Three-phase three-level converter

Abstract

The application provides a three-phase three-level converter, comprising: a DC input module for connecting a DC power supply and forming a stable DC bus voltage; a front-stage three-phase highest voltage generating module connected with the DC input module and used for forming a highest voltage required by three-phase output; a front-stage three-phase lowest voltage generating module connected with the DC input module and used for forming a lowest voltage required by three-phase output; a rear-stage three-phase intermediate voltage generating and three-phase voltage distributing module used for generating a three-phase intermediate voltage and dynamically mapping the highest, intermediate and lowest voltages to corresponding A, B and C phases according to real-time size relationship of each phase voltage; and a filtering output module used for filtering the finally output voltage, so that the three-phase three-level converter separates the high-frequency switch tube from the low-frequency switch tube, optimizes the cost and balances the conduction loss and the switching loss.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and more specifically to a three-phase three-level converter. Background Technology

[0002] In power systems, residential and industrial electricity is predominantly AC, while photovoltaic (PV) and battery-powered energy generation and storage devices primarily output DC. To achieve efficient utilization of clean energy, DC power must be converted to AC for grid connection or load supply. For example, in grid-connected PV systems, inverters convert DC power generated by solar panels into AC power for grid connection. In energy storage systems, the DC power stored in batteries also needs to be converted back to AC power by inverters. These DC-to-AC conversion devices—inverters—are core equipment in areas such as renewable energy integration into off-grid / microgrid power supply and power quality control. Since commercial, industrial, and power plant applications typically require connection to a three-phase grid, three-phase inverters play a crucial role. Furthermore, DC charging stations for electric vehicles are very popular; they convert three-phase AC power into high-voltage DC power to charge car batteries, with the three-phase bridge arms operating in rectification mode. Therefore, improving the conversion efficiency, power density, and reliability of three-phase converters while reducing their system costs is of great significance for promoting energy transition and advancing power electronics technology.

[0003] Existing three-phase three-level converters include many types such as ANPC, I-NPC, and T-NPC. Figure 1 The "T"-type three-level topology (T-NPC) shown is used as an example to illustrate the three-level structure. Taking phase A as an example: during the positive half-cycle of the grid voltage, S11 and S31 conduct complementaryly at their switching frequencies, S32 remains normally on, and S21 remains normally off; during the negative half-cycle of the grid voltage, S21 and S32 conduct complementaryly at their switching frequencies, S31 remains normally on, and S11 remains normally off. The control logic for phases B and C is the same. If it is necessary to control the voltage of DC-side capacitors C1 and C2 through independent bridge arms, then S14 and S24 will conduct complementaryly near a 50% duty cycle, and the neutral line (N line) is taken from the midpoint of the DC-side voltage. Compared with the two-level topology, this topology can reduce switching losses and reduce inductor costs. In the existing technology, each phase bridge arm requires 4 high-frequency switching transistors, and a total of 12 high-frequency switching transistors are required for the three phases. This type of structure has the following limitations: 1. It uses a relatively large number of high-frequency transistors, resulting in high cost. 2. High-frequency transistors typically sacrifice conduction losses to reduce switching losses, and it is difficult to balance conduction and switching losses. 3. The six vertical transistors (S11~S13, S21~S23) only operate for half of the power frequency cycle, and are normally off for the other half of the power frequency cycle. Therefore, these transistors are not being utilized to their fullest potential. Summary of the Invention

[0004] This invention was made to solve the above-mentioned problems, and its purpose is to provide a three-phase three-level converter.

[0005] This invention provides a three-phase three-level converter, characterized by: a DC input module for connecting to a DC power supply and forming a stable DC bus voltage; a front-stage three-phase highest voltage generation module connected to the DC input module for forming the three-phase highest voltage required for the three-phase output; a front-stage three-phase lowest voltage generation module connected to the DC input module for forming the three-phase lowest voltage required for the three-phase output; a rear-stage three-phase intermediate voltage generation and three-phase voltage distribution module connected to the front-stage three-phase highest voltage generation module and the front-stage three-phase lowest voltage generation module for generating the three-phase intermediate voltage and dynamically mapping the highest, intermediate, and lowest voltages to their corresponding A, B, and C phases according to the real-time magnitude relationship of each phase voltage; and a filter output module connected to the rear-stage three-phase intermediate voltage generation and three-phase voltage distribution module for filtering the final output voltage of the rear stage.

[0006] The three-phase three-level converter provided by this invention may also have the following features: the DC input module includes: a positive DC input terminal, used as the positive terminal of the DC power supply to introduce a positive DC bus voltage; a negative DC input terminal, used as the negative terminal of the DC power supply to introduce a negative DC bus voltage; a first supporting capacitor, the first end of which is connected to the positive DC input terminal to maintain the stability of the positive DC bus voltage; and a second supporting capacitor, the first end of which is connected to the second end of the first supporting capacitor, and the second end of which is connected to the negative DC input terminal to maintain the stability of the negative DC bus voltage.

[0007] The three-phase three-level converter provided by this invention may also have the following features: the front-stage three-phase highest voltage generation module includes: a first switching transistor unit, the first end of which is connected to the positive DC input terminal, for generating the three-phase highest voltage level; a second switching transistor unit, the first end of which is connected to the first switching transistor unit, and the second end of which is connected to the second end of the first supporting capacitor, for generating the three-phase highest voltage level; the front-stage three-phase lowest voltage generation module includes: a third switching transistor unit, the first end of which is connected to the first end of the second supporting capacitor, for generating the three-phase lowest voltage level; and a fourth switching transistor unit, the first end of which is connected to the third switching transistor unit, and the second end of which is connected to the negative DC input terminal, for generating the three-phase lowest voltage level.

[0008] The three-phase three-level converter provided by this invention may also have the following feature: the subsequent three-phase intermediate voltage generation and three-phase voltage distribution module includes: a fifth switching unit, the first terminal of which is connected to the second terminal of the second switching unit and the first terminal of the third switching unit respectively, for generating the three-phase intermediate voltage of phase A; a sixth switching unit, the first terminal of which is connected to the second terminal of the fifth switching unit, for generating the three-phase intermediate voltage of phase A; a seventh switching unit, the first terminal of which is connected to the second terminal of the second switching unit and the first terminal of the third switching unit respectively, for generating the three-phase intermediate voltage of phase B; and an eighth switching unit, the first terminal of which is connected to the second terminal of the fifth switching unit and the first terminal of the third switching unit respectively, for generating the three-phase intermediate voltage of phase B; and a seventh switching unit, the first terminal of which is connected to the second terminal of the second switching unit and the first terminal of the third switching unit respectively, for generating the three-phase intermediate voltage of phase B; and a twentieth switching unit, the first terminal of which is connected to the second terminal of the fifth ... The second terminal of the seventh switching transistor unit is connected to generate the three-phase intermediate level voltage of phase B; the first terminal of the ninth switching transistor unit is connected to the second terminal of the second switching transistor unit and the first terminal of the third switching transistor unit respectively, and is used to generate the three-phase intermediate level voltage of phase C; the first terminal of the tenth switching transistor unit is connected to the second terminal of the ninth switching transistor unit, and is used to generate the three-phase intermediate level voltage of phase C; the first terminal of the eleventh switching transistor unit is connected to the second terminal of the first switching transistor unit and the first terminal of the second switching transistor unit respectively, and the second terminal is connected to the second terminal of the sixth switching transistor unit, and is used to distribute the three-phase highest level voltage of phase A or generate a positive three-phase intermediate level voltage of phase A. The twelfth switching unit has its first terminal connected to the first terminal of the eleventh switching unit and its second terminal connected to the second terminal of the eighth switching unit. It is used to distribute the highest three-phase voltage to phase B or generate a positive three-phase intermediate voltage for phase B. The thirteenth switching unit has its first terminal connected to the first terminal of the twelfth switching unit and its second terminal connected to the second terminal of the tenth switching unit. It is used to distribute the highest three-phase voltage to phase C or generate a positive three-phase intermediate voltage for phase C. The fourteenth switching unit has its first terminal connected to the second terminal of the eleventh switching unit, and its second terminal connected to the second terminal of the third switching unit and the first terminal of the fourth switching unit. The fifteenth switch unit, with its first terminal connected to the second terminal of the twelfth switch unit and its second terminal connected to the second terminal of the third switch unit and the first terminal of the fourth switch unit, is used to distribute the three-phase minimum voltage to phase B or generate a negative three-phase intermediate voltage to phase B; the sixteenth switch unit, with its first terminal connected to the second terminal of the thirteenth switch unit and its second terminal connected to the second terminal of the third switch unit and the first terminal of the fourth switch unit, is used to distribute the three-phase minimum voltage to phase C or generate a negative three-phase intermediate voltage to phase C.

[0009] The three-phase three-level converter provided by this invention may also have the following feature: the filter output module includes: a first filter inductor, the first end of which is connected to the second end of the eleventh switching transistor unit and the first end of the fourteenth switching transistor unit, for filtering the output voltage; a second filter inductor, the first end of which is connected to the second end of the twelfth switching transistor unit and the first end of the fifteenth switching transistor unit, for filtering the output voltage; and a third filter inductor, the first end of which is connected to the second end of the thirteenth switching transistor unit and the first end of the sixteenth switching transistor unit, for filtering the output voltage.

[0010] The three-phase three-level converter provided by the present invention may also have the following feature: the types of switching transistor units include, but are not limited to, FET, IGBT, and BJT.

[0011] The three-phase three-level converter provided by the present invention may also have the following feature: the series connection point between the second end of the first supporting capacitor and the first end of the second supporting capacitor is the neutral point, and the neutral point is directly led out as an independent terminal.

[0012] The role and effect of invention

[0013] According to the three-phase three-level converter of the present invention, since it includes: a DC input module for connecting to a DC power supply and forming a stable DC bus voltage; a front-stage three-phase highest voltage generation module connected to the DC input module for forming the three-phase highest voltage required for the three-phase output; a front-stage three-phase lowest voltage generation module connected to the DC input module for forming the three-phase lowest voltage required for the three-phase output; a rear-stage three-phase intermediate voltage generation and three-phase voltage distribution module connected to the front-stage three-phase highest voltage generation module and the front-stage three-phase lowest voltage generation module for generating the three-phase intermediate voltage and dynamically mapping the highest, intermediate, and lowest voltages to their corresponding A, B, and C phases according to the real-time magnitude relationship of each phase voltage; and a filter output module connected to the rear-stage three-phase intermediate voltage generation and three-phase voltage distribution module for filtering the final output voltage of the rear stage, the three-phase three-level converter of the present invention uses high-frequency switching transistors and low-frequency switching transistors separately, optimizing costs and balancing conduction losses and switching losses. Attached Figure Description

[0014] Figure 1 This is a circuit diagram of a common T-type three-level topology circuit.

[0015] Figure 2 This is a schematic diagram of the topology of a three-phase three-level converter in Embodiment 1 of the present invention.

[0016] Figure 3 This is a schematic diagram of the three-phase voltage waveform of the three-phase three-level converter for two power frequency cycles in Embodiment 1 of the present invention.

[0017] Figure 4 This is a schematic diagram of the switching timing of a three-phase three-level converter in Embodiment 1 of the present invention.

[0018] Figure 5 This is a schematic diagram of the current flow path of the three-phase three-level converter in Embodiment 1 of the present invention.

[0019] Figure 6 This is a schematic diagram of the topology of a three-phase three-level converter in Embodiment 2 of the present invention.

[0020] Figure 7 This is a schematic diagram of the topology of the three-phase three-level converter in Embodiment 3 of the present invention.

[0021] Figure 8 This is a schematic diagram of the topology of the three-phase three-level converter in Embodiment 4 of the present invention.

[0022] Figure 9 This is a timing diagram of a switching transistor in the front-end voltage generation module of Embodiment 4 of the present invention.

[0023] Figure 10 This is a schematic diagram of the topology of the three-phase three-level converter in Embodiment 5 of the present invention.

[0024] Figure 11 This is a schematic diagram of the topology of a three-phase three-level converter in Embodiment 6 of the present invention.

[0025] Figure 12 This is a schematic diagram of the topology of the three-phase three-level converter in Embodiment 7 of the present invention.

[0026] Figure 13 This is a schematic diagram of the topology of the three-phase three-level converter in Embodiment 8 of the present invention.

[0027] Figure 14 This is a schematic diagram of the topology of the three-phase three-level converter in Embodiment 9 of the present invention. Detailed Implementation

[0028] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0029] To make the technical means, creative features, objectives and effects of the present invention easy to understand, the following embodiments, in conjunction with the accompanying drawings, will specifically illustrate the three-phase three-level converter of the present invention.

[0030] Example 1

[0031] Figure 2 This is a schematic diagram of the topology of a three-phase three-level converter in an embodiment of the present invention.

[0032] like Figure 2 As shown, this embodiment provides a three-phase three-level converter 100, including: a DC input module 1, a front-stage three-phase highest voltage generation module 2, a front-stage three-phase lowest voltage generation module 3, a rear-stage three-phase intermediate voltage generation and three-phase voltage distribution module 4, and a filter output module 5.

[0033] The DC input module 1 is used to connect to a DC power supply and form a stable DC bus voltage.

[0034] The DC input module 1 includes: a DC positive input terminal DC+, a DC negative input terminal DC-, a first supporting capacitor C1, and a second supporting capacitor C2.

[0035] The DC positive input terminal DC+ is used as the positive connection point of the DC power supply to introduce the positive voltage of the DC bus.

[0036] The DC negative input terminal (DC-) is used as the negative connection point of the DC power supply to introduce negative voltage to the DC bus.

[0037] The first supporting capacitor C1 is connected to the DC positive input terminal DC+ at its first end, and is used to maintain the stability of the positive DC bus voltage.

[0038] The first terminal of the second supporting capacitor C2 is connected to the second terminal of the first supporting capacitor C1, and the second terminal is connected to the DC negative input terminal DC-, which is used to maintain the stability of the negative DC bus voltage.

[0039] The series connection point between the second end of the first supporting capacitor C1 and the first end of the second supporting capacitor C2 is the neutral point, which is directly led out as an independent terminal.

[0040] The front-end three-phase maximum voltage generation module 2 is connected to the DC input module 1 and is used to generate the highest level voltage required for the three-phase output.

[0041] The front-end three-phase maximum voltage generation module 2 includes: a first switching transistor unit S1 and a second switching transistor unit S2.

[0042] The first terminal of the first switching transistor unit S1 is connected to the DC positive input terminal DC+, and is used to generate the highest level voltage of the three phases.

[0043] The first terminal of the second switching transistor unit S2 is connected to the first switching transistor unit S1, and the second terminal is connected to the second terminal of the first supporting capacitor C1, which is used to generate the highest level voltage of the three phases.

[0044] The front-end three-phase minimum voltage generation module 3 is connected to the DC input module 1 and is used to generate the minimum level voltage required for the three-phase output.

[0045] The front-end three-phase minimum voltage generation module 3 includes: a third switching transistor unit S3 and a fourth switching transistor unit S4.

[0046] The first terminal of the third switching transistor unit S3 is connected to the first terminal of the second supporting capacitor C2, and is used to generate the three-phase lowest level voltage.

[0047] The first terminal of the fourth switching transistor unit S4 is connected to the third switching transistor unit S3, and the second terminal is connected to the DC negative input terminal DC-, which is used to generate the three-phase lowest level voltage.

[0048] The three-phase intermediate voltage generation and three-phase voltage distribution module 4 is connected to the front-stage three-phase maximum voltage generation module 2 and the front-stage three-phase minimum voltage generation module 3. It is used to generate the three-phase intermediate voltage and dynamically map the maximum, intermediate and minimum voltages to their corresponding A, B and C phases according to the real-time magnitude relationship of each phase voltage.

[0049] The three-phase intermediate voltage generation and three-phase voltage distribution module 4 includes: the fifth switch unit S5, the sixth switch unit S6, the seventh switch unit S7, the eighth switch unit S8, the ninth switch unit S9, the tenth switch unit S10, the eleventh switch unit S11, the twelfth switch unit S12, the thirteenth switch unit S13, the fourteenth switch unit S14, the fifteenth switch unit S15, and the sixteenth switch unit S16.

[0050] The first terminal of the fifth switching transistor unit S5 is connected to the second terminal of the second switching transistor unit S2 and the first terminal of the third switching transistor unit S3, respectively, to generate the three-phase intermediate level voltage of phase A.

[0051] The first terminal of the sixth switching transistor unit S6 is connected to the second terminal of the fifth switching transistor unit S5, and is used to generate the three-phase intermediate voltage of phase A.

[0052] The first terminal of the seventh switching transistor unit S7 is connected to the second terminal of the second switching transistor unit S2 and the first terminal of the third switching transistor unit S3, respectively, to generate the three-phase intermediate level voltage of phase B.

[0053] The first terminal of the eighth switching transistor unit S8 is connected to the second terminal of the seventh switching transistor unit S7, and is used to generate the three-phase intermediate level voltage of phase B.

[0054] The first terminal of the ninth switching transistor unit S9 is connected to the second terminal of the second switching transistor unit S2 and the first terminal of the third switching transistor unit S3, respectively, to generate the three-phase intermediate level voltage of phase C.

[0055] The first terminal of the tenth switch unit S10 is connected to the second terminal of the ninth switch unit S9, and is used to generate the three-phase intermediate level voltage of phase C.

[0056] The first terminal of the eleventh switch unit S11 is connected to the second terminal of the first switch unit S1 and the first terminal of the second switch unit S2, and the second terminal is connected to the second terminal of the sixth switch unit S6. It is used to distribute the highest level voltage of the three phases to phase A or generate a positive intermediate level voltage of the three phases of phase A.

[0057] The first terminal of the twelfth switch unit S12 is connected to the first terminal of the eleventh switch unit S11, and the second terminal is connected to the second terminal of the eighth switch unit S8. It is used to distribute the highest three-phase voltage to phase B or generate a positive three-phase intermediate voltage for phase B.

[0058] The first terminal of the thirteenth switch unit S13 is connected to the first terminal of the twelfth switch unit S12, and the second terminal is connected to the second terminal of the tenth switch unit S10. It is used to distribute the highest level voltage of the three phases to the C phase or generate a positive three-phase intermediate level voltage of the C phase.

[0059] The first terminal of the fourteenth switch unit S14 is connected to the second terminal of the eleventh switch unit S11, and the second terminal is connected to the second terminal of the third switch unit S3 and the first terminal of the fourth switch unit S4, respectively. It is used to distribute the three-phase lowest level voltage to phase A or generate the negative three-phase intermediate level voltage of phase A.

[0060] The first terminal of the fifteenth switch unit S15 is connected to the second terminal of the twelfth switch unit S12. The second terminal is connected to the second terminal of the third switch unit S3 and the first terminal of the fourth switch unit S4, respectively. It is used to distribute the three-phase lowest level voltage to phase B or generate the negative three-phase intermediate level voltage of phase B.

[0061] The first terminal of the sixteenth switch unit S16 is connected to the second terminal of the thirteenth switch unit S13. The second terminal is connected to the second terminal of the third switch unit S3 and the first terminal of the fourth switch unit S4, respectively. It is used to distribute the three-phase lowest level voltage to the C phase or generate the negative three-phase intermediate level voltage of the C phase.

[0062] The filter output module 5 is connected to the subsequent three-phase intermediate voltage generation and three-phase voltage distribution module 4, and is used to filter the final output voltage of the subsequent stage.

[0063] The filter output module 5 includes: a first filter inductor L1, a second filter inductor L2, and a third filter inductor L3.

[0064] The first terminal of the first filter inductor L1 is connected to the second terminal of the eleventh switching transistor unit S11 and the first terminal of the fourteenth switching transistor unit S14, and is used to filter the output voltage.

[0065] The first terminal of the second filter inductor L2 is connected to the second terminal of the twelfth switching transistor unit S12 and the first terminal of the fifteenth switching transistor unit S15, and is used to filter the output voltage.

[0066] The first terminal of the third filter inductor L3 is connected to the second terminal of the thirteenth switching transistor unit S13 and the first terminal of the sixteenth switching transistor unit S16, and is used to filter the output voltage.

[0067] In this embodiment, the types of switching transistor units include, but are not limited to, FET (Field Effect Transistor), IGBT (Insulated Gate Bipolar Transistor), and BJT (Bipolar Transistor).

[0068] In this embodiment, the generated three-phase highest, lowest, and intermediate level voltages can be set according to specific requirements.

[0069] In this embodiment, the phase voltages of the 50Hz three-phase AC are all sine waves with an amplitude of 1. The N-line voltage is used as a reference. The three-phase voltages are represented by Ua, Ub, and Uc, and the N-line voltage is represented by Un. The maximum value of Ua, Ub, and Uc is Umax, the minimum value is Umin, and the middle value is Umid.

[0070] Figure 3 This is a schematic diagram of the three-phase voltage waveform of the three-phase three-level converter for two power frequency cycles in Embodiment 1 of the present invention.

[0071] The DC bus voltage Vdc is 2.

[0072] At a specific moment (e.g., 6ms in the waveform shown in the attached figure), the instantaneous values ​​of the three-phase output voltages are as follows: Phase A voltage Ua = 0.951, Phase B voltage Ub = -0.208, and Phase C voltage Uc = -0.743. Among these, the instantaneous maximum voltage Umax = Ua = 0.951, the instantaneous minimum voltage Umin = Uc = -0.743, and the instantaneous intermediate voltage Umid = Ub = -0.208.

[0073] The first switching transistor unit S1 and the second switching transistor unit S2 form the first bridge arm; the third switching transistor unit S3 and the fourth switching transistor unit S4 form the second bridge arm.

[0074] Since the voltage Ua of phase A is the instantaneous maximum value of the three phases, the eleventh switch unit S11 is turned on, and the fifth switch unit S5, the sixth switch unit S6, and the fourteenth switch unit S14 are turned off. The instantaneous maximum value of the three phases output of phase A is Umax=0.951.

[0075] Since the C-phase voltage Uc is the instantaneous minimum value of the three phases, the sixteenth switch unit S16 is turned on, and the thirteenth switch unit S13, the ninth switch unit S9, and the tenth switch unit S10 are turned off. The C-phase output three-phase instantaneous minimum value Umin = −0.743.

[0076] Ignoring dead time, the upper and lower switches of the first and second bridge arms are always complementary in conduction on the same half of the bridge. The highest voltage Umax is always generated by the first bridge arm, and the lowest voltage Umin is always generated by the second bridge arm.

[0077] In this embodiment, Umax = 0.951, therefore the duty cycle of the first switching transistor unit S1 in the first bridge arm is 0.951.

[0078] Umin = -0.743, therefore the duty cycle of the fourth switch unit S4 in the second bridge arm is 0.743.

[0079] The phase B voltage Ub is the instantaneous midpoint of the three phases, and the phase B midpoint Umid = -0.208. Because Ub < 0, the transverse double-pass switch bridge arm composed of the seventh switch unit S7 and the eighth switch unit S8, the fifteenth switch unit S15, and the second bridge arm composed of the third switch unit S3 and the fourth switch unit S4 jointly generate the phase B midpoint voltage Umid = -0.208.

[0080] Figure 4 This is a schematic diagram of the switching timing of a three-phase three-level converter in Embodiment 1 of the present invention. It is used to generate the intermediate voltage of phase B, such as... Figure 4As shown, t0-t0' is one complete cycle, and t0'-t0" is the second complete cycle. At time t1, S4 is off, S3, S7, and S8 are on, and the voltage across S15 is 0, achieving zero-voltage conduction. At time t2, S4 is off, and S3 and S15 are on. Since the voltage across S7 and S8 is 0, S7 and S8 achieve zero-voltage turn-off. Within a complete cycle, the time interval t3-t4 is the dead time of the second bridge arm. Simultaneously, S15 is on, and S7 and S8 are off. The output voltage of phase B is unknown, but its impact is negligible due to the extremely short dead time. During the time interval t5-t6, S4 is on, and S3 is off. To prevent a short circuit between DC- and N lines, S15, S7, and S8 are all kept off. The output voltage of phase B is unknown, but its impact is negligible due to the extremely short dead time. During the time interval t4-t5, S4 is on, S3 is off, and simultaneously S15 is on while S7 and S8 are off. The output voltage of phase B connected to DC- is -1. During other time intervals, the output voltage of phase B is 0. To generate Umid = -0.208 for phase B, given the negligible dead time, the time interval t4-t5 must account for 0.208 of the cycle. Figure 4 Timing is just one type of control timing; control timing is not unique.

[0081] Figure 5 This is a schematic diagram of the current flow path of the three-phase three-level converter in Embodiment 1 of the present invention.

[0082] Example 2

[0083] Figure 6 This is a schematic diagram of the topology of a three-phase three-level converter in Embodiment 2 of the present invention.

[0084] like Figure 6 As shown, the topology of Embodiment 2 adds a third and fourth bridge arm, as well as a ninth switch unit S9 and a tenth switch unit S10, to the structure of Embodiment 1. This completely decouples the generation and distribution of the three-phase voltage; the front-end becomes the voltage generation module, and the rear-end becomes the voltage distribution module. The newly added third and fourth bridge arms are used to generate three-phase intermediate voltages greater than and less than the neutral point, respectively. The first and second bridge arms are still used to generate the three-phase highest and lowest voltages. The rear-end voltage distribution module is only responsible for distributing the generated three-phase highest, lowest, and intermediate voltages to the corresponding A, B, and C phases. The newly added ninth and tenth switch units S9 and S10 are used to transmit the positive and negative three-phase intermediate voltages generated by the front-end to the rear-end, respectively. Eleventh to sixteenth switch units S16 are responsible for distributing the three-phase intermediate voltages to phases A, B, and C. Seventeenth to nineteenth switch units S19 are responsible for distributing the three-phase highest voltages to phases A, B, and C. Switching units S20 to S22 are responsible for distributing the three-phase minimum voltage to phases A, B, and C.

[0085] Example 3

[0086] Figure 7 This is a schematic diagram of the topology of the three-phase three-level converter in Embodiment 3 of the present invention.

[0087] like Figure 7 As shown, the topology of Embodiment 3 only changes the structure of the subsequent voltage distribution module in Embodiment 2. The distribution logic of Umax and Umin remains unchanged. The distribution method of Umid is as follows: if phase A is equal to Umid and greater than 0, then the ninth switch unit S9 and the tenth switch unit S10 are turned on, and the eleventh switch unit S11 to the twentieth switch unit S20 are all turned off. If phase A is equal to Umid and less than 0, then the nineteenth switch unit S19 and the twentieth switch unit S20 are turned on, and the ninth switch unit S9 to the eighteenth switch unit S18 are all turned off. The principle of phases B and C is similar.

[0088] Example 4

[0089] Figure 8 This is a schematic diagram of the topology of the three-phase three-level converter in Embodiment 4 of the present invention.

[0090] like Figure 8 As shown, the topology of Embodiment 4 is only modified in the front-end voltage generation module structure of Embodiment 2. In this embodiment, the upper half-bridge arm consists of the first switching transistor unit S1 to the third switching transistor unit S3. Ignoring dead time, only one of these transistors is in the off state at any given time. The lower half-bridge arm, consisting of the fourth switching transistor unit S4 to the sixth switching transistor unit S6, operates similarly; also ignoring dead time, only one of these transistors is in the off state at any given time. Umax is always generated by the upper half-bridge arm, Umin by the lower half-bridge arm, while Umid is generated by the upper half-bridge arm based on its sign. When Umid >= 0, it is generated by the upper half-bridge arm; when Umid < 0, it is generated by the lower half-bridge arm. To generate... Figure 3 Three-phase voltage waveform diagram Figure 6At time ms, the duty cycle of the first switching unit S1 in this embodiment is equal to Umax = 0.951, and the duty cycle of the sixth switching unit S6 is equal to -Umin = 0.743. Since Umid < 0, the eighth switching unit S8 is turned on and the seventh switching unit S7 is turned off. The upper half of the bridge arm does not need to generate an intermediate voltage. Therefore, the duty cycles of the second switching unit S2 and the third switching unit S3 are not subject to special requirements. It is sufficient that the proportion of the second switching unit S2 and the third switching unit S3 being turned on at the same time is equal to 1 - Umax. The lower bridge arm generates the intermediate voltage. The duty cycle of the fifth switching unit S5 and the sixth switching unit S6 being turned on at the same time, that is, the duty cycle of the fourth switching unit S4 being turned off, is equal to -Umid = 0.208. Figure 9 This is the switching timing diagram of the front-end voltage generation module in Embodiment 4 of the present invention. (See diagram below.) Figure 9 As shown, this timing diagram is just one example of timing; other timing diagrams are possible.

[0091] Example 5

[0092] Figure 10 This is a schematic diagram of the topology of the three-phase three-level converter in Embodiment 5 of the present invention.

[0093] like Figure 10 As shown, the topology of Embodiment 5 is modified only in the structure of the subsequent voltage distribution module of Embodiment 4. The distribution logic of Umax and Umin remains unchanged. The distribution method of Umid is as follows: if phase A is equal to Umid and greater than or equal to 0, then the seventh switch unit S7 and the eighth switch unit S8 are turned on, and the ninth switch unit S9 to the eighteenth switch unit S18 are all turned off. If phase A is equal to Umid and less than 0, then the seventeenth switch unit S17 and the eighteenth switch unit S18 are turned on, and the seventh switch unit S7 to the sixteenth switch unit S16 are all turned off. The principle of phases B and C is similar.

[0094] Example 6

[0095] Figure 11 This is a schematic diagram of the topology of a three-phase three-level converter in Embodiment 6 of the present invention.

[0096] like Figure 11 As shown, this embodiment modifies the structure of the front-end three-phase intermediate voltage generation section compared to Embodiment 2. This eliminates the cost of the ninth and tenth switching transistor units S9 and S10, which are used in Embodiment 2 to transmit three-phase intermediate voltages greater than or less than the neutral point voltage to the subsequent stages.

[0097] Example 7

[0098] Figure 12This is a schematic diagram of the topology of the three-phase three-level converter in Embodiment 7 of the present invention.

[0099] like Figure 12 As shown, the topology of this embodiment is modified only in the structure of the front-end voltage generation module of Embodiment 6. Compared with Embodiment 6, this embodiment reduces the cost of the lateral dual-pass switching transistor, and improves the control strategy to ensure that the intermediate level is still a three-level transition.

[0100] Example 8

[0101] Figure 13 This is a schematic diagram of the topology of the three-phase three-level converter in Embodiment 8 of the present invention.

[0102] like Figure 13 As shown, the topology of this embodiment is only modified in the structure of the front-end voltage generation module of embodiment 6, so that the number of switching transistors included in the intermediate level switching path is reduced, thereby reducing heat loss.

[0103] Example 9

[0104] Figure 14 This is a schematic diagram of the topology of the three-phase three-level converter in Embodiment 9 of the present invention.

[0105] like Figure 14 As shown, the only difference between this embodiment and embodiment 8 is the structure of the front-end voltage generation module. This embodiment reduces the cost of the lateral dual-pass switch compared to embodiment 8, and the intermediate level is a two-level transition.

[0106] The role and effect of the embodiments

[0107] According to the three-phase three-level converter involved in this embodiment, it includes: a DC input module for connecting to a DC power supply and forming a stable DC bus voltage; a front-stage three-phase highest voltage generation module connected to the DC input module for forming the three-phase highest voltage required for the three-phase output; a front-stage three-phase lowest voltage generation module connected to the DC input module for forming the three-phase lowest voltage required for the three-phase output; a rear-stage three-phase intermediate voltage generation and three-phase voltage distribution module connected to the front-stage three-phase highest voltage generation module and the front-stage three-phase lowest voltage generation module for generating the three-phase intermediate voltage and dynamically mapping the highest, intermediate, and lowest voltages to their corresponding A, B, and C phases according to the real-time magnitude relationship of each phase voltage; and a filter output module connected to the rear-stage three-phase intermediate voltage generation and three-phase voltage distribution module for filtering the final output voltage of the rear stage. Therefore, the three-phase three-level converter of this invention uses high-frequency switching transistors and low-frequency switching transistors separately, optimizing costs and balancing conduction losses and switching losses.

[0108] This embodiment separates the high-speed transistor and the low-speed transistor, maximizing the semiconductor characteristics of the material. Some semiconductors are suitable for making slow-speed but extremely low-frequency transistors, greatly reducing conduction losses; other semiconductor materials are suitable for making high-frequency transistors with very low switching losses, greatly reducing switching losses, thus overcoming the limitations of existing technologies.

[0109] Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A three-phase three-level converter, characterized in that, include: The DC input module is used to connect to a DC power supply and form a stable DC bus voltage; The front-end three-phase maximum voltage generation module is connected to the DC input module and is used to generate the three-phase maximum level voltage required for the three-phase output; The front-end three-phase minimum voltage generation module is connected to the DC input module and is used to generate the three-phase minimum level voltage required for the three-phase output; The downstream three-phase intermediate voltage generation and three-phase voltage distribution module is connected to the upstream three-phase maximum voltage generation module and the upstream three-phase minimum voltage generation module. It is used to generate the three-phase intermediate voltage and dynamically map the maximum, intermediate and minimum voltages to their corresponding A, B and C phases according to the real-time magnitude relationship of each phase voltage. The filtering output module is connected to the subsequent three-phase intermediate voltage generation and three-phase voltage distribution module, and is used to filter the final output voltage of the subsequent stage.

2. The three-phase three-level converter according to claim 1, Its features are: The DC input module includes: The DC positive input terminal is used as the positive connection point of the DC power supply to introduce the positive voltage of the DC bus. The DC negative input terminal is used as the negative connection point of the DC power supply to introduce the negative voltage of the DC bus. The first supporting capacitor has its first end connected to the DC positive input terminal to maintain the stability of the positive DC bus voltage. The second supporting capacitor has its first end connected to the second end of the first supporting capacitor and its second end connected to the DC negative input terminal, and is used to maintain the stability of the negative DC bus voltage.

3. The three-phase three-level converter according to claim 2, Its features are: The front-end three-phase maximum voltage generation module includes: The first switching transistor unit has its first terminal connected to the DC positive input terminal and is used to generate the highest level voltage of the three phases. The second switching transistor unit has a first end connected to the first switching transistor unit and a second end connected to the second end of the first supporting capacitor, and is used to generate the highest level voltage of the three phases. The front-end three-phase minimum voltage generation module includes: The third switching transistor unit has its first terminal connected to the first terminal of the second supporting capacitor, and is used to generate the three-phase lowest level voltage. The fourth switching transistor unit has its first terminal connected to the third switching transistor unit and its second terminal connected to the DC negative input terminal, and is used to generate the three-phase lowest level voltage.

4. The three-phase three-level converter according to claim 3, Its features are: The downstream three-phase intermediate voltage generation and three-phase voltage distribution module includes: The first terminal of the fifth switching transistor unit is connected to the second terminal of the second switching transistor unit and the first terminal of the third switching transistor unit, respectively, and is used to generate the three-phase intermediate level voltage of phase A; The sixth switching transistor unit, with its first terminal connected to the second terminal of the fifth switching transistor unit, is used to generate the three-phase intermediate voltage of phase A. The seventh switching transistor unit has its first terminal connected to the second terminal of the second switching transistor unit and the first terminal of the third switching transistor unit, respectively, to generate the three-phase intermediate level voltage of phase B. The eighth switching transistor unit, with its first terminal connected to the second terminal of the seventh switching transistor unit, is used to generate the three-phase intermediate level voltage of phase B. The ninth switching transistor unit has its first terminal connected to the second terminal of the second switching transistor unit and the first terminal of the third switching transistor unit, respectively, to generate the three-phase intermediate level voltage of phase C. The tenth switching transistor unit has its first terminal connected to the second terminal of the ninth switching transistor unit, and is used to generate the three-phase intermediate level voltage of phase C. The eleventh switching transistor unit has its first terminal connected to the second terminal of the first switching transistor unit and the first terminal of the second switching transistor unit, and its second terminal connected to the second terminal of the sixth switching transistor unit. It is used to distribute the highest three-phase voltage to phase A or generate a positive three-phase intermediate voltage for phase A. The twelfth switching transistor unit has its first terminal connected to the first terminal of the eleventh switching transistor unit and its second terminal connected to the second terminal of the eighth switching transistor unit. It is used to distribute the highest three-phase voltage to phase B or generate a positive three-phase intermediate voltage for phase B. The thirteenth switching transistor unit has its first terminal connected to the first terminal of the twelfth switching transistor unit and its second terminal connected to the second terminal of the tenth switching transistor unit. It is used to distribute the highest three-phase voltage to the C phase or generate a positive three-phase intermediate voltage for the C phase. The fourteenth switching transistor unit has its first terminal connected to the second terminal of the eleventh switching transistor unit, and its second terminal connected to the second terminal of the third switching transistor unit and the first terminal of the fourth switching transistor unit, respectively. It is used to distribute the three-phase lowest level voltage to phase A or generate the negative three-phase intermediate level voltage of phase A. The fifteenth switching transistor unit has its first terminal connected to the second terminal of the twelfth switching transistor unit, and its second terminal connected to the second terminal of the third switching transistor unit and the first terminal of the fourth switching transistor unit, respectively. It is used to distribute the three-phase lowest level voltage to phase B or generate the negative three-phase intermediate level voltage of phase B. The sixteenth switching transistor unit has its first terminal connected to the second terminal of the thirteenth switching transistor unit, and its second terminal connected to the second terminal of the third switching transistor unit and the first terminal of the fourth switching transistor unit, respectively. It is used to distribute the three-phase lowest level voltage to the C phase or generate the negative three-phase intermediate level voltage of the C phase.

5. The three-phase three-level converter according to claim 4, Its features are: The filtering output module includes: The first filter inductor has its first terminal connected to the second terminal of the eleventh switching transistor unit and the first terminal of the fourteenth switching transistor unit, and is used to filter the output voltage. The second filter inductor has its first terminal connected to the second terminal of the twelfth switching transistor unit and the first terminal of the fifteenth switching transistor unit, and is used to filter the output voltage. The third filter inductor has its first terminal connected to the second terminal of the thirteenth switching transistor unit and the first terminal of the sixteenth switching transistor unit, and is used to filter the output voltage.

6. The three-phase three-level converter according to claim 1, characterized in that: in, The types of switching transistor units include, but are not limited to, FET, IGBT, and BJT.

7. The three-phase three-level converter according to claim 2, characterized in that: in, The series connection point between the second end of the first supporting capacitor and the first end of the second supporting capacitor is the neutral point, which is directly led out as an independent terminal.

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