Novel AC / DC converter and DC side short circuit fault ride-through method

Abstract

The invention provides a novel AC / DC converter and a direct current side short circuit fault ride-through method, specifically, the novel AC / DC converter comprises a switch valve and an auxiliary shunt branch which are connected in parallel, the switch valve comprises three switch valve units which are connected in series, and the three switch valve units are connected in parallel. The switch valve unit comprises a switch capacitor valve string and two novel switch valve strings which are connected in parallel, and each switch capacitor valve string comprises a plurality of switch capacitor modules which are connected in series; the novel switch valve string comprises an upper bridge arm and a lower bridge arm, each of the upper bridge arm and the lower bridge arm comprises a single-bridge-arm type first power module and a double-bridge-arm type second power module which are connected in series, and the upper bridge arm and the lower bridge arm are symmetrically connected in series through a connecting midpoint; the auxiliary shunt branch comprises a series branch and two switch branches. According to the invention, the system cost is greatly reduced, and reactive power support and rapid fault recovery can be realized.

Description

Technical Field

[0001] The invention belongs to the technical field of power systems, and in particular relates to a novel AC / DC converter and a DC side short-circuit fault ride-through method. Background Art

[0002] Flexible DC transmission is an effective means of large-scale grid connection of renewable energy. The most common flexible DC transmission converter topology is modular multilevel converter (MMC). MMC technology is highly mature and has good power quality, and has been applied in several engineering projects. However, MMC is based on a half-bridge double star-connected circuit, which results in a large number of modules, resulting in a huge size and high cost, which is one of the important factors hindering the development of AC and DC power grids.

[0003] In case of instantaneous bipolar short-circuit fault on the DC side, MMC adopts a semi-full hybrid solution to achieve fault isolation on the AC side and rapid attenuation of fault current on the DC side, achieving rapid fault recovery, providing reactive power support for the AC system, and achieving fault ride-through. However, the semi-full hybrid solution requires the addition of a large number of full-bridge modules, which significantly increases the cost, volume, and loss.

[0004] Therefore, it is necessary to design a new AC / DC converter and a DC side short-circuit fault ride-through method to solve the above technical problems. Summary of the invention

[0005] In view of the above technical problems, the present invention provides a novel AC / DC converter, wherein the converter comprises a switch valve and an auxiliary shunt branch connected in parallel, wherein:

[0006] The switch valve comprises three switch valve units connected in series, the switch valve units comprise a switch capacitor valve string connected in parallel and two new switch valve strings, the switch capacitor valve string comprises a plurality of switch capacitor modules connected in series; the new switch valve string comprises an upper bridge arm and a lower bridge arm, the upper bridge arm and the lower bridge arm both comprise a first power module of a single bridge arm type connected in series and a second power module of a double bridge arm type, the upper bridge arm and the lower bridge arm are connected in series symmetrically by connecting the midpoint;

[0007] The auxiliary shunt branch includes a series branch and two switch branches, wherein the series branch is connected in parallel with the switch valve through the two switch branches; the series branch includes a capacitor C1 and a diode valve string connected in series, and a resistor R1 connected in parallel with the capacitor C1.

[0008] Furthermore, the converter further comprises two reactors, wherein one end of the two reactors are respectively connected to two ends of the series branch, and the other ends of the two reactors form a DC port of the converter.

[0009] Furthermore, the converter also includes at least three transformers connected one-to-one with at least three series valve strings, one end of each transformer is respectively connected to two connection midpoints of the corresponding series valve string, and the other ends of the three transformers are connected to form an AC port of the converter.

[0010] Further, the switch capacitor module is any one or more combinations of a half-bridge module, a full-bridge module and a hybrid module, wherein:

[0011] The hybrid module includes a first number of half-bridge modules connected in series and a second number of full-bridge modules connected in series. The first number of half-bridge modules connected in series and the second number of full-bridge modules connected in series are connected in series.

[0012] Furthermore, the first power module includes a first bridge arm, a voltage-equalizing capacitor C2 and an energy-consuming element H1 connected in parallel, wherein:

[0013] The first bridge arm includes a power switch device T1 and a diode D1, wherein the anode of the diode D1 is connected to the anode or collector of the power switch device T1;

[0014] One end of the voltage-equalizing capacitor C2 is connected to the cathode of the diode D1 , and the other end of the voltage-equalizing capacitor C2 is connected to the cathode or emitter of the power switch device T1 . The power switch device T1 is anti-parallel-connected with a diode D2 .

[0015] Furthermore, the second power module includes a voltage-sharing capacitor C3, an energy-consuming element H2 and two second bridge arms connected in parallel, wherein:

[0016] The second bridge arm includes a power switch device T2 and a diode D3, wherein the anode of the diode D3 is connected to the anode or collector of the power switch device T2, and a diode D4 is connected in anti-parallel to the power switch device T2;

[0017] One end of the voltage-equalizing capacitor C3 is connected to the cathode of the diode D3 of one of the second bridge arms, and the other end of the voltage-equalizing capacitor C3 is connected to the cathode or emitter of the power switch device T2 of one of the second bridge arms.

[0018] Furthermore, the diode valve string includes a plurality of diodes D connected in series. SN , where each diode D SN A voltage equalizing circuit is connected in parallel.

[0019] Furthermore, the voltage balancing circuit is one or more of a C voltage balancing circuit, an RC voltage balancing circuit and an RCD voltage balancing circuit.

[0020] Furthermore, the C voltage equalizing circuit includes a capacitor C4, wherein the capacitor C4 and the diode DSN in parallel.

[0021] Furthermore, the RC voltage equalizing circuit includes a capacitor C4 and a resistor R2, wherein the capacitor C4 and the diode D SN In parallel, resistor R2 and capacitor C4 are connected in parallel.

[0022] Furthermore, the RCD voltage balancing circuit includes a capacitor C4, a resistor R2 and a diode D5, wherein the resistor R2 is connected in series with the capacitor C4 and the diode D5. SN In parallel, the diode D5 is connected in parallel with the resistor R2.

[0023] Further, the switch branch includes switch K1 and / or switch K2. When switch K1 and switch K2 are included, K1 and K2 are connected in series.

[0024] On the one hand, the present invention also provides a novel method for riding through a DC side short-circuit fault of an AC / DC converter, wherein the converter adopts the above-mentioned converter, and the method is implemented based on a first operating condition, wherein the first operating condition is:

[0025] When the AC port is not connected to an AC power source, the second power module is bypassed;

[0026] The method comprises:

[0027] Step S1: a bipolar short circuit fault is detected at the DC port;

[0028] Step S2: the switch capacitor valve string of each phase outputs 0 voltage;

[0029] Step S3: disconnect K2;

[0030] Step S4: disconnect K1;

[0031] Step S5: Waiting for the DC side fault current of the converter to decay to 0;

[0032] Step S6: Waiting for the fault point to be freed;

[0033] Step S7: close K1;

[0034] Step S8: Close K2.

[0035] Further, the switch capacitor valve string outputs 0 voltage, including:

[0036] The fully controlled power switch devices of the upper bridge arms of all switch capacitor modules are turned off, and the fully controlled power switch devices of the lower bridge arms are turned on.

[0037] On the other hand, the present invention further provides a novel method for riding through a DC side short-circuit fault of an AC / DC converter, wherein the converter adopts the above-mentioned converter, and the method is implemented based on a second operating condition, wherein the second operating condition is:

[0038] When the AC port is connected to an AC power source, the sum of the DC voltages of the second power modules in any upper bridge arm of the novel switch valve is greater than the peak voltage of the AC power source connected to the AC port:

[0039] The method comprises:

[0040] Step S1: a bipolar short circuit fault is detected at the DC port;

[0041] Step S2: The switch capacitor valve string of each phase outputs a voltage, and the switch capacitor valve string output voltage of each phase satisfies the condition that the switch capacitor valve string output voltage of each phase is greater than the instantaneous value of the AC port voltage of the corresponding phase;

[0042] Step S3: When the current at any phase AC port decays to 0, the new switch valve string of the phase is turned off;

[0043] Step S4: After all the new switch valve strings of all phases are turned off, the switch capacitor valve string outputs 0 voltage;

[0044] Step S5: disconnect K2;

[0045] Step S6: disconnect K1;

[0046] Step S7: Wait for the DC side fault current to decay to 0;

[0047] Step S8: Waiting for the fault point to be freed;

[0048] Step S9: close K1;

[0049] Step S10: Close K2.

[0050] Further, the switch capacitor valve string outputs 0 voltage, including:

[0051] The fully controlled power switch devices of the upper bridge arms of all switch capacitor modules are turned off, and the fully controlled power switch devices of the lower bridge arms are turned on.

[0052] Furthermore, the novel switch valve string for shutting off the phase includes:

[0053] The fully controlled power switch devices of the first power module and the second power module power switch devices in the novel switch valve string are all turned off.

[0054] The present invention provides a novel AC / DC converter and a DC side short-circuit fault ride-through method, which greatly reduces the system cost compared with the semi-full hybrid solution of MMC and can achieve reactive power support and rapid fault recovery.

[0055] Other features and advantages of the present invention will be described in the following description, and partly become obvious from the description, or be understood by implementing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0057] Figure 1 A topology diagram of a novel AC / DC converter according to an embodiment of the present invention is shown.

[0058] Figure 2 A topological diagram of a first power module according to an embodiment of the present invention is shown.

[0059] Figure 3 A topology diagram of a second power module according to an embodiment of the present invention is shown.

[0060] Figure 4 FIG. 4 shows a topological diagram of an energy consumption element H1 according to an embodiment of the present invention.

[0061] Figure 5 FIG. 4 shows a topological diagram of a C voltage equalizing circuit according to an embodiment of the present invention.

[0062] Figure 6 A topology diagram of an RC voltage equalizing circuit according to an embodiment of the present invention is shown.

[0063] Figure 7 A topological diagram of an RCD voltage balancing circuit according to an embodiment of the present invention is shown.

[0064] Figure 8 A flow chart of a DC side short-circuit fault ride-through method of a novel AC / DC converter under a first working condition according to an embodiment of the present invention is shown.

[0065] Fig. 9 A flow chart of a DC side short-circuit fault ride-through method of a novel AC / DC converter under a second working condition according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0066] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0067] like Figure 1 As shown, the present invention provides a novel AC / DC converter, wherein the converter comprises a switch valve and an auxiliary shunt branch connected in parallel, wherein:

[0068] The switch valve includes three switch valve units connected in series, and the switch valve unit includes a switch capacitor valve string and two new switch valve strings in parallel, and the switch capacitor valve string includes multiple switch capacitor modules connected in series; the new switch valve string includes an upper bridge arm and a lower bridge arm, and the upper bridge arm and the lower bridge arm both include a first power module of a single bridge arm type and a second power module of a double bridge arm type connected in series, and the upper bridge arm and the lower bridge arm are connected in series symmetrically by connecting the midpoints.

[0069] The auxiliary shunt branch includes a series branch and two switch branches, wherein the series branch is connected in parallel with the switch valve through the two switch branches; the series branch includes a capacitor C1 and a diode valve string connected in series, and a resistor R1 connected in parallel with the capacitor C1.

[0070] A novel AC / DC converter of the present invention is described in detail below.

[0071] In some embodiments of the present invention, Figure 2 As shown, the first power module includes a first bridge arm, an equalizing capacitor C2 and an energy-consuming element H1 connected in parallel, wherein: the first bridge arm includes a power switching device T1 and a diode D1, the anode of the diode D1 is connected to the anode or collector of the power switching device T1; one end of the equalizing capacitor C2 is connected to the cathode of the diode D1, and the other end of the equalizing capacitor C2 is connected to the cathode or emitter of the power switching device T1, and a diode D2 is anti-parallel to the power switching device T1.

[0072] In some embodiments of the present invention, Figure 3 As shown, the second power module (ie Figure 1The dual-bridge-arm novel device series module) includes a parallel-connected equalizing capacitor C3, an energy-consuming element H2 and two second bridge arms, wherein: the second bridge arm includes a power switch device T2 and a diode D3, the anode of the diode D3 is connected to the anode or collector of the power switch device T2, and a diode D4 is anti-parallel connected to the power switch device T2; one end of the equalizing capacitor C3 is connected to the cathode of the diode D3 of one of the second bridge arms, and the other end of the equalizing capacitor C3 is connected to the cathode or emitter of the power switch device T2 of one of the second bridge arms.

[0073] That is, in the first power module, since only one first bridge arm has a power switch device, the first power module is defined as a single bridge arm type. In the second power module, both second bridge arms include power switch devices, so the second power module is defined as a dual bridge arm type.

[0074] In some embodiments of the present invention, Figure 4 As shown, the energy-consuming elements H1 and H2 are any one or combination of an energy-taking power supply, a first energy-consuming resistor, and a switchable energy-consuming resistor, wherein the energy-taking power supply is used to obtain energy from the corresponding voltage-equalizing capacitor to power the control circuit of the corresponding power module, and the switchable energy-consuming resistor includes a second energy-consuming resistor and a switch connected in series with the second energy-consuming resistor. (For example, the switch can be a relay, a contactor, a circuit breaker, a semiconductor switch, etc., which has a current that can be disconnected), one end of the switch is connected to one end of the second energy-consuming resistor, the other end of the switch is connected to the positive electrode of the corresponding voltage-equalizing capacitor, the other end of the second energy-consuming resistor is connected to the negative electrode of the corresponding voltage-equalizing capacitor, the energy-taking power supply is connected to both ends of the corresponding voltage-equalizing capacitor, and the switching control of the second energy-consuming resistor can be realized by setting the switch.

[0075] In one embodiment of the present invention, Figure 5 As shown, the switch capacitor module is any one or more combinations of a half-bridge module, a full-bridge module and a hybrid module, wherein:

[0076] The hybrid module includes a first number of half-bridge modules connected in series and a second number of full-bridge modules connected in series. The first number of half-bridge modules connected in series and the second number of full-bridge modules connected in series are connected in series.

[0077] The switched capacitor module is described in detail below.

[0078] In one embodiment of the present invention, in this embodiment, the power switching devices T1, T2 and T3 can all be fully controlled power switching devices such as insulated gate bipolar transistors (IGBT), integrated gate-commutated thyristors (IGCT), field-effect transistors (FET), etc.

[0079] In some embodiments of the present invention, Figure 2 As shown, a bypass switch can be configured in both the first power module and the second power module, that is, one end of the bypass switch S1 in the first power module is connected to the anode or collector of the power switch device T1, and the other end is connected to the cathode or emitter of the power switch device T1; Figure 3 As shown, two ends of the bypass switch S2 in the second power module are connected to two connection midpoints in the second power module.

[0080] In some embodiments of the present invention, Figure 1 As shown, the diode valve string includes a plurality of diodes D connected in series. SN , where each diode D SN A voltage balancing circuit is connected in parallel, wherein the voltage balancing circuit is one or more of a C voltage balancing circuit, an RC voltage balancing circuit and an RCD voltage balancing circuit.

[0081] In some embodiments of the present invention, Figure 5 As shown, the C voltage equalizing circuit includes a capacitor C4, wherein the capacitor C4 and the diode D SN in parallel.

[0082] In some embodiments of the present invention, Figure 6 As shown, the RC voltage equalizing circuit includes a capacitor C4 and a resistor R2, wherein the capacitor C4 and the diode D SN In parallel, resistor R2 and capacitor C4 are connected in parallel.

[0083] In some embodiments of the present invention, Figure 7 As shown, the RCD voltage balancing circuit includes a capacitor C4, a resistor R2 and a diode D5, wherein the resistor R2 is connected in series with the capacitor C4 and the diode D5. SN In parallel, the diode D5 is connected in parallel with the resistor R2.

[0084] In some embodiments of the present invention, Figure 1As shown, the switch branch includes switch K1 and / or switch K2. When K1 and K2 are included, K1 and K2 are connected in series, wherein K1 is a fast mechanical switch. The fast mechanical switch is similar to the isolating knife switch and does not have the current breaking capability, but has a fast breaking and closing speed, for example, the breaking can be completed in 1ms. K2 is a solid-state switch, and the rated voltage of K2 is lower than that of K1. The positions of K1 and K2 can be swapped, and K1 can be configured at both the positive and negative poles of the DC, or only at the positive pole of the DC, or only at the negative pole of the DC; K2 can be configured at both the positive and negative poles of the DC, or only at the positive pole of the DC, or only at the negative pole of the DC.

[0085] In some embodiments of the present invention, Figure 1 As shown, the converter also includes two reactors L, wherein one end of the two reactors L is respectively connected to the two ends of the series branch, and the other end of the two reactors L forms a DC port of the converter, that is, one end of the reactor L is connected between one end of the capacitor C1 and K1 or K2.

[0086] In some embodiments of the present invention, Figure 1 As shown, the converter also includes at least three transformers T connected one-to-one with at least three series valve strings, one end of each transformer T is respectively connected to two connection midpoints of the corresponding series valve string, and the other ends of the three transformers T are connected to form an AC port of the converter.

[0087] In the existing methods, no DC side bipolar short-circuit fault ride-through strategy has been proposed. If the semi-full hybrid solution is directly adopted by referring to MMC, the cost is high, the volume is large, and the efficiency is low, which seriously reduces the advantages of the new AC / DC converter topology. Therefore, the present invention also provides a DC side short-circuit fault ride-through method for the new AC / DC converter, which is described below.

[0088] In some embodiments of the present invention, a method for riding through a DC side short circuit fault of a novel AC / DC converter is also provided, wherein the converter adopts the above-mentioned converter, and the method is implemented based on a first operating condition, wherein the first operating condition is:

[0089] When the AC port is not connected to an AC power source, this parameter is not required. Figure 1 The dual-bridge-arm new device series module only configures a single-bridge-arm new device series module.

[0090] like Figure 8 As shown, the method includes:

[0091] Step S1: a bipolar short circuit fault is detected at the DC port;

[0092] Step S2: the switch capacitor valve string of each phase outputs 0 voltage, that is, the fully controlled power switch devices of the upper bridge arms of all switch capacitor modules are turned off, and the fully controlled power switch devices of the lower bridge arms are turned on;

[0093] Step S3: disconnect K2;

[0094] Step S4: disconnect K1;

[0095] Step S5: The converter is in STATCOM (static synchronous compensator) mode to support the AC port voltage;

[0096] Step S6: Waiting for the DC side fault current of the converter to decay to 0;

[0097] Step S7: Waiting for the fault point to be freed;

[0098] Step S8: close K1;

[0099] Step S9: close K2;

[0100] Step S10: The converter resumes normal operation.

[0101] The control principle of the first working condition is as follows: after a fault occurs on the DC side, the DC port voltage is 0, and the switch capacitor valve string outputs 0 voltage. During the disconnection of K2, the fault current is transferred to the diode series valve (i.e., diode valve string) to charge the capacitor C1. Since the capacitor voltage cannot change suddenly, and K2 is a solid-state switch with a very fast disconnection speed, after K2 is completely disconnected, the capacitor C1 voltage is still low, and K2 is turned off at approximately 0 voltage. Subsequently, K1 is disconnected. During the disconnection of K1, the C1 voltage is still rising, but it is all borne by K2. Therefore, K1 is disconnected at 0 voltage, and a fast mechanical switch without shunt capability can be used, which is much cheaper than a DC circuit breaker. After K1 is disconnected, C1 is continuously charged by the fault current, and the voltage continues to rise. Since the rated voltage of K1 is higher than that of K2, K1 bears most of the voltage of C1. K1 and K2 isolate the fault point of the DC port from the new AC / DC converter valve (i.e., the converter mentioned above), so the new AC / DC converter valve can be in STATCOM mode (i.e., working in STATCOM mode) to provide reactive voltage support to the AC system. Since C1 is charged, the voltage of C1 is added to the impedance of the fault circuit (mainly reactance, including line reactance, DC filter inductance or equivalent series reactance of DC filter at the DC port), so that the inductance of the fault circuit is quickly reduced to 0, thereby achieving rapid fault clearing. Then, after waiting for the time for the fault point to be freed and ensuring that the instantaneous fault is completely restored, K1 is closed first, and then K2 is closed to avoid overvoltage damage due to insufficient rated voltage of K2 when the fault still exists. Then, the converter resumes normal operation. The role of resistor R1 is to discharge C1 and prepare for the next fault crossing.

[0102] On the other hand, in some embodiments of the present invention, a DC side short circuit fault ride-through method of a novel AC / DC converter is provided, wherein the converter adopts the above-mentioned converter, and the method is implemented based on a second operating condition, wherein the second operating condition is:

[0103] When the AC port is connected to an AC power supply, a dual-bridge-arm new device series module needs to be configured, and the sum of the DC voltages of the second power modules in any upper bridge arm of the new switch valve must be greater than the peak voltage of the AC power supply connected to the AC port:

[0104] like Fig. 9 As shown, the method includes:

[0105] Step S1: a bipolar short circuit fault is detected at the DC port;

[0106] Step S2: The switch capacitor valve string of each phase outputs a voltage, and the switch capacitor valve string output voltage of each phase satisfies the condition that the switch capacitor valve string output voltage of each phase is greater than the instantaneous value of the AC port voltage of the corresponding phase;

[0107] Step S3: when the current at any phase AC port decays to 0, the new switch valve string of the phase is turned off, that is, the fully controlled power switch devices of the first power module and the second power module power switch devices in the new switch valve string are all turned off;

[0108] Step S4: After all phases of the new switch valve strings are turned off, the switch capacitor valve string outputs 0 voltage, that is, the fully controlled power switch devices of the upper bridge arms of all switch capacitor modules are turned off, and the fully controlled power switch devices of the lower bridge arms are turned on;

[0109] Step S5: disconnect K2;

[0110] Step S6: disconnect K1;

[0111] Step S7: The converter is in STATCOM (static synchronous compensator) mode to support the AC port voltage;

[0112] Step S8: Waiting for the DC side fault current to decay to 0;

[0113] Step S9: Waiting for the fault point to be freed;

[0114] Step S10: close K1;

[0115] Step S11: close K2;

[0116] Step 12: The converter resumes normal operation.

[0117] The particularity of the control of the above-mentioned second working condition compared with the control of the first working condition is that: the AC port is connected to an AC power supply, and the new switch valve string needs to be equipped with a double-bridge arm new device series module (i.e., the second power module) to block the AC voltage when the DC side voltage is 0, and then inject the fault current into the DC side fault point after the AC voltage is rectified by the new switch valve string.

[0118] In addition, the present invention also provides examples for exemplary description, as follows:

[0119] Take the bipolar short circuit at the DC port of the new ±15kV / 50MW AC / DC converter as an example. When a bipolar short circuit fault occurs on the DC side, the topology and control of the present invention are adopted, and the AC voltage is interrupted for about 3ms (i.e., the time required from the occurrence of the fault to the disconnection of K1), and then the new AC / DC series valve can provide reactive support. The fault current on the DC side decays to 0 in about 30ms, the fault point is freed for about 150ms, and the total fault clearing time is about 183ms. If the topology and control of the present invention are not adopted, the fault clearing time is in the second level, which is greatly increased, and the new AC / DC series valve needs to be locked, and it is impossible to provide reactive support to the AC port.

[0120] In summary, the present invention has the following advantages:

[0121] The novel DC side bipolar short-circuit fault ride-through method of the AC / DC converter proposed in the present invention only needs to add a few fully-controlled power switching devices and diodes, capacitors, and resistors compared to the MMC semi-full hybrid solution. The increased cost of the first operating condition is only about 20% of that of the MMC semi-full hybrid solution, and the increased cost of operating condition 2 is only about 66% of that of the MMC semi-full hybrid solution, which greatly reduces the system cost and can achieve reactive power support and rapid fault recovery.

[0122] The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A novel AC / DC converter, wherein: The converter comprises a switch valve and an auxiliary shunt branch connected in parallel, wherein: The switch valve comprises three switch valve units connected in series, the switch valve units comprise a switch capacitor valve string connected in parallel and two new switch valve strings, the switch capacitor valve string comprises a plurality of switch capacitor modules connected in series; the new switch valve string comprises an upper bridge arm and a lower bridge arm, the upper bridge arm and the lower bridge arm both comprise a first power module of a single bridge arm type connected in series and a second power module of a double bridge arm type, the upper bridge arm and the lower bridge arm are connected in series symmetrically by connecting the midpoint; The auxiliary shunt branch includes a series branch and two switch branches, wherein the series branch is connected in parallel with the switch valve through the two switch branches; the series branch includes a capacitor C1 and a diode valve string connected in series, and a resistor R1 connected in parallel with the capacitor C1.

2. A novel AC / DC converter according to claim 1, wherein: The converter further comprises two reactors, wherein one end of the two reactors is respectively connected to two ends of the series branch, and the other ends of the two reactors form a DC port of the converter.

3. A novel AC / DC converter according to claim 1 or 2, wherein: The converter also includes at least three transformers connected one-to-one with at least three series valve strings, one end of each transformer is respectively connected to two connection midpoints of the corresponding series valve string, and the other ends of the three transformers are connected to form an AC port of the converter.

4. A novel AC / DC converter according to claim 1 or 2, wherein: The switch capacitor module is any one or more combinations of a half-bridge module, a full-bridge module and a hybrid module, wherein: The hybrid module includes a first number of half-bridge modules connected in series and a second number of full-bridge modules connected in series. The first number of half-bridge modules connected in series and the second number of full-bridge modules connected in series are connected in series.

5. A novel AC / DC converter according to claim 1 or 2, wherein: The first power module includes a first bridge arm, a voltage-equalizing capacitor C2 and an energy-consuming element H1 connected in parallel, wherein: The first bridge arm includes a power switch device T1 and a diode D1, wherein the anode of the diode D1 is connected to the anode or collector of the power switch device T1; One end of the voltage-equalizing capacitor C2 is connected to the cathode of the diode D1 , and the other end of the voltage-equalizing capacitor C2 is connected to the cathode or emitter of the power switch device T1 . The power switch device T1 is anti-parallel-connected with a diode D2 .

6. A novel AC / DC converter according to claim 1 or 2, wherein: The second power module includes a voltage-equalizing capacitor C3, an energy-consuming element H2 and two second bridge arms connected in parallel, wherein: The second bridge arm includes a power switch device T2 and a diode D3, wherein the anode of the diode D3 is connected to the anode or collector of the power switch device T2, and a diode D4 is connected in anti-parallel to the power switch device T2; One end of the voltage-equalizing capacitor C3 is connected to the cathode of the diode D3 of one of the second bridge arms, and the other end of the voltage-equalizing capacitor C3 is connected to the cathode or emitter of the power switch device T2 of one of the second bridge arms.

7. A novel AC / DC converter according to claim 1 or 2, wherein: The diode valve string includes a plurality of diodes D connected in series. SN , where each diode D SN A voltage equalizing circuit is connected in parallel.

8. A novel AC / DC converter according to claim 7, wherein: The voltage balancing circuit is one or more of a C voltage balancing circuit, an RC voltage balancing circuit and an RCD voltage balancing circuit.

9. A novel AC / DC converter according to claim 8, wherein: The C voltage equalizing circuit includes a capacitor C4, wherein the capacitor C4 and the diode D SN in parallel.

10. A novel AC / DC converter according to claim 8, wherein: The RC voltage equalizing circuit includes a capacitor C4 and a resistor R2, wherein the capacitor C4 and the diode D SN In parallel, resistor R2 and capacitor C4 are connected in parallel.

11. A novel AC / DC converter according to claim 8, wherein: The RCD voltage balancing circuit includes a capacitor C4, a resistor R2 and a diode D5, wherein the resistor R2 is connected in series with the capacitor C4 and the diode D5. SN In parallel, the diode D5 is connected in parallel with the resistor R2.

12. A novel AC / DC converter according to any one of claims 8 to 11, wherein: The switch branch includes a switch K1 and / or a switch K2. When the switch branch includes K1 and K2, K1 and K2 are connected in series.

13. A novel method for riding through a DC side short-circuit fault of an AC / DC converter, wherein the converter is a converter according to any one of claims 3 to 12, and the method is implemented based on a first operating condition, wherein: The first working condition is: When the AC port of the converter is not connected to the AC power source, the second power module is bypassed; The method comprises: Step S1: detecting that a bipolar short circuit fault occurs at a DC port of the converter; Step S2: the switch capacitor valve string of each phase outputs 0 voltage; Step S3: disconnect K2; Step S4: disconnect K1; Step S5: Waiting for the DC side fault current of the converter to decay to 0; Step S6: Waiting for the fault point to be freed; Step S7: close K1; Step S8: Close K2.

14. A novel DC side short-circuit fault ride-through method for an AC / DC converter according to claim 13, wherein: The switched capacitor valve string outputs 0 voltage, including: The fully controlled power switch devices of the upper bridge arms of all switch capacitor modules are turned off, and the fully controlled power switch devices of the lower bridge arms are turned on.

15. A novel method for riding through a DC side short-circuit fault of an AC / DC converter, wherein the converter is a converter according to any one of claims 3 to 12, and the method is implemented based on a second operating condition, wherein: The second working condition is: When the AC port of the converter is connected to an AC power source, the sum of the DC voltages of the second power modules in any upper bridge arm of the novel switch valve is greater than the peak voltage of the AC power source connected to the AC port: The method comprises: Step S1: detecting that a bipolar short circuit fault occurs at a DC port of the converter; Step S2: The switch capacitor valve string of each phase outputs a voltage, and the switch capacitor valve string output voltage of each phase satisfies the condition that the switch capacitor valve string output voltage of each phase is greater than the instantaneous value of the AC port voltage of the corresponding phase; Step S3: When the current at any phase AC port decays to 0, the new switch valve string of the phase is turned off; Step S4: After all the new switch valve strings of all phases are turned off, the switch capacitor valve string outputs 0 voltage; Step S5: disconnect K2; Step S6: disconnect K1; Step S7: Wait for the DC side fault current to decay to 0; Step S8: Waiting for the fault point to be freed; Step S9: close K1; Step S10: Close K2.

16. A novel method for riding through a DC side short-circuit fault of an AC / DC converter according to claim 15, wherein: The switched capacitor valve string outputs 0 voltage, including: The fully controlled power switch devices of the upper bridge arms of all switch capacitor modules are turned off, and the fully controlled power switch devices of the lower bridge arms are turned on.

17. A novel DC side short-circuit fault ride-through method for an AC / DC converter according to claim 15 or 16, wherein: A new on-off valve train to shut off the phase includes: The fully controlled power switch devices of the first power module and the second power module power switch devices in the novel switch valve string are all turned off.

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