A hybrid modular multilevel grid-connected converter based on multi-terminal sharing of intensive redundant modules and its fault handling method

Abstract

This application provides a hybrid modular multilevel grid-connected converter based on multi-terminal sharing of intensive redundant modules, comprising: a three-phase circuit topology; the three-phase circuit topology includes three identical single-phase topologies, each single-phase topology including an upper bridge arm, an upper bridge arm inductor, an upper bridge arm switch, an intermediate module, an AC bridge arm, a lower bridge arm, a lower bridge arm inductor, and a lower bridge arm switch; the intermediate module includes a first switch, a second switch, a third switch, a fourth switch, a fifth switch, and a sixth switch, as well as a DC capacitor. By introducing the intermediate module, this application provides fault tolerance capability in the event of failures in the upper, lower, and AC bridge arm sub-modules. Compared to traditional redundant module configurations, the proposed topology significantly improves the utilization rate of redundant modules and enhances the operational reliability of the multilevel converter.

Description

Technical Field

[0001] This application relates to the field of power system technology, specifically to the field of voltage transformers. Background Technology

[0002] In recent years, Modular Multilevel Converters (MMCs) have been widely used in high-voltage direct current (HVDC) transmission systems due to their advantages such as low output harmonic content, high modularity, and strong scalability. Meanwhile, the application of MMCs in medium-voltage distribution networks has also attracted considerable attention, including in applications such as solid-state transformers, motor drives, unified power flow controllers, and static var compensators (SVCs).

[0003] To further expand the application of MMC in medium-voltage AC / DC distribution networks, some scholars have proposed a hybrid MMC topology with cascaded full bridges (HMMC-CFB), such as... Figure 1 As shown, the external full-bridge submodules of this topology can block and control DC fault current, ensuring that the topology can overcome external faults. However, the MMC is composed of multiple cascaded submodules, and its output function largely depends on each submodule. Once a submodule fails, it will affect the normal operation of the MMC, thereby reducing the reliability of the system. Therefore, a certain number of redundant submodules must be configured so that the damaged submodule can be replaced in the event of a fault, thereby ensuring the safe and stable operation of the system. Therefore, the redundancy configuration method of MMC is particularly critical. The traditional principle of redundancy unit configuration is to independently configure redundant submodules HSM in the upper and lower bridge arms respectively. r For the HMMC-CFB topology, an additional redundant FSM unit needs to be configured in the AC bridge arm. r However, the probability of simultaneous failure of submodules in the upper and lower arms and AC arms of HMMC-CFB is low. In contrast, the redundant submodule blocks configured in conventional topologies can only be activated when a submodule in its own arm fails, and cannot be used as backups when other arm submodules fail. Therefore, the existing configuration principle of independently configuring redundant units for each arm of MMC and HMMC-CFB uses a large number of redundant units with low utilization. Summary of the Invention

[0004] To overcome the aforementioned technical deficiencies, this application provides a hybrid modular multilevel grid-connected converter and fault handling method based on multi-terminal sharing of intensive redundant modules. To achieve the above objective, this application implements it according to the following technical solution:

[0005] In one aspect, this application provides a hybrid modular multilevel grid-connected converter based on multi-terminal sharing of intensive redundant modules, including: a three-phase circuit topology;

[0006] The three-phase circuit topology includes three identical single-phase topologies, each of which includes an upper bridge arm, an upper bridge arm inductor, an upper bridge arm switch, an intermediate module, an AC bridge arm, a lower bridge arm, a lower bridge arm inductor, and a lower bridge arm switch.

[0007] The AC bridge arm includes multiple full-bridge sub-modules, which are connected in series.

[0008] Both the upper bridge arm switch and the lower bridge arm switch are composed of two thyristors connected in reverse parallel.

[0009] Both the upper bridge arm and the lower bridge arm include multiple half-bridge sub-modules, which are connected in series. One end of the last half-bridge sub-module in the upper bridge arm is connected to one end of the upper bridge arm inductor, and one end of the first half-bridge module in the lower bridge arm is connected to one end of the lower bridge arm inductor.

[0010] The intermediate module includes a first switch, a second switch, a third switch, a fourth switch, a fifth switch, and a sixth switch, as well as a DC capacitor. Node A is formed by connecting the emitter node of the first switch, the collector node of the second switch, one end of the upper bridge arm switch, and the other end of the upper bridge arm inductor. Node B is formed by connecting the emitter node of the third switch, the collector node of the fourth switch, one end of the lower bridge arm switch, and the other end of the lower bridge arm inductor. Node C is formed by connecting the emitter node of the fifth switch, the collector node of the sixth switch, one end of the AC bridge arm, the other end of the upper bridge arm switch, and the other end of the lower bridge arm switch. The collector nodes of the first, third, and fifth switches are connected to the positive terminal of the DC capacitor, and the emitter nodes of the second, fourth, and sixth switches are connected to the negative terminal of the DC capacitor.

[0011] Secondly, this application provides a fault handling method for a multilevel converter. For a hybrid modular multilevel grid-connected converter based on multi-terminal sharing of intensive redundant modules as described in the first aspect, the fault handling method includes a first fault handling strategy, a second fault handling strategy, and a third fault handling strategy, wherein the first fault handling strategy includes:

[0012] When the upper bridge arm submodule fails, the faulty module is disconnected.

[0013] Turn off the upper and lower bridge arm switches;

[0014] The intermediate module is put into operation as a half-bridge sub-module of the upper bridge arm;

[0015] The third and fifth switching transistors remain normally closed.

[0016] The fourth and sixth switching transistors remain normally open.

[0017] The operating modes of the first and second switching transistors are the same as those of a traditional half-bridge submodule.

[0018] Optionally, the second fault handling strategy includes:

[0019] When a fault occurs in the lower bridge arm submodule, the faulty module is disconnected.

[0020] Close the upper and lower bridge arm switches;

[0021] The intermediate module is put into operation as a half-bridge sub-module of the lower bridge arm;

[0022] The first and fifth switching transistors remain normally open.

[0023] Optionally, the third fault handling strategy includes:

[0024] When a fault occurs in the AC bridge arm full-bridge submodule, the faulty module is disconnected.

[0025] Close the upper and lower bridge arm switches;

[0026] The intermediate module is put into operation as a full-bridge submodule of the AC bridge arm.

[0027] This application has the following beneficial effects:

[0028] The multi-port redundant modules in the multilevel converter topology proposed in this application have fault tolerance capabilities in the event of failures in the upper and lower bridge arms and AC bridge arm submodules. Compared with traditional redundant module configurations, the proposed topology significantly improves the utilization rate of redundant modules and enhances the operational reliability of the multilevel converter.

[0029] In addition to the purposes, features, and advantages described above, this application has other purposes, features, and advantages. The application will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0030] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0031] Figure 1 This is a schematic diagram of a hybrid MMC topology with cascaded full-bridge modules in existing technology.

[0032] Figure 2This is a schematic diagram of a hybrid modular multilevel grid-connected converter topology based on multi-terminal sharing of intensive redundant modules provided in an embodiment of this application;

[0033] Figure 3 This is an equivalent circuit diagram of the multilevel grid-connected converter provided in the embodiments of this application during normal operation;

[0034] Figure 4 This is an equivalent circuit diagram of the multilevel grid-connected converter provided in this application embodiment when the first fault handling strategy is adopted;

[0035] Figure 5 This is an equivalent circuit diagram of the multilevel grid-connected converter provided in this application embodiment when the second fault handling strategy is adopted;

[0036] Figure 6 This is the equivalent circuit diagram of the multilevel grid-connected converter provided in the embodiments of this application when the third fault handling strategy is adopted. Detailed Implementation

[0037] The embodiments of this application are described in detail below with reference to the accompanying drawings, but this application can be implemented in many different ways as defined and covered by the claims.

[0038] In order to solve the problems raised in the background art, such as Figure 2 As shown, this application provides a hybrid modular multilevel grid-connected converter (HMMC-MRM) based on multi-port redundancy module sharing, including: a three-phase circuit topology;

[0039] A three-phase circuit topology, comprising three identical single-phase topologies, each single-phase topology including an upper bridge arm and an upper bridge arm inductor. L 1. Upper bridge arm switch SW 1. Intermediate module, AC bridge arm, lower bridge arm, lower bridge arm inductor L 2. Lower bridge arm switch SW 2;

[0040] The AC bridge arm contains multiple full-bridge submodules (FSMs), which are connected in series.

[0041] upper bridge arm switch SW 1 and lower bridge arm switch SW 2. Both are composed of two thyristors connected in reverse parallel;

[0042] Both the upper and lower bridge arms contain multiple half-bridge submodules (HSMs), which are connected in series. One end of the last half-bridge module in the upper bridge arm is connected to the upper bridge arm inductor. LOne end of 1, one end of the first half-bridge submodule in the lower bridge arm is connected to the lower bridge arm inductor. L 2 at one end;

[0043] The intermediate module includes a first switching transistor. G 1. Second switching transistor G 2. Third switching transistor G 3. Fourth switching transistor G 4. Fifth switch G 5 transistors and the sixth switching transistor G 6, and DC capacitor C M First switching transistor G 1's emitter node, second switching transistor G The collector node of 2, and the upper bridge arm switch SW One end of 1 and the upper bridge arm inductor L The other end of 1 forms node A, the third switch. G 3 emitter node, fourth switch G 4 collector node, lower arm switch SW 2, one end of the lower bridge arm inductor L The other end of 2 is connected to form node B; the fifth switch. G 5's emitter node, sixth switch G The collector node of 6, one end of the AC bridge arm, and the upper bridge arm switch. SW The other end of 1, and the lower bridge arm switch SW The other end of 2 forms a node C; the first switch transistor G 1. Third switching transistor G 3 and the fifth switching transistor G The collector node of 5 is connected to the DC capacitor. C M The positive terminal, the second switching transistor G 2. Fourth switching transistor G 4 and the sixth switch G The emitter node of 6 is connected to the DC capacitor. C M The negative end.

[0044] Due to the structure of the full-bridge submodule and half-bridge submodule in this application, it has already been... Figure 1 As shown, the full-bridge submodule includes four switching transistors and submodule capacitors. C F The seventh switch S 1. Eighth switching transistor S 2. Ninth switch transistor S 3. Tenth switch transistor S 4. Seventh switch transistor S The emitter node of 1 and the eighth switchS The collector node of transistor 2 is connected, and the eighth switching transistor is connected. S The emitter of 2 and the tenth switch S The emitter node of 4 is connected to the submodule capacitor. C F The negative terminal, the seventh switch transistor S The collector of 1, the ninth switching transistor S The collector of 3 is connected to the submodule capacitor. C F The positive terminal of the ninth switch is connected to the emitter of the tenth switch.

[0045] The half-bridge submodule includes the eleventh switching transistor. D 1 and 12th switch D 2. Submodule capacitors C H Eleventh switch transistor D The emitter of transistor 1 and the twelfth switch. D The collector of transistor 2 is connected to the eleventh switching transistor. D 1 collector and submodule capacitor C H The positive terminal is connected to the twelfth switch. D Emitter and submodule capacitors of 2 C H Connect the negative ends.

[0046] It should be noted that the full-bridge submodule and half-bridge submodule, as well as the first switching transistor, in this application... G Switches 1 to 6 G All six are constructed using silicon-based insulated gate bipolar transistors (IGBTs).

[0047] The intermediate unit provided in this application can be used as a redundant backup module for the upper and lower bridge arms and the AC bridge arm, respectively. Compared with configuring a redundant unit for each phase, the configuration cost of the redundant unit can be greatly reduced.

[0048] This application proposes a redundant operation strategy shared by the upper, lower, and AC arms for the above-mentioned HMMC-MRM topology, and analyzes the operation modes of the HMMC-MRM in normal operation and three fault states.

[0049] (1) Normal operation

[0050] When the upper and lower bridge arms and the AC bridge arm submodules are all functioning correctly, the bridge arm switch... SW 1. SW When 2 is turned on, all six switches of the intermediate module are turned off, and the intermediate module is disconnected, such as... Figure 3 As shown. The upper and lower bridge arms are respectively connected via... SW 1. SW 2. Connect to the AC bridge arm. At this point, the HMMC-MRM can operate normally just like a traditional hybrid MMC.

[0051] (2) First fault handling strategy: Upper arm HSM fault

[0052] When the upper arm submodule fails (assuming upper arm HSM1 fails), the faulty module is disconnected, such as... Figure 4 As shown. At this time, the upper and lower bridge arm switches... SW 1. SW 2. The intermediate module is switched off and put into operation as a half-bridge sub-module of the upper bridge arm. Within the intermediate module, the third switch... G 3 and the fifth switching transistor G 5. Remains in the normally closed state; fourth switch transistor G 4 and the sixth switch G 6. Remain in the normally open state. First switching transistor. G 1 and second switching transistors G The operating mode of module 2 is the same as that of a traditional half-bridge submodule. The DC-side capacitor is switched appropriately. C M The switching schedule for the upper bridge arm is shown in Table 1. When... G 1. Conductivity G When 2 is turned off, the intermediate module is equivalent to the output voltage of the upper bridge arm. U c ;when G 1. Turn off G When 2 is turned on, the intermediate module output voltage is 0, and the DC capacitor... C M The bypass was removed.

[0053] Table 1 Intermediate Module Switching Modes

[0054] ,

[0055] (3) The second fault handling strategy includes: lower arm HSM fault

[0056] When a fault occurs in the lower bridge arm submodule (assuming a fault occurs in lower bridge arm HSM1), the faulty module is disconnected, such as... Figure 5 As shown. At this time, the bridge arm switch... SW 1. SW 2. The intermediate module is switched off and put into operation as a half-bridge sub-module of the lower bridge arm. In the intermediate module, the first switching transistor... G 1 and the fifth switch G 5. Keep the second switch in the normally open state. G 2 and the sixth switch G 6. Remains in the normally closed state. Third switching transistor.G 3 and the fourth switching transistor G The operating mode of module 4 is the same as that of a traditional half-bridge submodule. The DC-side capacitor is switched appropriately. C M The lower bridge arm is engaged, and the switching schedule is shown in Table 2. When... G 4 conduction, G When 3 is turned off, the intermediate module is equivalent to the lower bridge arm output voltage. U c ;when G 4. Shutdown G When 3 is turned on, the intermediate module output voltage is 0, and the DC capacitor... C M The bypass was removed.

[0057] Table 2 Intermediate Module Switching Modes

[0058] ,

[0059] (4) The third fault handling strategy includes AC bridge arm faults.

[0060] When the AC bridge arm submodule fails (assuming the AC bridge arm FSM) a1 (A fault occurs), the faulty module is removed, such as Figure 6 As shown. At this time, the bridge arm switch... SW 1. SW 2. When switched off, the intermediate module is switched on and put into operation as a full-bridge submodule of the AC bridge arm. The switching timetable is shown in Table 3. When G 1 、G 3 、G 6 conduction, G 2 、G 4 、G 5. When turned off, the intermediate module is equivalent to the output voltage of the AC bridge arm. U c ;when G 2 、G 4 、G 5 conduction, G 1 、G 3 、G When 6 is turned off, the intermediate module is equivalent to the AC bridge arm output voltage - U c Furthermore, when G 1 、G 3 、G 5 conduction, G 2 、G 4 、G When 6 is turned off, the intermediate module output voltage is 0, and the DC capacitor... C M The bypass was removed. Furthermore, when G 2 、G 4、G 6 conduction, G 1 、G 3 、G 5. When shut down, the intermediate module output voltage is also 0, and the DC capacitor... C M The bypass was removed.

[0061] Table 3 Intermediate Module Switching Modes

[0062] ,

[0063] In summary, the multi-port redundant modules in the HMMC-MRM topology proposed in this application possess fault tolerance capabilities in the event of failures in the upper and lower bridge arms and AC bridge arm submodules. Compared to traditional redundant module configurations, the proposed topology significantly improves the utilization rate of redundant modules and enhances the operational reliability of the HMMC-MRM.

[0064] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A hybrid modular multilevel grid-connected converter based on multi-terminal sharing of intensive redundant modules, characterized in that, include: Three-phase circuit topology; The three-phase circuit topology includes three identical single-phase topologies, each of which includes an upper bridge arm, an upper bridge arm inductor, an upper bridge arm switch, an intermediate module, an AC bridge arm, a lower bridge arm, a lower bridge arm inductor, and a lower bridge arm switch. The AC bridge arm includes multiple full-bridge sub-modules, which are connected in series. Both the upper bridge arm switch and the lower bridge arm switch are composed of two thyristors connected in reverse parallel. Both the upper bridge arm and the lower bridge arm include multiple half-bridge sub-modules, which are connected in series. One end of the last half-bridge sub-module in the upper bridge arm is connected to one end of the upper bridge arm inductor, and one end of the first half-bridge module in the lower bridge arm is connected to one end of the lower bridge arm inductor. The intermediate module includes a first switch, a second switch, a third switch, a fourth switch, a fifth switch, and a sixth switch, as well as a DC capacitor. Node A is formed by connecting the emitter node of the first switch, the collector node of the second switch, one end of the upper bridge arm switch, and the other end of the upper bridge arm inductor. Node B is formed by connecting the emitter node of the third switch, the collector node of the fourth switch, one end of the lower bridge arm switch, and the other end of the lower bridge arm inductor. Node C is formed by connecting the emitter node of the fifth switch, the collector node of the sixth switch, one end of the AC bridge arm, the other end of the upper bridge arm switch, and the other end of the lower bridge arm switch. The collector nodes of the first, third, and fifth switches are connected to the positive terminal of the DC capacitor, and the emitter nodes of the second, fourth, and sixth switches are connected to the negative terminal of the DC capacitor.

2. A fault handling method for a multilevel converter, characterized in that, For the hybrid modular multilevel grid-connected converter based on multi-terminal sharing of intensive redundant modules according to claim 1, the fault handling method includes a first fault handling strategy, a second fault handling strategy, and a third fault handling strategy, wherein the first fault handling strategy includes: When the upper bridge arm submodule fails, the faulty module is disconnected. Turn off the upper and lower bridge arm switches; The intermediate module is put into operation as a half-bridge sub-module of the upper bridge arm; The third and fifth switching transistors remain normally closed. The fourth and sixth switching transistors remain normally open. The operating modes of the first and second switching transistors are the same as those of a traditional half-bridge submodule.

3. The method according to claim 2, characterized in that, The second fault handling strategy includes: When a fault occurs in the lower bridge arm submodule, the faulty module is disconnected. Close the upper and lower bridge arm switches; The intermediate module is put into operation as a half-bridge sub-module of the lower bridge arm; The first and fifth switching transistors remain normally open. The second and sixth switching transistors remain normally closed. The operating states of the third and fourth switching transistors are the same as those of a traditional half-bridge sub-module.

4. The method according to claim 2, characterized in that, The third fault handling strategy includes: When a fault occurs in the AC bridge arm full-bridge submodule, the faulty module is disconnected. Close the upper and lower bridge arm switches; The intermediate module is put into operation as a full-bridge submodule of the AC bridge arm.

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