Modular commutation type converter with high overload capacity

Abstract

The invention belongs to the technical field of power electronics, and particularly relates to a modular commutated converter with high overload capacity. The modular commutation type converter is formed by connecting at least one large-current turn-off commutation bridge and at least one cascade module chain in parallel, wherein the large-current turn-off commutation bridge is an H-bridge circuit comprising four large-current turn-off commutation bridge arms; the large-current turn-off commutation bridge arm comprises at least one single switch device module SDM and at least one high-turn-off single switch device module HDM which are connected in series, and the current turn-off capacity of the high-turn-off single switch device module HDM is larger than the current at the turn-off moment of the large-current turn-off commutation bridge arm. According to the technical scheme of the invention, high-power overload operation can be realized in a short time, so that voltage and inertia support can be effectively carried out on a power grid. Compared with an existing structure, the topological structure has the advantage that the manufacturing cost is obviously reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronics, and in particular relates to a modular commutation converter with high overload capacity. Background Art

[0002] Compared with AC transmission technology, high-voltage direct current transmission technology has the advantages of low line cost, small line loss, high line corridor utilization, small impact of capacitance effect, and no need for synchronization of the power grids at both ends. It is particularly suitable for scenarios such as large-capacity long-distance transmission, submarine cable transmission, and asynchronous power grid interconnection.

[0003] In recent years, a high proportion of new energy and a high proportion of power electronic equipment have become the prominent features of new power systems. The large-scale development of new energy and DC transmission has brought about the problem of "hollowing out" of load center supporting power sources in the power system, especially in some load center areas, where the proportion of DC transmission as a power source for the power grid has increased year by year. However, in the existing DC transmission technology, both power electronic devices and converters are limited by inherent defects such as low overload capacity, low short-circuit capacity, and low inertia. The DC transmission system composed of them cannot provide support for the power grid. Instead, it requires the AC power grid to provide it with commutation voltage, or reduce output under fault transient conditions, resulting in a sharp increase in the safety risk of voltage and frequency instability in the power system, which seriously restricts the rapid development of new energy and new power systems.

[0004] Based on the above phenomenon, the stability of the power system and the efficiency of the power system can be improved by setting the power electronic equipment to have a short-term high overload operation capability. However, for conventional two-level VSC and MMC, it is usually necessary to increase the specifications of their switching devices proportionally to meet the device hard shutdown capability constraints and capacitor voltage fluctuation limits under high load, but this approach also causes the cost of power electronic equipment to increase proportionally. Summary of the invention

[0005] To solve the above problems, the present invention provides a modular commutation converter with high overload capacity. The modular commutation converter can achieve overload operation of the same proportion by simply setting the HDM to a device with a high shutdown capability whose current shutdown capability is greater than the current at the time when the large current shutdown commutation bridge arm is shut down, thereby lowering the manufacturing cost.

[0006] In the first aspect, the present invention discloses a modular commutation converter with high load capacity, which is composed of at least one large current shut-off commutation bridge and at least one cascade module chain connected in parallel. The large current shut-off commutation bridge is an H-bridge circuit, including four large current shut-off commutation bridge arms; the large current shut-off commutation bridge arms include at least one single switch device module SDM and at least one high shut-off single switch device module HDM connected in series, and the current shut-off capability of the high shut-off single switch device module HDM is greater than the current at the time when the large current shut-off commutation bridge arm is shut off.

[0007] In the above-mentioned high-current turn-off commutating bridge arm, there is at least one type of high turn-off single switch device module HDM; and / or, there is at least one type of single switch device module SDM.

[0008] The cascade module chain is composed of a plurality of submodules SM connected in series, and the cascade module chain is connected in parallel to the DC port of the modular commutated converter; the plurality of submodules SM connected in series are the same submodules or different submodules.

[0009] The single switch device module SDM includes a first auxiliary device group F1, which is composed of a first supporting capacitor C1 and a first static equalizing resistor R1 connected in parallel and then connected in series with a first auxiliary diode D1; and / or, the high-off single switch device module HDM includes a second auxiliary device group F2, which is composed of a second supporting capacitor C2 and a second static equalizing resistor R2 connected in parallel and then connected in series with a second auxiliary diode D2.

[0010] The single switch device module SDM further includes a first energy consumption circuit, which is connected in parallel to both ends of the first support capacitor C1; the high-off single switch device module HDM further includes a second energy consumption circuit, which is connected in parallel to both ends of the second support capacitor C2. Further, the second energy consumption circuit is connected in series with a fuse to protect the circuit.

[0011] In a second aspect, the present invention discloses an application based on the above modular commutation converter, specifically comprising:

[0012] A plurality of said modular commutation converters are cascaded to form a multi-phase converter; and / or,

[0013] An energy storage module is arranged at the DC port on the cascade module chain side in the modular commutation converter, and three modular commutation converters with energy storage modules arranged at the DC ports are star-connected or delta-connected to form an energy storage converter; and / or,

[0014] A plurality of the modular commutation converters are star-connected to form a multi-phase converter.

[0015] In a third aspect, the present invention further discloses a three-phase cascade modular commutation converter, which comprises a converter transformer with an auxiliary delta-connected winding, an auxiliary switch K, and three cascaded modular commutation converters of the first aspect; wherein the converter transformer with an auxiliary delta-connected winding is arranged at an AC port of the three-phase cascade modular commutation converter; the auxiliary windings of the converter transformer with an auxiliary delta-connected winding are W1, W2, and W3, and the auxiliary windings W1, W2, and W3 are delta-connected. The auxiliary switch K is located on the connection line between any two of the auxiliary windings W1, W2, and W3.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. In a modular commutation converter with high load capacity of the present invention, the high current shutoff commutation bridge utilizes the working characteristics of soft switching. It only needs to set all HDMs as devices with high shutoff capabilities, and set the current shutoff capability of the HDM to be greater than the current at the time when the bridge arm of the high current shutoff commutation bridge is shut off, so that the modular commutation converter can achieve high overload operation in a short time, thereby effectively supporting the voltage and inertia of the power grid. Compared with the setting of the traditional MMC topology (modular multi-level converter), the topology of the present invention significantly reduces the manufacturing cost.

[0018] 2. Multiple modular commutation converters can be cascaded to form a multiphase converter. Furthermore, the multiphase converter can be connected to a multiphase AC device through a converter transformer; multiple modular commutation converters connected in star or delta connection can be used to form a static VAR compensator or energy storage converter; multiple modular commutation converters can also be connected in other ways. The modular commutation converter of the present invention has various connection modes, which greatly increases its scope of application.

[0019] 3. When three modular commutated converters are cascaded to form a three-phase cascaded modular commutated converter, a converter transformer with an auxiliary delta-connected winding is provided at the AC port of the multi-phase converter, and an auxiliary switch is provided on the connecting line between any two of the auxiliary windings W1, W2 and W3. When an unbalanced fault occurs in the power grid, the auxiliary switch K is closed, and the delta-connected windings W1, W2 and W3 provide a zero-sequence current path, thereby achieving the effect of three-phase series voltage balancing.

[0020] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing 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, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative work.

[0022] Figure 1 This is a structural diagram of a single-phase modular commutation converter with high load capacity according to an embodiment of the present invention;

[0023] Figure 2 This is a structural diagram of a bridge arm of a large current shut-off commutator according to an embodiment of the present invention;

[0024] Figure 3 (a) is an internal structure diagram of a second energy consumption circuit of an HDM using a MOV according to an embodiment of the present invention;

[0025] Figure 3 (b) is an internal structure diagram of a second energy consumption circuit of an HDM using a TVS according to an embodiment of the present invention;

[0026] Figure 3 (c) is an internal structure diagram of a second energy consumption circuit of a HDM according to an embodiment of the present invention, in which an electronic switch is used to control a resistor;

[0027] Figure 4 This is a schematic diagram of a high current shut-off commutation bridge according to an embodiment of the present invention;

[0028] Figure 5 (a) is a structural diagram of a sub-module of a cascaded module chain using a half-bridge module according to an embodiment of the present invention;

[0029] Figure 5 (b) is a structural diagram of a submodule of a cascaded module chain using a full-bridge module according to an embodiment of the present invention;

[0030] Figure 5 (c) is a structural diagram of a battery or supercapacitor connected in parallel with a submodule of a cascade module chain according to an embodiment of the present invention;

[0031] Figure 5 (d) is a structural diagram of a battery or super capacitor and a control circuit in parallel with sub-modules of a cascade module chain according to an embodiment of the present invention;

[0032] Figure 6 This is a structural diagram of a three-phase cascaded modular commutation converter according to an embodiment of the present invention;

[0033] Figure 7 A structural diagram of an energy storage converter according to an embodiment of the present invention;

[0034] Figure 8 This is a structural diagram of another three-phase cascade modular commutation converter according to an embodiment of the present invention;

[0035] Fig. 9 This is a schematic diagram of a three-phase voltage balancing control based on zero-sequence current injection according to an embodiment of the present invention;

[0036] Fig.10 The present invention is a structural diagram of a static VAR compensator according to an embodiment of the present invention. DETAILED DESCRIPTION

[0037] 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.

[0038] Example 1

[0039] like Figure 1-2 As shown, this embodiment discloses a modular commutation converter with high load capacity, which is composed of at least one large current shutdown commutation bridge and at least one cascade module chain connected in parallel; wherein the large current shutdown commutation bridge is an H-bridge circuit including four large current shutdown commutation bridge arms, and the large current shutdown commutation bridge arms include at least one single switch device module SDM and at least one high shutdown single switch device module HDM connected in series, and the current shutdown capability of the high shutdown single switch device module HDM is greater than the current at the time when the large current shutdown commutation bridge arm is shut down. The modular commutation converter has both an AC port and a DC port. Exemplarily, a transformer or a filter can be set at the AC port, and / or a filter can be set at the DC port.

[0040] The current shutoff capability of the high-off single switch device module HDM is greater than the current shutoff capability of the single switch device module SDM. The current shutoff capability of the high-off single switch device module HDM is greater than the current shutoff capability of the single switch device module SDM in the following manners:

[0041] (1) HDM uses power electronic devices with higher current specifications than those in SDM. Specifically, the current shutoff capability of the power electronic devices in HDM is higher than that of the power electronic devices in SDM. For example, if the power electronic devices in SDM use thyristors, the current shutoff capability of the power electronic devices in HDM is higher than the average current-carrying capacity of the thyristors in SDM (Explanation: if fully controlled devices are used, the corresponding current shutoff capability is; if semi-controlled devices such as thyristors are used, the corresponding average current-carrying capacity is).

[0042] As a preferred embodiment, the current shutoff capability of the power electronic device in the HDM is 1.5-10 times the current shutoff capability of the power electronic device in the SDM. For example, if the power electronic device in the SDM adopts a thyristor, the current shutoff capability of the power electronic device in the HDM is 1.5-10 times the average current carrying capacity of the thyristor in the SDM.

[0043] (2) The power electronic devices in HDM are constructed by connecting power electronic devices with current specifications equivalent to or lower than those in SDM in parallel.

[0044] Optional, such as Figure 2 As shown, the proportion of the number of high-turnoff single switch device modules HDM in the high-current turn-off commutation bridge arm is 0.01% to 50%, where the calculation formula for the proportion of the number of HDM is as follows:

[0045] The proportion of the number of HDMs = (the number of HDMs in each high-current shutdown commutation bridge arm / (the number of HDMs in each high-current shutdown commutation bridge arm + the number of SDMs in each high-current shutdown commutation bridge arm)) × 100%.

[0046] Optionally, in each high-current turn-off commutation bridge arm, there is at least one type of HDM and / or at least one type of SDM.

[0047] Exemplarily, each high-current shut-off commutation bridge arm includes three types of HDM (respectively HDM1, HDM2 and HDM3) and two types of SDM (respectively SDM1 and SDM2). Assuming that the current at the time of shutting off the high-current shut-off commutation bridge arm is 2000A, the current shut-off capabilities of HDM1, HDM2 and HDM3 can be set to 5000A, 4000A and 3000A respectively (all greater than the current 2000A at the time of shutting off the high-current shut-off commutation bridge arm), and the current shut-off capabilities of SDM1 and SDM2 are set to 1500A and 1000A respectively (both less than the current 2000A at the time of shutting off the high-current shut-off commutation bridge arm).

[0048] In some embodiments, the single switch device module SDM includes a first auxiliary device group F1. Exemplarily, the first auxiliary device group F1 is composed of a first support capacitor C1 and a first static voltage balancing resistor R1 connected in parallel and then connected in series with a first auxiliary diode D1.

[0049] Further, the single switch device module SDM further comprises a first switch T1, which is connected in parallel with the first auxiliary device group F1. Exemplarily, the first switch T1 is composed of a fully controlled device G1 and a first diode DSDM connected in reverse parallel.

[0050] In some embodiments, the high turn-off single switch device module HDM includes a second auxiliary device group F2. Exemplarily, the second auxiliary device group F2 is composed of a second support capacitor C2 and a second static voltage balancing resistor R2 connected in parallel and then connected in series with a second auxiliary diode D2.

[0051] Furthermore, the high-off single switch device module HDM further includes a second switch T2, which is connected in parallel with the second auxiliary device group F2. Exemplarily, the second switch T2 is composed of a fully-controlled device G2 and a second diode DHDM connected in reverse parallel.

[0052] The structural setting of SDM and HDM in Example 1 of the present invention can achieve voltage balance between series modules. The principle is: the fully controlled device of the series module (SDM and / or HDM) with higher voltage in the bridge arm of the large current shut-off commutation bridge is always in a triggered state, and its supporting capacitor cannot be charged, and the voltage of the supporting capacitor will drop. The fully controlled device of the series module (SDM and / or HDM) with lower voltage in the bridge arm of the large current shut-off commutation bridge is turned on or off according to the actual situation. When the fully controlled device is in the off state, the current of the bridge arm of the large current shut-off commutation bridge charges the supporting capacitor through the auxiliary diode, and then the voltage across the supporting capacitor increases. Thereby achieving voltage balance between the series modules in the bridge arm of the large current shut-off commutation bridge.

[0053] In some other embodiments, the single switch device module SDM includes a first energy consumption circuit, and the first energy consumption circuit is connected in parallel to both ends of the first support capacitor C1 to prevent the energy charged by the stray inductance from accumulating in the first support capacitor C1 and causing overvoltage, thereby maintaining voltage balance across the first support capacitor C1. Exemplarily, the first energy consumption circuit includes any one or a combination of a first energy consumption resistor, a first energy source, and a first switchable energy consumption resistor.

[0054] Further, the above-mentioned high - turn - off single - switch device module HDM may further include a second energy - consuming circuit, which is connected in parallel across the second support capacitor C2 and the power of the second energy - consuming circuit is greater than that of the first energy - consuming circuit in the above - mentioned SDM. The second energy - consuming circuit can consume the energy charged into the second support capacitor C2 by the stray inductance during the turn - off process of the power electronic device in the HDM, and maintain the voltage balance across the second support capacitor C2. Exemplarily, the second energy - consuming circuit can be a metal - oxide varistor (MOV), a transient voltage suppression diode (TVS), or a energy - consuming resistor R3 controlled by an electronic switch K3, as Figure 3 (a)-(c) shown.

[0055] Exemplarily, as Figure 3 (c) shown, when the second energy - consuming circuit adopts an energy - consuming resistor R3 controlled by an electronic switch K3, the electronic switch K3 adopts a hysteresis control strategy, specifically: when the voltage across the second support capacitor C2 is higher than the first voltage threshold, the electronic switch K3 closes and the second support capacitor C2 discharges; when the voltage across the second support capacitor C2 is lower than the second voltage threshold, the electronic switch K3 opens and the second support capacitor C2 stops discharging. In terms of numerical relationship, the rated operating voltage of the HDM module < the second voltage threshold < the first voltage threshold < the maximum withstand voltage of the power electronic device in the HDM.

[0056] Further, the above - mentioned second energy - consuming circuit can also be connected in series with a fuse for protection.

[0057] Specifically, for the modular commutation converter in Embodiment 1, when the large - current commutation bridge arm current to be turned off is greater than the current turn - off ability of the SDM, the working principle of the large - current turn - off commutation bridge is as Figure 4 shown, including the following steps:

[0058] Step 1: Wait for the output voltage of the cascaded module chain to be less than the threshold voltage Uth, where the threshold voltage Uth≥0.

[0059] Step 2: When the output voltage of the cascaded module chain is less than the threshold voltage Uth, turn off all the HDMs in the bridge arm (the large - current commutation bridge arm to be turned off).

[0060] Step 3: Wait for the delay td.

[0061] Step 4: Turn off the SDM in the bridge arm (the large - current commutation bridge arm to be turned off).

[0062] The delay td in step 3 above can be a fixed constant or a variable. The function of the delay td is to prevent the first switch T1 in the SDM from being turned off under high current conditions, thereby causing turn-off failure or high loss; at the same time, the delay td can also prevent the first diode DSDM in the SDM from reverse hard recovery under high current conditions, causing damage.

[0063] Exemplarily, after the HDM in the high-current commutation bridge arm that needs to be shut down is shut down, the timing starts, and after the output voltage of the cascade module chain is greater than 0, the delay td2 is waited for, and step 4 is executed. In this way, the delay td is equal to the entire time period from the start of the timing to the end of waiting for td2.

[0064] The "turning off SDM" in the above step 4 can be all SDMs in the high-current commutation bridge arm that needs to be turned off, or it can be the high-current commutation bridge arm that needs to be turned off, and the voltages across the first supporting capacitor C1 of the SDM are sorted from high to low, and the part of the SDM corresponding to the lower voltage. When the voltages across the first supporting capacitor C1 in the SDM in the high-current commutation bridge arm that needs to be turned off are sorted from high to low, and the part of the SDM corresponding to the lower voltage is turned off, the turned-off SDM can be replenished from the DC port, and the voltage increases. The SDM that is not turned off cannot be replenished, and its static voltage equalizing resistor and energy source will consume energy, and the module voltage will decrease. Therefore, through the above control, the voltage equalization of the SDM module in the high-current commutation bridge arm that needs to be turned off is achieved.

[0065] From the working principle of the above-mentioned high-current shutdown commutation bridge, it can be known that when the high-current shutdown commutation bridge arm needs to be shut down during the commutation process of the modular commutation converter, all HDMs in the high-current commutation bridge arm that needs to be shut down are first controlled to be shut down. The high-current shutdown commutation bridge performs switching commutation only when the cascaded module chain outputs 0 voltage or is less than the threshold voltage Uth. Therefore, it is determined that the HDM shutdown process has zero voltage or low voltage characteristics, and the overvoltage spike generated by the shutdown is extremely low. When the shutdown reaches a steady state, the SDM in the bridge arm is controlled to be shut down, thereby achieving high voltage blocking.

[0066] It is worth noting that when the stray inductance follow-on energy is small, the SDM and HDM may not include the above-mentioned energy consumption circuit to further reduce the cost and volume.

[0067] like Figure 1 and Figure 5 As shown in (a)-(d), the cascade module chain in the modular commutation converter is composed of multiple sub-modules SM connected in series, and the cascade module chain is connected in parallel to the DC port of the modular commutation converter. Further, the multiple sub-modules SM connected in series are the same sub-modules or different sub-modules.

[0068] Optionally, the above-mentioned submodule SM is a half-bridge module, a half-bridge module with a power supply in parallel, a half-bridge module with a power supply and a control circuit in parallel, a full-bridge module, a full-bridge module with a power supply in parallel, a full-bridge module with a power supply and a control circuit in parallel, and any one or more combinations thereof. In some embodiments, the submodule SM can also be provided with at least one of a bypass switch and an energy-consuming element on any one or more combinations of the modules described above. Furthermore, when the submodule SM includes a current source type power semiconductor device, a clamping circuit can be configured at the same time according to actual needs to limit the current and time change rate of the power semiconductor switch device when it is turned on, so as to avoid damage to the power semiconductor switch device; if the submodule SM does not include a current source type power semiconductor device, there is no need to configure a clamping circuit.

[0069] The control circuit is used to control the charge and discharge of a battery (which may be a battery pack) or a supercapacitor. Compared with the direct parallel connection, the voltage configuration of the battery or supercapacitor of the present invention is more flexible, and the control circuit has a filtering function, so the service life of the battery or supercapacitor is longer. The control circuit is a prior art of energy storage converter, and this patent will not be repeated.

[0070] Example 2

[0071] This patent discloses the application of a modular commutation converter with high load capacity in Example 1.

[0072] 1. An energy storage converter

[0073] The energy storage converter comprises a three-phase bridge arm, each phase of the bridge arm comprises a modular commutation converter in Embodiment 1 and a plurality of energy storage modules, the plurality of energy storage modules correspond to the submodules SM of the cascade module chain in the modular commutation converter one by one and are connected in parallel. Further, the AC port of each modular commutation converter can be configured with a filter, such as Figure 7 shown.

[0074] Exemplarily, the energy storage module may be an energy storage battery.

[0075] 2. A static VAR compensator

[0076] Based on the modular commutated converter in Example 1, a plurality of the modular commutated converters are star-connected to form a multi-phase converter, and the multi-phase converter can be used as a static VAR compensator.

[0077] For example, Fig.10As shown, the static VAR compensator includes a three-phase bridge arm, each phase of the bridge arm includes a modular commutated converter, wherein the modular commutated converter is the modular commutated converter in embodiment 1. Furthermore, the AC port of the modular commutated converter can be configured with a filter.

[0078] 3. Based on the modular commutated converter in Example 1, a plurality of the modular commutated converters can be cascaded to form a multi-phase converter. Furthermore, a filter can be provided at the DC port and / or AC port of the multi-phase converter.

[0079] Exemplarily, the multi-phase converter may be connected to a multi-phase AC device via a converter transformer.

[0080] Optional, such as Figure 6 The three-phase cascaded modular commutated converter shown in the figure is composed of three groups of structures cascaded to form a three-phase cascaded commutated converter. Exemplarily, the AC port of the three-phase cascaded commutated converter is connected to the three-phase AC grid through a converter transformer, and the DC port of the cascaded module chain side is connected to the DC grid.

[0081] Finally, the connection method of multiple modular commutation converters in this patent is not limited to the above method, and can also be other connection methods, for example, it can also be a delta connection. In addition, the high current shutdown commutation bridge in this patent can also be used to form other devices.

[0082] Example 3

[0083] for Figure 6 In the three-phase cascade modular commutation converter structure shown in the figure, when an unbalanced fault occurs in the power grid, the three-phase power is seriously unbalanced, resulting in inconsistent module voltages of the three-phase sub-modules SM.

[0084] To this end, the present invention also discloses a three-phase cascade modular commutation converter. Figure 8 As shown, the three-phase cascaded modular commutated converter includes three cascaded modular commutated converters in Example 1, a converter transformer with an auxiliary delta-connected winding and an auxiliary switch K; wherein, the converter transformer with an auxiliary delta-connected winding is arranged at the AC port of the three-phase cascaded modular commutated converter; the auxiliary windings of the converter transformer with an auxiliary delta-connected winding are W1, W2 and W3, and the auxiliary windings W1, W2 and W3 are delta-connected; the auxiliary switch K is located on the connecting line between any two of the windings W1, W2 and W3.

[0085] When an unbalanced fault occurs in the power grid, the auxiliary switch K is closed, and the delta-connected windings W1, W2 and W3 provide a zero-sequence current path, thereby achieving three-phase series voltage balancing. The specific method is as follows (eg Fig. 9shown):

[0086] Assume that the three-phase positive-sequence voltages at the AC port of the three-phase high-current shutdown commutation bridge are Ua, Ub and Uc. By controlling the three-phase cascade module chain and the high-current shutdown commutation bridge, the zero-sequence voltage U0 is superimposed on the output voltage of the AC port of the three-phase high-current shutdown commutation bridge. Due to the existence of the converter transformer, there is a leakage reactance between the converter transformer and the three-phase high-current shutdown commutation bridge (it can also be an additional series reactance or the leakage reactance of the converter transformer). The zero-sequence voltage U0 is added between the above-mentioned reactances, thereby generating a zero-sequence current I0 in the auxiliary winding. By controlling the size of the zero-sequence current I0 and the phase relationship between the zero-sequence current I0 and Ua, Ub, and Uc, the three-phase power can be regulated.

[0087] When the power grid returns to normal, the auxiliary switch K is disconnected to prevent the zero-sequence third harmonic from generating third harmonic current.

[0088] It can be seen that the auxiliary switch K is closed only when an unbalanced fault occurs in the power grid, and the average current of the auxiliary winding and the auxiliary switch K is small. Therefore, it is not necessary to design the converter transformer according to the rated current of the converter transformer, and the cost is low.

[0089] It should be noted that the electrical connection between the above-mentioned units does not necessarily mean the connection between lines. An indirect connection method can be applied to the embodiments of the present invention as long as the purpose of the present invention is achieved.

[0090] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A modular commutation converter with high load capacity, wherein the modular commutation converter is composed of at least one high current cut-off commutation bridge and at least one cascade module chain connected in parallel, characterized in that: The large current shutdown commutating bridge is an H-bridge circuit, including four large current shutdown commutating bridge arms; the large current shutdown commutating bridge arms include at least one single switch device module SDM and at least one high shutdown single switch device module HDM connected in series, and the current shutdown capability of the high shutdown single switch device module HDM is greater than the current at the time when the large current shutdown commutating bridge arm is shut down.

2. The modular commutated converter according to claim 1, characterized in that: In the high current turn-off commutation bridge arm, the high turn-off single switch device module HDM is of at least one type; and / or, The single switch device module SDM is of at least one type.

3. The modular commutated converter according to claim 1, characterized in that: The cascade module chain is composed of a plurality of submodules SM connected in series, and the cascade module chain is connected in parallel to the DC port of the modular commutated converter.

4. The modular commutated converter according to claim 3, characterized in that: The multiple submodules SM connected in series are the same submodule or different submodules.

5. The modular commutated converter according to any one of claims 1 to 4, characterized in that: The single switch device module SDM includes a first auxiliary device group F1, wherein the first auxiliary device group F1 is formed by connecting a first support capacitor C1 and a first static voltage-sharing resistor R1 in parallel and then connecting a first auxiliary diode D1 in series; and / or, The high-off single switch device module HDM includes a second auxiliary device group F2, which is composed of a second supporting capacitor C2 and a second static voltage-sharing resistor R2 connected in parallel and then connected in series with a second auxiliary diode D2.

6. The modular commutated converter according to claim 5, characterized in that: The single switch device module SDM further includes a first energy consumption circuit, and the first energy consumption circuit is connected in parallel to both ends of the first support capacitor C1; The high-off single switch device module HDM further includes a second energy consumption circuit, which is connected in parallel to both ends of the second supporting capacitor C2.

7. The modular commutated converter according to claim 6, characterized in that: The second energy consumption circuit is connected in series with the fuse.

8. An application of a modular commutated converter according to any one of claims 1 to 7, characterized in that: include, A plurality of said modular commutation converters are cascaded to form a multi-phase converter; and / or, An energy storage module is arranged at a DC port on the cascade module chain side in the modular commutation converter, and three modular commutation converters with energy storage modules arranged at the DC ports are star-connected or delta-connected to form an energy storage converter; and / or, A plurality of the modular commutation converters are star-connected to form a multi-phase converter.

9. A three-phase cascaded modular commutation converter, characterized in that: The three-phase cascade modular commutation converter comprises: A converter transformer having an auxiliary delta-connected winding, an auxiliary switch K and three cascaded modular commutated converters according to any one of claims 1 to 7; The converter transformer with auxiliary delta-connected winding is arranged at the AC port of the three-phase cascade modular commutation converter; The auxiliary windings of the converter transformer with auxiliary delta-connected windings are W1, W2 and W3, and the auxiliary windings W1, W2 and W3 are delta-connected; The auxiliary switch K is located on a connection line between any two of the auxiliary windings W1 , W2 and W3 .

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