Hybrid modular multi-level grid-connected converter based on intensive redundant module multi-terminal sharing and fault processing method

Abstract

The invention provides a hybrid modular multi-level grid-connected converter based on intensive redundant module multi-terminal sharing. The hybrid modular multi-level grid-connected converter comprises a three-phase circuit topology; the three-phase circuit topology comprises three same single-phase topologies, and each single-phase topology comprises an upper bridge arm, an upper bridge arm inductor, an upper bridge arm switch, a middle module, an alternating current bridge arm, a lower bridge arm, a lower bridge arm inductor and a lower bridge arm switch; the intermediate module comprises a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube, a sixth switch tube and a direct current capacitor. According to the invention, by introducing the intermediate module, the fault-tolerant capability is provided when the upper and lower bridge arm sub-modules and the AC bridge arm sub-module have faults. Compared with a traditional redundant module configuration mode, the topology has the advantages that the utilization rate of the redundant module is greatly improved, and the operation reliability of the multi-level converter is improved.

Description

Technical Field

[0001] The present application relates to the technical field of power systems, and in particular to the field of voltage transformers. Background Art

[0002] In recent years, modular multilevel converters (MMC) have been widely used in high-voltage direct current transmission systems due to their advantages such as low output harmonic content, high modularity and strong scalability. At the same time, the application of MMC in the field of medium-voltage distribution networks has also attracted much attention, such as solid-state transformers, motor drives, unified power flow controllers and static VAR compensators.

[0003] In order to further expand the application of MMC in medium voltage AC and DC distribution networks, some scholars have proposed a hybrid MMC topology with cascaded full bridges (HMMC-CFB) topology, such as Figure 1 As shown. The external full-bridge submodule of this topology can block and control the DC fault current to ensure that the topology can achieve external fault crossing. However, the MMC is composed of multiple cascaded submodules, and its output function depends largely 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 when a fault occurs, thereby ensuring the safe and stable operation of the system. Therefore, the MMC redundant configuration method is particularly critical. The traditional redundant unit configuration principle is to independently configure the redundant submodule HSM in the upper and lower bridge arms respectively. r For the HMMC-CFB topology, it is also necessary to configure an additional redundant unit FSM in the AC bridge arm. r However, the probability of simultaneous failure of the submodules of the upper and lower bridge arms and the AC bridge arm in the HMMC-CFB is low, while the redundant submodule blocks configured in the conventional topology can only be put into use when the submodule of the bridge arm fails, and cannot be put into use as a backup when the submodules of other bridge arms fail. It can be seen that the existing MMC and the configuration principle of independently configuring redundant units for each bridge arm of the HMMC-CFB use a large number of redundant units and have a low utilization rate. Summary of the invention

[0004] In order to overcome the above technical defects, the present application provides a hybrid modular multi-level grid-connected converter and a fault handling method based on multi-terminal sharing of intensive redundant modules. To achieve the above purpose, the present application is implemented according to the following technical solutions: In a first aspect, the present application provides a hybrid modular multi-level 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, wherein the single-phase topology 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 comprises a plurality of full-bridge sub-modules, and the plurality of full-bridge sub-modules are connected in series; The upper bridge arm switch and the lower bridge arm switch are both composed of two thyristors connected in reverse parallel; The upper bridge arm and the lower bridge arm each include a plurality of half-bridge submodules, and the plurality of half-bridge submodules are connected in series; one end of the last half-bridge submodule in the upper bridge arm is connected to one end of the upper bridge arm inductor, and one end of the first half-bridge submodule in the lower bridge arm is connected to one end of the lower bridge arm inductor; The intermediate module includes a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube and a sixth switch tube, and a DC capacitor. The emitter node of the first switch tube, the collector node of the second switch tube, and one end of the upper bridge arm switch and the other end of the upper bridge arm inductor are connected to form a node A. The emitter node of the third switch tube, the collector node of the fourth switch tube, one end of the lower bridge arm switch, and the other end of the lower bridge arm inductor are connected to form a node B. The emitter node of the fifth switch tube, the collector node of the sixth switch tube, 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 form a node C. The collector nodes of the first switch tube, the third switch tube and the fifth switch tube are connected to the positive end of the DC capacitor, and the emitter nodes of the second switch tube, the fourth switch tube and the sixth switch tube are connected to the negative end of the DC capacitor.

[0005] In a second aspect, the present application provides a fault handling method for a multilevel converter. For the hybrid modular multilevel grid-connected converter based on multi-terminal sharing of an intensive redundant module according to 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: When the upper bridge arm submodule fails, the faulty module is removed; Turn off the upper and lower bridge arm switches; The middle module is put into operation and is put into operation as a half-bridge submodule of the upper bridge arm; The third switch tube and the fifth switch tube remain in a normally closed state; The fourth switch tube and the sixth switch tube remain in a normally open state; The operation modes of the first switch tube and the second switch tube are the same as those of the conventional half-bridge submodule.

[0006] Optionally, the second fault handling strategy includes: When the lower bridge arm submodule fails, the faulty module is removed; Close the upper and lower bridge arm switches; The middle module is put into operation and is put into operation as a half-bridge submodule of the lower bridge arm; The first switch tube and the fifth switch tube remain in a normally open state; Optionally, the third fault handling strategy includes: When a fault occurs in the full bridge submodule of the AC bridge arm, the faulty module is removed; Close the upper and lower bridge arm switches; The middle module is put into operation and is put into operation as a full-bridge submodule of the AC bridge arm.

[0007] This application has the following beneficial effects: The multi-port redundant module in the multi-level converter topology proposed in this application has fault tolerance when the upper and lower bridge arms and AC bridge arm submodules fail. Compared with the traditional redundant module configuration method, the proposed topology greatly improves the utilization rate of the redundant module and improves the operational reliability of the multi-level converter.

[0008] In addition to the above-described purposes, features and advantages, the present application has other purposes, features and advantages. The present application will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings: Figure 1 It is a schematic diagram of a hybrid MMC topology structure with a cascaded full-bridge module in the prior art; Figure 2 It is a schematic diagram of a topological structure of a hybrid modular multi-level grid-connected converter based on multi-terminal sharing of intensive redundant modules provided in an embodiment of the present application; Figure 3 is an equivalent circuit diagram of a multi-level grid-connected converter provided by an embodiment of the present application during normal operation; Figure 4 is an equivalent circuit diagram of a multi-level grid-connected converter provided in an embodiment of the present application when a first fault handling strategy is adopted; Figure 5 is an equivalent circuit diagram of a multi-level grid-connected converter provided in an embodiment of the present application when a second fault handling strategy is adopted; Figure 6 It is an equivalent circuit diagram of the multi-level grid-connected converter provided in the embodiment of the present application when the third fault handling strategy is adopted. DETAILED DESCRIPTION

[0010] The embodiments of the present application are described in detail below with reference to the accompanying drawings; however, the present application can be implemented in many different ways as defined and covered by the claims.

[0011] In order to solve the problems raised in the background technology, such as Figure 2 As shown, the present application provides a hybrid modular multi-level grid-connected converter (Hybrid MMC with multi-portredundancy module, HMMC-MRM) based on intensive redundant module multi-port sharing, including: a 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, and an L 1. Upper arm switch SW 1. Middle module, AC bridge arm, lower bridge arm, lower bridge arm inductor L 2. Lower arm switch SW 2; The AC bridge arm includes a plurality of full-bridge sub-modules FSM, and the plurality of full-bridge sub-modules are connected in series; High-side switch SW 1 and lower bridge arm switch SW 2. Both are composed of two thyristors connected in reverse parallel; Both the upper bridge arm and the lower bridge arm include multiple half-bridge submodules HSM, which are connected in series; one end of the last half-bridge submodule in the upper bridge arm is connected to the upper bridge arm inductor L 1, one end of the first half-bridge submodule in the lower bridge arm is connected to the lower bridge arm inductor L 2 one end; The middle module includes a first switch tube G 1. Second switch tube G 2. The third switch tube G 3. The fourth switch tube G 4. Fifth switch G 5th tube and the sixth switch tube G 6, and DC capacitors C M , the first switch G 1 emitter node, the second switch tube G 2 collector node, and the upper bridge switch SW One end of 1 and the upper bridge arm inductor L The other end of 1 is connected to the node A, and the third switch tube G 3 emitter node, the fourth switch tube G 4 collector node, lower bridge arm switch SW One end of 2, the lower bridge arm inductorL The other end of 2 is connected to form a node B; the fifth switch tube G 5 emitter node, the sixth switch tube G 6, one end of the AC bridge arm, and the upper bridge arm switch SW 1, and the lower bridge arm switch SW The other end of 2 forms a node C; the first switch tube G 1. The third switch tube G 3 and the fifth switch tube G The collector node of 5 is connected to a DC capacitor C M The positive terminal of the second switch G 2. The fourth switch tube G 4 and the sixth switch tube G The emitter node of 6 is connected to a DC capacitor C M The negative terminal.

[0012] Due to the structure of the full-bridge submodule and the half-bridge submodule in this application, Figure 1 As shown in the figure, the full-bridge submodule includes four switch tubes, submodule capacitors C F , the seventh switch tube S 1. The eighth switch tube S 2. The ninth switch tube S 3. The tenth switch tube S 4. The seventh switch tube S 1 emitter node and the eighth switch tube S 2, the collector node of the eighth switch tube S 2 emitter and the tenth switch tube S The emitter node of 4 is connected to the submodule capacitor C F The negative terminal of the seventh switch tube S 1 collector, the ninth switch tube S The collector of 3 is connected to the submodule capacitor C F The positive end of the ninth switch tube is connected to the collector of the tenth switch tube; The half-bridge submodule includes an eleventh switch D 1 and 12th switch tube D 2. Submodule capacitance C H , the eleventh switch D 1 emitter and the twelfth switch tube D 2, the collector of the eleventh switch tube D 1 collector and submodule capacitance C HThe positive terminal of the twelfth switch is connected to D 2 emitter and submodule capacitance C H The negative terminal is connected.

[0013] It should be noted that the full-bridge submodule and the half-bridge submodule, as well as the first switch tube in this application G 1 to the sixth switch tube G 6 are all constructed using silicon-based insulated gate bipolar transistors (IGBT).

[0014] The intermediate unit provided in the present application can be used as redundant backup modules for the upper and lower bridge arms and the AC bridge arm respectively. Compared with configuring redundant units for each phase, the configuration cost of the redundant units can be greatly reduced.

[0015] This application proposes a redundant operation strategy for sharing the upper and lower bridge arms and the AC bridge arm for the above-mentioned HMMC-MRM topology, and analyzes the operation modes of the HMMC-MRM in normal operation and three fault states.

[0016] (1) Normal operation When the upper and lower bridge arms and AC bridge arm submodules are not faulty, the bridge arm switch SW 1. SW 2 is turned on, the six switches of the middle module are all turned off, and the middle module is removed, such as Figure 3 As shown. The upper and lower bridge arms are respectively SW 1. SW 2 is connected to the AC bridge arm. At this point, the HMMC-MRM can operate normally like a traditional hybrid MMC.

[0017] (2) First fault handling strategy: upper bridge arm HSM fault When the upper bridge arm submodule fails (assuming that the upper bridge arm HSM1 fails), the faulty module is removed, such as Figure 4 At this time, the upper and lower bridge arm switches SW 1. SW 2 is turned off, the middle module is put into operation and operates as a half-bridge submodule of the upper bridge arm. G 3 and the fifth switch tube G 5 Keep the normally closed state, the fourth switch tube G 4 and the sixth switch tube G 6 Keep the normally open state. G 1 and the second switch tube G The operating mode of 2 is the same as that of the traditional half-bridge submodule. By appropriately switching the DC side capacitor C MPut into the upper bridge arm, the switching schedule is shown in Table 1. G 1 conduction, G 2When turned off, the intermediate module is equivalent to the output voltage of the upper bridge arm U c ;when G 1 Shutdown, G 2 is turned on, the output voltage of the intermediate module is 0, and the DC capacitor C M The bypass was removed.

[0018] Table 1 Intermediate module switch mode , (3) The second fault handling strategy includes: Lower bridge arm HSM fault When the lower bridge arm submodule fails (assuming that the lower bridge arm HSM1 fails), the faulty module is removed, such as Figure 5 At this time, the bridge arm switch SW 1. SW 2 is turned off, the middle module is put into operation and operates as a half-bridge submodule of the lower bridge arm. G 1 and the fifth switch tube G 5 Keep the normally open state, the second switch tube G 2 and the sixth switch tube G 6 Keep the normally closed state. The third switch tube G 3 and the fourth switch tube G The operating mode of 4 is the same as that of the traditional half-bridge submodule. By appropriately switching the DC side capacitor C M Put into the lower bridge arm, the switching schedule is shown in Table 2. G 4 conduction, G 3When turned off, the intermediate module is equivalent to the output voltage of the lower bridge arm U c ;when G 4 Shutdown, G 3 When the conduction is on, the output voltage of the intermediate module is 0, and the DC capacitor C M The bypass was removed.

[0019] Table 2 Intermediate module switch mode , (4) The third fault handling strategy includes AC bridge arm fault When the AC bridge arm submodule fails (assuming the AC bridge arm FSM a1 If a fault occurs), the faulty module is removed, such as Figure 6 At this time, the bridge arm switch SW 1. SW2 is turned off, the middle module is put into operation and is put into operation as a full-bridge submodule of the AC bridge arm. The switching schedule is shown in Table 3. G 1 、G 3 、G 6 conduction, G 2 、G 4 、G 5When 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 6 When turned off, the intermediate module is equivalent to the output voltage of the AC bridge arm - U c In addition, when G 1 、G 3 、G 5 conduction, G 2 、G 4 、G 6 When turned off, the output voltage of the intermediate module is 0, and the DC capacitor C M In addition, when G 2 、G 4 、G 6 conduction, G 1 、G 3 、G 5 When turned off, the output voltage of the intermediate module is also 0, and the DC capacitor C M The bypass was removed.

[0020] Table 3 Intermediate module switch mode , In summary, the multi-port redundant module in the HMMC-MRM topology proposed in this application has the fault tolerance capability when the upper and lower bridge arms and AC bridge arm submodules fail. Compared with the traditional redundant module configuration method, the proposed topology greatly improves the utilization rate of the redundant module and improves the operational reliability of the HMMC-MRM.

[0021] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A hybrid modular multi-level 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, wherein the single-phase topology 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 comprises a plurality of full-bridge sub-modules, and the plurality of full-bridge sub-modules are connected in series; The upper bridge arm switch and the lower bridge arm switch are both composed of two thyristors connected in reverse parallel; The upper bridge arm and the lower bridge arm each include a plurality of half-bridge submodules, and the plurality of half-bridge submodules are connected in series; one end of the last half-bridge submodule in the upper bridge arm is connected to one end of the upper bridge arm inductor, and one end of the first half-bridge submodule in the lower bridge arm is connected to one end of the lower bridge arm inductor; The intermediate module includes a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube and a sixth switch tube, and a DC capacitor. The emitter node of the first switch tube, the collector node of the second switch tube, and one end of the upper bridge arm switch and the other end of the upper bridge arm inductor are connected to form a node A. The emitter node of the third switch tube, the collector node of the fourth switch tube, one end of the lower bridge arm switch, and the other end of the lower bridge arm inductor are connected to form a node B. The emitter node of the fifth switch tube, the collector node of the sixth switch tube, 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 form a node C. The collector nodes of the first switch tube, the third switch tube and the fifth switch tube are connected to the positive end of the DC capacitor, and the emitter nodes of the second switch tube, the fourth switch tube and the sixth switch tube are connected to the negative end of the DC capacitor.

2. A fault handling method for a multi-level converter, characterized in that: For the hybrid modular multi-level 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 removed; Turn off the upper and lower bridge arm switches; The middle module is put into operation and is put into operation as a half-bridge submodule of the upper bridge arm; The third switch tube and the fifth switch tube remain in a normally closed state; The fourth switch tube and the sixth switch tube remain in a normally open state; The operation modes of the first switch tube and the second switch tube are the same as those of the conventional half-bridge submodule.

3. The method according to claim 2, characterized in that The second fault handling strategy includes: When the lower bridge arm submodule fails, the faulty module is removed; Close the upper and lower bridge arm switches; The middle module is put into operation and is put into operation as a half-bridge submodule of the lower bridge arm; The first switch tube and the fifth switch tube remain in a normally open state; The second switch tube and the sixth switch tube remain in a normally closed state; The operating states of the third switch tube and the fourth switch tube are the same as those of the 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 full bridge submodule of the AC bridge arm, the faulty module is removed; Close the upper and lower bridge arm switches; The middle module is put into operation and is put into operation as a full-bridge submodule of the AC bridge arm.

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