Three-phase llc power conversion circuit and control method thereof

Abstract

This application relates to a three-phase LLC power conversion circuit and its control method. The three-phase LLC power conversion circuit is configured to receive an input voltage and output an output voltage, and includes a three-phase transformer, an input switch group, an output switch group, and a resonant circuit group. The input switch group includes a plurality of input switches, and the output switch group includes a plurality of rectifier switches. The control method of this application includes the steps of: (S1) detecting the zero-crossing point of the input voltage, the output voltage, and the output current of each phase of the three-phase LLC power conversion circuit; and (S2) controlling the switching state of at least one rectifier switch to lead or lag the switching state of the corresponding input switch based on the ratio of the output voltage to the input voltage, and / or adjusting the duty cycle of all input switches to be increased, and adjusting the switching frequency of all input switches based on the output voltage, a reference voltage, and soft-switching setting conditions.

Description

Technical Field

[0001] This case belongs to the field of power conversion circuits, particularly a three-phase LLC power conversion circuit and its control method. Prior Art

[0002] The rapid development of information technology, particularly cloud computing, big data, and artificial intelligence, is driving increased energy consumption in data centers. Consequently, the power levels and power densities of the power conversion circuits that provide power to data centers have also increased significantly. Compared to unidirectional power conversion circuits, three-phase LLC power conversion circuits have become widely used in data centers due to their lower RMS current, lower peak current, and improved magnetic integration.

[0003] However, due to the interaction between the three phases, control of a three-phase LLC power conversion circuit is more complex than that of a unidirectional power conversion circuit. For example, in a unidirectional power conversion circuit, phase shift control can be used to narrow the switching frequency range, making the unidirectional power conversion circuit suitable for applications with a wide voltage range. However, in a three-phase LLC power conversion circuit, two control variables are required. Using a single control variable, such as phase shift control, cannot address changes in the resonant frequency. This results in significant reactive current and makes it difficult to accurately control the switches for soft switching. Therefore, there is still room for improvement in the control of three-phase LLC power conversion circuits.

[0004] Furthermore, three-phase LLC power conversion circuits typically include a three-phase transformer and a three-phase inductor. To reduce core and copper losses, the three-phase inductor and transformer are often integrated into a single magnetic component. However, conventional magnetic components integrating a three-phase inductor and transformer still have room for improvement in core losses and size reduction due to poor flux cancellation.

[0005] Therefore, it is necessary to develop a three-phase LLC power conversion circuit and a control method thereof to solve the problems and deficiencies faced by the prior art. Summary of the Invention

[0006] The present invention aims to provide a three-phase LLC power conversion circuit and its control method, which not only reduces the switching frequency range of the three-phase power conversion circuit but also achieves lower RMS current, lower peak current, and improved magnetic integration. Furthermore, because the control unit of the three-phase power conversion circuit controls two control variables: the phase shift and frequency of the switches, it can mitigate the increase in reactive current caused by changes in the resonant frequency and enable more precise soft switching.

[0007] To achieve the aforementioned objectives, a preferred embodiment of the present invention is a control method for use in a three-phase LLC power conversion circuit. The three-phase LLC power conversion circuit receives an input voltage and outputs an output voltage, and includes a three-phase transformer, an input switch group, an output switch group, and a resonant circuit group. The input switch group is electrically connected to a plurality of primary-side windings of the three-phase transformer and includes a plurality of input switches. The output switch group is electrically connected to a plurality of secondary-side windings of the three-phase transformer and includes a plurality of rectifier switches. The resonant circuit group is electrically connected between the input switch group and the plurality of primary-side windings. The control method of this case includes the steps of: (S1) detecting the zero crossing point of the input voltage, the output voltage, and the output current of each phase of the three-phase LLC power conversion circuit; and (S2) controlling a plurality of input switches to perform switching operations based on the detection results of step (S1), controlling a plurality of rectifier switches to perform synchronous rectification switching operations, and controlling the switching state of at least one rectifier switch in each phase output switch group to lead or lag the switching state of the corresponding input switch based on the ratio of the output voltage to the input voltage and / or adjusting the duty cycle of all input switches in each phase to increase the ratio of the output voltage to the input voltage, and adjusting the switching frequency of all input switches based on the output voltage, the reference voltage, and the soft switching setting conditions so that all input switches perform soft switching.

[0008] To achieve the above-mentioned objectives, another preferred embodiment of the present invention is a three-phase LLC power conversion circuit configured to receive an input voltage and output an output voltage, and comprising an input switch group, a three-phase transformer, a resonant circuit group, and an output switch group. The input switch group receives the input voltage and includes a plurality of input switches. The three-phase transformer includes a plurality of primary windings and a plurality of secondary windings, wherein the input switch group is electrically connected to the plurality of primary windings. The resonant circuit group is electrically connected between the input switch group and the plurality of primary windings and includes a plurality of first resonant elements and a plurality of second resonant elements, wherein the plurality of first resonant elements are star-connected and each comprised of an inductor or a capacitor, and the plurality of second resonant elements are delta-connected and each comprised of an inductor. The output switch group is electrically connected to the plurality of secondary windings and outputs the output voltage. Simple diagram description

[0009] FIG1 is a schematic flow chart of the steps of a control method according to an embodiment of the present invention.

[0010] FIG. 2 is a circuit topology diagram of a first embodiment of a three-phase LLC power conversion circuit to which the control method shown in FIG. 1 is applicable.

[0011] FIG3 to FIG6 are partial waveform timing diagrams of the operation of the three-phase LLC power conversion circuit when the control unit of the three-phase LLC power conversion circuit shown in FIG2 is controlled under different implementation modes.

[0012] FIG7 is a circuit topology diagram of the second embodiment of the three-phase LLC power conversion circuit of the present invention.

[0013] FIG8 is a circuit topology diagram of a third embodiment of the three-phase LLC power conversion circuit of the present invention.

[0014] FIG9 is a circuit topology diagram of a fourth embodiment of the three-phase LLC power conversion circuit of the present invention.

[0015] 10 and 11 are schematic diagrams of partial waveform timings of the operation of the three-phase LLC power conversion circuit when the control unit of the three-phase LLC power conversion circuit shown in FIG. 9 is controlled under different implementation modes.

[0016] FIG12 is a circuit topology diagram of the fifth embodiment of the three-phase LLC power conversion circuit of the present invention.

[0017] FIG13 is a waveform timing diagram of the operation of the control unit of the three-phase LLC power conversion circuit shown in FIG12.

[0018] FIG14 is a circuit topology diagram of the sixth embodiment of the three-phase LLC power conversion circuit of the present invention.

[0019] FIG. 15A is a circuit topology diagram of a first embodiment of a magnetic component suitable for a three-phase LLC power conversion circuit according to the present invention.

[0020] FIG. 15B is a schematic diagram illustrating the placement of the three-phase transformer and the three-phase resonant inductor of the magnetic assembly shown in FIG. 15A .

[0021] FIG. 15C is a schematic diagram illustrating a portion of the magnetic flux vectors of the magnetic assembly shown in FIG. 15B .

[0022] FIG. 16A is a schematic diagram showing another variation of the disposition of the three-phase transformer and the three-phase resonant inductor of the magnetic assembly shown in FIG. 15A .

[0023] FIG. 16B is a schematic diagram illustrating a portion of the magnetic flux vectors of the magnetic assembly shown in FIG. 16A .

[0024] FIG. 17A is a circuit topology diagram of a second embodiment of a magnetic component suitable for a three-phase LLC power conversion circuit according to the present invention.

[0025] FIG. 17B is a circuit topology diagram of a third embodiment of a magnetic component suitable for a three-phase LLC power conversion circuit according to the present invention.

[0026] FIG. 17C is a schematic diagram showing the placement of the three-phase transformer and the three-phase resonant inductor of the magnetic assembly shown in FIG. 17A or FIG. 17B .

[0027] FIG. 17D is a schematic diagram illustrating a portion of the magnetic flux vectors of the magnetic assembly shown in FIG. 17C .

[0028] FIG. 18A is a schematic diagram showing another variation of the disposition of the three-phase transformer and the three-phase resonant inductor of the magnetic assembly shown in FIG. 17A or FIG. 17B .

[0029] FIG. 18B is a schematic diagram illustrating a portion of the magnetic flux vectors of the magnetic assembly shown in FIG. 18A .

[0030] FIG. 19A is a circuit topology diagram of a fourth embodiment of a magnetic component suitable for a three-phase LLC power conversion circuit according to the present invention.

[0031] FIG19B is a schematic diagram showing the placement of the three-phase transformer and the three-phase resonant inductor of the magnetic assembly shown in FIG19A.

[0032] FIG. 19C is a schematic diagram illustrating a portion of the magnetic flux vectors of the magnetic assembly shown in FIG. 19B .

[0033] FIG20A is a schematic diagram showing another variation of the arrangement positions of the three-phase transformer and the three-phase resonant inductor of the magnetic assembly shown in FIG19A.

[0034] FIG. 20B is a schematic diagram illustrating a portion of the magnetic flux vectors of the magnetic assembly shown in FIG. 20A .

[0035] FIG. 21A is a circuit topology diagram of a fifth embodiment of a magnetic component suitable for a three-phase LLC power conversion circuit according to the present invention.

[0036] FIG. 21B is a schematic diagram illustrating the placement of the three-phase transformer and the three-phase resonant inductor of the magnetic assembly shown in FIG. 21A .

[0037] FIG. 21C is a schematic diagram illustrating a portion of the magnetic flux vectors of the magnetic assembly shown in FIG. 21B .

[0038] FIG. 22A is a schematic diagram showing another variation of the placement of the three-phase transformer and the three-phase resonant inductor of the magnetic assembly shown in FIG. 21A .

[0039] FIG. 22B is a schematic diagram illustrating a portion of the magnetic flux vectors of the magnetic assembly shown in FIG. 22A .

[0040] FIG. 23A is a circuit topology diagram of a sixth embodiment of a magnetic component suitable for a three-phase LLC power conversion circuit according to the present invention.

[0041] FIG. 23B is a circuit topology diagram of a seventh embodiment of the magnetic component of the present invention applicable to a three-phase LLC power conversion circuit.

[0042] FIG. 23C is a circuit topology diagram of an eighth embodiment of the magnetic component of the present invention applicable to a three-phase LLC power conversion circuit.

[0043] FIG. 23D is a circuit topology diagram of a ninth embodiment of the magnetic component of the present invention applicable to a three-phase LLC power conversion circuit.

[0044] FIG. 23E is a schematic diagram showing the locations of the three-phase transformer and the three-phase resonant inductor of the magnetic assembly shown in FIG. 23A , FIG. 23B , FIG. 23C or FIG. 23D .

[0045] FIG. 23F is a schematic diagram illustrating a portion of the magnetic flux vectors of the magnetic assembly shown in FIG. 23E .

[0046] FIG. 24 is a schematic diagram showing another variation of the placement of the three-phase transformer and the three-phase resonant inductor of the magnetic assembly shown in FIG. 15A .

[0047] FIG. 25 is a schematic diagram showing another variation of the placement of the three-phase transformer and the three-phase resonant inductor of the magnetic component shown in FIG. 23E . Implementation Method

[0048] Some typical embodiments that embody the features and advantages of this invention will be described in detail in the following sections. It should be understood that this invention is capable of various variations in various aspects without departing from the scope of this invention, and that the descriptions and drawings herein are intended to be illustrative in nature and not to limit this invention.

[0049] Figure 1 is a schematic flow chart of the steps of a control method according to one embodiment of the present invention. Figure 2 is a circuit topology diagram of a first embodiment of a three-phase LLC power conversion circuit applicable to the control method shown in Figure 1. Figures 3 through 6 are schematic timing diagrams of partial waveforms of the operation of the three-phase LLC power conversion circuit when the control unit of the three-phase LLC power conversion circuit shown in Figure 2 controls the circuit in different implementations. As shown in Figures 1, 2, 3, 4, 5, and 6, in this embodiment, the control method of the present invention can be applied to a conventional three-phase LLC power conversion circuit or to the three-phase LLC power conversion circuit 1 shown in Figure 2. Because there are many implementations of three-phase LLC power conversion circuits, it is impossible to describe them all in detail. Therefore, the control method of the present invention will be described below using the three-phase LLC power conversion circuit 1 shown in Figure 2 as an exemplary embodiment. The input end of the three-phase LLC power conversion circuit 1 is electrically connected to an input power source DC to receive an input voltage V in. The output end of the three-phase LLC power conversion circuit 1 is electrically connected to a load R to provide an output voltage V o to the load R. The three-phase LLC power conversion circuit 1 includes a three-phase transformer T, an input switch group 2, an output switch group 3, a control unit 4, and a resonant circuit group.

[0050] The input switch group 2 is electrically connected to the input end of the three-phase LLC power conversion circuit 1 and includes a first upper input switch Q1, a first lower input switch Q2, a second upper input switch Q3, a second lower input switch Q4, a third upper input switch Q5, and a third lower input switch Q6. The first upper input switch Q1 and the first lower input switch Q2 are connected in series to form a first input switch bridge arm, and the first upper input switch Q1 and the first lower input switch Q2 are connected in series to form a second input switch bridge arm, and the second upper input switch Q3 and the second lower input switch Q4 are connected in series to form a second input switch bridge arm, and the second upper input switch Q3 and the second lower input switch Q4 are connected in series to form a third input switch bridge arm, and the third upper input switch Q5 and the third lower input switch Q6 are connected in series to form a third input switch bridge arm, and the third upper input switch Q5 and the third lower input switch Q6 are connected in parallel to each other.

[0051] The three-phase transformer T includes a first transformer T1, a second transformer T2, and a third transformer T3. Each of the first transformer T1, the second transformer T2, and the third transformer T3 includes a primary winding and a secondary winding. In some embodiments, each of the first transformer T1, the second transformer T2, and the third transformer T3 includes a magnetizing inductor Lm1, Lm2, and Lm3, respectively, connected in parallel with the primary windings of the first transformer T1, the second transformer T2, and the third transformer T3.

[0052] The resonant circuit group is electrically connected between the input switch group 2 and the primary windings of the three-phase transformer T, and includes a plurality of first resonant elements RE A1, RE B1, and RE C1, and a plurality of second resonant elements RE A2, RE B2, and RE C2. The plurality of first resonant elements RE A1, RE B1, and RE C1 are star-connected (i.e., Y-connected) and can each be formed by an inductor or a capacitor. The first resonant element RE A1 is electrically connected between a first connection point and the first end of the primary winding of the first transformer T1, the first resonant element RE B1 is electrically connected between a second connection point and the first end of the primary winding of the second transformer T2, and the first resonant element RE C1 is electrically connected between a third connection point and the first end of the primary winding of the third transformer T3. The plurality of second resonant elements RE A2, RE B2, and RE C2 are connected in a delta configuration (i.e., Δ connection) and are each formed of an inductor. The endpoints of any two second resonant elements are electrically connected to each other and to the second ends of the primary windings of the corresponding transformers in the first transformer T1, the second transformer T2, and the third transformer T3. Because the plurality of second resonant elements RE A2, RE B2, and RE C2 are connected in a delta configuration (i.e., Δ connection) and are each formed of an inductor, the inductance of the second resonant elements RE A2, RE B2, and RE C2 increases by three times compared to a star connection, and the current decreases by 100% compared to a star connection. The cross-sectional area of ​​the wire is reduced by 3 times compared with the star connection method, and the number of winding turns is only increased by In some embodiments, the plurality of second resonant elements RE A2 , RE B2 , and RE C2 may also be formed by capacitors.

[0053] The output switch group 3 is electrically connected between a plurality of secondary windings of the three-phase transformer T and the output terminal of the three-phase LLC power conversion circuit 1. The output switch group 3 includes a first synchronous rectifier switch group, a second synchronous rectifier switch group, and a third synchronous rectifier switch group, each coupled to the secondary windings of the corresponding transformers among the first transformer T1, the second transformer T2, and the third transformer T3. In some embodiments, the first synchronous rectifier switch group includes a first upper rectifier switch SR1, a first lower rectifier switch SR2, a second upper rectifier switch SR3, and a second lower rectifier switch SR4. The first upper rectifier switch SR1 and the first lower rectifier switch SR2 are connected in series to form a first rectifier bridge arm, and the second upper rectifier switch SR3 and the second lower rectifier switch SR4 are connected in series to form a second rectifier bridge arm. The first rectifier bridge arm and the second rectifier bridge arm are connected in parallel. The second synchronous rectifier switch group includes a third upper rectifier switch SR5, a third lower rectifier switch SR6, a fourth upper rectifier switch SR7, and a fourth lower rectifier switch SR8. The third upper rectifier switch SR5 and the third lower rectifier switch SR6 are connected in series to form a third rectifier bridge arm, and the fourth upper rectifier switch SR7 and the fourth lower rectifier switch SR8 are connected in series to form a fourth rectifier bridge arm. The third rectifier bridge arm and the fourth rectifier bridge arm are connected in parallel. The third synchronous rectifier switch group includes a fifth upper rectifier switch SR9, a fifth lower rectifier switch SR10, a sixth upper rectifier switch SR11, and a sixth lower rectifier switch SR12. The fifth upper rectifier switch SR9 and the fifth lower rectifier switch SR10 are connected in series to form a fifth rectifier bridge arm, and the sixth upper rectifier switch SR11 and the sixth lower rectifier switch SR12 are connected in series to form a sixth rectifier bridge arm. The fifth rectifier bridge arm and the sixth rectifier bridge arm are connected in parallel. In other embodiments, the first upper rectifier switch SR1, the first lower rectifier switch SR2, the second upper rectifier switch SR3, the second lower rectifier switch SR4, the third upper rectifier switch SR5, the third lower rectifier switch SR6, the fourth upper rectifier switch SR7, the fourth lower rectifier switch SR8, the fifth upper rectifier switch SR9, the fifth lower rectifier switch SR10, the sixth upper rectifier switch SR11, and the sixth lower rectifier switch SR12 can each be an active switch, such as a metal oxide semiconductor field effect transistor (MOSFET). Because the first synchronous rectifier switch group, the second synchronous rectifier switch group, and the third synchronous rectifier switch group of the output switch group 3 of the three-phase LLC power conversion circuit 1 each have a full-bridge structure, the voltage stress of each rectifier switch in the first synchronous rectifier switch group, the second synchronous rectifier switch group, and the third synchronous rectifier switch group can be reduced, and the control freedom of the output switch group 3 can be increased. In the above embodiment, the first input switch bridge arm, the first transformer T1, the first resonant element RE A1, the second resonant element RE A2 and the first synchronous rectification switch group constitute the first phase of the three-phase LLC power conversion circuit 1.The second input switch bridge arm, the second transformer T2, the first resonant element RE B1, the second resonant element RE B2, and the second synchronous rectification switch group constitute the second phase of the three-phase LLC power conversion circuit 1. The third input switch bridge arm, the third transformer T3, the first resonant element RE C1, the second resonant element RE C2, and the third synchronous rectification switch group constitute the third phase of the three-phase LLC power conversion circuit 1.

[0054] The control unit 4 is electrically connected to the input switch group 2 and the output switch group 3 and is used to detect the zero-crossing points of the input voltage Vin, the output voltage Vo, and the output current of each phase. Based on the detection results, it controls the switching operation of the first upper input switch Q1 through the third lower input switch Q6 of the input switch group 2, and controls the first upper rectifier switch SR1 through the sixth lower rectifier switch SR12 of the output switch group 3 to perform synchronous rectification switching. Preferably, but not limited to, the switching operation of any two upper input switches in the input switch group 2 is 120 degrees out of phase; the switching operation of the upper input switch and the lower input switch in each input switch bridge arm of the input switch group 2 are complementary and have a dead time; and the switching operation of the upper rectifier switch and the lower rectifier switch in each rectifier bridge arm of the output switch group 3 are complementary and have a dead time. Furthermore, the control unit 4 further controls the switching state of at least one rectifier switch in each phase's output switch group 3 to lead or lag the switching state of the corresponding input switch in the input switch bridge arm of the same phase based on the ratio of the output voltage V o to the input voltage V in (i.e., the at least one rectifier switch leads or lags the input switch phase angle corresponding to the conduction), and / or adjusts the duty cycle of all input switches in each input switch bridge arm of the input switch group 2 to increase the ratio of the output voltage V o to the input voltage V in. Furthermore, the control unit 4 further adjusts the switching frequency of all input switches in the input switch group 2 based on the output voltage V o , the reference voltage V ref , and soft switching settings, so that all input switches in the input switch group 2 perform soft switching.

[0055] Because each phase of the three-phase LLC power conversion circuit 1 operates with a phase difference of 120 degrees, and the two switches in each phase's switching bridge arm operate in a complementary manner, Figure 3 illustrates only some operating parameters of the three-phase LLC power conversion circuit 1 to illustrate the present technology. In Figures 3 through 6, symbols Q1, Q3, and Q5 respectively represent the switching states of the first upper input switch Q1, the second upper input switch Q3, and the third upper input switch Q5 in the input switch group 2. Symbols Q7A and Q8A respectively represent the switching states of the synchronous rectifier switches (i.e., the diagonally opposite first upper rectifier switch SR1 and second lower rectifier switch SR4) that are in phase with and corresponding to the first upper input switch Q1. The switching state of the first upper rectifier switch SR1 leads the switching state of the first upper input switch Q1 by a first time ΔT1, and the switching state of the second lower rectifier switch SR4 lags the switching state of the first upper input switch Q1 by a second time ΔT2. Symbols Q9A and Q10A respectively represent the switching states of the synchronous rectifier switches corresponding to and in phase with the second upper input switch Q3 (i.e., the diagonally opposite third upper rectifier switch SR5 and fourth lower rectifier switch SR8). The switching state of the third upper rectifier switch SR5 leads the switching state of the second upper input switch Q3, while the switching state of the fourth lower rectifier switch SR8 lags the switching state of the second upper input switch Q3. Symbols Q11A and Q12A respectively represent the switching states of the synchronous rectifier switches corresponding to and in phase with the third upper input switch Q5 (i.e., the diagonally opposite fifth upper rectifier switch SR9 and sixth lower rectifier switch SR12). The switching state of the fifth upper rectifier switch SR9 leads the switching state of the third upper input switch Q5, while the switching state of the sixth lower rectifier switch SR12 lags the switching state of the third upper input switch Q5. I p1 is the current flowing through the primary side winding of the first transformer T1 of the first phase in the three-phase LLC power conversion circuit 1, I M1 is the current flowing through the excitation inductance L m1 of the first transformer T1 of the first phase in the three-phase LLC power conversion circuit 1, and I s1 is the current flowing through the secondary side winding of the first transformer T1 of the first phase in the three-phase LLC power conversion circuit 1.

[0056] As shown in FIG. 3 , control unit 4 controls the switching state of at least one rectifier switch in each phase's output switch group 3, based on the ratio of output voltage V o to input voltage V in, to lead the switching state of the corresponding input switch in the input switch bridge arm of the same phase, and controls the switching state of at least one remaining rectifier switch in each phase's output switch group 3, to lag the switching state of the corresponding input switch in the input switch bridge arm of the same phase. As shown in FIG. 4 , control unit 4 can also be modified to control at least one rectifier switch in each phase's output switch group 3 to perform synchronous rectification switching, and controls the switching state of at least one remaining rectifier switch in each phase's output switch group 3 to lag the switching state of the corresponding input switch in the input switch bridge arm of the same phase. As shown in Figures 5 and 6 , the control unit 4 can also be modified to control at least one rectifier switch in the synchronous rectifier switch group of each phase's output switch group 3 to perform synchronous rectification switching, and to control the switching state of at least one remaining rectifier switch in each phase's output switch group 3 to precede the switching state of the corresponding input switch in the input switch bridge arm of the same phase by a third time ΔT. Furthermore, as shown in Figure 6 , the control unit 4 further adjusts the switching frequency of all input switches in the input switch group 2 based on the soft switching setting conditions, so that all input switches in the input switch group 2 perform soft switching.

[0057] As can be seen from the above, the three-phase LLC power conversion circuit 1 of this embodiment not only reduces the switching frequency range, but also has lower RMS current, lower peak current, and better magnetic integration. Moreover, because the control unit 4 controls two control variables, namely the phase and switching frequency of the switch, it can solve the problem of increased reactive current due to changes in the resonant frequency and enable more precise soft switching of the switch.

[0058] In some embodiments, the control unit 4 includes a zero current detection circuit 41, a gain control circuit 42, a first driver 43, a subtractor 44, a compensation circuit 45, a voltage-controlled oscillator 46, and a second driver 47. The first driver 43 is configured to drive the first upper rectifier switch SR1 to the sixth lower rectifier switch SR12 of the output switch group 3. The zero current detection circuit 41 is electrically connected to the secondary windings of the first transformer T1, the second transformer T2, and the third transformer T3 to detect the zero-crossing point of the output current of each phase of the three-phase LLC power conversion circuit 1. The gain control circuit 42 is configured to detect the input voltage V in and the output voltage V o of the three-phase LLC power conversion circuit 1, and receive the detection results of the zero current detection circuit 41. Based on the detection results of the input voltage V in, the output voltage V o, and the zero-crossing point of the output current of each phase, the first driver 43 is controlled to drive the first upper rectifier switch SR1 to the sixth lower rectifier switch SR12 of the output switch group 3 to perform synchronous rectification switching. Gain control circuit 42 further controls the switching state of at least one rectifier switch in each phase's output switch group 3 to lead or lag the switching state of the corresponding input switch in the input switch bridge arm of the same phase based on the ratio of output voltage V o to input voltage V in (i.e., at least one rectifier switch leads or lags the corresponding input switch phase angle at which it is turned on), and / or adjusts the duty cycle of all input switches in each input switch bridge arm of input switch group 2 to increase the ratio of output voltage V o to input voltage V in. Subtractor 44 is configured to subtract output voltage V o from reference voltage V ref. Compensation circuit 45 is configured to receive soft switching settings and the result of subtractor 44 and output a compensation signal based on the soft switching settings and the result of subtractor 44. Voltage-controlled oscillator 46 generates a switching signal having the frequency of first upper input switch Q 1 through third lower input switch Q 6 based on the compensation signal. The second driver 47 is configured to drive the first upper input switch Q1 to the third lower input switch Q6 of the input switch group 2 of the output switch group 3 to perform a soft switching operation according to the switching signal.

[0059] Please refer to Figure 1 again. The control method of this case includes the following steps.

[0060] In step S1, the control unit 4 detects the input voltage Vin received by the three-phase LLC power conversion circuit 1, the output voltage Vo output by the three-phase LLC power conversion circuit 1, and the zero crossing point of the output current of each phase of the three-phase LLC power conversion circuit.

[0061] In step S2, the control unit 4 controls the switching operation of the first upper input switch Q1 to the third lower input switch Q6 of the input switch group 2 based on the detection results of the input voltage V in, the output voltage V o, and the zero-crossing point of the output current of each phase of the three-phase LLC power conversion circuit. It also controls the first upper rectifier switch S R1 to the sixth lower rectifier switch S R12 of the output switch group 3 to perform synchronous rectification switching. Furthermore, based on the ratio of the output voltage V o to the input voltage V in, the control unit 4 controls the switching state of at least one rectifier switch of the synchronous rectification switch group of each phase of the output switch group 3 to lead or lag the switching state of the corresponding input switch in the input switch bridge arm of the same phase and / or increases the duty cycle of all input switches in all input switch bridge arms of each phase of the input switch group 2, thereby increasing the ratio of the output voltage V o to the input voltage V in. Furthermore, the control unit 4 further adjusts the switching frequency of all input switches of the input switch group 2 based on the output voltage V o, the reference voltage V ref, and the soft switching setting conditions, so that all input switches of the input switch group 2 perform soft switching.

[0062] FIG7 is a circuit topology diagram of a second embodiment of the three-phase LLC power conversion circuit of the present invention. In this embodiment, the circuit structure of the three-phase LLC power conversion circuit 1a is similar to that of the three-phase LLC power conversion circuit 1 shown in FIG2 , and therefore its circuit structure will not be further described. However, in this embodiment, the first upper input switch Q1, first lower input switch Q2, second upper input switch Q3, second lower input switch Q4, third upper input switch Q5, and third lower input switch Q6 in the input switch group 2 of the three-phase LLC power conversion circuit 1a are electrically connected in cascade.

[0063] FIG8 is a circuit topology diagram of a third embodiment of the three-phase LLC power conversion circuit of this invention. In this embodiment, the circuit structure of the three-phase LLC power conversion circuit 1b is similar to that of the three-phase LLC power conversion circuit 1 shown in FIG2 , so its circuit structure will not be further described. However, the first synchronous rectifier switch group of the output switch group 3 of the three-phase LLC power conversion circuit 1b of this embodiment is modified to include a first upper rectifier switch SR1a and a first lower rectifier switch SR2a connected in series, forming a half-bridge structure. The second synchronous rectifier switch group of the output switch group 3 is modified to include a second upper rectifier switch SR3a and a second lower rectifier switch SR4a connected in series, forming a half-bridge structure. The third synchronous rectifier switch group of the output switch group 3 is modified to include a third upper rectifier switch SR5a and a third lower rectifier switch SR6a connected in series, forming a half-bridge structure.

[0064] Please refer to Figures 9, 10, and 11. Figure 9 is a circuit topology diagram of the fourth embodiment of the three-phase LLC power conversion circuit of the present invention. Figures 10 and 11 are partial waveform timing diagrams illustrating the operation of the three-phase LLC power conversion circuit when the control unit of the three-phase LLC power conversion circuit shown in Figure 9 is controlled under different implementations. In this embodiment, the circuit structure of the three-phase LLC power conversion circuit 1c is similar to that of the three-phase LLC power conversion circuit 1b shown in Figure 8, and therefore its circuit structure will not be further described. However, in this embodiment, the primary windings T1p, T2p, and T3p of the three-phase transformer T are connected in a delta configuration (i.e., Δ connection), and the secondary windings T1s, T2s, and T3s are connected in a delta configuration (i.e., Δ connection).

[0065] As shown in FIG. 10 , the control unit 4 controls the switching state of at least one rectifier switch in the synchronous rectifier switch group of each phase's output switch group 3 based on the ratio of the output voltage Vo to the input voltage Vin, so that the switching state of at least one rectifier switch leads the switching state of the corresponding input switch in the input switch bridge arm of the same phase (i.e., the switching states of the first upper rectifier switch SR1a, the second upper rectifier switch SR3a, and the third upper rectifier switch SR5a lead the switching states of the first upper input switch Q1, the second upper input switch Q3, and the third upper input switch Q5, respectively). As shown in FIG. 11 , the control unit 4 can also be modified to control the synchronous rectifier switch of at least one rectifier switch in the synchronous rectifier switch group of each phase's output switch group 3 to perform synchronous rectification switching based on the ratio of the output voltage Vo to the input voltage Vin, and to control the switching state of the remaining at least one rectifier switch in the synchronous rectifier switch group of each phase's output switch group 3 to lag the switching state of the corresponding input switch in the input switch bridge arm of the same phase (the switching state of the first upper rectifier switch SR1a lags the switching state of the first upper input switch Q1).

[0066] Please refer to Figures 12 and 13. Figure 12 is a circuit topology diagram of the fifth embodiment of the three-phase LLC power conversion circuit of this disclosure, and Figure 13 is a waveform timing diagram of the control unit of the three-phase LLC power conversion circuit shown in Figure 12 during operation. In this embodiment, the three-phase LLC power conversion circuit 1d shows the detailed circuit architecture of the three-phase LLC power conversion circuit 1b shown in Figure 8. Specifically, the plurality of first resonant elements RE A1, RE B1, and RE C1 of the three-phase LLC power conversion circuit 1c shown in Figure 8 are star-connected (i.e., Y-connected) and can be formed by capacitors Cr1, Cr2, and Cr3, respectively, as shown in Figure 12. The second resonant elements RE A2, RE B2, and RE C2 are delta-connected (i.e., Δ-connected) and are formed by resonant inductors L r1, L r2, and L r3, respectively. I c1, I c2, and I c3 are currents flowing through capacitors Cr1, Cr2, and Cr3, respectively; IL1, IL2, and IL3 are currents flowing through resonant inductors L r1, L r2, and L r3, respectively; and I s1, I s2, and I s3 are currents flowing through the secondary windings of the first transformer T1, the second transformer T2, and the third transformer T3, respectively.

[0067] FIG14 is a circuit topology diagram of a sixth embodiment of the three-phase LLC power conversion circuit of the present invention. In this embodiment, the circuit structure of the three-phase LLC power conversion circuit 1e is similar to that of the three-phase LLC power conversion circuit 1b shown in FIG8 , and therefore its circuit structure will not be further described. However, in this embodiment, the first upper input switch Q1, first lower input switch Q2, second upper input switch Q3, second lower input switch Q4, third upper input switch Q5, and third lower input switch Q6 in the input switch group 2 of the three-phase LLC power conversion circuit 1e are now electrically connected in cascade.

[0068] As can be seen from the above, the input switch group 2 of the three-phase LLC power conversion circuit can be either the input switch group circuit structure of the three-phase LLC power conversion circuit 1 shown in Figure 2 or the input switch group 2 circuit structure of the three-phase LLC power conversion circuit 1a shown in Figure 7. The output switch group of the three-phase LLC power conversion circuit can be either the output switch group circuit structure of the three-phase LLC power conversion circuit 1 shown in Figure 2 or the output switch group 3 circuit structure of the three-phase LLC power conversion circuit 1b shown in Figure 8. Furthermore, the plurality of first resonant elements RE A1, RE B1, and RE C1 can be star-connected (i.e., Y-connected) or delta-connected (i.e., Δ-connected) and can each be composed of a capacitor or a resonant inductor. The second resonant elements RE A2, RE B2, and RE C2 can be star-connected (i.e., Y-connected) or delta-connected (i.e., Δ-connected) and can each be composed of a capacitor or a resonant inductor. It should be emphasized that the circuit structure of the input switch group 2, the circuit structure of the output switch group 3, and the circuit structure of the resonant circuit group are not limited to the aforementioned embodiments and can be adjusted according to actual application requirements.

[0069] In order to enhance the magnetic flux cancellation between the three-phase transformer (e.g., the three-phase transformer T shown in FIG. 2 ) and the three-phase resonant inductor (e.g., the second resonant elements RE A2 , RE B2 , and RE C2 shown in FIG. 2 ) within the three-phase LLC power conversion circuits of the aforementioned embodiments, thereby improving core loss and reducing volume, the present invention further positions the three-phase transformer and the resonant inductor in the resonant element to achieve magnetic flux cancellation, thereby achieving the aforementioned objectives. The following describes various embodiments of positional matching between the three-phase transformer and the resonant inductor in the resonant element. The reference numerals A, B, and C appearing in the subsequent description represent the first phase A, the second phase B, and the third phase C, respectively. The first phase A leads the second phase B by 120 degrees, the second phase B leads the third phase C by 120 degrees, and the third phase C leads the first phase A by 120 degrees.

[0070] Please refer to Figures 15A, 15B, and 15C. Figure 15A is a circuit topology diagram of the first embodiment of the magnetic assembly suitable for a three-phase LLC power conversion circuit. Figure 15B is a schematic diagram illustrating the placement of the three-phase transformer and three-phase resonant inductor of the magnetic assembly shown in Figure 15A. Figure 15C is a schematic diagram illustrating a portion of the magnetic flux vectors of the magnetic assembly shown in Figure 15B. The magnetic assembly 5 of this embodiment includes a three-phase transformer, a three-phase resonant inductor, and a magnetic core assembly. The magnetic core assembly includes a single magnetic core 6. The three-phase transformer includes a first transformer TA, a second transformer TB, and a third transformer TC. The primary windings of the first, second, and third transformers TA, TB, and TC are star-connected (Y-connected). The three-phase resonant inductor includes a first resonant inductor L rBC (BC phase inductor), a second resonant inductor L rCA (CA phase inductor), and a third resonant inductor L rAB (AB phase inductor), each electrically connected to the primary windings of the corresponding transformers among the first transformer TA, the second transformer TB, and the third transformer TC. The first resonant inductor L rBC, the second resonant inductor L rCA, and the third resonant inductor L rAB are connected in a delta configuration. In some embodiments, the three-phase transformer further includes a first magnetizing inductor L mA, a second magnetizing inductor L mB, and a third magnetizing inductor L mC, each connected in parallel to the primary windings of the corresponding transformers among the first transformer TA, the second transformer TB, and the third transformer TC.

[0071] In the magnetic assembly 5, the first resonant inductor LrBC, the second resonant inductor LrCA, and the third resonant inductor LrAB are arranged horizontally adjacent to a first side of the magnetic core 6, and the first transformer TA, the second transformer TB, and the third transformer TC are arranged horizontally adjacent to a second side of the magnetic core 6, with the first side opposing the second side. Furthermore, when the ratio of the inductance of the resonant inductor to the inductance of the corresponding magnetizing inductor is greater than a set value, such as 10, the resonant inductors and transformers in different phases are arranged adjacent to each other: the first transformer TA is arranged horizontally adjacent to the first resonant inductor LrBC, the second transformer TB is arranged horizontally adjacent to the second resonant inductor LrCA, and the third transformer TC is arranged horizontally adjacent to the third resonant inductor LrAB. Furthermore, the phase angle between the magnetic flux direction of the adjacent resonant inductors and the magnetic flux direction of the transformers is greater than 90 degrees and less than 270 degrees. Furthermore, because the adjacent resonant inductors and transformers are arranged horizontally, the winding direction of the adjacent resonant inductors is opposite to that of the transformers.

[0072] FIG. 15C shows the magnetic fluxes Φ LrBC, Φ LrCA, and Φ LrAB of the first resonant inductor L rBC, the second resonant inductor L rCA, and the third resonant inductor L rAB, respectively. It also shows the magnetic fluxes Φ mA, Φ mB, and Φ mC of the first transformer TA, the second transformer TB, and the third transformer TC, respectively. Furthermore, the magnetic fluxes Φ LrA, Φ LrB, and Φ LrC of the resonant inductors in phases A, B, and C, respectively, are shown. The arrangement of the first transformer TA, the second transformer TB, and the third transformer TC with the first resonant inductor L rBC, the second resonant inductor L rCA, and the third resonant inductor L rAB enables magnetic flux cancellation between the resonant inductors and the transformers of different phases. For example, the magnetic flux of the first transformer TA partially cancels the magnetic flux of the first resonant inductor L rBC, forming a total magnetic flux Φ ΣA for phase A. This improves the loss of the magnetic core 6 and reduces the volume of the magnetic core 6.

[0073] Please refer to Figures 16A and 16B. Figure 16A is a schematic diagram of another variation of the placement of the three-phase transformer and three-phase resonant inductor of the magnetic assembly shown in Figure 15A, and Figure 16B is a schematic diagram of a portion of the magnetic flux vector of the magnetic assembly shown in Figure 16A. In some embodiments, when the ratio of the inductance of the resonant inductor to the inductance of the corresponding magnetizing inductor is less than a set value, the resonant inductors and transformers in the same phase are positioned adjacent to each other, i.e., the first transformer TA is positioned horizontally adjacent to the second resonant inductor LrCA, the second transformer TB is positioned horizontally adjacent to the third resonant inductor LrAB, and the third transformer TC is positioned horizontally adjacent to the first resonant inductor LrBC. Furthermore, the phase angle between the magnetic flux direction of the adjacent resonant inductors and the magnetic flux direction of the transformers is greater than 90 degrees and less than 270 degrees. Furthermore, because the adjacent resonant inductors are positioned horizontally with the transformers, the winding direction of the adjacent resonant inductors is opposite to that of the transformers.

[0074] Please refer to Figures 17A, 17B, 17C, and 17D. Figure 17A is a circuit topology diagram of a second embodiment of a magnetic assembly suitable for a three-phase LLC power conversion circuit. Figure 17B is a circuit topology diagram of a third embodiment of a magnetic assembly suitable for a three-phase LLC power conversion circuit. Figure 17C is a schematic diagram illustrating the placement of the three-phase transformer and three-phase resonant inductor of the magnetic assembly shown in Figures 17A or 17B. Figure 17D is a schematic diagram illustrating a portion of the magnetic flux vector of the magnetic assembly shown in Figure 17C. In the magnetic assembly 5a shown in Figure 17A, the primary windings of the first transformer TA, the second transformer TB, and the third transformer TC of the three-phase transformers are star-connected (Y-connected). The first resonant inductor L rA, the second resonant inductor L rB, and the third resonant inductor L rC of the three-phase resonant inductor are electrically connected to the primary windings of corresponding transformers in the first transformer TA, the second transformer TB, and the third transformer TC, respectively. The first resonant inductor L rA, the second resonant inductor L rB, and the third resonant inductor L rC are star-connected (Y-connected).

[0075] In the magnetic assembly 5b shown in FIG17B , the first transformer TA, the second transformer TB, and the third transformer TC of the three-phase transformer are independent and 120 degrees out of phase. The first resonant inductor L rA, the second resonant inductor L rB, and the third resonant inductor L rC of the three-phase resonant inductor are independent and 120 degrees out of phase, and are electrically connected to the primary windings of the corresponding transformers in the first transformer TA, the second transformer TB, and the third transformer TC, respectively.

[0076] In magnetic assembly 5a or 5b, the first resonant inductor LrA, the second resonant inductor LrB, and the third resonant inductor LrC are arranged horizontally adjacent to a first side of a magnetic core 6, while the first transformer TA, the second transformer TB, and the third transformer TC are arranged horizontally adjacent to a second side of the magnetic core 6, with the first side opposing the second side. Furthermore, the resonant inductors and transformers in different phases are arranged adjacent to each other: the first transformer TA and the third resonant inductor LrC, the second transformer TB and the first resonant inductor LrA, and the third transformer TC and the second resonant inductor LrB. Furthermore, the phase angle between the magnetic flux direction of the adjacent resonant inductors and the magnetic flux direction of the transformers is greater than 90 degrees and less than 270 degrees. Furthermore, because the adjacent resonant inductors are arranged horizontally with the transformers, the winding direction of the adjacent resonant inductors is opposite to that of the transformers.

[0077] FIG. 17D shows the magnetic fluxes Φ LrA, Φ LrB, and Φ LrC of the first resonant inductor L rA, the second resonant inductor L rB, and the third resonant inductor L rC, respectively. It also shows the magnetic fluxes Φ mA, Φ mB, and Φ mC of the first transformer TA, the second transformer TB, and the third transformer TC, respectively. The arrangement of the first transformer TA, the second transformer TB, and the third transformer TC with the first resonant inductor L rA, the second resonant inductor L rB, and the third resonant inductor L rC described above allows for magnetic flux cancellation between the resonant inductors and transformers of different phases. For example, the magnetic flux of the first transformer TA and the magnetic flux of the third resonant inductor L rC partially cancel each other out, forming a total magnetic flux Φ ΣA for phase A. This improves losses in the magnetic core 6 and reduces its volume.

[0078] Please refer to Figures 18A and 18B, wherein Figure 18A is a schematic diagram of another variation of the placement of the three-phase transformer and three-phase resonant inductor of the magnetic assembly shown in Figures 17A or 17B, and Figure 18B is a schematic diagram of a portion of the magnetic flux vectors of the magnetic assembly shown in Figure 18A. In some embodiments, the resonant inductors located in the same phase are adjacent to the transformers, i.e., the first transformer TA is horizontally adjacent to the first resonant inductor LrA, the second transformer TB is horizontally adjacent to the second resonant inductor LrB, and the third transformer TC is horizontally adjacent to the third resonant inductor LrC. Furthermore, the phase angle between the magnetic flux direction of the adjacent resonant inductors and the magnetic flux direction of the transformers is greater than 90 degrees and less than 270 degrees. Furthermore, because the adjacent resonant inductors are horizontally arranged with the transformers, the winding direction of the adjacent resonant inductors is opposite to that of the transformers.

[0079] Please refer to Figures 19A, 19B, and 19C. Figure 19A is a circuit topology diagram of a fourth embodiment of a magnetic component suitable for a three-phase LLC power conversion circuit. Figure 19B is a schematic diagram illustrating the placement of the three-phase transformer and three-phase resonant inductor of the magnetic component shown in Figure 19A. Figure 19C is a schematic diagram illustrating a portion of the magnetic flux vectors of the magnetic component shown in Figure 19B. The magnetic component 5c of this embodiment includes a three-phase transformer, a three-phase resonant inductor, and a magnetic core 6. The three-phase transformer includes a first transformer TAB, a second transformer TBC, and a third transformer TCA. The primary windings of the first transformer TAB, the second transformer TBC, and the third transformer TCA are connected in a delta configuration. The three-phase resonant inductor includes a first resonant inductor L rA, a second resonant inductor L rB, and a third resonant inductor L rC, each electrically connected to the primary windings of a corresponding two of the first transformer T AB, the second transformer T BC, and the third transformer T CA. The first resonant inductor L rA, the second resonant inductor L rB, and the third resonant inductor L rC are star-connected (Y-connected). In some embodiments, the three-phase transformer further includes a first magnetizing inductor L mB, a second magnetizing inductor L mBC, and a third magnetizing inductor L mCA, each connected in parallel to the primary windings of a corresponding two of the first transformer T AB, the second transformer T BC, and the third transformer T CA.

[0080] In the magnetic assembly 5c, the first resonant inductor L rA, the second resonant inductor L rB, and the third resonant inductor L rC are arranged horizontally adjacent to the first side of the magnetic core 6, while the first transformer T AB, the second transformer T BC, and the third transformer T CA are arranged horizontally adjacent to the second side of the magnetic core 6, with the first side opposing the second side. Furthermore, the resonant inductors and transformers in different phases are arranged adjacent to each other: the first transformer T AB and the third resonant inductor L rC are arranged horizontally adjacent to each other, the second transformer T BC and the first resonant inductor L rA are arranged horizontally adjacent to each other, and the third transformer T CA and the second resonant inductor L rB are arranged horizontally adjacent to each other. Furthermore, the phase angle between the magnetic flux direction of the adjacent resonant inductors and the magnetic flux direction of the transformers is greater than 90 degrees and less than 270 degrees. Furthermore, because the adjacent resonant inductors are arranged horizontally with the transformers, the winding direction of the adjacent resonant inductors is opposite to that of the transformers.

[0081] FIG. 19C shows the magnetic fluxes Φ LrA, Φ LrB, and Φ LrC of the first resonant inductor L rA, the second resonant inductor L rB, and the third resonant inductor L rC, respectively. It also shows the magnetic fluxes Φ mB, Φ mBC, and Φ mCA of the first transformer T AB, the second transformer T BC, and the third transformer T CA, respectively. Furthermore, the magnetic fluxes Φ LrAB, Φ LrBC, and Φ LrCA of the resonant inductors in the AB, BC, and CA phases, respectively, are shown. By configuring the first transformer T AB, the second transformer T BC, and the third transformer T CA with the first resonant inductor L rA, the second resonant inductor L rB, and the third resonant inductor L rC, the resonant inductors and transformers of different phases can achieve magnetic flux cancellation. For example, the magnetic flux of the first transformer T AB partially cancels the magnetic flux of the third resonant inductor L rC, thereby improving the loss of the magnetic core 6 and reducing the volume of the magnetic core 6.

[0082] Please refer to Figures 20A and 20B, wherein Figure 20A is a schematic diagram of another variation of the placement of the three-phase transformer and three-phase resonant inductor of the magnetic assembly shown in Figure 19A, and Figure 20B is a schematic diagram of a portion of the magnetic flux vector of the magnetic assembly shown in Figure 20A. In some embodiments, the resonant inductors located in the same phase are adjacent to the transformers, i.e., the first transformer TAB is horizontally adjacent to the first resonant inductor LrA, the second transformer TBC is horizontally adjacent to the second resonant inductor LrB, and the third transformer TCA is horizontally adjacent to the third resonant inductor LrC. Furthermore, the phase angle between the magnetic flux direction of the adjacent resonant inductors and the magnetic flux direction of the transformers is greater than 90 degrees and less than 270 degrees. Furthermore, because the adjacent resonant inductors are arranged horizontally with the transformers, the winding direction of the adjacent resonant inductors is opposite to that of the transformers.

[0083] Please refer to Figures 21A, 21B, and 21C. Figure 21A is a circuit topology diagram of a fifth embodiment of a magnetic component suitable for a three-phase LLC power conversion circuit. Figure 21B is a schematic diagram illustrating the placement of the three-phase transformer and three-phase resonant inductor of the magnetic component shown in Figure 21A. Figure 21C is a schematic diagram illustrating a portion of the magnetic flux vectors of the magnetic component shown in Figure 21B. The magnetic component 5d of this embodiment includes a three-phase transformer, a three-phase resonant inductor, and a magnetic core 6. The three-phase transformer includes a first transformer TAB, a second transformer TBC, and a third transformer TCA. The primary windings of the first transformer TAB, the second transformer TBC, and the third transformer TCA are connected in a delta configuration. The three-phase resonant inductor includes a first resonant inductor L rBC, a second resonant inductor L rCA, and a third resonant inductor L rAB. The third resonant inductor L rAB, the first resonant inductor L rBC, and the second resonant inductor L rCA are electrically connected to the primary windings of corresponding two transformers among the first transformer T AB, the second transformer T BC, and the third transformer T CA, respectively. The first resonant inductor L rBC, the second resonant inductor L rCA, and the third resonant inductor L rAB are connected in a delta configuration (Δ connection). In some embodiments, the three-phase transformer further includes a first magnetizing inductor L mAB, a second magnetizing inductor L mBC, and a third magnetizing inductor L mCA, each connected in parallel with the primary windings of corresponding transformers among the first transformer T AB, the second transformer T BC, and the third transformer T CA, respectively.

[0084] In the magnetic assembly 5d, the third resonant inductor LrAB, the first resonant inductor LrBC, and the second resonant inductor LrCA are arranged horizontally adjacent to each other on the first side of the magnetic core 6. The first transformer TAB, the second transformer TBC, and the third transformer TCA are arranged horizontally adjacent to each other on the second side of the magnetic core 6, with the first side opposing the second side. Furthermore, the resonant inductors and transformers in different phases are arranged adjacent to each other: the first transformer TAB and the second resonant inductor LrCA are arranged horizontally adjacent to each other, the second transformer TBC and the third resonant inductor LrAB are arranged horizontally adjacent to each other, and the third transformer TCA and the first resonant inductor LrBC are arranged horizontally adjacent to each other. Furthermore, the phase angle between the magnetic flux direction of the adjacent resonant inductors and the magnetic flux direction of the transformers is greater than 90 degrees and less than 270 degrees. Furthermore, because the adjacent resonant inductors are arranged horizontally with the transformers, the winding direction of the adjacent resonant inductors is opposite to that of the transformers.

[0085] FIG. 21C shows the magnetic fluxes Φ LrAB, Φ LrBC, and Φ LrCA of the third resonant inductor L rAB, the first resonant inductor L rBC, and the second resonant inductor L rCA, respectively. It also shows the magnetic fluxes Φ mAB, Φ mBC, and Φ mCA of the first transformer T AB, the second transformer T BC, and the third transformer T CA, respectively. By configuring the first transformer T AB, the second transformer T BC, and the third transformer T CA with the third resonant inductor L rAB, the first resonant inductor L rBC, and the second resonant inductor L rCA, the resonant inductors and transformers of different phases can achieve magnetic flux cancellation. For example, the magnetic flux of the first transformer T AB partially cancels the magnetic flux of the second resonant inductor L rCA, thereby improving the loss of the magnetic core 6 and reducing the volume of the magnetic core 6.

[0086] Please refer to Figures 22A and 22B, wherein Figure 22A is a schematic diagram of another variation of the placement of the three-phase transformer and three-phase resonant inductor of the magnetic assembly shown in Figure 21A, and Figure 22B is a schematic diagram of a portion of the magnetic flux vector of the magnetic assembly shown in Figure 16A. In some embodiments, the resonant inductors located in the same phase are adjacent to the transformers, i.e., the first transformer TAB is horizontally adjacent to the third resonant inductor LrAB, the second transformer TBC is horizontally adjacent to the first resonant inductor LrBC, and the third transformer TCA is horizontally adjacent to the second resonant inductor LrCA. Furthermore, the phase angle between the magnetic flux direction of the adjacent resonant inductors and the magnetic flux direction of the transformers is greater than 90 degrees and less than 270 degrees. Furthermore, because the adjacent resonant inductors are arranged horizontally with the transformers, the winding direction of the adjacent resonant inductors is opposite to that of the transformers.

[0087] Please refer to Figures 23A, 23B, 23C, 23D, 23E and 23F, wherein Figure 23A is a circuit topology diagram of the sixth embodiment of the magnetic component applicable to the three-phase LLC power conversion circuit of the present case, Figure 23B is a circuit topology diagram of the seventh embodiment of the magnetic component applicable to the three-phase LLC power conversion circuit of the present case, Figure 23C is a circuit topology diagram of the eighth embodiment of the magnetic component applicable to the three-phase LLC power conversion circuit of the present case, Figure 23D is a circuit topology diagram of the ninth embodiment of the magnetic component applicable to the three-phase LLC power conversion circuit of the present case, Figure 23E is a schematic diagram of the setting positions of the three-phase transformer and the three-phase resonant inductor of the magnetic component shown in Figure 23A, 23B, 23C or 23D, and Figure 23F is a schematic diagram of a portion of the magnetic flux vector of the magnetic component shown in Figure 23E. The magnetic assembly 5e shown in FIG. 23A includes a three-phase transformer, a first set of three-phase resonant inductors, a second set of three-phase resonant inductors, and a magnetic core 6. The primary windings of the first transformer TA, the second transformer TB, and the third transformer TC of the three-phase transformer are star-connected (Y-connected), while the secondary windings of the first transformer TA, the second transformer TB, and the third transformer TC of the three-phase transformer are star-connected (Y-connected). The first set of three-phase resonant inductors includes a first resonant inductor L rA1, a second resonant inductor L rB1, and a third resonant inductor L rC1. The first resonant inductor L rA1, the second resonant inductor L rB1, and the third resonant inductor L rC1 are electrically connected to the primary windings of the corresponding transformers in the first transformer TA, the second transformer TB, and the third transformer TC, respectively. The first resonant inductor L rA1, the second resonant inductor L rB1, and the third resonant inductor L rC1 are star-connected (Y-connected). The second set of three-phase resonant inductors includes a fourth resonant inductor L rA2, a fifth resonant inductor L rB2, and a sixth resonant inductor L rC2. The fourth resonant inductor L rA2, the fifth resonant inductor L rB2, and the sixth resonant inductor L rC2 are electrically connected to the secondary windings of corresponding transformers among the first transformer TA, the second transformer TB, and the third transformer TC, respectively. The fourth resonant inductor L rA2, the fifth resonant inductor L rB2, and the sixth resonant inductor L rC2 are star-connected (Y-connected).

[0088] In the magnetic assembly 5f shown in FIG. 23B , the first, second, and third three-phase transformers TA, TB, and TC are independent and 120 degrees out of phase with each other. The first, second, and third resonant inductors L rA1, L rB1, and L rC1 of the first set of three-phase resonant inductors are independent and 120 degrees out of phase with each other, and are electrically connected to the primary windings of the corresponding transformers in the first, second, and third transformers TC, respectively. The fourth, fifth, and sixth resonant inductors L rA2, L rB2, and L rC2 of the second set of three-phase resonant inductors are independent and 120 degrees out of phase with each other, and are electrically connected to the secondary windings of the corresponding transformers in the first, second, and third transformers TC, respectively.

[0089] The magnetic assembly 5g shown in FIG. 23C includes a three-phase transformer, a first set of three-phase resonant inductors, a second set of three-phase resonant inductors, and a magnetic core 6. The primary windings of the first transformer TA, the second transformer TB, and the third transformer TC of the three-phase transformer are star-connected (Y-connected). The first set of three-phase resonant inductors includes a first resonant inductor L rA1, a second resonant inductor L rB1, and a third resonant inductor L rC1. The first resonant inductor L rA1, the second resonant inductor L rB1, and the third resonant inductor L rC1 are electrically connected to the primary windings of the corresponding transformers in the first transformer TA, the second transformer TB, and the third transformer TC, respectively. The first resonant inductor L rA1, the second resonant inductor L rB1, and the third resonant inductor L rC1 are star-connected (Y-connected). The second set of three-phase resonant inductors includes a fourth resonant inductor L rA2, a fifth resonant inductor L rB2, and a sixth resonant inductor L rC2. The fourth resonant inductor L rA2, the fifth resonant inductor L rB2, and the sixth resonant inductor L rC2 are electrically connected between corresponding resonant inductors among the first resonant inductor L rA1, the second resonant inductor L rB1, and the third resonant inductor L rC1 and the primary windings of corresponding transformers among the first transformer TA, the second transformer TB, and the third transformer TC, respectively. Furthermore, the fourth resonant inductor L rA2, the fifth resonant inductor L rB2, and the sixth resonant inductor L rC2 are star-connected (Y-connected).

[0090] In the magnetic assembly 5h shown in FIG. 23D , the first transformer TA, the second transformer TB, and the third transformer TC of the three-phase transformer are independent and have a phase difference of 120 degrees. The first resonant inductor L rA1, the second resonant inductor L rB1, and the third resonant inductor L rC1 of the first set of three-phase resonant inductors are independent and have a phase difference of 120 degrees. The first resonant inductor L rA1, the second resonant inductor L rB1, and the third resonant inductor L rC1 are electrically connected to the primary windings of corresponding transformers in the first transformer TA, the second transformer TB, and the third transformer TC, respectively. The fourth resonant inductor L rA2, the fifth resonant inductor L rB2, and the sixth resonant inductor L rC2 of the second set of three-phase resonant inductors are independent and 120 degrees out of phase with each other. The fourth resonant inductor L rA2, the fifth resonant inductor L rB2, and the sixth resonant inductor L rC2 are electrically connected between the corresponding resonant inductor among the first resonant inductor L rA1, the second resonant inductor L rB1, and the third resonant inductor L rC1 and the primary winding of the corresponding transformer among the first transformer TA, the second transformer TB, and the third transformer TC, respectively.

[0091] In magnetic components 5e, 5f, 5g, or 5h, the first resonant inductor LrA1, the second resonant inductor LrB2, and the third resonant inductor LrC2 are arranged horizontally adjacent to the first side of the magnetic core 6, while the fourth resonant inductor LrA2, the fifth resonant inductor LrB2, and the sixth resonant inductor LrC2 are arranged horizontally adjacent to the second side of the magnetic core 6. The first transformer TA, the second transformer TB, and the third transformer TC are arranged horizontally between the first and second sides of the magnetic core 6 and between the first and second sets of three-phase resonant inductors, with the first side opposing the second side. Furthermore, resonant inductors in different phases are arranged adjacent to the transformers: the first transformer TA is arranged horizontally adjacent to the third resonant inductor LrC1 and the sixth resonant inductor LrC2, the second transformer TB is arranged horizontally adjacent to the first and fourth resonant inductors LrA1 and LrA2, and the third transformer TC is arranged horizontally adjacent to the second and fifth resonant inductors LrB1 and LrB2. Furthermore, the phase angle between the magnetic flux direction of the adjacent resonant inductor and the magnetic flux direction of the transformer is greater than 90 degrees and less than 270 degrees. Furthermore, because the adjacent resonant inductor and the transformer are arranged horizontally, the winding direction of the adjacent resonant inductor is opposite to that of the transformer.

[0092] FIG. 23F shows the magnetic fluxes Φ LrA1, Φ LrB1, Φ LrC1, Φ LrA2, Φ LrB2, and Φ LrC2 of the first, second, third, and fourth resonant inductors L rA1, L rB1, L rC1, L rA2, L rB2, and L rC2, respectively. Also shown are the magnetic fluxes Φ mA, Φ mB, and Φ mC of the first, second, and third transformers TA, TB, and TC, respectively. By configuring the first transformer TA, the second transformer TB, and the third transformer TC and the first resonant inductor L rA1, the second resonant inductor L rB1, the third resonant inductor L rC1, the fourth resonant inductor L rA2, the fifth resonant inductor L rB2, and the sixth resonant inductor L rC2, the resonant inductors and transformers of different phases can achieve magnetic flux cancellation. For example, the magnetic flux of the first transformer TA partially cancels out the magnetic flux of the third resonant inductor L rC1 and the magnetic flux of the sixth resonant inductor L rC2 to form the total magnetic flux Φ ΣA of the A phase. The magnetic flux of the second transformer TB partially cancels out the magnetic flux of the first resonant inductor L rA1 and the magnetic flux of the fourth resonant inductor L rA2 to form the total magnetic flux Φ ΣB of the B phase. The magnetic flux of the third transformer TC partially cancels out the magnetic flux of the second resonant inductor L rB1 and the magnetic flux of the fifth resonant inductor L rB2 to form the total magnetic flux Φ ΣC of the C phase. This improves the loss of the magnetic core 6 and reduces the volume of the magnetic core 6.

[0093] In the aforementioned embodiments, the three-phase transformers and three-phase resonant inductors of the magnetic assembly can also be stacked and arranged vertically on the magnetic core assembly, with the winding direction of adjacent resonant inductors being the same as that of the transformers. Several possible implementations are exemplified below. Referring to FIG. 24 , which is a schematic diagram illustrating another variation of the placement of the three-phase transformers and three-phase resonant inductors of the magnetic assembly of the embodiment shown in FIG. 15A , the circuit architecture of the magnetic assembly of this embodiment is similar to that of the magnetic assembly 5 shown in FIG. 15A . The magnetic core assembly of this embodiment comprises a first magnetic core 6a and a second magnetic core 6b, with the first magnetic core 6a arranged vertically above the second magnetic core 6b. The first resonant inductor L rBC, the second resonant inductor L rCA, and the third resonant inductor L rAB are disposed on the first magnetic core 6a. The first transformer TA, the second transformer TB, and the third transformer TC are disposed on the second magnetic core 6b. In addition, resonant inductors located in different phases are arranged adjacent to the transformers, that is, the first transformer TA is arranged perpendicularly adjacent to the first resonant inductor LrBC, the second transformer TB is arranged perpendicularly adjacent to the second resonant inductor LrCA, and the third transformer TC is arranged perpendicularly adjacent to the third resonant inductor LrAB. The phase angle between the magnetic flux direction of the perpendicularly adjacent resonant inductors and the magnetic flux direction of the transformers is between -90 degrees and +90 degrees, wherein the positive direction of the magnetic flux direction is from bottom to top, and the winding direction of the adjacent resonant inductors is the same as the winding direction of the transformers.

[0094] FIG25 is a schematic diagram illustrating another variation of the placement of the three-phase transformer and three-phase resonant inductor of the magnetic assembly shown in FIG23E. As shown in FIG25, the circuit architecture of the magnetic assembly of this embodiment is similar to that of magnetic assembly 5e, 5f, 5g, or 5h shown in FIG23A, FIG23B, FIG23C, or FIG23D. The magnetic core assembly of this embodiment comprises a first magnetic core 6a, a second magnetic core 6b, and a third magnetic core 6c. The first magnetic core 6a is disposed vertically above the second magnetic core 6b, and the second magnetic core 6b is disposed vertically above the third magnetic core 6c. The first resonant inductor LrA1, the second resonant inductor LrB1, and the third resonant inductor LrC1 are disposed on the first magnetic core 6a. The first transformer TA, the second transformer TB, and the third transformer TC are disposed on the second magnetic core 6b. The fourth resonant inductor LrA2, the fifth resonant inductor LrB2, and the sixth resonant inductor LrC2 are disposed on the third magnetic core 6c. Furthermore, resonant inductors located in different phases are positioned adjacent to the transformers. Specifically, the first transformer TA is positioned perpendicularly adjacent to the third resonant inductor LrC1 and the sixth resonant inductor LrC2; the second transformer TB is positioned perpendicularly adjacent to the first resonant inductor LrA1 and the fourth resonant inductor LrA2; and the third transformer TC is positioned perpendicularly adjacent to the second resonant inductor LrB1 and the fifth resonant inductor LrB2. The phase angle between the magnetic flux direction of the perpendicularly adjacent resonant inductors and the magnetic flux direction of the transformers is between -90 degrees and +90 degrees. The positive magnetic flux direction is from bottom to top, and the winding direction of the adjacent resonant inductors is the same as that of the transformers.

[0095] In summary, this invention provides a three-phase LLC power conversion circuit and control method thereof. These circuits not only reduce the switching frequency range of the three-phase power conversion circuit, but also achieve lower RMS current, lower peak current, and improved magnetic integration. Furthermore, because the control unit of the three-phase power conversion circuit controls two control variables—the phase shift and frequency of the switches—the circuit can mitigate the increase in reactive current caused by changes in the resonant frequency and enable more precise soft switching.

[0096] 1, 1a, 1b, 1c, 1d, 1e: Three-phase LLC power conversion circuit DC: Input power V in: input voltage R: Load V o: output voltage V ref: reference voltage T: Three-phase transformer 2: Input switch group 3: Output switch group 4: Control unit Q 1: First upper input switch Q 2: First input switch Q 3: Second upper input switch Q 4: Second input switch Q 5: Third input switch Q 6: The third input switch T1, TA, TAB: first transformer T 2, TB, T BC: Second transformer T 3, TC, T CA: The third transformer Lm1, Lm2, Lm3: magnetizing inductance RE A1, RE B1, RE C1: first resonant element RE A2, RE B2, RE C2: second resonant element SR1, SR1a: first upper rectifier switch SR2, SR2a: first lower rectifier switch SR3, SR3a: Second upper rectifier switch SR4, SR4a: Second lower rectifier switch S R5, S R5a: the third upper rectifier switch S R6, S R6a: the third lower rectifier switch S R7: Fourth upper rectifier switch S R8: the fourth lower rectifier switch S R9: Fifth upper rectifier switch S R10: Fifth lower rectifier switch S R11: Sixth upper rectifier switch S R12: Sixth lower rectifier switch △T 1: First time △T 2: Second time I p1, I M1, I s1, I s2, I s3, I C1, I C2, I C3, I L1, I L2, I L3: current 41: Zero current detection circuit 42: Gain control circuit 43: First Drive 44: Subtractor 45: Compensation circuit 46: Voltage Controlled Oscillator 47: Second Drive S1~S2: Steps of control method T1p, T2p, T3p: primary side winding T 1s, T 2s, T 3s: secondary side winding C r1, C r2, C r3: capacitors L r1, L r2 and L r3: resonant inductance L rBC, L rA, L rA1: first resonant inductor L rCA, L rB, L rB1: second resonant inductor L rAB, L rC, L rC1: third resonant inductor 5, 5a, 5b, 5c, 5d, 5e, 5f, 5g, 5h: Magnetic components 6: Magnetic core 6a: First magnetic core 6b: Second magnetic core 6c: The third magnetic core L mA, L mAB: first magnetizing inductance L mB, L mBC: Second magnetizing inductance L mC, L mCA: third magnetizing inductance Φ LrBC, Φ LrCA, Φ LrAB, Φ mA, Φ mB, Φ mC, Φ LrA, Φ LrB, Φ LrC, Φ ΣA, Φ ΣB, Φ ΣC, Φ mAB, Φ mBC, Φ mCA, Φ LrA1, Φ LrB1, Φ LrC1, Φ LrA2, Φ LrB2, Φ LrC2: magnetic flux L rA2: fourth resonant inductor L rB2: fifth resonant inductor L rC2: Sixth resonant inductor

Claims

1. A control method applied to a three-phase LLC power conversion circuit, the three-phase LLC power conversion circuit receiving an input voltage and outputting an output voltage, and including a three-phase transformer, an input switch group, an output switch group, and a resonant circuit group, the input switch group being electrically connected to a plurality of primary windings of the three-phase transformer and including a plurality of input switches, the output switch group being electrically connected to a plurality of secondary windings of the three-phase transformer and including a plurality of rectifier switches, the resonant circuit group being electrically connected between the input switch group and the plurality of primary windings, the control method comprising: S1: detecting a zero-crossing point of the input voltage, the output voltage, and an output current of each phase of the three-phase LLC power conversion circuit; and S2: Based on the detection result of S1, the plurality of input switches are controlled to perform switching operations, the plurality of rectifier switches are controlled to perform synchronous rectification switching operations, and based on the ratio of the output voltage and the input voltage, the switching state of at least one rectifier switch in the output switch group of each phase is controlled to lead or lag the switching state of the corresponding input switch and / or the duty cycle of all input switches in each phase is increased, thereby increasing the ratio of the output voltage and the input voltage, and the switching frequency of all input switches is adjusted based on the output voltage, a reference voltage and a soft switching setting condition, so that all input switches perform soft switching switching.

2. The control method as claimed in claim 1, wherein in S2, the switching state of at least one rectifier switch in each phase is controlled to lead the switching state of the corresponding input switch based on the ratio of the output voltage and the input voltage, and the switching state of the remaining at least one rectifier switch in each phase is controlled to lag the switching state of the corresponding input switch.

3. The control method as claimed in claim 1, wherein in S2, at least one rectifier switch of each phase is controlled to perform synchronous rectification switching, and the switching state of the remaining at least one rectifier switch of each phase is controlled to lead the switching state of the corresponding input switch.

4. The control method as claimed in claim 1, wherein in S2, at least one rectifier switch of each phase is controlled to perform synchronous rectification switching, and the switching state of the remaining at least one rectifier switch of each phase is controlled to lag behind the switching state of the corresponding input switch.

5. The control method as claimed in claim 1, wherein the plurality of input switches includes a first upper input switch, a first lower input switch, a second upper input switch, a second lower input switch, a third upper input switch, and a third lower input switch, wherein the first upper input switch and the first lower input switch are connected in series to form a first input switch bridge arm, the second upper input switch and the second lower input switch are connected in series to form a second input switch bridge arm, and the third upper input switch and the third lower input switch are connected in series to form a third input switch bridge arm, wherein the first input switch bridge arm, the second input switch bridge arm, and the third input switch bridge arm are connected in parallel to each other.

6. The control method as claimed in claim 1, wherein the plurality of input switches includes a first upper input switch, a first lower input switch, a second upper input switch, a second lower input switch, a third upper input switch, and a third lower input switch, wherein the first upper input switch and the first lower input switch are connected in series, the second upper input switch and the second lower input switch are connected in series, and the third upper input switch and the third lower input switch are connected in series, wherein the first upper input switch, the first lower input switch, the second upper input switch, the second lower input switch, the third upper input switch, and the third lower input switch are electrically connected in a cascaded manner.

7. The control method as claimed in claim 1, wherein the plurality of rectifier switches includes a first upper rectifier switch, a first lower rectifier switch, a second upper rectifier switch, a second lower rectifier switch, a third upper rectifier switch, a third lower rectifier switch, a fourth upper rectifier switch, a fourth lower rectifier switch, a fifth upper rectifier switch, a fifth lower rectifier switch, a sixth upper rectifier switch, and a sixth lower rectifier switch, wherein the first upper rectifier switch and the first lower rectifier switch are connected in series to form a first rectifier bridge arm, and the second upper rectifier switch and the second lower rectifier switch are connected in series to form a second upper rectifier bridge arm. The rectifier bridge arms are as follows: the first rectifier bridge arm and the second rectifier bridge arm are connected in parallel; the third upper rectifier switch and the third lower rectifier switch are connected in series to form a third rectifier bridge arm; the fourth upper rectifier switch and the fourth lower rectifier switch are connected in series to form a fourth rectifier bridge arm; the third rectifier bridge arm and the fourth rectifier bridge arm are connected in parallel; the fifth upper rectifier switch and the fifth lower rectifier switch are connected in series to form a fifth rectifier bridge arm; the sixth upper rectifier switch and the sixth lower rectifier switch are connected in series to form a sixth rectifier bridge arm; and the fifth rectifier bridge arm and the sixth rectifier bridge arm are connected in parallel.

8. The control method as described in claim 7, wherein the plurality of rectifier switches are each composed of active switches.

9. The control method as claimed in claim 1, wherein the resonant circuit comprises a plurality of first resonant elements and a plurality of second resonant elements, the plurality of first resonant elements being star-connected and each being composed of an inductor or a capacitor, and the plurality of second resonant elements being delta-connected and each being composed of another inductor or another capacitor.

10. The control method as claimed in claim 9, wherein the plurality of primary windings of the three-phase transformer are delta-connected and the plurality of secondary windings are delta-connected.

11. A three-phase LLC power conversion circuit, receiving an input voltage and outputting an output voltage, comprising: an input switch group receiving the input voltage and including a plurality of input switches; a three-phase transformer including a plurality of primary windings and a plurality of secondary windings, the input switch group being electrically connected to the plurality of primary windings; a resonant circuit group electrically connected between the input switch group and the plurality of primary windings, including a plurality of first resonant elements and a plurality of second resonant elements, the plurality of first resonant elements being star-connected and each consisting of an inductor or a capacitor, the plurality of second resonant elements being delta-connected and each consisting of another inductor or another capacitor; and an output switch group electrically connected to the plurality of secondary windings and including a plurality of rectifier switches for outputting the output voltage.

12. The three-phase LLC power conversion circuit as claimed in claim 11, wherein the three-phase LLC power conversion circuit further includes a control unit electrically connected to the input switch group and the output switch group, for detecting the input voltage, the output voltage and a zero-crossing point of an output current of each phase of the three-phase LLC power conversion circuit, so as to control the plurality of input switches to perform switching operation based on the detection result, control the plurality of rectifier switches to perform synchronous rectification switching operation, and control the switching state of at least one rectifier switch of the output switch group of each phase to lead or lag the switching state of the corresponding input switch according to the ratio of the output voltage and the input voltage and / or adjust the duty cycle of all input switches of each phase to increase, thereby increasing the ratio of the output voltage and the input voltage, and adjust the switching frequency of all input switches according to the output voltage, a reference voltage and a soft-switching setting condition, so that all input switches perform soft-switching switching.

13. The three-phase LLC power conversion circuit as claimed in claim 12, wherein the control unit controls the switching state of at least one rectifier switch in each phase to lead the switching state of the corresponding input switch based on the ratio of the output voltage and the input voltage, and controls the switching state of the remaining at least one rectifier switch in each phase to lag the switching state of the corresponding input switch.

14. The three-phase LLC power conversion circuit as claimed in claim 12, wherein the control unit controls at least one of the rectifier switches in each phase to perform synchronous rectification switching, and controls the switching state of the remaining at least one rectifier switch in each phase to lead the switching state of the corresponding input switch.

15. The three-phase LLC power conversion circuit as claimed in claim 12, wherein the control unit controls at least one of the rectifier switches in each phase to perform synchronous rectification switching, and controls the switching state of the remaining at least one rectifier switch in each phase to lag behind the switching state of the corresponding input switch.

16. The three-phase LLC power conversion circuit as claimed in claim 11, wherein the plurality of input switches includes a first upper input switch, a first lower input switch, a second upper input switch, a second lower input switch, a third upper input switch, and a third lower input switch, wherein the first upper input switch and the first lower input switch are connected in series to form a first input switch bridge arm, the second upper input switch and the second lower input switch are connected in series to form a second input switch bridge arm, and the third upper input switch and the third lower input switch are connected in series to form a third input switch bridge arm, wherein the first input switch bridge arm, the second input switch bridge arm, and the third input switch bridge arm are connected in parallel to each other.

17. The three-phase LLC power conversion circuit as claimed in claim 11, wherein the plurality of input switches includes a first upper input switch, a first lower input switch, a second upper input switch, a second lower input switch, a third upper input switch, and a third lower input switch, wherein the first upper input switch and the first lower input switch are connected in series, the second upper input switch and the second lower input switch are connected in series, and the third upper input switch and the third lower input switch are connected in series, wherein the first upper input switch, the first lower input switch, the second upper input switch, the second lower input switch, the third upper input switch, and the third lower input switch are electrically connected in a cascaded manner.

18. The three-phase LLC power conversion circuit as claimed in claim 11, wherein the plurality of rectifier switches includes a first upper rectifier switch, a first lower rectifier switch, a second upper rectifier switch, a second lower rectifier switch, a third upper rectifier switch, a third lower rectifier switch, a fourth upper rectifier switch, a fourth lower rectifier switch, a fifth upper rectifier switch, a fifth lower rectifier switch, a sixth upper rectifier switch, and a sixth lower rectifier switch, wherein the first upper rectifier switch and the first lower rectifier switch are connected in series to form a first rectifier bridge arm, and the second upper rectifier switch and the second lower rectifier switch are connected in series... A second rectifier bridge arm is formed, and the first rectifier bridge arm is connected in parallel with the second rectifier bridge arm. The third upper rectifier switch and the third lower rectifier switch are connected in series to form a third rectifier bridge arm. The fourth upper rectifier switch and the fourth lower rectifier switch are connected in series to form a fourth rectifier bridge arm. The third rectifier bridge arm and the fourth rectifier bridge arm are connected in parallel. The fifth upper rectifier switch and the fifth lower rectifier switch are connected in series to form a fifth rectifier bridge arm. The sixth upper rectifier switch and the sixth lower rectifier switch are connected in series to form a sixth rectifier bridge arm. The fifth rectifier bridge arm and the sixth rectifier bridge arm are connected in parallel.

19. The three-phase LLC power conversion circuit as claimed in claim 18, wherein the plurality of rectifier switches are each composed of active switches.

20. The three-phase LLC power conversion circuit as claimed in claim 11, wherein the resonant circuit includes a plurality of first resonant elements and a plurality of second resonant elements, the plurality of first resonant elements being star-connected and each consisting of an inductor or a capacitor, and the plurality of second resonant elements being delta-connected and each consisting of an inductor.

Images