CN106877717B - Flyback five-level inverter - Google Patents

Abstract

The invention discloses a flyback five-level inverter which is composed of an input direct-current power supply, a voltage dividing capacitor, a five-level conversion unit, a high-frequency isolation transformer, a frequency converter, an output filter and an output alternating-current load which are sequentially connected; the flyback five-level inverter can be well popularized to seven-level and nine-level by increasing the number of the voltage dividing capacitors and changing the five-level conversion units, so that a group of circuit topology families of the flyback multi-level inverter can be obtained. The invention has the advantages of simple circuit topology, bidirectional power flow, two-stage power conversion, small voltage stress of the power switch tube, good front-end voltage spectrum characteristic of the output filter, small volume of the output filter, strong load adaptability and the like, and is suitable for high-voltage input occasions.

Description

Flyback five-level inverter

technical field

The invention belongs to the technical field of power electronic conversion, in particular to a flyback five-level inverter.

Background technique

Direct-to-AC (DC-AC) conversion technology is a conversion technology that uses power semiconductor devices to convert DC power into constant-voltage and constant-frequency AC power, referred to as inverter technology. It is widely used in national defense, industrial and mining enterprises, scientific research institutes, university laboratories and daily life. With the development and application of new energy technology, the application of inverter technology in new energy is also increasing.

So far, research on DC-AC converters by power electronics researchers at home and abroad has mainly focused on non-electrically isolated, low-frequency and high-frequency electrically isolated two-level DC-AC converters; for multi-level converters Research mainly focuses on multi-level DC-DC, AC-AC and AC-DC converters, while research on multi-level DC-AC converters is very little, and is limited to non-isolated, low-frequency or intermediate-frequency isolated type multi-level direct-to-ac converter, but there are relatively few researches on high-frequency isolated multi-level two-stage power conversion inverters.

Traditional inverter technology usually adds a first-class power frequency transformer between the inverter and the output to adjust the voltage ratio and serve as electrical isolation, but the power frequency transformer has the characteristics of large size, audio noise, poor dynamic response characteristics and output filtering. There are many disadvantages such as large size. In 1977, Mr. ESPELAGE proposed a new concept of high-frequency chain inverter technology, using high-frequency transformers instead of power frequency transformers, which overcomes the shortcomings of low-frequency inverter technology, significantly improves the characteristics of the inverter, and has been widely used in the market .

In the traditional two-level inverter, the voltage stress of the switching tube is large, which is not suitable for high-voltage and high-power occasions. In 1977, the German scholar Holtz first proposed the main circuit of the three-level inverter using the switching tube to assist the neutral point clamping. In 1980, A Nabae and others in Japan developed it again and proposed the diode clamping multi-voltage inverter. Flat inverter circuit. After decades of development, there are currently three types of topologies in multi-level inverter technology: diode-clamped inverters, flying-capacitor-clamped inverters, and cascaded inverters with independent DC power supplies. device. Among them, the first two kinds of multilevel inverters are suitable for high input voltage and high power inverter occasions, and the latter multilevel inverter is suitable for low input, high output voltage and high power inverter occasions. However, the diode-clamped and capacitor-clamped multi-level multi-point flat inverter technologies have defects such as single topology and no electrical isolation, and the cascaded multi-level inverter technology with independent DC power supply has complex circuit topology and input The side power factor is low, the conversion efficiency is low, and the power density is low.

Contents of the invention

The object of the present invention is to provide a flyback five-level inverter.

The technical solution for realizing the object of the present invention is: a flyback five-level inverter, which consists of an input DC power supply unit, a voltage dividing capacitor, a five-level conversion unit, a high-frequency isolation transformer, a cycloconverter, an output filter and an output AC load composition;

The input DC power supply unit is used to input DC power;

The voltage dividing capacitor is used to divide the input DC power supply evenly;

The five-level conversion unit is used to modulate the average divided DC voltage into a high-frequency five-level SPWM wave;

The high-frequency isolation transformer is used to realize electrical isolation between the DC side and the AC side;

The cycloconverter is used to modulate the isolated high-frequency five-level SPWM wave into the required frequency SPWM wave;

The output filter is used to filter the SPWM wave output by the cycloconverter to obtain a sine wave.

Compared with the prior art, the present invention has the remarkable advantages of:

(1) The present invention applies the clamping multi-level topology and the construction idea of the loop construction method to the flyback inverter circuit, and inserts a high-frequency isolation transformer between the input DC power supply and the AC load, realizing the realization of the input side and the Electrical isolation on the load side, while realizing the miniaturization and weight reduction of the converter, and improving the efficiency of the converter;

(2) Compared with the traditional two-level inverter and the new three-level inverter, the converter can obtain U _i , (3/4) U _i , (2/4) U _i on the high-frequency transformer , (1/4)U _i , -(N ₁ /N ₂ )u _o five levels improve the output voltage waveform and are more suitable for high voltage and high power occasions;

(3) The present invention has the advantages of fewer power conversion stages (direct current DC-high frequency AC HFAC-low frequency AC LFAC), bidirectional power flow, and good spectral characteristics of the output filter front-end voltage, thereby improving conversion efficiency and power density, reducing Small size and weight.

Description of drawings

FIG. 1 is a circuit topology diagram of a flyback five-level inverter according to the present invention.

FIG. 2 is a circuit topology diagram of a full-wave rectification flyback five-level inverter according to the present invention.

Detailed ways

Combined with Figure 1 and Figure 2, a flyback five-level inverter consists of an input DC power supply unit 1, a voltage dividing capacitor 2, a five-level conversion unit 3, a high-frequency isolation transformer 4, a cycloconverter 5, and an output filter It is composed of an inverter 6 and an output AC load 7; the inverter can convert unstable high-voltage direct current into adjustable sinusoidal alternating current, reduce the number of power conversion stages, realize high-frequency electrical isolation, and is suitable for high-voltage DC/AC conversion occasions;

The input DC power supply unit 1 is used for inputting DC power;

The voltage dividing capacitor 2 is used to divide the input DC power supply evenly;

The five-level conversion unit 3 is used for modulating the average divided DC voltage into a high-frequency five-level SPWM wave;

The high-frequency isolation transformer 4 is used to realize electrical isolation between the DC side and the AC side;

The cycloconverter 5 is used to modulate the isolated high-frequency five-level SPWM wave into the SPWM wave of the required frequency;

The output filter 6 is used to filter the SPWM wave output by the cycloconverter 5 to obtain a sine wave.

Further, the input DC power supply unit 1 includes an input DC power supply U _i , and the voltage dividing capacitor 2 includes a first voltage dividing capacitor C ₁ , a second voltage dividing capacitor C ₂ , a third voltage dividing capacitor C ₃ and a fourth voltage dividing capacitor C ₄ ; the positive pole of the first voltage-dividing capacitor _C1 is connected to the positive pole of the input DC power supply _Ui , the negative pole of the first voltage-dividing capacitor _C1 is connected to the positive pole of the second voltage-dividing capacitor _C2 , and the positive pole of the second voltage-dividing capacitor _C2 The negative pole is connected to the positive pole of the third voltage dividing capacitor _C3 , the negative pole of the third voltage dividing capacitor _C3 is connected to the positive pole of the fourth voltage dividing capacitor _C4 , the negative pole of the fourth voltage dividing capacitor _C4 is connected to the input DC power supply _Ui Refer to negative connection.

Further, the five-level conversion unit 3 includes a first power switch S ₁ , a first diode D ₁ , a second power switch S ₂ , a second diode D ₂ , a first bidirectional switch S _A. The second bidirectional switch S _B , the third bidirectional switch S _C , the ninth power switch S ₉ , the ninth diode D ₉ , the tenth power switch S ₁₀ , the tenth diode D ₁₀ , The eleventh diode D ₁₁ , the twelfth diode D ₁₂ , the thirteenth diode D ₁₃ and the fourteenth diode D ₁₄ ; the two-way switches are composed of two single power The switch tubes are reversely connected in series to form a switch that withstands forward and reverse voltage stress and current stress, and has bidirectional blocking capability; the first bidirectional switch tube S _A includes a third power switch tube S ₃ , a third diode D _3. The fourth power switch S ₄ and the fourth diode D ₄ , the second bidirectional switch S _B includes the fifth power switch S ₅ , the fifth diode D ₅ , the sixth power switch S ₆ and The sixth diode D ₆ , the third bidirectional switch S _C includes a seventh power switch S ₇ , a seventh diode D ₇ , an eighth power switch S ₈ and an eighth diode D ₈ ; the The high-frequency isolation transformer 4 includes a primary winding N ₁ , a first secondary winding N ₂ and a second secondary winding N ₃ ;

The drain of the first power switch tube _S1 is connected to the anode of the first voltage dividing capacitor _C1 , and the first diode _D1 is connected in antiparallel to both ends of the first power switch tube _S1 , that is, the first diode D ₁ is connected to the drain of the first power switch tube _S1 , the anode of the first diode _D1 is connected to the source of the first power switch tube _S1 , and the source of the first power switch tube _S1 is connected to the original The terminal with the same name of the side winding _N1 is connected to the cathode of the eleventh diode _D11 ; the drain of the second power switch tube _S2 is connected to the terminal with the same name of the primary winding _N1 and the terminal of the tenth power switch tube _S10 The drain is connected to the cathode of the tenth diode _D10 , the source of the second power switch _S2 is connected to the cathode of the fourth voltage dividing capacitor _C4 , and the second diode _D2 is connected in antiparallel to the second Both ends of the power switch tube _S2 , that is, the cathode of the second diode _D2 is connected to the drain of the second power switch tube _S2 , and the anode of the second diode _D2 is connected to the source of the second power switch tube _S2 The tenth diode _D10 is connected in antiparallel to both ends of the tenth power switch tube _S10 , that is, the cathode of the tenth diode _D10 is connected to the drain of the tenth power switch tube _S10 , and the twelfth pole The anode of the tube D ₁₀ is connected to the source of the tenth power switch tube S ₁₀ , while the source of the tenth power switch tube S ₁₀ , the anode of the tenth diode D ₁₀ and the anode of the fourteenth diode D ₁₄ connected;

The cathode of the third diode _D3 and the drain of the third power switch _S3 are simultaneously connected to the negative pole of the first voltage dividing capacitor _C1 and the positive pole of the second voltage dividing capacitor _C2 , and the fourth diode D ₄ and the drain of the fourth power switch tube _S4 are simultaneously connected to the drain of the ninth power switch tube _S9 , the cathode of the ninth diode _D9 , and the cathode of the twelfth diode D12. The anode of the three diodes _D3 , the anode of the fourth diode _D4 , the source of the third power switch _S3 , and the source of the fourth power switch _S4 are connected together; the ninth diode D ₉ is connected in antiparallel to both ends of the ninth power switch tube _S9 , that is, the cathode of the ninth diode _D9 is connected to the drain of the ninth power switch tube S9, and the anode of the ninth diode _D9 is connected to the ninth power switch tube S9 _. The source of the switching tube _S9 is connected, and at the same time the source of the ninth power switching tube _S9 , the anode of the ninth diode _D9 and the anode of the eleventh diode _D11 are connected; the fifth diode D ₅ and the drain of the fifth power switch tube _S5 are simultaneously connected to the negative pole of the second voltage dividing capacitor _C2 and the positive pole of the third voltage dividing capacitor _C3 , and the cathode of the sixth diode _D6 and the sixth The drain of the power switch tube _S6 is connected to the cathode of the thirteenth diode _D13 and the anode of the twelfth diode D12 at the same _time , the anode of the fifth diode _D5 , the anode of the sixth diode D ₆ , the source of the fifth power switch _S5 , and the source of the sixth power switch _S6 are connected together; the cathode of the seventh diode _D7 and the drain of the seventh power switch _S7 are simultaneously It is connected with the negative pole of the third voltage dividing capacitor _C3 and the positive pole of the fourth voltage dividing capacitor _C4 , the cathode of the eighth diode _D8 and the drain of the eighth power switch tube _S8 are simultaneously connected with the thirteenth diode The anode of the tube D ₁₃ is connected to the cathode of the fourteenth diode D ₁₄ , the anode of the seventh diode D ₇ , the anode of the eighth diode D ₈ , the source of the seventh power switch tube S ₇ , The sources of the eighth power switch _S8 are connected together.

Further, the cycloconverter 5 includes a fourth bidirectional switch _SD and a fifth bidirectional switch _SE , the fourth bidirectional switch _SD and the fifth bidirectional switch _SE are composed of two single power switches The tubes are reversely connected in series to form a switch that bears forward and reverse voltage stress and current stress, and has a bidirectional blocking function; the fourth bidirectional switch tube S _D includes the eleventh power switch tube S ₁₁ , the twelfth power switch tube S ₁₂ , the fifteenth diode D ₁₅ and the sixteenth diode D ₁₆ , the fifth bidirectional switch S _E includes the thirteenth power switch S ₁₃ , the fourteenth power switch S ₁₄ , the seventeenth Diode D ₁₇ and the eighteenth diode D ₁₈ ; the cathode of the fifteenth diode D ₁₅ and the drain of the eleventh power switch S ₁₁ are all connected to the non-identical end of the first secondary winding N ₂ connected, the cathode of the sixteenth diode D ₁₆ and the drain of the twelfth power switch S ₁₂ are simultaneously connected to the cathode of the eighteenth diode D ₁₈ and the drain of the fourteenth power switch S ₁₄ , The cathode of the seventeenth diode D ₁₇ and the drain of the thirteenth power switch tube S ₁₃ are connected to the end of the same name of the second secondary winding N ₃ at the same time, the anode of the fifteenth diode D ₁₅ , the drain of the sixteenth The anode of the diode D ₁₆ , the source of the eleventh power switch S ₁₁ , and the source of the twelfth power switch S ₁₂ are connected together, the anode of the seventeenth diode D ₁₇ , the source of the eighteenth two The anode of the pole tube D ₁₈ , the source of the thirteenth power switch tube S ₁₃ , and the source of the fourteenth power switch tube S ₁₄ are connected together;

Further, the output filter 6 includes an output filter capacitor C _f , one end of the output filter capacitor C _f is simultaneously connected to the cathode of the sixteenth diode D ₁₆ , the drain of the twelfth power switch tube S ₁₂ , the tenth The cathode of the eighth diode _D18 is connected to the drain of the fourteenth power switch tube _S14 , and the other end of the output filter capacitor _Cf is connected to the terminal of the same name of the first secondary winding _N2 and the terminal of the second secondary winding _N3 Non-homogenous end connection.

Further, the output AC load 7 includes an AC load Z _L , one end of the AC load Z _L is connected to one end of the output filter capacitor C _f , and the other end of the AC load Z _L is connected to the other end of the output filter capacitor C _f .

The basic working principle of the high-frequency isolated five-level inverter of the present invention is as follows: the inverter can adopt the SPWM control mode. When the high-voltage DC input power supply U _i transmits power to the AC load Z _L , the input voltage U _i can get U _i , 3U _i /4, 2U _i /4, U _i /4 after passing through the voltage dividing capacitor and the five-level conversion unit , -(N ₁ /N ₂ )U _o five levels, after isolation and transmission by the high-frequency transformer, the cycloconverter will demodulate it into a low-frequency pulse voltage, and then get a stable or Adjustable sinusoidal AC voltage u _o .

There are four voltage-dividing capacitors on the DC side of the inverter. The closed-loop control needs to sample the voltages U _C1 , U _C2 , U _C3 , U _C4 of the four capacitors and the output voltage u _o to ensure that the four capacitors on the input side of the inverter work The voltage balance and the waveform quality of the output voltage u _o are good. The inverter adopts the active clamp pulse modulation (SPWM) chopping control method based on the voltage instantaneous value feedback control, and compares the sampling voltage of the voltage u _o output by the inverter with the sinusoidal reference voltage u _ref , the error voltage After the proportional-integral regulator, the error amplification signal _ue is obtained, and the error signal is intersected with the sawtooth carrier to obtain the SPWM signal wave, and the obtained SPWM signal and the sinusoidal basic signal wave are driven by a series of logic transformations to obtain the switch tube Signal. The voltages of the four capacitors are sampled as U _C1 , U _C2 , U _C3 , and U _C4 , and the four voltage values are compared to obtain the maximum value. This selects which capacitor has the longest working time in the switching cycle, and according to the optimal The selection principle of the switch sequence can select which switch tubes work and which switch tubes do not work. Select different capacitor combinations according to the voltage values of the four capacitors on the input side. If the value of U _C1 is the largest, C ₁ , C ₂ , C ₃ , and C ₄ provide the level U _i , and C ₁ , C ₂ , C ₃ Provide level (3/4) U _i , C ₁ , C ₂ provide 2/4 U _i , C ₁ provides (1/4) U _i ; if the value of U _C2 is the largest, C ₁ , C ₂ , C _3. C ₄ provides level U _i , C ₁ , C ₂ , C ₃ provide level (3/4) U _i , C ₁ , C ₂ provide (2/4) U _i , and C ₂ provides ( 1/4) U _i . If the value of U _C3 is the largest, C ₁ , C ₂ , C ₃ , C ₄ provide the level U _i , C ₂ , C ₃ , C ₄ provide the level (3/4) U _i , and C ₃ , C ₄ provides (2/4) U _i , C ₃ provides (1/4) U _i ; if the value of U _C4 is the largest, C ₁ , C ₂ , C ₃ , C ₄ provide the level U _i , and C ₂ , C ₃ , C ₄ provide level (3/4) U _i , C ₃ , C ₄ provide (2/4) U _i , and C ₄ provides (1/4) U _i .

Since the inverter has a four-quadrant working capability, it can carry resistive, capacitive, inductive and rectifying loads. In an output voltage cycle, the inverter has four working modes, corresponding to the four-quadrant work, each working mode is equivalent to a Buck/Boost type high-frequency isolation converter, and the inverter is under different load conditions The working sequence of the controller is also different.

Claims (5)

1. A flyback five-level inverter, characterized in that it consists of an input DC power supply unit (1), a voltage dividing capacitor (2), a five-level conversion unit (3), a high-frequency isolation transformer (4), Composed of a cycloconverter (5), an output filter (6) and an output AC load (7); The input DC power supply unit (1) is used for inputting DC power; The voltage dividing capacitor (2) is used to divide the input DC power evenly; The five-level conversion unit (3) is used to modulate the average divided DC voltage into a high-frequency five-level SPWM wave; The high-frequency isolation transformer (4) is used to realize electrical isolation between the DC side and the AC side; The cycloconverter (5) is used to modulate the isolated high-frequency five-level SPWM wave into a SPWM wave of the required frequency; The output filter (6) is used to filter the SPWM wave output by the cycloconverter (5) to obtain a sine wave; The five-level conversion unit (3) includes a first power switch tube (S ₁ ), a first diode (D ₁ ), a second power switch tube (S ₂ ), a second diode (D ₂ ) , the first bidirectional switch (S _A ), the second bidirectional switch (S _B ), the third bidirectional switch (S _C ), the ninth power switch (S ₉ ), the ninth diode (D ₉ ) , the tenth power switch tube (S ₁₀ ), the tenth diode (D ₁₀ ), the eleventh diode (D ₁₁ ), the twelfth diode (D ₁₂ ), the thirteenth diode ( D ₁₃ ) and the fourteenth diode (D ₁₄ ); the two-way switching tube is composed of two single power switching tubes in reverse series to form a switch that withstands forward and reverse voltage stress and current stress , with bidirectional blocking capability; the first bidirectional switch (S _A ) includes a third power switch (S ₃ ), a third diode (D ₃ ), a fourth power switch (S ₄ ) and a fourth two pole tube (D ₄ ), the second bidirectional switch tube (S _B ) includes the fifth power switch tube (S ₅ ), the fifth diode (D ₅ ), the sixth power switch tube (S ₆ ) and the sixth two pole tube (D ₆ ), the third bidirectional switch tube (S _C ) includes the seventh power switch tube (S ₇ ), the seventh diode (D ₇ ), the eighth power switch tube (S ₈ ) and the eighth two pole tube (D ₈ ); the high-frequency isolation transformer (4) includes a primary winding (N ₁ ), a first secondary winding (N ₂ ) and a second secondary winding (N ₃ ); The drain of the first power switch (S ₁ ) is connected to the anode of the first voltage dividing capacitor (C ₁ ), and the first diode (D ₁ ) is connected in antiparallel to both ends of the first power switch (S ₁ ). , that is, the cathode of the first diode (D ₁ ) is connected to the drain of the first power switch (S ₁ ), and the anode of the first diode (D ₁ ) is connected to the drain of the first power switch (S ₁ ). Source connection, the source of the first power switch tube (S ₁ ) is connected to the terminal with the same name of the primary winding (N ₁ ) and the cathode of the eleventh diode (D ₁₁ ); the second power switch tube (S ₂ ) The drain is connected to the non-identical terminal of the primary winding (N ₁ ), the drain of the tenth power switch tube (S ₁₀ ), and the cathode of the tenth diode (D ₁₀ ), and the second power switch tube The source of (S ₂ ) is connected to the cathode of the fourth voltage dividing capacitor (C ₄ ), and the second diode (D ₂ ) is antiparallel connected to both ends of the second power switch (S ₂ ), that is, the second two The cathode of the diode (D ₂ ) is connected to the drain of the second power switch (S ₂ ), and the anode of the second diode (D ₂ ) is connected to the source of the second power switch (S ₂ ). The tenth diode (D ₁₀ ) is connected in antiparallel to both ends of the tenth power switch tube (S ₁₀ ), that is, the cathode of the tenth diode (D ₁₀ ) is connected to the drain of the tenth power switch tube (S ₁₀ ), The anode of the tenth diode (D ₁₀ ) is connected to the source of the tenth power switch (S ₁₀ ), while the source of the tenth power switch (S ₁₀ ) and the tenth diode (D ₁₀ ) The anode is connected to the anode of the fourteenth diode (D ₁₄ ); The cathode of the third diode (D ₃ ) and the drain of the third power switch (S ₃ ) are in phase with the negative pole of the first voltage dividing capacitor (C ₁ ) and the positive pole of the second voltage dividing capacitor (C ₂ ). connection, the cathode of the fourth diode (D ₄ ) and the drain of the fourth power switch (S ₄ ) are simultaneously connected to the drain of the ninth power switch (S ₉ ), the ninth diode (D ₉ ) The cathode of the twelfth diode (D12) is connected, the anode of the third diode (D ₃ ), the anode of the fourth diode (D ₄ ), the third power switch tube (S ₃ ) The source of the fourth power switch (S ₄ ) is connected together; the ninth diode (D ₉ ) is connected in antiparallel to both ends of the ninth power switch (S ₉ ), that is, the ninth diode The cathode of (D ₉ ) is connected to the drain of the ninth power switch (S ₉ ), the anode of the ninth diode (D ₉ ) is connected to the source of the ninth power switch (S ₉ ), and the ninth The source of the power switch tube (S ₉ ), the anode of the ninth diode (D ₉ ) and the anode of the eleventh diode (D ₁₁ ) are connected; the cathode of the fifth diode (D ₅ ) and The drain of the fifth power switch tube (S ₅ ) is simultaneously connected to the negative pole of the second voltage dividing capacitor (C ₂ ) and the positive pole of the third voltage dividing capacitor (C ₃ ), and the sixth diode (D ₆ ) The cathode and the drain of the sixth power switch tube (S ₆ ) are simultaneously connected to the cathode of the thirteenth diode (D ₁₃ ) and the anode of the twelfth diode (D ₁₂ ), and the fifth diode ( The anode of D ₅ ), the anode of the sixth diode (D ₆ ), the source of the fifth power switch (S ₅ ), and the source of the sixth power switch (S ₆ ) are connected together; The cathode of the pole tube (D ₇ ) and the drain of the seventh power switch tube (S ₇ ) are simultaneously connected to the negative pole of the third voltage dividing capacitor (C ₃ ) and the positive pole of the fourth voltage dividing capacitor (C ₄ ). The cathode of the eighth diode (D ₈ ) and the drain of the eighth power switch tube (S ₈ ) are simultaneously connected to the anode of the thirteenth diode (D ₁₃ ) and the cathode of the fourteenth diode (D ₁₄ ) The anode of the seventh diode (D ₇ ), the anode of the eighth diode (D ₈ ), the source of the seventh power switch (S ₇ ), the eighth power switch (S ₈ ) The sources are connected together; When the high-voltage DC input power supply (U _i ) transmits power to the AC load (Z _L ), the input voltage U _i passes through the voltage dividing capacitor and the five-level conversion unit to obtain U _i , 3U _i /4, 2U _i /4, U _i /4, -(N ₁ /N ₂ ) U _o five levels, where U _o is the output voltage, N ₁ is the primary winding, and N ₂ is the first secondary winding. 2. The flyback five-level inverter according to claim 1, characterized in that the input DC power supply unit (1) includes an input DC power supply (U _i ), and the voltage dividing capacitor (2) includes a first voltage dividing capacitor (C ₁ ), the second voltage-dividing capacitor (C ₂ ), the third voltage-dividing capacitor (C ₃ ) and the fourth voltage-dividing capacitor (C ₄ ); the positive pole of the first voltage-dividing capacitor (C ₁ ) is connected to the input DC power supply The positive pole of (U _i ) is connected, the negative pole of the first voltage dividing capacitor (C ₁ ) is connected to the positive pole of the second voltage dividing capacitor (C ₂ ), the negative pole of the second voltage dividing capacitor (C ₂ ) is connected to the third voltage dividing capacitor (C ₃ ), the negative pole of the third voltage dividing capacitor (C ₃ ) is connected to the positive pole of the fourth voltage dividing capacitor (C ₄ ), the negative pole of the fourth voltage dividing capacitor (C ₄ ) is connected to the input DC power supply (U _i ) The reference negative connection. 3. The flyback five-level inverter according to claim 1, characterized in that the cycloconverter (5) includes a fourth bidirectional switch ( _SD ) and a fifth bidirectional switch ( _SE ) , the fourth bidirectional switch (S _D ) and the fifth bidirectional switch ( _SE ) are two single power switches in reverse series to form a switch that withstands forward and reverse voltage stress and current stress, It has a bidirectional blocking function; the fourth bidirectional switch tube (S _D ) includes the eleventh power switch tube (S ₁₁ ), the twelfth power switch tube (S ₁₂ ), the fifteenth diode (D ₁₅ ) and the The sixteenth diode (D ₁₆ ), the fifth bidirectional switch (S _E ) includes the thirteenth power switch (S ₁₃ ), the fourteenth power switch (S ₁₄ ), the seventeenth diode (D ₁₇ ) and the eighteenth diode (D ₁₈ ); the cathode of the fifteenth diode (D ₁₅ ) and the drain of the eleventh power switch tube (S ₁₁ ) are connected to the first secondary winding (N ₂ ), the cathode of the sixteenth diode (D ₁₆ ) and the drain of the twelfth power switch tube (S ₁₂ ) are simultaneously connected with the cathode of the eighteenth diode (D ₁₈ ) and the tenth The drains of the four power switch tubes (S ₁₄ ) are connected, the cathode of the seventeenth diode (D ₁₇ ) and the drain of the thirteenth power switch tube (S ₁₃ ) are simultaneously connected to the second secondary winding (N ₃ ) Connected to the end of the same name, the anode of the fifteenth diode (D ₁₅ ), the anode of the sixteenth diode (D ₁₆ ), the source of the eleventh power switch (S ₁₁ ), the twelfth power switch The sources of the tube (S ₁₂ ) are connected together, the anode of the seventeenth diode (D ₁₇ ), the anode of the eighteenth diode (D ₁₈ ), the source of the thirteenth power switch tube (S ₁₃ ) pole and the source of the fourteenth power switch tube (S ₁₄ ) are connected together. 4. The flyback five-level inverter according to claim 3, characterized in that the output filter (6) includes an output filter capacitor (C _f ), and one end of the output filter capacitor (C _f ) is simultaneously connected to The cathode of the sixteenth diode (D ₁₆ ), the drain of the twelfth power switch (S ₁₂ ), the cathode of the eighteenth diode (D ₁₈ ), and the fourteenth power switch (S ₁₄ ) The drain of the output filter capacitor (C _f ) is connected to the same-named end of the first secondary winding (N ₂ ) and the non-identical end of the second secondary winding (N ₃ ). 5. The flyback five-level inverter according to claim 4, characterized in that the output AC load (7) includes an AC load (Z _L ), one end of the AC load (Z _L ) and an output filter capacitor (C _f ) is connected at one end, and the other end of the AC load (Z _L ) is connected with the other end of the output filter capacitor (C _f ).

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