A low-loss electromagnetic system for an energy storage step-up transformer

Abstract

The application discloses a low-loss electromagnetic system of an energy storage step-up transformer, and relates to the technical field of transformer electromagnetic design.The system comprises a dynamic load sensing and electromagnetic parameter adaptive module, a harmonic loss suppression and magnetic flux regulation module, and a thermal-magnetic-force collaborative optimization design module.The dynamic load sensing module identifies the charging and discharging conditions in real time, and adaptively adjusts the magnetic flux density through the magnetic flux regulation winding tap connection tap.The harmonic loss suppression and magnetic flux regulation module uses a nanocrystalline bypass magnetic column and an adjustable air gap to realize the spatial decoupling of the fundamental wave and harmonic magnetic flux, and uses winding parallel branch transposition to suppress circulating loss.The thermal-magnetic-force collaborative optimization module establishes a full-loss analysis model, inversely optimizes the electromagnetic parameters with the hotspot temperature rise as the constraint, and collaboratively designs the short-circuit resistance and compact layout.The application effectively reduces the loss and temperature rise of the energy storage transformer under strong dynamic and high harmonic conditions, and improves the short-circuit resistance and compact installation adaptability.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic design technology for transformers, and in particular to a low-loss electromagnetic system for an energy storage step-up transformer. Background Technology

[0002] With the rapid growth of new energy installed capacity, electrochemical energy storage has become a key support for building new power systems. As the core equipment connecting the energy storage converter and the medium-voltage power grid, the energy storage step-up transformer's loss characteristics and operational reliability directly determine the overall efficiency of the energy storage system. However, existing energy storage transformers face severe challenges in practical applications: First, frequent charging and discharging switching of the energy storage system causes the transformer to endure severe load impacts, and traditional electromagnetic parameters based on steady-state conditions are difficult to adapt to strong dynamic load environments; second, the PWM voltage output by the energy storage converter is rich in high-frequency harmonics, generating significant additional losses in the core and windings, causing the total transformer loss to increase significantly compared to the power frequency condition; third, the compact integration space of the integrated inverter-step-up unit limits the transformer size, highlighting the contradiction between low loss, low temperature rise, and high reliability.

[0003] Therefore, it is necessary to design a low-loss electromagnetic system for energy storage step-up transformers. Through dynamic load sensing and adaptive adjustment of electromagnetic parameters, active suppression of high-frequency harmonic flux, and coordinated optimization of thermo-magnetic-force multi-physics fields, the technical challenges of low-loss and high-reliability operation of energy storage transformers under strong dynamic, high-harmonic, and compact space conditions can be fundamentally solved. Summary of the Invention

[0004] This invention proposes a low-loss electromagnetic system for an energy storage step-up transformer. Addressing the problems of high loss, large temperature rise, and insufficient short-circuit withstand capability of existing energy storage transformers under conditions of frequent start-stop, high harmonic content, and compact integration, a three-in-one architecture is constructed, which integrates dynamic electromagnetic parameter self-adaptation, active harmonic loss suppression, and thermo-magnetic-force multi-physics field collaborative optimization. This enables the energy storage transformer to operate efficiently and with low loss across the entire operating range.

[0005] The energy storage step-up transformer of this invention includes a transformer body, which comprises a transformer core, a low-voltage winding, a high-voltage winding, a flux control winding, an insulation structure, and an oil tank heat dissipation structure. The low-voltage winding is electrically connected to the energy storage converter, and the high-voltage winding is electrically connected to the medium-voltage power grid. The core forms a closed path for the magnetic flux, and the flux control winding is connected in series to the main magnetic circuit and is equipped with taps. This invention is an improvement upon the structure of this transformer body.

[0006] Based on the above-mentioned transformer body structure, the present invention provides a low-loss electromagnetic system for an energy storage step-up transformer. The system also includes the following three modules that cooperate with the transformer body: a dynamic load sensing and electromagnetic parameter adaptive module, a harmonic loss suppression and magnetic flux control module, and a thermal-magnetic-force collaborative optimization design module.

[0007] The dynamic load sensing and electromagnetic parameter adaptive module is electrically connected to the transformer's voltage sensing unit, current sensing unit, and temperature sensing unit. It collects real-time data on the transformer's primary and secondary voltages, currents, and winding hotspot temperatures of the low-voltage and high-voltage windings to construct a charging and discharging condition identification model for the energy storage system. This module processes the collected real-time data through a built-in lightweight time-series classification network, outputs the identification result of the current operating condition, and dynamically adjusts the equivalent excitation impedance through the taps of the flux control winding based on the identification result, so that the transformer's flux density adapts to load changes. The module also predicts the risk of transient overexcitation based on the load change rate and pre-adjusts the flux control strategy to suppress inrush current.

[0008] The harmonic loss suppression and flux control module is located between the transformer core and the low-voltage and high-voltage windings. It includes a high-frequency harmonic flux bypass structure, composed of a closed magnetic circuit made of nanocrystalline high-permeability thin strip material, providing a low-resistivity path for high-frequency harmonic flux and spatially decoupling the fundamental and harmonic fluxes. The module also includes a low-voltage winding harmonic loss suppression structure, which divides the low-voltage winding into several parallel branches and sets cross-transposition between them, balancing the impedance of each branch at high frequencies and suppressing circulating current losses. This module receives real-time operating condition identification results from the dynamic load sensing and electromagnetic parameter adaptive module. Based on the PWM harmonic spectrum distribution characteristics corresponding to the operating condition category, it dynamically adjusts the saturation depth of the flux bypass structure to achieve active suppression of harmonic losses.

[0009] The thermal-magnetic-force co-optimization design module, integrated into the structural design of the transformer, includes: a loss-temperature rise coupling calculation submodule based on the operating condition spectrum, which establishes a full-loss analytical model covering core loss, winding DC loss, and high-frequency additional loss, and performs inverse optimization of electromagnetic parameters with the winding hot spot temperature rise of the low-voltage and high-voltage windings as constraints; a short-circuit electromagnetic-structural co-design submodule, which calculates the winding electrodynamic force based on the leakage magnetic field distribution under bidirectional short-circuit conditions, and optimizes the radial and axial dimensional ratios and clamping force distribution of the low-voltage and high-voltage windings with the winding mechanical strength as constraints; and an integrated compact layout submodule, which uses the available installation space of the transformer as a boundary condition, and determines the optimal space occupation of the transformer body and the layout of the oil tank heat dissipation channel through multi-physics field iterative optimization of electromagnetic field, temperature field, and flow field.

[0010] Furthermore, the specific implementation of the high-frequency harmonic flux bypass structure in the harmonic loss suppression and flux control module is as follows:

[0011] Step B1: A bypass magnetic column made of nanocrystalline high permeability thin strips is set next to the main magnetic column of the transformer core. The bypass magnetic column is connected to the main magnetic column through an adjustable air gap.

[0012] Step B2: The fundamental magnetic flux flows along the main magnetic column because the magnetic reluctance of the bypass magnetic column is much greater than that of the main magnetic column. The high-frequency harmonic magnetic flux forms a low magnetic reluctance path in the bypass magnetic column due to the eddy current shielding effect, thereby achieving frequency domain decoupling of the fundamental and harmonic magnetic fluxes.

[0013] Step B3: An air gap adjustment mechanism driven by shape memory alloy is embedded in the bypass magnetic column. This mechanism adjusts the width of the adjustable air gap according to the current harmonic spectrum distribution characteristics to change the saturation depth of the bypass magnetic column, so that the harmonic flux bypass effect remains optimal within the operating frequency band.

[0014] Step B4: The bypassed harmonic flux forms a closed loop in the bypass magnetic column, and its energy is dissipated in the damping layer of the bypass magnetic column in the form of eddy current loss, so as to avoid the harmonic flux from passing through the main magnetic column and causing additional core loss.

[0015] Furthermore, the specific implementation of the low-voltage winding harmonic loss suppression structure is as follows:

[0016] Step C1: Divide the low-voltage winding into multiple parallel branches along the radial direction, with each branch using the same conductor cross-sectional area and number of turns;

[0017] Step C2: Set up a complete transposition structure between each parallel branch so that each branch occupies the inner, middle and outer radial positions in different positions in the winding height direction, ensuring that the leakage flux integral value of each branch is equal.

[0018] Step C3: Install impedance balancing reactors at the transposition nodes of each branch. The inductance value of the reactor is determined offline based on the high-frequency impedance difference between branches to further suppress the circulating current in the branches at high frequencies.

[0019] Step C4: The high-voltage winding adopts a graded insulation structure, and an electrostatic shielding layer is set in the inner layer near the iron core. This shielding layer is grounded to reduce the high-frequency resonance loss caused by the high-voltage winding's capacitance to ground.

[0020] Furthermore, the total loss analytical model in the thermal-magnetic-mechanical collaborative optimization design module is as follows:

[0021] Core losses consist of three components: hysteresis loss, classical eddy current loss, and abnormal loss. Each loss is related to the operating frequency, magnetic flux density amplitude, and material properties. Hysteresis loss is the product of the frequency and the magnetic flux density amplitude exponent. Classical eddy current loss is proportional to the square of the frequency and the square of the magnetic flux density amplitude. Abnormal loss is proportional to the 1.5th power of the frequency and the 1.5th power of the magnetic flux density amplitude.

[0022] The total winding losses of the low-voltage and high-voltage windings include DC losses, skin effect losses, proximity effect losses, and circulating current losses. Among them, skin effect losses and proximity effect losses are related to the harmonic spectrum distribution and are determined by superimposing the harmonic current components. Circulating current losses are caused by the unbalanced electromotive force between the parallel branches of the low-voltage winding and are calculated based on the deviation of the current in each branch from the average current.

[0023] With the constraint that the hot spot temperature of the low-voltage winding and the high-voltage winding does not exceed the allowable temperature of the insulation material, the optimization objective is to minimize the total loss, and the optimization variables are the magnetic flux density amplitude, the current density of the low-voltage winding and the high-voltage winding, the conductor diameter and the winding height. An inverse optimization objective function is constructed. The constraints of the optimization problem also include the volume constraint that the total volume of the transformer body does not exceed the volume constraint under the integrated compact layout.

[0024] By adopting the above solution, the beneficial effects achieved by the present invention are as follows:

[0025] This invention constructs a closed-loop electromagnetic design architecture of "dynamic sensing-harmonic suppression-cooperative optimization." The dynamic load sensing module identifies operating conditions in real time and outputs adjustment commands; the harmonic suppression module actively adjusts the magnetic flux bypass characteristics based on these commands; and the cooperative optimization module provides a full-condition parameter benchmark and feeds it back to the first two modules, forming an information closed loop. This overcomes the limitations of traditional transformer electromagnetic parameter design based on a single rated operating condition. The dynamic load sensing and electromagnetic parameter adaptive modules can identify the charging and discharging conditions of the energy storage system in real time and dynamically adjust the magnetic flux density setpoint, enabling the transformer to maintain minimum loss operation over a wide load range. This effectively solves the efficiency degradation problem caused by frequent start-ups and shutdowns and severe load fluctuations in energy storage systems.

[0026] This invention introduces a high-frequency harmonic flux bypass structure and a low-voltage winding harmonic loss suppression structure, achieving frequency domain decoupling between the fundamental flux and harmonic flux in space. This fundamentally suppresses the additional core losses caused by PWM harmonic injection and the high-frequency additional losses in the low-voltage and high-voltage windings. Compared with traditional solutions that rely on filter reactors, this invention integrates harmonic suppression functionality into the transformer's electromagnetic structure, eliminating the need for additional filtering equipment and reducing system size and cost.

[0027] This invention integrates losses, temperature rise, short-circuit withstand capability, and compact layout into a unified optimization framework through a thermo-magnetic-mechanical collaborative optimization design module. The full-loss analytical model allows the electromagnetic parameter design to be directly constrained by the temperature rise of the winding hot spots in the low-voltage and high-voltage windings, avoiding the fragmented process of "calculating losses first and then checking temperature rise" in traditional design. The electromagnetic-structural collaborative design for short-circuit withstand capability ensures the mechanical reliability of the transformer under bidirectional short-circuit impact. The integrated compact layout submodule achieves the best balance of electromagnetic, thermal, and mechanical performance within a limited space through multi-physics iterative optimization. Attached Figure Description

[0028] Figure 1 This is a block diagram of the module architecture of a low-loss electromagnetic system for an energy storage step-up transformer proposed in this invention.

[0029] Figure 2 This is a schematic diagram of the high-frequency harmonic flux bypass structure in Embodiment 2 of the present invention. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0031] Example 1:

[0032] according to Figure 1 This invention provides a low-loss electromagnetic system for an energy storage step-up transformer, which is particularly suitable for compact transformer installation scenarios. The system includes a dynamic load sensing and electromagnetic parameter adaptive module, a harmonic loss suppression and magnetic flux control module, and a thermal-magnetic-force collaborative optimization design module.

[0033] The dynamic load sensing and electromagnetic parameter adaptive module, the harmonic loss suppression and magnetic flux control module, and the thermo-magnetic-force co-optimization design module are connected via industrial fieldbus or hard-wired signals. The dynamic load sensing and electromagnetic parameter adaptive module outputs the operating condition identification results to the harmonic loss suppression and magnetic flux control module in the form of digital signals. The thermo-magnetic-force co-optimization design module stores the optimized electromagnetic parameter reference in the memory of each module in the form of a data table for dynamic adjustment and harmonic suppression.

[0034] The dynamic load sensing and electromagnetic parameter adaptive module is electrically connected to the transformer's voltage sensing unit, current sensing unit, and temperature sensing unit. It collects real-time data on the transformer's primary and secondary voltages, currents, and the hot spot temperatures of the low-voltage and high-voltage windings. This module incorporates a lightweight time-series classification network, using a sequence of operating condition feature vectors within a sliding time window as input to identify the current operating condition category (no-load standby, light-load charging, heavy-load charging, light-load discharging, heavy-load discharging, and power surge transition state). Based on the collected voltage, current, and temperature data, the lightweight time-series classification network extracts features such as the active power change rate, reactive power, total harmonic distortion rate of current, voltage deviation rate, and the winding temperature rise rate of the low-voltage and high-voltage windings. After network inference, the module outputs the identification result of the current operating condition category. Based on the identification result, the module dynamically adjusts the equivalent excitation impedance through the arc-free switching mechanism of the tap of the flux control winding (thyristor-assisted mechanical switch or vacuum circuit breaker in conjunction with transition resistor), so that the transformer flux density adapts to the load change. When a power change transient state is detected, the module predicts the risk of transient overexcitation based on the load change rate and pre-adjusts the flux control strategy to suppress the peak excitation inrush current. The transient overexcitation risk prediction adopts a threshold judgment method based on the load change rate: when the absolute value of the active power change rate exceeds 30% / s of the rated power, it is judged that there is a risk of transient overexcitation, and the tap pre-switching of the flux control winding is performed in advance.

[0035] The harmonic loss suppression and flux control module is located between the transformer core and the low-voltage and high-voltage windings. This module consists of two parts: a high-frequency harmonic flux bypass structure and a low-voltage winding harmonic loss suppression structure. The high-frequency harmonic flux bypass structure is composed of bypass magnetic pillars made of nanocrystalline high-permeability thin strips and an adjustable air gap, providing a low magnetic reluctance path for high-frequency harmonic flux and spatially decoupling the fundamental flux from the harmonic flux. An air gap adjustment mechanism driven by a shape memory alloy is embedded in the bypass magnetic pillar, which can dynamically adjust the saturation depth of the bypass magnetic pillar according to the current harmonic spectrum distribution characteristics. The low-voltage winding harmonic loss suppression structure suppresses the circulating current loss of the branches at high frequencies by dividing the low-voltage winding into several parallel branches and setting a fully transposed structure and an impedance balancing reactor.

[0036] The thermal-magnetic-mechanical co-optimization design module is integrated into the structural design of the transformer. This module includes a loss-temperature rise coupling calculation submodule based on the operating condition spectrum, a short-circuit electromagnetic-structural co-design submodule, and an integrated compact layout submodule. The loss-temperature rise coupling calculation submodule establishes a full-loss analytical model covering core losses, winding DC losses, and high-frequency additional losses, and performs inverse optimization of electromagnetic parameters with the winding hot spot temperature rise of the low-voltage and high-voltage windings as constraints. The short-circuit electromagnetic-structural co-design submodule calculates the electrodynamic forces of the low-voltage and high-voltage windings based on the leakage magnetic field distribution under bidirectional short-circuit conditions, and optimizes the radial and axial dimensional ratios and clamping force distribution of the low-voltage and high-voltage windings with the winding mechanical strength as constraints. The integrated compact layout submodule uses the available installation space of the transformer as a boundary condition, and determines the optimal space occupation of the transformer body and the layout of the oil tank heat dissipation channel through multi-physics field iterative optimization of electromagnetic field, temperature field, and flow field.

[0037] The three modules mentioned above work together through the following process to achieve low-loss operation of the energy storage step-up transformer:

[0038] First, the dynamic load sensing and electromagnetic parameter adaptive module identifies the operating conditions of the energy storage system in real time through a lightweight time-series classification network, and outputs the current operating condition category identifier and the corresponding optimal magnetic flux density setting value.

[0039] Secondly, the harmonic loss suppression and flux control module dynamically adjusts the saturation depth of the high-frequency harmonic flux bypass structure and the winding impedance equalization parameters according to the PWM harmonic spectrum distribution information corresponding to the operating condition category identifier, thereby achieving active suppression of harmonic losses.

[0040] Finally, the thermo-magnetic-mechanical co-optimization design module provides the electromagnetic parameter optimization benchmark and structural design constraints for the first two modules across the entire operating range, ensuring the effectiveness of dynamic adjustment and harmonic suppression throughout the entire life cycle.

[0041] Example 2:

[0042] This embodiment is based on Embodiment 1 and focuses on explaining the working principle and parameter design method of the high-frequency harmonic flux bypass structure.

[0043] according to Figure 2 The specific implementation of the high-frequency harmonic flux bypass structure is as follows:

[0044] A bypass magnetic column is arranged parallel to the main magnetic column of the transformer core. The bypass magnetic column is made of nanocrystalline high permeability thin strip (grade 1K107, initial permeability not less than 80000, saturation magnetic induction intensity of about 1.25 T) with a thickness of 0.02 mm. The bypass magnetic column is connected to the main magnetic column through an adjustable air gap. The width of the adjustable air gap is controlled by a shape memory alloy actuator, and the adjustment range is 0.1 mm to 2.0 mm.

[0045] The fundamental magnetic flux (50 Hz) flows along the main magnetic column because the magnetic reluctance of the bypass column is much greater than that of the main magnetic column; the high-frequency harmonic magnetic flux (2 kHz~10 kHz) forms a low magnetic reluctance path in the bypass column due to the high-frequency and low-loss characteristics and eddy current shielding effect of the nanocrystalline thin strip, thereby achieving frequency domain decoupling between the fundamental and harmonic magnetic fluxes.

[0046] The operating condition category identifier output by the dynamic load sensing and electromagnetic parameter adaptive module is first sent to the operating condition-harmonic spectrum mapping unit built into the harmonic loss suppression and magnetic flux control module. This unit stores a table of PWM harmonic spectrum characteristic parameters corresponding to typical operating conditions of the energy storage system, or has a built-in analytical mapping model (e.g., a harmonic analytical formula based on PWM double Fourier series analysis) that calculates the harmonic spectrum distribution based on operating condition characteristics (including modulation ratio, carrier ratio, and power factor angle). This model covers the carrier frequency under operating conditions such as no-load standby, light-load charging, heavy-load charging, light-load discharging, heavy-load discharging, and power transient states. The main harmonic order and its corresponding amplitude percentage are identified. The mapping unit obtains the corresponding harmonic spectrum distribution characteristic parameters based on the received current operating condition category identifier, and converts these parameters into an air gap width adjustment command, which is then sent to the control circuit of the shape memory alloy actuator. The control circuit outputs a corresponding excitation current to the shape memory alloy actuator according to the command, causing the actuator to operate and change the width of the adjustable air gap between the bypass magnetic column and the main magnetic column, thereby dynamically adjusting the saturation depth of the bypass magnetic column so that the harmonic flux bypass effect adapts to the harmonic spectrum distribution under the current operating condition. The response time of the entire signal link from operating condition identification to air gap adjustment completion is less than 100 ms, enabling real-time adjustment in response to changes in the operating condition of the energy storage system.

[0047] The width of the adjustable air gap is dynamically adjusted according to the current harmonic spectrum distribution characteristics output by the above process. When a high proportion of harmonic components is detected near the switching frequency, the shape memory alloy driver shrinks, reducing the width of the adjustable air gap, increasing the saturation depth of the bypass magnetic column, and widening the effective bandwidth of the harmonic flux bypass. When the harmonic components are low, the width of the adjustable air gap is increased, reducing the saturation degree of the bypass magnetic column and reducing the eddy current loss of the bypass magnetic column itself.

[0048] The bypassed harmonic flux forms a closed loop in the bypass magnetic column, and its energy is dissipated in the damping layer of the bypass magnetic column in the form of eddy current loss. The damping layer is made of a high resistivity alloy material (Fe-Cr-Al alloy) with a thickness of 0.5 mm. It is set between the laminations of the bypass magnetic column, which can effectively dissipate harmonic energy and prevent the harmonic flux from passing through the main magnetic column and causing additional core loss.

[0049] Actual measurements show that, under typical energy storage system operating conditions (PWM carrier frequency 5 kHz, harmonic distortion rate approximately 8%), this high-frequency harmonic flux bypass structure can reduce the high-frequency additional loss of the iron core by approximately 42% and the total transformer loss by approximately 18%.

[0050] Example 3:

[0051] This embodiment is based on Embodiment 1 and focuses on illustrating the workflow of the thermal-magnetic-force collaborative optimization design module.

[0052] The thermal-magnetic-mechanical collaborative optimization design module achieves global optimization of the electromagnetic parameters of the energy storage transformer through the following steps:

[0053] Step F1: Input design boundary conditions, including transformer rated capacity, voltage level, short-circuit impedance requirements, insulation class, available space volume constraints (available installation space for the transformer), and operating condition spectrum (obtained based on daily charge and discharge curves of typical energy storage power stations).

[0054] Step F2: Perform loss-temperature rise coupling calculation; establish a full loss analytical model covering core loss, winding DC loss, and high-frequency additional loss, core loss. Due to hysteresis loss Classical eddy current loss and abnormal losses Three components:

[0055] ;

[0056] in: ;

[0057] In the formula, The operating frequency is set to 50 Hz for the fundamental component and the corresponding harmonic frequency for each harmonic component. The magnitude of the magnetic flux density. This is the hysteresis loss coefficient. The Steinmetz exponent and the two together determine the characteristics of the hysteresis loop area as a function of frequency and magnetic flux density. The eddy current loss coefficient is proportional to the square of the material's electrical conductivity and the thickness of the laminate. The abnormal loss coefficient characterizes the additional losses caused by microscopic magnetization processes such as domain wall displacement.

[0058] For the 30ZH120 high magnetic orientation silicon steel sheet used (thickness) resistivity The above material property parameters were determined experimentally using the Epstein square method and then fitted using nonlinear least squares fitting. Their values ​​are as follows: , , , ;

[0059] Total winding losses of low-voltage and high-voltage windings Including DC losses In addition to high-frequency additional losses, high-frequency additional losses include skin effect losses. Proximity effect loss and circulating losses ,Right now:

[0060] ;

[0061] Skin effect loss and proximity effect loss Calculate as follows:

[0062] ;

[0063] ;

[0064] in, DC resistance of the winding; The highest harmonic order under consideration; and These are the skin effect coefficient and the proximity effect coefficient, respectively, both being frequency coefficients. The function; For the first RMS value of subharmonic current;

[0065] Circulation loss Caused by the unbalanced electromotive force between the parallel branches of the low-voltage winding, its calculation formula is:

[0066] ;

[0067] In the formula, This represents the number of parallel branches of the low-voltage winding. For the first The effective value of the current in each branch; This represents the effective value of the total current in the low-voltage winding.

[0068] The total loss model is embedded into the thermal network model to calculate the winding hot spot temperatures of the low-voltage and high-voltage windings. The thermal network model divides the transformer into multiple thermal nodes, including the core, low-voltage winding, high-voltage winding, insulation layer, and tank shell. The nodes are connected by thermal resistance and thermal capacity, and the node temperature is determined by the heat loss source and the heat dissipation boundary conditions.

[0069] Step F3: Perform reverse optimization of electromagnetic parameters; using the winding hot spot temperatures of the low-voltage and high-voltage windings. Not exceeding the allowable insulation temperature As a hard constraint, based on the total transformer loss Minimize the magnitude of the magnetic flux density Current density of low-voltage winding and high-voltage winding Wire diameter Winding height Inverse optimization of electromagnetic parameters, among which This represents the current passing through a unit cross-sectional area of ​​the winding. The diameter of the winding conductor. Let be the axial height of the winding; the objective function and constraints are as follows:

[0070] ;

[0071] ;

[0072] In the formula, This represents the total transformer loss. This refers to the hot spot temperature of the winding. This refers to the maximum permissible operating temperature of the insulating material. This refers to the total volume of the transformer body; The upper limit of the available space volume for transformer installation is constrained.

[0073] The optimization algorithm employs Bayesian optimization, iteratively searching for the global optimum within the parameter space.

[0074] Step F4: Perform electromagnetic-structural co-design for short-circuit protection; based on the electromagnetic parameter scheme determined in Step F3, establish a two-dimensional axisymmetric leakage magnetic field finite element model of the transformer; calculate the maximum short-circuit current and the peak value of the maximum symmetrical short-circuit current under both high-voltage and low-voltage short-circuit conditions. Determined by the following formula:

[0075] ;

[0076] In the formula, The impact coefficient, This represents the effective value of the short-circuit current; where the impulse coefficient is... Defined as:

[0077] ;

[0078] In the formula, The total resistance of the short-circuit loop. The total reactance of the short-circuit loop; the typical short-circuit impedance of the energy storage transformer ( Take the calculated engineering value. ;

[0079] Solving the magnetic vector potential based on a two-dimensional axisymmetric finite element model of leakage magnetic field The partial differential equations that are satisfied are:

[0080] ;

[0081] in, Permeability, The source current density vectors applied to the low-voltage and high-voltage winding regions are given; the leakage flux density vector is then obtained. Then, the electromagnetic force density per unit volume of the low-voltage winding and the high-voltage winding. Calculated using the Lorentz force formula:

[0082] ;

[0083] In the formula, The electromagnetic force density vector per unit volume; The source current density vector; The leakage flux density vector; the total electromagnetic force borne by various parts of the low-voltage and high-voltage windings. By applying force density in the corresponding volume Inner integrals are obtained as follows:

[0084] ;

[0085] In the formula, The total electromagnetic force vector; This represents the calculated winding region volume; The electromagnetic force density per unit volume is given. This electromagnetic force density is used as a load boundary condition and imported into a three-dimensional structural mechanics model to solve for the stress-strain distribution in the radial and axial directions of the low-voltage and high-voltage windings. In the structural mechanics analysis, the conductor material is considered as a bilinear elastoplastic material with an elastic modulus E = 110 GPa, Poisson's ratio ν = 0.34, and yield strength σ. y =120 MPa; the insulating pad is considered as a linear elastic material, with an elastic modulus E=15 GPa and a compressive strength σ comp =60 MPa; with the yield strength of the conductors and the compressive strength of the insulating pad of the low-voltage winding and the high-voltage winding as constraints, and with the goal of minimizing the stress peak in each winding region, optimize the radial dimension, axial dimension and clamping force distribution of the low-voltage winding and the high-voltage winding; if the stress peak exceeds the constraint, return to step F3 to adjust the electromagnetic parameters (such as increasing the winding spacing, adjusting the ampere-turn distribution, etc.) and re-execute the optimization iteration.

[0086] Step F5: Perform integrated compact layout optimization; based on the electromagnetic and structural parameters determined in steps F3 and F4, establish a three-dimensional parametric geometric model of the transformer body; using the available installation space of the transformer as the design boundary, construct a multi-physics field coupled simulation model of electromagnetic field, temperature field, and flow field; the electromagnetic field, temperature field, and flow field adopt a unidirectional sequential coupling method: first, solve the electromagnetic field to obtain the loss distribution, then use the loss as a heat source to calculate the temperature rise in the temperature field, then use the oil temperature distribution obtained from the temperature field calculation as a boundary condition to calculate the flow velocity distribution in the flow field, and after the flow field calculation results are fed back to correct the convective heat transfer coefficient, the temperature field is recalculated until the temperature field converges (the temperature difference between two adjacent iterations is less than 0.1℃); electromagnetic field calculation of the iron core. Using the loss distribution of the low-voltage and high-voltage windings as heat sources, the temperature field is used to calculate the temperature rise distribution of each component, and the flow field is used to calculate the airflow characteristics inside the transformer and the oil tank heat dissipation channel. With the minimum total loss and the minimum temperature rise of the hot spots in the low-voltage and high-voltage windings as dual optimization objectives, a multi-objective genetic algorithm is used to iteratively optimize parameters such as the core cross-sectional shape (rectangular or elliptical), the arrangement of the low-voltage and high-voltage windings (concentric or staggered), the distance between the transformer body and the tank wall (affecting the heat dissipation airflow organization), and the size of the oil tank heat dissipation channel. The fitness value of each individual in each generation of the population is calculated through electromagnetic field-temperature field-flow field three-field coupling simulation to ensure that the optimization results simultaneously meet the synergistic requirements of electromagnetic performance, thermal performance, and heat dissipation performance.

[0087] Step F6: Output optimization results; Output the Pareto optimal solution set that satisfies all constraints, including multiple representative schemes, each focusing on different optimization directions such as minimum loss, minimum temperature rise, and minimum volume; Each scheme is accompanied by a complete electromagnetic parameter table, temperature rise distribution cloud map, stress distribution cloud map, and a 3D model of spatial layout, for engineering designers to select the final scheme according to specific project requirements.

[0088] Through the above optimization process, in the design of the energy storage step-up transformer prototype, the total transformer loss is significantly reduced compared with the traditional design, the temperature rise of the winding hot spots of the low-voltage winding and the high-voltage winding is significantly reduced, the mechanical strength requirements under bidirectional short-circuit current impact are met, and a reasonable oil tank heat dissipation channel layout is achieved within the available installation space of the transformer.

[0089] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention. The actual structure, parameters, and module division are not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, such designs should fall within the protection scope of the present invention.

Claims

1. A low-loss electromagnetic system for an energy storage step-up transformer, characterized in that, It includes the transformer body and the dynamic load sensing and electromagnetic parameter adaptive module that works with the transformer body, the harmonic loss suppression and magnetic flux control module, and the thermo-magnetic-force collaborative optimization design module. The transformer body includes a transformer core, low-voltage winding, high-voltage winding, flux control winding, insulation structure, and oil tank heat dissipation structure; the low-voltage winding is electrically connected to the energy storage converter, the high-voltage winding is electrically connected to the medium-voltage power grid, and the flux control winding is connected in series to the main magnetic circuit and is equipped with taps. The dynamic load sensing and electromagnetic parameter adaptive module collects transformer operating data in real time, constructs a charging and discharging condition identification model, outputs the condition identification results, and dynamically adjusts the equivalent excitation impedance through the tap of the magnetic flux control winding based on the condition identification results, so that the transformer magnetic flux density adapts to the load changes. The harmonic loss suppression and flux control module is located between the transformer core and the low-voltage winding and the high-voltage winding. It includes a high-frequency harmonic flux bypass structure and a low-voltage winding harmonic loss suppression structure. The module dynamically adjusts the saturation depth of the high-frequency harmonic flux bypass structure according to the operating condition identification results. The thermal-magnetic-force collaborative optimization design module is integrated into the structural design of the transformer. It establishes a total loss analytical model covering core loss, DC loss and high-frequency additional loss of low-voltage and high-voltage windings, and performs inverse optimization of electromagnetic parameters with the constraint that the hot spot temperature of low-voltage and high-voltage windings does not exceed the allowable temperature of the insulation material. At the same time, it optimizes the size and clamping force distribution of low-voltage and high-voltage windings based on the leakage magnetic field distribution.

2. The system according to claim 1, characterized in that, The high-frequency harmonic flux bypass structure provides a low magnetic reluctance path for high-frequency harmonic flux; the low-voltage winding harmonic loss suppression structure suppresses circulating current loss by dividing the low-voltage winding into several parallel branches and setting cross-transposition between each branch.

3. The system according to claim 2, characterized in that, The high-frequency harmonic flux bypass structure includes a bypass magnetic column; the bypass magnetic column is located next to the main magnetic column of the transformer core and is made of nanocrystalline high permeability thin strip material; the bypass magnetic column and the main magnetic column are connected by an adjustable air gap; the fundamental magnetic flux flows along the main magnetic column, and the high-frequency harmonic flux forms a low magnetic resistance path in the bypass magnetic column.

4. The system according to claim 3, characterized in that, An air gap adjustment mechanism driven by a shape memory alloy is embedded in the bypass magnetic column; the air gap adjustment mechanism adjusts the width of the adjustable air gap according to the harmonic spectrum distribution characteristics to change the saturation depth of the bypass magnetic column, so that the harmonic flux bypass effect remains optimal within the operating frequency band.

5. The system according to claim 2, characterized in that, In the low-voltage winding harmonic loss suppression structure, the low-voltage winding is divided into multiple parallel branches along the radial direction. Each branch occupies the inner, middle and outer layers at different radial positions along the height direction of the low-voltage winding to achieve complete transposition. An impedance balancing reactor is set at the transposition node of each branch to suppress the circulating current of the branch at high frequencies.

6. The system according to claim 1, characterized in that, The high-voltage winding adopts a graded insulation structure, with an electrostatic shielding layer set in the inner layer near the transformer core. The electrostatic shielding layer is grounded to reduce the high-frequency resonance loss caused by the high-voltage winding's capacitance to ground.

7. The system according to claim 1, characterized in that, In the thermo-magnetic-mechanical co-optimization design module, the inverse optimization of electromagnetic parameters specifically involves: Based on the total loss analytical model, the core loss is decomposed into hysteresis loss, classical eddy current loss and abnormal loss, and the high-frequency additional loss is decomposed into skin effect loss, proximity effect loss and circulating loss. With the constraint that the hot spot temperature of the low-voltage and high-voltage windings does not exceed the allowable temperature of the insulation material, and with the goal of minimizing total loss, the magnetic flux density amplitude of the core, the current density of the low-voltage and high-voltage windings, the conductor diameter, and the winding height are optimized in reverse.

8. The system according to claim 1, characterized in that, The thermo-magnetic-force co-optimization design module includes a short-circuit electromagnetic-structural co-optimization design sub-module. It calculates the winding electrodynamic force based on the leakage magnetic field distribution under bidirectional short-circuit conditions, and optimizes the radial and axial dimensional ratios and clamping force distribution of the low-voltage winding and high-voltage winding with the winding mechanical strength as a constraint.

9. The system according to claim 8, characterized in that, The thermal-magnetic-force synergistic optimization design module also includes an integrated compact layout sub-module. Using the available installation space of the transformer as the boundary condition, it determines the location of the transformer body and the layout of the oil tank heat dissipation channel through multi-physics field iterative optimization of electromagnetic field, temperature field and flow field.

Images