Large-capacity high-frequency transformer test platform based on cascaded DAB and LC energy feedback and control method

Abstract

The application discloses a large-capacity high-frequency transformer test platform based on cascaded DAB and LC energy feedback and a control method, which comprises a rectification power supply unit for establishing a DC bus; a DAB secondary side cascaded module group is connected in parallel to the DC bus at the DC side and connected to a high-voltage side of a transformer to be tested after cascading at the AC side, and is used for synthesizing a high-frequency high-voltage square wave or a ladder wave with adjustable dv / dt; an AC side of a DAB primary side module group is connected in parallel to a low-voltage side of the transformer to be tested, and a DC side is connected with a primary side DC link capacitor; an LC bidirectional converter module group is connected between the primary side DC link and the DC bus, and is used for energy feedback; and a control and protection unit realizes multi-module synchronization, phase shift / duty ratio regulation and phased start-stop. The application realizes waveform synthesis and power regulation decoupling, significantly reduces the power supply capacity demand of a power grid, and improves test safety and scalability.

Description

Technical Field

[0001] This invention relates to the field of power electronic conversion and high-frequency transformer testing technology, specifically to a large-capacity high-frequency transformer testing platform and control method based on cascaded DAB and LC energy feedback. Background Technology

[0002] With the continuous advancement of power electronics applications such as new energy grid connection, energy storage systems, rail transit traction power supply, and medium- and high-voltage DC power distribution, the demand for equipment such as power electronic transformers (PETs) in terms of power conversion, bidirectional transmission, and electrical isolation is becoming increasingly prominent. As a key isolation and energy transfer component in such equipment, high-frequency transformers can reach capacities of hundreds of kilovolt-amperes, characterized by high operating frequencies and high power densities, and often need to operate for extended periods under complex electromagnetic and thermal stress coupling conditions. Therefore, in the process of product development and engineering applications, it is urgent to establish testing methods that can cover typical service conditions to comprehensively evaluate the electrical performance, temperature rise characteristics, operating efficiency, insulation performance, partial discharge characteristics, and long-term reliability of high-frequency transformers.

[0003] In medium- and high-voltage or modular series applications, high-frequency transformers, in addition to bearing high-frequency square wave voltage stress, may also experience additional voltage stress from low-frequency or DC components between their primary and secondary windings, and between the windings and the core, leading to a combined electrical stress on their insulation system. Traditional power frequency leakage current detection or single power frequency withstand voltage test methods are insufficient to accurately reflect the degradation behavior and partial discharge characteristics of insulation materials under high-frequency, non-sinusoidal, and combined voltage stress. Furthermore, the waveform characteristics of high-frequency square wave voltage (such as the voltage change rate dv / dt) have a significant impact on the initiation and development of partial discharge. Therefore, a test power supply and matching measurement system capable of outputting high frequency, high voltage, and flexibly adjustable waveform parameters (including amplitude, frequency, duty cycle, harmonic characteristics, and dv / dt) are needed to support the effective conduct of key tests such as insulation strength and partial discharge.

[0004] On the other hand, large-capacity high-frequency transformers consume significant amounts of electricity during temperature rise, efficiency, and reliability tests under full or near-full load conditions. If traditional "consumption-type" load methods (where electrical energy is directly converted into heat through energy-consuming components like resistors) are used, not only are high power supply capacity requirements and operating costs high, but it is also difficult to support long-term continuous accelerated aging or life tests, posing significant challenges to engineering implementation. Therefore, test platforms typically need energy feedback capabilities, meaning that while meeting test loading and waveform reproduction requirements, most of the electrical energy is fed back to the grid or DC bus, thereby significantly reducing the capacity requirements of external power sources and test operating costs.

[0005] In summary, to effectively reproduce the typical service conditions of large-capacity high-frequency transformers in an experimental environment, there is an urgent need for a test platform solution that can simultaneously achieve the following objectives: (i) It has scalable high-frequency square wave / staircase wave voltage synthesis capability and supports flexible control of duty cycle and dv / dt at high voltage levels; (ii) To achieve functional decoupling of waveform synthesis and power regulation, thereby improving the accuracy of operating condition reproduction and system stability; (iii) The integrated energy feedback mechanism makes the grid-side capacity demand significantly lower than the test capacity, effectively reducing energy consumption and equipment configuration costs; (iv) Provide control strategies such as phased pre-charging, group switching, and phase difference ramp start-up to suppress inrush current and improve system safety and reliability; (v) Achieve soft-switching operation as much as possible under a wide range of operating conditions, while taking into account system efficiency and thermal management requirements. Summary of the Invention

[0006] To address the aforementioned issues, this paper proposes a test platform topology and its control strategy based on cascaded DAB and LC energy feedback. This scheme integrates module-level synthesized output and phase-shift power regulation technology, and utilizes an LC bidirectional converter to achieve energy feedback and DC link voltage stability, thereby achieving comprehensive goals such as high-capacity output, low grid-side capacity requirements, controllable waveform, and safe commissioning.

[0007] The purpose of this invention is to provide a high-capacity high-frequency transformer test platform, comprising: The rectifier power supply unit is used to convert AC power into DC bus voltage; The DAB secondary-side cascaded module group includes multiple secondary-side full-bridge power modules. The DC terminals of each secondary-side full-bridge power module are connected in parallel to the DC bus. The midpoints of the bridge arms of each secondary-side full-bridge power module are connected in a cascaded manner to form an AC output terminal, which is used to connect to the high-voltage winding of the high-frequency transformer under test, so as to synthesize a high-frequency high-voltage square wave or stepped wave voltage on the high-voltage side of the high-frequency transformer under test. The DAB primary-side module group includes at least one primary-side full-bridge power module. The midpoint of the bridge arm of the primary-side full-bridge power module is connected to the low-voltage side winding of the high-frequency transformer under test, and the DC terminal of the primary-side full-bridge power module is connected to the DAB primary-side DC link capacitor. The LC bidirectional converter module group has its input terminal connected to the primary side DC link capacitor of the DAB and its output terminal connected to the DC bus, which is used to feed back the energy of the primary side of the high-frequency transformer under test to the DC bus. The control and protection unit is used to generate drive control signals for the DAB secondary cascade module group, the DAB primary module group and the LC bidirectional converter module group respectively, and to perform phased start-up, power regulation and shutdown control according to the bus voltage, primary and secondary voltage and current and protection threshold.

[0008] Furthermore, each of the secondary-side full-bridge power modules in the DAB secondary-side cascaded module group is equipped with a DC support capacitor, and the output voltage is cascaded and synthesized by means of synchronous timing or setting phase shift angle.

[0009] Furthermore, the DAB primary-side module group includes multiple primary-side full-bridge power modules connected in parallel to form a parallel current sharing structure.

[0010] Furthermore, the LC bidirectional converter module group includes a first full-bridge circuit, an LC resonant network, a high-frequency isolation transformer, and a second full-bridge circuit connected in sequence, and resonant capacitors are respectively provided on the primary side and the secondary side to realize the soft-switching operating range.

[0011] Furthermore, the control and protection unit is also configured to adjust the amplitude of the high-voltage side port voltage of the high-frequency transformer under test by adjusting the duty cycle of each of the secondary full-bridge power modules in the DAB secondary cascade module group.

[0012] Furthermore, the control and protection unit is also configured to continuously adjust the transmission power and current of the high-frequency transformer under test by adjusting the phase shift angle between the DAB primary-side module group and the DAB secondary-side cascaded module group.

[0013] Furthermore, the control and protection unit also includes a protection logic module for implementing overcurrent, overvoltage, overtemperature, asynchronous, or false triggering protection, and when protection is triggered, it performs shutdown in the following order: first, blocking the DAB secondary-side cascaded module group and the DAB primary-side module group; then, blocking the LC bidirectional converter module group; and finally, blocking the rectifier power supply unit.

[0014] Secondly, the present invention provides a control method based on the aforementioned experimental platform, comprising the following steps: Step 1: Complete the wiring and polarity verification of the DAB secondary-side cascaded module group, the DAB primary-side module group, and the LC bidirectional converter module group; Step 2: Set the output voltage frequency of the DAB secondary cascade module group to the rated frequency of the high-frequency transformer under test, and set the output voltage frequency of the LC bidirectional converter module group to its rated frequency. Step 3: Start the rectifier power supply unit to establish the DC bus voltage; Step 4: Enable the secondary circuit of the LC bidirectional converter module group, output a square wave using the duty cycle grouping adjustment method, and charge the primary DC link capacitor of the DAB and the supporting capacitor on the primary side of the LC bidirectional converter module group through the pre-charge rectification channel. Step 5: Enable the DAB primary-side module group and output the square wave voltage of the high-frequency transformer under test at the rated frequency by gradually putting the modules into operation in groups; Step 6: After the output voltage of the DAB primary-side module group stabilizes, adjust the duty cycle of the secondary-side circuit of the LC bidirectional converter module group to raise the voltage of the DC link capacitor of the DAB primary-side to the target bus voltage value. Step 7: Enable the DAB secondary cascaded module group, adjust the duty cycle of the secondary circuit of the LC bidirectional converter module group to 0.5, and enable the primary circuit of the LC bidirectional converter module group, so that the system enters the closed-loop energy feedback state. Step 8: Under closed-loop energy feedback, gradually increase the phase difference between the DAB primary side module group and the DAB secondary side cascaded module group until the primary side current of the high-frequency transformer under test reaches the set test current threshold. Step 9: Collect and record the voltage, current, and frequency data of the primary and secondary ports of the high-frequency transformer under test and the LC bidirectional converter module group to complete the test; Step 10: After the test, shut down the system in the following order: first, block the DAB secondary-side cascade module group and the DAB primary-side module group; then, block the LC bidirectional converter module group; and finally, block the rectifier power supply unit.

[0015] The beneficial effects of this invention are: (1) High voltage scalability: The system adopts a DAB secondary side cascade structure, and the number of modules can be flexibly expanded according to the requirements of different voltage levels; (2) Multiple dv / dt controllability: By using the module phase shifting to synthesize the stepped waveform, the output voltage change rate (dv / dt) can be adjusted to meet the test requirements of insulation stress testing, partial discharge detection, etc. (3) Power regulation decoupling design: DAB phase shift control is used for current / power regulation, and the secondary cascade module is responsible for voltage waveform synthesis. The control objectives of the two are independent of each other, which improves the system flexibility; (4) Energy feedback reduces energy consumption: The LC feedback structure is adopted so that the grid side mainly undertakes loss compensation, effectively reducing the external power supply capacity demand and system operation energy consumption; (5) Safe start-up mechanism: Combining LC pre-charging, DAB group commissioning and phase difference ramp control strategy, the DC link inrush current is significantly suppressed, the risk of false triggering is reduced, and the safety of system start-up is improved. Attached Figure Description

[0016] The present invention includes the following figures: Figure 1 This is a topology diagram of a high-frequency transformer test platform; Figure 2 Flowchart for starting the experiment. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0018] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this application should have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms "first," "second," and similar terms used in the embodiments of this application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are only used to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0019] Example 1: Test Platform Topology Reference Figure 1 This embodiment provides a test platform for a large-capacity high-frequency transformer, including: The rectifier power supply unit connects to the AC power grid on its AC side and outputs DC bus voltage on its DC side. In this embodiment, the rated value of the DC bus voltage is set to 750V.

[0020] The DAB secondary-side cascaded module group consists of N cascaded secondary-side full-bridge power modules, where N is determined based on the rated voltage level of the high-voltage side of the high-frequency transformer under test; in this embodiment, N=8. The DC terminals of each secondary-side full-bridge power module are connected in parallel to the DC bus. The midpoints of the bridge arms of each module are connected in series to form an AC output terminal, which is connected to the high-voltage winding of the high-frequency transformer under test. Each module contains a DC support capacitor, which can synthesize a high-frequency square wave through synchronous timing drive, and a stepped wave can be synthesized by setting the phase shift angle between modules, achieving adjustable dv / dt.

[0021] The DAB primary-side module group consists of M primary-side full-bridge power modules connected in parallel. M is determined based on the rated current level of the low-voltage side of the high-frequency transformer under test; in this embodiment, M=4. The midpoints of the bridge arms of each primary-side full-bridge power module are connected in parallel and then connected to the low-voltage side winding of the high-frequency transformer under test. The DC terminals of each module are connected in parallel to the DC link capacitor of the DAB primary side. This parallel structure is used to achieve current sharing and reduce the current stress on a single module.

[0022] The LC bidirectional converter module has its input connected to the DC link capacitor on the primary side of the DAB and its output connected to the DC bus. This module adopts a bidirectional full-bridge—LC resonant—high-frequency isolation transformer—full-bridge structure, with resonant capacitors on both the primary and secondary sides to achieve a soft-switching operating range. In this embodiment, the LC resonant frequency is set to 20kHz.

[0023] The control and protection unit is connected to the control terminals of the power switching transistors of the above-mentioned units to generate drive control signals; it is also connected to the bus voltage sensor, primary and secondary voltage and current sensors, and temperature sensor to collect operating status parameters; and performs phased start-up, power regulation, and shutdown control according to preset protection thresholds.

[0024] The control and protection unit also integrates a protection logic module to implement overcurrent, overvoltage, overtemperature, asynchronous or false triggering protection. When protection is triggered, the shutdown is performed in the following order: first, the DAB secondary cascade module group and the DAB primary module group are blocked; then the LC bidirectional converter module group is blocked; and finally the rectifier power supply unit is blocked.

[0025] Example 2: Specific Implementation of the Control Method Reference Figure 2 This embodiment provides a control method based on the experimental platform described in Embodiment 1, including the following steps: A) Wiring and polarity verification: Complete the wiring and polarity verification of the DAB secondary cascade module group, DAB primary module group and LC bidirectional converter module group according to the predetermined number of modules (N=8, M=4).

[0026] B) Parameter preset: Set the output voltage frequency of the DAB secondary cascade module group to the rated frequency of the high-frequency transformer under test, which is 10kHz in this embodiment; set the output voltage frequency of the LC bidirectional converter module group to its rated frequency, which is 20kHz in this embodiment.

[0027] C) DC bus establishment: Start the rectifier power supply unit to establish the DC bus voltage to the rated value of 750V.

[0028] D) LC Pre-charge: Enables the secondary circuit of the LC bidirectional converter module group (i.e., the second full-bridge circuit near the DC bus), and outputs a 20kHz square wave using a duty cycle grouping adjustment method. The duty cycle starts at 0.1 and gradually increases to 0.5 in 5 groups with a step size of 0.05, with each group maintaining 50 switching cycles. The DAB primary-side DC link capacitor and the supporting capacitor on the primary side of the LC bidirectional converter module group are charged through the pre-charge rectifier channel until the DAB primary-side DC link voltage rises to 50V.

[0029] E) DAB Primary-Side Grouping Startup: Enable the DAB primary-side module group, and output a 10kHz square wave voltage using a grouping and gradual activation method. In this embodiment, the four primary-side full-bridge power modules are divided into two groups, with two modules in each group. The first group is activated first, with a duty cycle set to 0.4. After the output current stabilizes, the second group is activated, and the duty cycle is gradually adjusted to 0.5.

[0030] F) DC link voltage boost: After the output voltage of the DAB primary side module group stabilizes, adjust the duty cycle of the secondary side circuit of the LC bidirectional converter module group, gradually increasing it from 0.5 to 0.65, thereby boosting the DC link capacitor voltage of the DAB primary side to the target bus voltage value of 700V.

[0031] G) Secondary-side commissioning and feedback closed-loop establishment: Enable the DAB secondary-side cascaded module group. The eight secondary-side full-bridge power modules output square waves with a duty cycle of 0.5 and a frequency of 10kHz in a synchronous timing manner. After cascading, a high-frequency high-voltage square wave is generated on the high-voltage side of the transformer under test. If it is necessary to simulate a specific dv / dt condition, a stepped wave is synthesized by setting the phase shift angle between modules (e.g., 2.5μs). At the same time, the duty cycle of the secondary circuit of the LC bidirectional converter module group is adjusted back to 0.5, and the primary circuit (first full-bridge circuit) of the LC bidirectional converter module group is enabled, and the system enters the closed-loop energy feedback state.

[0032] H) Phase-shifting loading: Under closed-loop feedback, the phase difference between the DAB primary side module group and the DAB secondary side cascaded module group is slowly increased at a rate of 1° / s until the primary side current of the high-frequency transformer under test reaches the set test current threshold, which is set to 500A in this embodiment.

[0033] I) Data Acquisition: The system operates under steady-state conditions, acquiring and recording the voltage, current, and frequency data of the primary and secondary terminals of the high-frequency transformer under test, as well as the voltage and current data of the LC bidirectional converter module group, to complete the capacity and operating condition tests.

[0034] J) Sequential shutdown: After the test, the shutdown shall be performed in the following order: first, shut down the DAB secondary cascade module group and the DAB primary module group; then, shut down the LC bidirectional converter module group; and finally, shut down the rectifier power supply unit.

[0035] In the above control method, the output voltage amplitude of the DAB secondary cascade module group can be adjusted by adjusting the duty cycle of each secondary full-bridge power module; the phase shift angle between the DAB primary module group and the DAB secondary cascade module group is continuously adjustable, realizing continuous adjustment of the transmission power and current of the high-frequency transformer under test; the LC bidirectional converter module group feeds the energy of the DAB primary DC link back to the DC bus in energy feedback mode, so that the rectifier power supply unit only needs to compensate for system losses.

[0036] It should be noted that any process or method description in the embodiments can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of the preferred embodiments of the invention includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order according to the functions involved, as should be understood by those skilled in the art to which the embodiments of the invention pertain.

[0037] It should be noted that the logic and / or steps in the embodiments, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Alternatively, the computer-readable medium may be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in a computer memory.

[0038] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0039] Those skilled in the art will understand that all or part of the steps of the methods described in the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, the program includes one or a combination of the steps of the method embodiments.

[0040] Furthermore, in the embodiments of the present invention, the functional modules can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module. The integrated module can be implemented in hardware or as a software functional module. If the integrated module is implemented as a software functional module and sold or used as an independent product, it can also be stored in a computer-readable storage medium. The aforementioned storage medium can be a read-only memory, a hard disk, or an optical disk, etc.

[0041] The above embodiments have provided a detailed description of the technical solutions of the present invention. Obviously, the present invention is not limited to the described embodiments. Based on the embodiments of the present invention, those skilled in the art can make various changes, but any changes that are equivalent or similar to the present invention fall within the scope of protection of the present invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A test platform for a large-capacity high-frequency transformer based on cascaded DAB and LC energy feedback, characterized in that, include: The rectifier power supply unit is used to convert AC power into DC bus voltage; The DAB secondary-side cascaded module group includes multiple secondary-side full-bridge power modules. The DC terminals of each secondary-side full-bridge power module are connected in parallel to the DC bus. The midpoints of the bridge arms of each secondary-side full-bridge power module are connected in a cascaded manner to form an AC output terminal, which is used to connect to the high-voltage winding of the high-frequency transformer under test, so as to synthesize a high-frequency high-voltage square wave or stepped wave voltage on the high-voltage side of the high-frequency transformer under test. The DAB primary-side module group includes at least one primary-side full-bridge power module. The midpoint of the bridge arm of the primary-side full-bridge power module is connected to the low-voltage side winding of the high-frequency transformer under test, and the DC terminal of the primary-side full-bridge power module is connected to the DAB primary-side DC link capacitor. The LC bidirectional converter module group has its input terminal connected to the primary side DC link capacitor of the DAB and its output terminal connected to the DC bus, which is used to feed back the energy of the primary side of the high-frequency transformer under test to the DC bus. The control and protection unit is used to generate drive control signals for the DAB secondary cascade module group, the DAB primary module group and the LC bidirectional converter module group respectively, and to perform phased start-up, power regulation and shutdown control according to the bus voltage, primary and secondary voltage and current and protection threshold.

2. The test platform according to claim 1, characterized in that, Each of the secondary-side full-bridge power modules in the DAB secondary-side cascaded module group is equipped with a DC support capacitor, and the output voltage is cascaded by means of synchronous timing or setting phase shift angle.

3. The test platform according to claim 1, characterized in that, The DAB primary-side module group includes multiple primary-side full-bridge power modules connected in parallel to form a parallel current sharing structure.

4. The test platform according to claim 1, characterized in that, The LC bidirectional converter module group includes a first full-bridge circuit, an LC resonant network, a high-frequency isolation transformer, and a second full-bridge circuit connected in sequence, and resonant capacitors are respectively provided on the primary and secondary sides to realize the soft-switching operating range.

5. The test platform according to claim 1, characterized in that, The control and protection unit is also configured to adjust the amplitude of the high-voltage side port voltage of the high-frequency transformer under test by adjusting the duty cycle of each of the secondary full-bridge power modules in the DAB secondary cascade module group.

6. The test platform according to claim 1, characterized in that, The control and protection unit is also configured to continuously adjust the transmission power and current of the high-frequency transformer under test by adjusting the phase shift angle between the DAB primary-side module group and the DAB secondary-side cascaded module group.

7. The test platform according to claim 1, characterized in that, The control and protection unit also includes a protection logic module for implementing overcurrent, overvoltage, overtemperature, asynchronous, or false triggering protection. When protection is triggered, the module performs shutdown in the following order: first, blocking the DAB secondary-side cascaded module group and the DAB primary-side module group; then, blocking the LC bidirectional converter module group; and finally, blocking the rectifier power supply unit.

8. A control method based on the test platform according to any one of claims 1 to 7, characterized in that, Includes the following steps: Step 1: Complete the wiring and polarity verification of the DAB secondary-side cascaded module group, the DAB primary-side module group, and the LC bidirectional converter module group; Step 2: Set the output voltage frequency of the DAB secondary cascade module group to the rated frequency of the high-frequency transformer under test, and set the output voltage frequency of the LC bidirectional converter module group to its rated frequency. Step 3: Start the rectifier power supply unit to establish DC bus voltage; Step 4: Enable the secondary circuit of the LC bidirectional converter module group, output a square wave using the duty cycle grouping adjustment method, and charge the primary DC link capacitor of the DAB and the supporting capacitor on the primary side of the LC bidirectional converter module group through the pre-charge rectification channel. Step 5: Enable the DAB primary-side module group and output the square wave voltage of the high-frequency transformer under test at the rated frequency by gradually putting the modules into operation in groups; Step 6: After the output voltage of the DAB primary-side module group stabilizes, adjust the duty cycle of the secondary-side circuit of the LC bidirectional converter module group to raise the voltage of the DC link capacitor of the DAB primary-side to the target bus voltage value. Step 7: Enable the DAB secondary cascaded module group, adjust the duty cycle of the secondary circuit of the LC bidirectional converter module group to 0.5, and enable the primary circuit of the LC bidirectional converter module group, so that the system enters the closed-loop energy feedback state. Step 8: Under closed-loop energy feedback, gradually increase the phase difference between the DAB primary side module group and the DAB secondary side cascaded module group until the primary side current of the high-frequency transformer under test reaches the set test current threshold. Step 9: Collect and record the voltage, current, and frequency data of the primary and secondary ports of the high-frequency transformer under test and the LC bidirectional converter module group to complete the test; Step 10: After the test, shut down the system in the following order: first, block the DAB secondary-side cascade module group and the DAB primary-side module group; then, block the LC bidirectional converter module group; and finally, block the rectifier power supply unit.

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