Energy storage system

Abstract

The embodiment of the invention relates to the technical field of power electronics, and discloses an energy storage system. The system comprises at least one first energy storage unit, the first energy storage unit is connected to an alternating current bus of an energy storage system through a first power conversion system, and a direct current bus bar of the first energy storage unit is connected to a direct current bus of the energy storage system through a direct current-direct current converter and a first switching device in sequence; the second energy storage unit is connected to the alternating current bus through a second power conversion system, and a direct current bus bar of the second energy storage unit is connected to the direct current bus through a second switching device; and the controller is configured to control the DC-DC converter, the first switching device and the second switching device to realize electric quantity balance between the first energy storage unit and the second energy storage unit. The problems of low reliability and limited flexibility of electric quantity equalization among different energy storage units in the prior art are solved.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of power electronics technology, and particularly to energy storage systems. Background Technology

[0002] Energy storage systems, as crucial peak-shaving, frequency regulation, and energy storage facilities in power systems, typically consist of multiple energy storage units connected in parallel. Each energy storage unit generally comprises multiple battery clusters, which are connected in parallel to a power conversion system and then to a high-voltage bus via a transformer. In the actual operation of energy storage facilities, scenarios often arise requiring power balancing between different energy storage units. For example, after several years of operation, the battery capacity of an energy storage facility may decline to varying degrees. To maintain the facility's capacity, new energy storage units need to be added to work in conjunction with existing units; or the facility may have been constructed in phases, resulting in the coexistence of old and new energy storage units; or a particular energy storage unit may have been out of service for an extended period, resulting in a low state of charge, requiring other energy storage units to replenish its power. All of these scenarios involve the need for compartment-level power balancing between energy storage units with different states of charge.

[0003] In related technologies, energy storage units are connected on the DC side via switching devices (such as contactors) to achieve power balancing. However, when there are significant differences in the port voltages of different energy storage units, the direct closing of the switching devices may generate large inrush currents, posing a risk of damaging the devices or triggering protection mechanisms, thus reducing the reliability of the balancing process. Furthermore, the switching devices can only perform on / off control and cannot actively adjust the power magnitude and direction during the balancing process, limiting the flexibility of the balancing control. Summary of the Invention

[0004] The purpose of this invention is to provide an energy storage system to solve the problems of low reliability and limited flexibility in power balance among different energy storage units in related technologies.

[0005] To address the aforementioned technical problems, embodiments of the present invention provide an energy storage system, comprising: at least one first energy storage unit, wherein the first energy storage unit is connected to the AC bus of the energy storage system via a first power conversion system, and the DC bus of the first energy storage unit is connected to the DC bus of the energy storage system sequentially via a DC-DC converter and a first switching device; at least one second energy storage unit, wherein the second energy storage unit is connected to the AC bus via a second power conversion system, and the DC bus of the second energy storage unit is connected to the DC bus via a second switching device; and a controller configured to control the DC-DC converter, the first switching device, and the second switching device to achieve power balancing between the first energy storage unit and the second energy storage unit.

[0006] In this embodiment of the invention, by setting a DC-DC converter between the first energy storage unit and the DC bus, the first energy storage unit can actively adjust its output voltage and power through the DC-DC converter. This allows for voltage regulation via the DC-DC converter when there is a significant voltage difference between the ports of the first and second energy storage units, avoiding the inrush current generated by directly closing the switching devices and improving the safety and reliability of the equalization process. Simultaneously, the DC-DC converter can actively control the magnitude and direction of the equalization power, making the equalization control more flexible and controllable compared to methods that only achieve equalization by switching devices on and off. Furthermore, the asymmetrical configuration of configuring a DC-DC converter for the first energy storage unit and only configuring switching devices for the second energy storage unit, compared to a scheme where each energy storage unit is equipped with a DC-DC converter, effectively reduces system costs while achieving controllable equalization.

[0007] Furthermore, the DC busbar of the first energy storage unit is connected to the common connection point of the DC busbar via a first switching device; the DC busbar of the second energy storage unit is connected to the common connection point of the DC busbar sequentially via a DC-DC converter and a second switching device; wherein the common connection point of the DC busbar is located inside either the first or the second energy storage unit. Therefore, the common connection point of the DC busbar can utilize the existing busbars within the energy storage units, eliminating the need to lay new common DC busbars during energy storage station expansion, achieving resource reuse, and reducing expansion costs and construction complexity.

[0008] Furthermore, the controller is configured to: detect the voltage difference between the first port voltage of the first energy storage unit and the second port voltage of the second energy storage unit; when the voltage difference exceeds a preset voltage difference threshold, control the first switching device to close and control the DC-DC converter to adjust the output voltage; when the voltage difference is less than or equal to the preset voltage difference threshold, control the second switching device to close. Thus, through a step-by-step control strategy, when the voltage difference is large, pre-regulation is performed through the DC-DC converter, and the second switching device is closed only after the voltage difference has decreased to a safe range. This further avoids the inrush current generated by directly closing the switch under large voltage differences, improving system safety.

[0009] In addition, this ensures that energy flows from the first energy storage unit with higher battery state parameters (such as higher state of charge) to the second energy storage unit with lower battery state parameters, thus guaranteeing the correctness of the balance direction and avoiding reverse energy flow.

[0010] In addition, the energy storage system also includes an overcurrent protection device, which is connected in series in the transmission path of the DC bus. Therefore, when a short-circuit fault occurs in the DC bus path, the overcurrent protection device can promptly trip to cut off the fault current, preventing the fault from escalating and improving the system's safety protection capability.

[0011] Furthermore, the DC bus of the second energy storage unit is connected to the DC bus in sequence via a second DC-DC converter and a second switching device. Thus, both the first and second energy storage units are equipped with DC-DC converters, enabling mutual balancing between any number and combination of energy storage units, improving the flexibility and applicability of the balancing process.

[0012] Furthermore, the battery state parameters include at least the state of charge (SOC). The controller is also configured to: after the second switching device is closed, acquire the second SOC of the second energy storage unit and the first SOC of the first energy storage unit; and control the output power of the DC-DC converter based on the SOC difference between the second and first SOCs to reduce the SOC difference. Thus, by dynamically adjusting the output power of the DC-DC converter based on the SOC difference between the two energy storage units, precise SOC balance control is achieved, making the SOC of each energy storage unit tend to be consistent.

[0013] Furthermore, the controller is configured to: acquire the power difference between the first operating power of the first power conversion system and the second operating power of the second power conversion system during the charging and discharging process of the first power conversion system and the second power conversion system to the AC bus; and adjust the output power of the DC-DC converter based on the power difference and the charge difference. This enables simultaneous pod-level equalization during normal charging and discharging operation of the energy storage station, allowing for immediate response to equalization needs without waiting for the station to come to a standstill, thus improving the timeliness of equalization and system operating efficiency.

[0014] Furthermore, the controller is configured to: upon detecting a fault in the second power conversion system, control the second switching device and the first switching device to close, thereby charging or discharging the second energy storage unit through the DC-DC converter. Thus, when a power conversion system of an energy storage unit fails, charging and discharging operations can continue for that energy storage unit through the DC bus and the DC-DC converter, achieving fault tolerance and improving the overall reliability and availability of the energy storage system. Attached Figure Description

[0015] One or more embodiments are illustrated by way of example with reference numerals in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0016] Figure 1 This is a structural diagram of an energy storage system provided according to an embodiment of this application; Figure 2 This is a structural diagram of an energy storage system equipped with an overcurrent protection device according to an embodiment of this application; Figure 3 This is a structural diagram of an energy storage system equipped with a second DC-DC converter according to an embodiment of this application. Detailed Implementation

[0017] As described in the background section, energy storage systems require power balancing between different energy storage units during actual operation. In related technologies, energy storage units are connected on the DC side via switching devices to achieve power balancing; however, this method suffers from low balancing reliability and limited control flexibility. The applicant's research revealed that the root causes of the aforementioned problems are as follows: First, the switching devices can only control on and off, lacking voltage regulation capabilities. When there are significant differences in the port voltages of different energy storage units, the direct closure of the switching devices will instantaneously create a low-impedance loop, generating a large inrush current driven by the voltage difference. This inrush current may exceed the rated withstand capacity of the switching devices and related electrical components, leading to device damage or triggering protection actions, thereby causing an interruption in the equalization process. Second, the switching devices cannot actively adjust the magnitude and direction of the equalization power. The equalization process relies entirely on the natural drive of the voltage difference between energy storage units. As the voltage difference gradually decreases, the equalization current also decreases, resulting in reduced equalization efficiency and prolonged equalization time. Third, if an AC-side equalization path via a power conversion system and transformer is adopted, the energy needs to pass through multiple power conversion stages. This not only results in a long path and high losses but also requires the power conversion system and transformer on the relevant links to be in a reliable working state, leading to high system complexity. Furthermore, this method can usually only be executed when the energy storage station is stationary and cannot respond to equalization needs during charging and discharging operations.

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details are presented in the various embodiments of the present invention to facilitate a better understanding of this application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments. The division of the various embodiments below is for ease of description and should not constitute any limitation on the specific implementation of the present invention. The various embodiments can be combined with and referenced by each other without contradiction.

[0019] One embodiment of the present invention relates to an energy storage system that can be applied to scenarios such as energy storage sites, energy storage power stations, industrial and commercial energy storage systems, and grid-side energy storage systems. The control logic of the energy storage system can run on an execution entity with data processing capabilities, such as the energy management system, energy storage unit controller, programmable logic controller, edge computing device, or cloud server of the energy storage site.

[0020] This invention provides an energy storage system, comprising: at least one first energy storage unit, the first energy storage unit being connected to the AC bus of the energy storage system via a first power conversion system, and the DC bus of the first energy storage unit being connected to the DC bus of the energy storage system sequentially via a DC-DC converter and a first switching device; at least one second energy storage unit, the second energy storage unit being connected to the AC bus via a second power conversion system, and the DC bus of the second energy storage unit being connected to the DC bus via a second switching device; and a controller configured to control the DC-DC converter, the first switching device, and the second switching device to achieve power balancing between the first energy storage unit and the second energy storage unit. In this embodiment of the invention, by setting a DC-DC converter between the first energy storage unit and the DC bus, the first energy storage unit can actively adjust its output voltage and power through the DC-DC converter. Therefore, when there is a large voltage difference between the ports of the first and second energy storage units, voltage regulation can be performed first through the DC-DC converter, avoiding the inrush current generated by directly closing the switching device, thus improving the safety and reliability of the balancing process. Meanwhile, the DC-DC converter can actively control the magnitude and direction of the equalization power, which is more flexible and controllable compared to the method of achieving equalization only by switching devices on and off. In addition, the asymmetrical configuration of using a DC-DC converter in the first energy storage unit and only a switching device in the second energy storage unit effectively reduces the system cost while achieving controllable equalization, compared to a scheme where each energy storage unit is equipped with a DC-DC converter.

[0021] like Figure 1As shown, the energy storage system provided in this embodiment includes at least one first energy storage unit, at least one second energy storage unit, and a controller. The first energy storage unit is connected to the AC bus of the energy storage system through a first power conversion system, and the DC bus of the first energy storage unit is connected to the DC bus of the energy storage system sequentially through a DC-DC converter and a first switching device. The second energy storage unit is connected to the AC bus through a second power conversion system, and the DC bus of the second energy storage unit is connected to the DC bus through a second switching device. The controller is configured to control the DC-DC converter, the first switching device, and the second switching device to achieve power balance between the first energy storage unit and the second energy storage unit.

[0022] Specifically, the first and second power conversion systems can be bidirectional energy storage converters used to achieve bidirectional conversion between direct current (DC) and alternating current (AC). The DC side of the first power conversion system is connected to the DC bus of the first energy storage unit, and the AC side is connected to the AC bus via a transformer. The DC side of the second power conversion system is connected to the DC bus of the second energy storage unit, and the AC side is connected to the AC bus via a transformer. The AC bus can be the high-voltage bus of the energy storage station, used to collect the AC power output from each energy storage unit and exchange power with the power grid.

[0023] A DC-DC converter is a power conversion device capable of transforming and regulating DC voltage, including but not limited to Buck converters, Boost converters, Buck-Boost converters, and bidirectional isolated DC-DC converters. The DC-DC converter is located between the DC bus and the DC bus of the first energy storage unit and can actively adjust the output voltage and output power according to the controller's instructions. Compared to switching devices that can only control on and off, the DC-DC converter has voltage regulation capabilities. When there is a large voltage difference between the ports of the first and second energy storage units, it can first adjust the output voltage to a level close to the DC bus voltage, thereby avoiding the inrush current caused by the voltage difference when directly closing the switching device.

[0024] The first and second switching devices are used to control the on / off connection between the corresponding energy storage units and the DC bus, including but not limited to contactors, circuit breakers, relays, and disconnect switches. Under normal operating conditions, both the first and second switching devices are in the off state, and each energy storage unit operates independently, exchanging power with the AC bus through its own power conversion system and transformer. When power balancing between energy storage units is required, the controller controls the closing of the corresponding switching devices according to the balancing strategy, enabling the participating energy storage units to form a DC-side connection through the DC bus, thereby achieving controllable energy transfer through a DC-DC converter.

[0025] The DC bus is a common combiner channel used to connect the DC sides of each energy storage unit, providing a DC power transmission path for the energy storage units participating in the balancing process. The voltage level of the DC bus matches the voltage level of the DC combiner bus of the energy storage unit; for example, it can be a 1500V DC bus.

[0026] The controller is used to coordinate and control the DC-DC converter and various switching devices in the energy storage system to achieve power balance among the energy storage units. The controller can be integrated into the energy management system of the energy storage site, or it can be a standalone balancing controller, or it can be distributed among the controllers of each energy storage unit and coordinate its operation through a communication network. The controller is connected to the DC-DC converter, the first switching device, and the second switching device via communication interfaces, including but not limited to CAN bus, RS485 bus, Ethernet, and wireless communication.

[0027] In a specific example, the DC bus of the first energy storage unit is connected to the common connection point of the DC bus through a first switching device; the DC bus of the second energy storage unit is connected to the common connection point of the DC bus through a DC-DC converter and a second switching device in sequence; wherein the common connection point of the DC bus is located inside the first energy storage unit or the second energy storage unit.

[0028] Specifically, the common connection point of the DC bus can reuse the existing busbar within the energy storage unit. For example... Figure 1 As shown, each energy storage unit is equipped with a DC busbar for collecting the outputs of each battery cluster. During normal operation, this DC busbar collects the DC power from each battery cluster and transmits it to the power conversion system. In this embodiment, the DC busbar within one energy storage unit can be used as a common connection point for the DC bus, with other energy storage units connected to this common connection point via cables. Therefore, when expanding the energy storage facility or operating with both new and old energy storage units, there is no need to lay an additional independent common DC busbar. The existing busbars within the existing energy storage units can be used to interconnect the DC sides of each energy storage unit, reducing expansion costs and construction complexity, and achieving resource reuse.

[0029] In an optional embodiment, the common connection point can also be configured as a common DC bus independent of each energy storage unit, with each energy storage unit connected to this common DC bus via a cable. This approach is suitable for newly built energy storage sites or scenarios requiring independent DC bus layout.

[0030] In a specific example, the first energy storage unit includes at least one first battery cluster, which is connected in parallel to the DC bus of the first energy storage unit via a first disconnect switch, and the DC bus of the first energy storage unit is connected to the DC side of the first power conversion system; and / or, the second energy storage unit includes at least one second battery cluster, which is connected in parallel to the DC bus of the second energy storage unit via a second disconnect switch, and the DC bus of the second energy storage unit is connected to the DC side of the second power conversion system.

[0031] Specifically, each energy storage unit typically comprises multiple battery clusters, each connected in parallel to the DC bus of the energy storage unit via its own isolating switch. The isolating switch controls the connection and disconnection between individual battery clusters and the DC bus, facilitating maintenance, repair, or fault isolation of individual battery clusters. The DC bus collects the DC power output from each battery cluster, connecting it to the DC side of the power conversion system for regular charging and discharging; and connecting it to the DC bus via switching devices and DC-DC converters for power balancing among energy storage units. Thus, the parallel structure of multiple battery clusters within the energy storage unit ensures sufficient capacity and power for each individual unit while enabling independent control and fault isolation of each battery cluster through the isolating switches, improving system flexibility and maintainability.

[0032] In a specific example, the energy storage system also includes an overcurrent protection device, which is connected in series in the transmission path of the DC bus.

[0033] Specifically, such as Figure 2 As shown, overcurrent protection devices can be fuses, DC circuit breakers, electronic protection switches, and other devices with overcurrent protection functions. When a short-circuit fault occurs in the DC bus path, the fault current will rise rapidly. The overcurrent protection device can act in time when the fault current reaches its operating threshold, cutting off the fault circuit and preventing the fault current from continuing to flow and causing damage to the DC-DC converter, switching devices, and battery packs, thereby preventing the fault from escalating and improving the system's safety protection capability.

[0034] In an optional embodiment, when only two energy storage units participate in balancing, short-circuit protection can be achieved using the existing fuses within each energy storage unit. When three or more energy storage units are connected via the DC bus, due to the large number of connected energy storage units, an additional overcurrent protection device can be added to the common transmission path of the DC bus to prevent the impact of a short-circuit fault from expanding. The overcurrent protection device is installed in the main path of the DC bus and can isolate the fault to a minimum extent when a short-circuit fault occurs.

[0035] In an optional example, the DC bus of the second energy storage unit is connected to the DC bus in sequence via a second DC-DC converter and a second switching device.

[0036] Specifically, such as Figure 3 As shown in this embodiment, both the first and second energy storage units are equipped with DC-DC converters. The DC bus of the first energy storage unit is connected to the DC bus via the first DC-DC converter and the first switching device in sequence; the DC bus of the second energy storage unit is connected to the DC bus via the second DC-DC converter and the second switching device in sequence. Thus, each energy storage unit has independent voltage regulation and power control capabilities, enabling mutual balancing between any number and combination of energy storage units. For example, when an energy storage station includes multiple energy storage units, any two or more energy storage units can be flexibly selected for balancing based on their state of charge. The controller controls the DC-DC converters and switching devices of the participating energy storage units respectively, achieving controllable energy transfer between the selected energy storage units. Although this symmetrical configuration increases the number of DC-DC converters compared to the asymmetrical configuration, it provides greater balancing flexibility and applicability.

[0037] In a specific example, the battery state parameters of the second energy storage unit are less than or equal to the battery state parameters of the first energy storage unit.

[0038] Specifically, battery state parameters characterize the current state of the batteries in the energy storage unit, including but not limited to state of charge, state of health, and port voltage. During charge balancing, energy flows from the energy storage unit with higher battery state parameters to the energy storage unit with lower battery state parameters. In this embodiment, the first energy storage unit is equipped with a DC-DC converter and has the ability to actively output power. Therefore, the energy storage unit with higher battery state parameters is designated as the first energy storage unit, and the energy storage unit with lower battery state parameters is designated as the second energy storage unit, so that energy is output from the first energy storage unit to the second energy storage unit through the DC-DC converter. This ensures the correctness of the balancing direction and avoids further expansion of the state difference caused by reverse energy flow.

[0039] In a specific example, the controller is configured to: detect the voltage difference between the first port voltage of the first energy storage unit and the second port voltage of the second energy storage unit; when the voltage difference exceeds a preset voltage difference threshold, control the first switching device to close and control the DC-DC converter to adjust the output voltage; when the voltage difference is less than or equal to the preset voltage difference threshold, control the second switching device to close.

[0040] Specifically, when the controller receives an equalization command or detects a condition requiring equalization, it first acquires the first port voltage of the first energy storage unit and the second port voltage of the second energy storage unit, and calculates the voltage difference between them. A preset voltage difference threshold is a pre-defined safe voltage difference range. If the voltage difference exceeds this threshold, directly closing the switching device to connect the DC sides of the two energy storage units would generate a large inrush current due to the voltage difference. Therefore, the controller first controls the first switching device to close, connecting the first energy storage unit to the DC bus via a DC-DC converter. At this time, since the second switching device is still open, the second energy storage unit is not yet connected to the DC bus, and no inrush current is generated. Subsequently, the controller controls the DC-DC converter to adjust the output voltage, gradually bringing the DC bus voltage closer to the port voltage of the second energy storage unit. When the voltage difference shrinks to within the preset voltage difference threshold, the controller then controls the second switching device to close, connecting the second energy storage unit to the DC bus. Thus, through a step-by-step control strategy and a pre-adjustment process, the inrush current generated by directly closing the switch under large voltage differences is avoided, improving system safety and device lifespan.

[0041] In an optional embodiment, the preset voltage difference threshold can be set according to factors such as the rated surge current withstand capability of the switching device and the impedance characteristics of the DC bus, for example, set to 20V, 50V or 100V.

[0042] In a specific example, the battery state parameters include at least the state of charge; the controller is also configured to: after the second switching device is closed, acquire the second state of charge of the second energy storage unit and the first state of charge of the first energy storage unit; and control the output power of the DC-DC converter to reduce the state of charge difference based on the charge difference between the second state of charge and the first state of charge.

[0043] Specifically, the state of charge (SOC) is a parameter characterizing the remaining capacity of a battery, usually expressed as a percentage. When both the first and second switching devices are closed, the first and second energy storage units are connected on the DC side via a DC bus. At this time, the controller acquires the SOC of the two energy storage units and calculates the SOC difference. The controller controls the output power of the DC-DC converter based on the SOC difference; the larger the SOC difference, the greater the output power to accelerate the balancing process; the smaller the SOC difference, the smaller the output power to achieve fine balancing and avoid overshoot. When the SOC difference decreases to a preset balancing completion threshold, the controller determines that balancing is complete, then controls the DC-DC converter to stop outputting and sequentially disconnects the second and first switching devices, allowing each energy storage unit to resume independent operation. Thus, by dynamically adjusting the output power based on the SOC difference between the two energy storage units, precise SOC balancing control is achieved, making the SOC of each energy storage unit tend to be consistent.

[0044] In a specific example, the controller is also configured to: during the charging and discharging process of the first power conversion system and the second power conversion system to the AC bus, acquire the power difference between the first operating power of the first power conversion system and the second operating power of the second power conversion system; and adjust the output power of the DC-DC converter according to the power difference and the charge difference.

[0045] Specifically, during the normal operation of an energy storage station, each energy storage unit charges or discharges to the AC bus through its respective power conversion system. When there are differences in the state of charge (SOC) of the energy storage units, if they are charged and discharged at the same power, the difference in SOC will persist or even increase. In this embodiment, while each energy storage unit is charging and discharging normally, the controller transfers energy between the energy storage units through the DC bus and the DC-DC converter, achieving synchronous charging, discharging, and balancing. Specifically, the controller obtains the first operating power of the first power conversion system and the second operating power of the second power conversion system, calculates the power difference, and comprehensively adjusts the output power of the DC-DC converter based on the SOC difference. For example, when the SOC of the first energy storage unit is higher than that of the second energy storage unit, the controller controls the DC-DC converter to output a certain power to the second energy storage unit. This power is added to the charging power obtained by the second energy storage unit from the AC side, making the charging speed of the second energy storage unit faster than that of the first energy storage unit, thereby gradually reducing the difference in SOC between the two. This enables simultaneous balancing of the storage tanks during normal charging and discharging operations, allowing for immediate response to balancing needs without waiting for the tanks to come to a standstill, thus improving the timeliness of balancing and the efficiency of system operation.

[0046] In a specific example, the controller is also configured to: in the event of a fault detected in the second power conversion system, control the second switching device and the first switching device to close, and charge or discharge the second energy storage unit through the DC-DC converter.

[0047] Specifically, during the operation of the energy storage system, if a fault is detected in the power conversion system of a certain energy storage unit—for example, if the second power conversion system fails to function properly due to device damage or protection activation—the second energy storage unit cannot be charged or discharged via the conventional AC side path. In this case, the controller closes the second and first switching devices, connecting the second energy storage unit to the first energy storage unit via the DC bus. The second energy storage unit is then charged or discharged through the DC-DC converter of the first energy storage unit. When charging the second energy storage unit, the controller controls the DC-DC converter to output power from the first energy storage unit to the second energy storage unit; when discharging the second energy storage unit, the controller controls the DC-DC converter to transfer energy from the second energy storage unit to the first energy storage unit, which then outputs power to the AC bus through the first power conversion system. Therefore, when a fault occurs in the power conversion system of a certain energy storage unit, charging and discharging operations can continue for that unit via the DC bus and DC-DC converter, achieving fault tolerance and improving the overall reliability and availability of the energy storage system.

[0048] In an optional embodiment, in the connection path between the DC busbar and the DC bus of the first energy storage unit, a backup switch is connected in series in addition to the first switching device; in the connection path between the DC busbar and the DC bus of the second energy storage unit, a backup switch is connected in series in addition to the second switching device. Specifically, the backup switch and the corresponding switching device are connected in series in the transmission path between the energy storage unit and the DC bus to form dual on / off control. The backup switch can be a contactor, circuit breaker, disconnector, or other device with on / off function, and its specifications can be the same as or different from the corresponding switching device. During normal balanced operation, the backup switch and the corresponding switching device operate synchronously; when one of the switching devices fails and cannot disconnect normally, the backup switch can act as a redundant protection measure to cut off the circuit, preventing safety hazards caused by the failure of a single switching device. In addition, the backup switch can also provide an additional isolation point during system maintenance, facilitating safe maintenance of the switching device or DC-DC converter. Thus, by setting a backup switch, the reliability and safety redundancy of the connection path between the energy storage unit and the DC bus are improved.

[0049] In this embodiment of the invention, by setting a DC-DC converter between the first energy storage unit and the DC bus, the first energy storage unit can actively adjust its output voltage and power through the DC-DC converter. This allows for voltage regulation via the DC-DC converter when there is a significant voltage difference between the ports of the first and second energy storage units, avoiding the inrush current generated by directly closing the switching devices and improving the safety and reliability of the equalization process. Simultaneously, the DC-DC converter can actively control the magnitude and direction of the equalization power, making the equalization control more flexible and controllable compared to methods that only achieve equalization by switching devices on and off. Furthermore, the asymmetrical configuration of configuring a DC-DC converter for the first energy storage unit and only configuring switching devices for the second energy storage unit, compared to a scheme where each energy storage unit is equipped with a DC-DC converter, effectively reduces system costs while achieving controllable equalization.

[0050] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0051] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. In addition, the character " / " in this document generally indicates that the related objects before and after it have an "or" relationship.

[0052] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0053] Furthermore, the examples mentioned in the above embodiments can be freely combined, and any combination can be understood as an embodiment. The terms "embodiment" or "example" appearing in various locations in the specification do not necessarily refer to the same embodiment, nor are they independent or alternative embodiments mutually exclusive with other embodiments. Those skilled in the art will understand that the embodiments described herein can be combined with other embodiments.

[0054] Those skilled in the art will understand that the above embodiments are specific embodiments for implementing the present invention, and in practical applications, various changes in form and detail may be made without departing from the spirit and scope of the present invention.

Claims

1. An energy storage system, characterized by, include: At least one first energy storage unit, the first energy storage unit is connected to the AC bus of the energy storage system through a first power conversion system, and the DC bus of the first energy storage unit is connected to the DC bus of the energy storage system in sequence through a DC-DC converter and a first switching device; At least one second energy storage unit is provided, the second energy storage unit is connected to the AC bus via a second power conversion system, and the DC bus of the second energy storage unit is connected to the DC bus via a second switching device. The controller is configured to control the DC-DC converter, the first switching device, and the second switching device to achieve power balance between the first energy storage unit and the second energy storage unit.

2. The energy storage system of claim 1, wherein, The DC bus of the first energy storage unit is connected to the common connection point of the DC bus through a first switching device; The DC bus of the second energy storage unit is connected to the common connection point of the DC bus in sequence through a DC-DC converter and a second switching device; The common connection point of the DC bus is located inside the first energy storage unit or the second energy storage unit.

3. The energy storage system of claim 1, wherein, The controller is configured as follows: The voltage difference between the first port voltage of the first energy storage unit and the second port voltage of the second energy storage unit is detected. When the voltage difference exceeds a preset voltage difference threshold, the first switching device is controlled to close, and the DC-DC converter is controlled to adjust the output voltage. When the voltage difference is less than or equal to the preset voltage difference threshold, the second switching device is controlled to close.

4. The energy storage system of claim 3, wherein, The battery state parameters of the second energy storage unit are less than or equal to the battery state parameters of the first energy storage unit.

5. The energy storage system according to claim 1, characterized in that, It also includes an overcurrent protection device, which is connected in series in the transmission path of the DC bus.

6. The energy storage system according to claim 1, characterized in that, The DC bus of the second energy storage unit is connected to the DC bus in sequence through the second DC-DC converter and the second switching device.

7. The energy storage system according to claim 1, characterized in that, The first energy storage unit includes at least one first battery cluster, which is connected in parallel to the DC bus of the first energy storage unit via a first disconnect switch. The DC bus of the first energy storage unit is connected to the DC side of the first power conversion system; and / or, The second energy storage unit includes at least one second battery cluster, which is connected in parallel to the DC bus of the second energy storage unit via a second disconnect switch. The DC bus of the second energy storage unit is connected to the DC side of the second power conversion system.

8. The energy storage system according to claim 4, characterized in that, The battery state parameters include at least the state of charge; the controller is also configured to: After the second switching device is closed, the second state of charge of the second energy storage unit and the first state of charge of the first energy storage unit are obtained. The output power of the DC-DC converter is controlled based on the charge difference between the second state of charge and the first state of charge, so as to reduce the charge difference.

9. The energy storage system according to claim 8, characterized in that, The controller is also configured to: During the charging and discharging process of the first power conversion system and the second power conversion system to the AC bus, the power difference between the first operating power of the first power conversion system and the second operating power of the second power conversion system is obtained; The output power of the DC-DC converter is adjusted according to the power difference and the charge difference.

10. The energy storage system according to claim 1, characterized in that, The controller is also configured to: If a fault is detected in the second power conversion system, the second switching device and the first switching device are controlled to close, and the second energy storage unit is charged or discharged through the DC-DC converter.

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