A new energy micro-grid off-grid and grid-connected power supply control method and system

Abstract

The application discloses a new energy micro-grid off-grid power supply control method and system, relates to the technical field of micro-grid power supply control, and comprises the following steps: acquiring the voltage, frequency and voltage phase angle of a micro-grid, determining a switching task, reading primary wiring information and switch opening / closing states, and forming a current operation topology; determining a power supply starting point according to the switching task, determining a power supply sequence according to load levels and load power, and searching for a candidate power supply path; dividing a protection section along the candidate power supply path, determining a setting interval according to the maximum load current and the minimum fault current, and deleting a path that does not meet protection requirements; rechecking common protection sections in the process of gradually adding the path, forming a target operation topology, and writing protection setting data into a backup setting value area; and after verification, performing a switch action, so that the safety and reliability of micro-grid off-grid operation are improved.

Description

Technical Field

[0001] This invention relates to the field of microgrid power supply control technology, and in particular to a method and system for controlling off-grid and on-grid power supply in a new energy microgrid. Background Technology

[0002] With the integration of new energy power generation, energy storage, and flexible loads into the distribution network, new energy microgrids are widely used in industrial parks, islands, industrial and commercial users, and emergency power supply scenarios. Microgrids typically need to operate in both grid-connected and off-grid states, and switch modes when there are external grid faults, voltage and frequency anomalies, or when the grid returns to normal. Existing control methods achieve off-grid disconnection, grid-connected restoration, and partial load power supply through voltage and frequency detection, synchronization judgment, distributed power source control, and switching sequence control.

[0003] However, distributed power sources in new energy microgrids are mostly power electronic interface power sources, and the fault current is limited and changes rapidly. After the operating topology changes, the magnitude, direction and power supply path of the fault current will also change. However, the existing technology does not adequately consider whether the switching conditions are met and whether the switch can operate, and does not adequately consider the protection coordination after the switching, which easily leads to the problem of mismatch between the protection settings and the actual operating topology. Summary of the Invention

[0004] In a first aspect, the present invention provides a method for controlling the off-grid and on-grid power supply of a new energy microgrid, the specific steps of which include: The system acquires the voltage, frequency, and voltage phase angle of the microgrid, determines the switching task, and forms the current operating topology based on the primary wiring information and the switch opening and closing status. The power supply starting point is determined according to the switching task, the load power supply sequence is determined according to the load level and load power, and candidate power supply paths from the power supply starting point to each load branch are searched. Divide the protection zone along the candidate power supply path, establish the path segment association between the candidate power supply path and the protection zone, determine the lower limit of operation based on the maximum load current of the protection zone, determine the upper limit of operation based on the minimum fault current of the protection zone, and determine the protection setting margin based on the difference between the upper limit of operation and the lower limit of operation. Candidate power supply paths are added in accordance with the load power supply sequence. When a candidate power supply path is added, the protection zone shared by the candidate power supply path and the reserved power supply path is determined according to the path segment association relationship. The new load corresponding to the candidate power supply path is included in the shared protection zone, the maximum load current of the shared protection zone is updated, and the minimum fault current is recalculated when the power supply circuit between the distributed power source and the shared protection zone changes. The lower limit, upper limit, and protection setting margin of the shared protection zone are redefined based on the updated maximum load current and minimum fault current. If the lower limit of any shared protection zone is not less than the upper limit, the attempt to add the candidate power supply path is cancelled and it is added to the restricted path set; otherwise, the candidate power supply path is retained. The target operating topology is formed from the reserved candidate power supply paths, protection setting data and switching action sequence are generated, the protection setting data is written into the backup setting area of ​​the protection device, and after verification, the device is switched to the backup setting area and the switching action sequence is executed. If the verification fails, the corresponding protection section is recorded in the restricted path set.

[0005] Preferably, the handover task includes off-grid handover task and on-grid handover task; When the microgrid voltage is lower than the preset lower limit voltage, exceeds the preset upper limit voltage, or the frequency is not within the preset frequency range, an off-grid switching task is generated. Once the voltage and frequency on both the microgrid side and the external grid side have returned to the allowable range, calculate the voltage difference, frequency difference, and voltage phase angle difference on both sides of the grid connection point. When all three are within the allowable range for synchronization, generate a grid connection switching task. Before closing the grid connection switch, recalculate the voltage difference, frequency difference, and voltage phase angle difference. If any one of them exceeds the allowable range for synchronization, cancel the closing and maintain the current switch state.

[0006] Preferably, the current operating topology, power supply starting point, and candidate power supply path are determined in the following manner: Obtain the primary wiring information and switch open / closed status of the microgrid, and construct the current operating topology using lines that are in the closed state and electrically connected at both ends; When performing off-grid switching tasks, the operating status and current available power of each grid-type power source are read, and the bus where the grid-type power source is located that is operating normally and whose current available power is greater than the preset minimum power is determined as the power supply starting point. When performing grid connection switching tasks, the grid connection point bus is determined as the power supply starting point; When determining the power supply sequence for loads, they should be arranged from high to low according to their load level, and if the load levels are the same, they should be arranged from small to large according to their load power.

[0007] Preferably, when searching for candidate power supply paths, the search starts from the power supply origin and proceeds step by step along the lines and switches that are in an operational state toward the bus where the load is located. After reaching the busbar where the load is located, the busbars, lines and switches along the way are recorded as candidate power supply paths; Read the active power, reactive power, and bus voltage of the lines connected to the candidate power supply path, and calculate the line operating current; when the operating current of any line is greater than the allowable current carrying capacity, delete the candidate power supply path passing through that line; when the candidate power supply path passes through the protection section in the restricted path set, delete the candidate power supply path.

[0008] Preferably, when dividing the protection zone, the installation location of the protection device and the circuit breaker it controls are read according to the power supply direction of the candidate power supply path; The line between two adjacent protection devices is called a double-end protection section; the line with a protection device at one end and a circuit breaker at the other end is called a single-end protection section. When a candidate power supply path contains a non-energized line, a topology change marker is set in the corresponding protection section of that line; Based on the topology change markers set for the corresponding protected area, the minimum fault current of the protected area is recalculated during the process of attempting to add a candidate power supply path.

[0009] Preferably, the path segment association relationship includes at least the circuit breaker, protection device, candidate power supply path passing through the protected segment, load branch powered by the protected segment, and distributed power source that provides fault current to the protected segment. When a candidate power supply path is attempted to be added, the protection zone affected by the new load, the protection zone shared with the existing power supply path, and the protection zone where the fault current needs to be recalculated are determined based on the path segment association relationship. When a candidate power supply path is withdrawn, the record of any new loads added to the shared protection zone by that candidate power supply path is simultaneously deleted.

[0010] Preferably, when determining the minimum fault current, fault points are set at the beginning and end of the protected section, and the total fault current for three-phase short circuit and two-phase short circuit is calculated respectively. Based on the candidate power supply path and the switch opening and closing status, the distributed power source of the closed electrical path is determined, the fault current during the protection device operation judgment period is read in real time, and the total fault current of the fault point is accumulated. The total fault currents corresponding to the three-phase short circuit at the beginning of the protected section, the two-phase short circuit at the beginning of the protected section, the three-phase short circuit at the end of the protected section, and the two-phase short circuit at the end of the protected section are obtained respectively. The minimum total fault current is selected as the minimum fault current of the protected section.

[0011] Preferably, when determining the protection setting margin, power flow calculation is performed on the candidate power supply path to obtain the maximum load current of the protected section, and the product of the maximum load current and the preset reliability coefficient is used as the lower limit value of the operation. Divide the minimum fault current by the preset sensitivity coefficient to obtain the upper limit value for operation; When the lower limit of the action is less than the upper limit of the action, the range between the lower and upper limits of the action is used as the setting interval, and the difference between the upper and lower limits of the action is used as the protection setting margin. Otherwise, the protected area is marked as a prohibited area.

[0012] Preferably, when there are multiple candidate power supply paths for the same load branch, an attempt is made to add each candidate power supply path to obtain the updated protection setting margin of the shared protection zone after the attempt is made. The minimum updated protection setting margin in each shared protection zone is used as the margin retention value for the candidate power supply path; Prioritize retaining the candidate power supply path with the largest margin retention value; if the margin retention values ​​are the same, prioritize retaining the candidate power supply path with the fewest required switching operations. If all candidate power supply paths for the current load branch are cancelled, skip the load branch and continue processing the next load branch, or stop the switching task when the preset power supply constraint requires the load branch to be powered.

[0013] Preferably, the protection setting data includes the protection positive direction, the main protection action setting value, the backup protection action setting value, the correspondence between the main protection device and the backup protection device, and the circuit breaker number for tripping. Specifically, the direction from the power supply starting point to the load branch is defined as the positive direction of protection; for double-ended protection sections, the protection devices corresponding to the circuit breakers at both ends are designated as the main protection devices; for single-ended protection sections, the protection device on the protection device side is designated as the main protection device; and the protection device encountered for the first time along the protection section towards the power supply starting point is designated as the backup protection device. When writing protection setting data, the protection setting data and the spare setting zone number are written to the protection device, and the setting zone number, verification result and self-test result returned by the protection device are read; when all three meet the preset verification conditions, the device is switched to the spare setting zone and the switching action sequence is executed; when any one of the preset verification conditions is not met, the setting zone switching is not executed, and the protection section corresponding to the protection device is recorded in the restricted path set. The sequence of switching actions is generated based on the difference in switching states between the current operating topology and the target operating topology. When performing an off-grid switching task, the opening action of the grid-connected switch is scheduled before the target topology activation action, and the line closing action is performed after the corresponding protection setting zone is successfully switched. When performing a grid-connected switching task, the grid-connected switch closing action is performed after the synchronization conditions are met. If any switch fails to return to the expected opening or closing state within a preset time, subsequent switching actions are stopped, and a switching blocking signal is output. For switches that have completed their actions and can be restored, restoration is performed according to the state before the switching. For switches that cannot be restored, the protection zone where they are located is recorded in the restricted path set for subsequent target operating topology reconstruction.

[0014] Secondly, the present invention provides a new energy microgrid off-grid and grid-connected power supply control system, comprising: The task analysis module is used to obtain the voltage, frequency, and voltage phase angle of the microgrid, determine the switching task, and form the current operating topology; The path search module is used to determine the power supply starting point and the power supply sequence to the load, and to search for candidate power supply paths; The segment association module is used to divide the protection segment and establish the path segment association relationship between the candidate power supply path and the protection segment; The margin calculation module is used to determine the lower limit of action, the upper limit of action, and the protection setting margin of the protected area. The path attempt addition module is used to attempt to add candidate power supply paths according to the load power supply sequence, determine the shared protection zone based on the path segment association, update the maximum load current and minimum fault current of the shared protection zone, and cancel the attempt to add candidate power supply paths when the protection setting interval disappears. The power supply control module is used to form the target operating topology from the reserved candidate power supply paths, generate protection setting data and switch action sequence, write the protection setting data into the spare setting area of ​​the protection device, and execute the switch action sequence after verification.

[0015] The beneficial effects of this invention are: Before switching between on-grid and off-grid, this invention assesses the load power supply path and the reliability of protection actions together, avoiding the formation of a target operating topology solely based on power supply accessibility. By calculating the maximum load current and minimum fault current of the protected area, it preemptively eliminates power supply paths whose protection settings cannot meet the requirements, effectively reducing the risk of protection maloperation, failure to operate, and expansion of the power outage range. Simultaneously, during the gradual addition of load paths, the shared protected area is re-verified, making the target operating topology more adaptable to scenarios with multiple power sources, multiple loads, and topology changes. Protection setting data is written and verified through the backup setting area before the switching action is executed, improving the safety and reliability of the on-grid and off-grid switching process. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a flowchart of the on-grid and off-grid power supply control for the new energy microgrid of the present invention. Detailed Implementation

[0018] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0019] This invention takes a new energy microgrid containing an external power grid, a grid connection point busbar, a grid-type distributed power source, load branches, lines, line switches, grid connection switches, circuit breakers, and protection devices as its application scenario.

[0020] The new energy microgrid is in both grid-connected and off-grid operation. When the voltage or frequency of the microgrid does not meet the preset operating conditions, an off-grid switching task is executed. When both the microgrid side and the external grid side recover to the allowable range and meet the synchronization conditions, a grid-connected switching task is executed.

[0021] The control method in this embodiment is executed by a microgrid central controller, a station control layer controller, an energy management controller, or a control device with data acquisition, topology analysis, protection setting, and switch control functions. The control device is communicatively connected to the voltage acquisition unit, frequency measurement unit, phase angle measurement unit, distributed power controller, protection device, and switch control unit. The protection device is preferably a digital protection device with at least two setpoint areas and supporting communication writing, verification, setpoint area switching, and self-test result return. For protection devices that do not support online writing or online switching of backup setpoint areas, the control device marks the corresponding protection section as a prohibited section.

[0022] The operation procedure of the backup setting area is as follows: The control device first keeps the current effective setting area of ​​the protection device unchanged, and writes the protection setting data corresponding to this switching task into the backup setting area; after writing, it reads the backup setting area number, data verification result and self-test result returned by the protection device; after all three meet the verification requirements, the control device sends a setting area switching command to switch the backup setting area to the current effective setting area; after the setting area switching is successful, the control device executes the opening or closing action according to the switching action sequence.

[0023] In this embodiment, the current operating topology refers to the electrical connectivity relationship formed based on the microgrid primary wiring information and the current switch on / off state; The power supply start point refers to the starting bus used to supply power to the target load when performing a switching task; the candidate power supply path refers to the electrical path formed from the power supply start point to the bus where the load is located, through available lines and switches. The protection zone refers to the range of protection action along the candidate power supply path according to the configuration of protection devices and circuit breakers; the setting range refers to the range of values ​​in which the protection action setting can simultaneously meet the requirements of avoiding the maximum load current and identifying the minimum fault current.

[0024] This method is executed according to a preset cycle of inspection, and is also triggered when voltage or frequency exceeds the limit, synchronization conditions are met, or an operation control command is received. When using periodic inspection, the sampling period is set together based on the refresh time of the measuring device, the operation time of the control device, and the requirements of the switch control response. In a scenario with a rated frequency of 50Hz, 20ms corresponds to one power frequency cycle, which is used to quickly detect voltage or frequency overruns, while 1s is used for routine inspections with slower load changes. 100ms to 500ms has better applicability between overrun identification speed and communication data volume, and is therefore the preferred sampling period.

[0025] Within the same judgment period, voltage, frequency, and voltage phase angle data should be time-aligned; a preset alignment threshold is used to limit the maximum allowed timestamp difference between different acquisition channels, which is less than or equal to the sampling period; In a 50Hz system, 20ms corresponds to one power frequency cycle, which can avoid the mixing of phase angle data across cycles. 100ms is suitable for the data refresh interval of general protection and control devices. Therefore, the preset alignment threshold is preferably set to 20ms to 100ms. When the timestamp difference between different acquisition channels exceeds the preset alignment threshold, the data set is marked as asynchronous data and is not used to generate new switching action commands.

[0026] When there is a short-term missing data but the number of missing data does not exceed the preset number, and the timestamp of the previous valid sample value is still within the allowable retention time, the control device uses the previous valid sample value to participate in the pre-judgment of the current cycle, but does not directly execute the switching action; When the number of consecutive missing values ​​exceeds the preset number or the previous valid sample value exceeds the allowed retention time, the data is marked as invalid, no new switching task is generated, and the current switch state is maintained; for devices with uncertain switch states, communication interruptions, or abnormal self-tests of protection devices, they participate in topology search as unusable.

[0027] For protection setting intervals, a valid setting interval is considered to exist only when the lower limit of the action is less than the upper limit of the action; when the lower limit of the action is equal to or greater than the upper limit of the action, the setting interval is treated as disappearing. For synchronization conditions, the synchronization conditions are deemed to be met when the voltage difference, frequency difference, and voltage phase angle difference do not exceed the corresponding allowable thresholds; if any one of them exceeds the corresponding allowable threshold, the synchronization conditions are deemed not to be met.

[0028] Example 1, referring to Figure 1 This embodiment provides a method for controlling the on-grid and off-grid power supply of a new energy microgrid, including the following steps: S1. Obtain the voltage, frequency, and voltage phase angle of the microgrid, determine the switching task, read the primary wiring information and switch open / closed status of the microgrid, and form the current operating topology.

[0029] In this step, the control device obtains voltage, frequency, and voltage phase angle from the grid connection point bus, microgrid side bus, or other preset key bus. When performing grid connection switching task judgment, the control device also reads the voltage, frequency, and voltage phase angle from the external grid side; the above data comes from voltage transformers, frequency measurement units, phase angle measurement units, protection and control devices, or synchronization phasor measurement units.

[0030] After acquiring the data, the control device first performs a validity check on the data; the validity check includes range check, timestamp check, communication status check, and abrupt change check. For example, if the sampled value of a bus voltage is 0, but the corresponding acquisition channel is in a communication interruption state, then the voltage value will not be used as real undervoltage data for the switching task judgment; if the frequency data has not been updated for three consecutive cycles, then the frequency data will be marked as invalid; for irreplaceable key data invalidation cases, the control device maintains the current switching state and saves the source of invalid data.

[0031] The control device compares the microgrid voltage with the preset lower limit voltage and the preset upper limit voltage, and compares the microgrid frequency with the preset frequency range; When the voltage of the microgrid is lower than the preset lower limit voltage, exceeds the preset upper limit voltage, or the frequency is not within the preset frequency range, an off-grid switching task is generated. If an external power grid anomaly causes the microgrid voltage to fall below the preset lower limit voltage or exceed the preset upper limit voltage, or causes the microgrid frequency to be outside the preset frequency range, an off-grid switching task will also be generated.

[0032] The preset lower voltage limit, preset upper voltage limit, and preset frequency range are pre-configured based on the rated operating parameters; For example, in an application scenario with a rated line voltage of 10kV and a rated frequency of 50Hz, the preset lower limit voltage is set to 9.0kV, the preset upper limit voltage is set to 11.0kV, and the preset frequency range is set to 49.5Hz to 50.5Hz. When the microgrid bus voltage is collected as 8.7kV and the frequency is 49.8Hz, although the frequency is still within the preset frequency range, the control device generates an off-grid switching task because the voltage is lower than the preset lower limit voltage.

[0033] Once the voltage and frequency on both the microgrid side and the external grid side have returned to their respective allowable ranges, the control device calculates the voltage difference, frequency difference, and voltage phase angle difference on both sides of the grid connection point. The voltage difference is calculated using the absolute value of the difference between the effective voltage values ​​on both sides, the frequency difference is calculated using the absolute value of the frequency difference on both sides, and the voltage phase angle difference is calculated using the absolute value of the phase angle difference on both sides after being converted to the range of 0° to 180°. A grid-connected switching task is generated when the voltage difference, frequency difference, and voltage phase angle difference are all within their respective allowable ranges for synchronization.

[0034] For example, the voltage on the microgrid side at the grid connection point is 10.02kV, and the voltage on the external grid side is 10.05kV, with a voltage difference of 0.03kV; the frequency on the microgrid side is 50.01Hz, and the frequency on the external grid side is 50.00Hz, with a frequency difference of 0.01Hz; the phase angle difference between the two sides is 4°. If the allowable ranges for the same period are voltage difference not greater than 0.5kV, frequency difference not greater than 0.2Hz, and phase angle difference not greater than 10°, then the control device generates a grid connection switching task.

[0035] Before the grid-connected switch performs the closing action, the control device recalculates the voltage difference, frequency difference, and voltage phase angle difference; if any of these are not within the allowable range during the recalculation, the closing action is canceled and the current switch state is maintained. For example, if the phase angle difference is 4° when the task is generated, but the phase angle difference is calculated again before closing and is 13°, which exceeds the allowable range of phase angle difference, then the grid-connected switch closing action will not be performed; this process is used to avoid asynchronous closing caused by changes in electrical quantities between task generation and switch action.

[0036] Subsequently, the control device reads the primary wiring information and switch open / close status of the microgrid; the primary wiring information includes the connection relationships between buses, lines, switches, circuit breakers, distributed power sources, and load branches; Switch open / closed status includes the open or closed status of grid-connected switches, line switches, and circuit breakers; the control device constructs the current operating topology based on lines that are in the closed state and electrically connected at both ends; If both switches at both ends of a line are closed and the line is not under maintenance or locked, the busbars at both ends of the line are considered electrically connected in the current operating topology; if either switch is open, the line is not electrically connected.

[0037] For example, a microgrid includes buses M0, M1, M2 and M3. The grid-connected switch is located between the external grid and M0. The grid-type power source is connected to M1, load L1 is connected to M2, and load L2 is connected to M3. If the M0-M1 line switch is closed, the M1-M2 line switch is closed, and the M1-M3 line switch is open, then in the current operating topology, M0, M1 and M2 are electrically connected, while M3 is not connected to M1.

[0038] This step outputs the switching task type, valid electrical quantities, primary wiring information, switch status, and current operating topology, and saves them as the basic status of this switching task before sending them to S2.

[0039] S2. Determine the power supply starting point according to the switching task, determine the load power supply sequence according to the load level and load power of each load branch, and search for candidate power supply paths; divide the protection zone along the candidate power supply path, and determine the lower limit of action according to the maximum load current of the protection zone and the upper limit of action according to the minimum fault current of the protection zone. Mark the protection zone with the lower limit of action not less than the upper limit of action as the prohibited selection zone and delete the candidate power supply path passing through the zone.

[0040] When performing off-grid switching tasks, the control device reads the operating status and current available power of each grid-type power source, and determines the bus where the grid-type power source is located that is operating normally and whose current available power is greater than the preset minimum power as the power supply starting point. The current available power is sent by the distributed power controller and is also determined by the control device based on the operating status, rated capacity, remaining energy storage capacity and current operating limitations of the distributed power source. The preset minimum power is used to determine whether the grid-type power supply has the minimum capacity to support off-grid and grid-connected power supply and power supply to important loads. Its value is determined based on the rated active power of the grid-type power supply, the minimum power supply of primary loads, the lower limit of the remaining energy storage capacity, and the reserved margin for grid control. In this embodiment, the preset minimum power is 5% to 30% of the rated active power of the grid-connected power source, preferably 10% to 20%. Among them, 5% is used to exclude power sources that can only maintain no-load or low-power operation, 30% is used to avoid insufficient available power supply starting point due to an excessively high minimum power threshold, and 10% to 20% is suitable for microgrid off-grid switching scenarios that take into account grid control margin and initial important load input. When the current available power is greater than the preset minimum power and the operating status is normal, the bus where the grid-connected power source is located is allowed to be used as the power supply starting point for the off-grid switching task.

[0041] For example, if the grid-connected power source DG1 is connected to bus M1, its current available power is 800kW, the preset minimum power is 200kW, and its operating status is normal, then bus M1 is determined as the power supply starting point; if the grid-connected power source DG2 has a current available power of 120kW, which is less than the preset minimum power, then its bus is not used as the power supply starting point.

[0042] When performing grid connection switching tasks, the control device uses the bus at the grid connection point as the power supply starting point; for example, if the inner bus of the grid connection switch is M0, then M0 is used as the power supply starting point in the grid connection switching task to search for candidate power supply paths in the load branches inside the microgrid; if the grid connection point bus is invalid or the grid connection switch is in an abnormal blocking state, then the grid connection target operating topology will not be generated.

[0043] The control device obtains the load level and load power of each load branch, and arranges them from high to low load level; if the load levels are the same, they are arranged from low to high load power to obtain the load power supply sequence. The load levels are pre-set as Level 1, Level 2, Level 3, etc., with Level 1 loads having a higher power supply priority than Level 2 loads, and Level 2 loads having a higher power supply priority than Level 3 loads. The load power is based on the most recent valid measurement value or the preset planned power. Loads of the same level are arranged in ascending order of load power. When the available power of the grid-type power supply is limited, more loads of the same level are restored first, and the impact of a single path addition on the maximum load current of the shared protection zone is reduced.

[0044] For example, if load L1 is a primary load with a power of 300kW, load L2 is a secondary load with a power of 100kW, and load L3 is a primary load with a power of 150kW, then the power supply order for the loads is L3, L1, L2. This order prioritizes power supply to higher-level loads and prioritizes the processing of branches with lower power among loads of the same level.

[0045] When searching for candidate power supply paths, the control device takes the power supply starting point as the search starting point and searches step by step along the lines and switches that are in the available state in the primary wiring information to the bus where the load is located. During the search process, buses already traversed along the same path are not re-entered. Expansion stops when the path length exceeds the preset maximum search level. Lines with maintenance lockouts, communication abnormalities, inoperable switches, or prohibited section markers are not further expanded. Upon reaching the busbar where the load is located, the control device records the traversed buses, lines, and switches as a single candidate power supply path. The preset maximum search level is the number of lines or switch levels that a candidate power supply path is allowed to pass through continuously. It is used to avoid unlimited searching in complex microgrids, forming excessively long power supply paths, and causing too many protection coordination levels. Its value is preset based on the number of microgrid buses, feeder levels, number of tie switches, number of allowable protection level differences, and number of backup paths. Among them, the number of feeder levels and tie switches determines the spatial search depth of candidate paths, and the number of allowable protection level differences determines the maximum number of coordination layers of main protection and backup protection that can be continuously configured in the path. If the number of search levels is too small, it cannot cover the necessary backup power supply paths. If the number of search levels is too large, it will significantly increase the number of candidate path combinations and lead to too many protection backup level differences and too long action time, which is not conducive to rapid fault clearing. In this embodiment, the preset maximum search level is typically set to 2 to 10 levels, preferably 3 to 6 levels. Level 2 is suitable for simple microgrids where there is only a direct feeder or a primary backup connection between the power supply start point and the load. Level 10 is used to limit the maximum search boundary of complex microgrids with multiple buses and multiple connections. Levels 3 to 6 are suitable for searching the main feeder and backup connection paths in general park-type and industrial and commercial microgrids. When the search level reaches this value and the load bus is still not reached, the control device stops expanding the search branch.

[0046] Optionally, for the same load branch, a preset number of candidate power supply paths are retained according to path length, number of switching operations, or search arrival order.

[0047] For example, in an off-grid task, with bus M1 as the power supply starting point, load L1 is located on bus M2, and there is a direct line K12 between M1 and M2, as well as a backup path M1-M4-M2; if K12 and the M1-M4 and M4-M2 lines are all in an operational state, the control device records two candidate power supply paths: the first is M1-K12-M2, and the second is M1-K14-M4-K42-M2; both paths are then entered into subsequent current carrying capacity verification and protection setting verification.

[0048] After the candidate power supply path is formed, the control device reads the active power, reactive power and corresponding bus voltage of the lines included in each candidate power supply path, and calculates the operating current of each line. If the operating current of any line exceeds its allowable current carrying capacity, the candidate power supply path is deleted. For three-phase lines, the operating current is calculated based on active power, reactive power, and line voltage. For example, if line K12 in a candidate path carries an active power of 300kW and a reactive power of 100kvar, with a corresponding line voltage of 10kV, then the apparent power is approximately 316kVA and the line operating current is approximately 18.2A. If the allowable current carrying capacity of this line is 120A, then the current carrying capacity is checked. If the operating current of a certain section of line in another candidate path is 135A and the allowable current carrying capacity is 120A, then the candidate power supply path passing through this line is deleted.

[0049] Subsequently, the control device divides the protection zone along the candidate power supply path; when dividing the protection zone, the installation position of the protection device and the circuit breaker controlled by each protection device are read sequentially according to the power supply direction of the candidate power supply path. When both ends of the same line are equipped with protection devices and the fault is cleared by the circuit breakers at both ends, the line between the protection devices at both ends is regarded as a double-end protection section, and the two protection devices and the circuit breakers they control are respectively associated with the double-end protection section; when only one end of the same line is equipped with a protection device and the other end is equipped with a controllable circuit breaker, the line between the protection device and the circuit breaker at the other end is regarded as a single-end protection section.

[0050] The line between two adjacent protection devices constitutes a double-end protection section, and the two protection devices and the circuit breakers they control correspond to the double-end protection section respectively; when a protection device is installed at one end of the line and a circuit breaker is installed at the other end, the line between the protection device and the circuit breaker is regarded as a single-end protection section.

[0051] For example, in the path M1-M2, a protection device P12A is installed on the M1 side and a circuit breaker B12A is controlled, and a protection device P12B is installed on the M2 side and a circuit breaker B12B is controlled. Then the M1-M2 line constitutes a double-end protection section Z12. In another example, in path M2-M3, a protection device P23A is installed on the M2 side and controls the circuit breaker B23A, while only a circuit breaker B23B is installed on the M3 side. In this case, the line between the protection device on the M2 side and the circuit breaker on the M3 side constitutes a single-end protection section Z23.

[0052] For lines that are not energized in the current operating topology but become energized after the candidate power supply path is used, the control device sets a topology change marker in the protection section corresponding to the line; the topology change marker is used to trigger the recalculation of the fault current after path superposition or switch status change. For example, if the current circuit breaker of line M1-M3 is open and the line is not energized, and if the candidate path selects M1-M3 as the load power supply, then the protection section Z13 is marked with a topology change. The control device also records the circuit breakers, protection devices, load branches powered by the protection section, and distributed power sources that provide fault current to the protection section at both ends of each protection section.

[0053] When determining the minimum fault current of the protected section, the control device sets fault points at the beginning and end of the protected section respectively, and calculates the total fault current for each fault point under three-phase short circuit and two-phase short circuit conditions. The beginning and end of the protection zone are determined based on the power supply direction of the candidate power supply path; for a single-end protection zone, the protection device side and the circuit breaker side at the other end are respectively taken as the beginning and end.

[0054] The control device determines whether there is a closed electrical path between each distributed power source and the fault point based on the candidate power supply path and the switch opening and closing status; for distributed power sources with closed electrical paths, the control device reads the fault current that the distributed power source can output during the protection device operation judgment period. The total fault current at the fault point under the corresponding short-circuit type is obtained by summing the fault currents of each distributed power source with a closed electrical path.

[0055] The control device determines the distributed power source that is electrically connected to the fault point based on the candidate power supply path and the switch opening and closing status; for the distributed power source that is electrically connected to the fault point, the control device reads the fault current output by it during the protection device operation judgment period, and adds up the fault currents to obtain the total fault current of the corresponding fault point. The effective current value within one to five power frequency cycles after the protection device starts is taken during the action discrimination period. In a system with a rated frequency of 50Hz, the action discrimination period corresponds to the effective current value within 20ms to 100ms after the protection starts. According to the action time limit requirements of the protection device, the action discrimination period can be extended to within 200ms after the protection starts.

[0056] The fault current output by the distributed power source during the protection device's operation judgment period is sent by the distributed power source controller according to the current control mode, current limiting factor, rated current and fault duration, and is also obtained by the control device by calling the pre-stored fault current characteristic curve. For inverter-type distributed power sources, the fault current is determined by multiplying the current limiting factor by the rated output current; for synchronous-type distributed power sources, the fault current is calculated based on transient reactance, line impedance, and fault location; for energy storage converters, the fault current is read from the energy storage converter's current limiting setting and the action judgment time window.

[0057] In one example, the rated current of the inverter-type distributed power supply DG1 is 200A, and the current limiting factor during the protection operation judgment period is 1.3. Therefore, the fault current that DG1 can provide during this period is calculated as 260A. If the rated current of another distributed power source DG2 is 100A and the current limiting factor is 0.9, then the fault current that DG2 can provide during this period is calculated as 90A; if both DG1 and DG2 are electrically connected to the fault point, then the total fault current of the distributed power sources at the corresponding fault point is 350A.

[0058] When performing grid connection switching tasks or when the target operating topology includes the grid connection point bus and there is an electrical connection loop between the grid connection point and the fault point, the grid connection point side participates in the verification as the equivalent fault current source; the control device reads the equivalent short-circuit capacity, equivalent impedance or short-circuit current contribution value sent by the protection and control device of the upstream system of the grid connection point, and uses it together with the fault current of the distributed power source that maintains electrical connection for the calculation of the total fault current; If the grid connection switch is not closed or there is no electrical connection between the grid connection point and the fault point, the equivalent fault current on the grid connection point side is not included.

[0059] When calculating the three-phase short-circuit and two-phase short-circuit currents, the control device determines the fault current based on the line impedance between the fault point and each power source, the transformer impedance, the switch opening and closing status, and the fault current characteristics of the distributed power source. For fault currents during the action discrimination period that have been sent by the distributed power controller or protection and monitoring device, the sent value is directly used for accumulation; for power supplies that have not sent fault currents but have pre-stored parameters, the fault current characteristic curve or equivalent impedance is used for calculation; for power supplies that have neither sent values ​​nor valid parameters, the control device marks the circuit where the power supply is located as an unverifiable circuit and marks the protection section involving the circuit as a prohibited section; when a preset conservative value can be obtained, the preset conservative value is used for minimum fault current calculation.

[0060] The preset conservative value refers to the alternative fault current lower limit used when both the real-time fault current transmitted value and the effective fault current parameter are unavailable, but there is still reliable lower limit data. The preset conservative value is determined based on the power supply rated current, the current limiting lower limit given by the manufacturer, or the minimum fault current during the historical operation judgment period, preferably the minimum value among the above available values. If there is no traceable and reliable lower limit data, the preset conservative value will not be used, and the protection section involving the power supply circuit will be directly marked as a prohibited section.

[0061] The control device obtains the total fault current corresponding to the three-phase short circuit at the beginning of the protected section, the two-phase short circuit at the beginning, the three-phase short circuit at the end, and the two-phase short circuit at the end; then compares the above total fault currents and determines the smallest total fault current as the minimum fault current of the protected section.

[0062] The control device compares the total fault current at the beginning and end of the protected section under different short-circuit types, and determines the minimum value as the minimum fault current of the protected section. For example, when the three-phase short circuit at the beginning of the protected section Z12 is 350A, the total fault current is 300A when the two-phase short circuit at the beginning is 300A, the total fault current is 330A when the three-phase short circuit at the end is 330A, and the total fault current is 280A when the two-phase short circuit at the end is 280A. Then the control device will determine 280A as the minimum fault current of the protected section Z12.

[0063] The control device performs power flow calculations on the candidate power supply paths to obtain the maximum load current of the protected section, and uses the product of the maximum load current and the preset reliability coefficient as the lower limit of the action; the control device divides the minimum fault current of the protected section by the preset sensitivity coefficient as the upper limit of the action. The preset reliability coefficient is used to cover load fluctuations, measurement errors, and current transformer errors, so that the protection action setting is higher than the maximum load current that occurs during normal operation. It is usually set to 1.10 to 1.20. The preset sensitivity coefficient is used to ensure that the minimum fault current can still be reliably identified by the protection device. It is usually set to 1.3 to 1.5 in microgrids where the fault current of distributed power sources is limited. When the field protection procedure or equipment manual gives a more stringent coefficient, the more stringent coefficient shall be configured.

[0064] When the lower limit of the action is less than the upper limit of the action, the control device establishes the setting range of the protection device and determines the main protection action setting value; The main protection action setting is calculated using the following formula: Main protection action setting value = lower limit of action value + preset value coefficient × (upper limit of action value - lower limit of action value); The preset value coefficient is greater than zero and less than one, with 0.5 being the preferred value. For example, if the maximum load current of the protected section Z12 is 120A and the preset reliability coefficient is 1.2, then the lower limit of the action is 144A; if the minimum fault current is 280A and the preset sensitivity coefficient is 1.4, then the upper limit of the action is 200A; since 144A is less than 200A, the setting range [144A, 200A] is formed. When the preset value coefficient is 0.5, the main protection action setting value is 172A; if the lower limit of the action is 210A and the upper limit of the action is 200A, then the lower limit of the action is not less than the upper limit of the action, the main protection action setting value is not generated, and the protected section is marked as a prohibited section.

[0065] When a protected section is marked as a prohibited section, the control device deletes all candidate power supply paths passing through that section; For example, if the Z12 protection zone disappears, the path M1-K12-M2 is deleted; if another path M1-K14-M4-K42-M2 does not pass through Z12 and its protection zones all have a protection zone, then the path can still be retained for subsequent target operation topology formation.

[0066] This step outputs the load power supply sequence, the set of candidate power supply paths, the results of the protection zone division, the protection zone setting interval, and the prohibited selection zone markers, and sends them to S3.

[0067] S3. Select candidate power supply paths according to the load power supply sequence. For each path added, redetermine the lower and upper limits of the action of the shared protection zone. If the setting interval disappears, cancel the added path. Otherwise, the target operating topology is formed by the retained paths, and protection setting data and switch action sequence are generated.

[0068] In this step, the control device calculates the difference between the upper limit and lower limit of the action of each protected section in each candidate power supply path, and takes the smallest difference as the protection setting margin of the candidate power supply path. The protection setting margin is used to indicate the space that can still be adjusted in the most unfavorable protected section of a candidate power supply path. The larger the setting margin, the less likely the setting range will disappear when the path is superimposed with subsequent loads.

[0069] For example, candidate path A includes protected sections Z1 and Z2, where the difference between the upper and lower limits of action for Z1 is 60A and the difference for Z2 is 40A. Therefore, the protection setting margin of candidate path A is 40A. Candidate route B includes protected sections Z3 and Z4, with differences of 55A and 50A respectively. Therefore, the protection setting margin of candidate route B is 50A. If both path A and path B can supply power to the same load, then path B, with a protection setting margin of 50A, should be selected first.

[0070] The control device processes each load branch sequentially according to the load power supply sequence; when the same load branch is connected to multiple candidate power supply paths, the candidate power supply path with the largest protection setting margin is selected; when the protection setting margins are the same, the candidate power supply path with the fewest required switching operations is selected. The required number of switch actions is determined based on the current operating topology and the number of switches whose states need to be changed after the candidate power supply path is put into operation. For example, if the protection setting margin of both paths is 45A, and path A requires closing 2 switches and opening 1 switch, while path B only requires closing 1 switch, then path B is selected.

[0071] Optionally, when the path selected according to the protection setting margin priority rule results in the subsequent loads being unable to form a feasible path, the control device reverts to the previous load branch in the selected path set and reads the next candidate power supply path of the corresponding load branch to recombine. This rollback process is used to improve the success rate of target operating topology formation; in implementations where rollback is not enabled, the control device still tries the next candidate power supply path one by one according to the load power supply sequence.

[0072] The preset power supply constraints are used to specify the power supply handling method for the load branch in this switching task, including three categories: mandatory power supply, power supply that can be delayed, and power supply prohibited. Preset power supply constraints are determined based on load level, user authorization, emergency power supply strategy, current available power of the power supply, and pre-configuration by operation and maintenance personnel; for example, fire protection, communication, or safety production loads can be configured to require power supply, general lighting loads can be configured to allow delayed power supply, and load branches under maintenance can be configured to prohibit power supply.

[0073] After the selected candidate power supply path is added to the provisional operating topology formed by the selected path, the control device includes the newly added load power of the path in the protection zone shared with the selected path, and updates the maximum load current of the shared protection zone. The shared protection zone refers to the protection zone through which multiple load branch power supply paths pass. For example, if the selected path supplies power to load L1 and passes through the protected section Z01, the current maximum load current of Z01 is 90A; if the candidate path for the newly added load L2 also passes through Z01, and the current through Z01 increases to 135A after the addition, the control device will use 135A as the updated maximum load current of Z01.

[0074] When the power supply loop between the distributed power source and the protected section changes, the control device recalculates the minimum fault current of the protected section. For example, in the original provisional topology, only DG1 is electrically connected to the protected section Z01, and the minimum fault current is 260A. After the new path is put into operation, DG2 forms an electrical connection with Z01 through a closed circuit. Then the control device recalculates the total fault current of the beginning and end of Z01 under three-phase short circuit and two-phase short circuit, and takes the minimum value as the updated minimum fault current. If a new path causes a previously unenergized line to become energized, the fault current in the protected section of that line will be recalculated due to the topology change marking.

[0075] The control device recalculates the lower and upper limits of action using the updated maximum load current and minimum fault current. If no setting interval exists in any shared protection zone, the candidate power supply path added this time will be cancelled, and the next candidate power supply path for that load branch will continue to be read. For example, if the maximum load current of Z01 after the update is 180A and the preset reliability coefficient is 1.2, then the lower limit of the action is 216A; if the minimum fault current after the update is 280A and the preset sensitivity coefficient is 1.4, then the upper limit of the action is 200A; since 216A is not less than 200A, the Z01 setting range disappears, the control device cancels the newly added path and tries other candidate paths for this load branch.

[0076] If all relevant protection zones have a set interval after adding a candidate power supply path, the control device retains the path and includes it in the provisional operating topology; after processing each load branch according to the load power supply sequence, the control device forms the target operating topology based on the retained candidate power supply path; The target operating topology includes the target energized busbar, target connected line, target switch status, power supply starting point, energized load branch, protected section, and the corresponding relationship of protection devices.

[0077] In a preferred embodiment, the target operating topology is stored in the form of radial power supply, and the control device avoids forming a closed-loop power supply path when combining candidate power supply paths, so as to form a definite coordination relationship between the positive direction protection, the main protection and the backup protection. The radial power supply method refers to avoiding the formation of closed loops in the target operating topology, but does not exclude the possibility that multiple distributed power sources are connected to different buses to contribute fault current to the same radial topology. When there are multiple distributed power sources supplying power in parallel or multiple fault current sources in the actual microgrid, the control device records the energized circuits of each fault current source to the protected section, and determines the protection device that can cut off the corresponding power supply circuit when searching for backup protection.

[0078] When generating protection setting data, the control device determines the direction from the power supply start point to the load branch as the positive protection direction; For double-ended protection sections, the protection devices corresponding to the circuit breakers at both ends of the protection section shall be used as the main protection devices. For single-end protection sections, the protection device on the protection device side shall be regarded as the main protection device; Search along the protected section towards the power supply starting point, and use the first protection device encountered that cuts off the power supply circuit of the protected section as a backup protection device.

[0079] When there are multiple sources of fault current in the protected section, the control device searches for a protection device that can cut off the corresponding power supply circuit along the direction of each source of fault current, and uses one or more of the found protection devices as backup protection devices for the protected section; if the same protection device is found in multiple directions, it is recorded together; if there is no backup protection device that can cut off the corresponding power supply circuit in a certain direction, the protected section is marked as a prohibited section.

[0080] For example, if the power supply start point in the target topology is M1, the load is located at M3, the protection section Z23 is located between M2 and M3, and the power supply direction is from M1 to M3, then the positive protection direction of Z23 is from M2 to M3. If Z23 is a double-ended protection section, both its two-ended protection devices P23A and P23B serve as the main protection devices; if protection device P12A is first encountered along Z23 towards the power supply starting point, and the circuit breaker controlled by P12A can cut off the power supply circuit of Z23, then P12A serves as the backup protection device for Z23.

[0081] The control device acquires the main protection operating settings within the corresponding setting range of the main protection device, and determines the backup protection operating settings based on the maximum load current and minimum fault current of the protection zone where the backup protection device is located. The backup protection operating settings are determined as follows: Backup protection action setting value = backup action lower limit value + backup value coefficient × (backup action upper limit value - backup action lower limit value). Among them, the lower limit of the backup action is the product of the maximum load current of the protection section where the backup protection device is located and the preset backup reliability coefficient, and the upper limit of the backup action is the minimum fault current of the protection section where the backup protection device is located divided by the preset backup sensitivity coefficient. The backup value coefficient is greater than zero and less than one. The preset backup reliability coefficient is the same as the preset reliability coefficient used by the main protection, and is also set separately according to the actual requirements of protection coordination; the preset backup sensitivity coefficient is the same as the preset sensitivity coefficient used by the main protection, and is also set separately according to the actual requirements of backup protection sensitivity.

[0082] In one implementation, the backup protection action time limit is longer than the main protection action time limit, and a preset time difference is set between the two; the preset time difference is determined based on the protection device action time, the circuit breaker tripping time, and the communication delay, and is between 0.1s and 0.5s. By setting time tiers, when the main protection correctly clears the fault, the backup protection does not expand the clearing range; when the main protection fails to clear the fault, the backup protection operates with a time delay to cut off the corresponding power supply circuit.

[0083] For example, the main protection action setting is 172A, the main protection action time limit is 0s or a fast action time limit; the backup action lower limit of the section where the backup protection device is located is 160A, the backup action upper limit is 230A, and the backup value coefficient is 0.5, then the backup protection action setting is 195A. If the preset time difference is 0.3s, the backup protection will send a trip command to the circuit breaker it controls after a delay of 0.3s when the backup protection action setting is reached and no disconnection feedback signal is received.

[0084] When the fault current flowing through the main protection device reaches the main protection action setting value, the main protection device of the double-end protection section sends a trip command to the circuit breakers at both ends of the protection section, and the main protection device of the single-end protection section sends a trip command to the circuit breaker it controls and sends a disconnection feedback signal to the outside. For a single-end protection section, if the circuit breaker at the other end has the conditions for remote control or inter-tripping, the main protection device sends a tripping command to the circuit breaker it controls, and at the same time sends an inter-tripping command to the circuit breaker at the other end through the control device or inter-tripping channel. If the circuit breaker at the other end does not have the interlocking trip capability, the control device will only allow the single-end protected section to be in a single-sided power supply state when forming the target operating topology.

[0085] When the fault current flowing through the backup protection device reaches the backup protection action setting value and no disconnection feedback signal is received, the backup protection device sends a single trip command to the circuit breaker it controls. For example, when Z23 fails and both P23A and P23B detect that the fault current has reached the main protection action setting, a trip command is sent to both ends of B23A and B23B; if the backup protection P12A reaches the backup protection action setting but does not receive the disconnection feedback signal from Z23 within the preset discrimination time, then P12A sends a single trip command to the circuit breaker it controls.

[0086] After the protection setting data is generated, the control device generates the switching action sequence based on the difference in switching status between the current operating topology and the target operating topology; when performing the off-grid switching task, the control device sends an off-grid operation preparation command to the distributed power source; after the distributed power source returns the preparation completion signal, the grid-connected switch tripping action is placed first. For line switches that do not belong to the target operating topology, the tripping action is performed first; for line switches that belong to the target operating topology and are currently in the tripping state, the closing action is performed after the corresponding protection setting area is successfully switched.

[0087] For example, in the current operating topology, grid-connected switch G is in the closed state, and line switches K12 and K23 are in the closed state. The target operating topology requires grid-connected switch G to be open, K12 to remain closed, K23 to be open, and K14 to be closed. Then the sequence of off-grid switching actions is as follows: After the distributed power source is ready for off-grid operation, grid-connected switch G is opened first; then K23, which does not belong to the target operating topology, is opened; after the protection setting area is successfully switched, K14, which belongs to the target operating topology and is currently open, is closed.

[0088] When performing grid connection switching tasks, the control device performs grid connection switch closing action on microgrids where the voltage difference, frequency difference and voltage phase angle difference are all within the allowable range of the same period, and sends grid connection operation mode switching instructions to distributed power sources; For example, during the pre-closing re-verification, if the voltage difference is 0.02kV, the frequency difference is 0.01Hz, and the phase angle difference is 3°, all within the allowable range for synchronization, the control device will execute the grid-connected switch closing action; after successful closing, it will send a grid-connected operation mode switching command to the distributed power source.

[0089] If any switch fails to return to the expected open / closed state within a preset time, the control device will stop executing subsequent switching actions, restore the switches that have already performed actions to their pre-switching state, mark the switches that cannot be restored and their protected areas as prohibited areas, and output a switching interlock signal or alarm signal. For grid-connected switches that have already been opened, if it is necessary to restore them to the closed state before switching, the voltage difference, frequency difference, and voltage phase angle difference must be rechecked. If any one of them does not meet the allowable range of synchronization, the restoration closing action will not be performed, and an alarm signal will be output.

[0090] For example, if the closing command for switch K14 is issued and it does not return to the closed state within a preset 5 seconds, then subsequent actions will stop; if K23, which has been previously opened, can be restored to the closed state before the switchover, then K23 will be restored; if the state of K14 cannot be confirmed, then K14 and its protected section will be marked as a prohibited section; if the grid-connected switch G, which has been opened, needs to be restored to the closed state, and the phase angle difference before the closing exceeds the allowable range for synchronization, then the grid-connected switch G will not be restored, and a switchover blocking signal or an alarm signal will be output.

[0091] This step outputs the target operating topology, protection setting data, and switch action sequence. The target operating topology is entered into S4 for writing protection setting data and executing switches. The protection setting data is used to write to the backup setting area of ​​the protection device, and the switch action sequence is used to implement switching after verification.

[0092] S4. Write the protection setting data into the backup setting area of ​​the protection device; after verification, switch the setting area and perform the switching action; if the verification fails, mark the corresponding protection section as a prohibited section and re-determine the target operating topology; if an alternative target operating topology cannot be formed, stop the current switching task and maintain the current switching state.

[0093] In this step, the control device combines the main protection action setting value, backup protection action setting value, the correspondence between the main protection device and the backup protection device, the tripping protection device and the corresponding circuit breaker number in the protection setting data into a data string to be written according to the preset writing order. The writing operation is performed in the following order: forming the data string to be written, calculating the target check code, writing to the backup setting area, reading the return information, judging the verification result, sending the setting area switching command, and verifying the effective setting area number. After forming the data string to be written, the current effective setting area of ​​the protection device remains unchanged. Only after the backup setting area is verified as qualified and the effective setting area number is verified as correct will the control device perform subsequent switching operations.

[0094] The preset writing order is determined according to the protection device number, protection section number, or power supply direction order in the target operating topology; the data string to be written includes fields such as protection section number, protection device number, setting type, setting value, tripped circuit breaker number, and backup protection correspondence.

[0095] For example, for protected section Z12, the main protection devices are P12A and P12B, with a main protection action setting of 172A. The backup protection device is P01A, with a backup protection action setting of 195A. The circuit breakers that trip together are B12A and B12B. The control device will combine the above data into a data string to be written according to the preset field order. This data string is used to write the backup setting area of ​​the corresponding protection device, without directly overwriting the setting area currently in use.

[0096] The control device performs cyclic redundancy check on the data string to be written to obtain the target check code; then, the control device writes the data string to be written, the target check code, and the spare set value area number into the protection device, and reads the set value area number, check code, and self-test result returned by the protection device. Cyclic redundancy check is used to determine whether the data before and after writing is consistent. The spare setting area number is used to ensure that the protection device writes the data into the predetermined spare area. The self-test result is used to determine whether the protection device has the conditions to perform setting area switching and protection actions.

[0097] The preset verification conditions include: whether the set value area number returned by the protection device is consistent with the backup set value area number issued by the control device, whether the returned verification code is consistent with the target verification code, and whether the self-test result of the protection device is normal.

[0098] When the returned setpoint zone number matches the spare setpoint zone number, the returned checksum matches the target checksum, and the self-test result is normal, the control device marks the protection device as verified and sends a setpoint zone switching command. After sending the setpoint zone switching command, the control device reads the currently effective setpoint zone number again; If all the effective setting zone numbers of the relevant protection devices are correct, the switching action sequence is executed. If the effective setting zone number is incorrect, the setting zone used before the switchover is restored, and the switching action sequence is not executed.

[0099] For example, if the control device writes the spare setpoint area 2 to the protection device P12A and the target verification code is C1, and the protection device returns the setpoint area number 2, the verification code C1, and the self-test result is normal, then P12A's verification is qualified; if P12B returns the setpoint area number 2 but the verification code is C2, which is inconsistent with the target verification code, then P12B's verification is unqualified, the control device does not send a setpoint area switching command to P12B, and marks the protection section corresponding to P12B as a prohibited section.

[0100] If any verification item is inconsistent or the self-test result is abnormal, the control device will not send a setting zone switching command to the corresponding protection device, and will mark the protection zone corresponding to the protection device as a prohibited selection zone. Subsequently, the control device re-executes the processes of candidate power supply path deletion, target operating topology formation, protection setting data generation, and switch action sequence generation; If an alternative target operating topology is formed, the protection setting data is rewritten and verified; if an alternative target operating topology cannot be formed, the current switching task is stopped and the current switch state is maintained.

[0101] For example, the original target operating topology uses the protected section Z12, but the verification of the protection device corresponding to Z12 fails; the control device marks Z12 as a prohibited section and deletes all candidate power supply paths passing through Z12; if there are still alternative paths that reach the same load via Z14 and Z42, and each protected section of the alternative path has a setting range, then the target operating topology is re-formed; if all alternative paths are deleted due to overload or the disappearance of the setting range, then the current switching task is stopped and the current switching state is maintained.

[0102] When performing a switching action, the control device issues control commands one by one in the order of switching actions, and reads the switch return status after each action; the next action is executed only when the return status matches the expected open / closed state. If any switch fails to return to the expected state within the preset time, subsequent actions will be stopped, and the activated switches will be restored according to the abnormal handling method in S3. Switches that cannot be restored and their protected sections will be marked as prohibited sections.

[0103] After this step is completed, the control device saves the final operating topology, the currently effective setpoint area, the execution result of the switch action, the prohibited selection section, and the switching task status. If the switch is successful, the final operating topology serves as the basis for judging the current operating topology in the next cycle. If the switch fails, the reason for the failure is saved and the current switch status is maintained to provide a basis for the next switching task or manual review.

[0104] Example 2, refer to Figure 1 This embodiment provides a new energy microgrid off-grid and grid-connected power supply control system to implement the above-mentioned new energy microgrid off-grid and grid-connected power supply control method; the system includes a task analysis module, a path search module, a segment association module, a margin calculation module, a path attempt addition module, and a power supply control module; The task analysis module is used to obtain the voltage, frequency, and voltage phase angle of the microgrid, determine the switching task, and form the current operating topology; The path search module is used to determine the power supply starting point and the power supply sequence to the load, and to search for candidate power supply paths; The segment association module is used to divide the protection segment and establish the path segment association relationship between the candidate power supply path and the protection segment; The margin calculation module is used to determine the lower limit of action, the upper limit of action, and the protection setting margin of the protected area. The path attempt addition module is used to attempt to add candidate power supply paths according to the load power supply sequence, determine the shared protection zone based on the path segment association, update the maximum load current and minimum fault current of the shared protection zone, and cancel the attempt to add candidate power supply paths when the protection setting interval disappears. The power supply control module is used to form the target operating topology from the reserved candidate power supply paths, generate protection setting data and switch action sequence, write the protection setting data into the spare setting area of ​​the protection device, and execute the switch action sequence after verification.

Claims

1. A method for controlling the on / off grid power supply of a new energy microgrid, characterized in that, include: The system acquires the voltage, frequency, and voltage phase angle of the microgrid, determines the switching task, and forms the current operating topology based on the primary wiring information and the switch opening and closing status. The power supply starting point is determined according to the switching task, the load power supply sequence is determined according to the load level and load power, and candidate power supply paths from the power supply starting point to each load branch are searched. Divide the protection zone along the candidate power supply path, establish the path segment association between the candidate power supply path and the protection zone, determine the lower limit of operation based on the maximum load current of the protection zone, determine the upper limit of operation based on the minimum fault current of the protection zone, and determine the protection setting margin based on the difference between the upper limit of operation and the lower limit of operation. Candidate power supply paths are added in accordance with the load power supply sequence. When a candidate power supply path is added, the protection zone shared by the candidate power supply path and the reserved power supply path is determined according to the path segment association relationship. The new load corresponding to the candidate power supply path is included in the shared protection zone, the maximum load current of the shared protection zone is updated, and the minimum fault current is recalculated when the power supply circuit between the distributed power source and the shared protection zone changes. The lower limit of operation, upper limit of operation, and protection setting margin of the shared protection zone are re-determined based on the updated maximum load current and minimum fault current. If the lower limit of the action for any shared protection zone is not less than the upper limit of the action, the attempt to add the candidate power supply path is cancelled and it is added to the restricted path set. Otherwise, retain the candidate power supply path; The target operating topology is formed from the reserved candidate power supply paths, protection setting data and switching action sequence are generated, the protection setting data is written into the backup setting area of ​​the protection device, and after verification, the device is switched to the backup setting area and the switching action sequence is executed. If the verification fails, the corresponding protection section is recorded in the restricted path set.

2. The method for controlling the off-grid and on-grid power supply of a new energy microgrid according to claim 1, characterized in that, The handover tasks include off-grid handover tasks and on-grid handover tasks; When the microgrid voltage is lower than the preset lower limit voltage, exceeds the preset upper limit voltage, or the frequency is not within the preset frequency range, an off-grid switching task is generated. Once the voltage and frequency on both the microgrid side and the external grid side have returned to the allowable range, calculate the voltage difference, frequency difference, and voltage phase angle difference on both sides of the grid connection point. When all three are within the allowable range for synchronization, generate a grid connection switching task. Before closing the grid connection switch, recalculate the voltage difference, frequency difference, and voltage phase angle difference. If any one of them exceeds the allowable range for synchronization, cancel the closing and maintain the current switch state.

3. The method for controlling the off-grid and on-grid power supply of a new energy microgrid according to claim 1, characterized in that, The current operating topology, power supply starting point, and candidate power supply path are determined in the following manner: Obtain the primary wiring information and switch open / closed status of the microgrid, and construct the current operating topology using lines that are in the closed state and electrically connected at both ends; When performing off-grid switching tasks, the operating status and current available power of each grid-type power source are read, and the bus where the grid-type power source is located that is operating normally and whose current available power is greater than the preset minimum power is determined as the power supply starting point. When performing grid connection switching tasks, the grid connection point bus is determined as the power supply starting point; When determining the power supply sequence for loads, they should be arranged from high to low according to their load level, and if the load levels are the same, they should be arranged from small to large according to their load power.

4. The method for controlling the off-grid and on-grid power supply of a new energy microgrid according to claim 1, characterized in that, When searching for candidate power supply paths, the search starts from the power supply origin and proceeds step by step along the lines and switches that are in an operational state toward the bus where the load is located. After reaching the busbar where the load is located, the busbars, lines and switches along the way are recorded as candidate power supply paths; Read the active power, reactive power, and bus voltage of the lines connected to the candidate power supply path, and calculate the line operating current; when the operating current of any line exceeds the allowable current carrying capacity, delete the candidate power supply path passing through that line. When a candidate power supply path passes through a protected section in the restricted path set, the candidate power supply path is deleted.

5. The method for controlling the off-grid and on-grid power supply of a new energy microgrid according to claim 1, characterized in that, When dividing the protection zone, the installation location of the protection device and the circuit breaker it controls are read according to the power supply direction of the candidate power supply path; The line between two adjacent protection devices is called a double-end protection section; the line with a protection device at one end and a circuit breaker at the other end is called a single-end protection section. When a candidate power supply path contains a non-energized line, a topology change marker is set in the corresponding protection section of that line; Based on the topology change markers set for the corresponding protected area, the minimum fault current of the protected area is recalculated during the process of attempting to add a candidate power supply path.

6. The method for controlling the off-grid and on-grid power supply of a new energy microgrid according to claim 5, characterized in that, The path segment association includes at least the circuit breaker, protection device, candidate power supply path passing through the protected segment, load branch powered by the protected segment, and distributed power source that provides fault current to the protected segment. When a candidate power supply path is attempted to be added, the protection zone affected by the new load, the protection zone shared with the existing power supply path, and the protection zone where the fault current needs to be recalculated are determined based on the path segment association relationship. When a candidate power supply path is withdrawn, the record of any new loads added to the shared protection zone by that candidate power supply path is simultaneously deleted.

7. The method for controlling the off-grid and on-grid power supply of a new energy microgrid according to claim 1, characterized in that, When determining the minimum fault current, fault points are set at the beginning and end of the protected section, and the total fault current is calculated for three-phase short circuit and two-phase short circuit respectively. Based on the candidate power supply path and the switch opening and closing status, the distributed power source of the closed electrical path is determined, the fault current during the protection device operation judgment period is read in real time, and the total fault current of the fault point is accumulated. The total fault currents corresponding to the three-phase short circuit at the beginning of the protected section, the two-phase short circuit at the beginning of the protected section, the three-phase short circuit at the end of the protected section, and the two-phase short circuit at the end of the protected section are obtained respectively. The minimum total fault current is selected as the minimum fault current of the protected section.

8. The method for controlling the off-grid and on-grid power supply of a new energy microgrid according to claim 1, characterized in that, When determining the protection setting margin, power flow calculation is performed on the candidate power supply path to obtain the maximum load current of the protected section, and the product of the maximum load current and the preset reliability coefficient is used as the lower limit value of the operation. Divide the minimum fault current by the preset sensitivity coefficient to obtain the upper limit value for operation; When the lower limit of the action is less than the upper limit of the action, the range of values ​​between the lower limit of the action and the upper limit of the action is used as the setting interval, and the difference between the upper limit of the action and the lower limit of the action is used as the protection setting margin. Conversely, the protected area section will be marked as a prohibited section.

9. The method for controlling the off-grid and on-grid power supply of a new energy microgrid according to claim 1, characterized in that, When there are multiple candidate power supply paths for the same load branch, attempt to add each candidate power supply path to obtain the updated protection setting margin of the shared protection zone after the attempt to add it. The minimum updated protection setting margin in each shared protection zone is used as the margin retention value for the candidate power supply path; Prioritize retaining the candidate power supply path with the largest margin retention value; When the margin retention values ​​are the same, the candidate power supply path with the fewest required switching operations is preferred; If all candidate power supply paths for the current load branch are cancelled, skip the load branch and continue processing the next load branch, or stop the switching task when the preset power supply constraint requires the load branch to be powered.

10. The method for controlling the off-grid and on-grid power supply of a new energy microgrid according to claim 1, characterized in that, The protection setting data includes the protection positive direction, main protection action setting value, backup protection action setting value, the correspondence between the main protection device and the backup protection device, and the circuit breaker number for tripping. Specifically, the direction from the power supply starting point to the load branch is defined as the positive direction of protection; for double-ended protection sections, the protection devices corresponding to the circuit breakers at both ends are designated as the main protection devices; for single-ended protection sections, the protection device on the protection device side is designated as the main protection device; and the protection device encountered for the first time along the protection section towards the power supply starting point is designated as the backup protection device. When writing protection setting data, the protection setting data and the spare setting zone number are written to the protection device, and the setting zone number, verification result and self-test result returned by the protection device are read; when all three meet the preset verification conditions, the device is switched to the spare setting zone and the switching action sequence is executed; when any one of the preset verification conditions is not met, the setting zone switching is not executed, and the protection section corresponding to the protection device is recorded in the restricted path set. The sequence of switching actions is generated based on the difference in switching states between the current operating topology and the target operating topology. When performing an off-grid switching task, the opening action of the grid-connected switch is scheduled before the target topology activation action, and the line closing action is performed after the corresponding protection setting zone is successfully switched. When performing a grid-connected switching task, the grid-connected switch closing action is performed after the synchronization conditions are met. If any switch fails to return to the expected opening or closing state within a preset time, subsequent switching actions are stopped, and a switching blocking signal is output. For switches that have completed their actions and can be restored, restoration is performed according to the state before the switching. For switches that cannot be restored, the protection zone where they are located is recorded in the restricted path set for subsequent target operating topology reconstruction.

11. A new energy microgrid off-grid and grid-connected power supply control system, used to implement the new energy microgrid off-grid and grid-connected power supply control method according to any one of claims 1 to 10, characterized in that, include: The task analysis module is used to obtain the voltage, frequency, and voltage phase angle of the microgrid, determine the switching task, and form the current operating topology; The path search module is used to determine the power supply starting point and the power supply sequence to the load, and to search for candidate power supply paths; The segment association module is used to divide the protection segment and establish the path segment association relationship between the candidate power supply path and the protection segment; The margin calculation module is used to determine the lower limit of action, the upper limit of action, and the protection setting margin of the protected area. The path attempt addition module is used to attempt to add candidate power supply paths according to the load power supply sequence, determine the shared protection zone based on the path segment association, update the maximum load current and minimum fault current of the shared protection zone, and cancel the attempt to add candidate power supply paths when the protection setting interval disappears. The power supply control module is used to form the target operating topology from the reserved candidate power supply paths, generate protection setting data and switch action sequence, write the protection setting data into the spare setting area of ​​the protection device, and execute the switch action sequence after verification.

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