CN102801349A - Single-phase nine-level converter - Google Patents

Abstract

A single-phase nine-level converter is composed of a diode-clamped three-level three-phase bridge and two coupled inductors. The midpoint of a bridge arm in the diode-clamped three-level three-phase bridge is used as a terminal of the output end of the single-phase nine-level converter; in the diode-clamped three-level three-phase bridge, The midpoints of the other two bridge arms are respectively connected to the two non-common connection points of the two coupled inductors, and the common connection points of the two coupled inductors are used as the output terminals of the single-phase nine-level converter. Another terminal; the two coupled inductors are connected in series. The present invention can be used as converters such as single-phase inverters and rectifiers, and can also constitute a three-phase nine-level converter so as to be applied to three-phase occasions; Connected to form a converter with more levels.

Description

Single Phase Nine Level Converter

technical field

The invention relates to a multilevel power electronic converter.

Background technique

In order to improve the voltage tolerance level, reduce the harmonic content of the output voltage, and reduce the electromagnetic interference caused by the high dv/dt (voltage rise rate), multi-level power electronic converters have always been obtained It has attracted extensive attention and research, and also produced a large number of practical application devices. Relevant research institutions and R&D enterprises and units at home and abroad have also proposed multi-level converters with various topological structures.

However, almost all current multilevel power electronic converters use multiple DC power supplies to achieve multiple (more than three) levels of output voltage. For example, the traditional cascaded H-bridge multilevel converter needs to use multiple independent DC power supplies; while the diode-clamped multilevel converter and the flying capacitor multilevel converter both use split capacitors to obtain multiple A level of DC voltage is obtained indirectly from multiple DC power sources.在已有专利中，美国专利US6005788、US7219673、US20060044857和US20090237962以及中专利200610019724、200710062642、200520044611.2、200720083744.X、200810204472、200710064575.X、200710114460.7、200710144523.3、200810105139.7、200810118834.7、200810118835.1、200910045506.3等等均是采用Multiple transformers are used to obtain independent DC power supplies or output voltages of multiple levels are obtained by splitting the DC capacitor voltage. For single-phase multi-level converters, in order to achieve nine levels of output voltage, traditional circuit topologies, such as cascaded H-bridge type, diode clamp type, flying capacitor type, etc., require four DC power supplies ( or four split DC capacitors) and at least sixteen fully-controlled power electronic devices. However, using multiple transformers to obtain an independent DC power supply will increase the volume and weight of the converter; while using multiple split DC capacitors will make the control system of the converter more complicated because the voltages of multiple capacitors need to be controlled and balanced with each other. It is complicated, which reduces the reliability of the system operation.

Contents of the invention

The invention aims to overcome the disadvantages of the existing single-phase nine-level converter, reduce the DC voltage and DC capacitance, and improve the reliability of the operation of the multi-level converter while reducing the harmonic content of the output voltage.

The invention is composed of a traditional diode-clamped three-level three-phase bridge and two coupled inductors. The three bridge arms of the diode-clamped three-level three-phase bridge are composed of power electronic power devices. The output end of a bridge arm in the three-phase bridge is used as a terminal of the output end of the single-phase nine-level voltage type converter of the present invention; The non-common connection point is connected, and the common connection point of the coupled inductor is used as another terminal of the output terminal of the single-phase nine-level converter of the present invention. At the same time, the connection mode of the two coupled inductors is sequential connection, that is, the common connection point of the two coupled inductors is the common connection point between the same-named end of one coupled inductor and the non-identical end of the other coupled inductor.

The single-phase nine-level converter of the present invention has the following characteristics and advantages:

1. Only two DC power supplies and twelve fully-controlled power electronic switching devices are needed to generate a nine-level output voltage. Compared with the traditional single-phase nine-level converter, the invention requires less fully-controlled devices, simple structure and high reliability.

2. The DC voltage stress of each power electronic power device is the same, which is convenient for device design and selection.

3. The minimum level of the output voltage is 1/4 of the DC bus voltage. Compared with the single-phase full-bridge converter, it can greatly reduce the harmonic content and the dv/dt of the output voltage, which can also reduce the system operating time. electromagnetic interference.

4. It only needs to add two coupled inductors on the basis of the common diode-clamped three-level three-phase bridge. The structure is simple and it is very convenient for manufacturing.

5. The present invention has flexible configuration and wide application range, and can be used in both single-phase systems and three-phase systems, such as rectifiers and inverters. When the modules are cascaded, they can also be applied to high-voltage systems, such as high-voltage DC transmission systems, high-voltage AC frequency conversion systems, etc.

Description of drawings

Fig. 1 is the circuit principle diagram of single-phase nine-level converter of the present invention;

Fig. 2 is the emulation waveform figure of output voltage u _ab of single-phase nine-level converter of the present invention;

Fig. 3 is the simulation calculation wave form of load current i _b ;

Fig. 4 is the spectrum analysis chart of u _ab .

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

As shown in Fig. 1, the single-phase nine-level converter of the present invention is composed of a diode-clamped three-level three-phase bridge and two coupled inductors. The diode-clamped three-level three-phase bridge is composed of two DC power supplies, a first bridge arm, a second bridge arm and a third bridge arm. The three bridge arms of the diode-clamped three-level three-phase bridge are composed of twelve fully-controlled power electronic switching devices S ₁₁ -S ₁₄ , S ₂₁ -S ₂₄ , S ₃₁ -S ₃₄ and eighteen diodes D ₁₁ -D ₁₄ , D ₂₁ -D ₂₄ , D ₃₁ -D ₃₄ , constitute. Taking the case of S ₁₁ -S ₁₄ using IGBT (insulated gate bipolar transistor) as an example, the connection mode between each device is:

The two DC power supplies _E1 and _E2 are connected in series, that is, the negative pole of the first DC power supply _E1 is connected to the positive pole of the second DC power supply _E2 at one point, and this connection point is marked as the midpoint n of the DC bus bar ; The positive pole of the first DC power supply _E1 is marked as the positive pole P of the DC bus bar; the negative pole of the second DC power supply _E2 is marked as the positive pole N of the DC bus bar.

The first bridge arm is composed of four IGBTs S ₁₁ , S ₁₂ , S ₁₃ , S ₁₄ and six diodes D ₁₁ , D ₁₂ , D ₁₃ , D ₁₄ , D ₁₅ and D ₁₆ ; four IGBTs S ₁₁ , S ₁₂ , S ₁₃ and S ₁₄ are connected in series in sequence, that is, the emitter of the first IGBT _{S 11} is connected to the collector of the second IGBT S 12, and the emitter of the second IGBT _{S 12 is} connected to the collector of the third IGBT S ₁₃ connected together, denoted as the midpoint 1 of the first bridge arm, the emitter of the third IGBT S ₁₃ and the collector of the fourth IGBT S ₁₄ are connected together; the first diode D ₁₁ and the first IGBT S ₁₁ is connected in anti-parallel, that is, the anode of the first diode D ₁₁ is connected together with the emitter of the first IGBT S ₁₁ , and the cathode of the first diode D ₁₁ is connected together with the collector of the first IGBT S ₁₁ ; The second diode D ₁₂ is connected in antiparallel with the first IGBT S ₁₂ , that is, the anode of the second diode D ₁₂ is connected with the emitter of the second IGBT S ₁₂ , and the cathode of the second diode D ₁₂ is connected with the second IGBT S The collectors of ₁₂ are connected together; the third diode D ₁₃ is connected in antiparallel with the third IGBT S ₁₃ , that is, the anode of the third diode D ₁₃ is connected with the emitter of the third IGBT S ₁₃ , and the third diode The cathode of the tube D ₁₃ is connected to the collector of the third IGBT S ₁₃ ; the fourth diode D ₁₄ is connected in antiparallel with the fourth IGBT S ₁₄ , that is, the anode of the fourth diode D ₁₄ is connected to the fourth IGBT S ₁₄ The emitters are connected together, the cathode of the fourth diode D ₁₄ is connected together with the collector of the fourth IGBT S ₁₄ ; the anode of the fifth diode D ₁₅ is connected with the cathode of the sixth diode D ₁₆ to the midpoint n of the DC bus; the cathode of the fifth diode D ₁₅ is connected to the emitter of the first IGBT S ₁₁ and the collector of the second IGBT S ₁₂ ; the anode of the sixth diode D ₁₆ is connected to the first The emitter of the third IGBT S ₁₃ and the collector of the fourth IGBT S ₁₄ ; the collector of the first IGBT _{S 11} is connected to the positive pole P of the DC bus; the emitter of the fourth IGBT S ₁₄ is connected to the negative pole N of the DC bus.

The second bridge arm is composed of four IGBTs S ₂₁ , S ₂₂ , S ₂₃ , S ₂₄ and six diodes D ₂₁ , D ₂₂ , D ₂₃ , D ₂₄ , D ₂₅ and D ₂₆ ; the fifth IGBT S ₂₁ , the sixth IGBT S ₂₂ , the seventh IGBT S ₂₃ , and the eighth IGBT S ₂₄ are connected in series in sequence, that is, the emitter of the fifth IGBT S ₂₁ and the collector of the sixth IGBT S ₂₂ are connected together, and the emitter of the sixth IGBT S ₂₂ The pole is connected with the collector of the seventh IGBT S ₂₃ , which is recorded as the midpoint 2 of the second bridge arm, and the emitter of the seventh IGBT S ₂₃ is connected with the collector of the eighth IGBT S ₂₄ ; D ₂₁ is connected in antiparallel with S ₂₁ , that is, the anode of D ₂₁ is connected with the emitter of S ₂₁ , the cathode of D ₂₁ is connected with the collector of S ₂₁ ; D ₂₂ is connected in antiparallel with S ₂₂ , that is, the anode of D ₂₂ is connected with S ₂₂ The emitter of D 22 is connected together, the cathode of D ₂₂ is connected with the collector of S ₂₂ ; D ₂₃ and S ₂₃ are connected in antiparallel, that is, the anode of D ₂₃ is connected with the emitter of S ₂₃ , and the cathode of D ₂₃ is connected with S ₂₃ The collectors of D ₂₄ and S ₂₄ are connected in antiparallel, that is, the anode of D ₂₄ is connected with the emitter of S ₂₄ , the cathode of D ₂₄ is connected with the collector of S ₂₄ ; the eleventh diode D The anode of ₂₅ and the cathode of the twelfth diode D ₂₆ are both connected to the midpoint n of the DC bus; the cathode of the eleventh diode D ₂₅ is connected to the emitter of the fifth IGBT S ₂₁ and the sixth IGBT The collector of S ₂₂ ; the anode of the twelfth diode D ₂₆ is connected to the emitter of the seventh IGBT S ₂₃ and the collector of the eighth IGBT S ₂₄ ; the collector of the fifth IGBT S ₂₁ is connected to the positive pole of the DC bus P; the emitter of the eighth IGBT S ₂₄ is connected to the negative pole N of the DC bus.

The third bridge arm is composed of four IGBTs S ₃₁ , S ₃₂ , S ₃₃ , S ₃₄ and six diodes D ₃₁ , D ₃₂ , D ₃₃ , D ₃₄ , D ₃₅ and D ₃₆ ; the ninth IGBT S ₃₁ , the tenth IGBT S ₃₂ , the eleventh IGBT S ₃₃ , and the twelfth IGBT S ₃₄ are connected in series in sequence, that is, the emitter of the ninth IGBT S ₃₁ and the collector of the tenth IGBT S ₃₂ are connected together, and the tenth IGBT S ₃₂ The emitter of the eleventh IGBT S ₃₃ and the collector of the eleventh IGBT S 33 are connected together, which is recorded as the midpoint 3 of the third bridge arm, the emitter of the eleventh IGBT S ₃₃ is connected with the collector of the twelfth IGBT S ₃₄ Connected together; D ₃₁ and S ₃₁ are anti-parallel, that is, the anode of D ₃₁ is connected with the emitter of S ₃₁ , and the cathode of D ₃₁ is connected with the collector of S ₃₁ ; D ₃₂ and S ₃₂ are anti-parallel, that is, D _The anode of ₃₂ is _{connected with the emitter of S 32, the cathode of D 32 is connected with the} collector of S _{32 ;} The cathode of D ₃₃ is connected to the collector of S 33; D ₃₄ is connected in antiparallel to S ₃₄ , that is, the anode of D ₃₄ is connected to the emitter of S ₃₄ , and the cathode of D ₃₄ is connected to the collector of S ₃₄ ; the tenth The anode of the seventh diode D ₃₅ and the cathode of the eighteenth diode D ₃₆ are both connected to the midpoint n of the DC bus; the cathode of the seventeenth diode D ₃₅ is connected to the emitter of the ninth IGBT S ₃₁ pole and the collector of the tenth IGBT S ₃₂ ; the anode of the eighteenth diode D ₃₆ is connected to the emitter of the eleventh IGBT S ₃₃ and the collector of the twelfth IGBT S ₃₄ ; the anode of the eleventh IGBT S ₃₁ The collector is connected to the positive pole P of the DC bus; the emitter of the twelfth IGBT S ₃₄ is connected to the negative pole N of the DC bus.

The midpoint 1 of the first bridge arm is used as the output terminal a of the single-phase nine-level converter of the present invention; the midpoint 2 of the second bridge arm and the midpoint 3 of the third bridge arm are respectively connected to two coupling inductors _L1 and L ₂ is two terminals of the non-common point; the common point terminal of the coupled inductor serves as another output terminal b of the single-phase nine-level converter of the present invention. The two coupled inductors are sequential, that is, the common connection point of the two coupled inductors is the common connection point between the same-named end of one coupled inductor and the non-identical end of the other coupled inductor, that is, the output of the single-phase nine-level converter of the present invention terminal b.

Said IGBT can be replaced by MOSFET, GTO and other fully controlled power electronic switching devices.

In order to further illustrate the working principle of the single-phase nine-level converter of the present invention, the effects of the two coupled inductors in FIG. 1 are firstly analyzed. Assuming that the two coupled inductors have the same number of turns and are wound on the same iron core, the main self-inductance of both is M; at the same time, it is assumed that the leakage self-inductance is very small, that is, it can be ignored. Assume that the coupling coefficient of the two coupled inductors is 1, which means that the mutual inductance of the two coupled inductors is also equal to M. Taking the middle connection point n of two DC power supplies as a reference point, the dynamic voltage equation is as follows:

Mdi ₂ /dt-Mdi ₃ /dt=u ₂ nu _bn (1)

Mdi ₃ /dt-Mdi ₂ /dt=u _3n -u _bn (2)

At the same time, according to Kirchhoff's law:

i ₂ +i ₃ +i _b =0 (3)

Solve equations (1)-(3) to get:

u _bn =(u _2n +u _3n )/2 (4)

It can be seen that the role of the coupled inductor is equivalent to connecting two input voltages in series. Therefore, the output voltage of the single-phase nine-level converter is:

u _ab =u _an -u _bn =u _an -(u _2n +u _3n )/2 (5)

It can be seen that the output voltage of the single-phase nine-level converter has nothing to do with the load current _ib . The meanings of the symbols in the above formulas are shown in Figure 1.

There are three switching states of the four switching devices in each bridge arm of the diode-clamped three-level three-phase bridge. The voltage of each bridge arm in different switching states is shown in Table 1 (assuming two DC power sources _E1 and _E2 The voltages are all E).

Table 1 Switching state and corresponding output voltage of each bridge arm of a diode-clamped three-level three-phase bridge (where x indicates the number of the bridge arm, x can be 1, 2 or 3, ON indicates that the corresponding switching device is turned on, OFF indicates that the corresponding switching device is off)

Permissible switching states for each bridge arm output voltage u _{xn Sx1} =ON, _Sx2 =ON, _Sx3 =OFF, _Sx4 =OFF +E S _x1 = OFF, S _x2 = ON, S _x3 = ON, S _x4 = OFF 0 _Sx1 =OFF, _Sx2 =OFF, _Sx3 =ON, _Sx4 =ON -E

It can be seen from Table 1 that u _an (ie u _1n ), u _2n and u _3n can output voltages of three levels, namely +E, 0 and -E. At the same time, according to the formula (5), it can be obtained that the voltage that u _ab can output is shown in Table 2.

Table 2 The output voltage u _ab can output when the output voltage u _an , u _2n , u _{3n of} the three bridge arms are combined in different ways

It can be seen from the rightmost column of Table 2 that u _ab can output nine levels of voltage, namely +2E, +3E/2, +E, +E/2, 0, -E/2, -E, -3E/2 and -2E. Therefore, by selecting an appropriate modulation method, the output voltage u _ab of the single-phase nine-level converter can be realized at nine levels.

Fig. 2 is the simulation calculation waveform diagram of the output voltage u _ab of the single-phase nine-level converter of the present invention, Fig. 3 is the simulation calculation waveform diagram of the load current i _b , and Fig. 4 is the spectrum analysis diagram of u _ab . The simulation parameters are: the DC voltage is 2E=400V, the modulation method is sinusoidal pulse width modulation, the carrier frequency is 2kHz, the reference voltage frequency is 50Hz, the modulation ratio is 0.9, the main self-inductance of the two coupled inductors is 3mH, and the load is RL resistor Inductive series load, where R=2Ω, L=2mH. From these simulation calculation results, it can be seen that the output voltage u _ab of the single-phase nine-level converter is a nine-level pulse width modulation waveform, and the spectrum analysis of u _ab shows that even when the carrier frequency is 2kHz, the THD of u _ab ( total harmonic distortion: total harmonic distortion rate) is only about 17%. Therefore, the nine-level converter can significantly reduce the harmonic content in the output voltage while reducing the switching frequency of the switching device. At the same time, the above simulation calculation results also show the correctness and feasibility of the present invention.

Claims (8)

1. A single-phase nine-level converter is characterized in that: said single-phase nine-level converter is made of a diode-clamped three-level three-phase bridge and two coupled inductors; said three-phase The output terminal of one bridge arm of the bridge is used as a terminal of the output terminal of the single-phase nine-level voltage-type converter; The common connection points are connected, and the common connection point of the two coupled inductors is used as the other terminal of the output terminal of the single-phase nine-level voltage-type converter; the two coupled inductors are connected in series. 2. single-phase nine-level converter as claimed in claim 1, is characterized in that: described diode-clamped three-level three-phase bridge consists of two DC power supplies, a first bridge arm, a second bridge arm and The third bridge arm is formed; the first bridge arm, the second bridge arm and the third bridge arm are all composed of twelve fully-controlled power electronic switching devices (S ₁₁ -S ₁₄ , S ₂₁ -S ₂₄ , S ₃₁ -S ₃₄ ) and eighteen diodes (D ₁₁ -D ₁₄ , D ₂₁ -D ₂₄ , D ₃₁ -D ₃₄ ). 3. The single-phase nine-level converter according to claim 2, characterized in that: the two DC power sources (E ₁ , E ₂ ) are connected in series, that is, the negative pole of the first DC power source (E ₁ ) It is connected to the positive pole of the second DC power supply (E ₂ ) at one point, and this connection point is marked as the midpoint (n) of the DC bus; the positive pole of the first DC power supply (E ₁ ) is marked as the positive pole of the DC bus (P); The negative pole of the second DC power supply (E ₂ ) is denoted as the positive pole (N) of the DC bus. 4. The single-phase nine-level converter according to claim 2, characterized in that: said first bridge arm consists of four IGBTs (S ₁₁ , S ₁₂ , S ₁₃ , S ₁₄ ) and six diodes ( D ₁₁ , D ₁₂ , D ₁₃ , D ₁₄ , D ₁₅ , D ₁₆ ); four IGBTs (S ₁₁ , S ₁₂ , S ₁₃ , S ₁₄ ) are connected in series in sequence, that is, the emitter of the first IGBT (S ₁₁ ) It is connected with the collector of the second IGBT (S ₁₂ ), and the emitter of the second IGBT (S ₁₂ ) is connected with the collector of the third IGBT (S ₁₃ ), denoted as the first bridge arm Midpoint (1), the emitter of the third IGBT (S ₁₃ ) is connected together with the collector of the fourth IGBT (S ₁₄ ); the first diode (D ₁₁ ) is antiparallel to the first IGBT (S ₁₁ ) , that is, the anode of the first diode (D ₁₁ ) is connected together with the emitter of the first IGBT (S ₁₁ ), and the cathode of the first diode (D ₁₁ ) is connected with the collector of the first IGBT (S ₁₁ ). Together; the second diode (D ₁₂ ) is connected in antiparallel with the second IGBT (S ₁₂ ), that is, the anode of the second diode (D ₁₂ ) is connected with the emitter of the second IGBT (S ₁₂ ), the second The cathode of the second diode (D _{12 )} is connected to the collector of the second IGBT (S ₁₂ ); the third diode (D ₁₃ ) is connected in antiparallel with the third IGBT (S ₁₃ ), that is, the third diode (D ₁₃ ) anode is connected with the emitter of the third IGBT (S ₁₃ ), the cathode of the third diode (D ₁₃ ) is connected with the collector of the third IGBT (S ₁₃ ); the fourth diode The tube (D ₁₄ ) is connected in antiparallel with the fourth IGBT (S ₁₄ ), that is, the anode of the fourth diode (D ₁₄ ) is connected with the emitter of the fourth IGBT (S ₁₄ ), and the fourth diode (D ₁₄ ) ) is connected together with the collector of the fourth IGBT (S ₁₄ ); the anode of the fifth diode (D ₁₅ ) is connected with the cathode of the sixth diode (D ₁₆ ) to the midpoint of the DC bus (n); the cathode of the fifth diode (D ₁₅ ) is connected to the emitter of the first IGBT (S ₁₁ ) and the collector of the second IGBT (S ₁₂ ); the anode of the sixth diode (D ₁₆ ) Connected to the emitter of the third IGBT (S ₁₃ ) and the collector of the fourth IGBT (S ₁₄ ); the collector of the first IGBT (S ₁₁ ) is connected to the positive pole (P) of the DC bus; the fourth IGBT (S ₁₄ ) is connected to the negative pole (N) of the DC bus. 5. The single-phase nine-level converter according to claim 2, characterized in that: said second bridge arm consists of four IGBTs (S ₂₁ , S ₂₂ , S ₂₃ , S ₂₄ ) and six diodes ( D ₂₁ , D ₂₂ , D ₂₃ , D ₂₄ , D ₂₅ , D ₂₆ ); the fifth IGBT (S ₂₁ ), the sixth IGBT (S ₂₂ ), the seventh IGBT (S ₂₃ ), the eighth IGBT (S ₂₄ ) in series in sequence, that is, the emitter of the fifth IGBT (S ₂₁ ) is connected to the collector of the sixth IGBT (S ₂₂ ), and the emitter of the sixth IGBT (S ₂₂ ) is connected to the collector of the seventh IGBT (S ₂₃ ). The electrodes are connected together, which is recorded as the midpoint of the second bridge arm), the emitter of the seventh IGBT (S ₂₃ ) is connected with the collector of the eighth IGBT (S ₂₄ ); the seventh diode ( D ₂₁ ) is anti-parallel with the fifth IGBT (S ₂₁ ), that is, the anode of the seventh diode (D ₂₁ ) is connected with the emitter of the fifth IGBT (S ₂₁ ), and the seventh diode (D ₂₁ ) The cathode is connected with the collector of the fifth IGBT and the fifth IGBT (S ₂₁ ); the eighth diode (D ₂₂ ) is connected in antiparallel with the sixth IGBT (S ₂₂ ), that is, the anode of the eighth diode (D ₂₂ ) The emitter of the sixth IGBT (S ₂₂ ) is connected together, the cathode of the eighth diode (D ₂₂ ) is connected with the collector of the sixth IGBT (S ₂₂ ); the ninth diode (D ₂₃ ) It is anti-parallel with the seventh IGBT (S ₂₃ ), that is, the anode of the ninth diode (D ₂₃ ) is connected with the emitter of the seventh IGBT (S ₂₃ ), and the cathode of the ninth diode (D 23 ) is connected with the emitter of the seventh IGBT (S ₂₃ ). The collectors of the seven IGBTs (S ₂₃ ) are connected together; the tenth electrode (D ₂₄ ) is connected in antiparallel with the eighth IGBT (S ₂₄ ), that is, the anode of the tenth electrode (D ₂₄ ) is connected to the eighth IGBT (S ₂₄ ) The emitters of the tenth diode (D ₂₄ ) are connected together with the collector of the eighth IGBT (S ₂₄ ); the anode of the eleventh diode (D ₂₅ ) is connected with the twelfth diode The cathodes of diodes (D ₂₆ ) are connected to the midpoint (n) of the DC bus; the cathodes of the eleventh diode (D ₂₅ ) are connected to the emitter of the fifth IGBT (S ₂₁ ) and the sixth IGBT (S ₂₂ ) collector; the anode of the twelfth diode (D ₂₆ ) is connected to the emitter of the seventh IGBT (S ₂₃ ) and the collector of the eighth IGBT (S ₂₄ ); the fifth IGBT (S ₂₁ ) The collector is connected to the positive pole (P) of the DC bus; the emitter of the eighth IGBT (S ₂₄ ) is connected to the negative pole (N) of the DC bus. 6. The single-phase nine-level converter according to claim 2, characterized in that: said third bridge arm consists of four IGBTs (S ₃₁ , S ₃₂ , S ₃₃ , S ₃₄ ) and six diodes ( D ₃₁ , D ₃₂ , D ₃₃ , D ₃₄ , D ₃₅ , D ₃₆ ); the ninth IGBT (S ₃₁ ), the tenth IGBT (S ₃₂ ), the eleventh IGBT (S ₃₃ ), the twelfth IGBT ( S ₃₄ ) are connected in series in sequence, that is, the emitter of the ninth IGBT (S ₃₁ ) is connected with the collector of the tenth IGBT (S ₃₂ ), and the emitter of the tenth IGBT (S ₃₂ ) is connected with the collector of the eleventh IGBT (S ₃₃ ) collectors are connected together, recorded as the midpoint (3) of the third bridge arm, the emitter of the eleventh IGBT (S ₃₃ ) is connected with the collector of the twelfth IGBT (S ₃₄ ) ; The thirteenth diode (D ₃₁ ) is connected in antiparallel with the ninth IGBT (S ₃₁ ), that is, the anode of the thirteenth diode (D ₃₁ ) is connected with the emitter of the ninth IGBT (S ₃₁ ), The cathode of the thirteenth diode (D ₃₁ ) is connected to the collector of the ninth IGBT (S ₃₁ ); the fourteenth diode (D ₃₂ ) is connected in antiparallel with the tenth IGBT (S ₃₂ ), that is, The anode of the fourteenth diode (D ₃₂ ) is connected together with the emitter of the tenth IGBT (S ₃₂ ), and the cathode of the fourteenth diode (D ₃₂ ) is connected with the collector of the tenth IGBT (S ₃₂ ) Together; the fifteenth diode (D ₃₃ ) is antiparallel to the eleventh IGBT (S ₃₃ ), that is, the anode of the fifteenth diode (D ₃₃ ) is connected to the emitter of the eleventh IGBT (S ₃₃ ) connected together, the cathode of the fifteenth diode (D ₃₃ ) is connected to the collector of the eleventh IGBT (S ₃₃ ); the sixteenth diode (D ₃₄ ) is connected to the collector of the twelfth IGBT (S ₃₄ ) in anti-parallel connection, that is, the anode of the sixteenth diode (D ₃₄ ) is connected to the emitter of the twelfth IGBT (S ₃₄ ), and the cathode of the sixteenth diode (D ₃₄ ) is connected to the twelfth IGBT (S ₃₄ ) collectors are connected together; the anode of the seventeenth diode (D ₃₅ ) and the cathode of the eighteenth diode (D ₃₆ ) are both connected to the midpoint (n) of the DC bus; The cathode of the seventeenth diode (D ₃₅ ) is connected to the emitter of the ninth IGBT (S ₃₁ ) and the collector of the tenth IGBT (S ₃₂ ); the anode of the eighteenth diode (D ₃₆ ) is connected to the The emitter of the eleventh IGBT (S ₃₃ ) and the collector of the twelfth IGBT (S ₃₄ ); the collector of the eleventh IGBT (S ₃₁ ) is connected to the positive pole (P) of the DC bus; the twelfth IGBT (S ₃₄ ) is connected to the negative pole (N) of the DC bus. 7. The single-phase nine-level converter as claimed in claim 1, characterized in that: two coupled inductors are sequentially connected, that is, the common connection point of the two coupled inductors is that the same-named end of one coupled inductor is not the same as the other coupled inductor. Common connection point for the end of the same name. 8. The single-phase nine-level converter according to claim 1, characterized in that the DC voltage stress of each power electronic power device is the same.

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