Hybrid three-level resonant converter circuit based on silicon carbide devices and control method thereof

Abstract

The application discloses a hybrid three-level resonant conversion circuit based on silicon carbide devices and a control method thereof, and relates to the technical field of power electronic conversion. The hybrid three-level resonant conversion circuit comprises a three-phase rectification circuit, a hybrid three-level bridge arm composed of four main switching tubes and two active clamping tubes, a resonant conversion circuit, a high-frequency isolation transformer, a secondary full-bridge rectification filter circuit and a digital control unit, and all the switching tubes are silicon carbide MOS tubes. The control method cooperatively controls each switching tube in six stages in one switching period, and introduces phase shift control at light load. The application can realize zero-current turn-on of all the main switching tubes and zero-current turn-off of the secondary rectification tubes, effectively solves the problems of uneven switching loss and excessively high voltage stress, and improves conversion efficiency and system reliability.

Description

Technical Field

[0001] This invention relates to the technical field of control circuits, and in particular to a hybrid three-level resonant converter circuit based on silicon carbide devices and its control method. Background Technology

[0002] With the rapid development of the new energy industry, DC fast charging piles and energy storage systems have placed higher demands on the efficiency, power density, and reliability of power conversion modules. Currently, power conversion modules widely adopt three-level neutral point clamped (NPC) topologies and LLC resonant topologies. The three-level NPC topology reduces device voltage stress and output harmonics through multi-level output. This is typically achieved by using multiple switches connected in series for voltage division and then using clamping diodes to bring out the midpoint potential. The LLC resonant topology utilizes the resonant characteristics of inductors and capacitors to achieve zero-current turn-on of the primary-side switch and zero-current turn-off of the secondary-side rectifier within a specific frequency range, thus achieving high conversion efficiency. In practical applications, these two topologies are often used in combination to adapt to a wide range of input and output voltage requirements and to utilize wide-bandgap semiconductor devices to increase the switching frequency.

[0003] However, in existing technologies, traditional three-level NPC topologies suffer from uneven loss distribution between internal and external switching transistors under high-frequency applications. This leads to excessively high temperatures in some devices during operation, limiting the system's power density and long-term reliability. Furthermore, the voltage stress experienced by some switching transistors at the moment of turn-off may exceed half of the bus voltage, increasing device selection costs. In addition, traditional LLC topologies struggle to maintain soft-switching across the entire load range under light loads or large input voltage variations, resulting in increased switching losses and decreased efficiency. Moreover, the high voltage change rate generated by high-frequency switching can easily trigger electromagnetic interference, affecting the system's electromagnetic compatibility. Therefore, existing technologies suffer from poor application reliability. Summary of the Invention

[0004] This invention provides a hybrid three-level resonant converter circuit based on silicon carbide devices and its control method, aiming to solve the problem of poor operational reliability of power conversion modules in the prior art.

[0005] In a first aspect, embodiments of the present invention disclose a hybrid three-level resonant converter circuit based on silicon carbide devices, wherein the hybrid three-level resonant converter circuit includes a three-phase rectifier circuit, a first switch, a second switch, a third switch, a fourth switch, a first diode, a second diode, a first active clamping diode, a second active clamping diode, a resonant converter circuit, a high-frequency isolation transformer, a secondary full-bridge rectifier and filter circuit, and a digital control unit; The input terminal of the three-phase rectifier circuit is connected to three-phase AC power. The positive terminal of the DC bus of the three-phase rectifier circuit is connected to the drain of the first switching transistor and the drain of the first active clamping transistor. The gate of the first switching transistor is connected to the negative terminal of the first diode. The source of the first switching transistor is connected to the drain of the second switching transistor and the gate of the first active clamping transistor. The source of the first active clamping transistor is connected to the drain of the second active clamping transistor and the second connection terminal of the resonant conversion circuit. The source of the second switching transistor is connected to the drain of the third switching transistor and the first connection terminal of the resonant conversion circuit. The anode of the first diode is connected to the midpoint potential of the three-phase rectifier circuit and the cathode of the second diode; the anode of the second diode is connected to the source of the third switch, the drain of the fourth switch, and the gate of the second active clamping transistor; the source of the fourth switch is connected to the negative terminal of the DC bus of the three-phase rectifier circuit. The third and fourth connection terminals of the resonant conversion circuit are respectively connected to the two ends of the primary side of the high-frequency isolation transformer, and the three winding connection points of the secondary side of the high-frequency isolation transformer are respectively connected to the first input terminal, the second input terminal, and the third input terminal of the secondary full-bridge rectifier and filter circuit; the two output terminals of the secondary full-bridge rectifier and filter circuit are respectively used as the positive output terminal and the negative output terminal. The first switch, the second switch, the third switch, the fourth switch, the first active clamping transistor, and the second active clamping transistor are all silicon carbide MOS transistors and are all equipped with temperature sensors. The input terminal of the digital control unit is connected to the positive terminal of the DC bus, the negative terminal of the DC bus, the positive output terminal, the first connection terminal of the resonant conversion circuit, each of the temperature sensors, the source of the first active clamping transistor, the source of the second active clamping transistor, the control input terminal of the first switching transistor, the control input terminal of the second switching transistor, the control input terminal of the third switching transistor, the control input terminal of the fourth switching transistor, the control input terminal of the first active clamping transistor, and the control input terminal of the second active clamping transistor.

[0006] In a second aspect, embodiments of the present invention disclose a control method for a hybrid three-level resonant converter circuit based on silicon carbide devices, wherein the current control method is applied to the hybrid three-level resonant converter circuit based on silicon carbide devices as described in the first aspect above. The control method, applied to the hybrid three-level resonant converter circuit based on silicon carbide devices as described in the first aspect above, includes: The first switch, the second switch, the third switch, the fourth switch, the first active clamp, and the second active clamp are switched on and off within one switching cycle. One of the switching cycles comprises the following six phases: S1. Control the first switch and the third switch to turn on, so that energy is transferred from the primary side to the secondary side, and the third diode, the fourth diode, the fifth diode and the sixth diode achieve zero current turn-off; S2. Control the first switch to turn off and the first active clamping transistor to turn on, so that the first switch to turn off with zero current and the first active clamping transistor clamps the drain-source voltage of the first switch. S3. Control the second switch to turn on and the first active clamp to turn off, so that the second switch can achieve zero current turn-on and the resonant inductor current reaches its peak value. S4. Control the third switch to turn off and the second active clamping transistor to turn on. The third switch to turn off with zero current, and the second active clamping transistor clamps the drain-source voltage of the third switch. S5. Control the fourth switch to turn on and the second active clamping transistor to turn off. The fourth switch to turn on with zero current and the resonant inductor current begins to decrease. S6. Control the second switch to turn off, the fourth switch to turn off, the first active clamping transistor to turn on, and the second active clamping transistor to turn on. The second switch and the fourth switch achieve zero-current turn-off, and the resonant inductor current freewheels through the first active clamping transistor and the second active clamping transistor.

[0007] This application discloses a hybrid three-level resonant converter circuit based on silicon carbide devices and its control method. The aforementioned hybrid three-level resonant converter circuit based on silicon carbide devices utilizes silicon carbide MOSFETs as core switching devices and integrates a temperature sensor to achieve real-time acquisition of bus voltage, output status, and temperature information at key points without causing control lag. At the same time, the active clamping transistor is used to coordinate the conduction and cutoff at specific stages to avoid the hidden danger of the main switch voltage peak exceeding half of the bus voltage, thereby improving the converter's operational stability, conversion efficiency, and power density across the entire load range. It can achieve zero-current turn-on of all main switches and zero-current turn-off of secondary rectifiers, effectively solving the problems of uneven switching losses and excessive voltage stress, and improving conversion efficiency and system reliability. Attached Figure Description

[0008] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0009] Figure 1A circuit structure diagram of a hybrid three-level resonant converter circuit based on silicon carbide devices provided in an embodiment of the present invention; Figure 2 The waveform diagram of the three-level square wave voltage provided in the embodiment of the present invention; Figure 3 The waveform diagram of the resonant inductor current provided in the embodiment of the present invention; Figure 4 A flowchart illustrating the control method for a hybrid three-level resonant converter circuit based on silicon carbide devices provided in an embodiment of the present invention.

[0010] Reference numerals: Q1, first switching transistor; Q2, second switching transistor; Q3, third switching transistor; Q4, fourth switching transistor; D1, first diode; D2, second diode; Q5, first active clamping transistor; Q6, second active clamping transistor; P1, digital control unit; P, positive terminal of DC bus; M, midpoint potential; N, negative terminal of DC bus; Lr, resonant inductor; Cr, resonant capacitor; Lm, magnetizing inductor; D3, third diode; D4, fourth diode; D5, fifth diode; D6, sixth diode; C o1 First output filter capacitor; C o2 P1, second output filter capacitor; P2, sampling module; P3, signal processor; P4, numerical control unit; P5, control chip; L1, first inductor; L2, second inductor; L3, third inductor; E INPUT Three-phase electromagnetic interference input filter; BR; Three-phase bridge rectifier; C bus1 First filter capacitor; C bus2 1. Second filter capacitor; 2. High-frequency isolation transformer. Detailed Implementation

[0011] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0012] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0013] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0014] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0015] This invention discloses a hybrid three-level resonant converter circuit based on silicon carbide devices, such as... Figure 1As shown, the hybrid three-level resonant converter circuit includes a three-phase rectifier circuit, a first switch Q1, a second switch Q2, a third switch Q3, a fourth switch Q4, a first diode D1, a second diode D2, a first active clamping transistor Q5, a second active clamping transistor Q6, a resonant converter circuit, a high-frequency isolation transformer T, a secondary-side full-bridge rectifier and filter circuit, and a digital control unit P1. The input terminal of the three-phase rectifier circuit is connected to three-phase AC power. The positive terminal P of the DC bus of the three-phase rectifier circuit is connected to the drain of the first switch Q1 and the drain of the first active clamping transistor Q5. The gate of the first switch Q1 is connected to the negative terminal of the first diode D1, and the source of the first switch Q1 is connected to the drain of the second switch Q2 and the gate of the first active clamping transistor Q5. The source of the first active clamping transistor Q5 is connected to the drain of the second active clamping transistor Q6 and the second connection terminal of the resonant conversion circuit. The source of the second switching transistor Q2 is connected to the drain of the third switching transistor Q3 and the first connection terminal of the resonant conversion circuit. The anode of the first diode D1 is connected to the midpoint potential M of the three-phase rectifier circuit and the cathode of the second diode D2. The anode of the second diode D2 is connected to the source of the third switching transistor Q3, the drain of the fourth switching transistor Q4, and the gate of the second active clamping transistor Q6. The source of the fourth switching transistor Q4 is connected to the negative DC bus N of the three-phase rectifier circuit. The third and fourth connection terminals of the resonant conversion circuit are respectively connected to the two ends of the primary side of the high-frequency isolation transformer T. The three winding connection points of the secondary side of the high-frequency isolation transformer T are respectively connected to the first, second, and third input terminals of the secondary full-bridge rectifier filter circuit. The two output terminals of the secondary full-bridge rectifier filter circuit serve as the positive and negative output terminals, respectively. The first switch Q1, the second switch Q2, the third switch Q3, the fourth switch Q4, the first active clamping transistor Q5, and the second active clamping transistor Q6 are all silicon carbide MOSFETs and each is equipped with a temperature sensor. The input terminal of the digital control unit P1 is connected to the positive terminal P of the DC bus, the negative terminal N of the DC bus, the positive output terminal, the first connection terminal of the resonant conversion circuit, each of the temperature sensors, the source of the first active clamping transistor Q5, the source of the second active clamping transistor Q6, the control input terminal of the first switch Q1, the control input terminal of the second switch Q2, the control input terminal of the third switch Q3, the control input terminal of the fourth switch Q4, the control input terminal of the first active clamping transistor Q5, and the control input terminal of the second active clamping transistor Q6.

[0016] The three-phase rectifier circuit is a circuit module used to convert the input three-phase AC power into DC power. In this application, the input terminal of the three-phase rectifier circuit is connected to the three-phase AC power grid, and its output terminal forms the positive DC bus P, the negative DC bus N, and the midpoint potential M, providing DC power and a potential reference point for the subsequent inverter and resonant circuit. The three-phase rectifier circuit is directly connected to active devices such as the first switch Q1 and the fourth switch Q4, forming the energy input stage of the entire converter. The stability of its output DC bus voltage directly affects the operating state of the subsequent resonant conversion circuit. The specific implementation of the three-phase rectifier circuit can be set according to the actual situation. For example, it can be a combination structure including an EMI filter and a three-phase bridge rectifier BR, or other rectifier topologies designed according to different input voltage levels. This application does not impose any special limitations on this.

[0017] The first switch Q1, the second switch Q2, the third switch Q3, and the fourth switch Q4 constitute the main power switching devices of the hybrid three-level bridge arm. In this embodiment, these four switches are connected in series between the positive and negative terminals of the DC bus. Specifically, the first switch Q1 and the second switch Q2 are connected in series between the positive terminal and the node related to the midpoint potential M, while the third switch Q3 and the fourth switch Q4 are connected in series between the node related to the midpoint potential M and the negative terminal. They work together to generate a three-level square wave voltage to excite the resonant conversion circuit. The specific waveform of the three-level square wave voltage is as follows: Figure 2 As shown, the horizontal axis t represents time, and the vertical axis U represents voltage amplitude; Figure 2 Figures (a) and (b) illustrate the waveform structures of two three-level square wave voltages, respectively. The source of the first switch Q1 is connected to the drain of the second switch Q2. The source of the second switch Q2 is connected to the drain of the third switch Q3, serving as the first connection terminal of the resonant converter circuit. The source of the third switch Q3 is connected to the drain of the fourth switch Q4. This series structure ensures that the voltage stress borne by each switch in the off state is approximately half that of the DC bus voltage, thereby reducing the requirements for the voltage withstand rating of the devices. All four switches are silicon carbide MOSFETs. Utilizing the high-frequency and low-loss characteristics of silicon carbide material, the switching frequency and efficiency of the converter can be significantly improved.

[0018] The first diode D1 and the second diode D2 are passive devices used to clamp the midpoint potential M. The cathode of the first diode D1 is connected to the gate of the first switching transistor Q1, and the anode of the first diode D1 is connected to the midpoint potential M of the three-phase rectifier circuit and the cathode of the second diode D2. The anode of the second diode D2 is connected to the source of the third switching transistor Q3, the drain of the fourth switching transistor Q4, and the gate of the second active clamping transistor Q6. During circuit operation, when a specific switching transistor is turned off, the first diode D1 or the second diode D2 conducts, clamping the potential of the switching node to the midpoint potential M of the DC bus to prevent voltage overshoot. This, together with the active clamping transistor, maintains the voltage balance of the three-level structure. The diodes can be selected based on current capacity and reverse withstand voltage requirements; for example, silicon carbide Schottky diodes can be used to reduce reverse recovery losses.

[0019] The first active clamping transistor Q5 and the second active clamping transistor Q6 are active control devices used to assist the main switching transistors in achieving zero-current switching (ZVS) and further clamping the voltage. The drain of the first active clamping transistor Q5 is connected to the drain of the first switching transistor Q1, and the source is connected to the drain of the second active clamping transistor Q6 and the second connection terminal of the resonant switching circuit. The source of the second active clamping transistor Q6 is connected to the source of the third switching transistor Q3 and related nodes. These two clamping transistors work together with the main switching transistors to provide a freewheeling path or a clamping path during the main switching transistor's turn-off period, absorb leakage inductance energy, and clamp the drain-source voltage of the main switching transistor within a safe range. By precisely controlling the turn-on and turn-off sequence of the first active clamping transistor Q5 and the second active clamping transistor Q6, it can be ensured that the drain-source voltage of all main switching transistors has dropped to zero before turn-on, thereby achieving zero-current switching and significantly reducing switching losses. The active clamping transistor also uses a silicon carbide MOSFET to accommodate high-frequency switching operations.

[0020] The resonant conversion circuit is an LC resonant network connected between the output of the three-level bridge arm and the primary side of the high-frequency isolation transformer T. The first connection terminal of the resonant conversion circuit is connected to the source of the second switch Q2 and the drain of the third switch Q3. The second connection terminal is connected to the source of the first active clamping transistor Q5 and the drain of the second active clamping transistor Q6. The third and fourth connection terminals are respectively connected to the two ends of the primary side of the high-frequency isolation transformer T. This circuit utilizes the resonant characteristics of inductors and capacitors to convert the square wave voltage generated by the three-level bridge arm into a sinusoidal current, creating conditions for soft switching. The specific components of the resonant conversion circuit may include a resonant inductor Lr, a resonant capacitor Cr, and a magnetizing inductor Lm, etc. Its parameters, such as inductance and capacitance, can be designed according to the target resonant frequency and gain characteristics. For example, the resonant frequency can be set between tens of kilohertz and hundreds of kilohertz; this embodiment does not impose any special limitations on this.

[0021] The high-frequency isolation transformer T is a magnetic component used to achieve electrical isolation and voltage transformation. Its primary winding is connected to the third and fourth terminals of the resonant converter circuit, respectively. The secondary winding has three connection points, which are connected to the first, second, and third input terminals of the secondary full-bridge rectifier and filter circuit. The high-frequency isolation transformer T not only achieves electrical isolation between the input and output sides, ensuring system safety, but also adjusts the voltage to the level required by the load through turns ratio changes. The transformer's core material can be selected from high-frequency, low-loss materials such as nanocrystalline and ferrite materials. The winding structure can be designed according to insulation withstand voltage requirements and leakage inductance control needs; for example, the insulation withstand voltage of the primary and secondary windings can be set to above 2500VAC.

[0022] The secondary-side full-bridge rectifier and filter circuit is located on the secondary side of the transformer and is used to convert high-frequency alternating current (AC) into smooth direct current (DC). Its three input terminals are connected to the three winding connection points of the secondary side of the high-frequency isolation transformer T, and its two output terminals serve as the positive and negative output terminals to supply power to the load. This circuit typically includes rectifier diodes and filter capacitors. The rectifier diodes rectify the AC into pulsating DC, while the filter capacitors filter out ripple and provide a stable DC voltage. Silicon carbide diodes can also be used as rectifiers in the secondary-side full-bridge rectifier and filter circuit to achieve zero-current switching (ZCS) and reduce reverse recovery losses. The capacitance and voltage rating of the filter capacitor can be configured according to the output ripple requirements and load power.

[0023] The digital control unit P1 is the core of the entire conversion circuit, responsible for signal acquisition, logic operations, and drive signal generation. The input terminals of the digital control unit P1 are widely connected to key nodes in the circuit, including the positive and negative terminals of the DC bus, the positive output terminal, the first connection terminal of the resonant conversion circuit, the temperature sensors integrated in each switch, the source of the active clamping transistor, and the control input terminals of all switches. By acquiring bus voltage, output voltage, resonant current, and temperature information of key components, the digital control unit P1 can monitor the system's operating status in real time and generate corresponding PWM drive signals according to a preset control algorithm to control the on / off timing of the first to fourth switches Q4 and the first and second active clamping transistors Q6. The digital control unit P1 can be composed of a DSP, FPGA, or microcontroller and its peripheral circuits; its specific hardware architecture and software algorithm can be adjusted according to the requirements of control accuracy and response speed.

[0024] Temperature sensors are integrated into the first switching transistor Q1, the second switching transistor Q2, the third switching transistor Q3, the fourth switching transistor Q4, the first active clamping transistor Q5, and the second active clamping transistor Q6. These temperature sensors are thermistors integrated inside the silicon carbide MOSFET package or attached to its heat dissipation surface, used to monitor the junction temperature or case temperature of the switching transistors in real time. The output signal of the temperature sensor is transmitted to the digital control unit P1. When the detected temperature exceeds a preset threshold, the control unit can take protective measures such as frequency reduction, current limiting, or shutdown to prevent the devices from being damaged due to overheating, thereby improving the long-term operational reliability of the system. The temperature sensors can be thermistors, thermocouples, or integrated temperature ICs, and their installation location and number can be flexibly set according to the thermal management strategy.

[0025] In a more specific embodiment, the resonant conversion circuit includes a resonant inductor Lr, a resonant capacitor Cr, and a magnetizing inductor Lm. One end of the resonant inductor Lr serves as the first connection terminal of the resonant conversion circuit. The other end of the resonant inductor Lr is connected to one end of the resonant capacitor Cr. The other end of the resonant capacitor Cr is connected to one end of the magnetizing inductor Lm, and this connection point serves as the third connection terminal of the resonant conversion circuit. The other end of the magnetizing inductor Lm serves as both the second and third connection terminals of the resonant conversion circuit.

[0026] The resonant conversion circuit is a module used to construct a resonant network on the primary side of the high-frequency isolation transformer T to achieve zero-current turn-on of the switching transistors and efficient energy transfer. It enables soft switching and voltage conversion, controlling the output voltage by adjusting the switching frequency. The resonant inductor Lr has a specification of 1μH; the resonant capacitor Cr has a specification of 2.5μF; the magnetizing inductor Lm has a specification of 60μH; and the resonant frequency of the resonant conversion circuit is 100kHz. This resonant conversion circuit works in conjunction with the first switching transistor Q1, the second switching transistor Q2, the third switching transistor Q3, the fourth switching transistor Q4, and the active clamping transistor as defined in the above embodiment. Through the oscillation characteristics of its internal inductance and capacitance, it converts the square wave voltage output from the hybrid three-level bridge arm into a sinusoidal or near-sinusoidal current waveform. The resonant inductor Lr is an inductor element connected in series in the power transmission path, used to limit the rate of current change and participate in determining the resonant frequency.

[0027] In this application, one end of the resonant inductor Lr serves as the first connection terminal of the resonant conversion circuit, which can be connected to the midpoint potential M of the aforementioned hybrid three-level bridge arm. The other end of the resonant inductor Lr is connected to one end of the resonant capacitor Cr. The specific inductance of the resonant inductor Lr can be set according to the power level, switching frequency range, and required gain characteristics of the actual application, for example, it can be from a few microhenries to tens of microhenries, and this application embodiment does not impose any special limitations on this. Its material can be selected from ferrite cores, powder cores, or nanocrystalline cores, etc., to meet the requirements of high-frequency and low-loss operation. The resonant capacitor Cr is a capacitor element connected in series with the resonant inductor Lr, which together determines the fundamental frequency of the resonant cavity. One end of the resonant capacitor Cr is connected to the resonant inductor Lr, and the other end is connected to one end of the excitation inductor Lm, and this connection point serves as the third connection terminal of the resonant conversion circuit. The third connection terminal is typically connected to one winding terminal of the primary side of the high-frequency isolation transformer T. The high-frequency isolation transformer T can be a transformer with a nanocrystalline magnetic core, a primary winding of Np=20 turns, and a secondary winding of Ns=40 turns (center tap). The high-frequency isolation transformer T is used to achieve electrical isolation and voltage matching, and the insulation withstand voltage of the primary and secondary sides is ≥2500VAC. The capacitance value of the resonant capacitor Cr can be calculated and determined according to the resonant frequency formula combined with the selected resonant inductance value Lr. For example, it can be from several hundred nanofarads to several microfarads. This application embodiment does not make any special limitation on this. The capacitor can be a film capacitor, a ceramic capacitor, or other capacitor types suitable for high-frequency and high-voltage environments. The magnetizing inductance Lm is the equivalent parallel inductance of the primary winding of the high-frequency isolation transformer T, or an inductor element that is independently set in the circuit and connected in parallel with the primary side of the transformer. It is used to store magnetic field energy and participate in the resonance process during the turn-off of the switching transistor to maintain soft-switching conditions. In this embodiment, one end of the magnetizing inductance Lm is connected to the other end of the resonant capacitor Cr, and the other end serves as the second and third connection terminals of the resonant conversion circuit. The magnitude of the magnetizing inductance Lm determines the gain characteristics and reactive circulating current of the converter. Its value can be set according to the transformer's turns ratio design and the required excitation current ratio; for example, it can be several to tens of times the resonant inductance Lr. This application does not impose any special limitations on this aspect. Figure 1 As shown, in Figure 1 The diagram clearly illustrates the connection relationship between the resonant inductor Lr, the resonant capacitor Cr, and the magnetizing inductor Lm: the resonant inductor Lr and the resonant capacitor Cr are connected in series, and then together with the magnetizing inductor Lm, they form a specific series-parallel combination structure, which together constitutes the LLC resonant cavity. This structure makes the current flowing through the primary side of the high-frequency isolation transformer T exhibit sinusoidal characteristics, thereby reducing switching losses and electromagnetic interference.

[0028] In a more specific embodiment, such as Figure 1 As shown, the secondary-side full-bridge rectifier and filter circuit includes a third diode D3, a fourth diode D4, a fifth diode D5, a sixth diode D6, and a first output filter capacitor C.o1 and the second output filter capacitor C o2 The anode of the third diode D3 serves as the first input terminal, connected to the first winding connection point. The cathode of the third diode D3 is connected to the cathode of the sixth diode D6. The anode of the sixth diode D6 is connected to the cathode of the fifth diode D5, and this connection point serves as the second input terminal, connected to the second winding connection point. The anode of the fifth diode D5 is connected to the anode of the fourth diode D4, and the cathode of the fourth diode D4 serves as the third input terminal, connected to the third winding connection point. The first output filter capacitor C... o1 and the second output filter capacitor C o2 They are respectively connected in parallel between the negative terminal of the sixth diode D6 and the positive terminal of the fifth diode D5.

[0029] In this circuit, the third diode, D3, can be a silicon carbide Schottky diode. Its anode serves as the first input terminal, connected to the first winding connection point of the secondary side of the high-frequency isolation transformer T. It conducts during the positive half-cycle of the AC voltage or within a specific phase interval, converting the AC output from the transformer into a unidirectional pulsating current. The third diode D3 is connected to the cathode of the sixth diode D6, forming an output arm node of the rectifier bridge. This connection establishes the basic path for current flow from the transformer to the load. The third diode D3, fourth diode D4, fifth diode D5, and sixth diode D6 in the secondary-side full-bridge rectifier filter circuit are all 1200V / 100A SiC diodes. The function of the secondary-side full-bridge rectifier filter circuit is to convert high-frequency AC power into smooth DC power.

[0030] In this application, the third diode D3 performs high-frequency rectification, utilizing the low reverse recovery charge characteristic of silicon carbide material to achieve near-zero current turn-off in conjunction with other diodes, reducing switching losses. The sixth diode D6 can also be a silicon carbide Schottky diode, with its anode connected to the cathode of the fifth diode D5. This connection point serves as the second input terminal, connecting to the second winding connection point of the secondary side of the high-frequency isolation transformer T. The sixth diode D6 conducts in another phase interval of the AC voltage, alternating with the third diode D3 to complete the full-wave or full-bridge rectification process. Both the cathode of the sixth diode D6 and the anode of the fifth diode D5 are internal nodes of the rectifier bridge and also serve as the first output filter capacitor C. o1 and the second output filter capacitor C o2The parallel connection point forms the reference potential or negative terminal of the output voltage, serving to collect the rectified current and guide it to the filtering stage. The fifth diode, D5, can be a silicon carbide Schottky diode. Its anode is connected to the anode of the fourth diode, D4, forming another input arm node of the rectifier bridge, while its cathode is connected to the anode of the sixth diode, D6. The fifth diode, D5, conducts under a specific voltage polarity, responsible for transferring energy from the other winding of the transformer secondary to the output. The connection between the fifth diode D5 and the anode of the fourth diode D4 allows them to respond collaboratively to potential changes at different winding terminals of the transformer secondary, ensuring that a diode is always conducting throughout the complete switching cycle, maintaining current continuity. The fourth diode, D4, can also be a silicon carbide Schottky diode. Its cathode serves as the third input terminal, connected to the third winding connection point of the high-frequency isolation transformer T. The fourth diode D4 and the anode of the fifth diode D5 are connected, together forming the input side structure of the rectifier bridge. Driven by the alternating voltage output from the high-frequency isolation transformer T, the fourth diode D4, along with the other three diodes, alternately turns on and off according to a preset timing sequence, converting the high-frequency alternating current into pulsating direct current. The introduction of the fourth diode D4 completes the full-bridge rectifier architecture, ensuring bidirectional or full-cycle coverage of energy transfer, and is one of the key components for achieving efficient rectification. The first output filter capacitor C... o1 It can be a film capacitor or an electrolytic capacitor, which, together with the second output filter capacitor C, o2 Parallel configuration. First output filter capacitor C o1 It is connected in parallel between the negative terminal of the sixth diode D6 and the positive terminal of the fifth diode D5. The first output filter capacitor C... o1 Its main function is to absorb high-frequency ripple components in the rectified voltage, smooth the output voltage, and provide a stable DC power supply to the load. Using a dual-capacitor parallel structure increases the total capacitance and reduces the equivalent series resistance, thereby further improving the filtering effect, sharing the ripple current stress, and enhancing system reliability. The second output filter capacitor C o2 It can be used with the first output filter capacitor C o1 Having the same or different parameter specifications, both are connected in parallel and work together at the rectified output. The second output filter capacitor C o2 This configuration not only enhances the filtering capacity but also suppresses noise across different frequency bands. In the first output filter capacitor C... o1 and the second output filter capacitor C o2 With a parallel architecture, the stability of the output voltage is significantly improved, which can effectively cope with voltage fluctuations caused by sudden load changes and meet the requirements of high-precision DC output.

[0031] In a more specific embodiment, the first output filter capacitor C o1 and the second output filter capacitor C o2 All are polarized capacitors. The first output filter capacitor Co1 The negative terminal and the second output filter capacitor C o2 The negative terminals are respectively connected to the positive terminals of the fifth diode D5. The first output filter capacitor C... o1 This refers to an energy storage element with positive and negative polarity differentiation capabilities. Its material can be aluminum electrolytic capacitors, tantalum capacitors, or polymer capacitors, etc., and this application does not impose any special limitations on this. For example, two 450V / 2200μF thin-film capacitors can be used as the first output filter capacitor C. o1 and the second output filter capacitor C o2 In this hybrid three-level resonant converter circuit, the first output filter capacitor C o1 Its primary function is to filter out the high-frequency ripple current after secondary-side rectification and smooth the DC output voltage. In the system linkage, the first output filter capacitor C... o1 The negative terminal is configured to be connected to the positive terminal of the fifth diode D5. This connection path ensures that the potential difference across the capacitor is aligned with its polarity markings; that is, the positive terminal is at a relatively high potential, while the negative terminal is at the low potential side determined by the common cathode of the rectifier bridge. This avoids increased leakage current, overheating, or even failure of the capacitor due to reverse bias. The second output filter capacitor C... o2 That is, with the first output filter capacitor C o1 The parameters of the other polarity energy storage element, which can be connected in parallel or independently, can be set according to the actual output power requirements. Second output filter capacitor C o2 Its function in the circuit is to work with the first output filter capacitor C. o1 They jointly undertake the filtering task at the output end and share the ripple current stress. In terms of their linkage, the second output filter capacitor C... o2 The negative terminal of the capacitor is also connected to the negative terminal of the fifth diode D5. This means that the negative terminals of the two polarized capacitors are connected to the same potential point, which is determined by the connection node potential of the fifth diode D5 and the sixth diode D6 in the secondary full-bridge rectifier filter circuit. Through this common negative terminal connection, the two capacitors can work together to ensure that the output voltage remains stable during the switching of the rectifier diodes on and off, and that the capacitors always operate in the forward voltage range.

[0032] In a more specific embodiment, such as Figure 1As shown, the digital control unit P1 includes a sampling module P2, a signal processor P3, a numerical control unit P4, and a control chip P5. The input terminal of the sampling module P2 is connected to the positive terminal P of the DC bus, the negative terminal N of the DC bus, the positive output terminal, the first connection terminal of the resonant conversion circuit, and each of the temperature sensors. The first output terminal of the sampling module P2 is connected to the input terminal of the signal processor P3. The second output terminal of the sampling module P2, the output terminal of the signal processor P3, the source of the first active clamping transistor Q5, the source of the second active clamping transistor Q6, and the first connection terminal of the resonant conversion circuit are respectively connected to the input terminal of the numerical control unit P4. The output terminal of the numerical control unit P4 is connected to the input terminal of the control chip P5. The output terminal of the control chip P5 is connected to the control input terminal of the first switching transistor Q1, the control input terminal of the second switching transistor Q2, the control input terminal of the third switching transistor Q3, the control input terminal of the fourth switching transistor Q4, the control input terminal of the first active clamping transistor Q5, and the control input terminal of the second active clamping transistor Q6.

[0033] The sampling module P2 is a hardware circuit or functional unit used to collect real-time operating status parameters of the conversion circuit. In this application, the input terminals of the sampling module P2 are electrically connected to the positive terminal P of the DC bus, the negative terminal N of the DC bus, the positive output terminal, the first connection terminal of the resonant conversion circuit, and the temperature sensors mounted on each switching transistor. The function of the sampling module P2 is to acquire the voltage feedback, current feedback, and temperature feedback of the system. Specifically, it collects the voltage between the positive and negative terminals of the DC bus to monitor the input energy status, collects the voltage at the positive output terminal to monitor the load demand, collects the current at the first connection terminal of the resonant conversion circuit to reflect the working status of the resonant cavity, and collects the real-time temperature of each silicon carbide MOSFET to prevent overheating damage. The sampling module P2 can convert analog signals into digital signals. For example, it can be a circuit structure including a voltage divider resistor network, an operational amplifier, and an analog-to-digital converter, or it can be a dedicated sampling chip with integrated signal conditioning functions. This application embodiment does not make any special limitations on this. Through the above connection relationship, the sampling module P2 transmits multi-source sensing data to the subsequent signal processor P3, forming the basic sensing link for closed-loop control. Signal processor P3 is the computational unit that preprocesses, filters, and extracts features from the raw data output by sampling module P2. The input of signal processor P3 is connected to the first output of sampling module P2. Its function is to digitally filter the received voltage, current, and temperature digital signals to remove high-frequency noise and perform standardization processing for subsequent algorithm calculations. In the system linkage, signal processor P3 is located between sampling module P2 and CNC unit P4, acting as a data buffer and performing preliminary processing to ensure that the data input to CNC unit P4 has a higher signal-to-noise ratio and reliability. Signal processor P3 can be a specific core within a digital signal processor P3 or a logic resource block in a field-programmable gate array; this embodiment does not impose any special limitations on this. CNC unit P4 is the logic operation unit that executes the core control algorithm and generates control strategies. For example, CNC unit P4 can use a TI TMS320F28379D DSP main controller. The input terminals of the CNC unit P4 are connected to the second output terminal of the sampling module P2, the output terminal of the signal processor P3, the source of the first active clamping transistor Q5, the source of the second active clamping transistor Q6, and the first connection terminal of the resonant conversion circuit. This multi-input configuration allows the CNC unit P4 to not only receive processed feedback signals but also directly acquire the potential state of key nodes and the instantaneous value of the resonant current, thereby more accurately determining the operating stage of the circuit. The functional positioning of the CNC unit P4 is to calculate the required duty cycle, frequency, or phase angle based on the preset control strategy and the real-time feedback.The numerical control unit P4 can internally run proportional-integral-derivative control algorithms, fuzzy control algorithms, or model predictive control algorithms. Its specific implementation can be embedded software code or logic circuits written in a hardware description language; this application does not impose any special limitations on this. The control chip P5 is the interface unit that converts the digital control instructions generated by the numerical control unit P4 into pulse signals that drive the switching transistors. The input terminal of the control chip P5 is connected to the output terminal of the numerical control unit P4, and its output terminals are respectively connected to the control input terminals of the first switching transistor Q1, the second switching transistor Q2, the third switching transistor Q3, the fourth switching transistor Q4, the first active clamping transistor Q5, and the second active clamping transistor Q6. The control chip P5 can use a Xilinx Artix-7 FPGA component, and its output terminal can output 6 channels of PWM drive signals to realize fault protection and communication control functions. In the system linkage, the control chip P5 acts as the execution bridge between the digital control logic and the main power circuit. The pulse width modulation signal it generates directly determines the turn-on and turn-off timing of the six silicon carbide MOSFETs, thereby achieving zero-current turn-on and voltage clamping functions. The control chip P5 can integrate dead-time generation, fault blocking, and level shifting functions. For example, it can be a dedicated gate driver chip or the internal control part of an intelligent power module with integrated drive functions. This application does not impose any special limitations on this aspect.

[0034] In a more specific embodiment, such as Figure 1 As shown, the three-phase rectifier circuit includes a first inductor L1, a second inductor L2, a third inductor L3, and a three-phase electromagnetic interference input filter E. INPUT Three-phase bridge rectifier BR, first filter capacitor C bus1 and the second filter capacitor C bus2 The first inductor L1, the second inductor L2, and the third inductor L3 are connected in series on the three input phase lines. One end of each input phase line is connected to a three-phase AC power supply, and the other end of each input phase line is connected to the three-phase electromagnetic interference input filter E. INPUT The three input terminals. The three-phase electromagnetic interference input filter E INPUT The three output terminals are respectively connected to the three input terminals of the three-phase bridge rectifier BR. The first output terminal of the three-phase bridge rectifier BR is connected to the first filter capacitor C. bus1 One end of the circuit is connected to the positive terminal P of the DC bus. The second output terminal of the three-phase bridge rectifier BR is connected to the second filter capacitor C. bus2 One end of the capacitor is connected to the DC bus negative terminal N. The first filter capacitor C bus1 The other end is connected to the second filter capacitor C bus2 The other end, and the connection point serves as the midpoint potential M.

[0035] The three-phase rectifier circuit is used to convert 380V three-phase AC power into 540V-800V DC power. The first inductor L1, the second inductor L2, and the third inductor L3 are magnetic components connected in series on the three-phase lines L1, L2, and L3 of the three-phase AC power grid input. Their function is to cooperate with subsequent circuits to form an input filter network, suppressing high-frequency noise from the power grid and preventing high-frequency harmonics generated by the converter from flowing back into the power grid. In practical applications, the inductance of these three inductors can be set according to the actual situation, for example, from tens to hundreds of microhenries. The specific value depends on the rated power of the system and the required filter cutoff frequency; this application does not impose any special limitations on this. These three inductors serve as the front-end impedance elements of the input stage, and work in conjunction with the three-phase electromagnetic interference input filter E. INPUT Working together, they form an attenuation path for both differential-mode and common-mode interference, ensuring the sinusoidal nature of the input current waveform and reducing electromagnetic interference to other devices. Three-phase electromagnetic interference input filter E INPUT This is a passive network component used to filter out electromagnetic interference signals in a specific frequency band. Its internal structure may include a combination of conventional devices such as common-mode inductors, X capacitors, and Y capacitors. The three input terminals of the filter are connected to the aforementioned first inductor L1, second inductor L2, and third inductor L3, respectively, and its three output terminals are connected to the AC input terminals of the three-phase bridge rectifier BR. In this application, the filter is located before the rectification stage and is mainly used to attenuate conducted interference caused by high-frequency dv / dt and di / dt due to switching operations. Its cutoff frequency and impedance characteristics can be designed according to the requirements of actual electromagnetic compatibility standards, and this application embodiment does not impose any special limitations on this. Through the cooperation of the filter and the input inductors, the function of suppressing electromagnetic noise at the source is achieved, providing a clean AC input environment for the subsequent power conversion circuit. The three-phase bridge rectifier BR is a power conversion unit that converts three-phase AC power into pulsating DC power. It can be composed of a full-bridge structure with six rectifier diodes, or a controlled rectifier bridge composed of thyristors or other controllable switching devices, and this application embodiment does not impose any special limitations on this. In a preferred implementation, the three-phase bridge rectifier BR is composed of six silicon carbide Schottky diodes to reduce rectification losses by utilizing their low reverse recovery charge and high-temperature characteristics. The three AC input terminals of the rectifier are connected to a three-phase electromagnetic interference input filter E. INPUT The rectifier outputs a positive pulsating DC voltage at its first output terminal and a negative pulsating DC voltage at its second output terminal. This rectifier performs the core function of AC-DC conversion in the system, and its output pulsating DC voltage waveform frequency is six times the grid frequency, providing charging pulses for the subsequent filter capacitors. The first filter capacitor C... bus1 and the second filter capacitor C bus2 This refers to an energy storage element used to smooth the DC bus voltage and establish a midpoint potential M. In this embodiment, the two capacitors are connected in series, with the first filter capacitor C...bus1 One end is connected to the first output terminal of the three-phase bridge rectifier BR, and the second filter capacitor C. bus2 One end is connected to the second output terminal of the three-phase bridge rectifier BR, while the first filter capacitor C bus1 The other end is connected to the second filter capacitor C bus2 The other ends of the capacitors are connected to each other, and this connection point forms the midpoint potential M. This series voltage divider structure not only acts as a filter, smoothing the pulsating DC voltage into a stable DC bus voltage, but more importantly, it provides the necessary zero-potential reference point for the subsequent hybrid three-level topology. The capacitance values ​​of these two capacitors can be set according to the system power level and the allowable bus voltage ripple range. For example, they can be film capacitors or electrolytic capacitors ranging from hundreds to thousands of microfarads, and their capacitance values ​​are usually kept consistent to maintain the balance of the midpoint potential M. This application does not impose any special limitations on this aspect.

[0036] In a more specific embodiment, the first filter capacitor C bus1 and the second filter capacitor C bus2 All are polarized capacitors. The first filter capacitor C bus1 The positive terminal is connected to the first output terminal of the three-phase bridge rectifier BR, and the second filter capacitor C bus2 The negative terminal is connected to the second output terminal of the three-phase bridge rectifier BR. The first filter capacitor C bus1 The negative terminal is connected to the second filter capacitor C. bus2 The positive terminal. Among them, the first filter capacitor C... bus1 This refers to energy storage elements such as electrolytic capacitors, film capacitors, or supercapacitors with clearly marked positive and negative polarities, whose positive terminal is configured to receive a high-potential DC voltage from the first output terminal of a three-phase bridge rectifier BR; for example, two 450V / 1000μF film capacitors can be used as the first filter capacitor C. bus1 and the second filter capacitor C bus2 In this application, the first filter capacitor C bus1 With the second filter capacitor C bus2 The series connection forms a DC bus filter network, with the first filter capacitor C bus1 This first filter capacitor, C, is responsible for filtering the voltage between the positive terminal P of the DC bus and the midpoint potential M. Its polarity must be consistent with the direction of the DC voltage applied across it to prevent capacitor breakdown or failure due to reverse voltage. bus1 The specific capacity and voltage rating can be set according to the actual situation. For example, it can be a 450V / 1000μF aluminum electrolytic capacitor or a high-voltage metallized polypropylene film capacitor. This application does not impose any special limitations on this. Second filter capacitor Cbus2 That is, with the first filter capacitor C bus1Capacitors of the same or different polarities have their negative terminals configured to be connected to the second output terminal of the three-phase bridge rectifier BR, i.e., the low-potential terminal or negative terminal of the DC bus. Second filter capacitor C bus2 This second filter capacitor C is responsible for filtering the voltage between the midpoint potential M and the negative terminal N of the DC bus. Its negative terminal is connected towards the low-potential end to ensure the correct direction of the internal electric field under normal operating conditions. bus2 With the first filter capacitor C bus1 Electrically, they form a series connection, working together to smooth the pulsating DC voltage after three-phase rectification and provide a stable DC input for the subsequent three-level inverter bridge arms. The second filter capacitor C... bus2 Specific parameters such as capacitance and equivalent series resistance can be set according to the system power level and ripple suppression requirements. For example, they can be related to the first filter capacitor C. bus1 Symmetrically configured capacitors of the same specification can also use different specifications depending on the balance requirement of the midpoint potential M; this application does not impose any special limitations on this. First filter capacitor C bus1 The negative terminal and the second filter capacitor C bus2 The positive terminals of the capacitors are connected, and this connection point naturally forms the midpoint potential M of the DC bus in the circuit topology. This connection establishes the zero-potential reference point or virtual neutral point required for the three-level topology, so that the DC bus voltage is evenly divided into upper and lower parts, providing working voltage references for the upper and lower bridge arms respectively. Through this specific series connection of polarized capacitors, not only is the storage and filtering of DC-side energy realized, but also the midpoint clamping foundation required for the hybrid three-level converter is constructed, ensuring that the three-level bridge arms can correctly clamp voltage stress during switching. The stability of the midpoint potential M directly depends on the leakage current balance and capacitance matching of the two polarized capacitors. In practical applications, the stability of the midpoint potential M can be maintained by selecting capacitor pairs with good consistency or adding equalizing resistors. This application does not specifically limit the specific means of maintaining the midpoint potential M.

[0037] In a more specific embodiment, such as Figure 1 As shown, the three-phase bridge rectifier BR consists of six rectifier diodes, which can be 1200V / 50A SiC diodes. The anodes of three of these rectifier diodes are connected to the three-phase electromagnetic interference input filter E. INPUT The three output terminals and the negative terminals of the three rectifier diodes are connected together to form the first output terminal of the three-phase bridge rectifier BR. The negative terminals of the other three rectifier diodes are respectively connected to the three-phase electromagnetic interference input filter E. INPUTThe three output terminals and the positive terminals of the three rectifier diodes are connected together and serve as the second output terminal of the three-phase bridge rectifier BR. The six rectifier diodes are six unidirectional conductive semiconductor devices constituting the three-phase full-bridge rectifier topology. Their material can be silicon carbide diodes or other wide-bandgap semiconductor diodes with fast recovery characteristics; this embodiment does not impose any special limitations on this. In this hybrid three-level resonant converter circuit, these six rectifier diodes are divided into a common-cathode group and a common-anode group. The three rectifier diodes in the common-cathode group are used to conduct during the positive half-cycle of the AC current or a specific phase interval, transferring the highest potential in the three-phase input to the positive terminal P of the DC bus; the three rectifier diodes in the common-anode group are used to conduct during the negative half-cycle of the AC current or a specific phase interval, transferring the lowest potential in the three-phase input to the negative terminal N of the DC bus. Through this coordination, the six rectifier diodes work together to convert the three-phase electromagnetic interference input filter E... INPUT The filtered three-phase AC power is converted into pulsating DC power to charge the subsequent filter capacitors and establish the DC bus voltage. Specifically, the positive terminals of the three rectifier diodes are connected to the three-phase electromagnetic interference input filter E. INPUT The three output terminals and the negative terminals of the other three rectifier diodes are respectively connected to the three-phase electromagnetic interference input filter E. INPUT The three output terminals describe the electrical connection between the rectifier diodes and the front-end filter. Three-phase electromagnetic interference input filter E INPUT The three output terminals correspond to phases A, B, and C of the three-phase AC power supply. For the three rectifier diodes in the common-cathode group, their anodes are independently connected to each of the three phases, while their cathodes converge at a single point. This convergence point forms the first output terminal of the three-phase bridge rectifier BR, which is also the positive potential point of the DC bus. For the three rectifier diodes in the common-anode group, their cathodes are independently connected to each of the three phases, while their anodes converge at a single point. This convergence point forms the second output terminal of the three-phase bridge rectifier BR, which is also the negative potential point of the DC bus. This connection method ensures that at any given time, current flows from the phase with the highest potential through the common-cathode group diodes to the load, and from the load back to the phase with the lowest potential through the common-anode group diodes, thus achieving full-wave rectification. Furthermore, the negative terminals of the three rectifier diodes are connected together as the first output terminal of the three-phase bridge rectifier BR, and the positive terminals of the three rectifier diodes are connected together as the second output terminal of the three-phase bridge rectifier BR, defining the formation method of the rectifier output terminals. The first and second output terminals serve as the positive and negative terminals of the DC bus, respectively, for connecting to the subsequent first filter capacitor C. bus1 and the second filter capacitor C bus2In practical applications, these six rectifier diodes can be integrated into a single rectifier bridge module or soldered onto a circuit board as discrete components. The specific packaging form, heat dissipation structure, and mounting method can be set according to the actual power level and space layout requirements. For example, they can be bolt-fixed packages to facilitate high-current heat dissipation or surface-mount packages to accommodate high-density integration. This application does not impose any special limitations on this. Regardless of the form used, the core function is to utilize the unidirectional conductivity of the diodes, combined with the phase difference of the three-phase AC power, to output a stable DC voltage, providing energy input to the subsequent hybrid three-level active clamp bridge arm.

[0038] This invention also discloses a control method for a hybrid three-level resonant converter circuit based on silicon carbide devices. The control method is applied to the hybrid three-level resonant converter circuit based on silicon carbide devices as described in the above embodiments. The method includes switching control of a first switch, a second switch, a third switch, a fourth switch, a first active clamping transistor, and a second active clamping transistor within one switching cycle. The switching cycle is divided into six consecutive operating stages. The turn-on and turn-off sequence of each switch is precisely controlled by a digital control unit to achieve zero-current turn-on of the main switch and zero-current turn-off of the secondary diode using the resonant inductor current. Figure 4 As shown, the following six actions are executed in one switching cycle, corresponding to steps S1 to S6 respectively.

[0039] Step 1: S1. Control the first and third switching transistors to turn on, transferring energy from the primary side to the secondary side. The third, fourth, fifth, and sixth diodes achieve zero-current turn-off. This stage is the energy transfer stage. The first and third switching transistors turn on simultaneously under the drive signal of the digital control unit. The DC bus voltage is applied across the resonant conversion circuit, and the resonant inductor current flows forward and is coupled to the secondary side through the high-frequency isolation transformer. At this time, the third, fourth, fifth, and sixth diodes in the secondary-side full-bridge rectifier filter circuit are in the conducting state, rectifying the high-frequency AC current into DC output. As the resonance process progresses, when the resonant current crosses zero and reverses, the secondary-side diodes naturally turn off. Since the current drops to zero at the moment of turn-off, zero-current turn-off is achieved, eliminating the reverse recovery loss of the diodes. For example, under a switching frequency of 100kHz, this stage lasts for approximately half a resonant cycle. During this period, the on-resistance of the primary-side SiCMOS transistor is extremely low, significantly reducing conduction losses. By coordinating the conduction of the first and third switching transistors, an energy transmission channel is established from the positive terminal of the DC bus through the resonant cavity to the negative terminal, thus reserving the necessary resonant energy for the soft switching action in the subsequent stage.

[0040] Step Two: S2, control the first switch to turn off and the first active clamping transistor to turn on. The first switch achieves zero-current turn-off, and the first active clamping transistor clamps the drain-source voltage of the first switch. This stage is the turn-off and voltage clamping stage of the first switch. The digital control unit first removes the drive signal to the first switch to turn it off. Since the resonant inductor current cannot change abruptly, this current quickly transfers to the body diode or channel of the first active clamping transistor, allowing the first switch to complete the turn-off action before the drain-source voltage rises, thus achieving zero-current turn-off. Subsequently, the first active clamping transistor is actively driven to turn on, its source connected to the midpoint potential of the three-phase rectifier circuit, and its drain connected to the source of the first switch, thereby strictly clamping the drain-source voltage of the first switch to half of the DC bus voltage. For example, when the DC bus voltage is 800V, the voltage stress on the first switch is limited to within 400V, avoiding the impact of high-voltage spikes on the device. The conduction of the first active clamping transistor not only protects the first switching transistor, but also creates a freewheeling loop for the resonant current, maintaining the continuity of the current and creating the voltage conditions for the zero-current turn-on of the second switching transistor in the next stage.

[0041] Step 3: S3, control the second switch to turn on and the first active clamp to turn off. The second switch achieves zero-current turn-on, and the resonant inductor current reaches its peak value. This stage is the turn-on and current peak stage of the second switch. During the conduction of the first active clamp, the resonant inductor current flows through it, pulling the drain-source voltage of the second switch down to near zero. At this time, the digital control unit sends a drive signal to turn on the second switch. Since the voltage across it is already zero, zero-current turn-on is achieved, completely eliminating turn-on losses. Subsequently, the first active clamp turns off, and the resonant circuit enters a free oscillation state. The resonant inductor current continues to increase until it reaches its positive peak value. For example, with a resonant inductance of 1μH and a resonant capacitor of 2.5μF, the peak current can reach tens of amperes, the specific value depending on the load power and input voltage. The zero-current turn-on of the second switch, in conjunction with the orderly turn-off of the first active clamp, ensures a smooth transition in the commutation process. At the same time, the peak value of the resonant current stores sufficient magnetic field energy to support energy release and reverse freewheeling in subsequent stages.

[0042] Step 4: S4. Control the third switch to turn off and the second active clamping transistor to turn on. The third switch achieves zero-current turn-off, and the second active clamping transistor clamps the drain-source voltage of the third switch. This stage involves the turn-off and voltage clamping of the third switch, and its working principle is symmetrical to the above. The digital control unit controls the third switch to turn off, and the resonant inductor current immediately transfers to the second active clamping transistor, allowing the third switch to turn off under zero-current conditions. Immediately afterwards, the second active clamping transistor turns on, connecting its source and drain, thereby clamping the drain-source voltage of the third switch to half of the DC bus voltage. For example, in high-frequency switching processes, this clamping effect effectively suppresses voltage oscillations caused by parasitic inductance in the line, reducing electromagnetic interference. The coordinated operation of the third switch and the second active clamping transistor not only achieves lossless turn-off of the third switch, but also fixes the potential of the lower half-bridge arm at the midpoint level, preventing voltage stress from exceeding the limit and ensuring the safe operation of the device under high-frequency conditions.

[0043] Step 5: S5, control the fourth switch to turn on and the second active clamp to turn off. The fourth switch achieves zero-current turn-on, and the resonant inductor current begins to decrease. This stage is the turn-on and current-decreasing phase of the fourth switch. Similar to the above, during the conduction of the second active clamp, the drain-source voltage of the fourth switch is clamped to zero. The digital control unit drives the fourth switch to turn on in a timely manner to achieve zero-current turn-on. Subsequently, the second active clamp turns off, and the energy in the resonant cavity begins to be released to the load or fed back through the transformer. The resonant inductor current gradually decreases from its peak value. For example, when the load power is at 50% of the rated value, the current decrease slope is determined by the resonant parameters, exhibiting a standard sinusoidal half-wave characteristic. The zero-current turn-on of the fourth switch and the turn-off of the second active clamp work closely together to complete the commutation process of the lower half of the bridge arm. At the same time, the decrease in current marks the formal start of the second half of the energy transfer cycle, preparing for the dead time.

[0044] Step Six: S6, control the second and fourth switches to turn off, and turn on the first and second active clamping transistors. The second and fourth switches achieve zero-current turn-off, and the resonant inductor current freewheels through the first and second active clamping transistors. This stage is the dead time and freewheeling stage. The digital control unit simultaneously turns off the second and fourth switches. Since the direction of the resonant inductor current has not yet changed or has just passed zero, the current will naturally flow into the body diodes or channels of the first and second active clamping transistors, causing the second and fourth switches to turn off under zero-current conditions. Subsequently, both the first and second active clamping transistors are driven to turn on, forming a bidirectional freewheeling loop. The resonant inductor current circulates between the midpoint potential and the switching node through these two clamping transistors. For example, under light load conditions, this stage lasts longer to maintain the continuity of the resonant current and ensure that all main switches have zero-current turn-on conditions at the start of the next cycle. The coordinated operation of the second and fourth switches and the two active clamping transistors not only achieves lossless turn-off of the main switches but also eliminates the voltage uncertainty problem of the dead time through the freewheeling mechanism, ensuring the stable realization of soft switching throughout the entire cycle. The waveform of the resonant inductor current during the above process is shown in the figure. Figure 3 As shown in the figure, the horizontal axis t represents time, and the vertical axis I represents the magnitude of the current.

[0045] In a more specific embodiment, the control method further includes steps for judging the load condition and adjusting the corresponding control strategy. Step 1: Determine whether the load power is under a light load condition. This step may involve the digital control unit acquiring the output voltage and output current of the conversion circuit in real time, calculating the current load power, and comparing the load power with a preset light load threshold to determine the current operating condition of the system. Specifically, the sampling module acquires real-time output electrical signals through voltage and current sensors connected to the positive and negative output terminals. The signal processor calculates the instantaneous load power based on the acquired voltage and current values. The digital control unit internally stores a light load judgment threshold, which is typically set to 20% of the rated power. For example, for a DC fast charging pile module with a rated power of 40kW, if the calculated load power is less than 8kW, the system is determined to be under a light load condition; conversely, if the load power is greater than or equal to 8kW, the system is determined not to be under a light load condition. This dynamic monitoring and threshold comparison mechanism accurately identifies whether the system is operating under heavy load, full load, standby, or light load conditions, providing a basis for selecting the optimal control mode and avoiding the problem of poor adaptability of a single control strategy across a wide load range. Step Two: If the load power is not under light load conditions, frequency conversion control is used to adjust the switching frequency corresponding to the switching cycle, resulting in stable output voltages at both the positive and negative output terminals. Specifically, when the load power is confirmed to be higher than the light load threshold, the digital control unit uses a pulse frequency modulation strategy to adjust the impedance characteristics of the resonant cavity by changing the frequency of the switching cycle, thereby stabilizing the output voltage. Specifically, the CNC unit adjusts the frequency of the drive signals output to the first to fourth switching transistors and the first and second active clamping transistors based on the deviation between the output voltage and the reference voltage. Under normal load conditions, the switching frequency typically varies around the resonant frequency, for example, within the range of 80kHz to 150kHz. When the output voltage is low, the switching frequency is reduced to decrease the resonant cavity impedance and increase energy transfer; when the output voltage is high, the switching frequency is increased to increase the impedance and reduce energy transfer. During this process, the first, second, third, and fourth switching transistors maintain a fixed complementary conduction relationship, with only the overall switching frequency changing. For example, when the load is 30kW and the output voltage is detected to be slightly lower than the set value of 750V, the control chip lowers the switching frequency from 120kHz to 100kHz, utilizing the gain characteristics of the LLC resonant cavity in the inductive region to increase the voltage gain, allowing the output voltage to quickly return to stability. Through this frequency conversion control method, zero-current turn-on of the primary-side switching transistors and zero-current turn-off of the secondary-side rectifier diodes can be achieved under heavy load and half-load conditions, ensuring that the system maintains high-efficiency operation within the main operating range. Step 3: If the load power is under light load conditions, adjust the phase shift angle between the first and second switching transistors and between the third and fourth switching transistors and expand the gain adjustment range.This step can refer to the digital control unit switching to a phase-shift modulation strategy when the load power is confirmed to be below the light load threshold, or adopting a hybrid control strategy combining frequency conversion and phase shifting. This involves adjusting the equivalent duty cycle by changing the phase difference of the conduction timing of the internal switches in the bridge arm, thereby expanding the voltage gain adjustment range. Specifically, the CNC unit no longer relies solely on a significant increase in frequency to adjust the voltage, but instead maintains the switching frequency at a low level while introducing a phase shift angle. This phase shift angle is defined as the phase difference between the drive signals of the first and second switches, and the phase difference between the drive signals of the third and fourth switches. The adjustment range of the phase shift angle is typically 0° to 90°. When it is necessary to further reduce the output voltage under light load or maintain voltage regulation, increasing the phase shift angle reduces the conduction overlap time of the upper and lower bridge arms, which is equivalent to reducing the amplitude of the fundamental voltage applied to the resonant cavity. For example, under extremely light load standby conditions of 5kW, using only frequency converter control might require increasing the frequency to over 300kHz to achieve voltage regulation, which would lead to a surge in iron losses and potentially loss of ZVS. In this case, the control chip locks the switching frequency at 100kHz and adjusts the phase shift angle between Q1 and Q2, and between Q3 and Q4 from 0° to 45°. By reducing the effective pulse width, the gain is lowered, maintaining output voltage stability while ensuring the switching transistors remain in a soft-switching state. This phase-shift control effectively solves the technical problems of frequency spikes and insufficient gain adjustment capability in traditional LLC converters under light loads, significantly improving the system's dynamic response and energy efficiency over a wide load range.

[0046] This invention discloses a hybrid three-level resonant converter circuit based on silicon carbide devices and its control method, relating to the field of power electronic conversion technology. The hybrid three-level resonant converter circuit includes a three-phase rectifier circuit, a hybrid three-level bridge arm composed of four main switches and two active clamping transistors, a resonant conversion circuit, a high-frequency isolation transformer, a secondary-side full-bridge rectifier and filter circuit, and a digital control unit. All switches are silicon carbide MOSFETs. The control method coordinates the control of each switch in six stages within one switching cycle, and introduces phase-shift control under light load conditions. This application can achieve zero-current turn-on of all main switches and zero-current turn-off of the secondary-side rectifier, effectively solving the problems of uneven switching losses and excessive voltage stress, and improving conversion efficiency and system reliability.

[0047] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A hybrid three-level resonant converter circuit based on silicon carbide devices, characterized in that, The hybrid three-level resonant converter circuit includes a three-phase rectifier circuit, a first switch, a second switch, a third switch, a fourth switch, a first diode, a second diode, a first active clamping diode, a second active clamping diode, a resonant converter circuit, a high-frequency isolation transformer, a secondary full-bridge rectifier and filter circuit, and a digital control unit. The input terminal of the three-phase rectifier circuit is connected to three-phase AC power. The positive terminal of the DC bus of the three-phase rectifier circuit is connected to the drain of the first switching transistor and the drain of the first active clamping transistor. The gate of the first switching transistor is connected to the negative terminal of the first diode. The source of the first switching transistor is connected to the drain of the second switching transistor and the gate of the first active clamping transistor. The source of the first active clamping transistor is connected to the drain of the second active clamping transistor and the second connection terminal of the resonant conversion circuit. The source of the second switching transistor is connected to the drain of the third switching transistor and the first connection terminal of the resonant conversion circuit. The anode of the first diode is connected to the midpoint potential of the three-phase rectifier circuit and the cathode of the second diode; the anode of the second diode is connected to the source of the third switch, the drain of the fourth switch, and the gate of the second active clamping transistor; the source of the fourth switch is connected to the negative terminal of the DC bus of the three-phase rectifier circuit. The third and fourth connection terminals of the resonant conversion circuit are connected to the secondary full-bridge rectifier and filter circuit after being transformed by the high-frequency isolation transformer. The secondary full-bridge rectifier and filter circuit has two output terminals as positive and negative output terminals. The first switch, the second switch, the third switch, the fourth switch, the first active clamping transistor, and the second active clamping transistor are all silicon carbide MOS transistors and are all equipped with temperature sensors. The input terminal of the digital control unit is connected to the positive terminal of the DC bus, the negative terminal of the DC bus, the positive output terminal, the first connection terminal of the resonant conversion circuit, each of the temperature sensors, the source of the first active clamping transistor, the source of the second active clamping transistor, the control input terminal of the first switch transistor, the control input terminal of the second switch transistor, the control input terminal of the third switch transistor, the control input terminal of the fourth switch transistor, the control input terminal of the first active clamping transistor, and the control input terminal of the second active clamping transistor. The first switch, the second switch, the third switch, the fourth switch, the first active clamp, and the second active clamp are switched on and off within one switching cycle. One of the switching cycles comprises the following six phases: S1. Control the first switch and the third switch to be turned on; S2, control the first switch to turn off and the first active clamping transistor to turn on; S3. Control the second switch to turn on and the first active clamping transistor to turn off; S4. Control the third switch to turn off and the second active clamping transistor to turn on; S5. Control the fourth switch to turn on and the second active clamping transistor to turn off; S6. Control the second switch to turn off, the fourth switch to turn off, the first active clamping transistor to turn on, and the second active clamping transistor to turn on.

2. The hybrid three-level resonant converter circuit based on silicon carbide devices according to claim 1, characterized in that, The resonant conversion circuit includes a resonant inductor, a resonant capacitor, and a magnetizing inductor. One end of the resonant inductor serves as the first connection terminal of the resonant conversion circuit, the other end of the resonant inductor is connected to one end of the resonant capacitor, and the other end of the resonant capacitor is connected to one end of the magnetizing inductor, with the connection point serving as the third connection terminal of the resonant conversion circuit. The other end of the excitation inductor serves as the second and third connection terminals of the resonant conversion circuit.

3. The hybrid three-level resonant converter circuit based on silicon carbide devices according to claim 2, characterized in that, The secondary-side full-bridge rectifier filter circuit includes a third diode, a fourth diode, a fifth diode, a sixth diode, a first output filter capacitor, and a second output filter capacitor; The positive terminal of the third diode is connected to the first winding connection point as the first input terminal, and the negative terminal of the third diode is connected to the negative terminal of the sixth diode; the positive terminal of the sixth diode is connected to the negative terminal of the fifth diode, and the connection point is connected to the second winding connection point as the second input terminal; the positive terminal of the fifth diode is connected to the positive terminal of the fourth diode, and the negative terminal of the fourth diode is connected to the third winding connection point as the third input terminal; the first output filter capacitor and the second output filter capacitor are respectively connected in parallel between the negative terminal of the sixth diode and the positive terminal of the fifth diode.

4. The hybrid three-level resonant converter circuit based on silicon carbide devices according to claim 3, characterized in that, Both the first output filter capacitor and the second output filter capacitor are polarized capacitors; The negative terminals of the first output filter capacitor and the second output filter capacitor are respectively connected to the positive terminal of the fifth diode.

5. The hybrid three-level resonant converter circuit based on silicon carbide devices according to any one of claims 1-4, characterized in that, The digital control unit includes a sampling module, a signal processor, a numerical control unit, and a control chip; The input terminal of the sampling module is connected to the positive terminal of the DC bus, the negative terminal of the DC bus, the positive output terminal, the first connection terminal of the resonant conversion circuit, and each of the temperature sensors; The first output terminal of the sampling module is connected to the input terminal of the signal processor. The second output terminal of the sampling module, the output terminal of the signal processor, the source of the first active clamping transistor, the source of the second active clamping transistor, and the first connection terminal of the resonant conversion circuit are respectively connected to the input terminal of the numerical control unit. The output terminal of the numerical control unit is connected to the input terminal of the control chip. The output terminal of the control chip is connected to the control input terminals of the first switching transistor, the second switching transistor, the third switching transistor, the fourth switching transistor, the first active clamping transistor, and the second active clamping transistor.

6. The hybrid three-level resonant converter circuit based on silicon carbide devices according to claim 5, characterized in that, The three-phase rectifier circuit includes a first inductor, a second inductor, a third inductor, a three-phase electromagnetic interference input filter, a three-phase bridge rectifier, a first filter capacitor, and a second filter capacitor. The first inductor, the second inductor, and the third inductor are connected in series on three input phase lines. One end of each input phase line is connected to three-phase AC power, and the other end of each input phase line is connected to the three input terminals of the three-phase electromagnetic interference input filter. The three output terminals of the three-phase electromagnetic interference input filter are connected to the three input terminals of the three-phase bridge rectifier. The first output terminal of the three-phase bridge rectifier is connected to one end of the first filter capacitor, and the connection point serves as the positive terminal of the DC bus. The second output terminal of the three-phase bridge rectifier is connected to one end of the second filter capacitor, and the connection point serves as the negative terminal of the DC bus. The other end of the first filter capacitor is connected to the other end of the second filter capacitor, and the connection point serves as the midpoint potential.

7. The hybrid three-level resonant converter circuit based on silicon carbide devices according to claim 6, characterized in that, Both the first filter capacitor and the second filter capacitor are polarized capacitors; the positive terminal of the first filter capacitor is connected to the first output terminal of the three-phase bridge rectifier, and the negative terminal of the second filter capacitor is connected to the second output terminal of the three-phase bridge rectifier; the negative terminal of the first filter capacitor is connected to the positive terminal of the second filter capacitor.

8. The hybrid three-level resonant converter circuit based on silicon carbide devices according to claim 6, characterized in that, The three-phase bridge rectifier consists of six rectifier diodes; The positive terminals of three rectifier diodes are respectively connected to the three output terminals of the three-phase electromagnetic interference input filter, and the negative terminals of the three rectifier diodes are connected together to serve as the first output terminal of the three-phase bridge rectifier; the negative terminals of the other three rectifier diodes are respectively connected to the three output terminals of the three-phase electromagnetic interference input filter, and the positive terminals of the three rectifier diodes are connected together to serve as the second output terminal of the three-phase bridge rectifier.

9. A control method for a hybrid three-level resonant converter circuit based on silicon carbide devices, characterized in that, The control method is applied to the hybrid three-level resonant converter circuit based on silicon carbide devices as described in any one of claims 1-8, and the control method includes: The first switch, the second switch, the third switch, the fourth switch, the first active clamp, and the second active clamp are switched on and off within one switching cycle. One of the switching cycles comprises the following six phases: S1. Control the first switch and the third switch to turn on, so that energy is transferred from the primary side to the secondary side, and the third diode, the fourth diode, the fifth diode and the sixth diode achieve zero current turn-off; S2. Control the first switch to turn off and the first active clamping transistor to turn on, so that the first switch to turn off with zero current and the first active clamping transistor clamps the drain-source voltage of the first switch. S3. Control the second switch to turn on and the first active clamp to turn off, so that the second switch can achieve zero current turn-on and the resonant inductor current reaches its peak value. S4. Control the third switch to turn off and the second active clamping transistor to turn on. The third switch to turn off with zero current, and the second active clamping transistor clamps the drain-source voltage of the third switch. S5. Control the fourth switch to turn on and the second active clamping transistor to turn off. The fourth switch to turn on with zero current and the resonant inductor current begins to decrease. S6. Control the second switch to turn off, the fourth switch to turn off, the first active clamping transistor to turn on, and the second active clamping transistor to turn on. The second switch and the fourth switch achieve zero-current turn-off, and the resonant inductor current freewheels through the first active clamping transistor and the second active clamping transistor.

10. The control method for the hybrid three-level resonant converter circuit based on silicon carbide devices according to claim 9, characterized in that, The control method further includes: Determine whether the load power is under light load conditions; If the load power is not under light load conditions, frequency conversion control is used to adjust the switching frequency corresponding to the switching cycle, and the positive output terminal and the negative output terminal output a stable voltage. If the load power is under light load conditions, adjust the phase shift angle between the first switch and the second switch, and between the third switch and the fourth switch, and expand the gain adjustment range.

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