A peak-to-peak current optimization method for dual active bridge converters

Abstract

The present invention relates to the technical field of DAB current optimization. The present invention provides a peak-to-peak current optimization method for a dual active bridge converter. The method comprises: establishing a mathematical model of the DAB converter; obtaining the peak-to-peak value of the current and the transmission power of the dual active bridge converter; P The mathematical expression of P Perform per-unit processing; take the minimum value of the per-unit inductor current peak-to-peak value as the optimization target, and the specified value of the per-unit transmission power as the constraint condition, and establish the mathematical expression of the nonlinear optimization problem of the DAB converter; use the KKT condition to solve the nonlinear optimization problem and construct the Lagrangian equation E And for this equation E The HTVM strategy of the present invention combines the wider zero voltage switching range of TVAM under light load and the lower current level of TVSM under heavy load, enriching the modulation strategy of 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 been widely used in the field of power electronics, especially in new energy applications, due to their simple structure, electrical isolation characteristics, wide voltage conversion ratio and bidirectional energy transmission capabilities. This converter controls the energy flow by adjusting the phase difference between the two full bridges, usually using a single phase shift (SPS) modulation strategy. However, when the input and output voltages do not match, SPS will cause high current stress and soft switching losses, affecting energy conversion efficiency.

[0003] To solve this problem, 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 zero levels, while reducing on-time and switching losses. Specifically, these strategies further reduce switching losses by optimizing switching logic and on-time, reducing current stress at light loads, improving energy conversion efficiency, and expanding the range of zero-voltage switching (ZVS).

[0004] However, multivariable symmetrical modulation and multivariable asymmetrical modulation each have their own advantages and disadvantages. Among them, multivariable symmetrical modulation can achieve the lowest current level, but the ZVS range is narrow under light load, and the strategy of expanding the ZVS range increases the difficulty of microcontroller implementation. Multivariable asymmetrical modulation provides a wider ZVS range, but faces great challenges at higher current levels, and five-variable modulation also brings 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 level, wide ZVS range and easy implementation. 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 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 Connected 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 Connected to the isolation transformer T The two ends of the secondary coil; point a With point b The voltage betweenv 1. Point c With point 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 the 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: 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 conducting delay; 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 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 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 value of the 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: for 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 pThe normalized peak-to-peak value of the inductor current is 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, constructing the Lagrangian equation E , and the Lagrangian 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 switch. 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:

[0010] 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;

[0011] 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:

[0012] (1).

[0013] Preferably, the step S1.3 specifically includes:

[0014] Step S1.31: The classification basis of the six modes of the hybrid three-variable modulation strategy is set as shown in Table 1:

[0015] Table 1 Classification basis of the six modes of the hybrid three-variable modulation strategy

[0016]

[0017] 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;

[0018] Step S1.33: Get the instantaneous value of the inductor current in mode 1 The expression is:

[0019] (2)

[0020] In formula (2):

[0021] (3)

[0022] In formula (3), T s It is expressed as a switching cycle.

[0023] Preferably, 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 current The expression is:

[0024] (4)

[0025] 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;

[0026] Step S2.12: Based on the volt-second balance principle, the mathematical expression (5) is obtained:

[0027] (5)

[0028] Step S2.13: Based on mathematical expression (5), the mathematical expression of the transmission power P is obtained as follows:

[0029] (6)

[0030] The step S2.2 specifically includes:

[0031] 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:

[0032] (7)

[0033] In formula (7), I N The expression is:

[0034] (8)

[0035] Step S2.22: The transmission power P Perform normalization to obtain the normalized transmission power p The normalized transmission power p The expression is:

[0036] (9)

[0037] In formula (9), P N The expression is:

[0038] (10).

[0039] 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:

[0040] min i P-P ( D 1 , D 2 , D 3 );

[0041] st p ( D 1 , D 2 , D 3 )- p* = 0;

[0042] g i ( D 1 , D 2 , D 3 )≤0,( i =1,2,… l )(11)

[0043] 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.

[0044] 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:

[0045] (12)

[0046] 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;

[0047] Step S4.2: Solve the Lagrange equations E The partial derivative of , we get the following expression:

[0048] (13)

[0049] And set the complementary relaxation condition:

[0050] (14)

[0051] 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:

[0052] Table 2 Optimization solutions for TVAM and TVSM

[0053]

[0054] Preferably, the control variable D 1, D 2, D The expression of the optimal solution of 3 is:

[0055] (15)

[0056] In formula (15), Indicates the dividing point between light load and heavy load; D 1, D 2, D 3 is the optimized control parameters.

[0057] Preferably, the peak-to-peak current optimization method of the dual active bridge converter further comprises: step S5.2: calculating the solved control parameter D 1, D 2, D 3. The optimal solution expression of 3 is used for real-time analysis of optimization results.

[0058] 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, explain p The value range is , then execute step S5.23; Step S5.22: adjust D 1, D 2, andD 3, so that the normalized peak-to-peak value of the inductor current Minimum fluctuation; Step S5.23: Adjust D 1, D 2, and D 3, so as to further reduce the normalized peak-to-peak value of the inductor current .

[0059] Beneficial effects of the present invention:

[0060] (1) The peak-to-peak current optimization method of the dual active bridge (DAB) converter of the present invention is based on the hybrid three-variable modulation (HTVM) strategy, that is, the optimization method provides an optimized HTVM strategy. Specifically, the HTVM strategy combines three-variable symmetric modulation (TVSM) and three-variable asymmetric modulation (TVAM), and combines the wider zero voltage switch (Zero Voltage Switch, ZVS) range of TVAM under light load and the lower current level of TVSM under heavy load, enriching the modulation strategy of the DAB converter.

[0061] (2) The peak-to-peak current optimization method of the dual active bridge (DAB) converter of the present invention is based on the hybrid three-variable modulation (HTVM) strategy, that is, the optimization method provides a steady-state optimization scheme based on HTVM. Specifically, a simple two-stage optimization method is adopted to maintain a good balance between improving the working efficiency of the DAB converter and facilitating system implementation, and the peak-to-peak current in the HTVM is optimized. At the same time, the working efficiency of the DAB converter under different load conditions is greatly optimized, and the working efficiency of the DAB converter in the entire power range is improved. In particular, the working efficiency of the DAB converter under light load is greatly optimized.

[0062] Additional aspects and advantages of the invention will become apparent from the following description, or may be learned by practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 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;

[0064] Figure 2 A typical topological structure schematic diagram of a DAB converter according to an embodiment of the present invention is shown;

[0065] 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 the principles of mode 1 of the HTVM, (b) shows a schematic diagram of the principles of mode 2 of the HTVM, (c) shows a schematic diagram of the principles of mode 3 of the HTVM, (d) shows a schematic diagram of the principles of mode 4 of the HTVM, (e) shows a schematic diagram of the principles of mode 5 of the HTVM, and (f) shows a schematic diagram of the principles of mode 6 of the HTVM;

[0066] 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

[0067] Figure 4b An embodiment of the present invention is shown in k TVAM and TVSM when the value is 1.75 I rms and p Schematic diagram of

[0068] Figure 5a FIG. 4 is a schematic diagram showing the ZVS range of a TVAM according to an embodiment of the present invention;

[0069] Figure 5b FIG. 4 is a schematic diagram showing the ZVS range of a TVSM according to an embodiment of the present invention. DETAILED DESCRIPTION

[0070] In order to more clearly understand the above-mentioned objectives, 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 the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0071] 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 protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0072] Figure 1 FIG. 1 is a schematic flow chart of 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 circuitH 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 Connected 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.

[0073] like Figure 1 As shown, the peak-to-peak current optimization method of the dual active bridge converter includes:

[0074] Step S1: Establishing a mathematical model of a dual active bridge converter;

[0075] The step S1 specifically includes:

[0076] Step S1.1: defining technical parameters of the dual active bridge converter;

[0077] 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;

[0078] 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

[0079] Step S2: Obtain the peak-to-peak value of the current and dual active bridge converters transfer power P The mathematical expression of the peak-to-peak current and 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 ;

[0080] 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

[0081] 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 is and the normalized transmission power p The control variables of the mathematical expression include D 1, D 2 and D 3;

[0082] 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;

[0083] 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;

[0084] Step S5: Optimizing the hybrid three-variable modulation strategy based on the optimization solutions of TVAM and TVSM;

[0085] The step S5 specifically includes:

[0086] 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.

[0087] With the rapid development of the new energy field in recent years, the Dual Active Bridge (DAB) converter has become an important DC-DC converter and is 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 2Through inductance L and isolation transformer T connected to form the DAB converter. L The high frequency voltage on the DAB converter determines the power transmission.

[0088] In this embodiment, the peak-to-peak current optimization method of the dual active bridge (DAB) converter of the present invention is based on the hybrid three-variable modulation (HTVM) strategy, that is, the optimization method provides an optimized HTVM strategy. Specifically, the HTVM strategy combines three-variable symmetric modulation (TVSM) and three-variable asymmetric modulation (TVAM), and combines the wider zero voltage switch (ZVS) range of TVAM under light load and the lower current level of TVSM under heavy load, enriching the modulation strategy of the DAB converter.

[0089] In this embodiment, the peak-to-peak current optimization method of the dual active bridge (DAB) converter of the present invention is based on the hybrid three-variable modulation (HTVM) strategy, that is, the optimization method provides a steady-state optimization scheme based on HTVM. Specifically, a simple two-stage optimization method is adopted to maintain a good balance between improving the working efficiency of the DAB converter and facilitating system implementation, and the peak-to-peak current in the HTVM is optimized, while the working efficiency of the DAB converter under different load conditions is greatly optimized, so as to improve the working efficiency of the DAB converter in the entire power range. In particular, the working efficiency of the DAB converter under light load is greatly optimized.

[0090] In one embodiment of the present invention, the step S1.1 specifically includes:

[0091] Step S1.11: Define the input voltage of the dual active bridge converter as V 1. The output voltage is V 2. Isolation transformer TThe turns ratio is N :1, inductance is L ;in, N is a positive integer;

[0092] 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:

[0093] (1).

[0094] 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 represents the additional inductance and transformer leakage inductance. a With point b The voltage between v 1. Point c With point 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 Nv 2. Here, V L represents the voltage drop across the inductor L, i L Indicates that the inductor L The current of v 1 and v 2 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.

[0095] 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 solved control parameters D 1, D 2,D 3. The optimal solution expression of 3 is used for real-time analysis of optimization results.

[0096] The peak-to-peak current optimization method of the dual active bridge converter of the present invention will be demonstrated below with a specific embodiment. The dual active bridge converter comprises: 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 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 Connected 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 Connected to the isolation transformer T The two ends of the secondary coil; point a With pointb The voltage between v 1. Point c With point d The voltage between v 2. Switching elements S 1 to S 8 are all silicon carbide (SiC) MOSFET switches.

[0097] 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:

[0098] (1) Step S1: Establishing a mathematical model of a dual active bridge converter;

[0099] The step S1 specifically includes:

[0100] Step S1.1: defining technical parameters of the dual active bridge converter;

[0101] The step S1.1 specifically includes:

[0102] 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;

[0103] 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:

[0104] (1).

[0105] Step S1.2: Setting a hybrid three-variable modulation strategy; wherein the hybrid three-variable modulation strategy includes using symmetrically modulated 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: using asymmetrically modulated 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 voltagev 2The duty cycle used for signal modulation; D 3 is for the first switch element S 1 and the fifth switching element S 5 and the duty cycle used for the turn-on delay of the signal.

[0106] 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

[0107] The step S1.3 specifically includes:

[0108] Step S1.31: The classification basis of the six modes of the hybrid three-variable modulation strategy is set as shown in Table 1:

[0109] Table 1 Classification basis of the six modes of the hybrid three-variable modulation strategy

[0110]

[0111] Figure 3 shows the schematic diagram of Hybrid Three-variable Modulation (HTVM) in different modes. Figure 3 As shown, (a), (b), and (c) in Figure 3 show three-variable asymmetric modulation (TVAM), and (d), (e), 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. Figure 3 classifies the HTVM into modes to obtain the steady-state characteristics. v 1 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 represent the duration of each stage. T The turns ratio is N :1, so Nv 2 means through an isolation transformer T After that the voltage.

[0112] 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 It explains how HTVM can achieve more efficient energy transmission by adjusting the timing of switches. It also shows that different modulation methods can optimize the conversion efficiency of the system 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.

[0113] 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;

[0114] Step S1.33: Get the instantaneous value of the inductor current in mode 1 The expression is:

[0115] (2)

[0116] In formula (2):

[0117] (3)

[0118] In formula (3), T s It is expressed as a switching cycle.

[0119] (2) Step S2: Obtaining the peak-to-peak value of the current and the transfer power of the dual active bridge converterP 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 ;

[0120] 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

[0121] The step S2.1 specifically includes:

[0122] Step S2.11: By taking the maximum value of the current Subtract the minimum current from , and obtain the peak-to-peak current The expression is:

[0123] (4)

[0124] 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;

[0125] Step S2.12: Based on the volt-second balance principle, the mathematical expression (5) is obtained:

[0126] (5)

[0127] Step S2.13: Based on mathematical expression (5), the mathematical expression of the transmission power P is obtained as follows:

[0128] (6)

[0129] 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 is and the normalized transmission powerp The control variables of the mathematical expression include D 1, D 2 and D 3;

[0130] The step S2.2 specifically includes:

[0131] 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:

[0132] (7)

[0133] In formula (7), I N The expression is:

[0134] (8)

[0135] Step S2.22: The transmission power P Perform normalization to obtain the normalized transmission power p The normalized transmission power p The expression is:

[0136] (9)

[0137] In formula (9), P N The expression is:

[0138] (10).

[0139] Further, 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 in six modes are shown in the following table:

[0140] Normalized transmission power p and the normalized peak-to-peak value of the inductor current

[0141]

[0142] (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 pThe specified value of is a constraint condition, and a mathematical expression of the nonlinear optimization problem of the dual active bridge converter is established;

[0143] 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:

[0144] min i P-P ( D 1 , D 2 , D 3 );

[0145] st p ( D 1 , D 2 , D 3 )- p * = 0;

[0146] g i ( D 1 , D 2 , D 3 )≤0,( i =1,2,… l )(11)

[0147] 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 andD 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.

[0148] (4) Step S4: Use the Karush-Kuhn-Tucker (KKT) condition 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;

[0149] 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:

[0150] (12)

[0151] 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;

[0152] Step S4.2: Solve the Lagrange equation E The partial derivative of , we get the following expression:

[0153] (13)

[0154] And set the complementary relaxation condition:

[0155] (14)

[0156] 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:

[0157] Table 2 Optimization solutions for TVAM and TVSM

[0158]

[0159] (5) Step S5: Optimizing the hybrid three-variable modulation strategy based on the optimization solutions of the TVAM and TVSM;

[0160] The step S5 specifically includes:

[0161] 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.

[0162] 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 simulations were performed using the following parameters: 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, there is a slight difference under medium load conditions, and the TVAM shows I rms Slightly higher than TVSM, although the difference is small.

[0163] Furthermore, the zero-voltage switching (ZVS) range has a great influence on the switching loss of the DAB converter. The more switches that achieve ZVS, the smaller the switching loss. Therefore, analyzing and comparing the ZVS range of TVAM and TVSM is also crucial to obtain the optimization solution for HTVM. Figure 5a and Figure 5b The ZVS ranges of TVAM (Fig. 5a) and TVSM (Fig. 5b) are shown respectively. A 1, S 1- S 3 can achieve ZVS, that is, ZVS is achieved by 3 switches, and in the area A 2, all switches S 1- S 8 can achieve ZVS. A 1 to A The conversion of 2 occurs at:

[0164] ;

[0165] On the contrary, in Figure 5b area, S 1 and S 2 can achieve ZVS (2 switches achieve ZVS). area, S 1- S 8 can achieve ZVS. and The boundary between is defined as:

[0166] .

[0167] Therefore, due to the p Less than or equal to When TVAM has one more switch than TVSM to achieve ZVS, the I rms The values ​​are not much different, so TVAM is the preferred solution. 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 peak value is less than 0.05. 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 respectively. For each mode, the control variable is obtained by analyzing the expression of the optimized current peak value. D 1, D 2, D The optimal solution of 3.

[0168] Specifically, the global optimization scheme of the DAB converter using HTVM is used to obtain the control variables D 1, D 2, D The expression of the optimal solution of 3 is:

[0169] (15)

[0170] 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 .

[0171] Next, the optimization results are analyzed. That is, step S5, which specifically includes: step S5.2: analyzing the solved control parameters D 1, D 2, D 3. The optimal solution expression of 3 is used for real-time analysis of optimization results.

[0172] 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, explain p The value range is , then execute step S5.23; Step S5.22: adjust D 1, D 2, and D 3, so that the normalized peak-to-peak value of the inductor current Minimal volatility;

[0173] 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 .

[0174] Specifically, when When the system is in a low power transmission stage, the duty cycle is adjusted to make the normalized peak-to-peak value of the inductor current Minimal 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 load and heavy load conditions can be improved, current stress can be reduced, and power loss can be reduced.

[0175] The peak-to-peak current optimization method of the dual active bridge (DAB) converter of the present invention is based on the hybrid three-variable modulation (HTVM) strategy, that is, the optimization method provides an optimized HTVM strategy. Specifically, the HTVM strategy combines three-variable symmetric modulation (TVSM) and three-variable asymmetric modulation (TVAM), and combines the wider zero voltage switch (Zero Voltage Switch, ZVS) range of TVAM under light load and the lower current level of TVSM under heavy load, enriching the modulation strategy of the DAB converter.

[0176] The peak-to-peak current optimization method of the dual active bridge (DAB) converter of the present invention is based on the hybrid three-variable modulation (HTVM) strategy, that is, the optimization method provides a steady-state optimization scheme based on HTVM. Specifically, a simple two-stage optimization method is adopted to maintain a good balance between improving the working efficiency of the DAB converter and facilitating system implementation, and the peak-to-peak current in the HTVM is optimized, while the working efficiency of the DAB converter under different load conditions is greatly optimized, so as to improve the working efficiency of the DAB converter in the entire power range. In particular, the working efficiency of the DAB converter under light load is greatly optimized.

[0177] 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, improves the energy efficiency and stability of the entire system, and is suitable for power electronic equipment for DC-DC power conversion.

[0178] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope 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: A primary side circuit H1, an isolation transformer T, an inductor L, and a secondary side circuit H2; the isolation transformer T couples the primary side circuit H1 and the secondary side circuit H2 together; the primary side circuit H1 includes: a first filter capacitor C1 and a first bridge circuit connected in parallel with each other; the secondary side circuit H2 includes: a second filter capacitor C2 and a second bridge circuit connected in parallel with each other; the first bridge circuit is a full bridge circuit formed by connecting a first branch connected in series with a first switching element S1 and a second switching element S2 in parallel with a second branch connected in series with a third switching element S3 and a fourth switching element S4; a connection point a between the first switching element S1 and the second switching element S2 is connected to a point between the third switching element S3 and the fourth switching element S4 The connection point b between the fifth switch element S5 and the sixth switch element S6 is respectively connected to the two ends of the primary coil of the isolation transformer T; the connection point a is connected to one end of the primary coil of the isolation transformer T via the inductor L; the second bridge circuit is a full bridge circuit formed by connecting the third branch connected in series with the fifth switch element S5 and the sixth switch element S6, and the fourth branch connected in series with the seventh switch element S7 and the eighth switch element S8 in parallel; the connection point c between the fifth switch element S5 and the sixth switch element S6, and the connection point d between the seventh switch element S7 and the eighth switch element S8 are respectively connected to the two ends of the secondary coil of the isolation transformer T; the voltage between point a and point b is v1, and the voltage between point c and point d is v2; it is 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 adopting symmetrically modulated TVSM for both the primary side circuit H1 and the secondary side circuit H2 of the dual active bridge converter; and the hybrid three-variable modulation strategy also includes: adopting asymmetrically modulated TVAM for both the primary side circuit H1 and the secondary side circuit H2 of the dual active bridge converter; the three variables are D1, D2 and D3 respectively; D1 is the duty cycle adopted for signal modulation of voltage v1 based on TVAM and TVSM; D2 is the duty cycle adopted for signal modulation of voltage v2 based on TVAM and TVSM; D3 is the duty cycle adopted for conducting delay of the signal between the first switch element S1 and the fifth switch element S5; Step S1.3: Based on the hybrid three-variable modulation strategy, establish the instantaneous value of the inductor current i of the dual active bridge converter L (t) is a mathematical expression; Step S2: Obtain the peak-to-peak value of the current I P-P The mathematical expression of the transmission power P of the dual active bridge converter and the peak-to-peak current I P-P and the transmission power P are respectively normalized; wherein the peak-to-peak value of the current I P-P is the instantaneous value of the inductor current i L The difference between the maximum and minimum values ​​of (t); Step S2.1: Based on the instantaneous value of the inductor current i L The peak-to-peak current I is obtained by the mathematical expression of (t) P-P A mathematical expression of the transmission power P is obtained based on the volt-second balance principle; Step S2.2: Calculate the peak-to-peak value of the current I P-P The normalized peak-to-peak value of the inductor current i is obtained by normalizing the peak-to-peak value of the inductor current i P-P , the transmission power P is normalized to obtain the normalized transmission power p; the normalized peak-to-peak value of the inductor current i P-P The control variables of the mathematical expression of the normalized transmission power p all include D1, D2 and D3; Step S3: Taking the normalized peak-to-peak value of the inductor current i P-P The minimum value of is the optimization target, and the specified value of the normalized transmission power p is used as the constraint condition to establish a mathematical expression for the nonlinear optimization problem of the dual-active bridge converter; Step S4: using the Karush-Kuhn-Tucker condition to solve the nonlinear optimization problem, constructing the Lagrangian equation E, and solving the Lagrangian equation E, and establishing the optimization solution of TVAM and TVSM according to the partial derivative results of the solved Lagrangian equation E; 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, by comprehensively considering the root mean square current and zero voltage switching, determine the optimal solution of the control parameters D1, D2, and D3 to achieve the normalized peak-to-peak value of the inductor current i P-P Reach a minimum value; The step S1.1 specifically includes: Step S1.11: define the input voltage of the dual active bridge converter as V1, the output voltage as V2, the turns ratio of the isolation transformer T as N:1, and the inductance as L; wherein N is a positive integer; Step S1.12: define the adaptation coefficient between the input voltage V1 and the output voltage V2 as k; the expression of the adaptation coefficient k is: 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 i of mode 1 of the dual active bridge converter is L (t) The time variation with time t in one cycle is divided into 6 corresponding time periods; Step S1.33: Get the instantaneous value of the inductor current i in mode 1 L The expression of (t) is: In formula (2): In formula (3), T s It is expressed as a switching cycle; The step S2.1 specifically includes: Step S2.11: By taking the maximum value of the current i L (t4) minus the minimum current value i L (t6), obtain the peak-to-peak current I P-P The expression is: In formula (4), i L (t4) is the instantaneous value of the inductor current corresponding to time point t4; i L (t6) is the instantaneous value of the inductor current corresponding to time point t6; f s is the switching frequency; Step S2.12: Based on the volt-second balance principle, the mathematical expression (5) is obtained: Step S2.13: Based on mathematical expression (5), the mathematical expression of the transmission power P is obtained as follows: The step S2.2 specifically includes: Step S2.21: Calculate the peak-to-peak value of the current I P-P Perform per-unit normalization to obtain the normalized peak-to-peak value of the inductor current i P-P The normalized peak-to-peak value of the inductor current i P-P The expression is: In formula (7), I N The expression is: Step S2.22: normalize the transmission power P to obtain the normalized transmission power p; the normalized transmission power p is expressed as: In formula (9), P N The expression is: Based on the normalized peak-to-peak value of the inductor current i P-P and the normalized transmission power p, a mathematical expression of the nonlinear optimization problem of the dual-active bridge converter is established; the mathematical expression of the nonlinear optimization problem is: mean i P-P (D1,D2,D3)? s.t.p(D1,D2,D3)-p * =0; <h2 style=";text-align:left;direction:ltr">g<h2 style=";text-align:left;direction:ltr"> i <h2 style=";text-align:left;direction:ltr"> (D1,D2,D3)≤0,(i=1,2,…l) (11) In formula (11), p * represents the expected transmission power of the dual active bridge converter; st is the abbreviation of subject to; p(D1, D2, D3) represents the power value calculated by the control variables D1, D2 and D3; stp(D1, D2, D3)-p * = 0 means that in the optimization process, the power value calculated by the control variables D1, D2 and D3 needs to be consistent with the target power p * Stay consistent; i represents the boundary conditions of the optimization variables; l represents the number of boundary conditions; The step S4 specifically includes: Step S4.1: Using the Karush-Kuhn-Tucker condition to solve the nonlinear optimization problem, construct the Lagrangian equation E; the expression of the Lagrangian equation E is: In formula (12), λ is the Lagrange multiplier associated with the equality constraint; μ i is the inequality constraint g i The associated Lagrange multiplier; μ is expressed as the inequality constraint g i The associated Lagrange multipliers are from μ1 to μ i A collection of; Step S4.2: Solve the partial derivative of the Lagrange equation E and obtain the following expression: And set the complementary relaxation condition: μ i g i (D1,D2,D3)=0,µ i ≥0,λ≠0 (14) Step S4.3: According to the partial derivative results of the Lagrange equation E, the optimization solutions of TVAM and TVSM are established as shown in Table 2: Table 2 Optimization solutions for TVAM and TVSM The optimal solution expression of the control variables D1, D2, D3 is: In formula (15), p b′ Indicates the dividing point between light load and heavy load; D1, D2, D3 are optimized control parameters; The peak-to-peak current optimization method of the dual active bridge converter further includes: Step S5.2: Real-time analysis of the optimization results of the expressions of the optimal solutions of the solved control parameters D1, D2, and D3; The step S5.2 specifically includes: Step S5.21: Determine whether the normalized transmission power p is greater than or equal to zero and less than or equal to p b′ ; When the judgment result is yes, execute step S5.22; when the judgment result is no, it means that the value range of p is p b′ <p≤1, then execute step S5.23; Step S5.22: Adjust D1, D2, and D3 so that the normalized peak-to-peak value of the inductor current i P-P Minimal volatility; Step S5.23: Adjust D1, D2, and D3 to further reduce the normalized peak-to-peak value of the inductor current i P-P .

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