Patent Publication Number: US-2019179387-A1

Title: Power storage apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefits of U.S. provisional application Ser. No. 62/598,449, filed on Dec. 13, 2017. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
    
    
     BACKGROUND 
     Technical Field 
     The disclosure relates to a power storage apparatus and more particularly relates to an expandable power storage apparatus. 
     Description of Related Art 
     With the advancement of technology, mobile devices are becoming more and more common. As to how to keep mobile devices operating for a long time, power supply and power storage play very important roles. 
     With the existing battery expansion technology, the battery of a power storage apparatus can be charged by an additional expansion battery to maintain the power of the power storage apparatus. The current expansion form requires the battery of the power storage apparatus and the battery of the expansion device to be connected in parallel. Moreover, the battery of the power storage apparatus and the battery of the expansion device need to be batteries of the same power specification. That is, since the power specifications need to be the same, the flexibility of the existing battery expansion technology is limited. 
     SUMMARY 
     The disclosure provides a power storage apparatus that improves battery expansibility. 
     The power storage apparatus of the disclosure includes a system host, a battery expansion module, and a communication interface. The system host includes a main controller, a main battery, a first switch set, and a main buck-boost converter. The first switch set is coupled between the main controller and the main battery. The main buck-boost converter is coupled to the main controller, the first switch set, and the main battery. The main buck-boost converter receives control of the main controller, and converts a first DC input voltage received by the first switch set and outputs a first DC output voltage to charge the main battery. The battery expansion module is adapted to be detachably assembled with the system host. The battery expansion module includes an expansion controller, an expansion battery, and a second switch set. The second switch set is coupled between the expansion controller and the expansion battery. When the system host and the battery expansion module are assembled, the expansion controller and the main controller communicate with each other through the communication interface and selectively control switches of the first switch set and the second switch set to charge the main battery or the expansion battery. 
     Based on the above, the power storage apparatus of the disclosure includes the system host, the battery expansion module, and the communication interface. When the system host and the battery expansion module are assembled, the expansion controller and the main controller communicate with each other through the communication interface and control the first switch set and the second switch set, so as to select to charge the main battery or the expansion battery. In addition, the main buck-boost converter converts the first DC input voltage received by the first switch set and outputs the first DC output voltage to charge the main battery. Thus, the expansibility of the power storage apparatus can increase expansion devices. 
     To make the aforementioned more comprehensible, several embodiments accompanied with drawings are described in detail as follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure. 
         FIG. 1  is a schematic diagram of the power storage apparatus according to the first embodiment of the disclosure. 
         FIG. 2  is a schematic diagram of the power storage apparatus according to the second embodiment of the disclosure. 
         FIG. 3  is a flowchart illustrating an operation that the power storage apparatus performs on the first switch set and the second switch set according to the second embodiment of the disclosure. 
         FIG. 4  is a schematic diagram of the power storage apparatus according to the third embodiment of the disclosure. 
         FIG. 5  is a schematic diagram of the power storage apparatus according to the fourth embodiment of the disclosure. 
         FIG. 6  is a flowchart illustrating an operation that the power storage apparatus performs on the first switch set and the second switch set according to the fourth embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS 
     Referring to  FIG. 1 ,  FIG. 1  is a schematic diagram of a power storage apparatus according to the first embodiment of the disclosure. In this embodiment, the power storage apparatus  100  includes a system host  110 , battery expansion modules  120 _ 1  and  120 _ 2 , and a communication interface CI. The system host  110  includes a main controller  111 , a main battery  112 , a first switch set  113 , and a main buck-boost converter  114 . The main controller  111  is used as the control core of the system host  110 . The main battery  112  is used to store a first DC output voltage VO_ 1 . The first switch set  113  is coupled between the main controller  111  and the main battery  112  and is controlled by the main controller. The main buck-boost converter  114  is coupled between the main controller  111 , the main battery  112 , and the first switch set  113 . The main buck-boost converter  114  is used to receive control of the main controller  111  and convert a first DC input voltage VI_ 1  received by the first switch set  113  or an external power EP 1  to output the first DC output voltage VO_ 1  to charge the main battery  112 . In the disclosure, the number of the battery expansion modules may be one or more and is not particularly limited. 
     In this embodiment, the battery expansion modules  120 _ 1  and  120 _ 2  are adapted to be detachably assembled with the system host  110 . The battery expansion module  120 _ 1  includes an expansion controller  121 _ 1 , an expansion battery  122 _ 1 , a second switch set  123 _ 1 , and an expansion buck-boost converter  124 _ 1 . The battery expansion module  120 _ 2  includes an expansion controller  121 _ 2 , an expansion battery  122 _ 2 , a second switch set  123 _ 2 , and an expansion buck-boost converter  124 _ 2 . Taking the battery expansion module  120 _ 1  as an example, the expansion controller  121 _ 1  is used as the control core of the battery expansion module  120 _ 1 , and the expansion controller  121 _ 1  and the main controller  111  communicate with each other through the communication interface CI. The expansion battery  122 _ 1  is used to store a second DC output voltage VO_ 2 . The second switch set  123 _ 1  is coupled between the expansion controller  121 _ 1  and the expansion battery  122 _ 1 . The second switch set  123 _ 1  is used to receive the power provided by an external power EP 2  or the expansion battery  122 _ 1  and provide the power received from the external power EP 2  or the expansion battery  122 _ 1  as the first DC input voltage VI_ 1 . The expansion buck-boost converter  124 _ 1  is coupled between the expansion controller  121 _ 1 , the second switch set  123 _ 1 , and the expansion battery  122 _ 1 . The expansion buck-boost converter  124 _ 1  is used to receive control of the expansion controller  121 _ 1  and convert a second DC input voltage VI_ 2  received by the first switch set  113  to output a second DC output voltage VO_ 2  to charge the expansion battery  122 _ 1 . 
     In this embodiment, the system host  110  of the power storage apparatus  100  may be connected to a load LD. The system host  110  is used to provide the power of the main battery  112  to the load LD. In some embodiments, the load LD may also be connected to the battery expansion modules  120 _ 1 / 120 _ 2 . The battery expansion modules  120 _ 1 / 120 _ 2  may provide the power of the expansion batteries  122 _ 1 / 122 _ 2  to the load LD. In some embodiments, the power storage apparatus  100  may further provide one of the external powers EP 1 , EP 2 , and EP 3  to the load LD. 
     In this embodiment, when the system host  110  and the battery expansion modules  120 _ 1  and  120 _ 2  are assembled, the main controller  111  and the expansion controllers  121 _ 1  and  121 _ 2  communicate with each other through the communication interface CI and the first switch set  113  and the second switch sets  123 _ 1  and  123 _ 2  are assembled to form a switch set. The main controller  111  may determine the power amount of the main battery  112  and determine whether the system host  110  receives the external power EP 1 . The expansion controller  121 _ 1  may determine the power amount stored in the expansion battery  122 _ 1  and determine whether the battery expansion module  120 _ 1  receives the external power EP 2 . In addition, the expansion controller  121 _ 2  may determine the power amount stored in the expansion battery  122 _ 2  and determine whether the battery expansion module  120 _ 2  receives the external power EP 3 . The main controller  111  and the expansion controllers  121 _ 1  and  121 _ 2  cooperatively control the first switch set  113  and the second switch sets  123 _ 1  and  123 _ 2  through the communication interface CI according to the above determination results, so as to selectively charge the main battery  112  or the expansion batteries  122 _ 1  and  122 _ 2 . 
     With the mechanism of cooperative control and selective charging as described above, the charging efficiency of the power storage apparatus  100  does not decrease as the number of battery expansion modules increases. With the mechanism of cooperative control and selective charging as described above, it is also possible to prevent imbalance caused by the assembly of multiple battery expansion modules  120 _ 1  and  120 _ 2 , thereby reducing a discharge surge of the main battery  112  or the expansion batteries  122 _ 1  and  122 _ 2  to extend the lifespan of the main battery  112  or the expansion batteries  122 _ 1  and  122 _ 2 . 
     The system host  110  converts the first DC input voltage VI_ 1  through the main buck-boost converter  114  to generate the first DC output voltage VO_ 1  that matches the power specification of the main battery  112 . The battery expansion modules  120 _ 1  and  120 _ 2  may respectively convert the second DC input voltage VI_ 2  through the expansion buck-boost converters  124 _ 1  and  124 _ 2  to generate the second DC output voltage VO_ 2  that matches the power specification of the expansion batteries  122 _ 1  and  122 _ 2 . Thus, the power storage apparatus  100  may receive power of different power specifications to charge the main battery  112  or the expansion batteries  122 _ 1  and  122 _ 2 , thereby improving the battery expansibility of the power storage apparatus  100 . 
     Hereinafter, the assembly of the system host  110  and the battery expansion module  120 _ 1  is taken as an example. When the main controller  111  and the expansion controller  121 _ 1  communicate with each other through the communication interface CI, the main controller  111  may determine whether the first switch set  113  is connected to the external power EP 1  and the expansion controller  121  may determine whether the first switch set  113  is connected to the external power EP 2 . The main controller  111  and the expansion controllers  121 _ 1  and  121 _ 2  control the first switch set  113  to receive the external power EP 1  or the first DC input voltage VI_ 1  that the second switch set  123 _ 1  provides by receiving the external power EP 1  according to the above determination results. The main buck-boost converter  114  converts the external power EP 1  or the first DC input voltage VI_ 1  received by the first switch set  113  to output the first DC output voltage VO_ 1  to charge the main battery  112 . 
     Hereinafter, the assembly of the system host  110  and the battery expansion module  120 _ 1  is taken as another example. When the main controller  111  and the expansion controller  121 _ 1  communicate with each other through the communication interface CI, the expansion controller  121 _ 1  may determine whether the power amount stored in the expansion battery  122 _ 1  is greater than a predetermined minimum discharge amount. If the power amount stored in the expansion battery  122 _ 1  is greater than the predetermined minimum discharge amount, the expansion controller  121 _ 1  controls the second switch set  123 _ 1  to provide the power of the expansion battery  122 _ 1  as the first DC input voltage VI_ 1 . The second switch set  123 _ 1  provides the first DC input voltage VI_ 1  to the first switch set  113 , and the main buck-boost converter  114  converts the first DC input voltage VI_ 1  received by the first switch set  113  to output the first DC output voltage VO_ 1  to charge the main battery  112 . On the other hand, if the power amount stored in the expansion battery  122 _ 1  is not greater than the predetermined minimum discharge amount, the expansion controller  121 _ 1  controls the second switch set  123 _ 1  not to provide the power of the expansion battery  122 _ 1  as the first DC input voltage VI_ 1 . 
     Hereinafter, the assembly of the system host  110  and the battery expansion module  120 _ 1  is taken as another example. When the main controller  111  and the expansion controller  121 _ 1  communicate with each other through the communication interface CI, the expansion controller  121 _ 1  is further used to determine whether the second switch set  123 _ 1  receives the external power EP 2  and the main controller  111  is further used to determine whether the power amount stored in the main battery  112  reaches a fully charged state. If the expansion controller  121 _ 1  determines that the second switch set  123 _ 1  receives the external power EP 2  and the main controller  111  determines that the power amount of the main battery  112  reaches the fully charged state, the expansion controller  121 _ 1  controls the second switch set  123 _ 1  to provide the external power EP 2  as the first DC input voltage VI_ 1  and provide the first DC input voltage VI_ 1  to the expansion buck-boost converter  124 _ 1 . The expansion buck-boost converter  124 _ 1  converts the external power EP 2 , so as to output the second DC output voltage VO_ 2  to charge the expansion battery  122 _ 1 . 
     Hereinafter, the assembly of the system host  110  and the battery expansion module  120 _ 1  is again taken as another example. The main controller  111  is further used to determine whether the first switch set  113  receives the external power EP 1 . If the main controller  111  determines that the first switch set  113  receives the external power EP 1  and determines that the main battery  112  reaches the fully charged state, the main controller  111  controls the first switch set  113  to provide the received second converted DC voltage as the second DC input voltage VI_ 2  and to provide the second DC input voltage VI_ 2  to the second switch set  123 _ 1 , and the expansion buck-boost converter  124 _ 1  converts the second DC input voltage VI_ 2  received by the second switch set  123 _ 1  to output the second DC output voltage VO_ 2  to charge the expansion battery  122 _ 1 . 
     An operation that the power storage apparatus performs on the first switch set and the second switch set is described in detail hereinafter. Referring to  FIG. 2  and FIG.  3 ,  FIG. 2  is a schematic diagram of the power storage apparatus according to the second embodiment of the disclosure.  FIG. 3  is a flowchart illustrating the operation that the power storage apparatus performs on the first switch set and the second switch set according to the second embodiment of the disclosure. In this embodiment, the power storage apparatus  200  includes a system host  210  and a battery expansion module  220 . 
     A first switch set  213  of the system host  210  includes a first switch set connection port CP 1 , a first switch S 1 , and a second switch S 2 . The first terminal of the first switch S 1  is used to receive the external power EP 1  and the second terminal of the first switch S 1  is coupled to a main buck-boost converter  214 . The first terminal of the second switch S 2  is coupled to the first switch set connection port CP 1  and the second terminal of the second switch S 2  is coupled to the second terminal of the first switch S 1  and the main buck-boost converter  214 . A second switch set  223  of the battery expansion module  220  includes a second switch set connection port CP 2 , a third switch S 3 , and a fourth switch S 4 . The first terminal of the third switch S 3  is coupled to the second switch set connection port CP 2  and the second temiinal of the third switch S 3  is coupled to the expansion battery  222 . The first terminal of the fourth switch S 4  is coupled to the second switch set connection port CP 2  and the first terminal of the third switch S 3 . The second terminal of the fourth switch S 4  is coupled to an expansion buck-boost converter  224 . The first switch S 1 , the second switch S 2 , the third switch S 3 , and the fourth switch S 4  of this embodiment may be transistor switches of any form. 
     In this embodiment, when the system host  210  and the battery expansion module  220  are assembled, the main controller  211  and the expansion controller  221  start to cooperatively control the first switch set  213  and the second switch set  223 . The system host  210  starts charging in step S 301 . In step S 302 , the main controller  211  determines whether the system host  210  receives the external power EP 1 , that is, determines whether the first terminal of the first switch S 1  receives the external power EP 1 . If the main controller  211  determines that the first terminal of the first switch S 1  receives the external power EP 1 , the procedure proceeds to step S 303 . In step S 303 , the main controller  211  turns on the first switch S 1  and turns off the second switch S 2 . In addition, if the expansion controller  221  determines that the system host  210  and the battery expansion module  220  are assembled, the third switch S 3  and the fourth switch S 4  are turned off. Thus, the first switch set  213  provides the power of the external power EP 1  to the main buck-boost converter  214  under control of the main controller  211 , and the main buck-boost converter  214  converts the power of the external power EP 1  to output the first DC output voltage VO_ 1  to charge the main battery  212 . 
     In step S 304 , if the main controller  211  determines that the first terminal of the first switch S 1  receives the external power, the main controller  211  further determines whether the main battery  212  reaches the fully charged state. If the main controller  211  determines that the main battery  212  reaches the fully charged state, the procedure proceeds to step S 305 . In step S 305 , the main controller  211  turns on the first switch S 1  and the second switch S 2 . In addition, if the expansion controller  221  determines that the system host  210  and the battery expansion module  220  are assembled, the fourth switch S 4  is turned on and the third switch S 3  is turned off. Thus, the first switch set  213  uses the external power EP 1  as the second DC input voltage V 1 _ 2  under control of the main controller  211  and provides the second DC input voltage VI_ 2  to the second switch set  223 . The expansion buck-boost converter  224  converts the second DC input voltage VI_ 2  received by the second switch set  223  to output the second DC output voltage VO_ 2  to charge the expansion battery  222 . In other words, if the main controller  211  deter wines that the first switch set  213  receives the external power EP 1  and determines that the main battery  212  reaches the fully charged state, the main controller  211  controls the first switch set  213  to provide the external power EP 1  to the battery expansion module  220  to charge the expansion battery  222 . 
     On the other hand, if the main controller  211  determines in step S 304  that the main battery  212  does not reach the fully charged state, the procedure returns to step S 301 . 
     Returning to step S 302 , if the main controller  211  determines that the system host  210  does not receive the external power EPI, the procedure proceeds to step S 306 . In step S 306 , the main controller  211  again confirms whether the system host  210  and the battery expansion module  220  are assembled. If the main controller  211  determines that the system host  210  and the battery expansion module  220  are assembled, the procedure proceeds to step S 307 . On the other hand, if the main controller  211  deteimines that the system host  210  is not connected to the battery expansion module  220 , the procedure returns to step S 301 . In step S 307 , the expansion controller  221  determines whether the battery expansion module  220  receives the external power EP 2 . If the expansion controller  221  determines that the battery expansion module  220  receives the external power EP 2 , that is, if the expansion controller  221  deteii  1 ines that the first terminal of the fourth switch S 4  receives the external power EP 2 , the procedure proceeds to step S 308 . In step S 308 , the expansion controller  221  turns off the third switch S 3  and the fourth switch S 4  and the main controller  211  turns on the second switch S 2  and turns off the first switch S 1 . Thus, the second switch set  223  uses the external power EP 2  as the first DC input voltage VI_ 1  under control of the expansion controller  221  and provides the first DC input voltage VI_ 1  to the first switch set  213 . The main buck-boost converter  214  converts the first DC input voltage VI_ 1  received by the first switch set  213  so as to output the first DC output voltage VO_ 1  to charge the main battery  212 . 
     Next, the main controller  211  determines in step S 309  whether the main battery  212  reaches the fiilly charged state. If the main controller  211  determines that the main battery  212  reaches the frilly charged state, the procedure proceeds to step S 310 . In step S 310 , the main controller  211  turns off the first switch S 1  and the second switch S 2  and the expansion controller  221  turns on the fourth switch S 4  and turns off the third switch S 3 . Thus, the second switch set  223  provides the external power EP 2  to the expansion buck-boost converter  224  under control of the expansion controller  221 . The expansion buck-boost converter  224  receives the external power EP 2  and converts the external power EP 2  to output the second DC output voltage VO_ 2  to charge the expansion battery  222 . In other words, if the expansion controller  221  determines that the second switch set  223  receives the external power EP 2  and the main controller  211  determines that the power amount of the main battery  212  reaches the fully charged state, the expansion controller  221  controls the second switch set  223  to provide the power of the external power EP 2  to the expansion battery  222  for charging. On the other hand, if the main controller  211  determines that the main battery  212  does not reach the fully charged state, the procedure returns to step S 301 . 
     Returning to step S 307 , if the expansion controller  221  determines that the battery expansion module  220  does not receive the external power EP 2 , the procedure proceeds to step S 311 . The expansion controller  221  determines in step S 311  whether the power amount stored in the expansion battery  222  is greater than the predetermined minimum discharge amount. If the expansion controller  221  determines that the power amount stored in the expansion battery  222  is greater than the predetermined minimum discharge amount, that is, if the expansion controller  221  determines that the first terminal of the fourth switch S 4  does not receive the external power EP 2 , the procedure proceeds to step S 312 . In step S 312 , the expansion controller  221  turns on the third switch S 3  and turns off the fourth switch S 4  and the main controller  211  turns on the second switch S 2  and turns off the first switch S  1 . Thus, the second switch set  223  provides the power of the expansion battery  222  as the first DC input voltage VI_ 1  under control of the expansion controller  221  and provides the first DC input voltage VI_ 1  to the first switch set  213 . The main buck-boost converter  214  converts the first DC input voltage VI_ 1  received by the first switch set  213  so as to output the first DC output voltage VO_ 1  to charge the main battery  212 . After step S 312  is completed, the procedure proceeds to step S 309 . Furthermore, in step S 311 , if the expansion controller  221  determines that the power amount stored in the expansion battery  222  is not greater than the predetermined minimum discharge amount, the procedure returns to step S 301 . 
     Referring to  FIG. 4 ,  FIG. 4  is a schematic diagram of the power storage apparatus according to the third embodiment of the disclosure. Different from the second embodiment, a system host  410  of this embodiment further includes an AC/DC converter  415  and a battery expansion module  420  further includes an AC/DC converter  425 . The AC/DC converter  415  of the system host  410  is coupled to a first switch set  413 . The AC/DC converter  415  is used to receive an external power EP 4  in the form of AC power and convert the external power EP 4  to generate power in the form of DC power. The AC/DC converter  425  of the battery expansion module  420  is coupled to a second switch set  423 . The AC/DC converter  425  is used to receive an external power 
     EP 5  in the form of AC power and convert the external power EP 5  to generate power in the form of DC power. 
     Referring to  FIG. 5  and  FIG. 6 ,  FIG. 5  is a schematic diagram of the power storage apparatus according to the fourth embodiment of the disclosure.  FIG. 6  is a flowchart illustrating an operation that the power storage apparatus performs on the first switch set and the second switch set according to the fourth embodiment of the disclosure. Different from the second embodiment, in a system host  510 , a first switch set  513  further includes a fifth switch S 5 . The first terminal of the fifth switch S 5  is coupled to the first terminal of the first switch S 1 . The second terminal of the fifth switch S 5  is coupled to the first terminal of the second switch S 2  and the first switch set connection port CP 1 . The fifth switch S 5  of this embodiment may be a transistor switch of any form. 
     In the operation procedure of this embodiment, the system host  510  starts charging in step S 601 . In step S 602 , the main controller  511  determines whether the system host  510  receives the external power EP 1 . If the main controller  511  determines that the system host  510  receives the external power EP 1 , the procedure proceeds to step S 603 . In step S 603 , the main controller  511  turns on the first switch S 1  and turns off the second switch S 2  and the fifth switch S 5 , so as to charge the main battery  512 . In addition, if the expansion controller  521  determines that the system host  510  and the battery expansion module  520  are assembled, the third switch S 3  and the fourth switch S 4  are turned off. 
     In step S 604 , the main controller  511  determines whether the main battery  512  reaches the fully charged state. If the main controller  511  determines that the main battery  512  reaches the fully charged state, the procedure proceeds to step S 605 . In step S 605 , the main controller  511  turns on the fifth switch S 5  and turns off the first switch S 1  and the second switch S 2 . In addition, if the expansion controller  521  determines that the system host  510  and the battery expansion module  520  are assembled, the fourth switch S 4  is turned on and the third switch S 3  is turned off, so as to charge the expansion battery  522 . 
     It is worth mentioning that, in step S 605 , the main controller  511  turns on the fifth switch S 5  instead of turning on the first switch S 1  and the second switch S 2 . As a result, the transmission loss of the external power EP 1  in the first switch set  513  is reduced. 
     If the main controller  511  determines in step S 604  that the main battery  512  does not reach the fully charged state, the procedure returns to step S 601 . 
     Returning to step S 602 , if the main controller  511  determines that the system host  510  does not receive the external power EP 1 , the procedure proceeds to step S 606 . In step S 606 , the main controller  511  again determines whether the system host  510  and the battery expansion module  520  are assembled. If the main controller  511  determines that the system host  510  and the battery expansion module  520  are assembled, the procedure proceeds to step S 607 . On the other hand, if the main controller  511  determines that the system host  510  and the battery expansion module  520  are not assembled, the procedure returns to step S 601 . In step S 607 , the expansion controller  521  determines whether the battery expansion module  520  receives the external power EP 2 . If the expansion controller  521  determines that the battery expansion module  520  receives the external power EP 2 , the procedure proceeds to step S 608 . In step S 608 , the expansion controller  521  turns off the third switch S 3  and the fourth switch S 4  and the main controller  511  turns on the second switch S 2  and turns off the first switch S 1  and the fifth switch S 5 , so as to charge the main battery  512 . 
     Next, the main controller  511  determines in step S 609  whether the main battery  512  reaches the fully charged state. If the main controller  511  determines that the main battery  512  reaches the fully charged state, the procedure proceeds to step S 610 . In step S 610 , the main controller  511  turns off the first switch S 1 , the second switch S 2 , and the fifth switch S 5  and the expansion controller  521  turns on the fourth switch S 4  and turns off the third switch S 3 , so as to charge the expansion battery  522 . 
     Returning to step S 607 , if the expansion controller  521  determines that the battery expansion module  520  does not receive the external power EP 2 , the procedure proceeds to step S 611 . The expansion controller  521  determines in step S 611  whether the power amount stored in the expansion battery  522  is greater than the predetermined minimum discharge amount. If the expansion controller  521  determines that the power amount stored in the expansion battery  522  is greater than the predetermined minimum discharge amount, the procedure proceeds to step S 612 . In step S 612 , the expansion controller  521  turns on the third switch S 3  and turns off the fourth switch S 4  and the main controller  511  turns on the second switch S 2  and turns off the first switch S 1  and the fifth switch S 5 , so as to charge the main battery  512 . After step S 612  is completed, the procedure proceeds to step S 609 . On the other hand, in step S 611 , if the expansion controller  521  determines that the power amount stored in the expansion battery  522  is not greater than the predetermined minimum discharge amount, the procedure returns to step S 601 . 
     To sum up, when the system host and the battery expansion module of the disclosure are assembled, the first switch set and the second switch set may be controlled cooperatively through the communication interface, so as to selectively charge the main battery or the expansion battery. In addition, the system host may convert the first DC input voltage through the main buck-boost converter to generate the first DC output voltage that matches the power specification of the main battery. The battery expansion module may convert the second DC input voltage through the expansion buck-boost converter to generate the second DC output voltage that matches the power specification of the expansion battery. Thus, the power storage apparatus may receive power of different power specifications to charge the main battery or the expansion batteries, thereby improving the battery expansibility of the power storage apparatus. Furthermore, with the mechanism of cooperative control and selective charging of the disclosure, the charging efficiency of the power storage apparatus does not decrease as the number of battery expansion modules increase, and the imbalance caused by assembly of multiple battery expansion modules may also be prevented to extend the lifespan of the main battery  112  or the expansion batteries  122 _ 1  and  122 _ 2 . 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure covers modifications and variations provided that they fall within the scope of the following claims and their equivalents.