Three-phase frequency converter and air conditioner

Abstract

The invention relates to the technical field of air conditioners, particularly provides a three-phase frequency converter and an air conditioner, and aims to solve the problems of improving the power factor of the three-phase air conditioner by using the frequency converter and reducing the electrical stress of a power device and the cost of the frequency converter. The three-phase frequency converter provided by the invention comprises a three-phase rectification module and a three-phase inversion module, wherein the three-phase rectification module comprises a three-phase rectification circuit, a three-phase harmonic current injection circuit and a step-down circuit; the three-phase rectifying circuit is used for converting first alternating current input by a three-phase alternating current power supply into first direct current, and the first alternating current comprises first harmonic current; the three-phase harmonic current injection circuit is used for injecting second harmonic current into the first alternating current, so that the second harmonic current and the first harmonic current counteract each other; the step-down circuit is used for carrying out step-down on the first direct current to form second direct current; the three-phase inversion module is used for converting the second direct current into second alternating current. Based on the structure, the power factor can be improved, and power device electrical stress and frequency converter cost are reduced.

Description

Technical Field

[0001] The present application relates to the technical field of air conditioning, and in particular to a three-phase inverter and an air conditioner. Background Art

[0002] An air conditioner using a three-phase AC power supply (hereinafter referred to as a three-phase air conditioner) usually uses a three-phase inverter to achieve frequency conversion. The three-phase inverter includes a three-phase rectifier module and a three-phase inverter module. The AC side of the three-phase rectifier module is connected to the three-phase AC power supply, the DC side of the three-phase rectifier module is connected to the DC side of the three-phase inverter module, and the AC side of the three-phase inverter module is connected to the load.

[0003] At present, in order to suppress the harmonic current in three-phase air conditioners and improve the power factor, there are mainly two ways:

[0004] The first method is to set a passive power factor correction (Power Factor Correction) circuit on the DC side of the three-phase rectifier module, but it is difficult to achieve a higher power factor in this way.

[0005] The second method is to use a Vienna rectifier circuit with a power factor correction function to construct a three-phase rectifier module. The Vienna rectifier circuit is actually a boost-type power factor correction circuit, which will cause a large increase in the bus voltage on the DC side of the three-phase rectifier module, which will increase the electrical stress of the subsequent power devices, where the subsequent power devices may include power devices in the three-phase inverter module, power devices in the fan drive circuit, power devices in the compressor drive circuit, etc. The increase in the electrical stress of the power device requires the use of a high-voltage power device, which not only increases the cost of the inverter, but is also not conducive to low-voltage drive of loads such as fans and compressors with low voltage levels.

[0006] Accordingly, the art needs a new technical solution to solve the above problems. Summary of the invention

[0007] In order to overcome the above-mentioned defects, the present application is proposed to solve or at least partially solve the technical problem of using a frequency converter to improve the power factor of a three-phase air conditioner and reduce the electrical stress of power devices and the cost of the frequency converter.

[0008] In a first aspect, a three-phase frequency converter is provided, the three-phase frequency converter comprising a three-phase rectifier module (1) and a three-phase inverter module (2), wherein the three-phase rectifier module (1) comprises a three-phase rectifier circuit (11), a three-phase harmonic current injection circuit (12) and a step-down circuit (13);

[0009] The three-phase rectifier circuit (11) includes an AC input terminal and a DC output terminal. The AC input terminal is connected to a three-phase AC power supply. The three-phase rectifier circuit (11) is configured to convert a first alternating current input from the three-phase AC power supply into a first direct current, and the first alternating current includes a first harmonic current;

[0010] A first end of the three-phase harmonic current injection circuit (12) is connected to the AC input terminal, and a second end of the three-phase harmonic current injection circuit (12) is connected to the DC output terminal. The three-phase harmonic current injection circuit (12) is configured to inject a second harmonic current into the first alternating current so that the second harmonic current cancels out the first harmonic current;

[0011] A first end of the buck circuit (13) is connected to the DC output terminal, and a second end of the buck circuit (13) is connected to the three-phase inverter module (2). The buck circuit (13) is configured to step down the first direct current to form a second direct current;

[0012] The three-phase inverter module (2) is configured to convert the second direct current into a second alternating current.

[0013] In a technical solution of the above three-phase frequency converter, the buck circuit (13) includes a first Buck sub-circuit (131), a second Buck sub-circuit (132), and a capacitor (133);

[0014] The first Buck sub-circuit (131) includes a first switching tube (1311), a first diode (1312), and a first inductor (1313);

[0015] The second Buck sub-circuit (132) includes a second switching tube (1321), a second diode (1322), and a second inductor (1323);

[0016] A first end of the first switching tube (1311) is connected to the positive pole of the DC output terminal, and a second end is connected to a first end of the first inductor (1313);

[0017] A first end of the second switching tube (1321) is connected to the negative pole of the DC output terminal, and a second end is connected to a first end of the second inductor (1323);

[0018] The capacitor (133) is connected in parallel between a second end of the first inductor (1313) and a second end of the second inductor (1323);

[0019] The cathode of the first diode (1311) is connected to the first end of the first inductor (1313), and the anode is connected to the cathode of the second diode (1322). The anode of the second diode (1322) is connected to the first end of the second inductor (1323).

[0020] Wherein, the first ends of the first switching tube (1311) and the second switching tube (1321) form the first end of the buck circuit (13), and the second ends of the first inductor (1313) and the second inductor (1323) form the second end of the buck circuit (13).

[0021] In a technical solution of the above three-phase frequency converter, the second end of the three-phase harmonic current injection circuit (12) is connected between the anode of the first diode (1311) and the cathode of the second diode (1322).

[0022] In a technical solution of the above three-phase frequency converter, the AC input end includes a first input end, a second input end, and a third input end. The three-phase harmonic current injection circuit (12) includes a first injection circuit (121), a second injection circuit (122), and a third injection circuit (123).

[0023] The first end of the first injection circuit (121) is connected to the first input end, and the first injection circuit (121) is used to inject a second harmonic current into the first alternating current flowing into the first input end.

[0024] The first end of the second injection circuit (122) is connected to the second input end, and the second injection circuit (122) is used to inject a second harmonic current into the first alternating current input into the second input end.

[0025] The first end of the third injection circuit (123) is connected to the third input end, and the third injection circuit (123) is used to inject a second harmonic current into the first alternating current input into the third input end.

[0026] Wherein, the second ends of the first injection circuit (121), the second injection circuit (122), and the third injection circuit (123) form the second end of the three-phase harmonic current injection circuit (12).

[0027] In a technical solution of the above three-phase frequency converter, the first injection circuit (121) includes two switching tubes connected in reverse.

[0028] The second injection circuit (122) includes two switching tubes connected in reverse.

[0029] The third injection circuit (123) includes two switching tubes connected in reverse.

[0030] In a technical solution of the above three-phase frequency converter, the three-phase rectifier circuit (11) is a three-phase full-bridge rectifier circuit composed of diodes.

[0031] In a technical solution of the above three-phase frequency converter, the three-phase inverter module (2) is an inverter module composed of an intelligent power module IPM.

[0032] In a technical solution of the above three-phase frequency converter, the three-phase frequency converter includes a switching power supply, and the switching power supply is connected to the second end of the buck circuit (13).

[0033] In a technical solution of the above three-phase frequency converter, the switching power supply is a flyback switching power supply.

[0034] In a second aspect, an air conditioner is provided, and the air conditioner includes the three-phase frequency converter provided in the first aspect.

[0035] One or more of the above technical solutions of the present application have at least one or more of the following beneficial effects:

[0036] In implementing a technical solution of the three-phase frequency converter provided by the present application, the three-phase frequency converter includes a three-phase rectification module and a three-phase inversion module. The three-phase rectification module includes a three-phase rectifier circuit, a three-phase harmonic current injection circuit, and a buck circuit. The three-phase rectifier circuit includes an AC input end and a DC output end. The AC input end is connected to a three-phase AC power supply. The three-phase rectifier circuit is used to convert the first alternating current input from the three-phase AC power supply into a first direct current. The first alternating current includes a first harmonic current. The first end of the three-phase harmonic current injection circuit is connected to the AC input end, and the second end of the three-phase harmonic current injection circuit is connected to the DC output end. The three-phase harmonic current injection circuit is used to inject a second harmonic current into the first alternating current so that the second harmonic current cancels out the first harmonic current. The first end of the buck circuit is connected to the DC output end, and the second end of the buck circuit is connected to the three-phase inversion module. The buck circuit is used to step down the first direct current to form a second direct current. The three-phase inversion module is used to convert the second direct current into a second alternating current.

[0037] In the above implementation, by injecting a second harmonic current into the first alternating current through the three-phase harmonic current injection circuit, the second harmonic current cancels out the first harmonic current, realizing the active suppression of harmonic current, and thus realizing the active power factor correction. Compared with the passive power factor correction adopted in the prior art, the above implementation can achieve a higher power factor. In addition, through the buck circuit, the bus voltage on the DC side of the three-phase rectification module can be reduced, reducing the electrical stress of the subsequent power devices, so that low-voltage withstand power devices can be used, not only reducing the cost of the frequency converter, but also enabling low-voltage driving of loads such as low-voltage fans and compressors. Brief Description of the Drawings

[0038] Referring to the accompanying drawings, the disclosure of the present application will become more readily understood. It is easily understood by those skilled in the art that these drawings are only for illustrative purposes and are not intended to limit the scope of protection of the present application. Among them:

[0039] Figure 1 is a schematic diagram of the main structure of a three-phase frequency converter according to an embodiment of the present application;

[0040] Figure 2 is a schematic diagram of the main structure of a buck circuit according to an embodiment of the present application;

[0041] Figure 3 is a schematic diagram of the main structure of a three-phase harmonic current injection circuit according to an embodiment of the present application;

[0042] Figure 4 is a schematic diagram of the main structure of a three-phase rectification module according to an embodiment of the present application;

[0043] Figure 5 is a schematic diagram of an intelligent power module IPM with a rated voltage of 650V;

[0044] Figure 6 is a schematic diagram of the connection of a three-phase frequency converter, a compressor drive module, and a fan drive module in an air conditioner according to an embodiment of the present application. Detailed Embodiments

[0045] The following describes some embodiments of the present application with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present application and are not intended to limit the scope of protection of the present application.

[0046] The following describes an embodiment of the three-phase frequency converter provided by the present application.

[0047] Referring to the attached Figure 1 , Figure 1 is a schematic diagram of the main structure of a three-phase frequency converter according to an embodiment of the present application. As Figure 1 shown, the three-phase frequency converter in the embodiment of the present application mainly includes a three-phase rectification module 1 and a three-phase inversion module 2. The three-phase rectification module 1 includes a three-phase rectification circuit 11, a three-phase harmonic current injection circuit 12, and a buck circuit 13.

[0048] Specifically, the three-phase rectifier circuit 11 includes an AC input terminal and a DC output terminal. The AC input terminal is connected to a three-phase AC power supply, and the DC output terminal is connected to the first terminal of the buck circuit 13. The first alternating current of the three-phase AC power supply flows into the three-phase rectifier circuit 11 through the AC input terminal. The three-phase rectifier circuit 11 is used to convert the first alternating current into a first direct current, and then input the first direct current into the buck circuit 13 for bucking to form a second direct current. The second terminal of the buck circuit 13 is connected to the three-phase inverter module 2, and the buck circuit 13 can input the second direct current into the three-phase inverter module 2. The three-phase inverter module 2 can convert the second direct current into a second alternating current.

[0049] The first alternating current input from the three-phase AC power supply to the three-phase rectifier circuit 11 includes a first harmonic current, and this harmonic current will reduce the power factor of the three-phase frequency converter.

[0050] The first terminal of the three-phase harmonic current injection circuit 12 is connected to the AC input terminal of the three-phase rectifier circuit 11, and the second terminal of the three-phase harmonic current injection circuit 12 is connected to the DC output terminal of the three-phase rectifier circuit 11. The three-phase harmonic current injection circuit 12 is used to inject a second harmonic current into the first alternating current flowing into the AC input terminal of the three-phase rectifier circuit 11, so that the second harmonic current cancels out the first harmonic current in the first alternating current. Based on this, the first alternating current flowing into the three-phase rectifier circuit 11 no longer contains the first harmonic current, thereby effectively improving the power factor of the three-phase frequency converter.

[0051] Based on the above embodiments, by injecting the second harmonic current into the first alternating current through the three-phase harmonic current injection circuit 12, the second harmonic current cancels out the first harmonic current, realizing the active suppression of harmonic current, and thus realizing the active power factor correction. Compared with the passive power factor correction adopted in the prior art, the above embodiments can achieve a higher power factor. In addition, through the buck circuit 13, the bus voltage on the DC side of the three-phase rectifier module 1 can be reduced, reducing the electrical stress of the subsequent power devices, so that low-voltage withstand power devices can be used, which not only reduces the cost of the frequency converter, but also can perform low-voltage drive on loads such as low-voltage fans and compressors.

[0052] The three-phase rectifier module 1 and the three-phase inverter module 2 will be further described below.

[0053] 1. Description of the three-phase rectifier module 1.

[0054] 1. Description of the three-phase rectifier circuit 11.

[0055] In some embodiments, a three-phase full-bridge rectifier circuit composed of diodes can be used as the three-phase rectifier circuit 11. Diodes can be understood as uncontrollable power electronic devices. Therefore, the above three-phase full-bridge rectifier circuit can be understood as an uncontrollable rectifier circuit.

[0056] 2. Describe the buck circuit 13.

[0057] Refer to the appendix Figure 2 , Figure 2 Exemplarily shows a schematic diagram of the main structure of the buck circuit 13 according to an embodiment of the present application. As Figure 2 shown, the buck circuit 13 includes a first Buck sub-circuit 131, a second Buck sub-circuit 132, and a capacitor 133.

[0058] Specifically, the first Buck sub-circuit 131 includes a first switching transistor 1311, a first diode 1312, and a first inductor 1313. The second Buck sub-circuit 132 includes a second switching transistor 1321, a second diode 1322, and a second inductor 1323.

[0059] The first end of the first switching transistor 1311 is connected to the positive pole of the DC output end of the three-phase rectifier circuit 11, and the second end of the first switching transistor 1311 is connected to the first end of the first inductor 1313. The first end of the second switching transistor 1321 is connected to the negative pole of the DC output end of the three-phase rectifier circuit 11, and the second end of the second switching transistor 1321 is connected to the first end of the second inductor 1323. The capacitor 133 is connected in parallel between the second ends of the first inductor 1313 and the second inductor 1323.

[0060] The cathode of the first diode 1311 is connected to the first end of the first inductor 1313, the anode of the first diode 1311 is connected to the cathode of the second diode 1322, and the anode of the second diode 1322 is connected to the first end of the second inductor (1323).

[0061] Next, describe the first end and the second end of the buck circuit 13.

[0062] The first ends of the first switching transistor 1311 and the second switching transistor 1321 form the first end of the buck circuit 13. Among them, the first end of the first switching transistor 1311 can be understood as the positive extreme, which is connected to the positive pole of the DC output end of the three-phase rectifier circuit 11; the first end of the second switching transistor 1321 can be understood as the negative extreme, which is connected to the negative pole of the DC output end of the three-phase rectifier circuit 11.

[0063] The second ends of the first inductor 1313 and the second inductor 1323 form the second end of the buck circuit 13. Among them, the second end of the first inductor 1313 can be understood as the positive extreme, which is connected to the positive pole of the DC input end of the three-phase inverter module 2; the second end of the second inductor 1323 can be understood as the negative extreme, which is connected to the negative pole of the DC input end of the three-phase inverter module 2.

[0064] The working principle of the buck circuit 13 will be described below.

[0065] The first switching tube 1311 and the second switching tube 1321 are fully controlled power electronic devices, and the first switching tube 1311 and the second switching tube 1321 can be controlled to turn on and off through a pulse modulation signal PWM. For example, the first switching tube 1311 and the second switching tube 1321 can be MOS tubes. When the buck circuit 13 works, the first switching tube 1311 and the second switching tube 1321 can be controlled to turn on and off simultaneously through the pulse modulation signal PWM (Pulse Width Modulation). By adjusting the on-time and off-time of the first switching tube 1311 and the second switching tube 1321, the voltage of the second direct current output at the second end of the buck circuit 13 can be changed. Among them, the longer the on-time, the smaller the voltage of the second direct current, and the longer the off-time, the larger the voltage of the second direct current.

[0066] When the first switching tube 1311 and the second switching tube 1321 are turned on simultaneously, the first direct current output from the DC output end of the three-phase rectifier circuit 11 flows through the first inductor 1313 and the second inductor 1323. The first inductor 1313 and the second inductor 1323 are magnetized, and the current flowing through the first inductor 1313 and the second inductor 1323 increases linearly. At the same time, the capacitor 133 is charged, and the second direct current is output through the second end of the buck circuit 13.

[0067] When the first switching tube 1311 and the second switching tube 1321 are turned off simultaneously, a conducting loop is formed by the first inductor 1313, the second inductor 1323, the first diode 1311, the second diode 1322, and the capacitor 133. The first inductor 1313 and the second inductor 1323 discharge through the first diode 1311 and the second diode 1322, and the inductor current on the first inductor 1313 and the second inductor 1323 decreases linearly, and the capacitor 133 also discharges. The second direct current output at the second end of the buck circuit 13 is maintained by the inductor current of the first inductor 1313 and the second inductor 1323 and the discharge of the capacitor 133.

[0068] 3. The three-phase harmonic current injection circuit 12 will be described.

[0069] Refer to the appendix Figure 3 , Figure 3An exemplary schematic diagram of the main structure of a three-phase harmonic current injection circuit 12 according to an embodiment of the present application is shown. As Figure 3 shown, the second end of the three-phase harmonic current injection circuit 12 is connected between the anode of the first diode 1311 and the cathode of the second diode 1322. The first end of the three-phase harmonic current injection circuit 12 is connected to the AC input terminal of the three-phase rectifier circuit 11 ( Figure 3 not shown).

[0070] In some embodiments, the AC input terminals of the three-phase rectifier circuit 11 include a first input terminal, a second input terminal, and a third input terminal, and the three-phase harmonic current injection circuit 12 includes a first injection circuit 121, a second injection circuit 122, and a third injection circuit 123.

[0071] The first end of the first injection circuit 121 is connected to the first input terminal, and the first injection circuit 121 is configured to inject a second harmonic current into the first alternating current flowing into the first input terminal, so that the second harmonic current cancels out the first harmonic current in the first alternating current.

[0072] The first end of the second injection circuit 122 is connected to the second input terminal, and the second injection circuit 122 is configured to inject a second harmonic current into the first alternating current input into the second input terminal, so that the second harmonic current cancels out the first harmonic current in the first alternating current.

[0073] The first end of the third injection circuit 123 is connected to the third input terminal, and the third injection circuit 123 is configured to inject a second harmonic current into the first alternating current input into the third input terminal, so that the second harmonic current cancels out the first harmonic current in the first alternating current.

[0074] In the above three-phase harmonic current injection circuit 12, the second ends of the first injection circuit 121, the second injection circuit 122, and the third injection circuit 123 form the second end of the three-phase harmonic current injection circuit 12. Specifically, the second ends of the first injection circuit 121, the second injection circuit 122, and the third injection circuit 123 are connected together to form a common terminal, and this common terminal is the second end of the three-phase harmonic current injection circuit 12.

[0075] In some embodiments, the first injection circuit 121 includes two switching tubes connected in reverse, the second injection circuit 122 includes two switching tubes connected in reverse, and the third injection circuit 123 includes two switching tubes connected in reverse. The above switching tubes can be fully controlled power electronic devices, and the above switching tubes can be controlled to turn on and off through a pulse modulation signal PWM. For example, the above switching tubes can be MOS tubes.

[0076] The working principle of the three-phase harmonic current injection circuit 12 will be described below.

[0077] Taking the first injection circuit 121 as an example, the first injection circuit 121 includes two switching transistors connected in reverse. The conduction and cutoff of these two switching transistors can be controlled respectively. Based on this, the first injection circuit 121 can be made to conduct with the first diode 1311 or the second diode 1322, and the current in the first diode 1311 or the second diode 1322 can flow into the first injection circuit 121. By changing the conduction and cutoff frequency (or time) of the switching transistors, the frequency of the current flowing through the first injection circuit 121 can also be changed. Therefore, the frequency of the second harmonic current can be obtained in advance. By setting the conduction and cutoff of the switching transistors according to this frequency, the current flowing through the first injection circuit 121 can be adjusted to the second harmonic current. It should be noted that each switching transistor is reversely connected in parallel with a freewheeling diode. Therefore, even when the switching transistor is cutoff, the current can be transmitted through the freewheeling diode.

[0078] The following combines with the attached Figure 4 to illustrate the three-phase rectification module 1 provided by the present application.

[0079] As Figure 4 shown, the three-phase rectification module 1 includes a three-phase rectification circuit 11, a three-phase harmonic current injection circuit 12, and a buck circuit 13. Among them, the three-phase rectification circuit 11 is a three-phase full-bridge rectification circuit composed of diodes D1 to D6. The three-phase harmonic current injection circuit 12 includes a first injection circuit 121, a second injection circuit 122, and a third injection circuit 123. The first injection circuit 121 includes switching transistors Q1 and Q2 connected in reverse, the second injection circuit 122 includes switching transistors Q3 and Q4 connected in reverse, and the third injection circuit 123 includes switching transistors Q5 and Q6 connected in reverse. In addition, the three-phase rectification module 1 further includes a current transformer T1 and a current transformer T2. The current of the first direct current output by the three-phase rectification circuit 11 can be detected through the current transformer T1, and the current of the second direct current output by the buck circuit 13 can be detected through the current transformer T2. Furthermore, the voltages of the first and second direct currents can be obtained according to the above-mentioned currents of the first and second direct currents.

[0080] Second, illustrate the three-phase inverter module 2.

[0081] In some embodiments, the three-phase inverter module 2 is an inverter module composed of an intelligent power module IPM (Intelligent Power Module).

[0082] For example, for an air conditioner using a 380V three-phase AC power supply, if a three-phase frequency converter provided by the prior art is used, only an inverter module with a rated voltage of 1200V can be used. However, if the three-phase frequency converter provided by the present application is used, the inverter module can use Figure 5The intelligent power module IPM with a rated voltage of 650V as shown. Compared with the inverter module of 1200V, the inverter module of 650V bears lower electrical stress. In addition, since the higher the rated voltage level, the higher the cost of the inverter module, therefore, the cost of the inverter module can also be reduced by the above method.

[0083] The three-phase frequency converter provided by the present application will be further described below.

[0084] In some embodiments, the three-phase frequency converter may include, in addition to the three-phase rectification module 1 and the three-phase inverter module 2, a switching power supply. The switching power supply is connected to the second end of the buck circuit 13. The switching power supply can convert the voltage of the second direct current output by the buck circuit 13 to obtain a third direct current. The switching power supply can be connected to a load and input the third direct current to the load to supply power to the load. The switching power supply may be a flyback switching power supply.

[0085] Another aspect of the present application also provides an air conditioner.

[0086] In the embodiment of the air conditioner provided by the present application, the air conditioner may include the three-phase frequency converter described in the above embodiment. For example, as Figure 6 shown, when the above three-phase frequency converter is applied to the air conditioner, the bus connected to the second end of the buck circuit 13 is a low-voltage DC bus, and this low-voltage DC bus can also be understood as the second end of the buck circuit 13. The compressor drive module and the fan drive module of the air conditioner can both be connected to the above low-voltage DC bus to obtain electrical energy from the low-voltage DC bus.

[0087] So far, the technical solution of the present application has been described in conjunction with an embodiment shown in the drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present application is obviously not limited to these specific embodiments. Without departing from the principle of the present application, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the protection scope of the present application.

Claims

1. A three-phase frequency converter, characterized in that, The three-phase frequency converter includes a three-phase rectification module (1) and a three-phase inversion module (2). The three-phase rectification module (1) includes a three-phase rectification circuit (11), a three-phase harmonic current injection circuit (12), and a buck circuit (13). The three-phase rectification circuit (11) includes an AC input end and a DC output end. The AC input end is connected to a three-phase AC power supply. The three-phase rectification circuit (11) is configured to convert a first alternating current input from the three-phase AC power supply into a first direct current. The first alternating current includes a first harmonic current. A first end of the three-phase harmonic current injection circuit (12) is connected to the AC input end, and a second end of the three-phase harmonic current injection circuit (12) is connected to the DC output end. The three-phase harmonic current injection circuit (12) is configured to inject a second harmonic current into the first alternating current so that the second harmonic current cancels out the first harmonic current. A first end of the buck circuit (13) is connected to the DC output end, and a second end of the buck circuit (13) is connected to the three-phase inversion module (2). The buck circuit (13) is configured to step down the first direct current to form a second direct current. The three-phase inversion module (2) is configured to convert the second direct current into a second alternating current.

2. The three-phase frequency converter according to claim 1, characterized in that The buck circuit (13) includes a first Buck sub-circuit (131), a second Buck sub-circuit (132), and a capacitor (133). The first Buck sub-circuit (131) includes a first switching tube (1311), a first diode (1312), and a first inductor (1313). The second Buck sub-circuit (132) includes a second switching tube (1321), a second diode (1322), and a second inductor (1323). A first end of the first switching tube (1311) is connected to the positive pole of the DC output end, and a second end is connected to a first end of the first inductor (1313). A first end of the second switching tube (1321) is connected to the negative pole of the DC output end, and a second end is connected to a first end of the second inductor (1323). The capacitor (133) is connected in parallel between a second end of the first inductor (1313) and a second end of the second inductor (1323). The cathode of the first diode (1311) is connected to the first end of the first inductor (1313), the anode is connected to the cathode of the second diode (1322), and the anode of the second diode (1322) is connected to the first end of the second inductor (1323). Wherein, the first ends of the first switching tube (1311) and the second switching tube (1321) form the first end of the buck circuit (13), and the second ends of the first inductor (1313) and the second inductor (1323) form the second end of the buck circuit (13).

3. The three-phase frequency converter according to claim 2, wherein The second end of the three-phase harmonic current injection circuit (12) is connected between the anode of the first diode (1311) and the cathode of the second diode (1322).

4. The three-phase frequency converter according to claim 3, characterized in that, The AC input terminal includes a first input terminal, a second input terminal, and a third input terminal, and the three-phase harmonic current injection circuit (12) includes a first injection circuit (121), a second injection circuit (122), and a third injection circuit (123); The first end of the first injection circuit (121) is connected to the first input terminal, and the first injection circuit (121) is configured to inject a second harmonic current into the first alternating current flowing into the first input terminal; The first end of the second injection circuit (122) is connected to the second input terminal, and the second injection circuit (122) is configured to inject a second harmonic current into the first alternating current input into the second input terminal; The first end of the third injection circuit (123) is connected to the third input terminal, and the third injection circuit (123) is configured to inject a second harmonic current into the first alternating current input into the third input terminal; Wherein, the second ends of the first injection circuit (121), the second injection circuit (122), and the third injection circuit (123) form the second end of the three-phase harmonic current injection circuit (12).

5. The three-phase frequency converter according to claim 4, wherein The first injection circuit (121) includes two switching tubes connected in reverse; The second injection circuit (122) includes two switching tubes connected in reverse; The third injection circuit (123) includes two switching tubes connected in reverse.

6. The three-phase frequency converter according to claim 1, wherein The three-phase rectifier circuit (11) is a three-phase full-bridge rectifier circuit composed of diodes.

7. The three-phase frequency converter according to claim 1, wherein The three-phase inverter module (2) is an inverter module composed of an intelligent power module IPM.

8. The three-phase frequency converter according to claim 1, characterized in that, The three-phase frequency converter includes a switching power supply, and the switching power supply is connected to the second end of the buck circuit (13).

9. The three-phase frequency converter according to claim 8, characterized in that, The switching power supply is a flyback switching power supply.

10. An air conditioner, characterized in that, The air conditioner includes the three-phase frequency converter according to any one of claims 1 to 9.

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