A dual-cllc converter based on modulated coupled inductance for improving bidirectional light load efficiency
By employing modulated coupled inductor technology in the CLLC converter, the switching sequence and the equivalent inductance value of the coupled inductor are changed, enabling switching between full-bridge series and half-bridge parallel modes. This solves the problems of high switching losses and narrow frequency range under light load, improves the efficiency and gain of electric vehicle energy storage systems, and is suitable for bidirectional energy transmission in electric vehicles.
Patent Information
- Application Number
- CN202610655547.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-05-13
- Publication Date
- 2026-07-31
AI Technical Summary
Traditional CLLC converters have large switching currents under light loads with wide input voltage and bidirectional full load ranges, which increases switching losses and makes it difficult to improve efficiency. In addition, they have a narrow operating frequency range and limited gain range.
By employing modulated coupled inductor technology, the system switches between full-bridge series mode and half-bridge parallel mode by changing the switching sequence and the equivalent inductance value of the coupled inductor, achieving a wide range of voltage gain and efficiency improvement, and enabling all switching transistors to achieve zero-voltage switching.
It significantly improves efficiency across the entire bidirectional load range, achieves wide-range voltage gain, reduces turn-off losses and reactive circulating current losses, and is suitable for scenarios such as on-board chargers, vehicle-to-grid, and grid-to-vehicle connections, without requiring additional hardware.
Smart Images
Figure CN122495860A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of DC-DC converters, and in particular to a dual CLLC converter based on a modulated coupled inductor to improve bidirectional light-load efficiency. Background Technology
[0002] With the rapid development of the electric vehicle industry and the continuous advancement of vehicle-to-grid (V2G) technology, the role of electric vehicle energy storage systems in energy management is becoming increasingly important. Especially in applications such as on-board chargers (OBC), vehicle-to-grid (V2G), and grid-to-vehicle (G2V), electrical energy needs to be efficiently and reliably transmitted bidirectionally between the grid and the power battery. This places higher demands on the efficiency, power density, and bidirectional operation capability of power conversion systems. The Dual CLLC Converter with Enhanced Bidirectional Light-Load Efficiency Based on Modulated Coupling Inductors (D-MCI-CLLC), a novel topology, significantly improves efficiency and adaptability across the entire bidirectional load range by flexibly switching resonant modes, making it a current research hotspot for high-density power solutions. While traditional CLLC converters offer advantages such as symmetrical primary and secondary sides, ease of bidirectional energy transfer, and soft-switching capabilities, they suffer from limitations in electric vehicle energy storage system charging and discharging scenarios across a wide input voltage range and bidirectional full load: high turn-off current of the switching transistors under light loads leads to increased switching losses and hinders efficiency improvement. Therefore, there is an urgent need for a design method for CLLC topologies that can effectively alter the circuit's equivalent inductance without introducing external components, inheriting soft-switching and wide-gain characteristics, addressing the efficiency loss caused by bidirectional operation under both light and heavy loads, and ultimately achieving a balance between efficiency and wide-gain optimization. Summary of the Invention
[0003] The main objective of this invention is to address the problems of narrow operating frequency range, limited gain range, and low efficiency under light load in traditional full-bridge CLLC topologies. It proposes a dual CLLC topology that utilizes coupled inductor modulation technology to change the switching sequence, allowing the converter to operate in either full-bridge series mode or half-bridge parallel mode across the entire bidirectional load range. The resonant frequency can be arbitrarily configured for both operating modes. When the resonant frequencies differ, by appropriately adjusting the coupled inductor, full-bridge buck and half-bridge boost voltages can be achieved within a narrow switching frequency range, thus achieving a wide-range voltage gain. Furthermore, the operating mode can be switched according to light or heavy load conditions to improve the converter's efficiency across the entire range while maintaining a wide gain.
[0004] The objective of this invention is achieved through the following technical solution: A dual CLLC converter based on modulated coupled inductors to improve bidirectional light-load efficiency includes an input power supply, split capacitors, an inverter unit, a first resonant cavity, a second resonant cavity, a first transformer, a second transformer, a third resonant cavity, a fourth resonant cavity, a rectifier unit, a filter capacitor, and an output terminal. The split capacitor is composed of a first capacitor and a second capacitor connected in series, with N nodes between the first capacitor and the second capacitor. The inverter unit consists of two bridge arms connected in parallel. Each bridge arm consists of two switching transistors connected in series. Nodes A and B are respectively provided between the two switching transistors in each bridge arm. The input power supply is connected in parallel with the split capacitor and the two bridge arms in sequence. The opposite-named end of the primary winding of the first transformer is connected to the same-named end of the primary winding of the second transformer to form node E; the opposite-named end of the secondary winding of the first transformer is connected to the same-named end of the secondary winding of the second transformer to form node F. Node A is connected sequentially to the same-named terminals of the first resonant cavity and the primary winding of the first transformer. Node B is connected in sequence to the opposite ends of the second resonant cavity and the primary winding of the second transformer. Node N and Node E are interconnected; The rectifier unit consists of two rectifier branches connected in parallel. Each rectifier branch consists of two switching transistors connected in series. A C node and a D node are respectively provided between the two switching transistors in each rectifier branch. The filter capacitor is connected in parallel with the two rectifier branches and then connected to the output terminal. The filter capacitor is composed of the third capacitor and the fourth capacitor connected in series, and there is an O node between the third capacitor and the fourth capacitor. The same-named terminals of the secondary winding of the first transformer are connected in sequence to the third resonant cavity and node C, and the opposite-named terminals of the secondary winding of the second transformer are connected in sequence to the fourth resonant cavity and node D. Node O and Node F are interconnected; The inductors in the first, second, third, and fourth resonant cavities are coupled inductors, wherein the first and third resonant cavities constitute the first resonant network, and the second and fourth resonant cavities constitute the second resonant network.
[0005] Furthermore, the turns ratio of both the first and second transformers is n:1, and the magnetizing inductances of the first and second transformers are respectively... L m1 and L m2 .
[0006] Furthermore, the first resonant cavity is composed of a first resonant capacitor and a coupling inductor connected in series, the second resonant cavity is composed of a second resonant capacitor and a coupling inductor connected in series, the third resonant cavity is composed of a third resonant capacitor and a coupling inductor connected in series, and the fourth resonant cavity is composed of a fourth resonant capacitor and a coupling inductor connected in series.
[0007] Furthermore, the coupling coefficient of the coupled inductor is set according to different operating conditions. The equivalent inductance value of the coupled inductor is changed by changing the switching sequence of the inverter unit switching transistors, so as to switch all resonant inductor parameters under light and heavy loads in bidirectional operation.
[0008] Furthermore, by setting different switching sequences for the switching transistors, the converter can operate in either full-bridge series mode or half-bridge parallel mode in both directions.
[0009] Furthermore, in full-bridge series mode, the converter's inductance ratio is increased and the quality factor is decreased to reduce the turn-off current under light load and improve light load efficiency.
[0010] Furthermore, in the half-bridge parallel mode, the converter's quality factor increases to expand the voltage gain range under heavy load and improve heavy load efficiency.
[0011] Furthermore, all switching transistors can achieve zero-voltage switching (ZVS).
[0012] Compared with the prior art, the beneficial effects of the technical solution of the present invention are: 1. High efficiency under light load: In the bidirectional full-bridge series mode, by reducing the equivalent inductance of the coupling inductor and increasing the circuit inductance ratio ( k and reducing the quality factor ( Q This significantly reduces turn-off losses and reactive circulating current losses, thereby improving the light load rate.
[0013] 2. High efficiency under heavy load: In the half-bridge parallel mode, by increasing the equivalent inductance value of the coupling inductor and reducing the circuit inductance ratio ( k ) and increase the quality factor ( Q This can broaden the voltage gain range, effectively reduce heavy-load switching losses, and improve heavy-load efficiency.
[0014] 3. Wide range gain: By flexibly switching between full-bridge series and half-bridge parallel modes, it can simultaneously meet the requirements of boost and buck conversion within a narrow switching frequency range, achieving a wide output gain with a wide input voltage range. It is suitable for scenarios such as on-board charger (OBC), vehicle-to-grid (V2G), and grid-to-vehicle (G2V).
[0015] 4. Continuous gain: The half-bridge parallel mode is equivalent to a half-bridge CLLC voltage multiplier circuit, and the full-bridge series mode is equivalent to a full-bridge CLLC circuit. The gain at the resonant point (where the switching frequency equals the resonant frequency) is 1, and the gain changes continuously during the mode switching process.
[0016] 5. Bidirectional high-efficiency operation: Through the symmetrical structure of CLLC, by changing the switching sequence of the primary and secondary sides, the two modes can be freely switched in both directions across the full load range, thereby improving the efficiency of the converter across the entire range while achieving a wide gain.
[0017] 6. Zero-voltage switching: All switching transistors can achieve ZVS in any operating mode, which can reduce switching losses and improve converter efficiency.
[0018] 7. Advantages of magnetic integration: The four ordinary resonant inductors in the primary and secondary resonant cavities of the transformer are replaced with two adjustable coupled inductors, which are integrated with the split capacitors and two transformers to reduce the impact of parasitic parameters on resonant performance and improve power density and reliability.
[0019] 8. No additional components required: This invention does not increase the number of switching transistors and diodes. It achieves mode switching only by changing the switching sequence and coupling inductor modulation technology. No additional hardware is required, which simplifies the circuit structure and reduces costs. Attached Figure Description
[0020] Figure 1 This is a schematic diagram of the dual CLLC resonant converter topology of the present invention; Figure 2 This is a schematic diagram of a traditional full-bridge CLLC converter topology; Figure 3 This is the fundamental equivalent circuit diagram of the dual CLLC converter of the present invention in full-bridge series mode; Figure 4 This is a schematic diagram of the waveforms of each switch drive, resonant cavity input voltage, resonant cavity current, and secondary current when the dual CLLC resonant converter of this invention is operating in the forward mode of the full-bridge series mode. Figure 5 This is a schematic diagram of the waveforms of each switch drive, resonant cavity input voltage, resonant cavity current, and secondary current when the dual CLLC resonant converter of this invention is operating in the forward half-bridge parallel mode. Figure 6 This is the fundamental equivalent circuit diagram of the dual CLLC converter of the present invention in half-bridge parallel mode; Figure 7 This is a schematic diagram of the switching transistor current waveform of the dual CLLC resonant converter of the present invention under light load (10% full load) during forward operation; Figure 8 This is a schematic diagram of the switching transistor current waveform of a traditional full-bridge CLLC converter under light load conditions (10% full load). Figure 9 This is a schematic diagram of the switching transistor current waveform of the dual CLLC resonant converter of the present invention under full load and forward operation. Figure 10 This is a schematic diagram of the switching transistor current waveforms of a traditional full-bridge CLLC converter under full load conditions during forward operation. Figure 11 This is a schematic diagram of the voltage gain curve of the dual CLLC resonant converter of the present invention. Detailed Implementation
[0021] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.
[0022] To address the requirements of CLLC converters in applications such as bidirectional energy storage systems, on-board chargers (OBCs) for electric vehicles, V2G energy exchange, photovoltaic energy storage interfaces, and DC microgrids for wide input / output voltage range, bidirectional energy flow, and high-efficiency power conversion, this embodiment provides a dual CLLC converter based on modulated coupled inductors to improve bidirectional light-load efficiency. Figure 1 As shown, it includes an input power supply, a split capacitor, an inverter unit, a first resonant cavity, a second resonant cavity, a first transformer, a second transformer, a third resonant cavity, a fourth resonant cavity, a rectifier unit, a filter capacitor, and an output terminal; The split capacitor consists of two input filter capacitors, namely the first capacitor. C i1 Second capacitor C i2 The first capacitor is connected in series. C i1 Second capacitor C i2 There are N nodes between them; The inverter unit consists of two bridge arms connected in parallel. One bridge arm consists of two switches Q1 and Q2 connected in series, and the other bridge arm consists of two switches Q3 and Q4 connected in series. Node A is set between switches Q1 and Q2, and node B is set between switches Q3 and Q4. The input power supply is connected in parallel with the split capacitor and the two bridge arms in sequence. The opposite-named terminals of the primary winding of the first transformer and the same-named terminals of the primary winding of the second transformer are connected to form node E; the opposite-named terminals of the secondary winding of the first transformer and the same-named terminals of the secondary winding of the second transformer are connected to form node F; the turns ratio of both the first and second transformers is n:1, and the magnetizing inductances of the first and second transformers are L and L, respectively. m1 and L m2 Node N and node E are interconnected.
[0023] Node A is connected sequentially to the corresponding terminals of the first resonant cavity and the primary winding of the first transformer; the first resonant cavity is composed of the first resonant capacitor C. r1 and the first coupled inductor L r1 Composed of series connections.
[0024] Node B is connected sequentially to the opposite-named terminals of the second resonant cavity and the primary winding of the second transformer; the second resonant cavity is composed of the second resonant capacitor C. r2 Second coupling inductor L r2 Composed of series connections.
[0025] The rectifier unit consists of two rectifier branches connected in parallel. The first rectifier branch consists of two switches Q5 and Q6 connected in series, and the second rectifier branch consists of two switches Q7 and Q8 connected in series. Node C is provided between switches Q5 and Q6, and node D is provided between switches Q7 and Q8.
[0026] The filter capacitor is connected in parallel with the two rectifier branches and then connected to the output terminal. The filter capacitor consists of two output filter capacitors, i.e., the third capacitor C. o1 and the fourth capacitor C o2 The three capacitors are connected in series, and the third capacitor C is formed by them. o1 and the fourth capacitor C o2 There is an O node between them; The same-named terminals of the secondary winding of the first transformer are connected in sequence to the third resonant cavity and node C; the opposite-named terminals of the secondary winding of the second transformer are connected in sequence to the fourth resonant cavity and node D; node O and node F are interconnected. The third resonant cavity is composed of the third resonant capacitor C. r3 and the third coupling inductor L r3 The fourth resonant cavity is composed of a fourth resonant capacitor C, which is connected in series. r4 and the fourth coupling inductor L r4 Composed of series connections.
[0027] Preferably, the topology proposed in this embodiment can switch between full-bridge series mode and half-bridge parallel mode by changing the switching sequence. A traditional full-bridge CLLC converter topology is as follows: Figure 2 As shown, it consists of two full-bridge CLLC converters connected in series.
[0028] When it operates in full-bridge cascade mode, the key waveform of this mode is as follows: Figure 4 As shown in the diagram. Here, drive1 and drive3 represent the drive signals for switching transistors Q1 and Q3, respectively. i LmThe waveform shows the excitation inductor current. It can be seen that in this mode, the drive signals for Q1 and Q4 are the same, and the drive signals for Q2 and Q3 are the same; Q1 and Q2, and Q3 and Q4 are complementary in conduction. In this mode, the voltage applied to points A and N... v AN With the voltage applied at points B and N v BN Conversely, the voltage applied at points C and O v AN With the voltage applied at points D and O v BN On the contrary, therefore there is v Ci1= v Ci2= v dc / 2, due to v AN = - v BN , v CO = - v DO ,so i r1 and i r2 The directions are opposite, so that current will not flow into nodes N and O. C r1 , C r2 , L r1 , L r2 Together they form a resonant cavity. C i1 , C i2 Together they form the input filter capacitor. C o1 , C o2 Together, they form the output filter capacitor. The mathematical model for the two positively coupled inductors in this converter can be expressed as: (1) (2) In the formula, v L1 and v L2 These are the voltages on the two windings of the primary-side coupled inductor, respectively. v L3 and vL4 These are the voltages on the two windings of the secondary-coupled inductor, respectively. L r1 and L r2 The self-inductance of the primary-side coupled inductor L r3 and L r4 For the self-inductance of the secondary-side coupled inductor, M This is the mutual inductance of the coupled inductors. Due to the symmetry of the converter... L r1 = L r2 = L r3 = L r4 = L r , L r This represents a resonant inductor; in this mode, i r1 and i r2 The amplitude and direction of the vibration are opposite, that is... i r1 = - i r2 Substituting into (1), we get: (3) (4) The equivalent resonant inductance of the dual CLLC in this mode is Let the coupling coefficient The resonant frequency of the converter is: (5) Representing the resonant capacitor, the fundamental equivalent circuit of a dual CLLC converter in full-bridge series mode based on modulated coupling inductors to improve bidirectional light-load efficiency is shown below. Figure 3 As shown, where u i,FHA It is the input voltage. i r,FHA It is the total current in the resonant cavity, which is composed of the first resonant network and the second resonant network connected in series. u o,FHA It is a secondary voltage. i rec It is the rectifier current. R o,acThis is the equivalent load resistance. In this mode, the two resonant networks are connected in series, equivalent to a full-bridge CLLC. The first and third resonant cavities constitute the first resonant network, and the second and fourth resonant cavities constitute the second resonant network located on the secondary side of the transformer.
[0029] The characteristic impedance of the full-bridge series mode is expressed as: (6) in f r This is the resonant frequency in the full-bridge series mode.
[0030] Let the quality factor Q The ratio of characteristic impedance to equivalent resistance: (7) make: (8) (9) in Angular velocity, n This refers to the transformer turns ratio.
[0031] At this time, the inductance of the circuit is... Quality factor Equivalent AC resistance , R o This represents the circuit load resistance. Compared to a traditional full-bridge CLLC circuit, this circuit has a larger inductance ratio and a smaller quality factor.
[0032] When it operates in half-bridge parallel mode, the key waveform of this mode is as follows: Figure 5 As shown. It can be seen that in this mode, the drive signals for Q1 and Q3 are the same, and the drive signals for Q2 and Q4 are the same; Q1 and Q2, and Q3 and Q4 are complementary in conduction. In this mode, because... v AN = v BN , v CO = v DO ,so i r1 and i r2 The directions are the same. C i1 , C i2 , C r1 , C r2 ,L r1 , L r2 They participate in resonance together. In this mode, i r1 and i r2 The amplitude and direction of the vibration are the same, that is... i r1 = i r2 Substituting (1) and (2), we get: (10) (11) The fundamental equivalent circuit of a dual CLLC converter in half-bridge parallel mode, based on modulated coupled inductors to improve bidirectional light-load efficiency, is as follows: Figure 6 As shown, where u i,FHA It is the input voltage. i r,FHA It is the total current in the resonant cavity formed by the parallel connection of the first and second resonant networks. u o,FHA It is a secondary voltage. i rec It is the rectifier current. R o,ac It is the equivalent load resistance. In this mode, the two resonant networks are connected in parallel, which is equivalent to two half-bridge CLLCs connected in parallel on the primary side and in parallel on the secondary side.
[0033] The characteristic impedance of the half-bridge parallel mode is expressed as: (12) in This is the resonant frequency of the half-bridge parallel mode.
[0034] Let the quality factor Q’ The ratio of characteristic impedance to equivalent resistance: (13) make: (14) (15) The equivalent resonant inductance of the dual CLLC in this mode is Let the coupling coefficient The resonant frequency of the converter is: (16) At this time, the inductance of the circuit is... Quality factor Equivalent AC resistance Compared to a typical full-bridge CLLC circuit, this circuit has a smaller inductance ratio, a wider voltage gain range, a higher quality factor, and improved efficiency.
[0035] This embodiment is based on a dual CLLC converter with symmetrical parameters that improves bidirectional light-load efficiency using modulated coupled inductors. The forward and reverse operation are the same, so the two reverse modes will not be described in detail.
[0036] The core of achieving soft switching lies in ensuring that the parasitic capacitance of the switching device has completed a full charging and discharging process before it is turned on. Based on the principle of charge conservation, the following relationship can be derived: (17) in, I r This is the current value of the switching transistor when it is turned off. T d Dead time, C oss This represents the junction capacitance between the drain and source of the switching transistor.
[0037] In the half-bridge parallel mode, when the switching frequency equals the resonant frequency, the turn-off current reaches its minimum value. At this time, the resonant current is approximately equal to the peak excitation current, i.e.: (18) The constraint condition for obtaining the magnetizing inductance is: (19) Similarly, in the full-bridge series mode, the constraint condition for the magnetizing inductor to achieve ZVS in this mode is: (20) because Therefore, the magnetizing inductance required to achieve ZVS in the half-bridge parallel mode is smaller, which means that the magnetizing inductance in the half-bridge parallel mode is sufficient to achieve ZVS in the full-bridge series mode.
[0038] The formula for the input impedance in the half-bridge parallel mode is: (twenty one) The necessary condition for achieving soft switching is that its resonant part exhibits inductive characteristics. Setting the imaginary part of the input impedance to zero, i.e., setting the imaginary part of equation (21) to 0, the resonant cavity exhibits resistive characteristics, which can be obtained as follows: (twenty one) in k x The circuit inductance ratio, x The values are 1 and 2; f n The normalized frequency is the ratio of the switching frequency to the resonant frequency.
[0039] Differentiating formula (21) and setting it to 0, we can obtain the following: hour, Q It has a maximum value: (twenty two) Will Q Substituting 0 into the voltage gain expression yields the inductance ratio. k Maximum value: (twenty three) in, M min This represents the minimum value of the voltage gain. f nmax This represents the maximum value of the normalized frequency.
[0040] Therefore, in order to comprehensively consider both converter switching losses and soft-switching implementation, and thus improve the overall efficiency of the CLLC converter, the inductance ratio... k The selection of numerical values requires a trade-off, and should be based on good frequency modulation capability and gain characteristics.
[0041] Next, select k Substitute value Finding the quality factor Q The maximum value of Q should be selected, and the largest possible Q value should be chosen based on the frequency modulation range and gain capability.
[0042] Finally, the resonant inductance value is obtained using formula (13). L r The resonant capacitance can be calculated using formula (16). C r .
[0043] like Figure 7 As shown in the figure, IQ1_D-MCI-CLLC is the current waveform of the Q1 transistor of the converter proposed in this embodiment under light load (10% full load). It can be seen from the figure that its turn-off current is about 5.45A. Figure 8 The figure shows the current waveform of transistor Q1 in a traditional full-bridge CLLC converter topology (without coupling and identical parameters) under light load (10% full load). As can be seen from the figure, its turn-off current is approximately 6.6A. Due to the implementation of soft switching, its turn-off loss and reactive circulating current loss are the main losses. The reactive circulating current and turn-off current can be effectively suppressed through the coupling inductor, resulting in higher efficiency under light load, as shown in the simulation.
[0044] like Figure 9 The figure shows the current waveform of transistor Q1 under full load of the converter proposed in this embodiment. As can be seen from the figure, its turn-off current is about 5.49A. Figure 10The figure shows the current waveform of transistor Q1 in a traditional full-bridge CLLC converter topology under the same full-load power. As can be seen from the figure, its turn-off current is approximately 6.73A. Due to the implementation of soft switching, turn-off loss and reactive circulating current loss are the main losses. A larger inductance can effectively suppress reactive circulating current and turn-off current, resulting in higher efficiency under light load, as shown in the simulation. Under heavy load, the current is high, and switching loss becomes the main loss. Simulation results show that the topology proposed in this embodiment has a smaller turn-off current and higher efficiency under heavy load.
[0045] The design parameters for this embodiment are shown in Table 1.
[0046] Table 1 The normalized voltage gain curves of the topology proposed in this embodiment in half-bridge parallel mode and full-bridge series mode are as follows: Figure 11 As shown.
[0047] In summary, the topology proposed in this embodiment effectively solves the efficiency loss problem caused by light and heavy loads, and ultimately balances the optimization problem of efficiency and wide gain.
[0048] This invention is not limited to the embodiments described above. The above description of specific embodiments is intended to illustrate and explain the technical solutions of this invention. The specific embodiments described above are merely illustrative and not restrictive. Without departing from the spirit and scope of the claims, those skilled in the art can make many specific modifications based on the teachings of this invention, and these modifications all fall within the scope of protection of this invention.
Claims
1. A dual CLLC converter with improved bidirectional light-load efficiency based on modulated coupled inductors, characterized in that, It includes an input power supply, a split capacitor, an inverter unit, a first resonant cavity, a second resonant cavity, a first transformer, a second transformer, a third resonant cavity, a fourth resonant cavity, a rectifier unit, a filter capacitor, and an output terminal; The split capacitor is composed of a first capacitor and a second capacitor connected in series, with N nodes between the first capacitor and the second capacitor. The inverter unit consists of two bridge arms connected in parallel. Each bridge arm consists of two switching transistors connected in series. Nodes A and B are respectively provided between the two switching transistors in each bridge arm. The input power supply is connected in parallel with the split capacitor and the two bridge arms in sequence. The opposite-named end of the primary winding of the first transformer is connected to the same-named end of the primary winding of the second transformer to form node E; the opposite-named end of the secondary winding of the first transformer is connected to the same-named end of the secondary winding of the second transformer to form node F. Node A is connected sequentially to the same-named terminals of the first resonant cavity and the primary winding of the first transformer. Node B is connected in sequence to the opposite ends of the second resonant cavity and the primary winding of the second transformer. Node N and Node E are interconnected; The rectifier unit consists of two rectifier branches connected in parallel. Each rectifier branch consists of two switching transistors connected in series. A C node and a D node are respectively provided between the two switching transistors in each rectifier branch. The filter capacitor is connected in parallel with the two rectifier branches and then connected to the output terminal. The filter capacitor is composed of the third capacitor and the fourth capacitor connected in series, and there is an O node between the third capacitor and the fourth capacitor. The same-named terminals of the secondary winding of the first transformer are connected in sequence to the third resonant cavity and node C, and the opposite-named terminals of the secondary winding of the second transformer are connected in sequence to the fourth resonant cavity and node D. Node O and Node F are interconnected; The inductors in the first, second, third, and fourth resonant cavities are coupled inductors, wherein the first and third resonant cavities constitute the first resonant network, and the second and fourth resonant cavities constitute the second resonant network.
2. The dual CLLC converter for improving bidirectional light-load efficiency according to claim 1, characterized in that, The turns ratio of both the first and second transformers is n:1, and the magnetizing inductances of the first and second transformers are respectively... L m1 and L m2 .
3. The dual CLLC converter for improving bidirectional light-load efficiency according to claim 1, characterized in that, The first resonant cavity is composed of a first resonant capacitor and a coupling inductor connected in series; the second resonant cavity is composed of a second resonant capacitor and a coupling inductor connected in series; the third resonant cavity is composed of a third resonant capacitor and a coupling inductor connected in series; and the fourth resonant cavity is composed of a fourth resonant capacitor and a coupling inductor connected in series.
4. The dual CLLC converter for improving bidirectional light-load efficiency according to claim 1, characterized in that, The coupling coefficient of the coupled inductor is set according to different operating conditions. The equivalent inductance value of the coupled inductor is changed by changing the switching sequence of the inverter unit switching transistors, so as to switch all resonant inductor parameters under light and heavy loads in bidirectional operation.
5. The dual CLLC converter for improving bidirectional light-load efficiency according to claim 1, characterized in that, By setting different switching sequences for the switching transistors, the converter can operate in either full-bridge series mode or half-bridge parallel mode in both directions.
6. The dual CLLC converter for improving bidirectional light-load efficiency according to claim 5, characterized in that, In full-bridge series mode, the converter's inductance ratio increases and its quality factor decreases, thereby reducing the turn-off current under light load and improving light load efficiency.
7. The dual CLLC converter for improving bidirectional light-load efficiency according to claim 5, characterized in that, In half-bridge parallel mode, the converter's quality factor increases, thereby expanding the voltage gain range under heavy load and improving heavy load efficiency.
8. The dual CLLC converter for improving bidirectional light-load efficiency according to claim 1, characterized in that, All switching transistors can achieve zero-voltage switching (ZVS).