Three-phase ac-dc converter and fault current suppression method

Abstract

The disclosure provides a three-phase AC-DC converter and a fault current suppression method. The three-phase AC-DC converter comprises an AC filter unit, a three-phase conversion bridge arm unit, and a DC filter capacitor. The AC filter unit comprises three-phase filter circuits, 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 comprises three-phase conversion bridge arms, 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 connected to the two ends of each phase conversion bridge arm, and the two ends of the DC filter capacitor are connected to two DC ports on the DC side. Each phase conversion bridge arm comprises 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 comprises a protection capacitor and a diode connected in series, and is used for suppressing the 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 an embodiment of this disclosure, the negative terminal of the protection capacitor is connected to the positive terminal of the diode. When a short-circuit fault occurs, the inductor current at the inductor can charge the protection capacitor. The negative terminal of the diode is connected between the two switching transistors of the first bridge arm, and the positive terminal of the protection capacitor is connected between the two switching transistors of the second bridge arm.

[0028] According to an embodiment of this disclosure, during normal operation, one switch in each of the first and second bridge arms of each phase-conversion bridge arm is turned on, and the other two switches are driven complementaryly according to a set modulation ratio.

[0029] According to embodiments of this disclosure, such as Figure 1As shown, the first arm of the A-phase conversion bridge consists of two series-connected switches Q1 and Q2 with opposite polarities, forming a bidirectional switching group. Switch Q1 has an anti-parallel diode Q1D, and switch Q2 has an anti-parallel diode Q2D. Switches Q1 and Q2 are connected in a common-source series configuration. The second arm of the A-phase conversion bridge consists of two series-connected switches Q3 and Q4 with opposite polarities, forming a bidirectional switching group. Switch Q3 has an anti-parallel diode Q3D, and switch Q4 has an anti-parallel diode Q4D. Switches Q3 and Q4 are connected in a common-drain series configuration. The protection branch of the A-phase conversion bridge includes a protection capacitor C3 and a diode D1 connected in series, with the negative terminal of protection capacitor C3 connected to the positive terminal of diode D1. The cathode of diode D1 is connected between the two switches Q1 and Q2 in the first arm of the A-phase converter bridge, and the anode of protection capacitor C3 is connected between the two switches Q3 and Q4 in the second arm. The first arm of the B-phase converter bridge consists of a bidirectional switching group composed of two switches Q5 and Q6 connected in series with opposite polarities. Switch Q5 has an anti-parallel diode Q5D, and switch Q6 has an anti-parallel diode Q6D. Switches Q5 and Q6 are connected in a common-source series configuration. The second arm of the B-phase converter bridge consists of a bidirectional switching group composed of two switches Q7 and Q8 connected in series with opposite polarities. Switch Q7 has an anti-parallel diode Q7D, and switch Q8 has an anti-parallel diode Q8D. Switches Q7 and Q8 are connected in a common-drain series configuration. The first arm of the C-phase converter bridge consists of a bidirectional switching transistor group composed of two anti-polarity series-connected transistors Q9 and Q10. Transistor Q9 has an anti-parallel diode Q9D, and transistor Q10 has an anti-parallel diode Q10D. Transistors Q9 and Q10 are connected in a common-source series configuration. The B-phase converter bridge includes a protection capacitor C4 and a diode D2 connected in series. The cathode of protection capacitor C4 is connected to the anode of diode D2. The cathode of diode D2 is connected between the two transistors Q5 and Q6 in the first arm of the B-phase converter bridge, and the anode of protection capacitor C4 is connected between the two transistors Q7 and Q8 in the second arm. The second arm of the C-phase converter bridge arm includes a bidirectional switching transistor group consisting of two series-connected switching transistors Q11 and Q12 with opposite polarity. Switch Q11 is equipped with an anti-parallel diode Q11D, and switch Q12 is equipped with an anti-parallel diode Q12D. Switches Q11 and Q12 are connected in a common-drain series configuration. The C-phase converter bridge arm includes a protection capacitor C5 and a diode D3 connected in series. The negative terminal of the protection capacitor C5 is connected to the positive terminal 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 converter arm, the fault current path is as follows: Figure 2 As shown, the fault current flows through inductor L, then through the anti-parallel diode Q4D of the switching transistor Q4 in the second bridge arm, into the protection branch, and then through the anti-parallel diode Q1D of the switching transistor Q1 in the first bridge arm to the DC port. At this time, assuming the DC bus voltage on the DC side is Vdc, and the midpoints of the three-phase AC ports A, B, and C on the AC side are at the same potential as the midpoint of the DC bus, then we have: 0.5Vdc + VC3 = -L·diL / dt + uA. Where VC3 is the voltage across the protection capacitor C3, L·diL / dt is the instantaneous voltage across inductor L connected to the A-phase switching bridge arm, t represents time, the inductor current is iL, and uA is the phase voltage of the A-phase AC port. As can be seen from the above formula, during a DC-side short circuit, although the DC bus voltage Vdc is close to 0, the presence of the voltage VC3 across the protective capacitor C3 prevents the inductor current iL from increasing. Furthermore, during normal operation, the voltage VC3 across the protective capacitor C3 is greater than the maximum phase voltage uAmax. Therefore, under the influence of the voltage VC3 across the protective capacitor C3, the inductor current iL will continuously and rapidly decrease to 0. The rate of decrease is related to the result of |0.5Vdc+VC3-uA(t0)|, where uA(t0) is the phase voltage of the A-phase AC port at time t0. Combining this with the current path, it can be seen that this is a process of the inductor charging the protective capacitor C3. While the inductor current iL decreases, the voltage VC3 across the protective capacitor C3 further increases, which in turn accelerates the decrease of the inductor current iL at a faster rate. This forms a positive feedback loop for fault current suppression.

[0035] (2) When the inductor current flows out of the A-phase converter arm, the current path is as follows: Figure 3As shown, the fault current flows through the DC port, through the anti-parallel diode Q3D of the second bridge arm switch Q3, into the protection branch, and then through the anti-parallel diode Q2D of the first bridge arm switch Q2, through the inductor L, and finally to the A-phase AC port. At this time, assuming the DC bus voltage is Vdc, and the midpoints of the three-phase AC ports A, B, and C on the AC side are at the same potential as the midpoint of the DC bus, then we have: -0.5Vdc + VC3 + L·diL / dt + uA = 0. Where 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 switching bridge arm, and uA is the phase voltage of the A-phase AC port. Similar to the analysis process when inductor current flows into the bridge arm, it can be seen from the above equation that during a DC-side short circuit, although the DC bus voltage Vdc is close to 0, the presence of the voltage VC3 across the protection capacitor C3 prevents the inductor current from increasing. Furthermore, during normal operation, the voltage VC3 across the protection capacitor C3 is greater than the maximum phase voltage uAmax. Therefore, under the influence of the voltage VC3 across the protection capacitor C3, the inductor current iL will continuously and rapidly decrease to 0. Its rate of decrease is related to |0.5Vdc-VC3-uA(t0)|, where uA(t0) is the phase voltage of the A-phase AC port at time t0. Combining the current path, it can be seen that, similar to the inductor current flowing into the bridge arm, this is also a process of the inductor charging the capacitor C3. While the inductor current decreases, the voltage VC3 across capacitor C3 will further increase, which in turn will accelerate the inductor current's decrease at a faster rate, thus forming a positive feedback loop for fault current suppression.

[0036] It should be noted that the three-phase AC-DC converter disclosed herein can suppress fault current in the event of a short circuit on the DC side, or in the event of a short circuit on the AC side, or in other abnormal situations that cause all the switching transistors in a certain phase converter arm to be disconnected.

[0037] Another aspect of this disclosure provides a fault current suppression method based on the above-described three-phase AC-DC converter, combined with... Figure 6 and Figure 1 As shown, the fault current suppression method includes:

[0038] Operation S1: Construct an AC filter unit including a three-phase filter circuit, each phase filter circuit including an inductor and a capacitor, and one end of each phase filter circuit is connected to the three-phase AC port on the AC side in a phase-corresponding manner.

[0039] Operation S2: Construct a three-phase conversion bridge arm unit including three-phase conversion bridge arms. The midpoint of each phase conversion bridge arm is connected to the other end of each phase filter circuit. 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.

[0040] Operation S3: Set up DC filter capacitors with their two ends connected to the two ends of each phase converter bridge arm, and connect the two ends of the DC filter capacitors to the two DC ports on the DC side.

[0041] Operation S4: A protection branch is obtained 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 can suppress the fault current when a short circuit fault occurs.

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

[0043] Simulation analysis was performed on the three-phase AC-DC converter and fault current suppression method disclosed in this paper:

[0044] The following is an example of the simulation results when the inductor current flows into the A-phase converter arm, such as... Figure 4 As shown, under normal conditions, switches Q2 and Q4 are normally on, while switches Q1 and Q3 alternately conduct or turn off. At t=0.5150s, a short circuit occurs. At this time, the instantaneous value of the inductor current iL is approximately 110A. After the short circuit, the current iC3 at the protection branch rises rapidly, and the inductor current iL also rises rapidly. At t=0.51505s, the overcurrent protection is triggered (the simulation sets the overcurrent protection value to 250A), and switches Q1~Q4 are all turned off. At this time, the inductor current iL charges the protection capacitor C3, causing the voltage VC3 of the protection capacitor C3 to rise rapidly and generate a large back electromotive force VL across the inductor. This causes the inductor current iL to drop rapidly, reaching zero at t≈0.51508s, effectively blocking the propagation of the fault current and achieving fault current suppression and fault isolation.

[0045] The following is an example of the simulation results when the inductor current flows out of the A-phase converter arm, such as... Figure 5 As shown, under normal conditions, switches Q2 and Q4 are normally on, while switches Q1 and Q3 alternately conduct or turn off. At t=0.5050s, a short circuit occurs. At this time, the instantaneous value of the inductor current iL is approximately -110A. After the short circuit, the current iC3 at the protection branch rises rapidly, and the inductor current iL also rises rapidly. At t=0.50505s, the overcurrent protection is triggered (the simulation sets the overcurrent protection value to 250A), and switches Q1~Q4 are all turned off. At this time, the inductor current iL charges the protection capacitor C3, causing the voltage VC3 of the protection capacitor C3 to rise rapidly and generate a large back electromotive force VL across the inductor. This causes the inductor current iL to drop rapidly, reaching zero at t≈0.50508s, effectively blocking the propagation of the fault current and achieving fault current suppression and fault isolation.

[0046] The embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. It should be noted that implementations not illustrated or described in the drawings or the main text of the specification are forms known to those skilled in the art and are not described in detail. Furthermore, the definitions of the various elements and methods described above are not limited to the specific structures, shapes, or methods mentioned in the embodiments, and those skilled in the art can easily modify or substitute them.

[0047] Furthermore, unless otherwise specified, the ordinal numbers such as "first," "second," etc., used herein are merely for distinguishing multiple elements with the same name and do not indicate any hierarchy, order of execution, or process sequence among them. A "first" element and a "second" element may appear together in the same component or separately in different components. The presence of an element with a higher ordinal number does not necessarily indicate the presence of another element with a lower ordinal number.

[0048] Furthermore, unless specifically described or required to occur in a specific order, the order of the above steps is not limited to those listed above and can be varied or rearranged according to the desired design. Moreover, the above embodiments can be used in combination with each other or with other embodiments based on design and reliability considerations; that is, technical features from 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 this disclosure. It should be understood that the above descriptions are merely specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A three-phase AC-DC converter, characterized in that, include: An AC filtering unit includes a three-phase filtering circuit, each phase of which includes an inductor and a capacitor, and one end of each phase of which is connected to a three-phase AC port on the AC side in a phase-corresponding manner. A three-phase converter bridge arm unit includes three-phase converter bridge arms, with the midpoint of each phase's converter bridge arm connected to the other end of each phase's filter circuit; and A DC filter capacitor is connected at both ends to the two ends of each phase of the converter bridge arm, and the two ends of the DC filter capacitor are connected to the two DC ports on the DC side. Each phase of the 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 arranged in series. The protection branch is used to suppress the 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 includes a switch group with bidirectional conduction capability, consisting of two switches connected in series with opposite polarities. Each switch is equipped with an anti-parallel diode. The two switches in the first bridge arm are connected in a common-source series configuration or a common-drain series configuration. The second bridge arm is located on the other side of the midpoint of the conversion bridge arm. The second bridge arm includes a switch group with bidirectional conduction capability, consisting of two switches connected in series with opposite polarities. Each switch is equipped with an anti-parallel diode. The two switches in the second bridge arm are connected in a common-source series configuration or a common-drain series configuration. The connection configuration of the two switches in the first bridge arm is different from that in the second bridge arm. The negative terminal of the protective capacitor is connected to the positive terminal of the diode. The negative terminal of the diode is connected between the two switching transistors of the first bridge arm, and the positive terminal of the protective capacitor is connected between the two switching transistors of the second bridge arm. When a short circuit fault occurs, the inductor current at the inductor can charge the protective capacitor.

2. The three-phase AC-DC converter according to claim 1, characterized in that, When a short-circuit fault occurs, the inductor current rises rapidly and triggers the overcurrent protection, causing the switching transistors in each phase conversion bridge arm to disconnect. As a result, the inductor current charges the protection capacitor, increasing the voltage of the protection capacitor and generating a back electromotive force applied to the inductor, causing the inductor current to decrease, thus achieving the goal of reducing and suppressing the fault current.

3. The three-phase AC-DC converter according to claim 1, characterized in that, When a short-circuit fault occurs, all the switching transistors in each phase conversion bridge arm are disconnected. When the inductor current at the inductor is flowing into the conversion bridge arm, the inductor current charges the protection capacitor through an anti-parallel diode on one side of the midpoint of the conversion bridge arm and then flows to the DC port connected to the other side of the midpoint of the conversion bridge arm, thereby suppressing the fault current.

4. The three-phase AC-DC converter according to claim 1, characterized in that, When a short-circuit fault occurs, all the switching transistors in each phase converter arm are disconnected. When the inductor current flows out of the converter arm, the inductor current charges the protection capacitor through an anti-parallel diode on one side of the midpoint of the converter arm and then flows to an anti-parallel diode on the other side of the midpoint of the converter arm. It then flows through the inductor to the AC port connected to each phase converter arm, thereby suppressing the fault current.

5. The three-phase AC-DC converter according to claim 1, characterized in that, During normal operation, one switch in each of the first and second bridge arms of each phase conversion bridge arm is always on, while the other two switches are turned on or off according to the set modulation ratio.

6. A fault current suppression method for a three-phase AC-DC converter according to any one of claims 1-5, characterized in that, include: An AC filtering unit is constructed, comprising a three-phase filtering circuit, wherein each phase of the filtering circuit includes an inductor and a capacitor, and one end of each phase of the filtering circuit is connected to the three-phase AC port on the AC side in a phase-corresponding manner. A three-phase conversion bridge arm unit is constructed, comprising three-phase conversion bridge arms. The midpoint of each phase conversion bridge arm is connected to the other end of the filter circuit of each phase. 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. A DC filter capacitor is provided, with its two ends connected to the two ends of each phase of the converter bridge arm, and the two ends of the DC filter capacitor are respectively connected to two DC ports on the DC side; and A protection branch is formed by connecting a protection capacitor and a diode in series between the first bridge arm and the second bridge arm, which suppresses the fault current when a short circuit fault occurs.

Images