AC-DC converter that realizes bidirectional current flow based on primary energy conversion

Abstract

The present invention provides an AC / DC converter that realizes bidirectional current flow based on a primary energy conversion, and relates to the technical field of converters. The AC / DC converter of the present invention is used to realize a single-phase rectification function or an inversion function; when realizing a single-phase rectification function, the first end and the second end of the AC / DC converter are respectively connected to the two ends of the AC power supply, and the third end and the fourth end of the AC / DC converter are respectively connected to the two ends of the load; when realizing an inversion function, the third end and the fourth end of the AC / DC converter are respectively connected to the two ends of the DC power supply; in an off-grid mode, the first end and the second end of the AC / DC converter are respectively connected to the two ends of the load; in a grid-connected mode, the first end and the second end of the AC / DC converter are respectively connected to the two ends of the grid. The present invention adopts a primary energy conversion to realize a forward rectification function and a reverse inversion function, uses fewer devices and sampling circuits, has a lower equipment cost, and is smaller in size.

Description

Technical Field

[0001] The present invention relates to the technical field of converters, and in particular to an AC / DC converter for realizing bidirectional current flow based on primary energy conversion. Background Art

[0002] In applications with high power demand, such as electric vehicle charging, data center and communication base station power supply, the converter must have a power factor correction (PFC) function, and is generally an isolated PFC converter. An isolated PFC converter usually consists of two stages. The front stage is an AC / DC converter, which mainly improves the power factor of the circuit, reduces the harmonic content of the converter input current, and thus reduces the converter's interference with the power grid; the rear stage is a DC / DC converter. In order to achieve safe and reliable power supply, the circuit contains a high-frequency transformer. The main functions of the rear stage converter are generally two points: one is to achieve electrical isolation between the input voltage and the output voltage, and the other is to adjust and stabilize the output voltage according to load requirements.

[0003] However, although the two-stage circuits of the two-stage PFC converter can be independently designed and controlled, and the input and output waveforms have good quality, the two-stage PFC converter is composed of a rectifier circuit and an LLC, and the two-stage energy conversion uses a large number of devices, requires more sampling circuits, has a relatively high cost, and has a large device size. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In view of the deficiencies of the prior art, the present invention provides an AC-DC converter that realizes bidirectional current flow based on one-stage energy conversion, solving the technical problem of a large number of components used in the existing two-stage PFC converter.

[0006] (II) Technical solution

[0007] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0008] In a first aspect, the present invention provides an AC-DC converter for realizing bidirectional current flow based on primary energy conversion, comprising: an H4 full-bridge circuit, a transformer, a first inductor, an intermediate capacitor, a second inductor, and a fifth switch connected in parallel with a freewheeling diode;

[0009] The H4 full-bridge circuit includes four bridge arms, the common end of the first bridge arm and the second bridge arm is the first end of the H4 full-bridge circuit, the common end of the third bridge arm and the fourth bridge arm is the second end of the H4 full-bridge circuit, the common end of the first bridge arm and the third bridge arm is the third end of the H4 full-bridge circuit, and the common end of the second bridge arm and the fourth bridge arm is the fourth end of the H4 full-bridge circuit;

[0010] The first end of the H4 full-bridge circuit is connected to the first end of the first inductor, and the second end of the first inductor is the first end of the AC-DC converter; the second end of the H4 full-bridge circuit is the second end of the AC-DC converter;

[0011] The third end of the H4 full-bridge circuit is connected to the first end of the first coil of the transformer via the intermediate capacitor, and the fourth end of the H4 full-bridge circuit is connected to the second end of the first coil of the transformer;

[0012] The first end of the second coil of the transformer is connected to the first end of the fifth switch tube, and the second end of the fifth switch tube is the third end of the AC-DC converter; the second end of the second coil of the transformer is the fourth end of the AC-DC converter;

[0013] The second inductor is connected in parallel with the first coil of the transformer;

[0014] The AC / DC converter is used to realize a single-phase rectification function or an inversion function;

[0015] When the single-phase rectification function is realized, the first end and the second end of the AC-DC converter are respectively connected to the two ends of the AC power source, and the third end and the fourth end of the AC-DC converter are respectively connected to the two ends of the load; and the AC-DC converter has a power factor correction function;

[0016] When the inverter function is realized, the third end and the fourth end of the AC-DC converter are connected to the two ends of the DC power supply respectively; in the off-grid mode, the first end and the second end of the AC-DC converter are connected to the two ends of the load respectively; in the grid-connected mode, the first end and the second end of the AC-DC converter are connected to the two ends of the grid respectively.

[0017] Preferably, each bridge arm of the H4 full-bridge circuit includes a switch tube, and each switch tube is connected in parallel with a freewheeling diode.

[0018] Preferably, when implementing the inversion function in off-grid mode, the AC / DC converter includes four operating modes;

[0019] Among them, when the output voltage is in the positive direction of the sine wave, there are two modes, namely:

[0020] Mode 1: When the fifth switch tube, the switch tube in the first bridge arm of the H4 full-bridge circuit, and the switch tube in the fourth bridge arm are all turned on, the input current passes through the fifth switch tube and the primary side of the transformer, and there will be current on the secondary side. On the one hand, the current directly charges the second inductor, and on the other hand, it passes through the intermediate capacitor, the first bridge arm, the first inductor, the load, the fourth bridge arm and returns to the transformer;

[0021] Mode 2: When the fifth switch tube and the switch tube in the fourth bridge arm are both disconnected, the circuit enters the freewheeling state, and the current of the second inductor flows through the freewheeling diode in the fourth bridge arm, the freewheeling diode in the third bridge arm, and the intermediate capacitor, and the current of the first inductor flows through the load, the freewheeling diode in the third bridge arm, and the switch tube in the first bridge arm;

[0022] When the output voltage is in the negative direction of the sine wave, there are two modes:

[0023] Mode 3: When the fifth switch tube, the switch tube in the second bridge arm, and the switch tube in the third bridge arm are all turned on, the input current passes through the fifth switch tube and the primary side of the transformer, and there is current on the secondary side. On the one hand, the current directly charges the second inductor, and on the other hand, it passes through the intermediate capacitor, the switch tube in the third bridge arm, the first inductor, the load, the switch tube in the second bridge arm and returns to the transformer;

[0024] Mode 4: When the fifth switch tube and the switch tube in the third bridge arm are disconnected, the circuit enters the freewheeling state, and the current of the second inductor flows through the freewheeling diode in the fourth bridge arm, the freewheeling diode in the third bridge arm, and the intermediate capacitor; the current of the first inductor flows through the switch tube in the second bridge arm, the freewheeling diode in the fourth bridge arm, and the load;

[0025] When the inverter function is realized, the first coil of the transformer is the secondary side, and the second coil of the transformer is the primary side.

[0026] Preferably, when realizing the single-phase rectification function, the AC-DC converter includes four working modes;

[0027] Among them, when the input voltage is in the positive direction of the sine wave, there are two modes, namely:

[0028] Mode 1: When the switch tube in the third bridge arm and the switch tube in the fourth bridge arm are turned on at the same time and the freewheeling diode on the fifth switch tube is turned off, the input current charges the first inductor through the first inductor, the freewheeling diode in the first bridge arm, and the switch tube in the third bridge arm, and the intermediate capacitor charges the second inductor through the switch tube in the third bridge arm and the switch tube in the fourth bridge arm;

[0029] Mode 2: When the switch tubes in the third bridge arm and the switch tubes in the fourth bridge arm are turned off at the same time and the freewheeling diodes on the fifth switch tube are turned on, the first inductor and the second inductor enter the freewheeling mode, and the current of the first inductor is freewheeling through the freewheeling diode in the first bridge arm, the intermediate capacitor, the primary side of the transformer, and the freewheeling diode in the fourth bridge arm, and the current of the second inductor is freewheeling through the primary side of the transformer, and the current of the secondary side of the transformer flows to the load through the freewheeling diode on the fifth switch tube;

[0030] When the input voltage is in the negative direction of the sine wave, there are two modes:

[0031] Mode three: when the switch tube in the third bridge arm and the switch tube in the fourth bridge arm are turned on at the same time and the flyback diode on the fifth switch tube is turned off, the input current charges the first inductor through the switch tube in the fourth bridge arm and the flyback diode in the second bridge arm, and the intermediate capacitor charges the second inductor through the switch tube in the third bridge arm and the switch tube in the fourth bridge arm;

[0032] Mode 4: When the switch tubes in the third bridge arm and the switch tubes in the fourth bridge arm are turned off at the same time and the freewheeling diode on the fifth switch tube is turned on, the inductor enters the freewheeling mode, and the current of the first inductor flows through the freewheeling diode in the third bridge arm, the intermediate capacitor, the primary side of the transformer, and the freewheeling diode in the second bridge arm. The current of the second inductor flows through the primary side of the transformer, and the current of the secondary side of the transformer flows to the load through the freewheeling diode on the fifth switch tube.

[0033] When the single-phase rectification function is realized, the first coil of the transformer is the primary side, and the second coil of the transformer is the secondary side.

[0034] Preferably, when the AC / DC converter realizes a single-phase rectification function, a filter capacitor is connected in parallel at both ends of the load.

[0035] Preferably, the AC / DC converter realizes an inversion function, and a filter capacitor is connected in parallel at both ends of the load.

[0036] In a second aspect, the present invention provides an AC-DC converter for realizing bidirectional current flow based on primary energy conversion, comprising: an H4 full-bridge circuit, a transformer, a first inductor, an intermediate capacitor, a second inductor, and a fifth switch connected in parallel with a freewheeling diode;

[0037] The H4 full-bridge circuit includes four bridge arms, the common end of the first bridge arm and the second bridge arm is the first end of the H4 full-bridge circuit, the common end of the third bridge arm and the fourth bridge arm is the second end of the H4 full-bridge circuit, the common end of the first bridge arm and the third bridge arm is the third end of the H4 full-bridge circuit, and the common end of the second bridge arm and the fourth bridge arm is the fourth end of the H4 full-bridge circuit;

[0038] The first end of the H4 full-bridge circuit is connected to the first end of the first inductor, and the second end of the first inductor is the first end of the AC-DC converter; the second end of the H4 full-bridge circuit is the second end of the AC-DC converter;

[0039] The third end of the H4 full-bridge circuit is connected to the first end of the first coil of the transformer via the intermediate capacitor, and the fourth end of the H4 full-bridge circuit is connected to the second end of the first coil of the transformer;

[0040] The first end of the second coil of the transformer is connected to the first end of the fifth switch tube, and the second end of the fifth switch tube is the third end of the AC-DC converter; the second end of the second coil of the transformer is the fourth end of the AC-DC converter;

[0041] The second inductor is connected in parallel with the second coil of the transformer;

[0042] The AC / DC converter is used to realize a single-phase rectification function or an inversion function;

[0043] When the single-phase rectification function is realized, the first end and the second end of the AC-DC converter are respectively connected to the two ends of the AC power supply, and the third end and the fourth end of the AC-DC converter are respectively connected to the two ends of the load; and the AC-DC converter has a power factor correction function;

[0044] When the inverter function is realized, the third end and the fourth end of the AC-DC converter are connected to the two ends of the DC power supply respectively; in the off-grid mode, the first end and the second end of the AC-DC converter are connected to the two ends of the load respectively; in the grid-connected mode, the first end and the second end of the AC-DC converter are connected to the two ends of the grid respectively.

[0045] In a third aspect, the present invention provides a three-phase AC-DC converter for realizing bidirectional current flow based on primary energy conversion, comprising three single-phase modules, each of which comprises an H4 full-bridge circuit, a transformer, a first inductor, an intermediate capacitor, a second inductor, and a fifth switch connected in parallel with a freewheeling diode;

[0046] The H4 full-bridge circuit includes four bridge arms, the common end of the first bridge arm and the second bridge arm is the first end of the H4 full-bridge circuit, the common end of the third bridge arm and the fourth bridge arm is the second end of the H4 full-bridge circuit, the common end of the first bridge arm and the third bridge arm is the third end of the H4 full-bridge circuit, and the common end of the second bridge arm and the fourth bridge arm is the fourth end of the H4 full-bridge circuit;

[0047] The third end of the H4 full-bridge circuit in each single-phase module is connected to the first end of the first coil of the transformer via the intermediate capacitor, and the fourth end of the H4 full-bridge circuit is connected to the second end of the first coil of the transformer;

[0048] The first end of the second coil of the transformer in each single-phase module is connected to the first end of the fifth switch tube; the second inductor in each single-phase module is connected in parallel with the first coil of the transformer, or the second inductor is connected in parallel with the second coil of the transformer;

[0049] The second ends of the H4 full-bridge circuits in the three single-phase modules are connected to each other; the first ends of the H4 full-bridge circuits in the three single-phase modules are connected to each other via one phase of the three-phase power grid, or are connected to each other via a load;

[0050] The second ends of the fifth switch tubes in the three single-phase modules are connected to each other, and the common end thereof is the third end of the AC-DC converter; the second ends of the second coils of the transformers in the three single-phase modules are connected to each other, and are the fourth end of the AC-DC converter;

[0051] The AC / DC converter is used to realize a three-phase rectification function or an inversion function;

[0052] When the three-phase rectification function is realized, the first ends of the H4 full-bridge circuits in the three single-phase modules are connected to each other via one phase of the three-phase power grid, and the third and fourth ends of the AC / DC converter are connected to the two ends of the load respectively; and the AC / DC converter has a power factor correction function;

[0053] When the inverter function is realized, the third end and the fourth end of the AC / DC converter are respectively connected to the two ends of the DC power supply; in the off-grid mode, the first ends of the H4 full-bridge circuits in the three single-phase modules are respectively connected to each other via a load; in the grid-connected mode, the first ends of the H4 full-bridge circuits in the three single-phase modules are respectively connected to each other via one phase of the three-phase power grid.

[0054] Preferably, there is no coupling between the three single-phase modules, and each single-phase module is controlled individually.

[0055] Preferably, each bridge arm of the H4 full-bridge circuit includes a switch tube, and each switch tube is connected in parallel with a freewheeling diode.

[0056] (III) Beneficial effects

[0057] The present invention provides an AC / DC converter that realizes bidirectional current flow based on primary energy conversion. Compared with the prior art, it has the following beneficial effects:

[0058] The AC / DC converter of the present invention is used to realize a single-phase rectification function or an inversion function; when realizing the single-phase rectification function, the first end and the second end of the AC / DC converter are respectively connected to the two ends of the AC power supply, and the third end and the fourth end of the AC / DC converter are respectively connected to the two ends of the load; when realizing the inversion function, the third end and the fourth end of the AC / DC converter are respectively connected to the two ends of the DC power supply; in the off-grid mode, the first end and the second end of the AC / DC converter are respectively connected to the two ends of the load; in the grid-connected mode, the first end and the second end of the AC / DC converter are respectively connected to the two ends of the grid. The present invention adopts a one-stage energy conversion to realize the forward rectification function and the reverse phase inversion function, uses fewer devices and sampling circuits, has lower equipment cost and smaller volume. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] 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.

[0060] Figure 1 It is a framework diagram of an existing two-stage PFC converter;

[0061] Figure 2 The present invention is a circuit diagram of an existing two-stage PFC converter capable of bidirectional operation;

[0062] Figure 3 This is a framework diagram of an AC-DC converter for realizing bidirectional current flow based on primary energy conversion proposed in Example 1;

[0063] Figure 4 A circuit diagram of an AC-DC converter for realizing bidirectional current flow based on primary energy conversion in Example 1;

[0064] Figure 5 A circuit diagram of an AC-DC converter in which the second inductor L2 can also be connected in parallel to both ends of the second coil of the transformer;

[0065] Figure 6 for Figure 4 The circuit diagram of the AC / DC converter shown in FIG. 1 when the converter realizes the inverter function and is in off-grid mode;

[0066] Figure 7 for Figure 4 The circuit diagram of the AC / DC converter shown in FIG. 1 when the converter realizes the inverter function and is in the grid-connected mode;

[0067] Figure 8 for Figure 6 The AC / DC converter shown is in inverter mode 1 when the output voltage is in the positive direction of the sine wave;

[0068] Fig. 9 for Figure 6 The AC / DC converter shown is in inverter mode 2 when the output voltage is in the positive direction of the sine wave;

[0069] Fig.10 for Figure 6 The AC / DC converter shown is in inverter mode mode 3 when the output voltage is in the negative direction of the sine wave;

[0070] Fig.11 for Figure 6 The AC / DC converter shown is in inverter mode mode 4 when the output voltage is in the negative direction of the sine wave;

[0071] Fig.12 for Figure 4 The circuit diagram of the AC / DC converter shown in FIG. 1 is used to realize the rectification function;

[0072] Fig.13 for Fig.12 The AC-DC converter shown is in rectification mode one when the input voltage is in the positive direction of the sine wave;

[0073] Fig.14 for Fig.12 The AC-DC converter shown is in rectification mode mode 2 when the input voltage is in the positive direction of the sine wave;

[0074] Fig.15 for Fig.12 The AC-DC converter shown is in rectification mode mode 3 when the input voltage is in the negative direction of the sine wave;

[0075] Fig.16 for Fig.12 The AC-DC converter shown is in rectification mode mode 4 when the input voltage is in the negative direction of the sine wave;

[0076] Fig.17 Output and input waveforms of the AC / DC converter in the rectification mode in the simulation experiment;

[0077] Fig.18 Output and input waveforms of the AC / DC converter in the inverter mode in the simulation experiment;

[0078] Fig.19 A circuit diagram of a three-phase AC / DC converter in Example 2 that realizes a three-phase rectification function based on a primary energy conversion to realize a bidirectional current flow;

[0079] Fig. 20 A circuit diagram of a three-phase AC / DC converter in Example 2 that realizes bidirectional current flow based on primary energy conversion when realizing an inversion function in a grid-connected mode;

[0080] Fig.21 A circuit diagram of the three-phase AC / DC converter in Example 2 in an off-grid mode when realizing an inverter function based on primary energy conversion to realize bidirectional current flow;

[0081] Fig. 22 The output and input waveforms of the AC / DC converter in Embodiment 2 of the simulation experiment under the rectification mode;

[0082] Fig.23 The waveforms related to the output and input of the AC / DC converter in Example 2 of the simulation experiment under the inverter mode are shown. DETAILED DESCRIPTION

[0083] 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.

[0084] 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.

[0085] The embodiment of the present application solves the technical problem of a large number of components used in an existing two-stage PFC converter by providing an AC-DC converter that realizes bidirectional current flow based on a one-stage energy conversion, thereby realizing forward power factor correction, chopping function, and reverse inversion function through a one-stage energy conversion, using fewer components, fewer sampling circuits, lower equipment cost, and smaller size.

[0086] The technical solution in the embodiment of the present application is to solve the above technical problems, and the overall idea is as follows:

[0087] like Figure 1 As shown in the figure, the existing two-stage PFC converter mainly uses a front-stage PFC circuit plus a rear-stage LLC converter (DC / DC converter). The front stage is generally a three-phase bridge uncontrolled rectifier circuit, the input is AC voltage, and the rectifier circuit is composed of 6 diodes. The output is connected to the BOOST converter to achieve AC / DC conversion and power factor correction. The rear-stage LLC converter realizes DC / DC conversion and controls the output voltage within the required voltage range. If bidirectional operation is required, the diodes need to be replaced with fully controlled devices, such as Figure 2 shown.

[0088] However, the two-stage energy conversion used by the existing two-stage PFC converter consists of a rectifier circuit and an LLC. The two-stage energy conversion uses a large number of devices, requires more sampling circuits, is relatively costly, and has a large device size. At the same time, the two-stage energy conversion needs to be implemented by AC-DC-DC or DC-DC-AC, and has low working efficiency.

[0089] In order to solve the above problems, an embodiment of the present invention proposes an AC-DC converter that realizes bidirectional current flow based on a primary energy conversion. The AC-DC converter uses a primary energy conversion to realize forward power factor correction, chopping function, and reverse phase inversion function, uses fewer devices, fewer sampling circuits, and has lower equipment cost and smaller volume. At the same time, the AC-DC converter is modularly composed of three single-phase AC-DC converters in which current can flow bidirectionally. There is no coupling between the three phases, and control is easier to achieve.

[0090] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0091] Embodiment 1:

[0092] The embodiment of the present invention proposes an AC-DC converter that realizes bidirectional current flow based on primary energy conversion, such as Figure 3 As shown, it includes: H4 full-bridge circuit, transformer, first inductor, middle capacitor, second inductor and fifth switch tube;

[0093] The H4 full-bridge circuit includes four bridge arms, the common end of the first bridge arm and the second bridge arm is the first end of the H4 full-bridge circuit, the common end of the third bridge arm and the fourth bridge arm is the second end of the H4 full-bridge circuit, the common end of the first bridge arm and the third bridge arm is the third end of the H4 full-bridge circuit, and the common end of the second bridge arm and the fourth bridge arm is the fourth end of the H4 full-bridge circuit;

[0094] The first end of the H4 full-bridge circuit is connected to the first end of the first inductor, and the second end of the first inductor is the first end of the AC-DC converter; the second end of the H4 full-bridge circuit is the second end of the AC-DC converter;

[0095] The third end of the H4 full-bridge circuit is connected to the first end of the first coil of the transformer via the intermediate capacitor, and the fourth end of the H4 full-bridge circuit is connected to the second end of the first coil of the transformer;

[0096] The first end of the second coil of the transformer is connected to the first end of the fifth switch tube, and the second end of the fifth switch tube is the third end of the AC-DC converter; the second end of the second coil of the transformer is the fourth end of the AC-DC converter;

[0097] The second inductor is connected in parallel with the first coil of the transformer, or the second inductor is connected in parallel with the second coil of the transformer;

[0098] The AC / DC converter is used to realize a single-phase rectification function or an inversion function;

[0099] When the single-phase rectification function is realized, the first end and the second end of the AC-DC converter are respectively connected to the two ends of the AC power supply, and the third end and the fourth end of the AC-DC converter are respectively connected to the two ends of the load; and the AC-DC converter has a power factor correction function;

[0100] When the inverter function is realized, the third end and the fourth end of the AC-DC converter are connected to the two ends of the DC power supply respectively; in the off-grid mode, the first end and the second end of the AC-DC converter are connected to the two ends of the load respectively; in the grid-connected mode, the first end and the second end of the AC-DC converter are connected to the two ends of the grid respectively.

[0101] The specific circuit, control strategy and working mode of the AC / DC converter are described in detail below:

[0102] like Figure 4 As shown, the H4 full-bridge circuit includes four switch tubes T 1 ~T 4 (It should be noted that, in the specific implementation process, the bridge arm of the H4 full-bridge circuit can use other switch tubes), the intermediate capacitor C f The third switch tube and the second inductor L connected in the H4 full bridge circuit 2 The first end and the middle capacitor C f Separate the first inductor L 1 and the second inductor L 2 The middle point between the two inductors is used to adjust the first inductor L 1 and the second inductor L 2 The effect of the intermediate potential. When the second inductor L 2 When connected in parallel at both ends of the second coil of the transformer, the specific circuit is as follows Figure 5 shown.

[0103] The following describes the control strategy and working mode of the AC / DC converter when it realizes the inverter function:

[0104] When implementing the inverter function, taking the off-grid model as an example, the first and second terminals of the AC / DC converter are connected to the two terminals of the load respectively, and the third and fourth terminals of the AC / DC converter are connected to the two terminals of the DC power supply respectively. Figure 4 Taking the AC-DC converter shown in the figure as an example, the specific circuit of the AC-DC converter when realizing the inverter function is as follows Figure 6 , Figure 7 As shown, Figure 6 In off-grid mode, a capacitor C is connected in parallel across the load. 0 To achieve voltage stabilization and filtering (in the specific implementation process, filter capacitors are selectively connected in parallel according to the filtering needs, that is, there may be no filter capacitor C at both ends of the load 0 ), Figure 7 It is grid-connected mode.

[0105] When the AC / DC converter works in the inverter mode, since the switching frequency is much greater than the frequency of the power grid, the output voltage is approximately a DC voltage in each switching cycle. In this way, in each switching cycle, the inverter circuit is equivalent to a DC / DC converter. In this way, the voltage gain in each switching cycle is known. As long as the duty cycle of the device conduction in each switching cycle is calculated, the inverter function in each switching cycle can be realized.

[0106] Combination Figure 6 , the output voltage is in the forward direction, for example, the transformer ratio is n , input voltage V DC Indicates that the output voltage is V out The voltage of the middle capacitor is V f ,switch T 4 and switch T 5 The on-duty ratio is D ,switch T 1 The switch is always on when the output voltage is positive. T 2 It is always turned off when the output voltage is positive, and one switching cycle is T , the integration time is from time 0 to the end of a switching cycle T.

[0107] In switch T 1 、T 4 、T 5 When conducting, as in mode 1 ( Figure 8 ), the inductance L 2 and inductor L 1 Yes, the potential at point A is 0. B The point potential is V DC / n , C The point potential is V DC / nV f , the potential at point D is V out ; In the switch T 1 、D 4 、D 5 When conducting, as in mode 2 ( Fig. 9 ), the potential at point A is 0, B The point potential isV f , C The potential at point A is 0, and the potential at point D is V out .

[0108] During this switching cycle, the inductor L 2 There are (the integration interval is the time variable 0-T, and the numbers or symbols in the integration correspond to the potentials at both ends of the inductor):

[0109]

[0110] For inductance L 1 have:

[0111]

[0112] In a switching cycle, the input voltage can be approximated to be constant, so the integral sign can be removed and the inductance L 2 , according to the inductor volt-second balance in one switching cycle, we can get (the 0 in the following formulas all represent the potential):

[0113]

[0114] For inductance L 1 , according to the inductor volt-second balance in one switching cycle:

[0115]

[0116] Combining the above two equations, we can get the duty cycle corresponding to each switching cycle:

[0117]

[0118] The voltage gain corresponding to each switching cycle is:

[0119]

[0120] Finally, by comparing with the carrier, a PWM control signal is generated to drive the switch tube to work, thus realizing the inverter mode of this topology.

[0121] by Figure 6 The working mode of the AC / DC converter when realizing the inverter function is analyzed in the off-grid mode shown, and the load is represented by an RC load.

[0122] When the output voltage is in the positive direction of the sine wave, there are two modes:

[0123] Mode 1: When switch T 5 , T 1 , T 4 When it is on, the input current flows through the switch T5 , the primary side of the transformer, and at the same time there will be current on the secondary side, which directly feeds the inductor L 2 Charging, on the one hand, through the intermediate capacitor C f , switch T 1 、Inductance L 1 , load, switch T 4 And back to the transformer. The modal diagram is as follows Figure 8 shown.

[0124] Mode 2: At switch T 5 , T 4 When it is turned off, the circuit enters the freewheeling state, and the inductor L 2 The current flows through diode D 4 , diode D 3 、Intermediate capacitor C f Freewheeling. Inductor L 1 The current passes through the load and diode D 3 , switch T 1 The modal diagram is as follows: Fig. 9 shown.

[0125] When the output voltage is on the negative side of the sine wave, there are two modes:

[0126] Mode 3: When switch T 5 , T 2 , T 3 When it is on, the input current flows through the switch T 5 , the primary side of the transformer, and at the same time there will be current on the secondary side, which directly feeds the inductor L 2 Charging, on the one hand, through the intermediate capacitor C f , switch T 3 、Inductance L 1 , load, switch T 2 And back to the transformer. The modal diagram is as follows Fig.10 shown.

[0127] Mode 4: On switch T 5 , T 3 When it is turned off, the circuit enters the freewheeling state, and the inductor L 2 The current flows through diode D 4 , diode D 3 、Intermediate capacitor C f Freewheeling. Inductor L 1 The current through the switch T 2 , diode D 4 , load continuous current. The modal diagram is as follows Fig.11 shown.

[0128] The DC converter can realize four-quadrant operation when inverting, so it can also be connected to the grid. Figure 7 shown.

[0129] The following describes the control strategy and working mode of the AC / DC converter when it realizes the single-phase rectification function:

[0130] When the single-phase rectification function is realized, the first and second ends of the AC / DC converter are connected to the two ends of the AC power source respectively, and the third and fourth ends of the AC / DC converter are connected to the two ends of the load respectively. Figure 4 Taking the AC / DC converter shown in the figure as an example, the specific circuit of the AC / DC converter when realizing the rectification function is as follows Fig.12 shown.

[0131] Fig.12 The AC-DC converter shown is in rectification mode, and the switch T 3 , switch T 4 Simultaneously turns on and off and is connected to the diode D 5 Complementary.

[0132] When the input voltage is in the positive direction of the sine wave, there are two modes:

[0133] Mode 1: At switch T 3 , switch T 4 At the same time, the diode D 5 When the input current is turned off, it flows through the inductor L 1 , diode D 1 , switch T 3 Give inductor L 1 Charging, capacitor C f Through switch T 3 , switch T 4 Give inductor L 2 Charging. The modal diagram is as follows Fig.13 shown.

[0134] Mode 2: At switch T 3 , switch T 4 At the same time, the diode D 5 The inductor enters the freewheeling mode, and the inductor L 1 The current flows through diode D 1 , capacitor C f , transformer primary side (called secondary side when inverting), diode D 4 Freewheeling, inductor L 2 The current of the transformer flows through the primary side of the transformer, and the current of the secondary side of the transformer flows through the diode D 5 Flow to load. The modal diagram is as follows Fig.14 shown.

[0135] When the input voltage is on the negative side of the sine wave, there are two modes:

[0136] Mode 3: At switch T 3 , switch T4 At the same time, the diode D 5 When turned off, the input current flows through switch T 4 , diode D 2 Give inductor L 1 Charging, capacitor C f Through switch T 3 , switch T 4 Give inductor L 2 Charging. The modal diagram is as follows Fig.15 shown.

[0137] Mode 4: On switch T 3 , switch T 4 At the same time, the diode D 5 The inductor enters the freewheeling mode, and the inductor L 1 The current flows through diode D 3 , capacitor C f , transformer primary side (called secondary side when inverting), diode D 2 Freewheeling, inductor L 2 The current of the transformer flows through the primary side of the transformer, and the current of the secondary side of the transformer flows through the diode D 5 Flow to load. The modal diagram is as follows Fig.16 shown.

[0138] Simulation experiment:

[0139] The AC / DC converter based on the first-stage energy conversion realizes the bidirectional flow of current. The same parameters are used for rectification and inversion. SIMULINK simulation verification is carried out. During rectification, the AC voltage is 220V effective value, the output is 345V and the power factor is corrected; during inversion, the DC voltage is 345V and the output is AC 220V effective value. The output and input related waveforms in the rectification mode are as follows Fig.17 As shown, the output and input related waveforms in the inverter mode are as follows Fig.18 shown.

[0140] Embodiment 2:

[0141] The embodiment of the present invention provides a three-phase AC-DC converter for realizing bidirectional current flow based on primary energy conversion, the AC-DC converter includes three single-phase modules; each single-phase module includes an H4 full-bridge circuit, a transformer, a first inductor, an intermediate capacitor, a second inductor and a fifth switch tube;

[0142] The H4 full-bridge circuit includes four bridge arms, the common end of the first bridge arm and the second bridge arm is the first end of the H4 full-bridge circuit, the common end of the third bridge arm and the fourth bridge arm is the second end of the H4 full-bridge circuit, the common end of the first bridge arm and the third bridge arm is the third end of the H4 full-bridge circuit, and the common end of the second bridge arm and the fourth bridge arm is the fourth end of the H4 full-bridge circuit;

[0143] The third end of the H4 full-bridge circuit in each single-phase module is connected to the first end of the first coil of the transformer via the intermediate capacitor, and the fourth end of the H4 full-bridge circuit is connected to the second end of the first coil of the transformer;

[0144] The first end of the second coil of the transformer in each single-phase module is connected to the first end of the fifth switch tube; the second inductor in each single-phase module is connected in parallel with the first coil of the transformer, or the second inductor is connected in parallel with the second coil of the transformer;

[0145] The second ends of the H4 full-bridge circuits in the three single-phase modules are connected to each other; the first ends of the H4 full-bridge circuits in the three single-phase modules are connected to each other via one phase of the three-phase power grid, or are connected to each other via a load;

[0146] The second ends of the fifth switch tubes in the three single-phase modules are connected to each other, and the common end thereof is the third end of the AC-DC converter; the second ends of the second coils of the transformers in the three single-phase modules are connected to each other, and are the fourth end of the AC-DC converter;

[0147] The AC / DC converter is used to realize a three-phase rectification function or an inversion function;

[0148] When the three-phase rectification function is realized, the first ends of the H4 full-bridge circuits in the three single-phase modules are connected to each other through one phase of the three-phase power grid, and the third and fourth ends of the AC / DC converter are connected to the two ends of the load respectively; when the single-phase rectification function is realized, it has a power factor correction function;

[0149] When the inverter function is realized, the third end and the fourth end of the AC / DC converter are respectively connected to the two ends of the DC power supply; in the off-grid mode, the first ends of the H4 full-bridge circuits in the three single-phase modules are respectively connected to each other via a load; in the grid-connected mode, the first ends of the H4 full-bridge circuits in the three single-phase modules are respectively connected to each other via one phase of the three-phase power grid.

[0150] Since the three-phase circuit is not coupled, the second ends of the H4 full-bridge circuits in the three single-phase modules are directly connected, but not connected to the grid or the load. The potential of the common end of the second end of the H4 full-bridge circuit in the three single-phase modules is the same as the common end of the first end of the H4 full-bridge circuit.

[0151] The potentials of the two sides (that is, the side of the power grid away from the first inductor or the side of the load away from the first inductor) are equal.

[0152] The three-phase AC-DC converter for realizing bidirectional current flow based on primary energy conversion proposed in this embodiment is modularly composed of three single-phase AC-DC converters with bidirectional current flow. There is no coupling between the three phases, and each phase is controlled separately.

[0153] When the three-phase rectification function is realized, the circuit connection mode of the three-phase AC-DC converter for realizing the bidirectional flow of current based on the primary energy conversion is as follows: Fig.19 shown.

[0154] When the inverter function is realized, in the grid-connected mode, the circuit connection method of the AC / DC converter in this embodiment is as follows Fig. 20 shown.

[0155] When the inverter function is realized, in the off-grid mode, the circuit connection method of the AC / DC converter in this embodiment is as follows Fig.21 In the specific implementation process, the filter capacitors connected in parallel at both ends of the load can be placed according to the requirements, that is, there may be no filter capacitors at both ends of the load.

[0156] When the inverter function is realized, the three-phase AC-DC converter realizes the bidirectional flow of current based on the primary energy conversion.

[0157] The working principle of the three-phase AC-DC converter that realizes bidirectional current flow based on one-stage energy conversion is the same as that of the single-phase AC-DC converter that realizes bidirectional current flow based on one-stage energy conversion in Example 1, which will not be repeated here.

[0158] Simulation experiment:

[0159] The same parameters are used for rectification and inversion, and SIMULINK simulation verification is performed. The output waveforms in the inversion mode are as follows: Fig. 22 As shown, the output waveform in rectification mode is as follows Fig.23 shown.

[0160] In summary, compared with the prior art, the present invention has the following beneficial effects:

[0161] 1. The use of one-stage energy conversion can realize forward power factor correction, chopping function, and reverse inversion function, using fewer devices and sampling circuits, lower equipment cost and smaller size.

[0162] 2. The circuit adopts one-stage energy conversion, which improves working efficiency.

[0163] 3. It can operate in four quadrants in inverter mode, and can work both off-grid and on-grid.

[0164] 4. The proposed three-phase AC-DC converter with bidirectional current flow is modularly composed of three single-phase AC-DC converters with bidirectional current flow. There is no coupling between the three phases, and control is easier to achieve.

[0165] 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.

[0166] 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. An AC-DC converter for realizing bidirectional current flow based on primary energy conversion, characterized in that: include: H4 full-bridge circuit, transformer, first inductor, intermediate capacitor, second inductor and fifth switch connected in parallel with a freewheeling diode; The H4 full-bridge circuit includes four bridge arms, the common end of the first bridge arm and the second bridge arm is the first end of the H4 full-bridge circuit, the common end of the third bridge arm and the fourth bridge arm is the second end of the H4 full-bridge circuit, the common end of the first bridge arm and the third bridge arm is the third end of the H4 full-bridge circuit, and the common end of the second bridge arm and the fourth bridge arm is the fourth end of the H4 full-bridge circuit; The first end of the H4 full-bridge circuit is connected to the first end of the first inductor, and the second end of the first inductor is the first end of the AC-DC converter; the second end of the H4 full-bridge circuit is the second end of the AC-DC converter; The third end of the H4 full-bridge circuit is connected to the first end of the first coil of the transformer via the intermediate capacitor, and the fourth end of the H4 full-bridge circuit is connected to the second end of the first coil of the transformer; The first end of the second coil of the transformer is connected to the first end of the fifth switch tube, and the second end of the fifth switch tube is the third end of the AC-DC converter; the second end of the second coil of the transformer is the fourth end of the AC-DC converter; The second inductor is connected in parallel with the first coil of the transformer; The AC / DC converter is used to realize a single-phase rectification function or an inversion function; When the single-phase rectification function is realized, the first end and the second end of the AC-DC converter are respectively connected to the two ends of the AC power source, and the third end and the fourth end of the AC-DC converter are respectively connected to the two ends of the load; and the AC-DC converter has a power factor correction function; When the inverter function is realized, the third end and the fourth end of the AC-DC converter are connected to the two ends of the DC power supply respectively; in the off-grid mode, the first end and the second end of the AC-DC converter are connected to the two ends of the load respectively; in the grid-connected mode, the first end and the second end of the AC-DC converter are connected to the two ends of the grid respectively.

2. The AC-DC converter for realizing bidirectional current flow based on primary energy conversion according to claim 1, characterized in that: Each bridge arm of the H4 full-bridge circuit includes a switch tube, and each switch tube is connected in parallel with a freewheeling diode.

3. The AC-DC converter for realizing bidirectional current flow based on primary energy conversion according to claim 2, characterized in that: When the inverter function is realized in off-grid mode, the AC / DC converter includes four working modes; Among them, when the output voltage is in the positive direction of the sine wave, there are two modes, namely: Mode 1: When the fifth switch tube, the switch tube in the first bridge arm of the H4 full-bridge circuit, and the switch tube in the fourth bridge arm are all turned on, the input current passes through the fifth switch tube and the primary side of the transformer, and there will be current on the secondary side. On the one hand, the current directly charges the second inductor, and on the other hand, it passes through the intermediate capacitor, the first bridge arm, the first inductor, the load, the fourth bridge arm and returns to the transformer; Mode 2: When the fifth switch tube and the switch tube in the fourth bridge arm are both disconnected, the circuit enters the freewheeling state, and the current of the second inductor flows through the freewheeling diode in the fourth bridge arm, the freewheeling diode in the third bridge arm, and the intermediate capacitor, and the current of the first inductor flows through the load, the freewheeling diode in the third bridge arm, and the switch tube in the first bridge arm; When the output voltage is in the negative direction of the sine wave, there are two modes: Mode 3: When the fifth switch tube, the switch tube in the second bridge arm, and the switch tube in the third bridge arm are all turned on, the input current passes through the fifth switch tube and the primary side of the transformer, and there is current on the secondary side. On the one hand, the current directly charges the second inductor, and on the other hand, it passes through the intermediate capacitor, the switch tube in the third bridge arm, the first inductor, the load, the switch tube in the second bridge arm and returns to the transformer; Mode 4: When the fifth switch tube and the switch tube in the third bridge arm are disconnected, the circuit enters the freewheeling state, and the current of the second inductor flows through the freewheeling diode in the fourth bridge arm, the freewheeling diode in the third bridge arm, and the intermediate capacitor; the current of the first inductor flows through the switch tube in the second bridge arm, the freewheeling diode in the fourth bridge arm, and the load; When the inverter function is realized, the first coil of the transformer is the secondary side, and the second coil of the transformer is the primary side.

4. The AC-DC converter for realizing bidirectional current flow based on primary energy conversion according to claim 2, characterized in that: When realizing the single-phase rectification function, the AC-DC converter includes four working modes; Among them, when the input voltage is in the positive direction of the sine wave, there are two modes, namely: Mode 1: When the switch tube in the third bridge arm and the switch tube in the fourth bridge arm are turned on at the same time and the freewheeling diode on the fifth switch tube is turned off, the input current charges the first inductor through the first inductor, the freewheeling diode in the first bridge arm, and the switch tube in the third bridge arm, and the intermediate capacitor charges the second inductor through the switch tube in the third bridge arm and the switch tube in the fourth bridge arm; Mode 2: When the switch tubes in the third bridge arm and the switch tubes in the fourth bridge arm are turned off at the same time and the freewheeling diodes on the fifth switch tube are turned on, the first inductor and the second inductor enter the freewheeling mode, and the current of the first inductor is freewheeling through the freewheeling diode in the first bridge arm, the intermediate capacitor, the primary side of the transformer, and the freewheeling diode in the fourth bridge arm, and the current of the second inductor is freewheeling through the primary side of the transformer, and the current of the secondary side of the transformer flows to the load through the freewheeling diode on the fifth switch tube; When the input voltage is in the negative direction of the sine wave, there are two modes: Mode three: when the switch tube in the third bridge arm and the switch tube in the fourth bridge arm are turned on at the same time and the flyback diode on the fifth switch tube is turned off, the input current charges the first inductor through the switch tube in the fourth bridge arm and the flyback diode in the second bridge arm, and the intermediate capacitor charges the second inductor through the switch tube in the third bridge arm and the switch tube in the fourth bridge arm; Mode 4: When the switch tubes in the third bridge arm and the switch tubes in the fourth bridge arm are turned off at the same time and the freewheeling diode on the fifth switch tube is turned on, the inductor enters the freewheeling mode, and the current of the first inductor flows through the freewheeling diode in the third bridge arm, the intermediate capacitor, the primary side of the transformer, and the freewheeling diode in the second bridge arm. The current of the second inductor flows through the primary side of the transformer, and the current of the secondary side of the transformer flows to the load through the freewheeling diode on the fifth switch tube. When the single-phase rectification function is realized, the first coil of the transformer is the primary side, and the second coil of the transformer is the secondary side.

5. The AC-DC converter for realizing bidirectional current flow based on primary energy conversion according to any one of claims 1 to 4, characterized in that: When the AC / DC converter realizes the single-phase rectification function, the two ends of the load are connected in parallel with a filter capacitor.

6. The AC-DC converter for realizing bidirectional current flow based on primary energy conversion according to any one of claims 1 to 4, characterized in that: The AC / DC converter realizes the inversion function, and the two ends of the load are connected in parallel with the filter capacitor.

7. An AC / DC converter for realizing bidirectional current flow based on primary energy conversion, characterized in that: include: H4 full-bridge circuit, transformer, first inductor, intermediate capacitor, second inductor and fifth switch connected in parallel with a freewheeling diode; The H4 full-bridge circuit includes four bridge arms, the common end of the first bridge arm and the second bridge arm is the first end of the H4 full-bridge circuit, the common end of the third bridge arm and the fourth bridge arm is the second end of the H4 full-bridge circuit, the common end of the first bridge arm and the third bridge arm is the third end of the H4 full-bridge circuit, and the common end of the second bridge arm and the fourth bridge arm is the fourth end of the H4 full-bridge circuit; The first end of the H4 full-bridge circuit is connected to the first end of the first inductor, and the second end of the first inductor is the first end of the AC-DC converter; the second end of the H4 full-bridge circuit is the second end of the AC-DC converter; The third end of the H4 full-bridge circuit is connected to the first end of the first coil of the transformer via the intermediate capacitor, and the fourth end of the H4 full-bridge circuit is connected to the second end of the first coil of the transformer; The first end of the second coil of the transformer is connected to the first end of the fifth switch tube, and the second end of the fifth switch tube is the third end of the AC-DC converter; the second end of the second coil of the transformer is the fourth end of the AC-DC converter; The second inductor is connected in parallel with the second coil of the transformer; The AC / DC converter is used to realize a single-phase rectification function or an inversion function; When the single-phase rectification function is realized, the first end and the second end of the AC-DC converter are respectively connected to the two ends of the AC power supply, and the third end and the fourth end of the AC-DC converter are respectively connected to the two ends of the load; and the AC-DC converter has a power factor correction function; When the inverter function is realized, the third end and the fourth end of the AC-DC converter are connected to the two ends of the DC power supply respectively; in the off-grid mode, the first end and the second end of the AC-DC converter are connected to the two ends of the load respectively; in the grid-connected mode, the first end and the second end of the AC-DC converter are connected to the two ends of the grid respectively.

8. A three-phase AC-DC converter that realizes bidirectional current flow based on primary energy conversion, characterized in that: It includes three single-phase modules, each of which includes an H4 full-bridge circuit, a transformer, a first inductor, an intermediate capacitor, a second inductor, and a fifth switch connected in parallel with a freewheeling diode; The H4 full-bridge circuit includes four bridge arms, the common end of the first bridge arm and the second bridge arm is the first end of the H4 full-bridge circuit, the common end of the third bridge arm and the fourth bridge arm is the second end of the H4 full-bridge circuit, the common end of the first bridge arm and the third bridge arm is the third end of the H4 full-bridge circuit, and the common end of the second bridge arm and the fourth bridge arm is the fourth end of the H4 full-bridge circuit; The third end of the H4 full-bridge circuit in each single-phase module is connected to the first end of the first coil of the transformer via the intermediate capacitor, and the fourth end of the H4 full-bridge circuit is connected to the second end of the first coil of the transformer; The first end of the second coil of the transformer in each single-phase module is connected to the first end of the fifth switch tube; the second inductor in each single-phase module is connected in parallel with the first coil of the transformer, or the second inductor is connected in parallel with the second coil of the transformer; The second ends of the H4 full-bridge circuits in the three single-phase modules are connected to each other; the first ends of the H4 full-bridge circuits in the three single-phase modules are connected to each other via one phase of the three-phase power grid, or are connected to each other via a load; The second ends of the fifth switch tubes in the three single-phase modules are connected to each other, and the common end thereof is the third end of the AC-DC converter; the second ends of the second coils of the transformers in the three single-phase modules are connected to each other, and are the fourth end of the AC-DC converter; The AC / DC converter is used to realize a three-phase rectification function or an inversion function; When the three-phase rectification function is realized, the first ends of the H4 full-bridge circuits in the three single-phase modules are connected to each other via one phase of the three-phase power grid, and the third and fourth ends of the AC / DC converter are connected to the two ends of the load respectively; and the AC / DC converter has a power factor correction function; When the inverter function is realized, the third end and the fourth end of the AC / DC converter are respectively connected to the two ends of the DC power supply; in the off-grid mode, the first ends of the H4 full-bridge circuits in the three single-phase modules are respectively connected to each other via a load; in the grid-connected mode, the first ends of the H4 full-bridge circuits in the three single-phase modules are respectively connected to each other via one phase of the three-phase power grid.

9. The three-phase AC-DC converter for realizing bidirectional current flow based on primary energy conversion as claimed in claim 8, characterized in that: There is no coupling between the three single-phase modules, and each single-phase module is controlled independently.

10. The three-phase AC-DC converter for realizing bidirectional current flow based on primary energy conversion as claimed in claim 8, characterized in that: Each bridge arm of the H4 full-bridge circuit includes a switch tube, and each switch tube is connected in parallel with a freewheeling diode.

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