Parameter determination method of transformer and magnetic element and dual active bridge circuit

Abstract

The invention discloses a parameter determination method of a transformer and a magnetic element and a dual-active bridge circuit, and the method comprises the steps: determining that the dual-active bridge circuit meets the ZVS soft switching requirement when an upper switching tube of a left bridge arm of a bridge circuit at an output end is switched on, a first correspondence of the switching frequency with respect to the input power supply, the output voltage, the load and the turn ratio; determining a second corresponding relation of the switching frequency relative to the input power supply, the output voltage, the load and the turn ratio when the dual active bridge circuit meets the ZVS soft switching requirement and an upper switching tube of a left bridge arm of the bridge circuit at the input end is cut off; determining a first switching frequency value when the input power supply is a first value; determining a second switching frequency value when the input power supply is a second value; determining a turn ratio according to the first switching frequency value and the second switching frequency value; the first value is Vimax, and the second value is Vimin. By means of the mode, the parameters of the transformer meeting the system characteristics can be quantitatively and accurately designed.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of dual-active bridge circuits, and in particular, to a method for determining parameters of a transformer and a magnetic component, and a dual-active bridge circuit. Background Art

[0002] Dual Active Bridge (DAB) circuits are widely used in power electronic converters due to their advantages such as bi-directional energy flow, high power density, and good soft-switching characteristics. The modulation methods of DAB circuits mainly include Single Phase Shift (SPS) modulation, dual phase shift modulation, extended phase shift modulation, triple phase shift modulation, etc. When the input and output voltages of a power electronic transformer are constant, SPS modulation can achieve high efficiency and simple control, and is the most widely used modulation method.

[0003] The magnetic components in a DAB circuit mainly include inductors and transformers. SPS modulation adjusts its output power by changing the phase shift ratio between the two full bridges on both sides of the DAB circuit. The phase shift angle is closely related to the parameters of the magnetic components, and has a crucial impact on the efficiency, power density, and reliability of the DAB circuit. In terms of efficiency, the value of the transformer affects the soft-switching characteristics of the converter. Moreover, the design of the magnetic component parameters of most transformers is based on power distribution and uses engineering experience to give and then design the corresponding circuit component parameters, which is not universal and practical. In view of this, it is crucial to quantitatively and accurately design the parameters of the transformer that conform to the system characteristics. Summary of the Invention

[0004] The embodiments of the present application provide a method for determining parameters of a transformer and a magnetic component, and a dual-active bridge circuit, which can quantitatively and accurately design the parameters of the transformer that conform to the system characteristics.

[0005] In a first aspect, an embodiment of the present application provides a method for determining transformer parameters, which is applied to a dual-active-bridge circuit. The method includes: determining a first correspondence relationship between the switching frequency of the dual-active-bridge circuit and the input power supply, output voltage, load, and turns ratio of the transformer when the dual-active-bridge circuit meets the ZVS soft-switching requirement and the upper switching tube of the left bridge arm of the bridge circuit at the output end of the dual-active-bridge circuit is turned on; determining a second correspondence relationship between the switching frequency and the input power supply, output voltage, load, and turns ratio when the dual-active-bridge circuit meets the ZVS soft-switching requirement and the upper switching tube of the left bridge arm of the bridge circuit at the input end of the dual-active-bridge circuit is turned off; determining a first switching frequency value corresponding to the first correspondence relationship when the voltage of the input power supply is a first value; determining a second switching frequency value corresponding to the second correspondence relationship when the voltage of the input power supply is a second value; determining the turns ratio according to the first switching frequency value and the second switching frequency value; wherein, the voltage range of the input power supply is [Vi_min, Vi_max], the first value is the maximum value Vi_max in the voltage range of the input power supply, and the second value is the minimum value Vi_min in the voltage range of the input power supply.

[0006] In one or more embodiments, the bridge circuit at the input end of the dual-active-bridge circuit and the bridge circuit at the output end of the dual-active-bridge circuit are respectively a first bridge circuit and a second bridge circuit; the first correspondence relationship is: determining the first correspondence relationship between the switching frequency and the input power supply, output voltage, load, and turns ratio according to the first external phase-shift angle and the output power of the dual-active-bridge circuit under single-phase-shift modulation; wherein, the first external phase-shift angle is the external phase-shift angle when the dual-active-bridge circuit meets the critical condition of ZVS soft-switching requirement and the upper switching tube of the left bridge arm of the second bridge circuit is turned on; the second correspondence relationship is: determining the second correspondence relationship between the switching frequency and the input power supply, output voltage, load, and turns ratio according to the second external phase-shift angle and the output power; wherein, the second external phase-shift angle is the external phase-shift angle when the dual-active-bridge circuit meets the critical condition of ZVS soft-switching requirement and the upper switching tube of the left bridge arm of the second bridge circuit is turned on.

[0007] In one or more embodiments, determining the turns ratio according to the first switching frequency value and the second switching frequency value includes: setting the first switching frequency value and the second switching frequency value to be equal to determine the turns ratio; Vi_max = N * Vi_min, 1 < N < 2.

[0008] In one or more embodiments, determining the first correspondence relationship between the switching frequency and the input power supply, output voltage, load, and turns ratio according to the first external phase-shift angle and the output power of the dual-active-bridge circuit under single-phase-shift modulation includes: the first correspondence relationship is: F1 = Ro × (Vi 2 -Vo 2 ×Ntr 2) / (8 × Ls × Vi × Vo × Ntr), where the voltage gain G = Vo × Ntr / Vi and G < 1, F1 is the first correspondence, Ro is the resistance value of the load, Vi is the voltage of the input power supply, Vo is the output voltage of the dual active bridge circuit, Ntr is the turns ratio, and Ls is the inductance value of the resonant inductor of the resonant network of the dual active bridge circuit; determine the second correspondence of the switching frequency with respect to the input power supply, output voltage, load, and turns ratio according to the second external phase shift angle and output power, including: The second correspondence is: F2 = Ro × Vi × (Vo 2 × Ntr 2 - Vi 2 ) / (8 × Ls × Vo 3 × Ntr 3 ), where the voltage gain G = Vo × Ntr / Vi and G ≥ 1, and F2 is the second correspondence.

[0009] In one or more embodiments, when the first switching frequency value and the second switching frequency value are equal, determine the turns ratio, including: The turns ratio is: , where Ntr is the turns ratio and Vo is the output voltage of the dual active bridge circuit.

[0010] In one or more embodiments, when the dual active bridge circuit meets the critical condition for ZVS soft switching requirement and the upper switching transistor of the left bridge arm of the second bridge circuit is turned on, the current value i1 of the resonant inductor of the resonant network of the dual active bridge circuit satisfies: i1 > 0, i1 = 0.5 × (2θ - (1 - Vo × Ntr / Vi)) × Vi / (2π × fs × Ls), where fs is the switching frequency; based on the critical condition i1 = 0 for the dual active bridge circuit to meet the ZVS soft switching requirement, determine the first external phase shift angle θ1 as: θ1 = 0.5 × (1 - Vo × Ntr / Vi), where Vi is the voltage of the input power supply, Vo is the output voltage of the dual active bridge circuit, and Ntr is the turns ratio.

[0011] In one or more embodiments, when the dual active bridge circuit meets the critical condition for ZVS soft switching requirement and the upper switching transistor of the left bridge arm of the first bridge circuit is turned off, the current value i2 of the resonant inductor of the resonant network of the dual active bridge circuit satisfies: i2 > 0, i2 = 0.5 × (2θ × Vo × Ntr / Vi + (1 - Vo × Ntr / Vi)) × Vi / (2π × fs × Ls), where fs is the switching frequency; based on the critical condition i2 = 0 for the dual active bridge circuit to meet the ZVS soft switching requirement, determine the second external phase shift angle θ2 as: θ2 = 0.5 × (1 - Vi / (Vo × Ntr)), where Vi is the voltage of the input power supply, Vo is the output voltage of the dual active bridge circuit, and Ntr is the turns ratio.

[0012] In one or more embodiments, the output power is Po = (Vi × Vo × θ × (1 - θ)) / (2 × Ls × fs × Ntr), where Po is the output power, Vi is the voltage of the input power supply, Ntr is the turns ratio, Vo is the output voltage of the dual active bridge circuit, θ is the external phase shift angle of the dual active bridge circuit, Ls is the inductance value of the resonant inductor of the resonant network of the dual active bridge circuit, and fs is the switching frequency.

[0013] In a second aspect, an embodiment of the present application provides a method for determining parameters of a magnetic component of a dual active bridge circuit. The magnetic component includes a transformer and a resonant inductor. The method for determining parameters of the magnetic component of the dual active bridge circuit includes: determining the turns ratio of the transformer by the method for determining transformer parameters as described above; determining the inductance value of the resonant inductor according to the input power supply, the maximum output power of the dual active bridge circuit, the switching frequency of the dual active bridge circuit, the external phase shift angle of the dual active bridge circuit, and the output power of the dual active bridge circuit under single phase shift modulation.

[0014] In a third aspect, an embodiment of the present application provides a dual active bridge circuit, including: an input power supply; a first bridge circuit, the input end of the first bridge circuit is connected to the input power supply; a resonant network, the input end of the resonant network is connected to the output end of the first bridge circuit; a second bridge circuit, the input end of the second bridge circuit is connected to the output end of the resonant network, and the output end of the second bridge circuit is connected to a load; the turns ratio of the transformer of the resonant network and the inductance value of the resonant inductor of the resonant network are determined by the method for determining parameters of the magnetic component of the dual active bridge circuit as described above.

[0015] The beneficial effects of the present application are as follows: The transformer parameter determination method of the embodiment of the present application is applied to a dual-active bridge circuit. The method includes: determining a first correspondence relationship between the switching frequency of the dual-active bridge circuit and the input power supply, output voltage, load, and turns ratio of the transformer when the dual-active bridge circuit meets the ZVS soft-switching requirement and the upper switch tube of the left bridge arm of the bridge circuit at the output end of the dual-active bridge circuit is turned on; determining a second correspondence relationship between the switching frequency and the input power supply, output voltage, load, and turns ratio when the dual-active bridge circuit meets the ZVS soft-switching requirement and the upper switch tube of the left bridge arm of the bridge circuit at the input end of the dual-active bridge circuit is turned off; determining a first switching frequency value corresponding to the first correspondence relationship when the voltage of the input power supply is a first value; determining a second switching frequency value corresponding to the second correspondence relationship when the voltage of the input power supply is a second value; determining the turns ratio according to the first switching frequency value and the second switching frequency value; wherein, the voltage range of the input power supply is [Vi_min, Vi_max], the first value is the maximum value Vi_max in the voltage range of the input power supply, and the second value is the minimum value Vi_min in the voltage range of the input power supply. Through the above process, the parameters of the transformer can be determined based on parameters related to the system operation characteristics such as the input power supply, output voltage, load, and switching frequency, thereby realizing the quantitative and accurate design of the parameters of the transformer that conforms to the system characteristics, which is beneficial to improving the versatility and practicality of the DAB circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] One or more embodiments are exemplarily illustrated by pictures in the corresponding drawings. These exemplary illustrations are not intended to limit the embodiments. Elements with the same reference numerals in the drawings represent similar elements.

[0017] Figure 1 is a schematic circuit structure diagram of the dual-active bridge circuit provided by the embodiment of the present application; Figure 2 is provided by the embodiment of the present application Figure 1 schematic diagram of each signal in the dual-active bridge circuit shown; Figure 3 is the flow of the transformer parameter determination method provided by the embodiment of the present application Figure 1 ; Figure 4 is the flow of the transformer parameter determination method provided by the embodiment of the present application Figure 2 ; Figure 5 is the relationship diagram composed of formula (5) and formula (6) provided by the embodiment of the present application and the fitted relationship diagram; Figure 6 is provided by the embodiment of the present application showing the change of fs3 (Vi, 400 2 / 500) with the change of the turns ratio; Figure 7 is the variation of the relationship curves fs4(Vi, 400 2 / 500) and fs5(Vi, 400 2 / 500) within the voltage range of the input power supply; Figure 8 is the variation of the relationship curves fs6(Vi, 400 2 / 500), fs7(Vi, 400 2 / 500) and fs8(Vi, 400 2 / 500) within the voltage range of the input power supply; Figure 9 is the flowchart of the method for determining the parameters of the magnetic element of the dual-active-bridge circuit provided by the embodiment of the present application; Figure 10 is the variation of the relationship curves fs9(Vi, 400 2 / 1000) and fs10(Vi, 400 2 / 500) within the voltage range of the input power supply; Figure 11 is the variation of the relationship curves θ_zvs(Vi, 400 2 / 1000) and θ_zvs(Vi, 400 2 / 500) within the voltage range of the input power supply. Detailed implementation manners

[0018] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and detailedly described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. It should be understood that the specific embodiments described herein are only used to explain the present application, rather than to limit the present application.

[0019] It should be noted that when an element is expressed as "connected" to another element, it can be directly connected to the other element, or there can be one or more intermediate elements therebetween.

[0020] In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0021] Please refer to Figure 1 , Figure 1 which is the schematic circuit diagram of the dual-active-bridge circuit provided by the embodiment of the present application. As Figure 1As shown, the dual-active bridge circuit 100 includes a first bridge circuit 110, a second bridge circuit 120, a resonant network 130, and an input power supply 140. Among them, the input power supply 140 is connected to the input end of the first bridge circuit 110. The output end of the first bridge circuit 110 and the input end of the second bridge circuit 120 are respectively connected to both ends of the resonant network 130. The output end of the second bridge circuit 120 is connected to the load.

[0022] Among them, the first bridge circuit 110 is the bridge circuit at the input end of the dual-active bridge circuit 100. The input end of the first bridge circuit 110 is connected to the input power supply 140, and the output end of the first bridge circuit 110 is connected to the input end of the resonant network 130. The first bridge circuit 110 is a full-bridge circuit. The first bridge circuit includes a left bridge arm and a right bridge arm. The left bridge arm of the first bridge circuit 110 includes a first switching tube Q1 and a second switching tube Q2. Among them, the first switching tube Q1 is called the upper switching tube of the left bridge arm, and the second switching tube Q2 is called the lower switching tube of the left bridge arm. The right bridge arm includes a third switching tube Q3 and a fourth switching tube Q4. Among them, the fourth switching tube Q4 is called the upper switching tube of the right bridge arm, and the third switching tube Q3 is called the lower switching tube of the right bridge arm. The circuit composed of the series connection of the first switching tube Q1 and the second switching tube Q2 and the circuit composed of the series connection of the third switching tube Q3 and the fourth switching tube Q4 are connected in parallel and are connected between the positive and negative poles of the input power supply 140. The connection point between the first switching tube Q1 and the second switching tube Q2 is connected to the first end of the primary side of the transformer T1, and the connection point between the third switching tube Q3 and the fourth switching tube Q4 is connected to the second end of the primary side of the transformer T1. The first switching tube Q1 and the third switching tube Q3 receive a drive signal g1, and the second switching tube Q2 and the fourth switching tube Q4 receive a drive signal g2.

[0023] The second bridge circuit 120 is a bridge circuit at the output end of the dual active bridge circuit 100. The input end of the second bridge circuit 120 is connected to the output end of the resonant network 130, and the output end of the second bridge circuit 120 is connected to the load. The second bridge circuit 120 is a full-bridge circuit. The second bridge circuit 120 includes a left bridge arm and a right bridge arm. The left bridge arm of the second bridge circuit 120 includes a fifth switching tube Q5 and a sixth switching tube Q6. Among them, the fifth switching tube Q5 is called the upper switching tube of the left bridge arm, and the sixth switching tube Q6 is called the lower switching tube of the left bridge arm. The right bridge arm of the second bridge circuit 120 includes a seventh switching tube Q7 and an eighth switching tube Q8. Among them, the eighth switching tube Q8 is called the upper switching tube of the right bridge arm, and the seventh switching tube Q7 is called the lower switching tube of the right bridge arm. The circuit formed by the series connection of the fifth switching tube Q5 and the sixth switching tube Q6 and the circuit formed by the series connection of the seventh switching tube Q7 and the eighth switching tube Q8 are connected in parallel. The connection point between the fifth switching tube Q5 and the sixth switching tube Q6 and the connection point between the seventh switching tube Q7 and the eighth switching tube Q8 are respectively connected to the resonant inductor Ls of the resonant network 130. The connection point between the seventh switching tube Q7 and the eighth switching tube Q8 is connected to the resonant capacitor Cs of the resonant network 130. The fifth switching tube Q5 and the seventh switching tube Q7 are input with a drive signal g3, and the sixth switching tube Q6 and the eighth switching tube Q8 are input with a drive signal g4.

[0024] The resonant network 130 includes a transformer T1, a resonant inductor Ls, and a resonant capacitor Cs. The first end of the secondary side of the transformer T1 is connected to the resonant inductor Ls, and the second end of the secondary side of the transformer T1 is connected to the resonant capacitor Cs. Among them, the turns ratio of the transformer T1 and the inductance value of the resonant inductor Ls are determined by the parameter determination method of the magnetic element of the dual active bridge circuit in any embodiment of the present application.

[0025] Please refer to Figure 2 , Figure 2 is Figure 1 the schematic diagram of each signal in the dual active bridge circuit when the dual active bridge circuit shown uses single-phase shift modulation. Among them, in Figure 2 , the abscissa is time, and the ordinate from top to bottom is the drive signal g1, the drive signal g2, the drive signal g3, the current ILs flowing through the resonant inductor Ls, and the current IQ1 flowing through the first switching tube Q1 (or the current IQ4 flowing through the fourth switching tube Q4).

[0026] As Figure 2As shown, the current i1 is the critical condition for the dual active bridge circuit 100 to meet the ZVS soft-switching requirement, and it is the current value of the resonant inductor Ls of the resonant network 130 of the dual active bridge circuit 100 when the upper switching tube (i.e., the fifth switching tube Q5) of the left bridge arm of the second bridge circuit 120 is turned on; it is the current value of the resonant inductor Ls corresponding to the moment Ts1. The current i2 is the critical condition for the dual active bridge circuit 100 to meet the ZVS soft-switching requirement, and it is the current value of the resonant inductor Ls of the resonant network 130 of the dual active bridge circuit 100 when the upper switching tube (i.e., the first switching tube Q1) of the left bridge arm of the first bridge circuit 110 is turned off; it is the current value of the resonant inductor Ls corresponding to the moment Ts2. In the dual active bridge circuit 100, the external phase-shift angle θ refers to the phase difference of the switch switching between the first bridge circuit 110 and the second bridge circuit 120. Specifically, it is the angle corresponding to the delay time of the switching tube in the first bridge circuit 110 relative to the corresponding switching tube in the second bridge circuit 120. For example, it is the angle corresponding to the delay time of the first switching tube Q1 in the first bridge circuit 110 relative to the fifth switching tube Q5 in the second bridge circuit 120.

[0027] In the related art, for Figure 1 the circuit structure shown, the parameter design of the magnetic components of the transformer in most of the dual active bridge circuits 100 is based on power distribution and uses engineering experience to give and then design the corresponding circuit element parameters, which is not universal and practical.

[0028] Based on this, the embodiment of the present application provides a method for determining the parameters of a transformer applied to a dual active bridge circuit, which can quantitatively and accurately design the parameters of a transformer that conforms to the system characteristics.

[0029] Please refer to FIG. 3, Figure 3 which is a flowchart of the method for determining the parameters of the transformer provided by the embodiment of the present application. Among them, the method for determining the parameters of the transformer is applied to a dual active bridge circuit, and the specific implementation process of the dual active bridge circuit can be referred to for Figure 1 and Figure 2 the description of Figure 3 As shown, the method for determining the parameters of the transformer includes the following steps S310 to S350: Step S310: Determine the first correspondence relationship between the switching frequency of the dual active bridge circuit and the input power supply, output voltage, load, and turns ratio of the transformer when the dual active bridge circuit meets the ZVS soft-switching requirement and the upper switching tube of the left bridge arm of the bridge circuit at the output end of the dual active bridge circuit is turned on.

[0030] Step S320: Determine the second corresponding relationship of the switching frequency with respect to the input power supply, output voltage, load, and turns ratio when the dual active bridge circuit meets the ZVS soft-switching requirement and the upper switch of the left bridge arm of the bridge circuit at the input end of the dual active bridge circuit is turned off.

[0031] Among them, ZVS (Zero Voltage Switching) is a soft-switching technology that can perform switching operations when the voltage of the power switch tube is zero, thereby reducing switching losses and electromagnetic interference (EMI). In Figure 1 , that the bridge circuit at the input end of the dual active bridge circuit meets the ZVS soft-switching requirement means that each switch tube among the first switch tube Q1 to the fourth switch tube Q4 completes the switching action when the voltage across its two ends (the two ends other than the control end) is zero; that the bridge circuit at the output end of the dual active bridge circuit meets the ZVS soft-switching requirement means that each switch tube among the fifth switch tube Q5 to the eighth switch tube Q8 completes the switching action when the voltage across its two ends (the two ends other than the control end) is zero. In Figure 2 , when the dual active bridge circuit meets the ZVS soft-switching requirement, and the moment when the upper switch of the left bridge arm of the bridge circuit at the output end of the dual active bridge circuit is turned on is moment Ts1; when the dual active bridge circuit meets the ZVS soft-switching requirement, and the moment when the upper switch of the left bridge arm of the bridge circuit at the input end of the dual active bridge circuit is turned off is moment Ts2. The first corresponding relationship or the second corresponding relationship refers to the corresponding relationship of the switching frequency with respect to the voltage Vi of the input power supply 140, the output voltage V0, the resistance value Ro of the load, and the turns ratio of the transformer T1.

[0032] In some embodiments, as Figure 4 shown, the specific implementation process of step S310 includes step S410, and the specific implementation process of step S320 includes step S420: Step S410: Determine the first corresponding relationship of the switching frequency with respect to the input power supply, output voltage, load, and turns ratio according to the first external phase shift angle and the output power of the dual active bridge circuit under single-phase shift modulation; wherein, the first external phase shift angle is the external phase shift angle when the dual active bridge circuit meets the critical condition of ZVS soft-switching and the upper switch of the left bridge arm of the second bridge circuit is conducting.

[0033] Step S420: Determine the second corresponding relationship of the switching frequency with respect to the input power supply, output voltage, load, and turns ratio according to the second external phase shift angle and the output power; wherein, the second external phase shift angle is the external phase shift angle when the dual active bridge circuit meets the critical condition of ZVS soft-switching and the upper switch of the left bridge arm of the second bridge circuit is conducting.

[0034] Specifically, in a specific implementation manner, the process of determining the output power of the dual active bridge circuit 100 is as follows: When the dual-active-bridge circuit 100 adopts single-phase-shift modulation, the output power of the dual-active-bridge circuit 100 is shown in the following formula (1): Po = (Vi × Vo × θ × (1 - θ)) / (2 × Ls × fs × Ntr) (1) Where, Po is the output power, Vi is the voltage of the input power supply 140, Ntr is the turns ratio, Vo is the output voltage of the dual-active-bridge circuit 100, θ is the external phase-shift angle of the dual-active-bridge circuit 100, and θ ∈ (0, 1), Ls is the inductance value of the resonant inductor of the resonant network 130 of the dual-active-bridge circuit 100, fs is the switching frequency, and Ro is the resistance value of the load.

[0035] When the output power Po = (Vo × Vo) / Ro, from this and formula (1), the following formula (2) can be obtained: Vo = (Vi × Ro × θ × (1 - θ)) / (2 × Ls × fs × Ntr) (2) The process of determining the first external phase-shift angle is as follows: When the dual-active-bridge circuit 100 meets the critical condition for ZVS soft-switching requirements and the upper switching tube (i.e., the fifth switching tube Q5) of the left bridge arm of the second bridge circuit 120 is conducting, the current value i1 of the resonant inductor of the resonant network 130 of the dual-active-bridge circuit 100 satisfies: i1 > 0, i1 = 0.5 × (2θ - (1 - Vo × Ntr / Vi)) × Vi / (2π × fs × Ls), where fs is the switching frequency. Taking the critical condition as i1 = 0, according to the critical condition for the second bridge circuit 120 to meet the ZVS soft-switching requirements, the first external phase-shift angle θ1 is shown in the following formula (3): θ1 = 0.5 × (1 - Vo × Ntr / Vi) (3) The process of determining the second external phase-shift angle is as follows: When the dual-active-bridge circuit 100 meets the critical condition for ZVS soft-switching requirements and the upper switching tube (i.e., the first switching tube Q1) of the left bridge arm of the first bridge circuit 110 is cut off, the current value i2 of the resonant inductor of the resonant network 130 of the dual-active-bridge circuit 100 satisfies: i2 > 0, i2 = 0.5 × (2θ × Vo × Ntr / Vi + (1 - Vo × Ntr / Vi)) × Vi / (2π × fs × Ls), where fs is the switching frequency. Taking the critical condition as i2 = 0, according to the critical condition for the first bridge circuit 110 to meet the ZVS soft-switching requirements, the second external phase-shift angle θ2 is shown in the following formula (4): θ2 = 0.5 × (1 - Vi / (Vo × Ntr)) (4) As can be seen from Equation (3) and Equation (4), when the voltage Vi of the input power supply 140 varies within the range of [Vi_min, Vi_max], the external phase shift angle must be greater than a value, and this value is related to the voltage Vi of the input power supply 140. The specific description is as follows. For the two inequalities (i1 > 0 and i2 > 0) that meet the ZVS soft-switching requirements above, the two inequalities for the external phase shift angle θ originally obtained are θ > 0.5×(1 - Vo×Ntr / Vi) and θ > 0.5×(1 - Vi / (Vo×Ntr)), respectively. Thus, as long as the external phase shift angle θ is greater than the maximum value of the right-hand sides of the above two inequalities (0.5×(1 - Vo×Ntr / Vi) and 0.5×(1 - Vi / (Vo×Ntr))), the ZVS soft-switching requirements of both the first bridge circuit 110 and the second bridge circuit 120 can be achieved simultaneously. Combining Equation (3) and Equation (4), at this time, if the external phase shift angle θ is smaller, the current i1 and the current i2 are also smaller, thereby ensuring that the dual-active-bridge circuit 100 can maintain a small loss while meeting the ZVS soft-switching requirements and improving the overall efficiency of the machine.

[0036] The process of determining the first correspondence and the second correspondence is as follows: Set the voltage gain G = Vo×Ntr / Vi, and the external phase shift angle θ is determined according to Equation (3) and Equation (4). Substitute Equation (3): θ1 = 0.5×(1 - Vo×Ntr / Vi) into Equation (2) to obtain the first correspondence F1: F1 = Ro×(Vi 2 - Vo 2 × Ntr 2 ) / (8×Ls×Vi×Vo×Ntr), where the voltage gain G < 1 (5) Among them, the first correspondence F1 can also be understood as an expression or function of the switching frequency with respect to the input power supply, output voltage, load, and turns ratio.

[0037] Substitute Equation (4) into Equation (2) to obtain the second correspondence F2, as shown in the following Equation (6): F2 = Ro×Vi×(Vo 2 × Ntr 2 - Vi 2 ) / (8×Ls×Vo 3 × Ntr 3 )), where the voltage gain G ≥ 1 (6) Among them, the second correspondence F2 can also be understood as an expression or function of the switching frequency with respect to the input power supply, output voltage, load, and turns ratio.

[0038] Step S330: Determine the first switching frequency value corresponding to the first correspondence relationship when the voltage of the input power supply is the first value, where the first value is the maximum value in the voltage range of the input power supply.

[0039] Step S340: Determine the second switching frequency value corresponding to the second correspondence relationship when the voltage of the input power supply is the second value, where the second value is the minimum value in the voltage range of the input power supply.

[0040] Step S350: Determine the turns ratio according to the first switching frequency value and the second switching frequency value.

[0041] Among them, the voltage range of the input power supply 140 is [Vi_min, Vi_max], the first value is the maximum value Vi_max in the voltage range of the input power supply 140, and the second value is the minimum value Vi_min in the voltage range of the input power supply 140.

[0042] Specifically, from formulas (5) and (6), it can be obtained that when the output voltage Vo is constant, the switching frequency fs is linearly related to the resistance value Ro of the load. The larger the resistance value Ro, the higher the required frequency; conversely, the smaller the resistance value Ro, the lower the required frequency. At the same time, the switching frequency fs is also related to the voltage Vi of the input power supply 140. According to formulas (5) and (6), it is possible to select an appropriate turns ratio according to the voltage range [Vi_min, Vi_max] of the input power supply 140 to reduce the adjustment range of the switching frequency fs.

[0043] In some embodiments, for the input power supply 140 with a small voltage range, for example, a single-cell lithium-ion battery with a voltage range of 2.5V to 3.6V, an appropriate turns ratio can be selected according to the voltage range [Vi_min, Vi_max] of the input power supply 140 to reduce the adjustment range of the switching frequency fs, thereby achieving efficiency optimization. Among them, for the input power supply 140 with a small voltage range, it can be limited by Vi_max = N * Vi_min, 1 < N < 2, that is, according to Vi_max = N * Vi_min, 1 < N < 2, it is determined that the voltage range of the input power supply 140 is small. For example, for a single-cell lithium-ion battery, N is 1.45, then the voltage range of the lithium-ion battery is [Vi_min, 1.45 × Vi_min], and it is determined that the single-cell lithium-ion battery is an input power supply 140 with a small voltage range.

[0044] The specific process of determining the turns ratio is as follows: Substitute the minimum voltage Vi_min of the input power supply 140 into formula (6), and denote the obtained switching frequency expression as the switching frequency fs1. The switching frequency fs1 is the first switching frequency value. Substitute the maximum voltage Vi_max of the input power supply 140 into formula (5), and denote the obtained switching frequency expression as the switching frequency fs2. The switching frequency fs2 is the second switching frequency value.

[0045] Let fs1 = fs2, and the following formula (7) can be obtained: (7) According to formula (7), a more appropriate turns ratio Ntr can be determined. On the one hand, it realizes the determination of the parameters (turns ratio Ntr) of the transformer based on the parameters related to the system operation characteristics such as the voltage Vi of the input power supply 140, the output voltage Vo, the resistance value Ro of the load, and the switching frequency fs. That is, it realizes the quantitative and accurate design of the parameters of the transformer that conforms to the system characteristics, which is beneficial to improving the versatility and practicality of the DAB circuit. On the other hand, it can narrow the adjustment range of the switching frequency fs. Thus, while meeting the requirements of the output range and the load, the optimization of efficiency can be achieved.

[0046] It should be noted that from formula (5) and formula (6), it can be seen that when the output voltage Vo is determined, the switching frequency fs is related to the resistance value Ro of the load. The larger the resistance value Ro of the load, the higher the switching frequency required to achieve the determined output voltage Vo; conversely, the smaller the resistance value Ro of the load, the lower the switching frequency required to achieve the determined output voltage Vo. Similarly, from formula (5) and formula (6), it can be seen that the switching frequency fs is also related to the voltage Vi of the input power supply 140. Therefore, within the determined voltage range of the input power supply 140, by adjusting the switching frequency fs, the output voltage and power required by the load can be achieved. That is, the frequency modulation range of the switching frequency fs during the frequency modulation process affects the adjustment efficiency of the output voltage. Based on this, in order to reduce the adjustment range of the switching frequency fs and achieve efficiency optimization, this application designs the relationship between the turns ratio Ntr parameter of the transformer of the magnetic component corresponding to formula (7) and the input of the input power supply.

[0047] The principle of designing formula (7) in this application to narrow the adjustment range of the switching frequency fs will be described below.

[0048] Understandably, from the above formulas (5) and (6), when the difference between Vi and Vo×Ntr is large, as the resistance value Ro of the load changes, the switching frequency fs will change significantly. This means that as the resistance value Ro of the load changes continuously, the switching frequency fs requires a large adjustment range to meet the output voltage and power provided to the load. In this way, the frequency modulation range of the frequency modulation process is too large and the efficiency is low. The turns ratio Ntr is selected to satisfy: Vi_min / Vo < Ntr < Vi_max / Vo.

[0049] When the resistance value Ro of the load and the required output voltage are determined, and the voltage Vi of the input power supply 140 changes, for formulas (5) and (6), it can be regarded as the relationship curve between the switching frequency fs and the voltage Vi of the input power supply. In the relationship curve graph, the abscissa is the voltage value of the input power supply 140 and the ordinate is the value of the switching frequency fs. And at this time, the switching frequency fs is a combination of a first-order function and a third-order function of the voltage Vi of the input power supply 140. Let formula (7) = 0, and we get Vi = Ntr×Vo, that is, for the relationship curve between the switching frequency fs and the voltage Vi of the input power supply represented by formulas (5) and (6), the abscissa corresponding to when the switching frequency fs is 0 is Ntr×Vo.

[0050] First, in Figure 5 , the abscissa is the voltage Vi of the input power supply 140, and the ordinate is the switching frequency fs. Specifically, in formula (5), by solving the derivative of the switching frequency fs with respect to the voltage Vi of the input power supply 140, the derivative is a positive constant after derivation. Therefore, in the first interval of [Ntr×Vo, Vi_max] of formula (5), the switching frequency fs is a monotonically increasing function of the voltage Vi of the input power supply 140. Second, in formula (6), by solving the derivative of the switching frequency fs with respect to the voltage Vi of the input power supply 140 and letting the derivative be 0, we can obtain the extreme point , and through derivative analysis, it can be obtained that formula (6) shows monotonic increase in the second interval of [0, ); it shows monotonic decrease in the third interval of ( , Ntr×Vo]. Thus, it can be known that: the relationship curve presented by formula (5) is a strictly monotonically increasing function curve of the switching frequency fs with respect to the input power supply; the relationship curve presented by formula (6) is a non-strictly monotonic function curve of the switching frequency fs with respect to the input power supply, which is a combined function curve of monotonic increase and monotonic decrease.

[0051] In some embodiments, the output voltage Vo is 400V, the output power is 500W, and the resistance value Ro of the load is 400 2 / 500, and the relationship curve fs(Vi, 400 2 / 500) composed of formula (5) and formula (6), the relationship curve fs(Vi, 4002 The increasing and decreasing conditions of ( / 500) are consistent with the foregoing description, as Figure 5 shown.

[0052] Moreover, since the voltage Vi of the input power supply 140 is a continuous range value and the switching frequency fs and the output voltage Vo are in one-to-one correspondence, the adjustable range of the switching frequency fs is set to the frequency corresponding to the input voltage Vo within the range of , Vi_max]. For the input power supply 140 with a relatively small voltage range, that is, for a lithium battery whose ratio of the maximum value to the minimum value of the voltage of the input power supply 140 does not exceed 1.45, the voltage Vi of the input power supply 140 is within a smaller interval within , Vi_max]. Therefore, at this time, the relationship curves corresponding to formula (5) and formula (6) will both show strict monotonicity. That is, for a lithium battery whose ratio of the maximum value to the minimum value of the voltage of the input power supply 140 does not exceed 1.45, with as the abscissa demarcation point, the relationship curve corresponding to formula (5) shows strict monotonic increase, and the relationship curve corresponding to formula (6) shows strict monotonic decrease.

[0053] In Figure 5 , obtain multiple points of the relationship curve fs(Vi, 400 2 / 500) within [Vo×Ntr - ((Vo×Ntr - ) / 3), Vo×Ntr] (multiple points on the left side with Vo×Ntr as the demarcation point), and fit them into a straight line (this straight line is Figure 5 the first straight line fs1(Vi, 400 formed by multiple left-side fitting points in 2 / 500), which represents the relationship diagram of the switching frequency fs and the input power supply); obtain multiple points of the curve fs(Vi, 400 2 / 500) within [Vo×Ntr, Vi_max] (multiple points on the left side with Vo×Ntr as the demarcation point), and fit them into another straight line (this straight line is Figure 5 the second straight line fs2(Vi, 400 formed by multiple right-side fitting points in 2 / 500), which represents the relationship diagram of the switching frequency fs and the input power supply). In this way, obtain two linear functions of the switching frequency fs with respect to the voltage Vi of the input power supply 140 with Vo×Ntr as the demarcation point, and the corresponding relationship diagram of this function is fs3(Vi, 400 2 / 500).

[0054] For a lithium battery whose ratio of the maximum value to the minimum value of the voltage of the input power supply 140 does not exceed 1.45, the relationship diagram fs3(Vi, 400 of its switching frequency with respect to the input power supply 2 / 500) is a strictly monotonic function. Therefore, when the voltage range is within [Vi_min, Vo×Ntr], the switching frequency fs is the highest at the endpoint Vi_min of the voltage Vi of the input power supply 140. Denote the switching frequency corresponding to the endpoint Vi_min as the switching frequency fs1; when the voltage range is within [Vo×Ntr, Vi_max], the switching frequency fs is the highest at the endpoint Vi_max of the voltage Vi of the input power supply 140. Denote the switching frequency corresponding to the endpoint Vi_max as the switching frequency fs2.

[0055] Refer to Figure 6 , during the change of the turns ratio Ntr, the demarcation point Vo×Ntr of fs3(Vi, 400 2 / 500) will change, but the included angle between the two straight lines remains unchanged. This is because the slope of the linear function of the voltage Vi of the input power supply 140 approximately obtained by fs3(Vi, 400 2 / 500) is a constant related to the inductance value Ls of the resonant inductor of the resonant network 130 of the dual-active-bridge circuit 100, the resistance value Ro of the load, and the output voltage Vo of the dual-active-bridge circuit 100. Therefore, the included angle where the two straight lines intersect is certain, that is, the included angle remains θ C . Please also refer to Figure 5 and Figure 6 , with the change of the demarcation point Vo×Ntr, for the input power supply 140 with the voltage within [Vi_min, Vi_max], in order to satisfy the output voltage provided to the load, the frequency modulation range of the switching frequency fs shows different situations. For example, as Figure 6 shown, when the demarcation point Vo×Ntr is at M1, the switching frequency fs at the endpoint Vi_min is denoted as fs1.2, the switching frequency fs at the endpoint Vi_max is denoted as fs2.2, and the maximum frequency modulation range is H2; when the demarcation point Vo×Ntr is at M2, the switching frequency fs at the endpoint Vi_min is denoted as fs1.1, the switching frequency fs at the endpoint Vi_max is denoted as fs2.1, and the maximum frequency modulation range is H1. It can be seen that the frequency modulation range when the demarcation point is at M1 is greater than the frequency modulation range when the demarcation point is at M2. From Figure 6 it can be determined that no matter how the demarcation point Vo×Ntr moves, only when the switching frequency fs at the endpoint Vi_min = the switching frequency fs at the endpoint Vi_max, that is, the switching frequency fs1.1 = the switching frequency fs2.1, that is, the first switching frequency value in the above embodiment is equal to the second switching frequency value, can the frequency modulation range of the output voltage be minimized and the efficiency be the highest.

[0056] Illustrated with a specific embodiment. In this embodiment, the voltage range of the input power supply 140 is [42V, 58V], the set required output voltage Vo is 400V, and the output power is 500W. On the one hand, in the input situation and the required output situation of this embodiment, in the related prior art, the turns ratio Ntr is usually set as: Ntr = (Vi_min + Vi_max) / Vo = 0.5×(42 + 58) / 400 = 0.125. The resistance value Ro of the load = 400 2 / 500. According to formulas (5) and (6), the relationship curve fs4 (Vi, 400 2 / 500) of the switching frequency fs with respect to the input power supply and the relationship curve fs5 (Vi, 400 2 / 500) are plotted. The variation of the first two relationship curves within the voltage range [42V, 58V] is as shown in Figure 7 . Among them, in Figure 7 , the abscissa is the voltage Vi of the input power supply 140, and the ordinate is the switching frequency fs. It can be seen from Figure 7 that the maximum value fsmax1 of the switching frequency at this time is approximately 223kHz. Furthermore, taking the boundary values of the turns ratio Ntr: Ntr = 42 / 400 and Ntr = 58 / 400, substituting the above two boundary values into the corresponding formula (5) or formula (6) respectively, the relationship curves fs6 (Vi, 400 Figure 8 / 500) and fs7 (Vi, 400 2 / 500) in 2 can be plotted. It can be seen from Figure 8 that for the relationship curve fs6, the maximum value fsmax2 of the switching frequency is approximately 413kHz, and for the relationship curve fs7, the maximum value fsmax3 of the switching frequency is approximately 299kHz. On the other hand, according to the design of the turns ratio in formula (7) of this application, when the voltage range of the input power supply 140 is [42V, 58V], the turns ratio Ntr is calculated according to formula (7), and then the turns ratio Ntr is substituted into formula (5) or formula (6) to obtain the relationship curve fs8 (Vi, 400 Figure 8 / 500) in 2 . It can be seen from Figure 8 that the maximum value fsmax4 of the switching frequency corresponding to the relationship curve fs8 is approximately 200KHZ.

[0057] In summary, fsmax4 < fsmax1, fsmax4 < fsmax2, fsmax4 < fsmax3, that is, the frequency modulation range of the method provided by the embodiment of this application is the smallest. Therefore, designing the dual-active-bridge circuit 100 according to the turns ratio Ntr provided by the embodiment of this application can meet the output voltage within a smaller frequency modulation range and has higher efficiency.

[0058] Please refer to Figure 9 , Figure 9 which is a flowchart of a method for determining parameters of a magnetic component of a dual-active-bridge circuit provided in an embodiment of this application. Among them, the magnetic component includes a transformer and a resonant inductor. The specific implementation process of the dual-active-bridge circuit can be referred to the description for Figure 1 and Figure 2 , and will not be elaborated here. As Figure 9 shown, the method for determining parameters of the magnetic component of the dual-active-bridge circuit includes the following steps S910 to step S920: Step S910: Determine the turns ratio of the transformer according to the transformer parameter determination method in any embodiment of this application.

[0059] Step S920: Determine the inductance value of the resonant inductor according to the input power supply, the maximum output power of the dual-active-bridge circuit, the switching frequency of the dual-active-bridge circuit, the external phase shift angle of the dual-active-bridge circuit, and the output power of the dual-active-bridge circuit under single-phase-shift modulation.

[0060] Specifically, the specific implementation process of step S910 can be referred to the description of the steps shown for Figure 3 and Figure 4 , and will not be elaborated here.

[0061] Illustrated by a specific embodiment. In this embodiment, the voltage range of the input power supply 140 is [42V, 58V], the output voltage Vo is 400V, and if the maximum output power Pmax required by the circuit is 3000W. According to formula (7), the turns ratio Ntr = 0.127 can be obtained.

[0062] Next, when Vi = Vo × Ntr = 50.8V, the voltage gain is 1, which meets the ZVS soft-switching requirement while maintaining high efficiency. At the same time, in order to reduce the circulating current and improve the efficiency under heavy load, Vi = 50.8V, the switching frequency fs = 80kHz, and the external phase shift angle θ = 0.2 can be set. The switching frequency 80kHz is selected according to the adjustable frequency range of the switching tubes of the dual-active-bridge circuit in actual application. The switching frequency 80kHz is one of the selection methods, and the value of the external phase shift angle 0.2 is the value taken to satisfy i1 > 0 and i2 > 0 at full load. Substitute the above parameters (including the voltage Vi of the input power supply 140, the output power Po of the dual-active-bridge circuit, the switching frequency fs of the dual-active-bridge circuit, and the external phase shift angle θ of the dual-active-bridge circuit) into formula (1), and the calculated inductance value of the resonant inductor Ls = 53.7uH can be obtained.

[0063] In summary, the process of determining the parameters of the magnetic component is realized.

[0064] Afterwards, substituting the parameters of the transformer Ntr and the resonant inductor Ls of the magnetic component determined in the above process into Formula (5) and Formula (6), a relationship curve graph of the switching frequency fs varying with the voltage Vi of the input power supply 140 can be obtained, as shown in Figure 10 shown. Among them, in Figure 10 , the abscissa is the voltage Vi of the input power supply 140, and the ordinate is the switching frequency fs. In Figure 10 , the relationship curve fs9(Vi, 400 2 / 1000) when the output voltage is 400V and the output power is 1000W and the relationship curve fs10(Vi, 400 2 / 500) when the output voltage is 400V and the output power is 500W are shown. It can be seen from Figure 10 that according to the turns ratio Ntr determined by the method for determining transformer parameters provided in the embodiments of the present application, when the voltage Vi of the input power supply 140 becomes smaller along the horizontal axis or becomes larger along the horizontal axis with the demarcation point Vi = Vo×Ntr, the change ranges of the frequencies to be adjusted on the vertical axis are the same.

[0065] Substituting the parameters of the magnetic component determined in the above process into Formula (3) and Formula (4) again, a curve graph of the external phase shift angle θ varying with the voltage Vi of the input power supply 140 can be obtained, as shown in Figure 11 shown. Among them, in Figure 11 , the abscissa is the voltage Vi of the input power supply 140, and the ordinate is the external phase shift angle. The curve θ_zvs(Vi, 400 2 / 1000) represents the relationship curve between the external phase shift angle and the voltage Vi of the input power supply 140 when the output voltage Vo is 400V and the output power is 1000W, and θ_zvs(Vi, 400 2 / 500) represents the relationship curve between the external phase shift angle and the voltage Vi of the input power supply 140 when the output voltage Vo is 400V and the output power is 500W. It can be seen from Figure 11 that the external phase shift angle is related to the voltage Vi of the input power supply 140 and has nothing to do with the load.

[0066] The above are only the embodiments of the present application, and do not limit the patent scope of the present application. Any equivalent structural or equivalent process transformation made using the content of the specification and drawings of the present application, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present application.

[0067] The above embodiments are only used to illustrate the technical solutions of the present application, rather than limiting them; under the concept of the present application, the technical features in the above embodiments or different embodiments can also be combined, and the steps can be implemented in any order. Those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for determining transformer parameters, applied to a dual-active bridge circuit, characterized in that The method includes: Determining a first correspondence relationship of the switching frequency of the dual-active-bridge circuit with respect to the input power supply, the output voltage, the load, and the turns ratio of the transformer when the dual-active-bridge circuit meets the ZVS soft-switching requirement and the upper switching transistor of the left bridge arm of the bridge circuit at the output end of the dual-active-bridge circuit is turned on; Determining a second correspondence relationship of the switching frequency with respect to the input power supply, the output voltage, the load, and the turns ratio when the dual-active-bridge circuit meets the ZVS soft-switching requirement and the upper switching transistor of the left bridge arm of the bridge circuit at the input end of the dual-active-bridge circuit is turned off; Determining a first switching frequency value corresponding to the first correspondence relationship when the voltage of the input power supply is a first value; Determining a second switching frequency value corresponding to the second correspondence relationship when the voltage of the input power supply is a second value; Determining the turns ratio according to the first switching frequency value and the second switching frequency value; Wherein, the voltage range of the input power supply is [Vi_min, Vi_max], the first value is the maximum value Vi_max in the voltage range of the input power supply, and the second value is the minimum value Vi_min in the voltage range of the input power supply.

2. The method according to claim 1, wherein The bridge circuit at the input end of the dual-active-bridge circuit and the bridge circuit at the output end of the dual-active-bridge circuit are a first bridge circuit and a second bridge circuit respectively; The first correspondence relationship is: determining the first correspondence relationship of the switching frequency with respect to the input power supply, the output voltage, the load, and the turns ratio according to a first external phase shift angle and the output power of the dual-active-bridge circuit under single-phase shift modulation; wherein, the first external phase shift angle is the external phase shift angle when the dual-active-bridge circuit meets the critical condition of ZVS soft-switching requirement and the upper switching transistor of the left bridge arm of the second bridge circuit is conducting; The second correspondence relationship is: determining the second correspondence relationship of the switching frequency with respect to the input power supply, the output voltage, the load, and the turns ratio according to a second external phase shift angle and the output power; wherein, the second external phase shift angle is the external phase shift angle when the dual-active-bridge circuit meets the critical condition of ZVS soft-switching requirement and the upper switching transistor of the left bridge arm of the second bridge circuit is conducting.

3. The method according to claim 2, wherein Determining the turns ratio according to the first switching frequency value and the second switching frequency value includes: Setting the first switching frequency value and the second switching frequency value to be equal to determine the turns ratio; Vi_max = N * Vi_min, 1 < N < 2.

4. The method according to claim 2 or 3, characterized in that, The determining the first correspondence relationship of the switching frequency with respect to the input power supply, the output voltage, the load, and the turns ratio according to the first external phase shift angle and the output power of the dual-active-bridge circuit under single-phase shift modulation includes: The first corresponding relationship is: F1 = Ro × (Vi 2 - Vo 2 × Ntr 2 ) / (8 × Ls × Vi × Vo × Ntr), where the voltage gain G = Vo × Ntr / Vi and G < 1, F1 is the first corresponding relationship, Ro is the resistance value of the load, Vi is the voltage of the input power supply, Vo is the output voltage of the dual-active-bridge circuit, Ntr is the turns ratio, and Ls is the inductance value of the resonant inductor of the resonant network of the dual-active-bridge circuit; The determining the second correspondence relationship of the switching frequency with respect to the input power supply, the output voltage, the load, and the turns ratio according to the second external phase shift angle and the output power includes: The second corresponding relationship is: F2 = Ro × Vi × (Vo 2 × Ntr 2 - Vi 2 ) / (8 × Ls × Vo 3 × Ntr 3 ), where the voltage gain G = Vo × Ntr / Vi and G ≥ 1, and F2 is the second corresponding relationship.

5. The method according to claim 3, wherein Setting the first switching frequency value and the second switching frequency value to be equal to determine the turns ratio includes: The turns ratio is: , where Ntr is the turns ratio and Vo is the output voltage of the dual active bridge circuit.

6. The method according to claim 2, wherein When the dual active bridge circuit meets the critical condition for ZVS soft-switching requirement and the upper switching tube of the left bridge arm of the second bridge circuit is turned on, the current value i1 of the resonant inductor of the resonant network of the dual active bridge circuit satisfies: i1 > 0, i1 = 0.5×(2θ - (1 - Vo×Ntr / Vi))×Vi / (2π×fs×Ls), where fs is the switching frequency; Based on the critical condition i1 = 0 when the dual active bridge circuit meets the ZVS soft-switching requirement, the first external phase shift angle θ1 is determined as: θ1 = 0.5×(1 - Vo×Ntr / Vi), where Vi is the voltage of the input power supply, Vo is the output voltage of the dual active bridge circuit, and Ntr is the turns ratio.

7. The method according to claim 2, wherein When the dual active bridge circuit meets the critical condition for ZVS soft-switching requirement and the upper switching tube of the left bridge arm of the first bridge circuit is turned off, the current value i2 of the resonant inductor of the resonant network of the dual active bridge circuit satisfies: i2 > 0, i2 = 0.5×(2θ×Vo×Ntr / Vi + (1 - Vo×Ntr / Vi))×Vi / (2π×fs×Ls), where fs is the switching frequency; Based on the critical condition i2 = 0 when the dual active bridge circuit meets the ZVS soft-switching requirement, the second external phase shift angle θ2 is determined as: θ2 = 0.5×(1 - Vi / (Vo×Ntr)), where Vi is the voltage of the input power supply, Vo is the output voltage of the dual active bridge circuit, and Ntr is the turns ratio.

8. The method according to claim 2, wherein The output power is: Po = (Vi×Vo×θ×(1 - θ)) / (2×Ls×fs×Ntr), where Po is the output power, Vi is the voltage of the input power supply, Ntr is the turns ratio, Vo is the output voltage of the dual active bridge circuit, θ is the external phase shift angle of the dual active bridge circuit, Ls is the inductance value of the resonant inductor of the resonant network of the dual active bridge circuit, and fs is the switching frequency.

9. A method for determining parameters of a magnetic component of a dual-active-bridge circuit, characterized in that, The magnetic component includes a transformer and a resonant inductor. The method for determining the parameters of the magnetic component of the dual active bridge circuit includes: Determining the turns ratio of the transformer by the transformer parameter determination method according to any one of claims 1 - 8; Determining the inductance value of the resonant inductor according to the input power supply, the maximum output power of the dual active bridge circuit, the switching frequency of the dual active bridge circuit, the external phase shift angle of the dual active bridge circuit, and the output power of the dual active bridge circuit under single-phase modulation.

10. A dual-active bridge circuit, characterized in that, Includes: Input power supply; The first bridge circuit, the input end of the first bridge circuit is connected to the input power supply; Resonant network, the input end of the resonant network is connected to the output end of the first bridge circuit; The second bridge circuit, the input end of the second bridge circuit is connected to the output end of the resonant network, and the output end of the second bridge circuit is connected to the load; The turns ratio of the transformer of the resonant network and the inductance value of the resonant inductor of the resonant network are determined by the method for determining the parameters of the magnetic element of the dual-active-bridge circuit as described in claim 9.

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