Three-phase AC-DC converter and fault current suppression method

Abstract

The invention provides a three-phase alternating current-direct current converter and a fault current suppression method. The three-phase alternating current-direct current converter comprises an alternating current filtering unit, a three-phase conversion bridge arm unit and a direct current filtering capacitor, the alternating current filtering unit comprises three phases of filtering circuits, and one end of each phase of filtering circuit is correspondingly connected to a three-phase alternating current port of an alternating current side; the three-phase conversion bridge arm unit comprises three-phase conversion bridge arms, and the midpoint of each phase of conversion bridge arm is connected to the other end of each phase of filter circuit; two ends of the direct current filter capacitor are respectively connected with two ends of each phase of conversion bridge arm, and two ends of the direct current filter capacitor are respectively connected with two direct current ports at the direct current side; wherein each phase of conversion bridge arm comprises a first bridge arm and a second bridge arm which are respectively located at two sides of the midpoint of the conversion bridge arm, and a protection branch connected between the first bridge arm and the second bridge arm, the protection branch comprises a protection capacitor and a diode which are connected in series, and the protection branch is used for inhibiting fault current when a short circuit fault occurs.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of rectifying conversion and power conversion, and in particular to a three-phase AC-DC converter and a fault current suppression method. BACKGROUND

[0002] At present, two-level, three-level and other circuit topologies are the mainstream technical solutions of AC-DC conversion and are widely used in energy storage converters, photovoltaic inverters, flexible interconnection and other medium and low voltage grid-connected scenarios. For example, the patent with publication number CN112332679B proposes an improved three-terminal power unit with DC fault blocking capability, which includes a power conversion loop and a commutation loop. The improved three-terminal power unit has three AC terminals, one DC terminal and one energy storage access terminal, realizing the connection of the AC side, the energy storage unit side and the DC side. At the same time, it also has the fault blocking capability when the modular multilevel converter system has a DC fault, which can realize rapid blocking and clearing of fault current. However, when a fault occurs on the DC side of the above-mentioned AC-DC conversion scheme, the AC system will charge the DC fault point through the antiparallel freewheeling diode in the converter, threatening the safe and stable operation of the DC bus and affecting other devices or equipment connected to the DC bus, such as DC-DC converters, batteries, photovoltaic cells, and DC-AC converters. SUMMARY

[0003] Therefore, the present disclosure provides a three-phase AC-DC converter and a fault current suppression method to solve the technical problem that in the existing AC-DC conversion technology, when a fault occurs on the DC side, the antiparallel freewheeling diode will charge the DC fault point, threatening the safe and stable operation of the DC bus. In order to achieve the above-mentioned purpose, the technical solution of the present disclosure is as follows:

[0004] According to an embodiment of one aspect of the present disclosure, a three-phase AC-DC converter is provided, which includes an AC filter unit, a three-phase conversion bridge arm unit and a DC filter capacitor.

[0005] The AC filter unit includes a three-phase filter circuit, each phase filter circuit includes an inductor and a capacitor, and one end of each phase filter circuit is connected to a three-phase AC port on the AC side in a phase corresponding manner. The three-phase conversion bridge arm unit includes a three-phase conversion bridge arm, and the midpoint of each phase conversion bridge arm is connected to the other end of each phase filter circuit. The two ends of the DC filter capacitor are respectively connected to the two ends of each phase conversion bridge arm, and the two ends of the DC filter capacitor are respectively connected to two DC ports on the DC side. Each phase conversion bridge arm includes a first bridge arm and a second bridge arm located on both sides of the midpoint of the conversion bridge arm, and a protection branch connected between the first bridge arm and the second bridge arm. The protection branch includes a protection capacitor and a diode connected in series, and is used to suppress fault current when a short circuit fault occurs.

[0006] According to the embodiment of the present disclosure, the first bridge arm is located on one side of the midpoint of the conversion bridge arm, the first bridge arm comprises a switch tube group with bidirectional conduction capability formed by two switch tubes in reverse polarity series, and each switch tube is provided with an anti-parallel diode, and the connection form of the two switch tubes in the first bridge arm is common-source series connection or common-drain series connection.

[0007] According to the embodiment of the present disclosure, the second bridge arm is located on the other side of the midpoint of the conversion bridge arm, the second bridge arm comprises a switch tube group with bidirectional conduction capability formed by two switch tubes in reverse polarity series, and each switch tube is provided with an anti-parallel diode, and the connection form of the two switch tubes in the second bridge arm is common-source series connection or common-drain series connection; the connection form of the two switch tubes in the first bridge arm is different from the connection form of the two switch tubes in the second bridge arm.

[0008] According to the embodiment of the present disclosure, the negative electrode of the protection capacitor is connected to the positive electrode of the diode, and when a short-circuit fault occurs, the inductive current at the inductor can charge the protection capacitor.

[0009] According to the embodiment of the present disclosure, the negative electrode of the diode is connected between the two switch tubes of the first bridge arm, and the positive electrode of the protection capacitor is connected between the two switch tubes of the second bridge arm.

[0010] According to the embodiment of the present disclosure, when a short-circuit fault occurs, the inductive current rapidly rises and triggers overcurrent protection, so that the switch tubes in each phase conversion bridge arm are all turned off, so that the inductive current charges the protection capacitor to make the protection capacitor voltage rise, and the counter electromotive force is applied to the inductor to make the inductive current decrease, thereby achieving the purpose of inhibiting the fault current.

[0011] According to the embodiment of the present disclosure, when a short-circuit fault occurs, the switch tubes in each phase conversion bridge arm are all turned off, when the direction of the inductive current at the inductor is flowing into the conversion bridge arm, the inductive current charges the protection capacitor through one anti-parallel diode on one side of the midpoint of the conversion bridge arm and then flows to the DC port connected on the other side of the midpoint of the conversion bridge arm, thereby inhibiting the fault current.

[0012] According to the embodiment of the present disclosure, when a short-circuit fault occurs, the switch tubes in each phase conversion bridge arm are all turned off, when the direction of the inductive current at the inductor is flowing out of the conversion bridge arm, the inductive current charges the protection capacitor through one anti-parallel diode on one side of the midpoint of the conversion bridge arm and then flows to the anti-parallel diode on the other side of the midpoint of the conversion bridge arm, and then flows to the AC port connected with the phase conversion bridge arm through the inductor, thereby inhibiting the fault current.

[0013] According to the embodiment of the present disclosure, when the three-phase AC-DC converter is in normal operation, one switch tube in the first bridge arm and one switch tube in the second bridge arm in each phase conversion bridge arm are always on, and the other two switch tubes are driven to be on or off according to the set modulation ratio.

[0014] According to an embodiment of the disclosure, a fault current suppression method based on the three-phase AC-DC converter is provided, comprising: constructing an AC filter unit comprising three-phase filter circuits, each phase filter circuit comprising an inductor and a capacitor, and one end of each phase filter circuit being connected to a three-phase AC port on the AC side in a phase corresponding manner; constructing a three-phase bridge arm unit comprising three-phase bridge arms, the midpoints of each phase bridge arm being connected to the other end of each phase filter circuit, and each phase bridge arm comprising a first bridge arm and a second bridge arm located on both sides of the midpoint of the bridge arm, respectively; arranging a DC filter capacitor with two ends connected to the two ends of each phase bridge arm, respectively, and the two ends of the DC filter capacitor being connected to two DC ports on the DC side, respectively; and arranging a protection branch by connecting a protection capacitor and a diode in series between the first bridge arm and the second bridge arm, so that the protection branch suppresses the fault current when a short circuit fault occurs. BRIEF DESCRIPTION OF DRAWINGS

[0015] The above and other objects, features and advantages of the disclosure will become more apparent from the following description of embodiments of the disclosure taken in conjunction with the accompanying drawings, in which:

[0016] Figure 1 FIG. 1 is a circuit structure schematic diagram of a three-phase AC-DC converter according to an embodiment of the disclosure.

[0017] Figure 2 FIG. 2 is a current path schematic diagram when the inductor current flows into the bridge arm in the three-phase AC-DC converter according to an embodiment of the disclosure when a fault occurs.

[0018] Figure 3 FIG. 3 is a current path schematic diagram when the inductor current flows out of the bridge arm in the three-phase AC-DC converter according to an embodiment of the disclosure when a short circuit fault occurs.

[0019] Figure 4 FIG. 4 is a simulation waveform schematic diagram when the inductor current flows into the bridge arm in the three-phase AC-DC converter according to an embodiment of the disclosure when a short circuit fault occurs.

[0020] Figure 5 FIG. 5 is a simulation waveform schematic diagram when the inductor current flows out of the bridge arm in the three-phase AC-DC converter according to an embodiment of the disclosure when a short circuit fault occurs.

[0021] Figure 6 FIG. 6 is a flowchart of a fault current suppression method of a three-phase AC-DC converter according to an embodiment of the disclosure. DETAILED DESCRIPTION

[0022] This disclosure provides a three-phase AC-DC converter with fault interruption capability and a fault current suppression method, which can effectively block the propagation of fault current when a short circuit fault occurs on the DC side or AC side, thereby achieving fault interruption and improving reliability and safety.

[0023] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0024] In this embodiment of the disclosure, a three-phase AC-DC converter is provided, such as... Figure 1 As shown, the three-phase AC-DC converter includes an AC filter unit, a three-phase converter arm unit, and a DC filter capacitor. The AC filter unit includes a three-phase filter circuit, with each phase filter circuit including an inductor L and a capacitor C2. One end of each phase filter circuit is connected in phase to one of the three-phase AC ports on the AC side. The three-phase converter arm unit includes three phase converter arms: phase A, phase B, and phase C, connected in parallel. The midpoint of each phase converter arm is connected to the other end of each phase filter circuit and to the inductor L. The two ends of the DC filter capacitor C1 are connected to the two ends of each phase converter arm and to the two DC ports on the DC side. Each phase converter arm includes a first arm and a second arm located on either side of the midpoint of the converter arm, and a protection branch connecting the first and second arms. The protection branch includes a protection capacitor and a diode connected in series, used to suppress fault current when a short-circuit fault occurs on the DC or AC side.

[0025] According to an embodiment of this disclosure, the first bridge arm is located on one side of the midpoint of the switching bridge arm. The first bridge arm includes a switching transistor group with bidirectional conduction capability, consisting of two switching transistors connected in series with opposite polarities. Each switching transistor is provided with an anti-parallel diode. The connection form of the two switching transistors in the first bridge arm is either a common source series connection or a common drain series connection.

[0026] According to an embodiment of this disclosure, the second bridge arm is located on the other side of the midpoint of the switching bridge arm. The second bridge arm includes a switching transistor group with bidirectional conduction capability, consisting of two switching transistors connected in series with opposite polarities. Each switching transistor is provided with an anti-parallel diode. The connection form of the two switching transistors in the second bridge arm is either a common source series connection or a common drain series connection. The connection form of the two switching transistors in the first bridge arm is different from the connection form of the two switching transistors in the second bridge arm.

[0027] According to the embodiment of the present disclosure, the negative electrode of the protection capacitor and the positive electrode of the diode are connected, and when a short circuit fault occurs, the inductive current at the inductor can charge the protection capacitor. The negative electrode of the diode is connected between the two switch tubes of the first bridge arm, and the positive electrode of the protection capacitor is connected between the two switch tubes of the second bridge arm.

[0028] According to the embodiment of the present disclosure, in normal operation, one switch tube in each of the first bridge arm and the second bridge arm in each phase conversion bridge arm is turned on, and the other two switch tubes are driven complementarily according to the set modulation ratio.

[0029] According to the embodiment of the present disclosure, as Figure 1As shown, the first bridge arm of the A-phase conversion bridge arm includes a switch tube group with bidirectional conduction capability formed by two switch tubes Q1 and Q2 connected in series in reverse polarity, the switch tube Q1 is provided with an anti-parallel diode Q1D, the switch tube Q2 is provided with an anti-parallel diode Q2D, and the switch tubes Q1 and Q2 are connected in a common-source series connection mode. The second bridge arm of the A-phase conversion bridge arm includes a switch tube group with bidirectional conduction capability formed by two switch tubes Q3 and Q4 connected in series in reverse polarity, the switch tube Q3 is provided with an anti-parallel diode Q3D, the switch tube Q4 is provided with an anti-parallel diode Q4D, and the switch tubes Q3 and Q4 are connected in a common-drain series connection mode. The protection branch of the A-phase conversion bridge arm includes a protection capacitor C3 and a diode D1 connected in series, and the negative electrode of the protection capacitor C3 is connected to the positive electrode of the diode D1. The negative electrode of the diode D1 is connected between the two switch tubes Q1 and Q2 of the first bridge arm of the A-phase conversion bridge arm, and the positive electrode of the protection capacitor C3 is connected between the two switch tubes Q3 and Q4 of the second bridge arm. The first bridge arm of the B-phase conversion bridge arm includes a switch tube group with bidirectional conduction capability formed by two switch tubes Q5 and Q6 connected in series in reverse polarity, the switch tube Q5 is provided with an anti-parallel diode Q5D, the switch tube Q6 is provided with an anti-parallel diode Q6D, and the switch tubes Q5 and Q6 are connected in a common-source series connection mode. The second bridge arm of the B-phase conversion bridge arm includes a switch tube group with bidirectional conduction capability formed by two switch tubes Q7 and Q8 connected in series in reverse polarity, the switch tube Q7 is provided with an anti-parallel diode Q7D, the switch tube Q8 is provided with an anti-parallel diode Q8D, and the switch tubes Q7 and Q8 are connected in a common-drain series connection mode. The first bridge arm of the C-phase conversion bridge arm includes a switch tube group with bidirectional conduction capability formed by two switch tubes Q9 and Q10 connected in series in reverse polarity, the switch tube Q9 is provided with an anti-parallel diode Q9D, the switch tube Q10 is provided with an anti-parallel diode Q10D, and the switch tubes Q9 and Q10 are connected in a common-source series connection mode. The B-phase conversion bridge arm includes a protection capacitor C4 and a diode D2 connected in series, and the negative electrode of the protection capacitor C4 is connected to the positive electrode of the diode D2. The negative electrode of the diode D2 is connected between the two switch tubes Q5 and Q6 of the first bridge arm of the B-phase conversion bridge arm, and the positive electrode of the protection capacitor C4 is connected between the two switch tubes Q7 and Q8 of the second bridge arm. The second bridge arm of the C-phase conversion bridge arm includes a switch tube group with bidirectional conduction capability formed by two switch tubes Q11 and Q12 connected in series in reverse polarity, the switch tube Q11 is provided with an anti-parallel diode Q11D, the switch tube Q12 is provided with an anti-parallel diode Q12D, and the switch tubes Q11 and Q12 are connected in a common-drain series connection mode. The C-phase conversion bridge arm includes a protection capacitor C5 and a diode D3 connected in series, and the negative electrode of the protection capacitor C5 is connected to the positive electrode of the diode D3.The cathode of diode D3 is connected between the two switching transistors Q9 and Q10 in the first arm of the C-phase converter bridge arm, and the anode of protection capacitor C5 is connected between the two switching transistors Q11 and Q12 in the second arm. It should be noted that the connection configuration of the switching transistors in the above three-phase converter bridge arms can be adjusted according to the actual application. For example, the two switching transistors in the first arm can be connected in series with a common drain, and the two switching transistors in the second arm can be connected in series with a common source, as long as the connection configuration of the two switching transistors in the first arm of each phase converter bridge arm is different from that in the second arm.

[0030] According to the embodiments of this disclosure, when a short circuit fault occurs, the inductor current in the three-phase AC-DC converter rises rapidly and triggers overcurrent protection, causing the switching transistors in each phase conversion arm to disconnect. As a result, the inductor current charges the protection capacitor, causing the protection capacitor voltage to rise and forming a back electromotive force applied to the inductor, which causes the inductor current to decrease, thereby achieving the reduction and suppression of fault current.

[0031] According to embodiments of this disclosure, during normal operation of the three-phase AC-DC converter, one switch in each of the first and second arms of each phase conversion arm is turned on, while the other two switches are turned on or off complementaryly according to a set modulation ratio. For example, taking the A-phase conversion arm as an example, switches Q2 and Q4 remain constantly on, while switches Q1 and Q3 operate under the drive of a complementary PMW signal according to the modulation ratio m. In this case, the three-phase AC-DC converter topology is no different from that of a conventional two-level AC-DC converter circuit, and its operating principle is similar.

[0032] According to embodiments of this disclosure, when a short-circuit fault occurs, all switches in each phase converter arm are disconnected. Considering that the inductor current cannot change abruptly, there are two current directions depending on the direction of the inductor current: When the inductor current flows into the converter arm, it charges the protective capacitor through an anti-parallel diode on one side of the midpoint of the converter arm and then flows to the DC port connected to the other side of the midpoint, thereby suppressing the fault current. When the inductor current flows out of the converter arm, it charges the protective capacitor through an anti-parallel diode on one side of the midpoint of the converter arm and then flows to the anti-parallel diode on the other side of the midpoint, and then flows through the inductor to the AC port connected to each phase converter arm, thereby suppressing the fault current.

[0033] According to embodiments of this disclosure, a short-circuit fault occurs on the DC side, and the A-phase converter bridge arm is used as an example for illustration. Figure 2 and Figure 3 As shown, all switches Q1 to Q4 are off. Let the moment when Q1 to Q4 are off be t0. Considering that the inductor current cannot change abruptly, there are two current directions based on the direction of the inductor current, as follows:

[0034] (1) When the inductor current flows into the A-phase conversion bridge arm, the fault current path is as shown in Figure 2 Figure 2, and the fault current flows through the anti-parallel diode Q4D of the switch tube Q4 of the second bridge arm after the inductor L, flows into the protection branch, and then flows to a DC port through the anti-parallel diode Q1D of the switch tube Q1 of the first bridge arm. At this time, assuming that the DC side DC bus voltage is Vdc, and the midpoint of the three-phase AC port A, B, C and the midpoint of the DC bus are equipotential points, then: 0.5Vdc+VC3=-L·diL / dt+uA. Wherein, VC3 is the voltage across the protection capacitor C3, L·diL / dt is the instantaneous voltage across the inductor L connected to the A-phase conversion bridge arm, t represents time, the inductor current is iL, and uA is the phase voltage of the A-phase AC port. It can be seen from the above formula that when the DC side is short-circuited, although the DC bus voltage Vdc is close to 0, the existence of the voltage VC3 across the protection capacitor C3 prevents the increase of the inductor current iL, and in normal operation, the voltage VC3 across the protection capacitor C3 is greater than the maximum phase voltage uAmax, so under the action of the voltage VC3 across the protection capacitor C3, the inductor current iL will continue to decrease rapidly to 0, and the decrease speed is related to the result of |0.5Vdc+VC3-uA(t0)|, uA(t0) is the phase voltage of the A-phase AC port at t0. It can be seen from the current path that this is a process of charging the protection capacitor C3 by the inductor, and at the same time the inductor current iL decreases, the voltage VC3 across the protection capacitor C3 will further increase, which in turn will accelerate the inductor current iL to decrease at a faster rate, forming a positive feedback of fault current suppression.

[0035] (2) When the inductor current flows out of the A-phase conversion bridge arm, the current path is as shown in Figure 3As shown, the fault current flows through the anti-parallel diode Q3D of the switch tube Q3 of the second bridge arm, flows into the protection branch, and then flows through the anti-parallel diode Q2D of the switch tube Q2 of the first bridge arm, and then flows to the A-phase alternating current port through the inductor L. At this time, assuming that the DC bus voltage is Vdc, and the midpoint of the three-phase alternating current port A, B and C and the midpoint of the DC bus are equipotential points, then -0.5Vdc+VC3+L·diL / dt+uA=0. Wherein, VC3 is the voltage across the protection capacitor C3, L·diL / dt is the instantaneous voltage across the inductor L connected to the A-phase conversion bridge arm, and uA is the phase voltage of the A-phase alternating current port. Similar to the analysis process when the inductor current flows into the bridge arm, it can be seen from the above formula that, when the DC side is short-circuited, although the DC bus voltage Vdc is close to 0, the existence of the voltage VC3 across the protection capacitor C3 prevents the increase of the inductor current, and in normal operation, the voltage VC3 across the protection capacitor C3 is greater than the maximum phase voltage uAmax, so under the action of the voltage VC3 across the protection capacitor C3, the inductor current iL will continue to decrease rapidly to 0, and the decreasing speed is related to |0.5Vdc-VC3-uA(t0)|, and uA(t0) is the phase voltage of the A-phase alternating current port at t0. It can be seen from the current path that, similar to the inductor current flowing into the bridge arm, it is also a process of charging the capacitor C3 by the inductor, and at the same time the inductor current decreases, the voltage VC3 across the capacitor C3 will further increase, which in turn will accelerate the inductor current to decrease at a faster rate, thus forming a positive feedback of fault current suppression.

[0036] It should be noted that the three-phase alternating current-direct current converter of the present disclosure can suppress the fault current when the DC side is short-circuited, can suppress the fault current when the AC side is short-circuited, or can suppress the fault current when other abnormal conditions cause the switch tubes in the conversion bridge arm of a certain phase to be completely disconnected.

[0037] In another aspect of the present disclosure, a fault current suppression method based on the above three-phase alternating current-direct current converter is provided, which combines Figure 6 and Figure 1 As shown, the fault current suppression method comprises the following steps.

[0038] Operation S1: constructing an alternating current filter unit comprising three-phase filter circuits, each phase filter circuit comprising an inductor and a capacitor, and one end of each phase filter circuit being connected to a three-phase alternating current port on the AC side in a phase corresponding manner;

[0039] Operation S2: constructing a three-phase conversion bridge arm unit comprising three-phase conversion bridge arms, the midpoints of each phase conversion bridge arm being connected to the other end of each phase filter circuit, and each phase conversion bridge arm comprising a first bridge arm and a second bridge arm located on both sides of the midpoint of the conversion bridge arm, respectively;

[0040] Operation S3: Set the two ends of the DC filter capacitor connected to the two ends of each phase conversion bridge arm, and the two ends of the DC filter capacitor connected to the two DC ports of the DC side.

[0041] Operation S4: Obtain the protection branch by setting the protection capacitor and diode in series between the first bridge arm and the second bridge arm, so that the protection branch inhibits the fault current when a short circuit fault occurs.

[0042] The above fault current suppression method can suppress the fault current when a short circuit fault occurs at the DC side or the AC side of the three-phase AC-DC converter, and achieve fault blocking.

[0043] The three-phase AC-DC converter and the fault current suppression method of the present disclosure are simulated and analyzed:

[0044] Take the simulation results when the inductor current flows into the A-phase conversion bridge arm as an example for illustration, as shown in Figure 4 In the initial normal condition, the switch tube Q2 and the switch tube Q4 are normally on, and the switch tube Q1 and the switch tube Q3 are alternately and complementarily on or off. At t=0.5150s, a short circuit fault occurs, at which time the instantaneous value of the inductor current iL is about 110A. After the short circuit occurs, the current iC3 at the protection branch rises rapidly, and the inductor current iL rises rapidly. At t=0.51505s, the overcurrent protection is triggered (the simulation sets the overcurrent protection value to 250A), and the switch tubes Q1-Q4 are all turned off. At this time, the inductor current iL charges the protection capacitor C3, the voltage VC3 of the protection capacitor C3 rises rapidly, and a larger back electromotive force VL is formed on the inductor, so that the inductor current iL decreases rapidly and decreases to zero at t≈0.51508s, effectively blocking the propagation of the fault current and achieving suppression and blocking of the fault current.

[0045] Take the simulation results when the inductor current flows out of the A-phase conversion bridge arm as an example for illustration, as shown in Figure 5 In the initial normal condition, the switch tube Q2 and the switch tube Q4 are normally on, and the switch tube Q1 and the switch tube Q3 are alternately and complementarily on or off. At t=0.5050s, a short circuit fault occurs, at which time the instantaneous value of the inductor current iL is about -110A. After the short circuit occurs, the current iC3 at the protection branch rises rapidly, and the inductor current iL rises rapidly. At t=0.50505s, the overcurrent protection is triggered (the simulation sets the overcurrent protection value to 250A), and the switch tubes Q1-Q4 are all turned off. At this time, the inductor current iL charges the protection capacitor C3, the voltage VC3 of the protection capacitor C3 rises rapidly, and a larger back electromotive force VL is formed on the inductor, so that the inductor current iL decreases rapidly and decreases to zero at t≈0.50508s, effectively blocking the propagation of the fault current and achieving suppression and blocking of the fault current.

[0046] So far, the embodiments of the present disclosure have been described in detail in conjunction with the drawings. It should be noted that the implementation manners not shown or described in the drawings or the text of the specification are known to those skilled in the art, and are not described in detail. In addition, the definitions of the elements and methods described above are not limited to the various specific structures, shapes or manners mentioned in the embodiments, and can be simply changed or replaced by those skilled in the art.

[0047] In addition, in this document, except for the specifically indicated, the ordinal numbers such as "first", "second", etc. are only used to distinguish multiple elements with the same name, and do not mean that there is a position, level, execution order, or process order between them. A "first" element and a "second" element can appear together in the same component, or separately in different components. The presence of an element with a larger ordinal number does not necessarily mean the presence of another element with a smaller ordinal number.

[0048] In addition, unless specifically described or steps must occur in sequence, the order of the above steps is not limited to the above list, and can be changed or rearranged according to the desired design. And the above embodiments can be mixed and used with each other or with other embodiments based on design and reliability considerations, that is, the technical features in different embodiments can be freely combined to form more embodiments.

[0049] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present disclosure. It should be understood that the above description is only a specific embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

1. A three-phase AC-DC converter, characterized by, The application relates to an alternating current filter unit, a three-phase conversion bridge arm unit and a direct current filter capacitor. The alternating current filter unit comprises three-phase filter circuits, one end of each phase of the filter circuits is connected to a three-phase alternating current port on an alternating current side in a phase corresponding manner, and the three-phase conversion bridge arm unit comprises three-phase conversion bridge arms, the midpoints of each phase of the conversion bridge arms are connected to the other end of each phase of the filter circuits. The direct current filter capacitor is connected to the two ends of each phase of the conversion bridge arms and the two direct current ports on a direct current side. Each phase of the conversion bridge arms comprises a first bridge arm and a second bridge arm located on the two sides of the midpoint of the conversion bridge arm and a protection branch connected between the first bridge arm and the second bridge arm, the protection branch comprises a protection capacitor and a diode arranged in series, and the protection branch is used for inhibiting a fault current when a short circuit fault occurs. The first bridge arm is located on one side of the midpoint of the conversion bridge arm, the first bridge arm comprises a switch tube group with bidirectional conduction capacity which is composed of two switch tubes in reverse polarity series connection, each switch tube is provided with an anti-parallel diode, and the two switch tubes in the first bridge arm are connected in a common source series connection mode or a common drain series connection mode.

2. The three-phase AC-DC converter of claim 1, wherein, The second bridge arm is located on the other side of the midpoint of the conversion bridge arm, the second bridge arm comprises a switch tube group with bidirectional conduction capacity which is composed of two switch tubes in reverse polarity series connection, each switch tube is provided with an anti-parallel diode, and the two switch tubes in the second bridge arm are connected in a common source series connection mode or a common drain series connection mode.

3. The three-phase AC-DC converter of claim 2, wherein, The connection mode of the two switch tubes in the first bridge arm is different from that of the two switch tubes in the second bridge arm. The negative electrode of the protection capacitor is connected to the positive electrode of the diode, and when a short circuit fault occurs, an inductance current at the inductor can charge the protection capacitor.

4. The three-phase AC-DC converter of claim 3, wherein, The negative electrode of the diode is connected between the two switch tubes of the first bridge arm, and the positive electrode of the protection capacitor is connected between the two switch tubes of the second bridge arm.

5. The three-phase AC-DC converter of claim 4, wherein, When a short circuit fault occurs, the inductance current rapidly rises and triggers overcurrent protection, so that the switch tubes in each phase of the conversion bridge arm are all disconnected, the protection capacitor is charged by the inductance current, the protection capacitor voltage is raised, a counter electromotive force is formed on the inductor, the inductance current is reduced, and the fault current is inhibited.

6. The three-phase AC-DC converter of claim 3, wherein, When a short circuit fault occurs, the switch tubes in each phase of the conversion bridge arm are all disconnected, when the inductance current at the inductor flows into the conversion bridge arm, the inductance current charges the protection capacitor through one anti-parallel diode on one side of the midpoint of the conversion bridge arm and then flows to the direct current port connected to the other side of the midpoint of the conversion bridge arm, so that the fault current is inhibited.

7. The three-phase AC-DC converter of claim 3, wherein, When a short circuit fault occurs, the switch tubes in each phase of the conversion bridge arm are all disconnected, when the inductance current at the inductor flows out of the conversion bridge arm, the inductance current charges the protection capacitor through one anti-parallel diode on one side of the midpoint of the conversion bridge arm and then flows to the anti-parallel diode on the other side of the midpoint of the conversion bridge arm and then flows to the alternating current port connected to each phase of the conversion bridge arm through the inductor, so that the fault current is inhibited.

8. The three-phase AC-DC converter of claim 3, wherein, ​ 9. The three-phase AC-DC converter of claim 3, wherein, In normal operation, one of the first bridge arm and the second bridge arm in each phase conversion bridge arm is always on, and the other two switching tubes are driven on or off according to the set modulation ratio.

10. A method of fault current suppression for a three-phase AC-DC converter according to any one of claims 1-9, characterized in that, The method comprises the steps of: constructing an alternating current filtering unit comprising three-phase filtering circuits, each phase of the filtering circuit comprising an inductor and a capacitor, and one end of each phase of the filtering circuit being connected to three-phase alternating current ports on the alternating current side in a phase corresponding manner; constructing a three-phase conversion bridge arm unit comprising three-phase conversion bridge arms, the midpoints of each phase of the conversion bridge arm being connected to the other end of each phase of the filtering circuit, and each phase of the conversion bridge arm comprising a first bridge arm and a second bridge arm located on both sides of the midpoint of the conversion bridge arm; connecting a direct current filtering capacitor with two ends to the two ends of each phase of the conversion bridge arm, and connecting the two ends of the direct current filtering capacitor to two direct current ports on the direct current side; and by connecting a protection capacitor and a diode in series between the first bridge arm and the second bridge arm to obtain a protection branch, so that the protection branch can inhibit the fault current when a short circuit fault occurs.

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