Patent Publication Number: US-2016226275-A1

Title: Overcharge protection apparatus for battery pack and overcharge protection system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2015-0015590, filed on Jan. 30, 2015, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Field 
     Aspects of one or more exemplary embodiments relate to an overcharge protection apparatus for a battery pack and an overcharge protection system. 
     2. Description of the Related Art 
     Much research has been conducted into rechargeable secondary batteries along with the development of portable electronic devices, such as mobile phones, laptop computers, camcorders, and personal digital assistants (PDAs). Particularly, various kinds of secondary batteries, such as nickel-cadmium batteries, lead storage batteries, nickel-hydride batteries, lithium-ion batteries, lithium-polymer batteries, metal lithium batteries, or zinc-air batteries, have been developed. 
     Such secondary batteries are manufactured in the form of cells, and then the cells are combined with charge/discharge circuits to form battery packs. Thereafter, the battery packs can be charged or discharged by connecting external terminals of the battery packs to external power sources or loads. 
     A battery pack generally includes battery cells and a peripheral circuit including a charge/discharge circuit. The peripheral circuit is a printed circuit board that is connected to the battery cells. If a component of the printed circuit board of the battery pack catches fire or emits smoke due to abnormal conditions, patterns formed on the printed circuit board may be burnt. 
     Apparatuses and methods for addressing such situations have been developed and used. Generally, such apparatuses and methods are designed to cut a charge path if a battery cell is overcharged. Such an overcharge protection apparatus including a protection circuit and a battery pack having battery cells may constitute an energy storage system (ESS). 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the present invention, and therefore, it may contain information that does not form prior art. 
     SUMMARY 
     One or more exemplary embodiments provide an overcharge protection apparatus for a battery pack and an overcharge protection system that are configured to protect a battery pack or an overall system from an overcharge even when a primary overcharge protection unit operates abnormally. 
     One or more exemplary embodiments provide an overcharge protection apparatus for a battery pack and an overcharge protection system that are configured to prevent or substantially prevent spreading of damage to the whole system when some of a plurality of energy storage systems connected in series are overcharged. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments. 
     According to one or more exemplary embodiments, an overcharge protection apparatus includes: a first battery manager configured to monitor whether or not a battery module including at least one battery cell is overcharged, the first battery manager including a first switch configured to be turned on when the battery module is overcharged; a second battery manager including a second switch configured to be turned on by an external cutoff signal; a cutoff switch connected to the first and second battery managers, and configured to be turned on by the first switch or the second switch; and an overcharge controller configured to receive a control signal by the cutoff switch, and to generate an internal cutoff signal in response to the control signal. 
     The internal cutoff signal may have a voltage level greater than a voltage level of the battery module. 
     The overcharge controller is configured to generate the internal cutoff signal, and to output the internal cutoff signal to the outside when the cutoff switch is turned on. 
     The overcharge protection apparatus may further include: an analog front end (AFE) connected in parallel with the first battery manager; and a charge cutoff switch configured to cut off a charge path of the battery module, wherein the first battery manager and the AFE may be configured to turn off the charge cutoff switch when the first battery manager and the AFE determine that the battery module is overcharged. 
     A voltage level utilized as a reference voltage level by the AFE to determine whether or not the battery module is overcharged may be less than a voltage level utilized as a reference voltage level by the first battery manager to determine whether or not the battery module is overcharged. 
     The second battery manager may further include a noise filter configured to remove noise from the external cutoff signal, and the second switch may be further configured to be turned on by the external cutoff signal that passed through the noise filter. 
     The second switch may include a non-contact switch. 
     The overcharge controller may be configured to output the internal cutoff signal having a constant voltage level in response to the control signal. 
     The overcharge protection apparatus may further include the battery module including the at least one battery cell. 
     According to one or more exemplary embodiments, an overcharge protection system includes: a plurality of energy storage systems connected in series, each of the energy storage systems includes: a battery module including at least one battery cell; a first battery manager configured to monitor whether or not the battery module is overcharged, the first battery manager including a first switch configured to be turned on when the battery module is overcharged; a second battery manager including a second switch configured to be turned on by an external cutoff signal input from a previous energy storage system; a cutoff switch connected to the first and second battery managers, and configured to be turned on by the first switch or the second switch; and an overcharge controller configured to receive a control signal by the cutoff switch, and to generate an internal cutoff signal in response to the control signal, wherein the battery modules of the energy storage systems are connected in series. 
     The internal cutoff signal may have a voltage level greater than a voltage level of the control signal. 
     The internal cutoff signal may be output to a second battery manager of a next energy storage system. 
     The overcharge protection system may further include: an analog front end (AFE) connected in parallel with the first battery manager; and a charge cutoff switch configured to cut off a charge path of the battery module, wherein the first battery manager and the AFE may be configured to turn off the charge cutoff switch when the first battery manager and the AFE determine that the battery module is overcharged. 
     The second battery manager may further include a noise filter configured to remove noise from the external cutoff signal, and the second switch may be configured to be turned on by the external cutoff signal that passed through the noise filter. 
     The second switch may include a non-contact switch. 
     The overcharge controller may be configured to output the internal cutoff signal having a constant voltage level in response to the control signal. 
     The overcharge protection system may further include: a cutoff signal receiver configured to receive an internal cutoff signal from a last energy storage system; and a main switch configured to connect the battery modules to external charge terminals, wherein the cutoff signal receiver may be configured to turn off the main switch when the cutoff signal receiver receives the internal cutoff signal from the last energy storage system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and/or other aspects and features will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings in which: 
         FIGS. 1 and 2  are schematic diagrams illustrating an overcharge protection apparatus for a battery pack according to an exemplary embodiment; 
         FIGS. 3 and 4  are schematic diagrams illustrating an overcharge protection apparatus for a battery pack according to another exemplary embodiment; 
         FIG. 5  is a schematic diagram illustrating an overcharge protection apparatus for a battery pack according to another exemplary embodiment; 
         FIG. 6  is a schematic diagram illustrating an overcharge protection system including a plurality of energy storage systems; and 
         FIG. 7  is a schematic diagram illustrating an overcharge protection system according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. In this regard, the present invention may be embodied in various different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided as examples so that this disclosure will be thorough and complete, and will fully convey the aspects and features of the present disclosure to those skilled in the art. Accordingly, the exemplary embodiments are merely described below, by referring to the figures, to explain aspects of the present disclosure. Thus, processes, elements, and techniques that are not necessary to those having ordinary skill in the art for a complete understanding of the aspects and features of the present disclosure may not be described. 
     In the drawings, the relative sizes of elements, layers, and regions may be exaggerated for clarity. Spatially relative terms, such as “beneath,” “below,” “lower,” “under,” “above,” “upper,” and the like, may be used herein for ease of explanation to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or in operation, in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” or “under” other elements or features would then be oriented “above” the other elements or features. Thus, the example terms “below” and “under” can encompass both an orientation of above and below. The device may be otherwise oriented (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein should be interpreted accordingly. 
     It will be understood that, although the terms “first,” “second,” “third,” etc., may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section described below could be termed a second element, component, region, layer or section, without departing from the spirit and scope of the present invention. 
     It will be understood that when an element or layer is referred to as being “on,” “connected to,” or “coupled to” another element or layer, it can be directly on, connected to, or coupled to the other element or layer, or one or more intervening elements or layers may be present. In addition, it will also be understood that when an element or layer is referred to as being “between” two elements or layers, it can be the only element or layer between the two elements or layers, or one or more intervening elements or layers may also be present. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms “a” and “an” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and “including,” when used in this specification, specify the presence of the stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
     As used herein, the term “substantially,” “about,” and similar terms are used as terms of approximation and not as terms of degree, and are intended to account for the inherent deviations in measured or calculated values that would be recognized by those of ordinary skill in the art. Further, the use of “may” when describing embodiments of the present invention refers to “one or more embodiments of the present invention.” As used herein, the terms “use,” “using,” and “used” may be considered synonymous with the terms “utilize,” “utilizing,” and “utilized,” respectively. Also, the term “exemplary” is intended to refer to an example or illustration. 
     The electronic or electric devices and/or any other relevant devices or components according to embodiments of the present invention described herein may be implemented utilizing any suitable hardware, firmware (e.g. an application-specific integrated circuit), software, or a combination of software, firmware, and hardware. For example, the various components of these devices may be formed on one integrated circuit (IC) chip or on separate IC chips. Further, the various components of these devices may be implemented on a flexible printed circuit film, a tape carrier package (TCP), a printed circuit board (PCB), or formed on one substrate. Further, the various components of these devices may be may be a process or thread, running on one or more processors, in one or more computing devices, executing computer program instructions and interacting with other system components for performing the various functionalities described herein. The computer program instructions are stored in a memory which may be implemented in a computing device using a standard memory device, such as, for example, a random access memory (RAM). The computer program instructions may also be stored in other non-transitory computer readable media such as, for example, a CD-ROM, flash drive, or the like. Also, a person of skill in the art should recognize that the functionality of various computing devices may be combined or integrated into a single computing device, or the functionality of a particular computing device may be distributed across one or more other computing devices without departing from the spirit and scope of the exemplary embodiments of the present invention. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and/or the present specification, and should not be interpreted in an idealized or overly formal sense, unless expressly so defined herein. 
     Hereinafter, an overcharge protection apparatus for a battery pack and an overcharge protection system will be described with reference to the accompanying drawings according to exemplary embodiments. In the drawings, unless otherwise noted, like reference numerals refer to like elements throughout, and thus, repeated descriptions thereof may be omitted. 
       FIGS. 1 and 2  are schematic diagrams illustrating an overcharge protection apparatus  100  for a battery pack according to an exemplary embodiment. 
     Referring to  FIG. 1 , the overcharge protection apparatus  100  of the present exemplary embodiment may include a battery module  110 , a first battery management unit (e.g., a first battery manager)  120 , a second battery management unit (e.g., a second battery manager)  130 , an overcharge control unit (e.g., an overcharge controller)  140 , and a cutoff switch  150 . 
     The battery module  110  may include one or more battery cells. In  FIG. 1 , the battery cells of the battery module  110  are not illustrated. However, the battery module  110  may include one or more battery cells. The number of the battery cells may vary according to a desired capacity of a system design. 
     The battery module  110  may be connected to an external power source through charge/discharge terminals P+ and P− to receive a charging current from the external power source, or may be connected to a load to supply a discharging current to the load. The battery modules  110  may be connected in series or in parallel to flexibly adjust an overall voltage or capacity. 
     The first battery management unit  120  may monitor whether the battery module  110  is overcharged or not and may include a first switch SW 1 . The first switch SW 1  may be turned on if it is determined that the battery module  110  is overcharged. The first battery management unit  120  may be connected to a positive electrode and a negative electrode of the battery module  110  to measure the voltage and current of the battery module  110 . The first battery management unit  120  may compare a measured voltage value with a preset voltage value to determine whether the battery module  110  is overcharged or not. 
     The first battery management unit  120  may be connected to positive and negative electrodes of each of the battery cells of the overcharge protection apparatus  100  to determine whether each battery cell is overcharged or not. When it is determined that any one of the battery cells of the battery module  110  is overcharged, the first switch SW 1  may be turned on. 
     The overcharge protection apparatus  100  for a battery pack may include a switch  125  connecting the battery module  110  and the charge/discharge terminals P+ and P−. When it is determined that the battery module  110  is overcharged, the switch  125  may be turned off to interrupt a charging current flowing from an external power source to the battery module  110 . 
     The second battery management unit  130  may include a second switch SW 2  (refer to  FIG. 2 ), and the second switch SW 2  is turned on by an external cutoff signal SIGex input from the outside (e.g., outside of or external to the overcharge protection apparatus  100 ). 
     The cutoff switch  150  is connected to the first battery management unit  120  and the second battery management unit  130  and is turned on by the first switch SW 1  or the second switch SW 2 . When the battery module  110  is overcharged, the cutoff switch  150  may be turned on by the first switch SW 1  that is turned on by the first battery management unit  120 . In addition, the cutoff switch  150  may be turned on by the second switch SW 2  when the second switch SW 2  is turned on by an external cutoff signal SIGex input from the outside of the overcharge protection apparatus  100 . That is, the cutoff switch  150  is turned on by a signal generated in the overcharge protection apparatus  100  or a signal input from the outside of the overcharge protection apparatus  100 . 
     The overcharge control unit  140  receives a control signal by the cutoff switch  150  and generates an internal cutoff signal SIGin in response to the control signal. 
     The overcharge protection apparatus  100  of the present exemplary embodiment will now be described in more detail with reference to  FIG. 2 . The same description as that given with reference to  FIG. 1  may not be repeated. 
     The battery module  110  may include a plurality of battery cells, and as shown in  FIG. 2 , the positive and negative electrodes of the battery module  110  are connected to the first battery management unit  120 , so that the first battery management unit  120  may measure the voltage and current of the battery module  110 . In  FIG. 2 , only the positive and negative electrodes of the entire battery module  110  are shown as being connected to the first battery management unit  120 . However, the present disclosure is not limited thereto, and the positive and negative electrodes of each of the battery cells of the battery module  110  may be connected to the first battery management unit  120 , so that the first battery management unit  120  may measure the voltage and current of each of the battery cells. 
     That is, the first battery management unit  120  may measure the voltage and current of the entire battery module  110  or each of the battery cells of the battery module  110 , and when it is determined that the battery module  110  or any one of the battery cells are overcharged, the first battery management unit  120  may turn on the first switch SW 1 . Then, the cutoff switch  150  is turned on when the first switch SW 1  is turned on. 
     The overcharge control unit  140  receives an input signal from the battery module  110  through an input terminal IN and receives a control signal from the cutoff switch  150 . When the first switch SW 1  is turned on, the cutoff switch  150  is turned on and applies a control signal to the overcharge control unit  140  through an enable terminal EN. 
     When the overcharge control unit  140  receives the control signal from the cutoff switch  150  through the enable terminal EN, the overcharge control unit  140  outputs an internal cutoff signal SIGin through an output terminal OUT in response to the control signal. Then, the internal cutoff signal SIGin output through the output terminal OUT is fed back to the overcharge control unit  140  through a feedback terminal FB, and the overcharge control unit  140  determines whether or not a voltage level of the internal cutoff signal SIGin is equal or substantially equal to that of a preset voltage. When the voltage level of the internal cutoff signal SIGin is not equal or substantially equal to that of the preset voltage, the overcharge control unit  140  may output an internal cutoff signal SIGin having the same or substantially the same voltage level as that of the preset voltage. 
     The voltage level of the internal cutoff signal SIGin may be preset according to a desired system design, for example, the voltage level of the internal cutoff signal SIGin may be preset to be greater than the voltage level of the battery module  110 . In addition, the voltage level of the internal cutoff signal SIGin may be set to be constant or substantially constant. 
     The second battery management unit  130  receives an external cutoff signal SIGex from an external device (e.g., external to the overcharge protection apparatus  100 ). Then, the second switch SW 2  is turned on by the external cutoff signal SIGex input from the external device, and when the second switch SW 2  is turned on, the cutoff switch  150  is turned on. When the cutoff switch  150  is turned on, a control signal is applied to the enable terminal EN of the overcharge control unit  140 . 
     When the overcharge control unit  140  receives the control signal from the cutoff switch  150  through the enable terminal EN, the overcharge control unit  140  outputs an internal cutoff signal SIGin through the output terminal OUT in response to the control signal. Then, the internal cutoff signal SIGin output through the output terminal OUT is fed back to the overcharge control unit  140  through the feedback terminal FB, and the overcharge control unit  140  determines whether or not the voltage level of the internal cutoff signal SIGin is equal or substantially equal to that of the preset voltage. When the voltage level of the internal cutoff signal SIGin is not equal or substantially equal to that of the preset voltage, the overcharge control unit  140  may output an internal cutoff signal SIGin having the same or substantially the same voltage level as that of the preset voltage. 
     The second battery management unit  130  may include a noise filter. The noise filter removes noise from an external cutoff signal SIGex input from an external device, and then applies the external cutoff signal SIGex to the second switch SW 2 . Then, the second switch SW 2  is turned on by the external cutoff signal SIGex from which the noise has been removed by the noise filter. 
     The second switch SW 2  may be a non-contact switch. For example, as shown in  FIG. 2 , the second switch SW 2  may include a photodiode and a phototransistor. When the external cutoff signal SIGex is applied to the photodiode after passing through the noise filter, the photodiode may radiate light, and the phototransistor may be turned on in response to the light radiated from the photodiode. 
     When the phototransistor is turned on, since a current path is formed between the cutoff switch  150  and ground, the cutoff switch  150  is turned on, and a control signal is applied to the enable terminal EN of the overcharge control unit  140  through the cutoff switch  150 . 
       FIGS. 3 and 4  are schematic diagrams illustrating an overcharge protection apparatus  100  for a battery pack according to another exemplary embodiment. 
     Referring to  FIG. 3 , a first battery management unit (e.g., a first battery manager)  120 ′ may include a first sensing terminal SE 1  to sense the voltage of an internal cutoff signal SIGin output through an output terminal OUT of an overcharge control unit (e.g., an overcharge controller)  140 . The first battery management unit  120  may measure a voltage V OUT  of an output node through the first sensing terminal SE 1 , and when it is determined that an internal cutoff signal SIGin is output from the overcharge control unit  140 , the first battery management unit  120  may turn off a switch  125  connecting a battery module  110  and external terminals P+ and P−. 
     Referring to  FIG. 4 , a first battery management unit (e.g., a first battery manager)  120 ″ may include a second sensing terminal SE 2  to sense a control signal applied from a cutoff switch  150  to an enable terminal EN of the overcharge control unit  140 . The first battery management unit  120  may sense a control signal through the second sensing terminal SE 2 , and when it is determined that a control signal is applied from the cutoff switch  150 , the first battery management unit  120  may turn off the switch  125  connecting the battery module  110  and external terminals P+ and P−. 
       FIG. 5  is a schematic diagram illustrating an overcharge protection apparatus  200  for a battery pack according to another exemplary embodiment. 
     Referring to  FIG. 5 , the overcharge prevention apparatus  200  for a battery pack may further include an analog front end (AFE)  160  connected in parallel to a first battery management unit (e.g., a first battery manager)  120 . In  FIG. 5 , only a battery module  110 , the first battery management unit  120 , and the AFE  160  are illustrated. However, the overcharge prevention apparatus  200  may include a second battery management unit (e.g., a second battery manager)  130 , an overcharge control unit (e.g., an overcharge controller)  140 , and a cutoff switch  150  as described above with reference to  FIGS. 1 to 4 . The elements not shown in  FIG. 5  may function as described with reference to  FIGS. 1 to 4 . Further, the first battery management unit  120  shown in  FIG. 5  may be the same or substantially the same as any one of the first battery management units  120 ,  120 ′, and  120 ″ as shown above with reference to  FIGS. 1 to 4 . 
     Like the first battery management unit  120 , the AFE  160  may be connected to a positive electrode and a negative electrode of the battery module  110  to measure the voltage and current of the battery module  110 . When it is determined that the battery module  110  is overcharged, a switch  125  connecting the battery module  110  and external terminals P+ and P− may be turned off to prevent the battery module  110  from being charged by an external power source (e.g., external to the overcharge protection apparatus  200 ). 
     In  FIG. 5 , the AFE  160  is shown as being connected to the positive and negative electrodes of the entire battery module  110 . However, the present disclosure is not limited thereto, and the AFE  160  may be connected to positive and negative electrodes of each of battery cells of the battery module  110 . Whether or not the battery module  110  or any one of the battery cells are overcharged may be monitored, and when it is determined that the battery module  110  or any one of the battery cells is overcharged, the switch  125  connecting the battery module  110  and the external terminals P+ and P− may be turned off. 
     A voltage level used as a reference voltage by the AFE  160  for determining whether or not the battery module  110  is overcharged may be less than a voltage level used as a reference voltage by the first battery management unit  120  for determining whether or not the battery module  110  is overcharged. 
     For example, when the AFE  160  uses a voltage level V 1  and the first battery management unit  120  uses a voltage level V 2 , when the AFE  160  and the first battery management unit  120  determine whether the battery module  110  is overcharged, the voltage levels V 1  and V 2  may satisfy V 1 &lt;V 2 . 
     The AFE  160  may monitor the voltage of the battery module  110 , and when the voltage of the battery module  110  is greater than or equal to V 1 , the AFE  160  may determine that the battery module  110  is overcharged. 
     Further, the first battery management unit  120  may determine that the battery module  110  is overcharged when the voltage of the battery module  110  is greater than or equal to V 2 . 
     In this case, the first battery management unit  120  may function as a secondary overcharge protection unit (e.g., a secondary overcharge protector) for the battery module  110 . That is, compared to the first battery management unit  120 , the AFE  160  may protect the battery module  110  when the battery module  110  is overcharged to a relatively low voltage. However, if the AFE  160  does not properly perform its overcharge protection function, the first battery management unit  120  may function as a secondary overcharge protection unit to protect the battery module  110  from overcharge. 
       FIG. 6  is a schematic diagram illustrating an overcharge protection system  300  including a plurality of energy storage systems. 
     In the overcharge protection system  300  shown in  FIG. 6 , a first energy storage system ESS 1 , a second energy storage system ESS 2 , and a third energy storage system ESS 3  are connected in series. The first to third energy storage systems ESS 1  to ESS 3  respectively include first to third battery modules BAT 1 , BAT 2 , and BAT 3 , each of the first to third battery modules BAT 1 , BAT 2 , and BAT 3  including at least one battery cell. 
     The first to third battery modules BAT 1  to BAT 3  are connected in series. The first battery module BAT 1  of the first energy storage system ESS 1  is connected to an external positive (+) terminal, and the third battery module BAT 3  of the third energy storage system ESS 3  is connected to an external negative (−) terminal. 
     A first relay REL 1  may be connected between the first energy storage system ESS 1  and the external positive (+) terminal, or between the first battery module BAT 1  and the external positive (+) terminal. A second relay REL 2  may be connected between the third energy storage system ESS 3  and the external negative (−) terminal, or between the third battery module BAT 3  and the external negative (−) terminal. 
     When any one of the first to third battery modules BAT 1  to BAT 3  is overcharged, if a charging current or voltage is supplied to the external positive and negative terminals, the overcharged battery module may be damaged or the lifespan of the overcharged battery module may be decreased. Since this situation may affect the other non-overcharged battery modules, if any one of the first to third battery modules BAT 1  to BAT 3  is overcharged, it may be desirable to break (e.g., cut or disconnect) the series connection between the external positive and negative terminals and the first to third battery modules BAT 1  to BAT 3 . 
     When any one of the first to third battery modules BAT 1  to BAT 3  is overcharged, the first and second relays REL 1  and REL 2  are turned off to cut the connection between the external positive and negative terminals and the first to third battery modules BAT 1  to BAT 3 , and thus, damage caused by overcharging may not spread. Further, when only one of the first and second relays REL 1  and REL 2  is turned off, the connection between the positive and negative external terminals and the first to third battery modules BAT 1  to BAT 3  may be broken (e.g., cut or disconnected). Thus, in some embodiments, only one of the first and second relays REL 1  and REL 2  may be included and used. 
     In  FIG. 6 , three energy storage systems ESS 1  to ESS 3  are illustrated. However, it will be apparent to those of skill in the art that the number of energy storage systems connected in series may be varied according to a required voltage level or electricity capacity of a system. 
       FIG. 7  is a schematic diagram illustrating an overcharge protection system  400  according to an exemplary embodiment. 
     Referring to  FIG. 7 , the overcharge protection system  400  of the present exemplary embodiment includes a first energy storage system ESS 1 , a second energy storage system ESS 2 , and a third energy storage system ESS 3 . 
     In  FIG. 7 , three energy storage systems ESS 1  to ESS 3  are shown. However, the number of energy storage systems included in the overcharge protection system  400  is not limited to three. It will be apparent to those of skill in the art that the number of energy storage systems may be varied according to a desired voltage level or capacity of a system. 
     As described with reference to  FIGS. 1 to 5 , each of the first to three energy storage systems ESS 1  to ESS 3  may include one or more elements having the same or substantially the same function as that of the overcharge protection apparatus  100  or  200  described above, and thus, the same description as given above may be omitted. 
     The first energy storage system ESS 1  includes a battery module BAT 1 , a first battery management unit (e.g., a first battery manager)  421 , an overcharge control unit (e.g., an overcharge controller)  441 , and a cutoff switch  451 . The battery module BAT 1  includes at least one battery cell. The first battery management unit  421  monitors whether or not the battery module BAT 1  is overcharged and includes a first switch SWa, which may be turned on when the battery module BAT 1  is overcharged. 
     The cutoff switch  451  is connected to the first battery management unit  421  and is turned on by the first switch SWa. When the first battery management unit  421  determines that the battery module BAT 1  is overcharged, the first battery management unit  421  turns on the first switch SWa. When the first switch SWa is turned on, the cutoff switch  451  is turned on. 
     The overcharge control unit  441  receives a control signal from the cutoff switch  451  and generates an internal cutoff signal SIGin 1  in response to the control signal. A voltage is applied from the battery module BAT 1  to an input terminal IN of the overcharge control unit  441 , and when the cutoff switch  451  is turned on, a control signal is applied from the cutoff switch  451  to an enable terminal EN of the overcharge control unit  441 . When a control signal is applied to the enable terminal, the overcharge control unit  441  outputs an internal cutoff signal SIGin 1  through an output terminal OUT. In this case, the voltage level of the internal cutoff signal SIGin 1  may be set to be constant or substantially constant. For example, the voltage level of the internal cutoff signal SIGin 1  may be constant and greater than that of a voltage input from the battery module BAT 1 . 
     The second energy storage system ESS 2  has the same or substantially the same structure as the first energy storage system ESS 1 , except that the second energy storage system ESS 2  includes a second battery management unit (e.g., a second battery manager)  432 . The second battery management unit  432  includes a second switch SW 2 , and the second switch SW 2  is turned on by a cutoff signal input from a previous energy storage system. Here, the previous energy storage system refers to the first energy storage system ESS 1 . That is, the second battery management unit  432  receives an external cutoff signal SIGex 1  from the first energy storage system ESS 1 . The external cutoff signal SIGex 1  is a signal obtained by removing noises from an internal cutoff signal SIGin 1  output from the overcharge control unit  441  of the first energy storage system ESS 1  by using a noise filter. 
     Referring to  FIG. 7 , the second battery management unit  432  of the second energy storage system ESS 2  includes the noise filter and the second switch SW 2  configured to be turned on by an external cutoff signal SIGex 1 . The second switch may be a non-contact switch. For example, the second switch may include a photodiode and a phototransistor. 
     When an internal cutoff signal SIGin 1  output from the first energy storage system ESS 1  passes through the noise filter and is applied to the second switch as an external cutoff signal SIGex 1 , the photodiode may radiate light, and the phototransistor may be turned on in response to the light. 
     When the second switch is turned on in this manner, a cutoff switch  452  of the second energy storage system ESS 2  is turned on, and a control signal is applied from the cutoff switch  452  to an enable terminal EN of an overcharge control unit (e.g., an overcharge controller)  442  of the second energy storage system ESS 2 . Then, the overcharge control unit  442  outputs an internal cutoff signal SIGin 2  through an output terminal OUT. 
     In this case, the voltage level of the internal cutoff signal SIGin 2  may be set to be constant or substantially constant. For example, the voltage level of the internal cutoff signal SIGin 2  may be constant and greater than that of a voltage input from a battery module BAT 2 . 
     A first battery management unit (e.g., a first battery manager)  422  of the second energy storage system ESS 2  has the same or substantially the same function as that of the first battery management unit  421  of the first energy storage system ESS 1  and protects the battery module BAT 2  from overcharge. 
     Like the second energy storage system ESS 2 , the third energy storage system ESS 3  includes a second battery management unit (e.g., a second battery manager)  433 . The second battery management unit  433  has the same or substantially the same structure and function as those of the second battery management unit  432  of the second energy storage system ESS 2 . 
     That is, the second battery management unit  433  filters a cutoff signal SIGin 2  input from the second energy storage system ESS 2  and applies the filtered cutoff signal SIGin 2  to a second switch as an external cutoff signal SIGex 2 . When the second switch is turned on by the external cutoff signal SIGex 2 , a cutoff switch  453  of the third energy storage system ESS 3  is turned on. Then, an overcharge control unit (e.g., overcharge controller)  443  of the third energy storage system ESS 3  outputs an internal cutoff signal SIGin 3  through an output terminal OUT. 
     The second battery management units  432  and  433  of the second and third energy storage systems ESS 2  and ESS 3  are configured to respectively receive internal cutoff signals SIGin 1  and SIGin 2  from previous energy storage systems. That is, the first and second energy storage systems ESS 1  and ESS 2  respectively apply external cutoff signals SIGex 1  and SIGex 2  to the second switches SW 2  and SW 2 ′. 
     When the second switches SW 2  and SW 2 ′ are turned on by the external cutoff signals SIGex 1  and SIGex 2 , the cutoff switches  452  and  453  are turned on, and the overcharge control units  442  and  443  output internal cutoff signals SIGin 2  and SIGin 3  to next energy storage systems. 
     When a cutoff signal is output from each of the first to third energy storage systems ESS 1  to ESS 3 , the voltage level of the cutoff signal is controlled to be constant by the overcharge control units  441  to  443 . Therefore, even though cutoff signals passes through the energy storage systems ESS 1  to ESS 3  connected in series, the voltage level of the cutoff signals are not decreased. In addition, since each of the energy storage systems ESS 1  to ESS 3  includes a device for removing noises from a cutoff signal input thereto, even though noises are included in a cutoff signal while the cutoff signal is transmitted, the noises may be effectively removed. 
     In addition, the overcharge protection system  400  includes a cutoff signal receiving unit (e.g., a cutoff signal receiver)  470 . Referring to  FIG. 7 , the cutoff signal receiving unit  470  receives an internal cutoff signal SIGin 3  from the third energy storage system ESS 3 . When the cutoff signal receiving unit  470  receives an internal cutoff signal, the cutoff signal receiving unit  470  determines that at least one of the battery modules BAT 1  to BAT 3  is overcharged. Then, the cutoff signal receiving unit  470  may turn off a main switch connecting the battery modules BAT 1  to BAT 3  and external charge terminals (+, −) to protect the battery modules BAT 1  to BAT 3  and the overcharge protection system  400  from overcharge damage. The main switch may include a first relay REL 1  or a second relay REL 2 . 
     In  FIG. 7 , the first energy storage system ESS 1  is illustrated as not including a second battery management unit. However, the first energy storage system ESS 1  is not limited thereto. That is, the first energy storage system ESS 1  may include a second battery management unit like the second and third energy storage systems ESS 2  and ESS 3 . 
     In a system including a plurality of energy storage systems connected in series, the first one of the energy storage systems does not have a previous energy storage system transmitting an internal cutoff signal thereto. Therefore, the first energy storage system may not include a second battery management unit. However, if the system is expanded by adding additional energy storage systems, each of the energy storage systems of the system may include a corresponding one or more second battery management units. 
     For example, if an overcharge protection system includes four or more energy storage systems connected in series, each of the energy storage systems may include an overcharge protection unit such as those described with reference to  FIGS. 1 to 5 , and the overcharge protection system may include a cutoff signal receiving unit. If at least one of the energy storage systems is overcharged, the cutoff signal receiving unit turns off a main switch in response to a cutoff signal received from the last energy storage system to interrupt a current supplied to the overcharge protection system. 
     As described above, according to the one or more of the above exemplary embodiments, the overcharge protection apparatus for a battery pack and the overcharge protection system may protect battery packs or the entire system from overcharge, even though a primary overcharge protection unit operates abnormally. 
     In addition, although some of the energy storage systems connected in series are overcharged, the overcharge protection apparatus for a battery pack and the overcharge protection system may prevent or substantially prevent spreading of damage to the whole system. 
     It should be understood that the exemplary embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each exemplary embodiment should typically be considered as available for other similar features or aspects in other exemplary embodiments. 
     While one or more exemplary embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims, and their equivalents.