Method for assisting synchronous grid connection by using local load

Abstract

The invention relates to a method for assisting synchronous grid connection by using an in-situ load, which comprises the following steps of: predicting an impact current generated by switching on an interconnecting circuit breaker, and executing switching-on operation of the interconnecting circuit breaker when an impact current predicted value is not greater than an impact current allowable value of the interconnecting circuit breaker; otherwise, the impact load and the capacitive reactive power compensation device are put into use while the closing operation of the interconnecting circuit breaker is executed, the difference value between the impact current predicted value and the impact current allowable value is compensated by the active power of the impact load, and the inductive reactive power of the impact load is compensated by the capacitive reactive power compensation device. Aiming at the requirement that synchronous grid connection needs to be quickly realized when a regional power grid or a generator set to be connected to the grid does not meet synchronous conditions and adjustable power generation resources or control means are insufficient, the impact of grid connection operation on a large power grid is absorbed by starting an in-situ impact load, and meanwhile, an in-situ capacitive reactive power compensation device is started to compensate voltage drop; therefore, the method for realizing synchronous grid connection is accelerated.

Description

Technical Field

[0001] The present invention belongs to the technical field of safe and stable control of electric power systems, and in particular, relates to a method for synchronously connecting a generator or a regional power grid to the grid by using local loads. Background Art

[0002] When a generator or a regional power grid is connected to a large power grid through synchronous control, it may cause an impact on the power grid, resulting in a large-scale voltage drop, affecting the power supply quality and safe operation of the power grid. Therefore, measures need to be taken to limit the impact current generated by the generator or regional power grid when it is connected to the large power grid synchronously.

[0003] In the prior art, synchronous grid connection relies on the voltage amplitude difference, voltage phase angle difference, and frequency difference of the synchronous device at both ends of the interconnecting circuit breaker to close the circuit breaker and achieve grid connection. For example, the condition for switching to the large power grid through the backup channel within 180ms after the regional power grid is disconnected is that the voltage phase angle difference on both sides is less than 20°, the frequency difference on both sides is less than 1Hz, and the voltage secondary value difference on both sides is less than 0.2 times the rated voltage. The condition for synchronous grid connection of the generator set is that the voltage amplitude difference is less than 1%, the angle difference is less than 2.5°, and the frequency difference is less than 0.2Hz. When these synchronous conditions are not met, the disconnected regional power grid or the started generator cannot be connected to the large power grid for operation. In the case of sufficient and flexible power generation resource adjustment capabilities, by increasing the generator output and phase angle, it is possible to achieve synchronous grid connection conditions in a short time. However, in the absence of adjustable power generation resources or available power generation adjustment means, it is difficult for the regional power grid or the started generator to complete grid connection in a short time. Therefore, in order to achieve rapid synchronous grid connection, it is necessary to study and develop new adjustment means to accelerate the synchronous grid connection process of the regional power grid or the generator set. Summary of the invention

[0004] In order to solve the deficiencies in the prior art, the present invention provides a method for utilizing local loads to assist synchronous grid-connection. When the power grid or generator set in the area to be connected to the grid does not meet the synchronization conditions and the adjustable power generation resources or control means are insufficient, it is desired to quickly achieve synchronous grid-connection. The method accelerates the realization of synchronous grid-connection by starting the local impact load to absorb the impact of the grid-connection operation on the large power grid, and at the same time starting the local reactive power compensation device to compensate for the voltage drop.

[0005] The present invention adopts the following technical solution.

[0006] The present invention proposes a method for utilizing local load to assist synchronous grid connection, predicting the impact current generated by closing a connecting circuit breaker, and executing the connecting circuit breaker closing operation when the impact current prediction value is not greater than the impact current allowable value of the connecting circuit breaker; otherwise, while executing the connecting circuit breaker closing operation, the impact load and reactive power compensation device are put into operation, wherein the difference between the impact current prediction value and the impact current allowable value is compensated by the active power of the impact load, and the reactive power of the impact load is compensated by the reactive power compensation device.

[0007] Preferably, while executing the closing operation of the interconnecting circuit breaker, the impact load and the capacitive reactive power compensation device are put into operation, and the capacitive reactive power compensation device is used to compensate the inductive reactive power of the impact load.

[0008] Preferably, predicting the impact current generated by closing the tie circuit breaker includes:

[0009] Obtain the voltage and current history data of the tie circuit breaker when it is closed; obtain the system-side open-circuit voltage data and the generation-side open-circuit voltage data of the tie circuit breaker when the regional power grid is disconnected;

[0010] Based on the real-time data obtained, the impact current generated by closing the tie circuit breaker is predicted.

[0011] Preferably, the inrush current generated by closing the tie circuit breaker is predicted based on the acquired real-time data, including:

[0012] When the frequency difference between the system side and the generation side of the tie circuit breaker is less than the frequency difference threshold, the synchronous closing judgment and control stage begins. Based on the system side equivalent circuit and the generation side equivalent circuit of the regional power grid, and using the voltage and current history data of the tie circuit breaker during closing operation, the system side impedance and the generation side impedance of the tie circuit breaker are determined respectively.

[0013] The system-side open-circuit voltage data of the interconnecting circuit breaker when the regional power grid is disconnected is used as the voltage phasor of the ideal voltage source on the system side, and the generator-side open-circuit voltage data of the interconnecting circuit breaker when the regional power grid is disconnected is used as the internal potential phasor of the generator;

[0014] According to the impedance on the system side, the impedance on the generator side, the potential phasor inside the generator and the voltage phasor of the ideal voltage source on the system side, the predicted value of the inrush current generated by closing the tie circuit breaker is calculated using the following relationship:

[0015]

[0016] In the formula, I r is the predicted value of the inrush current generated by closing the tie circuit breaker, is the potential phasor inside the generator, is the voltage phasor of the ideal voltage source on the system side, Xs is the system side impedance, X g is the impedance on the generating side.

[0017] Preferably, the frequency difference threshold is set to 1.1 Hz.

[0018] Preferably, when the predicted value of the impact current is greater than the allowable value of the impact current of the tie circuit breaker, the impact load and the capacitive reactive power compensation device are put into operation at the same time as the tie circuit breaker closing operation is performed, including:

[0019] Compare the relationship between the predicted value of the impact current generated by the closing of the interconnecting circuit breaker and the allowable value of the impact current of the interconnecting circuit breaker. If the predicted value of the impact current is not greater than the allowable value of the impact current, execute the interconnecting circuit breaker closing operation; if the predicted value of the impact current is greater than the allowable value of the impact current, determine the capacity of the impact load and the capacity of the capacitive reactive power compensation device to be put into operation at the same time as the interconnecting circuit breaker is closed based on the difference between the predicted value of the impact current and the allowable value of the impact current.

[0020] Preferably, according to the difference between the predicted value of the impact current and the permissible value of the impact current, determining the capacity of the impact load and the capacity of the capacitive reactive power compensation device to be put into operation when the tie circuit breaker is closed comprises:

[0021] Calculate the difference between the predicted value of the impact current and the allowable value of the impact current as the impact current overflow;

[0022] Calculate the active power overload using the inrush current overflow and set voltage;

[0023] The active power overload is taken as the lower limit and the set multiple of the active power overload is taken as the upper limit to form the value range of the active power of the impact load; the sum of the active power of the impact load put into operation is taken as the optimization target to determine the capacity of the impact load put into operation simultaneously with the closing operation of the tie circuit breaker, and the sum of the inductive reactive power of the impact load put into operation simultaneously;

[0024] The sum of the inductive reactive power of the impact loads put into operation at the same time is taken as the lower limit, and the set multiple of the sum of the inductive reactive power of the impact loads put into operation at the same time is taken as the upper limit, so as to form the value range of the capacity of the capacitive reactive compensation device; taking the sum of the capacitive reactive compensation device capacities put into operation within the value range as the optimization goal, the capacity of the capacitive reactive compensation device put into operation at the same time as the closing operation of the interconnecting circuit breaker is determined.

[0025] Preferably, the active power overload ΔP is used as the lower limit and 110% of the active power overload is used as the upper limit to form the value range of the impact load active power;

[0026] Determine the type of impact load that is put into operation at the same time as the tie circuit breaker closing operation, and take the sum of the active powers of the impact loads put into operation P buChang Satisfy △P <P buChang <1.1△P is the optimization target, and then active power is allocated to each impact load according to the determined impact load type; the capacity of each impact load is determined according to the active power allocated to each impact load, the power factor is determined according to the type of each impact load, and the sum of the inductive reactive power Q of the impact loads put into use at the same time is determined by using the capacity and power factor of each impact load L-buChang .

[0027] Preferably, the sum of the inductive reactive power of the impact loads put into operation at the same time is Q L-buChang The lower limit is 100% of the sum of the inductive reactive power of the impact loads put into operation at the same time, and the upper limit is 110% of the sum of the inductive reactive power of the impact loads put into operation at the same time, which constitutes the value range of the capacity of the capacitive reactive compensation device;

[0028] First, determine the type of capacitive reactive power compensation device that is put into operation at the same time as the tie circuit breaker closing operation, and the sum of the capacitive reactive power compensation devices that are put into operation at the same time, Q C-buChang Satisfy Q L-buChang C-buChang <1.1Q L-buChang For the optimization purpose, the capacity is then allocated to each capacitive reactive power compensation device according to the determined type of the capacitive reactive power compensation device.

[0029] Preferably, when the sum of the active powers of the impact loads to be put into operation is within the value range of the active powers of the impact loads, and the sum of the capacitive reactive power compensation devices to be put into operation is within the value range of the capacitive reactive power compensation devices, a closing signal is sent to the tie circuit breaker, and a start signal is sent to the impact loads to be put into operation and the capacitive reactive power compensation devices to be put into operation at the same time;

[0030] Otherwise, the impact current generated by closing the interconnecting circuit breaker is predicted again.

[0031] The beneficial effect of the present invention is that, compared with the prior art, at least the method proposed by the present invention includes that when the expected closing impact current of the synchronous grid-connected circuit breaker is greater than the allowable value, the local impact load and supporting capacitor supplement device are selected according to the overflow, and the circuit breaker is closed at the same time, thereby diverting the impact current on the power grid and supporting the grid voltage. Thus, the power grid or the generator set in the area to be connected to the grid does not meet the synchronous conditions, and the adjustable power generation resources or control means are insufficient, and the synchronous grid connection is realized quickly. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The present invention provides a flow chart of a method for utilizing local loads to assist synchronous grid connection. DETAILED DESCRIPTION​

[0033] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only embodiments of a part of the present invention, rather than all embodiments. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0034] Install and deploy synchronous grid-connected devices at the stations where the circuit breakers of the regional power grid or generator sets need to be synchronously connected to the grid. For local impact loads, you can choose motor loads with large starting currents, electric heat storage boilers, electrochemical energy storage, etc. Reactive compensation devices can be reactive devices such as capacitors, SVG, SVC, etc. According to the closing control interface of the controlled load and the reactive compensation device, such as state quantity control or communication control, select the appropriate control instruction issuance mode. The state quantity can be a 0-1 node signal or a gear signal; communication control can choose various communication protocols based on the IP protocol.

[0035] In order to meet the demand for a large amount of active and reactive support power for grid-connected control, the above-mentioned loads and reactive compensation devices that can be used to assist grid connection can be withdrawn before synchronous grid connection. After grid connection operation is achieved according to the method of the present invention, it can be adjusted to the desired operating point through manual or other production control systems according to the requirements of optimal operation.

[0036] The present invention provides a method for utilizing local load to assist synchronous grid connection, wherein the impact current generated by closing a connecting circuit breaker is predicted, and when the predicted impact current value is not greater than the allowable impact current value of the connecting circuit breaker, the connecting circuit breaker closing operation is performed; otherwise, while the connecting circuit breaker closing operation is performed, the impact load and reactive power compensation device are put into operation, wherein the difference between the predicted impact current value and the allowable impact current value is compensated by the active power of the impact load, and the reactive power of the impact load is compensated by the reactive power compensation device.

[0037] Wherein, while executing the closing operation of the interconnecting circuit breaker, the impact load and the capacitive reactive power compensation device are put into operation, and the capacitive reactive power compensation device is used to compensate the inductive reactive power of the impact load.

[0038] like Figure 1 As shown, the method includes:

[0039] Step 1, obtaining the voltage and current history data of the interconnecting circuit breaker when it is closed; obtaining the system side open circuit voltage data and the generation side open circuit voltage data of the interconnecting circuit breaker when the regional power grid is disconnected.

[0040] Step 2: predict the impact current generated by closing the tie circuit breaker based on the acquired real-time data.

[0041] Specifically, step 2 includes:

[0042] Step 2.1, when the frequency difference between the system side and the generation side of the tie circuit breaker is less than the frequency difference threshold, the synchronous closing judgment and control stage begins, based on the system side equivalent circuit and the generation side equivalent circuit of the regional power grid, and using the voltage and current history data of the tie circuit breaker during closing operation, the system side impedance and the generation side impedance of the tie circuit breaker are determined respectively;

[0043] In a non-limiting preferred embodiment, the Thevenin equivalent circuit of the system side of the regional power grid and the Thevenin equivalent circuit of the power generation side are established, and the voltage and current history data of the tie circuit breaker during the most recent closing operation are used to determine the system side impedance X based on the corresponding equivalent circuit. s and the generator impedance X g Those skilled in the art can use different methods to establish equivalent circuits on the system side and the power generation side of the regional power grid according to actual conditions.

[0044] In a non-limiting preferred embodiment, the frequency difference threshold is 1.1 Hz.

[0045] Step 2.2, using the system-side open-circuit voltage data of the tie circuit breaker when the regional power grid is in a disconnected state as the voltage phasor of the ideal voltage source on the system side, and using the generator-side open-circuit voltage data of the tie circuit breaker when the regional power grid is disconnected as the generator internal potential phasor;

[0046] Specifically, when the regional power grid is in the disconnected state, the open-circuit voltage phasor on both sides of the tie circuit breaker is measured at a millisecond period to obtain the internal potential phasor of the generator and the voltage phasor of the ideal voltage source on the system side

[0047] Step 2.3, based on the impedance on the system side, the impedance on the generator side, the potential phasor inside the generator, and the voltage phasor of the ideal voltage source on the system side, calculate the predicted value of the inrush current generated by closing the tie circuit breaker using the following relationship:

[0048]

[0049] In the formula, I r is the predicted value of the inrush current generated by closing the tie circuit breaker, is the potential phasor inside the generator, is the voltage phasor of the ideal voltage source on the system side, X s is the system side impedance, X g is the impedance on the generating side.

[0050] Step 3, when the predicted value of the impact current is not greater than the allowable value of the impact current of the interconnecting circuit breaker, the interconnecting circuit breaker closing operation is executed; otherwise, while the interconnecting circuit breaker closing operation is executed, the impact load and the reactive power compensation device are put into operation, wherein the difference between the predicted value of the impact current and the allowable value of the impact current is compensated by the active power of the impact load, and the reactive power of the impact load is supplemented by the capacity of the reactive power compensation device.

[0051] Specifically, step 3 includes:

[0052] Step 3.1, comparing the magnitude relationship between the predicted value of the inrush current generated by the closing of the tie circuit breaker and the allowable value of the inrush current of the tie circuit breaker, if the predicted value of the inrush current is not greater than the allowable value of the inrush current, executing the closing operation of the tie circuit breaker; if the predicted value of the inrush current is greater than the allowable value of the inrush current, proceeding to step 3.2;

[0053] Specifically, the permissible value of the inrush current is a standard technical parameter of the tie circuit breaker, and the specific value is determined according to regulations and specifications.

[0054] Step 3.2, according to the difference between the predicted value of the impact current and the permissible value of the impact current, determine the capacity of the impact load and the capacity of the reactive power compensation device to be put into operation when the interconnecting circuit breaker is closed.

[0055] Specifically, step 3.2 includes:

[0056] Step 3.2.1, calculate the difference between the predicted value of the impact current and the allowable value of the impact current as the impact current overflow;

[0057] Step 3.2.2, using the impulse current overload and the set voltage, calculate the active power overload;

[0058] Specifically, the set voltage includes but is not limited to the average voltage and the rated voltage; those skilled in the art may select different voltage values ​​as the set voltage according to actual needs.

[0059] Step 3.2.3, taking the active power overload as the lower limit and the set multiple of the active power overload as the upper limit, the value range of the active power of the impact load is formed; taking the sum of the active power of the impact load put into operation within the value range as the optimization target, the capacity of the impact load put into operation simultaneously with the closing operation of the tie circuit breaker is determined, and the sum of the inductive reactive power of the impact load put into operation simultaneously is determined;

[0060] Furthermore, the number of impact loads put into operation at the same time as the closing operation of the interconnecting circuit breaker in the regional isolated grid is limited, and the granularity of the power value is relatively large, making it difficult to achieve accurate active and reactive compensation for the impact current. Therefore, the active and reactive variable range of the compensation load is set according to the current or power overload. Within this range, the impact load or capacitive reactive load can be optimized to compensate for the impact current overflow caused by the synchronous closing to the power grid and support the voltage drop.

[0061] In a non-limiting preferred embodiment, the active power overload ΔP is used as the lower limit and 110% of the active power overload ΔP is used as the upper limit to form the value range of the impact load active power; the type of impact load that is put into operation simultaneously with the closing operation of the connecting circuit breaker is determined, and equipment with large starting current is used as the impact load that is put into operation simultaneously, including but not limited to: motors, electric heat storage boilers, and electrochemical energy storage; the sum of the active powers of the impact loads put into operation P buChang Satisfy △P <P buChang <1.1△P is the optimization target. Then, according to the determined type of impact load and the regional power grid constraints, active power is allocated to each impact load. The capacity of each impact load is determined according to the active power allocated to each impact load, and the power factor is determined according to the type of each impact load. The sum of the inductive reactive power Q of the impact loads put into operation at the same time is determined by using the capacity and power factor of each impact load. L-buChang .

[0062] By putting the impact load into operation at the same time as the connecting circuit breaker is closed, the active power of the impact load can be used to compensate for the active power overload caused by the impact current overflow. When the power grid or generator set in the area to be connected to the grid cannot meet the synchronization conditions and the adjustable power generation resources or control means are insufficient, there is no need to wait and synchronous grid connection can be achieved quickly. In addition, the impact of the grid connection operation on the large power grid can be absorbed by starting the local impact load.

[0063] Step 3.2.4, taking the sum of the inductive reactive power of the impact loads put into operation at the same time as the lower limit and taking the set multiple of the sum of the inductive reactive power of the impact loads put into operation at the same time as the upper limit, to form the value range of the capacity of the capacitive reactive compensation device; taking the sum of the capacitive reactive compensation device capacities put into operation within the value range as the optimization target, determine the capacity of the capacitive reactive compensation device put into operation at the same time as the closing operation of the tie circuit breaker;

[0064] Furthermore, when the reactive compensation device is put into operation at the same time as the closing operation of the interconnecting circuit breaker, it should be avoided to cause instability in the regional power grid. Therefore, when determining the value range of the reactive compensation device capacity, the regional power grid voltage stability is taken as the optimization goal, and the value of the set multiple is determined; at the same time, the regional power grid voltage stability is also taken as the optimization goal, and the capacity of the reactive compensation devices put into operation is allocated, which not only makes the sum of the capacities of the reactive compensation devices put into operation within the value range, but also ensures that the reactive compensation devices put into operation will not cause instability in the regional power grid voltage.

[0065] In a non-limiting preferred embodiment, the sum of the inductive reactive powers Q of the impact loads simultaneously input is used as L-buChang The lower limit is the sum of the inductive reactive power of the impact loads that are put into use at the same time, Q L-buChang 110% of is taken as the upper limit to constitute the range of the capacity of the capacitive reactive power compensation device; first determine the type of the capacitive reactive power compensation device that is put into operation at the same time as the tie circuit breaker is closed, including but not limited to: capacitors, SVG, SVC; the sum of the capacitive reactive power compensation devices that are put into operation at the same time Q C-buChang Satisfy Q L-buChang C-buChang <1.1Q L-buChang To optimize the objective, the capacity is then allocated to each capacitive reactive compensation device according to the determined type of the capacitive reactive compensation device and based on the regional grid voltage stability constraint.

[0066] Step 4: When the sum of the active powers of the impact loads to be put into operation is within the value range of the impact load active powers, and the sum of the capacitive reactive power compensation devices to be put into operation is within the value range of the capacitive reactive power compensation devices, a closing signal is sent to the interconnecting circuit breaker, and a start signal is sent to the impact loads to be put into operation and the capacitive reactive power compensation devices to be put into operation at the same time; otherwise, return to step 2 and re-predict the impact current generated by the closing of the interconnecting circuit breaker.

[0067] Specifically, according to the impact load to be put into operation and the closing control interface of the reactive compensation device to be put into operation, including but not limited to state quantity control or communication control, select the appropriate control instruction issuing mode. The state quantity can be a 0-1 node signal or a gear signal; the communication control can select various communication protocols based on the IP protocol.

[0068] The present disclosure may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0069] ​A computer-readable storage medium may be a tangible device that can hold and store instructions used by an instruction execution device. A computer-readable storage medium may be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples of computer-readable storage media (a non-exhaustive list) include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disk read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, such as a punch card or a raised structure in a groove on which instructions are stored, and any suitable combination of the foregoing. As used herein, a computer-readable storage medium is not to be interpreted as a transient signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse through a fiber optic cable), or an electrical signal transmitted through a wire.

[0070] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, optical fiber transmissions, wireless transmissions, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in the computer-readable storage medium in each computing / processing device.

[0071] The computer program instructions for performing the operation of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-related instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages, such as Smalltalk, C++, etc., and conventional procedural programming languages, such as "C" language or similar programming languages. Computer-readable program instructions may be executed completely on a user's computer, partially on a user's computer, as an independent software package, partially on a user's computer, partially on a remote computer, or completely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., using an Internet service provider to connect via the Internet). In some embodiments, an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), may be customized by utilizing the state information of the computer-readable program instructions, and the electronic circuit may execute the computer-readable program instructions, thereby realizing various aspects of the present disclosure.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for using local load to assist synchronous grid connection, It is characterized in that The impact current generated by closing the interconnecting circuit breaker is predicted. When the predicted impact current value is not greater than the allowable impact current value of the interconnecting circuit breaker, the interconnecting circuit breaker closing operation is performed; otherwise, while the interconnecting circuit breaker closing operation is performed, the impact load and the reactive power compensation device are put into operation, wherein the active power of the impact load is used to compensate for the difference between the predicted impact current value and the allowable impact current value, and the reactive power of the impact load is compensated by the reactive power compensation device.

2. The method for synchronous grid connection using local load assistance according to claim 1, It is characterized in that While executing the closing operation of the interconnecting circuit breaker, the impact load and the capacitive reactive power compensation device are put into operation, and the capacitive reactive power compensation device is used to compensate the inductive reactive power of the impact load.

3. The method for synchronous grid connection using local load assistance according to claim 2, It is characterized in that Predict the impact current generated by closing the tie circuit breaker, including: Obtain the voltage and current history data of the tie circuit breaker during closing operation; obtain the system-side open circuit voltage data and the generation-side open circuit voltage data of the tie circuit breaker when the regional power grid is disconnected; Based on the real-time data obtained, the impact current generated by closing the tie circuit breaker is predicted.

4. The method for synchronous grid connection using local load assistance according to claim 3, It is characterized in that Based on the real-time data obtained, the impact current generated by closing the tie circuit breaker is predicted, including: When the frequency difference between the system side and the generation side of the tie circuit breaker is less than the frequency difference threshold, the synchronous closing judgment and control stage begins. Based on the system side equivalent circuit and the generation side equivalent circuit of the regional power grid, and using the voltage and current history data of the tie circuit breaker during closing operation, the system side impedance and the generation side impedance of the tie circuit breaker are determined respectively. The system-side open-circuit voltage data of the interconnecting circuit breaker when the regional power grid is disconnected is used as the voltage phasor of the ideal voltage source on the system side, and the generator-side open-circuit voltage data of the interconnecting circuit breaker when the regional power grid is disconnected is used as the internal potential phasor of the generator; According to the impedance on the system side, the impedance on the generator side, the potential phasor inside the generator and the voltage phasor of the ideal voltage source on the system side, the predicted value of the inrush current generated by closing the tie circuit breaker is calculated using the following relationship: In the formula, I r is the predicted value of the inrush current generated by closing the tie circuit breaker, is the potential phasor inside the generator, is the voltage phasor of the ideal voltage source on the system side, X s is the system side impedance, X g is the impedance on the generating side.

5. The method for synchronous grid connection using local load assistance according to claim 4, It is characterized in that The frequency difference threshold is set to 1.1 Hz.

6. The method for synchronous grid connection using local load assistance according to claim 2, It is characterized in that When the predicted value of the impact current is greater than the allowable value of the impact current of the interconnecting circuit breaker, the impact load and capacitive reactive power compensation device are put into operation at the same time as the interconnecting circuit breaker closing operation is performed, including: Compare the relationship between the predicted value of the impact current generated by the closing of the interconnecting circuit breaker and the allowable value of the impact current of the interconnecting circuit breaker. If the predicted value of the impact current is not greater than the allowable value of the impact current, execute the interconnecting circuit breaker closing operation; if the predicted value of the impact current is greater than the allowable value of the impact current, determine the capacity of the impact load and the capacity of the capacitive reactive power compensation device to be put into operation at the same time as the interconnecting circuit breaker is closed based on the difference between the predicted value of the impact current and the allowable value of the impact current.

7. The method for using local load to assist synchronous grid connection according to claim 6, It is characterized in that According to the difference between the predicted value of the impact current and the permissible value of the impact current, determine the capacity of the impact load and the capacity of the capacitive reactive power compensation device to be put into operation when the tie circuit breaker is closed, including: Calculate the difference between the predicted value of the impact current and the allowable value of the impact current as the impact current overflow; Calculate the active power overload using the inrush current overflow and set voltage; The active power overload is taken as the lower limit and the set multiple of the active power overload is taken as the upper limit to form the value range of the active power of the impact load; the sum of the active power of the impact load put into operation is taken as the optimization target to determine the capacity of the impact load put into operation simultaneously with the closing operation of the tie circuit breaker, and the sum of the inductive reactive power of the impact load put into operation simultaneously; The sum of the inductive reactive power of the impact loads put into operation at the same time is taken as the lower limit, and the set multiple of the sum of the inductive reactive power of the impact loads put into operation at the same time is taken as the upper limit, so as to form the value range of the capacity of the capacitive reactive compensation device; taking the sum of the capacitive reactive compensation device capacities put into operation within the value range as the optimization goal, the capacity of the capacitive reactive compensation device put into operation at the same time as the closing operation of the interconnecting circuit breaker is determined.

8. The method for synchronous grid connection using local load assistance according to claim 7, It is characterized in that The range of active power values ​​for impact load active power is formed by taking active power overload △P as the lower limit and 110% of active power overload as the upper limit. Determine the type of impact load that is put into operation at the same time as the tie circuit breaker closing operation, and take the sum of the active powers of the impact loads put into operation P buChang Satisfy △P <P buChang <1.1△P is the optimization target, and then active power is allocated to each impact load according to the type of impact load determined; Determine the capacity of each impact load according to the active power allocated to each impact load, determine the power factor according to the type of each impact load, and use the capacity and power factor of each impact load to determine the sum of the inductive reactive power Q of the impact loads put into use at the same time. L-buChang .

9. The method for using local load to assist synchronous grid connection according to claim 8, It is characterized in that The sum of the inductive reactive power of the impact loads that are put into operation at the same time is Q L-buChang The lower limit is 100% of the sum of the inductive reactive power of the impact loads put into operation at the same time, and the upper limit is 110% of the sum of the inductive reactive power of the impact loads put into operation at the same time, which constitutes the value range of the capacity of the capacitive reactive compensation device; First, determine the type of capacitive reactive power compensation device that is put into operation at the same time as the tie circuit breaker closing operation, and the sum of the capacitive reactive power compensation devices that are put into operation at the same time, Q C-buChang Satisfy Q L-buChang C-buChang <1.1Q L-buChang For the optimization purpose, the capacity is then allocated to each capacitive reactive power compensation device according to the determined type of the capacitive reactive power compensation device.​ 10. The method for using local load to assist synchronous grid connection according to claim 9, It is characterized in that When the sum of the active powers of the impact loads to be put into operation is within the value range of the impact load active powers, and the sum of the capacitive reactive power compensation devices to be put into operation is within the value range of the capacitive reactive power compensation devices, a closing signal is sent to the interconnecting circuit breaker, and a start signal is sent to the impact loads to be put into operation and the capacitive reactive power compensation devices to be put into operation at the same time; Otherwise, the impact current generated by closing the interconnecting circuit breaker is predicted again.

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