A grid-connected control method and system for an active distributed intelligent microgrid

Abstract

The present application belongs to the technical field of distributed power grid, and particularly relates to a grid-connection control method and system of an active distributed intelligent microgrid. The method comprises: when the active distributed intelligent microgrid meets the starting grid-connection condition, the microgrid is controlled to grid-connection as follows: 1) adjusting the voltage amplitude and frequency of the microgrid to the range allowed for grid-connection, and adjusting the phase difference between the microgrid waveform and the power grid waveform to a decreasing trend, and then performing step 2); 2) calculating the time difference between the current time and the time of the next synchronous forward zero-crossing point, the synchronous forward zero-crossing point being the synchronous forward zero-crossing point of the microgrid waveform and the power grid waveform; and judging whether the time difference is within the time range allowed for grid-connection, if yes, then grid-connection is performed; otherwise, when the time difference is greater than the upper limit of the time range allowed for grid-connection, waiting until the time difference is within the time range allowed for grid-connection, and when the time difference is less than the lower limit of the time range allowed for grid-connection, performing step 1).

Description

Technical Field

[0001] This invention belongs to the field of distributed power grid technology, specifically relating to a grid connection control method and system for an active distributed smart microgrid. Background Technology

[0002] Distributed smart microgrids, especially smart microgrids, as local power grids integrating distributed power sources, energy storage systems, and controllable loads, have become key supports for improving renewable energy absorption capacity, enhancing energy efficiency, and strengthening power system reliability due to their core advantage of flexible switching between grid-connected and off-grid modes. Their applications in scenarios such as "hydrogen-solar complementary" power generation in industrial parks and "fishery-solar-storage" power generation in agriculture have demonstrated their significant value in ensuring stable power supply and promoting carbon emission reduction.

[0003] The current mainstream grid-connected control adopts a synchronous regulation strategy. The core process includes: the microgrid controller detects the status of the main grid and its internal operation to confirm the grid connection conditions; the grid-connected main control unit switches from V / F control to pre-synchronization mode; the synchronous control device calculates the voltage, frequency, and phase deviations and adjusts the energy storage system output to eliminate the deviations; and the system accurately closes the circuit after meeting the closing thresholds (such as voltage difference <5%, frequency difference <0.2Hz, and phase difference <10°). Finally, after the microgrid is connected to the grid, the grid-connected main control unit quickly switches to PQ control to achieve power exchange.

[0004] For example, Chinese invention patent application CN114784869A, published on July 22, 2022, proposes a technical means to adjust the voltage difference, frequency difference, and phase difference between the smart microgrid and the power grid to within the allowable range for grid connection before connecting to the grid.

[0005] However, this grid connection method faces several challenges in large-scale local independent power grid grid connection control scenarios where the grid connection point and the main control unit are geographically dispersed and multiple distributed multi-grid main control units exist. These challenges include communication delays leading to synchronization deviations in the main control units, communication delay errors causing asynchronous adjustments among multiple main control units that disrupt synchronization conditions, and fluctuations and oscillations easily triggered by the switching of the operating modes of the grid-connecting main control units during the grid connection process. Ultimately, this results in difficulties in synchronizing the distributed smart microgrid with the large power grid, making it difficult to meet grid connection conditions and increasing the likelihood of grid connection failure. Summary of the Invention

[0006] The purpose of this invention is to provide a grid-connected control method and system for an active distributed smart microgrid, in order to solve the technical problem of grid connection failure caused by the difficulty in pre-synchronizing the distributed smart microgrid and the grid voltage in scenarios where the grid connection point and the main control unit are far apart and there are multiple distributed multi-network main control units.

[0007] To address the aforementioned technical problems, this invention provides a grid-connected control method for an active distributed intelligent microgrid, the method comprising:

[0008] When an active distributed intelligent microgrid meets the start-up and grid connection conditions, the microgrid is controlled as follows:

[0009] 1) Determine whether the voltage amplitude and frequency of the microgrid are within the allowable range for grid connection and whether the phase difference between the microgrid waveform and the grid waveform is decreasing. If so, proceed to step 2). Otherwise, adjust the voltage amplitude and frequency of the microgrid to the allowable range for grid connection, and adjust the phase difference between the microgrid waveform and the grid waveform to a decreasing trend before proceeding to step 2).

[0010] 2) Calculate the time difference between the current time and the next synchronous positive zero-crossing point, where the synchronous positive zero-crossing point is the synchronous positive zero-crossing point of the microgrid waveform and the power grid waveform; and determine whether the time difference is within the allowed time range for grid connection. If so, grid connection is performed; otherwise, if the time difference is greater than the upper limit of the allowed time range for grid connection, wait until the time difference is within the allowed time range for grid connection; if the time difference is less than the lower limit of the allowed time range for grid connection, execute step 1).

[0011] Furthermore, the time difference between the current time and the next synchronous positive zero-crossing time is calculated as follows: Based on the formula below, the time difference between M and N is minimized. This is the time difference between the current time and the next synchronous positive zero crossing time;

[0012]

[0013] In the formula, For the power grid frequency, For microgrid frequencies, For the current time, This represents the initial phase of the grid voltage waveform. This represents the initial phase of the microgrid voltage waveform. M and N represent the time difference between the current time and the next positive zero-crossing time of synchronization, where M and N are both non-negative integers.

[0014] Furthermore, the method for calculating the time difference between the current time and the next synchronous positive zero-crossing time includes:

[0015] Calculate the time remaining until the next positive zero crossing of the power grid;

[0016] To determine whether the next positive zero-crossing point of the power grid is also the positive zero-crossing point of the microgrid, if it is, the time difference between the current time and the next synchronous positive zero-crossing point is equal to the time remaining until the next positive zero-crossing point of the power grid. If the next positive zero-crossing point is not the positive zero-crossing point of the microgrid, the time difference between the current time and the next synchronous positive zero-crossing point is as follows:

[0017]

[0018]

[0019] In the formula, The time difference between the current time and the next positive zero-crossing time. For the power grid frequency, This is the time until the next positive zero crossing of the power grid. Microgrid frequency, For the current time, This represents the initial phase of the microgrid voltage waveform.

[0020] Furthermore, the method for calculating the time remaining until the next positive zero crossing of the power grid is as follows:

[0021]

[0022] In the formula, This is the time until the next positive zero crossing of the power grid. For the power grid frequency, For the current time, This represents the initial phase of the grid voltage waveform.

[0023] Furthermore, the permitted time range for grid connection is: , among which, T b For the lead compensation time, T k The allowable time for grid connection to be ahead of or behind schedule.

[0024] Furthermore, the method for adjusting the voltage amplitude and frequency of the microgrid to within the allowable range for grid connection, and adjusting the phase difference between the microgrid waveform and the grid waveform to a decreasing trend, is as follows:

[0025] First, adjust the microgrid voltage and frequency to the allowable range for grid connection, and then adjust the phase difference between the microgrid waveform and the grid waveform to a decreasing trend.

[0026] Furthermore, the method for adjusting the voltage amplitude and frequency of the microgrid to the allowable range for grid connection is as follows: by performing active and reactive power compensation control on the controlled power sources within the microgrid, the voltage amplitude and frequency of the microgrid are adjusted to the allowable range for grid connection.

[0027] Furthermore, before the microgrid is officially put into operation, the pre-lead compensation time is the closing response time of the grid-connected circuit breaker obtained from the trial operation test; after the microgrid is officially put into operation, the pre-lead compensation time is the closing response time of the grid-connected circuit breaker during the actual closing process in actual operation.

[0028] Furthermore, the permissible grid connection lead or lag time T k The calculation method is as follows:

[0029]

[0030] In the formula, The frequency difference between the power grid and the microgrid. This refers to the phase difference allowed for grid connection.

[0031] Furthermore, the method to adjust the phase difference between the microgrid waveform and the grid waveform to a decreasing trend is as follows: by increasing the microgrid frequency, the phase of the active distributed smart microgrid waveform catches up with the phase of the grid waveform, thereby adjusting the phase difference between the active distributed smart microgrid waveform and the grid waveform to a decreasing trend, and then restoring the microgrid frequency.

[0032] Furthermore, when the phase difference between the waveform of the active distributed smart microgrid and the waveform of the power grid... At that time, the real-time phase difference between the two waveforms Trend of change To increase the trend, when the phase difference between the waveform of the active distributed smart microgrid and the power grid waveform... At that time, the real-time phase difference between the two waveforms Trend of change To reduce the trend, K is a non-negative integer.

[0033] The beneficial effects of this invention are as follows: After initial voltage and frequency regulation of the microgrid, this invention finds the synchronous zero-crossing point of the microgrid and grid waveforms, and performs grid connection near this point. This reduces the deviation between the microgrid and the grid during grid connection, improving the stability of the connected microgrid operation. Simultaneously, it does not require the microgrid and grid to have the same frequency and phase, allowing for different voltage waveforms between the microgrid and the grid. This enables grid connection control for distributed smart microgrids that are difficult to regulate due to multiple sources, improving their grid connection success rate and operational stability. It eliminates the need for pre-synchronous voltage source regulation and operating mode switching, effectively avoiding problems such as grid connection information transmission delays, asynchronous regulation of multiple grid units, and fluctuations caused by mode switching. It is particularly suitable for scenarios with multiple dispersed grid units and grid connection points located far apart from the grid units, providing fast and stable switching control support for the off-grid to on-grid transition of active smart grids, ensuring safe and reliable grid operation. Meanwhile, this method does not involve switching the operating mode of the main control unit of the grid connection, thus avoiding the problem of fluctuations and oscillations that are easily caused by switching the operating mode of the main control unit of the grid connection during the grid connection process of existing technologies.

[0034] To address the aforementioned technical problems, the present invention also provides a grid-connected control system for an active distributed smart microgrid, comprising a local execution layer, a local decision-making layer, and a system control layer. The local execution layer is used to execute the grid connection and disconnection actions of the active distributed smart microgrid, and the local decision-making layer is used to collect the status of the microgrid and the power grid and send it to the system control layer.

[0035] When an active distributed smart microgrid meets the start-up and grid connection conditions, the system control layer determines whether the voltage amplitude and frequency of the microgrid are within the allowable range for grid connection and whether the phase difference between the microgrid waveform and the grid waveform is decreasing. If so, it sends a quasi-grid connection command to the local decision layer; otherwise, it adjusts the voltage amplitude and frequency of the microgrid to the allowable range for grid connection, adjusts the phase difference between the microgrid waveform and the grid waveform to a decreasing trend, and then sends a quasi-grid connection command to the local decision layer.

[0036] The local decision-making layer is also used to calculate the time difference between the current time and the next synchronous positive zero-crossing point after receiving the quasi-grid connection command. The synchronous positive zero-crossing point is the synchronous positive zero-crossing point of the microgrid waveform and the grid waveform. It also determines whether the time difference is within the allowed time range for grid connection. If so, grid connection is performed. Otherwise, when the time difference is greater than the upper limit of the allowed time range for grid connection, it waits until the time difference is within the allowed time range for grid connection. When the time difference is less than the lower limit of the allowed time range for grid connection, the system control layer re-determines whether the voltage amplitude and frequency of the microgrid are within the allowed range for grid connection and whether the phase difference between the microgrid waveform and the grid waveform is decreasing.

[0037] Furthermore, the time difference between the current time and the next synchronous positive zero-crossing time is calculated as follows: Based on the formula below, the time difference between M and N is minimized. This is the time difference between the current time and the next synchronous positive zero crossing time;

[0038]

[0039] In the formula, For the power grid frequency, Microgrid frequency, For the current time, This represents the initial phase of the grid voltage waveform. This represents the initial phase of the microgrid voltage waveform. M and N represent the time difference between the current time and the next positive zero-crossing time of synchronization, where M and N are both non-negative integers.

[0040] Furthermore, the method for calculating the time difference between the current time and the next synchronous positive zero-crossing time includes:

[0041] Calculate the time remaining until the next positive zero crossing of the power grid;

[0042] To determine whether the next positive zero-crossing point of the power grid is also the positive zero-crossing point of the microgrid, if it is, the time difference between the current time and the next synchronous positive zero-crossing point is equal to the time remaining until the next positive zero-crossing point of the power grid. If the next positive zero-crossing point is not the positive zero-crossing point of the microgrid, the time difference between the current time and the next synchronous positive zero-crossing point is as follows:

[0043]

[0044]

[0045] In the formula, The time difference between the current time and the next positive zero-crossing time. For the power grid frequency, This is the time until the next positive zero crossing of the power grid. Microgrid frequency, For the current time, This represents the initial phase of the microgrid voltage waveform.

[0046] Furthermore, the method for calculating the time remaining until the next positive zero crossing of the power grid is as follows:

[0047]

[0048] In the formula, This is the time until the next positive zero crossing of the power grid. For the power grid frequency, For the current time, This represents the initial phase of the grid voltage waveform.

[0049] Furthermore, the permitted time range for grid connection is: , among which, T b For the lead compensation time, T k The allowable time for grid connection to be ahead of or behind schedule.

[0050] Furthermore, the method for adjusting the voltage amplitude and frequency of the microgrid to within the allowable range for grid connection, and adjusting the phase difference between the microgrid waveform and the grid waveform to a decreasing trend, is as follows:

[0051] First, adjust the microgrid voltage and frequency to the range allowed for grid connection, and then adjust the phase difference between the microgrid waveform and the grid waveform to a decreasing trend.

[0052] Furthermore, the method for adjusting the voltage amplitude and frequency of the microgrid to the allowable range for grid connection is as follows: by performing active and reactive power compensation control on the controlled power sources within the microgrid, the voltage amplitude and frequency of the microgrid are adjusted to the allowable range for grid connection.

[0053] Furthermore, before the microgrid is officially put into operation, the pre-lead compensation time is the closing response time of the grid-connected circuit breaker obtained from the trial operation test; after the microgrid is officially put into operation, the pre-lead compensation time is the closing response time of the grid-connected circuit breaker during the actual closing process in actual operation.

[0054] Furthermore, the permissible grid connection lead or lag time T k The calculation method is as follows:

[0055]

[0056] In the formula, The frequency difference between the power grid and the microgrid. This refers to the phase difference allowed for grid connection.

[0057] Furthermore, the method to adjust the phase difference between the microgrid waveform and the grid waveform to a decreasing trend is as follows: by increasing the microgrid frequency, the phase of the active distributed smart microgrid waveform catches up with the phase of the grid waveform, thereby adjusting the phase difference between the active distributed smart microgrid waveform and the grid waveform to a decreasing trend, and then restoring the microgrid frequency.

[0058] Furthermore, when the phase difference between the waveform of the active distributed smart microgrid and the waveform of the power grid... At that time, the real-time phase difference between the two waveforms Trend of change To increase the trend, when the phase difference between the waveform of the active distributed smart microgrid and the power grid waveform... At that time, the real-time phase difference between the two waveforms Trend of change To reduce the trend, K is a non-negative integer.

[0059] The beneficial effects of this invention are as follows: This invention proposes an active smart grid grid-connected control system, mainly including the design of a three-layer grid-connected control architecture of "local execution - local decision-making - system regulation" and the proposal of a non-fully synchronized off-grid to grid-connected control method that does not rely on voltage sources. The grid-connected control method proposed in this invention does not require voltage source pre-synchronization adjustment or operating mode switching, and can effectively avoid the problems of grid-connected information transmission delay, asynchronous adjustment of multiple grid units, and fluctuations and oscillations caused by mode switching. It is particularly suitable for scenarios with multiple dispersed grid units and grid connection points and grid units that are far apart, and can provide fast and stable switching control support for the off-grid to grid-connected transition of active smart grids, ensuring the safe and reliable operation of the power grid. At the same time, the grid-connected control does not involve the switching of the operating mode of the main grid control unit, avoiding the problem of fluctuations and oscillations easily caused by the switching of the operating mode of the main grid control unit during the grid connection process in existing technologies. Attached Figure Description

[0060] Figure 1 This is a schematic diagram of the grid-connected control system structure of the active distributed intelligent microgrid of the present invention. Detailed Implementation

[0061] The active distributed smart microgrid grid connection control method and system of the present invention are applicable to the grid connection control of large-scale new smart microgrids, especially to the grid connection control scenarios of large-scale local independent power grids with multiple distributed multi-network main control units and the grid connection point and main control unit being far apart. It can be used for off-grid to grid connection control of distributed smart microgrids and power grids that are not completely synchronized.

[0062] The inventive concept of this invention is as follows: First, the voltage amplitude and frequency of the active distributed grid are regulated to bring it within the allowable closing range. Since the frequencies and phases are not completely the same, this invention does not simply adjust the phase of the microgrid to be the same as the phase of the main grid. Instead, it directly finds the synchronous positive zero-crossing point of the microgrid and the main grid and closes the grid near this synchronous positive zero-crossing point to reduce the voltage deviation between the microgrid and the main grid and achieve grid connection control.

[0063] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0064] System Implementation Method:

[0065] This application discloses a grid-connected control system for an active distributed smart microgrid, such as... Figure 1 As shown, the system includes a local execution layer, a local decision-making layer, and a system control layer. In this embodiment, the system control layer is a microgrid management system, the local execution layer is a microgrid grid-connected circuit breaker, and the local decision-making layer is a microgrid grounding monitoring and control device. This control system is used for grid-connected and off-grid control of distributed smart microgrids (hereinafter referred to as microgrids).

[0066] The grid-connected circuit breaker interacts with the local monitoring and control device through electrical signal lines, and has the ability to send opening status information to the local monitoring and control device and receive closing signals and execute them quickly.

[0067] The local monitoring and control device is installed near the grid-connected circuit breaker and is electrically connected to the voltage and current signal acquisition modules of the upstream and downstream lines of the grid-connected circuit breaker and the grid-connected circuit breaker itself. It is capable of real-time acquisition of the voltage of the main power grid. microgrid voltage and the operating status of the microgrid Operating status of large power grid and circuit breaker status The ability to calculate large power grid frequencies. and microgrid frequency Voltage amplitude deviation Frequency deviation And the real-time phase difference between microgrid waveforms and large power grid waveforms. and its changing trends It also has the ability to determine on-site in real time whether the conditions for grid connection and closing are met and issue a closing command.

[0068] The local monitoring and control device is connected to the microgrid intelligent management system via network communication, supporting the uploading of collected voltage, current, frequency, and phase difference data of the main power grid and microgrid to the microgrid intelligent management system, while simultaneously receiving grid connection start-up commands issued by the microgrid intelligent management system. Pre-connection order And execute.

[0069] The microgrid intelligent management system of the system control layer is installed in the microgrid monitoring center and is connected to the local measurement and control devices and the network of each distributed resource control terminal. It collects the operation information of each resource and measurement and control device, and issues active power adjustment and reactive power adjustment commands. It supports the functions of starting grid connection process, collaborative control pre-judgment and command issuance.

[0070] The grid-connected control system for the active distributed intelligent microgrid of the present invention is used to implement the grid-connected control method for the active distributed intelligent microgrid of the present invention, the method comprising the following steps:

[0071] 1. Measure the leader compensation time T b .

[0072] During the microgrid trial operation, the response time from the on-site test and control device issuing the closing command to the completion of the grid-connected circuit breaker closing was measured. This response time is the pre-leader compensation time T. b .

[0073] 2. Determine whether the conditions for starting and connecting to the grid are met.

[0074] The microgrid intelligent management system is based on the operating status of the main power grid. Microgrid system operating status and circuit breaker status The system determines whether the conditions for grid connection to start are met. If the conditions are met, the microgrid intelligent management system sends a grid connection start command to the local monitoring and control device and proceeds to step 3. If the conditions are not met, the system proceeds to step 24.

[0075] 3. Local monitoring and control devices monitor the voltage of the main power grid in real time. ,frequency microgrid voltage ,frequency Calculate the real-time phase difference between the voltage waveforms of the large power grid and the microgrid. and its changing trends And send it to the microgrid intelligent management system.

[0076] 4. The microgrid intelligent management system determines the voltage deviation between the main grid and the microgrid. Is it less than or equal to the allowable voltage deviation for closing? ,like > Then proceed to step 5, if ≤ Then proceed to step 8.

[0077] Voltage deviation Less than or equal to the allowable voltage deviation for closing This indicates that the microgrid voltage is within the allowable voltage range for closing the circuit breaker.

[0078] 5. The microgrid intelligent management system is based on the voltage of the main power grid. To achieve the target, the PQ voltage regulation command is calculated, and the column disturbance regulation command is generated and sent to each distributed unit (distributed voltage source and distributed current source) in the microgrid. In this embodiment, voltage regulation is achieved by performing active and reactive power compensation control on the controlled power sources within the microgrid.

[0079] 6. Each distributed unit in the microgrid executes the received instructions, and the monitoring and control device feeds back the execution results to the microgrid intelligent management system in real time.

[0080] 7. Based on the execution results fed back by the local monitoring and control devices, the microgrid intelligent management system reassesses the voltage deviation between the main grid and the microgrid. Is it less than or equal to the allowable voltage deviation for closing? ,like > Then proceed to step 5, if ≤ Then proceed to step 8.

[0081] 8. The microgrid intelligent management system determines the frequency deviation between the microgrid and the main grid. Is it less than or equal to the allowable frequency deviation for closing? ,like > Then proceed to step 9, if ≤ Then proceed to step 12.

[0082] Frequency deviation between microgrids and main grid Less than or equal to the allowable frequency deviation for closing This indicates that the microgrid frequency is within the permissible frequency range for closing the circuit breaker.

[0083] 9. Microgrid intelligent management system, with To adjust the target, a PQ frequency adjustment command is generated and issued to each distributed unit (including distributed voltage sources and distributed current sources). The frequency is the main power grid frequency, where 0 < m < 1. In this embodiment, frequency regulation is achieved by controlling the active and reactive power sources within the microgrid through active and reactive power compensation.

[0084] 10. Each distributed unit receives and executes the PQ frequency adjustment command, and simultaneously feeds back the execution result to the microgrid intelligent management system.

[0085] 11. The microgrid intelligent management system reassesses the frequency deviation between the microgrid and the main grid based on the execution results received by each distributed unit. Is it less than or equal to the allowable frequency deviation for closing? ,like Then proceed to step 9, if Then proceed to step 12.

[0086] 12. The microgrid intelligent management system determines the real-time phase difference between the voltage waveforms of the main grid and the microgrid. Trend of change If the trend is decreasing, proceed to step 16; otherwise, proceed to step 13.

[0087] 13. The microgrid intelligent management system performs a frequency disturbance adjustment by increasing the microgrid's frequency to catch up with the phase of the main grid. Specifically: To achieve the objective, calculate the PQ adjustment command and disturbance time, and generate the column disturbance adjustment command. , , Distribute to each distributed unit.

[0088] When n is greater than 1, the microgrid frequency is increased, causing the phase of the active distributed smart microgrid waveform to catch up with the phase of the power grid waveform, thereby adjusting the phase difference between the active distributed smart microgrid waveform and the power grid waveform to a decreasing trend. In this embodiment, 1 < n < 1.2.

[0089] 14. Each distributed unit receives and executes the PQ adjustment command issued by the microgrid intelligent management system. After execution, the frequency of each distributed unit is adjusted to the frequency before the disturbance adjustment, and the execution result is fed back to the microgrid intelligent management system.

[0090] 15. Based on the execution results of feedback disturbance regulation, the microgrid intelligent management system determines the real-time phase difference between the main grid voltage waveform and the microgrid voltage waveform. Trend of change If the trend is decreasing, proceed to step 16; otherwise, proceed to step 13.

[0091] Determine the real-time phase difference Trend of change The principle behind whether it is a decreasing trend is as follows:

[0092] When the frequency of the large power grid With microgrid frequency When frequency deviation exists, the phase difference between the large power grid and the microgrid The trend analysis is as follows: Meeting by That is, the positive zero-crossing phase will be synchronized. Asynchronous (increased phase difference) Maximum phase difference ( (k is an odd number) Asynchronous (phase difference decreases) synchronous( (k is an even number) Asynchronous (increased phase difference) Maximum phase difference ( (k is an odd number) Asynchronous (phase difference decreases) synchronous( (k is an even number)..., continuously repeating.

[0093] Based on this principle, when Real-time phase difference Trend of change To increase the trend, when Real-time phase difference Trend of change To reduce the trend, K = 0, 1, 2...

[0094] 16. The microgrid intelligent management system determines whether the quasi-grid connection conditions are met. If the grid connection conditions are met, proceed to step 17; otherwise, proceed to step 3.

[0095] In this embodiment, the quasi-grid connection condition is: ,and ,and The trend of change is decreasing.

[0096] 17. The microgrid intelligent management system sends a quasi-grid connection command to the local monitoring and control device.

[0097] 18. After receiving the quasi-grid connection command, the local monitoring and control device will again determine whether the microgrid meets the quasi-grid connection conditions. If the grid connection conditions are met, proceed to step 19; otherwise, proceed to step 3.

[0098] 19. The local monitoring and control device calculates the time difference between the current time and the next positive zero-crossing point (from negative to positive zero) of the large power grid and microgrid, and determines whether the time difference between the current time and the next positive zero-crossing point of the large power grid and microgrid is within the allowable grid connection time range. If it is within the allowable grid connection time range, proceed to step 21; otherwise, execute step 20.

[0099] The methods for calculating the time difference between the current time and the next positive zero-crossing point of the large power grid and microgrid include:

[0100] The synchronous zero-crossing point of a microgrid and a large power grid is the point where their phases are both integer multiples of 2π, expressed by the formula:

[0101]

[0102] Right now:

[0103]

[0104] In the formula, For the time when the large power grid and microgrid synchronize positive zero crossing, for Large power grid waveform phase, for Microgrid waveform phase For the current time, This represents the initial phase of the large power grid voltage waveform. This represents the initial phase of the microgrid voltage waveform. The time required for the large power grid and microgrid to synchronize at the zero-crossing point (i.e., the time difference between the current time and the time of the positive zero-crossing point). The calculated value is obtained when the absolute value of the difference between M and N is at its minimum (usually 1). This is the time difference between the current time and the next positive zero-crossing point of the large power grid and microgrid.

[0105] The engineering calculation method is as follows:

[0106] Using the frequency of the main power grid as a reference, and making the frequency of the microgrid slightly higher than that of the main power grid, the time required for the main power grid to reach its next positive zero crossing is then determined. The calculation method is as follows:

[0107]

[0108] To determine whether a microgrid is also at a positive zero-crossing point when the main power grid is at a positive zero-crossing point, we need to determine whether its actual phase is an integer multiple of 2π.

[0109]

[0110] If the above formula is true, then After a certain period of time, the microgrid also reaches a positive zero-crossing point. In this case, .

[0111] If the above formula does not hold, then After a certain time, the microgrid is no longer at a positive zero-crossing point. Additional time needs to be added on top of the positive zero-crossing time of the main power grid. The calculation method is as follows:

[0112]

[0113] In this embodiment, the allowable grid connection time deviation range is: T b For the lead compensation time, T k The allowable grid connection lead time or allowable grid connection lag time is calculated as follows: , The allowable grid-connected phase difference.

[0114] 20. Determine whether the time between the most recent positive zero-crossing of the main grid and the microgrid exceeds the upper limit of the allowable grid connection time deviation range. If it exceeds the upper limit, proceed to step 18 and wait for the time between the most recent positive zero-crossing of the main grid and the microgrid to enter the allowable grid connection time deviation range. If the time between the most recent positive zero-crossing of the main grid and the microgrid is less than the lower limit of the allowable grid connection time deviation range, the most recent positive zero-crossing has been missed, and proceed to step 3 to recalculate the next most recent positive zero-crossing.

[0115] 21. The local monitoring and control device triggers the circuit breaker to close and open. The grid-connected circuit breaker receives the command and closes. At the same time, the local monitoring and control device receives the circuit breaker status and calculates the circuit breaker closing response time T. s And send it to the microgrid intelligent management system.

[0116] 22. The microgrid intelligent management system receives information and determines whether the microgrid is operating normally after grid connection. If it is operating normally, it then sets an additional lead compensation time T. b =T s If the grid connection process ends, proceed to step 23.

[0117] 23. Activate the emergency response mechanism, quickly disconnect the grid-connected circuit breaker, restart the off-grid operation, analyze the reasons for the grid connection failure, and wait for the next grid connection.

[0118] 24. Grid connection failed. The system reported that the conditions for grid connection were not met, requiring manual intervention.

[0119] Method implementation:

[0120] The grid-connected control method for an active distributed smart microgrid of the present invention includes the following steps:

[0121] 1. Measure the leader compensation time T b .

[0122] During the microgrid trial operation, the response time from the on-site test and control device issuing the closing command to the completion of the grid-connected circuit breaker closing was measured. This response time is the pre-leader compensation time T. b .

[0123] 2. Determine whether the conditions for starting and connecting to the grid are met.

[0124] If the conditions for grid connection to start are met, proceed to step 3; otherwise, proceed to step 24.

[0125] 3. Detect the voltage of the main power grid. ,frequency microgrid voltage ,frequency Calculate the real-time phase difference between the voltage waveforms of the large power grid and the microgrid. and its changing trends .

[0126] 4. Determine the voltage deviation between the main power grid and the microgrid. Is it less than or equal to the allowable voltage deviation for closing? ,like Then proceed to step 5, if Then proceed to step 8.

[0127] 5. Based on the voltage of the main power grid To achieve the goal, calculate the PQ voltage regulation command and generate the column disturbance regulation command, which is then sent to each distributed unit (distributed voltage source and distributed current source) in the microgrid.

[0128] 6. Each distributed unit in the microgrid executes the received instructions.

[0129] 7. Reassess the voltage deviation between the main power grid and the microgrid. Is it less than or equal to the allowable voltage deviation for closing? ,like Then proceed to step 5, if Then proceed to step 8.

[0130] 8. Determine the frequency deviation between the microgrid and the main power grid. Is it less than or equal to the allowable frequency deviation for closing? ,like Then proceed to step 9, if Then proceed to step 12.

[0131] 9. With To adjust the target, a PQ frequency adjustment command is generated and issued to each distributed unit (including distributed voltage sources and distributed current sources). For the main power grid frequency, 0 < m < 1.

[0132] 10. Each distributed unit receives and executes the PQ frequency adjustment command.

[0133] 11. Based on the execution results received by each distributed unit, reassess the frequency deviation between the microgrid and the main grid. Is it less than or equal to the allowable frequency deviation for closing? ,like Then proceed to step 9, if Then proceed to step 12.

[0134] 12. Determine the real-time phase difference between the voltage waveforms of the large power grid and the microgrid. Trend of change If the trend is decreasing, proceed to step 16; otherwise, proceed to step 13.

[0135] 13. Perform a frequency disturbance adjustment by increasing the microgrid's frequency to catch up with the phase of the main grid. Specifically: To achieve the objective, calculate the PQ adjustment command and disturbance time, and generate the column disturbance adjustment command. , , Distribute to each distributed unit.

[0136] 14. Each distributed unit receives and executes the PQ adjustment command.

[0137] 15. Reassess the real-time phase difference between the voltage waveforms of the main grid and the microgrid. Trend of change If the trend is decreasing, proceed to step 16; otherwise, proceed to step 13.

[0138] 16. Determine whether the quasi-grid connection conditions are met. If the grid connection conditions are met, proceed to step 17; otherwise, proceed to step 3. In this embodiment, the quasi-grid connection conditions are... ,and ,and The trend of change is decreasing.

[0139] 17. Send the pre-grid connection command.

[0140] 18. After receiving the quasi-grid connection instruction, determine again whether the microgrid meets the quasi-grid connection conditions. If it meets the grid connection conditions, proceed to step 19; otherwise, proceed to step 3.

[0141] 19. The local monitoring and control device calculates the time difference between the current time and the time of the next positive zero-crossing of the large power grid and the microgrid, and determines whether the time difference between the current time and the time of the next positive zero-crossing of the large power grid and the microgrid is within the allowed grid connection time range. If it is within the allowed grid connection time range, proceed to step 21; otherwise, proceed to step 20.

[0142] 20. Determine whether the time between the most recent positive zero-crossing of the main grid and the microgrid exceeds the upper limit of the allowable grid connection time deviation range. If it exceeds the upper limit, proceed to step 18 and wait for the time between the most recent positive zero-crossing of the main grid and the microgrid to enter the allowable grid connection time deviation range. If the time between the most recent positive zero-crossing of the main grid and the microgrid is less than the lower limit of the allowable grid connection time deviation range, the most recent positive zero-crossing has been missed, and proceed to step 3 to recalculate the next most recent positive zero-crossing.

[0143] 21. The local monitoring and control device triggers the circuit breaker to close and open. The grid-connected circuit breaker receives the command and closes. At the same time, the local monitoring and control device receives the circuit breaker status and calculates the circuit breaker closing response time T. s And send it to the microgrid intelligent management system.

[0144] 22. The microgrid intelligent management system receives information and determines whether the microgrid is operating normally after grid connection. If it is operating normally, it then sets an additional lead compensation time T. b =T s If the grid connection process ends, proceed to step 23.

[0145] 23. Activate the emergency response mechanism, quickly disconnect the grid-connected circuit breaker, restart the off-grid operation, analyze the reasons for the grid connection failure, and wait for the next grid connection.

[0146] 24. Grid connection failed. The system reported that the conditions for grid connection were not met, requiring manual intervention.

[0147] The specific method details have been described in detail in the system implementation method, and will not be repeated in this implementation method.

[0148] In summary, the grid-connected control method and system for an active distributed smart microgrid of the present invention can effectively avoid problems such as grid-connected information transmission delay, asynchronous adjustment of multiple grid units, and fluctuations and oscillations caused by mode switching. Simultaneously, the present invention proposes a moving frequency disturbance adjustment method, which can accelerate the grid-connected synchronization speed and meet the grid-connected time requirements. Furthermore, the present invention proposes a lead time compensation method based on real-time measurement to further ensure grid-connected closing at the voltage zero-crossing point, reducing the impact of grid-connected closing. It is applicable to scenarios containing multiple distributed grid units and where the grid-connected point is geographically dispersed from the grid units, providing fast and stable switching control support for the off-grid to on-grid transition of active smart grids, ensuring the safe and reliable operation of the power grid.

Claims

1. A grid-connected control method for an active distributed intelligent microgrid, characterized in that, The method includes: When an active distributed intelligent microgrid meets the start-up and grid connection conditions, the microgrid is controlled as follows: 1) Determine whether the voltage amplitude and frequency of the microgrid are within the allowable range for grid connection and whether the phase difference between the microgrid waveform and the grid waveform is decreasing. If so, proceed to step 2). Otherwise, adjust the voltage amplitude and frequency of the microgrid to the allowable range for grid connection, and adjust the phase difference between the microgrid waveform and the grid waveform to a decreasing trend before proceeding to step 2). 2) Calculate the time difference between the current time and the next synchronous positive zero-crossing point, where the synchronous positive zero-crossing point is the synchronous positive zero-crossing point of the microgrid waveform and the power grid waveform; and determine whether the time difference is within the allowed time range for grid connection. If so, grid connection is performed; otherwise, if the time difference is greater than the upper limit of the allowed time range for grid connection, wait until the time difference is within the allowed time range for grid connection; if the time difference is less than the lower limit of the allowed time range for grid connection, execute step 1).

2. The grid-connected control method for an active distributed intelligent microgrid according to claim 1, characterized in that, The method for calculating the time difference between the current time and the next positive zero-crossing time is as follows: Solve for the time when the difference between M and N is minimized using the following formula. This is the time difference between the current time and the next synchronous positive zero crossing time; In the formula, For the power grid frequency, For microgrid frequencies, For the current time, This represents the initial phase of the grid voltage waveform. This represents the initial phase of the microgrid voltage waveform. M and N represent the time difference between the current time and the next positive zero-crossing time of synchronization, where M and N are both non-negative integers.

3. The grid-connected control method for an active distributed intelligent microgrid according to claim 2, characterized in that, The methods for calculating the time difference between the current time and the next positive zero-crossing time include: Calculate the time remaining until the next positive zero crossing of the power grid; To determine whether the next positive zero-crossing point of the power grid is also the positive zero-crossing point of the microgrid, if it is, the time difference between the current time and the next synchronous positive zero-crossing point is equal to the time remaining until the next positive zero-crossing point of the power grid. If the next positive zero-crossing point is not the positive zero-crossing point of the microgrid, the time difference between the current time and the next synchronous positive zero-crossing point is as follows: In the formula, The time difference between the current time and the next positive zero-crossing time. For the power grid frequency, This is the time until the next positive zero crossing of the power grid. Microgrid frequency, For the current time, This represents the initial phase of the microgrid voltage waveform.

4. The grid-connected control method for an active distributed intelligent microgrid according to claim 3, characterized in that, The method for calculating the time from the current time to the next positive zero crossing of the power grid is as follows: In the formula, This is the time until the next positive zero crossing of the power grid. For the power grid frequency, For the current time, This represents the initial phase of the grid voltage waveform.

5. The grid-connected control method for an active distributed intelligent microgrid according to any one of claims 1-4, characterized in that, The permitted time range for grid connection is , among which, T b For the lead compensation time, T k The allowable time for grid connection to be ahead of or behind schedule.

6. The grid-connected control method for an active distributed intelligent microgrid according to any one of claims 1-4, characterized in that, The method to adjust the voltage amplitude and frequency of the microgrid to within the allowable range for grid connection, and to adjust the phase difference between the microgrid waveform and the grid waveform to a decreasing trend, is as follows: First, adjust the microgrid voltage and frequency to the allowable range for grid connection, and then adjust the phase difference between the microgrid waveform and the grid waveform to a decreasing trend.

7. The grid-connected control method for an active distributed intelligent microgrid according to any one of claims 1-4, characterized in that, The method to adjust the voltage amplitude and frequency of the microgrid to the allowable range for grid connection is as follows: by performing active and reactive power compensation control on the controlled power sources within the microgrid, the voltage amplitude and frequency of the microgrid are adjusted to the allowable range for grid connection.

8. The grid-connected control method for an active distributed intelligent microgrid according to claim 5, characterized in that, Before the microgrid is officially put into operation, the pre-lead compensation time is the closing response time of the grid-connected circuit breaker obtained from the trial operation test; after the microgrid is officially put into operation, the pre-lead compensation time is the closing response time of the grid-connected circuit breaker during the actual closing process in actual operation.

9. The grid-connected control method for an active distributed intelligent microgrid according to claim 5, characterized in that, Allowable grid connection lead or lag time T k The calculation method is as follows: In the formula, The frequency difference between the power grid and the microgrid. This refers to the phase difference allowed for grid connection.

10. The grid-connected control method for an active distributed intelligent microgrid according to any one of claims 1-4, characterized in that, The method to adjust the phase difference between the microgrid waveform and the grid waveform to a decreasing trend is as follows: by increasing the microgrid frequency, the phase of the active distributed smart microgrid waveform catches up with the phase of the grid waveform, thereby adjusting the phase difference between the active distributed smart microgrid waveform and the grid waveform to a decreasing trend, and then restoring the microgrid frequency.

11. The grid-connected control method for an active distributed intelligent microgrid according to any one of claims 1-4, characterized in that, When the phase difference between the waveform of the active distributed smart microgrid and the waveform of the power grid At that time, the real-time phase difference between the two waveforms Trend of change To increase the trend, when the phase difference between the waveform of the active distributed smart microgrid and the power grid waveform... At that time, the real-time phase difference between the two waveforms Trend of change To reduce the trend, K is a non-negative integer.

12. A grid-connected control system for an active distributed smart microgrid, comprising a local execution layer, a local decision-making layer, and a system control layer, wherein the local execution layer is used to execute the grid connection and disconnection actions of the active distributed smart microgrid, and the local decision-making layer is used to collect the status of the microgrid and the power grid and send it to the system control layer; characterized in that... The system control layer is used to determine whether the voltage amplitude and frequency of the microgrid are within the allowable range for grid connection and whether the phase difference between the microgrid waveform and the grid waveform is decreasing when the active distributed smart microgrid meets the start-up and grid connection conditions. If so, it sends a quasi-grid connection command to the local decision layer; otherwise, it adjusts the voltage amplitude and frequency of the microgrid to the allowable range for grid connection, adjusts the phase difference between the microgrid waveform and the grid waveform to a decreasing trend, and then sends a quasi-grid connection command to the local decision layer. The local decision-making layer is also used to calculate the time difference between the current time and the next synchronous positive zero-crossing point after receiving the quasi-grid connection command. The synchronous positive zero-crossing point is the synchronous positive zero-crossing point of the microgrid waveform and the grid waveform. It also determines whether the time difference is within the allowed time range for grid connection. If so, grid connection is performed. Otherwise, when the time difference is greater than the upper limit of the allowed time range for grid connection, it waits until the time difference is within the allowed time range for grid connection. When the time difference is less than the lower limit of the allowed time range for grid connection, the system control layer re-determines whether the voltage amplitude and frequency of the microgrid are within the allowed range for grid connection and whether the phase difference between the microgrid waveform and the grid waveform is decreasing.

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