Low-frequency transformer with direct current bias resistance and control method

Abstract

The application discloses a low-frequency transformer resistant to direct-current bias magnetism and a control method, and aims to solve the problems of high loss under normal working conditions and insufficient shunt capacity under bias magnetism conditions of an existing fixed magnetic shunt structure. The application sets an adaptive magnetic shunt structure outside a driving assembly, and can dynamically adjust the magnetic resistance of the magnetic shunt loop according to the direct-current bias magnetism state by moving close to or away from the side yoke, so as to realize the dual goals of low-loss operation under normal working conditions and strong shunt under bias magnetism conditions. Specifically, the application comprises a magnetic conductor array, an insulation transmission assembly and a driving assembly, the optimal structure parameters are determined through proxy model optimization, and adaptive adjustment is realized through closed-loop control.

Description

Technical Field

[0001] This invention relates to the field of low-frequency converters, and more specifically, to a low-frequency transformer and control method resistant to DC bias. Background Technology

[0002] Low-frequency converters are suitable for long-distance power transmission and flexible AC power transmission. During operation, external influences cause a DC component to be superimposed on the grid-side current of a low-frequency transformer, which in turn generates a DC bias magnetomotive force in the converter. Due to its low operating frequency, large core size, and high design magnetic flux density, low-frequency transformers are more prone to unidirectional saturation or even deep saturation after the addition of DC bias.

[0003] When the core saturates, it leads to an increase and distortion of the excitation current, generating low-order harmonics and reactive power fluctuations. Simultaneously, the core and clamps may experience electromagnetic vibrations, increasing transformer noise and increasing additional losses and localized temperature rise in metal structural components such as windings, clamps, and tank sidewalls. In severe cases, this can cause relay protection malfunctions, accelerated insulation aging, or equipment shutdowns. For oil-immersed low-frequency transformers with high voltage levels of 220kV and below, DC bias not only affects electromagnetic performance but also places higher demands on insulation safety, sealing reliability, and operation and maintenance.

[0004] Existing anti-DC bias measures mainly include series capacitor DC blocking, fixed magnetic shunts, increasing the core cross-sectional area, reducing the design magnetic flux density, or installing compensating windings. Series capacitor DC blocking requires additional high-voltage, large-capacity capacitors, resulting in high cost, large size, and potential impact on system transient stability. While fixed magnetic shunt structures can shunt bias flux to some extent, their shunt capacity is fixed and cannot adapt to real-time changes in DC bias intensity. Under normal, unbiased operating conditions, fixed magnetic shunts may introduce additional leakage flux and no-load losses; under severe bias conditions, they may have insufficient shunt capacity. Simply increasing the core cross-sectional area or reducing the design magnetic flux density can improve saturation resistance, but it significantly increases transformer size, weight, and manufacturing costs, hindering the engineering application of low-frequency transformers. Summary of the Invention

[0005] This invention overcomes the shortcomings of existing low-frequency converters that use a fixed magnetic shunt structure to counteract biased magnetic conditions, resulting in high power consumption under normal operating conditions. It provides a low-frequency transformer and control method that resists DC biased magnetic conditions, which can dynamically adjust the magnetic shunt status according to the biased magnetic state of the converter.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A low-frequency transformer resistant to DC bias includes an oil tank and a core body. The core body is disposed inside the oil tank and includes a main core column and a side yoke. The low-frequency transformer includes an adaptive magnetic shunt structure, which includes a magnetic conductor array, an insulating transmission assembly, and a drive assembly. The drive assembly is located outside the oil tank and is connected to the magnetic conductor array through an insulating transmission assembly that penetrates the side wall of the oil tank. Under the drive of the drive assembly, the insulating transmission assembly moves the magnetic conductor array closer to or away from the side yoke to change the magnetic reluctance of the magnetic shunt circuit on the side yoke side.

[0007] Under normal AC operation, the main magnetic flux closes along the main magnetic circuit formed by the iron core body, upper yoke, side yoke, and lower yoke. At this time, the magnetic conductor array is in the initial maximum air gap position. At this point, the air gap reluctance is relatively high, and the magnetic shunt circuit reluctance is also relatively high, so the main magnetic flux will not be significantly shunted. Under DC bias conditions, the magnetic conductor array moves closer to the side yoke, and the air gap distance... The magnetic reluctance of the magnetic shunt circuit is reduced, thereby providing a bypass shunt path for the DC bias flux in the main iron core column 21.

[0008] Preferably, the magnetic conductor array includes an insulating clamping frame and magnetic conductor stacks, wherein the magnetic conductors forming the magnetic conductor stacks are insulated from each other, and the magnetic conductors are stacked along the magnetic flux direction of the yoke to form the magnetic conductor stacks.

[0009] Preferably, the oil tank is equipped with a guide mechanism, and the insulating clamping frame slides with the guide mechanism so that the insulating clamping frame can move in a direction close to or away from the yoke.

[0010] Preferably, the insulated transmission assembly includes an insulated pull rod and a sealing sleeve. The insulated pull rod passes through the side wall of the oil tank, one end of which is located inside the oil tank and connected to the magnetic conductor array, and the other end of which is connected to the drive assembly. The sealing sleeve is disposed between the insulated pull rod and the side wall of the oil tank for guiding and sealing the insulated pull rod.

[0011] Preferably, the fuel tank is also equipped with a position detection element for detecting the position of the magnetic conductor array.

[0012] A control method for a low-frequency transformer resistant to DC bias magnetization includes: Obtain the initial electromagnetic parameters, structural parameters, and operational constraint parameters of the low-frequency transformer, and obtain the initial structural parameters of the adaptive magnetic shunt structure; Collect the grid-side DC current component during the operation of the low-frequency transformer. and the magnetic flux density of the main iron core ; According to the grid-side DC current component and the magnetic flux density of the main iron core Determine whether the low-frequency transformer is in a state of DC bias risk; In response to the assessment that the low-frequency transformer is in a state of DC bias risk, the drive assembly is controlled to operate, driving the insulated transmission assembly to move the magnetic conductor array closer to the side yoke of the converter, thereby reducing the air gap distance. and increase the effective cross-linking area A ; In response to the determination that the low-frequency transformer is no longer in a state of DC bias risk, the drive assembly is controlled to drive the insulating transmission assembly to move the magnetic conductor array away from the converter's side yoke until it returns to the initial maximum air gap position. .

[0013] Preferably, the initial structural parameters of the adaptive magnetic shunt structure are obtained through optimization using a surrogate model, wherein the surrogate model optimization includes: Define air gap distance Effective linkage area of ​​the magnetic conductor array A At least two of the following should be used as optimization variables: the thickness of the magnetic conductor array stack, the size of the iron core main column, the size of the side yoke, and the installation pose. Construct a fitness function that includes at least two of the following: leakage flux loss term, no-load loss term, bias magnetic adjustment margin term, temperature rise constraint term, insulation distance constraint term, and mechanism motion constraint term; Proxy models are constructed based on finite element simulation samples; The fitness function is solved based on the surrogate model, and the initial structural parameters of the adaptive magnetic shunt structure are output.

[0014] As a preferred approach, when constructing the surrogate model, a physical feature penalty factor W(x) is introduced. When the magnetic flux density predicted by the surrogate model falls into the critical range of the saturation risk threshold or exceeds the upper limit of the critical range of the saturation risk threshold, the weight of the physical feature penalty factor W(x) is increased to improve the sampling density of the surrogate model near the magnetic saturation boundary.

[0015] As a preferred option, based on the main core post rate of increase Adjust the drive speed of the drive component, when When the speed exceeds a preset rate threshold, the driving speed of the driving component is the first speed; when... Less than or equal to the preset rate threshold and If the speed is still higher than the warning threshold, the driving speed of the drive component is the second speed, which is less than the first speed.

[0016] Preferably, based on the grid-side DC current component Magnetic flux density of the main iron core and the rate of change of magnetic flux density in the main iron core Determine the target air gap distance And through closed-loop position control, the magnetic conductor array is moved to the corresponding position; when the grid-side DC current component Below the release threshold, main core magnetic flux density After the air gap falls below a safety threshold and remains below it for a preset time, the magnetic conductor array is controlled to return to its initial maximum air gap position. .

[0017] Compared with the prior art, the beneficial effects of the present invention are: The magnetic conductor array can be moved closer to or further away from the iron core side according to the DC bias state, thereby changing the air gap distance. and effective cross-link area A This causes the magnetic shunting capability to vary with the bias magnetic intensity; Under conditions without DC bias, the magnetic conductor array remains at its initial maximum air gap position. The equivalent magnetic reluctance of the magnetic shunt circuit is relatively large, which has little impact on the main magnetic flux. Under DC bias conditions, the magnetic conductor array is close to the side yoke, and the equivalent magnetic reluctance of the magnetic shunt circuit is reduced, thereby enhancing the shunt capability of the DC bias magnetic flux. By setting up an insulating clamping frame, guiding mechanism, limiting component, position detection element, sealing sleeve and leakage detection cavity, the magnetic conductor array can move in a controlled manner in the transformer oil environment, which is conducive to meeting the sealing and insulation requirements of oil-immersed high-voltage equipment. The drive assembly is located outside the oil tank and drives the magnetic array inside the oil tank to move through the insulated transmission assembly. This avoids directly arranging the motor or complex actuator inside the oil tank, thus improving high-voltage insulation safety and maintenance convenience. By introducing a physical feature penalty factor W(x) into the surrogate model optimization, the optimization sampling pays more attention to the region near the magnetic saturation boundary, which helps to improve the accuracy of the design of the anti-magnetic margin of low-frequency transformers. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the design phase of this invention; Figure 2 This is a flowchart illustrating the operational phases of the present invention; Figure 3 This is a schematic diagram of the structure of the present invention; Figure 4 This is a schematic diagram of the structure of the magnetically conductive laminate; Figure 5 This is a comparison diagram of the active learning optimization process of the fusion feature penalty factor of the present invention; Figure 6 This is a simulation curve diagram of the present invention.

[0019] In the picture: 1. Oil tank; 2. Iron core body; 21. Main iron core column; 3. Winding; 22. Side yoke; 4. Magnetic conductor array; 41. Insulating clamping frame; 42. Magnetic conductor lamination; 421. Magnetic conductor sheet; 422. Insulating layer; 5. Insulating transmission assembly; 51. Insulating tie rod; 52. Sealing sleeve; 6. Drive assembly; 7. Control module; 8. Position detection element; 9. Guide mechanism. Detailed Implementation

[0020] The present disclosure will be further described below with reference to the accompanying drawings and embodiments.

[0021] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0022] Example: A low-frequency transformer resistant to DC bias, such as Figure 3 As shown, Figure 3 The dashed lines in the diagram represent the main magnetic flux paths. Figure 3 The dashed line in the diagram represents the DC bias shunt path, which includes an oil tank 1 and an iron core body 2. The iron core body 2 is located inside the oil tank 1 and includes a main iron core column 21 and a side yoke 22. A winding 3 is also wound around the outside of the iron core body 2. The iron core body 2 includes the main iron core column 21, side column, upper yoke, lower yoke, and side yoke 22. The winding 3 can include a low-voltage winding 3, a high-voltage winding 3, and a necessary voltage regulating winding 3. This application does not limit the type of winding 3.

[0023] The low-frequency transformer includes an adaptive magnetic shunt structure, which comprises a magnetic conductor array 4, an insulated transmission assembly 5, and a drive assembly 6. The drive assembly 6 is located outside the oil tank 1 and is connected to the magnetic conductor array 4 via the insulated transmission assembly 5, which penetrates the wall of the oil tank 1. The drive assembly 6 moves the magnetic conductor array 4 closer to or further away from the yoke to change the magnetic reluctance of the magnetic shunt circuit on the yoke side. In some embodiments, the drive assembly 6 is a linear motor.

[0024] When the magnetic conductor array 4 is brought close to the side yoke, the air gap distance between the magnetic conductor array 4 and the iron core body 2 can be changed. And the effective linkage area A, thereby changing the magnetic reluctance of the magnetic shunt loop on the side yoke.

[0025] Under conditions without DC bias, the magnetic conductor array 4 remains at the initial maximum air gap position. At this time, the magnetic reluctance of the magnetic shunt circuit is relatively large, and it will not significantly shunt the main magnetic flux. Under DC bias conditions, the magnetic conductor array 4 moves closer to the side yoke 22, and the air gap distance... The magnetic reluctance of the magnetic shunt circuit is reduced, thereby providing a bypass shunt path for the DC bias magnetic flux in the core body 2, thus achieving anti-DC bias, preventing the core from entering bias saturation, generating harmonics and irrelevant power fluctuations, as well as electromagnetic vibrations.

[0026] In this embodiment, "low-frequency transformer" refers to a power transformer with an operating frequency below 50Hz, preferably 16.7Hz or 20Hz, but other operating frequencies below the power frequency are also acceptable. The voltage level of this low-frequency transformer can be 220kV and below, but can also be extended to other voltage levels according to actual engineering needs.

[0027] The magnetic conductor array 4 includes an insulating clamping frame 41 and magnetic conductor laminations 42, with the magnetic conductors 421 forming the magnetic conductor laminations 42 being mutually insulated. Insulation between adjacent magnetic conductors 421 is achieved by providing an insulating layer 422, an insulating coating, or an insulating spacer between adjacent magnetic conductor laminations 42, thereby reducing eddy current losses in the magnetic conductor array 4, reducing temperature rise, and energy consumption. The insulating clamping frame 41 is also designed to be insulated for this reason. Selecting magnetic conductor laminations 42 with higher magnetic permeability can improve the aforementioned anti-DC bias effect.

[0028] like Figure 4 As shown, the magnetically conductive laminate 42 is formed by stacking magnetically conductive sheets 421. The material of the magnetically conductive sheets 421 includes one or more of amorphous ribbon, nanocrystalline ribbon, silicon steel sheet, and soft magnetic composite material. In order to better improve the magnetic permeability, the magnetically conductive sheets 421 are stacked along the magnetic flux direction of the lateral yoke, thereby having better magnetic permeability.

[0029] Under normal AC operation, the main magnetic flux closes along the main magnetic circuit formed by the iron core body 2, the upper yoke, the side yoke 22, and the lower yoke. At this time, the magnetic conductor array 4 is in the initial maximum air gap position. At this point, the air gap reluctance is relatively high, and the magnetic shunt circuit reluctance is also relatively high, so the main magnetic flux will not be significantly shunted. Under DC bias conditions, the magnetic conductor array 4 moves closer to the side yoke 22, and the air gap distance... The magnetic reluctance of the magnetic shunt circuit is reduced, thereby providing a bypass shunt path for the DC bias flux in the main iron core column 21.

[0030] When the DC current component enters winding 3, winding 3 generates a DC bias magnetomotive force, causing the magnetic flux operating point in the main core column 21 to shift to one side. Without adjustment, the main core column 21 may enter deep saturation during some AC cycles. At this time, by controlling the drive assembly 6, the magnetic conductor array 4 is moved closer to the side yoke 22 of the core. With the air gap distance... As the magnetic flux density decreases, the air gap reluctance of the magnetic shunt circuit on the side of the yoke 22 decreases, and a relatively low reluctance flux bypass is formed between the magnetic conductor array 4 and the yoke 22. Part of the DC bias flux in the main core column 21 enters the magnetic conductor array 4 through the side of the yoke 22 and closes along the region of the magnetic conductor array 4 and the yoke 22, thereby reducing the DC bias flux component in the main core column 21.

[0031] In a simplified equivalent magnetic circuit model, the equivalent magnetic reluctance of the magnetic shunt loop is... It can be represented as:

[0032] in, The equivalent magnetic reluctance on the side 22 of the iron core yoke. The magnetic reluctance corresponds to the air gap between the magnetic conductor array 4 and the iron core body 2. The magnetic reluctance of the magnetic conductor array 4 is itself. The above equivalent magnetic reluctance model is used to explain the air gap distance. The effect on magnetic shunt capability does not limit the actual magnetic flux path to consist only of the three reluctances connected in series mentioned above.

[0033] Ignoring edge leakage magnetic field or converting edge effects to the effective linkage area A At that time, air gap magnetoresistance It can be represented as:

[0034] in, The distance between the magnetic conductor array 4 and the iron core body 2 is the air gap distance. The permeability of free space, The effective linkage area. According to the above formula, when the magnetic conductor array 4 is close to the side yoke and the air gap distance δ is reduced, Follow The equivalent magnetic reluctance of the magnetic shunt circuit is reduced by decreasing the magnetic reluctance. This decreases accordingly, thereby enhancing the ability to shunt DC bias flux.

[0035] The above structure provides an additional low magnetic reluctance branch for the existing transformer magnetic circuit. It increases the shunting capacity of the magnetic circuit under the risk of bias magnetization, while maintaining a high magnetic reluctance state under normal conditions, thus taking into account both the anti-bias magnetization capability and loss control under normal operating conditions.

[0036] In addition to positioning the various magnetically conductive laminations 42, the insulating clamping frame 41 also restricts the degrees of freedom of the magnetically conductive laminations 42. A guide mechanism 9 is provided inside the oil tank 1. The insulating clamping frame 41 slides in conjunction with the guide mechanism 9, allowing the insulating clamping frame 41 to move along a direction closer to or further away from the yoke. In some embodiments, the guide mechanism 9 includes an insulating guide rail fixedly connected to the inner wall of the oil tank 1 and a guide slider fixedly connected to the insulating clamping frame 41. The insulating slider is slidably connected to the insulating guide rail to restrict the degrees of freedom of the insulating clamping frame 41, limiting its movement only in a linear direction closer to or further away from the yoke. In other embodiments, by providing an integrally or fixedly connected column with the same cross-section on the insulating clamping frame 41, and a tube fixedly connected to the inner wall of the oil tank 1, the shape of the tube is adjusted so that the column is inserted into the tube and slides in conjunction with the tube, thereby restricting the degrees of freedom of the insulating clamping frame.

[0037] The insulating clamping frame 41 can be made of epoxy glass cloth board, oil-resistant insulating composite material, aramid reinforced insulating material or other high-strength insulating materials suitable for transformer oil environment.

[0038] The insulated transmission assembly 5 includes an insulated pull rod 51 and a sealing sleeve 52. The insulated pull rod 51 passes through the wall of the oil tank 1, with one end located inside the oil tank 1 and connected to the magnetic conductor array 4, and the other end connected to the drive assembly 6. The insulated pull rod 51 can be made of epoxy fiberglass, aramid-reinforced composite material, oil-resistant insulating composite material, or ceramic insulating material. To improve insulation margin, the outer surface of the insulated pull rod 51 can be provided with an insulating reinforcement layer or a surface structure for increasing creepage distance. The surface structure includes flanges and slots spaced along the axial direction. The insulated pull rod 51 is connected to the magnetic conductor array 4 using an insulated connector to avoid forming unnecessary metal conductive paths.

[0039] The sealing sleeve 52 is disposed between the insulating tie rod 51 and the wall of the oil tank 1, and is used to guide and seal the insulating tie rod 51. The sealing pipe can be a flange compression seal, an O-ring seal, a bellows compensation seal, or a combination thereof. In some embodiments, a guide bushing can be provided inside the sealing sleeve 52 to ensure the coaxiality of the insulating tie rod 51 during reciprocating motion and reduce uneven wear between the insulating tie rod 51 and the sealing element.

[0040] The sealing sleeve 52 includes at least two sealing structures, forming a leakage detection chamber between the two sealing structures. A detection device is connected to the leakage detection chamber to detect the sealing status of the sealing structures. The detection device is located at the opening on the side wall of the oil tank 1 for mounting the insulating pull rod 51, thereby slidably connecting with the sealing sleeve 52. The detection device communicates with a higher-level server to reflect the sealing status of the sealing structures. The detection device includes, but is not limited to, pressure sensors or leakage indicators. The detection principle for the sealing status can vary. If a pressure sensor is used, it is attached to the sealing sleeve 52. When friction increases significantly, the data is compared with the database. If the deviation exceeds the threshold, an alarm is triggered to the maintenance personnel. Taking an oil level detection element as an example, the leakage detection chamber forms a container for receiving oil. The detection end of the oil level detection element extends into the container. By detecting the level of oil flowing into the leakage detection chamber, if the oil level is higher than the threshold, it is determined that maintenance is required, and an alarm is triggered to the maintenance personnel. Alternatively, a more direct leakage indication device can be used, using oil as an indicator. When it detects oil, it communicates with the upper server to warn the maintenance personnel.

[0041] By arranging the drive assembly 6 outside the oil tank 1 and using the insulated pull rod 51 for transmission, this embodiment avoids directly arranging the motor or complex actuator inside the transformer oil tank 1, which helps to reduce the risk of high voltage internal insulation and improves the maintenance convenience of the drive assembly 6.

[0042] The oil tank 1 is also equipped with a position detection element 8 for detecting the position of the magnetic conductor array 4. The position detection element 8 can be at least one of a linear displacement sensor, encoder, magnetostrictive displacement sensor, Hall effect position sensor, or limit switch. The position detection element 8 detects the position of the magnetic conductor array 4. The position detection element 8 communicates with the control module 7, transmitting the obtained position of the high-permeability magnetic components to the control module 7. The control module 7 calculates the air gap distance based on the current position of the position detection element 8. and the distance from the target air gap By comparing the positions, closed-loop control is achieved. Specifically, based on the position of the high-permeability magnetic array provided by the position detection element 8, when it approaches the maximum or minimum air gap distance, the control module 7 adjusts the drive component 6, thereby slowing down the speed of the high-permeability magnetic array when it approaches its travel limit, thus preventing overshoot.

[0043] In some embodiments, the oil tank 1 is further provided with an air gap limiting component to limit the high permeability magnetic array.

[0044] like Figure 1As shown, in order to avoid significantly increasing power consumption under normal conditions and to have sufficient shunt capacity under biased magnetization, the initial parameters of the high-permeability array need to be optimized. The parameters of the high-permeability array are closely related to the initial parameters of the low-frequency transformer, which include initial electromagnetic parameters, structural parameters, and operational constraint parameters. The initial electromagnetic parameters may include rated capacity, rated voltage, rated current, operating frequency, BH curve of core material, design magnetic flux density, number of turns in winding 3, and current direction in winding 3. The structural parameters may include the dimensions of the core main column, the dimensions of the yoke 22, the window dimensions of winding 3, the internal space of the oil tank 1, the installation area on the side of the yoke 22, and the position of the oil flow channel. The operational constraint parameters may include allowable no-load loss, allowable leakage magnetic loss, allowable temperature rise, minimum insulation distance, maximum mechanism stroke, and preset DC biased magnetization conditions.

[0045] Then, a three-dimensional electromagnetic field or multiphysics simulation model of the low-frequency transformer is established. The model includes the core body 2, windings 3, oil tank 1, yoke region 22, magnetic conductor array 4, and air gap region. The core material is described using a nonlinear magnetization curve, and the magnetic conductor array 4 is modeled based on its equivalent magnetic permeability. Different air gap distances are considered. Effective cross-link area Calculate the maximum magnetic flux density of the main core under rated operating conditions and DC bias conditions, considering the thickness of the magnetically conductive lamination 42, the dimensions of the main core column, the dimensions of the side yoke 22, and their installation orientation. No-load loss Leakage loss , bias adjustment margin M, local temperature rise And the driving force F required by the mechanism.

[0046] Next, a surrogate model is constructed based on the finite element simulation samples. The surrogate model can be a Kriging surrogate model, a radial basis function surrogate model, a polynomial response surface model, a Gaussian process regression model, or a neural network surrogate model. The optimization variable can include the air gap distance. The output response may include at least two of the following: the effective linkage area A of the magnetic conductor array 4, the stacking thickness of the magnetic conductor array 4, the size of the main core column, the size of the side yoke 22, and the mounting orientation. The output response may include the maximum magnetic flux density of the main core, no-load loss, leakage loss, bias adjustment margin, temperature rise, and mechanism driving force.

[0047] In one implementation, fitness It can be represented as:

[0048] in, For magnetic leakage loss, For no-load loss, This represents the maximum magnetic flux density of the main core column 21 under DC bias conditions. To preset a safe magnetic flux density threshold, For the temperature rise, This is an evaluation metric for insulation distance constraints. For evaluating the motion constraints of the mechanism, to These are the weighting coefficients. to This is a normalized evaluation function. The weighting coefficients mentioned above can be set according to the capacity, voltage level, operating frequency, insulation requirements, and anti-magnetic requirements of the low-frequency transformer.

[0049] bias adjustment margin It can be determined based on the difference between the magnetic flux density of the main core and the safety threshold under DC bias conditions, expressed as follows:

[0050] in, To preset a safe magnetic flux density threshold, M represents the maximum magnetic flux density of the main core column 21 under DC bias conditions. A larger M indicates a larger bias adjustment margin; when M is less than or equal to zero, it indicates that the magnetic flux density of the main core column 21 has reached or exceeded the preset safety threshold, and this set of structural parameters should not be used as the final design parameters.

[0051] When constructing the proxy model, a physical feature penalty factor is introduced. In this embodiment, the physical feature penalty factor This can also be understood as a saturation boundary sampling enhancement factor. When the surrogate model predicts the magnetic flux density... When the value falls within the critical range of the saturation risk threshold or exceeds the upper limit of the critical range of the saturation risk threshold, the physical feature penalty factor is increased. The weights are adjusted to increase the sampling density of the surrogate model near the magnetic saturation boundary. When Significantly lower When the region is in a safe and flat area, the sampling weight of that region can be reduced, thereby reducing redundant calculations.

[0052] In one implementation, the physical feature penalty factor It can be represented as:

[0053] in, To find the optimal variable vector, The magnetic flux density predicted by the surrogate model. The saturation risk threshold The normalized scale for magnetic flux density For adjustment coefficients, For activation function, For minimum sampling weight, For the maximum sampling weight, and . It can be set according to the magnetization curve of the core material, the design magnetic flux density, and the allowable saturation margin.

[0054] like Figure 5 As shown, Figure 5 The subgraph 'a' represents the penalty factor for lacking this physical feature. Schematic diagram Figure 5 The b-subgraph introduces a physical feature penalty factor. The diagram illustrates the concept, where existing samples are represented by hollow circular points, dashed lines represent the saturation risk threshold, diagonal lines represent the saturation risk threshold interval, solid rectangular points represent newly added samples in this round, dotted areas represent safe zones, and intersecting lines represent saturation dividing lines. When the risk falls into the critical range of the saturation risk threshold, or exceeds the upper limit of the critical range of the saturation risk threshold. Increasing the value makes the active learning addition criterion more inclined to supplement sample points near the magnetic saturation boundary; when Significantly lower hour, )near This reduces redundant sampling in the safe and flat regions. In this way, the surrogate model optimization process can pay more attention to the combination of structural parameters near the saturation boundary, avoiding optimization results that remain only in safe but overly conservative regions.

[0055] In one implementation, the point-addition criteria are actively learned. It can be represented as:

[0056] in, The expected improvement function is used to characterize the potential contribution of sample points to the improvement of the optimization objective; is the physical failure probability, used to characterize the likelihood of a sample point approaching saturation, overheating, or insulation risk areas; W(x) is the physical feature penalty factor. In each iteration, select... Larger candidate sample points are recalculated using the finite element method, and the recalculation results are added to the training sample set to update the surrogate model.

[0057] After iterative optimization, one or more sets of structural parameters that satisfy the constraints are output, including the initial maximum air gap. Minimum working air gap 4. Effective linkage area of ​​the magnetic conductor array The parameters include the alloy array stack thickness, mounting orientation, and rated thrust of drive assembly 6. These parameters guide the specific structural design and control strategy setting of the adaptive magnetic shunt device.

[0058] like Figure 2As shown, during the operation of the low-frequency transformer, the control module 7 collects the DC current component on the grid side in real time. and the magnetic flux density of the main iron core .

[0059] Grid-side DC current component The current signal can be obtained through a zero-flux current transformer, Hall effect current sensor, fiber optic current sensor, or current sampling algorithm. Control module 7 can perform low-pass filtering, moving average, Fourier decomposition, or other signal processing on the acquired current signal to extract the DC component and suppress interference.

[0060] Main core magnetic flux density This can be obtained through induction coils, magnetic flux sensors, fiber optic magnetic field sensors, or voltage integration algorithms. Control module 7, based on... Calculate its rate of ascent The system combines load current, excitation current harmonic content, oil temperature, and the current position of the magnetic conductor array 4 to determine whether the core is close to saturation.

[0061] When the DC current component on the grid side The current exceeds the preset DC current threshold, and the magnetic flux density of the main iron core... When the magnetic flux density exceeds the preset threshold or approaches the saturation critical value, control module 7 determines that the low-frequency transformer is in a state of DC bias risk. rise but The saturation threshold has not yet been reached, so control module 7 can enter an early warning state, increase the sampling frequency, and prepare to execute the magnetic shunt action. If... and If all the operating conditions are met, the control module 7 enters the operating state and sends adjustment commands to the drive component 6.

[0062] To prevent the drive component 6 from frequently operating near the threshold, the control module 7 sets a trigger threshold and a release threshold. The release threshold is lower than the trigger threshold to create hysteresis control. When... and Magnetic shunt adjustment is initiated when the condition is higher than the trigger condition; when Below the release threshold The mechanism is only allowed to reset after the temperature drops below the safety threshold and remains below the preset time.

[0063] In one implementation, the hysteresis judgment logic is as follows: when Greater than the trigger threshold and Greater than the trigger magnetic flux density threshold When, activate magnetic shunt adjustment; when Less than the release threshold and Less than the release magnetic flux threshold And continue to reach the preset time. Afterwards, the mechanism is allowed to reset, whereby... .

[0064] In one implementation, the control module 7 determines the magnetic flux density of the main iron core. rate of increase Adjust the operating speed of drive component 6. When When the rate exceeds the preset threshold, it indicates that the magnetic flux of the iron core is rapidly approaching the saturation region. The control module 7 then controls the drive component 6 to rapidly reduce the air gap distance at the first speed. .when Less than or equal to the preset rate threshold and If the air gap distance is still higher than the warning threshold, the control module 7 controls the drive component 6 to continue reducing the air gap distance at the second speed. The second speed is less than the first speed. A graded action strategy can balance rapid response and mechanical shock control.

[0065] In another implementation, the control module 7 according to Calculate the target air gap distance from the current position of the magnet array 4 Generally speaking, The larger, The closer to the saturation critical value, The larger, the better The smaller; The smaller The further away from the saturation critical value, the more... The larger.

[0066] In one implementation, the target air gap distance It can be represented as:

[0067] in, This represents the initial maximum air gap. The DC current trigger threshold is... For the safety magnetic flux density threshold, To control the gain, sat[ ] is the limiting function, used to make the gain control... Stay to between. This represents the minimum working air gap. The above expression is only one implementation method; in actual control, lookup table control, segmented control, proportional control, or model predictive control can also be used to determine the target air gap distance. .

[0068] Control module 7 moves the magnet array 4 to the target air gap distance through closed-loop position control. The corresponding position. When Once the air gap distance falls below the safety threshold, control module 7 stops further reducing the air gap distance. And control the drive component 6 to maintain its current position. If subsequently... Continue to increase or Upon further ascent, control module 7 can further reduce the air gap distance. until the target air gap is reached. or minimum working air gap .

[0069] Once the risk of DC bias is eliminated, the control module 7 controls the drive assembly 6 to reverse its operation, causing the magnetic conductor array 4 to move away from the side yoke 22 of the iron core body 2 and return to its initial maximum air gap position. .

[0070] Specifically, when the grid-side DC current component Below the release threshold, the magnetic flux density of the main iron core Once the DC bias falls below the safety threshold and remains below it for a preset time, control module 7 determines that the risk of DC bias has been eliminated. Subsequently, control module 7 drives the magnetic conductor array 4 away from the side yoke 22 at a reset speed lower than the input speed. The reset speed is preferably slow to avoid magnetic flux disturbance caused by rapid changes in the air gap distance.

[0071] When the magnet array 4 returns to its initial maximum air gap position Then, the drive component 6 stops operating and enters a holding or locked state. Under no DC bias conditions, the magnetic conductor array 4 remains in... The location of the magnetic shunt circuit results in a higher equivalent magnetic reluctance, thereby reducing the impact of the adaptive magnetic shunt device on the rated main magnetic flux and reducing additional no-load losses.

[0072] To improve the reliability of equipment operation, this embodiment also includes an anomaly protection step. When the control module 7 detects an abnormal position feedback, abnormal drive current, jamming of the insulating transmission component 5, abnormal limit signal, seal leakage, excessive oil temperature, or continuous excessive magnetic flux density of the main iron core, the control system enters a protection state.

[0073] When an abnormal increase in drive current is detected, no change in position feedback after the drive command is issued, the position change speed is lower than the preset range, or the limit signal is abnormal, the control module 7 determines that the drive mechanism or transmission mechanism may be stuck, out of step, or have a mechanical fault. At this time, the control module 7 stops the drive component 6 from operating and issues an alarm signal. Depending on the current magnetic flux state, the control module 7 can choose to maintain the current position or attempt to return to the initial maximum air gap position. .

[0074] When the leakage detection chamber detects oil leakage, abnormal pressure or oil level in the sealing sleeve 52, the control module 7 issues a sealing abnormality alarm and restricts or stops unnecessary mechanical actions to prevent the sealing failure from escalating.

[0075] When the magnet array 4 has moved to the minimum working air gap position The magnetic flux density of the main iron core If the current DC bias intensity remains above the safety threshold, it indicates that the current DC bias intensity may exceed the adjustment capability of the adaptive magnetic shunt device. At this time, the control module 7 issues a severe bias alarm and can coordinate with the upper-level protection system to take measures such as reducing the load, adjusting the operating mode, cutting off the DC disturbance source, or shutting down for maintenance.

[0076] When the DC current sensor, magnetic flux sensor, or position detection element 89 experiences signal loss, abrupt changes, contradictions, or exceeds the physically reasonable range, the control module 7 determines that the sensor is abnormal. For single-channel abnormalities, a backup channel can be switched or an estimated value can be used for control; for multi-channel abnormalities, the control module 7 enters a conservative protection mode, limiting the operation of the drive component 6 to prevent malfunctions.

[0077] By modeling and simulating and introducing DC current, the obtained magnetic flux density curve and air gap distance curve are as follows: Figure 6 As shown, in Figure 6 A DC component is introduced into subgraph a, and at the same time Figure 6 The b-subplot shows the corresponding changes in the air gap distance, thereby maintaining... Figure 6 The magnetic flux density variation of the c-subgraph is nearly constant. This demonstrates that the method described in this application has good anti-DC bias magnetization capability and can effectively adjust the position of the magnetic conductor array 4 to maintain the magnetic flux density of the main iron core within a safe range.

[0078] Therefore, this invention can achieve a good balance between low loss under normal operating conditions, strong current shunting under biased magnetic conditions, high voltage insulation safety, engineering feasibility and optimized design efficiency, and is suitable for low frequency power transmission, offshore wind power grid connection, flexible AC power transmission and other low frequency transformer applications that are easily affected by DC biased magnetic fields.

Claims

1. A low-frequency transformer resistant to DC bias, comprising an oil tank and a core body, wherein the core body is disposed inside the oil tank, and the core body includes a main core column and a side yoke, characterized in that, The low-frequency transformer includes an adaptive magnetic shunt structure, which includes a magnetic conductor array, an insulating transmission assembly, and a drive assembly. The drive assembly is located outside the oil tank and is connected to the magnetic conductor array through an insulating transmission assembly that penetrates the side wall of the oil tank. Under the drive of the drive assembly, the insulating transmission assembly moves the magnetic conductor array closer to or further away from the yoke to change the magnetic resistance of the magnetic shunt circuit on the yoke side.

2. The low-frequency transformer against DC bias as described in claim 1, characterized in that, The magnetic conductor array includes an insulating clamping frame and magnetic conductor stacks. The magnetic conductors that make up the magnetic conductor stacks are insulated from each other, and the magnetic conductors are stacked along the magnetic flux direction of the yoke to form the magnetic conductor stacks.

3. A low-frequency transformer resistant to DC bias magnetism according to claim 1, characterized in that, The oil tank is equipped with a guide mechanism. The insulating clamping frame slides with the guide mechanism, allowing the insulating clamping frame to move in a direction that is closer to or further away from the yoke.

4. A low-frequency transformer resistant to DC bias magnetism according to claim 1, characterized in that, The insulated transmission assembly includes an insulated pull rod and a sealing sleeve. The insulated pull rod passes through the side wall of the oil tank. One end of the insulated pull rod is located inside the oil tank and connected to the magnetic conductor array. The other end of the insulated pull rod is connected to the drive assembly. The sealing sleeve is disposed between the insulated pull rod and the side wall of the oil tank for guiding and sealing the insulated pull rod.

5. A low-frequency transformer resistant to DC bias magnetism according to claim 1, characterized in that, The fuel tank is also equipped with a position detection element for detecting the position of the magnetic conductor array.

6. A control method for a low-frequency transformer resistant to DC bias, characterized in that, The low-frequency transformer with DC bias resistance as described in any one of claims 1 to 5 includes the following steps: Obtain the initial electromagnetic parameters, structural parameters, and operational constraint parameters of the low-frequency transformer, and obtain the initial structural parameters of the adaptive magnetic shunt structure; Collect the grid-side DC current component during the operation of the low-frequency transformer. and the magnetic flux density of the main iron core ; According to the grid-side DC current component and the magnetic flux density of the main iron core Determine whether the low-frequency transformer is in a state of DC bias risk; In response to the assessment that the low-frequency transformer is in a state of DC bias risk, the drive assembly is controlled to operate, driving the insulated transmission assembly to move the magnetic conductor array closer to the side yoke of the converter, thereby reducing the air gap distance of the core body. and increase the effective crosslinking area of ​​the iron core body A ; In response to the determination that the low-frequency transformer is no longer in a state of DC bias risk, the drive assembly is controlled to drive the insulating transmission assembly to move the magnetic conductor array away from the converter's side yoke until it returns to the initial maximum air gap position. .

7. The control method for a low-frequency transformer with anti-DC bias magnetization according to claim 6, characterized in that, The initial structural parameters of the adaptive magnetic shunt structure are obtained through surrogate model optimization, which includes: Define air gap distance Effective linkage area of ​​the magnetic conductor array A At least two of the following should be used as optimization variables: the thickness of the magnetic conductor array stack, the size of the iron core main column, the size of the side yoke, and the installation pose. Construct a fitness function that includes at least two of the following: leakage flux loss term, no-load loss term, bias magnetic adjustment margin term, temperature rise constraint term, insulation distance constraint term, and mechanism motion constraint term; Proxy models are constructed based on finite element simulation samples; The fitness function is solved based on the surrogate model, and the initial structural parameters of the adaptive magnetic shunt structure are output.

8. The control method for a low-frequency transformer resisting DC bias magnetization according to claim 7, characterized in that, in When constructing the surrogate model, a physical feature penalty factor W(x) is introduced. When the magnetic flux density predicted by the surrogate model falls into the critical range of the saturation risk threshold or exceeds the upper limit of the critical range of the saturation risk threshold, the weight of the physical feature penalty factor W(x) is increased to improve the sampling density of the surrogate model near the magnetic saturation boundary.

9. The control method for a low-frequency transformer resisting DC bias magnetization according to claim 6, characterized in that, According to the main iron core column rate of increase Adjust the drive speed of the drive component, when When the speed exceeds a preset rate threshold, the driving speed of the driving component is the first speed; when... Less than or equal to the preset rate threshold and If the speed is still higher than the warning threshold, the driving speed of the drive component is the second speed, which is less than the first speed.

10. The control method for a low-frequency transformer resisting DC bias magnetization according to claim 6, characterized in that, Based on the grid-side DC current component Idc and the main core magnetic flux density and the rate of change of magnetic flux density in the main iron core Determine the target air gap distance And through closed-loop position control, the magnetic conductor array is moved to the corresponding position; when the grid-side DC current component Below the release threshold, main core magnetic flux density After the air gap falls below a safety threshold and remains below it for a preset time, the magnetic conductor array is controlled to return to its initial maximum air gap position. .

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