DAB Converter Return Power Optimization Method and Device Based on Superhelical Sliding Mode Control

Abstract

This application relates to the technical field of dual-active-bridge converters, and particularly to a method and device for optimizing the reverse power of a DAB converter based on super-twisting sliding mode control. This method constructs the reverse power function and transmission power function of four operating modes under dual-phase-shift control, differentiates the reverse power function of each mode to determine the calculation of the optimal reverse power path, and optimizes it according to the intersection point with the actual optimal reverse power path, ensuring the accuracy of the reverse power path. At a fixed transmission power, based on the optimized reverse power path, the phase-shift ratio combination with the minimum reverse power is selected, significantly reducing the reverse power of the DAB converter. This method uses dual-phase-shift control, eliminating the need to switch control signals during bidirectional energy transmission, and has a wider power adjustment range, reducing the control difficulty. In addition, by introducing the super-twisting sliding mode control strategy to dynamically adjust and optimize the external-bridge phase-shift ratio, the stability and robustness of the system are further enhanced.

Description

Technical Field

[0001] The present application relates to the technical field of dual active bridge converters, and particularly to a method and device for optimizing the reverse power of a DAB converter based on super-twisting sliding mode control. Background Technique

[0002] The dual active bridge (DAB) DC-DC converter has characteristics such as bidirectional power flow, electrical isolation, high power density, and easy implementation of zero-voltage switching, and has gradually become the mainstream device in the construction of DC microgrids. However, the reverse power problem has always been one of the key factors affecting the efficiency and performance of the DAB converter. Reverse power not only increases the energy loss of the system but may also have an adverse impact on the stability and reliability of the power grid.

[0003] To effectively control the reverse power in the DAB converter, the patent with the existing publication number CN109256955A provides a method for suppressing and analyzing the reverse power of a dual active bridge based on modal analysis. By adopting the extended phase shift (EPS) control method, the phase shift duty ratio and the timing of the primary side switch drive signal are changed, and a freewheeling mode is added during the DAB modal evolution process to provide a freewheeling channel for the inductor to discharge energy, thereby avoiding the freewheeling current flowing into the input power supply and reducing or eliminating the reverse power. The extended phase shift control method adopted by this method, on the basis of single phase shift (SPS) control, introduces an additional internal phase shift angle in the secondary side bridge of the transformer, which can effectively reduce the reverse power and current stress of the transformer. However, during the process of changing the direction of power transmission by EPS control, it often leads to changes in the operating conditions, making the original control parameters may no longer be applicable and need to be readjusted and optimized, greatly increasing the control difficulty of the system. Summary of the Invention

[0004] Based on this, in view of the problem that the existing reverse power suppression method is relatively complex, it is necessary to provide a method and device for optimizing the reverse power of a DAB converter based on super-twisting sliding mode control.

[0005] In a first aspect, the present application provides a method for optimizing the reverse power of a DAB converter based on super-twisting sliding mode control, including:

[0006] Step S1, divide the working modes of the DAB converter under the dual phase shift control mode into four types according to the magnitude relationship between the in-bridge phase shift ratio and the out-of-bridge phase shift ratio, and construct the reverse power function and transmission power function of the four working modes;

[0007] Step S2, respectively take the derivative of the reverse power function of the four working modes to obtain the calculated optimal reverse power path of each working mode;

[0008] Step S3: Calculate the intersection points of the calculated optimal reflux power paths and the actual optimal reflux power paths for each working mode, and optimize the calculated optimal reflux power paths according to the intersection points to obtain the optimized calculated optimal reflux power paths for each working mode;

[0009] Step S4: Obtain the phase shift ratio combination with the minimum reflux power under the condition of a certain transmission power according to the optimized calculated optimal reflux power paths for each working mode;

[0010] Step S5: Define the input and sliding mode surface of the super-twisting sliding mode controller;

[0011] Step S6: Obtain the optimized phase shift ratio outside the bridge according to the input and sliding mode surface of the super-twisting sliding mode controller, the phase shift ratio inside the bridge in the phase shift ratio combination with the minimum reflux power, and the reflux power function and transmission power function under the four working modes.

[0012] In one embodiment, the phase shift ratio D 1 inside the bridge and the phase shift ratio D 2 outside the bridge under the four working modes have the following magnitude relationships respectively:

[0013] Mode a: 0 < D 1 , D 2 < 1, D 1 < D 2 , D 1 + D 2 ≥ 1;

[0014] Mode b: 0 < D 1 , D 2 < 1, D 1 < D 2 , D 1 + D 2 < 1;

[0015] Mode c: 0 < D 1 , D 2 < 1, D 1 ≥ D 2 , D 1 + D 2 < 1;

[0016] Mode d: 0 < D 1 , D 2 < 1, D 1 ≥ D 2 , D 1 + D 2 ≥ 1.

[0017] In one embodiment, for the four operating modes of the DAB converter, the reflux power function and the transmission power function are constructed according to the following steps:

[0018] Step S11: Obtain the inductor current value of the DAB converter within one period.

[0019] Step S12: Obtain the reflux power and the transmission power according to the inductor current value and the port voltage of the primary side H-bridge of the transformer.

[0020] Step S13: Perform per-unit normalization on the reflux power and the transmission power with the maximum value of the transmission power as the reference value for power per-unit normalization.

[0021] In one embodiment, the expressions of the reflux power function and the transmission power function for the four operating modes after per-unit normalization are respectively:

[0022]

[0023] In the formula, P 1a represents the transmission power of mode a, P DPS-bf-a represents the reflux power of mode a, P 1b represents the transmission power of mode b, P DPS-bf-b represents the reflux power of mode b, P 1c represents the transmission power of mode c, P DPS-bf-c represents the reflux power of mode c, P 1d represents the transmission power of mode d, P DPS-bf-d represents the reflux power of mode d, and k represents the voltage transmission ratio.

[0024] In one embodiment, when the DAB converter operates in mode b, the expression of the inductor current value of the DAB converter within one period is:

[0025]

[0026] In the formula, i L is the inductor current, t 0 =0, t 1 =D 1 T hs , t 2 =D 2 T hs , t 3 =(D 1 +D 2 )T hs , T hs is the half-switching period of the DAB converter, f s is the switching frequency, f s =1 / (2T hs), where \(L\) is the sum of the leakage inductance and the auxiliary inductance of the transformer, \(n\) is the number of turns of the primary side of the transformer, \(u\) 0 is the output side voltage, and \(k\) is the voltage transfer ratio;

[0027] The expressions of the reflux power function and the transmission power function of Mode b after per-unit processing are:

[0028]

[0029] In the formula, \(P\) 1b represents the transmission power of Mode b, and \(P\) DPS-bf-b represents the reflux power of Mode b.

[0030] In one embodiment, step S2 includes:

[0031] Step S21, taking the derivative of the reflux power function of Mode b after per-unit processing; the expression of the derivative result is:

[0032]

[0033] Step S22, setting the value of the derivative reflux power function to 0 to obtain the calculated optimal reflux power path of Mode b; the expression of the calculated optimal reflux power path of Mode b is:

[0034]

[0035] Step S3 includes:

[0036] Step S31, setting \(D1 = D2\) to obtain the intersection point of the calculated optimal reflux power path and the actual optimal reflux power path of Mode b; the expression of the intersection point is:

[0037]

[0038] In the formula, \(P'\) 1 represents the transmission power of the intersection point, and \(D'\) 2 represents the bridge outer shift ratio of the intersection point;

[0039] Step S32, optimizing the calculated optimal reflux power path obtained in step S22 according to the intersection point to obtain the optimized calculated optimal reflux power path of Mode b; among them, when , the optimized calculated optimal reflux power path of Mode b is:

[0040]

[0041] In the formula, \(P\) 1 represents the transmission power of the DAB converter.

[0042] In one of the embodiments, the phase shift ratio combination with the minimum return power and the return power corresponding to the phase shift ratio combination with the minimum return power include:

[0043] When 0 ≤ P 1 <0.5, the operating mode of the DAB converter is mode c, and the phase shift ratio combination is The return power is 0.25(k - 1) 2 P 1 k -1 ;

[0044] When , the operating mode of the DAB converter is mode b, and the phase shift ratio combination is The return power is

[0045] When , the operating mode of the DAB converter is mode b, and the phase shift ratio combination is: The return power is: Wherein, P 1 is the transmission power of the DAB converter.

[0046] In one of the embodiments, the expressions of the input of the super-twisting sliding mode controller and the sliding mode surface are:

[0047]

[0048] In the formula, p represents the input of the super-twisting sliding mode controller, L is the sum of the leakage inductance of the transformer and the auxiliary inductance, f s is the switching frequency, C o is the support capacitor on the output side of the transformer, n is the number of turns of the primary side of the transformer, u i is the voltage on the input side of the transformer, i o is the load current, k 1 and k 2 are both positive coefficients, sgn is the sign function, α and β are both positive parameters, e is the output voltage error, s is the sliding mode surface, represents the derivative of the sliding mode surface;

[0049] Among them, the expression of the sliding mode surface is: s = k 1 e + k 2 ∫(e)dt, and the expression of the output voltage error is: e = u o - u ref , u o is the voltage on the output side of the transformer, u ref is the reference voltage.

[0050] In one of the embodiments, the expression of the optimized phase shift ratio outside the bridge is:

[0051]

[0052] In the formula, D 1 is the in-bridge phase shift ratio in the phase shift ratio combination with the minimum reflux power in step S4.

[0053] In a second aspect, the present application provides a DAB converter reflux power optimization device based on super-twisting sliding mode control, including:

[0054] An optimal reflux power path calculation module, configured to divide the working modes of the DAB converter under the DPS control mode into four according to the magnitude relationship between the in-bridge phase shift ratio and the out-of-bridge phase shift ratio, and construct the reflux power function and the transmission power function of the four working modes; respectively take the derivative of the reflux power functions of the four working modes to obtain the calculated optimal reflux power paths of the respective working modes;

[0055] An optimal reflux power path optimization module, configured to calculate the intersection points of the calculated optimal reflux power paths of the respective working modes and the actual optimal reflux power paths, and optimize the calculated optimal reflux power paths according to the intersection points to obtain the optimized calculated optimal reflux power paths of the respective working modes;

[0056] A phase shift ratio combination and reflux power calculation module, configured to obtain, according to the optimized calculated optimal reflux power paths of the respective working modes, the phase shift ratio combination with the minimum reflux power and the reflux power corresponding to the phase shift ratio combination with the minimum reflux power under the condition that the transmission power is constant;

[0057] An out-of-bridge phase shift ratio optimization module, configured to define the input and the sliding mode surface of the super-twisting sliding mode controller; obtain the optimized out-of-bridge phase shift ratio according to the input and the sliding mode surface of the super-twisting sliding mode controller, the in-bridge phase shift ratio in the phase shift ratio combination with the minimum reflux power, and the reflux power functions and the transmission power functions under the four working modes.

[0058] The above DAB converter reverse power optimization method and device based on super-twisting sliding mode control construct the reverse power function and transmission power function of the DAB converter under four working modes in the dual-phase-shift control mode, derive the calculation of the optimal reverse power path by differentiating the reverse power function of each working mode, and optimize it through the intersection point with the actual optimal path to ensure the accuracy of the calculated optimal reverse power path. Then, under the condition of a certain transmission power, the phase-shift ratio combination with the minimum reverse power is determined according to the optimized calculated optimal reverse power path of each working mode, thus significantly reducing the reverse power of the DAB converter. The DAB converter in this method is controlled by the dual-phase-shift control method, and the dual-phase-shift control does not require switching control signals in the case of bidirectional energy transmission and has a wider power regulation range, so the control difficulty of the system is reduced. In addition, by introducing the super-twisting sliding mode control strategy, this method realizes the dynamic adjustment and optimization of the external-bridge phase-shift ratio, further improving the stability and robustness of the system. Description of the Drawings

[0059] Figure 1 It is a schematic structural diagram of a DAB converter in an embodiment;

[0060] Figure 2 It is a schematic flow diagram of a DAB converter reverse power optimization method based on super-twisting sliding mode control in an embodiment;

[0061] Figure 3 It is a working waveform diagram of a DAB converter in the global mode in an embodiment;

[0062] Figure 4 It is a normalized transmission power diagram of a DAB converter in the global mode in an embodiment;

[0063] Figure 5 It is a schematic diagram of the calculated optimal reverse power path of a DAB converter in mode b in an embodiment;

[0064] Figure 6 It is a structural block diagram of a DAB converter reverse power optimization device based on super-twisting sliding mode control in an embodiment;

[0065] Figure 7 It is a schematic structural diagram of a DAB converter reverse power optimization system based on super-twisting sliding mode control in an embodiment;

[0066] Figure 8 It is a working waveform diagram when a DAB converter under light load conditions is controlled by a traditional current stress optimization method in an embodiment;

[0067] Figure 9It is a working waveform diagram when the DAB converter reflux power optimization method without super-twisting sliding mode control is used to control the DAB converter under light load conditions in an embodiment;

[0068] Figure 10 It is a working waveform diagram when the DAB converter reflux power optimization method based on super-twisting sliding mode control is used to control the DAB converter under light load conditions in an embodiment;

[0069] Figure 11 It is a working waveform diagram when the traditional current stress optimization method is used to control the DAB converter under medium load conditions in an embodiment;

[0070] Figure 12 It is a working waveform diagram when the DAB converter reflux power optimization method without super-twisting sliding mode control is used to control the DAB converter under medium load conditions in an embodiment;

[0071] Figure 13 It is a working waveform diagram when the DAB converter reflux power optimization method based on super-twisting sliding mode control is used to control the DAB converter under medium load conditions in an embodiment;

[0072] Figure 14 It is a working waveform diagram when the traditional current stress optimization method is used to control the DAB converter under heavy load conditions in an embodiment;

[0073] Figure 15 It is a working waveform diagram when the DAB converter reflux power optimization method without super-twisting sliding mode control is used to control the DAB converter under heavy load conditions in an embodiment;

[0074] Figure 16 It is a working waveform diagram when the DAB converter reflux power optimization method based on super-twisting sliding mode control is used to control the DAB converter under heavy load conditions in an embodiment. Detailed implementation manners

[0075] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0076] The DAB converter reflux power optimization method based on super-twisting sliding mode control provided by the present application is used to control the DAB converter as Figure 1 shown. In the figure, the DAB converter includes two identical full-bridge units, an auxiliary inductor L, a high-frequency transformer T, an input-side support capacitor C i and an output-side support capacitor Co and the two full-bridge units are connected by a high-frequency transformer. Among them, the full-bridge unit consists of 4 identical power switching devices, and the input-side full-bridge is represented by S 1 ~S 4 and the output-side full-bridge is represented by S 5 ~S 8 . The turns ratio of the primary and secondary sides of the high-frequency transformer is n:1. The auxiliary inductor is the sum of the leakage inductance of the high-frequency transformer and the auxiliary inductor. u i is the input-side voltage, u o is the output-side voltage, v H1 is the port voltage of the H-bridge on the primary side of the transformer, v H2 is the port voltage of the H-bridge on the secondary side of the transformer, i L is the inductor current, and i o is the load current.

[0077] Embodiment 1

[0078] An embodiment of the present disclosure provides a method for optimizing the reflux power of a DAB converter based on super-twisting sliding mode control. As Figure 2 shown, the method specifically includes the following steps:

[0079] Step S1: Divide the working modes of the DAB converter under the dual-phase-shift control mode into four types according to the magnitude relationship between the in-bridge phase-shift ratio and the out-of-bridge phase-shift ratio, and construct the reflux power function and transmission power function of the four working modes.

[0080] Among them, dual-phase-shift (DPS) control adds a phase-shift angle simultaneously inside the bridges on both sides of the transformer, has two control degrees of freedom, does not require switching control signals in the case of bidirectional energy transmission, and has a wider power adjustment range. The in-bridge phase-shift ratio is the phase-shift ratio between the two half-bridge arms inside the input-side full-bridge unit or the output-side full-bridge unit, denoted as D1, and the out-of-bridge phase-shift ratio is the phase-shift ratio between the input-side full-bridge unit and the output-side full-bridge unit, denoted as D2.

[0081] Specifically, the working modes of the DAB converter under the DPS control mode are divided into four working modes: mode a, mode b, mode c, and mode d. The magnitude relationship between the in-bridge phase-shift ratio D1 and the out-of-bridge phase-shift ratio D2 of each working mode is shown in Equation (1):

[0082]

[0083] Figure 3 shows the working waveform diagram of the DAB converter in the four working modes. It can be seen from the figure that since the DAB converter has a symmetric structure, the inductor current i LIt also has symmetry. Below, starting with mode b as a typical mode, the analysis begins.

[0084] When the DAB converter operates in mode b, according to the relationship between the current and voltage across the inductor, the inductor current value within one working cycle as shown in Equation (2) can be obtained:

[0085]

[0086] In the formula, i L is the inductor current, t 0 = 0, t 1 = D 1 T hs , t 2 = D 2 T hs , t 3 = (D 1 + D 2 )T hs , T hs is the half-switching period of the DAB converter, f s is the switching frequency, f s = 1 / (2T hs ), L is the sum of the leakage inductance of the transformer and the auxiliary inductance, n is the number of turns of the primary side of the transformer, u 0 is the output-side voltage, k is the voltage transfer ratio, Among them, the maximum value of the inductor current is the current stress.

[0087] Then, substituting Equation (2) into the calculation formulas for the reverse power and transmission power of the DAB converter as shown in Equation (3), the reverse power and transmission power of mode b as shown in Equation (4) are obtained. To more intuitively compare and analyze the performance under different working modes, then the maximum value of the transmission power of mode b is obtained, and then the maximum value of the transmission power is used as the reference value for power per-unitization. The expression of the reference value for power per-unitization is as shown in Equation (5); then, based on Equation (5), the transmission power and reverse power of mode b are per-unitized, and the reverse power function and transmission power function of per-unitized mode b as shown in Equation (6) are obtained.

[0088] Among them, the calculation formulas for the reverse power and transmission power of the DAB converter under the DPS control method are:

[0089]

[0090] In the formula, P 1 represents the transmission power of the DAB converter, P DPS-bf represents the reverse power of the DAB converter, v H1(t) represents the port voltage of the H-bridge on the primary side of the transformer, t' 2is the time when the inductor current is first 0 within a period;

[0091]

[0092] In the formula, P 1b represents the transmission power of mode b, and P DPS-bf-b represents the reflux power of mode b.

[0093]

[0094] In the formula, P N is the base value for power per-unit normalization.

[0095]

[0096] In formula (6), the transmission power P 1b of mode b is the transmission power after per-unit normalization, and the reflux power P DPS-bf-b of mode b is the reflux power after per-unit normalization.

[0097] When the DAB converter operates in the other three modes, similarly, first obtain the inductor current value within a working period according to the relationship between the current and voltage at both ends of the inductor, then substitute the inductor current value into formula (3) to obtain the reflux power and transmission power in the corresponding working mode, and then perform per-unit normalization processing on both the reflux power and the transmission power based on formula (5) to obtain the final reflux power function and transmission power function. Formula (7) lists the reflux power functions and transmission power functions of the four working modes, and Figure 4 shows the per-unit normalization diagram of the transmission power in the global mode of the DAB converter. In the figure, "1" represents mode a, "2" represents mode b, "3" represents mode c, and "4" represents mode d:

[0098]

[0099] In the formula, P 1a represents the transmission power of mode a, P DPS-bf-a represents the reflux power of mode a, P 1b represents the transmission power of mode b, P DPS-bf-b represents the reflux power of mode b, P 1c represents the transmission power of mode c, P DPS-bf-c represents the reflux power of mode c, P 1d represents the transmission power of mode d, P DPS-bf-d represents the reflux power of mode d, and k represents the voltage transmission ratio.

[0100] Step S2: Differentiate the reflux power functions of the four working modes respectively to obtain the calculated optimal reflux power paths for each working mode.

[0101] When the output power is determined, the problem of minimizing the reflux power of the DAB converter is transformed into solving the minimum value of the reflux power function within a specified scope under specified constraint conditions. Here, the specified constraint conditions mean that the value of the output power is fixed, and the specified scope corresponds to the variable range of the transmission power.

[0102] Step S3: Calculate the intersection points of the calculated optimal reflux power paths and the actual optimal reflux power paths of each operating mode, and optimize the calculated optimal reflux power paths according to the intersection points to obtain the optimized calculated optimal reflux power paths of each operating mode.

[0103] Exemplarily, taking mode b as a typical mode, analyze the characteristics of the DAB converter under different phase shift ratio combinations, so as to optimize the reflux power. Specifically, first, after taking the derivative of the reflux power function in Equation (6), we can get:

[0104]

[0105] Let the value of Equation (8) be 0, and the calculated optimal reflux power path of mode b as shown in Equation (9) can be obtained:

[0106]

[0107] Figure 5 The calculated optimal reflux power path of mode b is shown. It can be seen from the figure that the calculated optimal reflux power path of mode b crosses other operating modes. Therefore, the actual optimal reflux power path is the intersection point of mode b and mode c under the calculated optimal reflux power path. Then, by combining Equation (9) and Equation (7), and making D1 = D2 at the same time, the intersection point of the calculated optimal reflux power path and the actual optimal reflux power path of mode b can be obtained as:

[0108]

[0109] In the formula, P′ 1 represents the transmission power of the intersection point, and D′ 2 represents the external-bridge phase shift ratio of the intersection point.

[0110] Then, optimize the calculated optimal reflux power path shown in Equation (9) according to the intersection point shown in Equation (10), and when the optimized calculated optimal reflux power path of mode b is:

[0111]

[0112]

[0113] Using the same analysis method, the optimized calculated optimal reflux power paths for the remaining three operating modes can be obtained.

[0114] Step S4: According to the optimized calculated optimal reflux power paths of each operating mode, obtain the phase shift ratio combination with the minimum reflux power under the condition of a certain transmission power.

[0115] Specifically, under the condition of a certain transmission power, by comparing the optimal reflux power paths of each operating mode of the DAB converter, determine the path with the minimum reflux power, and determine the phase shift ratio combination corresponding to this path. Table 1 lists the phase shift ratio combinations with the minimum reflux power and their corresponding reflux power values of the DAB converter under different operating modes and different transmission powers. Among them, when the DAB converter operates in Mode a and Mode d, the optimal operating conditions cannot be obtained.

[0116] Table 1

[0117]

[0118] Step S5: Define the input and sliding mode surface of the super-twisting sliding mode controller.

[0119] Among them, the super-twisting sliding mode controller is an advanced non-linear control strategy. In the design of the super-twisting sliding mode controller, the input p is usually calculated according to the sliding mode surface function and its derivative, as well as the system state variables and their dynamics. The controller adjusts the input p to make the system state converge to the expected value quickly and stably along the predetermined sliding mode surface, so as to achieve the control objective of the system. The derivative s' of the sliding mode surface function reflects the rate of change of the system state along the sliding mode surface, and it is an important basis for the controller to adjust the system state to maintain or approach the sliding mode surface.

[0120] Specifically, the energy stored in the output capacitor C on the right side of the transformer o can be expressed as:

[0121]

[0122] In the formula, P o is the output power of the DAB converter, P o = u o i o , E c is the energy stored in the output capacitor, and P is the transmission power of the DAB converter. After simplifying Equation (13), we get:

[0123]

[0124] In the formula, represents the derivative of u o with respect to.

[0125] Define the output voltage error e as:

[0126] e = u o - u ref (15)

[0127] where u ref is the reference voltage.

[0128] To ensure that the tracking error e = 0, design the sliding surface s of the super-twisting sliding mode controller as:

[0129] s = k 1 e + k 2 ∫(e)dt (16)

[0130] where k 1 and k 2 are positive coefficients that determine the convergence rate of the error e.

[0131] The input P of the super-twisting sliding mode controller consists of two parts, namely the model equivalent part u * and the switching control part u 1 , where the role of u * is to guide the system state trajectory to enter and remain on the sliding surface. In sliding mode control, due to factors such as external disturbances, internal uncertainties, or modeling errors in the system, the system state may deviate from the sliding variable. The purpose of u 1 is to ensure that the system state does not leave the sliding surface. This switching control strategy helps to enhance the robustness and stability of the system. The specific expression of the input P of the super-twisting sliding mode controller is shown in Equation (17):

[0132]

[0133] where α and β are both positive parameters.

[0134] When the output voltage error e reaches the fixed-time sliding surface, there is Then, according to Equation (16), we can obtain:

[0135]

[0136] Replace the transmission power P 1 with the input P of the controller, and substitute into Equation (14). After combining Equation (18), the final super-twisting sliding mode controller is obtained as:

[0137]

[0138] Step S6: Obtain the optimized external-bridge phase shift ratio based on the input of the super-twisting sliding mode controller, the sliding mode surface, the in-bridge phase shift ratio in the phase shift ratio combination with the minimum reflux power, and the reflux power function and transmission power function under four working modes.

[0139] Specifically, based on the in-bridge phase shift ratio D1 in the phase shift ratio combination with the minimum reflux power in Table 1, the reflux power function and transmission power function under four working modes shown in Equation (7), and the input and sliding mode surface of the super-twisting sliding mode controller shown in Equation (19), the optimized external-bridge phase shift ratio shown in Equation (20) can be obtained.

[0140]

[0141] In the method for optimizing the reflux power of a DAB converter based on super-twisting sliding mode control in this embodiment, by constructing the reflux power function and transmission power function of the DAB converter under four working modes in a dual-phase shift control mode, the derivative of the reflux power function of each working mode is obtained to calculate the optimal reflux power path, and the optimal reflux power path is optimized through the intersection point with the actual optimal path, ensuring the accuracy of the calculated optimal reflux power path. Then, under the condition of a certain transmission power, the phase shift ratio combination with the minimum reflux power is determined according to the optimized calculated optimal reflux power path of each working mode, thereby significantly reducing the reflux power of the DAB converter. Moreover, the DAB converter in this method is controlled by a dual-phase shift control method, and the dual-phase shift control does not require switching control signals in the case of bidirectional energy transmission and has a wider power adjustment range, thus reducing the control difficulty of the system. In addition, by introducing the super-twisting sliding mode control strategy, the dynamic adjustment and optimization of the external-bridge phase shift ratio are realized, further improving the stability and robustness of the system.

[0142] Based on the same inventive concept, an embodiment of the present application also provides a device for optimizing the reflux power of a DAB converter based on super-twisting sliding mode control for implementing the method for optimizing the reflux power of a DAB converter based on super-twisting sliding mode control described above. The implementation solution provided by this device for solving problems is similar to the implementation solution described in the above method. Therefore, the specific limitations in one or more embodiments of the device for optimizing the reflux power of a DAB converter based on super-twisting sliding mode control provided below can refer to the limitations on the method for optimizing the reflux power of a DAB converter based on super-twisting sliding mode control in the above text, and will not be repeated here.

[0143] Embodiment 2

[0144] An embodiment of the present disclosure provides a device 600 for optimizing the reflux power of a DAB converter based on super-twisting sliding mode control, as Figure 6 shown, including:

[0145] The optimal return power path calculation module 601 is configured to divide the operating modes of the DAB converter under the DPS control mode into four types according to the magnitude relationship between the in-bridge phase shift ratio and the out-of-bridge phase shift ratio, and construct the return power function and the transmission power function for the four operating modes; respectively take the derivative of the return power functions of the four operating modes to obtain the calculated optimal return power path for each operating mode;

[0146] The optimal return power path optimization module 602 is configured to calculate the intersection points between the calculated optimal return power paths of each operating mode and the actual optimal return power paths, and optimize the calculated optimal return power paths according to the intersection points to obtain the optimized calculated optimal return power paths for each operating mode;

[0147] The phase shift ratio combination and return power calculation module 603 is configured to obtain, according to the optimized calculated optimal return power paths of each operating mode, the phase shift ratio combination with the minimum return power and the return power corresponding to the phase shift ratio combination with the minimum return power under the condition that the transmission power is constant;

[0148] The out-of-bridge phase shift ratio optimization module 604 is configured to define the input and the sliding mode surface of the super-twisting sliding mode controller; obtain the optimized out-of-bridge phase shift ratio according to the input and the sliding mode surface of the super-twisting sliding mode controller, the in-bridge phase shift ratio in the phase shift ratio combination with the minimum return power, and the return power functions and the transmission power functions under the four operating modes.

[0149] Each module in the above DAB converter return power optimization device based on super-twisting sliding mode control can be implemented in whole or in part by software, hardware, and their combination. The above modules can be embedded in the processor in the computer device in the form of hardware or be independent of the processor, or can be stored in the memory in the computer device in the form of software, so as to facilitate the processor to call and execute the operations corresponding to the above modules.

[0150] Embodiment III

[0151] An embodiment of the present disclosure provides a DAB converter return power optimization system based on super-twisting sliding mode control, as Figure 7 shown. The system includes a return power global optimization module, a super-twisting sliding mode controller, and a PWM controller. Among them, the return power global optimization module is configured to obtain the auxiliary inductor L, the input side voltage u i , the output side voltage u o , the load current i o , and the switching frequency f s , and calculate the voltage transfer ratio k according to the input side voltage u i , the output side voltage u o , and the number of turns n of the primary side of the transformer, and calculate the transmission power P of the DAB converter according to Equation (3) 1, then obtain the phase shift ratio combination with the minimum reflux power corresponding to the voltage transfer ratio and transmission power from Table 1, including the in-bridge phase shift ratio D1 and the out-of-bridge phase shift ratio D2, and send the in-bridge phase shift ratio D1 to the super-twisting sliding mode controller and the PWM controller; the super-twisting sliding mode controller optimizes the out-of-bridge phase shift ratio D2 based on the in-bridge phase shift ratio D1 and Equations (14)-(20), and sends the optimized out-of-bridge phase shift ratio D2 to the PWM controller; the PWM controller controls the power switch devices in the DAB converter according to the in-bridge phase shift ratio D1 and the optimized out-of-bridge phase shift ratio D2.

[0152] Embodiment 4

[0153] Furthermore, in order to demonstrate the effectiveness of the DAB converter reflux power optimization method based on super-twisting sliding mode control of the present application, this embodiment is compared with the traditional current stress optimization method, and experiments are carried out according to three working conditions: light load, medium load, and heavy load.

[0154] When the resistance R of the DAB converter load is 20 Ω, the transmission power P at this time 1 = 0.256 w, and the DAB converter operates under light load conditions. Figure 8 Shows the output side voltage u of the traditional current stress optimization method (DPS-CS) under light load conditions o , the port voltage v of the primary side H-bridge of the transformer H1 , the inductor current i L and the reflux power P of the DAB converter DPS-bf . Figure 9 Shows the DAB converter reflux power optimization method (DPS-BF) without super-twisting sliding mode control of the present application for the output side voltage u under light load conditions o , the port voltage v of the primary side H-bridge of the transformer H1 , the inductor current i L and the reflux power P of the DAB converter DPS-bf . Figure 10 Shows the DAB converter reflux power optimization method (DPS-STSMC-BF) after adding super-twisting sliding mode control of the present application for the output side voltage u under light load conditions o , the port voltage v of the primary side H-bridge of the transformer H1 , the inductor current i L and the reflux power P of the DAB converter DPS-bf . From Figures 8 - 10It can be seen that the current stress of DPS-CS is 6.4 A, the reflux power is 110 W, the current stress of DPS-BF is 7.6 A, the reflux power is 50 W, and the current stress of DPS-STSMC-BF is 7.6 A, and the reflux power is 40 W. The current stress of DPS-BF and DPS-STSMC-BF increases by 1.2 A compared with DPS-CS, and the reflux power decreases by 60 W and 70 W respectively.

[0155] When the resistance R of the DAB converter load is 10 Ω, the transmission power P at this time 1 = 0.512 w, and the DAB converter operates under medium load conditions. Figure 11 Shows the output side voltage u of the traditional current stress optimization method (DPS-CS) under medium load conditions o , the port voltage v of the H-bridge on the primary side of the transformer H1 , the inductor current i L and the reflux power P of the DAB converter DPS-bf . Figure 12 Shows the reflux power optimization method (DPS-BF) of the DAB converter without adding super-twisting sliding mode control in this application under medium load conditions for the output side voltage u o , the port voltage v of the H-bridge on the primary side of the transformer H1 , the inductor current i L and the reflux power P of the DAB converter DPS-bf . Figure 13 Shows the reflux power optimization method (DPS-STSMC-BF) of the DAB converter after adding super-twisting sliding mode control in this application under medium load conditions for the output side voltage u o , the port voltage v of the H-bridge on the primary side of the transformer H1 , the inductor current i L and the reflux power P of the DAB converter DPS-bf . From Figures 11 - 13 It can be seen that the current stress of DPS-CS is 8.0 A, the reflux power is 180 W, the current stress of DPS-BF is 9.8 A, the reflux power is 75 W, and the current stress of DPS-STSMC-BF is 9.9 A, and the reflux power is 75 W. The current stress of the latter two increases by 1.8 A and 1.9 A compared with DPS-CS, and the reflux power decreases by 105 W.

[0156] When the resistance R of the DAB converter load is 7.3 Ω, the transmission power P at this time 1 = 0.7 w, and the DAB converter operates under heavy load conditions. Figure 14 Shows the output side voltage u of the traditional current stress optimization method (DPS-CS) under heavy load conditions o , the port voltage v of the H-bridge on the primary side of the transformer H1 , the inductor current iL and the reflux power P of the DAB converter DPS-bf . Figure 15 Shows the output side voltage u of the DAB converter reflux power optimization method (DPS-BF) without super-twisting sliding mode control in this application under heavy load conditions o , the port voltage v of the primary side H-bridge of the transformer H1 , the inductor current i L and the reflux power P of the DAB converter DPS-bf . Figure 16 Shows the output side voltage u of the DAB converter reflux power optimization method (DPS-STSMC-BF) after adding super-twisting sliding mode control in this application under heavy load conditions o , the port voltage v of the primary side H-bridge of the transformer H1 , the inductor current i L and the reflux power P of the DAB converter DPS-bf . From Figures 14 - 16 It can be seen that the current stress of DPS-CS is 9.5A and the reflux power is 200W; the current stress of DPS-BF is 9.9A and the reflux power is 180W; the current stress of DPS-STSMC-BF is 9.9A and the reflux power is 170W. The current stress of DPS-BF and DPS-STSMC-BF increases by 0.4A compared with DPS-CS, and the reflux power decreases by 20W and 30W respectively.

[0157] From the above experimental results, it can be seen that the DAB converter reflux power optimization method based on super-twisting sliding mode control proposed in this application can effectively optimize the reflux power under light load, medium load or heavy load conditions of the DAB converter, and its optimization effect is remarkable.

[0158] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0159] The above embodiments only represent several implementation manners of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of this application, several deformations and improvements can still be made, and these all belong to the protection scope of this application. Therefore, the protection scope of this application patent should be subject to the appended claims.

Claims

1. A DAB converter reflux power optimization method based on super-helical sliding mode control, characterized in that: The method comprises: Step S1, dividing the working modes of the DAB converter under the dual phase shift control mode into four types according to the size relationship between the inner bridge shift phase and the outer bridge shift phase, and constructing the return power function and the transmission power function of the four working modes; Step S2, respectively deriving the return power functions of the four working modes to obtain the calculated optimal return power path of each working mode; Step S3, calculating the intersection point between the calculated optimal return power path and the actual optimal return power path of each working mode, and optimizing the calculated optimal return power path according to the intersection point to obtain the calculated optimal return power path after optimization of each working mode; Step S4, obtaining a shift ratio combination with the minimum return power under a certain transmission power condition according to the calculated optimal return power path after optimization of each working mode; the return power corresponding to the shift ratio combination with the minimum return power and the shift ratio combination with the minimum return power include: When 0≤P1<0.5, the shift ratio combination is The reflux power is 0.25(k-1) 2 P1k -1 ; when When the shift ratio is The return power is when When the shift ratio is The return power is Wherein, P1 is the transmission power of the DAB converter, k is the voltage transmission ratio, D1 is the bridge inward shift ratio, and D2 is the bridge outward shift ratio; Step S5, defining the input and sliding surface of the super-helical sliding mode controller; Step S6, obtaining an optimized bridge outer shift ratio according to the input and sliding surface of the superhelical sliding mode controller, the bridge inner shift ratio in the shift ratio combination with the minimum return power, and the return power function and the transmission power function in the four working modes; the expression of the optimized bridge outer shift ratio is: Wherein, D1 is the bridge inner shift phase ratio in the shift phase ratio combination with the minimum reflux power in the step S4, D2 is the optimized bridge outer shift phase ratio, and p is the input of the super-helical sliding mode controller.

2. The DAB converter reflux power optimization method based on super spiral sliding mode control according to claim 1 is characterized in that: The magnitude relationships between the bridge inward displacement D1 and the bridge outward displacement D2 in the four working modes are as follows: Mode a, 0<D1, D2<1, D1<D2, D1+D2≥1; Mode b, 0<D1, D2<1, D1<D2, D1+D2<1; Mode c, 0<D1, D2<1, D1≥D2, D1+D2<1; Mode d, 0<D1, D2<1, D1≥D2, D1+D2≥1.

3. The DAB converter reflux power optimization method based on super spiral sliding mode control according to claim 2 is characterized in that: For the four working modes of the DAB converter, the return power function and the transmission power function are constructed according to the following steps: Step S11, obtaining the inductor current value of the DAB converter in one cycle; Step S12, obtaining the return power and the transmission power according to the inductor current value and the port voltage of the H-bridge on the primary side of the transformer; Step S13: normalizing the return power and the transmission power by taking the maximum value of the transmission power as a reference value for power normalization.

4. The DAB converter reflux power optimization method based on super spiral sliding mode control according to claim 3 is characterized in that: The expressions of the return power function and transmission power function of the four working modes after normalization are: Where P 1a represents the transmission power of mode a, P DPS-bf-a represents the return power of mode a, P 1b represents the transmission power of mode b, P DPS-bf-b represents the return power of mode b, P 1c represents the transmission power of mode c, P DPS-bf-c represents the return power of mode c, P 1d represents the transmission power of mode d, P DPS-bf-d represents the return power of mode d, and k represents the voltage transfer ratio.

5. The DAB converter reflux power optimization method based on super spiral sliding mode control according to claim 4 is characterized in that: When the DAB converter operates in mode b, the expression of the inductor current value of the DAB converter in one cycle is: In the formula, i L is the inductor current, t0=0, t1=D1T hs , t2=D2T hs , t3=(D1+D2)T hs , T hs is the half switching period of the DAB converter, f s is the switching frequency, f s =1 / (2T hs ), L is the sum of the leakage inductance and auxiliary inductance of the transformer, n is the number of turns on the primary side of the transformer, u0 is the output side voltage, and k is the voltage transfer ratio; The expressions of the return power function and transmission power function of mode b after normalization are: Where P 1b represents the transmission power of mode b, P DPS-bf-b Indicates the return power in mode b.

6. The DAB converter reflux power optimization method based on super spiral sliding mode control according to claim 5, characterized in that: The step S2 comprises: Step S21, deriving the return power function of mode b after normalization; the expression of the derivative result is: Step S22, setting the value of the derived return power function to 0, and obtaining the optimal return power path for mode b; the expression for calculating the optimal return power path for mode b is: The step S3 comprises: Step S31, let D1=D2, and obtain the intersection point between the calculated optimal return power path and the actual optimal return power path of the mode b; the expression of the intersection point is: Wherein, P'1 represents the transmission power of the junction point, D'2 represents the bridge outward displacement ratio of the junction point; Step S32, optimizing the calculated optimal return power path obtained in step S22 according to the intersection point, and obtaining the calculated optimal return power path after optimization of mode b; wherein, when When , the optimal return power path after optimization of mode b is: Wherein, P1 represents the transmission power of the DAB converter.

7. The DAB converter reflux power optimization method based on super spiral sliding mode control according to claim 2, characterized in that: The input and sliding surface expressions of the super-helical sliding mode controller are: Where p represents the input of the super-helical sliding mode controller, L is the sum of the leakage inductance and auxiliary inductance of the transformer, and f s is the switching frequency, C o is the transformer output side support capacitor, n is the number of turns on the primary side of the transformer, u i is the voltage at the input side of the transformer, i o is the load current, k1 and k2 are both positive coefficients, sgn is the sign function, α and β are both positive parameters, e is the output voltage error, s is the sliding surface, represents the derivative of the sliding surface; The expression of the sliding surface is: s = k1e + k2∫ (e) dt, and the expression of the output voltage error is: e = u o -u ref ,u o is the voltage at the output side of the transformer, u ref is the reference voltage.

8. A DAB converter reflux power optimization device based on super spiral sliding mode control, characterized in that: The device comprises: The optimal return power path calculation module is used to divide the working modes of the DAB converter under the DPS control mode into four types according to the size relationship between the bridge inward shift ratio and the bridge outward shift ratio, and construct the return power function and transmission power function of the four working modes; respectively derive the return power function of the four working modes to obtain the calculated optimal return power path of each working mode; An optimal return power path optimization module is used to calculate the intersection point between the calculated optimal return power path and the actual optimal return power path of each working mode, and optimize the calculated optimal return power path according to the intersection point to obtain the calculated optimal return power path after optimization of each working mode; The shift ratio combination and return power calculation module is used to obtain the shift ratio combination with the minimum return power and the return power corresponding to the shift ratio combination with the minimum return power under the condition of a certain transmission power according to the calculated optimal return power path after optimization of each working mode; the shift ratio combination with the minimum return power and the return power corresponding to the shift ratio combination with the minimum return power include: When 0≤P1<0.5, the shift ratio combination is The reflux power is 0.25(k-1) 2 P1k -1 ; when When the shift ratio is The return power is when When the shift ratio is The return power is Wherein, P1 is the transmission power of the DAB converter, k is the voltage transmission ratio, D1 is the bridge inward shift ratio, and D2 is the bridge outward shift ratio; The bridge outer shift ratio optimization module is used to define the input and sliding surface of the super spiral sliding mode controller; the optimized bridge outer shift ratio is obtained according to the input and sliding surface of the super spiral sliding mode controller, the bridge inner shift ratio in the shift ratio combination with the minimum return power, and the return power function and the transmission power function in the four working modes; the expression of the optimized bridge outer shift ratio is: Wherein, D1 is the bridge inner shift phase ratio in the shift phase ratio combination with the minimum reflux power in the step S4, D2 is the optimized bridge outer shift phase ratio, and p is the input of the super-helical sliding mode controller.

Images