Patent Publication Number: US-2023163626-A1

Title: Battery assembly and energy storage system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2020/102403, filed on Jul. 16, 2020, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The embodiments relate to the field of energy technologies, a battery assembly, and an energy storage system. 
     BACKGROUND 
     A battery assembly such as a lead-acid battery or a lithium battery is widely applied to various power backup scenarios. However, in an actual application process, usually, a load is short-circuited and/or a power supply encounters a power failure, and consequently, a system easily breaks down. 
     SUMMARY 
     The embodiments may provide a battery assembly and an energy storage system, to resolve a phenomenon that the energy storage system breaks down when a load is short-circuited and/or a power supply encounters a power failure. The battery assembly has a characteristic of a short-circuit current-limitation output when the load is short-circuited, and can output a discharge current whose amplitude is greater than a maximum nominal discharge current of the battery assembly and less than a short-circuit protection current of the battery assembly, so that the load is cut off from the energy storage system before the battery assembly, and a busbar voltage in the energy storage system can be automatically restored. In addition, the battery assembly has a short-time overload discharge capability after the power supply encounters the power failure. A discharge capability of the battery assembly can be improved in a time period from a time point at which the power supply encounters the power failure to a time point at which a secondary load is powered off, so that the battery assembly supplies power to both a primary load and the secondary load, to ensure that the energy storage system does not break down. In addition, a maximum nominal discharge capability of the battery assembly can be restored after the power supply encounters the power failure until the secondary load is powered off, so that the battery assembly supplies power to the primary load, to ensure power backup duration of the primary load. 
     According to a first aspect, the embodiments may provide a battery assembly, including a control unit and a DCDC converter. 
     The control unit is configured to: when a first load is short-circuited in a process in which the battery assembly supplies power to the first load, control the DCDC converter to output a first current. The first current is greater than a maximum nominal discharge current of the battery assembly, is used to break an electrical connection between the first load and a busbar, and is less than a short-circuit protection current of the battery assembly; the maximum nominal discharge current of the battery assembly is a maximum current allowed when the battery assembly is normally discharged; and the short-circuit protection current of the battery assembly is a current that can be used to break an electrical connection between the battery assembly and the busbar. 
     The battery assembly provided in the first aspect has a characteristic of a short-circuit current-limitation output. The battery assembly can continue current-limitation operation when any one load is short-circuited, an amplitude of a discharge current output by the battery assembly is greater than the maximum nominal discharge current of the battery assembly and less than the short-circuit protection current of the battery assembly, and duration of the discharge current of the battery assembly is stable and controllable, so that when the any one load is short-circuited, the short-circuited load is cut off from an energy storage system before the battery assembly, and a busbar voltage in the energy storage system can be automatically restored. 
     The battery assembly may further include a battery pack; a first end of the DCDC converter is electrically connected to a positive electrode of the battery pack, a second end of the DCDC converter is electrically connected to a negative electrode of the battery pack, a third end of the DCDC converter is electrically connected to a first busbar, a fourth end of the DCDC converter is electrically connected to a second busbar, a fifth end of the DCDC converter is electrically connected to the control unit, the first busbar and the second busbar are configured to provide a direct current, and the first load is electrically connected in parallel between the first busbar and the second busbar; the control unit may be configured to: when the first load is short-circuited, control, based on a third pulse width of a first signal, the DCDC converter to decrease equivalent output impedance of the battery assembly, to control a discharge current of the battery assembly to be the first current; and the first signal represents a duty cycle of a power switching transistor in the DCDC converter, and a pulse width of the first signal is used to adjust the equivalent output impedance of the battery assembly, to control the discharge current of the battery assembly. Therefore, the control unit in the battery assembly controls the duty cycle of the power switching transistor in the DCDC converter, so that the discharge current output by the battery assembly is the first current, to provide a possible implementation in which the battery assembly outputs the first current. 
     The control unit may be configured to: monitor a port voltage of the battery assembly in a discharging state; and when the port voltage of the battery assembly in the discharging state is less than or equal to a first preset voltage, determine that the first load is short-circuited, and control the battery assembly to output the first current. Therefore, the control unit in the battery assembly can determine, based on the port voltage of the battery assembly in the discharging state, whether a load is short-circuited, to control the discharge current output by the DCDC converter to be the first current in a timely manner. Therefore, the control unit can determine whether the load is short-circuited, to control, to be the first current in a timely manner, the discharge current that is of the battery assembly and that is output by the DCDC converter. 
     According to a second aspect, the embodiments may provide a battery assembly, including a control unit and a DCDC converter. 
     The control unit is configured to: after a power supply encounters a power failure, control a discharge capability of the battery assembly to be greater than a maximum nominal discharge capability of the battery assembly, and supply power to a first load and a second load by using a DCDC converter; and after the first load is powered off, control the discharge capability of the battery assembly to be restored to the maximum nominal discharge capability, and supply power to the second load by using the DCDC converter, where the power supply is configured to provide a direct current to the first load and the second load before the power supply encounters the power failure, and power is supplied to the second load before the first load. 
     Based on the battery assembly provided in the second aspect, a monitoring unit in an energy storage system controls, by using the power failure alarm signal, a secondary load to be powered off, to ensure power backup duration of a primary load. In addition, the battery assembly has a short-time overload discharge capability. In a time period from a time point at which the power supply encounters the power failure to a time point at which the secondary load is powered off, a discharge capability (for example, a discharge power or a discharge current) of the battery assembly is greater than the maximum nominal discharge capability (for example, a maximum nominal discharge power or a maximum nominal discharge current) of the battery assembly, and the discharge capability (for example, the discharge power or the discharge current) of the battery assembly is stable and controllable. Therefore, the battery assembly supplies power to both the primary load and the secondary load in the time period from the time point at which the power supply encounters the power failure to the time point at which the secondary load is powered off, to ensure that the energy storage system does not break down. After the power supply encounters the power failure until the secondary load is powered off, the discharge capability (for example, the discharge power or the discharge current) of the battery assembly is restored to the maximum nominal discharge capability (for example, the maximum nominal discharge power or the maximum nominal discharge current) of the battery assembly, so that the battery assembly supplies power to the primary load, to ensure the power backup duration of the primary load. 
     When the discharge capability of the battery assembly is represented by using a discharge power of the battery assembly, the control unit may be configured to: after the power supply encounters the power failure, control the discharge power of the battery assembly to be greater than a maximum nominal discharge power in a time period from a time point at which the power supply encounters the power failure to a time point at which the first load is powered off, where the maximum nominal discharge power is a maximum power allowed when the battery assembly is normally discharged; and after the first load is powered off, control the battery assembly to be restored to the maximum nominal discharge power. Therefore, the discharge power of the battery assembly is used to represent the discharge capability of the battery assembly, to provide a possible implementation of adjusting the discharge capability of the battery assembly. 
     Alternatively, when the discharge capability of the battery assembly is represented by using a discharge current of the battery assembly, the control unit is configured to: after the power supply encounters the power failure, control the discharge current of the battery assembly to be greater than a maximum nominal discharge current in a time period from a time point at which the power supply encounters the power failure to a time point at which the first load is powered off, where the maximum nominal discharge current is a maximum current allowed when the battery assembly is normally discharged; and after the first load is powered off, control the battery assembly to be restored to the maximum nominal discharge current. Therefore, the discharge current of the battery assembly is used to represent the discharge capability of the battery assembly, to provide another possible implementation of adjusting the discharge capability of the battery assembly. 
     The first load may be used to implement a 5G data service and the second load may be used to implement a voice service and a transmission service that are different from the 5G data service. 
     The control unit may be further configured to: when a port voltage of the battery assembly in a charging state or a standby state is less than or equal to a second preset voltage, control the discharge capability of the battery assembly to be greater than the maximum nominal discharge capability of the battery assembly. Therefore, the control unit can determine whether the power supply encounters the power failure, to improve the discharge capability of the battery assembly in a timely manner. 
     The battery assembly may further include a battery pack; a first end of the DCDC converter is electrically connected to a positive electrode of the battery pack, a second end of the DCDC converter is electrically connected to a negative electrode of the battery pack, a third end of the DCDC converter is electrically connected to a first busbar, a fourth end of the DCDC converter is electrically connected to a second busbar, a fifth end of the DCDC converter is electrically connected to the control unit, the first busbar and the second busbar are configured to provide a direct current by using the power supply, and the first load and the second load are electrically connected in parallel between the first busbar and the second busbar; the control unit may be configured to control, based on a first pulse width of a first signal, the DCDC converter to decrease equivalent output impedance of the battery assembly, to control the discharge capability of the battery assembly to be greater than the maximum nominal discharge capability of the battery assembly; and after preset duration, control, based on a second pulse width of the first signal, the DCDC converter to increase the equivalent output impedance of the battery assembly, to control the discharge capability of the battery assembly to be restored to the maximum nominal discharge capability of the battery assembly; and the first pulse width is greater than or equal to the second pulse width, and a pulse width of the first signal is used to adjust the equivalent output impedance of the battery assembly, to control the discharge power or the discharge current of the battery assembly. Therefore, the control unit in the battery assembly controls a duty cycle of a power switching transistor in the DCDC converter, to change the discharge capability of the battery assembly, so as to provide a possible implementation of adjusting the discharge capability of the battery assembly. 
     According to a third aspect, the embodiments may provide an energy storage system, including a power supply assembly, a first busbar, a second busbar, and the battery assembly in the first aspect; and/or the power supply assembly, the first busbar, the second busbar, and the battery assembly in the second aspect. 
     The energy storage system may further include a monitoring unit, and the monitoring unit is electrically connected to the power supply assembly; the power supply component is configured to send a power failure alarm signal to the monitoring unit after a power supply encounters a power failure; and the monitoring unit is further configured to: when receiving the power failure alarm signal, control a secondary load in an electrical load to be powered off. Therefore, when the power supply encounters the power failure, the monitoring unit can control the secondary load to be powered off in a timely manner, so that the battery assembly does not need to have a long-time overload discharge capability, to avoid damage to the battery assembly. 
     The energy storage system includes any one of the following: a data center, a communications station, or an energy storage power station. 
     For beneficial effects of the energy storage system provided in the third aspect, refer to beneficial effects brought by the first aspect and the second aspect. Details are not described herein again. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram of a structure of an energy storage system according to an embodiment; 
         FIG.  2 A  is a schematic diagram of a structure of a battery assembly according to an embodiment; 
         FIG.  2 B  is a schematic diagram of a structure of an existing lithium battery; 
         FIG.  3    is a schematic diagram of a time sequence of a short-circuit current-limitation output of a battery assembly according to an embodiment; 
         FIG.  4 A  is a schematic diagram of a time sequence from charging to discharging of a battery assembly according to an embodiment; 
         FIG.  4 B  is a diagram of a voltage U-current I external characteristic curve of a battery assembly according to an embodiment; and 
         FIG.  4 C  is a diagram of a voltage U-current I external characteristic curve of a battery assembly according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The embodiments may provide a battery assembly and an energy storage system and may be applied to various power backup scenarios such as a communications station, a data center, and an energy storage power station. The battery assembly has a characteristic of a short-circuit current-limitation output. The battery assembly can continue current-limitation operation when any one load is short-circuited, an amplitude of a discharge current output by the battery assembly is greater than a maximum nominal discharge current of the battery assembly and less than a short-circuit protection current of the battery assembly, and duration of the discharge current of the battery assembly is stable and controllable, so that when the any one load is short-circuited, the short-circuited load is cut off from the energy storage system before the battery assembly, and a busbar voltage in the energy storage system can be automatically restored. 
     In addition, a monitoring unit in the energy storage system controls, by using a power failure alarm signal, a secondary load to be powered off, to ensure power backup duration of a primary load. In addition, the battery assembly has a short-time overload discharge capability. In a time period from a time point at which a power supply encounters a power failure to a time point at which the secondary load is powered off, a discharge capability (for example, a discharge power or a discharge current) of the battery assembly may be greater than a maximum nominal discharge capability (for example, a maximum nominal discharge power or a maximum nominal discharge current) of the battery assembly, and the discharge capability (for example, the discharge power or the discharge current) of the battery assembly may be stable and controllable. Therefore, the battery assembly supplies power to both the primary load and the secondary load in the time period from the time point at which the power supply encounters the power failure to the time point at which the secondary load is powered off, to ensure that the energy storage system does not break down. After the power supply encounters the power failure until the secondary load is powered off, the discharge capability (for example, the discharge power or the discharge current) of the battery assembly is restored to the maximum nominal discharge capability (for example, the maximum nominal discharge power or the maximum nominal discharge current) of the battery assembly, so that the battery assembly supplies power to the primary load, to ensure the power backup duration of the primary load. 
     Whether power is preferentially supplied to a load may be set based on a degree of importance of a service of the load. Usually, power is preferentially supplied to a load corresponding to a higher degree of importance of a service. In other words, power is supplied to the primary load before the secondary load. In addition, types of the secondary load and the primary load are not limited. 
     The following separately describes in detail implementations of a battery assembly  12  and an energy storage system  10  with reference to the embodiments. 
       FIG.  1    is a schematic diagram of a structure of an energy storage system according to an embodiment. As shown in  FIG.  1   , an energy storage system  10  may include a power supply assembly  11 , a first busbar W 1 , a second busbar W 2 , and at least one battery assembly  12 . An implementation of the energy storage system  10  is not limited. In some embodiments, the energy storage system  10  may include any one of the following: a data center, a communications station, or an energy storage power station. 
     The first busbar W 1  and the second busbar W 2  are used to provide a direct current. A busbar voltage in the energy storage system  10  is a voltage between the first busbar W 1  and the second busbar W 2 . The battery assembly  12  may be electrically connected in parallel between the first busbar W 1  and the second busbar W 2 , so that the battery assembly  12  can be charged or discharged. In addition, an electrical load  20  is also electrically connected in parallel between the first busbar W 1  and the second busbar W 2 , so that the electrical load  20  can obtain electrical energy. It should be noted that an electrical connection between the battery assembly  12  and a busbar is broken is illustrated by using an example in which an electrical connection between the battery assembly  12  and the second busbar W 2  is broken, and that an electrical connection between the electrical load  20  and a busbar is illustrated by using an example in which an electrical connection between the electrical load  20  and the second busbar W 2  is broken. 
     A quantity of battery assemblies  12  and an implementation structure may not be limited. When there is more than one battery assembly  12 , still referring to  FIG.  1   , the energy storage system  10  may further include a battery shunt  13  and a battery low voltage down (BLVD) contactor K 1 . In addition, when the battery assembly  12  is electrically connected in parallel between the first busbar W 1  and the second busbar W 2 , a switching module K 2  is usually added between the battery assembly  12  and the second busbar W 2 , to protect the battery assembly  12 . For ease of description, two battery assemblies  12  are used for illustration in  FIG.  1   , and each battery assembly  12  is electrically connected to the second busbar W 2  by using the switching module K 2 , the BLVD contactor K 1 , and the battery shunt  13 . 
     The following describes an implementation structure of the battery assembly  12  with reference to  FIG.  2 A . It should be noted that the switching module K 2 , the battery shunt  13 , and the BLVD contactor K 1  in  FIG.  2 A  are not illustrated. 
       FIG.  2 A  is a schematic diagram of a structure of a battery assembly according to an embodiment. As shown in  FIG.  2 A , the battery assembly  12  may include a battery pack  121 , a direct current-direct current (DCDC) converter  122 ), and a control unit  123 . 
     A first end  1  of the DCDC converter  122  is electrically connected to a positive electrode (+) of the battery pack  121 , a second end  2  of the DCDC converter  122  is electrically connected to a negative electrode (−) of the battery pack  121 , a third end  3  of the DCDC converter  122  is electrically connected to the first busbar W 1 , a fourth end  4  of the DCDC converter  122  is electrically connected to the second busbar W 2 , and a fifth end  5  of the DCDC converter  122  is electrically connected to the control unit  123 . 
     An implementation of the battery pack  121  is not limited. In some embodiments, the battery pack  121  may include at least one electrochemical cell. When the battery pack  121  includes a plurality of electrochemical cells, the plurality of electrochemical cells may be electrically connected in series; or the plurality of electrochemical cells may be electrically connected in parallel; or the plurality of electrochemical cells may be electrically connected in series and in parallel. In addition, a type of the electrochemical cell is not limited. For example, the type of the electrochemical cell may be a lithium battery. 
     An implementation of the DCDC converter  122  is not limited. In some embodiments, the DCDC converter  122  may include any one of the following: a buck converter circuit (Buck circuit), a boost converter circuit (Boost circuit), a buck-boost converter circuit (Buck-Boost circuit), a flyback circuit, a forward circuit, a half-bridge topology, a full-bridge topology, and an isolated or non-isolated circuit including at least one of the topologies. 
     The control unit  123  may be an integrated chip, for example, a microcontroller unit (MCU) or a system on a chip SoC) or may be formed by combining a plurality of components or may be formed by combining an integrated chip and a peripheral circuit. This is not limited. 
     In some embodiments, the control unit  123  may include a sampling module  1231 , an adjustment module  1232 , and a battery management system (BMS)  1233 . 
     The sampling module  1231  is configured to: collect a discharge current of the battery assembly  12  and collect a port voltage of the battery assembly  12  based on the first busbar W 1  and the second busbar W 2  (for example, a voltage between the third end  3  and the fourth end  4  of the DCDC converter  122 ). The sampling module  1231  sends the discharge current and the port voltage of the battery assembly  12  to the adjustment module  1232 . The port voltage of the battery assembly  12  may include a port voltage of the battery assembly  12  in a discharging state, and a port voltage of the battery assembly  12  in a charging state or a standby state. 
     The adjustment module  1232  is configured to: determine, based on the port voltage of the battery assembly  12  in the discharging state and a first preset voltage, whether the electrical load  20  is short-circuited, and when the port voltage of the battery assembly  12  in the discharging state is less than or equal to the first preset voltage, determine that the electrical load  20  is short-circuited. The first preset voltage may be configured based on a length of a line between the battery assembly  12  and the second busbar W 2 . 
     The adjustment module  1232  is further configured to: calculate a first signal based on the discharge current of the battery assembly  12  or calculate a first signal based on the discharge current of the battery assembly  12  and the port voltage of the battery assembly  12  in the discharging state. For example, the adjustment module  1232  obtains the first signal through single-loop or multi-loop proportional-integral-derivative control (proportional-integral-derivative control, PID control). The adjustment module  1232  outputs the first signal to the DCDC converter  122 . 
     The first signal represents a duty cycle of a power switching transistor in the DCDC converter  122 , and the first signal is used to adjust equivalent output impedance of the battery assembly  12 , to control a discharge power or the discharge current of the battery assembly  12 . An implementation of the first signal is not limited. For example, the first signal may be a pulse width modulated (PWM) signal. 
     The adjustment module  1232  is further configured to determine, based on the port voltage of the battery assembly  12  in the charging state or the standby state, whether a power supply  30  encounters a power failure, so that the battery assembly  12  determines whether to be charged, to be in a standby state, or to be discharged. For example, the adjustment module  1232  may preconfigure a second preset voltage. A value of the second preset voltage is not limited. Usually, the second preset voltage is slightly less than the port voltage of the battery assembly  12  in the charging state or the standby state. When the port voltage of the battery assembly  12  in the charging state or the standby state is less than or equal to the second preset voltage, the adjustment module  1232  may determine that the power supply power  30  encounters the power failure, so that the battery assembly  12  may transition from the charging state or the standby state to the discharging state. The charging state may be understood as a float charging state or an equalized charging state, and the standby state may be understood as a case in which a charging channel of the battery assembly  12  is broken and a discharging channel of the battery assembly  12  is conducted, in other words, the battery assembly  12  cannot be charged and can be discharged. 
     The BMS  1233  is configured to manage a chargeable and dischargeable capacity of the battery pack  121  and another battery management function. The BMS  1233  may be implemented by using a software algorithm and/or a hardware circuit. 
     Based on the foregoing descriptions, the control unit  123  is configured to: determine, based on the port voltage of the battery assembly  12  in the discharging state and the first preset voltage, whether the electrical load  20  is short-circuited, and when the port voltage of the battery assembly  12  in the discharging state is less than or equal to the first preset voltage, determine that the electrical load  20  is short-circuited. Therefore, the control unit  123  may control the DCDC converter  122  to adjust the equivalent output impedance of the battery assembly  12  based on the first signal, so that the discharge current of the battery assembly  12  changes. 
     In addition, the control unit  123  may determine, based on the port voltage of the battery assembly  12  in the charging state or the standby state and the second preset voltage, whether the power supply power supply  30  encounters the power failure, so that the battery assembly  12  determines whether to be charged, to be in a standby state, or to be discharged. In addition, when the port voltage of the battery assembly  12  in the charging state or the standby state is less than or equal to the second preset voltage, the control unit  30  determines that the power supply  30  encounters the power failure, and the battery assembly  12  may transition from the charging state or the standby state to the discharging state. Therefore, the control unit  123  may control, based on the first signal, the DCDC converter  122  to adjust the equivalent output impedance of the battery assembly  12 , so that the discharge power or the discharge current of the battery assembly  12  changes. 
     Usually, a larger pulse width of the first signal leads to a smaller value of the equivalent output impedance of the battery assembly  12 , and a larger discharge power or a larger discharge current of the battery assembly  12 . A smaller pulse width of the first signal leads to a larger value of the equivalent output impedance of the battery assembly  12 , and a smaller discharge power and a smaller discharge current of the battery assembly  12 . 
     It should be noted that an implementation of the battery assembly  12  is not limited to the implementation. 
     A quantity of electrical loads  20  and a type are not limited. When a quantity of secondary loads in the electrical load  20  is greater than 1, still referring to  FIG.  1   , the energy storage system  10  may further include a load shunt  15  and a load low voltage down (LLVD) contactor K 3 . In addition, when the electrical load  20  is electrically connected in parallel between the first busbar W 1  and the second busbar W 2 , load circuit breakers (K 41  and K 42 ) are usually added between the electrical load  20  and the second busbar W 2 . 
     In some embodiments, when the electrical load  20  includes a first load  21 , a first end of the first load  21  is electrically connected to the first busbar W 1 , and a second end of the first load  21  is electrically connected to the second busbar W 2  by using the load circuit breaker K 41  of the first load  21 . The load circuit breaker K 41  of the first load  21  may be configured to avoid an overcurrent existing when the first load  21  is short-circuited. 
     In some other embodiments, when the electrical load  20  includes a first load  21  and a second load  22 , power is supplied to the second load  22  before the first load  21 . In other words, the first load  21  is a secondary load, and the second load  22  is a primary load. In some embodiments, the first load  21  is configured to implement a 5G data service, and the second load  22  is configured to implement a voice service and a transmission service different from a 5G data service, for example, 2G/3G/4G service. It should be noted that, that the first load  21  is a secondary load and the second load  22  is a primary load herein is merely an example. Types of the first load  21  and the second load  22  are not limited. 
     For ease of description, one primary load and two secondary loads, namely, one second load  22  and two first loads  21  are used for illustration in  FIG.  1   . The two first loads  21  each are electrically connected to the second busbar W 2  through the LLVD contactor K 3  and the load shunt  15  by using the load circuit breaker K 41 , and the second load  22  is electrically connected to the second busbar W 2  through the LLVD contactor K 3  and the load shunt  15  by using the load circuit breaker K 42 . The power supply  30  provides a direct current to the second busbar W 2  by using the power supply assembly  11 , and the power supply assembly  11  may further monitor a state of the power supply  30 . An implementation of the power supply assembly  11  is not limited. 
     In some embodiments, the power supply assembly  11  may include a rectifier unit. An input end of the rectifier unit is electrically connected to the power supply  30  (namely, an alternating current power supply), an output grounding end of the rectifier unit is electrically connected to the first busbar W 1 , and an output power supply end of the rectifier unit is electrically connected to the second busbar W 2 . The rectifier unit converts, into a direct current, an alternating current provided by the power supply  30 , and the rectifier unit provides the direct current to the second busbar W 2 . An implementation of the rectifier unit is not limited. For example, the rectifier unit includes a rectifier circuit and a filter circuit. In addition, the power supply  30  may be energy such as wind energy. 
     In some other embodiments, the power supply assembly  11  may alternatively include a DCDC power converter. An input end of the DCDC power converter is electrically connected to the power supply  30  (namely, a direct current power supply), an output grounding end of the DCDC power converter is electrically connected to the first busbar W 1 , an output power supply end of the DCDC power converter is electrically connected to the second busbar W 2 , and the DCDC power converter provides a direct current to the second busbar W 2 . An implementation of the DCDC power converter is not limited. The power supply  30  may be energy such as a high voltage direct current (HVDC) or a solar panel. 
     In addition, the energy storage system  10  may further include a monitoring unit  14 . The monitoring unit  14  is electrically connected to the power supply assembly  11 , and the monitoring unit  14  is further electrically connected to a control end of the LLVD contactor K 3  and the BLVD contactor K 1 . In addition, the monitoring unit  14  may be electrically connected in parallel between the first busbar W 1  and the second busbar W 2 , to obtain electrical energy, so that the monitoring unit  14  normally operates. 
     When the power supply  30  encounters the power failure, the power supply assembly  11  may send a power failure alarm signal to the monitoring unit  14 , so that the monitoring unit  14  controls the LLVD contactor K 3  to be disconnected, and the secondary load (namely, the first load  21 ) is cut off from the energy storage system  10 . A representation form of the power failure alarm signal is not limited. 
     In an actual application process, after the power supply  30  encounters the power failure, the battery assembly needs to supply power to the electrical load  20 , so that the electrical load  20  can maintain operation. That the electrical load  20  includes the first load  21  is used as an example. When the battery assembly supplies power to the first load  21 , the battery assembly, the first busbar W 1 , the second busbar W 2 , and the first load  21  may form a circuit loop. 
     When the battery assembly is an existing lead-acid battery, if the first load  21  is short-circuited, the existing lead-acid battery outputs a discharge current of hundreds to thousands of amperes, and the discharge current is uncontrollable, bringing a safety hazard to the entire energy storage system. Therefore, the existing lead-acid battery needs to be configured with an expensive direct current fuse (in other words, the switching module K 2  is a direct current fuse), and then hierarchical short-circuit protection is implemented based on tripping current thresholds of the direct current fuse and the load switch K 41  corresponding to the first load  21 , and a time difference between the direct current fuse and the load switch K 41  corresponding to the first load  21 . However, the direct current fuse has high costs and a large volume. 
     When the battery assembly is an existing lithium battery, as shown in  FIG.  2 B , the existing lithium battery may include the battery pack  121 , a bidirectional switch  200 , a charger  300 , and a controller  400 . A first end of the battery pack  121  is electrically connected to the second busbar W 2  by using the bidirectional switch  200 , and a second end of the battery pack  121  is electrically connected to the first busbar W 1 . The charger  300  is electrically connected in parallel to two sides of the bidirectional switch  200 . 
     It should be noted that  FIG.  2 B  shows only a feasible connection manner in which the existing lithium battery is connected to each of the first busbar W 1  and the second busbar W 2 . Another module may be further included between the existing lithium battery and the first busbar W 1  and/or between the existing lithium battery and the second busbar W 2 . This is not limited. 
     If the first load  21  is short-circuited, the bidirectional switch  200  cuts off the circuit loop when a discharge current output by the existing lithium battery reaches a threshold. The bidirectional switch  200  may include but is not limited to a component such as a contactor, a relay, or two power semiconductor devices (for example, a bidirectional MOS transistor) connected in series. 
     A current in the circuit loop is uncontrollable and duration is short (usually several hundreds of microseconds), and it may be understood that the load circuit breaker K 41  of the first load  21  is usually a mechanical switch. If the bidirectional switch  200  in the existing lithium battery is a bidirectional MOS transistor, the bidirectional MOS transistor is an electronic switch. Sensitivity of the electronic switch is higher than sensitivity of the mechanical switch. The mechanical switch may be tripped after a delay of a period of time and the electronic switch may be opened immediately after receiving a corresponding instruction. Therefore, the existing lithium battery may protect the existing lithium battery in advance and is electrically disconnected from the second busbar W 2  before the first load  21 , causing a risk that the busbar voltage in the energy storage system  10  is clamped by the short-circuited first load  21 , and causing a phenomenon that the energy storage system  10  breaks down. If the bidirectional switch  200  is a contactor or a relay, when the first load  21  is short-circuited, the contactor or the relay is forcibly tripped under a short-circuit current, seriously damaging a contact in the contactor or the relay, or even causing the contact in the contactor or the relay to melt and adhere. 
     When the existing lead-acid battery or the existing lithium battery is used, and a load is short-circuited, there may be a safety risk and a system breakdown risk. 
     When the battery assembly  12  is used as the battery assembly, the first current greater than a maximum nominal discharge current of the battery assembly  12  and less than a short-circuit protection current of the battery assembly  12  is set. The first current is the discharge current output by the battery assembly  12  when the first load  21  is short-circuited. The maximum nominal discharge current of the battery assembly  12  is a maximum current allowed when the battery assembly  12  is normally discharged, and the short-circuit protection current of the battery assembly  12  is a current that can be used to break the electrical connection between the battery assembly  12  and the second busbar W 2 . A second current is a current that is used to break an electrical connection between the first load  21  and the second busbar W 2 , namely, the tripping current threshold of the load circuit breaker K 41  of the first load  21 . A person skilled in the art may understand that the second current is usually less than or equal to a maximum nominal current of the battery assembly  12 . Therefore, the first current is greater than the second current. 
     Values of the first current, the second current, the short-circuit protection current of the battery assembly  12 , and the maximum nominal discharge current of the battery assembly  12  are not limited. In some embodiments, in a scenario in which there is a large load, when a capacity of the load circuit breaker (K 41  or K 42 ) is configured, the tripping current threshold may approach or even exceed the maximum nominal discharge current of the battery assembly  12 . The capacity of the load circuit breaker herein is a maximum current that is allowed to pass through the load switch when the load circuit breaker is not tripped. For example, the first current may be set to be greater than 50% of the maximum nominal discharge current of the battery assembly  12 , and the second current is set to be greater than 25% to 30% of the maximum nominal discharge current of the battery assembly  12 . 
     Based on the configuration, the battery assembly  12  has a characteristic of a short-circuit current-limitation output. When a load is short-circuited, an amplitude of the first current output by the battery assembly  12  may be greater than an amplitude of the maximum nominal discharge current of the battery assembly  12  and less than an amplitude of the short-circuit protection current of the battery assembly  12 , so that duration of the first current output by the battery assembly  12  may be controllable, the first load  21  may be electrically disconnected from the second busbar W 2  before the battery assembly  12 , and the busbar voltage in the energy storage system  10  can be automatically restored, to avoid a risk that the energy storage system  10  breaks down. 
     In some embodiments, the battery assembly  12  may determine, based on the port voltage of the battery assembly  12  in the discharging state and the first preset voltage, whether the first load  21  is short-circuited. When the port voltage of the battery assembly  12  in the discharging state is less than or equal to the first preset voltage, it may be determined that the first load  21  is short-circuited. If the first load  21  is short-circuited, because the first current is set to be greater than the maximum nominal discharge current of the battery assembly  12  and less than the short-circuit protection current of the battery assembly  12 , the battery assembly  12  may control, based on the first signal, the DCDC converter  122  to decrease the equivalent output impedance of the battery assembly  12 , so that the discharge current of the battery assembly  12  increases. Therefore, the battery assembly  12  can output the first current whose amplitude and duration are stable and controllable, and the first current is greater than the second current, so that the first load  21  is electrically disconnected from the second busbar W 2  before the battery assembly  12 . Therefore, the short-circuited first load  21  is cut off from the energy storage system  10 , and the busbar voltage in the energy storage system  10  is automatically restored. 
     In some embodiments, when the first load  21  is short-circuited, the control unit  123  in the battery assembly  12  may increase the pulse width of the first signal (namely, a third pulse width), so that the equivalent output impedance of the battery assembly  12  decreases, the first current output by the battery assembly  12  increases, and the first current output by the battery assembly  12  is greater than the maximum nominal current of the battery assembly  12 . 
     The third pulse width of the first signal may be set based on the maximum nominal current of the battery assembly  12  and the second current. 
     In some embodiments, the second current is the tripping current threshold of the load circuit breaker K 41  of the first load  21 . Therefore, the first load  21  is automatically disconnected by using the load circuit breaker K 41  of the first load  21 . In other words, the load circuit breaker K 41  of the first load  21  is tripped, so that the first load  21  is electrically disconnected from the second busbar W 2 , the first load  21  is cut off from the energy storage system  10 , and the DCDC converter  122  and the second busbar W 2  may continue to be electrically connected, to ensure that the battery assembly  12  can continue to supply power to another load In the electrical load  20 . 
     With reference to  FIG.  3   , the following provides an example description of a change in the discharge current of the existing lead-acid battery, the existing lithium battery, and the battery assembly  12 . 
       FIG.  3    is a schematic diagram of a time sequence of a short-circuit current-limitation output of a battery assembly according to an embodiment. In  FIG.  3   , a horizontal coordinate represents time t, and a vertical coordinate represents a current I. A curve 1 is a curve indicating that the discharge current of the existing lead-acid battery changes with time when the first load  21  is short-circuited, a curve 2 is a curve indicating that the discharge current of the existing lithium battery changes with time when the first load  21  is short-circuited, and a curve 3 is a curve indicating that the discharge current of the battery assembly  12  changes with time when the first load  21  is short-circuited. 
     As shown in  FIG.  3   , the first load  21  is short-circuited at a moment t1, so that amplitudes of the discharge current of the existing lead-acid battery, the discharge current of the existing lithium battery, and the discharge current of the battery assembly  12  all increase after the moment t1. For the battery assembly  12 , the DCDC converter  122  outputs a first current I3 at a moment t2, so that an amplitude of the first current I3 of the battery assembly  12  is greater than the amplitude of the maximum nominal discharge current of the battery assembly  12  and less than the amplitude of the short-circuit protection current of the battery assembly  12 , and duration of the first current I3 is stable and controllable. The first current I3 is greater than the second current, so that the load switch K 41  of the first load  21  is automatically tripped, and the busbar voltage in the energy storage system is automatically restored. For the existing lithium battery, at a moment t3, the bidirectional switch quickly cuts off an electrical connection between the existing lithium battery and the second busbar W 2 , so that the discharge current of the existing lithium battery becomes zero, causing the existing lithium battery to be deadlocked, and causing the phenomenon that the energy storage system breaks down. For the existing lead-acid battery, the direct current fuse breaks an electrical connection between the existing lead-acid battery and the second busbar W 2  at a moment t4, so that the discharge current of the existing lead-acid battery becomes zero. 
     Therefore, compared with the curve 1, the battery assembly  12  can automatically limit the current when the first load  21  is short-circuited, and does not need to be configured with an expensive direct current fuse as the existing lead-acid battery within a safe range. Compared with the curve 2, the battery assembly  12  resolves a problem that when the first load  21  is short-circuited, the existing lithium battery is deadlocked and consequently, the energy storage system breaks down, and normal operation of the battery assembly  12  does not need to be manually restored, or the short-circuited first load  21  does not need to be manually removed, to reduce maintenance costs. 
     Therefore, the battery assembly  12  and the electrical load  20  may cooperate, after the electrical load  20  is short-circuited, the electrical load  20  is cut off from the busbar voltage in the energy storage system  10  before the battery assembly  12 . In addition, the amplitude and duration of a short-circuit discharge current of the battery assembly  12  may be configured by a user, to increase flexibility of the energy storage system  10 . 
     In an actual application scenario, that a load is short-circuited poses a risk that the energy storage system breaks down, and that the power supply encounters the power failure also affects power backup reliability of the energy storage system. An existing energy storage system usually supports both the 5G data service and 2G/3G/4G voice and transmission services. That the electrical load  20  includes the first load  21  and the second load  22  is used as an example. The second load  22  supplies power before the first load  21 . In other words, the first load  21  is a secondary load, and the second load  22  is a primary load. When a battery assembly in the existing energy storage system is in the charging state or the standby state, and the power supply  30  encounters the power failure, the battery assembly may transition from the charging state or the standby state to the discharging state and the battery assembly may supply power to the electrical load  20 , and both the first load  21  and the second load  22 . 
     In the conventional technology, if the power supply  30  encounters the power failure, the monitoring unit in the existing energy storage system usually first controls the secondary load to be powered off, and then controls the primary load to be powered off, so that hierarchical powering off is performed, to ensure that the power backup duration of the primary load can be prolonged when a low battery capacity is configured. 
     An implementation process may include: After the power supply  30  encounters the power failure, an existing battery assembly in the existing energy storage system supplies power to both the primary load and the secondary load, and the monitoring unit detects the busbar voltage in real time. When the busbar voltage decreases to an LLVD point as discharge duration increases, the monitoring unit in the existing energy storage system controls the secondary load to be powered off, and until the busbar voltage reaches a BLVD point, the monitoring unit in the existing energy storage system controls the BLVD contactor K 1  to operate, to separate the existing battery assembly from the existing energy storage system. 
     Because the battery assembly is usually expensive, in many scenarios, in the existing energy storage system, a capacity of the existing battery assembly (namely, I2*T11) only needs to be configured based on a current I2 and power backup duration T11 of the primary load. In such a configuration condition, an initial discharge ratio existing after the power supply encounters the power failure is IL/(I2*T11), where IL is a sum of the current I2 of the primary load and a current I1 of the secondary load. If IL is far greater than I2, an actual discharge ratio (Ratio=Current/Capacity) of the existing battery assembly is to be very large. In this case, there are the following two problems: 
     Problem 1: A polarization characteristic of the existing battery assembly is very serious, a port voltage of the existing battery assembly drops fast, and a hierarchical powering off effect is not ideal. 
     Problem 2: If the actual discharge ratio of the existing battery assembly is far greater than 1C, overcurrent protection is performed on the existing battery assembly, causing the existing battery assembly to be automatically protected and to be separated from the existing energy storage system, and causing the phenomenon that the existing energy storage system breaks down. 
     When the power supply  30  encounters the power failure, the power supply assembly  11  may send the power failure alarm signal to the monitoring unit  14 . When receiving the power failure alarm signal, the monitoring unit  14  controls the LLVD contactor K 3  to be disconnected, so that the first load  21  is powered off. In addition, the battery assembly  12  transitions from the charging state or the standby state to the discharging state after determining that the power supply  30  encounters the power failure, so that the battery assembly  12  supplies power to the electrical load  20 . 
     Because the port voltage of the battery assembly  12  quickly drops when the power supply  30  encounters the power failure, the battery assembly  12  may determine, based on the port voltage of the battery assembly  12  in the charging state or the standby state, whether the power supply  30  encounters the power failure. For example, the control unit  123  in the battery assembly  12  may determine a value of the port voltage of the battery assembly  12  in the charging state or the standby state and a value of the second preset voltage, to determine whether the power supply  30  encounters the power failure, and further control the battery assembly  12  to transition from the charging state or the standby state to the discharging state. For example, when the port voltage of the battery assembly  12  in the charging state or the standby state is less than or equal to the second preset voltage, the battery assembly  12  may determine that the power supply  30  encounters the power failure, so that the battery assembly  12  transitions from the charging state or the standby state to the discharging state. 
     In addition, because the monitoring unit  14  controls a delay in disconnecting the LLVD contactor K 3 , a discharge capability (namely, the discharge power or the discharge current) of the battery assembly  12  in a time period from a time point at which the power supply  30  encounters the power failure to a time point at which the first load  21  is powered off is set to be greater than the maximum nominal discharge capability (namely, a maximum nominal discharge power or the maximum nominal discharge current). The maximum nominal discharge power of the battery assembly  12  is a maximum power allowed when the battery assembly  12  is normally discharged. After the first load  21  is powered off, the discharge capability of the battery assembly  12  is restored to the maximum nominal discharge capability. In other words, before the power supply  30  encounters the power failure, the discharge capability of the battery assembly  12  is the maximum nominal discharge capability. 
     In some embodiments, the battery assembly  12  adjusts the equivalent output impedance of the battery assembly  12  based on the first signal, so that a discharge power of the battery assembly  12  in the time period from the time point at which the power supply  30  encounters the power failure to the time point at which the first load  21  is powered off is greater than the maximum nominal discharge power of the battery assembly  12 , the battery assembly  12  is restored to the maximum nominal discharge power after the first load  21  is powered off, and an actual discharge power of the battery assembly  12  depends on a load amount of the primary load. 
     Alternatively, the battery assembly  12  adjusts the equivalent output impedance of the battery assembly  12  based on the first signal, so that a discharge current of the battery assembly  12  in the time period from the time point at which the power supply  30  encounters the power failure to the time point at which the first load  21  is powered off is greater than the maximum nominal discharge current of the battery assembly  12 , the battery assembly  12  is restored to the maximum nominal discharge current after the first load  21  is powered off, and an actual discharge current of the battery assembly  12  depends on a load amount of the primary load. 
     In some embodiments, when the battery assembly  12  transitions from the charging state or the standby state to the discharging state, the control unit  123  in the battery assembly  12  may increase the pulse width (namely, a first pulse width) of the first signal, so that the equivalent output impedance of the battery assembly  12  decreases, and the discharge power or the discharge current of the battery assembly  12  increases. After preset duration, the battery assembly  12  may decrease the pulse width of the first signal (namely, a second pulse width), so that the equivalent output impedance of the battery assembly  12  increases, and the discharge power or the discharge current of the battery assembly  12  decreases, in other words, the battery assembly  12  is restored to the maximum nominal discharge power, or the battery assembly  12  is restored to the maximum nominal discharge current, to restore normal operation of the battery assembly  12 . The first pulse is greater than the second pulse. 
     A start moment of the preset duration is a moment at which the battery assembly  12  transitions from the charging state or the standby state to the discharging state. A value of the preset duration is not limited. A discharge capability of the DCDC converter  122  in the battery assembly  12  may be controlled based on a power of a total load. Therefore, the discharge capability (namely, the discharge power or the discharge current) of the battery assembly  12  can support the total load. Based on this, a backup capacity of the battery assembly  12  may be configured based on only a power (or a current) and the power backup duration of the primary load. 
     Compared with the conventional technology, when the power supply  30  encounters the power failure, the monitoring unit  14  monitors the power failure alarm signal to control the secondary load to be powered off, without a need to collect the busbar voltage to control a sequence of performing hierarchical powering off, and without a need to depend on a setting of two parameters of the LLVD point and the BLVD point, to avoid a case in which the polarization characteristic of the existing battery assembly affects the hierarchical powering off effect in a case of large-rate discharging, and avoid a case in which the existing battery assembly triggers an overcurrent protection action in a case of short-time large-rate discharging. 
     In addition, after the battery assembly  12  transitions from the charging state or the standby state to the discharging state, the discharge capability is improved in a time period before the secondary load is powered off, and the power can be supplied to both the primary load and the secondary load, to ensure that the energy storage system  10  does not encounter the power failure, and avoid the phenomenon that the energy storage system breaks down. After the secondary load is powered off, the discharge capability of the battery assembly  12  is restored to the maximum nominal discharge capability, and in this case, the battery assembly  12  provides a power backup only for the primary load. Therefore, when the battery assembly  12  is configured with a small capacity, the power backup duration of the primary load is basically not affected. 
     That the first load  21  is a secondary load and the second load  22  is a primary load is used as an example. In the time period from the time point at which the power supply  30  encounters the power failure to the time point at which the first load  21  is powered off, the battery assembly  12  has a short-time overload discharge capability, so that the battery assembly  12  supplies power to the first load  21  and the second load  22 , and supports the total load in the energy storage system  10 , to avoid the phenomenon that the energy storage system breaks down. After the first load  21  is powered off, the battery assembly  12  supplies power to the second load  22 , to ensure the power backup duration of the primary load. Therefore, a capacity configuration of the battery assembly  12  in the energy storage system  10  is reduced, the quantity of battery assemblies  12  in the energy storage system  10  is reduced, and costs are reduced. 
     With reference to  FIG.  4 A  to  FIG.  4 C , the following provides an example description of an operating process of the battery assembly  12  after the power supply  30  encounters the power failure. 
       FIG.  4 A  is a schematic diagram of a time sequence from charging to discharging of a battery assembly according to an embodiment. In  FIG.  4 A , a horizontal coordinate represents time t, and a vertical coordinate represents a current I. 
     As shown in  FIG.  4 A , in a time period from 0 to t1, the battery assembly  12  is in the charging state. In other words, a curve indicating that the battery assembly  12  is in the charging state may be a curve 1 or a curve 2. The curve 1 represents that the battery assembly  12  is in a float charging state, and the curve 2 represents that the battery assembly  12  is in the equalized charging state. At a moment t1, the power supply  30  encounters the power failure. In this case, the battery assembly  12  supplies power to the first load  21  and the second load  22 , and the discharge current of the battery assembly  12  is I1+I2. At a moment t2, in other words, after a time period T1, the first load  21  is cut off from the energy storage system  10 , the battery assembly  12  supplies power to the second load  22 , and the discharge current of the battery assembly  12  becomes I2. I1 is a discharge current at which the battery assembly  12  supplies power to the first load  21 , and I2 is a discharge current at which the battery assembly  12  supplies power to the second load  22 . 
     Therefore, the battery assembly  12  has a short-time overload discharge capability in the time period T1, the discharge power (or the discharge current) of the battery assembly  12  is greater than a discharge power (or a discharge current) that is of the battery assembly  12  and that exists after the moment t2, and a discharge power (or a discharge current) of the battery assembly  12  in the time period T1 is also stable and controllable. A discharge capability that is of the battery assembly  12  and that exists after the moment t2 is restored to the maximum nominal discharge capability, so that the battery assembly  12  continues to supply power based on a discharge power (or a discharge current) of normal operation. 
       FIG.  4 B  and  FIG.  4 C  each are a diagram of a voltage U-current I external characteristic curve of a battery assembly according to an embodiment. In  FIG.  4 B  and  FIG.  4 C , a horizontal coordinate is a current I, and a vertical coordinate is a voltage V. 
     An operating mode of the battery assembly  12  may include any one of a constant voltage mode, a constant power mode, or a constant current mode shown in  FIG.  4 B . When the battery assembly  12  is in the constant voltage mode, the DCDC converter  122  may ensure that the battery assembly  12  can output a constant voltage. The operating mode of the battery assembly  12  may further include a simulated operating mode of a real battery shown in  FIG.  4 C . Ie port voltage may gradually decrease as discharge time is prolonged. 
     A curve 1 represents a battery assembly  12  having only a short-time overload discharge capability. A curve 2 represents a battery assembly  12  having both the characteristic of the short-circuit current-limitation output and the short-time overload discharge capability. 
     With reference to  FIG.  4 B  and  FIG.  4 C , regardless of an operating mode of the battery assembly  12 , after the power supply  30  encounters the power failure, in the time period from the time point at which the power supply  30  encounters the power failure to the time point at which the first load  21  is powered off, the voltage U-current I external characteristic curve of the battery assembly  12  changes from the curve 1 to the curve 2. Therefore, the battery assembly  12  has the short-time overload discharge capability, and the battery assembly  12  supplies power to the first load  21  and the second load  22 . After the first load  21  is powered off, the battery assembly  12  supplies power to the second load  22 . 
     In addition, when the port voltage of the battery assembly  12  in the discharging state drops to a voltage V 1  (namely, the first preset voltage), the battery assembly  12  may determine that the first load  21  is short-circuited. Therefore, the battery assembly  12  controls, based on the first signal, an amplitude of the discharge current of the battery assembly  12  below an operating point V 1  to be greater than a maximum nominal discharge current above the operating point V 1  and less than the short-circuit protection current of the battery assembly  12 , and controls an amplitude and duration of the discharge current of the battery assembly  12  below the operating point V 1  to be stable and controllable, in other words, the current of the battery assembly  12  increases from a current I4 to the current I3 (namely, the first current). The current I4 is a maximum nominal discharge current existing when the battery assembly  12  normally operates. 
     In conclusion, the battery assembly not only has the characteristic of the short-circuit current-limitation output, but also has the short-time overload discharge capability. It should be noted that the battery assembly may have only the characteristic of the short-circuit current-limitation output or may have only the short-time overload discharge capability or may have both the characteristic of the short-circuit current-limitation output and the short-time overload discharge capability. 
     For example, the embodiments may further provide user equipment. A device in the embodiments may include an electrical load  20  and an energy storage system  10 . 
     An implementation of the user equipment is not limited. 
     A power supply  30  is configured to supply power to the energy storage system  10  and the electrical load  20 . The energy storage system  10  supplies power to the electrical load  20 , to ensure that an electrical device normally operates. The electrical load  20  may include a transceiver device, and the transceiver device is configured to: receive a signal or transmit a signal. In addition, the electrical device may further include a control device, and the control device may control the transceiver device to receive a signal or send a signal. 
     The electrical device may be configured to perform the solutions in the embodiments shown in  FIG.  1    to  FIG.  4 C . Implementation principles and effects of the electrical device are similar. For an implementation operation of each module, refer to related descriptions of the method embodiments. Details are not described herein again. 
     The foregoing descriptions are merely implementations, but are not intended to limit the scope of the embodiments. Any variation or replacement readily figured out by a person skilled in the art shall fall within the scope of the embodiments.