Modular multi-level converter and control method thereof, storage medium and electronic device

Abstract

The present invention discloses a modular multi-level converter and a control method thereof, a storage medium and an electronic device, wherein the modular multi-level converter comprises: a multi-phase AC voltage input terminal located at the power frequency side, a plurality of level conversion control units and a multi-phase AC voltage output terminal located at the low frequency side, a plurality of level conversion sub-modules are arranged on each bridge arm branch, a first overvoltage protection device is connected in parallel to the output terminal of each level conversion sub-module, the input terminal and the output terminal of each bridge arm branch are connected through at least one second overvoltage protection device, and a voltage regulating controllable device is also connected in parallel to the output terminal of each level conversion sub-module. The present invention can realize that in the case where the first overvoltage protection device and the second overvoltage protection device perform overvoltage protection improperly, based on the voltage regulating controllable device, it can ultimately ensure that the entire modular multi-level converter is still in a safe state when an overvoltage fault occurs.

Description

Technical Field

[0001] The present invention relates to the technical field of low-frequency power transmission, and in particular to a modular multi-level converter and a control method thereof, a storage medium and an electronic device. Background Art

[0002] With the rapid development of power electronics technology, modular multilevel converters (MMC) are increasingly used in flexible AC low-frequency power transmission. MMC is a new type of voltage conversion circuit that forms a topological structure in the form of multiple sub-modules cascaded.

[0003] In the prior art, when a short circuit fault occurs in the flexible AC low-frequency power transmission system, generally only one overvoltage protection switch is separately connected in parallel at the output end of the submodule of each bridge arm of the MMC, thereby avoiding the overvoltage phenomenon caused by the short circuit fault in the flexible AC low-frequency power transmission system.

[0004] At present, after a fault occurs in the flexible AC low-frequency power transmission system, its transmission frequency decreases, which in turn causes the overvoltage protection switch to slow down, which will cause the MMC to lock in much faster than the overvoltage protection switch. At this time, the fault point of the MMC will continue to be injected with current, which will cause the internal nodes of the flexible AC low-frequency power transmission system to still have high overvoltages, eventually leading to the collapse of the flexible AC low-frequency power transmission system. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defect in the prior art that when an overvoltage protection switch is used for overvoltage protection, a high overvoltage phenomenon still exists at each internal node of the flexible AC low-frequency power transmission system, which eventually leads to the collapse of the flexible AC low-frequency power transmission system, thereby providing a modular multi-level converter and its control method, device and electronic equipment.

[0006] According to a first aspect, an embodiment of the present invention provides a modular multi-level converter, comprising: a multi-phase AC voltage input terminal located on the industrial frequency side, multiple groups of level conversion control units and a multi-phase AC voltage output terminal located on the low-frequency side, wherein each group of level conversion control units comprises: multiple bridge arm branches, each bridge arm branch is connected to each phase AC voltage input terminal through a freewheeling device, the output end of each group of level conversion control units is connected to each phase AC voltage output terminal, multiple level conversion sub-modules are arranged on each bridge arm branch, a first overvoltage protection device is connected in parallel to the output end of each level conversion sub-module, the input end and the output end of each bridge arm branch are connected through at least one second overvoltage protection device, and the output end of each level conversion sub-module is also connected in parallel to a voltage regulating controllable device.

[0007] In one implementation, the voltage-regulating controllable device includes: a bidirectional thyristor.

[0008] In one implementation, each level conversion submodule is a fully controlled H-bridge structure.

[0009] In one embodiment, the fully controlled H-bridge includes: two groups of power electronic device bridge arms and a DC capacitor, the two groups of power electronic device bridge arms are connected in parallel, each of the power electronic device bridge arms includes two power electronic devices connected in series, and the DC capacitor is connected in parallel with the two groups of power electronic device bridge arms.

[0010] In one implementation, the freewheeling device is a DC inductor, the first overvoltage protection device is a switch protection device, and the second overvoltage protection device is a lightning arrester.

[0011] According to a second aspect, an embodiment of the present invention provides a modular multi-level conversion control method, which is used for the modular multi-level converter described in the first aspect or any embodiment of the first aspect, comprising:

[0012] Acquire the current input voltage of each bridge arm branch input end of the multiple groups of level conversion control units and the current output voltage of the output ends of multiple level conversion submodules on each bridge arm branch;

[0013] Determining whether the current input voltage is greater than a first preset safety voltage;

[0014] If the current input voltage is greater than the first preset safety voltage, controlling the second overvoltage protection device to perform an overvoltage protection action;

[0015] Determining whether the current output voltage is greater than a second preset safety voltage;

[0016] If the current output voltage is greater than the second preset safety voltage, the voltage regulating controllable device connected in parallel to the output end of each level conversion submodule is controlled to perform an overvoltage protection action.

[0017] In one embodiment, before the step of obtaining the current input voltage of each bridge arm branch input end of the multiple groups of level conversion control units and the current output voltage of the output ends of the multiple level conversion submodules on each bridge arm branch, the step further includes:

[0018] If the multiple groups of level conversion control units detect that an overvoltage fault occurs in multiple level conversion submodules on each bridge arm branch, the first overvoltage protection device is controlled to perform an overvoltage protection action.

[0019] In one embodiment, the modular multi-level conversion control method further includes:

[0020] If the current input voltage is less than or equal to the first preset safety voltage, each bridge arm branch is controlled to be in a normal working state.

[0021] In one embodiment, the modular multi-level conversion control method further includes:

[0022] If the current output voltage is less than or equal to the second preset safety voltage, the voltage regulating controllable devices connected in parallel to the output end of each level conversion submodule are controlled to be in a normal working state.

[0023] In one embodiment, in the modular multi-level conversion control method, the first preset safety voltage is less than or equal to the sum of preset voltages of multiple level conversion sub-modules arranged on each bridge arm branch.

[0024] According to a third aspect, an embodiment of the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores computer instructions, and the computer instructions are used to enable the computer to execute the modular multi-level conversion control method described in the second aspect or any embodiment of the second aspect.

[0025] According to the fourth aspect, an embodiment of the present invention provides an electronic device, comprising: the modular multilevel converter, memory and processor described in the first aspect or any embodiment of the first aspect, the modular multilevel converter, the memory and the processor are communicatively connected with each other, the memory stores computer instructions, and the processor executes the modular multilevel conversion control method described in the second aspect or any embodiment of the second aspect by executing the computer instructions.

[0026] The technical solution of the present invention has the following advantages:

[0027] The present invention provides a modular multi-level converter, a control method thereof, a storage medium and an electronic device, wherein the modular multi-level converter comprises: a multi-phase AC voltage input terminal located at the power frequency side, a plurality of level conversion control units and a multi-phase AC voltage output terminal located at the low frequency side, wherein each level conversion control unit comprises: a plurality of bridge arm branches, each bridge arm branch is connected to each phase AC voltage input terminal through a freewheeling device, the output terminal of each level conversion control unit is connected to each phase AC voltage output terminal, a plurality of level conversion submodules are arranged on each bridge arm branch, a first overvoltage protection device is connected in parallel to the output terminal of each level conversion submodule, the input terminal and the output terminal of each bridge arm branch are connected through at least one second overvoltage protection device, and the output terminal of each level conversion submodule is also connected in parallel to a voltage regulating controllable device. The present invention can ultimately ensure that when an overvoltage fault occurs in the entire modular multi-level converter, it is still in a safe state, and all level conversion submodules in the entire modular multi-level converter can be quickly cut off. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 A schematic diagram of the structure of a modular multi-level converter according to an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the structure of the level conversion submodule in an embodiment of the present invention;

[0031] Figure 3 Flow chart of a modular multi-level conversion control method according to an embodiment of the present invention;

[0032] Figure 4 Schematic diagram of the hardware structure of the electronic device in the embodiment of the present invention.

[0033] Reference numerals:

[0034] 11-level conversion control unit; 12-freewheeling device; 13-first overvoltage protection device;

[0035] 14-a second overvoltage protection device; 15-a voltage regulating controllable device; 16-a DC capacitor;

[0036] 17-power electronic devices; 111-multiple level conversion sub-modules. DETAILED DESCRIPTION

[0037] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only 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] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0039] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, it can also be the internal connection of two components, it can be a wireless connection, or it can be a wired connection. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0040] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0041] The embodiment of the present invention discloses a modular multilevel converter, whose English name is Modular Multilevel Converters (MMC for short). MMC is usually used in application scenarios of flexible low-frequency AC power transmission systems or industrial production equipment. Since low-frequency power transmission is usually achieved in the form of high voltage in a flexible low-frequency AC power transmission system, overvoltage short-circuit faults are inevitable in the flexible low-frequency AC power transmission system. In order to avoid system collapse or device damage caused by overvoltage in a flexible low-frequency AC power transmission system, that is, to ensure that the flexible low-frequency AC power transmission system can be in a safe and stable operating state, an embodiment of the present invention discloses a modular multilevel converter.

[0042] In one embodiment, Figure 1 As shown, the modular multi-level converter disclosed in the embodiment of the present invention includes: multi-phase AC voltage input terminals A, B, and C located on the power frequency side. Multiple groups of level conversion control units 11 and multi-phase AC voltage output terminals D, E, and F located on the low-frequency side, wherein each group of level conversion control units 11 includes: multiple bridge arm branches, each bridge arm branch is connected to each phase AC voltage input terminal through a freewheeling device 12, the output terminal of each group of level conversion control units 11 is connected to each phase AC voltage output terminal, and multiple level conversion sub-modules 111 are arranged on each bridge arm branch. The first overvoltage protection device 13 is connected in parallel to the output terminal of each level conversion sub-module 111, and the input terminal and the output terminal of each bridge arm branch are connected through a second overvoltage protection device 14. The output terminal of each level conversion sub-module 111 is also connected in parallel to a voltage regulating controllable device 15. Figure 1 In the embodiment, the number of the second overvoltage protection device 14 is one. In another alternative implementation, the input end and the output end of each bridge arm branch may be connected to each other via a plurality of second overvoltage protection devices 14 connected in series.

[0043] exist Figure 1 In the modular multi-level converter disclosed in the embodiment of the present invention, for example, the power frequency side is the transmission side using 50 Hz as the power grid operating frequency. Figure 1 In the embodiment, the multi-phase AC voltage input terminal can be a three-phase AC voltage input terminal A, B, and C. For example, the three-phase AC input voltages are Vsu, Vsv, and Vsw, respectively. The three-phase AC input voltage is a three-phase voltage on the power frequency side, and the currents flowing through the three-phase AC transmission line are iu, iv, and iw, respectively. Figure 1 In the embodiment, multiple groups of level conversion control units 11 form a modular structure, each group of level conversion control units 11 includes three bridge arm branches a, b, c, and each bridge arm branch a, b, c is connected to the three-phase AC voltage input terminals A, B, and C via a freewheeling device 12. For example, the freewheeling device 12 may be a DC inductor, but is not limited thereto. Figure 1 In the embodiment, the multi-phase AC voltage output terminal can be a three-phase AC voltage output terminal D, E, and F. For example, the three-phase AC voltages are VIa, VIb, and VIc, respectively, and the three-phase AC output voltage is a low-frequency side three-phase voltage. The frequency range of the low-frequency side is preferably 2Hz-48Hz. Of course, other frequencies within the conventional low-frequency frequency range are also feasible. Figure 1 In each bridge arm branch, a plurality of level conversion submodules 111 are provided. For example, the number of the plurality of level conversion submodules 111 may be N, or the number of cascaded level conversion submodules 111 may be increased or decreased to be applied to different voltage levels according to grid requirements. Figure 1 In the embodiment, the three-phase input voltage on the power frequency side and the three-phase output voltage on the low frequency side are connected in pairs through 9 bridge arm branches, each bridge arm branch is composed of N level conversion submodules 111 and a freewheeling device 12 connected in series, and each level conversion submodule 111 is composed of a full-bridge inverter circuit. The modular multi-level converter provided by the embodiment of the present invention can realize output of any amplitude, frequency, and phase.

[0044] The modular multi-level converter disclosed in the embodiment of the present invention has Figure 1 In the embodiment, the first overvoltage protection device 13 is connected in parallel to the output end of each level conversion submodule 111. For example, the first overvoltage protection device 13 may be a switch protection device, but is not limited to this device. The function of the switch protection device is that when a short circuit occurs in multiple level conversion submodules 111 arranged on each bridge arm branch, the switch protection device performs a bypass switch action to bypass the current level conversion submodule 111. Therefore, the first overvoltage protection device 13 can play a role in pre-protecting the entire modular multilevel converter to operate safely.

[0045] exist Figure 1In the modular multi-level converter disclosed in the present invention, the input end and the output end of each bridge arm branch are connected through a second overvoltage protection device 14. For example, the second overvoltage protection device 14 can be a lightning arrester, but it is not limited to this device. Figure 1 In the example, multiple lightning arresters can be connected in series between the input and output ends of each bridge arm branch. Figure 1 In the figure, the lightning arresters are Aua, Ava, Awa, Aub, Avb, Awb, Auc, Avc, and Awc. The function of the lightning arrester is to control the lightning arrester to perform overvoltage protection when the current input voltage of each bridge arm branch is greater than the first preset safety voltage. The lightning arrester absorbs overvoltage energy exceeding the first preset safety voltage to protect the devices on each bridge arm branch from being damaged due to excessive voltage. Among them, the first preset safety voltage is less than or equal to the sum of the preset voltages of the multiple level conversion submodules 111 set on each bridge arm branch. Therefore, the second overvoltage protection device 14 plays a role in further ensuring that the entire modular multilevel converter can operate safely, and the safety of the entire modular multilevel converter can be further improved by the lightning arrester.

[0046] like Figure 1 or Figure 2 As shown, in the modular multi-level converter disclosed in the present invention, the output end of each level conversion submodule is also connected in parallel to a voltage regulating controllable device 15, for example: the voltage regulating controllable device 15 can be a bidirectional thyristor, but is not limited to this device. Figure 2In the embodiment, two output ends of the level conversion submodule 111 on each bridge arm branch are connected in parallel to a bidirectional thyristor. When the current output voltage of the multiple level conversion submodules 111 on each bridge arm branch is greater than the second preset safety voltage, the bidirectional thyristor is controlled to perform an overvoltage protection action, thereby ensuring that each level conversion submodule 111 is not damaged due to excessive voltage. Therefore, the voltage regulating controllable device 15 can realize the final overvoltage protection when the first overvoltage protection device 13 and the second overvoltage protection device 14 cannot completely ensure that the entire modular multilevel converter is in a safe state due to their own structural characteristics. After the flexible AC low-frequency power transmission system fails, the switching action speed of the first overvoltage protection device 13 and the second overvoltage protection device 14 in the modular multilevel converter is reduced, and there is no time to quickly perform the overvoltage protection action, in order to prevent the locking action time of the entire modular multilevel converter from being faster than the switching action speed of the first overvoltage protection device 13 and the second overvoltage protection device 14, and then a failure occurs, which eventually leads to the collapse of the flexible AC low-frequency power transmission system. Therefore, the voltage regulating controllable device 15 can control the bidirectional thyristor to perform overvoltage protection when the current output voltage of multiple level conversion sub-modules 111 on each bridge arm branch is greater than the second preset safety voltage, thereby ensuring that each level conversion sub-module 111 is not damaged due to excessive voltage.

[0047] In one implementation manner, the modular multi-level converter disclosed in the embodiment of the present invention is Figure 2 In the embodiment, each level conversion submodule is a fully controlled H-bridge structure. The fully controlled H-bridge structure includes: two groups of power electronic device bridge arms and a DC capacitor 16, the two groups of power electronic device bridge arms are connected in parallel, each power electronic device bridge arm includes two power electronic devices connected in series, and the DC capacitor 16 is connected in parallel with the two groups of power electronic device bridge arms. Among them, the two power electronic devices are two IGBB devices respectively.

[0048] The modular multi-level converter disclosed in the present invention has a specific working principle as follows: when a short-circuit overcurrent phenomenon occurs at the fault point of the modular multi-level converter, the current is continued through the freewheeling device 12, and then flows through multiple level conversion sub-modules 111 on each bridge arm branch. At this time, each group of level conversion control units 11 first determines whether the current input voltage on each bridge arm branch is greater than the first preset safety voltage. If the current input voltage on each bridge arm branch is less than or equal to the first preset safety voltage, then the DC capacitor 16 connected in parallel to each level conversion sub-module 111 is charged based on the current, so that when the current output voltage of each level conversion sub-module 111 is greater than the second preset safety voltage, after a preset time, the first overvoltage protection device 13 quickly performs a switching action, and the conversion sub-module 111 can be bypassed, and then the voltage regulating controllable device 15 connected in parallel to each level conversion sub-module 111 is triggered to perform an overvoltage protection action, so that the entire modular multi-level converter is in a safe state, that is, all level conversion sub-modules 111 of the entire modular multi-level converter are in a disconnected state. In the above description, if the current input voltage on each bridge arm branch is greater than the first preset safety voltage, all level conversion submodules 111 of the entire modular multi-level converter are directly and quickly cut off.

[0049] In the modular multilevel converter disclosed in the embodiment of the present invention, the input end and the output end of each bridge arm branch are connected through the second overvoltage protection device, and the output end of each level conversion submodule is also connected in parallel with the voltage regulating controllable device to work together, which can ultimately ensure that when an overvoltage fault occurs in the entire modular multilevel converter, it is still in a safe state, and all level conversion submodules in the entire modular multilevel converter can be quickly cut off.

[0050] Based on the same concept, the embodiment of the present invention also discloses a modular multi-level conversion control method, which is used for the modular multi-level converter in the above embodiment. Figure 3 As shown, the following steps are included:

[0051] Step S31: obtaining the current input voltage of each bridge arm branch input end of multiple groups of level conversion control units and the current output voltage of multiple level conversion submodule output ends on each bridge arm branch. Here, it means obtaining the current input voltage of each bridge arm branch input end of multiple groups of level conversion control units at the same time.

[0052] For example: Figure 1 For bridge arm branch a, the current input voltage of the input end of bridge arm branch a is 166 V, and the current input voltage of the input end of bridge arm branch b is 205 V. For example: the current output voltage of the output end of multiple level conversion submodules is 208 V. The current input voltage and the current output voltage can be collected by the voltage collection module.

[0053] Step S32: determining whether the current input voltage is greater than a first preset safety voltage.

[0054] The first preset safety voltage mentioned above is less than or equal to the sum of the preset voltages of the multiple level conversion submodules set on each bridge arm branch. The first preset safety voltage is the maximum reference safety voltage to ensure that the current input voltage at the input end of each bridge arm branch can be within the safety range voltage. For example: the first preset safety voltage is 200v, and the current input voltage 166v at the input end of the above-mentioned bridge arm branch a is compared with the first preset safety voltage of 200v, so that the judgment result is that the current input voltage is less than the first preset safety voltage. For example: the current input voltage 166v at the input end of the bridge arm branch a is compared with the first preset safety voltage of 200v, so that the judgment result is that the current input voltage is less than the first preset safety voltage. For example: the current input voltage 208v at the input end of the bridge arm branch b is compared with the first preset safety voltage of 200v, so that the judgment result is that the current input voltage is greater than the first preset safety voltage.

[0055] Step S33: If the current input voltage is greater than the first preset safety voltage, control the second overvoltage protection device to perform an overvoltage protection action.

[0056] For example: in the above example, the current input voltage 208v at the input end of the bridge arm branch b is compared with the first preset safety voltage of 200v, so that the judgment result is that the current input voltage is greater than the first preset safety voltage. At this time, the first overvoltage protection device (lightning arrester) is controlled to perform the overvoltage protection action, thereby cutting off all the level conversion sub-modules in the modular multilevel converter in the above embodiment, which can ensure that the modular multilevel converter is in a safe state, and further ensure that the flexible low-frequency AC power transmission system where the modular multilevel converter is located can operate safely.

[0057] Step S34: determining whether the current output voltage is greater than the second preset safety voltage.

[0058] The second preset safety voltage mentioned above is the maximum reference safety voltage to ensure that the current output voltage of the multiple level conversion submodules set on each bridge arm branch can be within the safety range voltage. For example: the second preset safety voltage is 220v, and the current output voltage of the three-phase AC voltage output terminals D, E, and F mentioned above is compared with the second preset safety voltage to obtain a judgment result. For example: the current output voltage of the three-phase AC voltage output terminal D is 200v, the current output voltage of the three-phase AC voltage output terminal E is 228v, and the current output voltage of the three-phase AC voltage output terminal E is 232v. It can be seen that 200v<220v, 228v>220v, 232v>220v. Therefore, by comparison, it can be seen that the current output voltage of the three-phase AC voltage output terminal D is less than the second preset safety voltage, the current output voltage of the three-phase AC voltage output terminal E is greater than the second preset safety voltage, and the current output voltage of the three-phase AC voltage output terminal F is greater than the second preset safety voltage.

[0059] Step S35: if the current output voltage is greater than the second preset safety voltage, the voltage regulating controllable device connected in parallel to the output end of each level conversion submodule is controlled to perform an overvoltage protection action.

[0060] It can be seen from the above example that because 228v>220v, 232v>220v, the current output voltage of the three-phase AC voltage output terminal E is greater than the second preset safety voltage, and the current output voltage of the three-phase AC voltage output terminal F is greater than the second preset safety voltage. Therefore, the current output voltages of the three-phase AC voltage output terminal E and the three-phase AC voltage output terminal F have an overvoltage phenomenon. At this time, the voltage regulating controllable device connected in parallel to each level conversion sub-module is controlled, that is, in Figure 2 In the process, the bidirectional thyristor is controlled to perform overvoltage protection action.

[0061] In one implementation manner, the modular multi-level conversion control method disclosed in the embodiment of the present invention, before step S31, further includes:

[0062] Step S30: If the multiple groups of level conversion control units detect that an overvoltage fault occurs in multiple level conversion sub-modules on each bridge arm branch, the first overvoltage protection device is controlled to perform an overvoltage protection action.

[0063] For example, when a fault occurs in the flexible AC low-frequency power transmission system where the modular multilevel converter is located, the first overvoltage protection device (switch protection device) is controlled to perform an overvoltage protection action, that is, the faulty level conversion submodule is quickly bypassed, and at the same time, all level conversion submodules are quickly disconnected. At this time, the modular multilevel converter is made to quickly perform a locking action, that is, the modular multilevel converter is in a disconnected state, and the drive signals of all level conversion submodules are blocked, that is, the power output is stopped. Therefore, by controlling the first overvoltage protection device to perform an overvoltage protection action, it can be quickly ensured that the flexible AC low-frequency power transmission system where the modular multilevel converter is located is in a safe state.

[0064] Therefore, when the current output voltage of the three-phase AC voltage output terminal is greater than the second preset safety voltage, the second overvoltage protection device can be controlled to perform a protection action to prevent the current output voltage of the three-phase AC voltage output terminal from still presenting an overvoltage phenomenon. It can be seen that the modular multi-level conversion control method disclosed in the embodiment of the present invention can ultimately ensure that when an overvoltage fault occurs in the entire modular multi-level converter, it is still in a safe state, and all level conversion sub-modules in the entire modular multi-level converter can be quickly cut off.

[0065] In one implementation manner, the modular multi-level conversion control method in the embodiment of the present invention comprises: Figure 3 Also included:

[0066] Step S36: If the current input voltage is less than or equal to the first preset safety voltage, each bridge arm branch is controlled to be in a normal working state. Here, it means that when the current input voltage at the input end of each bridge arm branch of the multiple groups of level conversion control units is less than or equal to the first preset safety voltage, each bridge arm branch is controlled to be in a normal working state. Once the current input voltage at the input end of any bridge arm branch is greater than the first preset safety voltage, it means that the entire modular multi-level converter is in an unsafe state.

[0067] For example: From the above example, it can be seen that the current input voltage of the input end of the bridge arm branch a is 166v, and the first preset safety voltage is 200v, 166v<200v. It can be seen that the current input voltage of the input end of the bridge arm branch a is less than the first preset safety voltage. It can be known that the current input voltage of the input end of the bridge arm branch a is within the safety voltage range.

[0068] In one implementation manner, the modular multi-level conversion control method in the embodiment of the present invention further includes:

[0069] Step S37: If the current output voltage is less than or equal to the second preset safety voltage, the voltage regulating controllable device connected in parallel to the output end of each level conversion submodule is controlled to be in a normal working state. Here, it means that when the current output voltage of each phase AC voltage output end of multiple groups of level conversion control units is less than or equal to the second preset safety voltage, the voltage regulating controllable device connected in parallel to the output end of each level conversion submodule is controlled to be in a normal working state. Once the current output voltage of any phase AC voltage output end is greater than the second preset safety voltage, it means that the entire modular multi-level converter is in an unsafe state.

[0070] For example, as can be seen from the above example, the current output voltage of the three-phase AC voltage output terminal E is 200v, 200v<220v, therefore, the current output voltage of the three-phase AC voltage output terminal E is within the safe voltage range. At this time, if the current output voltages of the remaining AC voltage output terminals are also less than or equal to the second preset safe voltage, it means that the entire modular multi-level converter is in a safe state.

[0071] Based on the same concept, an embodiment of the present invention further provides an electronic device, such as Figure 4 As shown, the electronic device may include a processor 41, a memory 42 and a modular multi-level converter 43, wherein the processor 41, the memory 42 and the modular multi-level converter 43 may be connected via a bus or other means. Figure 4 The example of connecting through bus is taken in the following.

[0072] The processor 41 may be a central processing unit (CPU). The processor 41 may also be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, or a combination of the above chips.

[0073] The memory 42 is a non-transient computer-readable storage medium, which can be used to store non-transient software programs, non-transient computer executable programs and modules, such as program instructions / modules corresponding to the modular multi-level conversion control method in the embodiment of the present invention. The processor 41 executes various functional applications and data processing of the processor by running the non-transient software programs, instructions and modules stored in the memory 42, that is, the modular multi-level conversion control method in the above method embodiment is implemented.

[0074] The memory 42 may include a program storage area and a data storage area, wherein the program storage area may store an operating system, an application required by at least one function; the data storage area may store data created by the processor 41, etc. In addition, the memory 42 may include a high-speed random access memory, and may also include a non-volatile memory, such as at least one disk storage device, a flash memory device, or other non-volatile solid-state storage device. In some embodiments, the memory 42 may optionally include a memory remotely arranged relative to the processor 41, and these remote memories may be connected to the processor 41 via a network. Examples of the above-mentioned network include, but are not limited to, a power grid, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0075] The one or more modules are stored in the memory 42 and when executed by the processor 41, perform the following steps: Figure 3 The modular multi-level conversion control method in the illustrated embodiment.

[0076] For details of the above electronic equipment, please refer to Figures 1 to 3 The corresponding related descriptions and effects in the illustrated embodiments can be understood and will not be repeated here.

[0077] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiments can be implemented by instructing the relevant hardware through a computer program, and the program can be stored in a computer-readable storage medium, and when the program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, the storage medium can be a disk, an optical disk, a read-only memory (ROM), a random access memory (RAM), a flash memory, a hard disk drive (HDD) or a solid-state drive (SSD), etc.; the storage medium can also include a combination of the above-mentioned types of memory.

[0078] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A modular multilevel conversion control method for a modular multilevel converter, the modular multilevel converter comprising: A multi-phase AC voltage input terminal located at the power frequency side, multiple groups of level conversion control units and a multi-phase AC voltage output terminal located at the low frequency side, wherein each group of level conversion control units includes: multiple bridge arm branches, each bridge arm branch is connected to each phase AC voltage input terminal through a freewheeling device, the output terminal of each group of level conversion control units is connected to each phase AC voltage output terminal, multiple level conversion sub-modules are arranged on each bridge arm branch, and a first overvoltage protection device is connected in parallel to the output terminal of each level conversion sub-module, characterized in that the input terminal and the output terminal of each bridge arm branch are connected through at least one second overvoltage protection device, and the The output end of each level conversion submodule is also connected in parallel to a voltage regulating controllable device; the voltage regulating controllable device includes: a bidirectional thyristor; each level conversion submodule is a fully controlled H-bridge structure; the fully controlled H-bridge includes: two groups of power electronic device bridge arms and a DC capacitor, the two groups of power electronic device bridge arms are connected in parallel, each of the power electronic device bridge arms includes two power electronic devices connected in series, and the DC capacitor is connected in parallel to the two groups of power electronic device bridge arms; the freewheeling device is a DC inductor, the first overvoltage protection device is a switch protection device, and the second overvoltage protection device is an arrester; it is characterized in that it includes: Acquire the current input voltage of each bridge arm branch input end of the multiple groups of level conversion control units and the current output voltage of the output ends of multiple level conversion submodules on each bridge arm branch; Determining whether the current input voltage is greater than a first preset safety voltage; If the current input voltage is greater than the first preset safety voltage, controlling the second overvoltage protection device to perform an overvoltage protection action; Determining whether the current output voltage is greater than a second preset safety voltage; If the current output voltage is greater than the second preset safety voltage, controlling the voltage regulating controllable device connected in parallel to the output end of each level conversion submodule to perform an overvoltage protection action; Before the step of obtaining the current input voltage of each bridge arm branch input end of the multiple groups of level conversion control units and the current output voltage of the output ends of the multiple level conversion submodules on each bridge arm branch, the method further includes: If the multiple groups of level conversion control units detect that an overvoltage fault occurs in multiple level conversion submodules on each bridge arm branch, the first overvoltage protection device is controlled to perform an overvoltage protection action.

2. The modular multi-level conversion control method according to claim 1, characterized in that: Also includes: If the current input voltage is less than or equal to the first preset safety voltage, each bridge arm branch is controlled to be in a normal working state.

3. The modular multi-level conversion control method according to claim 1, characterized in that: Also includes: If the current output voltage is less than or equal to the second preset safety voltage, the voltage regulating controllable devices connected in parallel to the output end of each level conversion submodule are controlled to be in a normal working state.

4. The modular multi-level conversion control method according to any one of claims 1 to 3, characterized in that: The first preset safety voltage is less than or equal to the sum of preset voltages of a plurality of level conversion submodules arranged on each bridge arm branch.

5. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer instructions, and the computer instructions are used to enable the computer to execute the modular multi-level conversion control method according to any one of claims 1 to 4.

6. An electronic device, characterized in that: include: The modular multilevel converter, memory and processor according to any one of claims 1 to 4, wherein the modular multilevel converter, the memory and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes the modular multilevel conversion control method according to any one of claims 1 to 4 by executing the computer instructions.

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