Intelligent grid connection device and method for wind power photovoltaic power station

Abstract

The invention relates to the field of electric power, in particular to an intelligent grid connection device and method for a wind power photovoltaic power station. The intelligent grid-connected device of the wind power photovoltaic power station can change the operation mode of the voltage stabilizing device according to the energy flow direction to adapt to the energy direction; the self-adaptive flexible voltage stabilizing device comprises a voltage control module and a current control module, and the current control module is located at the front end of the power supply compensation module and used for improving the three-phase imbalance phenomenon in the power transmission line, eliminating higher harmonics and conducting reactive compensation. All current and voltage adjusting devices are connected in parallel in a circuit, or the adjusting devices are separated in a main circuit through an isolation transformer, and the main circuit is not provided with any operation device.

Description

Technical Field

[0001] The present invention relates to the field of electric power, and in particular to an intelligent grid-connected device and method for a wind power and photovoltaic power station. Background Art

[0002] Current status of the confluence side of large-scale wind power and photovoltaic power stations:

[0003] Large-scale wind power and photovoltaic power stations occupy a large area. The power generation equipment and boosting equipment are far away from the boosting substation, and the distances vary, resulting in different line voltage drops. Due to the long distance between locations, different wind strengths, and different light, voltage fluctuations will occur, making the voltage of each bus line inconsistent. In photovoltaic power stations, clouds covering some photovoltaic panels will cause huge fluctuations in bus line voltage.

[0004] During actual operation, it was also found that the three-phase voltage was unbalanced, and sometimes the three-phase voltage unbalance rate reached 3%.

[0005] The existing power station has no voltage processing on the bus side, but is simply connected in parallel. This will cause bus line circulation, increase line losses, and in severe cases burn out equipment and lines, affecting the safe operation of the power station.

[0006] Due to the instability of wind power and photovoltaic power generation, the voltage fluctuation range of this type of power plant is large. The power grid company has strict voltage range requirements for power plants to access the grid. If it exceeds this range, it cannot access the grid. Therefore, it will cause the embarrassment of being able to generate electricity but not being able to transmit electricity, affecting the efficiency of the power plant.

[0007] The bus lines in power stations generally use 10kV and 35kV voltage levels. Therefore, it is necessary to develop 10kV and 35kV voltage stabilizing equipment to meet the needs of various power stations.

[0008] On November 20, 2024, a search was conducted in the Chinese Patent Publication Database with "grid connection and voltage stabilization and current stabilization and direction and coupling and compensation" as the abstract keywords, and the option of allowing synonym expansion was checked, but no relevant literature was found.

[0009] Then, the search scope was expanded, with "wind power and photovoltaic and voltage stabilization and grid connection" as the abstract keywords, and the option to allow synonym expansion was checked. A search was conducted in the Chinese Patent Publication Database, and the following were found: CN114188968A Isolated microgrid integration technology containing energy storage and distributed energy, which involves voltage stabilizers, biogas power generation, hydropower, photovoltaic off-grid inverters, dual power switching switches, wind power grid-connected inverters and wind turbines; and is unrelated to this patent; CN103956772A An isolated grid photovoltaic, wind and oil hybrid power generation system; this technology involves photovoltaic units, wind power units, oil-electric units, energy storage units, AC current sensors, surplus power charging units, etc.; and is unrelated to this patent.

[0010] On November 20, 2024, an abstract search for "grid connection and voltage stabilization and current stabilization and direction and coupling and compensation" was conducted on China National Knowledge Infrastructure, and no relevant literature was found.

[0011] On November 20, 2024, a search was conducted on the website of the United States Patent and Trademark Office for "Grid connection with voltage stabilization with current stabilization with direction with coupling with compensation", and no relevant literature was found; the search URL was https: / / ppubs.uspto.gov / pubwebapp / .

[0012] On November 20, 2024, a search was conducted on the Korean Patent Office for "Grid connection and voltage stabilization and current stabilization and direction and coupling and compensation", and no relevant literature was found; the search URL was http: / / eng.kipris.or.kr / enghome / main.jsp.

[0013] On November 20, 2024, a search was conducted on WIPO's https: / / patentscope2.wipo.int / for "Grid connection and voltage stabilization and current stabilization and direction and coupling and compensation", and no relevant documents were found.

[0014] On November 20, 2024, a search was conducted on the Japan Patent Office website https: / / www.j-platpat.inpit.go.jp / for "Grid connection and voltage stabilization and current stabilization and direction and coupling and compensation", but no relevant literature was found.

[0015] Completely different from the concept of this patent. Summary of the invention

[0016] Purpose of the invention: To provide a more effective intelligent grid-connected device and method for wind power and photovoltaic power stations. The specific purpose can be seen in the multiple substantial technical effects of the specific implementation part.

[0017] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0018] An intelligent grid-connected device for a wind power and photovoltaic power station, characterized in that:

[0019] The intelligent grid-connected device of the wind power and photovoltaic power station can change the operation mode of the voltage stabilizing device according to the energy flow direction and adapt to the energy direction;

[0020] The adaptive flexible voltage stabilization device includes a voltage control module;

[0021] The voltage control module is located at the back end of the system access and is used to compensate the voltage of the transmission line to the standard value. Since the three-phase voltage is regulated independently in the voltage regulation module, each phase is compensated for the single-phase voltage through the voltage compensation module and the voltage coupling module. When the sensor automatically detects that the voltage at both ends of the power supply is lower than the standard voltage range, the controller will control the IGBT device of the voltage compensation module to work according to the range of the voltage value at this time to achieve a smooth voltage compensation value, which is coupled to the line and superimposed with the original voltage, so as to achieve the grid-connected bus voltage of the rated voltage ±1%.

[0022] A further technical solution of the present invention is that the adaptive flexible voltage stabilization device also includes a current control module, which is located at the front end of the power compensation module and is used to improve the three-phase imbalance in the transmission line, eliminate high-order harmonics, and perform reactive power compensation.

[0023] A further technical solution of the present invention is that the current control module detects the harmonic, reactive and negative sequence current components in the compensation object current through the command current operation circuit, and then the compensation current generating circuit generates the actual compensation current according to the command signal of the compensation current obtained by the command current operation circuit. The compensation current offsets the negative sequence current to be compensated in the load current, and finally the desired power supply current is obtained; thereby achieving the purpose of compensating the negative sequence component and the reactive current on the system side.

[0024] A method for intelligent grid-connection of a wind power and photovoltaic power station, characterized in that the method comprises the following steps:

[0025] At the junction point of the step-up substation, an adaptive flexible voltage stabilizer is added to each line. The adaptive flexible voltage stabilizer can control the voltage amplitude deviation of each line within 1%, and the voltage value is ±1% of the rated voltage, and can also ensure that the voltage phase angle of each line is the same. The junction conductor is first connected to the voltage stabilizing device, and then connected to the junction switch of the step-up substation to ensure that the junction bus voltage value is within the range of ±1% of the rated voltage.

[0026] A further technical solution of the present invention is that the device automatically detects the current and voltage signals of the distribution network line, and the controller analyzes and calculates the positive sequence, negative sequence and zero sequence currents. A current regulating device generates a current of corresponding magnitude in the opposite direction except the positive sequence current, which is injected into the main circuit through the transformer T1 to offset the other currents in the main circuit except the positive sequence current, thereby achieving the purpose of power factor ≥ 0.95 and three-phase current imbalance rate ≤ 2%; the device takes the set voltage as the target, and the controller controls the voltage regulating device to generate the voltage to be compensated, which is coupled to the line through the isolation transformer T2 to stabilize the voltage to the set value; the voltage compensation adopts a single-phase compensation method with a compensation accuracy of 1%, thereby realizing three-phase voltage imbalance compensation, and making the output voltage within the set range of ±0.5%, and realizing the voltage difference of each line within 1%.

[0027] A further technical solution of the present invention is that an adaptive flexible voltage stabilizer is installed on each line, any one adaptive flexible voltage stabilizer is in the host operation mode, and the other adaptive flexible voltage stabilizers are in the auxiliary operation mode. The auxiliary devices automatically output voltage according to the phase angle of the host device to ensure that the phase angles of multiple devices are the same.

[0028] A further technical solution of the present invention is that the adaptive flexible voltage stabilization device has an energy direction detection function, can timely determine the voltage compensation direction according to the energy flow direction, and adaptively stabilize the voltage according to the energy flow direction.

[0029] A further technical solution of the present invention is that the adaptive flexible voltage stabilization device is connected in parallel in the line, or the regulating device is separated from the main line by an isolation transformer, and the main line has no operating devices; the voltage response time is not higher than 40ms, and the current response time is less than 5ms, and the response is rapid.

[0030] A further technical solution of the present invention is that it also includes the following central control system control strategy, which is based on the central control system of edge computing, with carrier communication or 5G communication as the communication carrier, and the output voltage set by the equipment as the control target. By using the control terminal, receiving and execution terminal, and control software, the voltage stabilizing device in each line can operate in local operation and remote control mode. It can independently process the parameters within the range of this equipment, and can operate according to the commands of the central control system and operate in the central control mode, thereby realizing the function of randomly determining the operation mode of one host machine and the operation mode of the others for multiple devices.

[0031] A further technical solution of the present invention is that the adaptive flexible voltage stabilization device is suitable for the busbar connection points in large wind power and photovoltaic power stations with a voltage fluctuation range of 10kV to 35kV of ±10%-±30%.

[0032] The present invention adopting the above technical scheme has the following beneficial effects compared with the prior art: it can ensure that the voltage amplitude and phase angle of each branch in the wind power and photovoltaic station are consistent when connected to the grid, solve the problems of circulating current and current delivery between the branches, improve the safety of equipment in the station, and reduce the line loss in the station by more than 10%; because the grid-connected voltage can be set within ±2.5% of the rated voltage when connected to the grid, it is guaranteed that under any circumstances, the substation outlet voltage meets the grid-connected voltage requirements of the power supply company, avoiding the inability to supply electricity to the grid due to unqualified voltage, resulting in wind and light abandonment, at least increasing the grid-connected rate of the power station by more than 10%, and increasing the efficiency of the power station by at least 10%. This technology has a broad market space. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to further illustrate the present invention, the following is further described in conjunction with the accompanying drawings:

[0034] Figure 1 A layout diagram of the invention;

[0035] Figure 2 The main circuit structure diagram of the invention;

[0036] Figure 3 A module diagram of the invention;

[0037] Figure 4 It is a schematic diagram of the single-phase voltage compensation principle;

[0038] Figure 5 It is the equivalent circuit diagram of the current control module;

[0039] Figure 6 This is a front view of the whole machine;

[0040] Figure 7 A side view of the overall appearance. DETAILED DESCRIPTION

[0041] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. In the description of the present invention, it should be noted that the orientation or position relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", "top", "bottom", etc. is based on the orientation or position relationship shown in the accompanying drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or it can be the internal connection of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood in specific circumstances.

[0042] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0043] This patent provides a variety of parallel solutions. The different expressions are improved solutions or parallel solutions based on the basic solution. Each solution has its own unique characteristics. In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. The fixing method not described in the text can be any fixing method such as thread fixing, bolt fixing or glue bonding.

[0044] Due to the operating conditions of wind power and photovoltaic power, when generating electricity, the energy direction is from the power generation side to the grid side. When not generating electricity, the energy direction is from the grid side to the power generation side. Therefore, the voltage stabilizer must change the operating mode of the voltage stabilizer according to the energy flow direction and adapt to the energy direction.

[0045] Solution

[0046] At the junction of the booster substation, an adaptive flexible voltage stabilizer is added to each line. The voltage stabilizer can control the voltage amplitude deviation of each line within 1%, and the voltage value is ±1% of the rated voltage, and can also ensure that the voltage phase angle of each line is the same. The bus conductor is first connected to the voltage stabilizer and then connected to the bus switch of the booster substation to ensure that the bus voltage value is within the range of ±1% of the rated voltage. Figure 1 ;

[0047] The system has the following features:

[0048] 1. The three-phase voltage unbalance rate is less than 1%

[0049] The three-phase imbalance rate of each line can be controlled by this device to achieve balanced output three-phase voltage, with an imbalance rate of less than 1%.

[0050] 2. Voltage balance of each line

[0051] There are multiple bus lines, and it is difficult to make the voltage consistent at the bus point. After passing through the equipment, the voltage difference of each line is less than 1%.

[0052] 3. Adaptive energy flow and voltage stabilization

[0053] It can automatically detect the direction of energy flow, automatically adapt to the direction of energy flow, and determine the direction of voltage stabilization, that is, when generating electricity, it stabilizes the voltage on the grid side, and when purchasing electricity from the grid side, it stabilizes the voltage on the original generating side.

[0054] 4. Stabilize the output voltage value of the step-up transformer

[0055] It can ensure that the output voltage of the step-up transformer meets the requirements of the power supply company for access to the Internet, ensure that electricity can be supplied to the Internet at any time, and improve the economic benefits of power generation.

[0056] 5. Reactive power compensation function

[0057] Due to the distributed parameters of the line, reactive current will be generated, and the device can compensate for the reactive current.

[0058] 6. Equipment response time: 40ms.

[0059] 7. The equipment adopts fully automatic maintenance-free design.

[0060] 8. Equipment life is 30 years.

[0061] Intelligent grid-connected device

[0062] 1. System overall plan

[0063] This device automatically detects the current and voltage signals of the distribution network line, and the controller analyzes and calculates the positive sequence, negative sequence, and zero sequence currents. The current regulating device generates a current of the corresponding magnitude in the opposite direction except the positive sequence current, which is injected into the main circuit through the transformer T1 to offset the other currents in the main circuit except the positive sequence current, thereby achieving the purpose of power factor ≥ 0.95 and three-phase current imbalance rate ≤ 2%; the device takes the set voltage as the target, and the controller controls the voltage regulating device to generate the voltage to be compensated, which is coupled to the line through the isolation transformer T2 to stabilize the voltage to the set value. The voltage compensation adopts a single-phase compensation method with a compensation accuracy of 1%, thereby realizing three-phase voltage imbalance compensation, and making the output voltage within the set range of ±0.5%, and achieving the voltage difference of each line within 1%.

[0064] The device has an energy direction detection function, which can timely determine the voltage compensation direction according to the energy flow direction and adaptively adjust the energy flow direction for voltage stabilization.

[0065] This device is installed on each line. Any one of them is in the host operation mode, and the others are in the auxiliary operation mode. It automatically outputs voltage according to the phase angle of the host to ensure that the phase angles of multiple units are the same.

[0066] The main circuit structure diagram is as follows Figure 2 ;

[0067] This device is a power electronic device with IGBT and high-power thyristor as core components. It is a typical application device of flexible power supply technology, which can solve the functions of voltage value, phase angle and power factor of each circuit at the same time. The device has a three-level bypass system with a bypass response time of 0.1ms. After a fault, the device automatically exits operation without affecting the normal power supply of the line.

[0068] 2. Main device selection

[0069] The main IGBT and high-power thyristor devices are made by Germany's Infineon or internationally renowned brands with high voltage resistance and high performance. The 2-6 times current margin increases the safety of the device.

[0070] The bus capacitor uses a film capacitor, which has strong ripple current resistance and a longer service life than electrolytic capacitors.

[0071] 3. Analysis of compensation algorithm principle (reference Figure 3 )

[0072] This technology is an innovative power electronics integration technology. It integrates the system through power electronics technology to solve the three-phase voltage imbalance and the voltage stability of each line. In order to achieve comprehensive compensation of voltage increase and power quality at the same time, the device as a whole consists of two major parts: voltage control module and current control module.

[0073] The voltage control module is located at the back end of the system access and is used to compensate the voltage of the transmission line to the standard value. Since the three-phase voltage is regulated independently in this voltage regulation module, the operation principle of the other two phases can be inferred by analyzing one phase. The single-phase schematic diagram is shown in Figure 4 shown.

[0074] When the sensor automatically detects that the voltage at both ends of the power supply is lower than the standard voltage range, the controller will control the IGBT device of the voltage compensation module to work according to the voltage value range at this time to achieve a smooth voltage compensation value, which is coupled to the line and superimposed with the original voltage, thereby achieving a grid-connected bus voltage of the rated voltage ±1%.

[0075] The current control module is located at the front end of the power compensation module, and is used to improve the three-phase imbalance in the transmission line, eliminate high-order harmonics, and perform reactive power compensation. Its topology and principle diagram are shown in the figure below. Figure 5 As shown;

[0076] The controller detects the harmonic, reactive and negative sequence current components in the compensation object current through the command current operation circuit, and then the compensation current generation circuit generates the actual compensation current according to the command signal of the compensation current obtained by the command current operation circuit. The compensation current offsets the negative sequence current to be compensated in the load current, and finally obtains the desired power supply current. Thus, the purpose of compensating the negative sequence component and reactive current on the system side is achieved.

[0077] 4. Central control system and control strategy

[0078] The central control system based on edge computing uses carrier communication or 5G communication as the communication carrier, and the equipment output voltage (settable) as the control target. It uses control terminals, receiving and execution terminals, and control software. The voltage stabilizers in each line can operate in local operation and remote control modes. It can independently process parameters within the range of this equipment, and can also operate according to the commands of the central control system and operate in the central control mode, realizing the function of randomly determining one host operation mode for multiple devices and the others in auxiliary operation mode.

[0079] Main functions and performance

[0080] 1) Voltage is stable to ±0.5% of the set voltage

[0081] 2) The three-phase voltage unbalance rate is less than 1%

[0082] 3) It is suitable for linear compensation of inductive and capacitive loads, and can realize fast and smooth conversion of capacitive and inductive loads, and the power factor is compensated to 0.95 (adjustable).

[0083] 4) Eliminate the system negative sequence current and zero sequence current, and make the system current three-phase balanced

[0084] 5) Reduce line loss

[0085] 6) Automatically detect energy direction and automatically adapt to energy flow and stabilize voltage

[0086] 8) Complete protection function

[0087] 9) Friendly human-machine interface

[0088] 10) Flexible communication interface, which can remotely monitor the equipment operation status and save the operation data

[0089] 11) Bypass dynamic response time ≤ 0.1ms

[0090] 12) Allow short-term overload capacity 1.2 times

[0091] Advantages of voltage stabilizer

[0092] All current and voltage regulators are connected in parallel in the circuit, or separated from the main circuit by an isolation transformer. The main circuit does not have any operating devices. The voltage response time is no more than 40ms, the current response time is less than 5ms, and the response time is

[0093] fast;

[0094] Ensure that the line does not shut down when the voltage or current is adjusted;

[0095] When equipment fails, it does not affect the power supply of the line, making the system safer and more reliable;

[0096] Adopt the flexible coordinated control system of the whole line comprehensive power quality to achieve flexible power supply

[0097] electricity;

[0098] Use power electronic device pre-diagnosis system to perform fault self-diagnosis on power electronic devices in the system;

[0099] Can reduce a large number of maintenance personnel and maintenance workload;

[0100] The equipment used in this technology has a design life of 30 years.

[0101] Environmental requirements

[0102] Rated voltage: (10kV---35kV) ±10% (optional)

[0103] Relative humidity: monthly average value not more than 90% (25°C), no condensation

[0104] Rated frequency: 50Hz

[0105] Altitude: <5000m

[0106] Rated capacity: 1000KVA-25000KVA (customized according to user requirements)

[0107] Protection level: IP43 (customizable)

[0108] Storage temperature: -40℃--+65℃

[0109] Earthquake intensity: 8 degrees

[0110] Operating temperature: -20℃--+40℃

[0111] Pollution level: Level IV

[0112] Cooling method: forced air cooling

[0113] 5. Equipment parameter selection

[0114] Adaptive flexible voltage stabilizer is generally applicable to the grid connection point of the bus circuit in large wind power and photovoltaic power stations with a voltage fluctuation range of ±10% (customizable) from 10kV to 35kV. It is used to stabilize the line voltage, three-phase voltage imbalance, reduce bus line losses, improve power station operation safety, and solve power quality problems. The voltage level, fluctuation range (up to +30% / -10% depending on the capacity), device capacity, external dimensions, installation method, etc. of the device can be determined according to the user's on-site conditions.

[0115] Comparison with other devices

[0116] The commonly used solutions for voltage three-phase imbalance and line voltage deviation control are SVG adjustment, DVR adjustment, and voltage stabilization device adjustment. The following is an analysis of the characteristics and applicable scenarios of various voltage regulation methods.

[0117] SVG mode regulation: Reactive current is injected into the line through the SVG device to support the line voltage. Due to the large energy of the system, the voltage stability is achieved by injecting reactive current, which requires a large capacity and the support effect is uncontrollable. The SVG in the system is mainly used to protect the grid from power failure on the power generation side and quickly lower the grid voltage. It has no effect on the voltage imbalance of the bus branch and the different voltages of each line.

[0118] DVR mode adjustment: This device uses an energy storage unit to add a voltage to the system when the line voltage is lower than the set value, so as to achieve the goal of three-phase voltage balance and equal voltage value of each line. Since this device requires an energy storage unit, it is best used in voltage disturbance conditions, that is, the conditions of charging with a small current and working for a short time. This application scenario requires long-term and high-power operation, which will inevitably increase the charging circuit power, energy storage capacity, large volume, high cost, and average cost performance. The device is connected in series in the line, which increases the difficulty of transformation.

[0119] Voltage stabilization device mode adjustment: The device extracts energy through a parallel transformer in the system and steps down the voltage to 400V. Through the AC-DC-AC mode, it generates compensation current and compensation voltage respectively, instantly compensates for the line reactive current and compensation voltage, and achieves the goal of three-phase voltage balance and equal voltage value on each line. The energy storage part of the device does not need to be considered, thereby greatly reducing the size of the equipment, reducing the equipment cost, improving the safety of equipment operation, and reducing the operation and maintenance costs.

[0120] The use of this technology can ensure that the voltage amplitude and phase angle of each branch in the wind power and photovoltaic station are consistent when connected to the grid, solve the problems of circulating current and current delivery between branches, improve the safety of equipment in the station, and reduce the line loss in the station by more than 10%; because the grid-connected voltage can be set within ±2.5% of the rated voltage when connected to the grid, it is guaranteed that under any circumstances, the substation outlet voltage meets the grid-connected voltage requirements of the power supply company, avoiding the inability to supply electricity to the grid due to unqualified voltage, resulting in wind and solar power abandonment, at least increasing the grid-connected rate of the power station by more than 10%, and increasing the efficiency of the power station by at least 10%. This technology has a broad market space.

[0121] The basic principle, main features and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the protection required.

Claims

1. An intelligent grid-connected device for a wind power and photovoltaic power station, characterized in that: The intelligent grid-connected device of the wind power and photovoltaic power station can change the operation mode of the voltage stabilizing device according to the energy flow direction and adapt to the energy direction; The adaptive flexible voltage stabilization device includes a voltage control module; The voltage control module is located at the back end of the system access and is used to compensate the voltage of the transmission line to the standard value. Since the three-phase voltage is regulated independently in the voltage regulation module, each phase is compensated for the single-phase voltage through the voltage compensation module and the voltage coupling module. When the sensor automatically detects that the voltage at both ends of the power supply is lower than the standard voltage range, the controller will control the IGBT device of the voltage compensation module to work according to the range of the voltage value at this time to achieve a smooth voltage compensation value, which is coupled to the line and superimposed with the original voltage, so as to achieve the grid-connected bus voltage of the rated voltage ±1%.

2. The intelligent grid-connected device for wind power and photovoltaic power station according to claim 1, characterized in that: The adaptive flexible voltage stabilization device also includes a current control module, which is located at the front end of the power compensation module and is used to improve the three-phase imbalance in the transmission line, eliminate high-order harmonics, and perform reactive power compensation.

3. The intelligent grid-connected device for wind power and photovoltaic power station according to claim 2, characterized in that: The current control module detects the harmonic, reactive and negative sequence current components in the compensation object current through the command current operation circuit, and then the compensation current generation circuit generates the actual compensation current according to the command signal of the compensation current obtained by the command current operation circuit. The compensation current offsets the negative sequence current to be compensated in the load current, and finally obtains the desired power supply current; Thereby achieving the purpose of compensating negative sequence components and reactive current on the system side.

4. A method for intelligent grid connection of wind power and photovoltaic power station, characterized in that: The intelligent grid-connected device for wind power and photovoltaic power stations according to any one of claims 1 to 3 comprises the following method: At the junction point of the step-up substation, an adaptive flexible voltage stabilizer is added to each line. The adaptive flexible voltage stabilizer can control the voltage amplitude deviation of each line within 1%, and the voltage value is ±1% of the rated voltage, and can also ensure that the voltage phase angle of each line is the same. The junction conductor is first connected to the voltage stabilizing device, and then connected to the junction switch of the step-up substation to ensure that the junction bus voltage value is within the range of ±1% of the rated voltage.

5. The intelligent grid-connected method for wind power and photovoltaic power station according to claim 4, characterized in that: This device automatically detects the current and voltage signals of the distribution network line, and the controller analyzes and calculates the positive sequence, negative sequence and zero sequence currents. The current regulating device generates a current of corresponding magnitude in the opposite direction except the positive sequence current, which is injected into the main circuit through the transformer T1 to offset the other currents in the main circuit except the positive sequence current, thereby achieving the purpose of power factor ≥ 0.95 and three-phase current imbalance rate ≤ 2%; the device takes the set voltage as the target, and the controller controls the voltage regulating device to generate the voltage to be compensated, which is coupled to the line through the isolation transformer T2 to stabilize the voltage to the set value; the voltage compensation adopts the single-phase compensation method with a compensation accuracy of 1%, thereby realizing the three-phase voltage imbalance compensation, and making the output voltage within the set range of ±0.5%, and realizing the voltage difference of each line within 1%.

6. The intelligent grid-connected method for wind power and photovoltaic power station according to claim 4, characterized in that: One adaptive flexible voltage stabilizer is installed on each line. Any one adaptive flexible voltage stabilizer is in the host operation mode, and the other adaptive flexible voltage stabilizers are in the auxiliary operation mode. The auxiliary devices automatically output voltage according to the phase angle of the host to ensure that the phase angles of multiple devices are the same.

7. The intelligent grid-connected method for wind power and photovoltaic power station according to claim 4, characterized in that: The adaptive flexible voltage stabilization device has the function of energy direction detection, which can timely determine the voltage compensation direction according to the energy flow direction, and adaptively stabilize the voltage according to the energy flow direction.

8. The intelligent grid-connected method for wind power and photovoltaic power station according to claim 4, characterized in that: The adaptive flexible voltage stabilizer is connected in parallel in the line, or the regulating device is separated from the main line through an isolation transformer, and the main line has no operating devices; the voltage response time is no higher than 40ms, and the current response time is less than 5ms.

9. The intelligent grid-connected method for wind power and photovoltaic power station according to claim 4, characterized in that: It also includes the following central control system control strategy, which is based on the edge computing central control system, with carrier communication or 5G communication as the communication carrier, and the output voltage set by the equipment as the control target. It uses the control terminal, receiving and execution terminal, and control software. The voltage stabilizer in each line can work in local operation and remote control mode. It can independently process the parameters within the range of this equipment, and can operate according to the commands of the central control system and operate in the central control mode, so as to realize the function of randomly determining the operation mode of one host machine and the operation mode of the others for multiple devices.

10. The intelligent grid-connected method for wind power and photovoltaic power station according to claim 4, characterized in that: The adaptive flexible voltage stabilizer is suitable for the grid connection points of the busbars in large wind power and photovoltaic power stations with a voltage fluctuation range of 10kV to 35kV of ±10%-±30%.

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