SiC-based three-phase interleaved bidirectional LLC direct current conversion system and control method

Abstract

The application provides a SiC-based three-phase interleaved bidirectional LLC direct-current conversion system and a control method in the field of power electronics, and the system comprises at least two power conversion units, the input ends of the power conversion units are parallel to each other, and the output ends are connected in series or parallel through switches; the power conversion unit comprises a resonant transformer T1, a resonant transformer T2, a resonant transformer T3, a resonant inductor Lr1, a resonant inductor Lr2, a resonant inductor Lr3, a resonant capacitor Cr1, a resonant capacitor Cr2, a resonant capacitor Cr3, a capacitor C1, a capacitor C2, a SiC MOSFET tube Q1, a SiC MOSFET tube Q2, a SiC MOSFET tube Q3, a SiC MOSFET tube Q4, a SiC MOSFET tube Q5, a SiC MOSFET tube Q6, a SiC MOSFET tube Q7, a SiC MOSFET tube Q8, a SiC MOSFET tube Q9, a SiC MOSFET tube Q10, a SiC MOSFET tube Q11 and a SiC MOSFET tube Q12. The application has the advantages that high-frequency high efficiency, high power density and high reliability bidirectional power conversion under a fixed voltage conversion ratio are achieved, and the problems of large output current ripple and complex control strategy are solved.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a SiC-based three-phase interleaved bidirectional LLC DC-DC converter system and its control method. Background Technology

[0002] With the rapid development of electric vehicle charging infrastructure, energy storage systems, and DC microgrids, there is an urgent need for DC transformers (DCTs) capable of achieving efficient, high-power-density, and highly reliable bidirectional energy flow. These applications typically require the converter to operate efficiently at a relatively fixed voltage transformation ratio and place extremely high demands on the system's power density, efficiency, and current-sharing reliability during multiphase expansion.

[0003] First, regarding topology, while traditional single-phase LLC resonant converters possess soft-switching characteristics, their output current ripple is significant, necessitating large filter capacitors, which severely limits the improvement of system power density. Furthermore, to increase system capacity, a multi-module parallel architecture is often employed. However, due to parameter deviations and uneven load distribution between independent modules, complex active current sharing control circuits or algorithms are typically required. This not only increases system complexity and cost but also reduces system reliability.

[0004] Secondly, at the device level, traditional silicon-based (Si) switching devices are limited by their switching losses and parasitic parameters, making it difficult to significantly increase their operating frequency. This results in larger sizes of magnetic components (such as transformers and inductors), restricting the high-frequency and compact design of the system. For applications that require fixed voltage transformation and extreme efficiency, the performance bottleneck of traditional solutions at high frequencies is particularly prominent.

[0005] Furthermore, in terms of control strategy, existing bidirectional LLC converters typically employ frequency conversion control to achieve wide voltage range regulation. However, during frequency conversion, it is difficult to guarantee that all switches can achieve optimal soft switching across the entire range, and electromagnetic interference may be introduced. More importantly, for multiphase structures, the current sharing characteristics under frequency conversion control deteriorate with frequency shift. In addition, if diodes are used in the rectification stage on the secondary side of the converter, the conduction losses are relatively large; if synchronous rectification is used, complex timing control is required to adapt to changing switching frequencies and duty cycles to ensure soft switching characteristics. The complex control strategy increases the difficulty of implementation and the risk of failure.

[0006] Therefore, how to provide a SiC-based three-phase interleaved bidirectional LLC DC-DC converter system and control method to achieve high-frequency, high-efficiency, high-power-density, and high-reliability bidirectional power conversion at a fixed voltage conversion ratio, and solve the problems of large output current ripple and complex control strategies, has become an urgent technical problem to be solved. Summary of the Invention

[0007] The technical problem to be solved by this invention is to provide a SiC-based three-phase interleaved bidirectional LLC DC-DC converter system and control method, which realizes high-frequency, high-efficiency, high-power-density, and high-reliability bidirectional power conversion under a fixed voltage conversion ratio, and solves the problems of large output current ripple and complex control strategy.

[0008] In a first aspect, the present invention provides a SiC-based three-phase interleaved bidirectional LLC DC-DC converter system, comprising: At least two power conversion units, the input terminals of each power conversion unit are connected in parallel, and the output terminals are connected in series or in parallel through switches; The power conversion unit includes a resonant transformer group, a resonant inductor group, a resonant capacitor group, a SiC MOSFET group, a capacitor C1, and a capacitor C2. The resonant transformer group includes a resonant transformer T1, a resonant transformer T2, and a resonant transformer T3; the resonant inductor group includes a resonant inductor Lr1, a resonant inductor Lr2, and a resonant inductor Lr3; the resonant capacitor group includes a resonant capacitor Cr1, a resonant capacitor Cr2, and a resonant capacitor Cr3; the SiC MOSFET group includes a SiC MOSFET Q1, a SiC MOSFET Q2, a SiC MOSFET Q3, a SiC MOSFET Q4, a SiC MOSFET Q5, a SiC MOSFET Q6, a SiC MOSFET Q7, a SiC MOSFET Q8, a SiC MOSFET Q9, a SiC MOSFET Q10, a SiC MOSFET Q11, and a SiC MOSFET Q12. The primary winding of the resonant transformer T1 is connected to one end of the resonant inductor Lr1, and the primary winding of T1 is connected to the primary windings of the resonant transformer T2 and T3. The secondary winding is connected to the source of the SiC MOSFET Q7 and the drain of the SiC MOSFET Q10, and the secondary winding is connected to the secondary windings of the resonant transformer T2 and T3. The primary winding of the resonant transformer T2 is connected to one end of the resonant inductor Lr2, and the secondary winding is connected to the source of the SiC MOSFET Q8 and the drain of the SiC MOSFET Q11. The primary winding of the resonant transformer T3 is connected to one end of the resonant inductor Lr3, and the secondary winding is connected to the source of the SiC MOSFET Q9 and the drain of the SiC MOSFET Q12. One end of capacitor C2 is connected to the drain of SiC MOSFET Q7, the drain of SiC MOSFET Q8 and the drain of SiC MOSFET Q9, and the other end is connected to the source of SiC MOSFET Q10, the source of SiC MOSFET Q11 and the source of SiC MOSFET Q12. One end of the capacitor C1 is connected to the drain of SiC MOSFET Q1, the drain of SiC MOSFET Q2 and the drain of SiC MOSFET Q3, and the other end is connected to the source of SiC MOSFET Q4, the source of SiC MOSFET Q5 and the source of SiC MOSFET Q6. One end of the resonant capacitor Cr1 is connected to the other end of the resonant inductor Lr1, and the other end is connected to the source of SiC MOSFET Q1 and the drain of SiC MOSFET Q4. One end of the resonant capacitor Cr2 is connected to the other end of the resonant inductor Lr2, and the other end is connected to the source of SiC MOSFET Q2 and the drain of SiC MOSFET Q5. One end of the resonant capacitor Cr3 is connected to the other end of the resonant inductor Lr3, and the other end is connected to the source of SiC MOSFET Q3 and the drain of SiC MOSFET Q6.

[0009] Furthermore, the capacitor C1 is a polarized capacitor, with its positive terminal connected to the drain of the SiC MOSFET Q1 and its negative terminal connected to the source of the SiC MOSFET Q4.

[0010] Furthermore, the SiC MOSFETs Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9, Q10, Q11, and Q12 are all NMOS transistors.

[0011] Furthermore, the input terminals of each power conversion unit are connected in parallel through capacitor C1.

[0012] Furthermore, the output terminals of each power conversion unit are connected in series or in parallel via a switch and a capacitor C2.

[0013] Secondly, the present invention provides a control method for a SiC-based three-phase interleaved bidirectional LLC DC-DC converter system, comprising the following steps: The SiC MOSFET group is controlled in an open-loop fixed-frequency manner so that it operates at the inherent resonant frequency of the resonant network composed of the resonant transformer group, the resonant inductor group, and the resonant capacitor group. The inherent resonant frequency is determined by the excitation inductance of the resonant transformer group, the resonant inductor group, and the resonant capacitor group, realizing stable voltage transformation with a constant circuit gain of 1 and bidirectional free flow of energy. The phase difference between the three-phase bridge arm drive signals of the control power conversion unit is 120° to reduce the current ripple on the input and output sides. The secondary-side SiC MOSFETs Q7, Q8, Q9, Q10, Q11, and Q12 are controlled to operate synchronously with the primary-side SiC MOSFETs Q1, Q2, Q3, Q4, Q5, and Q6, so that the SiC MOSFETs Q7, Q8, Q9, Q10, Q11, and Q12 operate in synchronous rectification mode to reduce conduction losses.

[0014] The advantages of this invention are: 1. By adopting a three-phase interleaved bidirectional LLC topology with SiC MOSFETs as the core device and combining it with an open-loop fixed-frequency control strategy, a high-performance target with a fixed voltage conversion ratio is achieved. Specifically, SiC MOSFETs lay the foundation for high-frequency operation of the system, significantly reducing the size of magnetic components and thus improving power density. The three-phase interleaved topology (power conversion unit) itself achieves mutual cancellation of input and output current ripples through a 120° phase difference drive, effectively reducing current ripple and dependence on filter capacitors, further improving power density. Its integrated structure also achieves natural current sharing among the three phases, improving reliability. The open-loop fixed-frequency control fixes the operating point at the resonant frequency, ensuring that the circuit gain is always 1 and achieving soft switching across the entire load range. This not only simplifies the control strategy and avoids current sharing and EMI problems caused by frequency conversion, but also allows the secondary-side SiC MOSFETs to operate in synchronous rectification mode with a simple drive method that is completely synchronized with the primary-side SiC MOSFETs, significantly reducing conduction losses. Ultimately, this achieves high-frequency, high-efficiency, high-power-density, and high-reliability bidirectional power conversion.

[0015] 2. Using SiC MOSFETs as switching devices, SiC material has high critical electric field strength, high electron saturation drift velocity, and high thermal conductivity, enabling the device to operate at high frequencies and reducing switching and conduction losses. Combined with the soft-switching characteristics of LLC resonant topology, the system can achieve zero-voltage switching (ZVS) or zero-current switching (ZCS) in both bidirectional energy flows, thereby significantly improving conversion efficiency. In addition, high-frequency operation allows the use of smaller resonant components (such as transformers and inductors), increasing the power density of the system and making it suitable for applications that are sensitive to size and weight, such as electric vehicles or data center power supplies.

[0016] 3. By using a three-phase interleaved structure, the phase difference of the three-phase bridge arm drive signals is controlled by 120°, so that the current ripple of each phase cancels each other in the time domain, significantly reducing the total current ripple on the input and output sides. This reduces the capacity requirements of filter capacitors and inductors, and reduces the size, cost and loss of passive components. At the same time, the smooth current waveform helps to improve system stability and meet the standards with strict electromagnetic compatibility (EMI) requirements, such as industrial or automotive electronic applications.

[0017] 4. The control method adopts an open-loop fixed-frequency approach, which keeps the system operating at the inherent resonant frequency determined by the resonant network (resonant transformer, inductor, and capacitor), achieving a constant circuit gain of 1. This avoids the complex frequency modulation or pulse width modulation control found in traditional LLC converters, simplifies the control logic and algorithm, reduces reliance on high-precision feedback loops, and thus improves the system's reliability and anti-interference capability. Open-loop control also reduces the computational burden on the control chip, which is beneficial for reducing costs and accelerating dynamic response.

[0018] 5. The system design supports bidirectional free flow of energy between input and output, thanks to the bidirectional LLC topology and the bidirectional conduction characteristics of SiC MOSFETs. Combined with synchronous rectification control (the secondary MOSFET operates synchronously with the primary side), the system maintains high efficiency in both rectification and inverter modes, making it suitable for applications requiring energy feedback or energy storage, such as renewable energy systems, electric vehicle charging stations, or uninterruptible power supplies (UPS), thus enhancing the system's functionality and applicability.

[0019] 6. The system consists of at least two power conversion units, with the input terminals of each unit connected in parallel and the output terminals connected in series or parallel via switches. This modular architecture allows for flexible expansion of power levels and voltage ranges by increasing or decreasing the number of units to adapt to different load requirements. At the same time, the modular design improves the redundancy and maintainability of the system. The failure of a single unit does not affect the overall operation, reducing the risk of downtime. It is particularly suitable for industrial or power systems with high reliability requirements.

[0020] 7. The LLC resonant topology achieves soft switching through resonance, significantly reducing voltage and current spikes during the switching process, thereby reducing high-frequency noise and EMI; the three-phase interleaved structure further smooths the current waveform and disperses harmonic energy, making the system easier to pass electromagnetic compatibility certification. This helps reduce interference to external circuits, improves the overall system's environmental adaptability, and meets the requirements of modern electronic equipment for low-noise design.

[0021] 8. SiC MOSFETs have excellent thermal stability and high-temperature operating capability. Combined with the uniform power distribution brought by the three-phase interleaved structure, the system heat is dispersed, reducing the risk of local overheating. The modular design is also conducive to heat dissipation layout, such as improving thermal management through independent heat dissipation units. This enhances the long-term reliability and lifespan of the system, making it suitable for high-temperature or harsh environments, such as outdoor energy equipment or aerospace power supplies.

[0022] 9. Although SiC devices have a higher initial cost, their high frequency and high efficiency characteristics can reduce the cost of passive components and heat dissipation systems, achieving cost optimization at the overall system level; open-loop fixed-frequency control simplifies control circuit design and reduces reliance on expensive control chips; in addition, the modular structure facilitates standardized production and testing, improves manufacturing efficiency, and is suitable for large-scale deployment. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Figure 1 This is a circuit diagram of a SiC-based three-phase interleaved bidirectional LLC DC-DC converter system according to the present invention.

[0025] Figure 2 This is a circuit diagram of the power conversion unit of the present invention.

[0026] Figure 3 This is a gain curve of the resonant network of the present invention.

[0027] Figure 4 This is a full-load test carrier diagram of the present invention in forward operation mode.

[0028] Figure 5 This is a carrier diagram of the no-load and full-load test in the reverse operation mode of the present invention. Detailed Implementation

[0029] The overall concept of the technical solution in this application embodiment is as follows: SiC MOSFETs lay the foundation for high-frequency operation, reduce the size of magnetic components, and improve power density; the three-phase interleaved topology itself, through a 120° phase difference drive, enables the input and output current ripples to cancel each other, reducing current ripple and dependence on filter capacitors, further improving power density; the integrated structure realizes natural current sharing among the three phases, improving reliability; open-loop fixed-frequency control fixes the operating point at the resonant frequency, making the circuit gain constant at 1 and ensuring soft switching across the entire load range. This not only simplifies the control strategy and avoids current sharing and EMI problems caused by frequency conversion, but also allows the secondary-side SiC MOSFETs to operate in synchronous rectification mode using a simple drive method that is completely synchronized with the primary-side SiC MOSFETs, significantly reducing conduction losses, thereby achieving high-frequency, high-efficiency, high-power-density, and high-reliability bidirectional power conversion.

[0030] Please refer to Figures 1 to 5 As shown, a preferred embodiment of the SiC-based three-phase interleaved bidirectional LLC DC-DC converter system of the present invention includes: At least two power conversion units, wherein the input terminals (defined as DC_A side) of each power conversion unit are connected in parallel, and the output terminals (defined as DC_B side) are connected through a switch (such as...). Figure 1 K1, K2_1, and K2_2 in the system can be connected in series or in parallel; this combination method can broaden the voltage range and constant power operation range of the DC_B side of the system. The power conversion unit includes a resonant transformer group, a resonant inductor group, a resonant capacitor group, a SiC MOSFET group, a capacitor C1, and a capacitor C2. The primary and secondary windings of the power conversion unit are both connected in a "Y" configuration, and the neutral point is left floating. This structure is the key to achieving automatic current sharing. The resonant transformer group includes a resonant transformer T1, a resonant transformer T2, and a resonant transformer T3; the resonant inductor group includes a resonant inductor Lr1, a resonant inductor Lr2, and a resonant inductor Lr3; the resonant capacitor group includes a resonant capacitor Cr1, a resonant capacitor Cr2, and a resonant capacitor Cr3; the SiC MOSFET group includes a SiC MOSFET Q1, a SiC MOSFET Q2, a SiC MOSFET Q3, a SiC MOSFET Q4, a SiC MOSFET Q5, a SiC MOSFET Q6, a SiC MOSFET Q7, a SiC MOSFET Q8, a SiC MOSFET Q9, a SiC MOSFET Q10, a SiC MOSFET Q11, and a SiC MOSFET Q12. The primary winding of the resonant transformer T1 is connected to one end of the resonant inductor Lr1, and the primary winding of T1 is connected to the primary windings of the resonant transformer T2 and T3. The secondary winding is connected to the source of the SiC MOSFET Q7 and the drain of the SiC MOSFET Q10, and the secondary winding is connected to the secondary windings of the resonant transformer T2 and T3. The primary winding of the resonant transformer T2 is connected to one end of the resonant inductor Lr2, and the secondary winding is connected to the source of the SiC MOSFET Q8 and the drain of the SiC MOSFET Q11. The primary winding of the resonant transformer T3 is connected to one end of the resonant inductor Lr3, and the secondary winding is connected to the source of the SiC MOSFET Q9 and the drain of the SiC MOSFET Q12. One end of capacitor C2 is connected to the drain of SiC MOSFET Q7, the drain of SiC MOSFET Q8 and the drain of SiC MOSFET Q9, and the other end is connected to the source of SiC MOSFET Q10, the source of SiC MOSFET Q11 and the source of SiC MOSFET Q12. One end of the capacitor C1 is connected to the drain of SiC MOSFET Q1, the drain of SiC MOSFET Q2 and the drain of SiC MOSFET Q3, and the other end is connected to the source of SiC MOSFET Q4, the source of SiC MOSFET Q5 and the source of SiC MOSFET Q6. One end of the resonant capacitor Cr1 is connected to the other end of the resonant inductor Lr1, and the other end is connected to the source of SiC MOSFET Q1 and the drain of SiC MOSFET Q4. One end of the resonant capacitor Cr2 is connected to the other end of the resonant inductor Lr2, and the other end is connected to the source of SiC MOSFET Q2 and the drain of SiC MOSFET Q5. One end of the resonant capacitor Cr3 is connected to the other end of the resonant inductor Lr3, and the other end is connected to the source of SiC MOSFET Q3 and the drain of SiC MOSFET Q6.

[0031] The capacitor C1 is a polarized capacitor, with its positive terminal connected to the drain of SiC MOSFET Q1 and its negative terminal connected to the source of SiC MOSFET Q4.

[0032] The SiC MOSFETs Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9, Q10, Q11, and Q12 are all NMOS transistors.

[0033] The input terminals of each power conversion unit are connected in parallel through capacitor C1.

[0034] The output terminals of each power conversion unit are connected in series or in parallel via a switch and a capacitor C2.

[0035] This invention achieves zero-voltage turn-on of the switching transistor and soft switching of the rectifier, significantly reducing switching losses. Synchronous rectification technology is used on the secondary side to further reduce conduction losses. The use of SiC MOSFETs with excellent switching characteristics supports efficient system operation at higher frequencies (e.g., 140kHz), with a measured system efficiency reaching up to 98.2%.

[0036] The unique structure of the resonant transformer, with its primary and secondary sides connected in a "Y" shape and the neutral point suspended, enables natural and automatic current sharing among the three phases and multiple conversion units. This eliminates the need for additional current sharing control circuits, simplifying system design and improving current sharing accuracy and reliability.

[0037] The use of high-frequency (above 100kHz) and SiC devices has significantly reduced the size of magnetic components such as resonant inductors and transformers. Low ripple characteristics have reduced the size of filter capacitors. The modular and compact design has resulted in higher overall power density.

[0038] By combining modular components and flexibly switching between series and parallel connections on the output side, it can adapt to a wider range of input / output voltages (e.g., 480V-960V on the DC_A side and 240V-960V on the DC_B side), providing a wider constant power operating range and a wider range of application scenarios.

[0039] A preferred embodiment of the control method for a SiC-based three-phase interleaved bidirectional LLC DC-DC converter system of the present invention includes the following steps: The SiC MOSFET group is controlled in an open-loop fixed-frequency manner so that it operates at the inherent resonant frequency of the resonant network composed of the resonant transformer group, the resonant inductor group, and the resonant capacitor group. The inherent resonant frequency is determined by the magnetizing inductance of the resonant transformer group, the resonant inductor group, and the resonant capacitor group, achieving stable voltage transformation with a constant circuit gain of 1 and bidirectional free flow of energy; bidirectional free flow of energy can be achieved without complex voltage or current closed-loop control. The phase difference between the three-phase bridge arm drive signals of the control power conversion unit is 120° to reduce the current ripple on the input and output sides. The secondary-side SiC MOSFETs Q7, Q8, Q9, Q10, Q11, and Q12 are controlled to operate synchronously with the primary-side SiC MOSFETs Q1, Q2, Q3, Q4, Q5, and Q6, so that the SiC MOSFETs Q7, Q8, Q9, Q10, Q11, and Q12 operate in synchronous rectification mode to reduce conduction losses.

[0040] By adopting a three-phase interleaved parallel technology, the three currents with a phase difference of 120° are superimposed on each other, which theoretically reduces the output current ripple to about 20% of that of the single-phase scheme, and significantly reduces the size and loss of the filter capacitor.

[0041] Let's take a 30kW bidirectional DC transformer prototype as an example: System architecture: Two identical 15kW power conversion units are used. The DC_A side is connected in parallel, and the DC_B side is switched between series (for high voltage output) or parallel (for high current output) through contactors K1 and K2.

[0042] Power conversion unit: adopts a three-phase interleaved BLLC topology, and the switching transistors Q1-Q12 are all 1200V / 32mΩ SiCMOSFETs, with a resonant frequency designed to be 140kHz.

[0043] Resonance parameter design: The resonance parameters were calculated and determined using the fundamental equivalent method. The resonant inductance Lr is 11μH, the resonant capacitor Cr is 117nF (composed of three 39nF capacitors connected in parallel), the resonant transformer turns ratio is 2:1 (14 turns on the primary side and 7 turns on the secondary side), and the magnetizing inductance Lm is 106.8μH.

[0044] Control method: Open-loop fixed-frequency control is adopted, with the switching frequency fixed at 140kHz. The controller generates six drive signals with a 120° phase difference, which drive the three-phase bridge arms respectively. The primary and secondary side switches operate synchronously to achieve synchronous rectification.

[0045] Test results: such as Figure 4 , 5 As shown in the test waveforms, under full load conditions, all switching transistors achieved zero-voltage turn-on, verifying the soft-switching characteristics. Actual test data shows that the system efficiency reached a peak of 98.2%, the power density reached 82 W / m³, and the output current ripple was significantly lower than that of the single-phase topology.

[0046] In summary, the advantages of this invention are as follows: 1. By adopting a three-phase interleaved bidirectional LLC topology with SiC MOSFETs as the core device and combining it with an open-loop fixed-frequency control strategy, a high-performance target with a fixed voltage conversion ratio is achieved. Specifically, SiC MOSFETs lay the foundation for high-frequency operation of the system, significantly reducing the size of magnetic components and thus improving power density. The three-phase interleaved topology (power conversion unit) itself achieves mutual cancellation of input and output current ripples through a 120° phase difference drive, effectively reducing current ripple and dependence on filter capacitors, further improving power density. Its integrated structure also achieves natural current sharing among the three phases, improving reliability. The open-loop fixed-frequency control fixes the operating point at the resonant frequency, ensuring that the circuit gain is always 1 and achieving soft switching across the entire load range. This not only simplifies the control strategy and avoids current sharing and EMI problems caused by frequency conversion, but also allows the secondary-side SiC MOSFETs to operate in synchronous rectification mode with a simple drive method that is completely synchronized with the primary-side SiC MOSFETs, significantly reducing conduction losses. Ultimately, this achieves high-frequency, high-efficiency, high-power-density, and high-reliability bidirectional power conversion.

[0047] 2. Using SiC MOSFETs as switching devices, SiC material has high critical electric field strength, high electron saturation drift velocity, and high thermal conductivity, enabling the device to operate at high frequencies and reducing switching and conduction losses. Combined with the soft-switching characteristics of LLC resonant topology, the system can achieve zero-voltage switching (ZVS) or zero-current switching (ZCS) in both bidirectional energy flows, thereby significantly improving conversion efficiency. In addition, high-frequency operation allows the use of smaller resonant components (such as transformers and inductors), increasing the power density of the system and making it suitable for applications that are sensitive to size and weight, such as electric vehicles or data center power supplies.

[0048] 3. By using a three-phase interleaved structure, the phase difference of the three-phase bridge arm drive signals is controlled by 120°, so that the current ripple of each phase cancels each other in the time domain, significantly reducing the total current ripple on the input and output sides. This reduces the capacity requirements of filter capacitors and inductors, and reduces the size, cost and loss of passive components. At the same time, the smooth current waveform helps to improve system stability and meet the standards with strict electromagnetic compatibility (EMI) requirements, such as industrial or automotive electronic applications.

[0049] 4. The control method adopts an open-loop fixed-frequency approach, which keeps the system operating at the inherent resonant frequency determined by the resonant network (resonant transformer, inductor, and capacitor), achieving a constant circuit gain of 1. This avoids the complex frequency modulation or pulse width modulation control found in traditional LLC converters, simplifies the control logic and algorithm, reduces reliance on high-precision feedback loops, and thus improves the system's reliability and anti-interference capability. Open-loop control also reduces the computational burden on the control chip, which is beneficial for reducing costs and accelerating dynamic response.

[0050] 5. The system design supports bidirectional free flow of energy between input and output, thanks to the bidirectional LLC topology and the bidirectional conduction characteristics of SiC MOSFETs. Combined with synchronous rectification control (the secondary MOSFET operates synchronously with the primary side), the system maintains high efficiency in both rectification and inverter modes, making it suitable for applications requiring energy feedback or energy storage, such as renewable energy systems, electric vehicle charging stations, or uninterruptible power supplies (UPS), thus enhancing the system's functionality and applicability.

[0051] 6. The system consists of at least two power conversion units, with the input terminals of each unit connected in parallel and the output terminals connected in series or parallel via switches. This modular architecture allows for flexible expansion of power levels and voltage ranges by increasing or decreasing the number of units to adapt to different load requirements. At the same time, the modular design improves the redundancy and maintainability of the system. The failure of a single unit does not affect the overall operation, reducing the risk of downtime. It is particularly suitable for industrial or power systems with high reliability requirements.

[0052] 7. The LLC resonant topology achieves soft switching through resonance, significantly reducing voltage and current spikes during the switching process, thereby reducing high-frequency noise and EMI; the three-phase interleaved structure further smooths the current waveform and disperses harmonic energy, making the system easier to pass electromagnetic compatibility certification. This helps reduce interference to external circuits, improves the overall system's environmental adaptability, and meets the requirements of modern electronic equipment for low-noise design.

[0053] 8. SiC MOSFETs have excellent thermal stability and high-temperature operating capability. Combined with the uniform power distribution brought by the three-phase interleaved structure, the system heat is dispersed, reducing the risk of local overheating. The modular design is also conducive to heat dissipation layout, such as improving thermal management through independent heat dissipation units. This enhances the long-term reliability and lifespan of the system, making it suitable for high-temperature or harsh environments, such as outdoor energy equipment or aerospace power supplies.

[0054] 9. Although SiC devices have a higher initial cost, their high frequency and high efficiency characteristics can reduce the cost of passive components and heat dissipation systems, achieving cost optimization at the overall system level; open-loop fixed-frequency control simplifies control circuit design and reduces reliance on expensive control chips; in addition, the modular structure facilitates standardized production and testing, improves manufacturing efficiency, and is suitable for large-scale deployment.

[0055] While specific embodiments of the present invention have been described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and not intended to limit the scope of the invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A SiC-based three-phase interleaved bidirectional LLC DC-DC converter system, characterized in that: include: At least two power conversion units, the input terminals of each power conversion unit are connected in parallel, and the output terminals are connected in series or in parallel through switches; The power conversion unit includes a resonant transformer group, a resonant inductor group, a resonant capacitor group, a SiC MOSFET group, a capacitor C1, and a capacitor C2. The resonant transformer group includes a resonant transformer T1, a resonant transformer T2, and a resonant transformer T3; the resonant inductor group includes a resonant inductor Lr1, a resonant inductor Lr2, and a resonant inductor Lr3; the resonant capacitor group includes a resonant capacitor Cr1, a resonant capacitor Cr2, and a resonant capacitor Cr3; the SiC MOSFET group includes a SiC MOSFET Q1, a SiC MOSFET Q2, a SiC MOSFET Q3, a SiC MOSFET Q4, a SiC MOSFET Q5, a SiC MOSFET Q6, a SiC MOSFET Q7, a SiC MOSFET Q8, a SiC MOSFET Q9, a SiC MOSFET Q10, a SiC MOSFET Q11, and a SiC MOSFET Q12. The primary winding of the resonant transformer T1 is connected to one end of the resonant inductor Lr1, and the primary winding of T1 is connected to the primary windings of the resonant transformer T2 and T3. The secondary winding is connected to the source of the SiC MOSFET Q7 and the drain of the SiC MOSFET Q10, and the secondary winding is connected to the secondary windings of the resonant transformer T2 and T3. The primary winding of the resonant transformer T2 is connected to one end of the resonant inductor Lr2, and the secondary winding is connected to the source of the SiC MOSFET Q8 and the drain of the SiC MOSFET Q11. The primary winding of the resonant transformer T3 is connected to one end of the resonant inductor Lr3, and the secondary winding is connected to the source of the SiC MOSFET Q9 and the drain of the SiC MOSFET Q12. One end of capacitor C2 is connected to the drain of SiC MOSFET Q7, the drain of SiC MOSFET Q8 and the drain of SiC MOSFET Q9, and the other end is connected to the source of SiC MOSFET Q10, the source of SiC MOSFET Q11 and the source of SiC MOSFET Q12. One end of the capacitor C1 is connected to the drain of SiC MOSFET Q1, the drain of SiC MOSFET Q2 and the drain of SiC MOSFET Q3, and the other end is connected to the source of SiC MOSFET Q4, the source of SiC MOSFET Q5 and the source of SiC MOSFET Q6. One end of the resonant capacitor Cr1 is connected to the other end of the resonant inductor Lr1, and the other end is connected to the source of SiC MOSFET Q1 and the drain of SiC MOSFET Q4. One end of the resonant capacitor Cr2 is connected to the other end of the resonant inductor Lr2, and the other end is connected to the source of SiC MOSFET Q2 and the drain of SiC MOSFET Q5. One end of the resonant capacitor Cr3 is connected to the other end of the resonant inductor Lr3, and the other end is connected to the source of SiC MOSFET Q3 and the drain of SiC MOSFET Q6.

2. The SiC-based three-phase interleaved bidirectional LLC DC-DC converter system as described in claim 1, characterized in that: The capacitor C1 is a polarized capacitor, with its positive terminal connected to the drain of the SiC MOSFET Q1 and its negative terminal connected to the source of the SiC MOSFET Q4.

3. The SiC-based three-phase interleaved bidirectional LLC DC-DC converter system as described in claim 1, characterized in that: The SiC MOSFETs Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9, Q10, Q11, and Q12 are all NMOS transistors.

4. The SiC-based three-phase interleaved bidirectional LLC DC-DC converter system as described in claim 1, characterized in that: The input terminals of each power conversion unit are connected in parallel through capacitor C1.

5. The SiC-based three-phase interleaved bidirectional LLC DC-DC converter system as described in claim 1, characterized in that: The output terminals of each power conversion unit are connected in series or in parallel via a switch and a capacitor C2.

6. A control method for a SiC-based three-phase interleaved bidirectional LLC DC-DC converter system, characterized in that: The method requires the use of the SiC-based three-phase interleaved bidirectional LLC DC-DC converter system as described in any one of claims 1 to 5, and includes the following steps: The SiC MOSFET group is controlled in an open-loop fixed-frequency manner so that it operates at the inherent resonant frequency of the resonant network composed of the resonant transformer group, the resonant inductor group, and the resonant capacitor group. The inherent resonant frequency is determined by the excitation inductance of the resonant transformer group, the resonant inductor group, and the resonant capacitor group, realizing stable voltage transformation with a constant circuit gain of 1 and bidirectional free flow of energy. The phase difference between the three-phase bridge arm drive signals of the control power conversion unit is 120° to reduce the current ripple on the input and output sides. The secondary-side SiC MOSFETs Q7, Q8, Q9, Q10, Q11, and Q12 are controlled to operate synchronously with the primary-side SiC MOSFETs Q1, Q2, Q3, Q4, Q5, and Q6, so that the SiC MOSFETs Q7, Q8, Q9, Q10, Q11, and Q12 operate in synchronous rectification mode to reduce conduction losses.

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