Active power distribution network spare power automatic switching action control strategy

Abstract

The invention discloses a spare power automatic switching action control strategy for an active power distribution network, which belongs to the field of power system automation and comprises the following steps: detecting electrical quantities of a main power supply and a spare power supply, and judging whether the spare power supply is charged or not; if the standby power supply finishes charging, preliminarily judging whether the main power supply loses power or not; secondly, secondary judgment is carried out on whether the main power supply loses power or not; if it is finally judged that the main power supply loses power, presetting splitting delay time, and waiting for automatic splitting of the distributed power supply on the line; after the splitting delay time is over, judging whether a switching-on action condition of the standby power supply is met or not according to the amplitude and frequency of the bus voltage and a phase relation between the bus and the standby power supply; when the switching-on action condition of the standby power supply is met, the main power supply with the fault is cut off and confirmed, and then the standby power supply is switched on; and after power supply is stable, grid connection is carried out. According to the invention, the safety of the active power distribution network during power supply switching can be effectively improved, and the power supply reliability is ensured.

Description

Technical Field

[0001] This invention belongs to the field of power system automation, and specifically relates to a control strategy for automatic transfer switching of active distribution networks. Background Technology

[0002] Backup power supplies, also known as automatic backup power supply switching devices, are widely used in various power distribution network systems, covering multiple fields such as industrial production, residential life, and public services. They are crucial equipment for ensuring the reliability of power supply to facilities. When the main power supply in the distribution network experiences a sudden power outage due to an accident or fault, the backup power supply quickly switches the power system to the backup power supply to restore power to critical loads, avoiding economic losses caused by power outages and ensuring power supply stability.

[0003] Traditional backup power supplies are suitable for single-source radial distribution networks. They primarily determine whether the main power supply is functioning normally by monitoring various operating parameters of the substation. If the main power supply is found to be out of power, the backup power supply is immediately switched on, i.e., the circuit breaker is closed. However, during the operation of the backup power supply, differences in bus voltage, frequency, and phase between the backup power supply and the bus may cause asynchrony between the two. This can result in a large inrush current during power switching, affecting power supply stability and threatening equipment safety.

[0004] Furthermore, with the large-scale integration of distributed generation, the distribution network has transformed from a traditional single-source network to a new type of interconnected multi-source network. In this scenario, after the main power supply fails, residual voltage is generated due to the voltage support provided by the distributed generation to the bus. Current traditional backup power supply operation control strategies only employ a simple "voltage exists, then lockout" logic, failing to distinguish between residual voltage and normal supply voltage. This can easily lead to misjudgment that the main power supply has not failed due to the presence of residual voltage, causing the backup power supply to fail to operate. Consequently, it cannot promptly restore power to the power system, cannot guarantee a stable and continuous power supply to users, and is ill-suited to the operational requirements of active distribution networks with interconnected multi-source power supplies. Therefore, there is an urgent need to provide an active distribution network backup automatic transfer control strategy that can solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide an active power distribution network automatic transfer switch control strategy to address the aforementioned shortcomings. This strategy aims to solve the problems of inrush currents caused by asynchrony between the busbar and the backup power supply during the current power distribution network switchover from the main power source to the backup power supply, as well as the failure of the backup power supply to operate due to residual voltage on the busbar, thus affecting the reliability of the power supply system. To achieve the above objective, this invention provides the following technical solution: An active distribution network automatic transfer switch control strategy includes the following steps: S1: Detect the electrical quantities of the main power supply and backup power supply, and determine whether the backup power supply has finished charging; S2: If the backup power supply is fully charged, a preliminary determination is made as to whether the main power supply has lost power. Then, based on the preliminary determination that the main power supply has lost power, a second determination is made as to whether the main power supply has lost power according to the preset auxiliary criteria. If the main power supply is ultimately determined to be lost, proceed to step S3; otherwise, exit the steps directly. S3: Preset disconnection delay time; waits for the distributed power supply on the line to automatically disconnect due to low voltage and low frequency protection action; S4: After the disconnection delay time ends, detect the amplitude and frequency of the bus voltage and the phase relationship between the bus and the backup power supply, and determine whether the backup power supply closing operation conditions are met based on the relevant values ​​obtained from the detection. S5: When the conditions for the backup power supply to close are met, first disconnect the faulty main power supply and confirm it, then make the backup power supply close to restore power supply to the bus; after the power supply is stable, perform grid connection operation.

[0006] Furthermore, in step S1, the backup power supply is determined to be fully charged when the following conditions are met simultaneously: the main power supply incoming switch is in the closed position; the backup power supply incoming switch is in the open position and the backup power supply line voltage is normal; and the backup power supply function board is engaged.

[0007] Furthermore, in step S2, the specific steps for initially determining whether the main power supply has lost power are as follows: when the current of the main power supply incoming line switch is detected to be zero, and the bus voltage U 母 When the voltage drops below the preset power failure voltage value U1, it is preliminarily determined that the main power supply has lost power.

[0008] Furthermore, the specific steps for the secondary determination of whether the main power supply has lost power are as follows: First, a first auxiliary criterion and second, a second auxiliary criterion are set; when either auxiliary criterion meets the power loss condition, the main power supply is ultimately determined to be lost. Further, Furthermore, among the two auxiliary criteria, the first auxiliary criterion is the attenuation rate of the bus voltage dU / dt within a preset time period t; a first power failure determination value dU / dt is set. set Calculate the absolute value of the current first auxiliary criterion |dU / dt|; if |dU / dt| is greater than the first power failure judgment value dU / dt set If so, it is determined that the main power supply has lost power.

[0009] Furthermore, among the two auxiliary criteria, the second auxiliary criterion is the frequency change rate of the bus voltage, df / dt; a second power failure judgment value, df / dt, is set. set Calculate the absolute value of the current second auxiliary criterion, |df / dt|; if |df / dt| continuously exceeds the second power failure judgment value df / dt within a preset time period t. set If so, it is determined that the main power supply has lost power.

[0010] Further, in step S4, the disconnection determination voltage value U2 is set, and the bus voltage U is determined. 母 The relationship between U2 and U2; if the bus voltage U 母 If <U2, then the backup power supply is determined to meet the closing operation conditions.

[0011] Furthermore, during the judgment process in step S4, if the bus voltage U 母 ≥U set Then, it is further determined whether the amplitude and frequency of the current bus voltage and the phase difference between the bus and the backup power supply are all within the allowable difference range; if their values ​​are all within the allowable difference range, then the backup power supply is still determined to meet the closing operation conditions.

[0012] Furthermore, during the judgment process in step S4, if the bus voltage U 母 ≥U set If any one of the following parameters—the amplitude and frequency of the current bus voltage, or the phase difference between the bus and the backup power supply—is not within the allowable range, then the backup power supply is determined not to meet the closing operation conditions, and the backup power supply is locked out.

[0013] Furthermore, an alarm signal is sent out simultaneously with the backup power supply being locked.

[0014] The beneficial effects of this invention are: 1. This invention, by employing a multi-criteria fusion strategy—instead of relying on a single criterion for determining the main power supply failure, and using preliminary judgment and secondary judgment with auxiliary criteria—can effectively solve the problem of traditional backup power supplies failing to operate due to residual voltage. It can also adapt to different types and penetration rates of distributed power supply access scenarios, exhibiting strong adaptability. Furthermore, by comprehensively determining the backup power supply's closing action conditions through relevant electrical parameters between the main and backup power supplies, it avoids the risk of asynchronous closing, ensuring the safety and reliability of power supply during power switching in active distribution networks. Attached Figure Description

[0015] Figure 1 This is a flowchart of the backup power supply operation control strategy of the present invention; Detailed Implementation In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0016] In the description of this invention, "first feature" and "second feature" may include one or more of the features.

[0017] In the description of this invention, "a plurality of" means two or more.

[0018] In the description of this invention, the first feature being "above" or "below" the second feature may include the first and second features being in direct contact, or it may include the first and second features not being in direct contact but being in contact through another feature between them.

[0019] In the description of this invention, the terms "above," "over," and "on top" for the first feature and the second feature include the first feature being directly above or diagonally above the second feature, or simply indicating that the first feature is at a higher horizontal level than the second feature.

[0020] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," and "some examples" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the present invention is not limited to the following embodiments.

[0022] Example 1: See attached Figure 1 An active distribution network automatic transfer switch control strategy includes the following steps: S1: Detect the electrical quantities of the main power supply and backup power supply, and determine whether the backup power supply has finished charging; S2: If the backup power supply is fully charged, a preliminary determination is made as to whether the main power supply has lost power. Then, based on the preliminary determination that the main power supply has lost power, a second determination is made as to whether the main power supply has lost power according to the preset auxiliary criteria. If the main power supply is ultimately determined to be lost, proceed to step S3; otherwise, exit the steps directly. S3: Preset disconnection delay time; waits for the distributed power supply on the line to automatically disconnect due to low voltage and low frequency protection action; S4: After the disconnection delay time ends, detect the amplitude and frequency of the bus voltage and the phase relationship between the bus and the backup power supply, and determine whether the backup power supply closing operation conditions are met based on the relevant values ​​obtained from the detection. S5: When the conditions for the backup power supply to close are met, first disconnect the faulty main power supply and confirm it, then make the backup power supply close to restore power supply to the bus; after the power supply is stable, perform grid connection operation.

[0023] As described above, in step S1, the electrical quantities of the main power supply and the backup power supply are first detected to confirm that the backup power supply is fully charged, ensuring that the power supply can be switched at any time during the operation of the power system to guarantee power supply. Step S2 uses a composite control logic combining preliminary judgment and auxiliary criteria to make two judgments on the main power supply failure situation, further ensuring the accuracy of the judgment on the main power supply failure, avoiding misjudgment caused by residual voltage on the bus, and solving the problem of traditional backup power supply failure due to residual voltage. Moreover, this step does not rely on a single criterion, but uses the fusion of multiple criteria for comprehensive judgment, which can adapt to different types and penetration rates of distributed power supply access scenarios and has strong adaptability. In step S3, by setting a disconnection delay, the distributed power supply on the line is disconnected due to low voltage and low frequency protection actions, so that its voltage support to the bus disappears and the residual voltage naturally dissipates, further avoiding the situation where the backup power supply fails to operate due to residual voltage. Moreover, the disconnection process is carried out automatically without manual intervention or forced tripping of distributed power supply to prevent risks caused by additional operations. Step S4 comprehensively judges whether the closing conditions of the backup power supply are met by using multiple parameters related to the busbar, avoiding large inrush currents caused by asynchrony with the busbar during closing, and significantly improving power supply safety and reliability. In step S5, the disconnection status of the main power supply is reconfirmed to ensure the safe operation of equipment during switching. After the backup power supply is restored, it is connected to the grid to restore the entire distribution network to normal operation.

[0024] Example 2: See attached Figure 1 Based on Example 1, in step S1, the backup power supply is determined to be fully charged when the following conditions are met simultaneously: the main power supply incoming switch is in the closed position; the backup power supply incoming switch is in the open position and the backup power supply line voltage is normal; and the backup power supply function board is engaged.

[0025] As can be seen from the above, before putting the backup power supply into use, the operating status of the equipment should be checked and the backup power supply should be fully charged. This can prevent power switching when the backup power supply is not ready or the power system is in an abnormal state, thus ensuring the stability and safety of the power system.

[0026] In step S2, the specific steps for initially determining whether the main power supply has lost power are as follows: when the current of the main power supply incoming line switch is detected to be zero, and the bus voltage U 母 When the voltage drops below the preset power failure voltage value U1, it is preliminarily determined that the main power supply has lost power.

[0027] The specific steps for secondary determination of whether the main power supply has lost power are as follows: set a first auxiliary criterion and a second auxiliary criterion; when any one of the auxiliary criteria meets the power loss condition, the main power supply is finally determined to be lost.

[0028] As described above, by monitoring the current of the main power supply, it can be determined whether the main power supply is outputting power. When the current is zero, it indicates that the main power supply has stopped outputting power. The preset power failure voltage value U1 is used to evaluate the bus voltage U. 母 Whether the electrical parameters that have lost voltage support, if U 母 If the value is less than U1, it proves that the main power supply has lost power. When both conditions are met simultaneously, it can be preliminarily determined that the main power supply has lost power. In addition, for residual voltage interference caused by distributed power sources, this invention introduces a secondary judgment. Through two newly added auxiliary criteria, it further confirms whether the current main power supply is truly in a state of power loss, making up for the limitations of the preliminary judgment, avoiding the failure of the backup power supply to start due to the influence of residual voltage on the bus, and ensuring the stability of subsequent power switching.

[0029] Example 3: See attached Figure 1 Based on Example 2, among the two auxiliary criteria, the first auxiliary criterion is the attenuation rate dU / dt of the bus voltage within a preset time period t; a first power failure determination value dU / dt is set. set Calculate the absolute value of the current first auxiliary criterion |dU / dt|; if |dU / dt| is greater than the first power failure judgment value dU / dt set If so, it is determined that the main power supply has lost power.

[0030] Of the two auxiliary criteria, the second auxiliary criterion is the frequency change rate of the bus voltage, df / dt; a second power failure judgment value, df / dt, is set. set Calculate the absolute value of the current second auxiliary criterion, |df / dt|; if |df / dt| continuously exceeds the second power failure judgment value df / dt within a preset time period t. set If so, it is determined that the main power supply has lost power.

[0031] As can be seen from the above, the first auxiliary criterion for selecting the bus voltage decay rate is based on the fact that when the main power supply fails, the power system loses stable support, causing the voltage to drop rapidly, ultimately resulting in a very rapid change in the initial decay rate dU / dt. Therefore, the first power failure judgment value dU / dt is set. set Furthermore, by comparing the current |dU / dt| with dU / dtset, if the initial decay rate dU / dt in the preset time period t is found to be greater than the first power failure judgment value dU / dt, then... set If the voltage drop is consistent with the characteristics of a power outage, it indicates that the voltage drop is consistent with the characteristics of a power outage. In addition, although the connection of normal loads will also cause a voltage drop, its rate of drop is relatively slow and may be accompanied by voltage recovery. Therefore, selecting the bus voltage decay rate as an auxiliary criterion and setting an appropriate first power outage judgment value can effectively eliminate misjudgments caused by load fluctuations and accurately determine whether the main power supply is in a true power outage state.

[0032] The second auxiliary criterion, the frequency change rate of the bus voltage (df / dt), is chosen because when the main power supply fails, a significant power imbalance occurs due to the loss of primary power support, resulting in a very large frequency change rate of the bus voltage. While ordinary disturbances within the system also cause frequency changes, their rates are typically smaller. Therefore, a suitable second power failure criterion value (df / dt) can be set. set And compare whether |df / dt| continuously exceeds the second power failure judgment value df / dt within the preset time period t. set Confirm whether the main power supply is actually in a state of power failure.

[0033] Example 4: See attached Figure 1 Based on Embodiment 3, in step S4, the decoupling determination voltage value U is set. set And determine the bus voltage U 母 with U set The relationship between them; if the bus voltage U 母 <U set If so, it is determined that the backup power supply meets the conditions for closing the circuit breaker.

[0034] During the judgment process in step S4, if the bus voltage U 母 ≥U set Then, it is further determined whether the amplitude and frequency of the current bus voltage and the phase difference between the bus and the backup power supply are all within the allowable difference range; if their values ​​are all within the allowable difference range, then the backup power supply is still determined to meet the closing operation conditions.

[0035] During the judgment process in step S4, if the bus voltage U 母 ≥U setIf any one of the following parameters—the amplitude and frequency of the current bus voltage, or the phase difference between the bus and the backup power supply—is not within the allowable range, then the backup power supply is determined not to meet the closing operation conditions, and the backup power supply is locked out.

[0036] At the same time as the backup power supply is locked, an alarm signal is sent out.

[0037] As can be seen from the above, step S4 analyzes different situations and comprehensively judges whether the backup power supply meets the closing operation conditions. This can avoid the backup power supply failure caused by residual voltage misjudgment and eliminate the equipment impact risk caused by asynchronous closing. First, the bus voltage U is judged. 母 Determination voltage value U set The relationship between them. Determination of voltage value U. set The value is adaptively set according to the power system conditions, and its value is close to zero. This parameter can directly and accurately reflect the disconnection status of the main power supply. When the bus voltage U 母 <U set When this occurs, it indicates that all distributed power sources have been disconnected, residual voltage has disappeared, and the conditions for backup power source reactivation have been met. Then, if the bus voltage U... 母 ≥U set The system then analyzes the measured amplitude and frequency of the bus voltage, as well as the phase difference between the bus and the backup power source. These values ​​are compared to preset, corresponding allowable differences. If all three values ​​are within the allowable range, it indicates that while the bus has residual voltage, this residual voltage is maintained by a few undisconnected but controllable distributed power sources, ensuring the safety of power switching. Therefore, the system is deemed to meet the backup power source closing conditions. If neither of these conditions is met, it indicates that the main power source and the backup power source are out of sync. Switching the power source would generate a huge inrush current, threatening equipment safety. Therefore, the backup power source is deemed not to meet the closing conditions, and the backup power source is locked out and the process is terminated. Furthermore, this situation also implies a risk of islanded operation. Blindly closing the backup power source would generate a huge inrush current. Therefore, after locking out the backup power source, an alarm is triggered to promptly notify manual intervention, ensuring the safety of the power system operation.

[0038] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A control strategy for automatic transfer switching in an active distribution network, characterized in that, Includes the following steps: S1: Detect the electrical quantities of the main power supply and backup power supply, and determine whether the backup power supply has finished charging; S2: If the backup power supply is fully charged, a preliminary determination is made as to whether the main power supply has lost power. Then, based on the preliminary determination that the main power supply has lost power, a second determination is made as to whether the main power supply has lost power according to the preset auxiliary criteria. If the main power supply is ultimately determined to be lost, proceed to step S3; otherwise, exit the steps directly. S3: Preset disconnection delay time; waits for the distributed power supply on the line to automatically disconnect due to low voltage and low frequency protection action; S4: After the disconnection delay time ends, detect the amplitude and frequency of the bus voltage and the phase relationship between the bus and the backup power supply, and determine whether the backup power supply closing operation conditions are met based on the relevant values ​​obtained from the detection. S5: When the conditions for the backup power supply to close are met, first disconnect the faulty main power supply and confirm it, then make the backup power supply close to restore power supply to the bus; after the power supply is stable, perform grid connection operation.

2. The active distribution network backup automatic transfer control strategy according to claim 1, characterized in that, In step S1, the backup power supply is determined to be fully charged when the following conditions are met simultaneously: the main power supply incoming switch is in the closed position; the backup power supply incoming switch is in the open position and the backup power supply line voltage is normal; and the backup power supply function board is engaged.

3. The active distribution network automatic transfer switch control strategy according to claim 1, characterized in that, In step S2, the specific steps for initially determining whether the main power supply has lost power are as follows: when the current of the main power supply incoming line switch is detected to be zero, and the bus voltage U 母 When the voltage drops below the preset power failure voltage value U1, it is preliminarily determined that the main power supply has lost power.

4. The active distribution network automatic transfer switch control strategy according to claim 3, characterized in that, The specific steps for secondary determination of whether the main power supply has lost power are as follows: set a first auxiliary criterion and a second auxiliary criterion; when any one of the auxiliary criteria meets the power loss condition, the main power supply is finally determined to be lost.

5. The active distribution network automatic transfer switch control strategy according to claim 4, characterized in that, Of the two auxiliary criteria, the first auxiliary criterion is the attenuation rate of the bus voltage dU / dt within a preset time period t; a first power failure determination value dU / dt is set. set Calculate the absolute value of the current first auxiliary criterion |dU / dt|; if |dU / dt| is greater than the first power failure judgment value dU / dt set If so, it is determined that the main power supply has lost power.

6. The active distribution network backup automatic transfer control strategy according to claim 4, characterized in that, Of the two auxiliary criteria, the second auxiliary criterion is the frequency change rate of the bus voltage, df / dt; a second power failure judgment value, df / dt, is set. set Calculate the absolute value of the current second auxiliary criterion, |df / dt|; if |df / dt| continuously exceeds the second power failure judgment value df / dt within a preset time period t. set If so, it is determined that the main power supply has lost power.

7. The active distribution network backup automatic transfer control strategy according to claim 1, characterized in that, In step S4, the tripping determination voltage value U2 is set, and the bus voltage U is determined. 母 The relationship between U2 and U2; if the bus voltage U 母 If <U2, then the backup power supply is determined to meet the closing operation conditions.

8. The active distribution network automatic transfer switch control strategy according to claim 7, characterized in that, During the judgment process in step S4, if the bus voltage U 母 ≥U set Then, it is further determined whether the amplitude and frequency of the current bus voltage and the phase difference between the bus and the backup power supply are all within the allowable difference range; if their values ​​are all within the allowable difference range, then the backup power supply is still determined to meet the closing operation conditions.

9. The active distribution network automatic transfer switch control strategy according to claim 8, characterized in that, During the judgment process in step S4, if the bus voltage U 母 ≥U set If any one of the following parameters—the amplitude and frequency of the current bus voltage, or the phase difference between the bus and the backup power supply—is not within the allowable range, then the backup power supply is determined not to meet the closing operation conditions, and the backup power supply is locked out.

10. The active distribution network automatic transfer switch control strategy according to claim 9, characterized in that, At the same time as the backup power supply is locked, an alarm signal is sent out.

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