High-adaptability modular multi-level energy storage system

Abstract

The utility model discloses a modular multi-level energy storage system with high adaptability, which comprises a modular multi-level converter connected with a power grid, the modular multi-level converter comprises a plurality of three-phase ports and converter modules formed by connecting power units in series, and the converter modules are connected in different modes and are respectively connected with the three-phase ports. The power unit comprises an energy storage subunit, a direct current conversion subunit and an alternating current conversion subunit which are sequentially connected in series, through the voltage regulation function of the direct current conversion subunit, the configuration flexibility of an energy storage medium in the energy storage subunit is improved, and the influence of secondary current on the power unit is reduced. The modular multilevel converter superposes the AC side voltages of the plurality of power units, thereby raising the voltage of the power conversion system, enabling the power conversion system to adapt to a middle-high voltage power grid, and solving the technical problem that an energy storage system cannot be directly connected to the middle-high voltage power grid.

Description

Technical Field

[0001] The utility model relates to the technical field of energy storage, and in particular to a highly adaptable modular multi-level energy storage system. Background Art

[0002] New energy storage represented by electrochemical batteries, flywheels and other energy storage media is an important technology and basic equipment to support the new power system. It is of great significance to promote green energy transformation, respond to extreme events, ensure energy security, promote high-quality energy development, and support the realization of climate change goals.

[0003] At the same time, in order to cope with the high proportion of new energy consumption and transmission, a large-capacity new energy storage system is needed. The existing new energy storage technology mostly uses multiple PCSs in parallel and then boosts the voltage through a transformer to increase the capacity of a single system. Under large capacity, it is difficult to coordinate and control a large number of PCSs. At the same time, since the voltage needs to be boosted by a transformer, the loss will increase and the reactive power regulation range will be reduced.

[0004] In terms of the composition of the power unit, existing products mostly use a unipolar structure, which lacks flexibility in the selection of energy storage media and is easily limited by the number of parallel connections. The wide voltage range makes it difficult to optimize the control of the converter modulation ratio. The DC side must have a sufficiently high voltage, and failures are prone to occur in large-capacity energy storage systems. It is not possible to charge and discharge multiple branches at the same time.

[0005] At present, conventional energy storage systems use energy storage media to access PCS. PCSs are connected in parallel and connected to the low-voltage side of the step-up transformer. After step-up, they are connected to the medium and high voltage power grid. A single PCS uses conventional two-level or three-level output, with an output voltage not higher than 900V and a single-machine power not higher than 2.5MW. However, two-level or three-level output has large harmonics and high requirements for filtering. It is necessary to pass through a step-up transformer to access the medium and high voltage power grid, which causes transformer losses and reduces the reactive power regulation range. Limited by the voltage on the AC side of the PCS, the access capacity of a single PCS is limited. In order to realize a large-capacity energy storage system, a large number of PCSs need to be connected in parallel. The differences between the PCSs in the system make coordinated control difficult and the response slow. Summary of the invention

[0006] The utility model provides a highly adaptable modular multi-level energy storage system to solve the technical problem that the energy storage system cannot be directly connected to a medium or high voltage power grid.

[0007] In order to solve the above technical problems, the embodiment of the utility model provides a highly adaptable modular multi-level energy storage system, including a modular multi-level converter connected to a power grid, wherein:

[0008] The modular multi-level converter comprises a plurality of three-phase ports and a converter module composed of power units connected in series, wherein the converter modules are respectively connected to the three-phase ports of the modular multi-level converter;

[0009] The power unit comprises an energy storage subunit, a DC conversion subunit and an AC conversion subunit which are connected in series in sequence.

[0010] Each phase of the modular multilevel converter includes multiple power units connected in series. The AC side voltages of multiple power units are superimposed, thereby raising the voltage of the power conversion system to adapt it to medium and high voltage power grids. At the same time, multi-level output is achieved through cascading between power units.

[0011] As a preferred solution, the DC conversion subunit includes a first capacitor, a first inductor and a switch tube assembly, and the switch tube assembly includes a first switch tube, a second switch tube, a third switch tube, a fourth switch tube and a plurality of first diodes connected in sequence to the non-control end;

[0012] Wherein, each of the first diodes corresponds to the first switch tube, the second switch tube, the third switch tube and the fourth switch tube respectively;

[0013] The first port of each of the first diodes is respectively connected to the first non-control end of each corresponding switch tube, the second port of each of the first diodes is respectively connected to the second non-control end of each corresponding switch tube, the first port of the first inductor is connected to the first port of the switch tube assembly, the second port of the first inductor is connected to the first port of the first capacitor, and the second port of the first capacitor is connected to the second port of the switch tube assembly.

[0014] The DC conversion subunit contains multiple controllable switch tubes, which change the connection state by opening and closing the switch tubes, thereby adjusting the output voltage and improving the flexibility of the energy storage medium configuration. At the same time, it avoids direct connection between the energy storage subunit and the AC conversion subunit, eliminating the secondary current on the AC side.

[0015] As a preferred embodiment, the DC conversion subunit also includes a second capacitor and a third capacitor, the first non-control end of the first switch tube is connected to the first port of the second capacitor, the second port of the second capacitor is connected to the second non-control end of the second switch tube, the first non-control end of the third switch tube is connected to the first port of the third capacitor, the second port of the third capacitor is connected to the second non-control end of the fourth switch tube, the first non-control end of the second switch tube is connected to the first port of the first inductor, and the second non-control end of the third switch tube is connected to the second port of the first capacitor.

[0016] At this time, the DC conversion subunits are connected in a non-common grounding manner. By controlling the voltage, the impact caused by the inconsistency of the energy storage medium between different energy storage subunits is reduced, and the impact of the secondary current generated on the AC side is eliminated.

[0017] As a preferred embodiment, the DC conversion subunit also includes a fourth capacitor and a fifth capacitor, the first non-control end of the first switch tube is connected to the first port of the fourth capacitor, the second port of the fourth capacitor is connected to the second non-control end of the fourth switch tube, the first non-control end of the second switch tube is connected to the first port of the fifth capacitor, the second port of the fifth capacitor is connected to the second non-control end of the third switch tube, the first non-control end of the third switch tube is connected to the first port of the first inductor, and the second non-control end of the fourth switch tube is connected to the second port of the first capacitor.

[0018] At this time, the DC conversion subunit is connected in a common ground mode, which improves the safety and anti-interference ability of the system and can adapt to the scenario of multiple machines in parallel.

[0019] As a preferred solution, the AC conversion subunit includes a fifth switch tube, a sixth switch tube, a seventh switch tube, an eighth switch tube and a plurality of second diodes;

[0020] Wherein, the fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch tube each correspond to a second diode;

[0021] The first port of each of the second diodes is respectively connected to the first non-control end of each corresponding switch tube, the second port of each of the second diodes is respectively connected to the second non-control end of each corresponding switch tube, the second non-control end of the fifth switch tube is connected to the first non-control end of the sixth switch tube, the second non-control end of the seventh switch tube is connected to the first non-control end of the eighth switch tube, the first non-control end of the fifth switch tube is connected to the first non-control end of the seventh switch tube, and the second non-control end of the sixth switch tube is connected to the second non-control end of the eighth switch tube.

[0022] The AC conversion subunit is used to convert the DC voltage output by the energy storage subunit into an AC voltage so that the output can be connected to the power grid.

[0023] As a preferred solution, the first switch tube, the second switch tube, the third switch tube, the fourth switch tube, the fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch tube are types of triodes, field effect tubes or thyristors.

[0024] As a preferred solution, the converter module includes a filter reactor connected in series with the power unit, and the converter modules are connected in a star or triangle manner, wherein:

[0025] When connected in the star-shaped manner, one end of the converter modules is connected to each other, and the other end is respectively connected to each three-phase port of the modular multi-level converter;

[0026] When connected in the triangle manner, the converter modules are connected end to end, and the connection points between the converter modules are respectively connected to the three-phase ports of the modular multi-level converter.

[0027] When the same number of power units are connected in series, star wiring can increase the line voltage of the system output, while delta wiring can reduce the impact of three-phase imbalance. The choice can be made according to the needs of the actual usage scenario.

[0028] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0029] 1. The utility model connects power units in series to form a modular multi-level converter, thereby realizing direct connection between the power conversion system and the medium and high voltage power grid, reducing the loss caused by the connection transformer;

[0030] 2. The utility model increases the flexibility of energy storage medium configuration and eliminates secondary current on the AC side of the power conversion system by adding a DC conversion subunit between the energy storage subunit and the AC conversion subunit and controlling voltage changes through the DC conversion subunit. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 : A connection diagram of a star connection mode of a modular multi-level converter provided in an embodiment of the utility model;

[0032] Figure 2 : A connection diagram of a triangle connection mode of a modular multi-level converter provided by an embodiment of the utility model;

[0033] Figure 3 : A schematic diagram of a module connection of a power unit provided in an embodiment of the utility model;

[0034] Figure 4 : A connection diagram of a non-common ground connection mode of a DC conversion subunit provided in an embodiment of the utility model;

[0035] Figure 5 : A connection diagram of a common ground connection mode of a DC conversion subunit provided in an embodiment of the utility model;

[0036] Figure 6 : A connection diagram of an AC conversion subunit provided in an embodiment of the utility model;

[0037] Among them, the figure numbers of the drawings in the specification are as follows: 1. Modular multi-level converter, 1.1. Converter module, 1.2. Power unit, 1.3. Three-phase port, 2. Energy storage subunit, 3. DC conversion subunit, 4. AC conversion subunit. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0039] Embodiment 1

[0040] Reference Figure 1 As shown, Figure 1 A connection diagram of the star connection mode of the modular multilevel converter provided by the embodiment of the utility model, as shown in the figure, the utility model provides a highly adaptable modular multilevel energy storage system, which includes a modular multilevel converter 1, the modular multilevel converter 1 includes a plurality of converter modules 1.1, the converter module 1.1 is composed of a plurality of power units 1.2 connected in series, the number of power units 1.2 can be selected according to the voltage required in the actual application scenario, the more power units 1.2 connected in series, the higher the output voltage of the modular multilevel converter 1. The converter module 1.1 also includes a filter reactor, the power unit 1.2 is connected in series with the filter reactor, and the harmonic current in the modular multilevel converter 1 is reduced by connecting the filter reactor, thereby reducing the power loss.

[0041] The converter modules 1.1 in the modular multilevel converter 1 are interconnected, and the AC side voltages of the multiple power units 1.2 contained in the converter modules 1.1 are superimposed, so that the voltage of the modular multilevel converter 1 is raised to medium and high voltage, so that the energy storage system does not need to be connected to a step-up transformer and can be directly connected to the medium and high voltage power grid, thereby reducing the loss caused by the transformer, improving the capacity of the energy storage system and the command response speed, and realizing multi-level output through the cascading between the power units 1.2.

[0042] In this embodiment, the connection between the converter modules 1.1 is in star shape, where the converter modules 1.1 are connected to each other at the same end, and the other end is respectively connected to each three-phase port 1.3 of the modular multilevel converter 1, and each three-phase port 1.3 of the modular multilevel converter 1 is connected to the power grid. Connecting the converter modules 1.1 in a star shape can increase the line voltage in the modular multilevel converter 1 and improve the output of the energy storage system.

[0043] Reference Figure 3 As shown, Figure 3 A schematic diagram of a module connection of a power unit provided in an embodiment of the utility model is shown in the figure. As shown in the figure, the power unit 1.2 includes an energy storage subunit 2, a DC conversion subunit 3 and an AC conversion subunit 4, and the above units are connected in series in sequence.

[0044] The energy storage subunit 2 contains energy storage medium. In this embodiment, the specific type and specification of the energy storage medium are not specifically limited. It can be determined according to the needs of the actual application scenario. Different types or different specifications of energy storage media of the same type have an impact on the voltage on the AC side of the energy storage system. The energy storage subunit 2 is connected to the DC conversion subunit 3. The DC conversion subunit 3 can adjust the voltage output by the energy storage subunit 2 so that it is compatible with the AC conversion subunit 4 in the power unit 1.2 and can be connected to each other.

[0045] When the energy storage subunit 2 is directly connected to the AC conversion subunit 4, a secondary current will exist between the two subunits, resulting in an increase in the power loss of the energy storage system. In the prior art, a capacitor is connected between the energy storage subunit 2 and the AC conversion subunit 4 to reduce the impact of the secondary current. When the DC side capacitor or capacitor voltage connected in parallel between the energy storage subunit 2 and the AC conversion subunit 4 is larger, the secondary current on the battery side is smaller; when the internal resistance of the battery is smaller, the secondary current on the battery side is larger. Increasing the capacitance can reduce the impact of the secondary current to a certain extent, but this method has limited effect.

[0046] In view of the above problems, in this embodiment, a DC conversion subunit 3 is provided to separate the energy storage subunit 2 and the AC conversion subunit 4, so as to avoid the direct connection between the two and the occurrence of secondary current. At the same time, through the regulation of the DC conversion subunit 3, the influence of the secondary current is further reduced, thereby reducing the power loss of the energy storage system.

[0047] Reference Figure 4 As shown, Figure 4 A connection schematic diagram of a non-common ground connection mode of a DC conversion subunit provided in an embodiment of the utility model, as shown in the figure, the DC conversion subunit 3 provided by the utility model includes a switch tube assembly, the switch tube assembly includes a first switch tube Q1, a second switch tube Q2, a third switch tube Q3 and a fourth switch tube Q4, the second non-control end of the first switch tube Q1 is connected to the first non-control end of the second switch tube Q2, the second non-control end of the second switch tube Q2 is connected to the first non-control end of the third switch tube Q3, the second non-control end of the third switch tube Q3 is connected to the first non-control end of the fourth switch tube Q4, the first non-control end of the first switch tube Q1 and the second non-control end of the fourth switch tube Q4 are respectively connected to the input end of the DC conversion subunit 3.

[0048] The switch tube assembly also includes a plurality of first diodes D1, D2, D3 and D4, the number of the first diodes is the same as the number of switch tubes in the switch tube assembly, and in this embodiment, the number of the first diodes is 4. The first port of each first diode is respectively connected to the first non-control end of each corresponding switch tube, the second port of each first diode is respectively connected to the second non-control end of each corresponding switch tube, and the directions of each first diode relative to each corresponding switch tube are the same.

[0049] The DC conversion subunit 3 also includes a first capacitor C1 and a first inductor L1, wherein the first port of the first inductor L1 is connected to the first port of the switch tube assembly, and the first port of the switch tube assembly in this embodiment is the first non-control terminal of the second switch tube Q2. The second port of the first inductor L1 is connected to the first port of the first capacitor C1. The second port of the first capacitor C1 is connected to the second port of the switch tube assembly, and the second port of the switch tube assembly in this embodiment is the second non-control terminal of the third switch tube Q3. The first port and the second port of the first capacitor C1 are respectively connected to the output end of the DC conversion subunit 3.

[0050] On the basis of the above connection, the DC conversion subunit 3 in this embodiment further includes a second capacitor C2 and a third capacitor C3, wherein a first port of the second capacitor C2 is connected to the first non-control end of the first switch tube Q1, a second port of the second capacitor C2 is connected to the second non-control end of the second switch tube Q2, a first port of the third capacitor C3 is connected to the first non-control end of the third switch tube Q3, and a second port of the third capacitor C3 is connected to the second non-control end of the fourth switch tube Q4.

[0051] During operation, the first switch tube Q1, the second switch tube Q2, the third switch tube Q3 and the fourth switch tube Q4 can be controlled according to the voltage level to be adjusted, and the connection state is changed by opening and closing the switch tube, thereby adjusting the output voltage. The control method includes controlling the duty cycle of the drive signal input to the control end of the switch tube, thereby changing the opening and closing time of the switch tube to achieve the purpose of voltage regulation. In this embodiment, during operation, the drive signals of the first switch tube Q1 and the fourth switch tube Q4 are complementary, that is, the first switch tube Q1 and the fourth switch tube Q4 are not turned on at the same time; the drive signals of the second switch tube Q2 and the third switch tube Q3 are complementary, that is, the second switch tube Q2 and the third switch tube Q3 are not turned on at the same time; the drive signals of the first switch tube Q1 and the second switch tube Q2 differ by 180° phase angle, and the drive signals of the third switch tube Q3 and the fourth switch tube Q4 differ by 180° phase angle.

[0052] It can be seen from the above description that the output of the DC conversion subunit 3 in this embodiment is fitted by three levels, that is, a three-level bidirectional DC converter is formed. This structure can reduce the pressure on the switch tube, enable the switch tube to withstand greater power, and reduce DC harmonics.

[0053] The DC conversion subunit 3 is connected to the AC conversion subunit 4. Figure 6 As shown, Figure 6 A connection schematic diagram of an AC conversion subunit provided for an embodiment of the utility model, as shown in the figure, the AC conversion subunit 4 includes a fifth switch tube Q5, a sixth switch tube Q6, a seventh switch tube Q7 and an eighth switch tube Q8, wherein the second non-control end of the fifth switch tube Q5 is connected to the first non-control end of the sixth switch tube Q6, the second non-control end of the seventh switch tube Q7 is connected to the first non-control end of the eighth switch tube Q8, the first non-control end of the fifth switch tube Q5 is connected to the first non-control end of the seventh switch tube Q7, and the second non-control end of the sixth switch tube Q6 is connected to the second non-control end of the eighth switch tube Q8.

[0054] The first non-control terminal of the fifth switch tube Q5 and the first non-control terminal of the seventh switch tube Q7 are connected to the first input terminal of the AC conversion sub-unit 4, and the second non-control terminal of the sixth switch tube Q6 and the second non-control terminal of the eighth switch tube Q8 are connected to the second input terminal of the AC conversion sub-unit 4. The second non-control terminal of the fifth switch tube Q5 and the first non-control terminal of the sixth switch tube Q6 are connected to the first output terminal of the AC conversion sub-unit 4, and the second non-control terminal of the seventh switch tube Q7 and the first non-control terminal of the eighth switch tube Q8 are connected to the second output terminal of the AC conversion sub-unit 4.

[0055] The AC conversion subunit 4 also includes a plurality of second diodes D5, D6, D7 and D8, the number of the second diodes is the same as the number of the switch tubes in the AC conversion subunit 4, and the number of the second diodes in this embodiment is 4. The first port of each second diode is respectively connected to the first non-control end of each corresponding switch tube, the second port of each second diode is respectively connected to the second non-control end of each corresponding switch tube, and the direction of each second diode relative to each corresponding switch tube is the same.

[0056] The AC conversion subunit 4 is used to convert the DC voltage output by the energy storage subunit 2 into an AC voltage, so that the output voltage can be connected to the power grid to realize the output of the energy storage system.

[0057] The types of switch tubes included in the DC conversion subunit 3 and the AC conversion subunit 4 are triodes, field effect tubes or thyristors, which can be selected according to the needs of actual application scenarios.

[0058] In summary, compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0059] 1. The utility model connects power units in series to form a modular multi-level converter, thereby realizing direct connection between the power conversion system and the medium and high voltage power grid, reducing the loss caused by the connection transformer;

[0060] 2. The utility model increases the flexibility of energy storage medium configuration and eliminates secondary current on the AC side of the power conversion system by adding a DC conversion subunit between the energy storage subunit and the AC conversion subunit and controlling voltage changes through the DC conversion subunit.

[0061] Embodiment 2

[0062] This embodiment is based on the first embodiment, and changes the connection mode between the converter modules 1.1 in the modular multi-level converter 1. Figure 2 As shown, Figure 2 A connection diagram of a triangle connection mode of a modular multilevel converter provided in an embodiment of the utility model is shown in the figure. In this embodiment, the converter modules 1.1 are connected end to end, and the connection between the converter modules 1.1 is respectively connected to each three-phase port 1.3 of the modular multilevel converter 1. Compared with the first embodiment, the influence of three-phase imbalance in the modular multilevel converter 1 is reduced by the triangle connection mode in this embodiment.

[0063] Embodiment 3

[0064] This embodiment changes the structure of the DC conversion subunit 3 on the basis of the first embodiment. Figure 5 As shown, Figure 5 A connection schematic diagram of a common ground connection mode of a DC conversion subunit provided for an embodiment of the utility model, as shown in the figure, at this time, the first port of the first inductor L1 is connected to the first non-control end of the third switch tube Q3, and the second port of the first capacitor C1 is connected to the second non-control end of the fourth switch tube Q4. In this embodiment, the DC conversion subunit 3 includes a fourth capacitor C4 and a fifth capacitor C5, wherein the first port of the fourth capacitor C4 is connected to the first non-control end of the first switch tube Q1, the second port of the fourth capacitor C4 is connected to the second non-control end of the fourth switch tube Q4, the first port of the fifth capacitor C5 is connected to the first non-control end of the second switch tube Q2, and the second port of the fifth capacitor C5 is connected to the second non-control end of the third switch tube Q3. At this time, the common ground connection mode is adopted in the DC conversion subunit 3, which improves the safety and anti-interference of the energy storage system and can adapt to the scenario of multiple machines in parallel.

[0065] Embodiment 4

[0066] This embodiment changes the structure of the DC conversion subunit 3 on the basis of the second embodiment. The structure of the DC conversion subunit 3 in this embodiment is the same as that described in the third embodiment.

[0067] In combination with all the embodiments, the utility model has the following beneficial effects compared with the prior art:

[0068] 1. The utility model connects power units in series to form a modular multi-level converter, thereby realizing direct connection between the power conversion system and the medium and high voltage power grid, reducing the loss caused by the connection transformer;

[0069] 2. The utility model increases the flexibility of energy storage medium configuration and eliminates secondary current on the AC side of the power conversion system by adding a DC conversion subunit between the energy storage subunit and the AC conversion subunit and controlling voltage changes through the DC conversion subunit.

[0070] The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the utility model in detail. It should be understood that the above description is only a specific embodiment of the utility model and is not intended to limit the protection scope of the utility model. It is particularly pointed out that for those skilled in the art, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the utility model should be included in the protection scope of the utility model.

Claims

1. A highly adaptable modular multi-level energy storage system, characterized in that: It comprises a modular multilevel converter connected to a power grid, wherein: The modular multi-level converter comprises a plurality of three-phase ports and a converter module composed of power units connected in series, wherein the converter modules are respectively connected to the three-phase ports of the modular multi-level converter; The power unit comprises an energy storage subunit, a DC conversion subunit and an AC conversion subunit which are connected in series in sequence.

2. The highly adaptable modular multi-level energy storage system according to claim 1, characterized in that: The DC conversion subunit includes a first capacitor, a first inductor and a switch tube assembly, wherein the switch tube assembly includes a first switch tube, a second switch tube, a third switch tube, a fourth switch tube and a plurality of first diodes connected in sequence to the non-control end; Wherein, each of the first diodes corresponds to the first switch tube, the second switch tube, the third switch tube and the fourth switch tube respectively; The first port of each of the first diodes is respectively connected to the first non-control end of each corresponding switch tube, the second port of each of the first diodes is respectively connected to the second non-control end of each corresponding switch tube, the first port of the first inductor is connected to the first port of the switch tube assembly, the second port of the first inductor is connected to the first port of the first capacitor, and the second port of the first capacitor is connected to the second port of the switch tube assembly.

3. The highly adaptable modular multi-level energy storage system according to claim 2, characterized in that: The DC conversion subunit also includes a second capacitor and a third capacitor, the first non-control end of the first switch tube is connected to the first port of the second capacitor, the second port of the second capacitor is connected to the second non-control end of the second switch tube, the first non-control end of the third switch tube is connected to the first port of the third capacitor, the second port of the third capacitor is connected to the second non-control end of the fourth switch tube, the first non-control end of the second switch tube is connected to the first port of the first inductor, and the second non-control end of the third switch tube is connected to the second port of the first capacitor.

4. The highly adaptable modular multi-level energy storage system according to claim 2, characterized in that: The DC conversion subunit also includes a fourth capacitor and a fifth capacitor. The first non-control end of the first switch tube is connected to the first port of the fourth capacitor, the second port of the fourth capacitor is connected to the second non-control end of the fourth switch tube, the first non-control end of the second switch tube is connected to the first port of the fifth capacitor, the second port of the fifth capacitor is connected to the second non-control end of the third switch tube, the first non-control end of the third switch tube is connected to the first port of the first inductor, and the second non-control end of the fourth switch tube is connected to the second port of the first capacitor.

5. The highly adaptable modular multi-level energy storage system according to claim 2, characterized in that: The AC conversion subunit includes a fifth switch tube, a sixth switch tube, a seventh switch tube, an eighth switch tube and a plurality of second diodes; Wherein, the fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch tube each correspond to a second diode; The first port of each of the second diodes is respectively connected to the first non-control end of each corresponding switch tube, the second port of each of the second diodes is respectively connected to the second non-control end of each corresponding switch tube, the second non-control end of the fifth switch tube is connected to the first non-control end of the sixth switch tube, the second non-control end of the seventh switch tube is connected to the first non-control end of the eighth switch tube, the first non-control end of the fifth switch tube is connected to the first non-control end of the seventh switch tube, and the second non-control end of the sixth switch tube is connected to the second non-control end of the eighth switch tube.

6. The highly adaptable modular multi-level energy storage system according to claim 5, characterized in that: The first switch tube, the second switch tube, the third switch tube, the fourth switch tube, the fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch tube are types of triodes, field effect tubes or thyristors.

7. The highly adaptable modular multi-level energy storage system according to claim 1, characterized in that: The converter module includes a filter reactor connected in series with the power unit, and the converter modules are connected in a star or triangle manner, wherein: When connected in the star-shaped manner, one end of the converter modules is connected to each other, and the other end is respectively connected to each three-phase port of the modular multi-level converter; When connected in the triangle manner, the converter modules are connected end to end, and the connection points between the converter modules are respectively connected to the three-phase ports of the modular multi-level converter.

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