Peak-to-peak value current optimization method for dual-active bridge converter

Abstract

The invention relates to the technical field of DAB current optimization. The invention provides a peak-to-peak value current optimization method of a dual-active bridge converter. The method comprises the following steps: establishing a mathematical model of the DAB converter; obtaining a mathematical expression of a current peak value # imgabs0 # and the transmission power P of the dual-active bridge converter, and carrying out per-unit processing on # imgabs1 # and P; establishing a mathematical expression of a nonlinear optimization problem of the DAB converter by taking the minimum value of the per-unit inductive current peak value as an optimization target and taking the specified value of the per-unit transmission power as a constraint condition; solving a nonlinear optimization problem by adopting a KKT condition, constructing a Lagrange equation E and solving the equation E, and establishing an optimization solution of TVAM and TVSM according to a solving result; a hybrid three-variable modulation strategy is optimized based on the solution. The HTVM strategy of the invention combines a wider zero voltage switching range when the TVAM is in light load and a lower current level when the TVSM is in heavy load, and enriches the modulation strategy of the DAB converter.

Description

Technical Field

[0001] The present invention relates to the technical field of DAB current optimization, and in particular to a peak-to-peak current optimization method for a dual active bridge converter. Background Art

[0002] Dual Active Bridge (DAB) converters have gained widespread application in power electronics, particularly in new energy applications, due to their simple structure, electrical isolation, wide voltage conversion ratio, and bidirectional energy transfer capabilities. These converters control energy flow by adjusting the phase difference between the two full-bridges, typically employing a single-phase shift (SPS) modulation strategy. However, when there is a mismatch between the input and output voltages, SPS can lead to high current stress and soft switching losses, compromising energy conversion efficiency.

[0003] To address this issue, researchers have developed multivariable modulation strategies, such as three-variable symmetric modulation (TVSM) and three-variable asymmetric modulation (TVAM). These multivariable modulation strategies increase modulation flexibility by introducing a zero level, while also reducing on-time and switching losses. Specifically, these strategies optimize switching logic and on-time, reduce current stress at light loads, improve energy conversion efficiency, and expand the zero-voltage switching (ZVS) range to further reduce switching losses.

[0004] However, both multivariable symmetrical modulation and multivariable asymmetrical modulation have their own advantages and disadvantages. Multivariable symmetrical modulation can achieve the lowest current levels, but the ZVS range is narrow at light loads, and strategies to expand the ZVS range increase the difficulty of microcontroller implementation. Multivariable asymmetrical modulation offers a wider ZVS range but faces significant challenges at higher current levels, and five-variable modulation also presents considerable implementation difficulties.

[0005] Since efficiency and ease of implementation are both key dimensions for DAB in practical applications, it is urgent to develop a modulation strategy that provides low current levels, wide ZVS range, and is easy to implement. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art or related art.

[0007] Therefore, the object of the present invention is to provide a peak-to-peak current optimization method for a dual active bridge converter.

[0008] In order to achieve the above object, the technical solution of the present invention provides a peak-to-peak current optimization method of a dual active bridge converter, the dual active bridge converter comprising: a primary side circuit H 1. Isolation transformer T ,inductance L , and secondary side circuit H 2; the isolation transformer T The primary side circuit H 1 and secondary side circuit H 2 are coupled together; the primary side circuit H 1 includes: first filter capacitors connected in parallel C 1 and a first bridge circuit; the secondary side circuit H 2 includes: a second filter capacitor connected in parallel C 2 and a second bridge circuit; the first bridge circuit is composed of a first switching element S 1 and the second switching element S 2 The first branch in series with the third switching element S 3 and the fourth switching element S 4 series second branches are connected in parallel to form a full bridge circuit; the first switching element S 1 and the second switching element S The connection point between 2 a , with the third switching element S 3 and the fourth switching element S 4 connection points between b Connected to the isolation transformer T Both ends of the primary coil; the connection point a Through the inductor L With isolation transformer T One end of the primary coil is connected; the second bridge circuit is composed of a fifth switching element S 5 and the sixth switching element S 6 The third branch connected in series with the seventh switch element S 7 and the eighth switching element S 8 series connected fourth branches in parallel to form a full bridge circuit; the fifth switch element S 5 and the sixth switching element S 6 connection points between c , and the seventh switching element S 7 and the eighth switching element S 8 connection points between d Connected to the isolation transformer T The two ends of the secondary coil; point a with dot b The voltage betweenv 1. Point c with dot d The voltage between v 2; The optimization method comprises: step S1: establishing a mathematical model of a dual active bridge converter; the step S1 specifically comprises: step S1.1: defining technical parameters of the dual active bridge converter; step S1.2: setting a hybrid three-variable modulation strategy; wherein the hybrid three-variable modulation strategy comprises the primary side circuit of the dual active bridge converter H 1 and secondary side circuit H 2 are all symmetrically modulated TVSM; and the hybrid three-variable modulation strategy also includes: the primary side circuit of the dual active bridge converter H 1 and secondary side circuit H 2 both use asymmetric modulation TVAM; the three variables are D 1, D 2 and D 3; D 1 is based on TVAM and TVSM voltage v 1The duty cycle used for signal modulation; D 2 is based on TVAM and TVSM voltage v 2. The duty cycle used for signal modulation; D 3 is the first switching element S 1 and the fifth switching element S 5 and the duty cycle used for the conduction delay of the signal between 5; Step S1.3: Based on the hybrid three-variable modulation strategy, establish the instantaneous value of the inductor current of the dual active bridge converter Mathematical expression of; Step S2: Get the peak-to-peak value of current and the transfer power of the dual active bridge converter P The mathematical expression of the peak-to-peak current and the transmission power P The peak-to-peak value of the current is is the instantaneous value of the inductor current The difference between the maximum value and the minimum value of the inductor current; Step S2.1: Based on the instantaneous value of the inductor current The mathematical expression to obtain the peak-to-peak current is The mathematical expression of the transmission power is obtained based on the volt-second balance principle. P Mathematical expression of: Step S2.2: the peak-to-peak value of the current Perform per-unit normalization to obtain the normalized peak-to-peak value of the inductor current. , for the transmission power P Perform per-unit normalization to obtain the normalized transmission power pThe normalized peak-to-peak value of the inductor current and the normalized transmission power p The control variables of the mathematical expression include D 1, D 2 and D 3; Step S3: taking the normalized peak-to-peak value of the inductor current The minimum value of the optimization target is the normalized transmission power p The specified value of is a constraint condition, and a mathematical expression of the nonlinear optimization problem of the dual active bridge converter is established; Step S4: Using the Karush-Kuhn-Tucker condition to solve the nonlinear optimization problem, construct the Lagrangian equation E , and the Lagrange equation E Solve it, according to the solved Lagrange equation E The partial derivative results of TVAM and TVSM are used to establish the optimization solution; Step S5: Based on the optimization solution of TVAM and TVSM, the hybrid three-variable modulation strategy is optimized; Step S5 specifically includes: Step S5.1: Under different modes of the hybrid three-variable modulation strategy, the control parameters are determined by comprehensively considering the root mean square current and zero voltage switching. D 1, D 2, D 3 to achieve the peak-to-peak value of the normalized inductor current. Reached minimum value.

[0009] Preferably, the step S1.1 specifically includes: Step S1.11: Define the input voltage of the dual active bridge converter as V 1. The output voltage is V 2. Isolation transformer T The turns ratio is N :1, inductance is L ;in, N is a positive integer; Step S1.12: Define the input voltage V 1 and the output voltage V The adaptation coefficient between 2 is k ; The adaptation coefficient k The expression is: (1).

[0010] Preferably, the step S1.3 specifically includes: Step S1.31: The classification basis of the six modes of the hybrid three-variable modulation strategy is set as shown in Table 1: Table 1 Classification basis of the six modes of the hybrid three-variable modulation strategy Step S1.32: Based on the working principle of the dual active bridge converter, the instantaneous value of the inductor current in mode 1 of the dual active bridge converter is converted to Over time within a cycle t The changing time of is divided into 6 corresponding time periods; Step S1.33: Obtain the instantaneous value of the inductor current in mode 1 The expression is: (2) In formula (2): (3) In formula (3), T s Expressed as a switching cycle.

[0011] Preferably, the step S2.1 specifically includes: step S2.11: by taking the maximum value of the current Subtract the minimum current from , get the peak-to-peak current The expression is: (4) In formula (4), for t 4. The instantaneous value of the inductor current corresponding to the time point; for t 6. The instantaneous value of the inductor current corresponding to the time point; f s is the switching frequency; Step S2.12: Based on the volt-second balance principle, the mathematical expression (5) is obtained: (5) Step S2.13: Based on mathematical expression (5), the mathematical expression of the transmission power P is obtained as follows: (6) The step S2.2 specifically includes: Step S2.21: Calculate the peak-to-peak value of the current Perform per-unit normalization to obtain the normalized peak-to-peak value of the inductor current. The normalized peak-to-peak value of the inductor current The expression is: (7) In formula (7), I N The expression is: (8) Step S2.22: The transmission power P Perform per-unit normalization to obtain the normalized transmission power p The normalized transmission power p The expression is: (9) In formula (9), P N The expression is: (10).

[0012] Preferably, based on the normalized peak-to-peak value of the inductor current and the normalized transmission power p , establish a mathematical expression for the nonlinear optimization problem of the dual-active bridge converter; the mathematical expression for the nonlinear optimization problem is: min i P-P ( D 1 , D 2 , D 3 ); st p ( D 1 , D 2 , D 3 )- p * = 0; g i ( D 1 , D 2 , D 3 )≤0,( i =1,2,… l )(11) In formula (11), p * It represents the expected transmission power of the dual active bridge converter; st is the abbreviation of subject to; p ( D 1, D 2 ,D 3) Indicates the control variable D 1, D 2 and D3 Calculated power value; st p ( D 1, D 2 ,D 3)- p * =0 means that in the optimization process, the control variables need to be D 1, D 2 and D 3 Calculated power value and target power p * Stay consistent; g i Represents the boundary conditions of the optimization variables; l Expressed as the number of boundary conditions.

[0013] Preferably, the step S4 specifically includes: Step S4.1: using the Karush-Kuhn-Tucker condition to solve the nonlinear optimization problem and construct the Lagrangian equation E ; The Lagrange equation E The expression is: (12) In formula (12), is the Lagrange multiplier associated with the equality constraint; For the inequality constraints the associated Lagrange multipliers; Expressed as an inequality constraint The associated Lagrange multipliers are given by to A collection of Step S4.2: Solve the Lagrange equation E The partial derivative of , we get the following expression: (13) And set the complementary slack conditions: (14) Step S4.3: According to the solved Lagrange equation E The partial derivative results of , and the optimization solutions of TVAM and TVSM are shown in Table 2: Table 2 Optimization solutions for TVAM and TVSM

[0014] Preferably, the control variable D 1, D 2, D The optimal solution of 3 is: (15) In formula (15), Indicates the dividing point between light load and heavy load; D 1, D 2, D 3 is the optimized control parameters.

[0015] Preferably, the peak-to-peak current optimization method of the dual active bridge converter further comprises: step S5.2: calculating the obtained control parameters D 1, D 2, D 3. Real-time analysis of the optimization results based on the expression of the optimal solution of

[0016] Preferably, the step S5.2 specifically includes: step S5.21: determining the normalized transmission power p Is it greater than or equal to zero and less than or equal to ; When the judgment result is yes, execute step S5.22; when the judgment result is no, p The value range is , then execute step S5.23; Step S5.22: Adjust D 1, D 2, and D 3, so that the peak-to-peak value of the normalized inductor current is Minimum fluctuation; Step S5.23: Adjust D 1, D 2, and D 3, so as to further reduce the peak-to-peak value of the normalized inductor current .

[0017] Beneficial effects of the present invention: (1) The peak-to-peak current optimization method for a dual active bridge (DAB) converter of the present invention is based on a hybrid three-variable modulation (HTVM) strategy. Specifically, the optimization method provides an optimized HTVM strategy. Specifically, the HTVM strategy combines three-variable symmetric modulation (TVSM) and three-variable asymmetric modulation (TVAM), combining the TVAM's wider zero voltage switching (ZVS) range at light loads with the TVSM's lower current level at heavy loads, thereby enriching the modulation strategy of the DAB converter.

[0018] (2) The peak-to-peak current optimization method for a dual active bridge (DAB) converter of the present invention is based on a hybrid three-variable modulation (HTVM) strategy. That is, the optimization method provides a steady-state optimization solution based on HTVM. Specifically, a simple two-stage optimization method is adopted to maintain a good balance between improving the operating efficiency of the DAB converter and facilitating system implementation. The peak-to-peak current within the HTVM is optimized, while the operating efficiency of the DAB converter under different load conditions is greatly optimized, thereby achieving an improvement in the operating efficiency of the DAB converter over the entire power range. In particular, the operating efficiency of the DAB converter under light load is greatly optimized.

[0019] Additional aspects and advantages of the invention will become apparent from the description which follows, or may be learned by practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic flow chart illustrating a peak-to-peak current optimization method for a dual active bridge converter according to an embodiment of the present invention is shown; Figure 2 A schematic diagram showing a typical topological structure of a DAB converter according to an embodiment of the present invention is shown; Figure 3 Schematic diagrams of the principles of HTVM according to an embodiment of the present invention are shown, wherein (a) shows a schematic diagram of mode 1 of the HTVM, (b) shows a schematic diagram of mode 2 of the HTVM, (c) shows a schematic diagram of mode 3 of the HTVM, (d) shows a schematic diagram of mode 4 of the HTVM, (e) shows a schematic diagram of mode 5 of the HTVM, and (f) shows a schematic diagram of mode 6 of the HTVM; Figure 4a An embodiment of the present invention is shown in k When the value is 1.5, TVAM and TVSM I rms and p Schematic diagram of; Figure 4b An embodiment of the present invention is shown in k When the value is 1.75, TVAM and TVSM I rms and p Schematic diagram of; Figure 5a FIG4 is a schematic diagram showing the ZVS range of a TVAM according to an embodiment of the present invention; Figure 5bFIG. 4 is a schematic diagram showing the ZVS range of a TVSM according to an embodiment of the present invention. DETAILED DESCRIPTION

[0021] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that, in the absence of conflict, the embodiments of the present application and the features therein can be combined with each other.

[0022] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0023] Figure 1 FIG1 is a schematic flow chart showing a peak-to-peak current optimization method for a dual active bridge converter according to an embodiment of the present invention. Figure 2 As shown, the dual active bridge converter includes: a primary side circuit H 1. Isolation transformer T ,inductance L , and secondary side circuit H 2; the isolation transformer T The primary side circuit H 1 and secondary side circuit H 2 are coupled together; the primary side circuit H 1 includes: first filter capacitors connected in parallel C 1 and a first bridge circuit; the secondary side circuit H 2 includes: a second filter capacitor connected in parallel C 2 and a second bridge circuit; the first bridge circuit is composed of a first switching element S 1 and the second switching element S 2 The first branch in series with the third switching element S 3 and the fourth switching element S 4 series second branches are connected in parallel to form a full bridge circuit; the first switching element S 1 and the second switching element S The connection point between 2 a , with the third switching element S 3 and the fourth switching element S 4 connection points between b Connected to the isolation transformer T Both ends of the primary coil; the connection point a Through the inductor L With isolation transformer T One end of the primary coil is connected; the second bridge circuit is composed of a fifth switching elementS 5 and the sixth switching element S 6 The third branch connected in series with the seventh switch element S 7 and the eighth switching element S 8 series connected fourth branches in parallel to form a full bridge circuit; the fifth switch element S 5 and the sixth switching element S 6 connection points between c , and the seventh switching element S 7 and the eighth switching element S 8 connection points between d Connected to the isolation transformer T The two ends of the secondary coil; point a with dot b The voltage between v 1. Point c with dot d The voltage between v 2.

[0024] like Figure 1 As shown, the peak-to-peak current optimization method of the dual active bridge converter includes: Step S1: Establishing a mathematical model of a dual-active bridge converter; The step S1 specifically includes: Step S1.1: defining technical parameters of the dual active bridge converter; Step S1.2: Setting a hybrid three-variable modulation strategy; wherein the hybrid three-variable modulation strategy includes the primary side circuit of the dual active bridge converter H 1 and secondary side circuit H 2 are all symmetrically modulated TVSM; and the hybrid three-variable modulation strategy also includes: the primary side circuit of the dual active bridge converter H 1 and secondary side circuit H 2 both use asymmetric modulation TVAM; the three variables are D 1, D 2 and D 3; D 1 is based on TVAM and TVSM voltage v 1The duty cycle used for signal modulation; D 2 is based on TVAM and TVSM voltage v 2. The duty cycle used for signal modulation; D 3 is the first switching element S 1 and the fifth switching element S 5 for the conduction delay of the signal; Step S1.3: Based on the hybrid three-variable modulation strategy, establish the instantaneous value of the inductor current of the dual active bridge converter The mathematical expression of Step S2: Obtain the peak-to-peak value of the current and the transfer power of the dual active bridge converter P The mathematical expression of the peak-to-peak current and transmission power P The peak-to-peak value of the current is is the instantaneous value of the inductor current The difference between the maximum and minimum values ​​of ; Step S2.1: Based on the instantaneous value of the inductor current The mathematical expression to obtain the peak-to-peak current is The mathematical expression of the transmission power is obtained based on the volt-second balance principle. P The mathematical expression of Step S2.2: Calculate the peak-to-peak value of the current Perform per-unit normalization to obtain the normalized peak-to-peak value of the inductor current. , for the transmission power P Perform per-unit normalization to obtain the normalized transmission power p The normalized peak-to-peak value of the inductor current and the normalized transmission power p The control variables of the mathematical expression include D 1, D 2 and D 3; Step S3: Take the normalized peak-to-peak value of the inductor current The minimum value of the optimization target is the normalized transmission power p The specified value of is a constraint condition, and a mathematical expression of the nonlinear optimization problem of the dual-active bridge converter is established; Step S4: Use Karush-Kuhn-Tucker conditions to solve the nonlinear optimization problem and construct the Lagrangian equation E , and the equation E Solve it, according to the solved Lagrange equation E The partial derivative results of are used to establish the optimal solutions of TVAM and TVSM; Step S5: Optimize the hybrid three-variable modulation strategy based on the optimization solutions of TVAM and TVSM; The step S5 specifically includes: Step S5.1: Under different modes of the hybrid three-variable modulation strategy, the control parameters are determined by comprehensively considering the root mean square current and zero voltage switching.D 1, D 2, D 3 to achieve the peak-to-peak value of the normalized inductor current. Reached minimum value.

[0025] With the rapid development of new energy in recent years, Dual Active Bridge (DAB) converter has become an important DC-DC converter and has been widely used in electric vehicles, renewable energy power generation systems, energy storage, DC power distribution systems, microgrids and other fields. Figure 2 As shown, the primary side circuit H 1. Secondary side circuit H 2 and the first filter capacitor C 1. Second filter capacitor C 2 through the inductor L and isolation transformer T connected to form the DAB converter. L The high frequency voltage on the DAB converter determines the power transmission.

[0026] In this embodiment, the present invention provides a peak-to-peak current optimization method for a Dual Active Bridge (DAB) converter based on a hybrid three-variable modulation (HTVM) strategy. Specifically, the optimization method provides an optimized HTVM strategy. Specifically, the HTVM strategy combines three-variable symmetric modulation (TVSM) and three-variable asymmetric modulation (TVAM), combining the TVAM's wider zero voltage switching (ZVS) range at light loads with the TVSM's lower current levels at heavy loads, enriching the modulation strategy for DAB converters.

[0027] In this embodiment, the present invention's peak-to-peak current optimization method for a Dual Active Bridge (DAB) converter is based on a hybrid three-variable modulation (HTVM) strategy. Specifically, this optimization method provides a steady-state optimization solution based on HTVM. Specifically, a simple two-stage optimization approach is employed, striking a good balance between improving DAB converter efficiency and facilitating system implementation. It prioritizes optimizing the peak-to-peak current within the HTVM, significantly improving the DAB converter's efficiency under varying load conditions, and ultimately improving the converter's efficiency across the entire power range. In particular, the DAB converter's efficiency is significantly improved under light load conditions.

[0028] In one embodiment of the present invention, step S1.1 specifically includes: Step S1.11: Define the input voltage of the dual active bridge converter as V 1. The output voltage is V 2. Isolation transformer T The turns ratio is N :1, inductance is L ;in, N is a positive integer; Step S1.12: Define the input voltage V 1 and the output voltage V The adaptation coefficient between 2 is k ; The adaptation coefficient k The expression is: (1).

[0029] In this embodiment, if Figure 2 As shown, the input voltage of the dual active bridge converter is V 1 , the output voltage is V 2 . Isolation transformer T The turns ratio is N :1, inductor L Indicates the additional inductance and transformer leakage inductance. a with dot b The voltage between v 1. Point c with dot d The voltage between v 2; v 1 and v 2 are both high frequency AC voltages. v 2 When referenced to the primary side, the voltage on the left side of the isolation transformer can be expressed as Nv2. Here, V L represents the voltage drop across the inductor L, i L Indicates that the inductor L The current. v 1 and v 2 are added to the inductor L Voltage on V L , and the resulting current i L , will determine the steady-state performance of the DAB converter. In a specific embodiment, the switching element S 1 to S 8 may be a silicon carbide (SiC) MOSFET switch.

[0030] In one embodiment of the present invention, the peak-to-peak current optimization method of the dual active bridge converter further includes: step S5.2: calculating the obtained control parameters D 1, D 2, D 3. Real-time analysis of the optimization results based on the expression of the optimal solution of

[0031] The following is a specific embodiment to illustrate the peak-to-peak current optimization method of the dual active bridge converter of the present invention. The dual active bridge converter includes: a primary side circuit H 1. Isolation transformer T ,inductance L , and secondary side circuit H 2; the isolation transformer T The primary side circuit H 1 and secondary side circuit H 2 are coupled together; the primary side circuit H 1 includes: first filter capacitors connected in parallel C 1 and a first bridge circuit; the secondary side circuit H 2 includes: a second filter capacitor connected in parallel C 2 and a second bridge circuit; the first bridge circuit is composed of a first switching element S 1 and the second switching element S 2 The first branch in series with the third switching element S 3 and the fourth switching element S 4 series second branches are connected in parallel to form a full bridge circuit; the first switching element S 1 and the second switching element S The connection point between 2 a , with the third switching element S 3 and the fourth switching element S 4 connection points betweenb Connected to the isolation transformer T Both ends of the primary coil; the connection point a Through the inductor L With isolation transformer T One end of the primary coil is connected; the second bridge circuit is composed of a fifth switching element S 5 and the sixth switching element S 6 The third branch connected in series with the seventh switch element S 7 and the eighth switching element S 8 series connected fourth branches in parallel to form a full bridge circuit; the fifth switch element S 5 and the sixth switching element S 6 connection points between c , and the seventh switching element S 7 and the eighth switching element S 8 connection points between d Connected to the isolation transformer T The two ends of the secondary coil; point a with dot b The voltage between v 1. Point c with dot d The voltage between v 2. Switching elements S 1 to S 8 are all silicon carbide (SiC) MOSFET switches.

[0032] The specific implementation steps of the peak-to-peak current optimization method of the dual-active bridge converter of the present invention are as follows: (1) Step S1: Establishing a mathematical model of the dual-active bridge converter; The step S1 specifically includes: Step S1.1: defining technical parameters of the dual active bridge converter; The step S1.1 specifically includes: Step S1.11: Define the input voltage of the dual active bridge converter as V 1. The output voltage is V 2. Isolation transformer T The turns ratio is N :1, inductance is L ;in, N is a positive integer; Step S1.12: Define the input voltage V 1 and the output voltage V The adaptation coefficient between 2 is k ; The adaptation coefficient k The expression is: (1).

[0033] Step S1.2: Setting a hybrid three-variable modulation strategy; wherein the hybrid three-variable modulation strategy includes adopting symmetrical modulation TVSM for both the primary side circuit and the secondary side circuit of the dual active bridge converter; and the hybrid three-variable modulation strategy also includes adopting asymmetrical modulation TVAM for both the primary side circuit and the secondary side circuit of the dual active bridge converter; the three variables are D 1, D 2 and D 3; D 1 is based on TVAM and TVSM voltage v 1The duty cycle used for signal modulation; D 2 is based on TVAM and TVSM voltage v 2. The duty cycle used for signal modulation; D 3 is the first switching element S 1 and the fifth switching element S 5 and the duty cycle used for the turn-on delay of the signal.

[0034] Step S1.3: Based on the hybrid three-variable modulation strategy, establish the instantaneous value of the inductor current of the dual active bridge converter The mathematical expression of The step S1.3 specifically includes: Step S1.31: The classification basis of the six modes of the hybrid three-variable modulation strategy is set as shown in Table 1: Table 1 Classification basis of the six modes of the hybrid three-variable modulation strategy Figure 3 shows the schematic diagram of Hybrid Three-variable Modulation (HTVM) in different modes. Figure 3 As shown, (a) in Figure 3, (b) in Figure 3, and (c) in Figure 3 show three-variable asymmetric modulation (TVAM), and (d) in Figure 3, (e) in Figure 3, and (f) in Figure 3 show three-variable symmetric modulation (TVSM). Figure 3 (a) to Figure 3 (f) in Fig. 3 illustrates the modes 1–6. Fig. 3 classifies the HTVM modes to obtain the steady-state characteristics. v1 Adoption D 1 duty cycle, the voltage v 2 Adoption D 2 duty cycle, and the first switching element S 1 and the fifth switching element S 5 using a duty cycle D 3 for turn-on delay, so they have three control variables D 1. D 2. And D 3. D 1. D 2. And D 3 are duty cycle parameters. T s Expressed as a switching cycle, that is, the time of one switching cycle. D 1 T s , D 2 T s , D 3 T s Respectively represents the length of time of each stage. T The turns ratio is N :1, so Nv 2 means through an isolation transformer T The voltage after that.

[0035] pass Figure 3 Learn how different operation modes achieve precise control of voltage and current under the HTVM modulation strategy. By showing the specific behavior of each switch in each mode, Figure 3 This paper explains how HTVM can achieve more efficient energy transmission by adjusting the switching timing. It also shows that different modulation methods can be used to optimize the system conversion efficiency and reduce current stress and switching losses. This has important guiding significance for understanding how to optimize the performance of DAB converters under complex working conditions. In summary, Figure 3 Through detailed timing diagrams, the effects of different modulation strategies on switching behavior and voltage and current waveforms are intuitively demonstrated, providing strong support for understanding the advantages and implementation methods of HTVM.

[0036] Step S1.32: Based on the working principle of the dual active bridge converter, the instantaneous value of the inductor current in mode 1 of the dual active bridge converter is converted to Over time within a cycle t The changing time of is divided into 6 corresponding time periods; Step S1.33: Obtain the instantaneous value of the inductor current in mode 1 The expression is: (2) In formula (2): (3) In formula (3), T s Expressed as a switching cycle.

[0037] (2) Step S2: Obtaining the peak-to-peak value of the current and the transfer power of the dual active bridge converter P The mathematical expression of the peak-to-peak current and the transmission power P The peak-to-peak value of the current is is the instantaneous value of the inductor current The difference between the maximum and minimum values ​​of ; Step S2.1: Based on the instantaneous value of the inductor current The mathematical expression to obtain the peak-to-peak current is The mathematical expression of the transmission power is obtained based on the volt-second balance principle. P The mathematical expression of The step S2.1 specifically includes: Step S2.11: By taking the maximum value of the current Subtract the minimum current from , get the peak-to-peak current The expression is: (4) In formula (4), for t 4 The instantaneous value of the inductor current corresponding to the time point; for t 6 The instantaneous value of the inductor current corresponding to the time point; f s is the switching frequency; Step S2.12: Based on the volt-second balance principle, the mathematical expression (5) is obtained: (5) Step S2.13: Based on mathematical expression (5), the mathematical expression of the transmission power P is obtained as follows: (6) Step S2.2: Calculate the peak-to-peak value of the current Perform per-unit normalization to obtain the normalized peak-to-peak value of the inductor current. , for the transmission power P Perform per-unit normalization to obtain the normalized transmission powerp The normalized peak-to-peak value of the inductor current and the normalized transmission power p The control variables of the mathematical expression include D 1, D 2 and D 3; The step S2.2 specifically includes: Step S2.21: Calculate the peak-to-peak value of the current Perform per-unit normalization to obtain the normalized peak-to-peak value of the inductor current. The normalized peak-to-peak value of the inductor current The expression is: (7) In formula (7), I N The expression is: (8) Step S2.22: The transmission power P Perform per-unit normalization to obtain the normalized transmission power p The normalized transmission power p The expression is: (9) In formula (9), P N The expression is: (10).

[0038] Furthermore, using the same analysis method, the normalized transmission power p and the normalized peak-to-peak value of the inductor current i P-P The expressions under the six modes are shown in the following table: Normalized transmission power p and the normalized peak-to-peak value of the inductor current (3) Step S3: The peak-to-peak value of the normalized inductor current The minimum value of the optimization target is the normalized transmission power p The specified value of is a constraint condition, and a mathematical expression of the nonlinear optimization problem of the dual-active bridge converter is established; Based on the normalized peak-to-peak value of the inductor current and the normalized transmission power p, establish a mathematical expression for the nonlinear optimization problem of the dual-active bridge converter; the mathematical expression for the nonlinear optimization problem is: min i P-P ( D 1 , D 2 , D 3 ); st p ( D 1 , D 2 , D 3 )- p * = 0; g i ( D 1 , D 2 , D 3 )≤0,( i =1,2,… l )(11) In formula (11), p * It represents the expected transmission power of the dual active bridge converter; st is the abbreviation of subject to; p ( D 1, D 2 ,D 3) Indicates the control variable D 1, D 2 and D 3 Calculated power value; st p ( D 1, D 2 ,D 3)- p * =0 means that in the optimization process, the control variables need to be D 1, D 2 and D 3 Calculated power value and target power p * Stay consistent; g i Represents the boundary conditions of the optimization variables; l Expressed as the number of boundary conditions.

[0039] (4) Step S4: Use the Karush-Kuhn-Tucker (KKT) condition to solve the nonlinear optimization problem and construct the Lagrangian equation E , and the Lagrange equation E Solve it, according to the solved Lagrange equation E The partial derivative results of are used to establish the optimal solutions of TVAM and TVSM; The step S4 specifically includes: Step S4.1: using the Karush-Kuhn-Tucker condition to solve the nonlinear optimization problem and construct the Lagrangian equation E ; The Lagrange equation E The expression is: (12) In formula (12), is the Lagrange multiplier associated with the equality constraint; For the inequality constraints the associated Lagrange multipliers; Expressed as an inequality constraint The associated Lagrange multipliers are given by to A collection of Step S4.2: Solve the Lagrange equation E The partial derivative of , we get the following expression: (13) And set the complementary slack conditions: (14) Step S4.3: According to the solved Lagrange equation E The partial derivative results of , and the optimization solutions of TVAM and TVSM are shown in Table 2: Table 2 Optimization solutions for TVAM and TVSM

[0040] (5) Step S5: Optimizing the hybrid three-variable modulation strategy based on the optimization solutions of the TVAM and TVSM; The step S5 specifically includes: Step S5.1: Under different modes of the hybrid three-variable modulation strategy, the control parameters are determined by comprehensively considering the root mean square current and zero voltage switching. D 1, D 2, D 3 to achieve the peak-to-peak value of the normalized inductor current. Reached minimum value.

[0041] RMS Current I rms ) is a key factor affecting the efficiency of dual active bridge converters because it directly affects the transmission loss. I rms , the following parameters were used for simulation: V 1 = 150 V (input voltage of dual active bridge converter), input voltage V 1 and output voltage V The adaptation coefficient between 2 k = 1.5 and k =1.75, N = 1, L = 87 µH and switching frequency f s = 50 k Hz The results are shown in Figure 4a and Figure 4b respectively. Figure 4a middle, k = 1.5, corresponding to 100V output voltage, at this time TVAM and TVSM I rms are almost identical, indicating that the conduction losses are very similar. Figure 4b middle, k = 1.75, corresponding to an output voltage of 85.7V, TVAM and TVSM I rms The light and heavy load conditions are almost the same. However, under medium load conditions, there is a slight difference, and the TVAM shows I rms Slightly higher than TVSM, although the difference is small.

[0042] Furthermore, the zero-voltage switching (ZVS) range significantly impacts the switching losses of DAB converters. The greater the number of switches achieving ZVS, the lower the switching losses. Therefore, analyzing and comparing the ZVS ranges of TVAMs and TVSMs is crucial for developing optimized solutions for HTVMs. Figure 5a and Figure 5b The ZVS ranges of TVAM (Fig. 5a) and TVSM (Fig. 5b) are shown respectively. A 1 in, S 1- S 3 can achieve ZVS, that is, ZVS is achieved by 3 switches, and in the region A 2, all switches S 1- S8 can achieve ZVS. A 1 to A The conversion of 2 occurs at: ; On the contrary, in Figure 5b area, S 1 and S 2 can achieve ZVS (2 switches to achieve ZVS). area, S 1- S 8 can achieve ZVS. and The boundary between is defined as: .

[0043] Therefore, due to the p Less than or equal to When TVAM has one more switch than TVSM to achieve ZVS, and the two I rms The values ​​are not much different, so TVAM is the preferred option. p Greater than and less than When , TVSM is a better choice because it has 8 switches to achieve ZVS, while TVAM has only 3 switches. p Greater than or equal to When the value is less than or equal to 1, although both TVAM and TVSM achieve complete ZVS, TVSM I rms Therefore, it is the preferred solution. When TVAM is used, TVSM is used when the current is high. This method is called the optimized HTVM scheme using a two-stage optimization method. According to the different modes of HTVM (hybrid three-variable modulation), the optimal control parameters in each mode are solved separately. For each mode, the control variable is obtained by analyzing the expression of the optimized current peak. D 1, D 2, D The optimal solution of 3.

[0044] Specifically, the global optimization scheme of the DAB converter using HTVM is used to obtain the control variables D 1, D 2, D The optimal solution of 3 is: (15) In formula (15), Indicates the dividing point between light load and heavy load; D 1, D 2, D 3 is the optimized control parameter. Under different load conditions, the optimal duty cycle is calculated by formula (15): D 1, D 2, D 3. To achieve the minimum normalized peak-to-peak value of the inductor current .

[0045] Next, we analyze the optimization results. Step S5 specifically includes: Step S5.2: Analyze the obtained control parameters D 1, D 2, D 3. Real-time analysis of the optimization results based on the expression of the optimal solution of

[0046] The step S5.2 specifically includes: step S5.21: determining the normalized transmission power p Is it greater than or equal to zero and less than or equal to ; When the judgment result is yes, execute step S5.22; when the judgment result is no, p The value range is , then execute step S5.23; Step S5.22: Adjust D 1, D 2, and D 3, so that the peak-to-peak value of the normalized inductor current is Minimal volatility; Step S5.23: Adjustment D 1, D 2, and D 3, so as to further reduce the peak-to-peak value of the normalized inductor current .

[0047] Specifically, when When the system is in the low power transmission stage, the duty cycle is adjusted to make the normalized peak-to-peak value of the inductor current Minimum fluctuation. When the system enters the higher power transmission stage, the duty cycle is adjusted to continue to reduce the normalized peak-to-peak value of the inductor current. Through the above optimization process, the efficient operation of the DAB converter under different load conditions can be achieved, its overall performance under light and heavy load conditions can be improved, current stress can be reduced, and power loss can be lowered.

[0048] The present invention's peak-to-peak current optimization method for a Dual Active Bridge (DAB) converter is based on a hybrid three-variable modulation (HTVM) strategy. Specifically, the optimization method provides an optimized HTVM strategy. Specifically, the HTVM strategy combines three-variable symmetric modulation (TVSM) and three-variable asymmetric modulation (TVAM), combining the TVAM's wider zero voltage switching (ZVS) range at light loads with the TVSM's lower current levels at heavy loads, enriching the modulation strategy for DAB converters.

[0049] The present invention's peak-to-peak current optimization method for a Dual Active Bridge (DAB) converter is based on a hybrid three-variable modulation (HTVM) strategy. This optimization method provides a steady-state optimization solution based on HTVM. Specifically, it employs a simple two-stage optimization approach, striking a balance between improving DAB converter efficiency and facilitating system implementation. It prioritizes peak-to-peak current optimization within the HTVM, significantly improving the DAB converter's efficiency under varying load conditions and achieving improved efficiency across the entire power range. In particular, it significantly improves the DAB converter's efficiency under light loads.

[0050] The peak-to-peak current optimization method of the dual active bridge converter of the present invention reduces the peak-to-peak current of the DAB converter by optimizing the control strategy, thereby improving the energy efficiency and stability of the entire system, and is suitable for power electronic equipment for DC-DC power conversion.

[0051] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A peak-to-peak current optimization method for a dual active bridge converter, the dual active bridge converter comprising: Primary side circuit H 1. Isolation transformer T ,inductance L , and secondary side circuit H 2; the isolation transformer T The primary side circuit H 1 and secondary side circuit H 2 are coupled together; the primary side circuit H 1 includes: first filter capacitors connected in parallel C 1 and a first bridge circuit; the secondary side circuit H 2 includes: a second filter capacitor connected in parallel C 2 and a second bridge circuit; the first bridge circuit is composed of a first switching element S 1 and the second switching element S 2 The first branch in series with the third switch element S 3 and the fourth switching element S 4 are connected in series with the second branch in parallel to form a full bridge circuit; the first switch element S 1 and the second switching element S The connection point between 2 a , and the third switching element S 3 and the fourth switching element S 4 connection points between b Connect to the isolation transformer T Both ends of the primary coil; the connection point a Through the inductor L With isolation transformer T The second bridge circuit is composed of a fifth switching element S 5 and the sixth switching element S 6 The third branch connected in series with the seventh switch element S 7 and the eighth switching element S 8 are connected in series with the fourth branch in parallel to form a full bridge circuit; the fifth switch element S 5 and the sixth switching element S 6 connection points between c , and the seventh switching element S 7 and the eighth switching element S 8 connection points between d Connect to the isolation transformer T The two ends of the secondary coil; point a With point b The voltage between v 1. Point c With point d The voltage between v 2; characterized in that the optimization method comprises: Step S1: Establishing a mathematical model of a dual active bridge converter; The step S1 specifically includes: Step S1.1: defining technical parameters of the dual active bridge converter; Step S1.2: Setting a hybrid three-variable modulation strategy; wherein the hybrid three-variable modulation strategy includes: H 1 and secondary side circuit H 2 both adopt symmetrically modulated TVSM; and the hybrid three-variable modulation strategy also includes: the primary side circuit of the dual active bridge converter H 1 and secondary side circuit H 2 both use asymmetric modulation TVAM; the three variables are D 1, D 2 and D 3; D 1 is based on TVAM and TVSM voltage v 1The duty cycle used for signal modulation; D 2 is based on TVAM and TVSM voltage v 2The duty cycle used for signal modulation; D 3 is for the first switch element S 1 and the fifth switching element S 5 for the conduction delay of the signal; Step S1.3: Based on the hybrid three-variable modulation strategy, establish the instantaneous value of the inductor current of the dual active bridge converter The mathematical expression of Step S2: Obtain the peak-to-peak value of the current and the transfer power of the dual active bridge converter P The mathematical expression for the peak-to-peak current and the transmission power P are respectively normalized; wherein the peak-to-peak value of the current is the instantaneous value of the inductor current The difference between the maximum and minimum values ​​of ; Step S2.1: Based on the instantaneous value of the inductor current The mathematical expression to obtain the peak-to-peak value of the current is The mathematical expression of the transmission power is obtained based on the volt-second balance principle. P The mathematical expression of Step S2.2: Calculate the peak-to-peak value of the current Perform normalization to obtain the normalized peak-to-peak value of the inductor current. , for the transmission power P Perform normalization to obtain the normalized transmission power p The normalized peak-to-peak value of the inductor current and the normalized transmission power p The control variables of the mathematical expression include D 1, D 2 and D 3; Step S3: taking the normalized peak-to-peak value of the inductor current The minimum value of the optimization target is the normalized transmission power p The specified value of is a constraint condition, and a mathematical expression of the nonlinear optimization problem of the dual active bridge converter is established; Step S4: Use Karush-Kuhn-Tucker conditions to solve the nonlinear optimization problem and construct the Lagrangian equation E , and the Lagrangian equation E Solve it according to the solved Lagrange equation E The partial derivative results of are used to establish the optimal solutions of TVAM and TVSM; Step S5: Optimizing the hybrid three-variable modulation strategy based on the optimization solutions of the TVAM and TVSM; The step S5 specifically includes: Step S5.1: Under different modes of the hybrid three-variable modulation strategy, control parameters are determined by comprehensively considering the root mean square current and zero voltage switching. D 1, D 2, D 3 to achieve the peak-to-peak value of the normalized inductor current. Reached minimum value.

2. The peak-to-peak current optimization method of a dual active bridge converter according to claim 1, characterized in that: The step S1.1 specifically includes: Step S1.11: Define the input voltage of the dual active bridge converter as V 1. The output voltage is V 2. Isolation transformer T The turns ratio is N :1, inductance is L ;in, N is a positive integer; Step S1.12: Define the input voltage V 1 and the output voltage V The adaptation coefficient between 2 is k The adaptation coefficient k The expression is: （1）。 3. The peak-to-peak current optimization method of the dual active bridge converter according to claim 2, characterized in that: The step S1.3 specifically includes: Step S1.31: The classification basis of the six modes of the hybrid three-variable modulation strategy is set as shown in Table 1: Table 1 Classification basis of the six modes of the hybrid three-variable modulation strategy Step S1.32: Based on the working principle of the dual active bridge converter, the instantaneous value of the inductor current of mode 1 of the dual active bridge converter is Over time within a cycle t The change time is divided into 6 corresponding time periods; Step S1.33: Get the instantaneous value of the inductor current in mode 1 The expression is: （2） In formula (2): （3） In formula (3), T s It is expressed as a switching cycle.

4. The peak-to-peak current optimization method of a dual active bridge converter according to claim 3, characterized in that: The step S2.1 specifically includes: Step S2.11: By taking the maximum value of the current Subtract the minimum current from , and obtain the peak-to-peak value of the current The expression is: （4） In formula (4), for t 4 The instantaneous value of the inductor current corresponding to the time point; for t 6 The instantaneous value of the inductor current corresponding to the time point; f s is the switching frequency; Step S2.12: Based on the volt-second balance principle, the mathematical expression (5) is obtained: （5） Step S2.13: Based on mathematical expression (5), the mathematical expression of the transmission power P is obtained as follows: （6） The step S2.2 specifically includes: Step S2.21: Calculate the peak-to-peak value of the current Perform per-unit normalization to obtain the normalized peak-to-peak value of the inductor current. The normalized peak-to-peak value of the inductor current is The expression is: （7） In formula (7), I N The expression is: （8） Step S2.22: The transmission power P Perform normalization to obtain the normalized transmission power p The normalized transmission power p The expression is: （9） In formula (9), P N The expression is: （10）。 5. The peak-to-peak current optimization method of a dual active bridge converter according to claim 4, characterized in that: Based on the normalized peak-to-peak value of the inductor current and the normalized transmission power p , establish a mathematical expression for the nonlinear optimization problem of the dual active bridge converter; the mathematical expression for the nonlinear optimization problem is: min i P-P ( D 1 , D 2 , D 3 ); s.t. p ( D 1 , D 2 , D 3 )- p * = 0; g i ( D 1 , D 2 , D 3 )≤0,( i =1,2,… l )（11） In formula (11), p * It represents the expected transmission power of the dual active bridge converter; st is the abbreviation of subject to; p ( D 1, D 2 ,D 3) Indicates the control variable D 1, D 2 and D 3 Calculated power value; st p ( D 1, D 2 ,D 3)- p * =0 means that in the optimization process, the control variable D 1, D 2 and D 3 Calculated power value and target power p * Stay consistent; g i Represents the boundary conditions of the optimization variables; l Expressed as the number of boundary conditions.

6. The peak-to-peak current optimization method of a dual active bridge converter according to claim 5, characterized in that: The step S4 specifically includes: Step S4.1: Solve the nonlinear optimization problem using the Karush-Kuhn-Tucker condition and construct the Lagrangian equation E ; The Lagrange equation E The expression is: （12） In formula (12), is the Lagrange multiplier associated with the equality constraint; For the inequality constraints The associated Lagrange multipliers; Expressed as and inequality constraints The associated Lagrange multipliers are given by to A collection of; Step S4.2: Solve the Lagrange equation E The partial derivative of , we get the following expression: （13） And set the complementary relaxation condition: （14） Step S4.3: According to the solved Lagrange equation E The partial derivative results of the optimization solutions for TVAM and TVSM are shown in Table 2: Table 2 Optimization solutions for TVAM and TVSM 7. The peak-to-peak current optimization method of a dual active bridge converter according to claim 6, characterized in that: The control variable D 1, D 2, D The expression of the optimal solution of 3 is: （15） In formula (15), Indicates the dividing point between light load and heavy load; D 1, D 2, D 3 is the optimized control parameters.

8. The peak-to-peak current optimization method of a dual active bridge converter according to claim 7, characterized in that: Also includes: Step S5.2: Solve the control parameters D 1, D 2, D 3. The optimal solution expression of 3 is used for real-time analysis of optimization results.

9. The peak-to-peak current optimization method of a dual active bridge converter according to claim 8, characterized in that: The step S5.2 specifically includes: Step S5.21: Determine the normalized transmission power p Is it greater than or equal to zero and less than or equal to ; When the judgment result is yes, execute step S5.22; when the judgment result is no, explain p The value range is , then execute step S5.23; Step S5.22: Adjustment D 1, D 2, and D 3, so that the normalized peak-to-peak value of the inductor current Minimal volatility; Step S5.23: Adjustment D 1, D 2, and D 3, so as to further reduce the normalized peak-to-peak value of the inductor current .

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