A seamless handover method for enhanced stable operation under microgrid main grid fault

Abstract

The application discloses a seamless switching method for enhanced stable operation under micro-grid main grid fault, and relates to the technical field of micro-grid management, which comprises the following steps: acquiring the voltage, current, frequency and phase of each node of the micro-grid, judging the operation state of the main grid through joint collection, and simultaneously acquiring the electrical parameter information of a plurality of set position monitoring devices; aligning the electrical parameters acquired in the first step according to a unified time reference benchmark, judging the response time difference of each monitoring device to the fault event, and selecting the node where the monitoring device is located as the main control node according to a preset rule; the main control node sends a control instruction to the auxiliary control node, and the auxiliary control node switches to the auxiliary control state according to a preset priority after receiving the control instruction. The application can realize the fast and stable switching of the micro-grid control structure under the main grid fault, and can ensure the consistency of the output of each control node through the coordinated regulation of the voltage, frequency and active power, so that the continuity and stability of the system operation are maintained.

Description

Technical Field

[0001] This invention relates to the field of microgrid management technology, specifically to a seamless switching method for enhanced stable operation under microgrid main grid failure. Background Technology

[0002] With the development of distributed energy and microgrid technology, microgrids have gradually acquired the ability to operate autonomously and flexibly connect to the main grid. When the main grid is operating normally, the microgrid usually operates in parallel with the main grid to obtain a stable power supply and realize bidirectional power flow. However, when the main grid fails, the microgrid needs to seamlessly switch to islanded operation to ensure continuous power supply to critical loads.

[0003] Existing seamless switching solutions typically rely on single-point fault detection and pre-configuration of control nodes. Some methods trigger islanding mode entry through voltage drop detection and then rely on energy storage systems to maintain system stability. However, due to the simple switching response mechanism of control nodes, insufficient prediction of grid connection process, and lack of participation of communication links in switching strategy evaluation, problems such as voltage fluctuations, frequency drift, or grid current surges are easily generated during the switching process, thereby affecting system stability and equipment safety.

[0004] Therefore, how to comprehensively consider control response time, energy storage capacity and communication quality, dynamically select the optimal control node, and improve the operational stability and grid connection reliability of microgrids under main grid failure scenarios by adjusting parameter consistency control and grid connection trend prediction judgment has become an important technical direction that needs to be solved in the current microgrid operation control field. Therefore, this invention proposes a seamless switching method for enhanced stable operation of microgrids under main grid failure. Summary of the Invention

[0005] The purpose of this invention is to provide a seamless switching method for enhanced stable operation under microgrid main network failure, so as to solve the problems mentioned in the background art.

[0006] This invention can be achieved through the following technical solution: a seamless switching method for enhanced stable operation under microgrid main network failure, comprising the following steps:

[0007] Step 1: Obtain the voltage, current, frequency, and phase of each node in the microgrid; determine the operating status of the main power grid through joint acquisition; and simultaneously acquire electrical parameter information from multiple monitoring devices at designated locations.

[0008] Step 2: Align the electrical parameters obtained in Step 1 with a unified time reference standard, determine the response time difference of each monitoring device to the fault event, and select the node where the monitoring device is located as the main control node according to the preset rules.

[0009] Step 3: The main control node sends control commands to the auxiliary control node. After receiving the commands, the auxiliary control node switches to auxiliary control mode according to the preset priority and tracks the voltage and frequency output of the main control node.

[0010] Step 4: After the control state switch is completed, adjust the voltage amplitude, frequency reference value and adjustment rate of the main control node and the auxiliary control node so that the output parameters of the control node tend to be consistent within the set time window.

[0011] Step 5: After the adjustment in Step 4 is completed, monitor the change in load-side current. Before the load current rises to the preset load current rise threshold, correct the active power reference value of each power conversion device and adjust the discharge power of the energy storage device to meet the energy storage adjustment threshold.

[0012] Step 6: After the microgrid is operating stably, detect the status, voltage amplitude difference, and phase difference of the switch connected to the main grid. If the voltage amplitude difference threshold and phase difference threshold are met, control the switch to be engaged and limit the instantaneous grid current. The limit is executed based on the grid current rise rate threshold.

[0013] A further technical improvement of the present invention lies in: step two, selecting preset rules for the main control node, including:

[0014] S1. Receive the local timestamp of each control node detecting a voltage drop event in the main grid, and calculate the time difference between the voltage drop event occurrence time and the local detection time based on the set unified time reference, so as to obtain the corresponding response time.

[0015] S2. Obtain the current voltage, current, nominal capacity, and remaining capacity of the energy storage device connected to each control node, and calculate the sustainable power supply time using the following formula:

[0016] Sustainable power supply time = Remaining capacity value ÷ Current value;

[0017] And this sustainable power supply time will be used as a score for energy storage output capacity;

[0018] S3. During the communication link initialization phase, a handshake request data frame containing number information is broadcast to all control nodes in sequence. Each control node immediately returns a handshake response data frame containing the same number information after receiving the handshake request data frame.

[0019] The number of handshake response data frames successfully returned by each control node within a set time window and the average round-trip communication time are counted, and the communication score is calculated according to the following formula:

[0020] Communication score = Number of handshake response data frames − Round-trip communication time × Penalty coefficient;

[0021] S4. Based on the response time, energy storage output capacity score and communication score of each control node, a comprehensive score is calculated according to the preset weighted calculation rules, and the control node with the highest score is selected as the main control node.

[0022] A further technical improvement of the present invention lies in the setting of the time window in step four, which includes the following steps:

[0023] A1. Set a baseline time window length;

[0024] A2. If any of the following conditions are met, then an extension amount is added to the base time window length:

[0025] a21. Communication quality does not meet requirements: The average number of retransmissions of the handshake request data frame is greater than the set handshake retransmission threshold, or the noise level of the communication channel is greater than the set communication noise level threshold, or the standard deviation of the round-trip communication time of the handshake response data frame of the control node is greater than the set communication stability judgment threshold.

[0026] a22. Short-term voltage disturbance exists: The duration of the voltage disturbance at the microgrid's point of common coupling is less than the set disturbance duration judgment threshold, and its voltage recovery slope is greater than the set voltage recovery slope threshold.

[0027] A3. If any of the extension conditions in a21 and a22 of A2 are not met, and the equivalent virtual moment of inertia of all connected power sources in the microgrid is less than the set equivalent moment of inertia threshold, and the total active power change rate is greater than the set active power change rate threshold, then the length of the reference time window will be reduced by a shortening amount.

[0028] A4. The final length of the time window is the result of adding or subtracting values ​​based on the baseline time window length set in A1, according to the extension amount corresponding to the extension condition satisfied in A2 and the shortening amount corresponding to the shortening condition satisfied in A3.

[0029] A further technical improvement of the present invention is that: in step six, the method of limiting the instantaneous grid-connected current includes:

[0030] At a preset advance time before the control switch is closed, the instantaneous grid-connected current value at the grid-connected switch is collected, and continuous sampling is performed according to a preset time interval. The current rise rate is calculated by the current difference between adjacent sampling points.

[0031] At the instant the switch is closed, the rate of change of the output voltage in the control loop is adjusted to suppress the rate of rise of the instantaneous grid-connected current.

[0032] The rate of change of the output voltage is set according to the current instantaneous rise rate of the grid-connected current;

[0033] When the current rise rate is between the first current change rate threshold and the second current change rate threshold, the output voltage change rate decreases as the current rise rate increases.

[0034] When the current rise rate exceeds the second current change rate threshold, the output voltage change rate is not lower than the preset change rate lower limit.

[0035] After detecting that the current rise rate is continuously lower than the current stability judgment threshold, and this state continues for more than the preset stability judgment time window, the original voltage regulation rate of the control loop is restored.

[0036] A further technical improvement of the present invention is that: after the auxiliary control node switches to the new control command receiving node, the auxiliary control node uses linear interpolation to proportionally decrease the control reference value before the switch at a fixed time step within the reference value switching transition time window, while simultaneously proportionally increasing the control reference value provided by the new receiving node, until the control output fully adopts the control reference value of the new receiving node.

[0037] A further technical improvement of the present invention is that: after communication is restored, the auxiliary control node determines whether to switch back to the original primary control node according to the control node priority table stored locally;

[0038] The priority table for control nodes determines the priority order based on a weighted average of the node identifier, historical stability score, and communication quality score.

[0039] A further technical improvement of the present invention is that: the auxiliary control node dynamically updates its communication path priority table according to the information broadcast by other control nodes in each broadcast cycle;

[0040] The broadcast information includes the node identifier, the current communication delay value, the data packet loss rate, and the communication channel noise level.

[0041] A further technical improvement of the present invention is that, in step six, the operation of determining whether the grid-connected voltage amplitude difference threshold and phase difference threshold are met includes:

[0042] After detecting that the current voltage amplitude difference and phase difference meet the set grid connection conditions, the voltage amplitude and phase values ​​of the target control node are periodically collected within the sampling time window, and the rate of change between each sampling time is calculated.

[0043] Based on the rate of change and the preset prediction time interval, the voltage amplitude and phase values ​​at the prediction time point are calculated, and the voltage amplitude difference and phase difference at the corresponding moment of the prediction time point are obtained accordingly.

[0044] When the calculation results show that the grid voltage amplitude difference threshold and phase difference threshold are still met at the predicted time point, a switch closing command is issued at an earlier time point before the predicted time point so that the switch can be closed at the predicted time point.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] This invention enables rapid and stable switching of the microgrid control structure in the event of a main grid failure, and ensures the consistency of the output of each control node through coordinated adjustment of voltage, frequency and active power, thereby maintaining the continuity and stability of system operation.

[0047] Furthermore, this invention introduces a scoring mechanism based on three dimensions—response time, energy storage support capability, and communication quality—during the selection of the main control node, and sets normalized weighted calculation rules. This makes the selection of the main control node more globally adaptable and stable, avoiding misjudgments and control failures caused by a single indicator. It also enhances the stability of the main control node under sudden disturbances and effectively improves the overall control reliability.

[0048] On the other hand, the grid-connected control mechanism based on trend prediction of the present invention can judge the voltage and phase change trend in the future time period based on the current grid connection conditions. When it is ensured that the grid connection conditions are still met at the predicted time, the control command is issued in advance to ensure that the switch closes at the appropriate time. At the same time, combined with the grid connection current rise rate limiting adjustment mechanism, it effectively avoids the instantaneous current impact of grid connection and improves the power quality and equipment protection level during the microgrid reclosing process. Attached Figure Description

[0049] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0050] Figure 1 This is a schematic diagram of the method logic of the present invention. Detailed Implementation

[0051] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following detailed description of the specific implementation methods, structures, features and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided.

[0052] Example 1

[0053] Please see Figure 1 As shown, this invention provides a seamless switching method for enhanced stable operation under microgrid main network failure, comprising the following steps:

[0054] Step 1: Obtain the voltage, current, frequency, and phase of each node in the microgrid; determine the operating status of the main power grid through joint acquisition; and simultaneously acquire electrical parameter information from multiple monitoring devices at designated locations.

[0055] Step 2: Align the electrical parameters obtained in Step 1 with a unified time reference standard, determine the response time difference of each monitoring device to the fault event, and select the node where the monitoring device is located as the main control node according to the preset rules.

[0056] The preset rules for selecting the main control node include:

[0057] S1. Receive the local timestamp of each control node detecting a voltage drop event in the main grid, and calculate the time difference between the voltage drop event occurrence time and the local detection time based on the set unified time reference, so as to obtain the corresponding response time.

[0058] Specifically, after a voltage drop event occurs in the main power grid, a unified reference time is set for the entire network, such as the Coordinated Universal Time standard provided by the network time synchronization module, and set as [time base]. ;

[0059] Each control node records the timestamp of the first local detection of a voltage drop. ;

[0060] Subsequently, for each control node, its response time is calculated. ;

[0061] For example, if the unified time reference is 1000.000 milliseconds, and the detection time of a certain control node is 1002.037 milliseconds, then the response time of that node is 2.037 milliseconds.

[0062] S2. Obtain the current voltage, current, nominal capacity, and remaining capacity of the energy storage device connected to each control node, and calculate the sustainable power supply time using the following formula:

[0063] Sustainable power supply time = Remaining capacity value ÷ Current value;

[0064] And this sustainable power supply time will be used as a score for energy storage output capacity;

[0065] Specifically, after obtaining the response time of each control node, the current status parameters of the energy storage devices connected to each control node are then obtained.

[0066] The current voltage and current values ​​are read directly by the local measuring device. The nominal capacity value is pre-stored as an inherent parameter of the device. The remaining capacity value can be obtained by multiplying the current remaining power by the nominal capacity value.

[0067] For example, the parameters of the energy storage device at a certain node are:

[0068] Current voltage: 48V;

[0069] Current current: 20A;

[0070] Nominal capacity: 100Ah;

[0071] Remaining capacity: 60Ah;

[0072] The sustainable power supply time is:

[0073] 60Ah ÷ 20A = 3 hours.

[0074] The 3-hour period is used as the energy storage output capacity score for this node, representing its ability to maintain power supply independently under the current load conditions.

[0075] S3. During the communication link initialization phase, a handshake request data frame containing number information is broadcast to all control nodes in sequence. Each control node immediately returns a handshake response data frame containing the same number information after receiving the handshake request data frame.

[0076] The number of handshake response data frames successfully returned by each control node within a set time window and the average round-trip communication time are counted, and the communication score is calculated according to the following formula:

[0077] Communication score = Number of handshake response data frames − (Round-trip communication time × penalty coefficient);

[0078] Specifically, handshake request data frames are sent to all control nodes according to their assigned numbers. The frame format includes a fixed identifier (such as 0xAA55) and a unique number (such as frame number 001).

[0079] Each control node immediately returns a handshake response data frame upon receiving the corresponding data frame. The response frame contains the same numbering information as the request frame.

[0080] For example: broadcast 10 handshake request data frames to control node A, of which A successfully returns 9 response frames, with an average round-trip communication time of 45 milliseconds and a penalty coefficient of 0.2.

[0081] The communication score is: 9 − (45 × 0.2) = 0;

[0082] If the other node B successfully responds with 10 frames, and the average round-trip communication time is 20 milliseconds, the communication score is: 10 − (20 × 0.2) = 6;

[0083] This communication score quantifies the timeliness and stability of the communication link, and together with steps one and two, serves as a key basis for subsequent election weight scoring.

[0084] S4. Based on the response time, energy storage output capacity score and communication score of each control node, a comprehensive score is calculated according to the preset weighted calculation rules, and the control node with the highest score is selected as the main control node.

[0085] Specifically, the weighting coefficients are set as follows in this embodiment:

[0086] Response time weight: W1 = 0.4;

[0087] Energy storage capacity weight: W2=0.3;

[0088] Communication scoring weight: W3=0.3;

[0089] Furthermore, the three core parameters used to calculate the comprehensive score in this embodiment—response score, energy storage output capacity score, and communication score—have different original dimensions (for example, response time is measured in milliseconds or seconds, and energy storage capacity is measured in hours); therefore, all parameters must be normalized before they are substituted into the weighted summation formula.

[0090] Normalization converts all parameters into dimensionless values, thus ensuring that the final weighted calculation is performed on a unified dimensional basis.

[0091] To ensure consistent scoring, the response time was normalized and its reciprocal was used (shorter response time, higher score). The final comprehensive scoring formula is:

[0092] Overall score = W1 × (1 / response time) + W2 × energy storage output capacity score + W3 × communication score;

[0093] For example, if the response time of a certain control node is rounded to 2 milliseconds, its energy storage score is 3 hours, and its communication score is 6.

[0094] Therefore, its overall score is:

[0095] 0.4×(1 / 2)+0.3×3+0.3×6=0.2+0.9+1.8=2.9.

[0096] If multiple nodes are calculated simultaneously, the node with the highest score is determined as the master control node, which will be used to dominate voltage and frequency control in the subsequent operation of the microgrid.

[0097] Step 3: The main control node sends control commands to the auxiliary control node. After receiving the commands, the auxiliary control node switches to auxiliary control mode according to the preset priority and tracks the voltage and frequency output of the main control node.

[0098] After the auxiliary control node switches to the new control command receiving node, the auxiliary control node uses linear interpolation to proportionally decrease the control reference value before the switch at a fixed time step within the reference value switching transition time window, while simultaneously proportionally increasing the control reference value provided by the new receiving node, until the control output fully adopts the control reference value of the new receiving node.

[0099] Specifically, when the auxiliary control node switches to a new control command receiving node after a communication interruption, the following linear interpolation mechanism is used to avoid control output shocks caused by rapid changes in control reference values:

[0100] First, obtain the control reference value output by the control command receiving node used by the auxiliary control node before the switch, and record it as the initial reference value; then obtain the control reference value output by the new control command receiving node, and record it as the target reference value.

[0101] Then, set a reference value switching transition time window, for example, dividing it into several equally spaced sampling points in seconds.

[0102] Within this time window, the control reference value is gradually changed from the initial reference value to the target reference value in a linear progression with equal time steps. Specifically, for each sampling point, the current reference value is calculated as the initial reference value plus the time step percentage multiplied by the target difference.

[0103] Throughout the transition process, the auxiliary control node performs control output based on the linearly interpolated reference value, thereby reducing the impact of instantaneous reference value changes and ensuring a smooth transition in the control process.

[0104] After communication is restored, the auxiliary control node determines whether to switch back to the original primary control node based on the locally stored control node priority table.

[0105] The priority table for control nodes determines the priority order based on a weighted average of the node identifier, historical stability score, and communication quality score.

[0106] Specifically, after the auxiliary control node switches to a new control command receiving node due to a communication interruption, the system continuously monitors the communication status of the main control node.

[0107] Once communication with the primary control node is restored, the secondary control node determines whether to perform a switchback operation based on the locally stored control node priority table.

[0108] In the control node priority table, the priority order of each control node is determined based on the following indicators: the control node's identifier, historical control stability score, and communication quality score.

[0109] The historical control stability score includes indicators such as the number of control switching times and the degree of fluctuation in voltage and frequency regulation; the communication quality score includes communication delay, data packet loss rate, and signal-to-noise ratio of the communication channel.

[0110] In this embodiment, it should be noted that the communication quality score item included in the control node priority table is a medium- to long-term, smoothed score value obtained after statistical averaging, standard deviation analysis, or filtering over a long window, based on the communication path priority table or the instantaneous broadcast data it depends on. This processing method avoids the control back-cutting decision from relying on instantaneous network fluctuation data, thereby ensuring the stability and reliability of the decision.

[0111] Each scoring item is assigned a preset weight, and a comprehensive score is obtained by weighted summation. The auxiliary control node compares the comprehensive score of the current control command receiving node with that of the original master control node. If the original master control node has a higher score and the score difference exceeds a preset priority difference threshold, a switchback operation is performed, causing the control flow to follow the original master control node again.

[0112] During each broadcast cycle, the auxiliary control node dynamically updates its communication path priority table based on the information broadcast by other control nodes.

[0113] The broadcast information includes the node identifier, the current communication delay value, the data packet loss rate, and the communication channel noise level.

[0114] Specifically, to ensure that the auxiliary control node can quickly and reliably select the best control command receiving node when communication with the main control node is interrupted, the following dynamic update mechanism for the communication path priority table is adopted:

[0115] During each broadcast cycle, the auxiliary control node listens for data packets broadcast by other control nodes in the network. The broadcast content includes the control node's identifier, current communication delay value, data packet loss rate, and communication channel noise level.

[0116] The auxiliary control node scores the above communication parameters. The scoring methods include: the communication delay value is scored linearly in segments, with a higher score for shorter delays; the data packet loss rate is calculated based on an inverse proportional function, with a higher score for lower packet loss rates; and the noise level value is graded and deducted according to preset levels.

[0117] Each score is weighted and summed according to preset weights to obtain the current communication quality score of the control node.

[0118] The score is used to update the priority ranking of all control nodes in the communication path priority table.

[0119] The node with higher priority will be selected as the control command receiving node in the event of a subsequent communication interruption.

[0120] The aforementioned dynamic update mechanism ensures that the communication path priority table can reflect the current network status in real time, thereby improving the reliability of the auxiliary control node's decision-making in abnormal situations.

[0121] Step 4: After the control state switch is completed, adjust the voltage amplitude, frequency reference value and adjustment rate of the main control node and the auxiliary control node so that the output parameters of the control node tend to be consistent within the set time window.

[0122] Setting the time window includes the following steps:

[0123] A1. Set a baseline time window length;

[0124] Specifically, a standard time window value is first preset as the maximum allowable response delay benchmark for synchronous switching between control nodes after a main grid fault occurs in the microgrid. The length of this benchmark time window can be set according to system design parameters, for example, an initial value of 100ms, and can be initialized and corrected based on microgrid scale, communication topology, load response characteristics, etc.

[0125] A2. If any of the following conditions are met, an extension amount is added to the length of the reference time window. In this embodiment, the extension amount is set to 30ms:

[0126] a21. Communication quality does not meet requirements: The average number of retransmissions of the handshake request data frame is greater than the set handshake retransmission threshold, or the noise level of the communication channel is greater than the set communication noise level threshold, or the standard deviation of the round-trip communication time of the handshake response data frame of the control node is greater than the set communication stability judgment threshold.

[0127] a22. Short-term voltage disturbance exists: The duration of the voltage disturbance at the microgrid's point of common coupling is less than the set disturbance duration judgment threshold, and its voltage recovery slope is greater than the set voltage recovery slope threshold.

[0128] A3. If any of the extension conditions in a21 and a22 of A2 are not met, and the equivalent virtual moment of inertia of all connected power sources in the microgrid is less than the set equivalent moment of inertia threshold, and the total active power change rate is greater than the set active power change rate threshold, then the length of the reference time window will be reduced by a shortening amount.

[0129] A4. The final length of the time window is the result of adding or subtracting values ​​based on the baseline time window length set in A1, according to the extension amount corresponding to the extension condition satisfied in A2 and the shortening amount corresponding to the shortening condition satisfied in A3.

[0130] In this embodiment, the base time window length is 100ms. If conditions a21 and A3 of A2 are triggered, the final time window length is: 100ms + 30ms - 30ms = 100ms, which remains unchanged.

[0131] If A2 is not triggered but A3 is triggered, the time is 70ms;

[0132] If A2 triggers both items but A3 does not trigger, the time is 160ms, and so on.

[0133] Step 5: After the adjustment in Step 4 is completed, monitor the change in load-side current. Before the load current rises to the preset load current rise threshold, correct the active power reference value of each power conversion device and adjust the discharge power of the energy storage device to meet the energy storage adjustment threshold.

[0134] Step 6: After the microgrid is running stably, detect the status, voltage amplitude difference, and phase difference of the switch connected to the main grid. If the voltage amplitude difference threshold and phase difference threshold are met, control the switch to be engaged and limit the instantaneous current connected to the grid. The limit is executed based on the grid current rise rate threshold.

[0135] The operations for determining whether the grid-connected voltage amplitude difference threshold and phase difference threshold are met include:

[0136] After detecting that the current voltage amplitude difference and phase difference meet the set grid connection conditions, the voltage amplitude and phase values ​​of the target control node are periodically collected within the sampling time window, and the rate of change between each sampling time is calculated.

[0137] Based on the rate of change and the preset prediction time interval, the voltage amplitude and phase values ​​at the prediction time point are calculated, and the voltage amplitude difference and phase difference at the corresponding moment of the prediction time point are obtained accordingly.

[0138] When the calculation results show that the grid voltage amplitude difference threshold and phase difference threshold are still met at the predicted time point, a switch closing command is issued at an earlier time point before the predicted time point so that the switch can be closed at the predicted time point.

[0139] Specifically, a sampling time window is set, and the voltage amplitude and voltage phase values ​​at the target control node are periodically collected within the time window according to a fixed time step, forming a continuous voltage sampling sequence and phase sampling sequence.

[0140] For each pair of adjacent sampling moments in the voltage and phase sampling sequences, the difference between the voltage and phase values ​​is calculated, and this difference is divided by the sampling interval to obtain the voltage change rate and phase change rate within that interval. The voltage change rate is defined as: the voltage value at the next moment minus the voltage value at the previous moment, divided by the time interval between the two moments; the phase change rate is calculated similarly.

[0141] Based on the current voltage change rate and phase change rate values, combined with a preset prediction time interval, and using the current sampling point as a basis, a numerical extrapolation method with equal step size (such as each step being equal to the current change rate multiplied by the step time) is used to recursively predict the voltage amplitude and phase value at the prediction time point.

[0142] Based on the predicted voltage and phase values, they are compared with the current grid reference voltage and reference phase to calculate the voltage amplitude difference and phase difference at the predicted time.

[0143] The predicted voltage amplitude difference and phase difference are compared with the grid-connected voltage amplitude difference threshold and phase difference threshold, respectively:

[0144] If both are within the set threshold range, it is considered that the voltage and phase conditions remain stable at the predicted time and have a tendency to continuously meet the grid connection conditions.

[0145] If any difference exceeds the set threshold, it is considered that although the current voltage and phase temporarily meet the conditions, the trend is unstable, and the grid connection operation is postponed.

[0146] When the difference between the predicted times meets the conditions, the control operation of the switch is triggered at a preset advance time point before the predicted time point arrives.

[0147] The advance timing is set to take into account the response delay time required for the grid-connected switch to physically close after receiving the control command, so as to ensure that the switch closes accurately before the predicted time and achieves disturbance-free grid connection.

[0148] Through the above steps, it is ensured that grid connection control not only considers the current state, but also incorporates the prediction and judgment of future short-term voltage and phase change trends, thereby improving the accuracy of grid connection timing selection and the stability of the grid connection process, and effectively reducing the risk of grid connection shock caused by sudden changes.

[0149] Methods for limiting and controlling the instantaneous current connected to the grid include:

[0150] At a preset advance time before the control switch is closed, the instantaneous grid-connected current value at the grid-connected switch is collected, and continuous sampling is performed according to a preset time interval. The current rise rate is calculated by the current difference between adjacent sampling points.

[0151] At the instant the switch is closed, the rate of change of the output voltage in the control loop is adjusted to suppress the rate of rise of the instantaneous grid-connected current.

[0152] The rate of change of the output voltage is set according to the current instantaneous rise rate of the grid-connected current;

[0153] When the current rise rate is between the first current change rate threshold and the second current change rate threshold, the output voltage change rate decreases as the current rise rate increases.

[0154] When the current rise rate exceeds the second current change rate threshold, the output voltage change rate is not lower than the preset change rate lower limit.

[0155] After detecting that the current rise rate is continuously lower than the current stability judgment threshold, and this state continues for more than the preset stability judgment time window, the original voltage regulation rate of the control loop is restored.

[0156] Specifically, in this embodiment, before the control switch is ready to close, for example, 20 milliseconds in advance, continuous sampling of the instantaneous grid-connected current begins at the grid-connected switch.

[0157] Sampling is performed at a time interval of once every millisecond, and the output current value is collected five times consecutively;

[0158] For any two adjacent sampling times, calculate the difference between their instantaneous grid-connected current values, and divide the difference by the corresponding time interval to obtain the rise rate sequence of the grid-connected current.

[0159] Then, the maximum value is selected from this sequence as the current representative grid-connected current rise rate, which is used as a reference for adjusting the subsequent voltage change rate.

[0160] Subsequently, at the instant the grid-connected switch is closed, the controller adjusts the rate of change of the output voltage reference value of the target control node according to the magnitude of the representative grid-connected current rise rate, so as to limit the magnitude of the grid-connected current change.

[0161] The rules for setting the output voltage change rate are as follows:

[0162] When the current rise rate is less than the first current change rate threshold, the output voltage changes at the default rate.

[0163] When the current rise rate is between the first current change rate threshold and the second current change rate threshold, the output voltage change rate gradually decreases as the current rise rate increases, and the decrease is linearly related to it.

[0164] When the current rise rate exceeds the second current change rate threshold, the output voltage change rate is limited to a preset minimum change rate to enhance the ability to suppress severe current surges.

[0165] The first current change rate threshold is used to identify moderate grid connection shocks, and the second current change rate threshold is used to identify severe shocks. Both can be set based on factors such as historical grid connection operation data, power supply access characteristics, and controller bandwidth, and can be dynamically updated.

[0166] After the switch is closed, the controller continuously monitors the change in the rate of increase of the grid-connected current;

[0167] When the current rise rate is detected to be lower than the current stability judgment threshold for multiple consecutive sampling cycles, and the duration of this state exceeds the preset stability judgment time window, it is determined that the grid-connected current has stabilized. At this time, the normal rate of change of the output voltage is restored, and the limiting control process is terminated.

[0168] Example 2

[0169] Compared to Example 1, Example 2 provides a seamless handover method for enhanced stable operation under microgrid main network failure, comprising the following steps:

[0170] Step 1: Obtain the voltage, current, frequency, and phase of each node in the microgrid; determine the operating status of the main power grid through joint acquisition; and simultaneously acquire electrical parameter information from multiple monitoring devices at designated locations.

[0171] A default master node mechanism is introduced during system initialization or offline startup, including:

[0172] During system construction, all control nodes store the same, pre-defined priority list, which is created based on hard metrics of node resources such as maximum battery storage capacity, unique hardware ID, or computing power assessment.

[0173] The node ranked first in the list is defined as the default master node.

[0174] The main function of the default master node is to provide a clear, decentralized startup anchor point in the event of system disconnection or lack of coordinated communication, ensuring that the system can perform basic control tasks.

[0175] Step 2: Align the electrical parameters obtained in Step 1 with a unified time reference standard, determine the response time difference of each monitoring device to the fault event, and select the node where the monitoring device is located as the main control node according to the preset rules.

[0176] Furthermore, after a main grid fault is detected, if a node does not receive any instruction or announcement from the main control node within the preset emergency timeout period, the node will initiate a local escalation arbitration procedure, including:

[0177] Local assessment: Nodes conduct assessments based on their own local, non-communication-dependent data (such as response time and current energy storage status).

[0178] Arbitration decision: Based on the ranking in the preset priority list, if a node is the highest-ranking node in the current list and is functioning normally, then the node will automatically be promoted to the master control node and begin broadcasting control commands to the entire network.

[0179] Dynamic adjustment: After establishing the basic master control, the system immediately uses the preset rules of S1-S4 in Example 1 to select the node with the best current performance as the master control node.

[0180] Step 3: The main control node sends control commands to the auxiliary control node. After receiving the commands, the auxiliary control node switches to auxiliary control mode according to the preset priority and tracks the voltage and frequency output of the main control node.

[0181] Without external communication connections, all nodes will follow the control commands of the currently promoted default master node based on the arbitration result of step two, ensuring system control consistency during a fault. Once the dynamic election is complete, auxiliary nodes will switch to track the new optimal master node.

[0182] Step 4: After the control state switch is completed, adjust the voltage amplitude, frequency reference value and adjustment rate of the main control node and the auxiliary control node so that the output parameters of the control node tend to be consistent within the set time window.

[0183] Step 5: After the adjustment in Step 4 is completed, monitor the change in load-side current. Before the load current rises to the preset load current rise threshold, correct the active power reference value of each power conversion device and adjust the discharge power of the energy storage device to meet the energy storage adjustment threshold.

[0184] Step 6: After the microgrid is operating stably, detect the status, voltage amplitude difference, and phase difference of the switch connected to the main grid. If the voltage amplitude difference threshold and phase difference threshold are met, control the switch to be engaged and limit the instantaneous grid current. The limit is executed based on the grid current rise rate threshold.

[0185] The above formulas are all dimensionless calculations. The formulas are derived from software simulations based on a large amount of collected data to obtain the most recent real-world results. The preset parameters and thresholds in the formulas are set by those skilled in the art according to the actual situation.

[0186] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A seamless handover method for enhanced stable operation under microgrid master grid failure, characterized in that, Includes the following steps: Step 1: Obtain the voltage, current, frequency, and phase of each node in the microgrid; determine the operating status of the main power grid through joint acquisition; and simultaneously acquire electrical parameter information from multiple monitoring devices at designated locations. Step 2: Align the electrical parameters obtained in Step 1 with a unified time reference standard, determine the response time difference of each monitoring device to the fault event, and select the node where the monitoring device is located as the main control node according to the preset rules. The preset rules for selecting the master control node include: S1. Receive the local timestamp of each control node detecting a voltage drop event in the main grid, and calculate the time difference between the voltage drop event occurrence time and the local detection time based on the set unified time reference, so as to obtain the corresponding response time. S2. Obtain the current voltage, current, nominal capacity, and remaining capacity of the energy storage device connected to each control node, and calculate the sustainable power supply time using the following formula: Sustainable power supply time = Remaining capacity value ÷ Current value; And this sustainable power supply time will be used as a score for energy storage output capacity; S3. During the communication link initialization phase, a handshake request data frame containing number information is broadcast to all control nodes in sequence. Each control node immediately returns a handshake response data frame containing the same number information after receiving the handshake request data frame. The number of handshake response data frames successfully returned by each control node within a set time window and the average round-trip communication time are counted, and the communication score is calculated according to the following formula: Communication score = Number of handshake response data frames − Round-trip communication time × Penalty coefficient; S4. Based on the response time, energy storage output capacity score and communication score of each control node, a comprehensive score is calculated according to the preset weighted calculation rules, and the control node with the highest score is selected as the main control node. Step 3: The main control node sends control commands to the auxiliary control node. After receiving the commands, the auxiliary control node switches to auxiliary control mode according to the preset priority and tracks the voltage and frequency output of the main control node. Step 4: After the control state switch is completed, adjust the voltage amplitude, frequency reference value and adjustment rate of the main control node and the auxiliary control node so that the output parameters of the control node tend to be consistent within the set time window. Step 5: After the adjustment in Step 4 is completed, monitor the change in load-side current. Before the load current rises to the preset load current rise threshold, correct the active power reference value of each power conversion device and adjust the discharge power of the energy storage device to meet the energy storage adjustment threshold. Step 6: After the microgrid is operating stably, detect the status, voltage amplitude difference, and phase difference of the switch connected to the main grid. If the voltage amplitude difference threshold and phase difference threshold are met, control the switch to be engaged and limit the instantaneous grid current. The limit is executed based on the grid current rise rate threshold.

2. The seamless handover method for enhanced stable operation under failure of a master network of a microgrid according to claim 1, characterized in that, Setting the time window in step four includes the following steps: A1. Set a baseline time window length; A2. If any of the following conditions are met, then add an extension amount to the base time window length; a21. Communication quality does not meet requirements: The average number of retransmissions of the handshake request data frame is greater than the set handshake retransmission threshold, or the noise level of the communication channel is greater than the set communication noise level threshold, or the standard deviation of the round-trip communication time of the handshake response data frame of the control node is greater than the set communication stability judgment threshold. a22. Short-term voltage disturbance exists: The duration of the voltage disturbance at the microgrid's point of common coupling is less than the set disturbance duration judgment threshold, and its voltage recovery slope is greater than the set voltage recovery slope threshold. A3. If any of the extension conditions in a21 and a22 of A2 are not met, and the equivalent virtual moment of inertia of all connected power sources in the microgrid is less than the set equivalent moment of inertia threshold, and the total active power change rate is greater than the set active power change rate threshold, then the length of the reference time window will be reduced by a shortening amount. A4. The final length of the time window is the result of adding or subtracting values ​​based on the baseline time window length set in A1, according to the extension amount corresponding to the extension condition satisfied in A2 and the shortening amount corresponding to the shortening condition satisfied in A3.

3. The seamless handover method for enhanced stable operation under failure of a master in a microgrid according to claim 1, characterized in that, In step six, the methods for limiting the instantaneous grid-connected current include: At a preset advance time before the control switch is closed, the instantaneous grid-connected current value at the grid-connected switch is collected, and continuous sampling is performed according to a preset time interval. The current rise rate is calculated by the current difference between adjacent sampling points. At the instant the switch is closed, the rate of change of the output voltage in the control loop is adjusted to suppress the rate of rise of the instantaneous grid-connected current. The rate of change of the output voltage is set according to the current instantaneous rise rate of the grid-connected current; When the current rise rate is between the first current change rate threshold and the second current change rate threshold, the output voltage change rate decreases as the current rise rate increases. When the current rise rate exceeds the second current change rate threshold, the output voltage change rate is not lower than the preset change rate lower limit. After detecting that the current rise rate is continuously lower than the current stability judgment threshold, and this state continues for more than the preset stability judgment time window, the original voltage regulation rate of the control loop is restored.

4. The seamless switching method for enhanced stable operation under microgrid main network failure as described in claim 1, characterized in that, After the auxiliary control node switches to the new control command receiving node, the auxiliary control node uses linear interpolation to proportionally decrease the control reference value before the switch at a fixed time step within the reference value switching transition time window, while simultaneously proportionally increasing the control reference value provided by the new receiving node, until the control output fully adopts the control reference value of the new receiving node.

5. The seamless switching method for enhanced stable operation under microgrid main network failure as described in claim 4, characterized in that, After communication is restored, the auxiliary control node determines whether to switch back to the original primary control node based on the locally stored control node priority table. The priority table for control nodes determines the priority order based on a weighted average of the node identifier, historical stability score, and communication quality score.

6. The seamless handover method for enhanced stable operation under failure of a master in a microgrid according to claim 5, characterized in that, During each broadcast cycle, the auxiliary control node dynamically updates its communication path priority table based on the information broadcast by other control nodes. The broadcast information includes the node identifier, the current communication delay value, the data packet loss rate, and the communication channel noise level.

7. The seamless handover method for enhanced stable operation under failure of a master in a microgrid according to claim 3, characterized in that, In step six, the operation of determining whether the grid-connected voltage amplitude difference threshold and phase difference threshold are met includes: After detecting that the current voltage amplitude difference and phase difference meet the set grid connection conditions, the voltage amplitude and phase values ​​of the target control node are periodically collected within the sampling time window, and the rate of change between each sampling time is calculated. Based on the rate of change and the preset prediction time interval, the voltage amplitude and phase values ​​at the prediction time point are calculated, and the voltage amplitude difference and phase difference at the corresponding moment of the prediction time point are obtained accordingly. When the calculation results show that the grid voltage amplitude difference threshold and phase difference threshold are still met at the predicted time point, a switch closing command is issued at an earlier time point before the predicted time point so that the switch can be closed at the predicted time point.

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