Hybrid modular multilevel converter with overshoot operation

Abstract

The invention relates to the technical field of high-voltage direct-current power transmission, and discloses an overshoot operation hybrid modular multilevel converter which comprises an A phase, a B phase and a C phase which are completely identical, the A phase comprises an upper bridge arm and a lower bridge arm which are identical in structure, an alternating-current side filter inductor and an alternating-current side power grid, and the upper bridge arm comprises a bridge arm inductor and a bridge arm cascade structure. The bridge arm cascade structure is formed by connecting a plurality of hybrid sub-modules in series, and each hybrid sub-module comprises a half-bridge module, a unipolar full-bridge module, a bipolar full-bridge module, an upper end diode, a lower end diode and a capacitance voltage sensor. According to the invention, the maximum utilization of the bipolar voltage output capability of the bipolar full-bridge module in normal operation of the system under the condition of no fault on the direct current side is realized, and the power switch device and system cost are further reduced on the basis of the traditional hybrid modular multi-level converter.

Description

Technical Field

[0001] The present application relates to the technical field of high voltage direct current transmission, and in particular to a hybrid modular multi-level converter with overshoot operation. Background Art

[0002] Modular multilevel converters have the excellent characteristics of high reliability, high voltage output quality, high ductility, high modularity and standardization, and have been widely used and practiced in the field of flexible DC transmission technology. At present, the most widely used sub-module topology of modular multilevel converters is half-bridge module, which has the advantages of simple structure, low cost and low loss. However, in overhead lines of high-voltage DC transmission, the most serious faults include high-voltage DC bus inter-pole short-circuit faults and pole-to-ground short-circuit faults, and the modular multilevel converter system based on half-bridge module does not have the ability to isolate and clear faults. On the other hand, the control design of modular multilevel converters of any structure requires a large number of voltage sensors, and the operation of voltage sensors depends on other external power supplies, which greatly increases power dissipation, design cost, and equipment volume, and further brings some problems such as poor anti-interference ability, reduced accuracy, and difficulty in integrated design. Under harsh working conditions or unstable power supply conditions, the reliability of voltage sensors will be reduced, which will also affect the operation of the converter.

[0003] In order to solve the above problems and take into account the system's fault isolation capability, economy and efficient operation capability, scholars have proposed a hybrid modular multilevel converter structure, that is, a certain proportion of bipolar full-bridge modules and half-bridge modules are used in each bridge arm. When the DC bus voltage is normal, the bipolar full-bridge module in the hybrid modular multilevel converter will be equivalent to a half-bridge module. Only when a fault occurs, the bipolar full-bridge module can block the short-circuit current. In fact, the bipolar full-bridge module has a more flexible voltage output capability than the half-bridge module, and the traditional operation mode cannot effectively utilize the bipolar voltage output capability of the bipolar full-bridge module. In addition, compared with the half-bridge module, the cost of the bipolar full-bridge module is still relatively high. Therefore, the cost of the traditional hybrid modular multilevel converter still needs to be further reduced.

[0004] Therefore, it is necessary to optimize the hybrid modular multilevel converter system from multiple aspects such as structure, operation and design, which can not only ensure its DC fault ride-through capability, but also reduce the number of voltage sensors required by the system, reduce equipment costs, increase system power density, and improve the operating reliability of the converter.

[0005] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the application and should not be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to ordinary technicians in the field. Summary of the invention

[0006] The object of the present invention is to provide a hybrid modular multilevel converter with overshoot operation, which maximizes the use of the bipolar voltage output capacity during normal operation of the system without faults on the DC side, and further reduces the power switching devices and system costs based on the traditional hybrid modular multilevel converter.

[0007] In order to achieve the above objectives, this application is implemented by adopting the following technical solutions: Provided is a hybrid modular multi-level converter for overshoot operation, comprising completely identical A phase, B phase and C phase, wherein the A phase, B phase and C phase all comprise an AC side filter inductor, an AC side power grid and an upper bridge arm and a lower bridge arm of the same structure, wherein the upper bridge arm and the lower bridge arm all comprise a bridge arm inductor and a bridge arm cascade structure, wherein the bridge arm cascade structure is composed of a plurality of hybrid sub-modules connected in series; The hybrid submodule includes a half-bridge module, a unipolar full-bridge module, a bipolar full-bridge module, an upper diode, a lower diode and a capacitive voltage sensor. The bipolar full-bridge module, the unipolar full-bridge module and the half-bridge module are connected in series in sequence. The upper diode is arranged between the bipolar full-bridge module and the unipolar full-bridge module, and the lower diode is arranged between the unipolar full-bridge module and the half-bridge module. The capacitive voltage sensor is installed in parallel in the bipolar full-bridge module.

[0008] Optionally, the A phase, B phase and C phase are connected in parallel.

[0009] Optionally, the upper bridge arm and the lower bridge arm are connected in series, and the AC side filter inductor and the AC side power grid are connected between the upper bridge arm and the lower bridge arm.

[0010] Optionally, the number of hybrid submodules in the upper bridge arm and the lower bridge arm is defined as N , N The value of

[0011] in, U dc is the DC voltage of the modular multilevel converter, U C is the rated value of the internal capacitor voltage of the hybrid submodule.

[0012] Optionally, the bipolar full-bridge module includes a first capacitor, a first switch, a second switch, a third switch and a fourth switch, the first switch and the second switch are connected in series to form a first branch, the third switch and the fourth switch are connected in series to form a second branch, the first branch, the second branch and the first capacitor are respectively connected in parallel, the midpoint of the first branch is the positive output electrode of the bipolar full-bridge module, the midpoint of the second branch is the negative output electrode of the bipolar full-bridge module, and the capacitor voltage sensor is connected in parallel with the first capacitor.

[0013] Optionally, the unipolar full-bridge module includes a second capacitor, a fifth switch, a sixth switch, a diode, and a seventh switch. The fifth switch and the sixth switch are connected in series to form a third branch, the diode and the seventh switch are connected in series to form a fourth branch, the third branch, the fourth branch and the second capacitor are respectively connected in parallel, the midpoint of the third branch is the positive output electrode of the unipolar full-bridge module, and the midpoint of the fourth branch is the negative output electrode of the unipolar full-bridge module.

[0014] Optionally, the half-bridge module includes a third capacitor, an eighth switch and a ninth switch, the eighth switch and the ninth switch are connected in series to form a fifth branch, the third capacitor and the fifth branch are connected in parallel, the midpoint of the fifth branch is the positive output electrode of the half-bridge module, and the negative electrode of the third capacitor is the negative output electrode of the half-bridge module.

[0015] Optionally, the hybrid submodule investment principle is as follows: The number of hybrid sub-modules put into use in a single bridge arm is

[0016] in, n SM Indicates the number of hybrid sub-modules that need to be invested. u ap Represents the bridge arm voltage of phase a.

[0017] If the bridge arm current is positive, the capacitor voltage output by the capacitor voltage sensor in all hybrid sub-modules u CF Sort from small to large, first n SM -1 hybrid sub-module, half-bridge module, unipolar full-bridge module, bipolar full-bridge module are all put into use, the first n SM The number of modules required for hybrid sub-modules n mod for

[0018] No. n SM The modules that need to be invested in the hybrid sub-module are: n mod=1, only the bipolar full-bridge module is put into use; n mod =2, put the bipolar full-bridge module and unipolar full-bridge module into operation; n mod =3, half-bridge modules, unipolar full-bridge modules, and bipolar full-bridge modules are all put into use.

[0019] If the bridge arm current is non-positive, the capacitor voltage output by the capacitor voltage sensor in all hybrid sub-modules u CF Sort from small to large, first n SM -1 hybrid sub-module, half-bridge module, unipolar full-bridge module, bipolar full-bridge module are all put into use, the first n SM The number of modules required for hybrid sub-modules n mod for

[0020] No. n SM The modules that need to be invested in the hybrid sub-module are: n mod =1, only half-bridge module is put into use; n mod =2, put half-bridge module and unipolar full-bridge module into operation; n mod =3, half-bridge modules, unipolar full-bridge modules, and bipolar full-bridge modules are all put into use.

[0021] Optionally, the hybrid sub-module capacitor voltage self-balancing method is as follows: when and only when the sixth switch inside the unipolar full-bridge module is closed, the first capacitor and the second capacitor are connected in parallel to achieve self-balancing; when and only when the ninth switch inside the half-bridge module is closed, the second capacitor and the third capacitor are connected in parallel to achieve self-balancing.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1. When a short circuit fault occurs on the DC side, the power switch devices of all hybrid sub-modules are turned off. At this time, the bipolar full-bridge sub-module and the unipolar full-bridge sub-module are connected to the circuit with negative level output, which can achieve short-circuit fault isolation, so that the entire level converter can achieve DC side short-circuit fault ride-through; 2. Each hybrid submodule includes three capacitors, but only requires one capacitor voltage sensor. Compared with the traditional modular multi-level converter solution, the number of hybrid submodule capacitor voltage sensors is reduced to 1 / 3, reducing system costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 It is a schematic diagram of the internal structure of a multi-level converter provided by an embodiment of a hybrid modular multi-level converter in overshoot operation of the present invention; Figure 2 It is a schematic diagram of the internal current path of a hybrid submodule provided by an embodiment of a hybrid modular multi-level converter in overshoot operation of the present invention; Figure 3 It is a schematic diagram of a process flow of putting a half-bridge submodule, a unipolar full-bridge submodule and a bipolar full-bridge submodule into operation provided by an embodiment of a hybrid modular multi-level converter in overshoot operation of the present invention; Figure 4 It is a schematic diagram of a process flow of putting a half-bridge submodule, a unipolar full-bridge submodule and a bipolar full-bridge submodule into operation provided by an embodiment of a hybrid modular multi-level converter in overshoot operation of the present invention; Figure 5 The present invention is a schematic diagram of a process flow of putting a half-bridge submodule, a unipolar full-bridge submodule and a bipolar full-bridge submodule into operation according to an embodiment of a hybrid modular multi-level converter in overshoot operation.

[0025] The markings in the figure are: 1. upper bridge arm; 2. lower bridge arm; 3. AC side filter inductor; 4. AC side power grid; 5. bridge arm inductor; 6. bridge arm cascade structure; 7. half-bridge module; 8. unipolar full-bridge module; 9. bipolar full-bridge module; 10. hybrid sub-module; 11. capacitor voltage sensor; 12. upper diode; 13. lower diode. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its application or use. Example

[0027] A hybrid modular multilevel converter with overshoot operation, such as Figure 1~Figure 2As shown, it includes completely identical A phase, B phase and C phase, and A phase, B phase and C phase all include AC side filter inductor 3, AC side power grid 4 and upper bridge arm 1 and lower bridge arm 2 with the same structure, and upper bridge arm 1 and lower bridge arm 2 all include bridge arm inductor 5 and bridge arm cascade structure 6, and bridge arm cascade structure 6 is composed of multiple hybrid sub-modules 10 connected in series, and hybrid sub-module 10 includes half-bridge module 7, unipolar full-bridge module 8, bipolar full-bridge module 9, upper diode 12, lower diode 13 and a capacitive voltage sensor 11, bipolar full-bridge module 9, unipolar full-bridge module 8 and half-bridge module 7 are connected in series in sequence, and upper diode 12 is arranged between bipolar full-bridge module 9 and unipolar full-bridge module 8, and unipolar full-bridge module 9 is connected in series in sequence. A single diode is arranged between the bridge module 8 and the half-bridge module 7, and the capacitor voltage sensor 11 is installed in parallel in the bipolar full-bridge module 9. By mixedly using the half-bridge sub-module, the unipolar full-bridge sub-module and the bipolar full-bridge sub-module, the modular multi-level converter system can realize AC / DC interconnection, energy buffering and maintaining grid stability when the distributed part is configured with energy storage. The capacitor voltages of the half-bridge sub-module, the unipolar full-bridge sub-module and the bipolar full-bridge sub-module inside the hybrid sub-module 10 can achieve self-balancing. Therefore, the three module capacitors inside the hybrid sub-module 10 only need to sample the voltage across the first capacitor of the bipolar full-bridge module 9, thereby reducing the number of capacitor voltage sensors 11 of the hybrid sub-module 10 and reducing costs.

[0028] Phase A, phase B and phase C are connected in parallel to ensure the internal stability of the entire level converter when it is working.

[0029] The upper bridge arm 1 and the lower bridge arm 2 are connected in series, and the AC side filter inductor 3 and the AC side power grid 4 are connected between the upper bridge arm 1 and the lower bridge arm 2. The AC side filter inductor 3 is an energy storage element that stores the electric energy provided by the AC side power grid 4, and at the same time plays a filtering role for the switching harmonics rich in the output voltage of the level converter.

[0030] The number of the 10 hybrid submodules in the upper bridge arm 1 and the lower bridge arm 2 is defined as N, and the value of N is

[0031] in, U dc is the DC voltage of the modular multilevel converter, U C is the rated value of the internal capacitor voltage of the hybrid submodule 10; The number of the hybrid submodules 10 is determined by the size of the DC voltage specifically processed by the level converter, thereby ensuring that the level converter can work normally while reducing the cost.

[0032] The bipolar full-bridge module 9 includes a first capacitor, a first switch, a second switch, a third switch and a fourth switch, wherein the first switch and the second switch are connected in series to form a first branch, the third switch and the fourth switch are connected in series to form a second branch, the first branch, the second branch and the first capacitor are connected in parallel respectively, the midpoint of the first branch is the positive output of the bipolar full-bridge module 9, the midpoint of the second branch is the negative output of the bipolar full-bridge module 9, and the capacitor voltage sensor 11 is connected in parallel with the first capacitor; The unipolar full-bridge module 8 includes a second capacitor, a fifth switch, a sixth switch, a diode, and a seventh switch. The fifth switch and the sixth switch are connected in series to form a third branch, the diode and the seventh switch are connected in series to form a fourth branch, the third branch, the fourth branch, and the second capacitor are connected in parallel respectively, the midpoint of the third branch is the positive output of the unipolar full-bridge module 8, and the midpoint of the fourth branch is the negative output of the unipolar full-bridge module 8; The half-bridge module 7 includes a third capacitor, an eighth switch and a ninth switch, the eighth switch and the ninth switch are connected in series to form a fifth branch, the third capacitor and the fifth branch are connected in parallel, the midpoint of the fifth branch is the positive output electrode of the half-bridge module 7, and the negative electrode of the third capacitor is the negative output electrode of the half-bridge module 7; The capacitor voltage self-balancing mode of the hybrid submodule 10 is as follows: when and only when the sixth switch inside the unipolar full-bridge module 8 is closed, the first capacitor and the second capacitor are connected in parallel to achieve self-balancing; when and only when the ninth switch inside the half-bridge module 7 is closed, the second capacitor and the third capacitor are connected in parallel to achieve self-balancing; The voltages of the three module capacitors inside the hybrid submodule 10 can achieve self-balancing. Therefore, the three module capacitors inside the hybrid submodule 10 only need to sample the voltage across the capacitor of the bipolar full-bridge module 9. u CF , the current path to achieve capacitor voltage self-balancing is as follows: When the bipolar full-bridge module 9 is bypassed, the states of the first switch, the second switch, the third switch and the fourth switch are defined as: F3=F4=1, F1=F2=0; The states of the eighth switch and the ninth switch when the unipolar full-bridge mode is bypassed are defined as: U3=U4=1, U1=U2=0; The bypass states of the eighth and ninth switches of the half-bridge module 7 are defined as follows: when H1=0 and H2=1, the half-bridge module 7 is bypassed; like Figure 3 As shown, when U3=1, the first capacitor C1 and the second capacitor C2 are connected in parallel. At this time, the direction of the internal current of the hybrid submodule 10 is from the second capacitor C2 to the first capacitor C1, that is, the second capacitor C2 charges the first capacitor C1, and the voltage of the first capacitor C1 is balanced with the voltage of the second capacitor C2.

[0033] like Figure 4As shown, when H2=1, the second capacitor C2 and the third capacitor C3 are connected in parallel. At this time, the direction of the internal current of the hybrid submodule 10 is from the third capacitor C3 to the second capacitor C2, that is, the third capacitor C3 charges the second capacitor C2, and the voltage of the second capacitor C2 and the third capacitor C3 achieve voltage balance.

[0034] like Figure 5 As shown, when U3=1 and H2=1, the first capacitor C1, the second capacitor C2, and the third capacitor C3 are connected in parallel, and the voltages of the first capacitor C1, the second capacitor C2, and the third capacitor C3 are balanced.

[0035] It can be seen from this that when different modules fail, this device can ensure the operation of the device by bypassing the relevant modules and achieve short-circuit fault ride-through. Example

[0036] Based on the first embodiment, a hybrid sub-module input implementation method of a hybrid modular multi-level converter in overshoot operation is provided: The principles for investing the hybrid submodule 10 are as follows: The number of hybrid sub-modules put into use in real time in a single bridge arm is 10.

[0037] in, n SM Indicates the number of 10 hybrid sub-modules that need to be invested. u ap Represents the bridge arm voltage of phase a.

[0038] If the bridge arm current is positive, the capacitor voltage output by the capacitor voltage sensor 11 in all hybrid submodules 10 is u CF Sort from small to large, first n SM -1 hybrid submodule 10, the half-bridge module 7, the unipolar full-bridge module 8, and the bipolar full-bridge module 9 are all put into use, n SM The number of modules required for hybrid submodules 10 n mod for

[0039] No. n SM The modules that need to be invested in the hybrid sub-module 10 are: n mod =1, only bipolar full-bridge module 9 is put into operation; n mod =2, put the bipolar full-bridge module 9 and the unipolar full-bridge module 8 into operation; n mod=3, half-bridge module 7, unipolar full-bridge module 8, and bipolar full-bridge module 9 are all put into operation.

[0040] If the bridge arm current is non-positive, the capacitor voltage output by the sensors in all hybrid submodules 10 u CF Sort from small to large, first n SM -1 hybrid submodule 10, the half-bridge module 7, the unipolar full-bridge module 8, and the bipolar full-bridge module 9 are all put into use, n SM The number of modules required for hybrid submodules 10 n mod for

[0041] No. n SM The modules that need to be invested in the hybrid sub-module 10 are: n mod =1, only half-bridge module 7 is put into operation; n mod =2, half-bridge module 7 and unipolar full-bridge module 8 are put into operation; n mod =3, half-bridge module 7, unipolar full-bridge module 8, and bipolar full-bridge module 9 are all put into operation.

[0042] Different from the first embodiment, the present invention performs comprehensive balanced control on each module in the hybrid sub-module 10, and adjusts the number of internal half-bridge modules 7, unipolar full-bridge modules 8, and bipolar full-bridge modules 9 under different working conditions of the control device to achieve voltage balanced control of the bridge arm sub-module. This strategy does not require the injection of additional circulating current or the addition of additional hardware circuits, which helps to further reduce system construction costs and operating costs.

[0043] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only used to explain the relative position relationship, movement, etc. between the components in a certain posture. If the specific posture changes, the directional indication will also change accordingly. It is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply 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 a limitation to the present application.

[0044] In the description of this application, 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, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood by specific circumstances.

[0045] The above is only a preferred implementation of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A hybrid modular multilevel converter with overshoot operation, comprising identical phases A, B and C, characterized in that: The A phase, the B phase and the C phase all comprise an AC side filter inductor (3), an AC side power grid (4) and an upper bridge arm (1) and a lower bridge arm (2) of the same structure, the upper bridge arm (1) and the lower bridge arm (2) all comprise a bridge arm inductor (5) and a bridge arm cascade structure (6), and the bridge arm cascade structure (6) is composed of a plurality of hybrid submodules (10) connected in series; The hybrid submodule (10) comprises a half-bridge module (7), a unipolar full-bridge module (8), a bipolar full-bridge module (9), an upper diode (12), a lower diode (13) and a capacitive voltage sensor (11); the bipolar full-bridge module (9), the unipolar full-bridge module (8) and the half-bridge module (7) are sequentially connected in series; the upper diode (12) is arranged between the bipolar full-bridge module (9) and the unipolar full-bridge module (8); a lower diode is arranged between the unipolar full-bridge module (8) and the half-bridge module (7); and the capacitive voltage sensor (11) is installed in parallel in the bipolar full-bridge module (9).

2. The hybrid modular multilevel converter with overshoot operation according to claim 1, characterized in that: The A phase, B phase and C phase are connected in parallel.

3. The hybrid modular multilevel converter with overshoot operation according to claim 1, characterized in that: The upper bridge arm (1) and the lower bridge arm (2) are connected in series, and the AC side filter inductor (3) and the AC side power grid (4) are connected between the upper bridge arm (1) and the lower bridge arm (2).

4. The hybrid modular multilevel converter with overshoot operation according to claim 1, characterized in that: The number of the hybrid submodules (10) in the upper bridge arm (1) and the lower bridge arm (2) is defined as N, and the value of N is in, U dc is the DC voltage of the modular multilevel converter, U C is the rated value of the internal capacitor voltage of the hybrid submodule (10).

5. The hybrid modular multilevel converter with overshoot operation according to claim 1, characterized in that: The bipolar full-bridge module (9) comprises a first capacitor, a first switch, a second switch, a third switch and a fourth switch, the first switch and the second switch are connected in series to form a first branch, the third switch and the fourth switch are connected in series to form a second branch, the first branch, the second branch and the first capacitor are respectively connected in parallel, the midpoint of the first branch is the positive output electrode of the bipolar full-bridge module (9), the midpoint of the second branch is the negative output electrode of the bipolar full-bridge module (9), and the capacitor voltage sensor (11) is connected in parallel with the first capacitor.

6. The hybrid modular multilevel converter with overshoot operation according to claim 1, characterized in that: The unipolar full-bridge module (8) comprises a second capacitor, a fifth switch, a sixth switch, a diode, and a seventh switch; the fifth switch and the sixth switch are connected in series to form a third branch; the diode and the seventh switch are connected in series to form a fourth branch; the third branch, the fourth branch, and the second capacitor are connected in parallel respectively; the midpoint of the third branch is the positive output electrode of the unipolar full-bridge module (8); and the midpoint of the fourth branch is the negative output electrode of the unipolar full-bridge module (8).

7. The hybrid modular multilevel converter with overshoot operation according to claim 1, characterized in that: The half-bridge module (7) comprises a third capacitor, an eighth switch and a ninth switch, the eighth switch and the ninth switch are connected in series to form a fifth branch, the third capacitor and the fifth branch are connected in parallel, the midpoint of the fifth branch is the positive output electrode of the half-bridge module (7), and the negative electrode of the third capacitor is the negative output electrode of the half-bridge module (7).

8. The hybrid modular multilevel converter with overshoot operation according to claim 1, characterized in that: The input principle of the mixing submodule (10) is as follows: The number of hybrid submodules (10) put into use in real time in a single bridge arm is in, n SM Indicates the number of hybrid submodules (10) that need to be invested, u ap represents the bridge arm voltage of the upper bridge arm (1) of phase a; If the bridge arm current is positive, the capacitor voltage output by the capacitor voltage sensor (11) in all hybrid submodules (10) is u CF Sort from small to large, first n SM - The half-bridge module (7), the unipolar full-bridge module (8), and the bipolar full-bridge module (9) in one hybrid submodule are all put into use. n SM The number of modules required for hybrid submodules (10) n mod for No. n SM The modules that need to be invested in the hybrid submodule (10) are: n mod =1, only the bipolar full-bridge module (9) is put into operation; n mod =2, put the bipolar full-bridge module (9) and the unipolar full-bridge module (8) into operation; n mod =3, half-bridge module (7), unipolar full-bridge module (8), and bipolar full-bridge module (9) are all put into operation; If the bridge arm current is non-positive, the capacitor voltage output by the capacitor voltage sensor in all hybrid submodules (10) is u CF Sort from small to large, first n SM - A half-bridge module (7), a unipolar full-bridge module (8), and a bipolar full-bridge module (9) in a hybrid submodule (10) are all put into use. n SM The number of modules required for hybrid submodules (10) n mod for No. n SM The modules that need to be invested in the hybrid submodule (10) are: n mod =1, only half-bridge module (7) is put into operation; n mod =2, put the half-bridge module (7) and the unipolar full-bridge module (8) into operation; n mod =3, the half-bridge module (7), the unipolar full-bridge module (8), and the bipolar full-bridge module (9) are all put into operation.

9. The hybrid modular multilevel converter with overshoot operation according to any one of claims 5 to 7, characterized in that: The capacitor voltage of the hybrid submodule (10) is self-balancing in the following manner: when and only when the sixth switch inside the unipolar full-bridge module (8) is closed, the first capacitor and the second capacitor are connected in parallel to achieve self-balancing; when and only when the ninth switch inside the half-bridge module (7) is closed, the second capacitor and the third capacitor are connected in parallel to achieve self-balancing.

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