An expanded T-type three-phase three-level converter and its modulation method

Abstract

The present invention discloses an expanded T-type three-phase three-level converter and a modulation method thereof. The first end of a three-phase input filter module in the expanded T-type three-phase three-level converter is electrically connected to an AC power supply module, the first end of a three-phase expansion module is electrically connected to a second end of the three-phase input filter module, and the second end is connected to a first DC capacitor and a second DC capacitor in a delta-connected DC capacitor module, connected to points P, O, and N. The first end of the delta-connected DC capacitor module is electrically connected to the second end of the three-phase expansion module, the first end of a T-type three-phase three-level three-phase inverter module and the second end of the delta-connected DC capacitor module are electrically connected to points P, O, and N, and the first end of a three-phase output filter module is electrically connected to the second end of the T-type three-phase three-level three-phase inverter module. The present application has the advantages of continuously adjustable output voltage, excellent input and output power quality, and low switching loss.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and more particularly to an expanded T-type three-phase three-level converter and a modulation method thereof. Background Art

[0002] To better meet the performance requirements of electrical equipment and mitigate the adverse effects of these devices on grid power quality, research on high-efficiency inverters continues. Among various AC-AC converters, phase-controlled voltage regulators offer advantages such as simple structure and low cost, but they suffer from significant waveform distortion, low efficiency, and a lack of frequency conversion capabilities. Matrix converters, due to their AC-AC frequency conversion structure, offer advantages such as simplicity, high power density, and bidirectional energy flow. However, they suffer from complex switching control, high voltage and current stresses, high switching losses, and are limited by input voltage, resulting in a narrow output voltage adjustment range.

[0003] AC-DC-AC converters, with their two-stage rectification and inversion structure, offer simple control and strong adaptability, enabling a wide range of frequency conversion and voltage regulation. Traditional diode-controlled rectification and thyristor-controlled rectification methods, due to their high harmonic content and poor power factor, are being gradually replaced by fully controlled PWM rectification. Therefore, the current mainstream frequency conversion system is a cascaded PWM rectification-PWM inverter system. However, because each stage utilizes PWM control using fully controlled devices, switching losses are high. Summary of the Invention

[0004] To solve the above technical problems, the present invention develops an expanded T-type three-phase three-level converter and a modulation method thereof. The expanded T-type three-phase three-level converter has the advantages of continuously adjustable output voltage, excellent input and output power quality, and low switching loss.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] An expandable T-type three-phase three-level converter, characterized by comprising an AC power supply module, a three-phase input filter module, a three-phase expansion module, a delta-connected DC capacitor module, a T-type three-phase three-level three-phase inverter module, and a three-phase output filter module, wherein a first end of the three-phase input filter module is electrically connected to the AC power supply module, a first end of the three-phase expansion module is electrically connected to a second end of the three-phase input filter module, and a second end thereof is connected to a first DC capacitor and a second DC capacitor in a delta-connected DC capacitor module to points P, O, and N, a first end of the delta-connected DC capacitor module is electrically connected to a second end of the three-phase expansion module, a first end of the T-type three-phase three-level three-phase inverter module and a second end of the delta-connected DC capacitor module are electrically connected to points P, O, and N, and a first end of the three-phase output filter module is electrically connected to a second end of the T-type three-phase three-level three-phase inverter module.

[0007] The AC power supply module includes: a first AC power supply, a second AC power supply, and a third AC power supply, wherein the negative terminal of the second AC power supply is electrically connected to the negative terminal of the first AC power supply, and the negative terminal of the third AC power supply is electrically connected to the negative terminal of the second AC power supply;

[0008] The three-phase input filter module includes: a first filter inductor, a second filter inductor, and a third filter inductor, wherein a first end of the first filter inductor is electrically connected to the positive terminal of the first AC power supply, a first end of the second filter inductor is electrically connected to the positive terminal of the second AC power supply, and a first end of the third filter inductor is electrically connected to the positive terminal of the third AC power supply;

[0009] The three-phase expansion module includes: a first diode, a second diode, a third diode, a fourth diode, a fifth diode, a sixth diode, and a first bidirectional switch unit, wherein an anode of the first diode is electrically connected to the second end of the first filter inductor, a cathode of the second diode is electrically connected to the anode of the first diode, a cathode of the third diode is electrically connected to the cathode of the first diode, an anode of the third diode is electrically connected to the second end of the second filter inductor, a cathode of the fourth diode is electrically connected to the anode of the third switch tube, an anode of the fourth diode is electrically connected to the anode of the second diode, a cathode of the fifth diode is electrically connected to the cathode of the third diode, an anode of the fifth diode is electrically connected to the second end of the third filter inductor, a cathode of the sixth switch tube is electrically connected to the anode of the fifth switch tube, an emitter of the sixth diode is electrically connected to the anode of the fourth diode, a first end of the first bidirectional switch unit is electrically connected to the anode of the first diode, a second end of the first bidirectional switch unit is electrically connected to the anode of the third diode, and a third end of the first bidirectional switch unit is electrically connected to the anode of the fifth diode;

[0010] The delta-connected DC capacitor module includes: a first DC capacitor, a second DC capacitor, and a third DC capacitor, wherein a first end of the first DC capacitor is electrically connected to the cathode of the first diode at point P, a first end of the second DC capacitor is electrically connected to the second end of the first DC capacitor at point O, a first end of the third DC capacitor is electrically connected to the first end of the first DC capacitor at point P, and a second end of the third DC capacitor is electrically connected to the second end of the second DC capacitor at point N;

[0011] The T-type three-phase three-level three-phase inverter module includes: a second bidirectional switch unit and a three-phase full-bridge unit, wherein the first end of the second bidirectional switch unit is electrically connected to the O end of the first DC capacitor, the first end of the three-phase full-bridge unit is electrically connected to the first end P of the first DC capacitor, and the second end of the three-phase full-bridge unit is electrically connected to the second end N of the second DC capacitor;

[0012] The three-phase output filter module includes: a fourth filter inductor, a fifth filter inductor and a sixth filter inductor, the fourth filter inductor is electrically connected to the first end of the first load, the fifth filter inductor is electrically connected to the first end of the second load, and the sixth filter inductor is electrically connected to the first end of the third load.

[0013] As a preferred technical solution of the present invention: the first bidirectional switch unit includes: a first switching tube, a second switching tube, a third switching tube, a fourth switching tube, a fifth switching tube and a sixth switching tube, the collector of the first switching tube is electrically connected to the anode of the first diode, the emitter of the second switching tube is electrically connected to the emitter of the first switching tube, the collector of the third switching tube is electrically connected to the anode of the third diode, the emitter of the fourth switching tube is electrically connected to the emitter of the third switching tube, the collector of the fifth switching tube is electrically connected to the anode of the fifth diode, and the emitter of the sixth switching tube is electrically connected to the emitter of the fifth switching tube.

[0014] As a preferred technical solution of the present invention: the second bidirectional switch unit includes: a seventh switch tube, an eighth switch tube, a ninth switch tube, a tenth switch tube, an eleventh switch tube and a twelfth switch tube, the collector of the seventh switch tube is electrically connected to the second end of the first DC capacitor, the emitter of the eighth switch tube is electrically connected to the emitter of the seventh switch tube, the collector of the ninth switch tube is electrically connected to the second end of the first DC capacitor, the emitter of the tenth switch tube is electrically connected to the emitter of the ninth switch tube, the collector of the eleventh switch tube is electrically connected to the second end of the first DC capacitor, and the emitter of the twelfth switch tube is electrically connected to the emitter of the eleventh switch tube.

[0015] As a preferred technical solution of the present invention: the three-phase full-bridge unit includes: a thirteenth switch tube, a fourteenth switch tube, a fifteenth switch tube, a sixteenth switch tube, a seventeenth switch tube and an eighteenth switch tube, the collector of the thirteenth switch tube is electrically connected to the first end of the first DC capacitor, the emitter of the thirteenth switch tube is electrically connected to the collector of the eighth switch tube, the collector of the fourteenth switch tube is electrically connected to the emitter of the thirteenth switch tube, the emitter of the fourteenth switch tube is electrically connected to the second end of the second DC capacitor, the collector of the fifteenth switch tube is electrically connected to the collector of the thirteenth switch tube The emitter of the fifteenth switching tube is electrically connected to the collector of the tenth switching tube, the collector of the sixteenth switching tube is electrically connected to the emitter of the fifteenth switching tube, the emitter of the sixteenth switching tube is electrically connected to the emitter of the fourteenth switching tube, the collector of the seventeenth switching tube is electrically connected to the collector of the fifteenth switching tube, the emitter of the seventeenth switching tube is electrically connected to the collector of the twelfth switching tube, the collector of the eighteenth switching tube is electrically connected to the emitter of the seventeenth switching tube, and the emitter of the eighteenth switching tube is electrically connected to the emitter of the sixteenth switching tube.

[0016] In the above-mentioned structure, the present invention proposes an expandable T-type three-phase three-level converter. Its expansion side utilizes triple-power-frequency switching, resulting in a six-pulse segmented sinusoidal voltage across the DC capacitor. To maximize voltage utilization, the T-type three-level inverter side uses the maximum and second-maximum line voltages across the DC capacitor to synthesize the inverter-stage voltage. The upper and lower transistors of the T-type three-level inverter perform inversion based on the maximum line voltage. If the upper capacitor serves as the second-maximum line voltage, the upper transistor and bidirectional switch of the T-type three-level inverter perform inversion based on the second-maximum voltage. Conversely, if the lower capacitor serves as the second-maximum line voltage, the bidirectional switch and lower transistor of the T-type three-level inverter perform inversion based on the second-maximum voltage.

[0017] A modulation method for an expanded T-type three-phase three-level converter is characterized by comprising the following steps:

[0018] S1. Determine the first and second duty ratios of the effective current vector in the expanded stage current space vector;

[0019] S2. Determine the third and fourth duty cycles of the effective voltage vector in the output voltage space vector of the inverter stage;

[0020] S3, determining a fifth duty cycle of the zero vector in the inverter output voltage space vector;

[0021] S4, select the transfer period;

[0022] S5. Determining first and second duty ratios of the effective current vector in the expanded-stage current space vector, including:

[0023] According to the current space vector modulation method, the expressions for determining the first and second duty cycles of the rectifier stage are:

[0024]

[0025] Among them, θ sc is the angle between the desired reference current vector and the current large sector vector

[0026] The first and second duty cycles of the effective current vector are equal to the maximum and second largest line voltage duty cycles on the DC capacitor. When the first small sector is turned on, there is a second largest line voltage u on the first DC capacitor. ab The on-duty cycle is d β , there is a maximum line voltage u on the third DC capacitor ac The on-duty cycle is d α , at this time, the first AC power supply current and the third AC power supply current synthesize a reference current vector;

[0027] S6. Determining the third and fourth duty ratios of the inverter stage of the effective voltage vector in the output voltage space vector of the inverter stage, comprising:

[0028] According to the voltage space vector modulation method, the expressions for determining the third and fourth duty cycles of the inverter stage are:

[0029]

[0030] Among them, m v is the modulation coefficient of the inverter, ranging from 0 to 1; θ sv is the angle between the desired reference voltage vector and the lower vector of the current sector.

[0031] In the above structure: the third DC capacitor always has a maximum line voltage, the three-phase full-bridge unit inverts the maximum line voltage on the third DC capacitor, and the second bidirectional switch unit is electrically disconnected from the second end of the first DC capacitor. Therefore, when the first DC capacitor has a second-maximum line voltage, the thirteenth, fifteenth, and seventeenth switching tubes and the second bidirectional switch unit invert the second-maximum line voltage on the first DC capacitor, and the fourteenth, sixteenth, and eighteenth switching tubes are electrically disconnected from the second end of the second DC capacitor. When the second DC capacitor has a second-maximum line voltage, the fourteenth, sixteenth, and eighteenth switching tubes and the second bidirectional switch unit invert the second-maximum line voltage on the second DC capacitor, and the thirteenth, fifteenth, and seventeenth switching tubes are electrically disconnected from the first end of the first DC capacitor.

[0032] Determining a fifth duty cycle of a zero vector of the inverter stage in the output voltage space vector of the inverter stage includes:

[0033] According to the effective duty cycle of voltage and current, the fifth duty cycle expression of the zero vector in the output voltage space vector is determined as: d0 = 1-dα d m -d α d n -d β d m -d β d n

[0034] Among them, d α is the first duty cycle of the rectifier stage, d β is the second duty cycle of the rectifier stage, d m is the second duty cycle of the inverter stage, d n is the second duty cycle of the inverter stage.

[0035] Several switching periods are selected within the modulation cycle, including:

[0036] The time period corresponding to the first modulation timing in the modulation cycle is selected as the first switching period, the time period corresponding to the modulation timing after the second change of any switch state of the expansion level in the modulation cycle is selected as the second switching period, and the time period corresponding to the last modulation in the modulation cycle is selected as the third switching period.

[0037] The duration of the first switching period is half of the product of the first duty cycle and the modulation period, the duration of the second switching period is half of the product of the second duty cycle and the modulation period, and the duration of the third switching period is half of the product of the first duty cycle and the modulation period.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The present invention provides an expandable T-type three-phase three-level converter and a modulation method thereof. Since the conduction frequency of the bidirectional switch on the expanded side is three times the industrial frequency, and the T-type three-level inverter side operates at a high frequency, the conduction loss is low, which effectively reduces the cost and improves the system efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is the topology of the unfolded T-type three-phase three-level converter;

[0041] Figure 2 It is the sector diagram of the rectifier stage output current space vector;

[0042] Figure 3 is the input current space vector;

[0043] Figure 4 is the input voltage space vector;

[0044] Figure 5 Modulation diagram of an expanded T-type three-phase three-level converter (inverter side);

[0045] Figure 6 is the input current and input voltage (phase voltage) waveform;

[0046] Figure 7 is the output current and output voltage (phase voltage) waveform;

[0047] Figure 8 is the DC capacitor voltage waveform;

[0048] Figure 9 It is the expanded side state table of the expanded T-type three-phase three-level converter;

[0049] Figure 10 It is the inverter side state table of the expanded T-type three-phase three-level converter.

[0050] Description of reference numerals:

[0051] 1. AC power supply module; 2. Three-phase input filter module; 3. Three-phase expansion module; 4. Delta-connected DC capacitor module; 5. T-type three-phase three-level three-phase inverter module; 6. Three-phase output filter module; 7. First AC power supply; 8. Second AC power supply; 9. Third AC power supply; 10. First filter inductor; 11. Second filter inductor; 12. Third filter inductor; 13. First diode; 14. Second diode; 15. Third diode; 16. Fourth diode; 17. Fifth diode; 18. Sixth diode; 19. First bidirectional switch unit; 20. First switch tube; 21. Second switch tube; 22. Third switch tube 15. The first switching transistor; 16. The second switching transistor; 17. The third switching transistor; 18. The fourth filtering inductor; 19. The sixth filtering inductor; 20. The seventh filtering inductor; 21. The eighth filtering inductor; 22. The ninth filtering inductor; 23. The fourth switching transistor; 24. The fifth switching transistor; 25. The sixth switching transistor; 26. The first DC capacitor; 27. The second DC capacitor; 28. The third DC capacitor; 29. ​​The second bidirectional switch unit; 30. The seventh switching transistor; 31. The eighth switching transistor; 32. The ninth switching transistor; 33. The tenth switching transistor; 34. The eleventh switching transistor; 35. The twelfth switching transistor; 36. The thirteenth switching transistor; 37. The fourteenth switching transistor; 38. The fifteenth switching transistor; 39. The sixteenth switching transistor; 40. The seventeenth switching transistor; 41. The eighteenth switching transistor; 42. The fourth filtering inductor; 43. The fifth filtering inductor; 44. The sixth filtering inductor. DETAILED DESCRIPTION

[0052] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0053] To address the shortcomings of existing converters, such as poor output waveform, large switching loss, and low overall efficiency, the present invention proposes an expanded T-type three-phase three-level converter and a modulation method thereof. The specific technical solutions are as follows:

[0054] like Figure 1-10As shown, the present invention proposes an expanded T-type three-phase three-level converter, including an AC power supply module 1, a three-phase input filter module 2, a three-phase expansion module 3, a delta-connected DC capacitor module 4, a T-type three-phase three-level three-phase inverter module 5 and a three-phase output filter module 6. The first end of the three-phase input filter module 2 is electrically connected to the AC power supply module 1, the first end of the three-phase expansion module 3 is electrically connected to the second end of the three-phase input filter module 2, and the second end is connected to the first DC capacitor 26 and the second DC capacitor 27 in the delta-connected DC capacitor module 4 to the P, O, and N points. The first end of the delta-connected DC capacitor module 4 is electrically connected to the second end of the three-phase expansion module 3, the first end of the T-type three-phase three-level three-phase inverter module 5 and the second end of the delta-connected DC capacitor module 4 are electrically connected to the P, O, and N points, and the first end of the three-phase output filter module 6 is electrically connected to the second end of the T-type three-phase three-level three-phase inverter module 5.

[0055] The AC power supply module 1 includes: a first AC power supply 7, a second AC power supply 8, and a third AC power supply 9, wherein the negative terminal of the second AC power supply 8 is electrically connected to the negative terminal of the first AC power supply 7, and the negative terminal of the third AC power supply 9 is electrically connected to the negative terminal of the second AC power supply 8;

[0056] The three-phase input filter module 2 includes: a first filter inductor 10, a second filter inductor 11, and a third filter inductor 12. The first end of the first filter inductor 10 is electrically connected to the positive terminal of the first AC power supply 7, the first end of the second filter inductor 11 is electrically connected to the positive terminal of the second AC power supply 8, and the first end of the third filter inductor 12 is electrically connected to the positive terminal of the third AC power supply 9.

[0057] The three-phase expansion module 3 includes: a first diode 13, a second diode 14, a third diode 15, a fourth diode 16, a fifth diode 17, a sixth diode 18 and a first bidirectional switch unit 19, wherein the anode of the first diode 13 is electrically connected to the second end of the first filter inductor 10, the cathode of the second diode 14 is electrically connected to the anode of the first diode 13, the cathode of the third diode 15 is electrically connected to the cathode of the first diode 13, the anode of the third diode 15 is electrically connected to the second end of the second filter inductor 11, the cathode of the fourth diode 16 is electrically connected to the anode of the third switch tube 22, and the anode of the fourth diode 16 is electrically connected to the cathode of the third switch tube 22. The anode of the fifth diode 17 is electrically connected to the anode of the third diode 15, the anode of the fifth diode 17 is electrically connected to the second end of the third filter inductor 12, the cathode of the sixth switching tube 25 is electrically connected to the anode of the fifth switching tube 24, the emitter of the sixth diode 18 is electrically connected to the anode of the fourth diode 16, the first end of the first bidirectional switch unit 19 is electrically connected to the anode of the first diode 13, the second end of the first bidirectional switch unit 19 is electrically connected to the anode of the third diode 15, and the third end of the first bidirectional switch unit 19 is electrically connected to the anode of the fifth diode 17;

[0058] The delta-connected DC capacitor module 4 includes: a first DC capacitor 26, a second DC capacitor 27, and a third DC capacitor 28. The first end of the first DC capacitor 26 is electrically connected to the cathode of the first diode at point P, the first end of the second DC capacitor 27 is electrically connected to the second end of the first DC capacitor 26 at point O, the first end of the third DC capacitor 28 is electrically connected to the first end of the first DC capacitor 26 at point P, and the second end is electrically connected to the second end of the second DC capacitor 27 at point N.

[0059] The T-type three-phase three-level three-phase inverter module 5 includes: a second bidirectional switch unit 29 and a three-phase full-bridge unit, wherein a first end of the second bidirectional switch unit 29 is electrically connected to the O end of the first DC capacitor 26, a first end of the three-phase full-bridge unit is electrically connected to the first end P of the first DC capacitor 26, and a second end of the three-phase full-bridge unit is electrically connected to the second end N of the second DC capacitor 27;

[0060] The three-phase output filter module 6 includes: a fourth filter inductor 42, a fifth filter inductor 43 and a sixth filter inductor 44. The fourth filter inductor 42 is electrically connected to the first end of the first load, the fifth filter inductor 43 is electrically connected to the first end of the second load, and the sixth filter inductor 44 is electrically connected to the first end of the third load.

[0061] The first bidirectional switch unit 19 includes: a first switching transistor 20, a second switching transistor 21, a third switching transistor 22, a fourth switching transistor 23, a fifth switching transistor 24 and a sixth switching transistor 25. The collector of the first switching transistor 20 is electrically connected to the anode of the first diode 13, the emitter of the second switching transistor 21 is electrically connected to the emitter of the first switching transistor 20, the collector of the third switching transistor 22 is electrically connected to the anode of the third diode 15, the emitter of the fourth switching transistor 23 is electrically connected to the emitter of the third switching transistor 22, the collector of the fifth switching transistor 24 is electrically connected to the anode of the fifth diode 17, and the emitter of the sixth switching transistor 25 is electrically connected to the emitter of the fifth switching transistor 24.

[0062] The second bidirectional switch unit 29 includes: a seventh switching transistor 30, an eighth switching transistor 31, a ninth switching transistor 32, a tenth switching transistor 33, an eleventh switching transistor 34 and a twelfth switching transistor 35. The collector of the seventh switching transistor 30 is electrically connected to the second end of the first DC capacitor 26, the emitter of the eighth switching transistor 31 is electrically connected to the emitter of the seventh switching transistor 30, the collector of the ninth switching transistor 32 is electrically connected to the second end of the first DC capacitor 26, the emitter of the tenth switching transistor 33 is electrically connected to the emitter of the ninth switching transistor 32, the collector of the eleventh switching transistor 34 is electrically connected to the second end of the first DC capacitor 26, and the emitter of the twelfth switching transistor 35 is electrically connected to the emitter of the eleventh switching transistor 34.

[0063] The three-phase full-bridge unit includes: a thirteenth switching transistor 36, a fourteenth switching transistor 37, a fifteenth switching transistor 38, a sixteenth switching transistor 39, a seventeenth switching transistor 40, and an eighteenth switching transistor 41. The collector of the thirteenth switching transistor 36 is electrically connected to the first end of the first DC capacitor 26, the emitter of the thirteenth switching transistor 36 is electrically connected to the collector of the eighth switching transistor 31, the collector of the fourteenth switching transistor 37 is electrically connected to the emitter of the thirteenth switching transistor 36, the emitter of the fourteenth switching transistor 37 is electrically connected to the second end of the second DC capacitor 27, and the collector of the fifteenth switching transistor 38 is electrically connected to the collector of the thirteenth switching transistor 36. The emitter of the fifteenth switching tube 38 is electrically connected to the collector of the tenth switching tube 33, the collector of the sixteenth switching tube 39 is electrically connected to the emitter of the fifteenth switching tube 38, the emitter of the sixteenth switching tube 39 is electrically connected to the emitter of the fourteenth switching tube 37, the collector of the seventeenth switching tube 40 is electrically connected to the collector of the fifteenth switching tube 38, the emitter of the seventeenth switching tube 40 is electrically connected to the collector of the twelfth switching tube 35, the collector of the eighteenth switching tube 41 is electrically connected to the emitter of the seventeenth switching tube 40, and the emitter of the eighteenth switching tube 41 is electrically connected to the emitter of the sixteenth switching tube 39.

[0064] In the implementation of the present invention: the AC power supply module 1 can provide stable voltage and frequency, the three-phase input filter module 2 is used to filter out ripples in the output voltage, the three-phase expansion module 3 is used to convert AC power into six-pulse DC power, and the T-type three-phase three-level three-phase inverter module 5 corresponds to the three-phase expansion module 3. The T-type three-phase three-level three-phase inverter module 5 is used to convert DC power into AC power.

[0065] In the embodiment of the present invention, the three-phase input filter module 2 filters the input current to eliminate harmonics and make the input current close to sinusoidal, so as to alleviate the voltage distortion of the power grid.

[0066] In the embodiment of the present invention: the modulation method of the three-phase expansion module 3 is as follows: Figure 2 、 Figure 3 As shown, the following steps are included: Considering that when the inverter stage is modulated, the three capacitors of the DC bus are connected to the inverter stage, and only two of the three lines have current flowing through them. Therefore, the rectifier stage can be compared to a current-type converter, using classic current vector modulation. For example, when the reference current is in the first small sector, the current of the first AC source 7 and the current of the third AC source 9 synthesize the reference current. According to the size and position of the desired input current vector, six effective vectors I1 to I6 are used to synthesize the desired vector. There is no zero vector. Each large sector has two small sectors. The effective current vectors used by the two small sectors are the same. The sector between I1 and I2 is the first large sector, and counterclockwise they are the twelfth small sector and the first small sector respectively. The sector between I2 and I3 is the second large sector, and counterclockwise they are the second small sector and the third small sector respectively. The sector between I3 and I4 is the third large sector. , counterclockwise they are the fourth small sector and the fifth small sector respectively, the sector between I4 and I5 is the fourth largest sector, counterclockwise they are the sixth small sector and the seventh small sector respectively, the sector between I5 and I6 is the fifth largest sector, counterclockwise they are the eighth small sector and the ninth small sector respectively, the sector between I6 and I1 is the sixth largest sector, counterclockwise they are the tenth small sector and the eleventh small sector respectively. For example, when the desired vector is located in the first largest sector, the I1 and I2 vectors are used to synthesize, and the duty ratios of the I1 current vector and the I2 current vector are the first duty ratio and the second duty ratio respectively. The three-phase expansion module 3 converts the sinusoidal AC voltage into six-pulse DC. At this time, the maximum line voltage u is present on the third DC capacitor. ac , there is a secondary large line voltage u on the first DC capacitor ab , there is a minimum line voltage u on the second DC capacitor bc According to Kirchhoff's voltage law, it is only necessary to control two-phase currents to control the remaining phase currents, so the purpose of inputting three-phase current sinusoidal can be achieved.

[0067] The first and second duty cycles d of the effective vectorα d β The expression is:

[0068]

[0069] Among them, θ sc is the angle between the desired reference current vector and the first effective current vector.

[0070] like Figure 9 As shown, D1, D2, D3, D4, D5, and D6 represent the first diode 13, the sixth diode 18, the third diode 15, the second diode 14, the fifth diode 17, and the fourth diode 16, respectively; Q a Represents the first switch tube 20, the second switch tube 21, Q b represents the third switch tube 22 and the fourth switch tube 23, Q c Represents the fifth switching tube 24 and the sixth switching tube 25;

[0071] In the embodiment of the present invention: the modulation strategy of the T-type three-phase three-level three-phase inverter module 5 includes the following steps: using the traditional voltage vector space control method, according to the size and position of the desired input voltage vector, using six effective vectors U1 to U6 and three zero vectors to synthesize the desired vector, U1 and U2 constitute the first sector, U2 and U3 constitute the first sector, U3 and U4 constitute the first sector, U5 and U6 constitute the first sector, U6 and U1 constitute the first sector, for example, when the reference voltage vector is in the first sector, using U1, U2 and a zero vector to synthesize the reference voltage vector, the third and fourth duty cycles of U1 and U2 are d respectively. m , d n .

[0072] According to the voltage space vector modulation method, the expressions for determining the third and fourth duty cycles are:

[0073]

[0074] Among them, m v is the modulation coefficient of the inverter, ranging from 0 to 1; θ sv is the angle between the desired reference voltage vector and the first effective voltage vector, and its value range is [0,π / 3].

[0075] In order to meet the maximum voltage utilization and inversion requirements over a wider range, the present invention selects the maximum line voltage and the second-maximum line voltage for inversion. The present invention is characterized in that the third DC capacitor 28 always has the maximum line voltage, the three-phase full-bridge unit inverts the maximum line voltage on the third DC capacitor 28, and the second bidirectional switch unit 29 is electrically disconnected from the second end of the first DC capacitor 26. When the first DC capacitor 26 has the second-maximum line voltage, the thirteenth, fifteenth, and seventeenth switching tubes and the second bidirectional switch unit 29 invert the second-maximum line voltage on the first DC capacitor 26, and the fourteenth, sixteenth, and eighteenth switching tubes are electrically disconnected from the second end of the second DC capacitor 27. When the second DC capacitor 27 has the second-maximum line voltage, the fourteenth, sixteenth, and eighteenth switching tubes and the second bidirectional switch unit 29 invert the second-maximum line voltage on the second DC capacitor 27, and the thirteenth, fifteenth, and seventeenth switching tubes are electrically disconnected from the first end of the first DC capacitor 26.

[0076] According to the voltage space vector modulation method, the remaining modulation time is used to arrange a reasonable zero voltage vector for transition. According to the effective duty cycle of the current vector and the effective duty cycle of the voltage vector, the fifth duty cycle expression of the zero vector in the output voltage space vector is determined as d0:

[0077] d0=1-d α d m -d α d n -d β d m -d β d n

[0078] Among them, d α is the first duty cycle, d β is the second duty cycle, d m is the second duty cycle, d n is the second duty cycle.

[0079] The present invention selects several switching time periods within the modulation cycle, including: selecting the time period corresponding to the first modulation timing within the modulation cycle as the first switching time period, selecting the time period corresponding to the modulation timing after the second change of any switch state of the expansion stage within the modulation cycle as the second switching time period, and selecting the time period corresponding to the last modulation within the modulation cycle as the third switching time period.

[0080] The duration of the first switching period is half of the product of the first duty cycle and the modulation period, the duration of the second switching period is half of the product of the second duty cycle and the modulation period, and the duration of the third switching period is half of the product of the first duty cycle and the modulation period.

[0081] In the embodiment of the present invention, the T-type three-level three-phase inverter module 5 converts the output direct current of the three-phase expansion module 3 into alternating current. At the same time, by controlling the T-type three-level three-phase inverter module 5, reasonable adjustment of the output voltage amplitude, phase and frequency can be achieved.

[0082] Taking the first small sector of current and the first sector of voltage as examples, the expression of the switching time of the switching action in each modulation cycle is:

[0083]

[0084] Among them, t x (x=1~11) represents the switching time, T s Represents one modulation cycle.

[0085] like Figure 10 As shown, SP represents the switch pair of the thirteenth switch tube 36, the fifteenth switch tube 38, and the seventeenth switch tube 40; SO represents the switch pair of the seventh switch tube 30, the eighth switch tube 31, the ninth switch tube 32, the tenth switch tube 33, the eleventh switch tube 34, and the twelfth switch tube 35; SN represents the switch pair of the fourteenth switch tube 37, the sixteenth switch tube 39, and the eighteenth switch tube 41.

[0086] The normal operation of the present invention is achieved by cooperating with a computer program product, which includes a computer program stored on a non-transitory computer-readable storage medium. The computer program includes program instructions, which, when executed by a computer, enable the computer to execute the modulation method described above.

[0087] The operating principle of the present invention is as follows: A triple-power frequency switch is used on the expansion side, resulting in a six-pulse segmented sinusoidal voltage across the DC capacitor. To achieve maximum voltage utilization, the T-type three-level inverter uses the maximum and second-maximum line voltages across the DC capacitor to synthesize the inverter-stage voltage. The upper and lower transistors of the T-type three-level inverter perform inversion based on the maximum line voltage. If the upper capacitor serves as the second-maximum line voltage, the upper transistor and bidirectional switch of the T-type three-level inverter perform inversion based on the second-maximum voltage. Conversely, if the lower capacitor serves as the second-maximum line voltage, the bidirectional switch and lower transistor of the T-type three-level inverter perform inversion based on the second-maximum voltage.

[0088] Specific case description: When the input grid voltage is 220V / 50Hz, the output reference voltage is 95V / 30Hz, the input side filter inductor L=1e-3mH, the DC capacitor size is C=5e-6uF, the output side filter inductor L=5e-3mH, the load is a 10Ω pure resistive load, the switching frequency is 20KHz, m v Take 0.5.

[0089] The system was simulated in Matlab / Simulink environment. Figure 6 The waveforms of input current and input voltage (phase voltage) are as follows: the input current is sinusoidal and has a basically unity power factor; Figure 7 The output current and output voltage (phase voltage) waveforms are sinusoidal and have a basically unity power factor. Figure 8 is the voltage on the DC capacitor, which can be seen as a six-pulse DC voltage.

[0090] A modulation method for an expanded T-type three-phase three-level converter comprises the following steps:

[0091] S1. Determine the first and second duty ratios of the effective current vector in the expanded stage current space vector;

[0092] S2. Determine the third and fourth duty cycles of the effective voltage vector in the output voltage space vector of the inverter stage;

[0093] S3, determining a fifth duty cycle of the zero vector in the inverter output voltage space vector;

[0094] S4, select the transfer period;

[0095] S5. Determining first and second duty ratios of the effective current vector in the expanded-stage current space vector, including:

[0096] According to the current space vector modulation method, the expressions for determining the first and second duty cycles of the rectifier stage are:

[0097]

[0098] Among them, θ sc is the angle between the desired reference current vector and the current large sector vector

[0099] The first and second duty cycles of the effective current vector are equal to the maximum and second largest line voltage duty cycles on the DC capacitor. When the first small sector is turned on, the second largest line voltage u ab The on-duty cycle is d β , there is a maximum line voltage u on the third DC capacitor 28 ac The on-duty cycle is d α , at this time, the first AC power supply current and the third AC power supply current synthesize a reference current vector;

[0100] S6. Determining the third and fourth duty ratios of the inverter stage of the effective voltage vector in the output voltage space vector of the inverter stage, comprising:

[0101] According to the voltage space vector modulation method, the expressions for determining the third and fourth duty cycles of the inverter stage are:

[0102]

[0103] Among them, m v is the modulation coefficient of the inverter, ranging from 0 to 1; θ sv is the angle between the desired reference voltage vector and the lower vector of the current sector.

[0104] The third DC capacitor 28 always has a maximum line voltage. The three-phase full-bridge unit inverts the maximum line voltage on the third DC capacitor 28, while the second bidirectional switch unit 29 is electrically disconnected from the second end of the first DC capacitor 26. Therefore, when the first DC capacitor 26 has a sub-maximum line voltage, the thirteenth, fifteenth, and seventeenth switch tubes and the second bidirectional switch unit 29 invert the sub-maximum line voltage on the first DC capacitor 26, while the fourteenth, sixteenth, and eighteenth switch tubes are electrically disconnected from the second end of the second DC capacitor 27. When the second DC capacitor 27 has a sub-maximum line voltage, the fourteenth, sixteenth, and eighteenth switch tubes and the second bidirectional switch unit 29 invert the sub-maximum line voltage on the second DC capacitor 27, while the thirteenth, fifteenth, and seventeenth switch tubes are electrically disconnected from the first end of the first DC capacitor 26.

[0105] Determining a fifth duty cycle of a zero vector of the inverter stage in the output voltage space vector of the inverter stage includes:

[0106] According to the effective duty cycle of voltage and current, the fifth duty cycle expression of the zero vector in the output voltage space vector is determined as follows:

[0107] d0=1-d α d m -d α d n -d β d m -d β d n

[0108] Among them, d α is the first duty cycle of the rectifier stage, d β is the second duty cycle of the rectifier stage, d m is the second duty cycle of the inverter stage, d n is the second duty cycle of the inverter stage.

[0109] Several switching periods are selected within the modulation cycle, including:

[0110] The time period corresponding to the first modulation timing in the modulation cycle is selected as the first switching period, the time period corresponding to the modulation timing after the second change of any switch state of the expansion level in the modulation cycle is selected as the second switching period, and the time period corresponding to the last modulation in the modulation cycle is selected as the third switching period.

[0111] The duration of the first switching period is half of the product of the first duty cycle and the modulation period, the duration of the second switching period is half of the product of the second duty cycle and the modulation period, and the duration of the third switching period is half of the product of the first duty cycle and the modulation period.

[0112] The present invention provides an expandable T-type three-phase three-level converter and a modulation method thereof. Since the conduction frequency of the bidirectional switch on the expanded side is three times the industrial frequency and the T-type three-level inverter side operates at a high frequency, it has the technical effects of low conduction loss, effective cost reduction and high system efficiency.

[0113] The above description is merely a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any modification or equivalent variation based on the technical essence of the present invention shall still fall within the scope of protection claimed by the present invention.

Claims

1. A modulation method for an expanded T-type three-phase three-level converter, characterized by: The expanded T-type three-phase three-level converter comprises an AC power supply module (1), a three-phase input filter module (2), a three-phase expansion module (3), a delta-connected DC capacitor module (4), a T-type three-phase three-level three-phase inverter module (5), and a three-phase output filter module (6), wherein a first end of the three-phase input filter module (2) is electrically connected to the AC power supply module (1), a first end of the three-phase expansion module (3) is electrically connected to a second end of the three-phase input filter module (2), and a second end of the three-phase expansion module (3) is electrically connected to a delta-connected DC capacitor module (4). The first DC capacitor (26) is electrically connected to the P and O points, and the second DC capacitor (27) is electrically connected to the O and N points. The third capacitor of the delta-connected DC capacitor module (4) is electrically connected to the P and N points. The first end of the T-type three-phase three-level three-phase inverter module (5) and the first DC capacitor (26) of the delta-connected DC capacitor module (4) are electrically connected to the P and O points, and the second DC capacitor (27) is electrically connected to the O and N points. The first end of the three-phase output filter module (6) is electrically connected to the second end of the T-type three-phase three-level three-phase inverter module (5). The AC power supply module (1) comprises: a first AC power supply (7), a second AC power supply (8) and a third AC power supply (9), wherein the negative terminal of the second AC power supply (8) is electrically connected to the negative terminal of the first AC power supply (7), and the negative terminal of the third AC power supply (9) is electrically connected to the negative terminal of the second AC power supply (8); The three-phase input filter module (2) comprises: a first filter inductor (10), a second filter inductor (11), and a third filter inductor (12), wherein a first end of the first filter inductor (10) is electrically connected to the positive terminal of the first AC power source (7), a first end of the second filter inductor (11) is electrically connected to the positive terminal of the second AC power source (8), and a first end of the third filter inductor (12) is electrically connected to the positive terminal of the third AC power source (9); The three-phase expansion module (3) comprises: a first diode (13), a second diode (14), a third diode (15), a fourth diode (16), a fifth diode (17), a sixth diode (18) and a first bidirectional switch unit (19), wherein the anode of the first diode (13) is electrically connected to the second end of the first filter inductor (10), the cathode of the second diode (14) is electrically connected to the anode of the first diode (13), the cathode of the third diode (15) is electrically connected to the cathode of the first diode (13), the anode of the third diode (15) is electrically connected to the second end of the second filter inductor (11), the cathode of the fourth diode (16) is electrically connected to the anode of the third diode (15), and the anode of the fourth diode (16) is electrically connected to the cathode of the second diode (11). The anode of the first bidirectional switch unit (19) is electrically connected to the anode of the first diode (13), the cathode of the fifth diode (17) is electrically connected to the cathode of the third diode (15), the anode of the fifth diode (17) is electrically connected to the second end of the third filter inductor (12), the cathode of the sixth diode (18) is electrically connected to the anode of the fifth diode (17), the anode of the sixth diode (18) is electrically connected to the anode of the fourth diode (16), the first end of the first bidirectional switch unit (19) is electrically connected to the anode of the first diode (13), the second end of the first bidirectional switch unit (19) is electrically connected to the anode of the third diode (15), the third end of the first bidirectional switch unit (19) is electrically connected to the anode of the fifth diode (17), and the fourth end of the first bidirectional switch unit (19) is connected to point O; The T-type three-phase three-level three-phase inverter module (5) comprises: a second bidirectional switch unit (29) and a three-phase full-bridge unit, wherein the first end of the second bidirectional switch unit (29) is electrically connected to the O end of the first DC capacitor (26), the second, third and fourth ends of the second bidirectional switch unit (29) are respectively connected to the midpoint of the bridge arm of the three-phase full-bridge unit, the first end of the three-phase full-bridge unit is electrically connected to the first end point P of the first DC capacitor (26), and the second end of the three-phase full-bridge unit is electrically connected to the second end point N of the second DC capacitor (27); The three-phase output filter module (6) comprises: a fourth filter inductor (42), a fifth filter inductor (43) and a sixth filter inductor (44), wherein the fourth filter inductor (42) is electrically connected to the first end of the first load, the fifth filter inductor (43) is electrically connected to the first end of the second load, and the sixth filter inductor (44) is electrically connected to the first end of the third load, and comprises the following steps: S1. Determine the first and second duty ratios of the effective current vector in the expanded stage current space vector; S2. Determine the third and fourth duty cycles of the effective voltage vector in the inverter stage output voltage space vector; S3, determining a fifth duty cycle of the zero vector in the output voltage space vector of the inverter stage; S4, select the transfer period; S5. Determining first and second duty ratios of the effective current vector in the expanded-stage current space vector, including: According to the current space vector modulation method, the expressions for determining the first and second duty cycles of the rectifier stage are: ； Among them, θ sc is the angle between the desired reference current vector and the current large sector lower vector; Since the first and second duty cycles of the effective current vector are equal to the maximum and second largest line voltage duty cycles on the DC capacitor, when the first small sector is turned on, the second largest line voltage u ab The on-duty cycle is d β , the third DC capacitor (28) has a maximum line voltage u ac The on-duty cycle is d α , at this time, the first AC power supply current and the third AC power supply current synthesize a reference current vector; S6. Determining the third and fourth duty ratios of the inverter stage of the effective voltage vector in the output voltage space vector of the inverter stage, comprising: According to the voltage space vector modulation method, the expressions for determining the third and fourth duty cycles of the inverter stage are: ； Among them, m v is the modulation coefficient of the inverter, ranging from 0 to 1; θ sv is the angle between the desired reference voltage vector and the lower vector of the current sector.

2. The modulation method of an expanded T-type three-phase three-level converter according to claim 1, characterized in that: The first bidirectional switch unit (19) comprises: a first switch tube (20), a second switch tube (21), a third switch tube (22), a fourth switch tube (23), a fifth switch tube (24) and a sixth switch tube (25); the collector of the first switch tube (20) is electrically connected to the anode of the first diode (13); the emitter of the second switch tube (21) is electrically connected to the emitter of the first switch tube (20); the collector of the third switch tube (22) is electrically connected to the anode of the third diode (15); the emitter of the fourth switch tube (23) is electrically connected to the emitter of the third switch tube (22); the collector of the fifth switch tube (24) is electrically connected to the anode of the fifth diode (17); and the emitter of the sixth switch tube (25) is electrically connected to the emitter of the fifth switch tube (24).

3. The modulation method of an expanded T-type three-phase three-level converter according to claim 1, characterized in that: The second bidirectional switch unit (29) comprises: a seventh switch tube (30), an eighth switch tube (31), a ninth switch tube (32), a tenth switch tube (33), an eleventh switch tube (34) and a twelfth switch tube (35); the collector of the seventh switch tube (30) is electrically connected to the second end of the first DC capacitor (26); the emitter of the eighth switch tube (31) is electrically connected to the emitter of the seventh switch tube (30); the collector of the ninth switch tube (32) is electrically connected to the second end of the first DC capacitor (26); the emitter of the tenth switch tube (33) is electrically connected to the emitter of the ninth switch tube (32); the collector of the eleventh switch tube (34) is electrically connected to the second end of the first DC capacitor (26); and the emitter of the twelfth switch tube (35) is electrically connected to the emitter of the eleventh switch tube (34).

4. The modulation method of an expanded T-type three-phase three-level converter according to claim 3, characterized in that: The three-phase full-bridge unit comprises: a thirteenth switch tube (36), a fourteenth switch tube (37), a fifteenth switch tube (38), a sixteenth switch tube (39), a seventeenth switch tube (40) and an eighteenth switch tube (41); the collector of the thirteenth switch tube (36) is electrically connected to the first end of the first DC capacitor (26); the emitter of the thirteenth switch tube (36) is electrically connected to the collector of the eighth switch tube (31); the collector of the fourteenth switch tube (37) is electrically connected to the emitter of the thirteenth switch tube (36); the emitter of the fourteenth switch tube (37) is electrically connected to the second end of the second DC capacitor (27); the collector of the fifteenth switch tube (38) is electrically connected to the collector of the thirteenth switch tube (36); The emitter of the fifteenth switching tube (38) is electrically connected to the collector of the tenth switching tube (33), the collector of the sixteenth switching tube (39) is electrically connected to the emitter of the fifteenth switching tube (38), the emitter of the sixteenth switching tube (39) is electrically connected to the emitter of the fourteenth switching tube (37), the collector of the seventeenth switching tube (40) is electrically connected to the collector of the fifteenth switching tube (38), the emitter of the seventeenth switching tube (40) is electrically connected to the collector of the twelfth switching tube (35), the collector of the eighteenth switching tube (41) is electrically connected to the emitter of the seventeenth switching tube (40), and the emitter of the eighteenth switching tube (41) is electrically connected to the emitter of the sixteenth switching tube (39).

Images