Applicable boundary evaluation method for current protection of new energy alternating current grid-connected system

Abstract

The invention discloses a new energy AC grid-connected system current protection applicable boundary evaluation method, and relates to the technical field of power system protection, and the method comprises the following steps: S1, in a weak power supply region, synchronously recording current phase angle data output by a plurality of inverters and a corresponding bus voltage fluctuation sequence along a time axis, the current phase angle data and the voltage fluctuation data are superposed point by point, and a continuous disturbance rhythm diagram of the corresponding relation between the voltage and the phase angle is constructed; and S2, on the basis of the continuous disturbance rhythm diagram, comparing the current phase angle tracks at adjacent time points, extracting a plurality of inverter phase angle synchronous jump segments with phase angle change consistency at the tail segment, and connecting the phase angle jump segments in series according to a time sequence to form a synchronous transition chain. According to the method, inverter fault synchronous response is broken through phase angle dislocation regulation and control, hierarchical guide current is converged along a set path, power flow back-stepping is inhibited, and the direction protection recognition accuracy and the grid-connected system stability are improved.

Description

Technical Field

[0001] This invention relates to the field of power system protection technology, specifically to a method for assessing the applicable boundaries of current protection in new energy AC grid-connected systems. Background Technology

[0002] The assessment of the applicable boundaries of current protection for renewable energy AC grid-connected systems refers to the process of determining and defining whether current protection can maintain reliable, sensitive, and rapid operation under different operating conditions in scenarios where renewable energy sources such as photovoltaics and wind power are connected to the smart grid through inverters. Due to the weak power source characteristics of renewable energy sources, the contribution of fault current is limited by control strategies, resulting in low short-circuit ratios and prominent inverter current limiting behavior. This can lead to problems such as insufficient sensitivity, failure of direction criteria, or delayed operation in traditional current protection. This assessment uses quantitative analysis of the amplitude, phase, and time characteristics of the fault current at the grid connection point, as well as the dynamic response of the inverter, to determine under what operating conditions the current protection can still effectively trigger and under what conditions its performance degrades. Ultimately, it establishes a set of applicable boundaries to guide protection setting configuration, operating mode adjustments, and renewable energy access planning, thereby ensuring the safe and stable operation of the AC grid-connected system under conditions of high renewable energy penetration.

[0003] Existing technologies have the following shortcomings: In existing new energy AC grid-connected operation scenarios, weak power supply areas generally rely on multiple parallel inverters to provide current support. However, when affected by dynamic disturbances such as voltage drops, frequency shifts, and cross-regional disturbances, the current control links of multiple inverters exhibit synchronous responses within millisecond time slices due to consistency adjustment mechanisms, resulting in synchronous transitions in the output current phase angle. This type of phase angle transition is a typical rapid transient behavior, which causes the existing technology's phase angle-based direction protection criteria to instantly lose their basis for judgment, making it impossible for the protection module to accurately identify the fault direction. When the line fault is located at the cross-regional power supply boundary, the protection failure to operate will further trigger power flow reverse push, and the fault current will spread to the healthy area along an unexpected path, resulting in a significant expansion of the fault energy propagation range. This causes the transmission section to bear transient thermal stress far exceeding the design range, and in severe cases, it may even induce chain tripping and regional voltage collapse.

[0004] The information disclosed in the background section is only intended to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a method for assessing the applicable boundaries of current protection in new energy AC grid-connected systems, in order to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for assessing the applicable boundaries of current protection in new energy AC grid-connected systems, comprising the following steps:

[0007] S1, In the weak power supply area, the current phase angle data and corresponding bus voltage fluctuation sequence of multiple inverters are recorded synchronously along the time axis, and the current phase angle data and voltage fluctuation data are superimposed point by point to construct a continuous disturbance rhythm diagram of the voltage and phase angle correspondence.

[0008] S2, based on the continuous disturbance rhythm diagram, compare the current phase angle trajectory at adjacent time points, extract multiple inverter phase angle synchronous jump segments with consistent phase angle changes in the final segment, and connect the phase angle jump segments in time sequence to form a synchronous transition chain;

[0009] S3 utilizes the phase angle concentration area formed at the end of the synchronous transition chain to superimpose the grid-connected line topology to identify the transition clustering location near the cross-regional power supply boundary and generate a directional protection risk boundary zone covering the cross-regional boundary area.

[0010] S4, insert a time-division sampling window based on the direction protection risk boundary band into the current acquisition link of multiple inverters. The time-division sampling window is used to construct a continuous hierarchical direction tracking trajectory containing the rhythm of current phase angle change, so as to realize the layer-by-layer tracking of the synchronous transition chain.

[0011] S5, based on the phase angle spatial distribution at the end of the hierarchical directional tracking trajectory, sends separately configured micro-time delay control commands to the inverter controllers in different regions. At the moment of fault response, the inverter current phase angle interval is widened to achieve phase angle misalignment at the moment of synchronous transition, guide the fault current to converge along the stable path, and suppress the fault current to push back the power flow to non-target regions.

[0012] Preferably, step S1 includes:

[0013] In areas with weak power sources, multiple inverters are connected to the grid, and synchronous sampling is used to collect the current phase angle data of each inverter and the bus voltage fluctuation data at the grid connection point.

[0014] The current phase angle data and the bus voltage fluctuation data are superimposed point by point along the time axis to form a continuous disturbance rhythm diagram of the relationship between voltage and phase angle;

[0015] In the continuous disturbance rhythm diagram, identify the abrupt phase angle change intervals where the phase angle change amplitude exceeds the preset threshold, compare the voltage fluctuation trend, and mark them to form a synchronous disturbance window;

[0016] The phase angle abrupt changes of multiple inverters in the synchronous disturbance window are connected in series in chronological order to form a complete disturbance response chain.

[0017] Preferably, buffer time windows of the same duration are set before and after the phase angle change interval. By comparing the current phase angle change trajectory before and after the buffer with the bus voltage fluctuation trend, it is determined whether the phase angle change is synchronized with the voltage disturbance rhythm, which is used to identify the effectiveness of the synchronization disturbance window.

[0018] Preferably, step S2 includes:

[0019] Based on the continuous disturbance rhythm diagram, the current phase angle data of multiple inverters are read at each sampling time point, and the phase angle data at each sampling time point is compared with the phase angle data at the previous time point to identify the candidate moment of phase angle jump.

[0020] The time window is extended forward and backward with the identified candidate moment of phase angle jump as the center. The inverter phase angle change curve is extracted and normalized to obtain the jump segment with consistent phase angle change.

[0021] The phase jump segments are concatenated in chronological order of the jump events to form a synchronous jump chain with temporal sequence and characteristics.

[0022] Inverter grid connection location numbers are superimposed on the synchronous jump chain to establish the correspondence between jump events and spatial location information.

[0023] Preferably, during the formation of the synchronous transition chain, by comparing the phase angle jump amplitude of each inverter with the bus voltage fluctuation trend, the jump segments whose phase angle jump direction is consistent with the main current flow direction are preferentially connected in series to ensure that the synchronous transition chain reflects the actual direction of disturbance propagation and is used to identify high-risk areas of directional protection failure.

[0024] Preferably, step S3 includes:

[0025] The phase angle change data of the last period is extracted in the synchronous transition chain and sorted according to the physical location number of the grid-connected branch to which the inverter belongs to form a phase angle transition spatial location mapping table.

[0026] Based on the phase angle transition spatial location mapping table, the grid-connected line topology diagram is superimposed, the inverter locations in the transition concentration are marked on the topology diagram, and the transition response range boundary is drawn.

[0027] The correlation characteristics between the core area of ​​the transition aggregation and the cross-regional power supply boundary are analyzed to identify high-risk areas for directional protection;

[0028] Based on the coupling relationship between the transition clustering region and the power supply topology, a directional protection risk boundary zone covering the cross-regional boundary area is generated.

[0029] Preferably, during the generation of the directional protection risk boundary zone, by comparing the phase angle transition amplitude of the inverter within the transition cluster area with the phase angle change difference of the adjacent branch inverter, the connection points of non-transition inverters with an electrical distance less than a preset threshold are included in the boundary zone range, so as to form the edge of the protection blind zone identification and limit the spatial expansion range of the risk area.

[0030] Preferably, step S4 includes:

[0031] In the directional protection risk boundary zone, inverters with dense current phase angle transitions and locations close to the protection critical section are selected as observation targets. A time-division sampling window is established in the current sampling link to lock the entire transition process.

[0032] Within the time-sharing sampling window, the current phase angle sampling values ​​are arranged in time sequence and compared with the transition chain timing data in the continuous disturbance rhythm diagram to obtain the directional consistency response trajectory.

[0033] Using the end point of the time axis of the first-layer directional response trajectory as a reference, the next window interval is selected, and the trajectory extraction operation is repeated to form a multi-layer directional tracking trajectory.

[0034] By combining the temporal structure and spatial distribution results of all hierarchical directional response trajectories, a complete directional tracking map is generated to describe the disturbance propagation process.

[0035] Preferably, the time range of the time-sharing sampling window is dynamically set according to the concentrated period of the inverter phase angle jump in the synchronous transition chain, and the time alignment error of the sampling data does not exceed the predetermined time interval, so as to ensure the correspondence accuracy between the current phase angle change sequence and the voltage fluctuation rhythm, thereby improving the recognition accuracy of the directional consistency response trajectory.

[0036] Preferably, step S5 includes:

[0037] Based on the hierarchical directional tracking trajectory, the inverter number, phase angle change amplitude, transition completion time and grid connection location corresponding to the end point of each layer trajectory are extracted to form a phase angle response distribution list and divide the response area;

[0038] Based on the natural phase angle misalignment characteristics between each response region, a millisecond-level micro-time delay control command is set in the inverter control path to widen the response trigger time of each region.

[0039] The phase angle interval was verified and a misalignment response spectrum was generated by recording the inverter current phase angle startup time using high-precision sampling equipment.

[0040] The direction of fault current convergence is analyzed based on phase angle misalignment diagrams to achieve current guidance and power flow reverse push suppression.

[0041] The technical effects and advantages provided by the present invention in the above technical solution are as follows:

[0042] This invention achieves ordered misalignment control of inverter current phase angles by constructing a continuous disturbance rhythm diagram, extracting synchronous transition chains, identifying directional protection risk boundary bands, hierarchically constructing directional tracking trajectories, and applying minute time-delay control commands between key inverters. This control strategy breaks the instantaneous synchronization of inverter current injection in the early stages of a fault, establishes a hierarchical response mechanism, promotes the preferential convergence of fault current along a set path in the grid topology, and effectively suppresses its reverse diffusion to non-fault areas. This significantly improves the identification accuracy and operational reliability of directional protection in high-penetration renewable energy scenarios, and enhances the safe and stable operation capability of AC grid-connected systems under complex disturbance environments. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0044] Figure 1 This is a flowchart of the method for evaluating the applicable boundary of current protection in a new energy AC grid-connected system according to the present invention. Detailed Implementation

[0045] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, they are provided so that the description of this disclosure will be more complete and fully convey the concept of the exemplary embodiments to those skilled in the art.

[0046] This invention provides, for example Figure 1 The method for assessing the applicable boundary of current protection in new energy AC grid-connected systems, as shown, includes the following steps:

[0047] S1, In the weak power supply area, the current phase angle data and corresponding bus voltage fluctuation sequence of multiple inverters are recorded synchronously along the time axis, and the current phase angle data and voltage fluctuation data are superimposed point by point to construct a continuous disturbance rhythm diagram of the voltage and phase angle correspondence.

[0048] To effectively assess the applicable boundaries of current protection in weak power source areas of new energy AC grid connection, it is necessary to first construct a voltage and phase angle coupling behavior map reflecting the response characteristics of multiple inverters, i.e., a continuous disturbance rhythm map, as the basis for subsequent extraction of synchronization transition characteristics and identification of protection risk boundaries. The following is a detailed implementation method for this process:

[0049] Within the selected weak-power grid connection area, establish a grid-connected environment containing at least three inverters. Install high-precision synchronous sampling equipment in this area to continuously collect the three-phase AC current phase angle data of each inverter's output side at fixed time intervals (e.g., every 2 milliseconds). Phase angle acquisition should be digitized and converted to a phase angle value consistent with the standard grid phase reference, for example, using zero degrees aligned with the voltage phase center point under daytime steady-state, disturbance-free operating conditions. Simultaneously, use a voltage acquisition device to synchronously collect the instantaneous amplitude change of the bus voltage at the grid connection point's main bus side. Each sampled voltage value should correspond one-to-one with the current phase angle at the current sampling moment. Taking actual sampling as an example, assuming that after a disturbance occurs, inverters A, B, and C experience drastic changes in current phase angle at 128 milliseconds, 130 milliseconds, and 131 milliseconds respectively, then at each sampling point within 128 to 140 milliseconds, the instantaneous phase angle values ​​of the three inverters and the corresponding voltage amplitude fluctuation data need to be listed side-by-side.

[0050] Based on the collected raw data sequence, the phase angle values ​​of each inverter are correlated point-by-point with the grid-connected point voltage fluctuation data in chronological order, establishing a correspondence between phase angle and voltage disturbance changes via a time axis. For example, in a disturbance response, when the voltage drops from a stable value of 220 volts to 204 volts, it rapidly recovers to 215 volts within approximately 5 milliseconds. Inverter B's phase angle exhibits an instantaneous jump from 35 degrees to 88 degrees at the voltage minimum point; this jump is then linked to the voltage trough. After performing the same operation on all inverters, a two-dimensional superimposed image is obtained, with the time axis as the horizontal axis and voltage changes and phase angle responses as the vertical axis—a continuous disturbance rhythm diagram. During image construction, to ensure data consistency, each set of current phase angle values ​​and voltage values ​​must be aligned using a unified timestamp, with a time error not exceeding 0.5 milliseconds, to ensure a clear causal relationship for abrupt changes. For example, in a wind farm fault event in June 2025, through the above-mentioned data collection and superposition operations, between 136 and 142 milliseconds, the phase angles of the three inverters rose by 40 to 60 degrees almost synchronously, and the corresponding voltage dropped to 203 volts and recovered around 139 milliseconds, forming a typical disturbance rhythm segment.

[0051] Based on the graph obtained after mapping the voltage and current phase angle data, the amplitude of phase angle change and the direction of voltage fluctuation within each time slice of the disturbance rhythm graph are further compared and analyzed. By selecting continuous time periods for sliding window processing, segments with phase angle change gradients greater than a set threshold (e.g., 40 degrees) can be extracted on the time axis. For each inverter phase angle curve, a 5-millisecond buffer window is extended before and after the abrupt change interval, and the phase angle trajectories before and after the buffer are marked as the pre-disturbance state and the post-disturbance state, respectively. At this time, the voltage fluctuation trend within 5 milliseconds before and after the disturbance should be approximated using a second-order difference to confirm whether the voltage change trend and the phase angle abrupt change are synchronized. If multiple inverters exhibit significant phase angle transitions within the same time period, and the corresponding voltage change curves show a rhythmic behavior of rapid drop followed by recovery, these time periods are defined as synchronization disturbance windows. Taking a sudden load drop in the region in July 2025 as an example, 7 out of 9 inverters simultaneously experienced phase angle jumps exceeding 45 degrees within 150 to 156 milliseconds, corresponding to the lowest voltage point at 151 milliseconds, which can be identified as a synchronization disturbance. By continuously plotting the above segments on the graph, a time interval segment with significant disturbance response characteristics can be constructed, laying the data foundation for the subsequent construction of the synchronization transition chain.

[0052] After segment labeling, the phase angle abrupt change characteristic segments extracted from the entire disturbance rhythm diagram are connected in chronological order to form the overall disturbance response chain of the inverter group. This chain should start from the first jump event and connect the main transition segments of each inverter at different time points to construct a complete response sequence. During the connection process, information such as the start and end time of each transition segment, phase angle transition amplitude, and corresponding voltage fluctuation pattern needs to be recorded. The transition behavior of each time period should be compared with the bus voltage fluctuation curve of the previous moment to ensure that it is a real disturbance response rather than data jitter. Through standardized image overlay, the transition behaviors of multiple inverters are stitched together in the same coordinate system in a parallel manner on the time axis to form a continuous disturbance rhythm diagram. The regular and visualized trajectory presented can be used to identify synchronous transition characteristics. The entire process forms a rhythm map with fine time resolution and significant voltage-phase angle coupling characteristics, which not only provides a clear basis for subsequent synchronous transition chain extraction but also lays the foundation for assessing the reliability of directional protection and identifying risks in boundary areas.

[0053] S2, based on the continuous disturbance rhythm diagram, compare the current phase angle trajectory at adjacent time points, extract multiple inverter phase angle synchronous jump segments with consistent phase angle changes in the final segment, and connect the phase angle jump segments in time sequence to form a synchronous transition chain;

[0054] To further identify the phase angle synchronous transition behavior caused by multiple inverters jointly responding to disturbances during the grid connection of new energy sources, based on the constructed continuous disturbance rhythm diagram, it is necessary to accurately extract synchronous jump segments with consistent phase angle changes and form a complete response trajectory chain arranged in chronological order, which will be used to subsequently construct the directional protection risk boundary. The following is a detailed implementation method for this process:

[0055] Based on the previously established continuous disturbance rhythm diagram, the current phase angle values ​​of all grid-connected inverters are sequentially read at each sampling time point and compared differentially with the phase angle value at the previous time point. The unit of difference is angle, and the calculation interval is two consecutive sampling periods. For example, with a sampling period of 2 milliseconds, the angle changes at 128 milliseconds and 130 milliseconds are compared. For each inverter, if its phase angle change amplitude exceeds a set threshold at a certain moment, such as exceeding 30 degrees, then that time point is marked as a candidate moment for phase angle jump. Further analysis is performed to determine if all inverters exhibit similar jump behavior at that moment. If more than two-thirds of the inverters have phase angle change amplitudes exceeding the threshold at that moment, then that time point is considered a potential synchronous phase angle jump event. Taking actual collected data as an example, suppose that in the test on August 4, 2025, the five inverters exhibited phase angle changes of 35 degrees to 85 degrees, 38 degrees to 90 degrees, 32 degrees to 84 degrees, 36 degrees to 83 degrees, and 34 degrees to 86 degrees respectively at 154 milliseconds, and that all of these transitions occurred at the same time point. Then, 154 milliseconds is marked as a valid synchronization jump moment.

[0056] After identifying potential synchronization jump moments, an observation window is established, extending forward and backward by several sampling periods from this moment. Typically, the extended window is set to ±10 milliseconds, meaning the complete observation interval is from 144 milliseconds to 164 milliseconds. Within this time period, the phase angle change curves of each inverter are extracted, and the phase angle change trends before and after the jump are reconstructed into a trajectory. To ensure consistency in the comparison between trajectories, all phase angle trajectories are normalized, with the jump start point set as the zero reference point and the maximum angle after the change used as the endpoint reference. By superimposing the normalized phase angle trajectories, it is possible to observe whether there are transition patterns with high overlap. If a rapidly rising curve with the same trend can be observed in most inverter trajectories, and the time span between the starting and ending points of the rise is within an allowable range (e.g., less than 6 milliseconds), then these trajectories are defined as jump segments with consistent phase angle changes. Taking a set of observation data as an example, if the phase angle of inverter A increases by 50 degrees within 4 milliseconds starting from 154 milliseconds, and B and C increase by 52 degrees and 48 degrees respectively within the same time period, and the trajectory shapes are almost identical, it can be determined that these trajectories have abrupt jump consistency.

[0057] After confirming the consistency of the jump segments, all consistent phase angle jump segments are sequentially connected according to the chronological order of their occurrence. The connection method starts with the earliest jump behavior based on the timestamp, connecting all satisfying jump segments in sequence to construct a complete trajectory chain from the occurrence of the disturbance to the end of the disturbance response. Each segment connection point records parameters such as the original sampling time, the number of participating inverters, the average transition amplitude, and the transition duration to form a dynamic trajectory with temporal sequence, characteristic features, and response strength. For example, if valid synchronous jump behaviors are detected at 150 ms, 154 ms, and 159 ms, and the interval between each event is less than 10 ms, with similar trajectory change directions, these three jump events can be merged into a synchronous transition chain. This chain reflects multiple concentrated jump behaviors experienced from the initial disturbance to the maximum response, providing a visual representation of the joint response of multiple inverters during a single disturbance.

[0058] To further enhance the spatial identification capability of the synchronous jump chain, the geographical location or grid connection location number of the inverter corresponding to each jump behavior is superimposed on the constructed trajectory chain to establish a correspondence between jump events and spatial location information. This operation can be recorded using a numbered list. For example, if inverters A, B, and C are located in bus segments 1, 2, and 3 respectively, when their jump behaviors are connected in the same jump chain, the jump origin and propagation direction can be indicated by additional labels. By jointly analyzing the time series and spatial distribution of the jump chain, it is possible to identify situations where certain jump behaviors are concentrated at cross-regional power supply boundaries or densely distributed inverter areas, thus providing data support for subsequent identification of high-risk areas for protection failure. In a set of actual simulation data, if it is found that subsequent jump events in the jump chain mostly occur in adjacent areas, and their direction is consistent with the main current flow direction, it can be further inferred that the jump chain may interfere with the protection direction determination. Therefore, the above method not only successfully constructs a complete synchronous jump chain but also lays a key foundation for subsequent identification of directional protection risk boundaries and guidance of fault diversion control strategies.

[0059] S3 utilizes the phase angle concentration area formed at the end of the synchronous transition chain to superimpose the grid-connected line topology to identify the transition clustering location near the cross-regional power supply boundary and generate a directional protection risk boundary zone covering the cross-regional boundary area.

[0060] Based on the established synchronous transition chain, to further pinpoint critical areas where directional protection may fail, it is necessary to integrate the phase angle change regions concentrated at the end of the transition chain with the spatial structure of the entire grid-connected line. This allows for the identification of power supply boundary locations with highly responsive coupling characteristics, and the delineation of directional protection risk boundary zones accordingly. The specific implementation method for this process is as follows:

[0061] The phase angle change data at the end of the completed synchronous transition chain is extracted and sorted according to the physical location number of the grid-connected branch to which the inverter belongs. Each inverter should have its connected bus number, grid-connected branch number, and relative position in the entire grid topology clearly defined; for example, inverter A is connected to bus 1 branch L1, inverter B is connected to bus 2 branch L3, etc. Subsequently, a one-to-one correspondence is established between the jump time points and phase angle change amplitudes of these inverters and their grid-connected positions, forming a phase angle transition-spatial location mapping table. During this process, special attention should be paid to inverter groups with large phase angle jump amplitudes and similar occurrence times in the transition chain, and these should be considered as candidate points for the core transition cluster area. Taking a set of measured data as an example, if inverters A, B, and C on the left side of the power supply boundary experience phase angle transitions exceeding 45 degrees between 154 milliseconds and 160 milliseconds, while inverters D and E on the right side show almost no phase angle change, it can be preliminarily determined that the transition response is concentrated in the left side of the boundary region.

[0062] Based on the completed phase angle transition-spatial location mapping table, the topology diagram of the entire AC grid-connected system is overlaid, including the connection relationships between each bus, the electrical distances between branches, the distribution of transformers, and the main power supply direction. The locations of inverters with transition clusters are marked on the topology diagram, and the transition response range boundary is drawn. The boundary should cover all inverter connection points that exhibit transition behavior within the same time period. In practical operation, this can be performed as follows: First, mark the locations of all inverters whose transition amplitude exceeds a set threshold (e.g., 40 degrees). Then, based on the electrical distances and topological connections between adjacent inverters, connect the jump points with dashed lines and enclose them in a closed region. For example, in a field test in September 2025, in a typical wind power transmission scenario, 6 out of 10 inverters were located at the grid connection point at the front end of the substation outgoing line. During a cross-regional disturbance, a phase angle synchronous transition occurred. The location formed a clear cluster in the topology map, which was less than the electrical distance of two branches from the regional boundary section. Therefore, this area can be preliminarily defined as the core area of ​​the transition cluster.

[0063] For the core area of ​​the transition cluster, the correlation characteristics between it and the cross-regional power supply boundary are further analyzed. Specifically, this includes: whether the cluster spans multiple substation outgoing lines; whether it is located at the convergence point in the main power supply direction; and whether it is adjacent to the branching node of the main line. By analyzing these relationships, it can be determined whether the transition response is related to the power flow interface. If the transition cluster is located at the critical position where power sources from different regions converge, or is adjacent to a junction node connected to a remote power receiving area, then this area has the potential to become a high-risk area for directional protection criterion failure. In a typical simulation case, the transition cluster point of a certain inverter group is located at the switching node between two load centers, and protection failure occurs at the time of disturbance, which can be identified as an actual weak protection area. By feeding these analysis results back onto the grid connection structure diagram and using different colors to mark the boundary between high-risk areas and normal areas, a preliminary sketch of the directional protection risk boundary can be generated.

[0064] Based on the coupling relationship between the formed transition cluster region and the power supply topology, the formal construction of the directional protection risk boundary zone is completed. The risk boundary zone should encompass all spatial areas where protection directional misjudgment, protection failure to operate, or power flow reverse propagation may occur. Its boundary should consist of two types of points: one type is inverter connection points with concentrated transition amplitudes and similar occurrence times; the other type is inverter connection points with an electrical distance less than a specific threshold (such as the length of two branches) and no obvious transitions, used to form the edge for identifying protection blind zones. The boundary zone can be drawn on the topology map in the form of distance contour lines, or represented using simplified shapes such as rectangles or trapezoids. In a verification of a high-proportion renewable energy access area, a high-risk area covering three outgoing lines and two busbar connection points was identified at the outlet of a wind farm, and the existence of potential misjudgment was confirmed during actual protection configuration adjustments. Therefore, this directional protection risk boundary zone not only clearly points out the potential failure areas of the current protection configuration, but also provides crucial spatial input basis for subsequent setting verification and control strategy optimization.

[0065] S4, insert a time-division sampling window based on the direction protection risk boundary band into the current acquisition link of multiple inverters. The time-division sampling window is used to construct a continuous hierarchical direction tracking trajectory containing the rhythm of current phase angle change, so as to realize the layer-by-layer tracking of the synchronous transition chain.

[0066] To more effectively identify the synchronous response process of multiple inverters under disturbances and dynamically track the current phase angle change trend in high-risk areas of directional protection, a time-division sampling window based on risk boundaries needs to be introduced into the current sampling chain. This allows for the extraction of the current phase angle rhythm layer by layer, forming a traceable directional trajectory. The specific implementation method of this process is as follows:

[0067] Within the identified directional protection risk boundary zone, inverters with dense current phase angle jumps and locations close to the critical protection section are selected as observation targets, and their time-domain processing strategy at the current sampling entry point is determined. Based on the characteristic segments at the end of the jump chain and their spatial distribution on the topology map, adjacent inverters are divided into multiple observation units, each corresponding to a continuous path on a risk boundary zone. In the current sampling channel corresponding to each group of inverters, an initial time window is established according to a fixed sampling period, for example, dividing each period into a 50-millisecond sampling segment, and retaining all instantaneous current phase angle sampling values ​​in each segment. This window setting does not depend on the fault trigger signal, but is triggered by the concentrated period of phase angle jumps of each inverter in the synchronous jump chain, enabling the sampling window to capture time-domain information around these high-frequency jump segments. Taking a certain disturbance as an example, if inverters A, B, and C experience phase angle transitions within 136 to 146 milliseconds, time-division sampling windows starting at 132 milliseconds and ending at 152 milliseconds are inserted into the sampling path of each inverter to lock the entire process before and after the transition.

[0068] After constructing the time-division sampling window, all current phase angle samples within the window are arranged in chronological order to form a fine-grained phase angle change sequence. This sequence is compared with the transition chain timing data in the continuous disturbance rhythm diagram, ensuring that each current phase angle data point can be mapped to a known transition event stage. To enhance the identification capability of disturbance response paths, the phase angle sequences of each group of inverters are arranged sequentially from near to far according to their physical location in the grid topology, and normalized according to their phase angle change trends. By comparing the slope, jump amplitude, and time delay characteristics of the normalized phase angle sequence changes, a set of phase angle curves with high similarity is extracted and defined as the directional consistency response trajectory. For example, if three inverters in the same window all exhibit a phase angle rise rate of 12 degrees per millisecond, a duration of approximately 5 milliseconds, and a final jump amplitude between 55 and 60 degrees, this is marked as the first-level directional response trajectory. Subsequently, the next-level phase angle change sequences with smaller jump response amplitudes but delays not exceeding 10 milliseconds are used as the second-level trajectories to further supplement the sequence.

[0069] After constructing the first layer of directional response trajectories, using its time axis endpoint as a new benchmark, the next window interval is selected in the subsequent sampling sequence of each inverter, and the above trajectory extraction operation is repeated, thereby extending the second, third, and even more layers of directional tracking trajectories along the time axis. Each layer of trajectory corresponds to a set of inverter phase angle sequences with similar response characteristics, and is numbered according to the transition time difference and phase angle change amplitude. All layers are connected by time intervals, and a layer-by-layer map of the directional protection influence range expansion is formed according to their spatial location. In a high-penetration wind farm test, actual sampling data showed that after a regional disturbance occurred, the first layer of trajectory appeared between 138 and 142 milliseconds, and the second layer of trajectory followed immediately, completing the transition response between 144 and 148 milliseconds. The spatial locations of the two sets of inverters exactly covered two adjacent branches of the high-voltage outgoing line, forming a typical protection blind zone expansion trajectory.

[0070] By integrating the temporal structure and spatial distribution results of all layered directional response trajectories, a complete directional tracking map is generated to dynamically describe the propagation of disturbances from the starting inverter to other areas. The differences in response characteristics between each trajectory layer are used to characterize the sensitivity of different areas to synchronization transitions. For example, the response start time of the trajectory is used to determine the order of protection triggering, and the change in transition amplitude is used to determine the degree of adaptation of directional protection settings. Ultimately, a three-dimensional directional protection risk assessment map is formed, with sampling time as the main axis, phase angle change amplitude as the magnitude, and spatial distribution as the extended dimension. This map can be directly used in actual power grid operation to assist in determining whether the directional protection blind zone has expanded to the critical region, and provides quantitative basis and judgment support for subsequent fault diversion control and protection strategy intervention.

[0071] S5, based on the phase angle spatial distribution at the end of the hierarchical directional tracking trajectory, sends separately configured micro-time delay control commands to the inverter controllers in different regions. At the moment of fault response, the inverter current phase angle interval is widened to achieve phase angle misalignment at the moment of synchronous transition, guide the fault current to converge along the stable path, and suppress the fault current to push back the power flow to non-target regions.

[0072] After constructing the multi-layer directional tracking trajectory, the control strategy of the inverters in each region can be further fine-tuned based on the phase angle spatial distribution characteristics at the end of each trajectory layer. By precisely applying a small time delay, the current phase angle of each inverter in the initial stage of fault response is controllably misaligned, thereby breaking the instantaneous synchronous transition trend and achieving directional guidance of the fault current. The following is a detailed implementation of this process:

[0073] Based on the previously constructed hierarchical directional tracking trajectories, the inverter number, phase angle change amplitude, transition completion time, and physical connection location in the grid topology corresponding to the endpoint of each trajectory are extracted. This information is combined into a phase angle response distribution list, and the inverters are classified by region. Each region corresponds to a directional tracking level, numbered from fastest to slowest response time as the first response zone, second response zone, third response zone, etc. Taking measured data from a wind farm as an example, if in a disturbance, inverters A, B, and C complete phase angle transitions 140 milliseconds in advance, D, E, and F complete transitions 145 milliseconds in advance, and G, H, and I complete transitions 150 milliseconds in advance, then the branch containing ABC can be classified as the first response zone, DEF as the second response zone, and GHI as the third response zone. Based on this, the average final phase angle value and response duration of the inverters within each response zone are statistically analyzed, and the phase angle difference between adjacent response zones is calculated. If the average phase angle of the first response zone is 85 degrees, the second response zone is 82 degrees, and the third response zone is 78 degrees, it indicates that there is a natural misalignment trend between the different levels, and subsequent regulation can be fine-tuned and strengthened based on this trend.

[0074] Based on the natural phase angle misalignment characteristics between response regions, adjustable micro-time delay control logic is designed in the inverter control path corresponding to each region. This time delay should be set at the millisecond level, generally controlled within the range of 0.5 milliseconds to 3 milliseconds, to artificially widen the trigger time of each region's response, thereby increasing the spatial distribution difference of current phase angles between inverters. Taking a specific implementation as an example, if the inverter control strategy for the first response region is set to no delay, the second response region is delayed by 1.5 milliseconds, and the third response region is delayed by 3 milliseconds, then at the instant a fault voltage drop occurs, the inverters in each region will sequentially initiate current support responses, forming a misalignment in the phase angle triggering sequence. This control command is injected through the grid-connected operation command channel and the parameters need to be issued during the steady-state phase before disturbance identification to ensure automatic triggering when a fault occurs. Each inverter control channel should have a delay timing logic unit to adjust the response start based on a preset delay value after receiving a voltage drop or frequency drift signal.

[0075] After implementing zoned delay control, high-precision sampling equipment is used to synchronously record the start-up time and rising trend of the current phase angle of each inverter at the moment of fault, verifying whether the phase angle interval between each zone reaches the expected misalignment range. For example, in a typical grid-connected point fault test, the collected results after implementing the delay strategy show that the phase angle of the first response zone rises to 80 degrees at 138 milliseconds, the second response zone rises to 83 degrees at 139.5 milliseconds, and the third response zone rises to 85 degrees at 141 milliseconds, forming a phase angle interval of about 2 to 3 degrees between the three zones, effectively avoiding the phenomenon of all inverters injecting symmetrical current simultaneously. By projecting these data into three-dimensional space, with time as the horizontal axis, phase angle as the vertical axis, and inverter position as the depth axis, the distribution trajectory of the current phase angle of each response zone can be clearly depicted, thereby establishing a realistic misalignment response spectrum. This spectrum will serve as an important basis for evaluating the fault current propagation path and help determine whether a current concentration direction conducive to protection action has been formed.

[0076] Based on the established phase angle misalignment pattern, the actual convergence direction and propagation path of fault current in the grid-connected system are further analyzed. By controlling the phase angle misalignment, the different current support response times lead to phase differences in the current output by each inverter in the initial stage of the fault, ultimately causing the total current to flow towards a specific main path, thus guiding the direction of the fault current. For example, in a scenario with a high proportion of photovoltaic grid connection, a delay strategy control ensures that the inverters on the main branch respond earliest, with the peripheral inverters responding sequentially later. This ultimately guides the fault current mainly to flow to the main branch, rather than spreading to the load-side branch, effectively preventing the protection device from misjudging the power supply direction at the load end. This current guidance result manifests in the protection device's current channel as a rapid stabilization of the current polarity and a clear direction at the moment of fault occurrence, facilitating the identification of protection setting actions. Simultaneously, phase angle misalignment can effectively reduce the risk of high-frequency oscillations caused by the instantaneous superposition of outputs from multiple inverters, improving the transient stability of the system. Ultimately, the entire phase angle misalignment strategy, with minimal time delay as its core, will constitute an important component of the grid-connected fault response and control mechanism, supporting the improvement of current-oriented control and protection reliability in new energy grid-connected areas under complex fault conditions.

[0077] This invention achieves ordered misalignment control of inverter current phase angles by constructing a continuous disturbance rhythm diagram, extracting synchronous transition chains, identifying directional protection risk boundary bands, hierarchically constructing directional tracking trajectories, and applying minute time-delay control commands between key inverters. This control strategy breaks the instantaneous synchronization of inverter current injection in the early stages of a fault, establishes a hierarchical response mechanism, promotes the preferential convergence of fault current along a set path in the grid topology, and effectively suppresses its reverse diffusion to non-fault areas. This significantly improves the identification accuracy and operational reliability of directional protection in high-penetration renewable energy scenarios, and enhances the safe and stable operation capability of AC grid-connected systems under complex disturbance environments.

[0078] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for assessing the applicable boundaries of current protection in new energy AC grid-connected systems, characterized in that, Includes the following steps: S1, In the weak power supply area, the current phase angle data and corresponding bus voltage fluctuation sequence of multiple inverters are recorded synchronously along the time axis, and the current phase angle data and voltage fluctuation data are superimposed point by point to construct a continuous disturbance rhythm diagram of the voltage and phase angle correspondence. S2, based on the continuous disturbance rhythm diagram, compare the current phase angle trajectory at adjacent time points, extract multiple inverter phase angle synchronous jump segments with consistent phase angle changes in the final segment, and connect the phase angle jump segments in time sequence to form a synchronous transition chain; S3 utilizes the phase angle concentration area formed at the end of the synchronous transition chain to superimpose the grid-connected line topology to identify the transition clustering location near the cross-regional power supply boundary and generate a directional protection risk boundary zone covering the cross-regional boundary area. S4, insert a time-division sampling window based on the direction protection risk boundary band into the current acquisition link of multiple inverters. The time-division sampling window is used to construct a continuous hierarchical direction tracking trajectory to achieve layer-by-layer tracking of the synchronous transition chain. S5, based on the phase angle spatial distribution at the end of the hierarchical directional tracking trajectory, sends separately configured micro-time delay control commands to the inverter controllers in different regions. At the moment of fault response, the inverter current phase angle interval is widened to achieve phase angle misalignment at the moment of synchronous transition, guide the fault current to converge along the stable path, and suppress the fault current to push back the power flow to non-target regions.

2. The method for assessing the applicable boundaries of current protection in a new energy AC grid-connected system according to claim 1, characterized in that, Step S1 includes: In areas with weak power supply, multiple inverters are connected to the grid, and synchronous sampling is used to collect the current phase angle data of each inverter and the bus voltage fluctuation data at the grid connection point. The current phase angle data and the bus voltage fluctuation data are superimposed point by point along the time axis to form a continuous disturbance rhythm diagram of the relationship between voltage and phase angle; In the continuous disturbance rhythm diagram, identify the abrupt phase angle change intervals where the phase angle change amplitude exceeds the preset threshold, compare the voltage fluctuation trend, and mark them to form a synchronous disturbance window; The phase angle abrupt changes of multiple inverters in the synchronous disturbance window are connected in series in chronological order to form a complete disturbance response chain.

3. The method for assessing the applicable boundary of current protection in a new energy AC grid-connected system according to claim 2, characterized in that, A buffer time window of the same duration is set before and after the phase angle change interval. By comparing the current phase angle change trajectory before and after the buffer with the bus voltage fluctuation trend, it is determined whether the phase angle change is synchronized with the voltage disturbance rhythm, which is used to identify the effectiveness of the synchronization disturbance window.

4. The method for assessing the applicable boundaries of current protection in a new energy AC grid-connected system according to claim 2, characterized in that, Step S2 includes: Based on the continuous disturbance rhythm diagram, the current phase angle data of multiple inverters are read at each sampling time point, and the phase angle data at each sampling time point is compared with the phase angle data at the previous time point to identify the candidate moment of phase angle jump. The time window is extended forward and backward with the identified candidate moment of phase angle jump as the center. The inverter phase angle change curve is extracted and normalized to obtain the jump segment with consistent phase angle change. The phase jump segments are concatenated in chronological order of the jump events to form a synchronous jump chain with temporal sequence and characteristics. Inverter grid connection location numbers are superimposed on the synchronous jump chain to establish the correspondence between jump events and spatial location information.

5. The method for assessing the applicable boundary of current protection in a new energy AC grid-connected system according to claim 4, characterized in that, During the formation of the synchronous transition chain, by comparing the phase angle jump amplitude of each inverter with the bus voltage fluctuation trend, the jump segments whose phase angle jump direction is consistent with the main current flow direction are preferentially connected in series to ensure that the synchronous transition chain reflects the actual direction of disturbance propagation and is used to identify high-risk areas of directional protection failure.

6. The method for assessing the applicable boundaries of current protection in a new energy AC grid-connected system according to claim 4, characterized in that, Step S3 includes: The phase angle change data of the last period is extracted in the synchronous transition chain and sorted according to the physical location number of the grid-connected branch to which the inverter belongs to form a phase angle transition spatial location mapping table. Based on the phase angle transition spatial location mapping table, the grid-connected line topology diagram is superimposed, the inverter locations in the transition concentration are marked on the topology diagram, and the transition response range boundary is drawn. The correlation characteristics between the core area of ​​the transition aggregation and the cross-regional power supply boundary are analyzed to identify high-risk areas for directional protection; Based on the coupling relationship between the transition clustering region and the power supply topology, a directional protection risk boundary zone covering the cross-regional boundary area is generated.

7. The method for assessing the applicable boundaries of current protection in a new energy AC grid-connected system according to claim 6, characterized in that, During the generation of the directional protection risk boundary zone, by comparing the phase angle transition amplitude of the inverter in the transition cluster area with the phase angle change difference of the adjacent branch inverter, the connection points of non-transition inverters with an electrical distance less than a preset threshold are included in the boundary zone range, so as to form the edge of the protection blind zone identification and limit the spatial expansion range of the risk area.

8. The method for assessing the applicable boundary of current protection in a new energy AC grid-connected system according to claim 6, characterized in that, Step S4 includes: In the directional protection risk boundary zone, inverters with dense current phase angle transitions and locations close to the protection critical section are selected as observation targets. A time-division sampling window is established in the current sampling link to lock the entire transition process. Within the time-sharing sampling window, the current phase angle sampling values ​​are arranged in time sequence and compared with the transition chain timing data in the continuous disturbance rhythm diagram to obtain the directional consistency response trajectory. Using the end point of the time axis of the first-layer directional response trajectory as a reference, the next window interval is selected, and the trajectory extraction operation is repeated to form a multi-layer directional tracking trajectory. By combining the temporal structure and spatial distribution results of all hierarchical directional response trajectories, a complete directional tracking map is generated to describe the disturbance propagation process.

9. The method for assessing the applicable boundaries of current protection in a new energy AC grid-connected system according to claim 8, characterized in that, The time range of the time-sharing sampling window is dynamically set according to the concentrated period of inverter phase angle jumps in the synchronous transition chain. The time alignment error of the sampling data does not exceed the predetermined time interval to ensure the correspondence accuracy between the current phase angle change sequence and the voltage fluctuation rhythm, thereby improving the recognition accuracy of the directional consistency response trajectory.

10. The method for assessing the applicable boundary of current protection in a new energy AC grid-connected system according to claim 8, characterized in that, Step S5 includes: Based on the hierarchical directional tracking trajectory, the inverter number, phase angle change amplitude, transition completion time and grid connection location corresponding to the end point of each layer trajectory are extracted to form a phase angle response distribution list and divide the response area; Based on the natural phase angle misalignment characteristics between each response region, a millisecond-level micro-time delay control command is set in the inverter control path to widen the response trigger time of each region. The phase angle interval was verified and a misalignment response spectrum was generated by recording the inverter current phase angle startup time using high-precision sampling equipment. The direction of fault current convergence is analyzed based on phase angle misalignment diagrams to achieve current guidance and power flow reverse push suppression.

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