Topological structure of T-type three-phase isolation type AC / DC converter and control method thereof

Abstract

The invention discloses a topological structure of a T-shaped three-phase isolation type AC / DC converter and a control method thereof, the topological structure comprises three groups of bidirectional switches connected in parallel, and the bidirectional switches are used for controlling bidirectional flow of energy; the transformer T1 and the transformer T2 are connected with the bidirectional switch and are used for realizing energy conversion and isolation; the group of H-bridge circuits connected in parallel or in series is connected with the transformer and is used for auxiliary energy conversion; wherein the external controller controls the mode of the bidirectional switch according to a control method, and calculates the duration of different modes according to the change trend of the leakage inductance current, thereby realizing the accurate control of the energy flow and the correction of the power factor. By accurately controlling energy flow and optimizing circuit design, the conversion efficiency and the power factor of the converter are remarkably improved, and the converter has wide application prospects and remarkable economic benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics, and particularly relates to a topological structure and a control method of a T-type three-phase isolated AC-DC converter. Background Art

[0002] As the power of single electrical equipment is getting larger and larger, the original single-phase power supply method is gradually changed to three-phase power supply. Without power factor correction (PFC) function, it will cause great damage to the power quality of the power grid, and even lead to the paralysis of the power grid in severe cases. Therefore, for the AC-DC conversion circuit with three-phase AC input, it is generally a two-stage circuit of PFC + DC / DC. Since the voltage after PFC rectification is relatively high, the design of the whole circuit will be more complex; therefore, some foreign counterparts have proposed a single-stage three-phase AC-DC converter before, such as the well-known single-cycle converter. For example, the invention patent WO2008 / 018802A2 is a relatively typical high-efficiency single-stage three-phase AC converter. This circuit simplifies the circuit on the basis of the traditional three-phase AC converter, and at the same time realizes soft switching. However, due to reasons such as grid adaptability, the control algorithm is complex, and this technology has not been widely applied to products.

[0003] There is an urgent need to propose a new topological structure and a control method of a three-phase isolated AC-DC converter. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a topological structure of a T-type three-phase isolated AC-DC converter aiming at the deficiencies in the above-mentioned prior art. By optimizing the circuit design, the conversion efficiency and power factor of the converter are significantly improved.

[0005] To solve the above technical problem, the technical solution adopted by the present invention is: a topological structure of a T-type three-phase isolated AC-DC converter, including:

[0006] Three groups of parallel bidirectional switches, which are used to control the bidirectional flow of energy;

[0007] Transformer T 1 and transformer T 2 , connected to the bidirectional switch, which is used to realize energy conversion and isolation;

[0008] A group of parallel or series-connected H-bridge circuits, connected to the transformer, which is used to assist energy conversion;

[0009] Wherein, an external controller controls the mode of the bidirectional switch according to the control method, calculates the duration of different modes according to the change trend of the leakage inductance current, so as to realize the precise control of energy flow and the correction of power factor.

[0010] The topological structure of the above-mentioned T-type three-phase isolated AC-DC converter, where the three groups of parallel bidirectional switches include parallel bidirectional switch A 1 , B 1 , and C 1 , parallel bidirectional switch A 2 , B 2 , and C 2 , and parallel bidirectional switch A 3 , B 3 , and C 3 ;

[0011] One end of the bidirectional switch A 1 , one end of the bidirectional switch B 1 , and one end of the bidirectional switch C 1 are all connected to one end of the primary coil of the transformer T 1 . The other end of the bidirectional switch A 1 , the other end of the bidirectional switch B 1 , and the other end of the bidirectional switch C 1 are respectively connected to the A-phase input terminal, the B-phase input terminal, and the C-phase input terminal;

[0012] One end of the bidirectional switch A 2 , one end of the bidirectional switch B 2 , and one end of the bidirectional switch C 2 are respectively connected to the A-phase input terminal, the B-phase input terminal, and the C-phase input terminal. The other end of the bidirectional switch A 2 , the other end of the bidirectional switch B 2 , and the other end of the bidirectional switch C 2 are all connected to one end of the primary coil of the transformer T 2 ;

[0013] One end of the bidirectional switch A 3 , one end of the bidirectional switch B 3 , and one end of the bidirectional switch C 3 are respectively connected to the A-phase input terminal, the B-phase input terminal, and the C-phase input terminal. The other end of the bidirectional switch A 3 , the other end of the bidirectional switch B 3 , and the other end of the bidirectional switch C 3 are all connected to the other end of the primary coil of the transformer T 1 and the other end of the primary coil of the transformer T 2 ;

[0014] The topological structure of the above-mentioned T-type three-phase isolated AC-DC converter, where a group of H-bridge circuits are in parallel. The two input terminals of one H-bridge circuit are respectively connected to the two ends of the secondary coil of the transformer T 1 , and the two input terminals of another H-bridge circuit are respectively connected to the transformer T2 are connected to both ends of the secondary coil.

[0015] For the topology of the above T-type three-phase isolated AC-DC converter, a group of H-bridge circuits are connected in series, and two input terminals of one H-bridge circuit are respectively connected to the transformer T 1 are connected to both ends of the secondary coil, and two input terminals of another H-bridge circuit are respectively connected to the transformer T 2 are connected to both ends of the secondary coil.

[0016] For the topology of the above T-type three-phase isolated AC-DC converter, the bidirectional switch is a MOSFET, IGBT, JFE or GaN HEMT.

[0017] The present invention also provides a control method for the topology of a T-type three-phase isolated AC-DC converter, and the method includes the following steps:

[0018] Step S1: Control three groups of parallel bidirectional switches to achieve bidirectional energy flow;

[0019] Step S2: Use the transformer T 1 and the transformer T 2 for energy conversion and isolation;

[0020] Step S3: Assist energy conversion through a group of H-bridge circuits;

[0021] Step S4: Calculate the duration of different levels according to the change trend of the leakage inductance current, so as to achieve precise control of energy flow and power factor correction.

[0022] For the control method of the topology of the above T-type three-phase isolated AC-DC converter, when controlling three groups of parallel bidirectional switches to achieve bidirectional energy flow in step S1, the following six different modes can be achieved: Mode a: t 0 -t 4 , A 1 , A 2 , C 3 are turned on, the primary voltage of the transformer T 1 is U ac , the primary voltage of the transformer T 2 is U ca ;

[0023] Mode b: t 4 -t 5 , A 1 , A 2 , B 3 are turned on, the primary voltage of the transformer T 1 is U ab , the primary voltage of the transformer T 2 is U ba;

[0024] Mode c: t 5 -t 6 , A 1 , A 2 , A 3 Turn on, transformer T 1 , T 2 The voltage on it is 0, and the transformer passes through A 1 , A 2 , A 3 Freewheeling;

[0025] Mode d: t 6 -t 10 , C 1 , C 2 , A 3 Turn on, transformer T 1 The primary voltage is U ca , transformer T 2 The primary voltage is U ac ;

[0026] Mode e: t 10 -t 11 , B 1 , B 2 , A 3 Turn on, transformer T 1 The primary voltage is U ba , transformer T 2 The primary voltage is U ab ;

[0027] Mode f: t 11 -t 12 , A 1 , A 2 , A 3 Turn on, transformer T 1 , T 2 The voltage on it is 0, and the transformer passes through A 1 , A 2 , A 3 Freewheeling.

[0028] For the control method of the topological structure of the above T-type three-phase isolated AC-DC converter, when calculating the duration of different modes according to the change trend of the leakage inductance current in step S4 to achieve precise control of energy flow and power factor correction, the time division method for each level is: [t 0 , t 0.5 ) is level 1, [t 0.5 , t 1 ) is level 2, [t 1 , t 4 is level 3, (t4 ,t 5 , the level at time t is 4, (t 5 ,t 6 , the level at time t is 5, (t 6 ,t 6.5 , the level at time t is 6, (t 6.5 ,t 7 , the level at time t is 7, (t 7 ,t 10 , the level at time t is 8, (t 10 ,t 11 , the level at time t is 9, (t 11 ,t 12 , the level at time t is 10;

[0029] Let the three-phase AC voltage be:

[0030]

[0031] U b = U N sinωt

[0032]

[0033] where U N is the peak value of the phase voltage, ω is the angular frequency, and t is the time;

[0034] In the first sector (0, 30°), assuming N modulations are performed in this sector, then at the k-th modulation, the three-phase voltages can be taken as:

[0035]

[0036] [t 0 ,t 0.5 ), at time t, the voltage difference across transformer T 1 is U ac + U bc , expressed as:

[0037]

[0038] [t 0.5 ,t 1 ), at time t, the voltage difference across transformer T 1 is U ac , expressed as:

[0039]

[0040] [t 1 ,t 4 ), at time t, the voltage difference across transformer T 1 is U ac - Ubc , expressed as:

[0041]

[0042] (t 4 , t 5 moment, the pressure difference across transformer T 1 is 0.

[0043] (t 5 , t 6 moment, the pressure difference across transformer T 1 is -U bc , expressed as:

[0044]

[0045] (t 6 , t 6.5 moment, the pressure difference across transformer T 1 is -U ac -U bc , expressed as:

[0046]

[0047] (t 6.5 , t 7 moment, the pressure difference across transformer T 1 is -U ac , expressed as:

[0048]

[0049] (t 7 , t 10 moment, the pressure difference across transformer T 1 is -U ac +U bc , expressed as:

[0050]

[0051] (t 10 , t 11 moment, the pressure difference across transformer T 1 is 0.

[0052] (t 11 , t 12 moment, the pressure difference across transformer T 1 is U bc , expressed as:

[0053]

[0054] The pressure difference across transformer T at the corresponding moment1 The current change trend on the leakage inductance is I m = voltage difference / L m , where L m is the leakage inductance of transformer T 1 .

[0055] For the control method of the above T-type three-phase isolated AC-DC converter topology, when calculating the duration of different levels according to the leakage inductance current change trend in step S4 to achieve precise control of energy flow and power factor correction, the calculation method of the duration of each level is as follows:

[0056] Let the start time of a certain level be t on , and the end time be t off . Integrating the current function on the leakage inductance, the area S enclosed by the leakage inductance current waveform and the coordinate axis at (t on , t off ) is:

[0057]

[0058] Then the duration of the level at (t on , t off ) is:

[0059]

[0060] where I Lr (t) represents the leakage inductance current, t on_x represents the start time of the x-th level, t off_x represents the end time of the x-th level, and T is the period.

[0061] Compared with the prior art, the present invention has the following advantages: The three-phase isolated AC-DC converter and its control method proposed by the present invention significantly improve the conversion efficiency and power factor of the converter through precise control of energy flow and optimization of circuit design; the use of MOSFET and IGBT as bidirectional switches not only improves the switching speed but also enhances the stability and durability of the device; the application of feedback control strategy and synchronous modulation technology effectively reduces current ripple and switching losses, further improving the overall performance of the system; in addition, this solution also supports the adjustment of the circuit topology in a specific working environment, enhancing the adaptability and flexibility of the device, and is applicable to various industrial and commercial scenarios, such as renewable energy power generation, electric vehicle charging stations, data center power management, etc., with broad application prospects and significant economic benefits.

[0062] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Description of the Drawings

[0063] Figure 1 It is a schematic structural diagram of the topological structure of the three-phase isolated AC-DC converter in Embodiment 1 of the present invention;

[0064] Figure 2 It is a schematic structural diagram of the topological structure of the three-phase isolated AC-DC converter in Embodiment 2 of the present invention;

[0065] Figure 3 It is a method flow block diagram of the control method for the topological structure of the three-phase isolated AC-DC converter of the present invention;

[0066] Figure 4 It is a control logic diagram of each mode and moment in Embodiment 1 and Embodiment 2 of the present invention;

[0067] Figure 5 It is a control schematic diagram of each mode in Embodiment 1 and Embodiment 2 of the present invention. Detailed implementation manners

[0068] Embodiment 1

[0069] As Figure 1 shown, the topological structure of the three-phase isolated AC-DC converter of the present invention includes:

[0070] Three groups of parallel bidirectional switches, and the bidirectional switches are used to control the bidirectional flow of energy;

[0071] Transformer T 1 and transformer T 2 , which are connected to the bidirectional switches and are used to achieve energy conversion and isolation;

[0072] A group of parallel or series-connected H-bridge circuits, which are connected to the transformer and are used to assist in energy conversion;

[0073] Among them, an external controller controls the mode of the bidirectional switches according to the control method, calculates the duration of different modes according to the change trend of the leakage inductance current, so as to achieve precise control of energy flow and correction of power factor.

[0074] In this embodiment, the three groups of parallel bidirectional switches include parallel bidirectional switch A 1 , B 1 and C 1 , parallel bidirectional switch A 2 , B 2 and C 2 , and parallel bidirectional switch A 3 , B 3 and C 3 ;

[0075] One end of the bidirectional switch A 1 , one end of the bidirectional switch B 1One end of and the two-way switch C 1 One end of both are connected to the transformer T 1 One end of the primary coil. The two-way switch A 1 The other end of, the two-way switch B 1 The other end of and the two-way switch C 1 The other end of are respectively connected to the A-phase input terminal, the B-phase input terminal and the C-phase input terminal;

[0076] The two-way switch A 2 One end of, the two-way switch B 2 One end of and the two-way switch C 2 One end of are respectively connected to the A-phase input terminal, the B-phase input terminal and the C-phase input terminal. The two-way switch A 2 The other end of, the two-way switch B 2 The other end of and the two-way switch C 2 The other end of are all connected to the transformer T 2 One end of the primary coil;

[0077] The two-way switch A 3 One end of, the two-way switch B 3 One end of and the two-way switch C 3 One end of are respectively connected to the A-phase input terminal, the B-phase input terminal and the C-phase input terminal. The two-way switch A 3 The other end of, the two-way switch B 3 The other end of and the two-way switch C 3 The other end of are all connected to the transformer T 1 The other end of the primary coil of the transformer T and the transformer T 2 The other end of the primary coil of are connected.

[0078] In this embodiment, a group of H-bridge circuits are connected in parallel. The two input terminals of one H-bridge circuit are respectively connected to both ends of the secondary coil of the transformer T 1 The two input terminals of another H-bridge circuit are respectively connected to both ends of the secondary coil of the transformer T 2 The two ends of the secondary coil of.

[0079] In this embodiment, the two-way switch is a MOSFET, IGBT, JFE or GaN HEMT.

[0080] Embodiment 2

[0081] As Figure 2 Shown, the difference between this embodiment and Embodiment 1 is that a group of H-bridge circuits are connected in series. The rest of the structures are the same as those in Embodiment 1.

[0082] Embodiment 3

[0083] As Figures 3 to 5As shown, this embodiment discloses a control method for the topology of a T-type three-phase isolated AC-DC converter, and this method includes the following steps:

[0084] Step S1, control three groups of parallel bidirectional switches to achieve bidirectional energy flow;

[0085] Step S2, utilize transformer T 1 and transformer T 2 to perform energy conversion and isolation;

[0086] Step S3, assist energy conversion through a group of H-bridge circuits;

[0087] Step S4, calculate the duration of different levels according to the change trend of the leakage inductance current, so as to achieve precise control of energy flow and power factor correction.

[0088] In this embodiment, when controlling the three groups of parallel bidirectional switches in step S1 to achieve bidirectional energy flow, the following six different modes can be achieved:

[0089] Mode a: t 0 -t 4 , A 1 , A 2 , C 3 is turned on, the primary voltage of transformer T 1 is U ac , the primary voltage of transformer T 2 is U ca ;

[0090] Mode b: t 4 -t 5 , A 1 , A 2 , B 3 is turned on, the primary voltage of transformer T 1 is U ab , the primary voltage of transformer T 2 is U ba ;

[0091] Mode c: t 5 -t 6 , A 1 , A 2 , A 3 is turned on, the voltage on transformer T 1 , T 2 is 0, and the transformer conducts freewheeling through A 1 , A 2 , A 3 ;

[0092] Mode d: t 6 -t 10 , C1 , C 2 , A 3 Turn on, transformer T 1 The primary voltage is U ca , transformer T 2 The primary voltage is U ac ;

[0093] Mode e: t 10 -t 11 , B 1 , B 2 , A 3 Turn on, transformer T 1 The primary voltage is U ba , transformer T 2 The primary voltage is U ab ;

[0094] Mode f: t 11 -t 12 , A 1 , A 2 , A 3 Turn on, transformer T 1 , T 2 The voltage on it is 0, and the transformer conducts freewheeling through A 1 , A 2 , A 3 Freewheeling.

[0095] In this embodiment, when calculating the duration of different modes according to the change trend of the leakage inductance current in step S4 to achieve precise control of energy flow and correction of power factor, the time division method for each level is as follows: [t 0 , t 0.5 ) is level 1, [t 0.5 , t 1 ) is level 2, [t 1 , t 4 is level 3, (t 4 , t 5 is level 4, (t 5 , t 6 is level 5, (t 6 , t 6.5 is level 6, (t 6.5 , t 7 is level 7, (t 7 , t 10 is level 8, (t 10 , t 11 is level 9, (t 11 , t 12 is level 10;

[0096] Let the three-phase AC voltage be:

[0097]

[0098] U b =U N sinωt

[0099]

[0100] where, U N is the peak value of the phase voltage, ω is the angular frequency, and t is the time;

[0101] In the first sector (0, 30°), assuming N modulations are performed in this sector, then at the k-th modulation, the three-phase voltages can be taken as:

[0102]

[0103] [t 0 ,t 0.5 ) moment, the voltage difference across transformer T 1 is U ac +U bc , expressed as:

[0104]

[0105] [t 0.5 ,t 1 ) moment, the voltage difference across transformer T 1 is U ac , expressed as:

[0106]

[0107] [t 1 ,t 4 moment, the voltage difference across transformer T 1 is U ac -U bc , expressed as:

[0108]

[0109] (t 4 ,t 5 moment, the voltage difference across transformer T 1 is 0.

[0110] (t 5 ,t 6 moment, the voltage difference across transformer T 1 is -U bc , expressed as:

[0111]

[0112] (t 6 ,t 6.5 moment, the pressure difference across transformer T 1 is -U ac -U bc , expressed as:

[0113]

[0114] (t 6.5 ,t 7 moment, the pressure difference across transformer T 1 is -U ac , expressed as:

[0115]

[0116] (t 7 ,t 10 moment, the pressure difference across transformer T 1 is -U ac +U bc , expressed as:

[0117]

[0118] (t 10 ,t 11 moment, the pressure difference across transformer T 1 is 0.

[0119] (t 11 ,t 12 moment, the pressure difference across transformer T 1 is U bc , expressed as:

[0120]

[0121] At the corresponding moment, the current change trend of the leakage inductance of transformer T 1 is I m = pressure difference / L m , L m is the leakage inductance of transformer T 1 .

[0122] In this embodiment, when calculating the duration of different levels according to the leakage inductance current change trend in step S4 to achieve precise control of energy flow and power factor correction, the calculation method of the duration of each level is as follows:

[0123] Let the start time of a certain level be t on , and the end time be t off . Integrating the current function of the leakage inductance, the leakage inductance current waveform in (ton , t off ) The area S enclosed by the moment and the coordinate axis is:

[0124]

[0125] Then (t on , t off ) The duration of the level at the moment is:

[0126]

[0127] Among them, I Lr (t) represents the leakage inductance current, t on_x represents the start time of the x-th level, t off_x represents the end time of the x-th level, and T is the period.

[0128] In summary, the three-phase isolated AC-DC converter and its control method proposed by the present invention not only achieve high-efficiency energy conversion and precise power factor control technically, but also improve the stability and adaptability of the equipment by optimizing the circuit design and control strategy. Its wide application scenarios range from industrial automation, electric vehicle charging, data center power management to medical equipment, aerospace, smart home and smart city, demonstrating its important value in modern science and technology and economic activities. By adopting high-speed switching elements such as MOSFET and IGBT, as well as advanced technologies such as synchronous modulation and feedback control, this solution can effectively cope with various complex environments and load changes, providing users with a stable, efficient and intelligent power conversion solution, with significant economic benefits and broad application prospects.

[0129] The above is only a preferred embodiment of the present invention, and does not impose any limitation on the present invention. Any simple modification, change and equivalent structural change made to the above embodiments according to the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A topological structure of a T-type three-phase isolated AC / DC converter, characterized in that: include: Three sets of bidirectional switches connected in parallel, the bidirectional switches are used to control the bidirectional flow of energy; Transformer T1 and transformer T2 are connected to the bidirectional switch to realize energy conversion and isolation; A set of parallel or series H-bridge circuits connected to the transformer for assisting energy conversion; The external controller controls the mode of the bidirectional switch according to the control method, and calculates the duration of different modes according to the variation trend of the leakage inductance current, thereby realizing accurate control of energy flow and correction of power factor.

2. The topological structure of the T-type three-phase isolated AC / DC converter according to claim 1, characterized in that: The three groups of parallel bidirectional switches include parallel bidirectional switches A1, B1 and C1, parallel bidirectional switches A2, B2 and C2, and parallel bidirectional switches A3, B3 and C3; One end of the bidirectional switch A1, one end of the bidirectional switch B1 and one end of the bidirectional switch C1 are connected to one end of the primary coil of the transformer T1, and the other ends of the bidirectional switch A1, the other ends of the bidirectional switch B1 and the other ends of the bidirectional switch C1 are connected to the A-phase input terminal, the B-phase input terminal and the C-phase input terminal respectively; One end of the bidirectional switch A2, one end of the bidirectional switch B2 and one end of the bidirectional switch C2 are respectively connected to the A-phase input terminal, the B-phase input terminal and the C-phase input terminal, and the other end of the bidirectional switch A2, the other end of the bidirectional switch B2 and the other end of the bidirectional switch C2 are all connected to one end of the primary coil of the transformer T2; One end of the bidirectional switch A3, one end of the bidirectional switch B3 and one end of the bidirectional switch C3 are respectively connected to the A-phase input terminal, the B-phase input terminal and the C-phase input terminal, and the other end of the bidirectional switch A3, the other end of the bidirectional switch B3 and the other end of the bidirectional switch C3 are all connected to the other end of the primary coil of the transformer T1 and the other end of the primary coil of the transformer T2.

3. The topological structure of the T-type three-phase isolated AC / DC converter according to claim 2, characterized in that: A group of H-bridge circuits are connected in parallel, wherein two input ends of one H-bridge circuit are respectively connected to two ends of the secondary coil of the transformer T1 , and two input ends of another H-bridge circuit are respectively connected to two ends of the secondary coil of the transformer T2 .

4. The topological structure of the T-type three-phase isolated AC / DC converter according to claim 2, characterized in that: A group of H-bridge circuits are connected in series, wherein two input ends of one H-bridge circuit are respectively connected to two ends of the secondary coil of the transformer T1 , and two input ends of another H-bridge circuit are respectively connected to two ends of the secondary coil of the transformer T2 .

5. The topological structure of the T-type three-phase isolated AC / DC converter according to claim 3 or 4, characterized in that: The bidirectional switch is MOSFET, IGBT, JFE or GaN HEMT.

6. A method for controlling the topological structure of the three-phase isolated AC / DC converter according to claim 3 or 4, characterized in that: The method comprises the following steps: Step S1, controlling three sets of bidirectional switches connected in parallel to achieve bidirectional flow of energy; Step S2, using transformer T1 and transformer T2 to perform energy conversion and isolation; Step S3, assisting energy conversion through a set of H-bridge circuits; Step S4: Calculate the duration of different levels according to the variation trend of the leakage inductance current, so as to achieve accurate control of energy flow and correction of power factor.

7. The method for controlling the topological structure of a T-type three-phase isolated AC / DC converter according to claim 6, characterized in that: When the three sets of bidirectional switches connected in parallel are controlled in step S1 to realize the bidirectional flow of energy, the following six different modes can be realized: Mode a: t0-t4, A1, A2, C3 are turned on, and the primary voltage of transformer T1 is U ac , the primary voltage of transformer T2 is U ca ; Mode b: t4-t5, A1, A2, B3 are turned on, and the primary voltage of transformer T1 is U ab , the primary voltage of transformer T2 is U ba ; Mode c: t5-t6, A1, A2, A3 are turned on, the voltage on transformers T1 and T2 is 0, and the transformers continue current through A1, A2, A3; Mode d: t6-t 10 , C1, C2, A3 are turned on, and the primary voltage of transformer T1 is U ca , the primary voltage of transformer T2 is U ac ; Modal e:t 10 -t 11 , B1, B2, A3 are turned on, and the primary voltage of transformer T1 is U ba , the primary voltage of transformer T2 is U ab ; Modal f:t 11 -t 12 , A1, A2, A3 are turned on, the voltage on transformers T1 and T2 is 0, and the transformer continues current through A1, A2, A3.

8. The method for controlling the topological structure of a T-type three-phase isolated AC / DC converter according to claim 7, characterized in that: When calculating the duration of different modes according to the leakage current variation trend in step S4 to achieve accurate control of energy flow and correction of power factor, the time division method of each level is: [t0,t 0.5 ) is level 1, [t 0.5 ,t1) is level 2, [t1,t4] is level 3, (t4,t5] is level 4, (t5,t6] is level 5, (t6,t 6.5 ] is level 6, (t 6.5 ,t7] is level 7, (t7,t 10 ] is level 8, (t 10 ,t 11 ] is level 9, (t 11 ,t 12 ] is level 10 at this moment; Assume the three-phase AC voltage is: The b =U N sinωt Among them, U N is the phase voltage peak value, ω is the angular frequency, and t is the time; In the first sector (0, 30°), assuming that N modulations are performed in this sector, the three-phase voltages that can be taken at the kth modulation are: [t0,t 0.5 ) at the moment, the voltage difference on transformer T1 is U ac +U bc , expressed as: [t 0.5 At t1), the voltage difference on transformer T1 is U ac , expressed as: At [t1, t4], the voltage difference on transformer T1 is U ac -U bc , expressed as: At (t4, t5], the voltage difference on transformer T1 is 0. At (t5, t6], the voltage difference on transformer T1 is -U bc , expressed as: (t6,t 6.5 ], the voltage difference on transformer T1 is -U ac -U bc , expressed as: (t 6.5 At t7], the voltage difference on transformer T1 is -U ac , expressed as: (t7,t 10 ], the voltage difference on transformer T1 is -U ac +U bc , expressed as: (t 10 ,t 11 ], the voltage difference across transformer T1 is 0. (t 11 ,t 12 ], the voltage difference on transformer T1 is U bc , expressed as: The current change trend of the leakage inductance of transformer T1 at the corresponding moment is I m = Pressure difference / L m , L m is the leakage inductance of transformer T1.

9. The method for controlling the topological structure of a T-type three-phase isolated AC / DC converter according to claim 8, characterized in that: When the duration of different levels is calculated according to the variation trend of the leakage inductance current in step S4, so as to realize the precise control of energy flow and the correction of power factor, the duration of each level is calculated as follows: Assume that the starting time of a certain level is t on , the end time is t off , integrating the current function on the leakage inductance, we can get the leakage inductance current waveform at (t on ,t off ) The area S enclosed by the coordinate axis at the moment is: Then (t on ,t off ) The duration of the level at the moment is: Among them, I Lr (t) represents the leakage inductance current, t on_x Indicates the time when the xth level starts, t off_x Indicates the time when the xth level ends, and T is the period.

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