CN216819454U

CN216819454U - Energy storage power module and energy storage system

Info

Publication number: CN216819454U
Application number: CN202123390672.2U
Authority: CN
Inventors: 冯亚东; 陈勇; 陈永奎; 桑煜; 陈永
Original assignee: Nanjing Hezhi Electric Power Technology Co ltd
Current assignee: Nanjing Hezhi Electric Power Technology Co ltd
Priority date: 2021-12-29
Filing date: 2021-12-29
Publication date: 2022-06-24
Anticipated expiration: 2031-12-29

Abstract

The application provides an energy storage power module and an energy storage system. The energy storage power module comprises a power conversion circuit and an energy storage unit which are connected in a cascading mode to form an energy storage system. The power conversion circuit comprises a bridge type current transformation unit and a DC-DC unit, wherein one side of the bridge type current transformation unit is a cascade side and is used for being cascaded so as to be connected with an alternating current power grid, and the other side of the bridge type current transformation unit is a direct current side and is connected with the energy storage unit and is used for providing electric energy for the energy storage unit or receiving the electric energy released by the energy storage unit. The energy storage capacitor is adopted in the bridge type current transformation unit to ensure that the cascade voltage output by the bridge type current transformation unit is relatively stable, and ripples carried by an alternating current power grid are reduced. The DC-DC unit controls the energy storage unit to charge and discharge so as to reduce ripples of charging and discharging current to the connected battery pack. The direct current ripple during charging and discharging is reduced, and the service life of the battery can be prolonged. Meanwhile, all the switch devices adopt MOSFET devices with low voltage and low on-resistance, so that the series connection scale of the connected battery packs can be reduced, and the energy conversion loss of the energy storage system can be reduced.

Description

Energy storage power module and energy storage system

Technical Field

The utility model relates to the field of energy storage of power systems, in particular to an energy storage power module and an energy storage system.

Background

In the existing energy storage system of the power system, a centralized battery pack composed of a plurality of series-parallel loops is mostly adopted, and the number of the battery packs connected in series is large, so that the defects of individual batteries may cause the fault of the whole battery pack, even the energy storage system is combusted and exploded, and the service life and the safety of the batteries have great hidden dangers.

At present, researches propose an energy storage system adopting a scheme of a modular multilevel power module, a required alternating current voltage waveform is formed by controllable superposition of output voltages of a plurality of modules, a power module of the modular multilevel energy storage system adopts a two-level or three-level high-capacity converter to realize charging or discharging of an alternating current power grid to a battery system, the current researches adopt high-voltage and high-current power devices, such as IGBT power devices, the high-power devices have the problems of high cost and high conduction voltage, and the power module usually needs to work in a high-voltage (such as 1-2 kV) and high-current (such as 1-2 kA) state to ensure reasonable cost and loss, so that the battery pack scale of each power module is still large, and the problems of battery service life and safety still exist. Meanwhile, the existing modular multilevel energy storage system power module rectifies alternating current power grid current and then directly charges and discharges the battery, and the charging and discharging voltage or current of the battery has large ripples, so that the service life of the battery is greatly influenced. In summary, the energy storage scheme of the currently adopted modular multilevel power module has the problems of large scale of the battery system, short service life of the battery, unsafe condition and the like.

SUMMERY OF THE UTILITY MODEL

Based on above-mentioned current situation, the main aim at of this application provides an energy storage power module and energy storage system, can reduce the scale of group battery, improves energy storage system's security, guarantees simultaneously that the life-span of group battery is not influenced.

In order to achieve the above purpose, the technical solutions adopted in the embodiments of the present application are as follows:

an energy storage power module is used for being connected in a cascading mode to form an energy storage system and comprises a power conversion circuit and an energy storage unit, wherein one side of the function conversion circuit is a cascading side and is used for being cascaded so as to be connected with an alternating current power grid, and the other side of the function conversion circuit is an energy storage side and is connected with the energy storage unit and is used for providing electric energy for the energy storage unit or receiving the electric energy released by the energy storage unit; the power conversion circuit comprises a bridge type current transformation unit and a DC-DC unit, wherein:

the bridge type current transformation unit comprises a bridge type current transformer mainly formed by a plurality of MOS (metal oxide semiconductor) tubes and an energy storage capacitor connected with the second side of the bridge type current transformer, wherein the first side of the bridge type current transformer is the cascade side, and the second side of the bridge type current transformer is a direct current side;

the DC-DC unit comprises a half-bridge converter mainly formed by a plurality of MOS (metal oxide semiconductor) tubes and a first inductor, and is provided with a first direct current side and a second direct current side, wherein the first direct current side is connected with the direct current side of the bridge type converter unit, and the second direct current side is connected with the anode and the cathode of the energy storage unit.

Optionally, the bridge converter is a single-phase full-bridge converter, and includes 4 MOS transistors, is first MOS transistor, second MOS transistor, third MOS transistor and fourth MOS transistor respectively, wherein:

after the source electrode of the first MOS tube is connected with the drain electrode of the third MOS tube, the first end of the bridge type converter is led out;

after the source electrode of the second MOS tube is connected with the drain electrode of the fourth MOS tube, the second end of the bridge type current transformer is led out, and the first end and the second end of the bridge type current transformer form the first side of the bridge type current transformer;

the drain electrode of the first MOS tube and the drain electrode of the second MOS tube are connected with the anode of the energy storage capacitor and then led out of a third end of the bridge type converter;

and after the source electrode of the third MOS tube and the source electrode of the fourth MOS tube are connected with the negative electrode of the energy storage capacitor, the fourth end of the bridge type converter is led out, and the third end and the fourth end of the bridge type converter form the second side of the bridge type converter.

Optionally, the bridge converter is a single-phase half-bridge converter, and includes 2 MOS transistors, a fifth MOS transistor and a sixth MOS transistor, where:

after the source electrode of the fifth MOS tube is connected with the drain electrode of the sixth MOS tube, the first end of the bridge type current converting unit is led out;

a source electrode of the sixth MOS tube is connected with a negative electrode of the energy storage capacitor and then led out of a second end of the bridge type current transformation unit, wherein the first end and the second end of the bridge type current transformation unit form a first side of the bridge type current transformation unit;

and after the drain electrode of the fifth MOS tube is connected with the anode of the energy storage capacitor, the third end of the bridge type current converting unit is led out, and the third end and the second end of the bridge type current converting unit form a second side of the bridge type current converting unit.

Optionally, the plurality of MOS transistors in the half-bridge converter are a seventh MOS transistor and an eighth MOS transistor, where:

the drain electrode of the seventh MOS tube is led out of the first end of the DC-DC unit, and the source electrode of the eighth MOS tube is led out of the second end of the DC-DC unit;

the source electrode of the seventh MOS tube, the drain electrode of the eighth MOS tube and one end of a first inductor are connected, and the other end of the first inductor leads out a third end of the DC-DC unit;

the first and second terminals of the DC-DC unit form a first direct current side of the DC-DC unit, and the second and third terminals form a second direct current side of the DC-DC unit.

a source electrode of the seventh MOS tube, a drain electrode of the eighth MOS tube and one end of a first inductor are connected, and the other end of the first inductor is led out of the first end of the DC-DC unit;

the drain electrode of the seventh MOS tube is led out of the third end of the DC-DC unit, and the source electrode of the eighth MOS tube is led out of the second end of the DC-DC unit;

Optionally, the DC-DC unit further includes a filter circuit, the filter circuit is connected in series with the half-bridge converter, the filter circuit mainly includes a second capacitor and a second inductor, the plurality of MOS transistors in the half-bridge converter are a seventh MOS transistor and an eighth MOS transistor, wherein:

the source electrode of the seventh MOS tube, the drain electrode of the eighth MOS tube and one end of a first inductor are connected, and the other end of the first inductor is connected with the third end of the DC-DC unit through the second inductor;

one end of the first inductor, which is connected with the second inductor, is connected with the second end of the DC-DC unit through the second capacitor;

the source electrode of the seventh MOS tube, the drain electrode of the eighth MOS tube and one end of a first inductor are connected, and the other end of the first inductor is connected with the first end of the DC-DC unit through the second inductor;

Optionally, the energy storage power module further includes a control unit, where the control unit is electrically connected to the bridge type current transforming unit, the DC-DC unit, and the energy storage unit, and is configured to monitor voltage information of the energy storage capacitor and energy storage information of the energy storage unit, and send a control signal to each MOS transistor of the bridge type current transforming unit and the DC-DC unit.

An energy storage system comprises a plurality of energy storage power modules and one or more reactors, wherein grid connection ends are formed at two cascaded ends, one or more bridge arms are formed by sequentially cascading the cascaded sides of the energy storage power modules, two ends of one or more bridge arms are connected with the grid connection ends of the energy storage system, and at least one reactor is connected in series between the cascaded sides of at least one part of the energy storage power modules in each bridge arm and/or between at least one of the two ends of the bridge arm and the grid connection ends.

Optionally, when the bridge converter is a single-phase full-bridge converter, the grid connection end is an ac grid connection end, and the energy storage power modules are cascaded in a manner that:

the cascade sides of the energy storage power modules are sequentially connected and cascaded to form a bridge arm, the first end of the bridge type converter in the first energy storage power module forms the first end of the bridge arm, the second end of the bridge type converter in the last energy storage power module forms the second end of the bridge arm, and the first end and the second end of the bridge arm are respectively connected with the alternating current power grid connecting end.

Optionally, when the bridge converter is a single-phase half-bridge converter, the grid connection end includes a dc grid connection end and an ac grid connection end, the energy storage system further includes a dc grid connection end, and the cascade connection manner of the plurality of energy storage power modules is as follows:

the energy storage power modules are cascaded to form two cascaded bridge arms which are an upper bridge arm and a lower bridge arm respectively, and the upper bridge arm and the lower bridge arm comprise energy storage power modules with the same number, wherein:

in the upper bridge arm, the cascade sides of the energy storage power modules are sequentially connected for cascade connection, the first end of a bridge type converter in the first energy storage power module forms the first end of the upper bridge arm, the first end of the upper bridge arm is connected with the voltage positive end of the direct current power grid connecting end, and the second end of the bridge type converter in the last energy storage power module forms the second end of the upper bridge arm;

in the lower bridge arm, the cascade sides of the energy storage power modules are sequentially connected for cascade connection, the first end of a bridge converter in the first energy storage power module forms the first end of the lower bridge arm, the second end of the bridge converter in the last energy storage power module forms the second end of the lower bridge arm, and the second end of the lower bridge arm is connected with the voltage negative end of the direct current power grid connection end;

the second end of the upper bridge arm is connected with the first end of the lower bridge arm to form a first connecting point, one end of the alternating current power grid connecting end is connected with the first connecting point, and the other end of the alternating current power grid connecting end is connected with a neutral point in the energy storage system.

An energy storage system comprising a multilevel converter comprising a three-phase circuit, each phase circuit comprising a plurality of energy storage power modules as described above and one or more reactors;

the voltage and current monitor is used for monitoring the working current and voltage of the three-phase circuit;

the controller can communicate with each energy storage power module through a communication interface so as to control the working state of each energy storage power module;

in each phase of circuit, the cascade sides of the energy storage power modules are sequentially cascaded to form one or more bridge arms, two ends of the one or more bridge arms are connected with the power grid connecting end of the energy storage system, and at least one reactor is connected in series between the cascade sides of at least one part of the energy storage power modules in each bridge arm and/or between at least one of the two ends of the bridge arm and the power grid connecting end.

Optionally, when the bridge converter is a single-phase full-bridge converter, the grid connection end is an ac grid connection end, and in each phase of circuit, the cascade connection mode of the energy storage power modules is as follows:

Optionally, when the bridge converter is a single-phase half-bridge converter, the grid connection end includes a dc grid connection end and an ac grid connection end, and the ac grid connection end includes three phase circuit connection points;

in each phase circuit, the cascade mode of the energy storage power modules is as follows:

the second end of the upper bridge arm is connected with the first end of the lower bridge arm to form a second connection point;

and the second connection point of each phase circuit is respectively connected with one phase circuit connection point of the alternating current network connection ends.

Has the advantages that:

the application provides an energy storage power module and energy storage system, energy storage power module connects through cascaded mode and forms energy storage system, and energy storage power module includes power conversion circuit and energy storage unit, and power conversion circuit includes bridge type conversion unit and DC-DC unit, and one side of power conversion circuit is for cascading the side for cascade so that be connected with alternating current electric wire netting, and the opposite side is the energy storage side, is connected with the energy storage unit, is used for providing the electric energy or receiving to the energy storage unit the electric energy of energy storage unit release. The bridge type current transformation unit adopts the energy storage capacitor to store electric energy firstly, and then outputs stable direct current voltage, so that the stability of the direct current voltage during the charging of the battery pack can be ensured, and the adverse effect of ripples carried by an alternating current power grid on the battery after the alternating current power grid is directly rectified is reduced; meanwhile, the DC-DC unit controls the energy storage unit to charge and discharge, and meanwhile, the DC-DC unit is matched with the switching frequency to carry out ripple processing on the charge and discharge current of the energy storage unit so as to reduce ripples. Direct current ripples during charging and discharging are reduced during rectification and DC-DC conversion, and the service life of the battery can be prolonged. Meanwhile, all the switching devices in the bridge type current transformation unit and the DC-DC unit adopt MOS devices with low voltage and low on-resistance, so that the scale of series connection of battery packs in the energy storage unit can be reduced, the safety of a battery system is improved, and meanwhile, the energy conversion loss of the energy storage system can be ensured to be low.

Other advantages of the present invention will be described in the detailed description, and those skilled in the art will understand the technical features and technical solutions presented in the description.

Drawings

Preferred embodiments according to the present application will be described below with reference to the accompanying drawings. In the figure:

fig. 1 is a schematic structural diagram of an energy storage power module according to an embodiment of the present application;

fig. 2 is a schematic circuit diagram of an energy storage power module according to an embodiment of the present disclosure;

fig. 3 is a schematic diagram illustrating a charging sequence of an energy storage unit according to an embodiment of the present disclosure;

FIG. 4 is a schematic diagram illustrating a discharge timing of an energy storage unit according to an embodiment of the present disclosure;

fig. 5 is a schematic circuit diagram illustrating an alternative embodiment of a bridge converter unit according to an embodiment of the present application;

fig. 6 is a schematic circuit diagram of a DC-DC unit according to an embodiment of the present disclosure;

fig. 7 is a schematic diagram illustrating another circuit structure of the DC-DC unit according to an embodiment of the present application;

fig. 8 is a schematic diagram illustrating an overall structure of an energy storage power module according to an embodiment of the present application;

fig. 9 is a schematic diagram illustrating an overall structure of an energy storage system when the bridge converter unit adopts the structure shown in fig. 2 according to an embodiment of the present application;

fig. 10 is a schematic diagram illustrating an overall structure of an energy storage system when the bridge converter unit adopts the structure shown in fig. 5 according to an embodiment of the present application.

Detailed Description

In order to describe the technical solutions of the present application in more detail and to facilitate further understanding of the present application, specific embodiments of the present application are described below with reference to the accompanying drawings. It should be understood, however, that all of the illustrative embodiments and descriptions thereof are intended to illustrate the application and are not to be construed as the only limitations of the application.

In this application, "first," "second," "third," "fourth," etc. are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

Referring to fig. 1, in the present application, the energy storage power module includes a power conversion circuit and an energy storage unit 30, the power conversion circuit includes a bridge type current transformation unit 10 and a DC-DC unit 20. The power conversion circuit is cascaded on one side for connection to an ac power grid, i.e. via the first end h1 and the second end h2 of the bridge converter unit 10 for connection to an ac power grid (not shown). The other side of the power conversion circuit is an energy storage side, and is connected to the energy storage unit 30 through the second terminal d2 and the third terminal d3 of the DC-DC unit 20, and is used for providing electric energy to the energy storage unit 30 or receiving electric energy released by the energy storage unit 30. For example, during a low-power consumption period, when the ac power grid is in a surplus, the power conversion circuit may charge the energy storage unit to provide power to the energy storage unit, so as to convert part of the grid power into power in the energy storage unit, and during a high-power consumption period or when the external power grid is interrupted, the power conversion circuit may receive the power released by the energy storage unit and convert the power into the ac power grid to compensate for the grid power.

The energy storage power modules are connected in a cascading mode to form an energy storage system, electric energy of a power grid is converted into electric energy in each energy storage unit, or electric energy released by each energy storage unit is received to compensate the electric energy of the power grid, wherein the cascade connection comprises the connection between two end points of the cascade side of the energy storage power modules in a hand-pulling mode, the connection is in series, a single-phase system is formed, or the connection of the energy storage power modules in series is in series with the hand-pulling mode, a one-phase circuit is formed, and a multi-phase system is formed by the multi-phase circuit, for example, a three-phase system. It will be appreciated that a cascaded single-phase system or a cascaded multi-phase system typically requires at least one reactor (e.g., inductor) to be passed through before being connected to the grid.

Referring also to fig. 2, in the present application, the bridge converter unit 10 includes a bridge converter mainly composed of a plurality of MOS transistors (e.g., Q1-Q4) and an energy storage capacitor C1. The first side of the bridge converter is a cascade side of the bridge converter unit 10, such as the first end h1 and the second end h2 shown in fig. 1 and fig. 2, for forming an energy storage system in a cascade manner and accessing the ac power grid. The second side of the bridge converter, which is the DC side of the bridge converter unit 10, is connected to two ends of the energy storage capacitor C1, such as the third end h3 and the fourth end h4 in fig. 1 and 2, and is connected to the first DC side of the DC-DC unit 20. The DC-DC unit 20 includes a half-bridge converter mainly formed by a plurality of MOS transistors (e.g., Q7, Q8) and a first inductor L1, the DC-DC unit 20 has a first DC side, such as a first end d1 and a second end d2 shown in fig. 1 and 2, connected to the second side of the bridge converter 10, and a second DC side, such as a second end d2 and a third end d3 shown in fig. 1 and 2, connected to the positive electrode and the negative electrode of the energy storage unit 30. The DC-DC unit 20 is configured to adapt a voltage between the bridge current transforming unit 10 and the energy storing unit 30, and filter a current ripple between the bridge current transforming unit 10 and the energy storing unit 30. For example, when the energy storage unit 30 is charged, the first inductor L1 may perform dc ripple processing on the output dc current of the bridge converter unit 10, so as to reduce the ripple. During charging and discharging, the direct current ripple of the charging and discharging current can be further reduced by controlling the switching frequency of the MOS tube, and the larger the switching frequency is, the smaller the direct current ripple of the finally formed charging and discharging current is.

In this embodiment, the energy storage power module adopts the energy storage capacitor in the bridge type current transforming unit to store the electric energy first, and then the bridge type current transforming unit outputs the stable dc voltage, so as to ensure the stability of the dc voltage when the battery pack is charged, and reduce the ripples carried by the ac power grid after the ac power grid is directly rectified. The DC-DC unit controls the energy storage unit to charge and discharge, and meanwhile, the DC-DC unit is matched with the switching frequency to carry out ripple processing on the charge and discharge current of the energy storage unit so as to reduce ripples. The direct current ripple during charging and discharging is reduced during rectification and DC-DC, and the service life of the battery can be prolonged. Meanwhile, all the switching devices in the bridge type current transformation unit and the DC-DC unit adopt MOS devices with low voltage and low on-resistance, so that the scale of the series connection of the connected battery packs can be reduced, and the energy conversion loss of the energy storage system can be reduced.

With reference to fig. 2, a schematic circuit diagram of an energy storage power module according to an embodiment of the present application is shown. In the present embodiment, as shown in fig. 2, the bridge converter may be a single-phase full-bridge converter, and includes 4 MOS transistors Q1-Q4. The single-phase full-bridge converter is formed by connecting two bridge arms in parallel, each bridge arm is formed by connecting two MOS tubes in series, and the energy storage capacitor C1 is connected to the second side of the single-phase full-bridge converter. As shown in the figure, after the source of the first MOS transistor Q1 is connected to the drain of the third MOS transistor Q3, the first end h1 of the bridge converter unit is led out, and after the source of the second MOS transistor Q2 is connected to the drain of the fourth MOS transistor Q4, the second end h2 of the bridge converter unit 10 is led out, and the first end h1 and the second end h2 form the first side of the bridge converter, that is, the cascade side. After the drain of the first MOS transistor Q1 and the drain of the third MOS transistor Q3 are connected to the anode of the energy storage capacitor C1, the third terminal h3 of the bridge converter unit 10 is led out, the source of the third MOS transistor Q3 and the source of the fourth MOS transistor Q4 are connected to the cathode of the energy storage capacitor C1, the fourth terminal h4 of the bridge converter unit 10 is led out, the third terminal h3 and the fourth terminal h4 form a second side of the bridge converter, the second side is also the dc side of the bridge converter unit 10, and the voltages at the two ends of the dc side are voltages at the two ends of the energy storage capacitor C1.

With continued reference to fig. 2, in the present embodiment, the DC-DC unit 20 is a half-bridge converter, wherein the plurality of MOS transistors are, for example, a seventh MOS transistor Q7, an eighth MOS transistor Q8, and 2 MOS transistors Q7, Q8 connected in series to form a bridge arm, as shown in the figure, a drain of the seventh MOS transistor Q7 leads to a first end d1 of the DC-DC unit, and a source of the eighth MOS transistor Q8 leads to a second end d2 of the DC-DC unit 20; the source of the seventh MOS transistor Q7, the drain of the eighth MOS transistor Q8, and one end of the first inductor L1 are connected, and the other end of the first inductor L1 leads out the third end d3 of the DC-DC unit 20. By this arrangement, a step-down DC-DC unit (for the charging process) can be realized.

In this embodiment, the first end d1 and the second end d2 of the DC-DC unit 20 form a first direct current side of the DC-DC unit 20, and are connected to the direct current sides of the bridge converter unit 10, i.e., the third end h3 and the fourth end h4, and the second end d2 and the third end d3 of the DC-DC unit 20 form a second direct current side of the DC-DC unit 20, and are connected to the positive electrode and the negative electrode of the energy storage unit 30. For the step-down DC-DC unit, since the voltage of the second DC side is lower than the voltage of the first DC side, it can be applied to the situation where the battery pack in the energy storage unit 30 is smaller in size, so that when used in the energy storage system, it can provide higher control accuracy and more diversified operation capabilities.

The operation principle of each part in the energy storage power module is described below by taking the circuit shown in fig. 2 as an example.

In the present application, the charging and discharging management of the energy storage capacitor C1 in the bridge converter unit 10 is managed by the bridge converter, the charging and discharging management of the energy storage unit 30 is managed by the DC-DC unit 20, and the charging and discharging of the energy storage capacitor C1 and the charging and discharging of the energy storage unit 30 are independent of each other.

Charging of energy storage capacitor C1: in the present application, the charging of the energy storage capacitor C1 mainly refers to that the ac power grid charges the capacitor C1 through the cascade side of the energy storage power module. The input current of the ac power grid is a sinusoidal current, when the first end h1 and the second end h2 of the bridge converter unit 10 input a positive half wave of the sinusoidal current, Q1 and Q4 are controlled to be turned on, and at this time, both ends of the capacitor C1 are charged, or when the first end h1 and the second end h2 of the bridge converter unit 10 input a negative half wave of the sinusoidal current, Q2 and Q3 are controlled to be turned on, and at this time, both ends of the capacitor are also in a charged state. During the charging process, the charging current of the energy storage capacitor C1 is a pulsating charging current, and the voltage across the C1 is relatively stable due to the existence of the energy storage capacitor C1. When the energy storage unit 30 is subsequently charged (controlled by the DC-DC unit 20), the DC side of the bridge converter unit 10 can provide a relatively stable DC voltage output for the energy storage unit to charge the energy storage unit 30.

It can be understood that, because the particularity of active and reactive power exchange may exist between the energy storage system and the ac power grid, in the charging process of the entire ac power grid to the energy storage capacitor, the energy storage capacitor also has a discharging transient process, but macroscopically, the ac power grid charges the energy storage capacitor, that is, the energy storage capacitor stores electric energy.

In this embodiment, the energy storage capacitor is used as a transfer station for energy conversion between the ac power grid and the energy storage unit 30, and the pulsating current with large ripple waves input by the power grid can be converted into the dc voltage with small ripple waves, so as to maintain the dc voltage output by the bridge type converter unit 10 in a relatively stable state, so as to reduce the dc ripple waves when the energy storage unit 30 is charged, thereby reducing the damage to the energy storage unit 30.

Charging of the energy storage unit 30: in this application, the energy storage unit 30 is charged from the side of the energy storage capacitor, and when the energy storage unit 30 needs to be charged, the seventh MOS transistor Q7 and the eighth MOS transistor Q8 are controlled to be turned on respectively by the control of the inverted PWM signal, in a switching period, the eighth MOS transistor Q8 is turned off first, the seventh MOS transistor Q7 is turned on, then the seventh MOS transistor Q7 is turned off, the eighth MOS transistor Q8 is turned on, and the pulsating direct current output from the direct current side of the bridge converter unit 10 charges the energy storage unit 30 after a part of ripples are eliminated by the inductor L1. For example, in a specific implementation scenario, assuming that the determined switching frequency of the MOS transistor is K, the charging current input to the energy storage unit 30 by the DC-DC unit 20 and the control signals of the seventh MOS transistor Q7 and the eighth MOS transistor Q8 are as shown in fig. 3, and the charging current at the energy storage unit 30 is approximately a direct current with a small triangular ripple.

Discharge of the energy storage unit 30: in this application, when the energy storage unit 30 discharges, it is realized by charging the energy storage capacitor C1, and finally, the energy storage capacitor C1 releases the electric energy to the ac power grid side. When the energy storage unit 30 discharges, in a switching period, the eighth MOS transistor Q8 is controlled to be turned on first, the seventh MOS transistor Q7 is turned off, at this time, the charging current output by the energy storage unit 30 flows through the inductor L1, energy is stored in the inductor L1, the seventh MOS transistor Q7 is controlled to be turned on, the eighth MOS transistor Q8 is turned off, and at this time, the inductor L1 charges the energy storage capacitor C1 through the seventh MOS transistor Q7. In the next switching cycle, the above process continues, and finally, the voltage across the energy storage capacitor C1 is maintained at a substantially constant value. It is understood that when the energy storage unit 30 is used to supply power to the ac power grid, the output voltage of the first end h1 and the second end h2 of the bridge converter unit 10 may be U, -U, or 0 through the control of the switch tubes in the bridge converter. For example, in a specific implementation scenario, assuming that the determined switching frequency of the MOS transistor is K, the discharge current input to the DC-DC unit 20 from the energy storage unit 30 and the control signals of the two MOS transistors Q7 and Q8 are as shown in fig. 4, and the discharge current at the energy storage unit 30 is approximately a direct current with a triangular ripple.

In this embodiment, through the matching of the inductor and the switching tube in the DC-DC unit 20 and the adjustment of the switching frequency, the ripple of the direct current when the energy storage unit 30 is charged and discharged can be reduced, thereby reducing the heat generated by the battery, reducing the voltage generated by the superposition of the internal resistance of the battery and the ripple, and reducing the damage to the energy storage unit.

Bypass of the energy storage unit: in the application, when a plurality of energy storage power modules are applied to the energy storage system after being cascaded, any one or more energy storage power modules can be bypassed from the energy storage system by controlling the conduction state of the MOS tube in the bridge type current conversion unit 10, and are isolated from other energy storage power modules in the system, so that each energy storage power module is relatively independent and does not influence each other. For example, still taking fig. 2 as an example, when a certain energy storage power module is in a fault, the third MOS transistor Q3 and the fourth MOS transistor Q4 are controlled to be turned on, at this time, the first end h1 and the second end h2 of the bridge converter unit 10 are directly turned on through the third MOS transistor Q3 and the fourth MOS transistor Q4, the energy storage capacitor C1, the DC-DC unit 20, and the energy storage unit 30 are all bypassed, and at this time, the energy storage power module is in a bypassed state as a whole and does not participate in energy storage and electric energy release.

In the present embodiment, the energy storage unit 30 is composed of a plurality of rechargeable batteries connected in series.

In this application, owing to chooseed low-voltage, low on-resistance's MOSFET device as the switch tube for use, consequently, no longer require to reach high-voltage heavy current to the energy storage battery group, the scale of energy storage unit 30 is compared in the energy storage scheme that adopts IGBT power device now, and the scale is obviously reduced to can keep apart the energy exchange of the energy storage unit in every power module and other parts in the energy storage system, the security problem of battery system obtains obviously improving. Illustratively, the number of cells of the series-connected rechargeable battery is 12, the voltage of the battery pack is 36V × 100AH, the MOSFET device is selected to have a withstand voltage of 60V, an on-resistance of 1 milliohm, an on-voltage of only 0.2V at 100A, and an on-voltage drop of only 0.55% for each energy storage power module consisting of the power conversion circuit and the energy storage unit 30, and the on-loss is very low.

In this embodiment, all the switching devices in the bridge type current transforming unit and the DC-DC unit employ MOSFET devices with low voltage and low on-resistance, which can reduce the series scale of the battery pack in the energy storage unit, reduce the overall loss of the energy storage system, and improve the energy conversion efficiency.

Referring to fig. 5, in an alternative embodiment of the present application, the bridge converter in the bridge converter unit may be a single-phase half-bridge converter, and as shown in the figure, the single-phase half-bridge converter includes 2 MOS transistors, that is, a fifth MOS transistor Q5 and a sixth MOS transistor Q6, two MOS transistors Q5 and Q6 form a bridge arm, and the energy storage capacitor C1 is connected to the second side of the single-phase half-bridge converter. The source of the fifth MOS transistor Q5 is connected to the drain of the sixth MOS transistor Q6, and then the first end h1 of the bridge converter unit 10 is led out, the source of the sixth MOS transistor Q6 is connected to the negative electrode of the energy storage capacitor C1, and then the second end h2 of the bridge converter unit 10 is led out, and the first end h1 and the second end h2 form the first side of the bridge converter. The drain of the fifth MOS transistor Q5 is connected to the anode of the energy storage capacitor C1, and then the third terminal h3 of the bridge converter unit 10 is led out, and the third terminal h3 and the fourth terminal h4 of the bridge converter unit form the second side of the bridge converter. In this embodiment, the fifth MOS transistor Q5 is turned on, the sixth MOS transistor Q6 is turned off, the energy storage capacitor C1 can be charged and discharged, and when the fifth MOS transistor Q5 is turned off and the sixth MOS transistor Q6 is turned on, the whole energy storage power module can be bypassed. Similarly to the full-bridge converter in the previous embodiment, the rectified voltage of the half-bridge converter in this embodiment is also a dc voltage with ripple due to the presence of the energy storage capacitor C1.

In the above embodiment, the bridge type current transforming unit adopts a half-bridge structure, and compared with a full-bridge structure, the number of switches used in a single module is less, and the switching loss of each module can be further reduced to a certain extent. Compared with a full-bridge structure, the energy storage system formed by the half-bridge structure can be suitable for the condition that the energy storage system is simultaneously connected with a power grid and a direct-current voltage source, for example, the energy storage system is simultaneously connected to the power grid and a bus voltage end provided by a wind energy system.

With continued reference to fig. 6, in an alternative embodiment of the present application, the positions of the switch sets in the half-bridge converter in the DC-DC unit 20 and the inductor L1 may be interchanged, as shown in the drawing, the drain of the seventh MOS transistor Q7 leads to the third end d3 of the DC-DC unit 20, and the source of the eighth MOS transistor Q8 leads to the second end d2 of the DC-DC unit 20; the source of the seventh MOS transistor Q7, the drain of the eighth MOS transistor Q8, and one end of the first inductor L1 are connected, and the other end of the first inductor L1 leads out the first end d1 of the DC-DC unit 20.

In this embodiment, the first end d1 and the second end d2 of the DC-DC unit 20 form a first direct current side of the DC-DC unit 20, and are connected to the direct current side of the bridge converter unit 10, that is, the third end h3 is connected to the fourth end h4, and the second end d2 and the third end d3 of the DC-DC unit 20 form a second direct current side of the DC-DC unit 20, and are connected to the positive electrode and the negative electrode of the energy storage unit 30. With this arrangement, a boost-type DC-DC unit (for charging process) can be realized, so that smooth charging of the battery pack can be realized even if the voltage across the storage capacitor C1 is lower than the voltage across the battery pack in the energy storage unit 30.

Optionally, in an embodiment, the DC-DC unit further comprises a filter circuit, which is connected in series with the half-bridge converter. The filter circuit is preferably an LC filter circuit, mainly includes a second inductor L2 and a second capacitor C2, and can form a T-shaped filter circuit together with the first inductor L1 in the half-bridge converter, so as to further filter the charging and discharging currents of the energy storage unit 30, and filter the ripple in the dc current.

Depending on the position of the first inductor L1 in the half-bridge converter, the filter circuit may be connected in series before or after the half-bridge converter.

When the half-bridge converter in the DC-DC unit 20 adopts the structure shown in fig. 2, the filter circuit is connected behind the half-bridge converter, as shown in fig. 7, at this time, the drain Q7 of the seventh MOS transistor leads out the first end d1 of the DC-DC unit 20, and the source of the eighth MOS transistor Q8 leads out the second end d2 of the DC-DC unit 20; the source of the seventh MOS transistor Q7, the drain of the eighth MOS transistor Q8, and one end of the first inductor L1 are connected, the other end of the first inductor L1 is connected to the third end d3 of the DC-DC unit 20 through the second inductor L2, and the end of the first inductor L1 connected to the second inductor L2 is connected to the second end d2 of the DC-DC unit 20 through the second capacitor C2; the first and second terminals d1 and d2 of the DC-DC unit 20 form a first direct current side of the DC-DC unit, and the second and third terminals d2 and d3 form a second direct current side of the DC-DC unit 20.

When the half-bridge converter in the DC-DC unit 20 adopts the structure shown in fig. 6, the filter circuit is connected in front of the half-bridge converter, and at this time, the drain Q7 of the seventh MOS transistor leads the third terminal d3 of the DC-DC unit 20, and the source Q8 of the eighth MOS transistor leads the second terminal d2 of the DC-DC unit 20; the source of the seventh MOS transistor Q7, the drain of the eighth MOS transistor Q8, and one end of the first inductor L1 are connected, the other end of the first inductor L1 is connected to the third end d1 of the DC-DC unit 20 through the second inductor L2, and the end of the first inductor L1 connected to the second inductor L2 is connected to the second end d2 of the DC-DC unit 20 through the second capacitor C2; the first and second terminals d1 and d2 of the DC-DC unit 20 form a first direct current side of the DC-DC unit, and the second and third terminals d2 and d3 form a second direct current side of the DC-DC unit 20.

At this time, the inductors L1 and L2 and the filter capacitor C2 form a T-shaped filter circuit to further eliminate ripples in the dc current during charging and discharging in the energy storage unit 30, ensure that current ripples at the d3 are as small as possible, protect the battery in the energy storage unit 30, and prolong the service life of the battery.

With continued reference to fig. 8, in a preferred embodiment of the present application, the energy storage power module further includes a control unit 40, where the control unit 40 is connected to the bridge current transforming unit 10 and the DC-DC unit 20, for example, connected through an I/O interface to control or monitor the bridge current transforming unit 10, the DC-DC unit 20, and the energy storage unit 30, monitor the voltage information of the energy storage capacitor C1 and the energy storage information of the energy storage unit 30, for example, monitor the voltage information, and send a control signal to each MOS transistor of the bridge current transforming unit 10 and the DC-DC unit 20 to control the on and off of each MOS transistor.

Because the energy storage power module comprises the control unit inside, the control unit can independently control the bridge type current transformation unit and the DC-DC unit inside the energy storage power module, and can monitor the energy storage unit (battery) inside the energy storage power module, thereby not only ensuring the control fineness, but also ensuring the control efficiency, and providing a foundation for the high-efficiency and safe work of an energy storage system. For example, in the case that a plurality of energy storage power modules are cascaded to form an energy storage system, the control unit in each energy storage power module only needs to monitor the battery in the energy storage power module to which it belongs, and once an abnormality is found, the control unit can immediately control the on-off state of the MOS transistor in the bridge type converter unit 10 to bypass the energy storage power module, thereby avoiding that the battery with the abnormality individually affects the entire energy storage system.

Furthermore, the monitoring among the current energy storage system is usually carried out by a controller, because group battery quantity is very big, can only carry out passive battery equalization detection usually, and in this application, the inside battery quantity of energy storage power module is less, after setting up the control unit in the module alone, can initiatively carry out battery equalization detection in the module to improve the utilization ratio to every battery, the utilization ratio of battery can obtain promoting among the whole energy storage system.

Further, as shown in fig. 9 or 10, the present application also provides an energy storage system including a multilevel converter 100, a plurality of reactors, a voltage current monitor 300, and a controller 200.

Among other things, the multilevel converter 100 preferably includes a three-phase circuit. In each phase of circuit, the cascade sides of a plurality of energy storage power modules are sequentially cascaded to form one or more bridge arms, and two ends of one or more bridge arms are connected with the power grid connecting end of the energy storage system, wherein at least one reactor is connected in series between the cascade sides of at least one part of energy storage power modules in each bridge arm and/or between at least one of the two ends of the bridge arm and the power grid connecting end. Illustratively, as in fig. 9 or 10, the two ends of the leg of each phase circuit are connected to the A, B, C phase access point of the ac power grid via a reactor (or multiple reactors). It can be understood that in this application, the position of the reactor may be connected in series between the bridge arm and the grid connection end as shown in fig. 9 or 10, or may be connected in series between the cascade sides of any one or more energy storage power modules in the bridge arm, and the number of the reactor may also be one or more, and may be selected according to the requirement, which is not limited in this application.

The voltage and current monitor 300 is used for monitoring the operating voltage and current of the three-phase circuit when the energy storage system is in operation, so as to determine the number of energy storage power modules which need to be connected to the energy storage system for charging or discharging in each phase circuit. Illustratively, the energy storage system selectively controls the multiple energy storage power modules to output different selectable voltage values according to the current value of the alternating voltage required to be output by each phase circuit, and the multiple energy storage power modules can superimpose the output voltage of each phase circuit to realize power exchange between the energy storage system and an alternating current power grid. Assuming that the output voltage of each energy storage power module is 50V, and the voltage output by a certain phase required by the energy storage system is 500V at this time, the number of the energy storage power modules in the input state in the phase can be controlled to be 10, and the other modules are in the bypass state, so that the phase cascade circuit can output a corresponding voltage value.

The controller 200 can communicate with each energy storage power module through the communication interface to control the working state of each energy storage power module, wherein the working state includes accessing the energy storage system for storing energy, releasing energy, or bypassing the energy storage system. For example, the controller 20 controls each energy storage power module to be connected to the energy storage system for storing energy and releasing energy, or to bypass from the energy storage system according to the voltage and current monitoring result of the voltage and current monitor 300, the voltage monitoring result of the energy storage capacitor provided by the control unit in the energy storage power module (or directly obtained by the controller 200), and the energy storage monitoring result of the energy storage unit. As mentioned above, when the number of the power modules connected to the system is 10, the controller 200 sends a control signal to each energy storage power module to connect 10 energy storage power modules to the energy storage system and bypass the remaining energy storage power modules from the energy storage system. When a certain energy storage power module has a fault and reports, the controller 200 also sends a corresponding control signal to bypass the energy storage power module from the energy storage system, and controls other energy storage power modules to access the system as required.

In this embodiment, because adopt many level modulation mode of modularization, the switching frequency greatly reduced of energy storage power module can reduce to below 1kHz, compares with the 16kHz that traditional level transverter adopted, and switching loss can be ignored, and energy storage system energy conversion efficiency is higher, has obvious advantage. And moreover, the battery pack of each energy storage power module is smaller in scale and safer, so that the safety of the whole energy storage system is further improved.

With continued reference to fig. 9, when the bridge converter of the bridge converter unit 10 is a single-phase full-bridge converter, the grid connection terminal is an ac grid connection terminal. In each phase of circuit, the energy storage power modules are cascaded in a manner shown in fig. 9, the cascade sides of the energy storage power modules are sequentially connected to form a bridge arm, that is, two ac access terminals h1 and h2 of the cascade side of each energy storage power module are respectively connected in series with two ac access terminals h1 and h2 of the cascade side of the adjacent energy storage power module, and two ends of the bridge arm are formed at two ends after the cascade. As shown in the figure, the first end h1 of the bridge converter in the first energy storage power module forms the first end of the bridge arm, the second end h2 of the bridge converter in the last energy storage power module forms the second end of the bridge arm, the first end and the second end of the bridge arm are respectively connected with the connecting end of the alternating current power grid, and at this time, one or more reactors are connected in series with the first end of the cascaded bridge arm and the connecting end of the alternating current power grid directly.

Referring to fig. 10, when the bridge converter of the bridge converter unit 10 is a single-phase half-bridge converter, the grid connection terminals include an ac grid connection terminal and a dc grid connection terminal (including a positive voltage terminal and a negative voltage terminal). The cascade of energy storage power modules in each phase circuit is as shown in fig. 10. In each phase of single circuit, the cascade mode of a plurality of energy storage power modules is as follows: the energy storage power modules are cascaded to form two bridge arms, namely an upper bridge arm and a lower bridge arm, and the upper bridge arm and the lower bridge arm comprise the same number of energy storage power modules.

In the upper bridge arm, the cascade sides of the energy storage power modules are connected in sequence for cascade connection, as shown in the figure, two ac access ends h1 and h2 at the cascade side of each energy storage power module are respectively connected in series with two ac access ends h1 and h2 at the cascade side of the adjacent energy storage power module, and two ends of the upper bridge arm are formed at two ends after cascade connection. The first end h1 of the bridge type converter in the first energy storage power module forms the first end of an upper bridge arm, the first end of the upper bridge arm is connected with the positive voltage end DC + of the direct current power grid connection end, and the second end h2 of the bridge type converter in the last energy storage power module forms the second end of the upper bridge arm.

In the lower bridge arm, the cascade sides of the energy storage power modules are connected in sequence for cascade connection, as shown in the figure, two ac access ends h1 and h2 at the cascade side of each energy storage power module are respectively connected in series with two ac access ends h1 and h2 at the cascade side of the adjacent energy storage power module, and two ends of the cascade connection form two ends of the lower bridge arm. The first end h1 of the bridge converter in the first energy storage power module forms the first end of the lower bridge arm, the first end of the lower bridge arm is connected in series with at least one reactor (such as an inductor in the figure), the second end h2 of the bridge converter in the last energy storage power module forms the second end of the lower bridge arm, and the second end of the lower bridge arm is connected with the negative voltage end DC-of the direct current grid connection end. The second end of the upper bridge arm is connected with the first end of the lower bridge arm to form a second connection point, and the second connection point of each phase circuit is respectively connected with one phase circuit connection point (such as an a-phase connection point, a B-phase connection point and a C-phase connection point in fig. 9 or fig. 10) of the alternating current power grid connection ends.

It can be understood that when the reactor is located in series between the bridge arms and the grid connection end as shown in fig. 9 or 10, at this time, the second end of the upper bridge arm and the first end of the lower bridge arm are respectively connected in series with one or more inductors and then connected to form the second connection point of each phase of circuit.

In an embodiment of the present application, another energy storage system is further provided, where the energy storage system includes a plurality of energy storage power modules and one or more reactors, cascade sides of the plurality of energy storage power modules are sequentially cascaded to form one or more bridge arms, and two ends of the one or more bridge arms are connected to a power grid connection end of the energy storage system, where at least one reactor is connected in series between the cascade sides of at least a part of the energy storage power modules in each bridge arm and/or between at least one of the two ends of the bridge arm and the power grid connection end. Likewise, the energy storage system may also include a voltage current monitor and a controller. Compared with the energy storage system shown in fig. 9 or fig. 10, the energy storage system in the present embodiment is different in that: in this embodiment, the energy storage system only includes a single-phase circuit composed of a plurality of energy storage power modules and one or more reactors. The energy storage system is only connected with one-phase circuit in the power grid, and can be applied to a single-phase alternating current power grid in a household mode, and the cascade modes of other voltage and current monitors, controller settings and energy storage power modules are the same as those of the energy storage system shown in fig. 9 or fig. 10, and are not described again here.

It can be understood that when the energy storage system only includes a single-phase circuit, when the bridge converter of the bridge converter unit 10 adopts a single-phase half-bridge converter, the second end of the upper bridge arm is connected to the first end of the lower bridge arm to form a first connection point, one end of the ac grid connection ends is connected to the first connection point, and the other end of the ac grid connection ends is connected to a neutral point (e.g., N shown in fig. 9) in the energy storage system.

It will be appreciated by those skilled in the art that the above-described preferred embodiments may be freely combined, superimposed, without conflict.

It will be understood that the embodiments described above are illustrative only and not restrictive, and that various obvious or equivalent modifications and substitutions for details described herein may be made by those skilled in the art without departing from the basic principles of the present application.

Claims

1. An energy storage power module is used for being connected in a cascading mode to form an energy storage system, and is characterized by comprising a power conversion circuit and an energy storage unit, wherein one side of the power conversion circuit is a cascading side and is used for being cascaded so as to be connected with an alternating current power grid, and the other side of the power conversion circuit is an energy storage side and is connected with the energy storage unit and is used for providing electric energy for the energy storage unit or receiving the electric energy released by the energy storage unit; the power conversion circuit comprises a bridge type current transformation unit and a DC-DC unit, wherein:

2. The energy storage power module of claim 1, wherein the bridge converter is a single-phase full-bridge converter, and comprises 4 MOS transistors, namely a first MOS transistor, a second MOS transistor, a third MOS transistor and a fourth MOS transistor, wherein:

3. The energy storage power module of claim 1, wherein the bridge converter is a single-phase half-bridge converter and comprises 2 MOS transistors, namely a fifth MOS transistor and a sixth MOS transistor, wherein:

after the source electrode of the fifth MOS tube is connected with the drain electrode of the sixth MOS tube, the first end of the bridge type current transforming unit is led out;

and after the drain electrode of the fifth MOS tube is connected with the anode of the energy storage capacitor, the third end of the bridge type current transforming unit is led out, and the third end and the second end of the bridge type current transforming unit form the second side of the bridge type current transforming unit.

4. The energy storage power module of claim 1, wherein the plurality of MOS transistors in the half-bridge converter are a seventh MOS transistor and an eighth MOS transistor, wherein:

5. The energy storage power module of claim 1, wherein the plurality of MOS transistors in the half-bridge converter are a seventh MOS transistor and an eighth MOS transistor, wherein:

6. The energy storage power module of claim 1, wherein the DC-DC unit further comprises a filter circuit, the filter circuit is connected in series with the half-bridge converter, the filter circuit mainly comprises a second capacitor and a second inductor, the plurality of MOS transistors in the half-bridge converter are a seventh MOS transistor and an eighth MOS transistor, wherein:

7. The energy storage power module of claim 1, wherein the DC-DC unit further comprises a filter circuit, the filter circuit is connected in series with the half-bridge converter, the filter circuit mainly comprises a second capacitor and a second inductor, the plurality of MOS transistors in the half-bridge converter are a seventh MOS transistor and an eighth MOS transistor, wherein:

8. The energy storage power module as claimed in any of claims 1-7, wherein the power module further comprises a control unit, the control unit is electrically connected to the bridge current transforming unit, the DC-DC unit and the energy storage unit, and is configured to monitor the voltage information of the energy storage capacitor and the energy storage information of the energy storage unit, and send a control signal to each MOS transistor of the bridge current transforming unit and the DC-DC unit.

9. An energy storage system, characterized by comprising a plurality of energy storage power modules according to any one of claims 1 to 8 and one or more reactors, wherein the cascade sides of the plurality of energy storage power modules are cascaded in sequence to form one or more bridge arms, and two ends of the one or more bridge arms are connected with the grid connection end of the energy storage system, wherein at least one reactor is connected in series between the cascade sides of at least a part of the energy storage power modules in each bridge arm and/or between at least one of the two ends of the bridge arm and the grid connection end.

10. The energy storage system of claim 9, wherein when the bridge converter is a single-phase full-bridge converter, the grid connection terminal is an ac grid connection terminal, and the plurality of energy storage power modules are cascaded in a manner that:

11. The energy storage system of claim 9, wherein when said bridge converter is a single-phase half-bridge converter, said grid connection terminals include a dc grid connection terminal and an ac grid connection terminal, and a plurality of said energy storage power modules are cascaded in a manner such that:

12. An energy storage system comprising a multilevel converter comprising three phase circuits, each phase circuit comprising a plurality of energy storage power modules according to any of claims 1 to 8 and one or more reactors;

in each phase of circuit, the cascade sides of the energy storage power modules are sequentially cascaded to form one or more bridge arms, two ends of each bridge arm are connected with the power grid connection end of the energy storage system, and at least one reactor is connected in series between the cascade sides of at least one part of the energy storage power modules in each bridge arm and/or between at least one of the two ends of each bridge arm and the power grid connection end.

13. The energy storage system of claim 12, wherein when the bridge converter is a single-phase full-bridge converter, the grid connection terminal is an ac grid connection terminal, and in each phase of the circuit, the energy storage power modules are cascaded in a manner that:

the cascade sides of the energy storage power modules are sequentially connected and cascaded to form a bridge arm, a first end of a bridge type converter in the first energy storage power module forms a first end of the bridge arm, a second end of the bridge type converter in the last energy storage power module forms a second end of the bridge arm, and the first end and the second end of the bridge arm are respectively connected with the alternating current power grid connection end.

14. The energy storage system of claim 12, wherein when said bridge converter is a single-phase half-bridge converter, said grid connection terminals comprise a dc grid connection terminal and an ac grid connection terminal, said ac grid connection terminal comprising three phase circuit connection points;

in each phase circuit, the cascade mode of a plurality of energy storage power modules is as follows:

the energy storage power modules are cascaded to form two bridge arms which are respectively an upper bridge arm and a lower bridge arm, the upper bridge arm and the lower bridge arm comprise energy storage power modules with the same number, and the energy storage power modules comprise:

in an upper bridge arm, the cascade sides of the energy storage power modules are connected in sequence for cascade connection, the first end of a bridge type converter in the first energy storage power module forms the first end of the upper bridge arm, the first end of the upper bridge arm is connected with the voltage positive end of the direct current power grid connection end, and the second end of the bridge type converter in the last energy storage power module forms the second end of the upper bridge arm;