Cascade multi-level energy storage system and configuration method thereof

Abstract

The invention discloses a cascaded multilevel energy storage system and a configuration method thereof. The cascaded multilevel energy storage system comprises an autotransformer, an energy storage module and an intelligent control unit, the autotransformer is connected with the energy storage module; the energy storage module is connected with the intelligent control unit. The autotransformer is divided into a primary winding and a secondary winding, the primary winding is connected to a power grid side, and the secondary winding is connected with the energy storage module; the intelligent control unit is a control and protection device of the system and is responsible for implementing a control strategy and a protection strategy. According to the invention, through cooperative control of the autotransformer and the cascade topology, the rigid coupling relationship between the voltage level and the number of modules of a traditional cascade energy storage system is broken through, and the compatibility of the system to different voltage scenes (such as low / medium / high voltage power grids, electric vehicle charging piles and the like) is significantly improved; meanwhile, differential capacity configuration and flexible capacity expansion of the energy storage module are supported, and the problems of voltage stiffness and low capacity utilization rate in the prior art are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics and new energy energy storage, and particularly relates to a cascaded multilevel energy storage system and a configuration method thereof. Background Art

[0002] As a new type of energy storage solution, the cascaded energy storage system is currently receiving extensive attention and application in the industry. At the same time, due to its modular, easy-to-expand, and high-redundancy characteristics, it has become one of the core technologies in the fields of new energy grid connection, microgrid, and industrial energy storage. The typical architecture of the cascaded energy storage system is to form a high-voltage output by connecting multiple energy storage sub-modules (such as battery packs, supercapacitor banks) in series, and each sub-module is equipped with an independent power conversion unit. However, in the prior art, the total voltage level of the system is directly determined by the product of the number of energy storage modules and the voltage of a single module, resulting in a rigid binding of the voltage level with the capacity and the number of modules, and it cannot be adjusted independently. For example, when the application scenario requires a voltage level adjustment, it must be achieved by increasing or decreasing the number of modules or changing the series-parallel structure of the modules, which severely limits the flexibility and economy of the system.

[0003] With the surging demand for cascaded energy storage devices in the new power system, there is an urgent need for a technical solution that can dynamically decouple the voltage level and the energy storage capacity configuration. In the existing technical solutions, some change the system voltage level by switching energy storage modules, but frequent switching is likely to cause power fluctuations, and redundant modules need to be configured, increasing the system volume and cost; also, a DC-DC converter is added at the front end or the back end of the cascaded topology to achieve voltage conversion. Although the voltage can be flexibly adjusted, the additional power devices lead to a decrease in efficiency, an increase in heat dissipation requirements, and the risk of electromagnetic interference introduced by high-frequency switches. There is also the use of a power frequency transformer for voltage matching, but it is bulky (the typical power density is less than 100 W / kg), has a slow response speed, and the redundant isolation characteristics result in cost waste.

[0004] Therefore, the present invention proposes a cascaded multilevel energy storage system and a configuration method thereof. Through the collaborative innovation of the autotransformer and the cascaded energy storage system, it breaks through the rigid dependence of the prior art on the number of modules and the voltage level, and provides a highly adaptable solution for multi-scenario energy storage applications. Summary of the Invention

[0005] Aiming at the technical bottleneck in the existing cascaded energy storage system that the voltage level is directly bound to the number and capacity of energy storage modules and it is difficult to flexibly adapt to the requirements of different application scenarios, the present invention proposes a cascaded multilevel energy storage system and a configuration method thereof. By introducing the collaborative design of the autotransformer and the cascaded topology, it realizes the dynamic matching of the voltage level and the flexible adjustment of power distribution.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: A cascaded multilevel energy storage system includes an autotransformer, an energy storage module, and an intelligent control unit. The autotransformer is connected to the energy storage module, and the energy storage module is connected to the intelligent control unit. The energy storage module consists of a bridge rectifier module, a DC capacitor, and a battery pack. The bridge rectifier module is connected to the DC capacitor, and the DC capacitor is connected to the battery pack. The bridge rectifier module is in an overall H-bridge structure, and a bypass switch K is electrically connected to the bridge rectifier module xN3 , which is used to convert a DC circuit into an AC circuit. The intelligent control unit is a control and protection device for the cascaded multilevel energy storage system, and is used to implement control strategies and protection strategies.

[0007] As a preferred solution, the bypass switch K xN3 short-circuits the H-bridge circuit when a fault occurs, thereby ensuring the normal operation of the entire system.

[0008] As a preferred solution, the autotransformer is divided into a primary winding and a secondary winding; The primary winding of the autotransformer is connected to the grid side, and the secondary winding of the autotransformer is connected to the energy storage module.

[0009] As a preferred solution, there are N energy storage modules, and N is greater than or equal to 1. The N energy storage modules form a cascaded topology in a series or mixed connection manner.

[0010] As a preferred solution, each bridge rectifier module uses the switching states of IGBT power devices: +Vdc, -Vdc, 0V. Under the modulation strategy control implemented by the intelligent control unit, the output voltages of each module are superimposed to synthesize a multilevel stepped wave to approximate the target sine waveform.

[0011] According to a configuration method proposed for a cascaded multilevel energy storage system, the cascaded multilevel energy storage system matches different voltage level requirements by configuring the turns ratio of the autotransformer. The specific configuration method is as follows: Step 1: Determine whether the application scenario of the cascaded multilevel energy storage system is a boost topology scenario or a buck topology scenario. Connect the battery pack to the DC side of the bridge rectifier module respectively, and form a multilevel output by connecting N bridge rectifier modules in series. Design the target output voltage U target ; Step 2: Determine the k value of the target voltage according to the turns ratio formula; Step 3: Determine the number N of energy storage modules required for the cascaded multilevel energy storage system according to Step 2; Step 4: Fix the turns ratio of the autotransformer and the number of energy storage modules, so that the output voltage of the cascaded multilevel energy storage system is locked at U target, it will no longer be dynamically adjusted during operation.

[0012] As a preferred solution, the turns ratio formula in step 2 is: where N1 is the number of turns of the primary winding, N2 is the effective number of turns of the secondary side, and U grid is the grid-side voltage, and U total is the total output voltage of the energy storage module.

[0013] As a preferred solution, the total output voltage U total of the energy storage module is determined by the number of modules N and the output voltage U sub of a single energy storage module, that is, U total = NU sub .

[0014] As a preferred solution, the k value for determining the target voltage in step 2 is specifically calculated by the formula: .

[0015] As a preferred solution, the number N of the energy storage modules is determined in step 3, and the specific formula is as follows: .

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Through the coordinated control of the autotransformer and the cascaded topology, the present invention breaks through the rigid coupling relationship between the voltage level and the number of modules of the traditional cascaded energy storage system, significantly improves the compatibility of the system with different voltage scenarios (such as low / medium / high voltage power grids, electric vehicle charging piles, etc.), and at the same time supports the differential capacity configuration and flexible expansion of the energy storage modules, solving the problems of voltage rigidity and low capacity utilization rate in the prior art.

[0017] 2. This system can be widely applied to scenarios such as new energy power station grid connection and microgrid energy management, and has the advantages of high flexibility, high efficiency, and low-cost expansion. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Topological diagram of a cascaded multilevel energy storage system and its configuration method; Figure 2 Boost autotransformer collaborative topology of a cascaded multilevel energy storage system and its configuration method; Figure 3 Buck autotransformer collaborative topology of a cascaded multilevel energy storage system and its configuration method. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0020] It should be understood that when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, wholes, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or their combinations.

[0021] It should also be understood that the terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" are intended to include the plural forms.

[0022] It should be further understood that the term "and / or" used in the specification of the present invention and the appended claims refers to any combination and all possible combinations of one or more of the related listed items, and includes these combinations.

[0023] Embodiment 1 As Figure 1 shown, a cascaded multilevel energy storage system and its configuration method include an autotransformer, an energy storage module, and an intelligent control unit; the autotransformer is connected to the energy storage module; the energy storage module is connected to the intelligent control unit.

[0024] The energy storage module consists of a bridge rectifier module, a DC capacitor, and a battery pack; the bridge rectifier module is connected to the DC capacitor, and the DC capacitor is connected to the battery pack; the bridge rectifier module converts the DC circuit into an AC circuit, and the overall structure is an H-bridge structure, and a bypass switch K is provided. xN3 ; The bypass switch is used to short-circuit the H-bridge when a fault occurs in the H-bridge, so that the entire system can operate normally.

[0025] The autotransformer is divided into a primary winding and a secondary winding; the primary winding of the autotransformer is connected to the grid side.

[0026] The autotransformer is connected to the energy storage module where it is located. Specifically, the secondary winding of the autotransformer is connected to the energy storage module.

[0027] There are N energy storage modules, and N is greater than or equal to 1; the N energy storage modules form a cascaded topology in series or parallel connection.

[0028] The intelligent control unit is the control and protection device of the system, responsible for implementing control strategies and protection strategies.

[0029] The system matches the requirements of different voltage levels by configuring the turns ratio of the autotransformer, realizing flexible energy interaction between the energy storage unit and the power grid. The specific configuration method is as follows: Step 1: Determine the system application scenario and design the target output voltage U target 。

[0030] Step 2: Determine the k value of the target voltage according to the turns ratio formula.

[0031] The turns ratio formula is: Where N1 is the number of turns of the primary winding, N2 is the effective number of turns of the secondary winding, U grid is the grid-side voltage, and U total is the total output voltage of the energy storage module.

[0032] The total output voltage U of the energy storage module total is determined by the number of modules N and the output voltage U of a single energy storage module sub , that is, U total = NU sub 。

[0033] The formula for determining the k value of the target voltage is: Step 3: According to Step 2, determine the number N of energy storage modules required for the system, 。

[0034] Step 4: Fix the turns ratio of the autotransformer and the number of energy storage modules, so that the system output voltage is locked at U target , and no dynamic adjustment is made during operation.

[0035] The system precisely matches the voltage ratio set by the autotransformer by adjusting the number N of energy storage modules or the output voltage of the energy storage module, ensuring the stability of the output voltage.

[0036] Embodiment 2 As Figure 2 shown, in the boost topology of a cascaded multilevel energy storage system and its configuration method, the primary winding of the autotransformer is connected to the power grid, and the secondary winding of the autotransformer is connected to the energy storage module.

[0037] In the boost topology, the primary winding is the high-voltage side and the secondary winding is the low-voltage side.

[0038] According to the configuration method of Embodiment 1, there are the following steps: Step 1: Determine that the system is a boost topology and design the target output voltage U target = 400V, grid voltage Ugrid = 800 V; Step 2: Determine the k value of the target voltage according to the turns ratio formula, k = 2.

[0039] Step 3: Determine the number N of energy storage modules required for the system according to Step 2; If a single energy storage module U sub = 50 V, then the number of energy storage modules N = 8.

[0040] Step 4: Fix the turns ratio k = 2 of the autotransformer and the number of energy storage modules to 8, so that the system output voltage is locked at 400 V. The fixed turns ratio of the autotransformer and the redundant design of the energy storage modules jointly ensure the stability of the system output voltage. Therefore, the specific formulas for the total power of the secondary winding, the total power of the primary winding, and the current of the primary winding are as follows: Total power of the secondary winding: Total power of the primary winding: Current of the primary winding: Embodiment 3 As Figure 3 shown, in the buck topology of a cascaded multilevel energy storage system and its configuration method, the primary winding of the autotransformer is connected to the power grid, and the secondary winding of the autotransformer is connected to the energy storage module.

[0041] In the buck topology, the primary winding is the low-voltage side and the secondary winding is the high-voltage side.

[0042] According to the configuration method of Embodiment 1, there are the following steps: Step 1: Determine that the system is a buck topology, and design the target output voltage U target = 10 kV, and the grid voltage U grid = 5 kV; Step 2: Determine the k value of the target voltage according to the turns ratio formula, k = 0.5.

[0043] Step 3: Determine the number N of energy storage modules required for the system according to Step 2; If a single energy storage module U sub = 200 V, then the number of energy storage modules N = 50.

[0044] Step 4: Fix the autotransformer turns ratio k = 0.5 and the number of energy storage modules to 50, so that the system output voltage is locked at 10 kV. The fixed turns ratio of the autotransformer restricts the adjustment range of the system output voltage. Therefore, the specific formulas for the total power of the secondary winding and the current of the primary winding are as follows: The total power of the secondary winding is: The current of the primary winding is: Those of ordinary skill in the art can realize that the units described in combination with the examples disclosed in this embodiment can be implemented by electronic hardware, computer software, or a combination of the two. To clearly illustrate the interchangeability of hardware and software, the components of each example have been generally described according to their functions in the above description. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Professional technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

[0045] In the embodiments provided in the present application, it should be understood that the division of units is only a logical function division, and there may be other division methods in actual implementation. For example, multiple units can be combined into one unit, one unit can be split into multiple units, or some features can be ignored, etc.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered by the scope of the claims and the description of the present invention.

Claims

1. A cascaded multilevel energy storage system, characterized in that, It includes an autotransformer, an energy storage module and an intelligent control unit. The autotransformer is connected to the energy storage module, and the energy storage module is connected to the intelligent control unit; The energy storage module consists of a bridge rectifier module, a DC capacitor and a battery pack; The bridge rectifier module is connected to the DC capacitor, and the DC capacitor is connected to the battery pack; The overall structure of the bridge-type current conversion module is an H-bridge structure, and a bypass switch K is electrically connected to the bridge-type current conversion module xN3 , which is used to convert a DC circuit into an AC circuit; The intelligent control unit is a control and protection device for a cascaded multilevel energy storage system, which is used to implement control strategies and protection strategies.

2. The cascade multi-level energy storage system according to claim 1, wherein The bypass switch K xN3 short - circuits the H - bridge circuit in case of a fault, thus ensuring the normal operation of the entire system.

3. The cascaded multi-level energy storage system according to claim 1, wherein The autotransformer is divided into a primary winding and a secondary winding; The primary winding of the autotransformer is connected to the grid side, and the secondary winding of the autotransformer is connected to the energy storage module.

4. A cascaded multi-level energy storage system according to claim 3, characterized in that There are N energy storage modules, and N is greater than or equal to 1. The N energy storage modules form a cascaded topology in a series or mixed connection manner.

5. The cascaded multi-level energy storage system according to claim 4, characterized in that, Each bridge rectifier module uses the switching states of IGBT power devices: +Vdc, -Vdc, 0V. Under the modulation strategy control implemented by the intelligent control unit, the output voltages of each module are superimposed to synthesize a multilevel stepped wave to approximate the target sine waveform.

6. A configuration method, the configuration method being used for a cascaded multi-level energy storage system according to any one of claims 1-5, characterized in that, The cascaded multilevel energy storage system matches the requirements of different voltage levels by configuring the turns ratio of the autotransformer. The specific configuration method is as follows: Step 1: Determine whether the application scenario of the cascaded multilevel energy storage system is a boost topology scenario or a buck topology scenario. Connect the battery packs to the DC side of the bridge converter module respectively, and form a multilevel output by connecting N bridge converter modules in series. The designed target output voltage is U target ; Step 2: Determine the k value of the target voltage according to the turns ratio formula; Step 3: Determine the number N of energy storage modules required for the cascaded multilevel energy storage system according to Step 2; Step 4: Fix the autotransformer turns ratio and the number of energy storage modules so that the output voltage of the cascaded multilevel energy storage system is locked at U target , and no dynamic adjustment is made during operation.

7. A configuration method according to claim 6, characterized in that, The turns ratio formula in Step 2 is: Among them, N1 is the number of turns of the primary winding, N2 is the effective number of turns of the secondary side, U grid is the grid-side voltage, U total is the total output voltage of the energy storage module.

8. A configuration method according to claim 7, wherein The total output voltage U of the energy storage module total is determined by the number of modules N and the output voltage U of a single energy storage module sub , that is total U = NU sub .

9. The configuration method according to claim 8, characterized in that, The formula for determining the k value of the target voltage in Step 2 is specifically: 。 10. The configuration method according to claim 9, characterized in that, The formula for determining the number N of the energy storage modules in Step 3 is as follows: 。

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