CN116937941A

CN116937941A - Three-phase single-stage isolated AC/DC converter and control method thereof

Info

Publication number: CN116937941A
Application number: CN202310933608.9A
Authority: CN
Inventors: 林景俊; 刘军; 蓝州
Original assignee: Shenzhen Yingkerui Digital Energy Technology Co ltd
Current assignee: Shenzhen Yingkerui Digital Energy Technology Co ltd
Priority date: 2023-07-27
Filing date: 2023-07-27
Publication date: 2023-10-24
Anticipated expiration: 2043-07-27
Also published as: CN116937941B

Abstract

The invention discloses a three-phase single-stage isolated AC/DC converter and a control method thereof, wherein the three-phase single-stage isolated AC/DC converter comprises an AC/DC rectifying circuit connected with three-phase alternating current and a DC/DC circuit connected with a direct current load, and the AC/DC rectifying circuit comprises a first terminal MA, a second terminal MB, a third terminal MC, a fourth terminal P and a fifth terminal N; the first terminal MA, the second terminal MB, the third terminal MC are configured to output a three-phase ac intermediate value Um, the fourth terminal P is configured to output a three-phase ac maximum value Up, and the fifth terminal N is configured to output a three-phase ac minimum value Un; compared with the prior art, the novel AC/DC converter and the control method thereof provided by the invention have the advantages that the overall efficiency and the power density are improved compared with the traditional AC/DC converter, and the full-range soft switching control is easier to realize.

Description

Three-phase single-stage isolated AC/DC converter and control method thereof

Technical Field

The invention relates to an AC/DC converter, in particular to a three-phase single-stage isolated AC/DC converter and a control method thereof.

Background

The isolated AC/DC converter generally adopts a two-stage structure, the front stage adopts a three-phase PFC converter structure, the three-phase current control task is completed, various power grid distortion problems are solved, the power quality of a power grid is ensured, the rear stage adopts an isolated DC/DC structure, the front stage circuit and the rear stage circuit are connected through a transformer, the electric isolation between a power supply side and a power utilization side is realized, and the stability of output voltage is realized under different load conditions. However, the structure has the defects of low conversion efficiency, high cost and the like due to the two-stage power conversion. In addition, the two-stage construction also requires a bulky bus capacitor to buffer the energy of the front-to-back stage converter, which reduces the reliability of the converter and limits its power density optimization.

Compared with a two-stage structure, the single-stage AC/DC converter structure can improve the overall efficiency and the power density of the converter by reducing the energy conversion level and removing the middle direct current bus capacitor, and is more in line with the design requirements of the current AC/DC power supply equipment.

Disclosure of Invention

Aiming at the problems of low conversion efficiency, high cost and the like of a two-stage AC/DC power converter in the prior art, the invention provides a three-phase single-stage isolated AC/DC converter and a control method thereof.

The technical scheme of the invention is that the three-phase single-stage isolated AC/DC converter comprises an AC/DC rectifying circuit connected with three-phase alternating current and a DC/DC circuit connected with a direct current load, wherein the AC/DC rectifying circuit comprises a first terminal MA, a second terminal MB, a third terminal MC, a fourth terminal P and a fifth terminal N;

the first terminal MA, the second terminal MB, the third terminal MC are configured to output a three-phase ac intermediate value Um, the fourth terminal P is configured to output a three-phase ac maximum value Up, and the fifth terminal N is configured to output a three-phase ac minimum value Un;

the first terminal MA, the second terminal MB and the third terminal MC are respectively connected to a first switch circuit, a second switch circuit and a third switch circuit, and the first switch circuit, the second switch circuit and the third switch circuit each have a first switch branch and a second switch branch, the first switch branch and the second switch branch are connected to a bridge arm midpoint of a bridge circuit in the DC/DC circuit, and the fourth terminal P and the fifth terminal N are respectively connected to an input positive terminal and an input negative terminal of the DC/DC circuit;

The three-phase single-stage isolated AC/DC converter can realize soft switching control by controlling switching tubes in the DC/DC circuit, the first switching branch and the second switching branch.

Further, the DC/DC circuit includes:

a first bridge circuit connected to the first switching leg and the second switching leg of the first, second and third switching circuits and having first and second legs, the first switching leg being connected to a midpoint of the first leg, the second switching leg being connected to a midpoint of the second leg, the fourth terminal P being connected to an input positive terminal of the first bridge circuit, the fifth terminal N being connected to an input negative terminal of the first bridge circuit;

a second bridge circuit connected to the dc load and having a third arm and a fourth arm;

a transformer communicating the first bridge circuit with the second bridge circuit and having a primary winding and a secondary winding, the primary winding having a first end connected to a midpoint of the first leg and a second end connected to a midpoint of the second leg, the secondary winding having a first end connected to a midpoint of the third leg and a second end connected to a midpoint of the fourth leg;

And a resonant circuit connected in series between the transformer and the first bridge circuit.

Further, the AC/DC rectifying circuit adopts a three-phase full-bridge circuit, and has a fifth bridge arm, a sixth bridge arm, and a seventh bridge arm, wherein a connection between a midpoint of the fifth bridge arm and the first switching circuit is used as the first terminal MA, a connection between a midpoint of the sixth bridge arm and the second switching circuit is used as the second terminal MB, and a connection between a midpoint of the seventh bridge arm and the second switching circuit is used as the third terminal MC;

the positive ends of the fifth bridge arm, the sixth bridge arm and the seventh bridge arm are connected with the fourth terminal P, and the negative ends of the fifth bridge arm, the sixth bridge arm and the seventh bridge arm are connected with the fifth terminal N;

the first switching circuit comprises a switching tube S5, a switching tube S6, a switching tube S7 and a switching tube S8, the second switching circuit comprises a switching tube S9, a switching tube S10, a switching tube S11 and a switching tube S12, and the third switching circuit comprises a switching tube S13, a switching tube S14, a switching tube S15 and a switching tube S16;

the switching tube S5 and the switching tube S6 are connected in series to form a first switching branch of the first switching circuit, one end of the first switching branch of the first switching circuit is connected to the midpoint of the fifth bridge arm, the other end of the first switching branch of the first switching circuit is connected to the midpoint of the first bridge arm, the switching tube S7 and the switching tube S8 are connected in series to form a second switching branch of the first switching circuit, and one end of the second switching branch of the first switching circuit is connected to the midpoint of the fifth bridge arm, and the other end of the second switching branch of the first switching circuit is connected to the midpoint of the second bridge arm;

The switching tube S9 and the switching tube S10 are connected in series to form a first switching branch of the second switching circuit, one end of the first switching branch of the second switching circuit is connected to the midpoint of the sixth bridge arm, the other end of the first switching branch of the second switching circuit is connected to the midpoint of the first bridge arm, the switching tube S11 and the switching tube S12 are connected in series to form a second switching branch of the second switching circuit, and one end of the second switching branch of the second switching circuit is connected to the midpoint of the sixth bridge arm, and the other end of the second switching branch of the second switching circuit is connected to the midpoint of the second bridge arm;

the switching tube S13 and the switching tube S14 are connected in series to form a first switching branch of the third switching circuit, one end of the first switching branch of the third switching circuit is connected to the midpoint of the seventh bridge arm, the other end of the first switching branch of the third switching circuit is connected to the midpoint of the first bridge arm, the switching tube S15 and the switching tube S16 are connected in series to form a second switching branch of the third switching circuit, and one end of the second switching branch of the third switching circuit is connected to the midpoint of the seventh bridge arm, and the other end of the second switching branch of the third switching circuit is connected to the midpoint of the second bridge arm.

Further, the switching tubes in the first bridge circuit, the first switching circuit, the second switching circuit and the third switching circuit are formed by connecting two single-phase controllable switching devices in series to form a bidirectional controllable switching device;

The switching tube in the second bridge circuit can adopt any one of a controllable switching device or a diode.

The invention also provides a control method applied to the three-phase single-stage isolated AC/DC converter, which comprises the following steps:

collecting voltages on the first terminal MA, the second terminal MB, and the third terminal MC;

judging the current working condition of the three-phase single-stage isolated AC/DC converter according to the absolute value of the maximum value Up of the three-phase alternating current and the absolute value of the minimum value Un of the three-phase alternating current;

and acquiring a first switching tube and a second switching tube which are conducted with the three-phase alternating current intermediate value Um when the three-phase single-stage isolated AC/DC converter is in the current working condition, and adjusting the conduction states of the first switching tube and the second switching tube according to the current working condition of the three-phase single-stage isolated AC/DC converter.

Further, the three-phase single-stage isolated AC/DC converter has a first working condition and a second working condition;

when the absolute value of the maximum value Up of the three-phase alternating current is larger than the absolute value of the minimum value Un of the three-phase alternating current, the three-phase single-stage isolated AC/DC converter is in a first working condition;

and when the absolute value of the maximum value Up of the three-phase alternating current is smaller than the absolute value of the minimum value Un of the three-phase alternating current, the three-phase single-stage isolated AC/DC converter is in a second working condition.

Further, when the current working condition of the three-phase single-stage isolated AC/DC converter is a first working condition, the three-phase single-stage isolated AC/DC converter includes a first working state, a second working state, a third working state, and a fourth working state;

the first working state is that the upper tube of the first bridge arm and the lower tube of the second bridge arm are conducted together;

the second working state is that the upper tube of the first bridge arm and the second switching tube are conducted together;

the third working state is that the upper tube of the second bridge arm and the lower tube of the first bridge arm are conducted together;

the fourth working state is that the upper tube of the second bridge arm and the first switch tube are conducted together;

or alternatively

The first working state is that the upper tube of the first bridge arm and the second switching tube are conducted together;

the second working state is that the upper tube of the first bridge arm and the lower tube of the second bridge arm are conducted together;

the third working state is that the upper tube of the second bridge arm and the first switch tube are conducted together;

the fourth working state is that the upper tube of the second bridge arm and the lower tube of the first bridge arm are conducted together;

the first switching tube is a switching tube of a first switching branch in a switching circuit connected with a phase voltage corresponding to the three-phase alternating current intermediate value Um;

the second switching tube is a switching tube of a second switching branch in the switching circuit connected with the phase voltage corresponding to the three-phase alternating current intermediate value Um.

Further, when the current working condition of the three-phase single-stage isolated AC/DC converter is the first working condition, the control method further includes:

collecting a controlled control quantity of the three-phase single-stage isolated AC/DC converter, wherein the controlled control quantity is at least one of output voltage, output current, input voltage and input current;

the controlled control quantity and the reference quantity of the three-phase single-stage isolated AC/DC converter are used as the input of a voltage ring control unit, and the output of the control unit is obtained;

taking the product of the output of the voltage loop control unit and the absolute value of the three-phase alternating current maximum value Up as a reference of a current value corresponding to the three-phase alternating current maximum value Up, entering the current loop control unit for operation with the current value corresponding to the three-phase alternating current maximum value Up, and performing frequency modulation and phase shift control on the three-phase single-stage isolated AC/DC converter by using the obtained current loop control unit output;

taking the product of the output of the voltage loop control unit and the absolute value of the three-phase alternating current minimum value Un as a reference of a corresponding current value of the three-phase alternating current minimum value Un, entering the current loop control unit for operation with the corresponding current value of the three-phase alternating current minimum value Un, and carrying out duty ratio adjustment on the three-phase single-stage isolated AC/DC converter by using the obtained current loop control unit output.

Further, when the current working condition of the three-phase single-stage isolated AC/DC converter is the second working condition, the characteristics of the three-phase single-stage isolated AC/DC converter include a fifth working state, a sixth working state, a seventh working state, and an eighth working state;

the fifth working state is that the lower tube of the second bridge arm and the upper tube of the first bridge arm are conducted together;

the sixth working state is that the lower tube of the second bridge arm and the first switch tube are conducted together;

the seventh working state is that the lower tube of the first bridge arm and the upper tube of the second bridge arm are conducted together;

the eighth working state is that the first bridge arm lower tube and the second switch tube are conducted together;

or alternatively

The fifth working state is that the lower tube of the second bridge arm and the first switch tube are conducted together;

the sixth working state is that the lower tube of the second bridge arm and the upper tube of the first bridge arm are conducted together;

Further, when the current working condition of the three-phase single-stage isolated AC/DC converter is the second working condition, the control method further includes:

the controlled control quantity and the reference quantity of the three-phase single-stage isolated AC/DC converter are used as the input of a voltage ring control unit, and the output of the voltage ring control unit is obtained;

taking the product of the output of the voltage loop control unit and the absolute value of the three-phase alternating current minimum value Un as a reference of a current value corresponding to the three-phase alternating current minimum value Un, entering the current loop control unit for operation with the current value corresponding to the three-phase alternating current minimum value Un, and carrying out frequency modulation and phase shift control on the three-phase single-stage isolated AC/DC converter by using the obtained current loop control unit output;

taking the product of the output of the voltage loop control unit and the absolute value of the three-phase alternating current maximum value Up as a reference of a corresponding current value of the three-phase alternating current maximum value Up, entering the current loop control unit for operation with the corresponding current value of the three-phase alternating current maximum value Up, and carrying out duty ratio adjustment on the three-phase single-stage isolated AC/DC converter by using the obtained current loop control unit output.

Compared with the prior art, the invention has at least the following beneficial effects:

the invention provides a novel three-phase single-stage isolated AC/DC converter which can realize soft switching control by controlling switching tubes in a first switching branch and a second switching branch.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments or the description of the prior art will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a schematic topology of a three-phase single-stage isolated AC/DC converter according to a first embodiment of the present invention;

FIG. 2 is a schematic diagram of a three-phase single-stage isolated AC/DC converter according to a second embodiment of the present invention;

FIG. 3 is a schematic diagram of a three-phase single-stage isolated AC/DC converter according to a third embodiment of the present invention;

FIG. 4 is a schematic diagram of a topology of a three-phase single-stage isolated AC/DC converter according to a fourth embodiment of the present invention;

FIG. 5 is a schematic diagram showing the selection of the maximum value, the intermediate value and the minimum value of the three-phase alternating current under the full working period;

FIG. 6 is a schematic diagram showing the selection of the first switching tube and the second switching tube for the second embodiment of the present invention under the full operation period;

FIG. 7 is a timing diagram of the control of the second embodiment of the present invention with the absolute value of the maximum value of the three-phase AC power greater than the absolute value of the minimum value of the three-phase AC power;

FIG. 8 is a schematic diagram of the voltage and current at each component in the 330-360 circuit for three-phase electrical input at the timing of FIG. 7;

FIG. 9 is a timing diagram of the control of the second embodiment of the present invention with the absolute value of the maximum value of the three-phase AC power less than the absolute value of the minimum value of the three-phase AC power;

FIG. 10 is a logic diagram of the present invention for dual loop control with an absolute value of the maximum value of three phase AC power greater than the absolute value of the minimum value of three phase AC power;

FIG. 11 is a logic diagram of a dual loop control in another embodiment of the present invention where the absolute value of the maximum value of the three phase AC power is greater than the absolute value of the minimum value of the three phase AC power;

FIG. 12 is a logic diagram of the present invention for dual loop control with an absolute value of the maximum value of three phase AC less than the absolute value of the minimum value of three phase AC;

FIG. 13 is a logic diagram of a dual loop control in another embodiment of the present invention where the absolute value of the maximum value of the three phase AC power is less than the absolute value of the minimum value of the three phase AC power;

Fig. 14 to 21 are control timing diagrams of phase shift control according to another embodiment of the present invention.

Detailed Description

In order to make the technical problems, technical schemes and beneficial effects to be solved more clear, the invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.

Thus, reference throughout this specification to one feature will be used in order to describe one embodiment of the invention, not to imply that each embodiment of the invention must be in the proper motion. Furthermore, it should be noted that the present specification describes a number of features. Although certain features may be combined together to illustrate a possible system design, such features may be used in other combinations not explicitly described. Thus, unless otherwise indicated, the illustrated combinations are not intended to be limiting.

The principles and structures of the present invention are described in detail below with reference to the drawings and the examples.

The traditional two-stage AC/DC power converter has the problems of low conversion efficiency, high cost and the like, is complex to control, and is difficult to realize full-range soft switching. The invention provides a single-stage isolated AC/DC converter, which can improve the overall efficiency and the power density of the converter by reducing energy conversion level and removing middle direct current bus capacitance compared with a two-stage AC/DC power converter, is provided with a first switch branch and a second switch branch, and can realize full-range soft switch control by adjusting switching tubes on the first switch branch and the second switch branch.

Specifically, the three-phase single-stage isolated AC/DC converter provided by the invention comprises an AC/DC rectifying circuit connected with three-phase alternating current and a DC/DC circuit connected with a direct current load, wherein the AC/DC rectifying circuit comprises a first terminal MA, a second terminal MB, a third terminal MC, a fourth terminal P and a fifth terminal N;

the first terminal MA, the second terminal MB and the third terminal MC are used for outputting a three-phase alternating current intermediate value Um, the fourth terminal P is used for outputting a three-phase alternating current maximum value Up, and the fifth terminal N is used for outputting a three-phase alternating current minimum value Un;

the first terminal MA, the second terminal MB and the third terminal MC are respectively connected to the first switch circuit, the second switch circuit and the third switch circuit, the first switch circuit, the second switch circuit and the third switch circuit are respectively provided with a first switch branch and a second switch branch, the first switch branch and the second switch branch are connected to the middle point of a bridge arm of a bridge circuit in the DC/DC circuit, and the fourth terminal P and the fifth terminal N are respectively connected to the positive input end and the negative input end of the DC/DC circuit;

the three-phase single-stage isolated AC/DC converter can realize soft switching control by controlling the DC/DC circuit, the switching tubes in the first switching branch and the second switching branch.

Referring to fig. 1, which is a schematic topology diagram of a three-phase single-stage isolated AC/DC converter according to a first embodiment of the present invention, the AC/DC rectifying circuit is a three-phase full-bridge circuit composed of a diode D1, a diode D2, a diode D3, a diode D4, a diode D5, and a diode D6, three-phase alternating currents are respectively connected to three bridge arms of the three-phase full-bridge circuit, and the DC-DC circuit is a DC/DC circuit of a rear stage;

the three-phase full-bridge circuit is provided with five connecting ends, namely a first terminal MA, a second terminal MB, a third terminal MC, a fourth terminal P and a fifth terminal N, wherein the first terminal MA, the second terminal MB and the third terminal MC are respectively connected with a switching circuit, for example, a switching tube S5, a switching tube S6, a switching tube S7 and a switching tube S8 form a first switching circuit, and the first switching circuit is connected to the first terminal MA;

the switching tube S9, the switching tube S10, the switching tube S11 and the switching tube S12 form a second switching circuit, and the second switching circuit is connected to the second terminal MB;

the switching tube S13, the switching tube S14, the switching tube S15, and the switching tube S16 constitute a third switching circuit, which is connected to the third terminal MC.

Here, since the voltages of the three-phase ac power vary at all times, the voltages at the first terminal MA, the second terminal MB, and the third terminal MC also vary, and when the first terminal MA outputs an intermediate voltage, the switching transistors S5 to S8 operate;

When the second terminal MB outputs the intermediate voltage, the switching transistors S9 to S12 operate;

when the third terminal MC outputs the intermediate voltage, the switching transistors S13 to S16 operate;

each switching circuit has a first switching leg connected to a first input terminal in the DC/DC circuit, and a second switching leg connected to a second input terminal in the DC/DC circuit, such as switching tube S5 and switching tube S6 being first switching legs of the first switching circuit, switching tube S7 and switching tube S8 being second switching legs of the first switching circuit, switching tube S9 and switching tube S10 being first switching legs of the second switching circuit, switching tube S11 and switching tube S12 being second switching legs of the second switching circuit, switching tube S13 and switching tube S14 being first switching legs of the third switching circuit, and switching tube S15 and switching tube S16 being second switching legs of the third switching circuit.

According to the invention, different three-phase alternating current conditions are matched, the on-off states of the switching tubes in the DC/DC circuit, the first switching branch and the second switching branch are regulated, and soft switching control in a full range can be realized.

Referring to fig. 2, a topology diagram of a three-phase single-stage isolated AC/DC converter according to a second embodiment of the present invention is shown, in which the DC/DC circuit includes:

A first bridge circuit connected to the first switching leg and the second switching leg of the first, second, and third switching circuits and having a first leg and a second leg, the first switching leg connected to a midpoint of the first leg, the second switching leg connected to a midpoint of the second leg, a fourth terminal P connected to an input positive terminal of the first bridge circuit, and a fifth terminal N connected to an input negative terminal of the first bridge circuit;

The first bridge circuit consists of a switching tube S1, a switching tube S2, a switching tube S3 and a switching tube S4, wherein the switching tube S1 and the switching tube S3 form a first bridge arm, and the switching tube S2 and the switching tube S4 form a second bridge arm;

The second bridge circuit is composed of a switching tube D7, a switching tube D8, a switching tube D9 and a switching tube D10, wherein the switching tube D7 and the switching tube D9 form a third bridge arm, and the switching tube D8 and the switching tube D10 form a fourth bridge arm.

The transformer is used for communicating the first bridge circuit with the second bridge circuit and is used for playing an isolating role, the first bridge circuit is used for converting direct current output by the AC/DC rectifying circuit into alternating current and providing the alternating current for a primary winding of the transformer, and the second bridge circuit is used for obtaining alternating current output by a secondary winding of the transformer and converting the alternating current into direct current and providing the direct current for a bus capacitor (capacitor Co) and a direct current load (resistor Ro) of a later stage. The resonant circuit is composed of a capacitor Cr, an inductor Lr and an inductor Lm and is used for providing resonant current for the circuit so as to control soft switching of the circuit.

Further, in this embodiment, the AC/DC rectifying circuit adopts a three-phase full-bridge circuit, and has a fifth bridge arm, a sixth bridge arm, and a seventh bridge arm, where a connection between the fifth bridge arm and the first switching circuit is used as the first terminal MA, a connection between the sixth bridge arm and the second switching circuit is used as the second terminal MB, and a connection between the seventh bridge arm and the second switching circuit is used as the third terminal MC;

The fifth bridge arm consists of a diode D1 and a diode D2, the sixth bridge arm consists of a diode D3 and a diode D4, and the seventh bridge arm consists of a diode D5 and a diode D6;

the switching tube S9 and the switching tube S10 are connected in series to form a first switching branch of the second switching circuit, one end of the first switching branch of the second switching circuit is connected to the midpoint of the sixth bridge arm, the other end of the first switching branch is connected to the midpoint of the first bridge arm, the switching tube S11 and the switching tube S12 are connected in series to form a second switching branch of the second switching circuit, and one end of the second switching branch of the second switching circuit is connected to the midpoint of the sixth bridge arm, and the other end of the second switching branch of the second switching circuit is connected to the midpoint of the second bridge arm;

The switching tube S13 and the switching tube S14 are connected in series to form a first switching branch of the third switching circuit, one end of the first switching branch of the third switching circuit is connected to the midpoint of the seventh bridge arm, the other end of the first switching branch is connected to the midpoint of the first bridge arm, the switching tube S15 and the switching tube S16 are connected in series to form a second switching branch of the third switching circuit, and one end of the second switching branch of the third switching circuit is connected to the midpoint of the seventh bridge arm, and the other end of the second switching branch of the third switching circuit is connected to the midpoint of the second bridge arm.

According to the invention, the first switching branch and the second switching branch are arranged and are respectively connected to the two input ends of the DC/DC circuit, so that the three-phase alternating current output by the first terminal MA, the second terminal MB and the third terminal MC can be distributed, the voltage output to the DC/DC circuit is regulated, and the condition for opening the zero voltage is provided.

The circuit shown in fig. 2 is a preferred embodiment of the present invention, and in other embodiments of the present invention, the three-phase single-stage isolated AC/DC converter may be designed to have a phase-shifting full-bridge or DAB structure, so as to achieve the same control effect.

Referring to fig. 3, a topology diagram of a three-phase single-stage isolated AC/DC converter according to a third embodiment of the present invention is shown, in which a resonant circuit is split into an inductor Lr and an inductor Lf, wherein one end of the inductor Lr is connected between a first end of a primary winding of a transformer and a midpoint of a first bridge arm, and the inductor Lf is connected between a second bridge circuit and a bus capacitor (capacitor Co), so that the circuit forms a phase-shifting full bridge structure;

In addition, referring to fig. 4, in the fourth embodiment of the present invention, a DAB structure may be further adopted, in which the inductor Lr and the capacitor Cr are connected between the first end of the primary winding of the transformer and the midpoint of the first bridge arm, and all the switching tubes in the second bridge circuit adopt MOS tubes for synchronous rectification.

Furthermore, for the first bridge circuit, the second bridge circuit, the first switch circuit, the second switch circuit and the switch tube in the third switch circuit provided by the invention, two single-phase controllable switch devices are connected in series to form a bidirectional controllable switch device;

likewise, the switching tubes in the second bridge circuit may be either controllable switching devices or diodes.

Furthermore, the invention also provides a control method applied to the three-phase single-stage isolated AC/DC converter, which comprises the following steps:

the method comprises the steps of obtaining a first switching tube and a second switching tube which are conducted with a three-phase alternating current intermediate value Um when the three-phase single-stage isolated AC/DC converter is in a current working condition, and adjusting the conduction states of the first switching tube and the second switching tube according to the current working condition of the three-phase single-stage isolated AC/DC converter.

The voltage collection at the first terminal MA, the second terminal MB, and the third terminal MC is used to obtain the maximum value Up, the intermediate value Um, and the minimum value Un of the three-phase ac at this time, and since the voltage of each phase of the three-phase ac changes, the current maximum value Up, the intermediate value Um, and the minimum value Un of the three-phase ac need to be sampled in real time.

As shown in fig. 5, for one operation period (360 degrees) of the three-phase alternating current, the three-phase alternating current can be split into 12 areas, each area is 30 degrees, and under each area, the maximum value Up, the intermediate value Um and the minimum value Un of the three-phase alternating current are all different. As shown in fig. 1, up represents a maximum value of the three-phase alternating current, um represents an intermediate value of the three-phase alternating current, un represents a minimum value of the three-phase alternating current, and as the three-phase alternating current operates, the selection of Up, um, un varies.

The control idea of the invention is that the current working condition of the three-phase single-stage isolated AC/DC converter is determined according to the absolute value of the maximum value Up of the three-phase alternating current and the absolute value of the minimum value Un of the three-phase alternating current, so that corresponding control is implemented.

The three-phase single-stage isolated AC/DC converter has a first working condition and a second working condition, and is in the first working condition when the absolute value of the maximum value Up of the three-phase alternating current is larger than the absolute value of the minimum value Un of the three-phase alternating current;

when the absolute value of the maximum value Up of the three-phase alternating current is smaller than the absolute value of the minimum value Un of the three-phase alternating current, the three-phase single-stage isolated AC/DC converter is in the second working condition.

After the current working condition of the three-phase single-stage isolated AC/DC converter is determined, a first switching tube and a second switching tube which conduct the intermediate value of three-phase alternating current under the current working condition are required to be obtained.

The selection process of the first switching tube and the second switching tube is that the current working condition of the three-phase single-stage isolated AC/DC converter is firstly obtained according to the maximum value Up and the minimum value Un of three-phase alternating current, then the region (12 regions divided by the previous operation period) corresponding to the current working condition is determined, and then the switching tube connected with the maximum value Up and the minimum value Un of three-phase alternating current is obtained according to the region.

Referring to fig. 6, according to the above method, the first switching tube and the second switching tube are selected as follows:

when the three-phase alternating current works at 330-30 degrees, smp corresponds to a switching tube S7 and a switching tube S8, and Smn corresponds to a switching tube S5 and a switching tube S6;

when the three-phase alternating current works at 30-90 degrees, smp corresponds to a switching tube S15 and a switching tube S16, and Smn corresponds to a switching tube S13 and a switching tube S14;

when the three-phase alternating current works at 90-150 degrees, smp corresponds to a switching tube S11 and a switching tube S12, and Smn corresponds to a switching tube S9 and a switching tube S10;

when the three-phase alternating current works at 150-210 degrees, smp corresponds to a switching tube S7 and a switching tube S8, and Smn corresponds to a switching tube S5 and a switching tube S6;

when the three-phase alternating current works at 210-270 degrees, smp corresponds to a switching tube S15 and a switching tube S16, and Smn corresponds to a switching tube S13 and a switching tube S14;

when the three-phase alternating current works at 270-330 degrees, smp corresponds to a switching tube S11 and a switching tube S12, and Smn corresponds to a switching tube S9 and a switching tube S10;

here, smp is a first switching tube, and Smn is a second switching tube.

The first working condition is that the absolute value of the maximum value Up of the three-phase alternating current is larger than that of the minimum value Un of the three-phase alternating current, please refer to FIG. 5, the requirements are met at 90 degrees to 120 degrees, 210 degrees to 240 degrees and 330 degrees to 360 degrees, wherein under the condition of 90 degrees to 120 degrees, the first switching tube is selected as a switching tube S11 and a switching tube S12, and the second switching tube is selected as a switching tube S9 and a switching tube S10;

Under the condition of 210-240 degrees, the first switching tube is selected as a switching tube S15 and a switching tube S16, and the second switching tube is selected as a switching tube S13 and a switching tube S14;

under the condition of 330-360 degrees, the first switching tube is selected as a switching tube S7 and a switching tube S8, and the second switching tube is selected as a switching tube S5 and a switching tube S6;

under the first working condition, the control thinking that the three-phase alternating current is in 90 degrees to 120 degrees, 210 degrees to 240 degrees and 330 degrees to 360 degrees is the same, the control thinking of the invention is illustrated by taking 330 degrees to 360 degrees as an example, in the case, the first switching tube is selected as a switching tube S7 and a switching tube S8, the second switching tube is selected as a switching tube S5 and a switching tube S6, please refer to fig. 7 and 8, and the three-phase monopole isolation type AC/DC converter comprises a first working state, a second working state, a third working state and a fourth working state;

Or alternatively

Specifically, the working process of the four stages is as follows:

first stage [ t0-t1]: at time t0, the switching tube S1 and the switching tube S4 are turned on, the input voltage of the resonant circuit is uPN, the inductance Lr and the capacitance Cr resonate, and the resonant current iLr changes from negative to positive. At this stage, the switching tube S8 is turned on at the same time, and since the switching tube S7 is not turned on and the body diode direction is the same as the voltage uYN direction, turning on the switching tube S8 at this stage can realize zero current turn-on. At the time t=dts, the switching tube S4 is turned off, the forward resonant current iLr charges the junction capacitance of the switching tube S4, simultaneously discharges the junction capacitance of the switching tube S7 until the voltage drop of the junction capacitance is 0, and simultaneously the body diode of the switching tube S7 is turned on to provide a zero-voltage on condition for the switching tube S7.

Second stage [ t1-t2]: at time t2, the switching tube S7 is turned on under the condition of zero voltage, the input voltage of the resonant circuit becomes uPY, the inductor Lr and the capacitor Cr continue to resonate, and if the resonant current iLr is equal to the exciting current iLm, the resonant current becomes Lr, lm and Cr three-element resonance. At the time t=ts/2, the switching tube S1, the switching tube S7 and the switching tube S8 are turned off simultaneously, at this time, the resonant current iLr is still positive, the junction capacitances of the switching tube S1, the switching tube S7 and the switching tube S8 are charged, and at the same time, the junction capacitances of the switching tube S2 and the switching tube S3 are discharged until the capacitance voltage drops to 0, so that a zero-voltage on condition is provided for the switching tube S2 and the switching tube S3.

The third stage [ t2-t3] and the fourth stage [ t3-t4] are exactly symmetrical with the input voltages of the first stage [ t0-t1] and the second stage [ t1-t2] (the input voltages become-uPN and-uPm), the waveform of the resonant current iLr is also positively symmetrical, the resonant current iLr is positively changed to negatively, the working process is similar, and the description is not repeated here.

Referring to fig. 10 and 11, under the first working condition, the control method of the three-phase single-stage isolated AC/DC converter further includes:

collecting a controlled control quantity of a three-phase single-stage isolated AC/DC converter, wherein the controlled control quantity is at least one of output voltage, output current, input voltage and input current;

taking the product of the output of the voltage loop control unit and the absolute value of the three-phase alternating current minimum value Un as a reference of the corresponding current value of the three-phase alternating current minimum value Un, enabling the current value corresponding to the three-phase alternating current minimum value Un to enter the current loop control unit for operation, and carrying out duty ratio adjustment on the three-phase single-stage isolated AC/DC converter by using the obtained current loop control unit output.

Further, the second working condition is that the absolute value of the maximum value Up of the three-phase alternating current is smaller than the absolute value of the minimum value Un of the three-phase alternating current, please refer to fig. 5, the requirements are met at 0 ° to 30 °, 120 ° to 150 °, 240 ° to 270 °, wherein under the condition of 0 ° to 30 °, the first switching tube is selected as a switching tube S7 and a switching tube S8, and the second switching tube is selected as a switching tube S5 and a switching tube S6;

Under the condition of 120-150 degrees, the first switching tube is selected as a switching tube S11 and a switching tube S12, and the second switching tube is selected as a switching tube S9 and a switching tube S10;

under the condition of 240-270 degrees, the first switching tube is selected as a switching tube S15 and a switching tube S16, and the second switching tube is selected as a switching tube S13 and a switching tube S14;

under the first working condition, the control thinking that the three-phase alternating current is in 0-30 degrees, 120-150 degrees and 240-270 degrees is the same, the control thinking of the invention is illustrated by taking 0-30 degrees as an example, in the case, the first switching tube is selected as a switching tube S7 and a switching tube S8, the second switching tube is selected as a switching tube S5 and a switching tube S6, please refer to FIG. 9, and the three-phase monopole isolated AC/DC converter is characterized by comprising a fifth working state, a sixth working state, a seventh working state and an eighth working state;

Or alternatively

The working flow under the second working condition is similar to that of the first working condition, only the lower arm switch of the second bridge arm is exchanged with the upper arm switch of the first bridge arm, the upper arm switch of the second bridge arm is exchanged with the lower arm switch of the second bridge arm, and the rest working flows are basically similar and are not repeated here.

Referring to fig. 12 and 13, under the second working condition, the control method of the three-phase single-stage isolated AC/DC converter further includes:

The controlled control quantity and the reference quantity of the three-phase single-stage isolated AC/DC converter are used as the input of the voltage ring control unit, and the output of the voltage ring control unit is obtained;

taking the product of the output of the voltage loop control unit and the absolute value of the three-phase alternating current minimum value Un as a reference of a current value corresponding to the three-phase alternating current minimum value Un, enabling the current value corresponding to the three-phase alternating current minimum value Un to enter the current loop control unit for operation, and carrying out frequency modulation and phase shift control on the three-phase single-stage isolated AC/DC converter by using the obtained current loop control unit output;

taking the product of the output of the voltage loop control unit and the absolute value of the three-phase alternating current maximum value Up as a reference of the corresponding current value of the three-phase alternating current maximum value Up, enabling the current value corresponding to the three-phase alternating current maximum value Up to enter the current loop control unit for operation, and carrying out duty ratio adjustment on the three-phase single-stage isolated AC/DC converter by using the obtained current loop control unit output.

Further, the present invention also provides a phase shift control method in another embodiment, which has two working conditions, and in the first working condition, the absolute value of the maximum value Up of the three-phase alternating current is greater than the absolute value of the minimum value Un of the three-phase alternating current, and in this case, four working states are shown in fig. 14 to 17, where the four states are respectively:

The first working state [ t 1-t 2] is that the upper pipe S1 of the first bridge arm is conducted with the lower pipe S4 of the second bridge arm, and UAB voltage is Vpn.

The second working state [ t 2-t 3] is that the upper tube S1 of the first bridge arm is conducted with the second switch tube Smp, and UAB voltage is Vpm.

In the third working state [ t 4-t 5 ]. The upper tube S2 of the second bridge arm is conducted with the lower tube S3 of the first bridge arm, and UAB voltage is-Vpn.

And in the fourth working state [ t 0-t 1], the upper tube S2 of the second bridge arm is conducted with the first switch tube Smn, and the UAB voltage is Vmn.

The phase-shifting control and the input power correction can be carried out by inserting different working states into the three-phase single-stage isolated AC/DC converter;

in the second working condition, the absolute value of the maximum value Up of the three-phase alternating current is smaller than the absolute value of the minimum value Un of the three-phase alternating current, and in this case, four working states are shown in fig. 18 to 21, wherein the four states are respectively:

the first working state [ t 1-t 2] is that the second bridge arm lower pipe S4 is conducted with the first bridge arm upper pipe S1, and UAB voltage is Vpn.

In the second working state [ t 2-t 3 ]. The second bridge arm lower tube S4 is conducted with the second switch tube Smn, and UAB voltage is Vmn.

The third working state [ t 4-t 5] is that the first bridge arm lower pipe S3 is conducted with the first bridge arm lower pipe S2, and UAB voltage is-Vpn.

The fourth working state [ t 0-t 1 ]. The first bridge arm lower tube S3 is conducted with the first switch tube Smp, and UAB voltage is Vpm.

The phase-shifting control and the input power correction can be carried out by inserting different working states into the three-phase single-stage isolated AC/DC converter.

In summary, compared with the prior art, the novel three-phase single-stage isolated AC/DC converter provided by the invention can realize soft switching control in a full range by controlling the switching tubes in the first switching branch and the second switching branch, and in addition, compared with the traditional two-stage AC/DC converter, the novel three-phase single-stage isolated AC/DC converter provided by the invention can reduce energy conversion level, improve overall efficiency and power density of the converter, and better meet the design requirements of current AC/DC power supply equipment.

The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.

Claims

1. The three-phase single-stage isolated AC/DC converter comprises an AC/DC rectifying circuit connected with three-phase alternating current and a DC/DC circuit connected with a direct current load, and is characterized in that the AC/DC rectifying circuit comprises a first terminal MA, a second terminal MB, a third terminal MC, a fourth terminal P and a fifth terminal N;

2. The three-phase single-stage isolated AC/DC converter of claim 1, wherein the DC/DC circuit comprises:

3. The three-phase single-stage isolated AC/DC converter according to claim 2, wherein the AC/DC rectifying circuit adopts a three-phase full-bridge circuit and has a fifth bridge arm, a sixth bridge arm, and a seventh bridge arm, and a connection point of a midpoint of the fifth bridge arm and the first switching circuit is used as the first terminal MA, a connection point of a midpoint of the sixth bridge arm and the second switching circuit is used as the second terminal MB, and a connection point of a midpoint of the seventh bridge arm and the second switching circuit is used as the third terminal MC;

4. The three-phase single-stage isolated AC/DC converter of claim 2 wherein the switching tubes in the first bridge circuit, the first switching circuit, the second switching circuit, and the third switching circuit are connected in series by two single-phase controllable switching devices to form a bidirectional controllable switching device;

5. A control method applied to the three-phase single-stage isolated AC/DC converter according to any one of claims 1 to 4, comprising:

6. The control method of claim 5, wherein the three-phase single-stage isolated AC/DC converter has a first operating mode and a second operating mode;

7. The control method according to claim 6, wherein when the current operating condition of the three-phase single-stage isolated AC/DC converter is a first operating condition, the three-phase single-stage isolated AC/DC converter includes a first operating state, a second operating state, a third operating state, and a fourth operating state;

or alternatively

8. The control method according to claim 7, wherein when the current operation condition of the three-phase single-stage isolated AC/DC converter is the first operation condition, the control method further comprises:

9. The control method according to claim 6, wherein when the current operating condition of the three-phase single-stage isolated AC/DC converter is the second operating condition, the three-phase single-stage isolated AC/DC converter is characterized by comprising a fifth operating state, a sixth operating state, a seventh operating state, and an eighth operating state;

or alternatively

10. The control method according to claim 9, wherein when the current operation condition of the three-phase single-stage isolated AC/DC converter is the second operation condition, the control method further comprises: