DAB converter control method based on double-integral sliding mode and current stress optimization

Abstract

The invention relates to a DAB converter control method based on a double-integral sliding mode and current stress optimization. The method comprises the following steps: establishing a DAB converter system order reduction model; designing a double-integral sliding mode controller; calculating a voltage transmission ratio, and dividing a power interval; judging a power interval, and selecting a control mode and an optimal bridge internal and external shift comparison combination; and control signal generation.

Description

Technical Field

[0001] The present invention relates to the field of power electronic converter control technology, specifically a dual-active bridge (DAB) DC-DC converter control method based on dual-integral sliding mode and current stress optimization. This method is suitable for DAB converter systems that require high power transmission efficiency and dynamic response performance. This method can be widely used in various fields, including renewable energy power generation, energy storage systems, electric vehicles, and microgrids. Background Art

[0002] As an important interface between new energy power generation units, energy storage systems, and DC buses, bidirectional DC-DC converters are widely used in a variety of fields, including renewable energy systems, electric vehicles, solid-state transformers, and DC microgrids. Among various DC-DC converter topologies, the DAB converter is widely considered to be an ideal bidirectional conversion topology for medium and high power scenarios due to its advantages such as zero-voltage switching capability, bidirectional energy flow, high power density, electrical isolation, and a wide voltage conversion gain range. Compared with traditional unidirectional DC-DC converters, the DAB converter can complete power transmission tasks with fewer power devices. In addition, the symmetrical full-bridge structure of the DAB converter facilitates modular implementation, providing a foundation for its circuit design and control method implementation.

[0003] Despite the numerous advantages of the DAB converter topology, its engineering applications still face several key technical challenges. First, the traditional single-phase shift (SPS) control has limited regulation capabilities and is unable to adapt to non-ideal operating conditions such as sudden input voltage changes and load variations. This is particularly true at light loads or when operating off-rated, where current stress can significantly increase, reducing system efficiency and increasing component design redundancy. Furthermore, current stress, a key factor affecting DAB converter conduction losses and component reliability, is not adequately considered in most control methods. Excessive current stress not only increases switching device conduction losses but can also lead to saturation of the energy storage inductor core, severely impacting system stability. Furthermore, while traditional PI-based control methods offer a simple structure and ease of implementation, they suffer from poor dynamic response speed and parameter adaptability, and their performance is highly dependent on the system operating point, limiting their applicability. In recent years, sliding mode control, a nonlinear variable structure control method, has been widely used in power electronics control due to its robustness and fast response. Compared to PI control, sliding mode control is more adaptable to non-ideal operating conditions such as sudden input voltage changes and load variations, and offers superior dynamic performance. However, the standard sliding mode control method still has problems such as obvious chattering and complex parameter adjustment, which need to be optimized and solved.

[0004] In summary, there is an urgent need to design a DAB converter control method with stronger anti-interference capability, better dynamic performance and smaller current stress, so as to improve system efficiency and operational reliability with stable output and fast response under non-ideal working conditions. Summary of the Invention

[0005] This invention addresses the shortcomings of existing DAB converter control methods in terms of current stress optimization and dynamic regulation capabilities. It proposes a DAB converter control method based on dual-integral sliding mode and current stress optimization. This method improves the system's dynamic response speed and interference rejection by designing dual-integral sliding mode control. Combined with current stress optimization, it effectively reduces switching device losses, thereby ensuring stable output, enhancing dynamic performance, and improving system transmission efficiency. It is suitable for bidirectional energy transmission scenarios under various complex loads and dynamic operating conditions. The technical solution is as follows:

[0006] A DAB converter control method based on dual-integral sliding mode and current stress optimization includes the following steps:

[0007] S1: Establish a reduced-order model of the DAB converter system;

[0008] S2: Design a dual-integral sliding mode controller based on a reduced-order model, including constructing a dual-integral sliding mode surface; design a reaching law and equivalent control input: use a hyperbolic tangent function instead of a sign function to ensure rapid convergence of the system state along the sliding mode surface and effectively suppress system chattering. Use an equivalent control method to derive a control law for closed-loop voltage regulation within the sliding mode surface; and verify stability.

[0009] S3: Calculate the voltage transfer ratio and divide the power range

[0010] According to the primary input voltage U1, the output reference voltage U 2ref Calculate the voltage transfer ratio k in steady state with the transformer ratio n = U1 / nU 2ref , the voltage transfer ratio k is used to divide the entire power transfer range [0,1] into three non-overlapping sub-intervals. Different sub-intervals correspond to different control modes and current stress optimization strategies. The three sub-intervals are specifically:

[0011] First power range:

[0012] Second power range:

[0013] The third power range:

[0014] S4: Determine the power range, select the control mode and the optimal bridge inward and outward shift combination

[0015] The dual-integral sliding mode controller is used as the front-stage controller to detect the output voltage tracking error of the DAB converter. The control law is constructed based on the set sliding mode surface and the system control input p is generated. u , which is numerically equal to the predicted per-unit value of the transmission power p at this time. The power interval to which this time belongs can be determined according to the value of p;

[0016] Let D1 be the ratio of the newly added phase shift angle in the primary full bridge to π, called the bridge internal phase shift ratio, and D2 be the ratio of the phase shift angle between the primary and secondary bridges to π, called the bridge external phase shift ratio; they are the bridge internal phase shift ratio and bridge external phase shift ratio when the minimum current stress is achieved, respectively;

[0017] If it is judged that p falls within the first power range, the DAB converter enters the EPS-I control mode, and the optimal bridge internal and external shift ratio combination is taken as

[0018]

[0019] If it is judged that p falls within the second power range, the DAB converter enters EPS-II control mode, and the optimal bridge internal and external shift ratio combination is taken as

[0020]

[0021] If it is judged that p falls within the second power range, the DAB converter enters EPS-II control mode, and the optimal bridge internal and external shift ratio combination is taken as

[0022]

[0023] If it is judged that p falls within the third power range, it still enters the EPS-II control mode and determines the optimal bridge inward and outward shift ratio combination as follows:

[0024]

[0025] S5: Control signal generation

[0026] The final optimal bridge internal and external shift phase combination is used as input and transmitted to the PWM modulation module to generate the driving signal of the original secondary bridge arm to realize the control of the DAB converter.

[0027] Furthermore, in S1, the average value modeling is used to establish the mathematical model of the DAB converter, considering the inductor current i L It is a pure AC component, and its average value within a switching cycle is 0, resulting in a reduced-order model of the DAB converter system:

[0028]

[0029] Where: U2 is the output voltage of the secondary full-bridge of the DAB converter, R is the output side load, C2 is the filter capacitor of the secondary full-bridge, n is the ratio of the high-frequency transformer T, p is the u It is the system control input, which is equal to the per-unit transmission power value p.

[0030] Furthermore, in S2, the method for constructing the double integral sliding surface is:

[0031] Define the DAB converter system output voltage u2 and reference voltage u ref The difference is the error signal e v , construct the double integral sliding surface, and design the state variable x and sliding surface s as follows:

[0032]

[0033] Where: α i represents the i-th sliding mode gain.

[0034] Furthermore, in the design of the reaching law of S2 and the equivalent control input, the equivalent control method is used to derive the control u for realizing voltage closed-loop regulation within the sliding mode surface:

[0035]

[0036] Where: I2 is the output current of the DAB converter secondary full-bridge side, η is the positive gain in the reaching law, and μ is the thickness of the fixed boundary layer of the chattering.

[0037] Furthermore, the stability verification in S2 includes: in order to verify that the state trajectory can remain near the desired sliding surface, Lyapunov's second method is used to define the Lyapunov function as follows:

[0038]

[0039] Furthermore, in S4, if it is determined that p falls within the first power range, the DAB converter enters the EPS-I control mode, and the method for obtaining the optimal bridge inward and outward shift ratio combination is:

[0040] The inductor current expression at each switching moment in EPS-I mode is:

[0041]

[0042] Where: t0-t6 are the moments when the DAB converter switches its working state, f s is the operating frequency of the DAB converter;

[0043] The transmission power model after per-unit processing in EPS-I control mode is:

[0044]

[0045] In EPS-I control mode, the current stress per unit value i is obtained by simplifying and eliminating D2. max for

[0046] i max =2[k(1-D1)+2D2-1] (40)

[0047] According to the transmission power model, D2 is expressed as a function of p and D1.

[0048]

[0049] Substitute back to the per-unit value of current stress i max Simplifying and eliminating D2, the objective function is:

[0050]

[0051] Take the per-unit value of current stress i max Derivative, find the maximum value to get the optimal bridge displacement compared to D 1min , substitute back into the function about D2 to obtain the optimal bridge outward shift compared to D 2min , and obtain the optimal bridge inward and outward displacement comparison combination.

[0052] Furthermore, in EPS-I control mode, after simplifying and eliminating D2, the per-unit current stress value i is obtained. max The method is:

[0053] Write the per-unit value of current stress

[0054] i max =2[k(1-D1)+2D2-1] (43)

[0055] According to the transmission power model, D2 is expressed as a function of p and D1.

[0056]

[0057] Substitute back to the per-unit value of current stress i max Simplifying and eliminating D2, the objective function is:

[0058]

[0059] Furthermore, in S4, if it is determined that p falls within the second power range, the DAB converter enters the EPS-II control mode, and the method for obtaining the optimal bridge inner and outer shift ratio combination is:

[0060] The inductor current expression at each switching moment in EPS-II control mode is:

[0061]

[0062] The transmission power model after per-unit processing in EPS-II control mode is:

[0063]

[0064] p falls within the second power range, and the per-unit current stress value i in EPS-II control mode max for

[0065] i max =2[k(1-D1)+2D2-1] (48)

[0066] According to the transmission power model, D2 is expressed as a function of p and D1.

[0067]

[0068] Substituting formula (13) back into formula (12) yields the per-unit current stress value i max , for the per-unit value of current stress i max Take the derivative to find the maximum value and get the optimal combination of bridge inward and outward displacement.

[0069] Furthermore, in S4, if it is determined that p falls within the third power range, the EPS-II control mode is still entered, and the method for determining the optimal bridge inward and outward shift ratio combination is:

[0070] Current stress per unit value i max for

[0071] i max =2[kD1+1-k] (50)

[0072] At this time, the magnitude of the current stress is only related to D1. After p is given, D1 reaches its maximum value on the section D2 = kD1-k+1, thereby determining the optimal bridge inward and outward displacement ratio combination.

[0073] Compared with the existing control method, the present invention has the following beneficial effects:

[0074] (1) This control method introduces minimum current stress optimization, which can effectively reduce the peak current in the converter and the conduction loss of the switching devices, thereby improving the system energy transmission efficiency.

[0075] (2) This control method can reduce the rated current and withstand voltage requirements of switching devices by optimizing current stress, thereby reducing hardware costs and improving the overall economy of the system.

[0076] (3) This control method adopts a dual-integral sliding mode controller, which has stronger anti-interference ability and faster dynamic response speed. It can effectively suppress output voltage fluctuations under disturbance conditions such as load mutation and input voltage fluctuation, ensuring stable operation of the system.

[0077] (4) This control method can almost completely eliminate the steady-state error of the output voltage, ensuring the output voltage accuracy, and is suitable for application scenarios with high requirements for output stability.

[0078] (5) This control method can achieve the dynamic response characteristics of the system with no overshoot and fast convergence, and improve the control performance and operating stability of the DAB converter under various complex working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Figure 1 is a flow chart of the control method of the present invention;

[0080] Figure 2 This is the topological diagram of the DAB converter;

[0081] Figure 3 This is the operating waveform of the DAB converter in EPS-I mode;

[0082] Figure 4 This is the operating waveform of the DAB converter in EPS-II mode;

[0083] Figure 5 This is the division diagram of the theoretical current stress value area under EPS-II mode;

[0084] Figure 6 This is the actual current stress value area division diagram under EPS-II mode;

[0085] Figure 7 It is a three-dimensional graph of the D1 constraint domain and the objective function;

[0086] Figure 8 It is the output voltage waveform of the startup process;

[0087] Figure 9 It is the energy storage inductor current waveform;

[0088] Figure 10 It is the output voltage waveform when the input voltage changes suddenly;

[0089] Figure 11 It is the output voltage waveform when the load changes step;

[0090] Figure 12 This is the output voltage waveform when the reference voltage changes suddenly (60V→70V→60V); DETAILED DESCRIPTION

[0091] The following will further elaborate on the specific implementation of the DAB converter control method based on double integral sliding mode and current stress optimization in conjunction with the accompanying drawings.

[0092] The overall control flow of the control method of the present invention is as shown in the attached Figure 1 figure, and the attached Figure 2 is the topology structure diagram of the DAB converter applicable to the control method of the present invention. Among them, U1 is the DC input voltage of the primary full-bridge of the DAB converter, U2 is the DC output voltage of the secondary full-bridge, R is the load on the output side, I2 is the output current, C1 - C2 are the filter capacitors on the primary and secondary full-bridge sides respectively, Q1 - Q8 are the drive signals of each switching device, V1 - V8 are the freewheeling diodes reversely connected in parallel on both sides of the switching device, L is the energy storage inductor connected in series on the primary full-bridge side, i L is the current of the energy storage inductor, U L is the voltage of the energy storage inductor, the voltage ratio of the high-frequency transformer T is n, U ab is the output voltage on the primary full-bridge side, and U cd is the input voltage on the secondary full-bridge side.

[0093] The present invention uses EPS control to drive the primary and secondary full-bridges. Compared with SPS control, EPS control adds an internal phase-shift angle in the primary full-bridge side, and the introduction of the new degree of freedom increases the flexibility of the control method. Define D1 as the ratio of the newly added internal phase-shift angle in the primary full-bridge to π, which is called the internal phase-shift ratio of the bridge, and D2 as the ratio of the phase-shift angle between the primary and secondary bridges to π, which is called the external phase-shift ratio of the bridge.

[0094] When 0 ≤ D1 ≤ D2 ≤ 1, the system is in the EPS-I mode; when 0 ≤ D2 < D1 ≤ 1, the system is in the EPS-II mode. The attached Figure 3 and the attached Figure 4 are the working waveform diagrams of the DAB converter in the EPS-I mode and the EPS-II mode. The abscissa is time t, and T hs is half of the working period of the DAB converter. Define t0 - t6 as the respective moments when the system working state switches. Considering that the waveform of the energy storage inductor current in the attached Figure 3 has half-cycle positive and negative symmetry, the expression of the inductor current at each switching moment in the EPS-I mode is obtained as

[0095]

[0096] In the formula: f s is the working frequency of the DAB converter, and k = U1 / nU2 is the voltage transfer ratio.

[0097] Similarly, according to the attached Figure 4 the inductor current at each switching moment in the EPS-II mode is obtained as

[0098]

[0099] The formula for calculating average power is:

[0100]

[0101] Where: p a is the system average transmission power.

[0102] In order to analyze the current stress optimization problem of DAB converter, the maximum transmission power under SPS control (at this time D1 = 0) is taken as the power reference value p N :

[0103]

[0104] The input current corresponding to this time is the current reference value i N :

[0105]

[0106] Based on the inductor current expressions at each moment in the two EPS control modes, the expression of the transmission power per unit value p of the corresponding mode DAB converter is obtained as follows:

[0107]

[0108] When the DAB converter operates in EPS-I mode, the per-unit current stress value i max for

[0109] i max =|i L (t0)|=2[k(1-D1)+2D2-1] (8)

[0110] When the DAB converter operates in EPS-II mode, the current stress situation is more complicated. According to the different ranges of the bridge internal and external shift ratio combinations, the absolute values ​​of the inductor current at the three turning moments may be current stress. In order to accurately optimize the current stress, the sequential comparison method is used to obtain the range of the bridge internal and external shift ratio combinations corresponding to different current stress values ​​in EPS-II mode.

[0111]

[0112] Attachment Figure 5 This is the division diagram of the theoretical current stress value area under the EPS-II mode.

[0113] Taking the given per-unit value of the transmission power in EPS-II mode as p=0, it can be seen that the spatial relationship curve between p and the inward and outward movement of the bridge at this time is projected on the plane boundary as D1=2D2. Therefore, when the EPS-II mode is in the forward power transmission direction, that is, p≥0, the constraint condition D1≤2D2 must be satisfied, and the current stress value excludes |i L (t2)|, attached Figure 6 The actual current stress value area division diagram under EPS-II mode, the current stress per unit value i under EPS-II mode max There are only two possible situations:

[0114]

[0115] The current stress optimization strategy is designed below. In EPS-I mode, according to the normalized transmission power model, D2 is expressed as a function of p and D1:

[0116]

[0117] Substitute back to the per-unit current stress value i in EPS-I mode max Simplify the expression and eliminate D2 to get

[0118]

[0119] The above formula is the objective function. By taking the derivative of the above formula and finding the maximum value, we can get the optimal bridge displacement D. 1min , substitute back into the function about D2 to obtain the optimal bridge outward shift compared to D 2min , the optimal bridge inward and outward displacement combination is

[0120]

[0121] Considering the inequality constraint of EPS-I mode: 0≤D1≤D2≤1, the optimal bridge internal and external shift ratio combination is substituted into the simplified equation to obtain the transmission power per unit value p applicable to the shift ratio combination. The value range is:

[0122]

[0123] In EPS-II mode, the current stress in region 1 is |i L (t0)|, according to the normalized transmission power model, D2 is expressed as a function of p and D1:

[0124]

[0125] Substitute into the per-unit current stress value i in EPS-II mode max Simplify the expression and eliminate D2, take this as the objective function and take the derivative to find the maximum value, and get the optimal bridge displacement D1min , substitute back into the functional equation for D2 in the same steps to obtain the optimal outer shift of the bridge compared to D 2min , at this time, the optimal inner and outer shift ratio combination of the bridge is

[0126]

[0127] Considering the inequality constraint conditions at this time: 0 ≤ D2 ≤ D1 ≤ 1 and kD1 - k + 1 < D2, substitute the optimal inner and outer shift ratio combination of the bridge and simplify to obtain the range of the per-unit value p of the transmission power applicable to this shift ratio combination as

[0128]

[0129] In the EPS-II mode region 2, that is, when the current stress value is |i L (t1)|, the magnitude of the current stress is only related to D1. To minimize the current stress, it should be based on satisfying the inequality constraint condition: kD1 - k + 1 > D2 and the equality constraint condition: the transmission power model equation (7). Select the smallest D1. According to the above constraint conditions, first obtain the range of the per-unit value p of the transmission power at this time as

[0130]

[0131] Appendix Figure 7 is a three-dimensional graph for the D1 constraint domain and the objective function. From the appendix Figure 7 it is known that after p is given, when D1 is on the section D2 = kD1 - k + 1, the smallest D1 value can be obtained, and then the smallest current stress can be obtained. Combining with D2 expressed as a function form of p and D1, the optimal inner and outer shift ratio combination of the bridge at this time is

[0132]

[0133] Next, model the DAB converter system.

[0134] Modeling is the representation of physical phenomena by mathematical means. The modeling process takes the EPS-I mode as an example. In the EPS-I mode, the DAB converter system has a total of 6 working states, and the working states of the system change periodically. According to Kirchhoff's law, establish a differential equation system for each working state:

[0135]

[0136]

[0137] Each differential equation group only represents the voltage-current relationship in this working state. Therefore, average value modeling can be used to establish a differential equation that can describe the dynamic characteristics of the DAB converter during the entire switching cycle. Note that in the DAB converter system, the energy storage inductor current i L It is a pure AC component, and its change speed is much faster than the secondary full-bridge output voltage U2, and its average value in one switching cycle is 0, so for i L It does not make sense to model the mean value of .

[0138] Considering that the primary control target of the DAB converter is the stability of the secondary full-bridge output voltage U2, we ignore i L , the reduced-order model of the system is established as

[0139]

[0140] Where: p u (D1, D2) is the system control input, which is numerically equal to the per-unit transmission power value p.

[0141] Based on the above DAB converter reduced-order model, the specific steps for designing a dual-integral sliding mode controller are as follows:

[0142] A single-input single-output nonlinear system without disturbance can be expressed as:

[0143]

[0144] Where: x is the system state variable, f(x) and g(x) are nonlinear functions, u a Input to the controller.

[0145] The design goal of sliding mode control is to ensure that the system state reaches the sliding surface and enters the sliding mode phase within a finite time. Introducing the integral term of the sliding mode state variable into the sliding surface design can further suppress steady-state error. This method is called integral sliding mode control. While single-integral sliding mode can effectively reduce steady-state error, it cannot completely eliminate steady-state deviation. Steady-state accuracy can be improved by increasing the order of the system controller. Based on this, the present invention adopts a dual-integral sliding mode control method.

[0146] Define the difference between the system output voltage and the reference voltage as the error signal e v , design the double integral sliding surface, integrate the system steady-state error and dynamic performance requirements, and finally design the state variable x and sliding surface s respectively

[0147]

[0148] s=α1x1+α2x2+α3x3 (29)

[0149] Where: e v=U2-U ref is the output voltage tracking error, α i represents the i-th sliding mode positive gain.

[0150] Traditional sliding mode control uses the sign function sgn(s) to design a reaching law to maintain the state variable near the sliding surface. However, the sign function has discontinuities, which can cause chattering. Consider replacing the sign function with the hyperbolic tangent function to ensure rapid convergence of the system state along the sliding surface and effectively suppress system chattering. Based on the sliding mode control principle, combining the system state equation and the sliding surface dynamic equation, an equivalent control method is used to derive the control law u for achieving closed-loop voltage regulation within the sliding surface:

[0151]

[0152] Where: η is the positive gain in the reaching law, and μ is the thickness of the fixed boundary layer of the buffeting.

[0153] In order to verify that the state trajectory can remain near the desired sliding surface during this period, the Lyapunov function V is defined:

[0154]

[0155] Using Lyapunov's second method, it is easy to know that the Lyapunov function is positive definite and its derivative is negative definite at this time, which can verify that the system is asymptotically stable under double-integral sliding mode control.

[0156] A two-stage cooperative control structure is constructed, and a dual-integral sliding mode controller is used as the front-stage controller to detect the output voltage tracking error of the DAB converter in real time. The control law is constructed based on the set sliding mode surface and the system control input p is generated. u (Its value is equal to the predicted per-unit value of the transmission power p at this time), which is used to achieve fast dynamic response and stable adjustment of the system to the output performance.

[0157] The current stress optimization controller is used as the post-stage controller. The entire power transmission range [0,1] is divided into three non-overlapping power ranges according to the calculated input voltage transfer ratio k. The power range segment is then determined by the front-stage input p. In the current stress optimization strategy, each power range corresponds to a set of optimal bridge internal and external shift ratio combinations. 1min and D 2min When the signal is sent to the PWM modulation module, the optimal control of the DAB converter can be achieved by the two-stage coordinated control method as required.

[0158] Next, we build a simulation model to verify the DAB converter control method based on dual-integral sliding mode and current stress coordinated optimization. The system reference output voltage is 60V. The simulation verification mainly includes the following contents:

[0159] Verify the system's response time and voltage overshoot during startup; evaluate the current stress in steady state; test the system's voltage regulation capability by introducing a sudden change in input voltage in steady state; observe the system's dynamic response when the load undergoes a step change; and evaluate the tracking performance of the control method by introducing a sudden change in reference voltage.

[0160] The above control performance was compared and analyzed using the two-stage collaborative optimization control method of the present invention and the PI control method. The comparison results verify the advantages of the control method of the present invention in terms of dynamic response performance, voltage stability, current stress suppression, etc., and prove the effectiveness and practicality of the control method of the present invention.

Claims

1. A DAB converter control method based on dual-integral sliding mode and current stress optimization, comprising the following steps: S1: Establish a reduced-order model of the DAB converter system; S2: Design a dual-integral sliding mode controller based on the reduced-order model, including constructing a dual-integral sliding mode surface. Design reaching laws and equivalent control inputs. Use a hyperbolic tangent function instead of a sign function to ensure rapid convergence of the system state along the sliding mode surface and effectively suppress system chattering. Use an equivalent control method to derive a control law for closed-loop voltage regulation within the sliding mode surface. Stability verification; S3: Calculate the voltage transfer ratio and divide the power range The voltage transfer ratio k is used to divide the entire power transfer range [0,1] into three non-overlapping sub-intervals. Different sub-intervals correspond to different control modes and current stress optimization strategies. The three sub-intervals are as follows: First power range: Second power range: The third power range: S4: Determine the power range, select the control mode and the optimal bridge inward and outward shift combination The dual-integral sliding mode controller is used as the front-stage controller to detect the output voltage tracking error of the DAB converter. The control law is constructed based on the set sliding mode surface and the system control input p is generated. u , which is numerically equal to the predicted per-unit value of the transmission power p at this time. The power interval to which this time belongs can be determined according to the value of p; Let D1 be the ratio of the newly added phase shift angle in the primary full bridge to π, called the bridge internal phase shift ratio, and D2 be the ratio of the phase shift angle between the primary and secondary bridges to π, called the bridge external phase shift ratio; they are the bridge internal phase shift ratio and bridge external phase shift ratio when the minimum current stress is achieved, respectively; If it is judged that p falls within the first power range, the DAB converter enters the EPS-I control mode, and the optimal bridge internal and external shift ratio combination is taken as If it is judged that p falls within the second power range, the DAB converter enters EPS-II control mode, and the optimal bridge internal and external shift ratio combination is taken as If it is judged that p falls within the second power range, the DAB converter enters EPS-II control mode, and the optimal bridge internal and external shift ratio combination is taken as If it is judged that p falls within the third power range, it still enters the EPS-II control mode and determines the optimal bridge inward and outward shift ratio combination as follows: S5: Control signal generation The final optimal bridge internal and external shift phase combination is used as input and transmitted to the PWM modulation module to generate the driving signal of the original secondary bridge arm to realize the control of the DAB converter.

2. The DAB converter control method based on dual-integral sliding mode and current stress optimization according to claim 1, characterized in that: In S1, the average value modeling is used to establish the mathematical model of the DAB converter, considering the inductor current i L It is a pure AC component, and its average value within a switching cycle is 0, resulting in a reduced-order model of the DAB converter system: Where: U2 is the output voltage of the secondary full-bridge of the DAB converter, R is the output side load, C2 is the filter capacitor of the secondary full-bridge, n is the ratio of the high-frequency transformer T, p is the u It is the system control input, which is equal to the per-unit transmission power value p.

3. The DAB converter control method based on dual-integral sliding mode and current stress optimization according to claim 1, characterized in that: In S2, the method for constructing the double integral sliding surface is: Define the DAB converter system output voltage u2 and reference voltage u ref The difference is the error signal e v , construct the double integral sliding surface, and design the state variable x and sliding surface s as follows: s=α1x1+α2x2+α3x3 (10) Where: α i represents the i-th sliding mode gain.

4. The DAB converter control method based on dual-integral sliding mode and current stress optimization according to claim 2, characterized in that: In the design of the reaching law of S2 and the equivalent control input, the equivalent control method is used to derive the control u for realizing voltage closed-loop regulation within the sliding surface: Where: I2 is the output current of the DAB converter secondary full-bridge side, η is the positive gain in the reaching law, and μ is the thickness of the fixed boundary layer of the chattering.

5. The DAB converter control method based on dual-integral sliding mode and current stress optimization according to claim 2, characterized in that: The stability verification in S2 includes: in order to verify that the state trajectory can remain near the desired sliding surface, Lyapunov's second method is used to define the Lyapunov function as follows:

6. The DAB converter control method based on dual-integral sliding mode and current stress optimization according to claim 1, characterized in that: In S3, the reference voltage U is output according to the primary input voltage U1. 2ref Calculate the voltage transfer ratio k in steady state with the transformer ratio n = U1 / nU 2ref .

7. The DAB converter control method based on dual-integral sliding mode and current stress optimization according to claim 1, characterized in that: In S4, if it is determined that p falls within the first power range, the DAB converter enters the EPS-I control mode. The method for obtaining the optimal bridge internal and external shift ratio combination is: The inductor current expression at each switching moment in EPS-I mode is: Where: t0-t6 are the moments when the DAB converter switches its working state, f s is the operating frequency of the DAB converter; The transmission power model after per-unit processing in EPS-I control mode is: In EPS-I control mode, the current stress per unit value i is obtained by simplifying and eliminating D2. max for i max =2[k(1-D1)+2D2-1] (15) According to the transmission power model, D2 is expressed as a function of p and D1. Substitute back to the per-unit value of current stress i max Simplifying and eliminating D2, the objective function is: Take the per-unit value of current stress i max Derivative, find the maximum value to get the optimal bridge displacement compared to D 1min , substitute back into the function about D2 to obtain the optimal bridge outward shift compared to D 2min , and obtain the optimal bridge inward and outward displacement comparison combination.

8. The DAB converter control method based on dual-integral sliding mode and current stress optimization according to claim 6, characterized in that: In EPS-I control mode, the current stress per unit value i is obtained by simplifying and eliminating D2. max The method is: Write the per-unit value of current stress i max =2[k(1-D1)+2D2-1] (18) According to the transmission power model, D2 is expressed as a function of p and D1. Substitute back to the per-unit value of current stress i max Simplifying and eliminating D2, the objective function is:

9. The DAB converter control method based on dual-integral sliding mode and current stress optimization according to claim 1, characterized in that: In S4, if it is determined that p falls within the second power range, the DAB converter enters the EPS-II control mode. The method for obtaining the optimal bridge internal and external shift ratio combination is: The inductor current expression at each switching moment in EPS-II control mode is: The transmission power model after per-unit processing in EPS-II control mode is: p falls within the second power range, and the per-unit current stress value i in EPS-II control mode max for i max =2[k(1-D1)+2D2-1] (23) According to the transmission power model, D2 is expressed as a function of p and D1. Substituting formula (13) back into formula (12) yields the per-unit current stress value i max , for the per-unit value of current stress i max Take the derivative to find the maximum value and get the optimal combination of bridge inward and outward displacement.

10. The DAB converter control method based on dual-integral sliding mode and current stress optimization according to claim 1, characterized in that: In S4, If p is determined to fall within the third power range, the EPS-II control mode is still entered. The method for determining the optimal bridge inward and outward shift ratio combination is: Current stress per unit value i max for i max =2[kD1+1-k] (25) At this time, the magnitude of the current stress is only related to D1. After p is given, D1 reaches its maximum value on the section D2 = kD1-k+1, thereby determining the optimal bridge inward and outward displacement ratio combination.

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