Flexible traction power supply system substation role and stage collaborative current-limiting voltage-maintaining control method

Abstract

The application discloses a flexible traction power supply system sub-role and sub-stage collaborative current-limiting voltage-maintaining control method for a substation, which comprises the following steps: dividing an active power supply area according to the equivalent line impedance from a traction substation to a fault point; comprehensively scoring the traction substation in the active power supply area; configuring the role of the traction substation according to the comprehensive score; the role comprises a main voltage supply role, an auxiliary voltage supply role and a current-limiting protection role; performing droop control on the traction substation with different roles and collaboratively limiting the current and maintaining the voltage in stages; the stages comprise a rapid peak suppression stage, a collaborative voltage maintenance stage and a smooth recovery stage. The application realizes comprehensive coordination of the voltage support capability of the fault point and the safety boundary of the flexible traction substation by constructing a dynamic role division mechanism based on the matching of the operation margin and the position, combining the three-stage control strategy of the rapid peak suppression, the collaborative voltage maintenance and the smooth recovery, and can improve the power supply continuity and reliability of the flexible traction power supply system under the fault working condition.

Description

Technical Field

[0001] This invention relates to the field of traction power supply control technology, and in particular to a method for role-based, phased, collaborative current limiting and voltage maintaining control of a flexible traction power supply system substation. Background Technology

[0002] The rail transit traction power supply system uses flexible traction substations along the line to jointly supply power to the trains via the overhead contact line. As the train is a moving load, its location changes in real time during operation, causing dynamic changes in the output power and line voltage drop of each flexible traction substation. In particular, when a local fault disturbance occurs in the system, significant power coupling and voltage support coupling effects will form between adjacent flexible traction substations.

[0003] Currently, various technical solutions and engineering applications have been developed for the coordinated power supply and fault condition operation assurance of flexible traction substations. These mainly focus on fault detection and segmented protection, power supply network reconstruction after fault section isolation, cross-regional or bilateral power supply restoration strategies, and inter-station coordinated control based on information interaction. For example, segmented protection enables rapid isolation of fault sections, cross-regional power supply restoration is achieved through tie switch switching, and inter-station coordinated control is realized based on multi-station information sharing. However, existing solutions still have certain limitations: existing technologies mostly focus on fault identification, isolation, and power supply topology reconstruction after fault occurrence, mainly addressing the power supply restoration problem after fault isolation. The technical means for continuous coordinated control of multiple flexible traction substations around the moving train load throughout the entire fault disturbance process are still imperfect. Furthermore, most existing solutions do not comprehensively consider the differences in operating margins of each flexible traction substation in terms of current, temperature rise, and capacity, making it difficult to dynamically adjust load distribution according to the real-time support capacity of each flexible traction substation. This can easily lead to overload or even shutdown of some flexible traction substations. In addition, a phased differentiated coordination mechanism is established for the initial disturbance stage, the continuous voltage holding stage, and the recovery stage after the fault is cleared. During the power supply restoration process, problems such as voltage fluctuations, unstable power distribution, and frequent switching of control modes are easily caused, which affect the stability of system operation and the continuity of power supply. Summary of the Invention

[0004] The purpose of this invention is to provide a multi-substation collaborative current limiting and voltage maintaining control method for flexible traction power supply systems, which combines the real-time operating status and support capabilities of each flexible traction substation for dynamic coordination, and takes into account disturbance suppression, continuous voltage maintaining and smooth recovery of multi-substation collaborative control, so as to improve the power supply continuity and reliability of flexible traction power supply systems under fault conditions.

[0005] The technical solution for achieving the objective of this invention is as follows:

[0006] A role-based, phased, collaborative current-limiting and voltage-maintaining control method for substations in flexible traction power supply systems, when a fault occurs in the contact network of the system, includes the following steps:

[0007] Active power supply zones are defined based on the equivalent line impedance from the traction substation to the fault point.

[0008] A comprehensive evaluation is conducted on traction substations within the active power supply area;

[0009] The roles of traction substations are configured based on comprehensive scores; these roles include main power supply role, auxiliary power supply role, and current limiting protection role.

[0010] Droop control is implemented for traction substations with different roles, and current limiting and voltage maintenance are carried out in stages; the stages include a rapid peak suppression stage, a coordinated voltage maintenance stage, and a smooth recovery stage.

[0011] Preferably, the division of the active power supply zone is as follows: [The text abruptly ends here, likely due to an incomplete sentence or a formatting error.] ≤β The traction substations are included in the active power supply area, among which, Let be the equivalent line impedance from the i-th traction substation to the fault point. β is the minimum equivalent line impedance from all traction substations to the fault point, and β>1 is the active power supply area expansion coefficient.

[0012] Preferably, the comprehensive score of the i-th traction substation within the active power supply area is: :

[0013]

[0014] in,

[0015] For location matching degree, , This is the distance between the traction substation and the fault point. This represents the maximum distance between the traction substation and the fault point within the active power supply area.

[0016] For current margin, , , These are the maximum allowable output current and the current equivalent output current of the traction substation, respectively.

[0017] For heat margin, , , , These are the maximum allowable junction temperature, the real-time estimated junction temperature, and the reference temperature of the power devices in the traction substation, respectively.

[0018] This is the equivalent line impedance from the traction substation to the fault point;

[0019] , , , These are the corresponding weights, and the preset values ​​satisfy... ;like Less than the preset threshold ,or Less than the preset threshold Then let , This is the preset minimum value.

[0020] Furthermore, the role of the traction substation configured according to the comprehensive score is as follows: the traction substation with the highest comprehensive score is designated as the main voltage supply role, the traction substation with the second highest comprehensive score is designated as the auxiliary voltage supply role, and the other traction substations are designated as current limiting protection roles.

[0021] Preferably, the conditions for the phased approach are:

[0022] Rapid peak suppression phase: Output current of any traction substation within the active power supply area Greater than or equal to the warning threshold or the voltage at the fault point Below the warning threshold ;

[0023] Collaborative pressure maintenance phase: The overhead contact line fault has not been cleared, and the output current of all traction substations is... Less than or equal to the warning threshold And the rate of change of output current of all traction substations satisfies And the voltage at the fault point satisfy ≤ ≤ ;in, The threshold for the rate of change of output current. To restore the voltage threshold;

[0024] Smooth recovery phase: Overhead contact network fault cleared, and ;in, To restore the current threshold, To restore the holding time.

[0025] Furthermore, the phased collaborative current limiting and pressure maintenance specifically refers to:

[0026] Once the rapid peak suppression phase begins, then:

[0027] For the reference value of the outer loop output current of the traction substation that is the main voltage supplier, the limiting threshold is increased, i.e.: ,in, This is the reference value for the outer voltage loop output current. This is the upper limit of the current constraint for the traction substation under the current fault condition. This is a limiting function;

[0028] For the reference value of the outer voltage loop output current of the traction substation that plays a supporting voltage supply role, first reduce the scaling factor, and then limit the amplitude, that is: ,in, This is the scaling factor, 0 < <1, This is the upper limit of the current constraint for the traction substation under the current fault condition.

[0029] The reference value of the outer loop output current of the traction substation, which plays a current-limiting protection role, is limited. ,in, This is the current limiting value for the traction substation under the current fault condition;

[0030] Upon entering the coordinated pressure-holding phase, then:

[0031] For traction substations with main and auxiliary power supply respectively, the reference output voltage value of the inner current loop is corrected based on the voltage deviation at the fault point, i.e.: , , , ,in, , These are the output voltage reference values ​​after correction for the main and auxiliary power supply roles, respectively. , These are the reference output voltage values ​​for the main and auxiliary voltage supply roles, respectively. , These are the voltage reference correction values ​​for the main and auxiliary voltage supply roles, respectively. , These are the proportional adjustment coefficients for the main and auxiliary pressure supply roles in PI control. , These are the integral adjustment coefficients for the main and auxiliary pressure supply roles in PI control, respectively. The reference value for the target voltage at the fault point;

[0032] For traction substations that play a current-limiting protection role, a smooth weighted average method is used to generate a total current reference value, which is then used as the current-limiting value for the outer loop output current of the traction substation's voltage. ,in, These are the weighting coefficients. This is the current limiting value for the traction substation under the current fault condition. This is the target current reference value under current constraint priority control;

[0033] Once the smooth recovery phase begins, then:

[0034] For traction substations with main and auxiliary voltage supply roles respectively, the reference output voltage value of the inner current loop is adjusted according to the voltage reference correction amount, that is: , ;in, This is the voltage reference correction amount. , This is the voltage reference correction amount at the initial moment when the traction substation enters the smooth recovery phase. The rate of decline of the voltage reference correction for this traction substation;

[0035] For traction substations with current limiting protection, update the total current reference value: ,in, , This is the current limiting value of the outer voltage loop output current reference value. The target current reference value is set under current-constrained priority control; and the outer voltage loop output current reference value is updated: .

[0036] This invention addresses the problems of voltage drop at the fault point, severe overcurrent in local flexible traction substations, and easy oscillation during the recovery process caused by traditional fault clearing methods in flexible traction power supply systems under fault disturbance conditions. By constructing a dynamic role division mechanism based on operating margin and location matching, combined with a three-stage control strategy of rapid peak suppression, coordinated voltage maintenance, and smooth recovery, this invention achieves comprehensive coordination of the voltage support capability at the fault point and the safety boundary of the flexible traction substation, thereby improving the power supply continuity and reliability of the flexible traction power supply system under fault conditions. Attached Figure Description

[0037] Figure 1 This is a schematic diagram showing the structure, status information collection, and active power supply zone division corresponding to fault points in a flexible traction power supply system.

[0038] Figure 2 This is a schematic diagram illustrating the logic of comprehensive score calculation and role classification.

[0039] Figure 3 A diagram illustrating the functional division of the main pressure supply role, auxiliary pressure supply role, and current limiting protection role.

[0040] Figure 4 This is a schematic diagram of the three-stage coordinated control switching logic under fault conditions. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0042] I. System Structure and Status Information Acquisition

[0043] Figure 1The diagram shows the structure and status information acquisition of the flexible traction power supply system. The system includes the main power grid, multiple flexible traction substations arranged along the line, the overhead contact line, and the running trains. Each flexible traction substation is connected to the external power grid via transformers and converters, and provides traction power supply voltage to the overhead contact line via feeders. The flexible traction substations exchange operational status information and coordinate control through a communication network.

[0044] The overhead contact line runs along the railway line. Trains, acting as mobile loads, draw current from the contact line via pantographs. During operation, the current-drawing location constantly changes, causing dynamic variations in the power load distribution, output current, and line voltage drop of each flexible traction substation. When a fault occurs in the contact line, the electrical distance and equivalent line impedance from each flexible traction substation to the fault point differ due to the different locations of the fault points within the line. This results in variations in the voltage support capacity and current distribution relationship of different flexible traction substations to the fault point, thus providing the foundation for implementing a role-based, phased, and coordinated control strategy for flexible traction substations.

[0045] Each flexible traction substation has a certain output regulation capability, and its output characteristics are affected by local operating conditions and line impedance. During system operation, each flexible traction substation collects the following information in real time: output current of each flexible traction substation, output power of each flexible traction substation, estimated junction temperature of power devices, fault point voltage, equivalent line impedance from each flexible traction substation to the fault point, and local fault-related quantities, including fault proximity, current change rate, and fault point voltage drop.

[0046] II. Construction of Comprehensive Evaluation Indicators

[0047] Figure 2 The diagram shows the overall character rating and character classification process.

[0048] To achieve a comprehensive evaluation of the collaborative support capability and operational safety boundary of flexible traction substations, this invention constructs the following indicators:

[0049] 1. Location matching degree

[0050]

[0051] in, Let be the distance between the i-th flexible traction substation and the fault point. This represents the maximum electrical distance between each flexible traction substation in the active power supply area corresponding to the current fault point and the fault point. The greater the location matching degree, the closer the flexible traction substation is to the current fault location, and the more effective it is in fulfilling its voltage support task.

[0052] 2. Current margin

[0053]

[0054] in, Let be the current equivalent output current of the i-th flexible traction substation. Set its maximum allowable output current.

[0055] 3. Heat margin

[0056]

[0057] in, This is the highest allowable junction temperature for power devices. To estimate junction temperature in real time, This is a reference temperature.

[0058] 4. Overall Score

[0059]

[0060] in, Let be the equivalent line impedance from the i-th flexible traction substation to the fault point. to For the corresponding weight coefficients, and satisfying Each weight coefficient is set according to the importance of the indicator to the system's operational safety and support capabilities. Under normal operating conditions, the initial weight coefficients for each evaluation indicator are set as follows: Location matching degree weight. Current margin weight Heat margin weight Line impedance weighting .

[0061] In this invention, when the current margin of the i-th flexible traction substation is... Less than the threshold or heat margin Less than the threshold At that time, the weight coefficient of the corresponding indicator and Dynamically weakened to a minimum The remaining weight coefficients remain at their initial values, significantly reducing their overall score and thus placing them in a lower priority position in the ranking. They are only assigned to limited support or rate-limiting roles to ensure a safety margin for system operation. A preset, extremely small positive number is used to characterize the degree of weakened participation of the corresponding indicator in the scoring; it can be taken as... .

[0062] III. Rules for Delineating Active Power Supply Zones and Assigning Roles

[0063] Figure 1 A schematic diagram showing the division of active power supply areas corresponding to fault points.

[0064] In traction power supply systems, the degree of support provided by different flexible traction substations to the current fault point varies significantly. Especially in the scenario of flexible substation clusters, some flexible traction substations, due to their large spatial distance from the fault point and weak electrical coupling, have limited actual support for the current undervoltage point. Including them in the comprehensive scoring and role allocation would not only reduce the relevance of role assignment but also potentially lead to an excessive number of current-limiting protection roles in the system, increasing control complexity without any significant practical benefits.

[0065] Therefore, before assigning roles, the system first divides the group of substations into active power supply zones based on the location of fault points, the spatial distribution of flexible traction substations, and the coupling relationship of power supply paths. For each fault point, the system uses the equivalent line impedance from each flexible traction substation to that fault point as the basis for dividing the active power supply zone, and calculates the corresponding active power supply zone for each flexible traction substation. and will satisfy ≤β The flexible traction substation is included in the active power supply area, among which, β is the minimum equivalent line impedance from all flexible traction substations to the current fault point, and β is the active power supply zone expansion coefficient, where β > 1. Therefore, not only can the flexible traction substation closest to the fault point in electrical distance be included in the active power supply zone, but also flexible traction substations slightly farther from the fault point but still providing strong support can be included if their equivalent line impedance does not exceed the threshold. Other flexible traction substations that do not meet the above conditions are considered to be far from the current fault point and have insignificant support functions; they do not participate in the comprehensive scoring and role classification of the current fault point, nor do they assume the corresponding current-limiting protection role, and remain in a normal power supply or standby state.

[0066] By using the above method, the scope of role division can be limited to the local group that has a real impact on the current fault point, thereby avoiding the problem of too many current-limiting roles in a large-scale power supply system and improving the effectiveness and simplicity of control.

[0067] Figure 3 A diagram illustrating the functional division of the main pressure supply role, auxiliary pressure supply role, and current limiting protection role.

[0068] Based on the above principles for dividing active power supply areas, the system can form the following two typical role division scenarios:

[0069] (1) Active power supply area scenario of dual substations

[0070] When an active power supply area contains only two flexible traction substations that have a significant supporting relationship with the current fault point, the system adopts a configuration of "1 main voltage supply role + 1 auxiliary voltage supply role". Specifically, the one with the higher comprehensive score serves as the main voltage supply role, undertaking the main voltage support task, while the other flexible traction substation serves as the auxiliary voltage supply role, providing auxiliary support.

[0071] (2) Active power supply areas of three substations and above

[0072] When an active power supply area contains three or more flexible traction substations, the configuration is generally "1 main voltage supply role + 1 auxiliary voltage supply role + the rest are current limiting protection roles". Specifically, within the active power supply area, the substation with the highest comprehensive score is designated as the main voltage supply role, the substation with the second highest comprehensive score is designated as the auxiliary voltage supply role, and the remaining flexible traction substations assume the current limiting protection role or are in standby protection status according to their operating status.

[0073] For a typical scenario with three flexible traction substations, a basic configuration of "1 main voltage supply role + 1 auxiliary voltage supply role + 1 current limiting protection role" can be formed. For active power supply areas with four or more flexible traction substations, the role structure of "1 main + 1 auxiliary + other current limiting protection" should be maintained in principle to ensure that the voltage protection responsibility is centralized, the control logic is clear, and to avoid too many units participating in strong support at the same time, which would complicate the power distribution.

[0074] IV. Stage Determination and Phased Control Methods in Three-Player Scenarios

[0075] Figure 4 This is a schematic diagram of the three-stage coordinated control switching logic under fault conditions.

[0076] To balance transient overcurrent suppression under fault disturbances, fault point voltage support, and smooth exit after fault mitigation, this invention constructs a phased collaborative control mechanism for fault scenarios, dividing the fault response process into a rapid peak suppression phase, a collaborative voltage maintenance phase, and a smooth recovery phase. The three-stage control dynamically switches according to the changes in fault point voltage, fault point voltage change rate, and output current of each flexible traction substation, following a progressive logic of "rapidly suppressing the impact in the initial stage of the fault—collaboratively maintaining voltage during the fault duration—smoothly returning to normal after fault mitigation."

[0077] The rapid peak suppression phase mainly corresponds to the transient process of rapid current surge and rapid voltage drop in the early stage of a fault. Its control objective is to prioritize suppressing the overcurrent peak, prevent further expansion of the disturbance, and avoid directly disconnecting the flexible traction substation in the early stage of the fault, which would lead to a significant drop in the voltage at the fault point. The coordinated voltage maintenance phase mainly corresponds to the process where the fault still exists, but the system has moved away from the strong impact state of the initial fault. Its control objective is to continuously maintain the voltage at the fault point while meeting the safety boundaries of each flexible traction substation, and prevent further deterioration of the power supply capacity during the fault. The smooth recovery phase mainly corresponds to the recovery process after the fault has been disconnected or the impact of the fault has left the enhanced support demand range. Its control objective is to gradually withdraw each role from the enhanced support state, and reduce the risks of voltage oscillation, repeated power transfer, and frequent role switching caused by direct withdrawal from control.

[0078] In this invention, the stage determination comprehensively considers the voltage amplitude at the fault point, the voltage change rate at the fault point, the output current of each flexible traction substation, the current change rate, and the duration of the fault.

[0079] When the output current of any flexible traction substation Reaching the warning threshold Or the voltage at the fault point is lower than the warning threshold. The system then enters a rapid peak suppression phase.

[0080] When the fault is not cleared, and the output current of each flexible traction substation is... Less than or equal to the warning threshold Its rate of change of current satisfies At the same time, the voltage at the fault point meets the requirements. ≤ ≤ At this point, the system enters the collaborative pressure-holding phase. In the formula, The threshold for the rate of change of output current (can be set to 0.05). / ms), To restore the voltage threshold (which can be set to 0.95). At this point, although the voltage at the fault point has not returned to the normal range, the current is no longer in a state of rapid surge, and the focus of system control has shifted from rapidly suppressing the surge to continuously maintaining voltage support.

[0081] When the fault is cleared, and the voltage at the fault point and the output current of each flexible traction substation recover to the preset range and continuously meet the holding time requirement, the system enters the smooth recovery phase. The criterion for this phase can be expressed as follows:

[0082]

[0083] in, To restore the current threshold (which can be set to 0.8). / ms), To restore the hold time (which can be set to 200ms).

[0084] To avoid frequent system switching due to fault disturbances near the stage switching boundary, this invention further introduces a recovery threshold, holding time, and hysteresis mechanism in the stage determination. When the system is in the coordinated voltage holding stage or the smooth recovery stage, if the triggering condition of the rapid peak suppression stage is met again, i.e., the output current of any flexible traction substation reaches the warning threshold... Or the voltage at the fault point is lower than the warning threshold. If the fault is not resolved and the recovery conditions are not met, the system will return to the rapid peak suppression phase. If the fault has not been resolved and the recovery conditions are not met, the system will continue to remain in the collaborative pressure holding phase, thus forming a progressive and reversible control logic that is oriented towards the entire fault process.

[0085] Based on the phased control concept under the above fault scenarios, and on the basis of droop control of traction substations, the following three typical control scenarios are formed:

[0086] (1) Rapid peak suppression control scenario at the initial stage of a fault

[0087] When the system is in the initial stage of a fault, and the output current of any flexible traction substation reaches the warning threshold. or the voltage at the fault point Below the warning threshold At this point, the system enters the rapid peak suppression phase. The core function of this phase is to quickly suppress the overcurrent surge at the initial stage of the fault, slow down the voltage deterioration trend at the fault point, and retain the necessary operating margin for the subsequent fault continuation phase.

[0088] During this phase, for the main voltage supply role, to ensure it can still undertake the main voltage support task in the early stages of a fault, the reference value of the outer voltage loop output current is subject to threshold limiting, i.e.:

[0089]

[0090] in, Reference value for the outer loop output current of the main voltage supply role voltage. The upper limit of current constraint for the main voltage supply role under the current fault condition.

[0091] The limiting function is as follows:

[0092]

[0093] For auxiliary voltage supply roles, to prevent them from prematurely entering an overcurrent state while providing auxiliary voltage support, the scaling factor of their outer voltage loop output current reference value is first reduced, and then amplitude limiting is applied, i.e.:

[0094]

[0095] in, The scaling factor for the auxiliary pressure supply role satisfies 0 < <1, The upper limit of current constraint for the auxiliary voltage supply role under the current fault condition.

[0096] For current limiting protection, the priority is to suppress local overcurrent peaks, and the reference value of the outer voltage loop output current is directly and strictly limited, i.e.:

[0097]

[0098] in, The current limiting value for the current limiting protection role under the current fault condition.

[0099] In one implementation, the current constraint thresholds for each of the above roles satisfy:

[0100]

[0101] The aforementioned differentiated control can prevent all flexible traction substations from adopting strong current-limiting responses in the early stages of a fault, which could lead to a sudden drop in voltage at the fault point.

[0102] (2) Collaborative pressure holding control scenario during fault duration

[0103] When the fault is not cleared, and the output current of each flexible traction substation meets the requirements... And its rate of change of current satisfies | |≤ At the same time, the voltage at the fault point meets the requirements. ≤ ≤ At this point, the system enters the collaborative voltage maintenance phase. The core function of this phase is to maintain the voltage at the fault point during the fault's duration, stabilize the support functions of each role, and prevent local units from exceeding safety boundaries due to continuous support.

[0104] In this stage, the voltage deviation at the fault point is incorporated into the AC side output voltage reference correction process. The main voltage supply and auxiliary voltage supply roles each generate voltage reference corrections of varying strengths based on the voltage deviation at the fault point.

[0105]

[0106]

[0107] in, and , , These are the proportional adjustment coefficients for the main and auxiliary pressure supply roles in PI control (which can be set to 0.8 and 0.4 respectively). , These are the integral adjustment coefficients for the main and auxiliary pressure supply roles in PI control (each can be set to 120). 60 ), The reference value for the target voltage at the fault point (can be taken as 27.5 kV).

[0108] The voltage reference correction is added to the original reference output voltage values ​​in the control of the main and auxiliary voltage supply roles, respectively, to obtain the corrected AC side output voltage reference values:

[0109]

[0110]

[0111] in, and These are the reference output voltage values ​​for the main voltage supply role and the auxiliary voltage supply role under normal operating conditions. and These serve as input references for the outer voltage loop of the corresponding flexible traction substation. After adjustment by the outer voltage loop, they generate the inner current loop reference quantity, thereby achieving layered and coordinated support for the voltage at the fault point.

[0112] By setting different support gains, the main voltage supply role obtains a larger voltage reference correction range and assumes the main voltage protection responsibility; the auxiliary voltage supply role obtains a smaller voltage reference correction range and assumes the auxiliary voltage protection responsibility, thus forming a collaborative voltage protection structure with main and auxiliary layers and different strengths.

[0113] For current limiting protection, when its output current continues to approach the forced current limiting threshold... At this time, the control objective gradually shifts from "considering voltage support" to "prioritizing current safety," and the control method further transitions from current-limiting voltage source control to current-constraint-priority control. To reduce the sudden current changes and voltage fluctuations caused by the direct switching between the two control methods, this invention uses a smooth weighted method to generate the total current reference value:

[0114]

[0115] in, This is the target current reference value under current-constrained priority control. To switch weight coefficients, and The output current varies continuously within the threshold range; The current limiting value for the current limiting protection role under the current fault condition.

[0116] In one implementation, satisfy:

[0117] Therefore, the current-limiting protection function can continuously transition between maintaining a certain voltage support capability and prioritizing its own safety, depending on the degree of approach of the output current during the fault. If the fault worsens further during this stage, and the output current of any flexible traction substation reaches the warning threshold... Or the voltage at the fault point is lower than the warning threshold. Then the system can return to the rapid peak suppression phase.

[0118] (3) Smooth recovery control scenario after fault mitigation or removal

[0119] If the fault is cleared, and the voltage at the fault point and the output current of each flexible traction substation simultaneously meet the requirements... And continue to meet the retention time When this happens, the system enters the smooth recovery phase. The core function of this phase is to ensure that all roles exit the fault enhancement support state in an orderly manner, suppress secondary disturbances during the recovery process, and ensure that the system smoothly returns to its normal operating state.

[0120] In this stage, to avoid voltage oscillations or repeated power shifts caused by the main voltage supply role, auxiliary voltage supply role, and current limiting protection role directly exiting coordinated control after the fault is cleared, this invention adopts a parameter gradual recovery method. The weight recovery and current limiting value recovery of the current limiting protection role, as well as the reduction of the voltage reference correction for the main voltage supply role and auxiliary voltage supply role, are respectively expressed as follows:

[0121]

[0122]

[0123]

[0124] in, , and These represent the recovery (fallback) rates for the corresponding parameters.

[0125] For the traffic-limiting protection role, after recovery and Substitute this value back into its control law. Specifically, the current reference value under current-limiting voltage source control is updated as follows:

[0126]

[0127] Its total current reference value has been updated as follows:

[0128]

[0129] Therefore, with As current limiting protection gradually recovers, the maximum allowable output current increases gradually; with... As the voltage increases gradually, the control method smoothly transitions from current constraint priority control back to current-limiting voltage source control, and then gradually returns to the conventional voltage source support state.

[0130] For the primary and secondary pressure supply roles, after recovery Substitute the AC side output voltage reference value back into the value for use, that is:

[0131]

[0132]

[0133] in, , These are the reference output voltage values ​​for the main and auxiliary power supply flexible traction substations under normal operating conditions. Therefore, the additional voltage support introduced by the main and auxiliary power supply roles during a fault gradually decreases over time until it returns to the reference voltage value under normal operating conditions, thus avoiding voltage oscillations and repeated power transfers caused by a sudden loss of voltage support.

[0134] To avoid the system frequently entering and exiting different control stages near the recovery boundary, this invention sets a hysteresis condition to ensure that the threshold is satisfied:

[0135]

[0136] and

[0137]

[0138] Through the aforementioned gradual recovery and hysteresis mechanisms, the system can gradually deactivate the main voltage supply role, auxiliary voltage supply role, and current limiting protection role from the fault enhancement support state, reducing the risks of voltage oscillation, repeated power transfer, and frequent role switching after the fault is cleared. If the fault recurs during the recovery process, or the voltage at the fault point drops again and the output current rises again, the system can stop the recovery process and switch back to the rapid peak suppression phase, thereby ensuring the continuity and reliability of power supply throughout the fault process.

[0139] V. Degradation Control Methods in Dual-Role Scenarios

[0140] When an active power supply area contains only two flexible traction substations, the system adopts a dual-role configuration of "1 main power supply role + 1 auxiliary power supply role", without setting a current limiting protection role. In this case, the control methods for the main power supply role and the auxiliary power supply role in the rapid peak suppression stage, the coordinated pressure maintenance stage, and the smooth recovery stage are the same as the control methods for the corresponding roles in the three-role scenario described in Part IV, and will not be repeated here.

[0141] Specifically, during the rapid peak suppression phase, the main voltage supply role continues to perform high threshold limiting control, while the auxiliary voltage supply role continues to perform support coefficient scaling and limiting control; during the coordinated voltage holding phase, the main voltage supply role and the auxiliary voltage supply role continue to generate voltage reference correction amounts and achieve layered coordinated voltage holding; during the smooth recovery phase, the main voltage supply role and the auxiliary voltage supply role continue to gradually exit the enhanced support state.

[0142] When the current margin or thermal margin of one flexible traction substation in a dual-role scenario is significantly insufficient, resulting in a significant decrease in its overall score, the corresponding flexible traction substation can degenerate into a protection priority state and enter a more stringent restricted support control to ensure the safe operation of the device; the other flexible traction substation continues to undertake the main voltage support task within the allowable range of its safety boundary. Specific Implementation

[0143] The present invention will be described below with reference to typical failure scenarios. The embodiments described are only for illustrating the control concept and implementation of the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0144] Example 1: Collaborative control of a single fault point in a scenario with a single train and multiple flexible traction substations

[0145] Taking the example of multiple flexible traction substations arranged sequentially along the line and jointly supplying power to the overhead contact system, a local fault occurs in the overhead contact system when a single train is running near the boundary power supply area between the first and second flexible traction substations.

[0146] After a fault occurs, the system first divides the active power supply area based on the location of the fault point, the spatial distribution of flexible traction substations, and the coupling relationship of the power supply path. Since the first and second flexible traction substations are relatively close to the fault point and have strong electrical coupling, and the third flexible traction substation still has some correlation, the active power supply area corresponding to this fault point can include the first, second, and third flexible traction substations. More distant flexible traction substations are not included in the current active power supply area and do not participate in the scoring and role classification of this fault point.

[0147] Subsequently, the system calculates the location matching degree, current margin, thermal margin, and comprehensive score for each flexible traction substation within the active power supply area. Since the fault point is located between the first and second flexible traction substations, their location matching degrees are relatively close. Therefore, the determination of the main and auxiliary power supply roles depends primarily on their real-time current margin, thermal margin, and line impedance level. If the first flexible traction substation has the highest comprehensive score, it is designated as the main power supply role, the second flexible traction substation as the auxiliary power supply role, and the third flexible traction substation as the current limiting protection role.

[0148] When the initial fault causes a rapid drop in voltage at the fault point, and the output current of either the first or second flexible traction substation reaches the warning threshold... At this time, the system enters the rapid peak suppression phase. At this time, the main voltage supply role maintains a strong voltage support capability, only moderately restricting the output current; the auxiliary voltage supply role executes limited voltage support control; the current limiting protection role enters current limiting voltage source control to suppress local overcurrent peaks as soon as possible, and avoid further deterioration of the fault point voltage caused by simultaneous deep current limiting of the three flexible traction substations.

[0149] When the fault has not yet been resolved, but the most severe overcurrent surge has been initially suppressed, and the voltage at the fault point remains low, the system enters the coordinated voltage holding phase. The main voltage supply takes on the primary voltage holding task, the auxiliary voltage supply takes on the secondary voltage holding task, and the current limiting protection measures the output current as it approaches the forced current limiting threshold. The control system can smoothly switch between current-limiting voltage source control and current constraint priority control to balance fault point voltage support and its own safety protection.

[0150] When the fault is cleared or significantly reduced, the voltage at the fault point recovers to above the set range, and the output current of each flexible traction substation falls below the recovery threshold and remains below it for the specified time, the system enters the smooth recovery phase. At this time, the enhanced support, current limiting values, and switching weights of each component gradually recover according to a preset slope, thus smoothly exiting the fault control state. If the voltage at the fault point drops again or the output current rises rapidly again during the recovery process, the system stops recovery and returns to the rapid peak suppression phase.

[0151] This embodiment demonstrates that the present invention can sequentially complete the active power supply area division, comprehensive scoring, role division, and three-stage progressive control in a single fault point scenario, thereby achieving coordinated current limiting and voltage protection control throughout the fault process.

[0152] Example 2: Zoned Cooperative Control in Multi-Train, Multi-Fault-Point Scenarios

[0153] Take a flexible traction power supply system composed of multiple flexible traction substations as an example. Suppose that a first fault point F1 occurs in the overhead contact line near the first train, and a second fault point F2 occurs in the overhead contact line near the second train. Since the two fault points are located in different sections, the support relationship and electrical coupling relationship of the surrounding flexible traction substations are also different. Therefore, the system does not uniformly score and assign roles to the entire group of substations, but instead divides the system into two active power supply zones around fault points F1 and F2 respectively.

[0154] For fault point F1, the system selects several nearby flexible traction substations with strong electrical connections and significant supporting functions to form an active power supply area. Within this active power supply area, a comprehensive evaluation and role assignment are performed to determine the main voltage supply role, auxiliary voltage supply role, and current limiting protection role. For fault point F2, the system independently completes the evaluation and role assignment for another active power supply area in the same manner. Flexible traction substations far from the fault point and with limited supporting functions do not participate in the evaluation of their corresponding areas, nor do they assume the current limiting protection role.

[0155] During the control process, the two active power supply areas independently experience the rapid peak suppression stage, the coordinated voltage maintenance stage, and the smooth recovery stage based on the development of their respective faults. For example, if the area where fault point F1 is located is still in the initial impact stage of the fault, it enters the rapid peak suppression stage; while if the overcurrent peak in the area where fault point F2 is located has been suppressed but the voltage is still low, it can be in the coordinated voltage maintenance stage. After fault point F1 is cleared, its corresponding active power supply area enters the smooth recovery stage; if fault point F2 is still not cleared, its corresponding active power supply area continues to maintain coordinated voltage maintenance control, and can return to the rapid peak suppression stage if necessary.

[0156] This embodiment demonstrates that, in a multi-fault-point parallel scenario, the present invention can achieve partitioned scoring, partitioned role division, and partitioned stage control by dividing the active power supply area, avoiding role redundancy, control mismatch, and too many current-limiting roles caused by unified control of the entire substation group, thereby improving the system's coordinated control capability and power supply continuity under complex fault conditions.

[0157] As can be seen from the above embodiments, the present invention can dynamically complete the division of active power supply areas, comprehensive scoring and role allocation based on the location of the fault point, the real-time operating margin of the flexible traction substation and the coupling relationship of the power supply path. Through progressive control of the rapid peak suppression stage, the coordinated voltage maintenance stage and the smooth recovery stage, it can achieve coordinated current limiting, fault point voltage support and smooth recovery under fault conditions, thereby improving the safety, reliability and power supply continuity of the flexible traction power supply system.

Claims

1. A method for coordinated current limiting and voltage maintaining control in a substation with different roles and stages in a flexible traction power supply system, characterized in that... When the overhead contact line of the system malfunctions, the following steps are included: Active power supply zones are defined based on the equivalent line impedance from the traction substation to the fault point. A comprehensive evaluation is conducted on traction substations within the active power supply area; The roles of traction substations are configured based on comprehensive scores; these roles include main power supply role, auxiliary power supply role, and current limiting protection role. Droop control is implemented for traction substations with different roles, and current limiting and voltage maintenance are carried out in stages; the stages include a rapid peak suppression stage, a coordinated voltage maintenance stage, and a smooth recovery stage.

2. The control method as described in claim 1, characterized in that, The active power supply zone is defined as follows: Will satisfy ≤β The traction substations are included in the active power supply area, among which, Let be the equivalent line impedance from the i-th traction substation to the fault point. β is the minimum equivalent line impedance from all traction substations to the fault point, and β>1 is the active power supply area expansion coefficient.

3. The control method as described in claim 1, characterized in that, The overall score of the i-th traction substation within the active power supply area is: : in, For location matching degree, , This is the distance between the traction substation and the fault point. This represents the maximum distance between the traction substation and the fault point within the active power supply area. For current margin, , , These are the maximum allowable output current and the current equivalent output current of the traction substation, respectively. For heat margin, , , , These are the maximum allowable junction temperature, the real-time estimated junction temperature, and the reference temperature of the power devices in the traction substation, respectively. This is the equivalent line impedance from the traction substation to the fault point; , , , These are the corresponding weights, and the preset values ​​satisfy... ; like Less than the preset threshold ,or Less than the preset threshold Then let , This is the preset minimum value.

4. The control method as described in claim 3, characterized in that, The role of the traction substation is configured based on the comprehensive score as follows: The traction substation with the highest overall score is designated as the main voltage supply substation, the traction substation with the second highest overall score is designated as the auxiliary voltage supply substation, and the other traction substations are designated as current limiting protection substations.

5. The control method as described in claim 1, characterized in that, The conditions for the phased approach are: Rapid peak suppression phase: Output current of any traction substation within the active power supply area Greater than or equal to the warning threshold or the voltage at the fault point Below the warning threshold ; Collaborative pressure maintenance phase: The overhead contact line fault has not been cleared, and the output current of all traction substations is... Less than or equal to the warning threshold And the rate of change of output current of all traction substations satisfies And the voltage at the fault point satisfy ≤ ≤ ;in, The threshold for the rate of change of output current. To restore the voltage threshold; Smooth recovery phase: Overhead contact network fault cleared, and ;in, To restore the current threshold, To restore the holding time.

6. The control method as described in claim 5, characterized in that, The phased collaborative current limiting and pressure maintenance specifically refers to: Once the rapid peak suppression phase begins, then: For the reference value of the outer loop output current of the traction substation that is the main voltage supplier, the limiting threshold is increased, i.e.: ,in, This is the reference value for the outer voltage loop output current. This is the upper limit of the current constraint for the traction substation under the current fault condition. This is a limiting function; For the reference value of the outer voltage loop output current of the traction substation that plays a supporting voltage supply role, first reduce the scaling factor, and then limit the amplitude, that is: ,in, This is the scaling factor, 0 < <1, This is the upper limit of the current constraint for the traction substation under the current fault condition. The reference value of the outer loop output current of the traction substation, which plays a current-limiting protection role, is limited. ,in, This is the current limiting value for the traction substation under the current fault condition; Upon entering the coordinated pressure-holding phase, then: For traction substations with main and auxiliary power supply respectively, the reference output voltage value of the inner current loop is corrected based on the voltage deviation at the fault point, i.e.: , , , ,in, , These are the output voltage reference values ​​after correction for the main and auxiliary power supply roles, respectively. , These are the reference output voltage values ​​for the main and auxiliary voltage supply roles, respectively. , These are the voltage reference correction values ​​for the main and auxiliary voltage supply roles, respectively. , These are the proportional adjustment coefficients for the main and auxiliary pressure supply roles in PI control. , These are the integral adjustment coefficients for the main and auxiliary pressure supply roles in PI control, respectively. The reference value for the target voltage at the fault point; For traction substations that play a current-limiting protection role, a smooth weighted average method is used to generate a total current reference value, which is then used as the current-limiting value for the outer loop output current of the traction substation's voltage. ,in, These are the weighting coefficients. This is the current limiting value for the traction substation under the current fault condition. This is the target current reference value under current constraint priority control; Once the smooth recovery phase begins, then: For traction substations with main and auxiliary voltage supply roles respectively, the reference output voltage value of the inner current loop is adjusted according to the voltage reference correction amount, that is: , ;in, This is the voltage reference correction amount. , This is the voltage reference correction amount at the initial moment when the traction substation enters the smooth recovery phase. The rate of decline of the voltage reference correction for this traction substation; For traction substations with current limiting protection, update the total current reference value: ,in, , This is the current limiting value of the outer voltage loop output current reference value. The target current reference value is set under current-constrained priority control; and the outer voltage loop output current reference value is updated: .

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