A modular energy storage system

Abstract

The present invention discloses a modular energy storage system, which comprises a ring-shaped superconducting magnet formed by connecting n arc-shaped magnet modules end to end. Each arc-shaped magnet module is connected in parallel to a DC power grid via a DC bidirectional current source power converter. The power converter controls the voltage and current sharing of each arc-shaped magnet module to generate equal magnetic flux and superimpose them in the arc direction. The power converter adopts a bidirectional current source two-level topology to reduce device current stress and bus current ripple. A phase-shift control strategy is adopted between the power converters to effectively reduce current and total magnetic flux ripple, reduce AC loss of the superconducting magnet, improve the efficiency of the superconducting system, and realize rapid conversion of high-efficiency, high-power electrical energy and magnetic energy. The system can be applied to energy conversion occasions such as new power grids and integrated power systems for ships.

Description

Technical Field

[0001] The present invention belongs to the fields of superconducting applications, power electronics, electrical engineering and new electric energy technologies, and relates to high-efficiency, large-capacity, fast-response superconducting energy storage technology, and specifically to a modular energy storage system. Background Art

[0002] As a new type of material with excellent electromagnetic properties and great application potential, superconducting materials have the advantages of low conductive losses and high current density. Superconducting magnetic energy storage systems can achieve rapid conversion of electrical and magnetic energy, achieving millisecond-level power response, effectively improving power quality and enhancing power system stability. Superconducting energy storage systems use superconducting magnets to store energy in the grid as electromagnetic energy, returning the electrical energy to the grid or for other purposes when needed. Essentially, they are an inductive energy storage technology consisting of energy storage magnets, converters, constant temperature dewars, cryogenic refrigeration equipment, quench protection devices, and monitoring systems.

[0003] The superconducting magnet is the core component of the superconducting magnetic energy storage device, and its stability is related to whether the entire device can operate safely. Superconducting energy storage magnets can be made of high-temperature superconducting materials or low-temperature superconducting materials. The structural form of superconducting magnets can be annular, parallel multi-solenoid and single solenoid: the single solenoid type has a simple structure and is easy to process and manufacture, but it has a large leakage magnetic field; the parallel multi-solenoid type has a smaller leakage magnetic field, but its energy storage density is very low; the annular energy storage magnet uses a medium amount of wire, and the tightly coupled structure confines the magnetic field to the inside of the annular coil, and the magnet leakage magnetic field is very small. The annular structure is the first choice for large-capacity energy storage magnets, but high power requires the magnet to withstand higher voltages, which poses a challenge to low-temperature thermal insulation.

[0004] The cooling methods and structures of magnets include immersion cooling, steam cooling, and conduction cooling. Conduction cooling does not require cryogenic liquid or steam, but instead conducts the heat of the magnet to the refrigerator through metal cooling materials. It has a compact structure and is easy to maintain. However, the introduction of cooling metal structural parts also brings problems of low-temperature insulation and eddy current loss, which may limit the power output of the energy storage magnet and reduce the energy storage efficiency.

[0005] On the other hand, due to the presence of pinning centers in high-temperature superconducting materials, when a varying current is applied to the superconductor, the Lorentz force overcomes the pinning force, generating heat energy known as AC losses. AC losses can adversely affect high-temperature superconductors, which require maintaining a low-temperature operating environment. They not only increase the cooling costs of superconducting magnets but also cause the magnet temperature to rise and the critical current to decrease, compromising the performance and stability of the magnet.

[0006] Because the DC-side energy storage element in superconducting energy storage is an inductor, a current source converter topology is ideal. This simplifies the converter structure and improves charging / discharging efficiency and safety. Multilevel current source converters, in addition to the advantages of traditional two-level current source converters, offer reduced switching stress on individual devices, large output capacity, and low harmonic content in the output waveform. They are particularly suitable for low-voltage, high-current applications. Furthermore, with the development of reverse-blocking switching devices (such as integrated gate-commutated thyristors), multilevel current source converters are experiencing new opportunities and possess promising application prospects and development trends. However, the multi-objective coordinated control of bidirectional multilevel current source converters and their integration with modular energy storage magnets increases the technical complexity of system development, hindering their development.

[0007] In principle, superconducting energy storage systems based on high-temperature superconducting materials have the advantages of low operating losses, large working capacity, and small device size. However, in reality, these advantages will be offset by refrigeration costs, and a considerable part of these costs comes from lead losses, mainly including conductive losses and heat leakage losses, which limits their application.

[0008] In summary, the expansion of superconducting energy storage systems is hampered by the difficulty in balancing multiple objectives, such as efficiency, power, insulation, and cooling. This is particularly true given the increased control dimension and complex control strategies, which increase the technical difficulty of system development and restrict its development. Analyzing this issue and seeking solutions is both theoretically and practically valuable. Summary of the Invention

[0009] The purpose of the present invention is to propose a modular energy storage system: design a new modular energy storage magnet to reduce the voltage of the unit energy storage magnet, reduce the difficulty of low-temperature insulation design of the conduction-cooled magnet, and achieve system redundancy and fault tolerance; design a new current source converter to reduce the switching stress of a single device, reduce the output waveform ripple content, reduce AC loss, and be suitable for low voltage and high current, and achieve high efficiency and high power; through coordinated control of the modular energy storage magnet and the converter, further reduce the output waveform ripple content, reduce AC loss, improve efficiency, and reduce refrigeration requirements; reduce cross-environment leads, fundamentally avoid unnecessary lead losses, improve the economy of superconducting application technology, and thus achieve efficient, safe, stable, and fast operation of a high-power superconducting energy storage system.

[0010] The technical solution adopted by the present invention to solve its technical problems is: a modular energy storage system, which adopts superconducting energy storage, includes a ring-shaped superconducting magnet formed by connecting n unit arc-shaped magnet modules end to end on the circumference, the arc of the arc-shaped magnet module is 2π / n, 2≤n≤10, each arc-shaped magnet module is connected in parallel to the bus of the DC power grid through its own independent DC bidirectional current source power converter, and controls the charging and discharging current of the arc-shaped magnet module to be equal to reduce the voltage pressure of the magnet; the power converter controls the equalization of voltage and current of each arc-shaped magnet module, generates equal magnetic flux and superimposes it in the arc direction, and each power converter has the function of serving as a backup for each other. After a unit module circuit fails, the remaining unit modules can continue to operate in fault-tolerant redundancy, thereby improving the reliability of the energy storage system; the power converter adopts a two-level topology, reduces the device current stress, reduces the bus current ripple, and the power switch tube T e The emitter of diode D e The negative electrodes are connected in series, marked as connection point E, forming bridge arm Q e , power switch tube T f The collector of the diode D f The positive electrodes are connected in series, marked as connection point F, forming a bridge arm Q f , connection points E and F are connected to the two ends of the arc magnet module respectively, and the bridge arm Q e With bridge arm Q f Connected in parallel to the DC bus support capacitor C, the bridge arm Q e Upper power switch tube T e The collector is connected to the positive bus P, the bridge arm Q e Upper diode D e The positive pole is connected to the negative bus N, and the bridge arm Q f The emitter of the upper power switch tube Tf is connected to the negative bus N, and the bridge arm Q f Upper diode D f The negative pole is connected to the positive bus P.

[0011] Furthermore, the arc magnet module is mainly composed of a superconducting coil, an inner ring, an outer ring, a radial support assembly, a cooling plate, a supporting side plate, a current lead assembly and a low-temperature glue.

[0012] Furthermore, the superconducting coil is a double-pancake coil wound on the inner ring, with a transition fit between the superconducting coil and the inner ring, the outer ring is sleeved on the outside of the superconducting coil, with a gap fit between the two, the gap between the outer ring and the superconducting coil is filled with a superconducting tape, and a radial support assembly is sleeved on the outside of the outer ring, with a transition fit between the two, the cold conduction plates are respectively located on both sides of the superconducting coil, and are fixedly connected to the inner ring and the radial support assembly by bolts, the support side plates are located on the outside of the cold conduction plates, and are fixedly connected to the inner ring and the radial support assembly by bolts, and the current lead assembly is located in the upper middle part of the magnet unit and is fixed on the radial support assembly.

[0013] Furthermore, the two-level power converter adopts a closed-loop control strategy to control the charging and discharging state of the arc-shaped magnetic module: the power switch tube T e Drive pulse trigger, power switch tube T e Turn on, power switch tube T f Drive pulse trigger, power switch tube T f The arc-shaped magnetic module is charged; the power switch tube T e Drive pulse trigger, power switch tube T e Turn on, power switch tube T f Drive pulse blocked, power switch tube T f Blocking, diode D e Blocking, diode D f The arc-shaped magnetic module is turned on and continues to flow; the power switch tube T e Drive pulse blocked, power switch tube T e Blocking, power switch tube T f Drive pulse trigger, power switch tube T f Conducting, diode D e Conducting, diode D f Blocking, arc-shaped magnetic module continuous flow; power switch tube T e Drive pulse blocked, power switch tube T e Blocking, power switch tube T f Drive pulse blocked, power switch tube T f Blocking, diode D e , diode D f The arc magnet module is turned on and discharged.

[0014] Furthermore, the arc magnet module current adopts closed loop control, and the regulator realizes fast tracking and error-free regulation of charge and discharge current, and maintains the current balance of each module: The reference instruction is output by the PI current regulator, and the absolute value of the signal is used as the common reference modulation wave of each converter. D , each power switch tube is turned on and off according to the multi-level DC pulse width modulation strategy.

[0015] In the modular energy storage system, the power switch tube adopts a multi-level carrier phase-shift pulse width modulation strategy, and generates a PWM wave by comparing a plurality of triangular carriers with the same phase shift and amplitude with the modulation wave to control each group of power units respectively, and then superimposes them to form a multi-level PWM waveform.

[0016] The modular energy storage system adopts a phase shift control strategy between each power converter, namely power converter Ck, k∈{1,…,n}, which effectively reduces the total magnet synthetic flux ripple, reduces the arc magnet module induced potential and current ripple, and reduces the superconducting magnet AC loss; reduces the bus current ripple, power converters C1, C n Each cluster triggers a pulse sequence, which shifts phase by 2π / n in a switching cycle T. The converter modules C1 and C n Each cluster of trigger pulse sequences is delayed by T / n in sequence.

[0017] Furthermore, the power switch tube T e , T f It is a reverse-blocking switching device with reverse blocking capability but no reverse conducting capability; or it is a reverse-conducting switching device with reverse conducting capability with a diode connected in series in the forward direction at the emitter.

[0018] Furthermore, the switching device may be one of a power transistor GTR, an insulated gate bipolar transistor IGBT, an integrated gate-commutated thyristor IGCT, and a metal oxide semiconductor field effect transistor MOSFET.

[0019] The beneficial effects of the present invention are as follows: the present invention uses a combination of multiple arc-shaped magnet modules to form a ring-shaped superconducting magnet. Each arc-shaped magnet module is connected in parallel to the DC power grid through its own independent power converter, reducing voltage stress. The power converter adopts a bidirectional current source two-level topology, which reduces device current stress and bus current ripple. A phase-shift control strategy is adopted between the power converters, effectively reducing current and total magnetic flux ripple, and reducing the AC loss of the superconducting magnet. The converter's current sharing / shunting inductor uses superconducting materials, reducing losses and improving the efficiency of the superconducting system. The ring-shaped superconducting magnet can achieve high-efficiency and high-power rapid conversion of electrical energy and magnetic energy, and can be applied to energy conversion occasions such as new power grids and integrated ship power systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0021] Figure 2 is a partial cross-sectional view of the annular superconducting magnet of the present invention;

[0022] Figure 3 Schematic diagram of three traditional superconducting magnet structures;

[0023] Figure 4 Schematic diagram of the structure of the annular superconducting magnet of the present invention;

[0024] Figure 5 A partial cross-sectional view of the arc-shaped magnet module of the present invention;

[0025] Figure 6 Schematic diagram of the decomposition of the arc magnet module;

[0026] Figure 7 This is a schematic diagram of the structure of the arc-shaped magnet module cooling plate and supporting side plates;

[0027] Figure 8 The inner and outer ring structures of the present invention and their relationship with the superconducting coil;

[0028] Figure 9 This is a structural diagram of the radial support assembly of the present invention;

[0029] Figure 10 This is a diagram of the cold conduction plate structure and its fixing structure of the present invention;

[0030] Figure 11 The supporting side panel structure and its installation method of the present invention;

[0031] Figure 12 This is a structural diagram of the current lead assembly of the present invention;

[0032] Figure 13 2 is a schematic structural diagram of a power converter according to the present invention;

[0033] Figure 14 It is a bidirectional current source multi-level energy storage power converter power device;

[0034] Figure 15 Adopting phase shift control strategy between power converters;

[0035] Figure 16 The current waveform adopts phase-shift control strategy between magnet modules.

[0036] The reference numerals of the figures are: 01 - superconducting coil, 02 - inner ring, 03 - outer ring, 04 - radial support assembly, 05 - cooling plate, 06 - support side plate, 07 - current lead assembly. DETAILED DESCRIPTION

[0037] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0038] Reference Figure 1 As shown, the present invention discloses a current-type energy conversion system that uses superconducting energy storage. The system uses n arc-shaped magnet modules, 2≤n≤10, and each arc-shaped magnet module has a radian of 2π / n. They are combined on the circumference to form a ring-shaped magnet overall. The tightly coupled structure confines the magnetic field to the inside of the ring coil, and the magnet leakage field is very small. Each arc-shaped magnet module is connected in parallel to the busbar of the DC grid through its own independent DC bidirectional current source power converter. The arc-shaped magnet module controls the voltage and current of each arc-shaped magnet module to generate equal magnetic flux, and superimposes them in the arc direction, as shown in FIG. Figure 2 shown.

[0039] Conventional superconducting magnet structures such as Figure 3 As shown in the figure, a is a single solenoid, b is a multi-(quadruple) solenoid, and c is a ring magnet. Different from the traditional superconducting magnet structure, the arc-shaped magnet module of the present invention has a radian of 2π / n, 2≤n≤10, as shown in the figure. Figure 4 and Figure 5 As shown, the tightly coupled structure confines the magnetic field within the toroidal coil, minimizing magnetic leakage field. The power converter controls the voltage and current distribution of each arc-shaped magnet module, generating equal magnetic flux that overlaps along the arc. Each power converter functions as a backup for the others. If one module fails, the remaining modules can continue to operate with fault-tolerant redundancy, improving the reliability of the energy storage system. The converter's shunt inductor uses superconducting material and is integrated with the superconducting magnet into a cryostat dewar, reducing lead losses.

[0040] Reference Figure 6 As shown, the arc magnet module is mainly composed of superconducting coil 01, inner ring 02, outer ring 03, radial support assembly 04, cold plate 05, support side plate 06, current lead assembly 07 and low temperature glue. The structure of cold plate 05 and support side plate 06 is as shown in FIG. Figure 7 shown.

[0041] The superconducting coil 01 is a double-pancake coil, wound around the inner ring 02, with a transition fit between the two. The outer ring 03 fits over the coil, with a gap between the two, filled with superconducting tape. The radial support assembly 04 fits over the outer ring 03, with a transition fit between the two. The cold plate 05 is located on either side of the superconducting coil 01 and is bolted to the inner ring 02 and radial support assembly 04. The support side plate 06 is located outside the cold plate 05 and is bolted to the inner ring 02 and radial support assembly 04. The current lead assembly 07 is located in the upper middle portion of the magnet unit and is fixed to the radial support assembly 04. After the entire arc magnet module is assembled, it is filled and cured with low-temperature glue using a room-temperature vacuum impregnation process. To reduce eddy current losses, the inner ring 02, outer ring 03, and support side plates 06 are all made of non-metallic composite materials. The cold plate 05 is made of copper and is located on both sides of the superconducting coil 01.

[0042] The inner ring 02 and the outer ring 03 are both made of composite materials. Their structure and the assembly relationship with the superconducting coil 01 are shown in the figure. Figure 8 The inner ring 02 is a stepped structure on which the superconducting coil 01 is wound; the outer ring 03 is a circular ring structure, which is sleeved outside the superconducting coil 01 and is used to withstand the electromagnetic force of the superconducting coil 01 in the radial direction outward.

[0043] The radial support assembly 04 is located outside the outer ring 03 and is mainly composed of an aluminum alloy frame, composite material tie rods and pressure blocks, such as Figure 9 As shown, the radial support assembly 04 primarily supports and secures the arc-shaped magnet module, while also connecting to the external cooling element. To reduce eddy current losses in the aluminum alloy frame, it is divided into two parts, connected by composite tie rods and compressed with a pressure block. This reduces eddy current losses in the frame while also enhancing the shrinkage consistency between the aluminum alloy frame and the outer ring 03.

[0044] The magnet unit cold plate 05 is located on both sides of the superconducting coil 01 and is used for heat conduction of the superconducting coil 01. The cold plate 05 is made of copper material and its structure is as follows: Figure 10 As shown in the figure, considering that the cold plate 05 is located in a relatively large magnetic field and generates eddy current losses during the charging and discharging process, the cold plate 05 is slotted to reduce the eddy current losses generated by the cold plate 05. The cold plate 05 is fixedly connected to the radial assembly and the inner ring 02 by bolts.

[0045] The supporting side plates 06 are made of non-metallic composite materials. The two supporting side plates 06 are installed on both sides of the superconducting coil 01. Their dimensions are consistent with those of the cold plate 05 and they are aligned with the cold plate 05. This allows the cold plate 05 to fit tightly with the superconducting coil 01 and also enhances the lateral strength of the entire magnet unit. Considering the low strength of composite materials and aluminum alloys, a pre-embedded stainless steel screw sleeve with internal thread is used to achieve threaded connection. The external structure and installation method of the magnet unit supporting side plates 06 are as follows: Figure 11 shown.

[0046] In order not to destroy the integrity of the composite material outer ring 03, the current lead assembly 07 of the superconducting coil 01 is Figure 12 In the structure shown, the outermost turns of the superconducting coil 01 are led to the upper end of the magnet unit. The external leads are horizontal, facilitating series connections between adjacent magnet units. The current lead assembly 07 primarily consists of an epoxy plate, an oxygen-free copper plate, and a superconducting broadband. The broadband overlaps the outermost turns of the superconducting coil 01 and is welded to the oxygen-free copper plate. The oxygen-free copper plate is bolted to the epoxy plate, which is bolted to the radial support assembly 04 and the outer ring 03. Each magnet unit is equipped with two sets of current lead assemblies 07, aligned and fixed to the upper portion of the magnet unit.

[0047] The DC bidirectional current source power converter adopts a two-level topology, which reduces the device current stress and bus current ripple. Figure 13 As shown. Power switch tube T e The emitter of diode D e The negative electrodes are connected in series, marked as connection point E, forming bridge arm Q e , power switch tube Tf The collector of the diode D f The positive electrodes are connected in series, marked as connection point F, forming a bridge arm Q f , connection points E and F are connected to the two ends of the arc magnet module respectively, and the bridge arm Q e With bridge arm Q f Connected in parallel to the DC bus support capacitor C, the bridge arm Q e Upper power switch tube T e The collector is connected to the positive bus P, the bridge arm Q e Upper diode D e The positive pole is connected to the negative bus N, and the bridge arm Q f The emitter of the upper power switch tube Tf is connected to the negative bus N, and the bridge arm Q f Upper diode D f The negative pole is connected to the positive bus P.

[0048] The power switch tube T e , T f It is a reverse blocking type switching device with reverse blocking capability but no reverse conducting capability; or it is a reverse conducting type switching device with reverse conducting capability with a diode connected in series in the forward direction of the emitter. The switching device can be a power transistor GTR, an insulated gate bipolar transistor IGBT, an integrated gate commutated thyristor IGCT, a metal oxide semiconductor field effect transistor MOSFET, such as Figure 14 The shunt inductor uses superconducting materials to reduce the loss of the shunt inductor.

[0049] The two-level power converter adopts a closed-loop control strategy to control the charging and discharging state of the arc-shaped magnet module.

[0050] Power switch tube T e Drive pulse trigger, power switch tube T e Turn on, power switch tube T f Drive pulse trigger, power switch tube T f Turn on and the arc magnet module is charged.

[0051] Power switch tube T e Drive pulse trigger, power switch tube T e Turn on, power switch tube T f Drive pulse blocked, power switch tube T f Blocking, diode D e Blocking, diode D f The arc magnet module is turned on and continues to flow.

[0052] Power switch tube T e Drive pulse blocked, power switch tube T e Blocking, power switch tube T f Drive pulse trigger, power switch tube Tf Conducting, diode D e Conducting, diode D f Blocked, arc magnet module continues current.

[0053] Power switch tube T e Drive pulse blocked, power switch tube T e Blocking, power switch tube T f Drive pulse blocked, power switch tube T f Blocking, diode D e , diode D f The arc magnet module is turned on and discharged.

[0054] The arc magnet module current is controlled by closed loop, such as Figure 15 As shown, the regulator can achieve fast tracking and error-free regulation of charge and discharge currents and maintain current balance among modules: The reference instruction is output by the PI current regulator, and the absolute value of the signal is used as the common reference modulation wave of each converter. D , each power switch tube is turned on and off according to the multi-level DC pulse width modulation strategy.

[0055] A phase-shift control strategy is adopted between each power converter, that is, the power converter Ck, k∈{1,…,n} effectively reduces the total magnet composite flux ripple, reduces the magnet module induced potential and current ripple, reduces the superconducting magnet AC loss, and reduces the bus current ripple. The trigger pulse sequence of each cluster of power converters C1 and Cn is phase-shifted by 2π / n within a switching cycle T. The trigger pulse sequence of each cluster of converter modules C1 and Cn is sequentially delayed by T / n, as shown in Figure 16 shown.

[0056] The present invention employs a pulse synchronization control strategy between the arc-shaped magnet modules to ensure current balance among them. The converter's shunt inductor utilizes superconducting materials to reduce losses. The shunt inductor and superconducting magnet are integrated into a cryogenic, constant-temperature Dewar vessel, significantly reducing cross-environmental wiring, fundamentally avoiding unnecessary wiring losses and improving the economic efficiency of superconducting applications.

[0057] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments. The above-mentioned specific embodiments are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can make many variations without departing from the scope of protection of the present invention and the claims, and these all fall within the scope of protection of the present invention.

Claims

1. A modular energy storage system, characterized in that: The invention relates to a ring-shaped superconducting magnet formed by connecting n arc-shaped magnet modules end to end. The arc-shaped magnet module is assembled by a superconducting coil (01), an inner ring (02), an outer ring (03), a radial support assembly (04), a cold plate (05), a support side plate (06), a current lead assembly (07), and low-temperature glue, and then vacuum impregnated, filled, and cured at room temperature. The superconducting coil (01) is a double-pancake coil wound on the inner ring (02). The superconducting coil (01) and the inner ring (02) are in transition fit. The outer ring (03) is sleeved on the outer gap of the superconducting coil (01). A superconducting tape is used between the outer ring (03) and the superconducting coil (01). The outer ring (03) is filled with a radial support assembly (04) and is a transition fit. The cold conduction plates (05) are respectively located on both sides of the superconducting coil (01). The support side plates (06) are located outside the cold conduction plates (05). The current lead assembly (07) is fixed on the radial support assembly (04). The arc angle of the arc magnet module is 2π / n, 2≤n≤10. Each arc magnet module is connected to the busbar of the DC grid in parallel through a DC bidirectional current source power converter to control the equalization of voltage and current of each arc magnet module, generate equal magnetic flux and superimpose in the arc direction. The power converter adopts a two-level topology, and the power switch tube T e The emitter of diode D e The negative electrodes are connected in series, marked as connection point E, forming bridge arm Q e , power switch tube T f The collector of the diode D f The positive electrodes are connected in series, marked as connection point F, forming the bridge arm Q f , connection points E and F are connected to the two ends of the arc magnet module respectively, and the bridge arm Q e With bridge arm Q f Connected in parallel to the DC bus support capacitor C, the power switch tube T e The collector of diode D is connected to the positive bus. e The positive electrode is connected to the negative bus, the emitter of the power switch tube Tf is connected to the negative bus N, and the diode D f The negative pole is connected to the positive bus.

2. A modular energy storage system according to claim 1, characterized in that: The power converter adopts a closed-loop control strategy to control the charging and discharging state of the arc-shaped magnetic module: the power switch tube T e Drive pulse trigger, power switch tube T e Turn on, power switch tube T f Drive pulse trigger, power switch tube T f The arc-shaped magnetic module is charged; the power switch tube T e Drive pulse trigger, power switch tube T e Turn on, power switch tube T f Drive pulse blocked, power switch tube T f Blocking, diode D e Blocking, diode D f The arc-shaped magnetic module is turned on and continues to flow; the power switch tube T e Drive pulse blocked, power switch tube T e Blocking, power switch tube T f Drive pulse trigger, power switch tube T f Conducting, diode D e Conducting, diode D f Blocking, arc-shaped magnetic module continuous flow; power switch tube T e Drive pulse blocked, power switch tube T e Blocking, power switch tube T f Drive pulse blocked, power switch tube T f Blocking, diode D e , diode D f The arc magnet module is turned on and discharged.

3. A modular energy storage system according to claim 2, characterized in that: The arc magnet module current adopts closed loop control, and the regulator realizes fast tracking and error-free regulation of charge and discharge current, and maintains the current balance of each module: the reference instruction of charge and discharge current is output by the PI current regulator as the absolute value of the signal common to each converter. D , each power switch tube is turned on and off according to the multi-level DC pulse width modulation strategy.

4. A modular energy storage system according to claim 2, characterized in that: The power switch tube adopts a multi-level carrier phase-shift pulse width modulation strategy. By comparing multiple triangular carriers with the same phase shift and amplitude with the modulation wave, a PWM wave is generated to control each group of power units respectively, and then superimposed to form a multi-level PWM waveform.

5. A modular energy storage system according to claim 4, characterized in that: The power converters Ck, k∈{1,…,n} adopt a phase shift control strategy, and the power converters C1, C n Each cluster triggers a pulse sequence, which shifts phase by 2π / n in a switching cycle T. The converter modules C1 and C n Each cluster of trigger pulse sequences is delayed by T / n in sequence.

6. A modular energy storage system according to claim 5, characterized in that: The power switch tube T e , T f It is a reverse-blocking switching device with reverse blocking capability but no reverse conducting capability; or it is a reverse-conducting switching device with reverse conducting capability with a diode connected in series in the forward direction at the emitter.

7. A modular energy storage system according to claim 6, characterized in that: The switching device is a power transistor GTR, an insulated gate bipolar transistor IGBT, an integrated gate commutated thyristor IGCT or a metal oxide semiconductor field effect transistor MOSFET.

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