Three-phase single-stage AC / DC converter

Abstract

The invention provides a three-phase single-stage AC / DC converter, and relates to the field of converters. The three-phase single-stage alternating-current and direct-current converter comprises three alternating-current modules with transformers and a direct-current module, circuit structures of the three alternating-current modules are the same, each alternating-current module comprises a first inductor, an intermediate capacitor, a second inductor, a bidirectional switch and a transformer, the direct-current module comprises five ports, the first port and the second port are common ports, and the first port and the second port are common ports. Connecting to two ends of a load; when the three-phase single-stage AC / DC converter works, current in the DC module flows from the second port to the third port, and flows from the third port to the first port. The second port flows to the fourth port, and the fourth port flows to the first port; the second port flows to the fifth port, and the fifth port flows to the first port. According to the invention, AC / DC conversion is realized by adopting one-stage energy conversion, and a mainstream AC / DC + DC / DC two-stage framework is replaced, so that high efficiency and low cost are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of converters, and in particular to a three-phase single-stage AC / DC converter. Background Art

[0002] The existing three-phase two-stage PFC rectifier structure is usually as follows Figure 1 As shown, the front stage realizes the power factor correction function, and the rear stage realizes the isolation of the output end and the power supply while adjusting the output voltage. This method can better realize input rectification and output voltage regulation, with high power factor and small THD, but the two-stage circuit increases the use of components, thereby increasing the production cost of the whole machine. Summary of the invention

[0003] 1. Technical issues to be resolved In view of the deficiencies in the prior art, the present invention provides a three-phase single-stage AC-DC converter, which solves the technical problem of high cost of the existing three-phase two-stage PFC rectifier.

[0004] (II) Technical solution To achieve the above objectives, the present invention is implemented through the following technical solutions: In a first aspect, an embodiment of the present invention provides a three-phase single-stage AC / DC converter, comprising three AC modules with transformers and a DC module; in, The three AC modules each include two input terminals and two output terminals, wherein the first input terminals of the three AC modules are respectively connected to the A, B, and C phases of the three-phase power grid, the second input terminals of the three AC modules are connected together, and the first output terminals of the three AC modules are respectively connected to the third port, the fourth port, and the fifth port of the DC module; the fourth ports are connected together; the DC module includes five ports, wherein the first port and the second port are both common terminals, connected to both ends of the load; The circuit structures of the three AC modules are the same, and all include a first inductor, an intermediate capacitor, a second inductor, a bidirectional switch and a transformer; wherein the first end of the first inductor is the first input end of the AC module, the second end of the first inductor is connected to the first connection end of the primary side of the transformer via the intermediate capacitor, the second connection end of the primary side of the transformer is connected to the second input end of the AC module through a wire, and two connection ports a and b are arranged on the wire; wherein the connection port a is connected to the second end of the bidirectional switch, and the first end of the bidirectional switch is connected to the common end of the first inductor and the intermediate capacitor; the connection port b is connected to the second end of the second inductor, and the first end of the second inductor is connected to the common end of the intermediate capacitor and the transformer; the first connection end of the secondary side of the transformer is the first output end of the AC module, and the second connection end of the secondary side of the transformer is the second output end of the AC module; the bidirectional switch is connected to a plurality of control ends, and is suitable for being in one of the following three modes under the control of a control signal connected to the control end: mode one, conduction from the first end of the bidirectional switch to the second end of the bidirectional switch; mode two, conduction from the second end of the bidirectional switch to the first end of the bidirectional switch; mode three, disconnection between the first end and the second end of the bidirectional switch.

[0005] Preferably, the three-phase single-stage AC-DC converter is a three-phase three-wire single-stage AC-DC converter or a three-phase four-wire single-stage AC-DC converter; Wherein, when it is a three-phase four-wire single-stage AC / DC converter, the first end of the neutral line is connected to the common end of the three-phase electricity, and the second end is connected to the common end of the second input ends of the three AC modules.

[0006] Preferably, the bidirectional switch includes two IGBTs or two MOSFETs connected to each other from top to top.

[0007] Preferably, the three switching modes of the two IGBTs facing each other or the two MOSFETs facing each other include: The first switch tube is turned on, and the flyback diode connected in reverse parallel to the second switch tube is turned on; The second switch tube is turned on, and the freewheeling diode connected in reverse parallel to the first switch tube is turned on; The first switch tube and the second switch tube are both turned off.

[0008] Preferably, when the three-phase single-stage AC / DC converter is working, the current direction in the DC module is from the second port to the third port, and from the third port to the first port; from the second port to the fourth port, and from the fourth port to the first port; from the second port to the fifth port, and from the fifth port to the first port.

[0009] Preferably, the DC module includes six diodes, wherein the cathodes of the first diode, the second diode and the third diode are all connected to the first port of the DC module, and the anodes of the first diode, the second diode and the third diode are respectively connected to the third port, the fourth port and the fifth port of the DC module; the anodes of the fourth diode, the fifth diode and the sixth diode are all connected to the second port of the DC module, and the cathodes of the fourth diode, the fifth diode and the sixth diode are respectively connected to the third port, the fourth port and the fifth port of the DC module.

[0010] Preferably, the output voltage step-up and step-down control is achieved by changing the duty ratio of the bidirectional switches in the three AC modules; or the output voltage step-up and step-down control is achieved by the coil ratio of the transformers in the three AC modules.

[0011] Preferably, the three-phase single-stage AC-DC converter further includes a filter capacitor, and the filter capacitor is connected in parallel across the load.

[0012] In a second aspect, the present invention provides a three-phase single-stage AC / DC converter, comprising three AC modules with transformers and a DC module; The three AC modules each include two input terminals, wherein the first input terminals of the three AC modules are respectively connected to the A, B, and C phases of the three-phase power grid, and the second input terminals of the three AC modules are connected together; the DC module includes 6 diodes; The circuit structures of the three AC modules are the same, and all include a first inductor, an intermediate capacitor, a second inductor, a bidirectional switch, and a transformer with a center tap; wherein the first end of the first inductor is the first input end of the AC module, the second end of the first inductor is connected to the first connection end of the primary side of the transformer via the intermediate capacitor, the second connection end of the primary side of the transformer is connected to the second input end of the AC module through a wire, and two connection ports a and b are arranged on the wire; wherein the connection port a is connected to the second end of the bidirectional switch, and the first end of the bidirectional switch is connected to the common end of the first inductor and the intermediate capacitor; the connection port b is connected to the second end of the second inductor, and the first end of the second inductor is connected to the common end of the intermediate capacitor and the transformer; The output ends and common ends of the secondary sides of the three center-tapped transformers are respectively connected to the anodes of the six diodes in the DC module; the center taps of the secondary sides are connected together to form a common terminal P1, and the cathodes of the six diodes are connected together to form a common terminal P2. The common terminals P1 and P2 are connected to the two ends of the load.

[0013] Preferably, the three-phase single-stage AC-DC converter is a three-phase three-wire single-stage AC-DC converter or a three-phase four-wire single-stage AC-DC converter; Wherein, when it is a three-phase four-wire single-stage AC / DC converter, the first end of the neutral line is connected to the common end of the three-phase electricity, and the second end is connected to the common end of the second input ends of the three AC modules.

[0014] (III) Beneficial effects The present invention provides a three-phase single-stage AC / DC converter. Compared with the prior art, it has the following beneficial effects: The three-phase single-stage AC / DC converter provided by the present invention includes three AC modules with transformers and a DC module, wherein the circuit structures of the three AC modules are the same, and all include a first inductor, an intermediate capacitor, a second inductor, a bidirectional switch and a transformer, and the DC module includes five ports, wherein the first port and the second port are both common ports, connected to both ends of the load; when the three-phase single-stage AC / DC converter is working, the current direction in the DC module is that the second port flows to the third port, and the third port flows to the first port; the second port flows to the fourth port, and the fourth port flows to the first port; the second port flows to the fifth port, and the fifth port flows to the first port. The present invention realizes AC / DC conversion by adopting a one-stage energy conversion, replacing the mainstream AC / DC+DC / DC two-stage architecture, thereby achieving high efficiency and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 It is a structural diagram of an existing three-phase two-stage PFC rectifier; Figure 2 is based on Figure 1 A circuit diagram of a specific circuit example of the structure design shown; Figure 3 is a structural diagram of a three-phase three-wire single-stage AC-DC converter in an embodiment of the present invention; Figure 4 is a structural diagram of a three-phase four-wire single-stage AC-DC converter in an embodiment of the present invention; Figure 5 is a specific circuit diagram of a three-phase single-stage AC / DC converter in an embodiment of the present invention; Figure 6 for Figure 5 The circuit diagram shown is a schematic diagram of working mode 1 in DCM mode; Figure 7 for Figure 5 The circuit diagram shown is a schematic diagram of working mode 2 in DCM mode; Figure 8 for Figure 5 The circuit diagram shown is a schematic diagram of working mode 3 in DCM mode; Fig. 9 for Figure 5 The circuit diagram shown is a schematic diagram of working mode 4 in DCM mode; Fig.10 for Figure 5 The circuit diagram shown is a schematic diagram of working mode 5 in DCM mode; Fig.11 for Figure 5 The circuit diagram shown is a schematic diagram of working mode 6 in DCM mode; Fig.12 for Figure 5 The circuit diagram shown is a schematic diagram of the working mode 7 in the DCM mode; Fig.13 for Figure 5 The circuit diagram shown is a schematic diagram of the working mode 8 in the DCM mode; Fig.14 for Figure 5 The circuit diagram shown is a mathematical simplified model 1; Fig.15 for Figure 5 The circuit diagram shown is a mathematical simplified model 2; Fig.16 The circuit diagram of a three-phase three-wire single-stage AC / DC converter when the transformer has a center tap; Fig.17 The circuit diagram of a three-phase four-wire single-stage AC / DC converter when the transformer has a center tap; Fig.18 The circuit diagram of the output H4 bridge type three-phase three-wire single-stage AC-DC converter; Fig.19 The circuit diagram of the output H4 bridge type three-phase four-wire single-stage AC-DC converter; Fig. 20 for Fig.18 Single-phase circuit diagram of the circuit diagram shown. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] It should be noted that, for the convenience of description, the switch IGBT is used to represent the controllable (on and off) switch tube in the embodiment of the present invention, but the switch tube in the present invention is not limited to IGBT. Take IGBT as an example for explanation. The first end of the IGBT refers to the collector, the second end refers to the emitter, and the control end refers to the gate. A driving control signal is applied to the control end of each switch tube in the embodiment of the present invention. For the sake of brevity, it will not be repeated later. The power switch tube in the embodiment of the present invention can also be implemented by other controllable switch tube devices other than IGBT, such as MOSFET. At the same time, in order to ensure the normal operation of each switch device in the embodiment of the present invention, a freewheeling diode needs to be connected in parallel to each switch device. The parallel connection direction of the freewheeling diode is related to the type of the switch device. The technician can set it according to the type of the switch device, which is not limited here. If not specified, the switch device defaults to including a freewheeling diode, which will be pointed out in this embodiment in special cases.

[0019] The embodiment of the present application solves the technical problem of high cost of the existing three-phase two-stage PFC rectifier by providing a three-phase single-stage AC / DC converter, adopts one-stage energy conversion to realize AC / DC conversion, replaces the mainstream AC / DC+DC / DC two-stage architecture, and achieves high efficiency and low cost.

[0020] The technical solution in the embodiment of the present application is to solve the above technical problems, and the overall idea is as follows: When dealing with the problem of high-order harmonics generated by nonlinear power electronic equipment, active harmonic suppression schemes, that is, power factor correction technology, are one of the commonly used means. The existing method is generally to convert the AC voltage of the power grid into a DC voltage through the front-stage AC / DC converter, and then convert it into the required DC voltage through the DC / DC converter. This two-stage architecture has significant advantages. It enables the front and rear stages to be independently controlled, and the waveform quality of the input and output is relatively ideal. However, this solution also has certain limitations. Since the electric energy needs to undergo two conversions during the entire processing process, there is still room for further optimization in terms of efficiency and power density.

[0021] The existing three-phase two-stage PFC rectifier structure is usually as shown in 1. The front stage realizes the current power factor correction function, and the rear stage realizes the isolation of the output end and the power supply while adjusting the output voltage. This structure of the three-phase two-stage PFC rectifier can better achieve the tasks of input rectification and output voltage regulation, and has the advantages of high power factor and low total harmonic distortion (THD). However, this two-stage circuit increases the use of components, thereby increasing the cost of the whole machine. In addition, the front and rear stage circuits require more voltage and current sensors, and the control circuit is complicated, which reduces the reliability of the system. Figure 2 The three-phase two-stage PFC rectifier shown is based on Figure 1A specific circuit example of the structure design shown. Figure 2 In the circuit layout, the front stage adopts three-phase six-switch PFC, and the back stage is equipped with an isolated DC / DC converter. Figure 2 It can be seen that the circuit has a large number of switching components, requiring 8 switches and 3 diodes, which greatly increases the cost of the circuit.

[0022] To solve the above problems, the embodiment of the present invention proposes a three-phase single-stage AC / DC converter, which uses a single-stage energy conversion to achieve AC / DC conversion, replacing the mainstream AC / DC+DC / DC two-stage architecture, achieving high efficiency and low cost. Figure 3 As shown, it includes three AC modules with transformers and a DC module; in, The three AC modules each include two input terminals and two output terminals, wherein the first input terminals of the three AC modules are respectively connected to the A, B, and C phases of the three-phase power grid, the second input terminals of the three AC modules are connected together, and the first output terminals of the three AC modules are respectively connected to the third port, the fourth port, and the fifth port of the DC module; the second output terminals of the three AC modules are connected together; The circuit structures of the three AC modules are the same, and all include a first inductor, an intermediate capacitor, a second inductor, a bidirectional switch and a transformer, wherein the first end of the first inductor is the first input end of the AC module, the second end of the first inductor is connected to the first connection end of the primary side of the transformer via the intermediate capacitor, the second connection end of the primary side of the transformer is connected to the second input end of the AC module through a wire, and two connection ports a and b are set on the wire; wherein the connection port a is connected to the second end of the bidirectional switch, and the first end of the bidirectional switch is connected to the common end of the first inductor and the intermediate capacitor; the connection port b is connected to the second end of the second inductor, and the first end of the second inductor is connected to the common end of the intermediate capacitor and the transformer; the first connection end of the secondary side of the transformer is the first output end of the AC module, and the second connection end of the secondary side of the transformer is the second output end of the AC module; the bidirectional switch is connected to a plurality of control ends, and is suitable for being in one of the following three modes under the control of a control signal connected to the control end: mode one, conduction from the first end of the bidirectional switch to the second end of the bidirectional switch; mode two, conduction from the second end of the bidirectional switch to the first end of the bidirectional switch; mode three, disconnection between the first end and the second end of the bidirectional switch; The DC module includes five ports, among which the first port and the second port are both common ports, connected to both ends of the load; when the three-phase single-stage AC / DC converter is working, the current direction in the DC module is from the second port to the third port, and from the third port to the first port; the second port flows to the fourth port, and the fourth port flows to the first port; the second port flows to the fifth port, and the fifth port flows to the first port.

[0023] In the specific implementation process, the bidirectional switch can be two IGBTs facing each other, or two MOSFETs facing each other, or a composite bidirectional switch (such as an IGBT in series with a diode), a mechanical combination switch, etc. The switch combination only needs to meet the three working modes of the bidirectional switch, which will not be listed here one by one.

[0024] In a specific implementation process, the third port, the fourth port, the fifth port in the DC module are connected to the first port and the second port respectively to achieve unidirectional conduction by connecting a switch or a diode.

[0025] In a specific implementation process, a filter capacitor is connected in parallel across the load, and the filter capacitor has an energy storage function.

[0026] In a specific implementation process, the three-phase single-stage AC-DC converter can be used as a three-phase three-wire single-stage AC-DC converter, such as Figure 3 As shown, another conductor can be connected to form a three-phase four-wire single-stage AC-DC converter, such as Figure 4 shown.

[0027] like Figure 5 As shown, in this embodiment, the bidirectional switches in the three AC modules use two IGBTs facing each other, and the third port, the fourth port, the fifth port in the DC module are connected to the first port and the second port respectively to achieve unidirectional conduction by connecting a diode.

[0028] Below Figure 5 The modal analysis of the three-phase single-stage AC-DC converter shown is performed: It should be noted that although there are many forms of converters, such as replacing diodes with switches, using top-to-top MOSFET tubes for bidirectional switches, and three-phase four-wire circuits, the working modes are basically the same, so the following mainly focuses on Figure 5 The three-phase single-stage AC-DC converter shown is analyzed: The circuit consists of six switch devices S1, S2, S3, S4, S5, S6, which are paired with top switch groups, three input inductors, three transformers, three intermediate capacitors, six output diodes D1~D6 and output filter C o Each pair of switch groups has the modes shown in Table 1: Table 1 Three switching modes of switch group Each switch group will have three modes in the table. Mode 1 and Mode 2 are conduction modes with different current flow directions, and Mode 3 is a completely shut-off mode. If Mode 1 and Mode 2 are used as conduction modes, and Mode 3 is used as a shut-off mode, the switch group in each working mode of the converter will have different switch combinations of switch group modes 1, 2, and 3.

[0029] The circuit can work in DCM (discontinuous conduction mode). Switching devices S1, S2, S3, S4, S5, and S6 form a switch group in pairs. Since each switch tube is connected in parallel with a diode, in order to facilitate the representation, the signals of the S1-S6 switch tubes are the same, and one power frequency cycle of the input sinusoidal AC voltage is divided into 12 parts, and one of them is selected 30°: |V c| >|V a |>|V b |, and V c <0,V a >V b >0.

[0030] Take DCM as an example: Working mode 1: Figure 6 As shown, the switch tubes S1-S6 are turned on. The current flow path of phase A is V a →L 11 →S1→S2, C1→S→S2→L 12 , C o → Load, at this time the grid provides inductance L 11 Charging energy storage, C1 to inductor L 12 Discharge, IL 12 IL 22 IL 32 Under the action of reverse voltage, the capacitance C o Supply power to the load. Similarly, the current flow path analysis of phases B and C is the same as that of phase A.

[0031] Working mode 2: Figure 7 As shown, the switch tubes S1-S6 are still turned on. The difference from mode 1 is that IL 12 IL 22 IL 32 Reverse flow, at this time S1-S6 conduction phase ends.

[0032] Working mode 3: Figure 8 As shown, the switch tubes S1-S6 are turned off. The current flow path of phase A is V a →L 11 →C1→L 12 And the transformer primary side, transformer secondary side → D1 → C o And the load, at this time the grid and inductance L11 For C1 and L 12 And transfer energy to the secondary side of the transformer, at this time IL 12 IL 22 IL 32 gradually decreases, and at this time L 12 , L 22 , L 32 Respectively withstand (1 / 3)nV o 、(1 / 3)nV o 、(2 / 3)nV o Similarly, the current flow path analysis of phases B and C is the same as that of phase A.

[0033] Working mode 4: Fig. 9 As shown, the switch tubes S1-S6 are turned off. The difference between the current flow path of phase A and mode 3 is that due to V b The absolute value is the smallest, then L 22 The current IL 22 First it decreases to zero and then reverses.

[0034] Working mode 5: Fig.10 As shown, the switches S1-S6 are turned off. The difference between the current flow path of phase A and mode 4 is that when the inductor L 22 The current IL 22 Increase in the opposite direction to L 21 When the currents on the A and C phases are the same and in the same direction, the primary current of the transformer is zero. At this time, the current on the diode D3 is zero, and D3 is forced to turn off. The energy is then transmitted to the load through the A and C phases.

[0035] Working mode 6: Fig.11 As shown, the switch tubes S1-S6 are turned off. c |>|V a |, then the inductance L 32 The current IL 32 Reverse direction first, energy transmission is still from A and C to the load.

[0036] Working mode 7: Fig.12 As shown, the switches S1-S6 are turned off. 12 The current IL 12 In the reverse direction, the energy transmission is still from phases A and C to the load.

[0037] Working mode 8: Fig.13 As shown, the switches S1-S6 are turned off. 12 The current on the inductor increases in the reverse direction to the inductor L 11 The current on the inductor L 32 The current on the inductor increases in the reverse direction to the inductor L 31When the current on the A and C phase transformers is on, there is no current on the primary side, and all the diodes in the rear stage are turned off. o Provides energy to the load.

[0038] In DCM mode, there should be 8 circuit modes in each switching cycle, and 96 different modes will appear in one grid cycle.

[0039] Next, we give a mathematical proof that the converter has the function of automatic power factor correction. The single-phase equivalent model of the three-phase single-stage AC / DC converter is as follows: Fig.14 , Fig.15 As shown: The input voltage is V in , the output voltage is n V out , the switching period is T, the switch conduction duty cycle is D, and the current and voltage reference flow of the inductor and capacitor are as follows Fig.14 , Fig.15 shown.

[0040] Taking the positive half cycle of AC as an example, since the circuit works in DCM mode, before a switching cycle starts, i L1 =-i Lm =i0, the voltage of inductor L1 is the input voltage V in , inductance L m The voltage is the capacitor voltage V Cf , when the switch is on: i L1 =i1+V in / L1 t1→i L1.Max =i1+V in / L1 D T(1) i Lm =-i1+V Cf / L m t1→i Lm.Max =-i1+V Cf / L m D T(2) When the switch is turned off, the energy of the two inductors begins to flow to the load, and the voltage of inductor L1 is (V in -V Cf -n V out ), inductance L m The voltage is -n V out ,but: i L1 =i1+Vin / L1 D T+(V in -V Cf -n V out ) / L1 t2 (3) i Lm =-i1+V Cf / L m D T+(-n V out ) / L m t2 (4) According to the volt-ampere balance of inductance and capacitance: V in T=(1-D) T (V Cf +n V out )(5) 0=-V Cf D T+n V out (1-D) T(6) According to formula (5) and (6), we can get: V in =V Cf (7) According to formulas (3), (4) and (7), the time of freewheeling current to the load and the maximum and average values ​​of freewheeling current are: t2=V in D T / (n V out )(8) i 0.Max =V in / L1 D T+V in / L m D T(9) i 0.avg =(V in / L1 D T+V in / Lm D T) (V in D T / (n V out )) 0.5 T (10) According to the law of conservation of energy, the average value of the input current is: i L1.avg =((V in / L1 D T+V in / L m D T) (V in D T / (n V out )) 0.5 T) n V out / V in =0.5 V in D^ 2 T (L1+L m ) / (L1 L m )=K V in (11) Among them, D When T is fixed, K=0.5 D^ 2 T (L1+L m ) / (L1 L m ) is a constant, so it can be seen from formula (11) that the input current waveform is a sine waveform and is in phase with the input voltage. The circuit has an automatic power factor correction function.

[0041] It should be noted that, in the specific implementation process, the three-phase single-stage AC-DC converter can be transformed into a three-phase three-wire or three-phase four-wire topology with a transformer with a center tap, such as Fig.16 , 17As shown, the three-phase single-stage AC-DC converter includes three AC modules and a DC module, wherein: The three AC modules each include two input terminals, wherein the first input terminals of the three AC modules are respectively connected to the A, B, and C phases of the three-phase power grid, and the second input terminals of the three AC modules are connected together; the DC module includes 6 diodes; The circuit structures of the three AC modules are the same, and all include a first inductor, an intermediate capacitor, a second inductor, a bidirectional switch, and a transformer with a center tap; wherein the first end of the first inductor is the first input end of the AC module, the second end of the first inductor is connected to the first connection end of the primary side of the transformer via the intermediate capacitor, the second connection end of the primary side of the transformer is connected to the second input end of the AC module through a wire, and two connection ports a and b are arranged on the wire; wherein the connection port a is connected to the second end of the bidirectional switch, and the first end of the bidirectional switch is connected to the common end of the first inductor and the intermediate capacitor; the connection port b is connected to the second end of the second inductor, and the first end of the second inductor is connected to the common end of the intermediate capacitor and the transformer; The output ends and common ends of the secondary sides of the three center-tapped transformers are respectively connected to the anodes of the six diodes in the DC module; the center taps of the secondary sides are connected together to form a common terminal P1, and the cathodes of the six diodes are connected together to form a common terminal P2. The common terminals P1 and P2 are connected to the two ends of the load.

[0042] It should be noted that Fig.16 , Fig.17 The circuit shown not only Figure 5 The circuits shown have similar characteristics and can operate in both CCM and DCM modes.

[0043] It should be noted that, in the specific implementation process, three H4 bridges are used in the DC module, such as Fig.18 and 19 As shown, an output H4 bridge-type three-phase single-stage AC-DC converter is formed.

[0044] In addition, the three-phase single-stage AC-DC converter of the embodiment of the present invention can be operated in a single-phase mode, and its circuit structure is as follows: Fig. 20 shown.

[0045] In summary, compared with the prior art, the present invention has the following beneficial effects: 1. The embodiment of the present invention realizes AC / DC conversion by adopting one-stage energy conversion, replacing the mainstream AC / DC+DC / DC two-stage architecture, thereby achieving high efficiency and low cost.

[0046] 2. Compared with the existing two-stage energy conversion converter, the embodiment of the present invention does not use bus capacitors and is not affected by the service life of the bus, thereby increasing the service life of the converter.

[0047] 3. The switch devices of the three-phase single-stage AC / DC converter of the embodiment of the present invention are mainly located at the primary side of the transformer, which can make the design of the converter peripheral circuits, such as the drive circuit and the protection circuit, more centralized.

[0048] 4. The three-phase single-stage AC-DC converter of the embodiment of the present invention can be used in both a three-phase three-wire circuit and a three-phase four-wire circuit, and has a wide range of application scenarios.

[0049] 5. The three-phase single-stage AC-DC converter of the embodiment of the present invention can realize the automatic power factor correction function, so the design of the current loop can be omitted.

[0050] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0051] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A three-phase single-stage AC / DC converter, characterized in that: Includes three AC modules with transformers and a DC module; in, The three AC modules each include two input terminals and two output terminals. The first input terminals of the three AC modules are respectively connected to the A, B, and C phases of the three-phase power grid. The second input terminals of the three AC modules are connected together. The first output terminals of the three AC modules are respectively connected to the third port, the fourth port, and the fifth port of the DC module; the fourth ports are connected together; the DC module includes five ports, among which the first port and the second port are both common ports, connected to both ends of the load; The circuit structures of the three AC modules are the same, and all include a first inductor, an intermediate capacitor, a second inductor, a bidirectional switch and a transformer; wherein the first end of the first inductor is the first input end of the AC module, the second end of the first inductor is connected to the first connection end of the primary side of the transformer via the intermediate capacitor, the second connection end of the primary side of the transformer is connected to the second input end of the AC module through a wire, and two connection ports a and b are arranged on the wire; wherein the connection port a is connected to the second end of the bidirectional switch, and the first end of the bidirectional switch is connected to the common end of the first inductor and the intermediate capacitor; the connection port b is connected to the second end of the second inductor, and the first end of the second inductor is connected to the common end of the intermediate capacitor and the transformer; the first connection end of the secondary side of the transformer is the first output end of the AC module, and the second connection end of the secondary side of the transformer is the second output end of the AC module; the bidirectional switch is connected to a plurality of control ends, and is suitable for being in one of the following three modes under the control of a control signal connected to the control end: mode one, conduction from the first end of the bidirectional switch to the second end of the bidirectional switch; mode two, conduction from the second end of the bidirectional switch to the first end of the bidirectional switch; mode three, disconnection between the first end and the second end of the bidirectional switch.

2. The three-phase single-stage AC-DC converter according to claim 1, characterized in that: The three-phase single-stage AC-DC converter is a three-phase three-wire single-stage AC-DC converter or a three-phase four-wire single-stage AC-DC converter; Wherein, when it is a three-phase four-wire single-stage AC / DC converter, the first end of the neutral line is connected to the common end of the three-phase electricity, and the second end is connected to the common end of the second input ends of the three AC modules.

3. The three-phase single-stage AC-DC converter according to claim 1, characterized in that: The bidirectional switch includes two IGBTs or two MOSFETs connected top to top.

4. The three-phase single-stage AC-DC converter according to claim 3, characterized in that: The three switching modes of the two IGBTs or two MOSFETs facing each other include: The first switch tube is turned on, and the flyback diode connected in reverse parallel to the second switch tube is turned on; The second switch tube is turned on, and the freewheeling diode connected in reverse parallel to the first switch tube is turned on; The first switch tube and the second switch tube are both turned off.

5. The three-phase single-stage AC-DC converter according to claim 1, characterized in that: When the three-phase single-stage AC / DC converter is working, the current direction in the DC module is that the second port flows to the third port, and the third port flows to the first port; the second port flows to the fourth port, and the fourth port flows to the first port; the second port flows to the fifth port, and the fifth port flows to the first port.

6. The three-phase single-stage AC-DC converter according to claim 5, characterized in that: The DC module includes six diodes, wherein the cathodes of the first diode, the second diode and the third diode are all connected to the first port of the DC module, and the anodes of the first diode, the second diode and the third diode are respectively connected to the third port, the fourth port and the fifth port of the DC module; the anodes of the fourth diode, the fifth diode and the sixth diode are all connected to the second port of the DC module, and the cathodes of the fourth diode, the fifth diode and the sixth diode are respectively connected to the third port, the fourth port and the fifth port of the DC module.

7. The three-phase single-stage AC-DC converter according to claim 1, characterized in that: The output voltage step-up and step-down control is achieved by changing the duty ratio of the bidirectional switches in the three AC modules; or the output voltage step-up and step-down control is achieved by the coil ratio of the transformers in the three AC modules.

8. The three-phase single-stage AC-DC converter according to any one of claims 1 to 7, characterized in that: The three-phase single-stage AC-DC converter also includes a filter capacitor, which is connected in parallel across the load.

9. A three-phase single-stage AC / DC converter, characterized in that: Includes three AC modules with transformers and a DC module; The three AC modules each include two input terminals, wherein the first input terminals of the three AC modules are respectively connected to the A, B, and C phases of the three-phase power grid, and the second input terminals of the three AC modules are connected together; the DC module includes 6 diodes; The circuit structures of the three AC modules are the same, and all include a first inductor, an intermediate capacitor, a second inductor, a bidirectional switch, and a transformer with a center tap; wherein the first end of the first inductor is the first input end of the AC module, the second end of the first inductor is connected to the first connection end of the primary side of the transformer via the intermediate capacitor, the second connection end of the primary side of the transformer is connected to the second input end of the AC module through a wire, and two connection ports a and b are arranged on the wire; wherein the connection port a is connected to the second end of the bidirectional switch, and the first end of the bidirectional switch is connected to the common end of the first inductor and the intermediate capacitor; the connection port b is connected to the second end of the second inductor, and the first end of the second inductor is connected to the common end of the intermediate capacitor and the transformer; The output ends and common ends of the secondary sides of the three center-tapped transformers are respectively connected to the anodes of the six diodes in the DC module; the center taps of the secondary sides are connected together to form a common terminal P1, and the cathodes of the six diodes are connected together to form a common terminal P2. The common terminals P1 and P2 are connected to the two ends of the load.

10. The three-phase single-stage AC-DC converter according to claim 9, characterized in that: The three-phase single-stage AC-DC converter is a three-phase three-wire single-stage AC-DC converter or a three-phase four-wire single-stage AC-DC converter; Wherein, when it is a three-phase four-wire single-stage AC / DC converter, the first end of the neutral line is connected to the common end of the three-phase electricity, and the second end is connected to the common end of the second input ends of the three AC modules.

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