Three-phase staggered four-switch buck-boost integrated LLC DCDC isolation converter

Abstract

The invention discloses a three-phase staggered four-switch buck-boost integrated LLC (Logical Link Control) DCDC (Direct Current to Direct Current) isolation converter. The converter comprises a transformer based on magnetic integration design and a primary side circuit and a secondary side circuit which are connected with two sides of the transformer, the primary side circuit comprises a three-phase staggered parallel four-switch boost-buck circuit and a three-phase LLC resonant circuit, and each stage of four-switch boost-buck circuit comprises four switch tubes and a preceding-stage inductor. The front two switch tubes are located between the positive electrode and the negative electrode of the direct-current bus and form a front bridge arm, the rear two switch tubes are located between the middle bus and the negative electrode of the direct-current bus and form a rear bridge arm, and the front-stage inductor is connected between the middle point of the front bridge arm and the middle point of the rear bridge arm. The three ends of the three-phase LLC resonant circuit are correspondingly connected with the midpoints of the three rear axle arms respectively; the resonant capacitors of the LLC circuits are in angular connection, and other circuits of the LLC circuits are in star connection; the secondary side circuit is composed of a three-phase interleaved parallel full-wave rectification circuit. The invention has the advantages of wide input, high efficiency, high power density and high switching frequency.

Description

Technical Field

[0001] This invention relates to DC-DC converter technology for power conversion devices, and in particular to a DC-DC isolated converter with a three-phase interleaved four-switch buck-boost integrated LLC. Background Technology

[0002] In recent years, with the rise of industries such as new energy vehicles, photovoltaics, energy storage, green data centers, next-generation sites, and supercomputing, system power supply solutions are being driven to continuously break through and innovate in the direction of wide input, wide output, ultra-high density, and ultra-high efficiency. The full-bridge LLC resonant converter can achieve zero-voltage switching (ZVS) of the switching transistors across the entire load range, and can achieve zero-current switching (ZCS) of the secondary-side synchronous rectifier transistors when the switching frequency is lower than the resonant frequency.

[0003] Currently, LLC resonant converters commonly employ frequency conversion control, adjusting the voltage gain by controlling the converter's switching frequency. However, when the gain variation range is wide, the switching frequency variation range is also wide, posing challenges to the design of magnetic components and even failing to meet voltage regulation requirements. Considering LLC fixed-frequency operation, in constant-gain mode (i.e., LLC DCX mode), a non-isolated circuit stage is needed to achieve voltage regulation, with this stage using PWM for voltage adjustment. However, due to the increased number of power transfer stages, efficiency inevitably decreases. Therefore, researchers have proposed an integrated two-stage solution. The extremely high efficiency and power density of the LLC DCX stage contribute to the overall converter's excellent efficiency and power density performance; therefore, the focus of research is on improving the efficiency and power density of the non-isolated voltage regulation stage. Summary of the Invention

[0004] The purpose of this invention is to provide a DC-DC isolated converter with wide input, high efficiency, high power density, low conduction loss and core loss, and high switching frequency.

[0005] The technical solution to achieve the purpose of this invention is: a DC-DC isolated converter with a three-phase interleaved four-switch step-up and step-down integrated LLC, including a transformer based on magnetic integration design, and a primary side circuit and a secondary side circuit connected on both sides of the transformer;

[0006] The primary circuit includes a three-phase interleaved parallel four-switch buck-boost circuit and a three-phase LLC resonant circuit. Each four-switch buck-boost circuit includes four switching transistors and a pre-stage inductor. The first two switching transistors are located between the positive and negative terminals of the DC bus and form the front bridge arm. The last two switching transistors are located between the middle bus and the negative terminal of the DC bus and form the rear bridge arm. The pre-stage inductor is connected between the midpoint of the front bridge arm and the midpoint of the rear bridge arm. The three terminals of the three-phase LLC resonant circuit are respectively connected to the midpoints of the three rear bridge arms. The connection method between the LLC circuits is star-connected for both the primary and secondary sides, except for the resonant capacitor, and delta-connected for the resonant capacitor. The secondary circuit is composed of a three-phase interleaved parallel full-wave rectifier circuit.

[0007] Furthermore, the transformer includes first to third transformers T1 to T3, and the primary circuit includes an input DC voltage source V. in First to third inductors L b1 ~L b3 The first to twelfth switching transistors Q1~Q 12 The first to twelfth body diodes D1 to D2 12 Parasitic capacitances C from the first to the twelfth oss1 ~C oss12 Bus capacitor C bus The first to third resonant inductors L r1 ~L r3 The first to third resonant capacitors C r1 ~C r3 First to third magnetizing inductors L m1 ~L m3 Control unit;

[0008] The drain of the first switching transistor Q1, the cathode of the first body diode D1, and the first parasitic capacitance C oss1 One end is connected to the source of the first switching transistor Q1, the anode of the first body diode D1, and the first parasitic capacitance C. oss1 The other end is connected; the drain of the second switching transistor Q2 is connected to the cathode of the second body diode D2 and the second parasitic capacitance C. oss2 One end is connected, the source of the second switching transistor Q2 is connected to the anode of the second body diode D2 and the second parasitic capacitance C. oss2 The other end is connected; the drain of the third switch Q3 is connected to the cathode of the third body diode D3 and the third parasitic capacitance C. oss3 One end is connected, the source of the third switching transistor Q3 is connected to the anode of the third body diode D3 and the third parasitic capacitance C. oss3 The other end is connected; the drain of the fourth switch Q4 is connected to the cathode of the fourth body diode D4 and the fourth parasitic capacitance C. oss4 One end is connected to the source of the fourth switching transistor Q4, the anode of the fourth body diode D4, and the fourth parasitic capacitance C. oss4The other end is connected; the drain of the fifth switch Q5 is connected to the cathode of the fifth body diode D5 and the fifth parasitic capacitance C. oss5 One end is connected to the source of the fifth switching transistor Q5, the anode of the fifth body diode D5, and the fifth parasitic capacitance C. oss5 The other end is connected; the drain of the sixth switch Q6 is connected to the cathode of the sixth body diode D6 and the sixth parasitic capacitance C. oss6 One end is connected to the source of the sixth switch Q6, the anode of the sixth body diode D6, and the sixth parasitic capacitance C. oss6 The other end is connected; the drain of the seventh switch Q7 is connected to the cathode of the seventh body diode D7 and the seventh parasitic capacitance C. oss7 One end is connected to the source of the seventh switch Q7, the anode of the seventh body diode D7, and the seventh parasitic capacitance C. oss7 The other end is connected; the drain of the eighth switch Q8 is connected to the cathode of the eighth body diode D8 and the eighth parasitic capacitance C. oss8 One end is connected to the source of the eighth switch Q8, the anode of the eighth body diode D8, and the eighth parasitic capacitance C. oss8 The other end is connected; the drain of the ninth switch Q9 is connected to the cathode of the ninth body diode D9 and the ninth parasitic capacitance C. oss9 One end is connected to the source of the ninth switch Q9, the anode of the ninth body diode D9, and the ninth parasitic capacitance C. oss9 The other end is connected; the tenth switch Q 10 The drain and the tenth body diode D 10 The cathode and the tenth parasitic capacitance C oss10 One end is connected to the tenth switch Q. 10 The source and the tenth body diode D 10 The anode and the tenth parasitic capacitance C oss10 The other end is connected; the eleventh switch Q 11 The drain of the eleventh diode D 11 The cathode and the eleventh parasitic capacitance C oss11 One end is connected to the eleventh switch Q. 11 The source and the eleventh integrated diode D 11 The anode and the eleventh parasitic capacitance C oss11 The other end is connected; the twelfth switch Q 12 The drain of the twelfth body diode D 12 The cathode and the twelfth parasitic capacitance C oss12 One end is connected to the twelfth switch Q. 12 The source of the twelfth body diode D 12 The anode and the twelfth parasitic capacitance C oss12 The other end is connected;

[0009] The input DC voltage source Vin One end is connected to the drain of the first switch Q1, the fifth switch Q5, and the ninth switch Q9, and the other end is connected to the drain of the second switch Q2, the sixth switch Q6, and the tenth switch Q9. 10 The source of the first switch Q1 is connected to the drain of the second switch Q2 and the first inductor L. b1 One end is connected to the source of the fifth switch Q5, the drain of the sixth switch Q6, and the second inductor L. b2 One end is connected, and the source of the ninth switch Q9 is connected to the tenth switch Q. 10 The drain and the third inductor L b3 One end is connected; the first inductor L b1 The other end is connected to the source of the third switch Q3, the drain of the fourth switch Q4, and the first resonant inductor L. r1 One end is connected, the second inductor L b2 The other end is connected to the source of the seventh switch Q7, the drain of the eighth switch Q8, and the second resonant inductor L. r2 One end is connected, and the third inductor L b3 The other end is connected to the eleventh switch Q. 11 The source and the twelfth switch Q 12 The drain and the third resonant inductor L r3 One end is connected; the third switch Q3, the seventh switch Q7, and the eleventh switch Q 11 The drains of all terminals are connected to the bus capacitor C. bus At one end, the fourth switch Q4, the eighth switch Q8, and the twelfth switch Q 12 The sources of all are connected to the bus capacitor C. bus The other end; the first to third resonant inductors L r1 ~L r3 The other end is connected to the first to third magnetizing inductors L respectively. m1 ~L m3 One end is connected to one end of the first to third transformers T1 to T3, and the first to third magnetizing inductors L m1 ~L m3 The three phases are connected in parallel to the primary windings of the first to third transformers T1 to T3, and are connected together in a star configuration; the first to third resonant capacitors C r1 ~C r3 The first to third resonant capacitors C are connected together via a delta connection. r1 ~C r3 One end is connected to the first to third magnetizing inductors L respectively. m1 ~L m3 The other end and the other ends of the first to third transformers T1 to T3;

[0010] The control unit is used to control the first to twelfth switching transistors Q1 to Q2. 12 The on / off state.

[0011] Furthermore, the secondary circuit includes the first to sixth rectifier diodes SR1 to SR6 and the output capacitor C. o Load R Ld ;

[0012] One end of the first rectifier diode SR1 and the second rectifier diode SR2 are connected to the secondary side of the first transformer T1 to form a first full-wave rectifier circuit. One end of the third rectifier diode SR3 and the fourth rectifier diode SR4 are connected to the secondary side of the second transformer T2 to form a second full-wave rectifier circuit. One end of the fifth rectifier diode SR5 and the sixth rectifier diode SR6 are connected to the secondary side of the third transformer T3 to form a third full-wave rectifier circuit. The first to third full-wave rectifier circuits are connected together in a star configuration. The center tap of each of the first to third transformers T1 to T3 is connected to the output capacitor C. o and load R Ld One end of the first to sixth rectifier diodes SR1 to SR6 are connected to the output capacitor C. o and load R Ld The other end.

[0013] Furthermore, the conduction times of the first switch Q1 and the second switch Q2 are complementary; the conduction times of the third switch Q3 and the fourth switch Q4 are complementary; the conduction times of the fifth switch Q5 and the sixth switch Q6 are complementary; the conduction times of the seventh switch Q7 and the eighth switch Q8 are complementary; the conduction times of the ninth switch Q9 and the tenth switch Q6 are complementary. 10 Their conduction times are complementary; the eleventh switch Q 11 and the twelfth switch Q 12 Their conduction times are complementary.

[0014] Furthermore, the first to third resonant inductors L r1 ~L r3 The first to third transformers T1 to T3 are integrated into an LLC resonant cavity, using the leakage inductance of the transformer as the resonant inductor. Through the principle of three-phase magnetic flux cancellation, it integrates the first transformer T1 and the first resonant inductor L. r1 The second transformer T2 and the second resonant inductor L r2 The third transformer T3 and the third resonant inductor L r3 Each phase is integrated into a single magnetic component, forming a three-column structure. Two additional side columns are added as non-wound columns, allowing each phase flux to close through the non-wound columns, providing a closed path for the three-phase flux, and completely decoupling each phase flux. The three-phase superimposed flux is then closed through the side columns.

[0015] Furthermore, the first to fourth switching transistors Q1 to Q4 and the first front-end inductor L b1 The first phase four-switch buck-boost circuit is composed of the first switch Q1 and the second switch Q2 located between the positive and negative terminals of the DC bus and forming the front bridge arm, and the third switch Q3 and the fourth switch Q4 located between the middle bus and the negative terminal of the DC bus and forming the rear bridge arm. The first front-stage inductor L... b1 Connected between the midpoint of the front axle arm and the midpoint of the rear axle arm; the fifth to eighth switching transistors Q5 to Q8 and the second pre-stage inductor L b2 The second-phase four-switch step-up / step-down circuit is configured such that the fifth switch Q5 and the sixth switch Q6 are located between the positive and negative terminals of the DC bus and form the front bridge arm, while the seventh switch Q7 and the eighth switch Q8 are located between the middle bus and the negative terminal of the DC bus and form the rear bridge arm. The second front-stage inductor L... b2 Connected between the midpoint of the front axle arm and the midpoint of the rear axle arm; the ninth to twelfth switching transistors Q9~Q 12 and the third pre-stage inductor L b3 This forms the third-phase four-switch buck-boost circuit, in which the ninth switch Q9 and the tenth switch Q... 10 Located between the positive and negative terminals of the DC bus and forming the front bridge arm, the eleventh switching transistor Q 11 and the twelfth switch Q 12 Located between the intermediate bus and the negative terminal of the DC bus, forming the rear bridge arm, the third front-stage inductor L b3 It connects the midpoint of the front axle arm and the midpoint of the rear axle arm;

[0016] In the first to third phase four-switch buck-boost circuit, the phase shift angle between the front bridge arm and the rear bridge arm is the minimum phase shift angle δ required for each switch to achieve soft switching. When the phase shift angle is less than the minimum phase shift angle δ, the absolute value of the current flowing through each switch decreases, and soft switching cannot be achieved. When the phase shift angle is greater than the minimum phase shift angle δ, the absolute value of the current flowing through each switch increases, and the loss increases.

[0017] The minimum phase shift angle is:

[0018]

[0019] Where δ is the minimum phase shift angle, D is the duty cycle of the switch on the front axle arm, and f s L is the switching frequency. b P is the inductance value of the preceding stage inductor. o V is the output power of the converter. in C is the input voltage of the converter. oss t is the junction capacitance of the switching transistor. dead For dead time, L m This is the magnetizing inductance value of the transformer.

[0020] Furthermore, the control unit controls the first to twelfth switching transistors Q1 to Q2. 12 The switching on and off of the transistors in the first to third phase four-switch buck-boost circuits allows the two switching transistors in the front arm to conduct complementaryly with adjustable duty cycles to handle different input voltages; the two switching transistors in the rear arm conduct complementaryly with a fixed duty cycle of 0.5; the phase shift angle between the front and rear arms is the minimum phase shift angle δ; the conduction phase difference between the corresponding switching transistors in the first to third phase four-switch buck-boost circuits is 120°.

[0021] Furthermore, the first to sixth rectifier diodes SR1 to SR6 and the output filter capacitor C o To form a three-phase interleaved parallel full-wave rectifier circuit;

[0022] The first rectifier SR1, the second rectifier SR2, the third rectifier SR3, the fourth rectifier SR4, the fifth rectifier SR5, and the sixth rectifier SR6 are connected to a common ground and are located in two winding branches of the secondary windings of the first transformer T1, the second transformer T2, and the third transformer T3, respectively, forming a first-phase full-wave rectifier circuit, a second-phase full-wave rectifier circuit, and a third-phase full-wave rectifier circuit; the three full-wave rectifier circuits are connected in a star configuration; the output filter capacitor C... o It is connected in parallel to the output ports of three full-wave rectifier circuits.

[0023] Furthermore, the three-phase connection method of the primary and secondary circuits on both sides of the first to third transformers T1 to T3, except for the first to third resonant capacitors C... r1 ~C r3 All external connections are star-connected. Because the neutral point is floating, star connections naturally possess self-current sharing capability; however, for the first to third resonant capacitors C... r1 ~C r3 When a star connection is used, the resonant capacitor has a DC bias voltage. By moving the resonant capacitor from in front of the resonant inductor to behind the transformer and through the star-delta equivalent transformation, a delta connection structure for the resonant capacitor is obtained. In this structure, since the average voltage across the transformer and the inductor is zero, and the resonant capacitor is connected between the two transformers, the DC component of the resonant capacitor voltage is the difference between the DC components of the voltage at the two phase bridge arms. Since the DC components of the voltage at the two phase bridge arms cancel each other out, the resonant capacitor has no DC bias voltage.

[0024] Furthermore, when the input voltage is greater than the bus voltage, the control unit is used to control the duty cycle D of the upper switch in the front axle arm to be less than 0.5, so that the converter can realize the step-down function.

[0025] When the input voltage is less than the bus voltage, the control unit is used to control the duty cycle D of the upper switch in the front axle arm to be greater than 0.5, so that the converter can realize the boost function.

[0026] Compared with the prior art, the present invention has the following significant advantages: (1) Under wide voltage conditions, it has better efficiency and power density than similar circuits; (2) Within a wide range of input voltage and output power, it can achieve zero voltage turn-on (ZVS) of all switching transistors and zero current turn-off (ZCS) of all secondary synchronous rectifier transistors, thereby improving the switching frequency; (3) The rear bridge arm is a multiplexed structure, and the inductor current of the four-switch Buck-Boost can flow directly into the resonant cavity, reducing conduction loss and core loss; (4) The LLC resonant cavity part is magnetically integrated. The converter uses the transformer leakage inductance as the resonant inductor to integrate the resonant inductor into the transformer. At the same time, through the principle of three-phase magnetic flux cancellation, it integrates the three-phase transformer into a single magnetic component, realizing the high-efficiency and high-density design of the converter and improving the overall power density of the converter. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the DC-DC isolated converter of the present invention, which is a three-phase interleaved four-switch buck-boost integrated LLC.

[0028] Figure 2 This is a schematic diagram of the topology of a single four-switch Buck-Boost in this invention.

[0029] Figure 3 This is a waveform diagram of the inductor current and magnetizing current during one switching cycle of the four-switch Buck-Boost in an embodiment of the present invention.

[0030] Figure 4a This is a schematic diagram of the working mode of the converter in an embodiment of the present invention.

[0031] Figure 4b This is a schematic diagram of the second working mode of the converter in an embodiment of the present invention.

[0032] Figure 4c This is a schematic diagram of the working mode three of the converter in an embodiment of the present invention.

[0033] Figure 4d This is a schematic diagram of the fourth working mode of the converter in an embodiment of the present invention.

[0034] Figure 4e This is a schematic diagram of the fifth working mode of the converter in an embodiment of the present invention.

[0035] Figure 4f This is a schematic diagram of the sixth working mode of the converter in an embodiment of the present invention.

[0036] Figure 4g This is a schematic diagram of the seventh working mode of the converter in an embodiment of the present invention.

[0037] Figure 4hIt is a schematic diagram of the eighth working mode of the converter in the embodiment of the present invention.

[0038] Figure 4i It is a schematic diagram of the ninth working mode of the converter in the embodiment of the present invention.

[0039] Figure 4j It is a schematic diagram of the tenth working mode of the converter in the embodiment of the present invention.

[0040] Figure 4k It is a schematic diagram of the eleventh working mode of the converter in the embodiment of the present invention.

[0041] Figure 4l It is a schematic diagram of the twelfth working mode of the converter in the embodiment of the present invention.

[0042] Figure 5 It is the key waveforms within one switching period of the converter in the embodiment of the present invention. From top to bottom, they are the drive signal, resonant current and magnetizing current signals, and three-phase inductor current signals.

[0043] Figure 6 It is the current waveform diagram of each phase flowing through four switching tubes within one period in the embodiment of the present invention.

[0044] Figure 7 It is the variation diagram of the inductor current i Lb with the phase-shift angle δ when 0 < D < 0.5 and 0 < δ < D in the embodiment of the present invention.

[0045] Figure 8 It is the effective value curve of the inductor current relative to the phase-shift angle when the output powers are 2400W, 1200W, 600W and the input voltages are 300V, 400V, 500V respectively in the embodiment of the present invention.

[0046] Figure 9 It is the three-dimensional view of the new magnetic core structure of the three-phase interleaved four-switch buck-boost integrated LLC DCDC isolation converter in the embodiment of the present invention. Detailed implementation manners

[0047] Next, in combination with the accompanying drawings and specific embodiments, the present invention will be further described in detail.

[0048] This invention discloses a DC-DC isolated converter with a three-phase interleaved four-switch buck-boost integrated LLC circuit. The primary-side circuit includes a three-phase interleaved parallel four-switch buck-boost circuit and a three-phase LLC resonant circuit. Each stage of the four-switch buck-boost circuit includes four switching transistors and a pre-stage inductor. The first two switching transistors are located between the positive and negative terminals of the DC bus and form the front arm, while the last two switching transistors are located between the middle bus and the negative terminal of the DC bus and form the rear arm. The pre-stage inductor is connected between the midpoint of the front arm and the midpoint of the rear arm. The three terminals of the three-phase LLC resonant circuit are respectively connected to the midpoints of the three rear arms. The connection method between the LLC circuits is star-connected for both the primary and secondary sides, except for the resonant capacitor, which is delta-connected. The secondary-side circuit is composed of a three-phase interleaved parallel full-wave rectifier circuit.

[0049] Combination Figure 1 , Figure 2 This invention discloses a three-phase interleaved four-switch buck-boost integrated LLC DC-DC isolated converter, including an input DC voltage source V. in First to third inductors L b1 ~L b3 The first to twelfth switching transistors Q1~Q 12 The first to twelfth body diodes D1 to D2 12 Parasitic capacitances C from the first to the twelfth oss1 ~C oss12 Bus capacitor C bus The first to third resonant inductors L r1 ~L r3 The first to third resonant capacitors C r1 ~C r3 First to third magnetizing inductors L m1 ~L m3 Transformers T1-T3 (first to third), rectifier diodes SR1-SR6 (first to sixth), and output capacitor C. o Load R Ld Control unit;

[0050] The drain of the first switching transistor Q1, the cathode of the first body diode D1, and the first parasitic capacitance C oss1 One end is connected to the source of the first switching transistor Q1, the anode of the first body diode D1, and the first parasitic capacitance C. oss1 The other end is connected; the drain of the second switching transistor Q2 is connected to the cathode of the second body diode D2 and the second parasitic capacitance C. oss2 One end is connected, the source of the second switching transistor Q2 is connected to the anode of the second body diode D2 and the second parasitic capacitance C. oss2 The other end is connected; the drain of the third switch Q3 is connected to the cathode of the third body diode D3 and the third parasitic capacitance C. oss3One end is connected, the source of the third switching transistor Q3 is connected to the anode of the third body diode D3 and the third parasitic capacitance C. oss3 The other end is connected; the drain of the fourth switch Q4 is connected to the cathode of the fourth body diode D4 and the fourth parasitic capacitance C. oss4 One end is connected to the source of the fourth switching transistor Q4, the anode of the fourth body diode D4, and the fourth parasitic capacitance C. oss4 The other end is connected; the drain of the fifth switch Q5 is connected to the cathode of the fifth body diode D5 and the fifth parasitic capacitance C. oss5 One end is connected to the source of the fifth switching transistor Q5, the anode of the fifth body diode D5, and the fifth parasitic capacitance C. oss5 The other end is connected; the drain of the sixth switch Q6 is connected to the cathode of the sixth body diode D6 and the sixth parasitic capacitance C. oss6 One end is connected to the source of the sixth switch Q6, the anode of the sixth body diode D6, and the sixth parasitic capacitance C. oss6 The other end is connected; the drain of the seventh switch Q7 is connected to the cathode of the seventh body diode D7 and the seventh parasitic capacitance C. oss7 One end is connected to the source of the seventh switch Q7, the anode of the seventh body diode D7, and the seventh parasitic capacitance C. oss7 The other end is connected; the drain of the eighth switch Q8 is connected to the cathode of the eighth body diode D8 and the eighth parasitic capacitance C. oss8 One end is connected to the source of the eighth switch Q8, the anode of the eighth body diode D8, and the eighth parasitic capacitance C. oss8 The other end is connected; the drain of the ninth switch Q9 is connected to the cathode of the ninth body diode D9 and the ninth parasitic capacitance C. oss9 One end is connected to the source of the ninth switch Q9, the anode of the ninth body diode D9, and the ninth parasitic capacitance C. oss9 The other end is connected; the tenth switch Q 10 The drain and the tenth body diode D 10 The cathode and the tenth parasitic capacitance C oss10 One end is connected to the tenth switch Q. 10 The source and the tenth body diode D 10 The anode and the tenth parasitic capacitance C oss10 The other end is connected; the eleventh switch Q 11 The drain of the eleventh diode D 11 The cathode and the eleventh parasitic capacitance C oss11 One end is connected to the eleventh switch Q. 11 The source and the eleventh integrated diode D 11 The anode and the eleventh parasitic capacitance C oss11 The other end is connected; the twelfth switch Q 12 The drain of the twelfth body diode D 12The cathode and the twelfth parasitic capacitance C oss12 One end is connected to the twelfth switch Q. 12 The source of the twelfth body diode D 12 The anode and the twelfth parasitic capacitance C oss12 The other end is connected;

[0051] The input DC voltage source V in One end is connected to the drain of the first switch Q1, the fifth switch Q5, and the ninth switch Q9, and the other end is connected to the drain of the second switch Q2, the sixth switch Q6, and the tenth switch Q9. 10 The source of the first switch Q1 is connected to the drain of the second switch Q2 and the first inductor L. b1 One end is connected to the source of the fifth switch Q5, the drain of the sixth switch Q6, and the second inductor L. b2 One end is connected, and the source of the ninth switch Q9 is connected to the tenth switch Q. 10 The drain and the third inductor L b3 One end is connected; the first inductor L b1 The other end is connected to the source of the third switch Q3, the drain of the fourth switch Q4, and the first resonant inductor L. r1 One end is connected, the second inductor L b2 The other end is connected to the source of the seventh switch Q7, the drain of the eighth switch Q8, and the second resonant inductor L. r2 One end is connected, and the third inductor L b3 The other end is connected to the eleventh switch Q. 11 The source and the twelfth switch Q 12 The drain and the third resonant inductor L r3 One end is connected; the third switch Q3, the seventh switch Q7, and the eleventh switch Q 11 The drains of all terminals are connected to the bus capacitor C. bus At one end, the fourth switch Q4, the eighth switch Q8, and the twelfth switch Q 12 The sources of all are connected to the bus capacitor C. bus The other end; the first to third resonant inductors L r1 ~L r3 The other end is connected to the first to third magnetizing inductors L respectively. m1 ~L m3 One end is connected to one end of the first to third transformers T1 to T3, and the first to third magnetizing inductors L m1 ~L m3 The three phases are connected in parallel to the primary windings of the first to third transformers T1 to T3, and are connected together in a star configuration; the first to third resonant capacitors C r1 ~C r3The first to third resonant capacitors C are connected together via a delta connection. r1 ~C r3 One end is connected to the first to third magnetizing inductors L respectively. m1 ~L m3 The other end and the other ends of the first to third transformers T1 to T3;

[0052] One end of the first rectifier diode SR1 and the second rectifier diode SR2 are connected to the secondary side of the first transformer T1 to form a first full-wave rectifier circuit. One end of the third rectifier diode SR3 and the fourth rectifier diode SR4 are connected to the secondary side of the second transformer T2 to form a second full-wave rectifier circuit. One end of the fifth rectifier diode SR5 and the sixth rectifier diode SR6 are connected to the secondary side of the third transformer T3 to form a third full-wave rectifier circuit. The first to third full-wave rectifier circuits are connected together in a star configuration. The center tap of each of the first to third transformers T1 to T3 is connected to the output capacitor C. o and load R Ld One end of the first to sixth rectifier diodes SR1 to SR6 are connected to the output capacitor C. o and load R Ld The other end;

[0053] The control unit is used to control the first to twelfth switching transistors Q1 to Q2. 12 The on / off state.

[0054] As a specific example, the conduction times of the first switch Q1 and the second switch Q2 are complementary; the conduction times of the third switch Q3 and the fourth switch Q4 are complementary; the conduction times of the fifth switch Q5 and the sixth switch Q6 are complementary; the conduction times of the seventh switch Q7 and the eighth switch Q8 are complementary; the conduction times of the ninth switch Q9 and the tenth switch Q6 are complementary. 10 Their conduction times are complementary; the eleventh switch Q 11 and the twelfth switch Q 12 Their conduction times are complementary.

[0055] As a specific example, the first to third resonant inductors L r1 ~L r3 The first to third transformers T1 to T3 are integrated into an LLC resonant cavity, using the leakage inductance of the transformer as the resonant inductor. Through the principle of three-phase magnetic flux cancellation, it integrates the first transformer T1 and the first resonant inductor L. r1 The second transformer T2 and the second resonant inductor L r2 The third transformer T3 and the third resonant inductor L r3Each phase is integrated into a single magnetic component, forming a three-column structure. Two additional side columns are added as non-wound columns, allowing each phase flux to be closed through the non-wound columns, providing a closed path for the three-phase flux, and completely decoupling each phase flux. The three-phase flux after superposition can be closed through the side columns.

[0056] As a specific example, the first to fourth switching transistors Q1 to Q4 and the first front-end inductor L b1 The first phase four-switch buck-boost circuit is composed of the first switch Q1 and the second switch Q2 located between the positive and negative terminals of the DC bus and forming the front bridge arm, and the third switch Q3 and the fourth switch Q4 located between the middle bus and the negative terminal of the DC bus and forming the rear bridge arm. The first front-stage inductor L... b1 Connected between the midpoint of the front axle arm and the midpoint of the rear axle arm; the fifth to eighth switching transistors Q5 to Q8 and the second pre-stage inductor L b2 The second-phase four-switch step-up / step-down circuit is configured such that the fifth switch Q5 and the sixth switch Q6 are located between the positive and negative terminals of the DC bus and form the front bridge arm, while the seventh switch Q7 and the eighth switch Q8 are located between the middle bus and the negative terminal of the DC bus and form the rear bridge arm. The second front-stage inductor L... b2 Connected between the midpoint of the front axle arm and the midpoint of the rear axle arm; the ninth to twelfth switching transistors Q9~Q 12 and the third pre-stage inductor L b3 This forms the third-phase four-switch buck-boost circuit, in which the ninth switch Q9 and the tenth switch Q... 10 Located between the positive and negative terminals of the DC bus and forming the front bridge arm, the eleventh switching transistor Q 11 and the twelfth switch Q 12 Located between the intermediate bus and the negative terminal of the DC bus, forming the rear bridge arm, the third front-stage inductor L b3 It connects the midpoint of the front axle arm and the midpoint of the rear axle arm;

[0057] In the first to third phase four-switch buck-boost circuit, the phase shift angle between the front bridge arm and the rear bridge arm is the minimum phase shift angle δ required for each switch to achieve soft switching. When the phase shift angle is less than the minimum phase shift angle δ, the absolute value of the current flowing through each switch decreases, and soft switching cannot be achieved. When the phase shift angle is greater than the minimum phase shift angle δ, the absolute value of the current flowing through each switch increases, and the loss increases.

[0058] The minimum phase shift angle is:

[0059]

[0060] Where δ is the minimum phase shift angle, D is the duty cycle of the switch on the front axle arm, and f s L is the switching frequency. b P is the inductance value of the preceding stage inductor. oV is the output power of the converter. in C is the input voltage of the converter. oss t is the junction capacitance of the switching transistor. dead For dead time, L m This is the magnetizing inductance value of the transformer.

[0061] As a specific example, the control unit controls the first to twelfth switching transistors Q1 to Q2. 12 The switching on and off of the transistors in the first to third phase four-switch buck-boost circuits allows the two switching transistors in the front arm to conduct complementaryly with adjustable duty cycles to handle different input voltages; the two switching transistors in the rear arm conduct complementaryly with a fixed duty cycle of 0.5; the phase shift angle between the front and rear arms is the minimum phase shift angle δ; the conduction phase difference between the corresponding switching transistors in the first to third phase four-switch buck-boost circuits is 120°.

[0062] As a specific example, the first to sixth rectifier diodes SR1 to SR6 and the output filter capacitor C o To form a three-phase interleaved parallel full-wave rectifier circuit;

[0063] The first rectifier SR1, the second rectifier SR2, the third rectifier SR3, the fourth rectifier SR4, the fifth rectifier SR5, and the sixth rectifier SR6 are connected to a common ground and are located in two winding branches of the secondary windings of the first transformer T1, the second transformer T2, and the third transformer T3, respectively, forming a first-phase full-wave rectifier circuit, a second-phase full-wave rectifier circuit, and a third-phase full-wave rectifier circuit; the three full-wave rectifier circuits are connected in a star configuration; the output filter capacitor C... o It is connected in parallel to the output ports of three full-wave rectifier circuits.

[0064] As a specific example, the three-phase connection method of the primary and secondary circuits on both sides of the first to third transformers T1 to T3, excluding the first to third resonant capacitors C... r1 ~C r3 All external connections are star-connected. Because the neutral point is floating, star connections naturally possess self-current sharing capability; however, for the first to third resonant capacitors C... r1 ~C r3 When a star connection is used, the resonant capacitor has a DC bias voltage. Therefore, by moving the resonant capacitor from in front of the resonant inductor to behind the transformer and through the star-delta equivalent transformation, a delta connection structure for the resonant capacitor can be obtained. In this structure, since the average voltage across the transformer and the inductor is zero, and the resonant capacitor is connected between the two transformers, the DC component of the resonant capacitor voltage is the difference between the DC components of the voltages at the two bridge arm points. Since the DC components of the voltages at the two bridge arm points cancel each other out, the resonant capacitor does not have a DC bias voltage.

[0065] As a specific example, when the input voltage is greater than the bus voltage, the control unit is used to control the duty cycle D of the upper switch in the front axle arm to be less than 0.5, so that the converter can achieve the step-down function.

[0066] As a specific example, when the input voltage is less than the bus voltage, the control unit is used to control the duty cycle D of the upper switch in the front axle arm to be greater than 0.5, so that the converter can realize the boost function.

[0067] Example

[0068] This embodiment provides a three-phase interleaved four-switch buck-boost integrated LLC DC-DC isolated converter. The main circuit of the converter is as follows: Figure 1 As shown, the following settings are made: 1. The switching transistor capacitor is linearly ideal; 2. The inductor current is defined as positive from left to right; 3. The dead time is short enough; 4. The output capacitor is large enough.

[0069] Although the four-switch Buck-Boost and LLC share the rear axle arm, their gains do not affect each other; Figure 2 This is a circuit diagram for a single four-switch Buck-Boost converter. The DC voltage of the front arm is V. in Let the duty cycle of Q1 be D, then the voltage v at point A is... A The average value V over one switching cycle A for:

[0070]

[0071] The DC voltage of the rear axle arm, also known as the LLC axle arm, is V. bus If the duty cycles of Q3 and Q4 are both 0.5, then the voltage v at point B is... B The average value V over one switching cycle B for:

[0072]

[0073] According to the volt-second balance law of inductance L, V A = V B Substituting, we get:

[0074]

[0075] When an LLC-class transformer operates at its resonant frequency and its load effect is neglected, its gain is related to the transformer turns ratio n. For a three-phase LLC with full-wave rectification on the secondary side, the gain G... LLC for:

[0076]

[0077] The gain G of the entire converter is then:

[0078]

[0079] Figure 3 The waveforms of the inductor current and magnetizing current during one switching cycle of a four-switch Buck-Boost converter are given by... Figure 3 The expression for the inductor current can be obtained as follows:

[0080]

[0081] According to the conservation of input and output power of the converter during one cycle:

[0082]

[0083] Therefore, I1 can be expressed as:

[0084]

[0085] Therefore, the inductor current at other times can be obtained as follows:

[0086]

[0087] Figures 4a to 4l The operating mode diagram of the converter is given. Figure 5 The key waveforms of the converter during one switching cycle are presented, from top to bottom: drive signal, resonant current and magnetizing current signals, and three-phase inductor current signal. Because the LLC operates in open-loop fixed-frequency mode, and the switching frequency equals the resonant frequency, the secondary side can be equivalently represented by an inductor R connected in parallel with the magnetizing inductor. eq Before performing modal analysis, the positive directions of the two-phase inductor current and resonant current, as shown in the diagram, are first defined. Based on the relative magnitudes of the input voltage and the bus voltage, there are two operating modes: buck mode and boost mode. Each operating mode is further divided into twelve modes. Since buck mode and boost mode are essentially the same, this embodiment takes buck mode as an example, combined with... Figures 4a to 4l and Figure 5 A detailed modal analysis was conducted.

[0088] Mode 1 (t0-t1): such as Figure 4a For phase I: at time t0, Q2 is turned off, i Lb1 When the voltage across Q1 is negative, C1 discharges and C2 charges. When the voltage across Q1 becomes 0, Q1 turns on with zero voltage, Q3 remains off, and Q4 remains on. For phases II and III: the switching transistors do not operate, and Q6, Q7 and Q9... 11 The service will remain available on Q5, Q8, and Q6. 10 Q 12 Keep it off.

[0089] Mode 2 (t1-t2): such as Figure 4b For phase II: at time t1, Q7 is turned off, i Lb2 If negative, i Lr2 When the voltage across Q8 is positive, C8 discharges and C7 charges. When the voltage across Q8 becomes 0, Q8 turns on with zero voltage, Q5 remains off, and Q6 remains on. For phases I and III: the switching transistors do not operate, and Q1, Q4, Q9, and Q6 remain on. 11 The service will remain operational in Q2, Q3, and Q4. 10 Q 12 Keep it off.

[0090] Mode 3 (t2-t3): such as Figure 4c For phase III: at time t2, Q9 is turned off, i Lb3 If positive, then C 10 Discharge, C9 charges, when Q 10 When the voltage across the terminals becomes 0, Q 10 Zero-voltage turn-on, Q 11 Stay open, Q 12 Maintain off. For phases I and II: the switching transistors do not operate, Q1, Q4 and Q6, Q8 remain on, and Q2, Q3 and Q5, Q7 remain off.

[0091] Mode 4 (t3-t4): such as Figure 4d For phase I: at time t3, Q4 is turned off, i Lb1 For positive, i Lr1 When the voltage across Q3 is negative, C3 discharges and C4 charges. When the voltage across Q3 becomes 0, Q3 turns on with zero voltage, Q1 remains on, and Q2 remains off. For phases II and III: the switching transistors do not operate, and Q6, Q8, and Q... 10 Q 11 The service will remain open for Q5, Q7, Q9, and Q1. 12 Keep it off.

[0092] Mode 5 (t4-t5): such as Figure 4e For phase II: at time t4, Q6 is turned off, i Lb2 When the voltage across Q5 is negative, C5 discharges and C6 charges. When the voltage across Q5 becomes 0, Q5 turns on with zero voltage, Q7 remains off, and Q8 remains on. For phases I and III: the switching transistors do not operate, and Q1, Q3, and Q... 10 Q 11 The service will remain open in Q2, Q3, Q9, and Q1. 12 Keep it off.

[0093] Modal 6 (t5-t6): such as Figure 4f For phase III: at time t5, Q 11 Turn off, i Lb3 For positive, i Lr3If it is negative, then C 12 Discharge, C 11 Charging, when Q 12 When the voltage across the terminals becomes 0, Q 12 Zero-voltage turn-on, Q9 remains off, Q 10 Maintain operation. For phases I and II: the switching transistors do not operate, Q1, Q3 and Q5, Q8 remain on, and Q2, Q4 and Q6, Q7 remain off.

[0094] Mode 7 (t6-t7): such as Figure 4g For phase I: at time t6, Q1 is turned off, i Lb1 When the voltage across Q2 is positive, C2 discharges and C1 charges. When the voltage across Q2 becomes 0, Q2 turns on with zero voltage, Q3 remains on, and Q4 remains off. For phases II and III: the switching transistors do not operate, and Q5, Q8, and Q... 10 Q 12 The service will remain open in Q6, Q7, Q9, and Q1. 11 Keep it off.

[0095] Modal 8 (t7-t8): such as Figure 4h For phase II: at time t7, Q8 is turned off, i Lb2 For positive, i Lr2 When the voltage across Q7 is negative, C7 discharges and C8 charges. When the voltage across Q7 becomes 0, Q7 turns on with zero voltage, Q5 remains on, and Q6 remains off. For phases I and III: the switching transistors do not operate, and Q2, Q3, and Q... 10 Q 12 The service will remain open in Q1, Q4, Q9, and Q1. 11 Keep it off.

[0096] Mode 9 (t8-t9): such as Figure 4i For phase III: at time t8, Q 10 Turn off, i Lb3 The value is negative, causing C9 to discharge, C 10 When charging, Q9 turns on at zero voltage when the voltage across it becomes 0. 11 Maintain shutdown, Q 12 Maintain operation. For phases I and II: the switching transistors do not operate, Q2, Q3 and Q5, Q7 remain on, and Q1, Q4 and Q6, Q8 remain off.

[0097] Modal 10 (t9-t) 10 ):like Figure 4j For phase I: at time t9, Q3 is turned off, i Lb1 If negative, i Lr1When the voltage across Q4 is positive, C4 discharges and C3 charges. When the voltage across Q4 becomes 0, Q4 turns on with zero voltage, Q1 remains off, and Q2 remains on. For phases II and III: the switching transistors do not operate, and Q5, Q7, Q9, and Q2 remain on. 12 The service will remain available in Q6, Q8, and Q9. 10 Q 11 Keep it off.

[0098] Modal 11 (t) 10 -t 11 ):like Figure 4k For phase II: at t 10 At that moment, Q5 is turned off, i Lb2 When the voltage across Q6 is positive, C6 discharges and C5 charges. When the voltage across Q6 becomes 0, Q6 turns on with zero voltage, Q7 remains on, and Q8 remains off. For phases I and III: the switching transistors do not operate, and Q1, Q3, and Q... 10 Q 11 The service will remain open in Q2, Q3, Q9, and Q1. 12 Keep it off.

[0099] Modal Twelve (t) 11 -t 12 ):like Figure 4l For phase III: at t 11 At that moment, Q 12 Turn off, i Lb3 If negative, i Lr3 If positive, then C 11 Discharge, C 12 Charging, when Q 11 When the voltage across the terminals becomes 0, Q 11 Zero-voltage turn-on, Q9 remains on, Q 10 Maintain off. For phases I and II: the switching transistors do not operate, Q2, Q4 and Q6, Q7 remain on, and Q1, Q3 and Q5, Q8 remain off.

[0100] To achieve high converter efficiency, all switching transistors employ soft-switching technology during the switching process. By introducing resonance before and after the switching action, the turn-on voltage of the switching transistors drops to zero first, eliminating the overlap of voltage and current during switching, thereby significantly reducing or even eliminating switching losses. From the above modal analysis, the conditions for achieving soft switching of the switching transistors can be determined as follows:

[0101]

[0102] Where I Q t is the current flowing into the switching transistor at the moment of switching on. dead For dead time, C oss For the parasitic capacitance of the switching transistor, V dsIt is the voltage across the drain and source terminals when the switching transistor is turned off.

[0103] For a three-phase interleaved structure, the conditions for realizing soft switching of the four switching transistors corresponding to each phase are the same. Therefore, only the conditions for realizing soft switching of the four switching transistors in one phase need to be analyzed. Here, taking the first phase as an example:

[0104] For Q1 and Q2, the current provided by the pre-stage inductor current i Lb1 provides the current for realizing their soft switching. For Q3 and Q4, the current provided by the pre-stage inductor current i Lb1 and the resonant cavity excitation current i Lm1 together provide the current for realizing their soft switching. Figure 6 It is the current waveform diagram of each phase flowing through the four switching transistors in one period.

[0105] The phase shift angle δ has an important influence on the modulation inductor current waveform. Figure 7 When 0 < D < 0.5 and 0 < δ < D, the variation of the inductor current i Lb with the phase shift angle δ is simply given, where I1~I4 are the inductor currents at the turn-on moments of Q1-Q4 respectively. Intuitively, when the phase shift angle δ increases, the absolute values of I1~I4 all increase, and the loss increases. Therefore, it is expected that δ is as small as possible; when the phase shift angle δ decreases, the absolute values of I1~I4 all decrease, and the soft switching may fail. Therefore, it is expected that δ is larger. Therefore, in order to achieve high efficiency and high power density, the phase shift angle needs to be designed by compromise.

[0106] By联立所有条件并化简可得移相角需要满足的条件为:

[0107]

[0108] From the inductor current expression, the effective value of the inductor current in one switching period can be obtained as:

[0109]

[0110] Where:

[0111]

[0112] In order to minimize the conduction losses of the switching transistors and the inductor, and at the same time realize the soft switching of all switching transistors, the effective value of the inductor current must be minimized. From the inductor current effective value expression, Figure 8 . Figure 8 It respectively gives the effective value curves of the inductor current with respect to the phase shift angle when the output powers are 2400W, 1200W, 600W, and the input voltages are 300V, 400V, 500V.

[0113] Figure 8 It should be noted that the part "联立所有条件并化简可得移相角需要满足的条件为:" in the original text seems to be an unfinished or incorrect expression. I translated it as literally as possible. You may need to check and correct this part according to the actual situation.The dashed lines represent phase shift angles at which the converter cannot achieve soft switching for all switching transistors, while the solid lines represent phase shift angles at which soft switching for all switching transistors can be achieved. The intersection of the solid and dashed lines represents the critical phase shift angle at which all switching transistors can be achieved. This phase shift angle is obtained by taking the equality sign from the previous formula. As can be seen from the figure, the effective value of the inductor current has a minimum under all operating conditions. However, the phase shift angle chosen at this point causes the switching transistors to operate in a hard-switching state, resulting in significant switching losses. Choosing a critical phase shift angle minimizes the effective value of the inductor current while still enabling soft switching for all switching transistors. Therefore, the value of the phase shift angle is determined.

[0114] For a single transformer, a magnetic flux loop is typically formed by wound and unwound columns. Placing three independent transformers together requires at least three wound columns and three unwound columns. If the three-phase transformer cores are arranged at 120° intervals, the three unwound columns can be grouped together and integrated. Through the integration of the unwound columns, the three discrete cores are integrated into a single magnetic component. Furthermore, since the three-phase circuits are staggered by 120°, there is also a 120° phase difference between the magnetic fluxes of the three-phase transformers, allowing for flux cancellation. Based on the principle of three-phase flux cancellation, the three-phase transformer and three-phase inductor are integrated into a single magnetic component. The specific design includes upper and lower magnetic plates, three winding posts, and two non-winding side posts. This eliminates the need for the non-winding magnetic posts in the integrated magnetic core of the three-phase transformer, and the magnetic core is planarized, ultimately resulting in a three-phase integrated transformer core structure with three magnetic posts. In this structure, the side posts do not have air gaps; the air gap only exists between the three-phase winding posts and the upper magnetic plate. The leakage inductance of the transformer is used as the resonant inductance, achieving a high-efficiency and high-density design for the converter.

[0115] In fact, if a three-phase transformer is excited by a three-phase sinusoidal voltage with a phase difference of 120°, its three-phase magnetic flux also exhibits a sine wave with a phase difference of 120°, and the sum of the three-phase magnetic flux is always zero, achieving complete magnetic flux cancellation. However, for the DC-DC isolation converter with a three-phase interleaved four-switch step-up / step-down integrated LLC provided in this invention, the excitation of its three-phase transformer is a three-phase square wave voltage with a phase difference of 120°. Since the square wave voltage has rich harmonic content, the three-phase magnetic flux will inevitably have a large number of harmonic components, and the sum of the three phases is no longer zero, thus failing to achieve complete magnetic flux cancellation. For the three-pillar core structure, since the non-wound pillars are omitted, most of the magnetic flux of each phase must be closed through the magnetic circuits of the other two phases, thus there is a magnetic coupling relationship between the three phases. Since the three-pillar structure cannot provide a closed path for the three-phase superimposed tertiary magnetic flux, this tertiary magnetic flux can only be closed through air. This increases the transformer's leakage flux, and the high-frequency magnetic flux at three times the switching frequency induces high-frequency eddy currents in the PCB windings. Since the AC resistance of the windings is high at high frequencies, the tertiary magnetic flux introduces significant eddy current losses, reducing the overall efficiency of the transformer. An improvement to the three-pillar design involves adding two side pillars as non-wound pillars, allowing each phase's magnetic flux to close through these pillars individually. The presence of these pillars also provides a closed path for the tertiary magnetic flux. A three-dimensional view of the new core structure is shown below. Figure 9 As shown in the diagram. In this structure, the side posts do not have air gaps; the air gaps only exist between the three-phase winding posts and the upper magnetic plate, ignoring the magnetic core reluctance. Analysis shows that the presence of the side posts completely decouples the magnetic flux of each phase, and the three-phase superimposed magnetic flux can be closed through the side posts, avoiding the drawbacks of the original structure.

[0116] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A DC-DC isolated converter with a three-phase interleaved four-switch buck-boost integrated LLC, characterized in that, This includes transformers based on magnetic integration design, as well as the primary and secondary circuits connected on both sides of the transformer; The primary circuit includes a three-phase interleaved parallel four-switch buck-boost circuit and a three-phase LLC resonant circuit. Each four-switch buck-boost circuit includes four switching transistors and a pre-stage inductor. The first two switching transistors are located between the positive and negative terminals of the DC bus and form the front bridge arm. The last two switching transistors are located between the middle bus and the negative terminal of the DC bus and form the rear bridge arm. The pre-stage inductor is connected between the midpoint of the front bridge arm and the midpoint of the rear bridge arm. The three terminals of the three-phase LLC resonant circuit are respectively connected to the midpoints of the three rear bridge arms. The connection method between the LLC circuits is star-connected for both the primary and secondary sides, except for the resonant capacitor, and delta-connected for the resonant capacitor. The secondary circuit is composed of a three-phase interleaved parallel full-wave rectifier circuit.

2. The DC-DC isolated converter with a three-phase interleaved four-switch buck-boost integrated LLC according to claim 1, characterized in that, The transformers include first to third transformers T1 to T3, and the primary circuit includes an input DC voltage source V. in First to third inductors L b1 ~L b3 The first to twelfth switching transistors Q1~Q 12 The first to twelfth body diodes D1 to D2 12 Parasitic capacitances C from the first to the twelfth oss1 ~C oss12 Bus capacitor C bus The first to third resonant inductors L r1 ~L r3 The first to third resonant capacitors C r1 ~C r3 First to third magnetizing inductors L m1 ~L m3 Control unit; The drain of the first switching transistor Q1, the cathode of the first body diode D1, and the first parasitic capacitance C oss1 One end is connected to the source of the first switching transistor Q1, the anode of the first body diode D1, and the first parasitic capacitance C. oss1 The other end is connected; the drain of the second switching transistor Q2 is connected to the cathode of the second body diode D2 and the second parasitic capacitance C. oss2 One end is connected, the source of the second switching transistor Q2 is connected to the anode of the second body diode D2 and the second parasitic capacitance C. oss2 The other end is connected; the drain of the third switch Q3 is connected to the cathode of the third body diode D3 and the third parasitic capacitance C. oss3 One end is connected, the source of the third switching transistor Q3 is connected to the anode of the third body diode D3 and the third parasitic capacitance C. oss3 The other end is connected; the drain of the fourth switch Q4 is connected to the cathode of the fourth body diode D4 and the fourth parasitic capacitance C. oss4 One end is connected to the source of the fourth switch Q4, the anode of the fourth body diode D4, and the fourth parasitic capacitance C. oss4 The other end is connected; the drain of the fifth switch Q5 is connected to the cathode of the fifth body diode D5 and the fifth parasitic capacitance C. oss5 One end is connected to the source of the fifth switching transistor Q5, the anode of the fifth body diode D5, and the fifth parasitic capacitance C. oss5 The other end is connected; the drain of the sixth switch Q6 is connected to the cathode of the sixth body diode D6 and the sixth parasitic capacitance C. oss6 One end is connected to the source of the sixth switch Q6, the anode of the sixth body diode D6, and the sixth parasitic capacitance C. oss6 The other end is connected; the drain of the seventh switch Q7 is connected to the cathode of the seventh body diode D7 and the seventh parasitic capacitance C. oss7 One end is connected to the source of the seventh switch Q7, the anode of the seventh body diode D7, and the seventh parasitic capacitance C. oss7 The other end is connected; the drain of the eighth switch Q8 is connected to the cathode of the eighth body diode D8 and the eighth parasitic capacitance C. oss8 One end is connected to the source of the eighth switch Q8, the anode of the eighth body diode D8, and the eighth parasitic capacitance C. oss8 The other end is connected; the drain of the ninth switch Q9 is connected to the cathode of the ninth body diode D9 and the ninth parasitic capacitance C. oss9 One end is connected to the source of the ninth switch Q9, the anode of the ninth body diode D9, and the ninth parasitic capacitance C. oss9 The other end is connected; the tenth switch Q 10 The drain and the tenth body diode D 10 The cathode and the tenth parasitic capacitance C oss10 One end is connected to the tenth switch Q. 10 The source and the tenth body diode D 10 The anode and the tenth parasitic capacitance C oss10 The other end is connected; the eleventh switch Q 11 The drain of the eleventh diode D 11 The cathode and the eleventh parasitic capacitance C oss11 One end is connected to the eleventh switch Q. 11 The source and the eleventh integrated diode D 11 The anode and the eleventh parasitic capacitance C oss11 The other end is connected; the twelfth switch Q 12 The drain of the twelfth body diode D 12 The cathode and the twelfth parasitic capacitance C oss12 One end is connected to the twelfth switch Q. 12 The source of the twelfth body diode D 12 The anode and the twelfth parasitic capacitance C oss12 The other end is connected; The input DC voltage source V in One end is connected to the drain of the first switch Q1, the fifth switch Q5, and the ninth switch Q9, and the other end is connected to the drain of the second switch Q2, the sixth switch Q6, and the tenth switch Q9. 10 The source of the first switch Q1 is connected to the drain of the second switch Q2 and the first inductor L. b1 One end is connected to the source of the fifth switch Q5, the drain of the sixth switch Q6, and the second inductor L. b2 One end is connected, and the source of the ninth switch Q9 is connected to the tenth switch Q. 10 The drain and the third inductor L b3 One end is connected; the first inductor L b1 The other end is connected to the source of the third switch Q3, the drain of the fourth switch Q4, and the first resonant inductor L. r1 One end is connected, the second inductor L b2 The other end is connected to the source of the seventh switch Q7, the drain of the eighth switch Q8, and the second resonant inductor L. r2 One end is connected, and the third inductor L b3 The other end is connected to the eleventh switch Q. 11 The source and the twelfth switch Q 12 The drain and the third resonant inductor L r3 One end is connected; the third switch Q3, the seventh switch Q7, and the eleventh switch Q 11 The drains of all terminals are connected to the bus capacitor C. bus At one end, the fourth switch Q4, the eighth switch Q8, and the twelfth switch Q 12 The sources of all are connected to the bus capacitor C. bus The other end; the first to third resonant inductors L r1 ~L r3 The other end is connected to the first to third magnetizing inductors L respectively. m1 ~L m3 One end is connected to one end of the first to third transformers T1 to T3, and the first to third magnetizing inductors L m1 ~L m3 The three phases are connected in parallel to the primary windings of the first to third transformers T1 to T3, and are connected together in a star configuration; the first to third resonant capacitors C r1 ~C r3 The first to third resonant capacitors C are connected together via a delta connection. r1 ~C r3 One end is connected to the first to third magnetizing inductors L respectively. m1 ~L m3 The other end and the other ends of the first to third transformers T1 to T3; The control unit is used to control the first to twelfth switching transistors Q1 to Q2. 12 The on / off state.

3. The DC-DC isolated converter with a three-phase interleaved four-switch buck-boost integrated LLC according to claim 2, characterized in that, The secondary circuit includes the first to sixth rectifier diodes SR1 to SR6 and the output capacitor C. o Load R Ld ; One end of the first rectifier diode SR1 and the second rectifier diode SR2 are connected to the secondary side of the first transformer T1 to form a first full-wave rectifier circuit. One end of the third rectifier diode SR3 and the fourth rectifier diode SR4 are connected to the secondary side of the second transformer T2 to form a second full-wave rectifier circuit. One end of the fifth rectifier diode SR5 and the sixth rectifier diode SR6 are connected to the secondary side of the third transformer T3 to form a third full-wave rectifier circuit. The first to third full-wave rectifier circuits are connected together in a star configuration. The center tap of each of the first to third transformers T1 to T3 is connected to the output capacitor C. o and load R Ld One end of the first to sixth rectifier diodes SR1 to SR6 are connected to the output capacitor C. o and load R Ld The other end.

4. The DC-DC isolated converter with a three-phase interleaved four-switch buck-boost integrated LLC according to claim 3, characterized in that, The conduction times of the first switch Q1 and the second switch Q2 are complementary; the conduction times of the third switch Q3 and the fourth switch Q4 are complementary; the conduction times of the fifth switch Q5 and the sixth switch Q6 are complementary; the conduction times of the seventh switch Q7 and the eighth switch Q8 are complementary; the conduction times of the ninth switch Q9 and the tenth switch Q6 are complementary. 10 Their conduction times are complementary; the eleventh switch Q 11 and the twelfth switch Q 12 Their conduction times are complementary.

5. The DC-DC isolated converter with a three-phase interleaved four-switch buck-boost integrated LLC according to claim 3, characterized in that, The first to third resonant inductors L r1 ~L r3 The first to third transformers T1 to T3 are integrated into an LLC resonant cavity, using the leakage inductance of the transformer as the resonant inductor. Through the principle of three-phase magnetic flux cancellation, it integrates the first transformer T1 and the first resonant inductor L. r1 The second transformer T2 and the second resonant inductor L r2 The third transformer T3 and the third resonant inductor L r3 Each phase is integrated into a single magnetic component, forming a three-column structure. Two additional side columns are added as non-wound columns, allowing each phase flux to close through the non-wound columns, providing a closed path for the three-phase flux, and completely decoupling each phase flux. The three-phase superimposed flux is then closed through the side columns.

6. The DC-DC isolated converter with a three-phase interleaved four-switch buck-boost integrated LLC according to claim 3, characterized in that, The first to fourth switching transistors Q1 to Q4 and the first pre-stage inductor L b1 The first phase four-switch buck-boost circuit is composed of the first switch Q1 and the second switch Q2 located between the positive and negative terminals of the DC bus and forming the front bridge arm, and the third switch Q3 and the fourth switch Q4 located between the middle bus and the negative terminal of the DC bus and forming the rear bridge arm. The first front-stage inductor L... b1 Connected between the midpoint of the front axle arm and the midpoint of the rear axle arm; the fifth to eighth switching transistors Q5 to Q8 and the second pre-stage inductor L b2 The second-phase four-switch step-up / step-down circuit is configured such that the fifth switch Q5 and the sixth switch Q6 are located between the positive and negative terminals of the DC bus and form the front bridge arm, while the seventh switch Q7 and the eighth switch Q8 are located between the middle bus and the negative terminal of the DC bus and form the rear bridge arm. The second front-stage inductor L... b2 Connected between the midpoint of the front axle arm and the midpoint of the rear axle arm; the ninth to twelfth switching transistors Q9~Q 12 and the third pre-stage inductor L b3 This forms the third-phase four-switch buck-boost circuit, in which the ninth switch Q9 and the tenth switch Q... 10 Located between the positive and negative terminals of the DC bus and forming the front bridge arm, the eleventh switching transistor Q 11 and the twelfth switch Q 12 Located between the intermediate bus and the negative terminal of the DC bus, forming the rear bridge arm, the third front-stage inductor L b3 It connects the midpoint of the front axle arm and the midpoint of the rear axle arm; In the first to third phase four-switch buck-boost circuit, the phase shift angle between the front bridge arm and the rear bridge arm is the minimum phase shift angle δ required for each switch to achieve soft switching. When the phase shift angle is less than the minimum phase shift angle δ, the absolute value of the current flowing through each switch decreases, and soft switching cannot be achieved. When the phase shift angle is greater than the minimum phase shift angle δ, the absolute value of the current flowing through each switch increases, and the loss increases. The minimum phase shift angle is: ； Where δ is the minimum phase shift angle, D is the duty cycle of the switch on the front axle arm, and f s L is the switching frequency. b P is the inductance value of the preceding stage inductor. o V is the output power of the converter. in C is the input voltage of the converter. oss t is the junction capacitance of the switching transistor. dead For dead time, L m This is the magnetizing inductance value of the transformer.

7. The DC-DC isolated converter with a three-phase interleaved four-switch buck-boost integrated LLC according to claim 6, characterized in that, The control unit controls the first to twelfth switching transistors Q1 to Q2. 12 The switching on and off of the transistors in the first to third phase four-switch buck-boost circuits allows the two switching transistors in the front arm to conduct complementaryly with adjustable duty cycles to handle different input voltages; the two switching transistors in the rear arm conduct complementaryly with a fixed duty cycle of 0.5; the phase shift angle between the front and rear arms is the minimum phase shift angle δ; the conduction phase difference between the corresponding switching transistors in the first to third phase four-switch buck-boost circuits is 120°.

8. The DC-DC isolated converter with a three-phase interleaved four-switch buck-boost integrated LLC according to claim 6, characterized in that, The first to sixth rectifier diodes SR1 to SR6 and the output filter capacitor C o To form a three-phase interleaved parallel full-wave rectifier circuit; The first rectifier SR1, the second rectifier SR2, the third rectifier SR3, the fourth rectifier SR4, the fifth rectifier SR5, and the sixth rectifier SR6 are connected to a common ground and are located in two winding branches of the secondary windings of the first transformer T1, the second transformer T2, and the third transformer T3, respectively, forming a first-phase full-wave rectifier circuit, a second-phase full-wave rectifier circuit, and a third-phase full-wave rectifier circuit; the three full-wave rectifier circuits are connected in a star configuration; the output filter capacitor C... o It is connected in parallel to the output ports of three full-wave rectifier circuits.

9. The DC-DC isolated converter with a three-phase interleaved four-switch buck-boost integrated LLC according to claim 6, characterized in that, The three-phase connection method of the primary and secondary circuits on both sides of the first to third transformers T1 to T3, excluding the first to third resonant capacitors C r1 ~C r3 All external connections are star-connected. Because the neutral point is floating, star connections naturally possess self-current sharing capability; however, for the first to third resonant capacitors C... r1 ~C r3 When a star connection is used, the resonant capacitor has a DC bias voltage. By moving the resonant capacitor from in front of the resonant inductor to behind the transformer and through the star-delta equivalent transformation, a delta connection structure for the resonant capacitor is obtained. In this structure, since the average voltage across the transformer and the inductor is zero, and the resonant capacitor is connected between the two transformers, the DC component of the resonant capacitor voltage is the difference between the DC components of the voltage at the two phase bridge arms. Since the DC components of the voltage at the two phase bridge arms cancel each other out, the resonant capacitor has no DC bias voltage.

10. The DC-DC isolated converter with a three-phase interleaved four-switch buck-boost integrated LLC according to claim 1, characterized in that, When the input voltage is greater than the bus voltage, the control unit is used to control the duty cycle D of the upper switch in the front axle arm to be less than 0.5, so that the converter can realize the step-down function. When the input voltage is less than the bus voltage, the control unit is used to control the duty cycle D of the upper switch in the front axle arm to be greater than 0.5, so that the converter can realize the boost function.

Images