CN111726022B

CN111726022B - Nine-bridge-arm single-stage isolated three-phase bidirectional AC/DC converter

Info

Publication number: CN111726022B
Application number: CN202010176017.8A
Authority: CN
Inventors: 顾玲; 常松
Original assignee: Nanjing University of Science and Technology
Current assignee: Nanjing University of Science and Technology
Priority date: 2020-03-13
Filing date: 2020-03-13
Publication date: 2022-09-06
Anticipated expiration: 2040-03-13
Also published as: CN111726022A

Abstract

The invention discloses a nine-leg single-stage isolation three-phase bidirectional AC/DC converter which comprises an AC side filter inductor, an AC side three-phase leg, an isolation transformer, a DC side three-phase leg and a DC side filter capacitor, wherein the AC side filter inductor comprises an A-phase inductor, a B-phase inductor and a C-phase inductor; the alternating-current side three-phase bridge arm comprises six bridge arms, and each bridge arm is formed by connecting two switching tubes in series; the isolation transformer comprises an A-phase transformer, a B-phase transformer and a C-phase transformer; the direct-current side three-phase bridge arm comprises three bridge arms, and each bridge arm is formed by connecting two switching tubes in series. The invention reduces the number of power devices, reduces the switching loss of the switching tube and improves the conversion efficiency of electric energy while realizing the electrical isolation between the load and the power grid.

Description

Nine-bridge-arm single-stage isolated three-phase bidirectional AC/DC converter

Technical Field

The invention relates to an AC/DC converter, in particular to a nine-bridge-arm single-stage isolated three-phase bidirectional AC/DC converter.

Background

Renewable energy sources such as solar energy, wind energy and the like are easily affected by natural conditions and are unstable, and an interface AC/DC converter needs to be arranged between a direct current micro-grid and an alternating current grid to realize energy bidirectional transfer and regulate and control the energy balance of the whole micro-grid. In high power applications, a three-phase bidirectional AC/DC converter is typically used.

The three-phase bidirectional AC/DC converter usually adopts a three-phase voltage type PWM rectifier, and because the voltage type bidirectional converter has a boosting characteristic in the rectifying process, namely the output voltage of a direct current side is higher than the voltage peak value of an alternating current side, and the converter does not realize electrical isolation, certain potential safety hazards exist. Some schemes realize voltage matching and safe isolation of an alternating current side and a direct current side by adding an isolation transformer, for example, adding a power frequency isolation transformer at the alternating current side, or adopting a topological structure of a two-stage converter and adding a high-frequency isolation bidirectional DC/DC converter at the later stage. However, the first method described above has a high requirement for the working space of the converter due to the large size of the power frequency transformer; the second approach results in a reduction in converter efficiency and power density due to the use of two-stage power conversion and large coupling capacitance. In other schemes, electrical isolation is realized through an isolated three-phase AC/DC converter, but the number of switching tubes is large, so that the conversion efficiency and the power density of electric energy are reduced.

Disclosure of Invention

The invention aims to provide a nine-leg single-stage isolated three-phase bidirectional AC/DC converter.

The technical solution for realizing the purpose of the invention is as follows: a nine-leg single-stage isolation three-phase bidirectional AC/DC converter comprises an alternating current side filter inductor, an alternating current side three-phase leg, an isolation transformer, a direct current side three-phase leg and a direct current side filter capacitor, wherein the alternating current side filter inductor comprises an A-phase inductor, a B-phase inductor and a C-phase inductor; the alternating-current side three-phase bridge arm comprises six bridge arms, each bridge arm is formed by connecting two switching tubes in series, the first bridge arm is formed by a first switching tube and a second switching tube, the second bridge arm is formed by a third switching tube and a fourth switching tube, the third bridge arm is formed by a fifth switching tube and a sixth switching tube, the fourth bridge arm is formed by a seventh switching tube and an eighth switching tube, the fifth bridge arm is formed by a ninth switching tube and a tenth switching tube, and the sixth bridge arm is formed by an eleventh switching tube and a twelfth switching tube; the isolation transformer comprises an A-phase transformer, a B-phase transformer and a C-phase transformer; the direct-current side three-phase bridge arm comprises three bridge arms, each bridge arm is formed by connecting two switching tubes in series, wherein the seventh bridge arm is formed by a thirteenth switching tube and a fourteenth switching tube, the eighth bridge arm is formed by a fifteenth switching tube and a sixteenth switching tube, and the ninth bridge arm is formed by a seventeenth switching tube and an eighteenth switching tube;

the emitter of the first switch tube is connected with the collector of the second switch tube, and the connection point is connected with one end of the A-phase inductor; the emitter of the third switching tube is connected with the collector of the fourth switching tube, and the connection point is connected with one end of the B-phase inductor; an emitter of the fifth switching tube is connected with a collector of the sixth switching tube, and a connection point is connected with one end of the C-phase inductor; the other ends of the A-phase inductor, the B-phase inductor and the C-phase inductor are respectively connected with an alternating-current side power supply or a three-phase load; an emitter of the seventh switching tube is connected with a collector of the eighth switching tube, a connection point is used as a first common port, an emitter of the ninth switching tube is connected with a collector of the tenth switching tube, the connection point is used as a second common port, an emitter of the eleventh switching tube is connected with a collector of the twelfth switching tube, and the connection point is used as a third common port; the collector electrode of the first switching tube is connected with the collector electrode of the third switching tube, the collector electrode of the fifth switching tube, the collector electrode of the seventh switching tube, the collector electrode of the ninth switching tube and the collector electrode of the eleventh switching tube; an emitter of the second switching tube is connected with an emitter of the fourth switching tube, an emitter of the sixth switching tube, an emitter of the eighth switching tube, an emitter of the tenth switching tube and an emitter of the twelfth switching tube;

an emitter of the thirteenth switching tube is connected with a collector of the fourteenth switching tube, and a connection point is used as a fourth common port; an emitter of the fifteenth switching tube is connected with a collector of the sixteenth switching tube, and a connection point is used as a fifth common port; an emitter of the seventeenth switching tube is connected with a collector of the eighteenth switching tube, and a connection point is used as a sixth common port; a collector electrode of the thirteenth switching tube is connected with a collector electrode of the fifteenth switching tube and a collector electrode of the seventeenth switching tube, and a connection point is connected with the positive end of the direct-current side filter capacitor; an emitting electrode of the fourteenth switching tube is connected with an emitting electrode of the sixteenth switching tube and an emitting electrode of the eighteenth switching tube, and a connection point is connected with the negative end of the direct-current side filter capacitor;

the primary windings of the three transformers are respectively connected with the first public port, the second public port and the third public port, and the secondary windings are respectively connected with the fourth public port, the fifth public port and the sixth public port.

Furthermore, the primary winding and the secondary winding of the transformer have two connection modes: star connection and delta connection, the isolation transformer has four combination modes: a primary side star-secondary side delta connection, a primary side star-secondary side star connection, a primary side triangle-secondary side star connection, and a primary side triangle-secondary side delta connection.

Furthermore, when the isolation transformer is connected in a primary side star-secondary side delta connection mode, the first common port is connected with the dotted terminal of the primary side winding of the phase-A transformer, the second common port is connected with the dotted terminal of the primary side winding of the phase-B transformer, and the third common port is connected with the dotted terminal of the primary side winding of the phase-C transformer; the different-name end of the primary winding of the phase-A transformer is connected with the different-name end of the primary winding of the phase-B transformer and the different-name end of the primary winding of the phase-C transformer; the fourth public port is connected with a connection point of a homonymous end of the secondary winding of the phase-A transformer and a heteronymous end of the secondary winding of the phase-B transformer, the fifth public port is connected with a connection point of a homonymous end of the secondary winding of the phase-B transformer and a heteronymous end of the secondary winding of the phase-C transformer, and the sixth public port is connected with a connection point of a homonymous end of the secondary winding of the phase-C transformer and a heteronymous end of the secondary winding of the phase-A transformer.

Furthermore, when the isolation transformer is connected in a primary side star-secondary side star connection mode, the first common port is connected with the dotted terminal of the primary side winding of the phase-A transformer, the second common port is connected with the dotted terminal of the primary side winding of the phase-B transformer, and the third common port is connected with the dotted terminal of the primary side winding of the phase-C transformer; the different-name end of the primary winding of the phase-A transformer is connected with the different-name end of the primary winding of the phase-B transformer and the different-name end of the primary winding of the phase-C transformer; the fourth public port is connected with the homonymous end of the secondary winding of the phase-A transformer, the fifth public port is connected with the homonymous end of the secondary winding of the phase-B transformer, and the sixth public port is connected with the homonymous end of the secondary winding of the phase-C transformer; and the different-name end of the secondary winding of the phase-A transformer is connected with the different-name end of the secondary winding of the phase-B transformer and the different-name end of the secondary winding of the phase-C transformer.

Furthermore, when the isolation transformer is connected in a primary side triangle-secondary side star connection mode, the first common port is connected with a connection point of a homonymous end of the primary side winding of the phase-A transformer and a synonym end of the primary side winding of the phase-B transformer, the second common port is connected with a connection point of a homonymous end of the primary side winding of the phase-B transformer and a synonym end of the primary side winding of the phase-C transformer, and the third common port is connected with a connection point of a homonymous end of the primary side winding of the phase-C transformer and a synonym end of the primary side winding of the phase-A transformer; the fourth public port is connected with the homonymous end of the secondary winding of the phase-A transformer, the fifth public port is connected with the homonymous end of the secondary winding of the phase-B transformer, and the sixth public port is connected with the homonymous end of the secondary winding of the phase-C transformer; and the different-name end of the secondary winding of the phase-A transformer is connected with the different-name end of the secondary winding of the phase-B transformer and the different-name end of the secondary winding of the phase-C transformer.

Furthermore, when the isolation transformer is connected in a primary side triangle-secondary side triangle manner, the first common port is connected with a connection point of a homonymous end of the primary side winding of the phase-A transformer and a synonym end of the primary side winding of the phase-B transformer, the second common port is connected with a connection point of a homonymous end of the primary side winding of the phase-B transformer and a synonym end of the primary side winding of the phase-C transformer, and the third common port is connected with a connection point of a homonymous end of the primary side winding of the phase-C transformer and a synonym end of the primary side winding of the phase-A transformer; the fourth public port is connected with a connection point of a homonymous end of the secondary winding of the phase-A transformer and a heteronymous end of the secondary winding of the phase-B transformer, the fifth public port is connected with a connection point of a homonymous end of the secondary winding of the phase-B transformer and a heteronymous end of the secondary winding of the phase-C transformer, and the sixth public port is connected with a connection point of a homonymous end of the secondary winding of the phase-C transformer and a heteronymous end of the secondary winding of the phase-A transformer.

Furthermore, all the switch tubes are formed by connecting a one-way switch tube and a diode in parallel in an anti-phase mode.

Further, the diode is an IGBT reverse diode or a MOSFET parasitic diode, and the unidirectional switch tube is a triode, an IGBT or a MOSFET.

The SVPWM modulation method based on the nine-leg single-stage isolated three-phase bidirectional AC/DC converter comprises the following steps:

step 1, defining a switch state;

by using

Of the format defining a switch state, wherein S _a 、S _b 、S _c Respectively represent six switching tubes Q in three-phase bridge arms at alternating current side _a1 、Q _a2 、Q _a3 、Q _a4 、Q _a5 、Q _a6 When the switch tube Q is in the on-off state _a1 Definition of S at conduction _a Is 1, when the switch tube Q _a2 Definition of S at conduction _a Is 0; when the switch tube Q _a3 Define S when conducting _b Is 1, when the switch tube Q _a4 Define S when conducting _b Is 0; when the switch tube Q _a5 Define S when conducting _c Is 1, when the switch tube Q _a6 Define S when conducting _c Is 0. S _d 、S _e 、S _f Respectively represent six switching tubes Q in three-phase bridge arm at alternating current side _p1 、Q _p2 、Q _p3 、Q _p4 、Q _p5 、Q _p6 Switch (2)State when the switch tube Q is turned on _p1 Define S when conducting _d Is 1, when the switch tube Q _p2 Definition of S at conduction _d Is-1, when the switch tube Q _p1 、Q _p2 All define S when not conducting _d Is 0; when the switch tube Q _p3 Define S when conducting _e Is 1, when the switch tube Q _p4 Define S when conducting _e Is-1, when the switch tube Q _p3 、Q _p4 All define S when not conducting _e Is 0; when the switch tube Q _p5 Definition of S at conduction _f Is 1, when the switch tube Q _p6 Define S when conducting _f Is-1, when the switch tube Q _p5 、Q _p6 All define S when not conducting _f Is 0. S _x 、S _y 、S _z Respectively represent six switching tubes Q in a direct-current side three-phase bridge arm _s1 、Q _s2 、Q _s3 、Q _s4 、Q _s5 、Q _s6 When the switch tube Q is in a switched state _s1 Define S when conducting _x Is 1, when the switch tube Q _s2 Definition of S at conduction _x Is-1, when the switch tube Q _s1 、Q _s2 All define S when not conducting _x Is 0; when the switch tube Q _s3 Define S when conducting _y Is 1, when the switch tube Q _s4 Define S when conducting _y Is-1, when the switch tube Q _s3 、Q _s4 All define S when not conducting _y Is 0; when the switch tube Q _s5 Define S when conducting _z Is 1, when the switch tube Q _s6 Define S when conducting _z Is-1, when the switch tube Q _s5 、Q _s6 All define S when not conducting _z Is 0. A. B, C respectively represents the voltage direction at two ends of A, B, C three-phase transformer, when the dotted terminal of the voltage at two ends of the A-phase transformer is positive, A is positive, when the dotted terminal of the voltage at two ends of the A-phase transformer is negative, A is negative, when the voltage at two ends of the A-phase transformer is zero, A is 0, when the dotted terminal of the voltage at two ends of the B-phase transformer is positive, B is negative, when the voltage at two ends of the B-phase transformer is zero, B is 0, when the dotted terminal of the voltage at two ends of the C-phase transformer is positive, C is negative, when the dotted terminal of the voltage at two ends of the C-phase transformer is positive, C is positive, and when the voltage at two ends of the C-phase transformer is negative, C is 0;

step 2, dividing sectors

Synthesizing space voltage vectors by using different combinations of switch states, forming the space voltage vectors into a hexagon, wherein the hexagon comprises zero voltage vectors and 6 non-zero voltage vectors, and the whole hexagon is divided into 6 sectors by 6 non-zero voltage vector directions;

step 3, establishing the corresponding relation between the switch state and the basic voltage vector

The corresponding relation between the switching state and the voltage vector in the sectors 1-6 is shown in tables 1-6, a basic voltage vector diagram of each sector comprises 2 non-zero voltage vectors and 1 zero voltage vector, 3 switching states correspond to each non-zero voltage vector, and 2 switching states correspond to the zero voltage vector, so that the basic voltage vector of each sector corresponds to 8 switching states;

step 4, determining the switching sequence of the switch states

Firstly, two basic voltage vectors in an interval where a reference voltage vector u is positioned are considered, and 8 switch states corresponding to the basic voltage vectors are selected

In the method, A, B, C identical 2 switch states are selected to be divided into one group, the switch states corresponding to non-zero voltage vectors can be divided into 3 groups, and 1 corresponding switch state corresponding to a zero vector is added to each group;

the total action time of each group of 3 switch states is distributed to be one third of the switch period, and the action time of 2 switch states corresponding to non-zero voltage vectors is one third of the total action time of the voltage vectors in the corresponding vector direction, so that the volt-second balance of three transformers is ensured;

then, determining a specific switch switching sequence according to the principle that the switching times of the switches are minimum and the voltage-second balance of the transformer in one switching period is guaranteed;

step 5, calculating vector time

Firstly, determining the action time of a basic voltage vector of a sector where a reference voltage vector is located;

then, combining the principle of vector synthesis and the principle of volt-second balance of the transformer, obtaining a relation equation set between the action time of each switch state and the action time of the basic voltage vector;

and finally solving the equation set to obtain the action time of each switch state.

Further, step 4, the switching order of the switch states is determined to be replaced by the following scheme:

firstly, respectively placing 2 switch states corresponding to a zero voltage vector at the beginning and the end of each switch period, and placing 6 switch states corresponding to a non-zero voltage vector between 2 switch states corresponding to the zero voltage vector;

the action time of 3 switch states distributed in the same non-zero voltage vector direction is equal and is one third of the total action time of the voltage vectors in the corresponding vector direction, so that the volt-second balance of three transformers is ensured;

and then determining a specific switch switching sequence according to the principle that the switching times of the switches are minimum and the voltage-second balance of the transformer in one switching period is guaranteed.

Compared with the prior art, the invention has the remarkable advantages that: the number of power devices is reduced, the switching loss of the switching tube is reduced, and the conversion efficiency of electric energy is improved while the electric isolation between the load and the power grid is realized.

Drawings

Fig. 1 is a schematic circuit structure diagram of a nine-leg single-stage isolated three-phase bidirectional AC/DC converter of the present invention, where (a) is a schematic circuit structure diagram of a primary side star-secondary side triangle, (b) is a schematic circuit structure diagram of a primary side star-secondary side star, (c) is a schematic circuit structure diagram of a primary side triangle-secondary side star, and (d) is a schematic circuit structure diagram of a primary side triangle-secondary side triangle.

Fig. 2 is a basic voltage space vector diagram of the nine-leg single-stage isolated three-phase bidirectional AC/DC converter of the present invention in sector 1.

Fig. 3 is a basic vector diagram of the nine-leg single-stage isolated three-phase bidirectional AC/DC converter of the present invention.

Fig. 4 is a waveform diagram of the driving waveforms of the switching tube in sector 1 of the control scheme of the nine-leg single-stage isolated three-phase bidirectional AC/DC converter of the present invention.

Fig. 5 is a waveform diagram of the driving waveforms of the switching tubes in sector 1 of the control scheme two of the nine-leg single-stage isolated three-phase bidirectional AC/DC converter of the present invention.

Detailed Description

The invention is further described below with reference to the following figures and specific examples.

As shown in fig. 1, the nine-leg single-stage isolated three-phase bidirectional AC/DC converter of the present invention includes an AC-side filter inductor 1, an AC-side three-phase leg 2, an isolation transformer 3, a DC-side three-phase leg 4, and a DC-side filter capacitor 5, where the AC-side filter inductor 1 includes an a-phase inductor L _a B phase inductor L _b C-phase inductor L _c (ii) a The AC side three-phase bridge arm 2 comprises six bridge arms, each bridge arm is formed by connecting two switching tubes in series, wherein the first bridge arm is formed by a first switching tube Q _a1 A second switch tube Q _a2 The second bridge arm is composed of a third switching tube Q _a3 And a fourth switching tube Q _a4 The third bridge arm is composed of a fifth switch tube Q _a5 And a sixth switching tube Q _a6 The fourth bridge arm is composed of a seventh switch tube Q _p1 The eighth switch tube Q _p2 The fifth bridge arm is composed of a ninth switching tube Q _p3 The tenth switch tube Q _p4 The sixth bridge arm consists of an eleventh switch tube Q _p5 And a twelfth switching tube Q _p6 Composition is carried out; the isolation transformer 3 comprises an a-phase transformer T _ra B-phase transformer T _rb C-phase transformer T _rc (ii) a The direct current side three-phase bridge arm 4 comprises three bridge arms, each bridge arm is formed by connecting two switching tubes in series, wherein the seventh bridge arm is formed by a thirteenth switching tube Q _s1 And a fourteenth switching tube Q _s2 The eighth bridge arm is composed of a fifteenth switching tube Q _s3 Sixteenth switching tube Q _s4 The ninth bridge arm consists of a seventeenth switching tube Q _s5 Eighteenth switch tube Q _s6 Composition is carried out;

first switch tube Q _a1 Emitter and second switch tube Q _a2 Is connected with the collector of the A-phase inductor L _a One end of the two ends are connected; third switch tube Q _a3 Emitter and fourth switchTube Q _a4 Is connected with the collector of the phase B inductor L _b One end of the two is connected; fifth switch tube Q _a5 Emitter of and sixth switching tube Q _a6 Is connected with the collector of the inductor, and the connection point is connected with the C-phase inductor L _c One end of the two ends are connected; a phase inductance L _a B phase inductor L _b C-phase inductor L _c The other end of the three-phase inverter is respectively connected with an alternating-current side power supply (rectification or grid-connected inversion) or a three-phase load (independent inversion); seventh switch tube Q _p1 Emitter of (2) and eighth switching tube Q _p2 Is connected to the collector of the first switch, the connection point being a first common port a _p The ninth switching tube Q _p3 Emitter of (2) and tenth switching tube Q _p4 Is connected to the collector of the first switch, the connection point is used as a second common port b _p The eleventh switch tube Q _p5 Emitter and twelfth switching tube Q _p6 Is connected to the collector of (b), the connection point being a third common port c _p (ii) a First switch tube Q _a1 Collector and third switching tube Q _a3 Collector electrode of (1), and a fifth switching tube Q _a5 Collector electrode of (1), and seventh switching tube Q _p1 Collector electrode of (1), ninth switching tube Q _p3 Collector electrode of (2), eleventh switching tube Q _p5 The collector electrodes are connected; second switch tube Q _a2 Emitter and fourth switching tube Q _a4 Emitter of (2) and a sixth switching tube Q _a6 Emitter of (2) and eighth switching tube Q _p2 Emitter and tenth switching tube Q _p4 Emitter of, and twelfth switching tube Q _p6 Are connected.

Thirteenth switch tube Q _s1 Emitter of and fourteenth switching tube Q _s2 Is connected to the collector of the first switch, the connection point is used as a fourth common port a _s (ii) a Fifteenth switch tube Q _s3 Emitter and sixteenth switching tube Q _s4 Is connected to the collector of the first switch, the connection point is used as a fifth common port b _s (ii) a Seventeenth switching tube Q _s5 Emitter of (2) and eighteenth switching tube Q _s6 Is connected to the collector of the first switch, the connection point being a sixth common port c _s (ii) a Thirteenth switch tube Q _s1 Collector and fifteenth switching tube Q _s3 Collector electrode of (1), seventeenth switching tube Q _s5 Is connected with the collector, and the connection point is connected with the direct currentThe positive end of the side filter capacitor 5 is connected; fourteenth switching tube Q _s2 Emitter and sixteenth switching tube Q _s4 Emitter and eighteenth switching tube Q _s6 Is connected to the emitter of the dc side filter capacitor 5, and the connection point is connected to the negative terminal of the dc side filter capacitor 5.

Three transformers T _ra 、T _rb 、T _rc The primary windings are respectively connected with the first common port a _p A second common port b _p A third common port c _p The secondary windings are respectively connected with a fourth public port a _s Fifth common port b _s Sixth common port c _s 。

As a specific embodiment, the primary winding and the secondary winding of the transformer have two connection modes: star connection and delta connection, the isolation transformer has four combination modes: a primary side star-secondary side delta connection, a primary side star-secondary side star connection, a primary side triangle-secondary side star connection, and a primary side triangle-secondary side delta connection, as shown in fig. 1 (a) to (d).

In fig. 1, (a) the connection mode of the isolation transformer of the nine-leg single-stage isolation three-phase bidirectional AC/DC converter is primary side star-secondary side delta connection. First common port a _p A second common port b connected with the same name end of the primary winding of the A-phase transformer _p The same-name end and a third common port c of the primary winding of the B-phase transformer are connected _p Connecting the dotted terminal of the primary winding of the phase-C transformer; the different-name end of the primary winding of the phase-A transformer is connected with the different-name end of the primary winding of the phase-B transformer and the different-name end of the primary winding of the phase-C transformer; fourth common port a _s A fifth common port B for connecting the homonymous terminal of the secondary winding of the phase-A transformer with the heteronymous terminal of the secondary winding of the phase-B transformer _s A connection point for connecting the homonymous terminal of the secondary winding of the B-phase transformer and the heteronymous terminal of the secondary winding of the C-phase transformer, and a sixth common port C _s And the connecting point is connected with the homonymous end of the secondary winding of the phase-C transformer and the heteronymous end of the secondary winding of the phase-A transformer.

In fig. 1, (b) the connection mode of the isolation transformer of the nine-leg single-stage isolation three-phase bidirectional AC/DC converter is primary side star-secondary side star connection.First common port a _p A second common port b connected with the same name end of the primary winding of the A-phase transformer _p The same-name end and a third common port c of the primary winding of the B-phase transformer are connected _p Connecting the dotted terminal of the primary winding of the phase-C transformer; the different name end of the primary winding of the phase-A transformer is connected with the different name end of the primary winding of the phase-B transformer and the different name end of the primary winding of the phase-C transformer; fourth common port a _s The same name end of the secondary winding of the phase A transformer is connected with a fifth public port b _s The same-name end and a sixth common port c of the secondary winding of the phase-B transformer are connected _s Connecting the dotted terminal of the secondary winding of the phase C transformer; and the different-name end of the secondary winding of the phase-A transformer is connected with the different-name end of the secondary winding of the phase-B transformer and the different-name end of the secondary winding of the phase-C transformer.

In fig. 1, (c) the connection mode of the isolation transformer of the nine-leg single-stage isolation three-phase bidirectional AC/DC converter is primary side triangle-secondary side star connection. First common port a _p A connection point for connecting the homonymous terminal of the primary winding of the phase-A transformer with the synonym terminal of the primary winding of the phase-B transformer, and a second common port B _p A connection point between the homonymous terminal of the primary winding of the phase-B transformer and the heteronymous terminal of the primary winding of the phase-C transformer, and a third common port C _p The connection point is connected with the homonymous end of the primary winding of the phase-C transformer and the synonym end of the primary winding of the phase-A transformer; fourth common port a _s The same name end of the secondary winding of the phase A transformer is connected with a fifth public port b _s The same-name end and a sixth common port c of the secondary winding of the phase-B transformer are connected _s Connecting the dotted terminal of the secondary winding of the phase C transformer; and the different-name end of the secondary winding of the phase-A transformer is connected with the different-name end of the secondary winding of the phase-B transformer and the different-name end of the secondary winding of the phase-C transformer.

In fig. 1, (d) the connection mode of the isolation transformer of the nine-leg single-stage isolation three-phase bidirectional AC/DC converter is primary side triangle-secondary side triangle connection. First common port a _p A connection point for connecting the homonymous terminal of the primary winding of the phase-A transformer with the synonym terminal of the primary winding of the phase-B transformer, and a second common port B _p Connecting the homonymous terminal of the primary winding of the B-phase transformer with the synonym terminal of the primary winding of the C-phase transformerContact, third common port c _p The connection point is connected with the homonymous end of the primary winding of the phase-C transformer and the heteronymous end of the primary winding of the phase-A transformer; fourth common port a _s A fifth common port B for connecting the homonymous terminal of the secondary winding of the phase-A transformer with the heteronymous terminal of the secondary winding of the phase-B transformer _s A connection point for connecting the homonymous terminal of the secondary winding of the B-phase transformer and the heteronymous terminal of the secondary winding of the C-phase transformer, and a sixth common port C _s And the connection point is connected with the homonymous end of the secondary winding of the phase-C transformer and the heteronymous end of the secondary winding of the phase-A transformer.

The four combinations of the isolation transformers described above can provide different equivalent voltage ratios other than their turn ratios. The star-secondary delta connection on the primary side additionally provides a 2:1 transformer transformation ratio, and is suitable for voltage reduction occasions; the primary side triangle-secondary side star connection additionally provides a 1:2 transformer transformation ratio, and is suitable for boosting occasions; the primary side star-to-secondary star connection and the primary side delta-to-secondary delta connection do not provide additional transformer transformation ratios.

As a more specific implementation mode, the switch tubes are formed by connecting a one-way switch tube and a diode in parallel in an anti-phase mode, wherein Q is _a1 Comprising a unidirectional switching tube and a diode D _a1 Are connected in parallel to form _a2 Comprising a unidirectional switching tube and a diode D _a2 Are connected in parallel to form _a3 Comprising a unidirectional switching tube and a diode D _a3 Are connected in parallel to form _a4 Comprising a unidirectional switching tube and a diode D _a4 Are connected in parallel to form _a5 Comprising a unidirectional switching tube and a diode D _a5 Are connected in parallel to form _a6 Comprising a unidirectional switching tube and a diode D _a6 Are connected in parallel to form Q _p1 Comprising a unidirectional switching tube and a diode D _p1 Are connected in parallel to form _p2 Comprising a unidirectional switching tube and a diode D _p2 Are connected in parallel to form _p3 Comprising a unidirectional switching tube and a diode D _p3 Are connected in parallel to form _p4 Comprising a unidirectional switching tube and a diode D _p4 Are connected in parallel to form _p5 Comprising a unidirectional switching tube and a diode D _p5 Are connected in parallel to form _p6 Comprising a unidirectional switching tube and a diode D _p6 Are connected in parallel to form the composite material,Q _s1 comprising a unidirectional switching tube and a diode D _s1 Are connected in parallel to form _s2 Comprising a unidirectional switching tube and a diode D _s2 Are connected in parallel to form _s3 Comprising a unidirectional switching tube and a diode D _s3 Are connected in parallel to form _s4 Comprising a unidirectional switching tube and a diode D _s4 Are connected in parallel to form _s5 Comprising a unidirectional switching tube and a diode D _s5 Are connected in parallel to form _s6 Comprising a unidirectional switching tube and a diode D _s6 Are connected in parallel. When the two-way switch tube is connected in parallel, the emitting electrode of the one-way switch tube is connected with the anode of the diode, and the collecting electrode of the one-way switch tube is connected with the cathode of the diode.

As a more specific implementation, diode D _a1 、D _a2 、D _a3 、D _a4 、D _a5 、D _a6 、D _p1 、D _p2 、D _p3 、D _p4 、D _p5 、D _p6 、D _s1 、D _s2 、D _s3 、D _s4 、D _s5 、D _s6 Is an IGBT anti-parallel diode or a MOSFET parasitic diode. When the switching frequency is low, a common rectifier diode is adopted, and when the switching frequency is high, a fast recovery diode or a Schottky diode is adopted.

As a more specific implementation manner, the unidirectional switch tube may be a triode, an IGBT or an MOSFET, and for the triode and the IGBT, a collector of the unidirectional switch tube corresponds to a collector of the triode or the IGBT, and an emitter of the unidirectional switch tube corresponds to an emitter of the triode or the IGBT; for the MOSFET, a collector of the unidirectional switch tube corresponds to a drain electrode of the MOSFET, and an emitter of the unidirectional switch tube corresponds to a source electrode of the MOSFET.

When the converter works in a rectification mode, the alternating current side of the converter is an input side and is connected with a three-phase alternating current voltage source, and the direct current side of the converter is an output side and is connected with a load; when the converter works in an inversion mode, the direct current side of the converter is an input side and is connected with a direct current voltage source, and the alternating current side of the converter is an output side and is connected with a three-phase load or a three-phase alternating current voltage source. Because three high-frequency transformers are introduced into the converter, the problem of magnetic reset of the three transformers needs to be considered at the same time, and the implementation process of the existing SVPWM modulation technology is not applicable to the converter of the invention, so that an SVPWM modulation strategy applicable to the converter of the invention needs to be provided. Four combination modes of the isolation transformer are all suitable for the SVPWM modulation strategy of the converter. In the following, taking (a) a nine-leg single-stage isolated three-phase bidirectional AC/DC converter in fig. 1 as an example, an SVPWM modulation strategy of the nine-leg single-stage isolated three-phase bidirectional AC/DC converter is described with reference to fig. 2 to 5.

For convenience of analysis, all switching tubes and diodes are assumed to be ideal devices; all inductors, capacitors and transformers are ideal elements; the filter capacitance on the DC side is large enough to be approximately considered as a voltage source V _dc ，V _dc Is the dc side voltage. The number of turns of primary and secondary windings of three transformers in the isolation transformer 3 are assumed to be the same, and are n respectively _p 、n _s 。i _ap 、i _bp 、i _cp Current of primary winding of A, B, C phase transformer, v _Ta 、v _Tb 、v _Tc A, B, C phase-change transformer primary winding voltage, i _as 、i _bs 、i _cs Current of secondary winding of A, B, C phase transformer, i _a 、i _b 、i _c Respectively three-phase inductive current, e _a 、e _b 、e _c Respectively, three-phase ac side voltages. The SVPWM modulation method of the single-stage isolation three-phase bidirectional AC/DC converter provided by the invention comprises the following steps:

step 1, defining the switch state

By using

Of the format defining a switch state, wherein S _a 、S _b 、S _c Respectively represent six switching tubes Q in three-phase bridge arms at alternating current side _a1 、Q _a2 、Q _a3 、Q _a4 、Q _a5 、Q _a6 When the switch tube Q is in the on-off state _a1 Define S when conducting _a Is 1, when the switch tube Q _a2 Define S when conducting _a Is 0; when the switch tube Q _a3 Definition of S at conduction _b Is 1, when the switch tube Q _a4 Define S when conducting _b Is 0; when the switch tube Q _a5 Definition of S at conduction _c Is 1, when the switch tube Q _a6 Define S when conducting _c Is 0. S _d 、S _e 、S _f Respectively represent six switching tubes Q in three-phase bridge arms at alternating current side _p1 、Q _p2 、Q _p3 、Q _p4 、Q _p5 、Q _p6 When the switch tube Q is in the on-off state _p1 Define S when conducting _d Is 1, when the switch tube Q _p2 Definition of S at conduction _d Is-1, when the switch tube Q _p1 、Q _p2 All define S when not conducting _d Is 0; when the switch tube Q _p3 Define S when conducting _e Is 1, when the switch tube Q _p4 Define S when conducting _e Is-1, when the switch tube Q _p3 、Q _p4 All define S when not conducting _e Is 0; when the switch tube Q _p5 Define S when conducting _f Is 1, when the switch tube Q _p6 Define S when conducting _f Is-1, when the switch tube Q _p5 、Q _p6 All define S when not conducting _f Is 0. S _x 、S _y 、S _z Respectively represent six switching tubes Q in a direct-current side three-phase bridge arm _s1 、Q _s2 、Q _s3 、Q _s4 、Q _s5 、Q _s6 When the switch tube Q is in a switched state _s1 Define S when conducting _x Is 1, when the switch tube Q _s2 Define S when conducting _x Is-1, when the switch tube Q _s1 、Q _s2 All define S when not conducting _x Is 0; when the switch tube Q _s3 Define S when conducting _y Is 1, when the switch tube Q _s4 Define S when conducting _y Is-1, when the switch tube Q _s3 、Q _s4 All define S when not conducting _y Is 0; when the switch tube Q _s5 Define S when conducting _z Is 1, when the switch tube Q _s6 Define S when conducting _z Is-1, when the switch tube Q _s5 、Q _s6 All define S when not conducting _z Is 0. A. B, C respectively represent voltage directions at two ends of A, B, C three-phase transformer, when the dotted terminal of the voltage at two ends of the A-phase transformer is positive, A is positive, and when the dotted terminal of the voltage at two ends of the A-phase transformer is negativeWhen the voltage across the two ends of the phase-A transformer is negative, A is 0 when the voltage across the two ends of the phase-A transformer is zero, when the homonymous end of the voltage across the two ends of the phase-B transformer is positive, B is negative when the homonymous end of the voltage across the two ends of the phase-B transformer is negative, B is 0 when the voltage across the two ends of the phase-B transformer is zero, C is positive when the homonymous end of the voltage across the two ends of the phase-C transformer is negative, C is negative when the homonymous end of the voltage across the two ends of the phase-C transformer is negative, and C is 0 when the voltage across the two ends of the phase-C transformer is zero.

Step 2, dividing sectors

And synthesizing space voltage vectors by using different combinations of switch states, forming the space voltage vectors into a hexagon, wherein the hexagon comprises zero voltage vectors and 6 non-zero voltage vectors, and the whole hexagon is divided into 6 sectors by 6 non-zero voltage vector directions.

Tables 1-6 show the corresponding relationship between the switch states and the voltage vectors in sectors 1-6. Because of the rectification mode, the secondary side switch tube Q _s1～6 The current may flow through the anti-parallel diode D of the switching tube without applying a driving signal _s1～6 Finish the rectification, at this time S _x ＝0，S _y ＝0，S _z 0. In the inversion mode, the implementation mode of the basic control method is similar to that of the rectification mode, but a driving signal is required to be applied to the switching tube on the direct current side, so that in the invention, the secondary side switching tube Q is also supplied in the rectification mode _s1～6 A drive signal is applied.

TABLE 1 correspondence of switch states to voltage vectors in sector 1

S _a	S _b	S _c	S _d	S _e	S _f	S _x	S _y	S _z	A	B	C	v
														0	0	0	0	0	0	0	0	0	0	0	0	0
1	0	0	1	-1	0	1	-1	-1	+	-	0	(4n _p /3n _s )V _dc
													1	0	0	0	1	-1	-1	1	-1	0	+	-	(4n _p /3n _s )V _dc
1	0	0	-1	0	1	-1	-1	1	-	0	+	(4n _p /3n _s )V _dc
													1	1	0	1	-1	0	1	-1	-1	+	-	0	-α ² (4n _p /3n _s )V _dc
1	1	0	0	1	-1	-1	1	-1	0	+	-	-α ² (4n _p /3n _s )V _dc
													1	1	0	-1	0	1	-1	-1	1	-	0	+	-α ² (4n _p /3n _s )V _dc
1	1	1	0	0	0	0	0	0	0	0	0	0

Wherein, the first and the second end of the pipe are connected with each other,

n _p refers to the number of turns of the primary winding of the transformer, n _s Refers to the number of turns of the secondary winding of the transformer, V _dc Refers to the dc side voltage value.

Table 2 correspondence of switch states and voltage vectors in sector 2

S _a	S _b	S _c	S _d	S _e	S _f	S _x	S _y	S _z	A	B	C	v
														0	0	0	0	0	0	0	0	0	0	0	0	0
0	1	0	1	-1	0	1	-1	-1	+	-	0	α(4n _p /3n _s )V _dc
													0	1	0	0	1	-1	-1	1	-1	0	+	-	α(4n _p /3n _s )V _dc
0	1	0	-1	0	1	-1	-1	1	-	0	+	α(4n _p /3n _s )V _dc
													1	1	0	1	-1	0	1	-1	-1	+	-	0	-α ² (4n _p /3n _s )V _dc
1	1	0	0	1	-1	-1	1	-1	0	+	-	-α ² (4n _p /3n _s )V _dc
													1	1	0	-1	0	1	-1	-1	1	-	0	+	-α ² (4n _p /3n _s )V _dc
1	1	1	0	0	0	0	0	0	0	0	0	0

Wherein the content of the first and second substances,

TABLE 3 correspondence of switch states to voltage vectors in sector 3

S _a	S _b	S _c	S _d	S _e	S _f	S _x	S _y	S _z	A	B	C	v
														0	0	0	0	0	0	0	0	0	0	0	0	0
0	1	0	1	-1	0	1	-1	-1	+	-	0	α(4n _p /3n _s )V _dc
													0	1	0	0	1	-1	-1	1	-1	0	+	-	α(4n _p /3n _s )V _dc
0	1	0	-1	0	1	-1	-1	1	-	0	+	α(4n _p /3n _s )V _dc
													0	1	1	1	-1	0	1	-1	-1	+	-	0	-(4n _p /3n _s )V _dc
0	1	1	0	1	-1	-1	1	-1	0	+	-	-(4n _p /3n _s )V _dc
													0	1	1	-1	0	1	-1	-1	1	-	0	+	-(4n _p /3n _s )V _dc
1	1	1	0	0	0	0	0	0	0	0	0	0

Wherein the content of the first and second substances,

TABLE 4 correspondence of switch states to voltage vectors in sector 4

S _a	S _b	S _c	S _d	S _e	S _f	S _x	S _y	S _z	A	B	C	v
														0	0	0	0	0	0	0	0	0	0	0	0	0
0	0	1	1	-1	0	1	-1	-1	+	-	0	α ² (4n _p /3n _s )V _dc
													0	0	1	0	1	-1	-1	1	-1	0	+	-	α ² (4n _p /3n _s )V _dc
0	0	1	-1	0	1	-1	-1	1	-	0	+	α ² (4n _p /3n _s )V _dc
													0	1	1	1	-1	0	1	-1	-1	+	-	0	-(4n _p /3n _s )V _dc
0	1	1	0	1	-1	-1	1	-1	0	+	-	-(4n _p /3n _s )V _dc
													0	1	1	-1	0	1	-1	-1	1	-	0	+	-(4n _p /3n _s )V _dc
1	1	1	0	0	0	0	0	0	0	0	0	0

n _p refers to the number of turns of the primary winding of the transformer, n _s Refers to the secondary winding of the transformerNumber of turns, V _dc Refers to the dc side voltage value.

TABLE 5 correspondence of switch states to voltage vectors in sector 5

S _a	S _b	S _c	S _d	S _e	S _f	S _x	S _y	S _z	A	B	C	v
														0	0	0	0	0	0	0	0	0	0	0	0	0
0	0	1	1	-1	0	1	-1	-1	+	-	0	α ² (4n _p /3n _s )V _dc
													0	0	1	0	1	-1	-1	1	-1	0	+	-	α ² (4n _p /3n _s )V _dc
0	0	1	-1	0	1	-1	-1	1	-	0	+	α ² (4n _p /3n _s )V _dc
													1	0	1	1	-1	0	1	-1	-1	+	-	0	-α(4n _p /3n _s )V _dc
1	0	1	0	1	-1	-1	1	-1	0	+	-	-α(4n _p /3n _s )V _dc
													1	0	1	-1	0	1	-1	-1	1	-	0	+	-α(4n _p /3n _s )V _dc
1	1	1	0	0	0	0	0	0	0	0	0	0

Wherein the content of the first and second substances,

TABLE 6 correspondence of switch states to voltage vectors in sector 6

S _a	S _b	S _c	S _d	S _e	S _f	S _x	S _y	S _z	A	B	C	v
														0	0	0	0	0	0	0	0	0	0	0	0	0
1	0	0	1	-1	0	1	-1	-1	+	-	0	(4n _p /3n _s )V _dc
													1	0	0	0	1	-1	-1	1	-1	0	+	-	(4n _p /3n _s )V _dc
1	0	0	-1	0	1	-1	-1	1	-	0	+	(4n _p /3n _s )V _dc
													1	0	1	1	-1	0	1	-1	-1	+	-	0	-α(4n _p /3n _s )V _dc
1	0	1	0	1	-1	-1	1	-1	0	+	-	-α(4n _p /3n _s )V _dc
													1	0	1	-1	0	1	-1	-1	1	-	0	+	-α(4n _p /3n _s )V _dc
1	1	1	0	0	0	0	0	0	0	0	0	0

Fig. 2 is a diagram of the fundamental voltage vector within sector 1, including 2 non-zero voltage vectors (i.e., sector boundaries) and 1 zero voltage vector, with 6 switch states corresponding to the non-zero voltage vectors and 2 switch states corresponding to the zero voltage vectors, thus sector 1 fundamental voltage vector corresponds to 8 switch states. And similarly, obtaining basic voltage vector diagrams of other sectors, and synthesizing to obtain the basic voltage vector diagram of the SVPWM method of the nine-bridge-arm single-stage isolated three-phase bidirectional AC/DC converter, which is shown in figure 3.

Step 4, determining the switching sequence of the switch states

When the switching sequence of the switch states is determined, only two basic voltage vectors in the interval where the reference voltage vector u is positioned are considered, and 8 switch states corresponding to the basic voltage vectors are selected

In the method, A, B, C identical 2 switch states are selected to be divided into one group, the switch states corresponding to non-zero voltage vectors can be divided into 3 groups, and 1 corresponding switch state corresponding to a zero vector is added in each group; the total action time of each group of 3 switch states is one third of the switch period, and the action time of 2 switch states corresponding to non-zero voltage vectors is one third of the total action time of the voltage vectors in the corresponding vector direction, so that the volt-second balance of three transformers is ensured; and finally, determining a specific switch switching sequence according to the principle that the switching times of the switches are minimum and the voltage-second balance of the transformer in one switching period is guaranteed. Taking the reference voltage vector in sector 1 as an example, the switching order of the switch states is:

step 5, calculating vector time

Determining the action time of the basic voltage vector of the sector where the reference voltage vector is located, combining the principle of vector synthesis and the principle of volt-second balance of the transformer to obtain a relational equation set between the action time of each switch state and the action time of the basic voltage vector, and solving the equation set to obtain the action time of each switch state. Taking sector 1 as an example, a specific method for calculating the action time of each switch state comprises the following steps:

firstly, defining the action time of each switch state as follows;

assuming that the reference voltage vector u is located in the first sector, the component in α β coordinate is v _α 、v _β Therefore, it is necessary to calculate the action time of the 0-degree directional voltage vector, the 60-degree directional voltage vector and the zero vector, which are T ₁ 、T ₂ 、T ₀ ：

According to the principle of vector synthesis and the principle of volt-second balance of the transformer, the following expression can be obtained:

selecting a special set of solutions of the above equation set:

wherein the switching period T _s ＝T ₁ +T ₂ +T ₀ From which it is possible to calculateAnd outputting the time corresponding to each switch state, thereby accurately controlling the converter. Figure 4 shows the switching tube drive waveforms in sector 1 of the scheme and the voltage waveforms across the transformer. Switch tube Q in the above scheme _a1～6 The operating frequency of (2) being the switching tube Q _p1～6 Twice the operating frequency of (c);

the invention also has a second modulation scheme, which specifically comprises the following steps:

step 1, using

The format of (1), defining the switch state;

step 2, synthesizing space voltage vectors by using different combinations of switching states, and forming the space voltage vectors into a hexagon, wherein the hexagon comprises zero voltage vectors and 6 non-zero voltage vectors, the whole hexagon is divided into 6 sectors by 6 non-zero voltage vector directions, each non-zero voltage vector corresponds to 3 switching states in two basic voltage vector directions of each sector boundary, and the zero voltage vector corresponds to 2 switching states, namely the basic voltage vector of each sector corresponds to 8 switching states;

step 3, when the switching sequence of the switch states is determined, 2 switch states corresponding to the zero voltage vector are respectively placed at the starting position and the ending position of each switch period, and 6 switch states corresponding to the non-zero voltage vector are placed between the 2 switch states corresponding to the zero voltage vector; the action time of 3 switch states in the same non-zero voltage vector direction is equal and is one third of the total action time of the voltage vectors in the corresponding vector direction, so that the volt-second balance of the three transformers is ensured; and finally, determining a specific switch switching sequence according to the principle that the switching times of the switches are minimum and the voltage-second balance of the transformer in one switching period is guaranteed.

And 4, determining the action time of the basic voltage vector of the sector where the reference voltage vector is located, combining the vector synthesis principle and the transformer volt-second balance principle to obtain a relational equation set between the action time of each switch state and the action time of the basic voltage vector, and solving the equation set to obtain the action time of each switch state. Similarly, the reference voltage vector is located in the 1 st sector, and the switching order of the switch states under the second scheme is as follows:

the specific method for calculating the action time of each switch state comprises the following steps:

firstly, defining the action time of each switch state as follows;

since the reference voltage vector u is located in the first sector, the component in α β coordinate is v _α 、v _β Therefore, it is necessary to calculate the action time of the 0-degree directional voltage vector, the 60-degree directional voltage vector and the zero vector, which are T ₁ 、T ₂ 、T ₀ ：

selecting a group of special solutions of the equation set:

wherein the switching period T _s ＝T ₁ +T ₂ +T ₀ Therefore, the time corresponding to each switch state can be calculated, and the converter can be accurately controlled. FIG. 5 shows the driving waveforms of the switch tube in sector 1 under scheme twoAnd the voltage waveform across the transformer. In the second scheme, the switch tube Q is controlled _p1～6 Is a switching tube Q _a1～6 Twice the operating frequency of (c).

Claims

1. The nine-leg single-stage isolated three-phase bidirectional AC/DC converter is characterized by comprising an AC side filter inductor (1), an AC side three-phase leg (2), an isolation transformer (3), a DC side three-phase leg (4) and a DC side filter capacitor (5), wherein the AC side filter inductor (1) comprises an A-phase inductor (L) _a ) Phase B inductor (L) _b ) C phase inductance (L) _c ) (ii) a The alternating current side three-phase bridge arm (2) comprises six bridge arms, each bridge arm is formed by connecting two switching tubes in series, and the first bridge arm is formed by connecting a first switching tube (Q) _a1 ) A second switch tube (Q) _a2 ) The second bridge arm is composed of a third switching tube (Q) _a3 ) And a fourth switching tube (Q) _a4 ) The third bridge arm is composed of a fifth switch tube (Q) _a5 ) And a sixth switching tube (Q) _a6 ) The fourth bridge arm is composed of a seventh switch tube (Q) _p1 ) An eighth switching tube (Q) _p2 ) The fifth bridge arm is composed of a ninth switching tube (Q) _p3 ) The tenth switch tube (Q) _p4 ) The sixth bridge arm is composed of an eleventh switch tube (Q) _p5 ) And a twelfth switching tube (Q) _p6 ) Composition is carried out; the isolation transformer (3) comprises an A-phase transformer (T) _ra ) phase-B transformer (T) _rb ) C phase transformer (T) _rc ) (ii) a The direct current side three-phase bridge arm (4) comprises three bridge arms, each bridge arm is formed by connecting two switching tubes in series, and the seventh bridge arm is formed by connecting a thirteenth switching tube (Q) _s1 ) Fourteenth switching tube (Q) _s2 ) The eighth bridge arm is composed of a fifteenth switching tube (Q) _s3 ) Sixteenth switching tube (Q) _s4 ) The ninth bridge arm is composed of a seventeenth switching tube (Q) _s5 ) Eighteenth switch tube (Q) _s6 ) Composition is carried out;

first switch tube (Q) _a1 ) Emitter and second switching tube (Q) _a2 ) Is connected with the collector of the A-phase inductor (L) _a ) One end of the two ends are connected; third switch tube (Q) _a3 ) Emitter and fourth switching tube (Q) _a4 ) Is connected to the collector electrodeThe contact point is connected with a B-phase inductor (L) _b ) One end of the two ends are connected; fifth switch tube (Q) _a5 ) Emitter and sixth switching tube (Q) _a6 ) Is connected with the collector of the inductor, and the connection point is connected with the C-phase inductor (L) _c ) One end of the two ends are connected; a phase inductor (L) _a ) Phase B inductor (L) _b ) C phase inductor (L) _c ) The other end of the three-phase power supply is respectively connected with an alternating-current side power supply or a three-phase load; seventh switch tube (Q) _p1 ) Emitter and eighth switching tube (Q) _p2 ) Is connected to the collector of (b), the connection point being a first common port (a) _p ) Ninth switching tube (Q) _p3 ) Emitter and tenth switching tube (Q) _p4 ) Is connected to the collector of the first switch, the connection point being a second common port (b) _p ) Eleventh, tenth switching tube (Q) _p5 ) Emitter and twelfth switching tube (Q) _p6 ) Is connected to the collector of the first switching element, the connection point being a third common port (c) _p ) (ii) a First switch tube (Q) _a1 ) Collector and third switching tube (Q) _a3 ) Collector electrode of (1), and fifth switching tube (Q) _a5 ) Collector electrode of (1), and seventh switching tube (Q) _p1 ) Collector electrode of (2), ninth switching tube (Q) _p3 ) Collector of (2), eleventh switching tube (Q) _p5 ) The collector electrodes are connected; second switch tube (Q) _a2 ) Emitter and fourth switching tube (Q) _a4 ) Emitter electrode of (1), sixth switching tube (Q) _a6 ) Emitter electrode of (1), eighth switching tube (Q) _p2 ) Emitter electrode of (1), tenth switching tube (Q) _p4 ) Emitter electrode of (1), twelfth switching tube (Q) _p6 ) The emitting electrodes are connected;

thirteenth switch tube (Q) _s1 ) Emitter and fourteenth switching tube (Q) _s2 ) Is connected to the collector of the first switch, the connection point being a fourth common port (a) _s ) (ii) a Fifteenth switch tube (Q) _s3 ) Emitter and sixteenth switching tube (Q) _s4 ) Is connected to the collector of (b), the connection point being a fifth common port (b) _s ) (ii) a Seventeenth switching tube (Q) _s5 ) Emitter and eighteenth switching tube (Q) _s6 ) Is connected to the collector of (c), the connection point being a sixth common port (c) _s ) (ii) a Thirteenth switch tube (Q) _s1 ) Collector and fifteenth switching tube (Q) _s3 ) Collector electrode of (1), seventeenth switching tube (Q) _s5 ) Is connected with the collector, and the connection point is connected with the direct currentThe positive end of the side filter capacitor (5) is connected; fourteenth switching tube (Q) _s2 ) Emitter and sixteenth switching tube (Q) _s4 ) Emitter, eighteenth switching tube (Q) _s6 ) The emitter of the filter is connected, and the connection point is connected with the negative end of the direct current side filter capacitor (5);

the primary windings of the three transformers are respectively connected with a first common port (a) _p ) A second common port (b) _p ) A third common port (c) _p ) The secondary windings are respectively connected with a fourth common port (a) _s ) A fifth common port (b) _s ) Sixth common port (c) _s )；

The SVPWM modulation method of the nine-leg single-stage isolated three-phase bidirectional AC/DC converter comprises the following steps:

step 1, defining a switch state;

by using

Of the format defining a switch state, wherein S _a 、S _b 、S _c Respectively represent a first to a sixth switching tube (Q) in a three-phase bridge arm at an alternating current side _a1 、Q _a2 、Q _a3 、Q _a4 、Q _a5 、Q _a6 ) When the first switching tube (Q) is in the on-off state _a1 ) Define S when conducting _a 1, when the second switch tube (Q) _a2 ) Define S when conducting _a Is 0; when the third switch tube (Q) _a3 ) Define S when conducting _b 1 when the fourth switch tube (Q) _a4 ) Define S when conducting _b Is 0; when the fifth switch tube (Q) _a5 ) Define S when conducting _c 1, when the sixth switch tube (Q) _a6 ) Define S when conducting _c Is 0; s _d 、S _e 、S _f Respectively represent the seventh to twelfth switching tubes (Q) in the three-phase bridge arm at the AC side _p1 、Q _p2 、Q _p3 、Q _p4 、Q _p5 、Q _p6 ) When the seventh switching tube (Q) is in the on-off state _p1 ) Definition of S at conduction _d Is 1 when the eighth switch tube (Q) _p2 ) Define S when conducting _d Is-1, when the seventh and eighth switching tubes (Q) _p1 、Q _p2 ) Are all not conductedDefinition of S _d Is 0; when the ninth switch tube (Q) _p3 ) Define S when conducting _e Is 1, when the tenth switch tube (Q) _p4 ) Definition of S at conduction _e Is-1, when the ninth and tenth switching tubes (Q) _p3 、Q _p4 ) All define S when not conducting _e Is 0; when the eleventh switch tube (Q) _p5 ) Definition of S at conduction _f Is 1, when the twelfth switching tube (Q) _p6 ) Define S when conducting _f Is-1, when the eleventh and twelfth switching tubes (Q) _p5 、Q _p6 ) All define S when not conducting _f Is 0; s _x 、S _y 、S _z Respectively represent thirteenth to eighteenth switching tubes (Q) in a three-phase bridge arm at a direct current side _s1 、Q _s2 、Q _s3 、Q _s4 、Q _s5 、Q _s6 ) When the thirteenth switching tube (Q) is in the on-off state _s1 ) Define S when conducting _x Is 1, when the fourteenth switch tube (Q) _s2 ) Define S when conducting _x Is-1, when the thirteenth and fourteenth switching tubes (Q) _s1 、Q _s2 ) All define S when not conducting _x Is 0; when the fifteenth switch tube (Q) _s3 ) Define S when conducting _y Is 1, when the sixteenth switch tube (Q) _s4 ) Definition of S at conduction _y Is-1, when the fifteenth and sixteenth switching tubes (Q) _s3 、Q _s4 ) All define S when not conducting _y Is 0; when the seventeenth switch tube (Q) _s5 ) Define S when conducting _z Is 1 when the eighteenth switch tube (Q) _s6 ) Define S when conducting _z Is-1, when the seventeenth and eighteenth switching tubes (Q) _s5 、Q _s6 ) All define S when not conducting _z Is 0; A. b, C respectively represent voltage directions at two ends of a A, B, C three-phase transformer, when the homonymous ends of voltages at two ends of the phase-A transformer are positive, A is positive, when the homonymous ends of voltages at two ends of the phase-A transformer are negative, A is negative, when the voltages at two ends of the phase-A transformer are zero, A is 0, when the homonymous ends of voltages at two ends of the phase-B transformer are positive, B is negative, when the voltages at two ends of the phase-B transformer are zero, B is 0, when the homonymous ends of voltages at two ends of the phase-C transformer are positive, C is positive, when the homonymous ends of voltages at two ends of the phase-C transformer are negative, C is negative, and when the voltages at two ends of the phase-C transformer are zero, C is 0;

step 2, dividing sectors

Synthesizing space voltage vectors by using different combinations of switch states, forming the space voltage vectors into a hexagon, wherein the hexagon comprises zero voltage vectors and 6 non-zero voltage vectors, and dividing the whole hexagon into 6 sectors in 6 non-zero voltage vector directions;

The corresponding relation between the switch state and the voltage vector in the sector 1-6 is shown in the table 1-6;

TABLE 1 correspondence of switch states to voltage vectors in sector 1

Wherein the content of the first and second substances,

n _p refers to the number of turns of the primary winding of the transformer, n _s Refers to the number of turns of the secondary winding of the transformer, V _dc Refers to the value of the voltage on the direct current side;

TABLE 2 correspondence of switch states to voltage vectors in sector 2

TABLE 3 correspondence of switch states and voltage vectors in sector 3

TABLE 4 correspondence of switch states to voltage vectors in sector 4

TABLE 5 correspondence of switch states to voltage vectors in sector 5

TABLE 6 correspondence of switch states to voltage vectors in sector 6

The basic voltage vector diagram of each sector comprises 2 non-zero voltage vectors and 1 zero voltage vector, 3 switch states corresponding to each non-zero voltage vector and 2 switch states corresponding to the zero voltage vector, so that each sector basic voltage vector corresponds to 8 switch states;

step 4, determining the switching sequence of the switch states

Firstly, two basic voltage vectors in an interval where a reference voltage vector v is positioned are considered, and 8 switch states corresponding to the basic voltage vectors are selected

In the method, A, B, C identical 2 switch states are selected to be divided into one group, the switch states corresponding to non-zero voltage vectors are divided into 3 groups, and 1 corresponding switch state corresponding to a zero vector is added in each group;

the total action time of each group of 3 switch states is one third of the switch period, and the action times of 2 switch states corresponding to non-zero voltage vectors are all one third of the total action time of the voltage vectors in the corresponding vector direction, so that the volt-second balance of three transformers is ensured;

step 5, calculating vector time

then, combining a vector synthesis principle and a transformer volt-second balance principle to obtain a relation equation set between the action time of each switch state and the action time of the basic voltage vector;

2. The nine-leg single-stage isolated three-phase bidirectional AC/DC converter according to claim 1, wherein the primary winding and the secondary winding of the transformer have two connection modes: star connection and delta connection, the isolation transformer has four combination modes: a primary side star-secondary side delta connection, a primary side star-secondary side star connection, a primary side triangle-secondary side star connection, and a primary side triangle-secondary side delta connection.

3. The nine leg single stage isolated three phase bidirectional AC/DC converter according to claim 2 wherein the isolation transformers are connected in a primary side star-to-secondary side delta connection with the first common port (a) _p ) The same-name end and a second common port (b) of the primary winding of the phase-A transformer are connected _p ) The same name end and a third common port (c) of the primary winding of the B-phase transformer are connected _p ) Connecting the dotted terminal of the primary winding of the phase-C transformer; the different-name end of the primary winding of the phase-A transformer is connected with the different-name end of the primary winding of the phase-B transformer and the different-name end of the primary winding of the phase-C transformer; fourth common port (a) _s ) A connection point for connecting the homonymous terminal of the secondary winding of the phase-A transformer and the heteronymous terminal of the secondary winding of the phase-B transformer, and a fifth common port (B) _s ) A connection point for connecting the homonymous terminal of the secondary winding of the B-phase transformer and the heteronymous terminal of the secondary winding of the C-phase transformer, and a sixth common port (C) _s ) And the connection point is connected with the homonymous end of the secondary winding of the phase-C transformer and the heteronymous end of the secondary winding of the phase-A transformer.

4. The nine-leg single-stage isolated three-phase bidirectional AC/DC converter according to claim 2, wherein the isolation transformer is connected in a manner such that when a primary side star-to-secondary side star connection is made, the first common port (a) is connected in a manner such that _p ) The same-name end and a second common port (b) of the primary winding of the phase-A transformer are connected _p ) The same name end and a third common port (c) of the primary winding of the B-phase transformer are connected _p ) The same-name end of the primary winding of the phase-C transformer is connected; the different-name end of the primary winding of the phase-A transformer is connected with the different-name end of the primary winding of the phase-B transformer and the different-name end of the primary winding of the phase-C transformer; fourth common port (a) _s ) Connecting the dotted terminal of the secondary winding of the phase A transformer and a fifth common port (b) _s ) The same-name end and a sixth common port (c) of a secondary winding of the phase-B transformer are connected _s ) Connecting the dotted terminal of the secondary winding of the phase C transformer; and the different-name end of the secondary winding of the phase-A transformer is connected with the different-name end of the secondary winding of the phase-B transformer and the different-name end of the secondary winding of the phase-C transformer.

5. The nine-leg single-stage isolated three-phase bidirectional AC/DC converter according to claim 2, wherein the isolation transformer is connected in a manner such that when the primary side of the isolation transformer is connected in a delta-star configuration, the first common port (a) is connected in a delta-star configuration _p ) A connection point between the homonymous terminal of the primary winding of the phase-A transformer and the synonym terminal of the primary winding of the phase-B transformer, and a second common port (B) _p ) A connection point for connecting the homonymous terminal of the primary winding of the B-phase transformer and the synonym terminal of the primary winding of the C-phase transformer, and a third common port (C) _p ) The connection point is connected with the homonymous end of the primary winding of the phase-C transformer and the synonym end of the primary winding of the phase-A transformer; fourth common port (a) _s ) Connecting the dotted terminal of the secondary winding of the phase A transformer and a fifth common port (b) _s ) The same-name end and a sixth common port (c) of a secondary winding of the phase-B transformer are connected _s ) Connecting the dotted terminal of the secondary winding of the phase C transformer; and the different-name end of the secondary winding of the phase-A transformer is connected with the different-name end of the secondary winding of the phase-B transformer and the different-name end of the secondary winding of the phase-C transformer.

6. The nine-leg single-stage isolated three-phase bidirectional AC/DC converter according to claim 2, wherein the isolation transformer is connected in a primary-secondary delta connection mode, and the first common port (a) is connected to the secondary delta connection mode _p ) A connection point for connecting the homonymous terminal of the primary winding of the phase-A transformer and the synonym terminal of the primary winding of the phase-B transformer, and a second common port (B) _p ) A connection point for connecting the homonymous terminal of the primary winding of the B-phase transformer and the synonym terminal of the primary winding of the C-phase transformer, and a third common port (C) _p ) The connection point is connected with the homonymous end of the primary winding of the phase-C transformer and the synonym end of the primary winding of the phase-A transformer; fourth common port (a) _s ) A connection point for connecting the homonymous terminal of the secondary winding of the phase-A transformer and the heteronymous terminal of the secondary winding of the phase-B transformer, and a fifth common port (B) _s ) A connection point for connecting the homonymous terminal of the secondary winding of the B-phase transformer and the heteronymous terminal of the secondary winding of the C-phase transformer, and a sixth common port (C) _s ) The connection between the homonymous terminal of the secondary winding of the phase-C transformer and the heteronymous terminal of the secondary winding of the phase-A transformerAnd (6) contact points.

7. The nine-leg single-stage isolated three-phase bidirectional AC/DC converter according to claim 2, wherein all the switching tubes are formed by connecting a unidirectional switching tube and a diode in parallel in an inverted manner.

8. The nine-leg single-stage isolated three-phase bidirectional AC/DC converter according to claim 7, wherein the diode is an IGBT anti-parallel diode or a MOSFET parasitic diode, and the unidirectional switching tube is a triode, an IGBT or a MOSFET.

9. The nine-leg single-stage isolated three-phase bidirectional AC/DC converter according to claim 1, wherein the switching state switching sequence determined in step 4 is replaced by the following scheme: