A method and system for determining the turn-on current of a thyristor of a converter valve

Abstract

The application discloses a method and system for determining the opening current of a thyristor of a converter valve, wherein the method comprises: obtaining local temperatures, dividing a plurality of core units into at least two local temperature magnetic state calculation units, and determining the magnetization characteristic parameters of each local temperature magnetic state calculation unit according to the temperature corresponding to each local temperature magnetic state calculation unit; determining the magnetic flux density of each local temperature magnetic state calculation unit respectively; determining the total magnetic chain of the winding of the current discrete calculation time step; determining the winding current of the current discrete calculation time step according to the change amount of the total magnetic chain of the winding and the port voltage balance relationship of the discharge circuit containing the same winding; and sequentially advancing each discrete calculation time step, and determining the thyristor opening current according to the winding current determined by each discrete calculation time step. The application overcomes the defects of flattening the magnetization difference caused by the local temperature difference, and improves the determination accuracy of the thyristor opening current under the condition of uneven local temperature distribution.

Description

Technical Field

[0001] This application relates to the field of electromagnetic transient simulation technology for power systems, and in particular to a method and system for determining the turn-on current of a converter valve thyristor. Background Technology

[0002] Saturated reactors for converter valves are crucial protective components in thyristor converter valves. During the initial turn-on phase of the thyristor, the core of the saturated reactor is unsaturated, exhibiting a large inductance to limit the rate of change of the thyristor current. As the thyristor current increases, the core gradually enters the saturation region, and the incremental inductance of the reactor decreases accordingly, reducing its resistance to the normal conduction current. The initial maximum rate of change of current during the thyristor turn-on process is a vital parameter for evaluating the thyristor turn-on current stress. An excessively large initial maximum rate of change of current may cause uneven current distribution within the thyristor chip. Therefore, accurately calculating the thyristor turn-on current containing the saturated reactor is of great significance for saturated reactor parameter matching, thyristor turn-on current stress verification, and converter valve design. Saturated reactors for shell-type converter valves typically consist of a common winding and multiple core units magnetically coupled to that winding. Due to factors such as the spatial position, cooling boundary, insulation structure, and internal heat dissipation path of each core unit, there are often local temperature differences between different core units. Since the magnetization characteristics of soft magnetic materials change with temperature, the magnetization state of each core unit is not the same during the thyristor turn-on process.

[0003] Existing calculation models for saturated reactors used in converter valves typically treat the entire reactor as a combination of coil resistance, air-core inductance, nonlinear core inductance, and equivalent iron loss resistance, or use piecewise functions or exponential functions to describe the change in inductance with winding current. Even when the influence of temperature on magnetization characteristics is introduced into the model, it is often based on an average temperature to establish a unified magnetization model for all cores. However, these models, based on overall equivalent parameters or unified magnetization characteristics, struggle to reflect the differences in magnetization history, saturation time, and flux changes caused by local temperature differences in each core unit. This leads to deviations in the calculated thyristor turn-on current from reality, affecting the accuracy of thyristor turn-on current stress verification. Summary of the Invention

[0004] This application provides a method and system for determining the turn-on current of a converter valve thyristor to solve the above-mentioned problems.

[0005] In a first aspect, embodiments of this application provide a method for determining the turn-on current of a converter valve thyristor, applied to a saturated reactor for a converter valve. The saturated reactor includes a common winding and multiple core units magnetically coupled to the common winding. The method includes: acquiring local temperatures corresponding to the spatial positions of the multiple core units; dividing the multiple core units into at least two local temperature magnetic state calculation units based on their local temperatures; and determining the magnetization characteristic parameters of each local temperature magnetic state calculation unit based on its corresponding temperature; wherein local temperature magnetic state calculation units at different temperatures have different magnetization characteristic parameters; within the current discrete calculation time step, the method is based on the winding... The product of the group current and the number of turns of the same winding is used as the common ampere-turn excitation of each of the local temperature magnetic state calculation units. Based on the magnetization characteristic parameters of each of the local temperature magnetic state calculation units, the magnetic flux density of each local temperature magnetic state calculation unit is determined. Based on the magnetic flux density of each local temperature magnetic state calculation unit, the number of core units it represents, the effective cross-sectional area, and the linkage relationship between the magnetic flux and the same winding, the total winding flux of the current discrete calculation step is determined. Based on the change in the total winding flux and the port voltage balance relationship of the discharge circuit containing the same winding, the winding current of the current discrete calculation step is determined. The discrete calculation steps are advanced sequentially, and the thyristor turn-on current is determined based on the winding current determined in each discrete calculation step.

[0006] In the above scheme, multiple core units are divided into at least two local temperature magnetic state calculation units according to local temperature. This allows calculation units at different temperatures to have different magnetization characteristic parameters. The magnetic flux density of each calculation unit is determined under a common ampere-turn excitation. The magnetic flux from each calculation unit is then summed to form the total winding flux linkage, which participates in the determination of the winding current. Therefore, the differences in magnetization history, saturation time, and magnetic flux change caused by local temperature differences between different core units are preserved in the determination of the turn-on current. This overcomes the shortcomings of overall equivalent modeling and unified magnetization characteristic modeling, which smooth out these differences, and improves the accuracy of thyristor turn-on current determination under uneven local temperature distribution. Furthermore, the magnetic flux density of each local temperature magnetic state calculation unit is not calculated unidirectionally from a pre-given current, but rather is related to the winding current in each discrete calculation. The winding current is determined by the mutual coupling within the step. The magnetization state of each calculation unit is determined by the common ampere-turn excitation, and the change in the total magnetic flux of the winding is combined with the port voltage balance of the discharge circuit. Therefore, the obtained winding current truly reflects the reaction of the nonlinear magnetization of the iron core on the port voltage of the discharge circuit, avoiding the deviation caused by the decoupling of the local magnetic state from the opening process when calculating the magnetic field with a preset equivalent inductance or a given current. Furthermore, the number of iron core units represented by each calculation unit, the effective cross-sectional area, and the magnetic flux linkage relationship all participate in the determination of the total magnetic flux of the winding. Therefore, the scheme can be applied to the saturated reactor structure for converter valves with different numbers of iron core units, different degrees of linkage between units, and even inconsistent directions of magnetic flux linkage. It can be implemented by simply adjusting the division of the calculation units and the corresponding structural parameters, and has universal applicability to actual shell-type multi-core reactors.

[0007] Further, determining the winding current in the current discrete calculation time step includes: setting the winding current as the variable to be solved in the current discrete calculation time step, setting current candidate values ​​for the winding current, and using the product of the current candidate value and the number of turns of the same winding as the common ampere-turn excitation; determining the magnetization state and magnetic flux density of each local temperature magnetic state calculation unit under the corresponding magnetic circuit constraints, and determining the total flux linkage of the winding; correcting the current candidate values ​​based on the deviation between the magnetization state of each local temperature magnetic state calculation unit and the corresponding magnetic circuit constraints, and the deviation between the port voltage of the saturated reactor and the port voltage balance relationship of the discharge circuit determined by the change in the total flux linkage of the winding; repeating the above correction process until the magnetization state of each local temperature magnetic state calculation unit satisfies the corresponding magnetic circuit constraints and the port voltage satisfies the port voltage balance relationship, and determining the current candidate value when the conditions are met as the winding current in the current discrete calculation time step.

[0008] In the above scheme, by setting the winding current as the variable to be solved, and repeatedly correcting the candidate current value based on the deviation between the magnetization state and the magnetic circuit constraint, as well as the deviation between the balance relationship between the saturated reactor port voltage and the discharge circuit port voltage, the winding current satisfies the nonlinear magnetization constraint of all core units while also satisfying the electrical constraint of the discharge circuit. This overcomes the defect of the magnetization process and the electrical process being disconnected when the winding current is preset to a known excitation. The obtained turn-on current truly reflects the reaction of the local temperature magnetic state to the port voltage through the total magnetic flux, improving the accuracy of determining the turn-on current and the maximum current change rate before saturation. On the other hand, by using the magnetic circuit constraint deviation and the port voltage balance deviation to jointly drive the correction, and using the simultaneous satisfaction of both types of deviations as the convergence criterion, the solution process has clear convergence criteria on both the magnetization and electrical sides. This avoids divergence and oscillation caused by unidirectional calculation or inconsistent convergence criteria on both sides, ensuring stable convergence of the nonlinear solution within each discrete calculation time step. Moreover, the correction mechanism does not depend on specific iterative algorithms and residual construction forms, making it easy to implement in combination with different numerical solution methods.

[0009] Furthermore, each of the local temperature magnetic state calculation units stores its own magnetization history state; the determination of the magnetic flux density of each of the local temperature magnetic state calculation units includes: within the current discrete calculation time step, taking the magnetization state of each of the local temperature magnetic state calculation units in the previous discrete calculation time step as its respective magnetization history state; under the common ampere-turn excitation, determining the magnetization state of each of the local temperature magnetic state calculation units in the current discrete calculation time step based on the magnetization history state and the magnetization characteristic parameters of the corresponding local temperature magnetic state calculation unit, and then determining the corresponding magnetic flux density; updating the magnetization state of the current discrete calculation time step to the magnetization history state of the corresponding local temperature magnetic state calculation unit for use in the next discrete calculation time step; wherein, the magnetization history state of each of the local temperature magnetic state calculation units evolves independently with the advancement of the discrete calculation time step.

[0010] In the above scheme, by saving and independently evolving the magnetization history state for each local temperature magnetic state calculation unit, the magnetization state of each calculation unit at the current time step is determined by its own magnetization state at the previous time step and the current common ampere-turn excitation. The path dependence of core magnetization is fully reflected in the solution process. The differences in magnetization process, saturation time, and flux change of different temperature core units are continuously preserved along the time axis, avoiding the loss of magnetization history information caused by the overall equivalent model representing the entire core with a single magnetic state, and improving the accuracy of determining the turn-on current and current change rate before and after saturation. On the other hand, by rolling the magnetization state of the current time step to the magnetization history state of the next time step, each calculation unit only needs to save its own current magnetization history to support the determination of subsequent time steps, without storing the entire history trajectory. Moreover, the magnetization history evolution of each unit is uncoupled and can be promoted independently, which is convenient for parallel implementation by calculation unit, taking into account both storage overhead and solution efficiency.

[0011] Further, dividing the plurality of core units into at least two local temperature magnetic state calculation units includes: comparing the local temperatures of each core unit, merging multiple core units with the same local temperature or local temperature differences that meet preset similarity conditions into the same local temperature magnetic state calculation unit; determining the representative temperature of the local temperature magnetic state calculation unit based on the local temperatures of the multiple core units merged into the same local temperature magnetic state calculation unit, and using the representative temperature as the temperature corresponding to the local temperature magnetic state calculation unit; wherein, each local temperature magnetic state calculation unit uniformly represents the merged multiple core units in determining the total flux linkage of the winding.

[0012] In the above scheme, by merging multiple core units with the same local temperature or whose temperature differences meet the preset similarity conditions into the same local temperature magnetic state calculation unit, the number of magnetic states that need to be solved independently is less than the actual number of core units. While ensuring that the temperature differences between each calculation unit are preserved, the solution scale is compressed, the amount of computation required to determine the magnetic state in each discrete calculation step is reduced, and the efficiency of determining the thyristor turn-on current is improved. On the other hand, by using the local temperature of the merged core units to determine the representative temperature, and having the calculation unit uniformly represent the merged core units in determining the total flux linkage of the winding, the magnetization characteristic deviation introduced by merging is limited to the range defined by the preset similarity conditions. The sum of the total flux linkage can still reflect the weighted contribution of the number and cross-sectional area of ​​core units, so that the improvement of computational efficiency is not at the expense of the accuracy of the turn-on current determination.

[0013] Furthermore, the structural parameters, cooling boundaries, and local temperatures of the plurality of core units are approximately symmetrical about the middle of the arrangement of the plurality of core units; the division of the plurality of core units into at least two local temperature magnetic state calculation units includes: for the plurality of core units located symmetrical about the middle of the arrangement, when the local temperatures of the plurality of core units are the same or the local temperature differences meet a preset similarity condition, the plurality of core units are merged into the same local temperature magnetic state calculation unit; when the local temperature differences of the plurality of core units do not meet the preset similarity condition, the plurality of core units are assigned to different local temperature magnetic state calculation units; and the core unit located in the middle of the arrangement is separately divided into a local temperature magnetic state calculation unit.

[0014] In the above scheme, by utilizing the approximate symmetry of multiple core units in terms of structural parameters, cooling boundaries, and local temperatures about the middle of the arrangement, core units in symmetrical positions with similar temperatures are merged into the same local temperature magnetic state calculation unit, while core units in the middle of the arrangement are divided separately. This ensures that the division of calculation units matches the spatial distribution of the actual temperature field of the reactor. While further reducing the number of independently solved magnetic states, it ensures that the central region with the highest temperature is independently characterized, balancing the efficiency of current determination and the ability to distinguish temperature gradients. On the other hand, by not merging core units in symmetrical positions but whose temperature differences do not meet the preset similarity condition, and assigning them to different calculation units, the mechanical application of structural symmetry is avoided to smooth out the actual local temperature differences. Symmetrical merging is always based on similar temperatures, preventing additional magnetization characteristic deviations introduced by improper merging, and ensuring that the division results are consistent with the actual temperature distribution.

[0015] Further, obtaining the local temperatures corresponding to the spatial positions of the plurality of core units includes: establishing a heat conduction model corresponding to the actual structure of the saturated reactor, wherein the heat conduction model includes at least the plurality of core units, the same winding, the insulation structure, and the cooling boundary; setting heat sources in the corresponding regions of the heat conduction model according to the predetermined core losses of the plurality of core units and the winding losses of the same winding, and setting the heat dissipation conditions of the cooling boundary according to the actual cooling conditions of the saturated reactor; performing steady-state thermal solution on the heat conduction model to obtain a steady-state temperature field; and extracting the representative region temperature of each core unit from the steady-state temperature field to obtain the local temperature of each core unit.

[0016] In the above scheme, a heat conduction model covering multiple core units, windings, insulation structures, and cooling boundaries is established. Core losses and winding losses are used as heat sources for steady-state thermal solutions. The local temperature of each core unit is determined by the actual structure, loss distribution, and cooling conditions of the reactor. The obtained local temperature truly reflects the temperature distribution formed by differences in spatial location, insulation structure, and heat dissipation path. This provides an input consistent with actual operating conditions for determining magnetization characteristic parameters based on temperature, ensuring that the result of determining the turn-on current reflects the influence of actual temperature differences. On the other hand, the local temperature is obtained by extracting the representative area temperature of each core unit from the steady-state temperature field. This eliminates the need to arrange temperature measurement points point by point inside the reactor to obtain the local temperature of all core units, overcoming the engineering limitation that it is difficult to directly measure the internal temperature of the core and reducing the implementation cost and difficulty of obtaining local temperature.

[0017] Furthermore, the linkage relationship between the magnetic flux and the same winding is characterized by the effective linkage coefficient; the effective linkage coefficient corresponding to each local temperature magnetic state calculation unit is determined according to the actual linkage ratio and linkage direction of the magnetic flux of the corresponding local temperature magnetic state calculation unit with the same winding; the absolute value of the effective linkage coefficient is not greater than 1, and the sign of the effective linkage coefficient corresponds to the linkage direction of the corresponding magnetic flux relative to the positive direction of the magnetic flux of the same winding; for local temperature magnetic state calculation units where the magnetic flux is not fully linked with the same winding, the effective linkage coefficient is determined according to the ratio of the effective number of turns of the same winding actually surrounding the corresponding magnetic circuit to the number of turns of the same winding, or according to the ratio of the contribution of the magnetic flux of the corresponding local temperature magnetic state calculation unit to the actual magnetic flux of the same winding to the fully linked magnetic flux.

[0018] In the above scheme, the effective linkage coefficient is used to characterize the actual linkage ratio and direction of the magnetic flux of each local temperature magnetic state calculation unit with the same winding. The difference in linkage ratio and direction is included in the sum of the total magnetic flux of the winding. The partial linkage caused by leakage flux and the situation of inconsistent magnetic flux linkage direction can be truly reflected in the total magnetic flux. This avoids the overestimation or misdirection of the total magnetic flux caused by the ideal assumption that all magnetic flux is completely linked in the same direction, and improves the accuracy of determining the total magnetic flux of the winding and the start-up current. On the other hand, by providing two ways to determine the effective linkage coefficient for the calculation unit with incomplete linkage, namely the ratio of effective turns or the ratio of actual magnetic flux contribution, the scheme can be flexibly implemented according to the structural data conditions or magnetic field analysis conditions of the reactor. It is applicable to the case where only the geometric parameters of the winding are known, as well as the case where static magnetic field analysis methods are available, thus expanding the applicability of the scheme to different structural design stages and data conditions.

[0019] Furthermore, the sequential advancement of each discrete calculation time step includes: advancing each discrete calculation time step from the closing of the switch of the discharge circuit; during the advancement process, using the magnetization characteristic parameters corresponding to the acquired local temperature as fixed inputs for each local temperature magnetic state calculation unit to determine the magnetization state and winding current of each discrete calculation time step, without updating the local temperature; terminating the advancement when the winding current reaches the first current peak value to obtain the thyristor turn-on current from the closing of the switch to the first current peak value.

[0020] In the above scheme, by using the magnetization characteristic parameters corresponding to the local temperature as fixed inputs and not updating the local temperature during the process from the switch closing to the first current peak, the solution process does not need to simultaneously determine the core loss, temperature rise, and cooling process, thus avoiding the establishment of a thermal feedback loop between magnetization and heating. While retaining the influence of local temperature differences on the magnetization state and turn-on current, it reduces the number of state variables and thermal parameters to be determined, thereby reducing computational complexity and improving the solution efficiency and convergence stability of transient turn-on current determination. On the other hand, by using the winding current reaching the first current peak as the termination condition, the solution interval is limited to the process of the most concentrated current stress in the early stage of thyristor turn-on, eliminating the need for invalid calculations of the current decay process after the peak. This ensures that the investment of computational resources is precisely matched with the time interval of interest for thyristor turn-on current stress verification, further improving the determination efficiency.

[0021] Further, determining that the winding current has reached the first current peak includes: comparing the winding current in adjacent discrete calculation time steps; when the winding current changes from increasing step-by-step to no longer increasing for the first time with the discrete calculation time steps, it is determined that the winding current has reached the first current peak between the corresponding adjacent discrete calculation time steps; the method further includes: determining the maximum current change rate before saturation and the current value corresponding to the first current peak based on the thyristor turn-on current from the switch closing to the first current peak; wherein, the maximum current change rate before saturation is the maximum value of the current increment per unit time of the thyristor turn-on current within the current rise interval before the multiple core units enter saturation, excluding the initial influence of the switch closing.

[0022] In the above scheme, the first current peak is determined by comparing the winding current of adjacent discrete calculation time steps and the current change first changes from increasing step by step to no longer increasing. The determination of the peak position does not depend on the overall fitting of the current waveform or manual observation. It can be objectively determined only based on the current sequence obtained in the discrete calculation time step progression. It is naturally connected with the solution process of step by step progression, ensuring that the determination of the termination time has consistency and repeatability. On the other hand, by defining the maximum current change rate before saturation as the maximum value of the current increment per unit time in the current rise interval before the core unit enters saturation, excluding the initial influence of switch closing, the obtained index eliminates the boundary effect at the moment of switch closing and the interference of the inductance decrease after the core saturation on the current change rate. It objectively characterizes the maximum current rise stress borne by the thyristor when the core has not yet obviously entered the saturation transition, so that it can be directly used for the verification of the current distribution uniformity of the thyristor chip and the evaluation of the parameter matching of the saturated reactor.

[0023] Secondly, embodiments of this application provide a system for determining the turn-on current of a thyristor in a converter valve, applied to a saturated reactor for a converter valve. The saturated reactor for the converter valve includes a common winding and multiple core units magnetically coupled to the common winding. The system includes: A temperature acquisition module is used to acquire the local temperature corresponding to the spatial positions of the plurality of core units; The unit configuration module is used to divide the plurality of core units into at least two local temperature magnetic state calculation units according to the local temperature of each core unit, and to determine the magnetization characteristic parameters of each local temperature magnetic state calculation unit according to the temperature corresponding to each local temperature magnetic state calculation unit; wherein, local temperature magnetic state calculation units at different temperatures have different magnetization characteristic parameters. The magnetic state determination module is used to determine the magnetic flux density of each local temperature magnetic state calculation unit by using the product of the winding current and the number of turns of the same winding as the common ampere-turn excitation of each local temperature magnetic state calculation unit within the current discrete calculation time step, and by determining the magnetic flux density of each local temperature magnetic state calculation unit according to the magnetization characteristic parameters of each local temperature magnetic state calculation unit. The total flux linkage determination module is used to determine the total flux linkage of the winding at the current discrete calculation time step based on the magnetic flux density of each local temperature magnetic state calculation unit, the number of core units it represents, the effective cross-sectional area, and the linkage relationship between the magnetic flux and the same winding. The current determination module is used to determine the winding current at the current discrete calculation time step based on the change in the total flux linkage of the winding and the port voltage balance relationship of the discharge circuit containing the same winding. The time-stepping module is used to sequentially advance each discrete calculation time step and determine the thyristor turn-on current based on the winding current determined by each discrete calculation time step.

[0024] Other features and advantages of this application will be set forth in the following description. Attached Figure Description

[0025] Figure 1 A flowchart illustrating the method for determining the thyristor turn-on current of a converter valve provided in an embodiment of this application; Figure 2 A flowchart illustrating a method for determining the turn-on current of a converter valve thyristor in a specific application scenario provided in this application embodiment; Figure 3 The equivalent circuit diagram for thyristor turn-on with an anode saturated reactor provided in the embodiments of this application; Figure 4 A diagram showing the coupling relationship between the local temperature magnetic state and the thyristor turn-on current provided in the embodiments of this application; Figure 5 This is a schematic diagram of the structure and temperature grouping of a multi-core unit anode saturated reactor provided in an embodiment of this application; Figure 6 This is a comparison chart of the turn-on current calculation results under different temperature modeling methods in the calculation examples provided in this application embodiment; Figure 7 This is a schematic diagram of the architecture of the converter valve thyristor turn-on current determination system provided in the embodiments of this application. Detailed Implementation

[0026] Before introducing the specific implementation methods of this application, we will further explain the existing solutions related to the embodiments of this application in order to better understand the technical concept of this application.

[0027] Existing scheme one uses an overall equivalent approach to model the saturated reactor for the converter valve. This involves equating the entire reactor to a combination of coil resistance, air-core inductance, nonlinear core inductance, and equivalent iron loss resistance. Alternatively, it uses piecewise functions or exponential functions to describe the inductance variation with winding current, and then solves for the voltage and current during thyristor turn-on, or extracts parameters from the equivalent model. While this approach can characterize the nonlinear electrical characteristics of the saturated reactor to varying degrees, its inductance parameters correspond to the overall magnetization behavior of the entire core. A single inductance value or inductance-current curve can only reflect a uniform magnetization state at any given time. When there are local temperature differences between the core units of the reactor, the magnetization characteristics of each core unit are different, and their saturation times and flux changes also differ. The overall equivalent parameters cannot capture the spatial distribution differences mentioned above. The turn-on current obtained from this approach essentially corresponds to a non-existent "average core," and its calculation deviation increases with the degree of temperature non-uniformity.

[0028] Existing scheme two establishes a temperature-parameterized hysteresis model, setting saturation magnetization, hysteresis-free magnetization curve shape parameters, pinning parameters, reversible magnetization ratio, and mean field coupling parameters as functions of temperature to describe the magnetization characteristics of magnetic materials at different temperatures. This scheme solves the problem of characterizing magnetization characteristics with temperature, but it focuses on the hysteresis characteristics and core loss calculations of magnetic material samples or individual cores; the temperature in the model is the overall temperature of the material or core. For shell-type converter valves with saturated reactors where multiple core units are magnetically coupled to the same winding, the magnetic flux of each core unit collectively forms the total winding flux linkage, and changes in the total flux linkage affect the thyristor turn-on current. This scheme neither addresses the aggregation relationship of the magnetic flux from multiple core units to the winding ports nor the interaction between the magnetization process and the turn-on circuit, and therefore cannot be directly used for calculating the thyristor turn-on current.

[0029] Existing scheme three calculates the local magnetic field of electromagnetic devices under non-uniform temperature conditions. This involves matching the local temperature of each finite element unit to the magnetization curve at the corresponding temperature, using the winding current as a known excitation, and calculating the magnetic field distribution and losses within the continuous iron core. While this scheme considers the influence of local temperature on magnetization characteristics, its calculation mode is based on a given current and solving for the magnetic field. The current is a predetermined input quantity, not an unknown quantity determined by both the magnetic state and loop constraints. The total flux linkage increment formed by multiple local magnetic states does not participate in the synchronous solution of the winding current, thus failing to reflect the reaction of the local magnetization state through the total winding flux linkage on the thyristor turn-on current. Furthermore, this scheme uses a finite element mesh to describe the temperature and magnetic field distribution within the continuous iron core, primarily serving iterative calculations of electromagnetic fields, losses, and temperature fields in transformer-type equipment. Directly applying it to the transient calculation of the turn-on of a saturated reactor for a converter valve with multiple iron core units results in a large modeling and solution scale, making it difficult to meet the computational efficiency requirements for engineering verification.

[0030] In summary, existing solutions either calculate the turn-on current but fail to retain the magnetization differences caused by local temperature variations, or characterize the magnetization characteristics at local temperatures but are not coupled with the turn-on current calculation. These two approaches are currently separate. Therefore, this application provides a method for determining the turn-on current of a converter valve thyristor. This method divides multiple core units into at least two local temperature magnetic state calculation units based on local temperature, allowing calculation units at different temperatures to have different magnetization characteristic parameters. Under a common ampere-turn excitation, the magnetic flux density of each calculation unit is determined separately. The magnetic flux from each calculation unit is then summed to form the total winding flux linkage, which participates in the determination of the winding current. Therefore, the differences in magnetization history, saturation time, and magnetic flux change caused by local temperature variations between different core units are retained during the turn-on current determination process. This overcomes the shortcomings of overall equivalent modeling and unified magnetization characteristic modeling, which smooth out these differences, and improves the accuracy of determining the thyristor turn-on current under uneven local temperature distribution conditions. Furthermore, the magnetic flux density of each local temperature magnetic state calculation unit is not calculated unidirectionally from a pre-given current, but rather... The winding current is determined by mutual coupling within each discrete calculation time step. The winding current is determined by the magnetization state of each calculation unit through common ampere-turn excitation, and also by the change in the total winding flux combined with the port voltage balance of the discharge circuit. Therefore, the obtained winding current truly reflects the reaction of the nonlinear magnetization of the iron core on the port voltage of the discharge circuit, avoiding the deviation caused by the decoupling of the local magnetic state and the opening process when calculating the magnetic field with a preset equivalent inductance or a given current. Furthermore, the number of iron core units represented by each calculation unit, the effective cross-sectional area, and the magnetic flux linkage relationship all participate in the determination of the total winding flux. Therefore, the scheme can be applied to the saturated reactor structure for converter valves with different numbers of iron core units, different degrees of linkage between units, and even inconsistent magnetic flux linkage directions. It can be implemented by simply adjusting the division of the calculation units and the corresponding structural parameters, and has universal applicability to actual shell-type multi-core reactors.

[0031] like Figure 1 As shown, this application provides a method for determining the turn-on current of a thyristor in a converter valve, applied to a saturated reactor for a converter valve. The saturated reactor for the converter valve includes a common winding and multiple core units magnetically coupled to the same winding, including: Step S110: Obtain the local temperature corresponding to the spatial position of each of the multiple core units.

[0032] The aforementioned local temperature refers to the steady-state temperature of each core unit before the thyristor turn-on event, and it corresponds to the spatial position of each core unit. In a shell-type converter valve saturated reactor, multiple core units are arranged sequentially along the winding direction. The cooling conditions, contact relationships with the insulation structure, and internal heat dissipation paths of each core unit are different, resulting in variations in the steady-state temperature distribution along their spatial positions. The local temperature is the input provided in this step for subsequent calculations, and its function is to determine the magnetization characteristic parameters corresponding to each core unit. The magnetization characteristics of soft magnetic materials change with temperature; core units at different temperatures will exhibit different magnetization states under the same ampere-turn excitation. Therefore, accurate acquisition of the local temperature is a prerequisite for subsequently distinguishing the magnetization behavior of each core unit.

[0033] The local temperature is obtained before the start-up current is determined. This temperature can be obtained through at least one of the following methods: core temperature measurement results, thermal steady-state simulation results, and a pre-set operating condition temperature table. When using core temperature measurement results, temperature sensing elements can be placed on or near the surface of each core unit. The temperature readings of each core unit are read after the reactor reaches thermal steady state. When using a pre-set operating condition temperature table, a correspondence between operating conditions and the temperature of each core unit can be established in advance for typical operating conditions. During calculation, the corresponding value is retrieved from the temperature table according to the current operating condition. The local temperature can also be obtained through thermal analysis; the corresponding modeling and solution process will be explained in subsequent steps. These methods can be used individually or in combination. For example, measurement results can be used to correct table lookup values, and temperatures obtained through multiple methods can be cross-checked during the determination process.

[0034] Since the time from the closing of the discharge circuit switch to the winding current reaching the first peak current is extremely short, typically on the order of microseconds, the temperature rise of the core unit during this time interval is negligible. Therefore, each local temperature is treated as a given parameter throughout the entire calculation time interval, and each local temperature remains constant. This approach aligns with the physical process of the turn-on transient: the temperature change caused by core losses during turn-on requires the accumulation of heat conduction time to manifest, while the electrical process has already completed within this time interval. The influence of temperature on magnetization characteristics can be considered constant within this time interval, thus avoiding the simultaneous solution of the thermal process in the calculation while preserving the influence of local temperature differences on the turn-on current.

[0035] In one optional embodiment, the local temperature of the nine core units increases from the sides towards the center along the arrangement direction. The local temperature of the core units on the sides is approximately 63.8°C, and the local temperature of the core unit in the center is approximately 73.8°C, with a temperature difference of approximately 10°C. This difference in local temperature among the core units at different locations directly reflects the differences in their magnetization characteristic parameters. For example, the shape parameter of the hysteresis-free magnetization curve changes accordingly with increasing temperature, and this is subsequently reflected in the differences in the magnetization process and saturation time of each core unit in calculations.

[0036] Optionally, step S110 includes: establishing a heat conduction model corresponding to the actual structure of the saturated reactor, wherein the heat conduction model includes at least multiple core units, the same winding, insulation structure, and cooling boundary; setting heat sources in the corresponding regions of the heat conduction model according to the predetermined core losses of multiple core units and the winding losses of the same winding, and setting the heat dissipation conditions of the cooling boundary according to the actual cooling conditions of the saturated reactor; performing steady-state thermal solution on the heat conduction model to obtain the steady-state temperature field; and extracting the representative region temperature of each core unit from the steady-state temperature field to obtain the local temperature of each core unit.

[0037] When the local temperature is obtained through thermal analysis, a heat conduction model corresponding to the actual structure of the saturated reactor is first established. The heat conduction model is a mathematical description of the heat generation, conduction, and dissipation processes within the reactor. In this embodiment, a two-dimensional or three-dimensional steady-state heat conduction finite element model is used. The model dimension can be selected based on the symmetry of the reactor structure and the distribution characteristics of the temperature field: when the temperature distribution along a certain direction can be ignored, a two-dimensional model can be used to reduce the solution scale; when the structure or cooling conditions do not possess simplifiable symmetry, a three-dimensional model is used. The solution domain of the heat conduction model includes at least multiple core units, the same winding, the insulation structure, and the cooling boundary. The insulation structure is located between the core units and the winding, and between each core unit and the external structure. Its thermal conductivity is significantly lower than that of the core material and the winding conductor, and it is a crucial factor in the temperature differences among the core units; therefore, it needs to be reflected in the model. The cooling boundary is used to describe the heat transfer relationship between the reactor and the external cooling medium.

[0038] The heat source settings reflect the heat generation sources during reactor operation. Core losses and winding losses are predetermined before establishing the heat conduction model. These can be obtained through electromagnetic calculations, such as calculating core losses based on the core's hysteresis characteristics and operating magnetic flux density, and winding losses based on winding current and conductor parameters. Alternatively, they can be obtained through experimental measurements of actual reactors or prototypes. The predetermined core losses are applied to the regions where each core unit is located, and the winding losses are applied to the regions where the windings are located. The application can be a volumetric heat source, i.e., distributed throughout the entire volume of the corresponding region according to the unit volume heat generation rate, or a regional heat source, where the total losses of the corresponding region are applied as overall heat generation to that region. Since the losses of each core unit are related to its magnetization state, the spatial distribution difference of losses is one of the direct causes of temperature distribution differences. Therefore, heat sources should be set separately according to the actual losses of each region, rather than being uniformly applied based on the average loss.

[0039] The heat dissipation conditions at the cooling boundary are set based on the actual cooling conditions of the saturated reactor, including the temperature and flow rate of the cooling medium and the convective heat transfer conditions on the equipment surface. The convective heat transfer coefficient and ambient temperature can be determined based on design parameters, operating records, or thermal calibration results. Thermal calibration involves applying a load to the actual reactor and measuring the steady-state temperature rise at characteristic locations, thereby inverting the convective heat transfer coefficient to ensure the model's heat dissipation conditions match the actual heat dissipation capacity. The temperature and flow rate of the cooling medium determine the heat dissipation intensity at the boundary. The heat dissipation path length and heat transfer conditions differ for core elements located at different positions along the arrangement direction, thus creating spatial differences in temperature distribution within the model.

[0040] After setting the heat source and boundary conditions, a steady-state thermal solution is performed on the heat conduction model to obtain the steady-state temperature field. The steady-state thermal solution does not consider temperature changes over time; the resulting temperature field corresponds to the temperature distribution after the reactor reaches equilibrium between heat generation and dissipation under continuous operating conditions, and corresponds to the temperature state already formed in each core unit before the thyristor turn-on event. The representative region temperature of each core unit is extracted from the steady-state temperature field to obtain the local temperature of each core unit. The representative region temperature can be the volume average temperature of the corresponding core unit, i.e., the value obtained by averaging the temperature within the solution domain of that core unit by volume, or it can be the temperature at a characteristic location, such as the temperature value at the middle or highest temperature position of the core unit. The volume average temperature reflects the overall thermal state of the core unit, while the characteristic location temperature reflects the local extreme thermal state of the core unit. Both can be used as temperature inputs for subsequent determination of magnetization characteristic parameters. In practical applications, the appropriate temperature input can be selected based on the sensitivity of the magnetization characteristics to temperature distribution.

[0041] Step S120: Based on the local temperature of each core unit, divide the multiple core units into at least two local temperature magnetic state calculation units, and determine the magnetization characteristic parameters of each local temperature magnetic state calculation unit according to the temperature corresponding to each local temperature magnetic state calculation unit; wherein, local temperature magnetic state calculation units at different temperatures have different magnetization characteristic parameters.

[0042] The aforementioned local temperature magnetic state calculation unit refers to an object treated as an independent magnetization entity in the calculation. Each calculation unit corresponds to a representative temperature and represents one or more core units in subsequent calculations. The purpose of dividing multiple core units into at least two calculation units is to ensure that core regions at different temperatures correspond to different magnetization characteristics in the calculation, thereby transforming local temperature differences into differences in magnetization behavior. The number of calculation units is denoted as... , Take an integer not less than 2; the first... Each calculation unit corresponds to a temperature representation. and represent Each iron core unit The value is a positive integer. The representative temperature of each calculation unit is determined based on the local temperature of the core unit it represents. The correspondence between the representative temperature and the local temperature can be selected in combination with the temperature distribution of the core unit.

[0043] The basis for determining the magnetization characteristic parameters is the correspondence between temperature and magnetization characteristics. In this embodiment, the Jiles-Atherton hysteresis model is used to describe the magnetization behavior of the core material. The magnetization characteristic parameters of each local temperature magnetic state calculation unit constitute a parameter vector: ; In the formula, The saturation magnetization is expressed in A / m. The shape parameter of the hysteresis-free magnetization curve is expressed in A / m. These are pinning parameters, in A / m. The reversible magnetization ratio; These are the average field coupling parameters; The temperature parameter mapping relationship is established based on multi-temperature magnetization data; For the first The representative temperature of each computational unit is expressed in °C. The above formula shows that the magnetization parameter of the computational unit is not a constant, but a function of its representative temperature. Different representative temperatures result in different parameter vectors, thus temperature differences are translated into differences in magnetization characteristics. To ensure the parameters have physical meaning, the above parameters satisfy the following constraints: ; Temperature parameter mapping relationship The form of expression can be flexibly selected. Optional forms include lookup table functions, piecewise linear interpolation functions, spline functions, and low-order polynomial functions: lookup table functions are suitable for situations with a large number of temperature points, directly retrieving the temperature point closest to the representative temperature during calculation; piecewise linear interpolation functions use a linear transition of parameters between adjacent temperature points, offering a concise form while maintaining parameter continuity within the temperature range; spline functions and low-order polynomial functions are suitable for situations requiring smooth parameter changes with temperature.

[0044] The temperature parameter mapping relationship can be established in advance as follows: Magnetization tests are performed on the core material at multiple temperature points covering the expected operating temperature range of the saturated reactor. These multiple temperature points must include at least the lower limit, typical temperature, and upper limit of the expected operating temperature. The magnetic field strength range at each temperature point must at least cover the unsaturated magnetization region, the magnetization transition region, and the saturation region, obtaining the first-rise magnetization curve or a hysteresis loop containing the first-rise branch. For the first... There are 10 temperature points, and their temperatures are denoted as _____. The corresponding parameter vector of the Jiles-Atherton model is denoted as: ; The weighted squared error between the model calculation results and the magnetization test results is used as the objective function: ; In the formula, For the first Identify the objective function based on the parameters corresponding to each temperature point; This refers to the serial number of the magnetization test data point; The total number of magnetization test data points involved in parameter identification; For the first The weight of each data point; For the first The magnetic field strength corresponding to each data point is expressed in A / m. To use parameter vectors The magnetic flux density calculated using the Jiles-Atherton model; For temperature The lower magnetic field strength is The magnetic flux density was obtained during the test. Under the above constraints and with the mean field coupling parameters... Within the pre-defined physical allowable range, the objective function is minimized using a constrained nonlinear least squares method, thus determining the model parameters for each temperature point. For model parameters between adjacent temperature points, piecewise linear interpolation is preferred, ensuring the interpolation results pass through the identified discrete temperature parameter points while maintaining the aforementioned physical constraints. This establishes a temperature parameter mapping relationship between temperature and the Jiles-Atherton model parameters. .

[0045] It should be noted that the Jiles-Atherton model is the preferred hysteresis model in the above implementation method. Its five parameters correspond to the saturation level, transition region morphology, hysteresis loss, reversible magnetization component and coupling effect between magnetic domains in the magnetization process, respectively. The physical meaning is clear and easy to identify through magnetization test. In other implementation methods, other magnetization models that can describe the changes in magnetization characteristics with temperature can also be used instead. As long as the model parameters can be determined based on the representative temperature of the calculation unit, the transformation of temperature difference into magnetization characteristic difference in this step can be realized.

[0046] When the number of core units is large, if each core unit is treated as a separate local temperature magnetic state calculation unit, the number of magnetic states that need to be solved independently will increase accordingly, and the computational workload will increase accordingly. Considering that the local temperatures of some core units in actual reactors are the same or very close, and the differences in their magnetization behavior can be ignored, in order to reduce the solution scale while retaining the main temperature differences, the embodiments of this application provide the following solution: Optionally, the above-mentioned division of multiple core units into at least two local temperature magnetic state calculation units includes: comparing the local temperatures of each core unit, merging multiple core units with the same local temperature or local temperature differences that meet preset similar conditions into the same local temperature magnetic state calculation unit; determining the representative temperature of the local temperature magnetic state calculation unit based on the local temperatures of the multiple core units merged into the same local temperature magnetic state calculation unit, and using the representative temperature as the temperature corresponding to the local temperature magnetic state calculation unit; wherein, each local temperature magnetic state calculation unit uniformly represents the multiple core units merged into the unit in determining the total flux linkage of the winding.

[0047] The aforementioned merging refers to combining multiple core units into a single local temperature and magnetic state calculation unit during computation. The merging criterion is that the local temperatures are the same, or the local temperature differences meet a preset similarity condition. The preset similarity condition defines a negligible range of temperature differences; for example, it can be set to ensure the absolute value of the temperature difference does not exceed a preset threshold. This threshold can be selected based on the sensitivity of the magnetization parameters to temperature: when the impact of temperature-induced changes in magnetization parameters on the turn-on current calculation results is negligible, the corresponding temperature differences can be considered similar. After comparing the local temperatures of each core unit, multiple core units that meet the merging criterion are assigned to the same calculation unit, while core units that do not meet the merging criterion are assigned to different calculation units. The final number of calculation units is determined by this criterion. The number shall not exceed the actual number of core units, and shall not be less than 2.

[0048] After merging, a representative temperature needs to be determined for each computational unit, serving as the temperature corresponding to that unit. The representative temperature is determined based on the local temperatures of the multiple core units merged into that unit. In one implementation, the average of the local temperatures of the merged core units can be used; when the volume or loss weights of the core units differ, a corresponding weighted average can also be used. The representative temperature of each computing unit is denoted as When determining the magnetization characteristic parameters of this computational unit later, that is, using As input to the temperature parameter mapping relationship, since the merging criterion has limited the temperature differences within the unit to a similar range, the multiple core units merged are characterized by a single representative temperature, and the introduced magnetization deviation is controlled within an acceptable range.

[0049] After merging, each calculation unit uniformly represents the multiple core units merged to participate in the determination of the total flux linkage of the winding. The number of core units represented by each computing unit is denoted as When the total flux linkage of the winding is subsequently formed, the magnetic flux density of this calculation unit is determined according to the value it represents. Each core element is included, meaning the contribution of that element to the total flux linkage is equal to the sum of its individual magnetic flux densities. The product of the effective cross-sectional area and the linkage relationship. This approach ensures that the total physical amount of magnetic flux remains unchanged before and after merging: the merged core elements are not deleted from the calculation, and their magnetic flux contribution is still processed through... The solution is fully retained; only the repeated solution of core elements with similar temperatures is omitted.

[0050] Taking a reactor with nine core units as an example, the nine core units are merged into five computational units. The number of core units represented by each computational unit is 2, 2, 2, 2, and 1, respectively, and the corresponding representative temperatures are 63.8091℃, 70.1727℃, 71.2636℃, 72.9000℃, and 73.8091℃. Even after merging, the representative temperatures of each computational unit remain distinct, preserving the main temperature differences between the core units. The number of independently solvable magnetic states is reduced from nine to five, thus compressing the solution scale. The average temperature of the five representative temperatures, weighted by the number of core units they represent, is: In the formula, The average temperature is weighted by the number of core units, and the unit is °C. to These represent the temperatures of the five computational units; each coefficient represents the number of core units represented by the corresponding computational unit. This weighted average temperature can be used to compare with a control scheme modeled using a single average temperature to verify the effectiveness of grouped modeling in preserving local temperature differences.

[0051] The above merging method relies solely on the similarity of local temperatures and does not utilize the spatial relationship of the core units. For saturated reactors used in shell-type converter valves, multiple core units are typically arranged sequentially along the winding direction. Their structure, cooling conditions, and temperature distribution often exhibit approximately symmetrical characteristics about the center of the arrangement. Utilizing this symmetry, candidate units can be directly determined based on their spatial position during merging, further simplifying the partitioning process. Based on this, the embodiments of this application provide the following solution: Optionally, the structural parameters, cooling boundaries, and local temperatures of the multiple core units are approximately symmetrical about the middle of the arrangement of the multiple core units; the above-mentioned division of the multiple core units into at least two local temperature magnetic state calculation units includes: for multiple core units located symmetrical about the middle of the arrangement, when the local temperatures of the multiple core units are the same or the local temperature differences meet the preset similarity conditions, the multiple core units are merged into the same local temperature magnetic state calculation unit; when the local temperature differences of the multiple core units do not meet the preset similarity conditions, the multiple core units are assigned to different local temperature magnetic state calculation units; and the core unit located in the middle of the arrangement is separately divided into a local temperature magnetic state calculation unit.

[0052] The aforementioned "middle position" refers to the central location formed by multiple core units arranged sequentially along the winding direction. When the number of core units is odd, the middle position corresponds to the core unit in the very center; when the number of core units is even, the middle position corresponds to the position between the two middle core units. Symmetry of structural parameters means that core units in symmetrical positions have the same magnetic circuit structure dimensions. Symmetry of cooling boundaries means that core units in symmetrical positions have similar heat dissipation conditions. Symmetry of local temperature means that core units in symmetrical positions have the same or similar temperatures. When all three aspects of symmetry are approximately true, core units in symmetrical positions have similar magnetization behaviors, providing a physical basis for merging them into the same computational unit.

[0053] During the division process, pairs or groups of core units located symmetrically about the center of the layout are first identified, and their local temperatures are then compared. When multiple core units at symmetrical positions have the same local temperature or their local temperature differences meet a preset similarity condition, they are merged into the same local temperature magnetic state calculation unit. When the local temperature differences of core units at symmetrical positions do not meet the preset similarity condition, they are not merged, and the corresponding core units are assigned to different calculation units. This approach indicates that symmetrical positions only provide candidate objects for merging; whether to merge ultimately depends on the degree of temperature similarity. When the actual temperature distribution deviates from the symmetrical state, for example, when a change in cooling conditions on one side causes a significant temperature difference at the symmetrical position, forcibly merging and smoothing out this difference by assigning them to different calculation units can avoid the magnetization characteristic deviation introduced by this.

[0054] The core unit located in the middle of the arrangement is divided into a separate calculation unit because there is no symmetrical pairing for the central core unit. In an approximately symmetrical temperature distribution, the central position usually corresponds to the turning point of the temperature gradient change, and its temperature is often higher than that of the core units on both sides. Dividing this core unit separately allows the region with the highest temperature to be independently characterized in the calculation.

[0055] Taking a shell-type reactor with nine core units as an example, the nine core units are arranged from left to right as L4, L3, L2, L1, M, R1, R2, R3, and R4, with M located in the middle. L1 and R1, L2 and R2, L3 and R3, and L4 and R4 are symmetrically positioned about the middle. The local temperature of each core unit increases from both sides towards the middle. The local temperature of L4 and R4 is approximately 63.8℃, and the local temperature of M is approximately 73.8℃. The core units at symmetrical positions have approximately the same temperature. Based on this, L1 and R1, L2 and R2, L3 and R3, and L4 and R4 are grouped into the same calculation unit, while M forms a separate calculation unit, resulting in five local temperature magnetic state calculation units. The number of core units represented by each calculation unit is 2, 2, 2, 2, and 1, respectively. The division result is consistent with the result obtained by grouping only according to similar temperature, but the process of determining the grouping object directly utilizes the spatial symmetry relationship of the structure, without having to compare the temperature pairwise among all core units, making the division process simpler.

[0056] Step S130: Within the current discrete calculation time step, the product of the winding current and the number of turns of the same winding is used as the common ampere-turn excitation of each local temperature magnetic state calculation unit. Based on the magnetization characteristic parameters of each local temperature magnetic state calculation unit, the magnetic flux density of each local temperature magnetic state calculation unit is determined.

[0057] Optionally, each local temperature magnetic state calculation unit stores its own magnetization history state. The above-mentioned determination of the magnetic flux density of each local temperature magnetic state calculation unit includes: within the current discrete calculation time step, taking the magnetization state of each local temperature magnetic state calculation unit in the previous discrete calculation time step as its respective magnetization history state; under common ampere-turn excitation, determining the magnetization state of each local temperature magnetic state calculation unit in the current discrete calculation time step based on the magnetization history state and the magnetization characteristic parameters of the corresponding local temperature magnetic state calculation unit, and then determining the corresponding magnetic flux density; updating the magnetization state of the current discrete calculation time step to the magnetization history state of the corresponding local temperature magnetic state calculation unit for use in the next discrete calculation time step; wherein, the magnetization history state of each local temperature magnetic state calculation unit evolves independently with the advancement of the discrete calculation time step.

[0058] The aforementioned ampere-turn excitation refers to the product of the winding current and the number of turns in the winding, denoted as... ,in The number of turns in the winding. The winding current is used. Since multiple core units are magnetically coupled to the same winding, all local temperature magnetic state calculation units experience the same ampere-turn excitation at the same time. The differences in magnetization behavior among the calculation units stem from differences in their magnetization characteristic parameters, not differences in the excitation. It should be noted that the winding current is not a pre-given external excitation during the determination of the turn-on current, but rather an unknown quantity that needs to be determined together with the magnetization state. Within each discrete calculation time step, candidate values ​​of the winding current are first used to form the ampere-turn excitation, and then its value is determined through subsequent corrections.

[0059] Within each computational unit, the magnetic flux density is determined by both the magnetic circuit constraint and the magnetization relationship. For the first... Each computational unit has an ampere-turn excitation equal to the sum of the core magnetomotive force drop and the air gap magnetomotive force drop. ; In the formula, For the first The magnetic field strength inside the ferromagnetic material of each calculation unit; The effective magnetic circuit length of the ferromagnetic material; The air gap magnetic field strength; This represents the total equivalent air gap length. The air gap magnetic field strength is determined by the magnetic flux density in the air gap, i.e. ,in For the first The magnetic flux density of each computing unit; Let be the vacuum permeability, and take . When the air gap cross-sectional area is approximately the same as the effective cross-sectional area of ​​the iron core and the air gap edge effect is neglected, the magnetic field strength inside the ferromagnetic material can also be written as: This formula links magnetic field strength with magnetic flux density and is an equivalent form of magnetic circuit constraint.

[0060] The magnetization relationship is described using the Jiles-Atherton model, whose physical picture decomposes the total magnetization into reversible and irreversible components. The effective magnetic field strength of each computing unit is ,in The total magnetization is Let be the mean field coupling parameter; let Then the hysteresis-free magnetization is: ; In the formula, It represents the hysteresis-free magnetization, used to characterize the ideal magnetization level when hysteresis is neglected; The saturation magnetization; These are the shape parameters of the hysteresis-free magnetization curve. The total magnetization is a synthesis of reversible and irreversible components: ; In the formula, It is the irreversible magnetization intensity; This represents the reversible magnetization ratio. The irreversible magnetization intensity varies with the effective magnetic field according to the differential equation: ; in, Pinning parameters; For the magnetization direction parameter, take This is used to ensure the non-negativity of hysteresis loss. The magnetic flux density is ultimately determined by... Confirmed. During the initial current rise interval from the closing of the discharge switch to the first current peak, the effective magnetic field monotonically increases in the positive direction. .

[0061] The above relationships constitute a nonlinear equation. When solving this equation, the effective magnetic field strength is selected. As local iteration variables, for a given candidate value of winding current and the irreversible magnetization at the current time step, the hysteresis-free magnetization relation, the total magnetization relation, and the effective magnetic field relation can be used to sequentially... , , and Represented as The function, when substituted with the magnetic circuit constraints, forms a single-variable nonlinear equation: ; The above equations can be solved using Newton's method or damped Newton's method. The initial value for iteration is preferentially the effective magnetic field strength after convergence in the previous discrete calculation step, with zero initial value used for the first discrete calculation step. When the equation has multiple numerical roots, the root with the smallest difference from the magnetic state in the previous step is selected to ensure the continuity of the magnetization process. Local convergence is considered achieved when the local magnetopotential residual, after normalization according to the characteristic magnitude of the current ampere-turn excitation, is not greater than the preset relative tolerance. Subsequently, based on the converged effective magnetic field strength, the hysteresis-free magnetization, total magnetization, internal magnetic field strength of the ferromagnetic material, and magnetic flux density are determined sequentially.

[0062] In numerical processing, when When the value is less than the preset threshold, the hyperbolic cotangent difference is calculated directly. This can cause numerical instability, so a series expansion is used for approximation: ; The above approximate threshold is determined based on the relative error between the direct calculation formula of hyperbolic cotangent and the series expansion formula. When the relative error is not greater than the preset series calculation tolerance, the above approximate formula is used to ensure the calculation accuracy while avoiding numerical problems near the singularity.

[0063] The preservation and independent evolution of the magnetization history are achieved through the discretization of the irreversible magnetization differential equation. This differential equation is then transformed into a state equation relating to time: ; And adopting the backward Euler scheme, in the first... Constructing the first discrete computation time step within the nth time step The irreversible magnetization state residuals of each computational unit: ; For the initial current rise interval The residual can be written as: ; And require In the formula, the superscript... and These represent the previous discrete computation time step and the current discrete computation time step, respectively. The irreversible magnetization intensity after convergence at the previous time step is the known historical state at the current time step; , , All of these are quantities to be determined at the current time step. As can be seen from the above formula, the irreversible magnetization intensity at the current time step is jointly determined by the value of the previous time step and the magnetization increment at the current time step, thus introducing the path dependence of the magnetization process into the calculation. Each computational unit only stores its own magnetization history state at its most recent time step. After the current time step is determined, it is updated to a new history state for use in the next time step. The history states of each computational unit evolve independently with each time step, without interfering with each other. Ignoring the residual magnetism before the activation event, the initial magnetic state of each computational unit is set to... , , This refers to the demagnetization zero state.

[0064] The physical basis for adopting the above processing method is that the magnetization of the core material is irreversible. The magnetic flux change produced when the same ampere-turn excitation is applied to a core with different magnetization histories is different. Therefore, only by allowing each calculation unit to participate in the calculation with its own historical state can the differences in the magnetization process and saturation time of core units at different temperatures be truly reflected. Since each calculation unit shares the same ampere-turn excitation but solves the magnetization state independently, the magnetic flux density obtained by different calculation units in the same time step is generally different from each other. This difference is the manifestation of local temperature differences at the magnetization level and provides a block-based magnetic flux basis for the subsequent summarization of the total flux linkage of the winding.

[0065] Step S140: Determine the total flux linkage of the winding in the current discrete calculation step based on the magnetic flux density of each local temperature magnetic state calculation unit, the number of iron core units it represents, the effective cross-sectional area, and the linkage relationship between the magnetic flux and the same winding.

[0066] Optionally, the linkage relationship between the above magnetic flux and the same winding is characterized by the effective linkage coefficient; The effective linkage coefficient corresponding to each local temperature magnetic state calculation unit is determined based on the actual linkage ratio and linkage direction of the magnetic flux of the corresponding local temperature magnetic state calculation unit with the same winding; the absolute value of the effective linkage coefficient is not greater than 1, and the sign of the effective linkage coefficient corresponds to the linkage direction of the corresponding magnetic flux relative to the positive direction of the magnetic flux of the same winding; For a local temperature magnetic state calculation unit where the magnetic flux is not fully linked to the same winding, the effective linkage coefficient is determined based on the ratio of the effective number of turns of the same winding actually surrounding the corresponding magnetic circuit to the number of turns of the same winding, or based on the ratio of the contribution of the magnetic flux of the corresponding local temperature magnetic state calculation unit to the actual magnetic flux linkage of the same winding to the fully linked magnetic flux linkage.

[0067] The total winding flux linkage refers to the sum of the flux linkages formed on the same winding after the magnetic flux of all core units links with it. The total winding flux linkage is an intermediate quantity resulting from the magnetization of each local temperature magnetic state calculation unit acting on the discharge circuit: the magnetic flux density of each calculation unit is different, but the magnetic flux of all core units links with the same winding, and the effect produced at the winding ports is manifested as a change in the total flux linkage. The subsequent port voltage is determined by this change in total flux linkage. The total winding flux linkage at the current discrete calculation time step is determined by the following formula: ; In the formula, This represents the total flux linkage of the windings at the current discrete calculation time step; This refers to the number of turns in the winding. The number of units used for calculating the local temperature magnetic state; For the first The number of core units represented by each computing unit; For the first The effective cross-link coefficients corresponding to each computational unit; For the first The effective cross-sectional area corresponding to each calculation unit; For the first The magnetic flux density of each computational unit at the current time step. As can be seen from the above formula, the contribution of each computational unit is the product of its magnetic flux density and the number of core units it represents, the effective cross-sectional area, and the effective linkage coefficient. The contributions of each computational unit are added at the winding port. Therefore, computational units with a larger number of core units or a larger cross-sectional area have a correspondingly greater impact on the total flux linkage. Local temperature differences are directly introduced into the total flux linkage through the differences in magnetic flux density of each computational unit.

[0068] The effective linkage coefficient is used to characterize the actual linkage relationship between the magnetic flux of a computational unit and the same winding, and is defined as follows: ; In the formula, For the first The actual contribution of each calculation unit to the total flux linkage of the winding; denominator This refers to the flux linkage that can be formed when the magnetic flux of the calculation unit is fully linked to the winding. The effective linkage coefficient includes information on both the linkage ratio and the linkage direction. Its absolute value reflects the actual degree of linkage, and the absolute value is no greater than 1. It is taken as 1 when the magnetic flux of the corresponding core unit is fully linked to the winding and in the same direction. Its positive or negative sign reflects the linkage direction; when the magnetic flux reference direction is consistent with the positive direction of the winding flux linkage... When the directions are opposite Generally meets By introducing an effective linkage coefficient, the actual electromagnetic relationships, such as partial linkage caused by leakage flux and inconsistent magnetic flux directions, can be reflected in the total magnetic flux summary, avoiding the deviation introduced by the ideal assumption of complete unidirectional linkage of all magnetic fluxes.

[0069] For calculation units where the magnetic flux is not fully linked to the same winding, the effective linkage coefficient can be determined in two ways. One way is to determine it based on the effective number of turns that the winding actually surrounds the corresponding magnetic circuit, i.e. ,in For the actual surrounding of the winding One method involves calculating the effective number of turns in the magnetic circuit of each calculation unit. This method is suitable when the encirclement relationship between the winding and each magnetic circuit can be directly obtained from the structural parameters. Another method is to determine the effective linkage coefficient based on the ratio of the actual flux contribution of the corresponding calculation unit to the winding's flux linkage to the fully linkage case. This can be achieved by establishing a finite element model of the core-winding static magnetic field, calculating the actual flux linkage generated by the corresponding core unit on the winding, and then comparing it with the flux linkage under the fully linkage case. This method is suitable when the linkage relationship is difficult to determine directly from the geometric structure. The choice between these two methods depends on the data available during the design phase.

[0070] To find the difference between the total flux linkage and that of adjacent time steps, let the first step be denoted as . The total flux linkage of the windings at each discrete calculation time step is , No. The total flux linkage of the windings at each discrete calculation time step is Then the total flux increment at the current time step is The total flux linkage increment is used to determine the magnetic port voltage of the current time-step saturated reactor. Although each local temperature magnetic state calculation unit has different magnetic flux density and magnetization state, they are all aggregated to the same winding port through the total flux linkage, and the port voltage reacts to the winding current.

[0071] Step S150: Determine the winding current for the current discrete calculation step based on the change in the total flux linkage of the winding and the port voltage balance relationship of the discharge circuit containing the same winding.

[0072] Optionally, determining the winding current for the current discrete calculation time step includes: setting the winding current as the variable to be solved for the current discrete calculation time step; setting candidate values ​​for the winding current; using the product of the candidate values ​​and the number of turns of the same winding as a common ampere-turn excitation; determining the magnetization state and magnetic flux density of each local temperature magnetic state calculation unit under the corresponding magnetic circuit constraints; and determining the total flux linkage of the winding; correcting the candidate values ​​for the current based on the deviation between the magnetization state of each local temperature magnetic state calculation unit and the corresponding magnetic circuit constraints, and the deviation between the port voltage of the saturated reactor and the port voltage balance relationship of the discharge circuit determined by the change in the total flux linkage of the winding; repeating the above correction process until the magnetization state of each local temperature magnetic state calculation unit satisfies the corresponding magnetic circuit constraints and the port voltage satisfies the port voltage balance relationship; and determining the candidate values ​​for the current when the conditions are met as the winding current for the current discrete calculation time step.

[0073] The winding current must be treated as a variable to be solved, rather than a pre-defined excitation, because of its bidirectional dependence on the core magnetization. Given a current value, the magnetization state of each core unit and the total winding flux linkage can be determined. However, the given current is not equivalent to the actual current flowing through the discharge circuit: the actual current must also satisfy the constraints of the discharge capacitor's charge release and the circuit's voltage balance. Since core magnetization is nonlinear, there is no pre-defined functional relationship between the total flux linkage and the current. The aforementioned constraints cannot be satisfied by unidirectional substitution; therefore, the winding current and each local magnetic state must be solved together within the same discrete calculation time step.

[0074] The constraint of the discharge circuit on the winding current is given by two equations, which specify the winding current. The positive direction is from the positive terminal of the discharge capacitor, and the capacitor voltage is... This is the voltage across the positive terminal of the discharge capacitor relative to its negative terminal. The capacitor's state equation describes the law governing the discharge of charge: ; In the formula, C is the discharge capacitor; t is time. The port voltage equation describes the voltage balance relationship of the loop: ; In the formula, The circuit is connected in series with the resistor; It is a hollow residual inductor; This represents the total magnetic flux linkage of the winding. The right-hand side of the above equation represents, in order, the voltage across the resistor, the voltage across the air-core inductor, and the magnetic port voltage caused by the magnetization of the iron core, where... One factor is determined by the change in magnetic flux of each local temperature magnetic state calculation unit. The local magnetic state participates in the constraint of the winding current through this factor.

[0075] Discretizing the above equations using the fully implicit backward Euler scheme allows us to construct the current equation. Capacitor state residuals and port consistency residuals for each discrete computation time step: ; ; And require as well as In the formula, the superscript... and These represent the previous time step and the current time step, respectively. For discrete calculation of time step intervals; and These are capacitor state residual and port consistency residual, respectively. That is, the change in total flux linkage of the winding, divided by the time step interval, corresponds to the magnetic port voltage. The two residuals measure the degree of deviation of the current time step value from the capacitor charge constraint and the loop voltage balance, respectively. When the residual is zero, it indicates that the value satisfies both constraints simultaneously.

[0076] The correction process based on the above residuals is organized as follows: In the first... Within each discrete calculation time step, the variables to be solved include winding current. capacitor voltage and the irreversible magnetization of each computing unit to The internal magnetic field strength, effective magnetic field strength, hysteresis-free magnetization, total magnetization, and magnetic flux density of the ferromagnetic material in each computational unit can all be further calculated from the variables to be solved. For the candidate values ​​of winding current in the current nonlinear iteration, the following process is executed sequentially: Calculate the ampere-turn excitation shared by all computational units based on the candidate values; calculate the magnetic circuit state and hysteresis state of each computational unit based on the magnetization characteristic parameters corresponding to each representative temperature; obtain the magnetic flux density of each computational unit and form the total flux linkage of the winding at the current time step; calculate the total flux linkage increment based on the difference between the total flux linkage of the current time step and the previous time step; calculate the capacitor state residual and port consistency residual based on the total flux linkage increment, the capacitor state equation, and the port voltage equation; correct the candidate values ​​of winding current, capacitor voltage, and each local magnetic state variable based on the port consistency residual, capacitor state residual, and each local hysteresis state residual. Repeat the above process until the following conditions are met: ; In the formula, For the first The irreversible magnetization state residual of each computational unit; , and These are the preset magnetic state residual threshold, capacitor state residual threshold, and port residual threshold, respectively. The candidate current value that meets the convergence condition is determined as the winding current at the current time step.

[0077] Because the magnetic state residual and the two types of electrical residuals have different dimensions, the convergence thresholds need to be set separately. In one implementation, the magnetic state residual threshold is taken as the corresponding saturation magnetization. of The capacitor state residual threshold and the port consistency residual threshold are taken as the initial capacitor voltage. of times, equivalent to and The characteristic magnitude and normalized relative tolerance of the corresponding residuals are both taken as... For other computational accuracy requirements, the above relative tolerances can be adjusted according to the computer's floating-point accuracy and the required output accuracy. Joint solutions can be obtained using Newton's method, damped Newton's method, quasi-Newton's method, or other iterative solutions to nonlinear equations. The maximum number of iterations per discrete computation step can be set based on convergence, for example, to 30.

[0078] It should be noted that in each nonlinear iteration, the total flux linkage and its increment are recalculated based on the updated candidate values ​​of the winding current and each local magnetic state. This allows each local temperature magnetic state to directly participate in the determination of the winding current through the magnetic port voltage. This mechanism ensures that the final obtained winding current simultaneously satisfies the nonlinear magnetization relationship of the core and the external circuit constraints. If the value of the winding current deviates from the actual value, the increment of the total flux linkage formed by the sum of each local magnetic state will generate a corresponding magnetic port voltage deviation. This deviation is fed back to the current correction through the port consistency residual until the constraints on the magnetization side and the electrical side are simultaneously satisfied. Compared with the method of calculating the magnetic field unidirectionally using the current as a known quantity, the above-mentioned coupling determination mechanism eliminates the disconnect between the local magnetic state and the turn-on process, allowing the influence of local temperature differences on the turn-on current to be fully reflected.

[0079] Step S160: Proceed sequentially through each discrete calculation time step, and determine the thyristor turn-on current based on the winding current determined by each discrete calculation time step.

[0080] Optionally, the above-mentioned sequential advancement of each discrete calculation time step includes: advancing each discrete calculation time step from the closing of the self-discharge circuit switch; during the advancement process, using the magnetization characteristic parameters corresponding to the acquired local temperature as fixed inputs for each local temperature magnetic state calculation unit to determine the magnetization state and winding current of each discrete calculation time step without updating the local temperature; and terminating the advancement when the winding current reaches the first current peak value to obtain the thyristor turn-on current from the closing of the switch to the first current peak value.

[0081] The aforementioned determination of the winding current reaching the first current peak includes: comparing the winding current in adjacent discrete calculation time steps; when the winding current changes from increasing step-by-step to no longer increasing for the first time with the discrete calculation time steps, it is determined that the winding current has reached the first current peak between the corresponding adjacent discrete calculation time steps. The aforementioned method for determining the thyristor turn-on current of the converter valve also includes: determining the maximum current change rate before saturation and the current value corresponding to the first current peak based on the thyristor turn-on current from the switch closing to the first current peak; wherein, the maximum current change rate before saturation is the maximum value of the unit-time current increment of the thyristor turn-on current within the current rise interval before multiple core units enter saturation, excluding the initial influence of switch closing.

[0082] The progression of discrete computation time steps involves repeating the aforementioned single-time-step solution process sequentially along the time axis. The progression begins at the moment the self-discharge circuit switches closes; this moment is denoted as _____. After each time step converges, the converged winding current, capacitor voltage, and local magnetic states are accepted as the calculation results for the current time step and used as the known historical states for the next discrete calculation time step, before proceeding to the solution of the next time step. Due to the path dependence of core magnetization, each time step must proceed sequentially in chronological order and cannot be skipped or processed in parallel; however, the solution structure within each time step is exactly the same, with the only difference being the historical states and excitation levels.

[0083] During the process, the magnetization parameters of each local temperature and magnetic state calculation unit are used as fixed inputs in the solution of each time step, and the local temperature itself is not updated. This approach is based on the extremely short duration of the switching process: the time interval from switch closure to the winding current reaching the first current peak is typically on the order of microseconds. Temperature changes caused by core losses require the accumulation of heat conduction time to manifest, and the core temperature does not have time to change within this time interval. Therefore, the magnetization parameters remain constant throughout the entire process. Consequently, the solution process does not require simultaneous determination of core losses, temperature rise, and cooling processes. The state variables to be determined are limited to winding current, capacitor voltage, and each local magnetic state, thus reducing computational complexity and dependence on thermal parameters.

[0084] Time step interval The selection of [a specific parameter] affects the resolution and computational load of the propulsion system. The shortest electrical transient characteristic time in the capacitor discharge circuit, determined by the discharge capacitor, series resistance, air-core residual inductance, and nonlinear magnetization of the iron core, is selected based on the principle of being able to distinguish changes in winding current and local magnetic state during the initial turn-on phase. For example, 1.25 ns can be chosen. The rationality of the time step selection can be verified by halving: after halving the calculated time step and recalculating, if the relative changes in the first current peak value and the maximum current change rate before saturation are both no greater than the preset tolerance, it indicates that the current time step can sufficiently distinguish the transient process, and the current calculated time step can be used.

[0085] The termination of the propulsion is triggered by the determination of the first current peak value. After convergence at each time step, the discrete rate of change of the winding current is calculated: ; In the formula, , The first The and the first The winding current at each discrete moment; For the first The discrete rate of change of current at discrete moments. When the discrete rate of change first changes from a positive value to a non-positive value, i.e., satisfies... and When the first current peak value is reached, it indicates that the winding current has reached its first peak value between adjacent discrete calculation time steps, thus terminating the calculation. The first current peak value is located between the aforementioned adjacent time steps and can be determined by interpolating the current or current derivative of adjacent discrete calculation time steps, thereby obtaining the current value corresponding to the first current peak value. After the calculation is terminated, the winding currents of each time step are arranged in sequence, thus obtaining the thyristor turn-on current waveform from the switch closing to the first current peak value.

[0086] Determining the maximum rate of change of current before saturation requires first defining its value range. To eliminate the initial boundary effect at the instant the switch closes, the moment when the rate of change of current first changes from decreasing to non-decreasing is determined according to the discrete rate of change mentioned above, and this moment is taken as the starting moment for linear fitting. Starting from the starting moment of linear fitting, the fitting endpoint is gradually expanded, and a linear least squares fit is performed on the current-time data within the current fitting interval, and the coefficient of determination R is calculated. 2 When R 2 continuous The judgment time is lower than the preset threshold. When the current rise deviates from the linear law, the iron core begins to enter the saturation transition. The first judgment moment in this continuous interval is determined as the starting point of the saturation transition, and the number of data points involved in the fitting is no less than [number missing]. In one implementation, take , , Within the interval between the start of linear fitting and the start of saturation transition, the maximum current change rate before saturation is obtained by calculating the discrete current change rate point by point according to the formula and taking the maximum value. This index characterizes the maximum current rise stress borne by the thyristor after excluding the initial boundary effect of switch closure and before the core has obviously entered the saturation transition.

[0087] In one optional implementation, the saturation transition start point determined according to the above criteria is 1.36625 μs in the uniform temperature control model and 1.35125 μs in the grouped modeling method considering local temperature; the corresponding maximum current change rates before saturation are 224.813 A / μs and 249.414 A / μs, respectively; the first current peak values ​​are 2835.299 A and 2731.280 A, respectively; and the times of the first current peak are 5.049656 μs and 5.018493 μs, respectively. The above comparison shows that the maximum current change rate before saturation, the first current peak value, and its time can all be completely output by this step, directly serving the verification of the thyristor turn-on current stress.

[0088] To facilitate understanding of the working principle of the above-described method for determining the thyristor turn-on current of the converter valve, this application also provides specific application examples of this method in a certain application scenario. For example... Figure 2 As shown, in this application scenario, the method for determining the thyristor turn-on current of the converter valve mainly includes: Step 1: Obtain calculation parameters and local temperature; Figure 3 This diagram shows the equivalent circuit for thyristor turn-on containing an anode saturated reactor. The circuit consists of a discharge capacitor C and a series resistor R. Σ 1. Hollow residual inductance L σ And a closed discharge circuit is formed by connecting the equivalent inductance of the saturated reactor for the converter valve in series. The discharge capacitor C, charged to its initial voltage U0 before the discharge switch is closed, is the sole source of energy during the turn-on process; its positive terminal voltage is denoted as u. C The positive direction of the winding current i is defined as flowing out from the positive terminal of the discharge capacitor; the series resistor R in the circuit... Σ Characterizing the total loss resistance of all components and connections in the discharge circuit, the hollow residual inductance L σ Characterizes the leakage flux (excluding the contribution of core magnetization) and the inductance corresponding to the wiring in the circuit; the equivalent inductance of the saturated reactor is connected to the circuit in the form of winding ports, and its port voltage u m Equal to the total flux linkage λ of the winding m The rate of change with respect to time, i.e., u m =dλ m / dt, this port voltage centrally reflects the reaction effect of the nonlinear magnetization of multiple core units on the circuit. After the discharge switch is closed, the energy stored in the capacitor is released through the circuit, and the winding current rises under the drive of the capacitor voltage. Each core unit is magnetized under the ampere-turn excitation generated by the winding current, and the change in the total magnetic flux linkage forms the port voltage. The voltage balance relationship of the circuit is u. C =R Σ ·i+L σ ·(di / dt)+dλ m / dt, the current during the thyristor turn-on process is determined by revolving around this circuit.

[0089] Step one above mainly obtains the capacitor discharge circuit parameters, winding parameters, magnetic circuit structure parameters of multiple core units, and the local temperature corresponding to the spatial position of each core unit. The capacitor discharge circuit parameters include at least the discharge capacitor C, the initial capacitor voltage U0, and the circuit series resistance R. Σ and hollow residual inductance L σ The winding parameters must include at least the number of turns N. The magnetic circuit structure parameters must include at least the effective magnetic circuit length l of the ferromagnetic material in each core unit. Fe Total equivalent air gap length l gap Effective cross-sectional area A e The calculation parameters include the number of core units and the effective linkage coefficient between the core flux and the windings. Local temperatures are pre-obtained inputs before the turn-on current calculation and can be obtained from core temperature measurements, thermal steady-state simulation results, or at least one of a preset operating temperature table. Within the calculation time window from the closing of the discharge switch to the first current peak, each local temperature is used as a given parameter and remains constant throughout the calculation time window.

[0090] When the local temperature is obtained through thermal steady-state simulation, a two-dimensional or three-dimensional steady-state heat conduction finite element model corresponding to the actual structure is established. The model includes core elements, windings, insulation structures, and cooling boundaries. The core loss and winding loss, obtained in advance through electromagnetic calculations or experiments, are set as the volume heat source or regional heat source for the corresponding area. The cooling boundaries are set according to the actual cooling medium temperature, flow rate, and convective heat transfer conditions on the equipment surface. The convective heat transfer coefficient and ambient temperature are determined based on design parameters, operating records, or thermal test calibration results. After solving the steady-state temperature field, the volume average temperature or characteristic location temperature of each core element is extracted as the local temperature of the corresponding core element.

[0091] Step 2: Establish a local temperature and magnetic state calculation unit; Based on the local temperature and spatial location of multiple core units, the multiple core units are divided into G local temperature magnetic state calculation units, where G≥2.

[0092] The g-th local temperature magnetic state calculation unit corresponds to a representative temperature T. g,0, and represent n g A core unit with a local temperature that is the same or a temperature difference that is less than a preset threshold.

[0093] For multiple core elements whose structural parameters, cooling boundaries, and local temperatures are approximately symmetrical about the central position, core elements located at symmetrical positions can be grouped into the same local temperature magnetic state calculation unit, while core elements located at the center of symmetry can be grouped separately. When the local temperatures at symmetrical positions cannot be approximated as the same, the corresponding core elements are grouped into different local temperature magnetic state calculation units. This reduces the number of magnetic states that need to be solved independently while preserving the main local temperature differences.

[0094] Step 3: Determine the temperature parameterized hysteresis model parameters for each calculation unit; Based on the representative temperature of each local temperature magnetic state calculation unit, the corresponding temperature parameterized hysteresis model parameters are determined.

[0095] The hysteresis model parameter vector of the g-th local temperature magnetic state calculation unit is expressed as: ; Among them, M s,g a is the saturation magnetization; g The shape parameter of the hysteresis-free magnetization curve; k g For pinning parameters; c g The reversible magnetization ratio; α g M represents the mean-field coupling parameter; F represents the temperature parameter mapping relationship established based on multi-temperature magnetization data. The temperature parameter mapping relationship can be achieved using a lookup table function, a piecewise linear interpolation function, a spline function, or a low-order polynomial function. The parameters satisfy: M s,g >0, a g >0, k g >0, 0≤c g ≤1.

[0096] Preferably, the temperature parameterized hysteresis model adopts the Jiles-Atherton hysteresis model.

[0097] The temperature parameter mapping relationship can be established in advance as follows: magnetization test of core material is carried out at multiple temperature points covering the expected operating temperature range of saturated reactor. The multiple temperature points include at least the lower limit of the expected operating temperature, the typical temperature and the upper limit. The magnetic field strength range of each temperature point covers at least the unsaturated magnetization region, the magnetization transition region and the saturation region, and the first rise magnetization curve or hysteresis loop containing the first rise branch is obtained.

[0098] For the p-th temperature point, its temperature is denoted as T. p The corresponding parameter vector of the Jiles-Atherton model is denoted as: ; Among them, M s,p a is the saturation magnetization; p The shape parameter of the hysteresis-free magnetization curve; k p For pinning parameters; c p The reversible magnetization ratio; α p The mean field coupling parameter.

[0099] The weighted squared error between the calculation results of the Jiles-Atherton model and the magnetization test results is used as the objective function: ; in, Let be the objective function for parameter identification at the p-th temperature point; q is the index of the magnetization test data point; Q is the total number of magnetization test data points participating in parameter identification. H represents the weight of the q-th data point; q Let be the magnetic field strength corresponding to the q-th data point; To use the parameter vector θ p The magnetic flux density calculated using the Jiles-Atherton model; For temperature T p The lower magnetic field strength is H q The magnetic flux density obtained during the test.

[0100] In satisfying M s,q >0, a q >0, k q >0, 0≤c q ≤1 and α p Under the constraints of a preset physical allowable range, the model parameters corresponding to each temperature point are determined using the constrained nonlinear least squares method. For the model parameters between adjacent temperature points, piecewise linear interpolation is preferred to ensure that the interpolation results pass through the identified discrete temperature parameter points while maintaining the aforementioned physical constraints, thereby forming a temperature parameter mapping relationship F(T) between temperature T and the Jiles-Atherton model parameters.

[0101] Step 4: Divide the calculation time steps and set the initial state; The opening process from the closing of the discharge switch to the first current peak is divided into multiple discrete calculation time steps, and the r-th discrete time step is denoted as t. r The interval between adjacent time steps is Δt.

[0102] The discrete calculation time step interval Δt is selected based on the shortest electrical transient characteristic time determined by the discharge capacitor, the series resistance of the circuit, the air-core residual inductance, and the nonlinear magnetization of the iron core in the capacitor discharge circuit, with the principle of being able to distinguish the winding current and local magnetic state changes in the initial stage of turn-on. It can be verified by reducing the calculation time step; when the relative changes in the first current peak value and the maximum current change rate before saturation obtained after halving the calculation time step are both no greater than the preset tolerance, the current calculation time step is adopted.

[0103] The initial capacitor voltage and winding current are set as follows: U c (0)=U0, i(0)=0. Ignoring residual magnetism before the turn-on event, the initial magnetic state of each local temperature magnetic state calculation unit is set as: M irr,g (0)=0, M g (0) = 0, B g (0) = 0. Where M irr,g M represents the irreversible magnetization of the g-th local temperature magnetic state calculation unit. g B is the total magnetization. g denoted as magnetic flux density.

[0104] Step 5: Set the candidate values ​​for the winding current at the current time step; In the (r+1)th discrete calculation time step, set the candidate value i of the winding current. r+1 The candidate value of the winding current is not a pre-given external excitation, but rather an unknown quantity that needs to be determined within the current discrete calculation step using both the local magnetic state equation and the port equation. The product of the candidate value and the number of winding turns is used as the common ampere-turn excitation for all local temperature magnetic state calculation units: F coil =N*i r+1 .

[0105] Step 6: Establish the magnetic circuit and hysteresis relationship of each local temperature magnetic state calculation unit; For the g-th local temperature magnetic state calculation unit, the magnetic circuit constraint is established based on the common ampere-turn excitation, the core magnetomotive force drop, and the air gap magnetomotive force drop: N*i=H Fe,g l Fe,g +H gap,g l gap,g Among them, H gap,g =B g / μ0. Where: H Fe,g H represents the magnetic field strength inside the ferromagnetic material. gap,g Let be the air gap magnetic field strength; μ0 be the free permeability. When the air gap cross-sectional area is approximately the same as the effective cross-sectional area of ​​the iron core and the air gap edge effect is neglected, the magnetic field strength inside the ferromagnetic material can also be written as: The Jiles-Atherton model is used to describe the magnetization process of the g-th local temperature magnetic state calculation unit in the first rising branch: ; ; ; ; ; ; ; Among them, H e,g For the effective magnetic field strength, M an,g The magnetization intensity is hysteresis-free. During the initial current rise interval from the closing of the discharge switch to the first current peak, the effective magnetic field increases in the positive direction, taking... .when When the value is less than a preset threshold, to avoid numerical instability caused by directly calculating the hyperbolic cotangent difference, the following formula is used to approximate and calculate M. an,g : ; Given the current candidate values ​​of winding current and irreversible magnetization at the current time step in the nonlinear iteration, the effective magnetic field strength H will be... e,g Selected as a local iteration variable. Based on the aforementioned hysteresis-free magnetization relationship, total magnetization relationship, and effective magnetic field relationship, M is sequentially... an,g M g H Fe,g and B g Represented as H e,g The function is denoted by and substituted into the magnetic circuit constraints, resulting in the following single-variable nonlinear equation: ; The above equations can be solved using Newton's method or damped Newton's method. The initial value is preferentially the effective magnetic field strength after convergence in the previous discrete calculation step, with zero initial value used for the first discrete calculation step. When multiple numerical roots exist, the root with the smallest difference from the magnetic state in the previous step is selected. Local convergence is considered achieved when the local magnetomotive force residual, after normalization to the characteristic magnitude of the current ampere-turn excitation, does not exceed a preset relative tolerance. Subsequently, the hysteresis-free magnetization, total magnetization, internal magnetic field strength of the ferromagnetic material, and magnetic flux density are determined sequentially based on the converged effective magnetic field strength. Small approximation thresholds are determined based on the relative error between the direct calculation formula of the hyperbolic cotangent and the series expansion formula; the approximation formula is used when the relative error does not exceed a preset series calculation tolerance.

[0106] Step 7: Discretize the local hysteresis differential equation into state residuals; The irreversible magnetization differential equation in step six is ​​transformed into a state equation with respect to time: ; Using the backward Euler scheme, the irreversible magnetization state residual of the g-th local temperature magnetic state calculation unit is constructed within the (r+1)-th discrete calculation time step: ; And require .

[0107] For the aforementioned upward range, since The above residuals can be simplified to: ; The previous step and Given the known historical state; the current time step , and The hysteresis history varies along with the candidate values ​​of the winding current. Therefore, the hysteresis history of each local temperature magnetic state calculation unit is used in the joint solution of the current time step through the state residual.

[0108] Step 8: Form the total winding flux at the current time step; like Figure 4 As shown, based on the magnetic flux density of each local temperature magnetic state calculation unit, the number of core units it represents, the effective cross-sectional area, the number of winding turns, and the effective linkage coefficient, the total winding flux linkage at the current time step is formed: ; Where G is the number of local temperature magnetic state calculation units, n g κ represents the number of core elements represented by the g-th local temperature magnetic state calculation unit. g A is the effective linkage coefficient that includes the actual linkage ratio and the magnetic flux reference direction. e,g is the effective cross-sectional area corresponding to the g-th local temperature magnetic state calculation unit.

[0109] Effective crosslinking coefficient κ g The actual linkage ratio and linkage direction between the magnetic flux generated by the g-th local temperature magnetic state calculation unit and the same winding are represented by the following definition: ; Where λ m,g This represents the actual contribution of this calculation unit to the total flux linkage of the winding. κ is defined when the magnetic flux reference direction is aligned with the positive direction of the winding flux linkage. g >0, κ when the direction is opposite g <0, generally satisfying -1≤κ g ≤1; When the magnetic flux of the corresponding core unit is fully linked to the winding and in the same direction, κ g =1. For non-fully linked cases, the effective number of turns N surrounding the corresponding magnetic circuit can be determined based on the actual number of turns N of the winding. eff,g Determine κg =N eff,g / N; Alternatively, a finite element model of the static magnetic field of the core-winding system can be established, and κ can be determined based on the ratio of the actual flux linkage generated by the corresponding core element on the winding to the fully coupled flux linkage. g .

[0110] The total flux linkage increment at the (r+1)th discrete computation time step is: .

[0111] The total flux linkage increment is used to calculate the magnetic port voltage at the current time step. Although each local temperature magnetic state calculation unit has different magnetic flux density and hysteresis state, they are all aggregated to the same winding port through the total flux linkage.

[0112] Step 9: Establish the capacitor state equation and port voltage equation; Steps five through eight above address the candidate value i of the winding current given the current time step. r+1 Afterwards, what magnetization state will the core be in at each local temperature, and how large will the total winding flux linkage be formed by these local magnetic states? However, providing a candidate current value does not mean that this current is the actual current in the capacitor discharge circuit. The actual current must also satisfy the law of capacitor charge release and the voltage balance relationship of the circuit.

[0113] The positive direction of the winding current i is defined as flowing out from the positive terminal of the discharge capacitor, and the capacitor voltage u C This is the voltage between the positive terminal and the negative terminal of the discharge capacitor.

[0114] The state equation for a capacitor is: ; The port voltage equation is: ; Using a fully implicit backward Euler scheme, the capacitance state residuals for r+1 discrete computation time steps are constructed: and demand .

[0115] Construct port consistency residuals: and demand .

[0116] Step 10: Solve the local magnetic state and winding current simultaneously within the same time step; Step 7 Constrain the hysteresis state of the g-th local temperature magnetic state calculation unit; Step nine uses , Constrain the capacitor discharge state and balance the loop port voltage. Step ten aims to simultaneously find a set of winding currents, capacitor voltages, and local magnetic states such that the above equations hold true at the same time.

[0117] In the (r+1)th discrete computation time step, the variables to be solved include: i r+1 , , ,..., ;Calculation units for local temperature and magnetic states , , , , All of them can be further calculated from the variables to be solved, and are regarded as explicit variables to be solved in the system of equations.

[0118] For the candidate winding current values ​​in the current nonlinear iteration, perform the following procedure: (1) Calculate the ampere-turn excitation shared by all local temperature magnetic state calculation units based on the candidate values; (2) Calculate the magnetic circuit state and hysteresis state of each local temperature magnetic state calculation unit according to the hysteresis model parameters corresponding to each representative temperature; (3) Obtain the magnetic flux density of each local temperature magnetic state calculation unit and form the total winding flux linkage at the current time step; (4) Calculate the total flux increment based on the difference between the total flux at the current time step and the previous time step; (5) Calculate the capacitor state residual and port consistency residual based on the total flux increment, capacitor state equation and port voltage equation; (6) Based on the port consistency residual, capacitor state residual and local hysteresis state residual, correct the candidate values ​​of winding current, capacitor voltage and local magnetic state variables.

[0119] Repeat the above process until the following condition is met: ; in, , , These are preset threshold values ​​for magnetic state residuals, capacitance state residuals, and port residuals, respectively. A joint solution can be achieved using Newton's method, damped Newton's method, quasi-Newton's method, or other iterative solutions to nonlinear equations.

[0120] In each nonlinear iteration, the total flux linkage of the winding and its increment are recalculated based on the updated candidate values ​​of the winding current and each local magnetic state, so that each local temperature magnetic state can directly participate in the solution of the winding current through the magnetic port voltage.

[0121] Step 11: Proceed the calculation step until the first current peak value is reached; When the port consistency residual, capacitor state residual, and local hysteresis state residual in the (r+1)th discrete calculation time step simultaneously meet the preset convergence conditions, the converged winding current, capacitor voltage, and local magnetic states are accepted and used as the known historical states for the next discrete calculation time step.

[0122] By sequentially advancing each discrete calculation step, the change of winding current over time is obtained. When the discrete derivative of the winding current first changes from positive to negative, i.e., the following condition is met: and When the winding current reaches the first current peak value between adjacent discrete calculation time steps, it is determined that the winding current reaches the first current peak value.

[0123] By interpolating the current or current derivative of adjacent discrete calculation time steps, the time of the first current peak is determined, and the turn-on current waveform, the maximum current change rate before saturation, and the first current peak value are obtained from the closing of the discharge switch to the first current peak value.

[0124] To further explain the working principle of the above-mentioned method for determining the thyristor turn-on current of the converter valve, this application embodiment also provides a specific calculation case of the method. This calculation case is a case of calculating the initial turn-on current of a nine-core saturated reactor considering five sets of local temperature magnetic states, and mainly includes: 1. Calculation objects and modeling scope; The computational object in this case is modeled as a set of five-turn windings and nine complete closed magnetic circuit units magnetically coupled to these windings. For example... Figure 5 As shown, the nine magnetic circuit units are labeled L4, L3, L2, L1, M, R1, R2, R3, and R4 from left to right, with a single port current i(t) flowing through the winding. Each complete closed magnetic circuit unit is assembled with two U-shaped iron cores facing each other and includes two connecting air gaps.

[0125] During the initial turn-on of the thyristor, all nine magnetic circuit units are subjected to the same ampere-turn excitation Ni(t). The magnetic state calculation units at different local temperatures save and advance their own magnetization history states. After each group of magnetic fluxes links with the same winding, they are added together to form the total winding flux linkage. The change in the total winding flux linkage then reacts on the unique winding current through the port voltage equation.

[0126] This case study only calculates the initial positive rise process from the closing of the discharge switch to the moment the winding current reaches its first peak value. Within this calculation time window, the core temperature of each group remains constant; the initial core state is taken as the demagnetized zero state, and the previous pulse, residual magnetism, and hysteresis are not considered; no thermal feedback loop is established between core losses, temperature rise, and magnetic parameters, and no additional equivalent resistance for core losses is set. (Except for the air-core residual inductance L...) σ Furthermore, the main inductor is no longer connected in series in the circuit, and the nonlinear inductance generated by the magnetization of the iron core is entirely controlled by the total magnetic flux linkage λ of the winding. m The time-varying process is reflected.

[0127] 2. Parameters of the capacitor discharge circuit and the core structure; The parameters of the capacitor discharge circuit are shown in Table 1: Table 1 Parameters of capacitor discharge circuit ; The structural parameters of the winding and a single complete iron core unit are shown in Table 2: Table 2 Winding and Core Structure Parameters ; In this case, the effective cross-sectional area of ​​the air gap is taken to be the same as that of the iron core, the edge effect of the air gap is ignored, and the gross cross-sectional area of ​​the iron core is taken as the effective cross-sectional area. All nine complete closed magnetic circuits in this case are surrounded by the same five-turn winding, and the total flux linkage of the winding is calculated according to the same magnetic flux reference direction. Therefore, the effective linkage coefficient of each group is taken as κ. g =1.

[0128] 3. Establish a local temperature magnetic state calculation unit; Considering the approximate symmetry of the structure and temperature distribution of the nine core units about the central position, L4 and R4, L3 and R3, L2 and R2, and L1 and R1 are each assigned to the same local temperature and magnetic state calculation unit. The central core unit M constitutes a separate local temperature and magnetic state calculation unit, thus forming five local temperature and magnetic state calculation units, G1 to G5. The position represented by each calculation unit, the number of core units, and the representative temperature are shown in Table 3.

[0129] Table 3 Local Temperature Magnetic State Calculation Unit ; The average temperature of the five representative temperatures, weighted by the number of core units, is:

[0130] The temperatures listed in Table 3 are the preset non-uniform temperature conditions used in this embodiment. In practical applications, the local temperature can be obtained from the core temperature measurement results, thermal steady-state simulation results, or the preset operating condition temperature table.

[0131] Because the time from the closing of the discharge switch to the first current peak is short, the local temperature of each group is used as a given parameter within this calculation time window, and is set as follows: .

[0132] 4. Determine the JA model parameters at different temperatures; This embodiment uses the Jiles-Atherton model to describe the initial positive magnetization process of each local temperature magnetic state calculation unit. Based on the representative temperature of each calculation unit, the corresponding JA model parameters are directly obtained from a pre-established temperature parameter table; the fitting function of the parameters as a function of temperature is not provided in this embodiment.

[0133] No. The parameter vector of the JA model for each local temperature magnetic state calculation unit is: .

[0134] The specific parameters used in this case are shown in Table 4.

[0135] Table 4. JA model parameters used at different temperatures ; In practical applications, the correspondence between temperature and JA model parameters can be established using the aforementioned multi-temperature magnetization test, constrained nonlinear least squares identification, and piecewise linear interpolation method. In this embodiment, the parameters listed in Table 4 are directly used as known calculation inputs.

[0136] 5. Divide the calculation time steps and set the initial state; The opening process from the closing of the discharge switch to the first current peak is divided into multiple discrete calculation steps, denoted as the first step. The discrete time intervals are The interval between adjacent time steps is: The initial capacitor voltage and winding current are set as follows: This case study ignores residual magnetism prior to the activation event, and the initial magnetic state of each local temperature magnetic state calculation unit is set to... .in, For the first The irreversible magnetization intensity of a local temperature magnetic state calculation unit The total magnetization is denoted as magnetic flux density.

[0137] 6. Set candidate values ​​for winding current and calculate the local magnetic state for each group; In the Within each discrete calculation step, candidate values ​​for the winding current are set. The candidate values ​​for the winding current are not predetermined external excitations, but rather unknowns that need to be determined jointly by the local magnetic state equations and the capacitor discharge loop port equations. All local temperature magnetic state calculation units are subjected to the same winding ampere-turn excitation: For the first Each local temperature magnetic state calculation unit, the core magnetopotential drop and the air gap magnetopotential drop satisfy... .in, Let be the magnetic field strength inside the ferromagnetic material. The JA model is used to describe the first... The first rising branch of a local temperature magnetic state calculation unit:

[0138]

[0139]

[0140]

[0141]

[0142] in, For effective magnetic field strength, This represents the hysteresis-free magnetization. This case study calculates the first positive upward process under the demagnetization zero-state, taking the magnetization direction parameter... .

[0143] when To avoid numerical instability caused by directly calculating the hyperbolic cotangent difference, the following formula is used to calculate the hysteresis-free magnetization: , .

[0144] This case takes |H e,g / a g |<10 -4 The aforementioned fifth-order series expansion is used. The threshold is determined based on the relative error between the direct calculation formula and the series expansion. Within the threshold range, the series truncation error is lower than the numerical solution tolerance in this case. The effective magnetic field strength after convergence of the previous discrete calculation time step is used as the initial value for the current time step of each local temperature magnetic state calculation unit. The first discrete calculation time step takes a zero initial value.

[0145] The irreversible magnetization differential equation is transformed into a time-state equation, and the backward Euler scheme is used to construct the first... The local temperature and magnetic state calculation unit in the first The irreversible magnetization state residual within each discrete computation time step: ; And require .

[0146] Thus, the five local temperature magnetic state calculation units retain the hysteresis history state of the previous time step, and update the magnetic state of the current time step under the common ampere-turn excitation generated by the same winding current candidate value.

[0147] 7. Form the total flux linkage of the winding and establish the capacitance state and port equations; Based on the magnetic flux density, the number of core units represented, the effective cross-sectional area, the number of winding turns, and the effective linkage coefficient of each local temperature magnetic state calculation unit, the first... Total winding flux linkage at each discrete calculation time step: ; In this case, The sequence is 2, 2, 2, 2, 1, and each group... ,therefore: ; The total flux increment at the current time step is: ; The positive direction of the winding current is defined as flowing out from the positive terminal of the discharge capacitor, and the capacitor voltage is... Let be the voltage across the positive terminal of the discharge capacitor relative to its negative terminal. The capacitor's state equation is: ; The port voltage equation is: ; Using a fully implicit backward Euler scheme, construct the first... Capacitor state residuals for each discrete computation time step: ; And require: ; Construct port consistency residuals: ; And require: ; 8. Solve the local magnetic state and winding current together within the same discrete calculation time step; In the Within each discrete calculation step, the winding current needs to be determined simultaneously. capacitor voltage The current magnetic state of the five local temperature magnetic state calculation units ensures that the magnetic circuit relationships, JA magnetization relationships, irreversible magnetization state residuals, capacitance state residuals, and port consistency residuals are all valid simultaneously.

[0148] For the candidate winding current values ​​in the current nonlinear iteration, the following process is executed sequentially: (1) Calculate the ampere-turn excitation shared by the five local temperature magnetic state calculation units based on the candidate values ​​of the winding current; (2) Based on the JA model parameters corresponding to each representative temperature, calculate the magnetic circuit state and hysteresis state of the five local temperature magnetic state calculation units respectively; (3) Obtain the magnetic flux density of each local temperature magnetic state calculation unit and form the total winding flux linkage at the current time step; (4) Calculate the total flux increment based on the difference between the total flux of the windings at the current time step and the previous time step; (5) Calculate the capacitor state residual and the port consistency residual based on the total flux increment, the capacitor state equation and the port voltage equation; (6) Based on the port consistency residual, capacitor state residual and irreversible magnetization state residual of each local temperature magnetic state calculation unit, correct the candidate values ​​of winding current, capacitor voltage and each local magnetic state variable.

[0149] Because the magnetic state residual, capacitance state residual, and port consistency residual have different dimensions, this case sets corresponding convergence thresholds for each. Among them, the... The magnetic state residual threshold for each local temperature magnetic state calculation unit is taken as the corresponding saturation magnetization. of The capacitor state residual threshold and port consistency residual threshold are both taken as the initial capacitor voltage. of The time step of the current discrete computation is considered to have converged when the absolute values ​​of the residuals of each local magnetic state, capacitance state, and port consistency are all no greater than the corresponding thresholds.

[0150] The above thresholds are respectively expressed in M s,g U0, as the characteristic magnitude of the corresponding residual, is equivalent to taking a normalized relative tolerance of 10. -10 For other calculation accuracy requirements, the relative tolerance can be adjusted according to the computer's floating-point accuracy and the required output accuracy.

[0151] This case study employs the damped Newton method for the combined solution described above, with a maximum of 30 iterations per discrete calculation step. In each nonlinear iteration, five sets of magnetic flux densities, total winding flux linkage, and their increments are recalculated based on the updated candidate winding current values ​​and local magnetic states. This allows the local temperature magnetic states to directly participate in the determination of the winding current through the magnetic port voltage.

[0152] 9. Advance the calculation time step and determine the first current peak value and the maximum current change rate before saturation; When the When the port consistency residual, capacitor state residual, and residuals of each local irreversible magnetization state within a discrete calculation time step simultaneously meet the preset convergence conditions, the converged winding current, capacitor voltage, and each local magnetic state are accepted and used as the known historical state for the next discrete calculation time step.

[0153] By sequentially advancing each discrete calculation step, the change in winding current over time is obtained. The discrete current change rate is calculated using the following formula: When the discrete derivative of the winding current first changes from a positive value to a non-positive value, i.e., satisfies... and When the winding current reaches the first current peak value between adjacent discrete calculation time steps, it is determined that the winding current reaches the first current peak value.

[0154] The first current peak time and the first current peak value are determined by interpolating the current or current derivative of adjacent discrete calculation time steps.

[0155] To objectively determine the saturation transition point, the moment when the discrete current change rate first transitions from decreasing to non-decreasing is determined according to the aforementioned discrete current change rate. This moment is then used as the starting point for linear fitting after excluding the initial boundary effect of switch closure. From this starting point, the fitting endpoint is gradually expanded, and a linear least-squares fit is performed on the current-time data within the current fitting interval, and the coefficient of determination R is calculated. 2 When R 2 When q consecutive judgment times are below a preset threshold ρ, the first judgment time in that consecutive interval is determined as the saturation transition start point. The fitting interval contains no less than m data points. min .

[0156] This case takes m. min With values ​​of 10, ρ=0.999, and q=2, the saturation transition starting points for the uniform temperature model and the local temperature grouping model are 1.36625 μs and 1.35125 μs, respectively. Between the start of the linear fitting and the saturation transition starting point, the maximum value is calculated point-by-point according to the discrete current change rate calculation formula and taken as the maximum current change rate before saturation. This rate characterizes the maximum current change rate before the core has clearly entered the saturation transition, after excluding the initial boundary effect of the switch closure.

[0157] 10. Comparison of the uniform temperature model and calculation results; To illustrate the impact of local temperature magnetic state on the calculation results of the turn-on current, a uniform temperature model is set up as a control in this case. The uniform temperature model and the local temperature grouping model in this case use the same capacitor discharge circuit parameters, winding parameters, core structure parameters, initial conditions, time steps, and numerical solution methods.

[0158] The uniform temperature model sets the nine core elements to a weighted average temperature: All parameters were taken from the JA model in the "Uniform Temperature Comparison" row of Table 4, and the nine core units were represented by a single uniform magnetic state. The total winding flux linkage of the uniform temperature model was...

[0159] The turn-on current calculation results for the local temperature grouping model and the uniform temperature model in this case are as follows: Figure 6 As shown in Table 5.

[0160] Table 5. Calculation results of maximum current change rate and first current peak value before saturation under two temperature modeling methods. ; As shown in Table 5, under the condition that the weighted average temperature of the nine core units is 70.0111℃, the maximum current change rate before saturation obtained by the local temperature grouping model in this case is 249.414A / μs, while the maximum current change rate before saturation obtained by the uniform temperature model is 224.813A / μs, with a difference of 24.601A / μs. The calculation result of the local temperature grouping model in this case is about 10.94% higher than that of the uniform temperature model.

[0161] The first peak current obtained from the local temperature grouping model in this case is: The first peak current time is The first peak current obtained from the uniform temperature model is The first peak current time is The first current peaks of the two models differ by a factor of two. Approximately 10% of the results calculated by the mean temperature model .

[0162] The above results indicate that, under the same weighted average temperature, using a single average temperature and a uniform magnetic state will ignore the differences in magnetization states between different core units. The method provided in this application calculates five sets of local temperature magnetic states respectively, and introduces the total flux linkage increment of the winding formed by the magnetic flux of each set into the capacitor discharge circuit port equation, thus reflecting the influence of local temperature differences on the calculation results of the maximum current change rate before saturation and the first current peak value.

[0163] like Figure 7 As shown, based on the same inventive concept, this application also provides a converter valve thyristor turn-on current determination system 200, applied to a saturated reactor for a converter valve. The saturated reactor for the converter valve includes a common winding and multiple iron core units magnetically coupled to the same winding. The system includes: Temperature acquisition module 210 is used to acquire the local temperature corresponding to the spatial positions of multiple core units; The unit configuration module 220 is used to divide multiple core units into at least two local temperature magnetic state calculation units according to the local temperature of each core unit, and to determine the magnetization characteristic parameters of each local temperature magnetic state calculation unit according to the temperature corresponding to each local temperature magnetic state calculation unit; wherein, local temperature magnetic state calculation units at different temperatures have different magnetization characteristic parameters. The magnetic state determination module 230 is used to use the product of the winding current and the number of turns of the same winding as the common ampere-turn excitation of each local temperature magnetic state calculation unit within the current discrete calculation time step, and to determine the magnetic flux density of each local temperature magnetic state calculation unit according to the magnetization characteristic parameters of each local temperature magnetic state calculation unit. The total flux linkage determination module 240 is used to determine the total flux linkage of the winding in the current discrete calculation step based on the magnetic flux density of each local temperature magnetic state calculation unit, the number of iron core units it represents, the effective cross-sectional area, and the linkage relationship between the magnetic flux and the same winding. The current determination module 250 is used to determine the winding current in the current discrete calculation step based on the change in the total flux linkage of the winding and the port voltage balance relationship of the discharge circuit containing the same winding. The time-stepping module 260 is used to sequentially advance each discrete calculation time step and determine the thyristor turn-on current based on the winding current determined by each discrete calculation time step.

[0164] It should be noted that the converter valve thyristor turn-on current determination system 200 provided in this application embodiment can realize any of the functions of the above-mentioned converter valve thyristor turn-on current determination method. For the method embodiment section, please refer to the method embodiment section for the way each function is realized and the working principle. The system embodiment section will not repeat it here.

[0165] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for determining the turn-on current of a converter valve thyristor, characterized in that, A method for use in saturated reactors for converter valves, wherein the saturated reactor for converter valves comprises a common winding and multiple core units magnetically coupled to the common winding, the method comprising: Obtain the local temperature corresponding to the spatial position of the plurality of core units; Based on the local temperature of each core unit, the plurality of core units are divided into at least two local temperature magnetic state calculation units, and the magnetization characteristic parameters of each local temperature magnetic state calculation unit are determined based on the temperature corresponding to each local temperature magnetic state calculation unit; wherein, local temperature magnetic state calculation units at different temperatures have different magnetization characteristic parameters. Within the current discrete calculation time step, the product of the winding current and the number of turns of the same winding is used as the common ampere-turn excitation of each of the local temperature magnetic state calculation units. Based on the magnetization characteristic parameters of each of the local temperature magnetic state calculation units, the magnetic flux density of each of the local temperature magnetic state calculation units is determined respectively. Based on the magnetic flux density of each local temperature magnetic state calculation unit, the number of core units it represents, the effective cross-sectional area, and the linkage relationship between the magnetic flux and the same winding, the total magnetic flux of the winding in the current discrete calculation step is determined. The winding current at the current discrete calculation step is determined based on the change in the total flux linkage of the winding and the port voltage balance relationship of the discharge circuit containing the same winding. The discrete calculation time steps are advanced sequentially, and the thyristor turn-on current is determined based on the winding current determined in each discrete calculation time step.

2. The method for determining the thyristor turn-on current of the converter valve according to claim 1, characterized in that, Determining the winding current at the current discrete calculation time step includes: The winding current is set as the variable to be solved in the current discrete calculation time step. A current candidate value is set for the winding current, and the product of the current candidate value and the number of turns of the same winding is used as the common ampere-turn excitation. The magnetization state and magnetic flux density of each local temperature magnetic state calculation unit under the corresponding magnetic circuit constraint are determined, and the total magnetic flux linkage of the winding is determined. The candidate current value is corrected based on the deviation between the magnetization state of each local temperature magnetic state calculation unit and the corresponding magnetic circuit constraint, and the deviation between the port voltage of the saturated reactor and the port voltage balance relationship of the discharge circuit determined by the change in the total flux linkage of the winding. Repeat the above correction process until the magnetization state of each local temperature magnetic state calculation unit satisfies the corresponding magnetic circuit constraint and the port voltage satisfies the port voltage balance relationship. Then, determine the current candidate value when the condition is met as the winding current of the current discrete calculation step.

3. The method for determining the thyristor turn-on current of the converter valve according to claim 1, characterized in that, Each of the local temperature magnetic state calculation units stores its own magnetization history; the determination of the magnetic flux density of each of the local temperature magnetic state calculation units includes: Within the current discrete calculation time step, the magnetization state of each local temperature magnetic state calculation unit in the previous discrete calculation time step is taken as its respective magnetization history state. Under the common ampere-turn excitation, the magnetization state of each local temperature magnetic state calculation unit in the current discrete calculation time step is determined according to the magnetization history state and the magnetization characteristic parameters of the corresponding local temperature magnetic state calculation unit, and then the corresponding magnetic flux density is determined. The magnetization state of the current discrete calculation time step is updated to the magnetization history state of the corresponding local temperature magnetic state calculation unit for use in the next discrete calculation time step; wherein, the magnetization history state of each local temperature magnetic state calculation unit evolves independently with the progress of the discrete calculation time step.

4. The method for determining the thyristor turn-on current of the converter valve according to any one of claims 1 to 3, characterized in that, The step of dividing the plurality of core units into at least two local temperature magnetic state calculation units includes: Compare the local temperatures of each core unit, and merge multiple core units with the same local temperature or local temperature differences that meet the preset similar conditions into the same local temperature magnetic state calculation unit. Based on the local temperatures of multiple core units merged into the same local temperature magnetic state calculation unit, the representative temperature of the local temperature magnetic state calculation unit is determined, and the representative temperature is used as the temperature corresponding to the local temperature magnetic state calculation unit. Each local temperature magnetic state calculation unit uniformly represents multiple core units that have been merged and participates in the determination of the total flux linkage of the winding.

5. The method for determining the thyristor turn-on current of the converter valve according to any one of claims 1 to 3, characterized in that, The structural parameters, cooling boundaries, and local temperatures of the multiple core units are approximately symmetrical about the middle of the arrangement of the multiple core units; The step of dividing the plurality of core units into at least two local temperature magnetic state calculation units includes: For multiple core units located symmetrically about the middle of the arrangement, when the local temperatures of the multiple core units are the same or the local temperature differences meet the preset similarity conditions, the multiple core units are merged into the same local temperature magnetic state calculation unit; when the local temperature differences of the multiple core units do not meet the preset similarity conditions, the multiple core units are assigned to different local temperature magnetic state calculation units respectively. The core unit located in the middle of the arrangement is divided into a separate local temperature and magnetic state calculation unit.

6. The method for determining the turn-on current of the converter valve thyristor according to any one of claims 1 to 3, characterized in that, The step of obtaining the local temperature corresponding to the spatial positions of the plurality of core units includes: A heat conduction model corresponding to the actual structure of the saturated reactor is established. The heat conduction model includes at least the multiple core units, the same winding, the insulation structure, and the cooling boundary. Based on the predetermined core losses of the multiple core units and the winding losses of the same winding, a heat source is set in the corresponding region of the heat conduction model, and the heat dissipation conditions of the cooling boundary are set according to the actual cooling conditions of the saturated reactor. The steady-state thermal solution is performed on the heat conduction model to obtain the steady-state temperature field; The representative region temperature of each core unit is extracted from the steady-state temperature field to obtain the local temperature of each core unit.

7. The method for determining the turn-on current of the converter valve thyristor according to any one of claims 1 to 3, characterized in that, The linkage relationship between the magnetic flux and the same winding is characterized by the effective linkage coefficient; The effective linkage coefficient corresponding to each local temperature magnetic state calculation unit is determined based on the actual linkage ratio and linkage direction between the magnetic flux of the corresponding local temperature magnetic state calculation unit and the same winding; the absolute value of the effective linkage coefficient is not greater than 1, and the sign of the effective linkage coefficient corresponds to the linkage direction of the corresponding magnetic flux relative to the positive direction of the magnetic flux of the same winding; For a local temperature magnetic state calculation unit where the magnetic flux is not fully linked to the same winding, the effective linkage coefficient is determined based on the ratio of the effective number of turns of the same winding actually surrounding the corresponding magnetic circuit to the number of turns of the same winding, or based on the ratio of the actual magnetic flux contribution of the magnetic flux of the corresponding local temperature magnetic state calculation unit to the magnetic flux of the same winding to the fully linked magnetic flux.

8. The method for determining the turn-on current of the converter valve thyristor according to any one of claims 1 to 3, characterized in that, The sequential advancement of each discrete calculation step includes: Since the switch of the discharge circuit is closed, each discrete calculation time step is advanced. During the advancement process, the magnetization characteristic parameters corresponding to the local temperature are used as fixed inputs for each local temperature magnetic state calculation unit to determine the magnetization state and winding current of each discrete calculation time step, without updating the local temperature. The process is terminated when the winding current reaches the first current peak value, thus obtaining the thyristor turn-on current from the time the switch is closed until the first current peak value.

9. The method for determining the thyristor turn-on current of the converter valve according to claim 8, characterized in that, Determining that the winding current has reached the first current peak value includes: comparing the winding current in adjacent discrete calculation time steps; when the winding current changes from increasing step by step to no longer increasing for the first time as the discrete calculation time step changes, it is determined that the winding current has reached the first current peak value between the corresponding adjacent discrete calculation time steps. The method further includes: determining the maximum current change rate before saturation and the current value corresponding to the first current peak based on the thyristor turn-on current from the closing of the switch to the first current peak value; wherein, the maximum current change rate before saturation is the maximum value of the current increment per unit time of the thyristor turn-on current within the current rise range before the plurality of core units enter saturation, excluding the initial influence of the switch closing.

10. A system for determining the turn-on current of a converter valve thyristor, characterized in that, A saturated reactor for converter valves, the saturated reactor for converter valves comprising a common winding and multiple core units magnetically coupled to the common winding, the system comprising: A temperature acquisition module is used to acquire the local temperature corresponding to the spatial positions of the plurality of core units; The unit configuration module is used to divide the plurality of core units into at least two local temperature magnetic state calculation units according to the local temperature of each core unit, and to determine the magnetization characteristic parameters of each local temperature magnetic state calculation unit according to the temperature corresponding to each local temperature magnetic state calculation unit; wherein, local temperature magnetic state calculation units at different temperatures have different magnetization characteristic parameters. The magnetic state determination module is used to determine the magnetic flux density of each local temperature magnetic state calculation unit by using the product of the winding current and the number of turns of the same winding as the common ampere-turn excitation of each local temperature magnetic state calculation unit within the current discrete calculation time step, and by determining the magnetic flux density of each local temperature magnetic state calculation unit according to the magnetization characteristic parameters of each local temperature magnetic state calculation unit. The total flux linkage determination module is used to determine the total flux linkage of the winding at the current discrete calculation time step based on the magnetic flux density of each local temperature magnetic state calculation unit, the number of core units it represents, the effective cross-sectional area, and the linkage relationship between the magnetic flux and the same winding. The current determination module is used to determine the winding current at the current discrete calculation time step based on the change in the total flux linkage of the winding and the port voltage balance relationship of the discharge circuit containing the same winding. The time-stepping module is used to sequentially advance each discrete calculation time step and determine the thyristor turn-on current based on the winding current determined by each discrete calculation time step.

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