Quick seamless start control method and system for dual-active full-bridge DC-DC converter

Abstract

The invention discloses a rapid seamless start control method and system for a dual-active full-bridge DC-DC converter, and belongs to the technical field of power electronic converter control. According to the method, by traversing all possible operation stage tracks, a switching sequence is optimized under the limitation of preset inductive current, and two starting modes of constant frequency (CF) and variable frequency (VF) are realized. In the starting process, control parameters (a phase shift angle alpha and duty ratios phi 1 and phi 2 of the primary side and the secondary side) are dynamically adjusted based on an iterative algorithm, direct-current magnetic bias of the transformer is avoided, zero-voltage conduction (ZVS) of all power switches is ensured, and meanwhile inductive current is restrained within a preset peak value. Complex controller parameter setting is not needed, the starting speed is increased by 60%-80% compared with a traditional method, seamless transition to steady-state triple phase shift (TPS) modulation can be achieved, excellent dynamic performance is achieved under different working conditions such as a buck-boost mode and light and heavy loads, and the method is suitable for scenes such as new energy grid connection, an energy storage system and electric vehicle charging.

Description

Technical Field

[0001] This invention relates to the field of power electronic converter control technology, and in particular to a fast and seamless start-up control method and system for a dual active full-bridge DC-DC converter. Background Technology

[0002] Dual-active-bridge (DAB) DC-DC converters are widely used in modern power electronic systems due to their high power density, high efficiency, bidirectional power transfer capability, and electrical isolation characteristics. An efficient DAB DC-DC converter must meet four core requirements during startup: fast startup speed, transformerless DC bias, controllable peak current, and zero-voltage switching (ZVS) for all power switches. Existing research on the startup of DAB DC-DC converters has significant limitations: most schemes focus only on suppressing inrush current, lacking comprehensive analysis and classification, and lacking theoretical support for minimizing startup time; some studies simplify the secondary bridge arm to a diode rectifier bridge and use open-loop control with linearly increasing primary duty cycle, which cannot guarantee optimal startup performance; the selection of modulation strategies relies heavily on experience rather than theoretical derivation, easily leading to problems such as DC bias and excessive current stress during startup; a few closed-loop startup schemes have excessively long startup times when the output voltage is far below the reference value, and it is difficult to balance ZVS achievement and seamless transition to steady-state operation. In traditional startup methods, the fixed duty cycle control in constant frequency mode can cause DC bias and increased current stress in the inductor, while simply increasing the duty cycle can shorten the startup time but exacerbates these problems; under varying load conditions, heavy load will prolong the startup time, while light load can easily lead to voltage overshoot, making it impossible to achieve a balance between startup speed, current stress, and ZVS achievement. Therefore, there is an urgent need for an optimized method that can adapt to different operating modes, avoid DC bias, accurately control peak current, and achieve fast and seamless startup. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a fast and seamless start-up control method and system for a dual active full-bridge DC-DC converter, which achieves a fast, unbiased, and fully ZVS start-up process by optimizing the switching sequence and control parameters.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: a fast and seamless start-up control method for a dual active full-bridge DC-DC converter, comprising the following steps:

[0005] Step 1: Establish a mathematical model for the startup phase of the dual active full-bridge DC-DC converter, and clarify the circuit parameters, operating constraints, and control objectives. The circuit parameters include the input voltage, output voltage reference value, switching frequency, inductance value, transformer turns ratio, and output capacitor value. The control objectives include fast startup, no DC bias, inductor current peak limitation, and zero-voltage conduction of all switches.

[0006] Step 2: Traverse all possible start-up phase trajectories and solve the duration and control parameters of each phase based on the iterative algorithm. The control parameters are phase shift angle α, primary side duty cycle φ1, and secondary side duty cycle φ2.

[0007] Step 3: Select the starting mode according to the operating conditions: constant frequency mode CF has a fixed switching frequency of the rated value; variable frequency mode VF has an initial frequency of 1.2 to 1.5 times the rated frequency, and smoothly transitions to the rated frequency during the start-up process;

[0008] Step 4: During startup, control parameters are dynamically updated to meet current peak constraints and ZVS conditions in real time. When the output voltage reaches the preset threshold, it seamlessly switches to steady-state TPS modulation.

[0009] Step 5: Execute the optimized switching sequence through the digital controller to achieve a seamless connection between rapid startup and steady-state operation of the dual active full-bridge DC-DC converter.

[0010] In a preferred embodiment, in step 1, under steady state, the input power P in Output power P out and the relationship between control parameters;

[0011]

[0012]

[0013] Among them, I A I B I C I D I F I G I H I I These represent the normalized inductor current values ​​for each steady-state stage, A, B, C, D, E, F, G, H, and I, respectively. M = Vo / (nVin) represents the normalized voltage gain, and n represents the turns ratio of the transformer secondary to the primary side.

[0014] (3)

[0015] In the expression, θ A θ B θ C θD θ E θ F θ G θ H θ I Let A, B, C, D, E, F, G, H, and I represent the normalized durations of each steady-state stage. The normalized duty cycle of the original side bridge arm. This is the normalized duty cycle of the original side bridge arm.

[0016]

[0017] During startup, each switching cycle contains nine stages from a to i, and the voltage gain of each stage is represented by M. a (θ), M b θ), M c (θ), M d (θ), M e (θ), M f (θ), M g (θ), M h (θ) and M i (θ), in the expression I a (θ) represents the normalized inductor current during the startup phase a, I o (θ) represents the normalized output current during startup, I a0 V is the initial inductor current. a0 is the initial output capacitor voltage; r is the output capacitor coefficient reflecting the normalized impedance of the output capacitor; q is the load coefficient representing the load state. A larger r corresponds to a lower output capacitor impedance, which means a smaller capacitor size; while a larger q indicates a stronger load condition.

[0018]

[0019] In a preferred embodiment, the circuit parameters in step 1 are as follows: input voltage 240V, output voltage reference value 170V ~ 340V, rated switching frequency 100kHz, inductance value 57μH, transformer ratio 1:1, output capacitor 33μF, film capacitor 560nF, rated output power 1.2kW, and preset inductor current peak value 3A ~ 4A.

[0020] In a preferred embodiment, the iterative algorithm in step 2 includes:

[0021] Step 21: Initialize startup parameters: Initial output voltage gain M a (0)=M Init =0, initial inductor current I a (0)=I Init =0, preset peak current Ipeak Target output voltage gain M End ;

[0022] Step 22: Traverse all possible combinations of stage trajectories and solve for the duration θ of each stage. a ~θ i This satisfies the stage transition conditions and current constraints;

[0023] Step 23: Calculate the target output voltage gain corresponding to each trajectory, and select the control parameter combination corresponding to the maximum gain;

[0024] Step 24: Iteratively update the control parameters until the output voltage gain reaches M. End It outputs the optimal control parameter trajectory.

[0025] In a preferred embodiment, the constraint condition for the control parameters in step 2 is:

[0026] Constant frequency mode: θ a +θ c +θ f = θ i +θ g +θ d = π, φ1(θ) is dynamically adjusted to avoid DC bias;

[0027] Variable frequency mode: Initial switching frequency 127 kHz ~ 161 kHz, satisfying ZVS current constraint I. c (0) ≤ I ZVS I g (0) ≥ -I ZVS Peak current constraint I c (θ c ) = I peak I g (θ g )=- I peak ;

[0028] Full-condition ZVS: Primary-side switch satisfies I a (0) < 0、I c (0) > 0, the secondary switch meets the current polarity and conduction requirements matching.

[0029] In a preferred embodiment, the stage trajectory selection rule for the startup mode in step 3 is as follows:

[0030] Constant frequency mode: During the low-voltage startup phase, the “acfigd” trajectory is used, and when the voltage gain is close to 1, it switches to the “abcihg” trajectory.

[0031] Variable frequency mode: During the low-voltage start-up phase, the “acig” trajectory is used. When the voltage gain is close to 1, the trajectory is switched to “abcihg” and transitioned to the rated frequency.

[0032] Boost mode, M > 1: Current peaks occur at the end of stages b and h, constraining I. b (θ b ) = I peak I h (θ h ) =- I peak ;

[0033] Buck mode, M<1: Current peak occurs at the end of stages c and g, constraining I. c (θ c )= I peak I g (θ g )= -I peak .

[0034] In a preferred embodiment, the seamless switching condition in step (4) is that the difference between the output voltage and the reference value is less than 1V, the switching process is completed within one switching cycle, and steady-state power transmission is achieved by using TPS modulation.

[0035] In a preferred embodiment, the digital controller in step (5) is a DSP T MS320F28377D, the control algorithm execution time is less than or equal to 4.6μs, and it supports startup control with a maximum switching frequency of 217kHz.

[0036] This invention also provides a fast and seamless start-up control system for a dual active full-bridge DC-DC converter, which applies the aforementioned fast and seamless start-up control method for a dual active full-bridge DC-DC converter. The system includes an input DC power supply, a dual active full-bridge DC-DC converter main circuit, an output capacitor, a digital controller, and a load. The digital controller stores the optimized control parameter trajectory and generates PWM drive signals in real time.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) Fast startup speed: 60% ~ 80% faster than traditional methods, with heavy-load startup time as low as 0.84 Ms;

[0039] (2) High reliability: No DC bias magnetism, controllable peak current, and full-switch ZVS conduction;

[0040] (3) High adaptability: It can adapt to different working conditions such as boosting and deboosting modes, light and heavy loads;

[0041] (4) Simple implementation: No complex parameter tuning is required, and the controller execution time is ≤ 4.6μs;

[0042] (5) Seamless transition: There are no obvious oscillations or sudden changes during startup and steady state. Attached Figure Description

[0043] Figure 1 This is a topology diagram of a DAB DC-DC converter;

[0044] Figure 2 Typical waveforms of positive and negative power transfer in a DAB DC-DC converter are shown, where (a) is the waveform of positive power transfer and (b) is the waveform of reverse power transfer.

[0045] Figure 3 The equivalent circuit for the nine operating stages of the DAB DC-DC converter under steady state;

[0046] Figure 4 This is the equivalent circuit for the nine operating stages of the DAB DC-DC converter during startup;

[0047] Figure 5 This is a typical startup waveform diagram of a DAB DC-DC converter in constant frequency mode;

[0048] Figure 6 Flowchart of the iterative startup optimization algorithm for the DAB DC-DC converter;

[0049] Figure 7 Here is the flowchart of the DAB DC-DC converter control algorithm;

[0050] Figure 8 The waveform diagrams for the traditional startup method are shown below, where (a) is the overall waveform diagram, (b) is the magnified waveform diagram during the initial startup, (c) is the magnified waveform diagram during switching, and (d) is the waveform diagram after startup is completed.

[0051] Figure 9 The waveform diagrams for constant frequency mode startup are shown below. (a) is the overall waveform, (b) is the magnified waveform during initial startup, and (c) is the V waveform. o =150V magnified waveform diagram, (d) is the waveform diagram after startup;

[0052] Figure 10 The waveform diagrams for inverter mode startup are shown below. (a) is the overall waveform diagram, (b) is the magnified waveform diagram during initial startup, and (c) is the waveform diagram for V. o =150V magnified waveform diagram, (d) is the waveform diagram after startup; Detailed Implementation

[0053] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0054] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0055] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application; as used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise; furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0056] A fast and seamless start-up control method for a dual active full-bridge DC-DC converter, referenced Figure 1-10 The process includes the following steps:

[0057] Step (1) Establish a mathematical model for the startup phase of the dual active full-bridge DC-DC converter, and clarify the circuit parameters, operating constraints and control objectives. The control objectives include fast startup, no DC bias, inductor current peak limitation and zero-voltage conduction of all switches. The circuit parameters include input voltage, output voltage reference value, switching frequency, inductance value, transformer turns ratio and output capacitance value.

[0058] Under steady state, the input power P in Output power P out and the relationship between control parameters;

[0059]

[0060] Among them, I A I B I C I D I F I G I H I I These represent the normalized inductor current values ​​for each steady-state stage, A, B, C, D, E, F, G, H, and I, respectively. M = Vo / (nVin) represents the normalized voltage gain, and n represents the turns ratio of the transformer secondary to the primary side.

[0061]

[0062] (3)

[0063] In the expression, θ A θ B θ C θD θ E θ F θ G θ H θ I Let A, B, C, D, E, F, G, H, and I represent the normalized durations of each steady-state stage. The normalized duty cycle of the original side bridge arm. This is the normalized duty cycle of the original side bridge arm.

[0064]

[0065] During startup, each switching cycle contains nine stages from a to i, and the voltage gain of each stage is represented by M. a (θ), M b θ), M c (θ), M d (θ), M e (θ), M f (θ), M g (θ), M h (θ) and M i (θ), in the expression I a (θ) represents the normalized inductor current during the startup phase a, I o (θ) represents the normalized output current during startup, I a0 V is the initial inductor current. a0 is the initial output capacitor voltage; r is the output capacitor coefficient reflecting the normalized impedance of the output capacitor; q is the load coefficient representing the load state. A larger r corresponds to a lower output capacitor impedance, which means a smaller capacitor size; while a larger q indicates a stronger load condition.

[0066]

[0067] Taking stage a as an example, where I a0 V is the initial inductor current. a0 This represents the initial output capacitor voltage. The output capacitance coefficient c reflects the normalized impedance of the output capacitor, and the load coefficient g represents the load condition. A larger c corresponds to a lower output capacitor impedance, which means a smaller capacitor size; while a larger g indicates a stronger load condition.

[0068] Step (2) Traverse all possible start-up stage trajectories and solve the duration and control parameters of each stage based on the iterative algorithm. The stage trajectory includes combinations such as “acfIgd”, “abcIhg”, and “acIg”. The control parameters are phase shift angle α, primary side duty cycle φ1, and secondary side duty cycle φ2.

[0069] Step (3) Select the starting mode according to the working conditions: constant frequency mode (CF) fixes the switching frequency to the rated value; variable frequency mode (VF) sets the initial frequency to 1.2 to 1.5 times the rated frequency and smoothly transitions to the rated frequency during the start-up process;

[0070] During the startup process of step (4), the control parameters are dynamically updated to meet the current peak constraint and ZVS condition in real time. When the output voltage reaches the preset threshold, it seamlessly switches to steady-state TPS modulation.

[0071] Step (5) executes the optimized switching sequence through the digital controller to achieve seamless connection between fast start-up and steady-state operation of the dual active full-bridge DC-DC converter.

[0072] Specifically, the main circuit of the dual active full-bridge DC-DC converter described in step (1) includes a primary and secondary full-bridge, a high-frequency transformer, a transmission inductor, and input and output capacitors. Its circuit parameters are: input voltage 240V, output voltage reference value 170V (step-down) ~ 340V (step-up), rated switching frequency 100kHz, inductance value 57μH, transformer ratio 1:1, output capacitor 33μF (aluminum electrolytic capacitor) + 560nF (film capacitor), rated output power 1.2kW, and preset inductor current peak value 3A ~ 4A.

[0073] The control objective is to reduce startup time by 60% to 80% compared to traditional methods, with a startup time of ≤ 0.96ms for light load (120W) and ≤ 0.84ms for heavy load (1.2kW); the operating constraints are: peak inductor current ≤ 3A to 4A, no transformer DC bias, and all switches achieving ZVS conduction.

[0074] Transition performance: Seamlessly switches to TPS steady-state modulation after startup, without voltage surges or current oscillations.

[0075] Specifically, the iterative algorithm described in step (2) includes:

[0076] Initial startup parameters: Initial output voltage gain M a (0)=M Init =0, initial inductor current I a (0)=I Init =0, preset peak current I peak Target output voltage gain M End ;

[0077] Iterate through all possible combinations of stage trajectories and solve for the duration θ of each stage. a ~θ i This satisfies the stage transition conditions and current constraints;

[0078] Calculate the target output voltage gain for each trajectory and select the control parameter combination corresponding to the maximum gain;

[0079] Iteratively update the control parameters until the output voltage gain reaches M. End It outputs the optimal control parameter trajectory.

[0080] Specifically, the constraints on the control parameters in step (2) are as follows:

[0081] Constant frequency mode: θ a +θ c +θ f = θ i +θ g +θ d = π, φ1(θ) is dynamically adjusted to avoid DC bias;

[0082] Variable frequency mode: Initial switching frequency 127 kHz ~ 161 kHz, satisfying ZVS current constraint I. c (0) ≤ I ZVS I g (0) ≥ -I ZVS Peak current constraint I c (θ c ) =I peak I g (θ g )=- I peak ;

[0083] Full-condition ZVS: Primary-side switch satisfies I a (0) < 0、I c (0) > 0, the secondary switch meets the current polarity and conduction requirements matching.

[0084] Specifically, the stage trajectory selection rule for the startup mode described in step (3) is as follows:

[0085] Constant frequency mode: During the low-voltage startup phase, the “acfigd” trajectory is used, and when the voltage gain is close to 1, it switches to the “abcihg” trajectory.

[0086] Variable frequency mode: During the low-voltage start-up phase, the “acig” trajectory is used. When the voltage gain is close to 1, the trajectory is switched to “abcihg” and transitioned to the rated frequency.

[0087] Boost mode (M > 1): The current peak occurs at the end of stages b and h, constraining I. b (θ b ) = I peak I h (θ h ) =- I peak ;

[0088] Buck mode (M<1): The current peak occurs at the end of the c and g stages, constraining I. c (θ c )= I peak I g (θ g )= -I peak .

[0089] Specifically, the seamless switching condition in step (4) is that the difference between the output voltage and the reference value is less than 1V. The switching process is completed within one switching cycle. TPS modulation is used to achieve steady-state power transmission, ensuring no voltage surges and current oscillations.

[0090] Specifically, the digital controller mentioned in step (5) is a DSP T MS320F28377D, the control algorithm execution time is less than or equal to 4.6μs, and it supports startup control with a maximum switching frequency of 217kHz.

[0091] Specific implementation methods include:

[0092] 1. Hardware platform setup

[0093] A 1.2kW DAB DC-DC converter experimental platform was built, including: power device: CREEC3 M0021120K (1.2kV / 21 MΩ); controller: DSPT MS320F28377D (200 MHz); key components: 57μH transmission inductor, 18T / 18T high-frequency transformer, 33μF+560nF output capacitor; measurement equipment: oscilloscope, power analyzer, current probe.

[0094] 2. Software Implementation Steps

[0095] (1) Offline optimization stage

[0096] 1) Establish a mathematical model for the DAB DC-DC startup phase and traverse all phase trajectories; 2) Solve the optimal control parameter trajectory under different operating conditions based on an iterative algorithm and store it in the controller lookup table; 3) Fit the relationship function between control parameters and output voltage and load for real-time calculation.

[0097] (2) Online startup phase

[0098] 1) Controller initialization: Read operating parameters (output voltage reference value, load, preset peak current);

[0099] Set reference value: V Base (Reference voltage), I Base (Reference current), Z Base (Reference impedance), fBase (Reference frequency);

[0100] The initial voltage ratio M Init and initial current I Init Set to 0, and iterate through the preset peak current I. Peak The system iterates through each phase angle, solving the iterative state equations for each combination of angles. It verifies whether the solution satisfies all set constraints (such as current and voltage safety ranges). Among all solutions that satisfy the constraints, it finds the one that makes the system's terminal voltage ratio M... End The largest set of control parameters, until the condition is met: M End > M Set .

[0101] 2) Select startup mode: Choose CF or VF mode based on the load and voltage gain;

[0102] 3) Real-time update of control parameters: Read the output voltage and inductor current every switching cycle, and update α, φ1, and φ2 through a fitting function;

[0103] 4) Seamless switching: When the voltage error meets the conditions, switch to TPS steady-state modulation.

[0104] 3. Experimental verification

[0105] Verify the effectiveness of the method under two typical operating conditions:

[0106] Operating Condition 1: Boost Mode (V) oref =340V, M=1.4), light load 120W operating condition: VF mode startup time 0.96 ms, CF mode startup time 1.1 ms, traditional method startup time 1.52 ms;

[0107] Operating Condition 2: Buck Mode (V) oref =170V, M=0.7), heavy load 1.2kW operating condition: VF mode start-up time 0.84 ms, CF mode start-up time 1.2ms, traditional method start-up time 1.56 ms;

[0108] Key performance indicators: peak inductor current ≤ 4A, no DC bias, all switches ZVS conduction, and no oscillation during switching.

Claims

1. A fast and seamless start-up control method for a dual active full-bridge DC-DC converter, characterized in that, Includes the following steps: Step 1: Establish a mathematical model for the startup phase of the dual active full-bridge DC-DC converter, and clarify the circuit parameters, operating constraints and control objectives. The circuit parameters include the input voltage, the reference value of the output voltage, the switching frequency, the inductance value, the transformer turns ratio and the output capacitor value. Step 2: Traverse all possible start-up phase trajectories and solve the duration and control parameters of each phase based on the iterative algorithm. The control parameters are phase shift angle α, primary side duty cycle φ1, and secondary side duty cycle φ2. Step 3: Select the starting mode according to the operating conditions: constant frequency mode CF has a fixed switching frequency of the rated value; variable frequency mode VF has an initial frequency of 1.2 to 1.5 times the rated frequency, and smoothly transitions to the rated frequency during the start-up process; Step 4: During startup, control parameters are dynamically updated to meet current peak constraints and ZVS conditions in real time. When the output voltage reaches the preset threshold, it seamlessly switches to steady-state TPS modulation. Step 5: Execute the optimized switching sequence through the digital controller to achieve a seamless connection between rapid startup and steady-state operation of the dual active full-bridge DC-DC converter.

2. The fast and seamless start-up control method for a dual active full-bridge DC-DC converter according to claim 1, characterized in that, In step 1, under steady state, the input power P in Output power P out and the relationship between control parameters; Among them, I A I B I C I D I F I G I H I I These represent the normalized inductor current values ​​for each steady-state stage, A, B, C, D, E, F, G, H, and I, respectively. M = Vo / (nVin) represents the normalized voltage gain, and n represents the turns ratio of the transformer secondary to the primary side. (3) In the expression, θ A θ B θ C θ D θ E θ F θ G θ H θ I Let A, B, C, D, E, F, G, H, and I represent the normalized durations of each steady-state stage. The normalized duty cycle of the original side bridge arm. The normalized duty cycle of the original side bridge arm; During startup, each switching cycle contains nine stages from a to i, and the voltage gain of each stage is represented by M. a (θ), M b θ), M c (θ), M d (θ), M e (θ), M f (θ), M g (θ), M h (θ) and M i (θ), in the expression I a (θ) represents the normalized inductor current during the startup phase a, I o (θ) represents the normalized output current during startup, I a0 V is the initial inductor current. a0 is the initial output capacitor voltage; r is the output capacitor coefficient reflecting the normalized impedance of the output capacitor; q is the load coefficient representing the load state. A larger r corresponds to a lower output capacitor impedance, which means a smaller capacitor size; while a larger q indicates a stronger load condition.

3. The fast and seamless start-up control method for a dual active full-bridge DC-DC converter according to claim 1, characterized in that, The circuit parameters mentioned in step 1 are as follows: input voltage 240V, output voltage reference value 170V ~ 340V, rated switching frequency 100kHz, inductance value 57μH, transformer ratio 1:1, output capacitor 33μF, film capacitor 560nF, rated output power 1.2kW, and preset inductor current peak value 3A ~ 4A.

4. The fast and seamless start-up control method for a dual active full-bridge DC-DC converter according to claim 1, characterized in that, The iterative algorithm described in step 2 includes: Step 21: Initialize startup parameters: Initial output voltage gain M a (0)=M Init =0, initial inductor current I a (0)=I Init =0, preset peak current I peak Target output voltage gain M End ; Step 22: Traverse all possible combinations of stage trajectories and solve for the duration θ of each stage. a ~θ i This satisfies the stage transition conditions and current constraints; Step 23: Calculate the target output voltage gain corresponding to each trajectory, and select the control parameter combination corresponding to the maximum gain; Step 24: Iteratively update the control parameters until the output voltage gain reaches M. End It outputs the optimal control parameter trajectory.

5. The fast and seamless start-up control method for a dual active full-bridge DC-DC converter according to claim 1, characterized in that, The constraints on the control parameters mentioned in step 2 are as follows: Constant frequency mode: θ a +θ c +θ f = θ i +θ g +θ d = π, φ1(θ) is dynamically adjusted to avoid DC bias; Variable frequency mode: Initial switching frequency 127 kHz ~ 161 kHz, satisfying ZVS current constraint I. c (0) ≤ I ZVS I g (0)≥ -I ZVS Peak current constraint I c (θ c ) = I peak I g (θ g )=- I peak ; Full-condition ZVS: Primary-side switch satisfies I a (0) < 0、I c (0) > 0, the secondary switch meets the current polarity and conduction requirements matching.

6. The fast and seamless start-up control method for a dual active full-bridge DC-DC converter according to claim 1, characterized in that, The stage trajectory selection rule for the startup mode described in step 3 is as follows: Constant frequency mode: During the low-voltage startup phase, the "acfigd" trajectory is used, and when the voltage gain is close to 1, it switches to the "abcihg" trajectory; Variable frequency mode: During the low-voltage start-up phase, the "acig" trajectory is used. When the voltage gain is close to 1, the trajectory is switched to "abcihg" and transitioned to the rated frequency. Boost mode, M > 1: Current peaks occur at the end of stages b and h, constraining I. b (θ b ) =I peak I h (θ h ) = -I peak ; Buck mode, M<1: Current peak occurs at the end of stages c and g, constraining I. c (θ c )= I peak I g (θ g )= - I peak .

7. The fast and seamless start-up control method for a dual active full-bridge DC-DC converter according to claim 1, characterized in that, The seamless switching condition mentioned in step (4) is that the difference between the output voltage and the reference value is less than 1V. The switching process is completed within one switching cycle, and steady-state power transmission is achieved by using TPS modulation.

8. The fast and seamless start-up control method for a dual active full-bridge DC-DC converter according to claim 1, characterized in that, The digital controller mentioned in step (5) is a DSP T MS320F28377D, the control algorithm execution time is less than or equal to 4.6μs, and it supports startup control with a maximum switching frequency of 217kHz.

9. A fast and seamless start-up control system for a dual active full-bridge DC-DC converter, applying the fast and seamless start-up control method for a dual active full-bridge DC-DC converter as described in any one of claims 1-8, characterized in that, It includes an input DC power supply, a dual active full-bridge DC-DC converter main circuit, an output capacitor, a digital controller, and a load. The digital controller stores the optimized control parameter trajectory and generates PWM drive signals in real time.

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