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

Abstract

The invention discloses a topological structure of a triangular three-phase isolation type AC / DC converter and a control method thereof, and the topological structure comprises three groups of switches which are connected in parallel, and the switches are used for controlling the flow of energy; the transformer T1, the transformer T2 and the transformer T3 are connected with the switch and are used for realizing energy conversion and isolation; the three-phase full-control bridge rectifier circuit is connected with the transformer and is used for auxiliary energy conversion; wherein the external controller controls the modes of the switch according to a control method, and calculates the duration of different modes according to the change trend of the leakage inductance current, so that the accurate control of energy flow and the correction of a power factor are realized. 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 delta three-phase isolated AC-DC converter. Background Art

[0002] At present, the mainstream power supply line is still the AC power grid. With the wide application of power electronic devices, the harmonic current components in the power grid are increasing, bringing a series of hazards to the power grid itself and other electrical equipment, such as misoperation of relay protection and automatic devices, and mismeasurement of instruments. In addition, current harmonics will also cause additional losses, resulting in problems such as transformer heating and cable aging. For this reason, governments and international organizations have formulated a series of standards, such as IEC 61000-302 Class D, to limit the input current harmonics and power factor of the converter.

[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 and a control method of a delta three-phase isolated AC-DC converter for 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 delta three-phase isolated AC-DC converter, including:

[0006] Three groups of parallel switches for controlling the flow of energy;

[0007] A transformer T, the primary coil of the transformer T is connected in delta, the secondary coil of the transformer T is connected in star, and the primary coil of the transformer T is connected to the switch for energy conversion and isolation;

[0008] A three-phase fully controlled bridge rectifier circuit, connected to the secondary coil of the transformer T for assisting energy conversion;

[0009] Wherein, an external controller controls the mode of the 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 achieve precise control of the energy flow and correction of the power factor.

[0010] The above topological structure of the delta three-phase isolated AC-DC converter is characterized in that: the three groups of parallel switches include parallel switches A1, B1 and C1, parallel switches A2, B2 and C2, and parallel switches A3, B3 and C3;

[0011] One end of switch A1, one end of switch B1, and one end of switch C1 are all connected to the positive homonymous end of the first coil and the negative homonymous end of the third coil of the primary coil of transformer T. The other end of switch A1, the other end of switch B1, and the other end of switch C1 are respectively connected to the A-phase input terminal, the B-phase input terminal, and the C-phase input terminal;

[0012] One end of switch A2, one end of switch B2, and one end of switch C2 are respectively connected to the A-phase input terminal, the B-phase input terminal, and the C-phase input terminal. The other end of switch A2, the other end of switch B2, and the other end of switch C2 are all connected to one end of the positive homonymous end of the second coil and the negative homonymous end of the first coil of the primary coil of transformer T;

[0013] One end of switch A3, one end of switch B3, and one end of switch C3 are respectively connected to the A-phase input terminal, the B-phase input terminal, and the C-phase input terminal. The other end of switch A3, the other end of switch B3, and the other end of switch C3 are all connected to the positive homonymous end of the third coil and the negative homonymous end of the second coil of the primary coil of transformer T.

[0014] For the above triangular three-phase isolated AC-DC converter topology, it is characterized in that: the switch is a MOSFET, IGBT, JFE or GaN HEMT.

[0015] The present invention also discloses a control method for the above triangular three-phase isolated AC-DC converter topology, and this method includes the following steps:

[0016] Step S1, control three groups of parallel switches to achieve bidirectional energy flow;

[0017] Step S2, use transformer T for energy conversion and isolation;

[0018] Step S3, assist energy conversion through a three-phase fully controlled bridge rectifier circuit;

[0019] Step S4, calculate 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 power factor correction.

[0020] For the control method of the above triangular three-phase isolated AC-DC converter topology, when controlling three groups of parallel switches to achieve bidirectional energy flow in step S1, the following six different modes can be achieved:

[0021] Mode a: t0 - t1, A1, B2, C3 are turned on, and the voltage of the first coil of the primary coil of transformer T is U ab , the voltage of the second coil of the primary coil of transformer T is U bc , the voltage of the third coil of the primary coil of transformer T is Uca ;

[0022] Mode b: From t1 to t2, A1, C2, and B3 are turned on. The voltage of the first coil of the primary coil of transformer T is U ac , and the voltage of the second coil of the primary coil of transformer T is U cb , and the voltage of the third coil of the primary coil of transformer T is U ba ;

[0023] Mode c: From t2 to t3, B1, C2, and A3 are turned on. The voltage of the first coil of the primary coil of transformer T is U bc , and the voltage of the second coil of the primary coil of transformer T is U ca , and the voltage of the third coil of the primary coil of transformer T is U ab ;

[0024] Mode d: From t3 to t4, C1, B2, and A3 are turned on. The voltage of the first coil of the primary coil of transformer T is U ca , and the voltage of the second coil of the primary coil of transformer T is U ba , and the voltage of the third coil of the primary coil of transformer T is U ac ;

[0025] Mode e: From t4 to t5, C1, A2, and B3 are turned on. The voltage of the first coil of the primary coil of transformer T is U ca , and the second coil of the primary coil of transformer T is U ab , and the voltage of the third coil of the primary coil of transformer T is U bc ;

[0026] Mode f: From t5 to t6, B1, A2, and C3 are turned on. The voltage of the first coil of the primary coil of transformer T is U ba , and the voltage of the second coil of the primary coil of transformer T is U ac , and the voltage of the third coil of the primary coil of transformer T is U cb .

[0027] For the control method of the topological structure of the above triangular 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 as follows:

[0028] The time period from [t0, t1) is level 1, the time period from [t1, t2) is level 2, the time period from [t2, t3] is level 3, the time period from (t3, t4] is level 4, the time period from (t4, t5] is level 5, and the time period from (t5, t6] is level 6;

[0029] Assume the three-phase AC voltage is:

[0030]

[0031] U B = A 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, the three-phase voltages taken at the k-th modulation can be:

[0035]

[0036] As shown at the moment [t0, t1), the voltage difference across the transformer T at this time is U ab -U bc , that is:

[0037]

[0038] Then the current change trend in the leakage inductance of the transformer T at the corresponding moment is I m = voltage difference / L m L m is the leakage inductance of the transformer T.

[0039] For the control method of the topological structure of the above triangular three-phase isolated AC-DC converter, 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:

[0040] Let the start time of a certain mode be t on , and the end time be t off . Integrating the current function of the leakage inductance, the area S enclosed by the leakage inductance current waveform and the coordinate axis at the moment (t on , t off ) is:

[0041]

[0042] Then the duration of the mode at the moment (t on , t off ) is:

[0043]

[0044] where I Lr (t) represents the leakage inductance current, t on_x represents the start time of the x-th level, toff_x Indicates the time when the x - level ends. T is the period. Are the current references corresponding to a, b, and c three - phases.

[0045] For the control method of the topological structure of the above - mentioned triangular three - phase isolated AC - DC converter, when calculating the duration of different levels 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 specific process is as follows:

[0046] Step S401: Compare the measured output voltage u pn with the set - point value u * pn and input it to the controller G u to normalize the output current;

[0047] Step S402: Take the average voltage to calculate the normalized signal required for interpolation The measured DC voltage u pn is readjusted to the primary side, and the normalized voltage u' pn is calculated and input to the interpolation link;

[0048] The measured main voltage is used to determine the sector. The sector and the pulse - width modulator (PWM) are input with four relative switching times to control the primary - side and secondary - side MOSFETs;

[0049] Taking the transformer T1 as an example, assuming the primary - side voltage of the transformer is u1(t) and the secondary - side voltage of the transformer is u2(t), then the transformer voltage is:

[0050] u T (t)=u1(t)-u2(t)

[0051] Then the slope of the transformer leakage inductance current function is:

[0052]

[0053] In modes a - f, the voltage difference across the transformer is:

[0054]

[0055] Then the transformer leakage inductance current function can be expressed as where i0 is the leakage inductance current value at the starting moment of each mode;

[0056] Then the average value of the current within the corresponding mode time is:

[0057]

[0058] where t a ,tb are the start and end time of the corresponding mode respectively.

[0059] Then the a-phase current I in one cycle a The average value is:

[0060]

[0061] Then the b-phase current I in one cycle b The average value is:

[0062]

[0063] Then the phase c current I c The average value is:

[0064]

[0065] By combining the above equations and assuming the coefficients of each unknown number, we can get the equation:

[0066]

[0067] Assuming t4-t8 are free variables, we can get:

[0068]

[0069] Then the duration of each mode can be expressed as:

[0070]

[0071] Among them, x4, x5, x6 are arbitrary real numbers.

[0072] Compared with the prior art, the present invention has the following advantages: the triangular three-phase isolated AC / DC converter and control method proposed in the present invention significantly improve the conversion efficiency and power factor of the converter by accurately controlling the energy flow and optimizing the circuit design; the application of feedback control strategy and synchronous modulation technology effectively reduces current ripple and switching loss, and further improves the overall performance of the system; in addition, the scheme also supports the adjustment of circuit topology structure under specific working environment, enhances the adaptability and flexibility of the equipment, and is suitable for various industrial and commercial scenarios, such as renewable energy power generation, electric vehicle charging stations, data center power management, etc., and has broad application prospects and significant economic benefits.

[0073] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 It is a schematic diagram of the topological structure of the three-phase isolated AC-DC converter in Embodiment 1 of the present invention;

[0075] Figure 2 This is the method flow block diagram of the control method for the topology structure of the three-phase isolated AC-DC converter of the present invention;

[0076] Figure 3 This is the control logic of each mode and moment of the present invention Figure 1 ;

[0077] Figure 4 This is the control logic of each mode and moment of the present invention Figure 2 ;

[0078] Figure 5 This is the control schematic diagram of each mode of the present invention;

[0079] Figure 6 This is the block diagram of the DC output voltage control scheme in the specific embodiment of the present invention. Detailed implementation manners

[0080] Embodiment 1

[0081] As Figure 1 shown, the topology structure of the triangular three-phase isolated AC-DC converter of the present invention includes:

[0082] Three groups of parallel switches, and the switches are used to control the flow of energy;

[0083] Transformer T, the primary coil of the transformer T is in delta connection, the secondary coil of the transformer T is in star connection, and the primary coil of the transformer T is connected to the switches for realizing energy conversion and isolation;

[0084] Three-phase fully controlled bridge rectifier circuit, which is connected to the secondary coil of the transformer T for assisting energy conversion;

[0085] Among them, the external controller controls the mode of the 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 realize the precise control of the energy flow and the correction of the power factor.

[0086] In this embodiment, the three groups of parallel switches include parallel switches A1, B1 and C1, parallel switches A2, B2 and C2, and parallel switches A3, B3 and C3;

[0087] One end of switch A1, one end of switch B1 and one end of switch C1 are all connected to the positive homonymous end of the first coil and the negative homonymous end of the third coil of the primary coil of transformer T, and the other ends of switch A1, switch B1 and switch C1 are respectively connected to the A-phase input terminal, the B-phase input terminal and the C-phase input terminal;

[0088] One end of switch A2, one end of switch B2, and one end of switch C2 are respectively connected to the A-phase input terminal, B-phase input terminal, and C-phase input terminal. The other ends of switch A2, switch B2, and switch C2 are all connected to one end of the positive homonymous end of the second coil and the negative homonymous end of the first coil of the primary coil of transformer T.

[0089] One end of switch A3, one end of switch B3, and one end of switch C3 are respectively connected to the A-phase input terminal, B-phase input terminal, and C-phase input terminal. The other ends of switch A3, switch B3, and switch C3 are all connected to the positive homonymous end of the third coil and the negative homonymous end of the second coil of the primary coil of transformer T.

[0090] In this embodiment, the switch is a MOSFET, IGBT, JFE, or GaN HEMT.

[0091] Embodiment 2

[0092] As Figures 2 to 5 shown, the control method of the topology structure of the triangular three-phase isolated AC-DC converter of the present invention includes the following steps:

[0093] Step S1: Control three groups of parallel switches to achieve bidirectional energy flow;

[0094] Step S2: Use transformer T for energy conversion and isolation;

[0095] Step S3: Assist energy conversion through a three-phase fully controlled bridge rectifier circuit;

[0096] Step S4: Calculate 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 power factor correction.

[0097] In this embodiment, when controlling three groups of parallel switches in step S1 to achieve bidirectional energy flow, the following six different modes can be achieved:

[0098] Mode a: t0 - t1, A1, B2, C3 are turned on, and the voltage of the first coil of the primary coil of transformer T is U ab , the voltage of the second coil of the primary coil of transformer T is U bc , the voltage of the third coil of the primary coil of transformer T is U ca ;

[0099] Mode b: t1 - t2, A1, C2, B3 are turned on, and the voltage of the first coil of the primary coil of transformer T is U ac , the voltage of the second coil of the primary coil of transformer T is U cb , the voltage of the third coil of the primary coil of transformer T is Uba ;

[0100] Mode c: t2 - t3, B1, C2, A3 are turned on, the voltage of the first coil of the primary coil of transformer T is U bc , the voltage of the second coil of the primary coil of transformer T is U ca , the voltage of the third coil of the primary coil of transformer T is U ab ;

[0101] Mode d: t3 - t4, C1, B2, A3 are turned on, the voltage of the first coil of the primary coil of transformer T is U ca , the voltage of the second coil of the primary coil of transformer T is U ba , the voltage of the third coil of the primary coil of transformer T is U ac ;

[0102] Mode e: t4 - t5, C1, A2, B3 are turned on, the voltage of the first coil of the primary coil of transformer T is U ca , the second coil of the primary coil of transformer T is U ab , the voltage of the third coil of the primary coil of transformer T is U bc ;

[0103] Mode f: t5 - t6, B1, A2, C3 are turned on, the voltage of the first coil of the primary coil of transformer T is U ba , the voltage of the second coil of the primary coil of transformer T is U ac , the voltage of the third coil of the primary coil of transformer T is U cb .

[0104] 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: the time period [t0, t1) is level 1, the time period [t1, t2) is level 2, the time period [t2, t3] is level 3, the time period (t3, t4] is level 4, the time period (t4, t5] is level 5, and the time period (t5, t6] is level 6;

[0105] Assume the three-phase AC voltage is:

[0106]

[0107] U B = A sinωt

[0108]

[0109] where U N is the peak value of the phase voltage, ω is the angular frequency, and t is the time;

[0110] 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 k-th modulation are as follows:

[0111]

[0112] As shown at the moment of [t0, t1), the pressure difference on the transformer T at this time is U ab -U bc , that is:

[0113]

[0114] Then the change trend of the current on the leakage inductance of the transformer T at the corresponding moment is I m = pressure difference / L m , L m is the leakage inductance of the transformer T.

[0115] In this embodiment, when calculating the duration of different levels 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 calculation method of the duration of each level is as follows:

[0116] Let the start time of a certain mode 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 the moment of (t on , t off ) is:

[0117]

[0118] Then the duration of the level at the moment of (t on , t off ) is:

[0119]

[0120] 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, T is the period, is the current reference corresponding to a, b, c, obtained from the control loop.

[0121] In this embodiment, as Figure 6 shown, when calculating the duration of different levels 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 specific process is as follows:

[0122] Step S401. The measured output voltage upn is compared with the setpoint value u * pn and input into the closed-loop controller G u to obtain the normalized reference value of the alternating current;

[0123] Step S402: Take the average voltage (such as u bc ) in Sector 1 to calculate the normalized signal required for interpolation The measured DC voltage u pn is readjusted to the primary side, and the normalized voltage u' pn is calculated and input to the interpolation section;

[0124] Combining the normalized signal with the calculation formulas of Claims 6 and 7, the relative switching times t1 - t8 can be determined; the measured main voltage is used to determine the sector, and the sector and the pulse width modulator (PWM) are input with four relative switching times to control the primary and secondary side MOSFETs; since the primary side input current is generated by open-loop control, the proposed control scheme does not require a current sensor, and the corresponding sensor losses can be avoided;

[0125] Taking the transformer T1 as an example, assuming the primary side voltage of the transformer is u1(t) and the secondary side voltage of the transformer is u2(t), then the transformer voltage is:

[0126] u T (t) = u1(t) - u2(t)

[0127] Then the slope of the transformer leakage inductance current function is:

[0128]

[0129] For modes a - f, the voltage difference across the transformer is:

[0130]

[0131] Then the transformer leakage inductance current function can be expressed as where i0 is the leakage inductance current value at the start time of each mode.

[0132] Then the average value of the current within the corresponding mode time is:

[0133]

[0134] where t a , t b are the start and end times of the corresponding mode respectively.

[0135] Then the average value of the a-phase current I a within one period is:

[0136]

[0137] Then the b-phase current I in one cycle b The average value is:

[0138]

[0139] Then the phase c current I c The average value is:

[0140]

[0141] By combining the above equations and assuming the coefficients of each unknown number, we can get the equation:

[0142]

[0143] Assuming t4-t8 are free variables, we can get:

[0144]

[0145] Then the duration of each mode can be expressed as:

[0146]

[0147] Among them, x4, x5, x6 are arbitrary real numbers.

[0148] In summary, the triangular three-phase isolated AC / DC converter and control method proposed in the present invention significantly improve the conversion efficiency and power factor of the converter by accurately controlling energy flow and optimizing circuit design; the application of feedback control strategy and synchronous modulation technology effectively reduces current ripple and switching loss, and further improves the overall performance of the system; in addition, this solution also supports the adjustment of circuit topology structure under specific working environment, enhances the adaptability and flexibility of the equipment, and is suitable for various industrial and commercial scenarios, such as renewable energy power generation, electric vehicle charging stations, data center power management, etc., and has broad application prospects and significant economic benefits.

[0149] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural change made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A topological structure of a triangular three-phase isolated AC-DC converter, characterized in that Including: Three groups of parallel switches for controlling the flow of energy; Transformer T, with the primary coil of the transformer T connected in delta and the secondary coil of the transformer T connected in star. The primary coil of the transformer T is connected to the switches for energy conversion and isolation; Three-phase fully controlled bridge rectifier circuit, connected to the secondary coil of the transformer T for assisting energy conversion; Among them, the external controller controls the mode of the 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 the energy flow and correction of the power factor.

2. The topology of the triangular three-phase isolated AC-DC converter according to claim 1, characterized in that: The three groups of parallel switches include parallel switches A1, B1, and C1, parallel switches A2, B2, and C2, and parallel switches A3, B3, and C3; One end of switch A1, one end of switch B1, and one end of switch C1 are all connected to the positive homonymous end of the first coil and the negative homonymous end of the third coil of the primary coil of transformer T. The other ends of switch A1, switch B1, and switch C1 are respectively connected to the A-phase input terminal, B-phase input terminal, and C-phase input terminal; One end of switch A2, one end of switch B2, and one end of switch C2 are respectively connected to the A-phase input terminal, B-phase input terminal, and C-phase input terminal. The other ends of switch A2, switch B2, and switch C2 are all connected to one end of the positive homonymous end of the second coil and the negative homonymous end of the first coil of the primary coil of transformer T; One end of switch A3, one end of switch B3, and one end of switch C3 are respectively connected to the A-phase input terminal, B-phase input terminal, and C-phase input terminal. The other ends of switch A3, switch B3, and switch C3 are all connected to the positive homonymous end of the third coil and the negative homonymous end of the second coil of the primary coil of transformer T.

3. The topological structure of the triangular three-phase isolated AC-DC converter according to claim 1, characterized in that: The switch is a MOSFET, IGBT, JFE or GaN HEMT.

4. A control method for the topology of the triangular three-phase isolated AC-DC converter as described in claim 2, characterized in that, The method includes the following steps: Step S1: Control three groups of parallel switches to achieve bidirectional energy flow; Step S2: Use transformer T for energy conversion and isolation; Step S3: Assist energy conversion through a three-phase fully controlled bridge rectifier circuit; Step S4: Calculate the duration of different modes according to the change trend of the leakage inductance current, so as to achieve precise control of the energy flow and correction of the power factor.

5. The control method of the topology structure of the triangular three-phase isolated AC-DC converter according to claim 4, characterized in that: When controlling the three groups of parallel switches in step S1 to achieve bidirectional energy flow, the following six different modes can be achieved: Mode a: From t0 to t1, A1, B2, and C3 are turned on, and the voltage of the first coil of the primary coil of transformer T is U ab , and the voltage of the second coil of the primary coil of transformer T is U bc , and the voltage of the third coil of the primary coil of transformer T is U ca ; Mode b: From t1 to t2, A1, C2, and B3 are turned on, and the voltage of the first coil of the primary coil of transformer T is U ac , and the voltage of the second coil of the primary coil of transformer T is U cb , and the voltage of the third coil of the primary coil of transformer T is U ba ; Mode c: t2 - t3, B1, C2, A3 are turned on, and the voltage of the first coil of the primary coil of transformer T is U bc , and the voltage of the second coil of the primary coil of transformer T is U ca , and the voltage of the third coil of the primary coil of transformer T is U ab ; Mode d: From t3 to t4, C1, B2, and A3 are turned on, and the voltage of the first coil of the primary coil of transformer T is U ca , and the voltage of the second coil of the primary coil of transformer T is U ba , and the voltage of the third coil of the primary coil of transformer T is U ac ; Mode e: t4 - t5, C1, A2, B3 are turned on, and the voltage of the first coil of the primary coil of transformer T is U ca , and the voltage of the second coil of the primary coil of transformer T is U ab , and the voltage of the third coil of the primary coil of transformer T is U bc ; Mode f: t5 - t6, B1, A2, C3 are turned on, and the voltage of the first coil of the primary coil of transformer T is U ba , and the voltage of the second coil of the primary coil of transformer T is U ac , and the voltage of the third coil of the primary coil of transformer T is U cb .

6. The control method of the topological structure of the triangular three-phase isolated AC-DC converter according to claim 5, characterized in that: 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 the energy flow and correction of the power factor, the time division method of each level is: the time period from [t0, t1) is level 1, the time period from [t1, t2) is level 2, the time period from [t2, t3] is level 3, the time period from (t3, t4] is level 4, the time period from (t4, t5] is level 5, and the time period from (t5, t6] is level 6; Assume the three-phase AC voltage is: U B = Asinωt where U N is the peak value of the phase voltage, ω is the angular frequency, and t is the time; In the first sector (0, 30°), assuming N modulations are performed in this sector, then the three-phase voltages that can be taken during the kth modulation are: As shown in the figure, at the time of [t0, t1), the pressure difference across the transformer T is U ab -U bc , that is: Then the current change trend on the leakage inductance of transformer T at the corresponding moment is I m = pressure difference / L m , L m is the leakage inductance of transformer T.

7. The control method of the topological structure of the triangular three-phase isolated AC-DC converter according to claim 6, 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: Let the starting time of a certain mode be \(t\). on , and the ending time be \(t\). off , by integrating the current function on the leakage inductance, the area \(S\) enclosed by the leakage inductance current waveform and the coordinate axis at the time \((t\). on , \(t\). off ) is as follows: Then (t on , t off ) The duration for which the level persists is: Among them, I Lr (t) represents the leakage inductance current, where t on_x represents the start time of the x-th level, and t off_x represents the end time of the x-th level. T is the period, is the current reference corresponding to the three phases a, b, and c.

8. The control method of the topological structure of the triangular three-phase isolated AC-DC converter according to claim 7, characterized in that: When calculating the duration of different levels according to the leakage inductance current variation trend in step S4, so as to achieve accurate control of energy flow and correction of power factor, the specific process is as follows: Step S401, measure the output voltage u pn and compare it with the setpoint value u * pn and input it into the closed-loop controller G u to obtain the normalized reference value of the alternating current; Step S402: Take the average voltage to calculate the normalized signal required for interpolation Measured DC voltage u pn Is readjusted to the primary side, and the normalized voltage u’ is calculated pn , and is input to the interpolation section; The measured main voltage is used to determine the sectors, which together with the pulse width modulator (PWM) input four relative switching times to control the primary and secondary MOSFETs; Assume that the primary voltage of the transformer is u1(t) and the secondary voltage of the transformer is u2(t), then the transformer voltage is: u T u(t) = u1(t) - u2(t) Then the slope of the transformer leakage inductance current function is: Mode a~f, the voltage difference across the transformer is: Then the transformer leakage inductance current function can be expressed as where i0 is the leakage inductance current value at the starting moment of each mode; Then the average value of the current in the corresponding modal time is: where t a , t b are the start and end times of the corresponding mode, respectively. Then the average value of the phase-a current I a in one period is as follows: Then the average value of the b-phase current I b in one period is: Then, the average value of the c-phase current I c in one period is: By combining the above equations and assuming the coefficients of each unknown number, we can get the equation: Assuming t4-t8 are free variables, we can get: Then the duration of each mode can be expressed as: Among them, x4, x5, x6 are arbitrary real numbers.

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