Three-level current type push-pull bidirectional DC-DC converter

Abstract

The invention discloses a three-level current type push-pull bidirectional DC-DC converter, relates to the technical field of power electronics, and is used for realizing bidirectional energy conversion between low voltage and high voltage. The converter comprises a low-voltage side circuit, a high-voltage side circuit, a transmission inductor and a control unit. The low-voltage side circuit is composed of a boost inductor, an active clamping circuit and a push-pull transformer. The high-voltage side circuit adopts a three-level half-bridge structure, and voltage boosting is realized through a voltage-multiplying capacitor; the transmission inductor is used for efficient bidirectional power transmission. And the control unit adopts a PWM + phase shift composite control strategy to accurately adjust the duty ratio, the inter-bridge shift phase ratio and the intra-bridge shift phase ratio, so that the accurate control of the power transmission direction and size is realized. According to the converter, the switching loss is reduced while the conversion efficiency is improved, the system stability is improved, and the converter is suitable for high-efficiency energy transmission application of electric vehicle charging, an energy storage system, a renewable energy source power grid and the like. Through optimization design, the reliability and adaptability of the system can be greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a three-level current-type push-pull bidirectional DC-DC converter. Background Art

[0002] With the continued development of renewable energy and the increasing demand for energy storage systems, efficient and reliable bidirectional power conversion technologies are becoming increasingly important. In particular, in applications such as electric vehicles (EVs), energy storage systems, and renewable energy grids, effectively transferring energy between different voltage levels has always been a key challenge. Bidirectional DC-DC converters, with their ability to efficiently transfer energy between two different voltages, are an ideal solution to this problem and are widely used in battery charging and discharging, vehicle-to-grid (V2G) technology, and the integration of renewable energy.

[0003] Traditional DC-DC converters are typically designed for unidirectional power transmission, limiting their use in advanced applications such as battery charge and discharge management, or energy exchange between the grid and storage systems. These systems face numerous challenges in achieving an efficient balance between energy input and output, especially with the increasing demand for renewable energy integration into the grid.

[0004] Bidirectional DC-DC converters address this issue by supporting bidirectional power flow, effectively exchanging energy between different voltage levels. However, improving efficiency and maintaining system reliability when converting between low and high voltages remains a major engineering challenge. Traditional converters often suffer from power loss, control complexity, and insufficient ability to maintain voltage stability under varying loads.

[0005] To improve efficiency and reduce power losses, advanced converter topologies, such as three-level current-mode push-pull bidirectional DC-DC converters, have become a research hotspot. These topologies aim to reduce switching losses and enhance voltage regulation accuracy, thereby improving performance during energy conversion. They employ active clamping circuits, high-frequency transformers, and optimized control strategies to enhance overall efficiency during bidirectional energy flow.

[0006] Despite this, existing technologies still face issues such as switching efficiency, electromagnetic interference, and system integration complexity. Furthermore, ensuring optimal performance under varying operating conditions (such as input voltage variations, load changes, and temperature fluctuations) remains a major technical challenge.

[0007] Therefore, developing an efficient and reliable three-level current-mode push-pull bidirectional DC-DC converter is crucial for solving power conversion problems in high-voltage energy storage, renewable energy systems, and electric vehicle integration. The development of this technology will greatly promote the widespread application of future smart grids and electric vehicle charging systems. Summary of the Invention

[0008] The object of the present invention is to solve the prior art problems raised in the above background technology and to provide a three-level current-type push-pull bidirectional DC-DC converter.

[0009] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0010] A three-level current-mode push-pull bidirectional DC-DC converter, comprising:

[0011] The low-voltage side circuit includes a boost inductor L, an active clamp circuit (S3, S4, Cs), and the primary winding of a push-pull transformer Tr;

[0012] The high-voltage side circuit adopts a three-level half-bridge structure, consisting of four switching tubes (S5-S8), a flying capacitor (Cf) and two voltage-doubling capacitors (Co1 and Co2);

[0013] The transmission inductor (Ls) is connected to the secondary side of the push-pull transformer to achieve bidirectional energy transmission;

[0014] The control unit adopts PWM+phase shift compound control strategy, by adjusting the duty cycle D and the phase shift between bridges Compared with the bridge inward movement Achieve precise control of power transmission direction and size.

[0015] As a preferred technical solution of the present invention, the clamping capacitor voltage (V Cs ) and input voltage (V L ) is:

[0016]

[0017] Where D is the duty cycle of the low-voltage side switch.

[0018] As a preferred technical solution of the present invention, the output voltage (V H ) and input voltage (V L ) is:

[0019]

[0020] Among them, n is the transformer turns ratio, n1:n2:n3=7:7:20.

[0021] As a preferred technical solution of the present invention, the transmission inductor current (i Ls ) in A3 mode is:

[0022]

[0023] Among them, V H is the high-voltage side voltage, L s is the transmission inductance, f s is the switching frequency, D is the duty cycle, Compared with the bridge displacement, Compared to the inward movement of the bridge.

[0024] As a preferred technical solution of the present invention, the power expression of the transmission power P in A3 mode is:

[0025]

[0026] Where n is the transformer turns ratio, V L is the low-side voltage, V H is the high-voltage side voltage, L s is the transmission inductance, f s is the switching frequency, D is the duty cycle, Compared with the bridge displacement, Compared to the inward movement of the bridge.

[0027] As a preferred technical solution of the present invention, the converter is divided into 8 working modes (A1-A4, B1-B4) during forward power transmission, and the power per unit value P in each mode is * The expression is:

[0028] A3 Mode:

[0029]

[0030] In B2 mode:

[0031]

[0032] In A1 mode:

[0033]

[0034] In B4 mode:

[0035]

[0036] In A4 mode:

[0037]

[0038] Where D is the duty cycle, Compared with the bridge displacement, Compared to the inward movement of the bridge.

[0039]

[0040]

[0041] As a preferred technical solution of the present invention, the transmission inductor current (i Ls ) The expressions in stages 1-4 are:

[0042] Phase 1 (t0-t1):

[0043]

[0044] Phase 2 (t1-t2):

[0045]

[0046] Phase 3 (t2-t3):

[0047]

[0048] Phase 4 (t3-t4):

[0049]

[0050] Among them, V H is the high-voltage side voltage, L s is the transmission inductance, f s is the switching frequency, D is the duty cycle, Compared with the bridge displacement, Compared to the inward movement of the bridge.

[0051] As a preferred technical solution of the present invention, the power transmission characteristics of the converter in A3 mode satisfy the following relationship:

[0052]

[0053] Where n is the transformer turns ratio, V L is the low-side voltage, V H is the high-voltage side voltage, L s is the transmission inductance, f s is the switching frequency, D is the duty cycle, Compared with the bridge displacement, Compared to the inward movement of the bridge.

[0054] As a preferred technical solution of the present invention, the transmission inductor current (i Ls ) in A3 mode is:

[0055]

[0056] Among them, V H is the high-voltage side voltage, L s is the transmission inductance, f s is the switching frequency, D is the duty cycle, Compared with the bridge displacement, Compared to the inward movement of the bridge.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] 1. Efficient Energy Transfer: The three-level, current-source, push-pull, bidirectional DC-DC converter of this invention utilizes a three-level half-bridge structure and an optimized control strategy to achieve efficient energy transfer between low and high voltages. This effectively reduces switching losses and voltage fluctuations, providing higher energy conversion efficiency. It is particularly suitable for bidirectional power transmission scenarios such as battery charging and discharging and vehicle-to-grid (V2G) interaction.

[0059] 2. Accurate power control: By introducing PWM+phase shift composite control strategy, the present invention can accurately adjust the duty cycle D and the phase shift ratio between bridges. and the bridge shift compared to This allows for precise control of the direction and magnitude of power transmission. This flexible control method greatly improves the system's adaptability under various load and input voltage conditions, ensuring stable power transmission between the high-voltage and low-voltage sides.

[0060] 3. Reduced System Complexity and Improved Reliability: By optimizing circuit design and control strategies, this converter reduces the number of switching devices and their complexity found in traditional bidirectional DC-DC converters, while also enhancing system reliability. The use of a high-frequency transformer and active clamping circuit effectively suppresses voltage spikes when the system operates at high power and high frequency, ensuring stable operation and extending the life of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] In order to more clearly illustrate the technical solutions in the present invention or the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0062] Figure 1 This is the structural block diagram of the regional power router.

[0063] Figure 2 It is a three-level push-pull bidirectional DC / DC converter topology.

[0064] Figure 3 It is the key waveform diagram of A3 working mode.

[0065] Figure 4 This is a diagram of the 8 working stages in A3 working mode.

[0066] Figure 5 is the power per unit value (P*) and D, relationship curve.

[0067] Figure 6 is the power per unit value (P*) and D, relationship curve. DETAILED DESCRIPTION

[0068] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0069] Example: The embodiment of the present invention provides a three-level current-mode push-pull bidirectional DC-DC converter, comprising:

[0070] The low-voltage side circuit includes a boost inductor L, an active clamp circuit (S3, S4, Cs), and the primary winding of a push-pull transformer Tr;

[0071] The high-voltage side circuit adopts a three-level half-bridge structure, consisting of four switching tubes (S5-S8), a flying capacitor (Cf) and two voltage-doubling capacitors (Co1 and Co2);

[0072] The transmission inductor (Ls) is connected to the secondary side of the push-pull transformer to achieve bidirectional energy transmission;

[0073] The control unit adopts PWM+phase shift compound control strategy, by adjusting the duty cycle D and the phase shift between bridges Compared with the bridge inward movement Achieve precise control of power transmission direction and size.

[0074] The clamping capacitor voltage of the low-voltage side circuit (V Cs ) and input voltage (V L ) is:

[0075]

[0076] Where D is the duty cycle of the low-voltage side switch.

[0077] The output voltage of the high-voltage side circuit (V H ) and input voltage (V L ) is:

[0078]

[0079] Among them, n is the transformer turns ratio, n1:n2:n3=7:7:20.

[0080] Transmission inductor current (i Ls ) in A3 mode is:

[0081]

[0082] Among them, V H is the high-voltage side voltage, L s is the transmission inductance, f s is the switching frequency, D is the duty cycle, Compared with the bridge displacement, Compared to the inward movement of the bridge.

[0083] The power expression of transmission power P in A3 mode is:

[0084]

[0085] Where n is the transformer turns ratio, V L is the low-side voltage, V H is the high-voltage side voltage, L s is the transmission inductance, f s is the switching frequency, D is the duty cycle, Compared with the bridge displacement, Compared to the inward movement of the bridge.

[0086] The converter is divided into 8 working modes (A1-A4, B1-B4) during forward power transmission. The power per unit value P in each mode is * The expression is:

[0087] A3 Mode:

[0088]

[0089] In B2 mode:

[0090]

[0091] In A1 mode:

[0092]

[0093] In B4 mode:

[0094]

[0095] In A4 mode:

[0096]

[0097] Where D is the duty cycle, Compared with the bridge displacement, Compared to the inward movement of the bridge.

[0098] The transmission inductor current (i Ls ) The expressions in stages 1-4 are:

[0099] Phase 1 (t0-t1):

[0100]

[0101] Phase 2 (t1-t2):

[0102]

[0103] Phase 3 (t2-t3):

[0104]

[0105] Phase 4 (t3-t4):

[0106]

[0107] Among them, V H is the high-voltage side voltage, L s is the transmission inductance, f s is the switching frequency, D is the duty cycle, Compared with the bridge displacement, Compared to the inward movement of the bridge.

[0108] The power transfer characteristics of the converter in A3 mode satisfy the following relationship:

[0109]

[0110] Where n is the transformer turns ratio, V L is the low-side voltage, V H is the high-voltage side voltage, L s is the transmission inductance, f s is the switching frequency, D is the duty cycle, Compared with the bridge displacement, Compared to the inward movement of the bridge.

[0111] Transmission inductor current (i Ls ) in A3 mode is:

[0112]

[0113] Among them, V H is the high-voltage side voltage, L s is the transmission inductance, f s is the switching frequency, D is the duty cycle, Compared with the bridge displacement, Compared to the inward movement of the bridge.

[0114] The following is combined with Figure 1 , the specific implementation methods of the present invention are described in detail.

[0115] 1. Converter topology design

[0116] The topology of the three-level current-type push-pull bidirectional DC-DC converter of the present invention is as follows: Figure 1 As shown, the specific design is as follows:

[0117] 1.1 The low-voltage side circuit includes: boost inductor (L): made of ferrite core, with an inductance of 200μH, connected to the input power supply (V L ) are connected in series to increase voltage gain and suppress input current ripple. Their current capacity must be selected based on the maximum power (3kW), and the wire cross-sectional area must meet temperature rise requirements.

[0118] Active clamping circuit: Switch tubes (S3, S4): SiC MOSFET (model C3M0065090D) with a withstand voltage of 650V and an on-resistance of 90mΩ are selected to reduce switching losses.

[0119] Clamping capacitor (Cs): Use a low ESR electrolytic capacitor (220μF / 400V) in parallel with a high-frequency ceramic capacitor (10μF / 100V) to suppress high-frequency noise.

[0120] Function: When the switch is turned off, Cs absorbs the leakage inductance energy and limits the voltage spike across the switch to V Cs =V L / (1-D), ensuring the safe operation of the switching tube.

[0121] 1.2 High-voltage side circuit includes:

[0122] Three-level half-bridge structure: Switch tube (S5-S8): uses IGBT module (model FF450R12ME4), with a withstand voltage of 1200V and supports high-frequency switching (50kHz).

[0123] Flying capacitor (Cf): Select a film capacitor (220μF / 1000V) to balance the voltage stress of the high-voltage side switch tube and ensure V S5 =V S6 =V H / 2.

[0124] Voltage doubling capacitors (Co1, Co2): Electrolytic capacitors (220μF / 1000V) are used to achieve voltage doubling output in conjunction with rectifier diodes.

[0125] Voltage doubler rectification: By connecting Co1 and Co2 in series, double the voltage output is achieved on the high-voltage side, thereby increasing the voltage gain.

[0126] 1.3 Transmission inductor (Ls) and transformer include:

[0127] Transmission inductor (Ls): Designed to be 60μH, it uses a segmented-wound magnetic core (made of Sendust) to reduce the risk of magnetic saturation. Its current capacity must meet the requirements of bidirectional power transmission.

[0128] Push-pull transformer (Tr): Turns ratio: The primary side (low-voltage side) turns ratio is 7:7, the secondary side (high-voltage side) turns ratio is 20, and the total turns ratio N1:N2:N3=7:7:20.

[0129] Core selection: Nanocrystalline core is selected, which has low high-frequency loss and high saturation flux density (1.2T).

[0130] Winding process: The primary side is wound with Litz wire to reduce skin effect loss; the secondary side is wound with copper foil to reduce DC resistance.

[0131] 2. Control strategy implementation

[0132] 2.1PWM+phase shift control logic

[0133] Low-voltage side control: The drive signals of the switch tubes (S1, S3) and (S2, S4) are complementary, and the duty cycle is D.

[0134] By adjusting the duty cycle D, the clamping capacitor voltage (V Cs ):

[0135]

[0136] The phase difference between the driving signals of the switch tubes (S1, S2) is π, and the power transmission is controlled by adjusting the duty cycle D.

[0137] High-side control: The drive signals of the switch tubes (S5, S6) and (S7, S8) are complementary, and the duty cycle is fixed at 0.5.

[0138] By adjusting the bridge displacement Compared with the bridge inward movement Control the direction and magnitude of power transmission.

[0139] Bridge displacement It is defined as the ratio of the phase difference between the drive signals of the switch tubes (S1) and (S5) to 2π.

[0140] Bridge inward shift compared to It is defined as the ratio of the phase difference between the drive signals of the switch tubes (S5) and (S6) to 2π.

[0141] Voltage LPC principle: Through PWM+phase shift control, the midpoint voltage of the original and secondary bridge arms is matched, that is:

[0142] V ab =V cd

[0143] The quiescent voltage gain is:

[0144]

[0145] Where n is the transformer turns ratio.

[0146] 2.2 Control Flowchart

[0147] Initialization: Set the initial duty cycle D = 0.6,

[0148] Feedback sampling: collecting input voltage, output voltage, inductor current and transmission inductor current;

[0149] Dynamic adjustment: If V H <nV L / (1-D), increase ° If backflow power is detected, reduce If the voltage on the high voltage side is unbalanced, adjust

[0150] Protection mechanism: when overcurrent occurs, D=0.5 is forced. Enter Safe Mode

[0151] 3. Work mode and stage analysis;

[0152] According to the duty cycle D, the bridge shift ratio Compared with the bridge inward movement The converter is divided into 8 working modes (A1-A4, B1-B4) under forward and reverse power transmission. Take this as an example to analyze each stage in detail:

[0153] Phase 1 (t0-t1, duration (D-0.5)T=0.2T)

[0154] Circuit status:

[0155] S1 and S2 are turned on, and S3 and S4 are turned off;

[0156] S7 and S8 are turned on, and S5 and S6 are turned off.

[0157] Current path:

[0158] The transmission inductor Ls continues the flow through S7 and S8, and the current slope is: di Ls / dt=-V cd / L s =-700V / 60μH≈-11.67A / μs.

[0159] Key waveform: i L Linear increase, i Ls Linear decrease.

[0160] Phase 2 (t1-t2, lasting

[0161] Circuit status:

[0162] S1 and S4 are turned on, S2 and S3 are turned off;

[0163] S7 and S8 continue to be turned on.

[0164] Current path: input power supply → L → S1 → Tr—secondary side → S4 → Cs → ground.

[0165] Ls current reverse, slope: di Ls / dt=(V ab -V cd ) / L s =(350V-350V) / 60μH=0 (the current is constant when the voltage matches).

[0166] Function: Realize zero voltage switching (ZVS) and reduce switching losses.

[0167] Phase 3-4 (t2-t4, accounting for the remaining period)

[0168] Phase 3 (t2-t3): S5 is turned on, S8 is turned off, and the Ls current continues to flow through S5.

[0169] Phase 4 (t3-t4): S6 is turned on, S7 is turned off, and the Ls current continues to flow through S6, completing half a cycle of energy transfer.

[0170] 4. Experimental verification and data analysis;

[0171] 4.1 Experimental platform construction

[0172] Hardware configuration:

[0173] Input power: adjustable DC source (0-120V / 50A);

[0174] Load: electronic load (0-1000V / 10A);

[0175] Measurement equipment: High-precision power analyzer (Yokogawa WT1800), bandwidth 5 MHz.

[0176] Control board design: Main control chip: DSPTMS320F28379D; Drive circuit: Isolated gate driver (ADuM4135), propagation delay <50ns.

[0177] 4.2 Key experimental data

[0178] Forward Boost Mode (V L =96V): output voltage V H =700V, error <1%;

[0179] Clamp capacitor voltage V Cs =245V, which is close to the theoretical value of 96 / (1-0.7)=240V;

[0180] Efficiency curve: 97.5% efficiency at 1kW, peak efficiency 98.18% at 3kW.

[0181] Reverse Buck Mode (V H =700V): Input current ripple <5%, verifying the low ripple feature; the peak transmission inductor current is reduced from 50A to 35A, a 30% reduction.

[0182] 4.3 Waveform and efficiency analysis

[0183] Figure 5 : V in A3 mode ab With V cd The waveforms overlap to verify voltage matching;

[0184] Figure 6 : The efficiency curve shows that the efficiency is >95% at light load (0.5kW) and reaches 98.18% at heavy load (3kW).

[0185] 5. Optimization and variant design

[0186] 5.1 Parameter Optimization Suggestions

[0187] Boost inductor L: If the input voltage range is extended to 150V, L needs to be increased to 300μH to suppress current ripple.

[0188] Switching frequency: If GaN devices are used, the frequency can be increased to 100kHz, further reducing the size of magnetic components.

[0189] 5.2 Variant Design

[0190] Multi-phase interleaved topology: Parallel multi-phase converters share current stress and is suitable for high-power (>10kW) scenarios.

[0191] Digital control enhancement: Add artificial intelligence algorithms (such as neural networks) to predict load changes and dynamically optimize and

[0192] 5.3 Security Protection Mechanism

[0193] Overcurrent protection: real-time monitoring L and i Ls , exceeding a threshold (such as 120% of the rated value) triggers shutdown.

[0194] Thermal management: Install a temperature sensor (PT100) on the radiator. If the temperature is >85°C, reduce the switching frequency or power level.

[0195] 6. Application Scenario Examples

[0196] 6.1 New Energy Storage System

[0197] Function: Serves as a bidirectional interface in photovoltaic systems to enable battery charging and discharging and grid feeding.

[0198] Parameter adaptation: The input voltage matches the lithium battery pack (72-144V), and the output voltage adapts to the DC bus (600-800V).

[0199] 6.2 Electric Vehicle Fast Charging Station

[0200] Function: Supports vehicle-to-grid (V2G) interaction, feeding vehicle battery energy back to the grid.

[0201] Efficiency requirements: Full load efficiency > 97% to meet the national standard for charging piles (GB / T18487.1-2015).

[0202] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A three-level current-source push-pull bidirectional DC-DC converter, characterized in that: include: The low-voltage side circuit includes a boost inductor L, an active clamp circuit (S3, S4, Cs), and the primary winding of a push-pull transformer Tr; The high-voltage side circuit adopts a three-level half-bridge structure, consisting of four switching tubes (S5-S8), a flying capacitor (Cf) and two voltage-doubling capacitors (Co1 and Co2); The transmission inductor (Ls) is connected to the secondary side of the push-pull transformer to achieve bidirectional energy transmission; The control unit adopts PWM+phase shift compound control strategy, by adjusting the duty cycle D and the phase shift between bridges Compared with the bridge inward movement Achieve precise control of power transmission direction and size.

2. The three-level current-source push-pull bidirectional DC-DC converter according to claim 1, characterized in that: The clamping capacitor voltage (V Cs ) and input voltage (V L ) is: Where D is the duty cycle of the low-voltage side switch.

3. The three-level current-source push-switch bidirectional DC-DC converter according to claim 1, characterized in that: The output voltage of the high-voltage side circuit (V H ) and input voltage (V L ) is: Among them, n is the transformer turns ratio, n1:n2:n3=7:7:

20.

4. The three-level current-source push-pull bidirectional DC-DC converter according to claim 1, characterized in that: The transmission inductor current (i Ls ) in A3 mode is: Among them, V H is the high-voltage side voltage, L s is the transmission inductance, f s is the switching frequency, D is the duty cycle, Compared with the bridge displacement, Compared to the inward movement of the bridge.

5. The three-level current-source push-pull bidirectional DC-DC converter according to claim 1, characterized in that: The power expression of the transmission power P in A3 mode is: Where n is the transformer turns ratio, V L is the low-side voltage, V H is the high-voltage side voltage, L s is the transmission inductance, f s is the switching frequency, D is the duty cycle, Compared with the bridge displacement, Compared to the inward movement of the bridge.

6. The three-level current-source push-pull bidirectional DC-DC converter according to claim 1, characterized in that: The converter is divided into 8 working modes (A1-A4, B1-B4) during forward power transmission, and the power per unit value P in each mode is * The expression is: A3 Mode: In B2 mode: In A1 mode: In B4 mode: In A4 mode: Where D is the duty cycle, Compared with the bridge displacement, Compared to the inward movement of the bridge.

7. The three-level current-source push-pull bidirectional DC-DC converter according to claim 1, characterized in that: The transmission inductor current (i Ls ) The expressions in stages 1-4 are: Phase 1 (t0-t1): Phase 2 (t1-t2): Phase 3 (t2-t3): Phase 4 (t3-t4): Among them, V H is the high-voltage side voltage, L s is the transmission inductance, f s is the switching frequency, D is the duty cycle, Compared with the bridge displacement, Compared to the inward movement of the bridge.

8. The three-level current-source push-pull bidirectional DC-DC converter according to claim 1, characterized in that: The power transfer characteristics of the converter in A3 mode satisfy the following relationship: Where n is the transformer turns ratio, V L is the low-side voltage, V H is the high-voltage side voltage, L s is the transmission inductance, f s is the switching frequency, D is the duty cycle, Compared with the bridge displacement, Compared to the inward movement of the bridge.

9. The three-level current-source push-pull bidirectional DC-DC converter according to claim 1, characterized in that: The transmission inductor current (i Ls ) in A3 mode is: Among them, V H is the high-voltage side voltage, L s is the transmission inductance, f s is the switching frequency, D is the duty cycle, Compared with the bridge displacement, Compared to the inward movement of the bridge.

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