Matrix expandable modular multilevel battery energy storage system and control method

Abstract

The application provides a matrix expandable modular multilevel battery energy storage system, comprising: a direct current power grid and a three-phase power grid; an energy storage bridge arm, the energy storage bridge arm comprising an energy storage upper bridge arm and an energy storage lower bridge arm, a first port of the energy storage upper bridge arm being connected with a positive terminal of the direct current power grid, a second port of the energy storage lower bridge arm being connected with a negative terminal of the direct current power grid, a second port of the energy storage upper bridge arm and a first port of the energy storage lower bridge arm being connected with the three-phase power grid; the energy storage bridge arm is formed into a matrix net structure by using a matrix arrangement mode of energy storage units, and an independent controller is arranged in the energy storage unit and used for executing a control instruction; the energy storage bridge arm comprises 1 to X parallel energy storage units arranged in a horizontal direction and 1 to N series energy storage units arranged in a vertical direction. The matrix arrangement of the energy storage units realizes high expandability and flexibility of the system, the independent controller in each energy storage unit can accurately execute the control instruction, and the overall performance and reliability of the system are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery energy storage and system control, in particular to a matrix expandable modular multilevel battery energy storage system and a control method. BACKGROUND

[0002] High-efficiency, stable and large-capacity energy storage systems have become a core component in power systems. However, how to further improve the capacity and fault tolerance of the energy storage system while ensuring efficient operation of the system has become a key research direction. The existing large-capacity energy storage system topologies mainly include three-level, CHB structure and conventional MMC structure. The above traditional battery energy storage system topologies have the following technical problems:

[0003] 1. Poor expansion capacity

[0004] For the three-level topology, the expansion of the system is mainly achieved by increasing the battery voltage or paralleling the same topology of the energy storage converter to increase the current. However, this method has the following defects: the battery voltage level needs to be improved; a power frequency transformer must be used for voltage boosting; and the parallel connection of multiple energy storage converters will affect the overall output of the system, which brings difficulties to the design of system efficiency, size, cost, etc. For the CHB structure, the synchronization of control signals is particularly important. With the increase in the number of modules, the delay and phase difference of control signals between modules can cause a decrease in system performance, and even resonance, affecting the stability and reliability of the system. For the conventional MMC structure, the expansion process increases the difficulty of voltage and power balancing between sub-modules.

[0005] 2. Insufficient fault tolerance of the system

[0006] The shortcoming of the three-level structure lies in the battery system. Once a battery fails, the system energy balancing management is complex, and the fault recovery time is longer, which poses a challenge to the continuous operation and fault tolerance of the system. Some technologies use matrix reconfigurable battery systems to flexibly connect batteries in a matrix, which can solve the battery energy control problem to some extent, but the direct connection of batteries (without relying on inductors and other devices) will cause circulating current problems. For the CHB structure, since multiple modules are connected in series, a single module failure can affect the stability of the entire system, so the fault tolerance in large-scale applications is limited. For the conventional MMC structure, the increase in sub-modules in the energy storage unit can cause the system response time to become longer and the system to fail to respond in time under fault conditions. SUMMARY

[0007] In view of the defects in the prior art, the purpose of the present application is to provide a matrix expandable modular multilevel battery energy storage system and a control method, which can increase the voltage level and the rated current of the battery energy storage system by combining the energy storage units, and can adapt to different power scales and capacity requirements without redesigning different voltage levels and power levels.

[0008] In one aspect of the present application, a matrix expandable modular multilevel battery energy storage system is provided, comprising a direct current grid and a three-phase grid.

[0009] An energy storage bridge arm, comprising an energy storage upper bridge arm and an energy storage lower bridge arm, a first port of the energy storage upper bridge arm being connected to a positive terminal of the direct current grid, a second port of the energy storage lower bridge arm being connected to a negative terminal of the direct current grid, a second port of the energy storage upper bridge arm and a first port of the energy storage lower bridge arm being connected to the three-phase grid.

[0010] The energy storage bridge arm is formed by arranging the energy storage units in a matrix manner to form a matrix network structure, and the energy storage units are provided with independent controllers for executing control instructions.

[0011] The energy storage bridge arm comprises 1 to X energy storage units connected in parallel in the horizontal direction and 1 to N energy storage units connected in series in the vertical direction.

[0012] Further, one end of the 1 to X energy storage units connected in parallel in the horizontal direction is connected to each other, the other end is connected to one end of the energy storage units connected in series below the 1 to N energy storage units connected in series in the vertical direction, forming NxX energy storage units, and constituting the matrix network structure.

[0013] The energy storage upper bridge arm has the same structure as the energy storage bridge arm, and both are formed by arranging the energy storage units in a matrix manner.

[0014] Further, the energy storage upper bridge arm comprises a first energy storage upper bridge arm, a second energy storage upper bridge arm and a third energy storage upper bridge arm, and the energy storage lower bridge arm comprises a first energy storage lower bridge arm, a second energy storage lower bridge arm and a third energy storage lower bridge arm.

[0015] The first energy storage upper bridge arm and the first energy storage lower bridge arm form a first phase cluster, a first port of the first energy storage upper bridge arm being connected to the positive terminal of the direct current grid, a second port of the second energy storage lower bridge arm being connected to the negative terminal of the direct current grid, and a second port of the first energy storage upper bridge arm and a first port of the second energy storage lower bridge arm being connected to a first phase of the three-phase grid.

[0016] The second energy storage upper bridge arm and the second energy storage lower bridge arm form a second phase cluster, a first port of the second energy storage upper bridge arm is connected with a positive terminal of the direct current power grid, a second port of the second energy storage lower bridge arm is connected with a negative terminal of the direct current power grid, and a second port of the second energy storage upper bridge arm and a first port of the second energy storage lower bridge arm are connected with a second phase of the three-phase power grid.

[0017] The third energy storage upper bridge arm and the third energy storage lower bridge arm form a third phase cluster, a first port of the third energy storage upper bridge arm is connected with a positive terminal of the direct current power grid, a second port of the third energy storage lower bridge arm is connected with a negative terminal of the direct current power grid, and a second port of the third energy storage upper bridge arm and a first port of the third energy storage lower bridge arm are connected with a third phase of the three-phase power grid.

[0018] Further, the first energy storage upper bridge arm, the second energy storage upper bridge arm, the third energy storage upper bridge arm, the first energy storage lower bridge arm, the second energy storage lower bridge arm and the third energy storage lower bridge arm have the same number of energy storage units in the same phase cluster, and each of them is composed of NxX energy storage units to form a matrix net structure.

[0019] Further, the energy storage unit comprises 1 to n energy storage sub-modules and a bridge energy storage inductor, the energy storage sub-module has a first end and a second end; the second end of the last energy storage sub-module of the 1 to n energy storage sub-modules is connected with the first end of the next energy storage sub-module;

[0020] The second end of the nth energy storage sub-module is connected with the first end of the bridge energy storage inductor;

[0021] The first end of the first energy storage sub-module serves as the first end of the energy storage unit, and the second end of the bridge energy storage inductor serves as the second end of the energy storage unit.

[0022] Further, the energy storage sub-module comprises a first switching device, a second switching device, a third switching device, a fourth switching device, a first freewheeling diode, a second freewheeling diode, a third freewheeling diode, a fourth freewheeling diode, a filter capacitor and an energy storage device.

[0023] The control end of the first switch device, the second switch device, the third switch device and the fourth switch device is connected with an external modulation function port; the first end of the first switch device is connected with the cathode of the first freewheeling diode, the first end of the filter capacitor and the first end of the energy storage device, and the second end of the first switch device is connected with the anode of the first freewheeling diode and the first end of the third switch device; the first end of the second switch device is connected with the cathode of the second freewheeling diode, the first end of the filter capacitor and the first end of the energy storage device, and the second end of the second switch device is connected with the anode of the second freewheeling diode and the first end of the fourth switch device; the first end of the third switch device is connected with the cathode of the third freewheeling diode, and the second end of the third switch device is connected with the anode of the third freewheeling diode, the second end of the filter capacitor and the second end of the energy storage device; the first end of the fourth switch device is connected with the cathode of the fourth freewheeling diode, and the second end of the fourth switch device is connected with the anode of the fourth freewheeling diode, the second end of the filter capacitor and the second end of the energy storage device.

[0024] The connection between the second end of the first switch device and the third switch device serves as the first end of the energy storage unit, and the connection between the second end of the second switch device and the fourth switch device serves as the second end of the energy storage unit.

[0025] In a second aspect, the application provides a control method for a matrix-type scalable modular multi-level battery energy storage system, comprising:

[0026] Receiving a system capacity expansion demand signal, determining a target capacity after capacity expansion according to the capacity of the original battery energy storage circuit, the voltage level of the AC / DC side, the U characteristics of the energy storage device of the energy storage unit, defining the rated power of the energy storage unit, and determining the number of added energy storage units;

[0027] Judging whether a fault occurs in the energy storage unit of the energy storage system, and if yes, executing a re-distribution process, and if not, executing a distribution process.

[0028] Further, the receiving of the system capacity expansion demand signal, the determination of the target capacity after capacity expansion according to the capacity of the original battery energy storage circuit, the voltage level of the AC / DC side, the U characteristics of the energy storage device of the energy storage unit, the definition of the rated power of the energy storage unit, and the determination of the number of added energy storage units, comprises:

[0029] Receiving a system capacity expansion demand signal and a target capacity, determining the target capacity after capacity expansion as P target , according to the capacity of the original battery energy storage circuit, the voltage level of the AC / DC side, the U characteristics of the energy storage device of the energy storage unit, and the capacity of the system before capacity expansion being P origin .

[0030] The energy storage device U with the same voltage level as the original energy storage device U is selected as the energy storage device U of the energy storage unit in the increased energy storage bridge arm, and the rated power of one energy storage unit is defined;

[0031] The rated capacity of the energy storage device U of the original energy storage unit is calculated according to the capacity before expansion, and the number of the increased energy storage units is determined.

[0032] Further, the judgment of whether the energy storage unit in the energy storage system fails is performed, and if so, a re-distribution process is performed, including:

[0033] The number N of the energy storage units and the rated discharge current I of the energy storage device U in the energy storage unit are obtained N ;

[0034] The other energy storage units are distributed to the current I D satisfying the relationship: and the rated current value of the switching device in the energy storage unit should also satisfy the relationship I mosN ≥I D ;

[0035] In the formula, I D is the current distributed to the other energy storage units; N is the number of the energy storage units; I N is the rated discharge current of the energy storage device U in the energy storage unit;

[0036] I mosN is the rated current value of the switching device in the energy storage unit.

[0037] Further, the execution of the distribution process includes that the main controller sends the voltage and current control signals distributed to each SET to the SET controller based on the voltage and current of each bridge arm of the three phases, and outputs the voltage and current through closed-loop control.

[0038] The SET controller receives the voltage and current control signals distributed by the main controller, performs voltage modulation on the voltage of each SET, outputs the voltage and current distribution result, and sends the switching control signal to the energy storage submodule controller;

[0039] The energy storage submodule executes the switching control signal, and samples the temperature and battery energy information of the energy storage submodule, and sends them to the SET controller for energy balancing and power distribution.

[0040] Compared with the prior art, the present application has at least one of the following beneficial effects:

[0041] 1. The application can be combined in the form of energy storage units, which can increase the voltage level and the rated current of the battery energy storage system. The battery energy storage system can adapt to different power scales and capacity requirements without redesigning different voltage levels and power levels.

[0042] 2. When the system capacity is expanded or reduced, the control system structure does not need to be adjusted (including the control resources and control strategies of the system), the expansion method is simple and easy to implement, which avoids the problem of repeated design when the energy storage system needs to adapt to different power levels, reduces the design difficulty of the energy storage system, and the matrix structure helps to balance the energy inside the system. And the system can run with faults through reasonable power distribution when a few modules fail, so it has strong scalability and reliability. BRIEF DESCRIPTION OF DRAWINGS

[0043] Other features, objects and advantages of the application will become more apparent after reading the detailed description of the non-limiting embodiments with reference to the following drawings:

[0044] Figure 1 A structure diagram of a matrix expandable modular multilevel battery energy storage system in an embodiment of the application.

[0045] Figure 2 A structure diagram of a scheme in which the energy storage bridge arm has only a single energy storage unit in an embodiment of the application.

[0046] Figure 3 A structure diagram of the connection mode of the energy storage unit in an embodiment of the application.

[0047] Figure 4 A basic structure diagram of the energy storage unit in an embodiment of the application.

[0048] Figure 5 A structure diagram of a full-bridge structure of the energy storage unit in an embodiment of the application.

[0049] Figure 6 A framework diagram of a matrix expandable modular multilevel battery energy storage system in an embodiment of the application.

[0050] Figure 7 A flowchart of a control method of a matrix expandable modular multilevel battery energy storage system in an embodiment of the application.

[0051] Figure 8 A structure diagram of a battery energy storage circuit connected by a specific embodiment in an embodiment of the application. DETAILED DESCRIPTION

[0052] The application will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be pointed out that those skilled in the art can make several modifications and improvements without departing from the concept of the application. These all belong to the protection scope of the application.

[0053] Referring to Figure 1 As shown in FIG. 1, the matrix expandable modular multilevel battery energy storage system according to an embodiment of the application comprises a direct current power grid and a three-phase power grid; an energy storage bridge arm, which comprises an energy storage upper bridge arm and an energy storage lower bridge arm, the first port of the energy storage upper bridge arm is connected to the positive terminal of the direct current power grid, the second port of the energy storage lower bridge arm is connected to the negative terminal of the direct current power grid, and the second port of the energy storage upper bridge arm and the first port of the energy storage lower bridge arm are connected to the three-phase power grid; the energy storage bridge arm is formed into a matrix network structure by using a matrix arrangement of energy storage units, and each energy storage unit is provided with an independent controller for executing control instructions.

[0054] The energy storage bridge arm comprises 1 to X parallel energy storage units arranged in the horizontal direction and 1 to N series energy storage units arranged in the vertical direction.

[0055] The matrix arrangement of the energy storage units realizes high expandability and flexibility of the system, the combination of the energy storage units can increase the voltage level and the rated current of the battery energy storage system. Without redesigning for different voltage levels and power levels, the battery energy storage system can adapt to different power scales and capacity requirements, and the independent controller in each energy storage unit can accurately execute control instructions, thereby improving the overall performance and reliability of the system and being suitable for large-scale battery energy storage applications. At the same time, the matrix structure helps to balance the energy inside the system. Moreover, the system can realize fault operation through reasonable power distribution when a small number of modules fail, so it has strong expandability and reliability.

[0056] The direct current power grid receives electric energy and distributes it to the energy storage bridge arm. The energy storage bridge arm is composed of an energy storage upper bridge arm and an energy storage lower bridge arm, which are respectively connected to the positive terminal and the negative terminal of the direct current power grid and connected to the three-phase power grid through their respective ports. Inside the energy storage bridge arm, the energy storage units are arranged in a matrix form to form a network structure, 1 to X energy storage units are arranged in parallel in the horizontal direction, and 1 to N energy storage units are arranged in series in the vertical direction to adapt to different energy storage requirements. Each energy storage unit is provided with an independent controller for receiving and executing control instructions, thereby realizing accurate control and management of the energy storage system.

[0057] In some specific embodiments, one end of 1 to X parallel energy storage units arranged in the transverse direction are connected to each other, and the other end are connected to each other in series with one end of 1 to N series energy storage units arranged in the longitudinal direction, forming NxX energy storage units, constituting a matrix network structure.

[0058] Specifically, the system includes NxX matrix arranged energy storage units. The energy storage units are X units in parallel in the transverse direction (the first end of the X energy storage units are connected together, and the second end are connected together), and N units in series in the longitudinal direction (the second end of the upper energy storage units are connected together with the first end of the lower energy storage units), and NxX units constitute a matrix network structure. The first port of the first row of energy storage units is connected to the first port of the energy storage structure, and the second port of the Nth row of energy storage units is connected to the second port of the energy storage structure.

[0059] Wherein, the energy storage upper bridge arm and the energy storage bridge arm have the same structure, both of which are composed of energy storage units in a matrix arrangement.

[0060] In some specific embodiments, the energy storage upper bridge arm includes a first energy storage upper bridge arm, a second energy storage upper bridge arm, and a third energy storage upper bridge arm; and the energy storage lower bridge arm includes a first energy storage lower bridge arm, a second energy storage lower bridge arm, and a third energy storage lower bridge arm.

[0061] The first energy storage upper bridge arm and the first energy storage lower bridge arm form a first phase cluster, the first port of the first energy storage upper bridge arm is connected to the positive terminal of the DC power grid, the second port of the second energy storage lower bridge arm is connected to the negative terminal of the DC power grid, and the second port of the first energy storage upper bridge arm and the first port of the second energy storage lower bridge arm are connected to the first phase of the three-phase power grid.

[0062] The second energy storage upper bridge arm and the second energy storage lower bridge arm form a second phase cluster, the first port of the second energy storage upper bridge arm is connected to the positive terminal of the DC power grid, the second port of the second energy storage lower bridge arm is connected to the negative terminal of the DC power grid, and the second port of the second energy storage upper bridge arm and the first port of the second energy storage lower bridge arm are connected to the second phase of the three-phase power grid.

[0063] The third energy storage upper bridge arm and the third energy storage lower bridge arm form a third phase cluster, the first port of the third energy storage upper bridge arm is connected to the positive terminal of the DC power grid, the second port of the third energy storage lower bridge arm is connected to the negative terminal of the DC power grid, and the second port of the third energy storage upper bridge arm and the first port of the third energy storage lower bridge arm are connected to the third phase of the three-phase power grid.

[0064] The matrix expandable modular multilevel battery energy storage structure can not only be applied to MMC, but also be used in other cascaded multilevel energy storage system structures, such as CHB, etc.

[0065] In some specific embodiments, the first energy storage upper bridge arm, the second energy storage upper bridge arm, the third energy storage upper bridge arm, the first energy storage lower bridge arm, the second energy storage lower bridge arm and the third energy storage lower bridge arm have the same number of energy storage units in the same phase cluster, and each has NxX energy storage units to form a matrix network structure.

[0066] Specifically, the first energy storage upper bridge arm and the first energy storage lower bridge arm have the same structure and each includes NxX matrix-arranged energy storage units. In the first energy storage upper bridge arm and the first energy storage lower bridge arm, the energy storage units are in parallel in the horizontal direction (the first ends of X energy storage units are connected together, and the second ends are connected together) and in series in the vertical direction (the second end of an upper energy storage unit is connected to the first end of a lower energy storage unit), and NxX units form a matrix network structure. In the first energy storage upper bridge arm, the first port of the first row of energy storage units is connected to the positive terminal of the DC power grid, and the second port of the Nth row of energy storage units is connected to the first phase of the AC power grid; in the first energy storage lower bridge arm, the first port of the first row of energy storage units is connected to the first phase of the AC power grid, and the second port of the Nth row of energy storage units is connected to the negative terminal of the DC power grid.

[0067] The second energy storage upper bridge arm and the second energy storage lower bridge arm have the same structure and each includes NxX matrix-arranged energy storage units. In the second energy storage upper bridge arm and the second energy storage lower bridge arm, the energy storage units are in parallel in the horizontal direction (the first ends of X energy storage units are connected together, and the second ends are connected together) and in series in the vertical direction (the second end of an upper energy storage unit is connected to the first end of a lower energy storage unit), and NxX units form a matrix network structure. In the second energy storage upper bridge arm, the first port of the first row of energy storage units is connected to the positive terminal of the DC power grid, and the second port of the Nth row of energy storage units is connected to the second phase of the AC power grid; in the second energy storage lower bridge arm, the first port of the first row of energy storage units is connected to the second phase of the AC power grid, and the second port of the Nth row of energy storage units is connected to the negative terminal of the DC power grid.

[0068] The third energy storage upper bridge arm and the third energy storage lower bridge arm have the same structure and each includes NxX matrix-arranged energy storage units. In the third energy storage upper bridge arm and the third energy storage lower bridge arm, the energy storage units are in parallel in the horizontal direction (the first ends of X energy storage units are connected together, and the second ends are connected together) and in series in the vertical direction (the second end of an upper energy storage unit is connected to the first end of a lower energy storage unit), and NxX units form a matrix network structure. In the third energy storage upper bridge arm, the first port of the first row of energy storage units is connected to the positive terminal of the DC power grid, and the second port of the Nth row of energy storage units is connected to the third phase of the AC power grid; in the third energy storage lower bridge arm, the first port of the first row of energy storage units is connected to the third phase of the AC power grid, and the second port of the Nth row of energy storage units is connected to the negative terminal of the DC power grid.

[0069] By increasing the number of units in parallel in the transverse direction, the rated current that the energy storage system can withstand can be increased, and by increasing the number of units in series in the longitudinal direction, the voltage level of the energy storage system can be increased. In the case where the internal structure of the energy storage unit, the control system, and the voltage withstand level remain unchanged, the energy storage circuit has a large enough expansion interval. The above expansion method is flexible and easy to implement. The internal energy storage unit series inductance avoids the direct series and parallel connection of a large number of energy storage devices, can reduce the circulating current between devices, and can realize redundancy and self-regulation in the event of system failure, thus having strong expansion capacity and fault tolerance.

[0070] In one embodiment, each of the energy storage units includes a plurality of energy storage units in the same series number, and the number of parallel energy storage units is not completely the same.

[0071] Specifically, in the scheme of the present embodiment, the NxX energy storage units in the first energy storage bridge arm form a matrix mesh structure, X units are connected in parallel in the transverse direction, and N units are connected in series in the longitudinal direction. The remaining energy storage bridge arms adopt similar structures. By increasing the number of units in parallel in the transverse direction, the rated current that the energy storage system can withstand can be increased, and by increasing the number of units in series in the longitudinal direction, the voltage level of the energy storage system can be increased. In the case where the internal structure of the energy storage unit, the control system, and the voltage withstand level remain unchanged, the energy storage circuit has a large enough expansion interval.

[0072] As shown in Figure 4 In some specific embodiments, the energy storage unit includes 1 to n energy storage sub-modules and a bridge arm energy storage inductor, and the energy storage sub-module has a first end and a second end. The second end of the last energy storage sub-module of the 1 to n energy storage sub-modules is connected to the first end of the next energy storage sub-module. The second end of the nth energy storage sub-module is connected to the first end of the bridge arm energy storage inductor. The first end of the first energy storage sub-module serves as the first end of the energy storage unit, and the second end of the bridge arm energy storage inductor serves as the second end of the energy storage unit.

[0073] As shown in Figure 2 In the above embodiment, the scheme can be realized by adding new energy storage units in the original energy storage bridge arm with only a single energy storage unit. Figure 2 As shown in the energy storage system, the first energy storage upper bridge arm includes only one energy storage unit, the second energy storage upper bridge arm includes only one energy storage unit, and the third energy storage upper bridge arm includes only one energy storage unit. The first energy storage lower bridge arm includes only one energy storage unit, the second energy storage lower bridge arm includes only one energy storage unit, and the third energy storage lower bridge arm includes only one energy storage unit. At this time, in order to improve the capacity of the energy storage system, the number of parallel energy storage units or the number of series energy storage units or the number of series and parallel energy storage units can be increased in the first energy storage upper bridge arm, the first energy storage lower bridge arm, the second energy storage upper bridge arm, the second energy storage lower bridge arm, the third energy storage upper bridge arm, and the third energy storage lower bridge arm to realize the expansion operation of the energy storage system.

[0074] Specifically, the energy storage units have the same basic structure, each of which includes n energy storage sub-modules and an energy storage bridge arm inductor, the n energy storage sub-modules and the energy storage bridge arm inductor are connected in series, the second end of an upper energy storage sub-module is connected to the first end of a lower energy storage sub-module, and the second end of an nth energy storage sub-module is connected to the first end of the bridge arm energy storage inductor. The first end of the first energy storage sub-module serves as the first end of the energy storage unit, and the second end of the bridge arm energy storage inductor serves as the second end of the energy storage unit.

[0075] In the present application, it should be pointed out that in one embodiment, the number of energy storage units can also be increased in the case of originally having multiple energy storage units in the energy storage bridge arm (the number of energy storage units in the energy storage bridge arm is NxX, N and X are greater than 1). That is, the number of parallel and series energy storage units in the energy storage bridge arm increases, and the more the number of parallel or series energy storage units, the larger the capacity of the battery energy storage system. When increasing the number of energy storage units to realize the expansion operation of the energy storage, a bridge arm energy storage inductor is added for each added energy storage unit to ensure that each energy storage unit has a corresponding bridge arm energy storage inductor for filtering and suppressing inter-unit circulating current, and to ensure the working reliability of the battery energy storage circuit after the addition of the energy storage unit.

[0076] As shown in FIG. 1, the energy storage system of the present application includes a first energy storage upper bridge arm, a second energy storage upper bridge arm, a third energy storage upper bridge arm, a first energy storage lower bridge arm, a second energy storage lower bridge arm, and a third energy storage lower bridge arm. Figure 3 As shown in FIG. 1, the energy storage system of the present application includes a first energy storage upper bridge arm, a second energy storage upper bridge arm, a third energy storage upper bridge arm, a first energy storage lower bridge arm, a second energy storage lower bridge arm, and a third energy storage lower bridge arm.

[0077] As shown in FIG. 1, the energy storage system of the present application includes a first energy storage upper bridge arm, a second energy storage upper bridge arm, a third energy storage upper bridge arm, a first energy storage lower bridge arm, a second energy storage lower bridge arm, and a third energy storage lower bridge arm. Figure 5 As shown in FIG. 1, the energy storage system of the present application includes a first energy storage upper bridge arm, a second energy storage upper bridge arm, a third energy storage upper bridge arm, a first energy storage lower bridge arm, a second energy storage lower bridge arm, and a third energy storage lower bridge arm.

[0078] The control ends of the first switch device, the second switch device, the third switch device and the fourth switch device are respectively connected with external modulation function ports; the first end of the first switch device is connected with the cathode of the first freewheeling diode, the first end of the filter capacitor and the first end of the energy storage device, and the second end of the first switch device is connected with the anode of the first freewheeling diode and the first end of the third switch device; the first end of the second switch device is connected with the cathode of the second freewheeling diode, the first end of the filter capacitor and the first end of the energy storage device, and the second end of the second switch device is connected with the anode of the second freewheeling diode and the first end of the fourth switch device; the first end of the third switch device is connected with the cathode of the third freewheeling diode, and the second end of the third switch device is connected with the anode of the third freewheeling diode, the second end of the filter capacitor and the second end of the energy storage device; the first end of the fourth switch device is connected with the cathode of the fourth freewheeling diode, and the second end of the fourth switch device is connected with the anode of the fourth freewheeling diode, the second end of the filter capacitor and the second end of the energy storage device.

[0079] The connection between the second end of the first switch device and the third switch device is the first end of the energy storage unit, and the connection between the second end of the second switch device and the fourth switch device is the second end of the energy storage unit.

[0080] In the present application, the structure of the energy storage sub-module is also not unique, and can be a single polarity topology or a double polarity topology. When the energy storage unit is a full-bridge structure of double polarity topology, please refer to Figure 5 , the output positive end of which is the midpoint of the left half-bridge, and the output negative end of which is the midpoint of the right half-bridge.

[0081] Specifically, the first end of the energy storage sub-module is the output positive end of the energy storage sub-module, and the second end of the energy storage sub-module is the output negative end of the energy storage. In order to realize the series connection between the energy storage sub-modules, only the output positive end of the energy storage sub-module is connected with the output negative end of another energy storage sub-module, so that the series connection of the two energy storage sub-modules is realized.

[0082] The specific type of the energy storage device U is not unique, and in an embodiment, a lithium battery can be directly used. Through this scheme, the direct series and parallel connection of the energy storage device (i.e. the battery) is avoided, and the difference between the batteries is isolated in the form of a module. Even if different types of batteries are used in each energy storage unit, as long as a suitable and perfect battery management system is supplemented, even if the battery capacities are different, they can also be mixedly used in the multi-level structure energy storage system.

[0083] Among them, the device voltage level of the energy storage sub-module is consistent.

[0084] As Figure 6As shown in the above battery energy storage system uses a distributed control structure, namely each set uses a controller for control, each SET in the n sub-modules have a sub-module controller to execute control instructions, responsible for the switch tube in the sub-module of SET opening.

[0085] In a second aspect of the present application, a control method of a matrix expandable modular multilevel battery energy storage system is provided, comprising: receiving a system expansion demand signal, determining a target capacity after expansion according to the capacity of the original battery energy storage circuit, the voltage level of the AC and DC sides, the energy storage device U characteristics of the energy storage unit, defining the rated power of the energy storage unit, and determining the number of added energy storage units;

[0086] Judging whether a fault occurs in the energy storage unit of the energy storage system, if yes, executing a re-distribution process, and if not, executing a distribution process.

[0087] In some specific embodiments, receiving a system expansion demand signal, determining a target capacity after expansion according to the capacity of the original battery energy storage circuit, the voltage level of the AC and DC sides, the energy storage device U characteristics of the energy storage unit, defining the rated power of the energy storage unit, and determining the number of added energy storage units, comprises: receiving a system expansion demand signal and a target capacity, determining a target capacity after expansion as P origin according to the capacity of the original battery energy storage circuit, the voltage level of the AC and DC sides, the energy storage device U characteristics of the energy storage unit, and the capacity before system expansion as P target ; selecting an energy storage device U with the same voltage level as the original energy storage device U as the energy storage device U of the energy storage unit in the added energy storage bridge arm, defining the rated power of one energy storage unit; calculating the rated capacity of the energy storage device U of the original energy storage unit according to the capacity before expansion, and determining the number of added energy storage units.

[0088] In the above embodiment, the power of the energy storage unit is the same, so only the rated power of one energy storage unit needs to be defined.

[0089] Specifically, when the battery energy storage circuit has an expansion demand, first, the target capacity after expansion is determined as P origin according to the capacity of the original battery energy storage circuit, the voltage level of the AC and DC sides, the energy storage device U characteristics of the energy storage unit, and the capacity before system expansion as P t arg et . An energy storage device U with the same voltage level as the original energy storage device U is selected as the energy storage device U of the energy storage unit in the added energy storage bridge arm, and the rated power of one energy storage unit is defined as: P N = nU N I N . Wherein, I N is the rated discharge current of the energy storage device U in the energy storage unit, and U NThe rated voltage level of the energy storage device U in the energy storage unit.

[0090] In some specific embodiments, after capacity expansion, it is determined whether the energy storage unit has failed, and if so, a re-distribution process is performed, including: obtaining the number N of energy storage units and the rated discharge current I N of the energy storage device U in the energy storage unit D satisfying the relationship: and the rated current value of the switching device in the energy storage unit should also satisfy the relationship: mosN ≥I D .

[0091] In the formula, I D is the current allocated to other energy storage units; N is the number of energy storage units; I N is the rated discharge current of the energy storage device U in the energy storage unit; and I mosN is the rated current value of the switching device in the energy storage unit.

[0092] Specifically, the rated capacity of the energy storage device U in the original energy storage unit is calculated according to the capacity before expansion wherein k=N·X is the number of energy storage units contained in one energy storage bridge arm, and n is the number of energy storage sub-modules in one energy storage unit. The number of added energy storage units should satisfy: and the rated current value I mosN of the switching device in the energy storage unit should satisfy the relationship: When one energy storage unit in the energy storage system fails, other energy storage units in parallel with the failed energy storage unit will additionally bear the power of the failed energy storage unit, and the system will run with the fault. Other energy storage units will be allocated to the current I D satisfying the relationship: and the rated current value of the switching device in the energy storage unit should also satisfy the relationship: I mosN ≥I D .

[0093] As shown in Figure 7 some specific embodiments, the distribution process includes: the main controller sends the voltage and current control signals allocated to each SET to the SET controller based on the voltage and current of each bridge arm in three phases through closed-loop control of the external output voltage and current; the SET controller receives the voltage and current control signals allocated by the main controller, modulates the voltage of each SET, outputs the voltage and current distribution result, and sends the switching control signal to the energy storage sub-module controller; the energy storage sub-module executes the switching control signal and samples the energy storage sub-module temperature and battery energy information, and sends them to the SET controller for energy balancing and power distribution.

[0094] Specifically, during operation, the main controller first performs closed-loop control on the output voltage and current of the system based on the voltage and current information of each bridge arm of the three-phase. Then, the main controller calculates and sends the voltage value allocated to each SET to the lower SET controller. After receiving the voltage value, the SET controller in the first column modulates the voltage of the respective SET, while the other SET controllers allocate and control the current of the respective SET branch. At the same time, the SET controller also collects the temperature and battery energy information of the sub-modules and uploads it to itself for energy balancing and power distribution decision-making. Finally, the SET controller sends the switch control signal to the sub-module according to the voltage and current allocation results and the energy and temperature state information of the sub-module. The sub-module controller executes these control signals and continues to collect the temperature and battery energy information of the sub-module and uploads it to the SET controller for subsequent optimization.

[0095] Wherein, the SET controller is the controller of the energy storage unit; SET is the energy storage unit; the rated power of the energy storage unit is defined as the rated power of the newly added energy storage unit.

[0096] The present application realizes accurate closed-loop control of the three-phase bridge arm voltage and current through the cooperative work of the main controller, SET controller and sub-module controller, improves the stability and accuracy of the output voltage and current, and realizes the optimization of energy balancing and power distribution through the collection of the temperature and battery energy information of the sub-modules.

[0097] In some specific embodiments, the SET controller receives the voltage and current control signals allocated by the main controller, modulates the voltage of each SET, outputs the voltage and current allocation results, and sends the switch control signal to the energy storage sub-module controller, which includes: obtaining the voltage and current control signal; sampling the voltage and current in each SET for voltage and current control; sampling the sub-module temperature and battery energy information and uploading it to the SET controller for energy balancing and power distribution; the SET controller sends the switch tube control signal to the sub-module in the SET according to the above voltage and current allocation results and the energy and temperature state information of each sub-module.

[0098] Finally, the control signal issued by the SET controller is executed, the sub-module temperature and battery energy information is collected and uploaded to the SET controller for energy balancing and power distribution.

[0099] The sub-module controller uploads the sub-module temperature and battery energy information to the SET controller, and the SET controller uploads the information to the uppermost controller after integration processing, for overall scheduling control of the entire system. The system-level voltage and current control is completed at the uppermost level, and the information is sent to the SET controller, which adds energy balance control for more detailed processing. The sub-module temperature and energy information are related to the output power capability, and the energy balance refers to the distribution of more power to the sub-module with high energy state during discharging, and the opposite during charging.

[0100] The SET controller obtains and integrates the information sampled by the n sub-module controllers.

[0101] To facilitate understanding of the scheme of expanding the capacity of the energy storage units in the battery energy storage system by increasing the number of energy storage units, the expansion operation is explained and described in detail below. The voltage level of each energy storage device U is set to be the same, for example, in one embodiment, a 51.2V rated voltage and 38Ah nominal capacity energy storage device U is used in each energy storage unit.

[0102] Referring to FIG. 1, Figure 8 For example, in a more detailed embodiment, when the 200kW energy storage system needs to be expanded to 400kW, the DC side voltage is 800V, the AC side voltage is 380V, and each energy storage bridge arm of the energy storage system before expansion contains 4 energy storage units (the energy storage units are connected in a 2X2 matrix), each energy storage unit contains 6 energy storage sub-modules and 1 energy storage bridge arm inductor, in this embodiment, the target capacity is 400kW, each energy storage bridge arm of the expanded system contains 9 energy storage units (the energy storage units are connected in a 3X3 matrix), each energy storage unit contains 6 energy storage sub-modules and 1 energy storage bridge arm inductor, and the energy storage circuit is connected in the manner of Figure 6 Assuming that after expansion, the energy storage unit Set1-1 fails, the system current is distributed by the parallel energy storage units Set1-2 and Set1-3.

[0103] The energy storage sub-module in this embodiment includes a switching device, a capacitor, and an energy storage device U (i.e., a battery), which are connected in the manner of Figure 5The structure shown is connected to constitute an energy storage sub-module. Meanwhile, the selected energy storage bridge arm inductance and AC side inductance value in the embodiment is 1 mH, the energy storage device U used is a lithium iron phosphate battery with a nominal voltage of 51.2 V / 38 AH, and the power MOSFET used is SFG180N10PF. The main controller uses a Beckoff CX2020 controller, the set controller uses a xilinx K7 series FPGA, and the sub-module controller uses a pango PGL12G series FPGA. The voltage allocated to each SET in the original upper bridge arm is 200+311 / 2sinwt V, and the voltage allocated to the lower bridge arm is 200-311 / 2sinwt V. The current allocated in each SET is 27.13 A

[0104] In the embodiment, a power decoupling control method can be used to control the power of the AC side and the power of the DC side respectively, and then indirectly control the charging and discharging state of the battery. A carrier phase shift modulation method is used to realize switching control of the energy storage unit.

[0105] According to the foregoing operation, the system is expanded: the original capacity of the system P origin = 200 kW, the rated capacity of the energy storage device U of the original energy storage unit is calculated according to the capacity before expansion After expansion, the number of added energy storage units should satisfy: That is, the number of added energy storage units on each energy storage bridge arm In this case, 5 energy storage units will be added in each energy storage bridge arm to meet the above condition of increasing the number of energy storage units. At this time, the current passing through the switching device in each energy storage unit At this time, it satisfies

[0106] After expansion, the rated current of the system I N , assuming that SET1-1 fails to operate, the current allocated to SET1-2 to SET1-3 is At this time, the switching device in the energy storage unit satisfies the relationship: I mosN ≥ I D From the control level of the system, after the system is expanded by 5 energy storage units, 5 SET controllers need to be added. After the expansion of the energy storage system, the voltage and current allocated to each SET change. The voltage allocated to each SET in the upper bridge arm is 400 / 3+311 / 3sinwt V, and the voltage allocated to the lower bridge arm is 400 / 3-311 / 3sinwt V. The current allocated in each SET is 24.1 A. After the above system assumes that SET1-1 fails, the voltage allocated to the SET in parallel with SET1-1 remains unchanged, but the allocated current is modified to 36.2 A.

[0107] The specific embodiments of the present application have been described. It is to be understood that the application is not limited to particular details of the embodiments described, as various modifications can be made therein without departing from the spirit and scope of the application. The specific features of the various embodiments can be used in any combination without departing from the spirit and scope of the application.

Claims

1. A control method of a matrix expandable modular multilevel battery energy storage system, characterized in that, The energy storage system comprises a direct-current power grid and a three-phase power grid; The energy storage bridge arm comprises an upper energy storage bridge arm and a lower energy storage bridge arm, a first port of the upper energy storage bridge arm is connected with a positive terminal of the direct-current power grid, a second port of the lower energy storage bridge arm is connected with a negative terminal of the direct-current power grid, and a second port of the upper energy storage bridge arm and a first port of the lower energy storage bridge arm are connected with the three-phase power grid; The energy storage bridge arm is formed by arranging the energy storage units in a matrix manner to form a matrix network structure, and the energy storage units are provided with independent controllers for executing control instructions; The energy storage bridge arm comprises 1 to X parallel energy storage units arranged in the transverse direction and 1 to N series energy storage units arranged in the longitudinal direction, wherein X>1 and N>1; One end of the 1 to X parallel energy storage units arranged in the transverse direction is connected with each other, the other end is connected with one end of the 1 to N series energy storage units arranged in the longitudinal direction, and the 1 to X parallel energy storage units and the 1 to N series energy storage units form NxX energy storage units to form the matrix network structure; The upper energy storage bridge arm has the same structure as the energy storage bridge arm and is formed by arranging the energy storage units in a matrix manner; The control method comprises the following steps: receiving a system capacity expansion demand signal, determining a target capacity after expansion according to the capacity of the original battery energy storage circuit, the voltage level of the AC / DC side, the U characteristics of the energy storage units, defining the rated power of the energy storage units, and determining the number of added energy storage units; Judging whether the energy storage units in the energy storage system have faults, if yes, executing a re-distribution process, and if not, executing a distribution process.

2. The control method of a matrix expandable modular multilevel battery energy storage system according to claim 1, characterized in that, The upper energy storage bridge arm comprises a first upper energy storage bridge arm, a second upper energy storage bridge arm and a third upper energy storage bridge arm, and the lower energy storage bridge arm comprises a first lower energy storage bridge arm, a second lower energy storage bridge arm and a third lower energy storage bridge arm; The first upper energy storage bridge arm and the first lower energy storage bridge arm form a first phase cluster, a first port of the first upper energy storage bridge arm is connected with a positive terminal of the direct-current power grid, a second port of the second lower energy storage bridge arm is connected with a negative terminal of the direct-current power grid, and a second port of the first upper energy storage bridge arm and a first port of the second lower energy storage bridge arm are connected with a first phase of the three-phase power grid; The second upper energy storage bridge arm and the second lower energy storage bridge arm form a second phase cluster, a first port of the second upper energy storage bridge arm is connected with a positive terminal of the direct-current power grid, a second port of the second lower energy storage bridge arm is connected with a negative terminal of the direct-current power grid, and a second port of the second upper energy storage bridge arm and a first port of the second lower energy storage bridge arm are connected with a second phase of the three-phase power grid; The third upper energy storage bridge arm and the third lower energy storage bridge arm form a third phase cluster, a first port of the third upper energy storage bridge arm is connected with a positive terminal of the direct-current power grid, a second port of the third lower energy storage bridge arm is connected with a negative terminal of the direct-current power grid, and a second port of the third upper energy storage bridge arm and a first port of the third lower energy storage bridge arm are connected with a third phase of the three-phase power grid.

3. The control method of a matrix expandable modular multilevel battery energy storage system according to claim 2, characterized in that, The first energy storage upper bridge arm, the second energy storage upper bridge arm, the third energy storage upper bridge arm, the first energy storage lower bridge arm, the second energy storage lower bridge arm and the third energy storage lower bridge arm have the same number of energy storage units in the same phase cluster, and each has NxX energy storage units to form a matrix net structure.

4. The control method of a matrix expandable modular multilevel battery energy storage system according to claim 1, characterized in that, The energy storage unit comprises 1 to n energy storage sub-modules and a bridge energy storage inductor, and the energy storage sub-modules have first ends and second ends; the second end of the last energy storage sub-module of the 1 to n energy storage sub-modules is connected to the first end of the next energy storage sub-module; The second end of the nth energy storage sub-module is connected to the first end of the bridge energy storage inductor; The first end of the first energy storage sub-module serves as the first end of the energy storage unit, and the second end of the bridge energy storage inductor serves as the second end of the energy storage unit.

5. The control method of a matrix expandable modular multilevel battery energy storage system according to claim 4, characterized in that, The energy storage sub-module comprises a first switching device, a second switching device, a third switching device, a fourth switching device, a first freewheeling diode, a second freewheeling diode, a third freewheeling diode, a fourth freewheeling diode, a filter capacitor and an energy storage device; The control ends of the first switching device, the second switching device, the third switching device and the fourth switching device are respectively connected to external modulation function ports; the first end of the first switching device is connected to the cathode of the first freewheeling diode, the first end of the filter capacitor and the first end of the energy storage device, and the second end of the first switching device is connected to the anode of the first freewheeling diode, the first end of the third switching device; the first end of the second switching device is connected to the cathode of the second freewheeling diode, the first end of the filter capacitor and the first end of the energy storage device, and the second end of the second switching device is connected to the anode of the second freewheeling diode, the first end of the fourth switching device; the first end of the third switching device is connected to the cathode of the third freewheeling diode, and the second end of the third switching device is connected to the anode of the third freewheeling diode, the second end of the filter capacitor and the second end of the energy storage device; the first end of the fourth switching device is connected to the cathode of the fourth freewheeling diode, and the second end of the fourth switching device is connected to the anode of the fourth freewheeling diode, the second end of the filter capacitor and the second end of the energy storage device; The connection between the second end of the first switching device and the third switching device serves as the first end of the energy storage unit, and the connection between the second end of the second switching device and the fourth switching device serves as the second end of the energy storage unit.

6. The control method of a matrix expandable modular multilevel battery energy storage system of claim 1, wherein, The receiving system receives a capacity expansion demand signal, determines a target capacity after expansion according to the capacity of the original battery energy storage circuit, the voltage level of the AC and DC sides, the U characteristics of the energy storage device of the energy storage unit, defines the rated power of the energy storage unit, and determines the number of added energy storage units, including: The receiving system receives a capacity expansion demand signal and a target capacity, and according to the capacity of the original battery energy storage circuit, AC / DC voltage level, and energy storage device U characteristics of the energy storage unit, the capacity before the system capacity expansion is P origin , and the target capacity after the capacity expansion is P target . selecting an energy storage device U with the same voltage level as the original energy storage device U as the energy storage device U of the energy storage unit in the added energy storage bridge arm, and defining the rated power of one energy storage unit; calculating the rated capacity of the energy storage device U of the original energy storage unit according to the capacity before expansion, and determining the number of added energy storage units.

7. The control method of a matrix expandable modular multilevel battery energy storage system of claim 1, wherein, The application judges whether a fault occurs in the energy storage unit of the energy storage system, and if so, a redistribution process is executed, including: Obtaining the number N of energy storage units and the rated discharge current I of the energy storage device U in the energy storage unit N ; The other energy storage units will be allocated to the current I D The relationship is satisfied: The rated current value of the switching device in the energy storage unit should also satisfy the relationship I mosN ≥ I D ; where I D is the current assigned to other energy storage units; N is the number of energy storage units; I N is the rated discharge current of the energy storage device U in the energy storage unit. I mosN The rated current value for the switching device in the energy storage unit.

8. The control method of a matrix expandable modular multilevel battery energy storage system of claim 1, wherein, The execution of the distribution process includes that the main controller sends voltage and current control signals allocated to each SET to the SET controller based on the voltage and current of each bridge arm of the three phases through closed-loop control of the output voltage and current. The SET controller receives the voltage and current control signals allocated by the main controller, modulates the voltage of each SET, outputs the voltage and current distribution results, and sends switch control signals to the energy storage submodule controller. The energy storage submodule executes the switch control signals and samples the temperature and battery energy information of the energy storage submodule, and sends them to the SET controller for energy balancing and power distribution.

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