Multi-objective optimization method and system for dual-active bridge converter based on frequency conversion modulation

Abstract

The invention discloses a multi-objective optimization method and system for a dual active bridge converter based on frequency conversion modulation, and the method comprises the steps: determining the characteristic parameters and design variables of a DAB converter, calculating the transformation ratio of a transformer according to the characteristic parameters, selecting a proper MOSFET model, designing a drive circuit according to the MOSFET model, and selecting the magnetic core materials of the transformer and an inductor, determining the upper and lower limits of switching frequency according to the type of the MOSFET, the driving power of the driving circuit and the material of the magnetic core; calculating an inductance value range and a switching frequency range under different inductance values and powers based on the upper and lower limits of the switching frequency according to a required soft switching range to obtain a design range of frequency conversion modulation; the minimum inductance value is selected in the design range, and efficiency and power density multi-objective optimization design is carried out under the full-load working condition; and the optimal switching frequency under different load working conditions is found in a design range. A solution is provided for efficiency and power density optimization of the DAB converter under the working condition that the input and output bus voltages are constant.

Description

Technical Field

[0001] The present invention relates to the technical field of optimal design of power electronic converters, and particularly to a multi-objective optimization method and system for a dual active bridge converter based on variable frequency modulation. Background Art

[0002] At present, devices such as photovoltaic and energy storage are widely connected to the power grid. These devices mainly perform energy conversion and grid connection through power electronic devices. DC power electronic transformers represented by dual active bridge (DAB) converters play an increasingly important role. The DAB converter can achieve bidirectional energy transmission. Compared with resonant converters, it has advantages such as high power density and fast energy transmission speed.

[0003] Efficiency and power density are important optimization objectives in the design of DAB converters. To improve efficiency, the converter can achieve soft switching and lower losses by optimizing the modulation method and circuit parameters. To improve power density, it is necessary to optimize the design of magnetic components such as inductors and transformers in the converter. When the DAB converter is used as a DC transformer, if the input and output bus voltages are constant, single-phase shift modulation is the most widely used modulation method. This modulation method controls power transmission by controlling the phase shift angle between the primary full-bridge and the secondary full-bridge. However, due to the parasitic capacitance of the switching tubes, the converter cannot achieve soft switching under light load, resulting in low efficiency. To expand the soft switching range, based on traditional single-phase shift modulation, the switching frequency can be used as another controllable variable to adjust the inductor current value at the commutation moment, so as to achieve soft switching under light load conditions.

[0004] The DAB converter based on variable frequency modulation can improve light load efficiency. How to select the switching frequency and circuit parameters, and how to optimize magnetic components under variable frequency modulation are important issues in the design. Summary of the Invention

[0005] The purpose of the present invention is to provide a multi-objective optimization method and system for a dual active bridge converter based on variable frequency modulation to solve the problem that the DAB converter cannot achieve light load soft switching under traditional single-phase shift modulation and the lack of a multi-objective optimization design method for the DAB converter based on variable frequency modulation at present. The present invention provides a solution for optimizing the efficiency and power density of the DAB converter under the condition of constant input and output bus voltages, which can promote the popularization and application of the DAB converter in scenarios such as power electronic transformers.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A multi-objective optimization method for a dual active bridge converter based on variable frequency modulation, comprising the following steps: Step 1: Determine the characteristic parameters and design variables of the DAB converter, calculate the transformer turns ratio according to the characteristic parameters, select a suitable MOSFET model, design the drive circuit according to the MOSFET model, and select the magnetic core materials for the transformer and inductor. Determine the upper and lower limits of the switching frequency according to the MOSFET model, the drive power of the drive circuit, and the magnetic core materials; Step 2: Based on the upper and lower limits of the switching frequency, calculate the range of the inductor value and the range of the switching frequency at different inductor values and powers according to the required soft-switching range, and obtain the design range of the variable-frequency modulation; Step 3: Select the minimum inductor value in the design range and perform multi-objective optimization design of efficiency and power density under full-load conditions; Step 4: Find the optimal switching frequency under different load conditions within the design range.

[0007] Furthermore, the characteristic parameters of the DAB converter include the input voltage V in , the output voltage V out , and the rated power P max ; The design variables of the DAB converter include the switching frequency f s , the inductor value L , the inductor core shape, the inductor winding specifications and turns N L , the transformer core shape, the transformer winding specifications and the transformer turns; The inductor value L includes the external inductor L ex and the transformer leakage inductance L σ ; The transformer turns include the primary turns N T1 and the secondary turns N T2 .

[0008] Furthermore, the calculation of the transformer turns ratio according to the characteristic parameters is specifically as follows: Obtain the transformer turns ratio n = V in / V out according to the input and output voltages; The selection of a suitable MOSFET model is specifically as follows: Select a suitable MOSFET model according to the rated voltage and rated current requirements; The determination of the upper and lower limits of the switching frequency according to the MOSFET model, the drive power of the drive circuit, and the magnetic core materials is specifically as follows: Determine the upper limit of the switching frequency according to the MOSFET model, the driving power of the driving circuit, and the core material f up , and determine the lower limit of the switching frequency according to the saturation requirement of the core material f low .

[0009] Furthermore, the specific steps of step 2 are as follows: Step 2.1: List the maximum switching frequency according to the rated power requirement f smax and the inductance value L and the power P relationship, and list the minimum switching frequency according to the soft-switching requirement f smin relationship with the inductance value and power;

[0010]

[0011] wherein, t margin is the margin of the dead time, C eq is the equivalent capacitance of the switch tube charge; Step 2.2: Based on the relationship in step 2.1, list the inequality according to the soft-switching range, the upper limit of the switching frequency f up and the lower limit of the switching frequency f low requirements, and solve to obtain the inductance value range; Step 2.3: For each feasible inductance value, calculate the curves of the maximum switching frequency and the minimum switching frequency in the required soft-switching range varying with the power, and obtain the design range of the variable-frequency modulation.

[0012] Furthermore, the inequality in step 2.2 is specifically:

[0013] wherein, represents f smin = f smax the corresponding power , represents the lower limit of the soft-switching power, represents that the output power is P min the corresponding minimum switching frequency f smin ( P = P min) Indicates the maximum switching frequency corresponding to P max when the output power is f smax ( P = P max ) Indicates the upper limit of the switching frequency, Indicates the lower limit of the switching frequency.

[0014] Furthermore, step 3 is specifically as follows: Step 3.1: Select the minimum inductance value, and obtain the curves of the maximum switching frequency and the minimum switching frequency varying with power at this minimum inductance value; Step 3.2: For the full-load condition, with the transformer core shape, the inductor core shape, the transformer winding current density j T , the inductor winding current density j L , the switching frequency f s as decision variables, construct a magnetic component data set, where the value range of the switching frequency f s is obtained through step 3.1. With the constraints of non-saturation of the core, sufficient window area, and not too high temperature rise, and with the converter efficiency and the volume of the magnetic component as the optimization objectives, solve the multi-objective optimization problem to obtain the Pareto front; Step 3.3: Select a set of design results on the Pareto front, calculate the winding specifications, and fabricate the transformer and the inductor.

[0015] Furthermore, step 3.2 is specifically as follows: Calculate the minimum number of turns of the primary side of the transformer according to the requirement of non-saturation of the core N T1min ; calculate the maximum number of turns of the primary side of the transformer according to the requirement of the window area N T1max :

[0016]

[0017] Among them, A eT is the effective cross-sectional area of the transformer core, A wT is the window area of the transformer core, I Lrms is the effective value of the inductor current, is the saturation margin of the magnetic induction intensity, is the saturation magnetic induction intensity, is the window area margin; If N T1min < N T1max , it indicates that the transformer can meet the requirements of non - saturation of the magnetic core and sufficient window area, and calculate the primary turns to minimize the transformer loss N T1 :

[0018] Among them, N T1opt is the loss pole of the transformer without considering the constraint conditions, and the expression is:

[0019] Among them, V T(core) is the volume of the transformer magnetic core, ρ is the resistivity of the winding, l T0 is the average length of each turn of the transformer winding, α is the frequency loss index, β is the magnetic induction loss index, is the magnetic core loss coefficient, is the ratio of the AC and DC resistance of the winding; After determining the number of turns of the transformer, according to the transformer loss P T , and the thermal resistance R th(T) , judge whether the temperature rise of the transformer meets the requirements. If it meets, calculate the inductance. Otherwise, this set of decision variables is not feasible and re - select the decision variables; Calculate the inductance turns L when the inductance value is N L ; According to the requirement of non - saturation of the magnetic core, calculate the minimum number of turns of the inductor N Lmin ; Calculate the maximum number of turns of the inductor according to the requirement of the window area N Lmax :

[0020]

[0021]

[0022] Among them, A L is the inductance factor, which is determined by the shape of the inductance magnetic core, I Lmax is the maximum value of the inductor current, AeL is the effective cross-sectional area of the inductance magnetic core, A wL is the window area of the inductance magnetic core; If N Lmin < N L < N Lmax , it indicates that the inductor can meet the requirements of non-saturation of the magnetic core and sufficient window area. Then, according to the inductor loss P L , and the thermal resistance R th(L) , judge whether the inductor temperature rise meets the requirements. If it meets the requirements, calculate the total loss of the converter, as well as the total volume of the inductor and transformer, and save the design, and plot the corresponding points in the loss-volume coordinate diagram; Repeat the above process until all data in the dataset are traversed to obtain the Pareto front.

[0023] Further, step 3.3 is specifically as follows: According to the actual requirements for efficiency and power density, select a set of design results from the Pareto front to obtain the corresponding magnetic core shape, current density, and switching frequency. Calculate the winding wire diameter according to the current density, and manufacture the transformer and inductor according to the selected magnetic core shape and winding wire diameter.

[0024] Further, step 4 is specifically as follows: According to the design ranges of the MOSFET, inductor, transformer, and variable-frequency modulation, calculate the losses at different switching frequencies under different loads, and select the switching frequency with the minimum loss as the optimal switching frequency to obtain the curve of the switching frequency varying with the load.

[0025] The multi-objective optimization system for a dual-active-bridge converter based on variable-frequency modulation includes: Parameter determination module: used to determine the characteristic parameters and design variables of the DAB converter, calculate the transformer turns ratio according to the characteristic parameters, select a suitable MOSFET model, design the drive circuit according to the MOSFET model, and select the magnetic core materials for the transformer and inductor. Determine the upper and lower limits of the switching frequency according to the MOSFET model, the drive power of the drive circuit, and the magnetic core materials; Design range determination module: used to calculate the inductor value range and the switching frequency range at different inductor values and powers based on the upper and lower limits of the switching frequency according to the required soft-switching range to obtain the design range of variable-frequency modulation; Optimized design module: used to select the minimum inductor value in the design range and perform multi-objective optimization design of efficiency and power density under full-load conditions; Optimal switching frequency design module: used to find the optimal switching frequency under different load conditions within the design range.

[0026] Compared with the prior art, the present invention has the following beneficial technical effects: The present invention proposes a design method for a DAB converter under variable-frequency modulation. Compared with the traditional single-phase-shift method, this method modulates the inductor current value at the switching moment by changing the switching frequency, thereby expanding the soft-switching range and improving the light-load efficiency of the converter. The present invention gives a set of comprehensive design processes for the DAB converter under variable-frequency modulation. Based on the rated power requirement and the soft-switching requirement, the design range of variable-frequency modulation is calculated; multi-objective optimization design of efficiency and power density is carried out under full-load conditions to determine the hardware parameters of the converter; the switching frequency that maximizes the efficiency of the converter is calculated under different loads. This design process can improve the power density and the efficiency under different loads of the DAB converter, and is easy to apply in practice. Description of the Drawings

[0027] The accompanying drawings in the specification are used to provide a further understanding of the present invention, and constitute a part of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0028] Figure 1 is the circuit diagram of the DAB converter; Figure 2 is the design range of variable-frequency modulation for a specific inductor value; Figure 3 is the multi-objective optimization process under full-load conditions; Figure 4 is the comparison of the measured efficiencies of variable-frequency modulation and traditional single-phase-shift modulation. Detailed Embodiments

[0029] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0030] It should be noted that the terms "first", "second", etc. in the description, claims and above-mentioned drawings of the present invention are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0031] Embodiment 1 The present invention provides a multi-objective optimization method for a dual-active-bridge converter based on frequency modulation, including the following steps: Step 1: Calculate the transformer turns ratio according to the converter characteristic parameters, select a suitable MOSFET model, design a drive circuit, select a core material, and determine the upper and lower limits of the switching frequency; The converter characteristic parameters include the input voltage V in , output voltage V out , power P . According to the rated voltage and rated current requirements, select a suitable MOSFET model. Determine the upper limit of the switching frequency f up according to factors such as the type of switching device, drive power, and core material, and determine the lower limit of the switching frequency f low according to the core material saturation requirement.

[0032] Step 2: Calculate the inductance value range and the switching frequency range at different inductance values according to the required soft-switching range, and obtain the design range of frequency modulation; specifically: Step 2.1: List the relationship between the maximum switching frequency f smax , inductance value L and power according to the rated power requirement, and list the relationship between the minimum switching frequency f smin and inductance value and power according to the soft-switching requirement; Step 2.2: List inequalities according to the soft-switching range and the upper and lower limits of the switching frequency requirements, and solve to obtain the inductance value range. If the inequality has no solution, it means that there is no inductance value that meets the requirements; Step 2.3: For each feasible inductance value, calculate the curves of the maximum switching frequency and the minimum switching frequency varying with power within the required soft-switching range, and obtain the design range of frequency modulation.

[0033] Step 3: Select the minimum inductance value within the design range, and perform multi-objective optimization design of efficiency and power density under full-load conditions; specifically: Step 3.1: Select the minimum inductance value, and obtain the curves of the maximum switching frequency and the minimum switching frequency versus power under this parameter; Step 3.2: For the full-load condition, with the shapes of the transformer and inductor cores, the current density of the transformer winding j T , the current density of the inductor winding j L , the switching frequency f s as decision variables, with the constraints of non-saturation of the core, sufficient window area, and not too high temperature rise, and with the converter efficiency and the volume of the magnetic components as the optimization objectives, solve the multi-objective optimization problem to obtain the Pareto front; Step 3.3: Select a set of design results on the Pareto front, calculate the winding specifications, and fabricate the transformer and inductor.

[0034] Step 4: Find the optimal switching frequency under different load conditions within the design range to achieve the highest efficiency.

[0035] Embodiment 2 A multi-objective optimization method for a dual-active-bridge converter based on variable-frequency modulation, the specific steps are as follows: (1) Determine the characteristic parameters of the DAB converter, including the input voltage V in , the output voltage V out , the rated power P max . Determine the design variables, including the switching frequency f s , the inductance value L (including the external inductance L ex and the leakage inductance of the transformer L σ ), the shape of the inductor core, the winding specifications and turns of the inductor N L , the shape of the transformer core, the winding specifications and turns of the transformer (primary side N T1 , secondary side N T2 ). Figure 1 The circuit diagram of the DAB converter is given, and the meanings of the parameters are as Figure 1 shown.

[0036] According to the input and output voltages, obtain the transformer turns ratio n which is the ratio of the input voltage to the output voltage.

[0037] Select a suitable MOSFET model according to the rated voltage and rated current requirements. Design the drive circuit based on the MOSFET model, and select the core materials for the transformer and inductor. Determine the upper limit of the MOSFET switching frequency based on factors such as the type of switching device, drive power, and core material characteristics f up , and determine the lower limit of the switching frequency according to the saturation requirement of the core material f low .

[0038] Taking silicon carbide MOSFET as an example, the upper limit of its switching frequency can reach 500 kHz. It is determined by the drive power P driver , the gate voltage swing Δ V gs of the MOSFET, and the gate charge Q g of the MOSFET that the upper limit of the switching frequency can reach P driver / ( Q g Δ V gs ). Taking the ferrite N87 core material as an example, the upper limit of its frequency can reach 500 kHz. The upper limit of the switching frequency f up is determined by the minimum value among the upper limits of the switching frequencies of the silicon carbide MOSFET, the drive power supply, and the core material

[0039] The lower limit of the switching frequency f low can be set according to actual needs f low , the larger it is, the smaller the maximum magnetic induction intensity of the transformer core, and thus the smaller the volume of the transformer

[0040] (2) Calculate the design range of the variable-frequency modulation, including the inductor value range and the switching frequency range for each inductor value and power

[0041] (1) The converter needs to meet two constraint conditions: the rated power requirement and the soft-switching requirement, and is related to the inductor value and the switching frequency. Existing methods can be used to list the relationship between the maximum switching frequency f smax and the inductor value L and power according to the rated power requirement, and list the relationship between the minimum switching frequency f smin and the inductor value and power according to the soft-switching requirement

[0042] (1) (2) Among them, t margin is the margin of the dead time, C eq is the equivalent capacitance of the switching device charge.

[0043] For a specific inductance value, f smax and f smin vary with power P The curve is as Figure 2 shown.

[0044] (2) List the inequalities according to the soft-switching range and the upper and lower limits of the switching frequency. It can be seen from Figure 2 that if a suitable solution can be found within the given soft-switching range and the upper and lower limits of the switching frequency, the following conditions need to be met: Condition 1: f smin = f smax The corresponding power P 1 needs to be less than the lower limit of the soft-switching power P min ; Condition 2: Within the soft-switching power range, the required frequency range is within the frequency limit, that is, f 1 < f up and f 2 > f low . In summary, the inductance value range can be obtained by solving the inequality (1): (3) Among them, represents f smin = f smax The corresponding power , represents the lower limit of the soft-switching power, represents the output power of P min The corresponding minimum switching frequency f smin ( P = P min ), represents the output power of P max The corresponding maximum switching frequency f smax ( P = P max ), Represents the upper limit of the switching frequency obtained in step 1, Represents the lower limit of the switching frequency obtained in step 1.

[0045] If the inequality has no solution, it means that there is no inductance value that meets the requirements, and it is necessary to expand the frequency limit or narrow the required soft-switching range.

[0046] (3) For each feasible inductance value, calculate the curves of the maximum and minimum switching frequencies within the required soft-switching range versus power to obtain the design range of variable-frequency modulation.

[0047] (III) Conduct multi-objective optimization design of efficiency and power density under full-load conditions.

[0048] (1) Using the existing method, it can be known that the larger the inductance value, the lower the efficiency and power density of the converter. Therefore, select the minimum inductance value. According to the variable-frequency modulation design range calculated in the previous step, obtain the curves of the maximum and minimum switching frequencies versus power under this parameter.

[0049] (2) Conduct multi-objective hardware optimization design of the inductor and transformer in the converter under full-load conditions. The design process is as Figure 3 shown. The converter parameters include the input voltage V in , the output voltage V out , the rated power P max and the inductance value L . The fixed parameters include the frequency loss index of the magnetic core material α , the magnetic induction loss index β , the loss coefficient k i , the ratio of the AC and DC resistances of the Litz wire F R , the magnetic core saturation margin λ sat , the window area margin λ win , the saturation magnetic induction intensity B sat , the maximum allowable temperature rise Δ of the transformer and inductor T max . The variable parameters (decision variables) include the shapes of the transformer and inductor magnetic cores, the winding current density of the transformer j T , the winding current density of the inductor j L , the switching frequency f s (the value range of the switching frequency f s is obtained from the previous step). Different decision variables constitute the magnetic component data set.

[0050] The constraints of this problem include that the magnetic core is not saturated, the window area is sufficient, and the temperature rise is not too high. For each set of variable parameters, according to the requirement of non-saturation of the magnetic core, the minimum number of turns of the primary side of the transformer is calculated. N T1min ; According to the requirement of the window area, the maximum number of turns of the primary side of the transformer is calculated. N T1max : (4) (5) In the formula, A eT is the effective cross-sectional area of the transformer magnetic core, A wT is the window area of the transformer magnetic core, I Lrms is the effective value of the inductor current, is the saturation margin of the magnetic induction intensity, is the saturation magnetic induction intensity, is the window area margin.

[0051] If N T1min < N T1max , it indicates that the transformer can meet the requirements of non-saturation of the magnetic core and sufficient window area, and calculate the number of turns that minimizes the transformer loss. N T1 : (6) In the formula, N T1opt is the loss pole of the transformer without considering the constraints, and the expression is (7) In the formula, V T(core) is the volume of the transformer magnetic core, ρ is the resistivity of the winding, l T0 is the average length of each turn of the transformer winding, α is the frequency loss index, β is the magnetic induction loss index, is the magnetic core loss coefficient, is the ratio of the AC and DC resistances of the winding.

[0052] After determining the number of turns of the transformer, according to the transformer loss P T , the thermal resistance R th(T), determine whether the transformer temperature rise meets the requirements. If it meets, calculate the inductance; otherwise, the set of decision variables is infeasible, and reselect the decision variables.

[0053] Calculate the inductance value as L The number of turns of the inductor when N L ; According to the requirement of non-saturation of the magnetic core, calculate the minimum number of turns of the inductor N Lmin ; Calculate the maximum number of turns of the inductor according to the requirement of the window area N Lmax : (8) (9) (10) In the formula, A L is the inductance factor, which is determined by the shape of the inductor magnetic core, I Lmax is the maximum value of the inductor current, A eL is the effective cross-sectional area of the inductor magnetic core, A wL is the window area of the inductor magnetic core.

[0054] If N Lmin < N L < N Lmax , it means that the inductor can meet the requirements of non-saturation of the magnetic core and sufficient window area. Then, according to the inductor loss P L , thermal resistance R th(L) , determine whether the inductor temperature rise meets the requirements. If it meets the requirements, calculate the total loss of the converter, as well as the total volume of the inductor and the transformer, and save the design, and plot the corresponding point in the loss-volume coordinate diagram.

[0055] Repeat this process until all data in the dataset are traversed to obtain the Pareto front.

[0056] (3) According to the actual requirements for efficiency and power density, select a set of design results from the Pareto front to obtain the corresponding decision variables such as the magnetic core shape, current density, and switching frequency. Calculate the winding wire diameter according to the current density, and manufacture the transformer and inductor according to the selected magnetic core shape and winding wire diameter.

[0057] (IV) Optimize the switching frequency under different loads According to the design results of MOSFET, inductor and transformer, as well as the design range of variable-frequency modulation, calculate the losses at each switching frequency under different loads, select the switching frequency with the minimum loss as the optimal switching frequency, and obtain the variation curve of the switching frequency with the load.

[0058] Verify the accuracy and effectiveness of the multi-objective optimization method for the DAB converter based on variable-frequency modulation proposed in the present invention by using a DAB converter with an input bus voltage of 700V, an output bus voltage of 800V, a rated power of 6.4kW, and a soft-switching range requirement of 1.28kW - 6.4kW. Compare the converter efficiencies of traditional single-phase-shift modulation and variable-frequency modulation under different loads, as Figure 4 shown. It can be seen that the converter using variable-frequency modulation has higher efficiency under each load.

[0059] Embodiment 3 The present invention provides a multi-objective optimization system for a dual-active-bridge converter based on variable-frequency modulation, including: A parameter determination module: used to determine the characteristic parameters and design variables of the DAB converter, calculate the transformer turns ratio according to the characteristic parameters, select a suitable MOSFET model, design a drive circuit according to the MOSFET model, select the magnetic core materials of the transformer and inductor, and determine the upper and lower limits of the switching frequency according to the MOSFET model, the drive power of the drive circuit, and the magnetic core materials; A design range determination module: used to calculate the inductor value range and the switching frequency range at different inductor values and powers based on the upper and lower limits of the switching frequency and according to the required soft-switching range, so as to obtain the design range of variable-frequency modulation; An optimal design module: used to select the minimum inductor value in the design range and perform multi-objective optimal design of efficiency and power density under full-load conditions; An optimal switching frequency design module: used to find the optimal switching frequency under different load conditions within the design range.

[0060] Those skilled in the art should understand that the embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0061] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and combinations of flows and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to the processors of general-purpose computers, special-purpose computers, embedded processors, or other programmable data processing devices to produce a machine, such that the instructions executed by the processors of the computer or other programmable data processing devices produce means for implementing the functions specified in the Figure 1 one or more flows and / or blocks Figure 1 one or more blocks.

[0062] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory produce a manufactured article including instruction means that implement the functions specified in the Figure 1 one or more flows and / or blocks Figure 1 one or more blocks.

[0063] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operational steps are performed on the computer or other programmable device to produce a computer-implemented process, so that the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in the Figure 1 one or more flows and / or blocks Figure 1 one or more blocks.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the scope of its protection. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that after reading the present invention, various changes, modifications, or equivalent replacements can still be made to the specific implementation manners of the invention, but these changes, modifications, or equivalent replacements are all within the scope of the claims of the invention pending approval.

Claims

1. A multi-objective optimization method for a dual-active-bridge converter based on variable-frequency modulation, characterized in that It includes the following steps: Step 1: Determine the characteristic parameters and design variables of the DAB converter, calculate the transformer turns ratio according to the characteristic parameters, select a suitable MOSFET model, design the drive circuit according to the MOSFET model, select the magnetic core materials for the transformer and inductor, and determine the upper and lower limits of the switching frequency according to the MOSFET model, the drive power of the drive circuit, and the magnetic core materials; Step 2: Based on the upper and lower limits of the switching frequency, calculate the inductor value range and the switching frequency range at different inductor values and powers according to the required soft-switching range, and obtain the design range of variable-frequency modulation; Step 3: Select the minimum inductor value in the design range and perform multi-objective optimization design of efficiency and power density under full-load conditions; Step 4: Find the optimal switching frequency under different load conditions within the design range.

2. The multi-objective optimization method of the dual-active-bridge converter based on variable-frequency modulation according to claim 1, wherein The characteristic parameters of the DAB converter include the input voltage V in , the output voltage V out , the rated power P max ; The design variables of the DAB converter include the switching frequency f s , the inductance value L , the inductor core shape, the inductor winding specifications and the number of turns N L , the transformer core shape, the transformer winding specifications and the number of turns of the transformer; The inductance value L includes an external inductor L ex and the leakage inductance of the transformer L σ ; The number of turns of the transformer includes the number of primary turns N T1 and the number of secondary turns N T2 .

3. The multi-objective optimization method for a dual-active-bridge converter based on variable-frequency modulation according to claim 2, wherein, The calculation of the transformer turns ratio according to the characteristic parameters is specifically: Obtain the transformer turns ratio based on the input and output voltages n = V in / V out ; The selection of a suitable MOSFET model is specifically: Select a suitable MOSFET model according to the rated voltage and rated current requirements; The determination of the upper and lower limits of the switching frequency according to the MOSFET model, the drive power of the drive circuit, and the magnetic core materials is specifically: Determine the upper limit of the switching frequency based on the MOSFET model, the driving power of the driving circuit, and the magnetic core material f up , and determine the lower limit of the switching frequency according to the saturation requirement of the magnetic core material f low .

4. The multi-objective optimization method of the dual-active-bridge converter based on variable-frequency modulation according to claim 2, wherein The specific content of Step 2 is: Step 2.1: List the maximum switching frequency according to the rated power requirement f smax and the inductance value L and the power P relationship, list the minimum switching frequency according to the soft-switching requirement f smin relationship with the inductance value and the power; Among them, t margin is the margin of the dead time, C eq is the equivalent capacitance of the switch tube charge; Step 2.2: Based on the relational expression in Step 2.1, list inequalities according to the soft-switching range, the upper limit of the switching frequency f up and the lower limit of the switching frequency f low requirements, and solve to obtain the range of the inductor value; Step 2.3: For each feasible inductor value, calculate the curves of the maximum switching frequency and the minimum switching frequency within the required soft-switching range versus power, and obtain the design range of variable-frequency modulation.

5. The multi-objective optimization method of the dual-active-bridge converter based on variable-frequency modulation according to claim 4, wherein The specific inequality in Step 2.2 is: Among them, represents f smin = f smax the corresponding power when , represents the lower limit of the soft-switching power, represents that the output power is P min the corresponding minimum switching frequency when f smin ( P = P min ), represents that the output power is P max the corresponding maximum switching frequency when f smax ( P = P max ), represents the upper limit of the switching frequency, represents the lower limit of the switching frequency.

6. The multi-objective optimization method of a dual-active-bridge converter based on variable-frequency modulation according to claim 2, characterized in that The specific content of Step 3 is: Step 3.1: Select the minimum inductor value and obtain the curves of the maximum switching frequency and the minimum switching frequency versus power at this minimum inductor value; Step 3.2: For the full-load condition, with the transformer core shape, inductor core shape, transformer winding current density j T , inductor winding current density j L , switching frequency f s as decision variables, construct a magnetic component data set. Among them, the value range of the switching frequency f s is obtained through Step 3.

1. With the constraints of non-saturation of the core, sufficient window area, and not too high temperature rise, and the converter efficiency and magnetic component volume as the optimization objectives, solve the multi-objective optimization problem to obtain the Pareto front; Step 3.3: Select a set of design results on the Pareto front, calculate the winding specifications, and fabricate the transformer and inductor.

7. The multi-objective optimization method of the dual-active-bridge converter based on variable-frequency modulation according to claim 6, wherein The specific content of Step 3.2 is: Calculate the minimum number of turns of the primary side of the transformer according to the requirement of core non-saturation N T1min ; Calculate the maximum number of turns of the primary side of the transformer according to the requirement of window area N T1max : Among them, A eT is the effective cross-sectional area of the transformer core, A wT is the window area of the transformer core, I Lrms is the effective value of the inductor current, is the saturation margin of the magnetic induction intensity, is the saturation magnetic induction intensity, is the window area margin; If N T1min < N T1max , it indicates that the transformer can meet the requirements of non-saturation of the magnetic core and sufficient window area, and calculate the primary turns to minimize the transformer loss N T1 : Among them, N T1opt is the loss pole of the transformer without considering the constraint conditions, and the expression is: Among them, V T(core) is the volume of the transformer core, ρ is the resistivity of the winding, l T0 is the average length of each turn of the transformer winding, α is the frequency loss index, β is the magnetic induction loss index, is the core loss coefficient, is the ratio of the AC and DC resistances of the winding; After determining the number of turns of the transformer, according to the transformer loss P T , thermal resistance R th(T) , judge whether the temperature rise of the transformer meets the requirements. If it meets, perform inductance calculation; otherwise, this set of decision variables is infeasible and reselect the decision variables; Calculate the number of turns of the inductor when the inductance value is L ; According to the requirement of non-saturation of the magnetic core, calculate the minimum number of turns of the inductor N L ; Calculate the maximum number of turns of the inductor according to the requirement of the window area N Lmin ; N Lmax : Among them, A L is the inductance factor, which is determined by the shape of the inductor core, I Lmax is the maximum value of the inductor current, A eL is the effective cross-sectional area of the inductor core, A wL is the window area of the inductor core; If N Lmin < N L < N Lmax , it indicates that the inductor can meet the requirements of non-saturation of the magnetic core and sufficient window area. Then, based on the inductor loss P L , and the thermal resistance R th(L) , judge whether the inductor temperature rise meets the requirements. If it meets the requirements, calculate the total loss of the converter, as well as the total volume of the inductor and the transformer, and save the design. Plot the corresponding points in the loss-volume coordinate diagram; Repeat the above process until all data in the dataset are traversed to obtain the Pareto front.

8. The multi-objective optimization method of the dual-active-bridge converter based on variable-frequency modulation according to claim 7, wherein The specific content of Step 3.3 is: According to the actual requirements for efficiency and power density, select a set of design results from the Pareto front to obtain the corresponding magnetic core shape, current density, and switching frequency. Calculate the winding wire diameter according to the current density, and fabricate the transformer and inductor according to the selected magnetic core shape and winding wire diameter.

9. The multi-objective optimization method for a dual-active-bridge converter based on variable-frequency modulation according to claim 6, wherein The specific content of Step 4 is: According to the MOSFET, inductor, transformer, and the design range of variable-frequency modulation, calculate the losses of each switching frequency under different loads, and select the switching frequency with the minimum loss as the optimal switching frequency to obtain the curve of the switching frequency versus the load.

10. A multi-objective optimization system for a dual-active-bridge converter based on variable-frequency modulation, characterized in that, It includes: Parameter determination module: Used to determine the characteristic parameters and design variables of the DAB converter, calculate the transformer turns ratio according to the characteristic parameters, select a suitable MOSFET model, design the drive circuit according to the MOSFET model, select the magnetic core materials for the transformer and inductor, and determine the upper and lower limits of the switching frequency according to the MOSFET model, the drive power of the drive circuit, and the magnetic core materials; Design range determination module: Used to calculate the inductor value range and the switching frequency range at different inductor values and powers based on the upper and lower limits of the switching frequency according to the required soft-switching range, and obtain the design range of variable-frequency modulation; Optimization Design Module: used to select the minimum inductance value within the design range and perform multi-objective optimization design of efficiency and power density under full-load conditions; Optimal Switching Frequency Design Module: used to find the optimal switching frequency under different load conditions within the design range.

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