously. Therefore, it is stipulated that when the receiving-end grid voltage drops below 0.9 pu, the system is at risk of failure. At this point, the VRPI value of each reactive power source is calculated. Otherwise, grid AC voltage monitoring is resumed.

[0045] The method for calculating the VRPI value of each reactive power source is:

[0046]

[0047] Where ΣQ is the maximum remaining reactive power output value of the reactive power source, ΔQ is the system reactive power loss under grid fault, Δt is the time required for the reactive power source to output ΣQ, K is the compensation coefficient, and f() satisfies the expression:

[0048]

[0049] Step 4: Allocate reactive power output tasks proportionally based on the VRPI value of each reactive power source

[0050] Reactive sources with larger VRPI values ​​are selected to participate in voltage regulation and output more reactive power, while reactive sources with smaller VRPI values ​​are selected to participate in voltage regulation and output less reactive power. If the reactive power output by the reactive source exceeds the limit, there is a risk of the new energy unit being tripped after a fault, and the system needs to reconfigure the capacity of the reactive compensation device. At this time, the excess will be redistributed according to the VRPI values ​​of other reactive sources. If the reactive power output by the reactive source does not exceed the limit, there is no risk of the new energy unit being tripped after a fault, and there is no need to reconfigure the reactive compensation capacity.

[0051] Step 5: Determine whether the reactive power output by the reactive source exceeds the limit. If so, the excess will be redistributed according to the VRPI value of other reactive sources. If not, the process ends.

[0052] The application of multi-reactive source coordinated control method in fault risk assessment of AC system at the sending end of renewable energy grid connection includes:

[0053] Application Example 1:

[0054] The simulation system topology is as follows Figure 2 As shown in the figure, the fault is set as a three-phase short circuit fault in the sending-end power grid, the voltage drops by 30%, the fault occurs at 1.5s, the duration is 0.1s, and the compensation factor K is 4.5. In this scenario, the voltage curve of the sending-end power grid and the reactive output curves of each reactive power source are as follows: Figure 3-Figure 6 As shown in Figure 1, at 1.5s, a short circuit fault occurs in the sending-end power grid, the voltage drops rapidly, and the wind turbine enters the LVRT process; Figure 3 As shown, the voltage is at least 0.7pu, which meets the LVRT specifications for wind turbines and will not cause tripping accidents.

[0055] Among all reactive power sources, synchronous condensers have strong overload capacity and the largest VRPI value, so they are assigned the most reactive power guarantee tasks. Figure 4 As shown in Figure 2, when a fault occurs, the synchronous condenser generates an additional 277 MVar reactive output. Since the reactive output capability of SVG is reduced in low-voltage scenarios, its VRPI value should be smaller than that of the synchronous condenser. Figure 5 As shown in Figure 2, the SVG generated 18 MVar of reactive power output during the fault. During the simulation, the wind turbine was set to a high power factor operation state, and the reactive power output was less than that of the synchronous condenser and SVG. Figure 6 As shown in the figure, the reactive power of DFIG and PMSG is 4Mvar and 2MVar respectively; after the fault is cleared, the reactive output of each reactive power source decreases, and the transient overvoltage can be effectively suppressed under the coordinated control strategy. In this case, the maximum transient overvoltage is 1.06pu, and the wind turbine will not trip.

[0056] Application Example 2:

[0057] The fault is set to a three-phase short circuit fault in the sending-end power grid, with a voltage drop of 55%. The fault occurs at 2s and lasts for 0.2s.

[0058] In this scenario, the voltage curve of the sending-end grid and the reactive output curves of each reactive power source are as follows: Figure 7-10 As shown in Figure 1, at 1.5s, a short circuit fault occurs in the sending-end power grid, the voltage drops rapidly, and the wind turbine enters the LVRT process; Figure 7 As shown, the voltage is at least 0.45pu, which meets the LVRT specifications for wind turbines and will not cause tripping accidents.

[0059] In this case, the synchronous condenser also has the largest VRPI value and generates an additional 372 MVar reactive output during the fault. The VRPI value of the SVG is smaller than that of the synchronous condenser, and the additional reactive output is 37 MVar. Figure 10 As shown in the figure, the DFIG unit and PMSG unit generate additional 8MVar and 6MVar reactive power respectively; the highest transient overvoltage in the three-phase short-circuit fault scenario of the sending-end grid is 1.07pu, and the wind turbine will not trip.

[0060] A computer-readable storage medium stores instructions. When the instructions are executed, the aforementioned reactive power output evaluation index of the sending-end AC system and its application method can be implemented. More specifically, the instructions can be in a computer-readable language. The aforementioned computer can be a general-purpose computer device or a dedicated computer device. In a specific implementation, the computer can be a desktop computer, a portable computer, a network server, a personal digital assistant (PDA), a mobile phone, a tablet computer, a wireless terminal device, a communication device, or an embedded device. The aforementioned storage medium can be any available medium that can be accessed by the computer or a data storage device such as a server or data center that integrates one or more available media. For example, the aforementioned storage medium is, but is not limited to, magnetic media (e.g., floppy disks, hard disks, magnetic tapes), optical media (e.g., digital versatile discs (DVDs)), or semiconductor media (e.g., solid-state drives (SSDs)).

[0061] 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 application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the 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 embodiment of the present application can be implemented in various computer languages, for example, object-oriented programming language Java and literal translation scripting language JavaScript, etc.

[0062] 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 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 steps in the process. 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.

[0063] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work 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 The function specified in one or more boxes.

[0064] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0065] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional 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 that fall within the scope of the present application.

[0066] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims

1. A multi-reactive source coordinated control method, characterized in that: The control method comprises the following steps: Step 1: Obtain the AC side voltage of the power grid; Step 2: Obtain the maximum remaining output reactive power of each reactive source; Step 3: Determine whether the wind turbine is at risk of disconnection based on the AC voltage of the grid and calculate the voltage regulation participation index VRPI value of each reactive power source; Step 4: Allocate reactive power output tasks in proportion to the VRPI value of each reactive power source; Step 5: Determine whether the reactive power output by the reactive source exceeds the limit. If so, the excess is redistributed according to the VRPI values ​​of other reactive sources. If not, the process ends. The method for calculating the voltage regulation participation index VRPI value of each reactive source includes: Where ΣQ is the maximum remaining reactive power output value of the reactive power source, ΔQ is the system reactive power loss under grid fault, Δt is the time required for the reactive power source to output ΣQ, K is the compensation coefficient, and f() satisfies the expression:

2. A multi-reactive source coordinated control method according to claim 1, characterized in that: The method for determining whether a wind turbine has a risk of disconnection based on the AC voltage of the power grid and calculating the voltage regulation participation index VRPI value of each reactive power source is as follows: Monitor the AC side voltage of the power grid in real time and calculate the remaining maximum output reactive power of each reactive source. When the AC side grid voltage drops below 0.9pu, calculate the VRPI value of each reactive power source. Otherwise, re-monitor the AC voltage of the power grid.

3. The multi-reactive source coordinated control method according to claim 1, characterized in that: The method for performing reactive power source coordinated control according to the VRPI value in step 4 is as follows: The VRPI values ​​of each reactive source obtained in step 3 are used to proportionally distribute the reactive power output of each reactive source. Reactive sources with larger VRPI values ​​participate in voltage regulation and output more reactive power, while reactive sources with smaller VRPI values ​​participate in voltage regulation and output less reactive power. When the reactive power output of a reactive source exceeds the limit, there is a risk that the new energy unit will be tripped after a fault. The system will reconfigure the capacity of the reactive compensation device, and at this time, the excess will be redistributed according to the VRPI values ​​of other reactive sources. When the reactive power output of a reactive source does not exceed the limit, there is no risk that the new energy unit will be tripped after a fault, and there is no need to reconfigure the reactive compensation capacity.

4. A computer-readable storage medium storing one or more programs, characterized in that: The one or more programs include instructions that, when executed by a computing device, cause the computing device to perform any one of the methods according to claims 1 to 3.

5. A computing device, characterized in that include: One or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the one or more programs comprising instructions for executing any one of the methods according to claims 1 to 3.

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