Control method and control device of DAB converter

Abstract

The invention provides a control method and a control device of a DAB converter. The method comprises the following steps: acquiring a relation curve of switching tube turn-off loss and switching frequency of the DAB converter, a relation curve of switching tube on-state loss and switching frequency, a relation curve of transformer magnetic core loss and switching frequency and a relation curve of transformer coil loss and switching frequency; acquiring the change trend of the comprehensive loss and the switching frequency of the DAB converter according to the relation curve; searching the optimal switching frequency of the DAB converter according to the change trend; and controlling the operation of the DAB converter according to the optimal switching frequency. According to the method, the comprehensive loss is obtained through the single loss curve of the DAB converter, and the optimal switching frequency is searched according to the change trend of the comprehensive loss, so that the DAB converter operates in the optimal state, the overall efficiency of the DAB converter is improved, and particularly, the efficiency is improved in a light load state.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, specifically to a control method for a DAB (Dual-Active-Bridge) converter and a control device for a DAB converter. Background Technology

[0002] In recent years, with the development of highly integrated bidirectional DC charging piles, increasingly important requirements have been placed on high-efficiency, high-power-density power modules, especially in the area of ​​efficiency improvement in DAB topologies. Due to its advantages in electrical conversion, high-frequency isolation, bidirectional mode, and high conversion efficiency, the DAB converter has become the core power conversion circuit of DC / DC modules. Furthermore, the multi-phase-shift tuning strategy of the DAB converter has three degrees of control freedom, thus enabling various operating modes.

[0003] However, due to the fixed losses and conversion losses of the power modules in the overall system architecture, the efficiency improvement capability of DAB (Digital Animation Block) under light load is very limited. In the context of improving efficiency in DAB bidirectional topologies, existing technologies have proposed multi-phase shift control strategies to achieve efficiency improvements under light loads. However, under medium and heavy loads, single-phase shift is still chosen, and this function is only achieved through soft switching of the switching transistors, resulting in limited efficiency improvements. Given these challenges, finding the optimal switching frequency trajectory strategy for power module losses during the initial design phase has become a pressing technical problem for those skilled in the art. Summary of the Invention

[0004] To address the aforementioned technical problems, the first objective of this invention is to propose a control method for a DAB converter.

[0005] The second objective of this invention is to provide a control device for a DAB converter.

[0006] The technical solution adopted in the present invention is as follows: An embodiment of the first aspect of the present invention proposes a control method for a DAB converter, comprising the following steps: obtaining the relationship curves between the turn-off loss of the switching transistor and the switching frequency, the relationship curve between the on-state loss of the switching transistor and the switching frequency, the relationship curve between the transformer core loss and the switching frequency, and the relationship curve between the transformer coil loss and the switching frequency of the DAB converter; obtaining the trend of the change in the overall loss of the DAB converter and the switching frequency based on the relationship curves between the turn-off loss of the switching transistor and the switching frequency, the relationship curve between the on-state loss of the switching transistor and the switching frequency, the relationship curve between the transformer core loss and the switching frequency, and the relationship curve between the transformer coil loss and the switching frequency; finding the optimal switching frequency of the DAB converter based on the trend; and controlling the operation of the DAB converter according to the optimal switching frequency.

[0007] The control method for the DAB converter proposed in this invention may also have the following additional technical features: According to one embodiment of the present invention, the above control method further includes: designing and selecting the transformer and switching transistor of the DAB converter based on the transformer's magnetic flux density, the transformer's core volume, the transformer's weight, and the cost of the DAB converter.

[0008] According to one embodiment of the present invention, the on-state loss of the switching transistor is obtained based on the energy of the equivalent resistance loss during the switching process.

[0009] According to one embodiment of the present invention, the core loss of the transformer is obtained based on hysteresis loss, eddy current loss and residual loss.

[0010] A second aspect of the present invention provides a control device for a DAB converter, comprising: a first acquisition module, configured to acquire curves showing the relationship between the turn-off loss of the switching transistor and the switching frequency, the relationship between the on-state loss of the switching transistor and the switching frequency, the relationship between the transformer core loss and the switching frequency, and the relationship between the transformer coil loss and the switching frequency of the DAB converter; a second acquisition module, configured to acquire the trend of the change in the overall loss of the DAB converter and the switching frequency based on the curves showing the relationship between the turn-off loss of the switching transistor and the switching frequency, the on-state loss of the switching transistor and the switching frequency, the relationship between the transformer core loss and the switching frequency, and the relationship between the transformer coil loss and the switching frequency; a search module, configured to search for the optimal switching frequency of the DAB converter based on the trend; and a control module, configured to control the operation of the DAB converter based on the optimal switching frequency.

[0011] The control device for the DAB converter described above may also have the following additional technical features: According to one embodiment of the present invention, the control device further includes a selection module, which is used to select the transformer and switching transistor of the DAB converter based on the transformer's magnetic flux density, the transformer's core volume, the transformer's weight, and the cost of the DAB converter.

[0012] According to one embodiment of the present invention, the on-state loss of the switching transistor is obtained based on the energy of the equivalent resistance loss during the switching process.

[0013] According to one embodiment of the present invention, the core loss of the transformer is obtained based on hysteresis loss, eddy current loss and residual loss.

[0014] Beneficial effects of the present invention: This invention obtains the comprehensive loss through the single loss curve of the DAB converter, and finds the optimal switching frequency based on the changing trend of the comprehensive loss, so that the DAB converter operates in the best state and improves the overall efficiency of the DAB converter, especially the efficiency improvement under light load conditions.

[0015] This invention combines cost, size, weight, and electrical parameters of components to design and select transformers and switching transistors for DAB converters, achieving optimal power module performance while meeting user needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a flowchart of a control method for a DAB converter according to an embodiment of the present invention; Figure 2 This is a topology diagram of a DAB converter according to an embodiment of the present invention; Figure 3 This is a curve showing the relationship between the turn-off loss of the switching transistor and the switching frequency according to an embodiment of the present invention; Figure 4 This is a curve showing the relationship between the on-state loss of a switching transistor and the switching frequency according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the transformer equivalent circuit according to an embodiment of the present invention; Figure 6 This is a curve showing the relationship between transformer core loss and switching frequency according to an embodiment of the present invention; Figure 7 This is a curve showing the relationship between transformer coil loss and switching frequency according to an embodiment of the present invention; Figure 8 This is a schematic diagram illustrating the variation trend of the overall loss and switching frequency of a DAB converter according to an embodiment of the present invention; Figure 9 This is a graph showing the relationship between different switching frequencies and load rates according to an embodiment of the present invention; Figure 10 This is a block diagram of a control device for a DAB converter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0017] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0018] To improve the overall conversion efficiency of the DAB converter, especially in the light load range (10%-30% of maximum power), which is crucial for improving the efficiency of bidirectional charging pile discharge mode, especially since the AC load during discharge is a household load, higher efficiency leads to greater energy savings. From a switching frequency perspective, light loads are highly sensitive to the switching losses of the switching transistors (SiC MOSFETs), while the medium-to-heavy load power range is highly sensitive to the losses of the high-frequency transformer. Therefore, achieving a light load efficiency of over 93% without sacrificing medium-to-heavy load efficiency requires careful selection of the optimal switching frequency.

[0019] Figure 1 This is a flowchart of a control method for a DAB converter according to an embodiment of the present invention. The topology of the DAB converter is as follows: Figure 2 As shown, the topology mainly includes a primary-side H-bridge and a secondary-side H-bridge. Vin is the transformer input voltage, Lr is the input-side resonant leakage inductance, Lm is the input-side magnetizing inductance, and Tr is the high-frequency isolation transformer. P1-P4 are primary-side SiC MOSFETs (silicon carbide metal-oxide-semiconductor field-effect transistors), S1-S4 are secondary-side SiC MOSFETs, and A, B, C, and D are four nodes.

[0020] like Figure 1 As shown, the control method of this DAB converter includes the following steps: S1, obtain the curves showing the relationship between the switching transistor turn-off loss and the switching frequency, the switching transistor on-state loss and the switching frequency, the transformer core loss and the switching frequency, and the transformer coil loss and the switching frequency of the DAB converter.

[0021] The following describes how to obtain the relationship curves of various losses using specific examples.

[0022] 1. Switching transistor losses The losses of switching devices in a DAB converter include switching losses and conduction losses. As a specific example, the switching transistors in a DAB module are N-type SiC MOSFETs. The losses of the switching transistor are caused by parasitic capacitances and resistances between different ports within the transistor, typically including conduction loss Pcon, cross-conduction loss Pon, and turn-off loss Poff. Due to the distributed capacitance between the control ports of the switching transistor, there is energy loss during charging and discharging during the switching process between steady-state and on / off states. Furthermore, there is a parasitic on-resistance Rds(on) between the source and drain of the switching transistor, resulting in resistive heat loss during the steady-state conduction process. Theoretically, due to the presence of the reverse current Ineg, the primary-side SiC MOSFETs in the DAB converter can achieve zero-voltage switching (ZVS), and the cross-conduction loss Pon is negligible.

[0023] Based on the fundamental formula for the turn-off loss Poff of a switching transistor, with the switching frequency fs as the independent variable and the turn-off loss Poff as the dependent variable, the driving resistance, input junction capacitance, threshold voltage, and Miller plateau voltage are experimentally verified, and plotted as follows: Figure 3 The curve shown represents the relationship between the turn-off loss of the switching transistor and the switching frequency.

[0024] Current flowing through the on-resistance of a switching transistor generates heat. In one embodiment of this invention, the on-state loss Pcon of the switching transistor is obtained based on the energy of the equivalent resistance loss during the switching process. The corresponding on-state loss is calculated according to the current formulas for different modes. The independent variable is the switching frequency fs, and the dependent variable is the on-state loss of the switching transistor. Experiments are conducted based on the driving resistance, input junction capacitance, threshold voltage, and Miller plateau voltage, and the results are plotted as shown below. Figure 4 The curve shown represents the relationship between the on-state loss of the switching transistor and the switching frequency.

[0025] 2. Transformer losses Due to leakage inductance and parasitic parameters, transformers generate significant losses in high-frequency switching power supplies, making transformer losses a major source of loss in DAB converters. The transformer core material and structure, winding method, and wire diameter all affect losses. This invention utilizes an equivalent transformer model to approximate relatively accurate transformer losses using a relatively simple method. For ease of description, Figure 5 The equivalent circuit of a transformer is shown, where U1 and U2 represent the voltages on the primary and secondary sides of the transformer, respectively; Rdc is the equivalent DC resistance of the core; Rac1 and Rac2 are defined as the AC resistances on the primary and secondary sides of the transformer; C1, C2, and C12 represent the distributed capacitance of the transformer's primary and secondary windings themselves and the distributed capacitance of their coupling, respectively; Lr1 and Lr2 represent the leakage inductance of the primary and secondary windings, respectively; and Lm represents the equivalent magnetizing inductance. Because the skin effect and proximity effect of the transformer are more pronounced at higher frequencies, the effect of AC resistance is significantly enhanced compared to DC resistance. Therefore, AC resistance needs to be considered more in the equivalent circuit.

[0026] Transformer losses primarily originate from the iron losses generated by the magnetic core and the copper losses caused by the winding resistance. Core losses mainly include hysteresis losses, eddy current losses, and residual losses. Copper losses are composed of both primary and secondary winding copper losses. Hysteresis losses arise because alternating current flowing through the transformer changes the direction and magnitude of the magnetic field lines, causing friction between molecules within the core and releasing heat. Eddy current losses occur when a closed-loop current flows through the transformer, generating a changing magnetic flux in the core, thus inducing an electromotive force and producing loop currents called "eddy currents." These eddy currents flow through the equivalent resistance of the core, generating heat that is dissipated. Residual losses occur during the excitation and demagnetization processes of the core, where the magnetization state has a lag time, resulting in residual losses.

[0027] based on Figure 5 The equivalent circuit of the transformer, with the switching frequency fs as the independent variable and the transformer core loss as the dependent variable, can be drawn according to the basic formula for core loss as follows. Figure 6 The curve shown represents the relationship between transformer core loss and switching frequency.

[0028] When current flows through a transformer coil, copper wire loss occurs due to the coil's resistance. This copper wire loss originates from two sources: DC loss and AC loss. DC loss can be calculated using the effective value of the current. AC loss is related to many factors, primarily the current waveform itself. If the current waveform has high harmonic content, the AC loss in the same coil will inevitably be high. Therefore, in evaluating certain application scenarios, an equivalent effective value of the current can be used for judgment. When considering the skin effect and proximity effect, the skin current is calculated as the surface thickness of the trace. The independent variable is the switching frequency fs, and the dependent variable is the transformer coil loss. Based on the basic formula for coil loss, the following can be plotted: Figure 7 The curve shown represents the relationship between transformer coil loss and switching frequency.

[0029] S2. Based on the curves showing the relationship between the turn-off loss of the switching transistor and the switching frequency, the curves showing the relationship between the on-state loss of the switching transistor and the switching frequency, the curves showing the relationship between the transformer core loss and the switching frequency, and the curves showing the relationship between the transformer coil loss and the switching frequency, the trend of the change in the overall loss and switching frequency of the DAB converter is obtained.

[0030] S3, find the optimal switching frequency of the DAB converter based on the changing trend.

[0031] S4 controls the operation of the DAB converter according to the optimal switching frequency.

[0032] Specifically, in combination Figure 3 , Figure 4 , Figure 6 , Figure 7It can be seen that the turn-off loss of a switching transistor is directly proportional to the switching frequency, while the on-state loss is basically independent of the switching frequency. The core loss of a transformer is inversely proportional to the switching frequency, and the coil loss is directly proportional to the switching frequency. Integrating the curves showing the relationships between the turn-off loss and switching frequency, the on-state loss and switching frequency, the core loss and switching frequency, and the coil loss and switching frequency forms a... Figure 8 The diagram shows the trend of combined losses and switching frequency in a DAB converter. As a specific example, it is derived from... Figure 8 As shown in the curves, keeping other conditions constant, based on empirical values ​​for the switching frequency, the total loss of all four components decreases in the 50kHz-70kHz range. In the 70kHz-100kHz range, the total loss increases, reaching a low point near 70kHz. Therefore, 70kHz is considered the optimal switching frequency for the DAB converter. Thus, this invention obtains the comprehensive loss using a single loss curve of the DAB converter and finds the optimal switching frequency based on the trend of the comprehensive loss, thereby ensuring the DAB converter operates at its best and improving its overall efficiency.

[0033] In one embodiment of the present invention, the control method of the DAB converter described above may further include: designing and selecting the transformer and switching transistor of the DAB converter based on the magnetic flux density of the transformer, the core volume of the transformer, the weight of the transformer and the cost of the DAB converter.

[0034] Specifically, before the DAB converter goes online, the transformer and switching transistors are designed and selected. During the selection process, based on the transformer's size requirements, a transformer that meets the relevant requirements is initially selected. Generally, given sufficient core permeability, a core with a larger B value is chosen. Considering electrical performance factors such as high frequency, wide temperature range, and low loss, as well as structural characteristics such as core size, weight, and windings, a compromise is made regarding the core. Then, based on this, switching transistors with the lowest possible on-state resistance are selected. Since on-state loss and switching loss are inherently contradictory, devices with lower switching losses are chosen while minimizing on-state resistance. Simultaneously, cost must be considered to ensure that the total cost of the DAB converter's transformer and switching transistors remains within the required range.

[0035] It should be noted that, in the embodiments of the present invention, the selection of the optimal switching frequency should be comprehensively considered. It is necessary to ensure that the switching frequency will not generate EMI (Electromagnetic Interference) problems, and the overall loss of the switching frequency should not exceed the maximum loss index.

[0036] To verify the effectiveness of the control method described above in this invention, the inventors conducted the following related experiments: Keeping other conditions constant, the impact of changing the switching frequency on the combined losses of transformer core loss, transformer coil loss, switch turn-off loss, and switch on-state loss is investigated. First, ensuring the original conditions remain consistent, the analysis focuses on improving the efficiency of the DAB converter to select the optimal switching frequency. Experiments are conducted using a complete system (system module, AC / DC module, and DC / DC module) for verification. By changing the switching frequency of the DAB converter, operating it at four switching frequencies (100kHz, 85kHz, 70kHz, and 55kHz), efficiency is verified across the full load range. Figure 9 shown.

[0037] like Figure 9 As shown in the figure, the horizontal axis represents the load rate and the vertical axis represents the efficiency. Under the condition that other conditions are the same, the efficiency curves for four operating conditions are plotted. It can be concluded that: (1) The overall efficiency is low when the switching frequency is 100kHz. Relatively speaking, as the switching frequency increases, the core loss decreases, but the turn-off loss of the switching transistor increases. The primary and secondary sides of the DAB are composed of a bridge circuit, and the number of switching transistors will lead to the turn-off loss accounting for a large proportion, so the overall efficiency is low; (2) The same applies when the switching frequency is 85kHz; (3) The efficiency curves of the switching frequency is similar to those of the switching frequency of 55kHz and 70kHz, but the overall curve of the switching frequency of 70kHz is still slightly higher than that of the switching frequency of 55kHz. Compared with 100kHz, the switching frequency is lower, the core loss is slightly higher, the turn-off loss of the switching transistor is very low, and the core loss accounts for a very small proportion, so the overall efficiency is higher.

[0038] Considering the actual requirements of the manufacturer's core material properties, and taking into account electrical performance such as high frequency, wide temperature range, and low loss, as well as structural characteristics such as core size, weight, and windings, while also taking EMC requirements into account, the switching frequency will be optimized. According to the optimal switching frequency trajectory diagram, the efficiency at a switching frequency of 70kHz is significantly higher than other switching frequency points at a 10% load rate, thus greatly improving light-load efficiency. This is highly beneficial for grid-connected discharge mode and V2L mode of household bidirectional chargers, allowing for full utilization of energy. Based on the above loss analysis and experimental verification, 70kHz was ultimately selected as the optimal switching frequency for the DAB converter.

[0039] The control method described above in this invention can be applied to DC / DC circuits with high-frequency transformer isolation, especially in active clamp flyback converters, phase-shifted full-bridge converters, LLC converters (resonant converters), dual active bridge converters, etc.

[0040] In summary, the control method for the DAB converter according to embodiments of the present invention obtains the comprehensive loss through the single loss curve of the DAB converter, finds the optimal switching frequency based on the changing trend of the comprehensive loss, thereby enabling the DAB converter to operate in the best state and improving the overall efficiency of the DAB converter; by combining cost, size, weight and electrical parameters of components to design and select the transformer and switching transistor of the DAB converter, the optimal working performance of the power module can be achieved while meeting user needs.

[0041] Corresponding to the control method for the DAB converter described above, this invention also proposes a control device for the DAB converter. Since the device embodiments of this invention correspond to the method embodiments described above, details not disclosed in the device implementation can be found in the method embodiments described above, and will not be repeated here.

[0042] Figure 10 This is a block diagram of a control device for a DAB converter according to an embodiment of the present invention, as shown below. Figure 10 As shown, the device includes: a first acquisition module 1, a second acquisition module 2, a search module 3, and a control module 4.

[0043] The first acquisition module 1 is used to acquire the relationship curves between the turn-off loss of the switching transistor and the switching frequency, the relationship curve between the on-state loss of the switching transistor and the switching frequency, the relationship curve between the core loss of the transformer and the switching frequency, and the relationship curve between the coil loss of the transformer and the switching frequency of the DAB converter; the second acquisition module 2 is used to acquire the trend of the change of the overall loss of the DAB converter and the switching frequency based on the relationship curves between the turn-off loss of the switching transistor and the switching frequency, the on-state loss of the switching transistor and the switching frequency, the core loss of the transformer and the switching frequency, and the coil loss of the transformer and the switching frequency; the search module 3 is used to find the optimal switching frequency of the DAB converter based on the trend; and the control module 4 is used to control the operation of the DAB converter based on the optimal switching frequency.

[0044] According to one embodiment of the present invention, the control device further includes: a selection module, which is used to select the transformer and switching transistor of the DAB converter based on the transformer's magnetic flux density, the transformer's core volume, the transformer's weight, and the cost of the DAB converter.

[0045] According to one embodiment of the present invention, the on-state loss of the switching transistor is obtained based on the energy of the equivalent resistance loss during the switching process.

[0046] According to one embodiment of the present invention, the transformer core loss is obtained based on hysteresis loss, eddy current loss and residual loss.

[0047] In summary, the control device for the DAB converter according to embodiments of the present invention obtains the comprehensive loss through the single loss curve of the DAB converter, finds the optimal switching frequency based on the changing trend of the comprehensive loss, thereby enabling the DAB converter to operate in the best state and improving the overall efficiency of the DAB converter; by combining cost, size, weight and electrical parameters of components to design and select the transformer and switching transistor of the DAB converter, the optimal working performance of the power module can be achieved while meeting user needs.

[0048] In the description of this invention, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Any process or method description in the flowcharts or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing custom logical functions or processes, and the scope of 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 embodiments of the invention pertain.

[0049] The logic and / or steps represented in the flowchart or otherwise described herein, 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). Furthermore, the computer-readable medium may even be paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium and then editing, interpreting or processing it in another suitable manner if necessary, and then storing it in a computer memory.

[0050] Those skilled in the art will understand that all or part of the steps of the methods 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.

[0051] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A control method for a DAB converter, characterized in that: The following steps are involved: Obtain the relationship curve between the switch-off loss and the switching frequency of the DAB converter, the relationship curve between the switch-on loss and the switching frequency, the relationship curve between the transformer core loss and the switching frequency, and the relationship curve between the transformer coil loss and the switching frequency; Obtain the change trend of the comprehensive loss of the DAB converter and the switching frequency according to the relationship curve between the switch tube turn-off loss and the switching frequency, the relationship curve between the switch tube on-state loss and the switching frequency, the relationship curve between the transformer core loss and the switching frequency, and the relationship curve between the transformer coil loss and the switching frequency; Finding the optimal switching frequency of the DAB converter according to the change trend; The DAB converter is controlled to operate according to the optimal switching frequency.

2. The control method of the DAB converter according to claim 1, characterized in that: Also includes: The transformer and switch tube of the DAB converter are designed and selected according to the magnetic flux density of the transformer, the core volume of the transformer, the weight of the transformer and the cost of the DAB converter.

3. The control method of the DAB converter according to claim 1, characterized in that: The on-state loss of the switch tube is obtained according to the energy of the equivalent resistance loss during the conduction process of the switch tube.

4. The control method of the DAB converter according to claim 1, characterized in that: The transformer core loss is obtained according to the hysteresis loss, eddy current loss and residual loss.

5. A control device for a DAB converter, characterized in that: include: A first acquisition module, the first acquisition module is used to obtain a relationship curve between the switch-off loss of the DAB converter and the switching frequency, a relationship curve between the switch-on loss and the switching frequency, a relationship curve between the transformer core loss and the switching frequency, and a relationship curve between the transformer coil loss and the switching frequency; A second acquisition module, the second acquisition module is used to obtain the change trend of the comprehensive loss of the DAB converter and the switching frequency according to the relationship curve between the switch tube turn-off loss and the switching frequency, the relationship curve between the switch tube on-state loss and the switching frequency, the relationship curve between the transformer core loss and the switching frequency, and the relationship curve between the transformer coil loss and the switching frequency; A searching module, the searching module is used to search for an optimal switching frequency of the DAB converter according to the change trend; A control module is used to control the operation of the DAB converter according to the optimal switching frequency.

6. The control device for a DAB converter according to claim 5, characterized in that: Also includes: The selection module is used to design and select the transformer and switch tube of the DAB converter according to the magnetic flux density of the transformer, the core volume of the transformer, the weight of the transformer and the cost of the DAB converter.

7. The control device for a DAB converter according to claim 5, characterized in that: The on-state loss of the switch tube is obtained according to the energy of the equivalent resistance loss during the conduction process of the switch tube.

8. The control device for a DAB converter according to claim 5, characterized in that: The transformer core loss is obtained according to the hysteresis loss, eddy current loss and residual loss.

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