Patent Publication Number: US-2022223925-A1

Title: Power receiving apparatus, battery unit, electric power unit, and work machine

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of International Patent Application No. PCT/JP2019/040294 filed on Oct. 11, 2019, the entire disclosure of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention mainly relates to a power receiving apparatus and a battery unit. 
     BACKGROUND ART 
     Patent Literature 1 describes the configuration of an electric work machine (electric tool) in which a plurality of battery units (battery packs) are individually electrically connected. A work machine body includes a plurality of connection portions configured to electrically connect the plurality of battery units. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL1: Japanese Patent Laid-Open No. 2011-161603 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In general, any battery unit may be electrically connected to the plurality of connection portions described above. That is, the battery unit detached from the work machine body can be optionally replaced with another battery unit having a similar configuration. In such a configuration, it is conceivable that a processor configured to control the power feeding function of each battery unit is mounted on the battery unit. In order to achieve the appropriate control of the power feeding function, it may be necessary for the processor to appropriately detect which of the plurality of connection portions the battery unit is electrically connected to. Therefore, a technique for achieving this with a relatively simple configuration is required. 
     An exemplary object of the present invention is to provide a power receiving apparatus and a plurality of battery units electrically connectable to the power receiving apparatus, in which the appropriate control of the power feeding function of each of the battery units is achieved with a relatively simple configuration. 
     Solution to Problem 
     A first aspect of the present invention relates to a power receiving apparatus. The power receiving apparatus is configured to be able to receive electric power from a plurality of battery units each including a processor configured to control a power feeding function. The power receiving apparatus includes a plurality of connection portions capable of electrically connecting the plurality of battery units. The plurality of connection portions are configured such that voltages supplied to the plurality of processors corresponding to the plurality of battery units have different values when the plurality of battery units are electrically connected to the connection portions. 
     Advantageous Effects of Invention 
     The present invention makes it possible to achieve the appropriate control of the power feeding function of each battery unit. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram illustrating a configuration example of an electric work machine. 
         FIG. 2  is a circuit block diagram illustrating a configuration example of a battery unit and a power receiving apparatus. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments will be described in detail with reference to the attached drawings. Note, the following embodiments are not intended to limit the scope of the claimed invention, and limitation is not made to an invention that requires a combination of all features described in the embodiments. Two or more of the multiple features described in the embodiments may be combined as appropriate. Furthermore, the same reference numerals are given to the same or similar configurations, and redundant description thereof is omitted. 
     (Configuration Example of Work Machine) 
       FIG. 1  is a block diagram illustrating a system configuration example of a work machine  1  according to an embodiment. The work machine  1  is an electric work machine (for example, a trowel or a sweeper or the like) that includes a work mechanism  11 , an electric motor  12 , a battery unit  13 , and a power receiving apparatus  14 , to cause the work mechanism  11  to perform predetermined work using the electric power of the battery unit  13 . 
     The work mechanism  11  executes the above-described work based on motive power (rotation) generated by the electric motor  12 . The battery unit  13  is configured to be able to store electric power. In the present embodiment, a plurality of battery units are arranged in parallel. The power receiving apparatus  14  incorporates a power drive unit (PDU) or the like, converts electric power received from the battery unit  13  into a predetermined mode, and supplies the electric power to the electric motor  12 . 
     Here, the electric motor  12  is illustrated as an electric power supply target, but the work machine  1  may further include an electric device such as a display device or a light source device as other electric power supply target. 
     The configuration of the work machine  1  is not limited to the above-described example, and various modifications may be made within a range that does not departing from the gist thereof. The electric motor  12 , the battery unit  13 , and the power receiving apparatus  14  may be unitized separately from the work mechanism  11 , and thus can be used in various applications as an electric power unit PU. 
       FIG. 2  is a circuit block diagram illustrating a system configuration example of the battery unit  13  and the power receiving apparatus  14 . Here, for ease of description, two battery units  13  are arranged in parallel. For distinction, one of them is referred to as “battery unit  13   a ” and the other is referred to as battery unit  13   b″.    
     (Configuration Example of Battery Unit) 
     The battery unit  13   a  includes a battery (battery body)  130   a , a processor  131   a , a communication unit  132   a , a regulator  133   a , a plurality of resistance elements  136   a , R 1   a , and R 2   a , a plurality of switch elements  134   a ,  135   a , and  137   a , and a rectifying element D 1   a . The battery unit  13   a  is configured by unitizing these elements  130   a  and the like, and includes a housing in which terminal groups T 1   a  to T 4   a  configured to electrically connect the battery unit  13   a  to the power receiving apparatus  14  are provided. 
     The battery  130   a  outputs a direct current (DC) voltage of 48 [V] in the present embodiment. The battery  130   a  typically can be configured by connecting a plurality of battery cells in series, but may be configured by a single battery cell. In the figure, a positive electrode-side power supply line of the battery  130   a  is represented by a line VH 13   a , and a negative electrode-side power supply line thereof is represented by a line VL 13   a . The power supply line VL 13   a  is electrically connected to the terminal T 1   a.    
     Although the details of the processor  131   a  will be described later, the processor  131   a  is an electronic component (for example, a semiconductor package) configured to control the power feeding function of the battery  130   a . The processor  131   a  may be a semiconductor device such as an application specific integrated circuit (ASIC) or a programmable logic device (PLD), but may be configured by a central processing unit (CPU) and a memory so as to be able to achieve the same function. That is, the function of the processor  131   a  can be achieved by either hardware or software. 
     The communication unit  132   a  is an electronic component configured to be able to communicate with elements outside the battery unit  13   a  via the terminal T 4   a , and enables external communication of the processor  131   a  by mutual communication with the processor  131   a  as represented by a broken line in the figure. 
     The regulator  133   a  outputs a predetermined voltage (here, 3.3 [V]) to a line VH 13   a ′ based on the voltage (here, 48 [V]) of the power supply line VH 13   a . The resistance elements R 1   a  and R 2   a  are connected in series between the line VH 13   a ′ and a line VH 13   a ″ electrically connected to the terminal T 2   a , and although the details thereof will be described later, voltage division based on the resistance ratio is generated at the node between the resistance elements R 1   a  and R 2   a.    
     In the present embodiment, a metal oxide semiconductor (MOS) transistor is used as the switch element  134   a , and a gate terminal thereof is electrically connected to the node between the resistance elements R 1   a  and R 2   a . A drain terminal is electrically connected to the line VH 13   a ′, and a source terminal is electrically connected to the processor  131   a.    
     The switch element  135   a  and the resistance element  136   a  are connected in series between the power supply line VH 13   a  and a line VH 13   ao  electrically connected to the terminal T 3   a . The switch element  137   a  is connected in parallel to the switch element  135   a  and the resistance element  136   a  connected in series. That is, the voltage (here, 48 [V]) of the power supply line VH 13   a  can be output from the terminal T 3   a  via the switch element  135   a  and the resistance element  136   a  and/or via the switch element  137   a . A known transistor withstanding high voltages may be used for the switch elements  135   a  and  137   a.    
     The rectifying element D 1   a  is disposed such that it includes an anode electrically connected to the line VH 13   a  (terminal T 1   a ) and a cathode electrically connected to the line VH 13   ao  (terminal T 3   a ). 
     As illustrated in  FIG. 2 , the battery unit  13   b  has the same configuration as that of the above-described battery unit  13   a , that is, includes an element  130   b  and the like corresponding to the above-described element  130   a  and the like. In particular, the battery  130   b  is configured similarly to the battery  130   a ; the processor  131   b  is configured similarly to the processor  131   a ; the communication unit  132   b  is configured similarly to the communication unit  132   a ; and the regulator  133   b  is configured similarly to the regulator  133   a . These are disposed. The resistance elements  136   b , Rib, and R 2   b  are configured similarly to the resistance elements  136   a , R 1   a , and R 2   a , respectively, and the switch elements  134   b ,  135   b , and  137   b  are configured similarly to the switch elements  134   a ,  135   a , and  137   a , respectively. These are disposed. Lines VH 13   b , VH 13   bo , VL 13   b , VH 13   b ′, and VH 13   b ″ in the figure correspond to the VH 13   a , the VH 13   ao , the VL 13   a , the VH 13   a ′, and the VH 13   a ″, respectively. A rectifying element D 1   b  is configured and arranged similarly to the rectifying element D 1   a . The battery unit  13   b  includes a housing in which terminal groups Tlb to T 4   b  capable of electrically connecting the battery unit  13   b  to the power receiving apparatus  14  are provided. These terminal groups correspond to the terminal groups T 1   a  to T 4   a.    
     (Configuration Example of Power Receiving Apparatus) 
     The power receiving apparatus  14  includes a capacitor  140 , a control unit  141 , a communication unit  142 , resistance elements R 3   a  and R 3   b , switch elements  143   a  and  143   b , and an activation switch  145 . The power receiving apparatus  14  is configured by unitizing these elements  140  and the like, and includes a housing in which terminal groups T 5   a  to T 8   a  and T 5   b  to T 8   b  configured to electrically connect the battery units  13   a  and  13   b  are provided. The terminal groups T 1   a  to T 4   a  are electrically connected to the terminal groups T 5   a  to T 8   a , respectively, and the terminal groups Tlb to T 4   b  are electrically connected to the terminal groups T 5   b  to T 8   b , respectively. 
     Although the details will be described later, the terminal groups T 5   a  to T 8   a , the resistance element R 3   a , and the switch element  143   a  form a connection portion  144   a  that can electrically connect the battery unit  13   a . The terminal groups T 5   b  to T 8   b , the resistance element R 3   b , and the switch element  143   b  form a connection portion  144   b  that can electrically connect the battery unit  13   b.    
     The capacitor  140  is provided between a line VH 14  electrically connected to the terminal T 7   b  and a line VL 14  electrically connected to the terminal T 5   a , and can hold a voltage received from the battery unit  13   a  (and  13   b ). 
     The control unit  141  controls the entire power receiving apparatus  14 , and can communicate with each of the processors  131   a  and  131   b , for example, although the details will be described later. The function of the control unit  141  can be achieved by either hardware or software similarly to the processor  131   a  and the like. The control unit  141  further has a function as the PDU, and can convert the voltage held by the capacitor  140  into a predetermined mode and supply the converted voltage to the electric motor  12 . 
     The communication unit  142  is an electronic component configured to be able to communicate with the communication units  132   a  and  132   b  via the terminals T 8   a  and T 8   b , respectively, and enables external communication of the control unit  141  by mutual communication with the control unit  141  as represented by a broken line in the figure. Such a connection aspect can also provide mutual communication between the communication units  132   a  and  132   b . This also allows, for example, the processor  131   a  of the battery unit  13   a  to output an instruction signal (or an instruction command) to the processor  131   b  of the battery unit  13   b  to directly control the power feeding function of the battery unit  13   b.    
     The resistance element R 3   a  and the switch element  143   a  are connected in series between the terminals T 5   a  and T 6   a . In the present embodiment, a bipolar transistor is used as the switch element  143   a , and a base terminal can be controlled by the control unit  141 . With such a configuration, the connection portion  144   a  capable of electrically connecting the battery unit  13   a  is formed. For example, when the switch element  143   a  is brought into a conductive state, a predetermined voltage is generated in the line VH 13   a ″. This voltage may be substantially determined by the voltage between the lines VH 13   a ′ and VL 13   a  and the resistance values of the resistance elements R 1   a , R 2   a , and R 3   a.    
     Similarly, the resistance element R 3   b  and the switch element  143   b  are connected in series between the terminals T 5   b  and T 6   b . In the present embodiment, a bipolar transistor is used as the switch element  143   b , and a base terminal can be controlled by the control unit  141 . With such a configuration, the connection portion  144   b  that can electrically connect the battery unit  13   b  is formed. 
     In the present embodiment, the activation switch  145  is connected in parallel to the resistance element R 3   a  and the switch element  143   a  connected in series. In the present embodiment, the activation switch  145  is a press-type switch. That is, the activation switch  145  is in a conductive state while being pressed, and is in a non-conductive state while not being pressed. When the activation switch  145  is pressed (is in a conductive state), a voltage determined by the voltage between the lines VH 13   a ′ and VL 13   a  and the resistance values of the resistance elements R 1   a  and R 2   a  is generated between the lines VH 13   a ″ and VL 13   a.    
     In the present embodiment, the activation switch  145  is described as a part of the power receiving apparatus  1 , but may be provided separately from the apparatus  1 . For example, the activation switch  145  may be externally attached to an electric path (that is, between the connection portion between the terminals T 1   a  and T 5   a  and the connection portion between the terminals T 2   a  and T 6   a ) between the battery unit  13   a  and the connection portion  144   a.    
     With such a configuration, the battery units  13   a  and  13   b  can be electrically connected to the power receiving apparatus  14  (to the connection portions  144   a  and  144   b , respectively). Although the details will be described later, in the present system configuration, the battery units  13   a  and  13   b  are connected in series and electrically connected to the power receiving apparatus  14 . As described above, the battery units  13   a  and  13   b  have the same configurations, whereby they can be replaced with each other, or one or both of them can be replaced with other battery unit (new/charged battery unit) having the same configuration. 
     (Activation Mechanism) 
     In the present system configuration, the power supply lines VL 13   a  and VL 14  (the terminals T 1   a  and T 5   a ) are fixed/grounded to the ground voltage (0 [V]). The voltage described below generally indicates a potential difference generated between two elements (terminal and node and the like), but for ease of description, may indicate a potential difference from this ground voltage. 
     Before the activation (stop state) of the work machine  1 , both the battery units  13   a  and  13   b  and the power feeding apparatus  14  are in a resting state. That is, the processors  131   a  and  131   b , the communication units  132   a  and  132   b , the control unit  141 , and the communication unit  142  are all in a resting state, and the switch elements  135   a ,  137   a ,  143   a ,  135   b ,  137   b , and  143   b , and the activation switch  145  are all in a non-conductive state. 
     The user (the owner of the work machine  1  or the like) presses the activation switch  145  to achieve the activation of the work machine  1 . The activation switch  145  is brought into a conductive state by pressing, whereby the line VH 13   a ″ (terminals T 2   a  and T 6   a ) has the same potential as that of the power supply line VL 13   a  (terminals T 1   a  and T 5   a ). That is, the line VH 13   a ″ (terminals T 2   a  and T 6   a ) is grounded. As a result, voltage division (defined as voltage Vdiv 1 ) based on the voltage (3.3 [V]) between the lines VH 13   a ′ and VL 13   a  and the resistance ratio of the resistance elements R 1   a  and R 2   a , that is, 
         V div1 =VDD×R 2 a /( R 1 a+R 2 a ),  [Expression 1]
         VDD: voltage between lines VH 13   a ′ and VL 13   a  ( 3 . 3  [V]),   R 1   a : resistance value of resistance element R 1   a,      R 2   a : resistance value of resistance element R 2   a,      is generated at the node between the resistance elements R 1   a  and R 2   a.          

     As a result, the voltage Vdiv 1  is applied to the gate terminal of a MOS transistor which is the switch element  134   a , and accordingly, the switch element  134   a  is brought into a conductive state, and a voltage VDD supplied to the drain terminal is supplied to the processor  131   a  via the source terminal. In response, the processor  131   a  is brought into an active state. 
     Then, the processor  131   a  in the active state brings the switch element  135   a  into a conductive state. As a result, the voltage (48 [V]) of the power supply line VH 13   a  is transmitted to the line VH 13   ao  via the resistance element  136   a  and the switch element  135   a , and is output from the battery unit  13   a  via the terminal T 3   a . At substantially the same time (alternatively, at the timing before/after the outputting), the processor  131   a  brings the communication unit  132   a  into an active state. 
     The voltage output from the battery unit  13   a  is transmitted to the line VH 14  via the terminals T 7   a  and T 5   b  of the power receiving apparatus  14 , via the terminal T 1   b , the rectifying element D 1   b , and the terminal T 3   b  of the battery unit  13   b , and via the terminal T 7   b  of the power receiving apparatus  14 . As a result, the capacitor  140  is charged, and the voltage between the lines VH 14  and VL 14  increases with the lapse of time. 
     After a lapse of a predetermined time from the start of charging of the capacitor  140 , the processor  131   a  further brings the switch element  137   a  into a conductive state. At this time, the processor  131   a  may maintain the switch element  135   a  in a conductive state or a non-conductive state. As a result, it is possible to increase the charging speed after the charging is stabilized while suppressing a steep potential difference that may be generated after the start of the charging. 
     When the voltage between the lines VH 14  and VL 14  is sufficiently increased (up to the voltage (48 [V]) of the power supply line VH 13   a ) by charging the capacitor  140 , the control unit  141  is accordingly brought into an active state, and at substantially the same time, the communication unit  142  is also brought into an active state. 
     Then, the control unit  141  in the active state brings the switch elements  143   a  and  143   b  into a conductive state. After the pressing of the activation switch  145  is released, in the battery unit  13   a , voltage division (defined as voltage Vdiv 2 ) based on the voltage between the lines VH 13   a ′ and VL 13   a  and the resistance ratio of the resistance elements R 1   a , R 2   a , and R 3   a  is performed, that is, 
         V div2 =VDD×R 3 a /( R 1 a+R 2 a+R 3 a ),  [Expression 2]
         R 3   a : resistance value of resistance element R 3   a,      is generated between the lines VH  13   a ″ and VL 13   a  by the switch element  143   a  in the conductive state.       

     Meanwhile, in the battery unit  13   b , voltage division (defined as voltage Vdiv 3 ) based on the voltage (3.3 [V]) between the line VH 13   b ′ and the line VL 13   b  and the resistance ratio of the resistance elements Rib, R 2   b , and R 3   b , that is, 
         V div3 =VDD ×( R 2 b+R 3 b )/( R 1 b+R 2 b+R 3 b ),  [Expression 3]
         VDD: voltage between lines VH 13   b ′ and VL 13   b  ( 3 . 3  [V]),   Rlb: resistance value of resistance element Rib,   R 2   b : resistance value of resistance element R 2   b,      R 3   b : resistance value of resistance element R 23 ,   are generated between the node between the resistance elements Rlb and R 2   b  and the line VL 13   b  by the switch element  143   b  in the conductive state.       

     As a result, the voltage Vdiv 3  is applied to the gate terminal of a MOS transistor which is the switch element  134   b , and accordingly, the switch element  134   b  is brought into a conductive state, and a voltage VDD supplied to the drain terminal is supplied to the processor  131   b  via the source terminal. In response, the processor  131   b  is brought into an active state, and at substantially the same time, the communication unit  132   b  is also brought into an active state. 
     Similarly, voltage division (defined as voltage Vdiv 4 ) based on the voltage between the lines VH 13   b ′ and VL 13   b  and the resistance ratio of the resistance elements Rib, R 2   b , and R 3   b , that is, 
         V div4 =VDD×R 3 b /( R 1 b+R 2 b+R 3 b ),  [Expression 4]
         is generated between the lines VH 13   b ″ and VL 13   b.          

     Although the details will be described later, the processor  131   a  can detect the voltage of the line VH 13   a ″, which makes it possible to determine that the battery unit  13   a  is electrically connected to the connection portion  144   a . Similarly, the processor  131   b  can detect the voltage of the line VH 13   b ″, which makes it possible to determine that the battery unit  13   b  is electrically connected to the connection portion  144   b.    
     Then, the processor  131   b  controls the switch elements  135   b  and  137   b  in the same procedure as that of the processor  131   a , and outputs the voltage of the power supply line VH 13   b  connected to the battery  130   b  via the line VH 13   bo . The voltage between the power supply lines VH 13   b  and VL 13   b  is 48 [V]. 
     As can be seen from  FIG. 2 , the battery units  13   a  and  13   b  are connected in series and electrically connected to the power receiving apparatus  14 . Therefore, a voltage (total 96 [V]) obtained by adding the output voltage (48 [V]) of the battery  130   b  to the output voltage (48 [V]) of the battery  130   a  is supplied to the power receiving apparatus  14 . As described above, the work machine  1  can be brought into an operating state. 
     In order to bring the work machine  1  in the operating state into a resting state again, the activation switch  145  may be pressed again. When the activation switch  145  is pressed again, the processor  131   a  detects that the line VH 13   a ″ is grounded to bring the battery unit  13   a  into a resting state. Prior to this, the processor  131   a  can also output an instruction signal for instructing the battery unit  13   b  and the power receiving apparatus  14  to be brought into a stop state by external communication via the communication unit  132   a.    
     When the battery unit  13   a  and/or  13   b  are/is removed while the work machine  1  is in an operating state, mutual communication via the corresponding communication unit  132   a  and/or  132   b  is interrupted. At substantially the same time, the voltage (the voltage between the lines VH 13   a ″ and VL 13   a  and/or the voltage between the lines VH 13   b ″ and VL 13   b ) supplied to the processor  131   a  and/or  131   b  is 3.3 [V], whereby the processor  131   a  and/or  131   b  can detect that the battery unit  13   a  and/or  13   b  are/is removed. The voltage of the terminal T 6   a  and/or T 6   b  is a floating state in the power receiving apparatus  14 , whereby the control unit  141  can detect that the removal is performed. 
     That is, both the processors  131   a  and  131   b  and the control unit  141  can detect that the removal is performed based on the communication result by the communication unit  132   a  or the like and the voltage supplied to the processor  131   a  or the like. As a result, for example, when the battery unit  13   a  ( 13   b ) is removed, the processor  131   b  ( 131   a ) can bring the battery unit  13   b  ( 13   a ) into a resting state by itself, and the control unit  141  can bring the power receiving apparatus  14  into a resting state by itself. 
     By referring to the communication results among the communication units  132   a ,  132   b , and  142 , in the case where the mutual communication is interrupted even though the battery unit  13   a  and/or  13   b  are/is not removed, this can be detected. For example, when the battery units  13   a  and  13   b  are not removed, the voltage supplied to the processors  131   a  and  131   b  and the voltage received by the power receiving apparatus  14  (the voltage of the terminals T 6   a  and T 6   b ) do not fluctuate (the value when the work machine  1  is in an operating state remains). Nevertheless, when a desired communication result cannot be obtained, the mutual communication can be said to be interrupted, whereby the processors  131   a  and  131   b  and the control unit  141  can detect that an unpredicted communication failure is generated among the communication units  132   a ,  132   b , and  142 . 
     Alternatively, in the case where the mutual communication is not interrupted even though the battery unit  13   a  and/or  13   b  are/is removed, this can be detected. As described above, when the battery unit  13   a  and/or  13   b  are/is removed, the voltage supplied to the processor  131   a  and/or  131   b  is 3.3 [V], and the voltage of the terminal T 6   a  and/or T 6   b  is in a floating state in the power receiving apparatus  14 . Nevertheless, when the mutual communication is continued, an unpredicted operation can be said to occur in the power receiving apparatus  14 , and the processors  131   a  and  131   b  and the control unit  141  can detect this. 
     It is sufficient that whether or not the battery units  13   a  and/or  13   b  are/is appropriately electrically connected can be detected on the side of the processors  131   a  and  131   b  and the control unit  141 , and the above-described removal includes removal not intended by the user, such as a contact failure. 
     (Control of Power Feeding Function by Processor) 
     As described above, the communication units  132   a  and  132   b  and the communication unit  142  enable mutual communication between the processors  131   a  and  131   b  and the control unit  141 . As a result, for example, based on a load situation or the like applied to the battery unit  13   a  and/or  13   b , it is possible to control the power feeding function thereof by itself/themselves. 
     Meanwhile, in the present system configuration, the power supply lines VL 13   a  and VL 14  (the terminals T 1   a  and T 5   a ) are fixed to the ground voltage. In contrast, in the present system configuration, the power supply line VL 13   b  associated as the ground line in the battery unit  13   b  has a voltage (48 [V] in the present embodiment) higher than the ground voltage when the work machine  1  is used (in the operating state of the work machine  1 ). 
     In general, in a system in which a plurality of power supply systems are present, a system configuration is made on the basis of the ground voltage or a voltage closest thereto in order to ensure operation stability on the system. This similarly applies to the present system configuration, and for example, even if the battery unit  13   b  is an active state while the battery unit  13   a  is in a resting state, the circuit constituting the battery unit  13   b  is not appropriately operated. Therefore, for example, a superior-subordinate relationship such as master/slave (parent/child) may be provided between the processors  131   a  and  131   b  and the control unit  141 , and priority may be incidentally set to these instruction signals. 
     As an example, a case where the control unit  141  is set as the master and the processors  131   a  and  131   b  are set as the slave will be considered. For example, it may be necessary to bring the battery unit  13   a  into a resting state while the work machine  1  is in an operating state. In this case, the processor  131   a  can output a resting instruction to the battery unit  13   b  (processor  131   b ) and the power receiving apparatus  14  (control unit  141 ) before bringing the battery unit  13   a  into a resting state. By setting this resting instruction to have higher priority than that of mutual communication between the battery unit  13   b  and the power receiving apparatus  14 , both the processors  131   a  and  131   b  and the control unit  141  can be appropriately brought into a resting state (for example, in a predetermined order). 
     As other example, it is also possible to set the processor  131   a  as the master and the processor  131   b  and the control unit  141  as the slave, and in this case, the same can be achieved. 
     In short, in the present system configuration, the battery units  13   a  and  13   b  include the processors  131   a  and  131   b  that can control the power feeding function by themselves, respectively, and perform mutual communication with the power receiving apparatus  14  (control unit  141 ). Meanwhile, in order to secure operation stability on the system, it may be required to provide a superior-subordinate relationship between the processors  131   a  and  131   b  and the control unit  141 , and to provide priority to the instruction systems. 
     Here, as described above, the battery units  13   a  and  13   b  have the same configurations, and may be electrically connected to any of the connection portions  144   a  and  144   b . Therefore, in order to be able to set the priority of the superior-subordinate relationship and the instruction system described above, the processor  131   a  ( 131   b ) is required to be able to determine by itself which of the connection portions  144   a  and  144   b  the battery unit  13   a  ( 13   b ) is electrically connected to. This is preferably achieved with a relatively simple configuration without unnecessarily increasing the number of terminals or complicating the structures of the connection portions  144   a  and  144   b.    
     Therefore, in the present embodiment, the resistance elements R 3   a  and R 3   b  are provided so that their resistance values are different from each other. The battery units  13   a  and  13   b  have the same configurations, whereby the resistance elements R 1   a  and Rlb have the same resistance values, and the resistance elements R 2   a  and R 2   b  have the same resistance values. That is, 
         R 1 a=R 1 b,    
         R 2 a=R 2 b , and 
         R 3 a≠R 3 b   [Expression 5]
         are set.       

     As described above (see [Expression 2] and [Expression 4]), the voltage Vdiv 2  applied between the lines VH 13   a ″ and VL 13   a  is 
         V div2 =VDD×R 3 a /( R 1 a+R 2 a+R 3 a ),         and the voltage Vdiv 4  applied between the lines VH 13   b ″ and VL 13   b  is       
       V div4 =VDD×R 3 b /( R 1 b+R 2 b+R 3 b ). According to the above [Expression 5], 
         V div2 ≠V div4,         is set.       
     Therefore, the processor  131   a  ( 131   b ) can determine which of the connection portions  144   a  and  144   b  the battery unit  13   a  ( 13   b ) is electrically connected to, when the line VH 13   a ″ (VH 13   b ″) detects any of the voltages Vdiv 2  and Vdiv 4 . In the present system configuration, the processor  131   a  detects the voltage Vdiv 2  of the line VH 13   a ″, whereby the processor  131   a  can determine that the battery unit  13   a  is electrically connected to the connection portion  144   a . The processor  131   b  detects the voltage Vdiv 4  of the line VH 13   b ″, whereby the processor  131   b  can determine that the battery unit  13   b  is electrically connected to the connection portion  144   b.    
     Therefore, according to the present embodiment, the control of the individual power feeding functions of the battery units  13   a  and  13   b  can be appropriately achieved while the operation stability on the system is secured. This is realized by the configurations of the connection portions  144   a  and  144   b  while the battery units  13   a  and  13   b  have the same configurations. In the present embodiment, the connection portions  144   a  and  144   b  include resistance elements R 3   a  and R 3   b  configured to be able to receive a DC voltage from the battery units  13   a  and  13   b , respectively, and allowing a current corresponding to the DC voltage to flow. The resistance elements R 3   a  and R 3   b  have resistance values different from each other, whereby, as a result, the voltages supplied to the processors  131   a  and  131   b  can be made different from each other. Therefore, the above can be said to be achievable with a relatively simple configuration. As other embodiment, alternatively/incidentally, the switch elements  143   a  and  143   b  may be configured to have on-resistances different from each other, whereby the same can be achieved. 
     In order to ensure the operation stability on the system, the activation switch  145  may be provided at the ground voltage or a power supply system closest thereto. In the present embodiment, the activation switch  145  is provided for the connection portion  144   a  located on the ground voltage side among the connection portions  144   a  and  144   b . As a result, an unpredicted voltage is not applied to the processor  131   a  at the time of activation. Therefore, according to the present embodiment, the control of the individual power feeding functions of the battery units  13   a  and  13   b  can be said to be more appropriately achievable. 
     In the present embodiment, the number of the battery units  13  is 2, but the contents of the embodiment can also be applied to a case where the number of the battery units  13  is 3 or more. In the present embodiment, the aspect in which the plurality of battery units  13  are electrically connected to the power receiving apparatus  14  in series connection has been exemplified, but the contents of the embodiment can also be applied to a case where the connection aspect thereof is parallel connection. 
     As described above, according to the present embodiment, each of the plurality of (two in the embodiment) battery units  13   a  and  13   b  includes the processors  131   a  and  131   b  configured to control the power feeding function. The power receiving apparatus  14  includes a plurality of (two in the embodiment) connection portions  144   a  and  144   b  that can electrically connect the battery units  13   a  and  13   b , respectively. The connection portions  144   a  and  144   b  are configured such that voltages supplied to the corresponding processors  131   a  and  131   b  have different values when the battery units  13   a  and  13   b  are electrically connected to the connection portions. This can be appropriately achieved, for example, by configuring the resistance elements R 3   a  and R 3   b  with resistance values different from each other. According to the present embodiment, the processor  131   a  ( 131   b ) can detect which of the connection portions  144   a  and  144   b  the battery unit  13   a  ( 13   b ) is electrically connected to. As a result, the processor  131   a  ( 131   b ) can appropriately control the power feeding function according to the electrically-connected connection portion  144   a  or  144   b.    
     In the above description, each element has been given a name related to its functional aspect for ease of understanding. Meanwhile, each element is not limited to one having, as a main function, the function described in the embodiment, and may be one having the function as an auxiliary function. 
     Summary of Embodiment 
     The features of the embodiment can be summarized as follows. 
     A first aspect relates to a power receiving apparatus (for example, 14). The power receiving apparatus is configured to be able to receive electric power from a plurality of battery units (for example.  13   a ,  13   b ) each including a processor (for example,  131   a ,  131   b ) configured to control a power feeding function. The power receiving apparatus includes a plurality of connection portions (for example,  144   a ,  144   b ) capable of electrically connecting the plurality of battery units. The plurality of connection portions are configured such that voltages supplied to the plurality of processors of the plurality of battery units have different values when the plurality of battery units are electrically connected to the connection portions. 
     According to such a configuration, in each battery unit, the processor can detect which of the plurality of connection portions the battery unit is electrically connected to, and can appropriately control a power feeding function according to the connection portion. 
     In a second aspect, each of the plurality of connection portions includes a resistance element (for example. R 3   a , R 3   b ) configured to be capable of receiving a DC voltage (for example, 48 [V]) from a corresponding battery unit and causing a current corresponding to the DC voltage to flow, and resistance values of the resistance elements are different from each other among the plurality of connection portions. 
     Such a configuration can relatively easily achieve the first aspect. 
     In a third aspect, the power receiving apparatus further includes a communication unit (for example,  142 ) configured to communicate with the plurality of processors, and a control unit (for example,  141 ) configured to individually control the plurality of processors via the communication unit. 
     Such a configuration makes it possible to individually control the power feeding function of each battery unit. 
     In a fourth aspect, the communication unit further enables the plurality of processors to communicate with each other, to allow at least one (for example,  131   a ) of the plurality of processors to control another processor (for example,  131   b ). 
     Such a configuration also makes it possible to cause a certain battery unit to control the power feeding function of the other battery unit. 
     In a fifth aspect, the communication unit allows the at least one processor to control the other processor based on the voltage supplied by a corresponding connection portion. 
     Such a configuration makes it possible to appropriately achieve the fourth aspect. 
     In a sixth aspect, the control unit determines whether or not the plurality of battery units are appropriately electrically connected in the plurality of connection portions, based on a communication result by the communication unit and a voltage supplied to the plurality of processors. 
     Such a configuration makes it possible to individually determine whether or not the electrical connection of the battery unit is appropriately performed. 
     In a seventh aspect, the plurality of connection portions are configured such that when the plurality of battery units are electrically connected to the plurality of connection portions, the plurality of battery units are connected in series. 
     Such a configuration makes it possible to supply a relatively large voltage to the power receiving apparatus. 
     In an eighth aspect, when a battery unit closest to a ground voltage among the plurality of battery units is defined as a first battery unit (for example,  13   a ), and a connection portion corresponding to the first battery unit among the plurality of connection portions is defined as a first connection portion (for example,  144   a ), the power receiving apparatus further includes an activation switch (for example,  145 ) provided for the first connection portion and configured to activate the processor of the first battery unit. 
     According to such a configuration, when the processor is activated, an unpredicted voltage is not applied to the processor. 
     A ninth aspect relates to an electric power unit (for example, PU). The electric power unit includes: the power receiving apparatus (for example,  14 ); and an electric motor (for example,  12 ) that generates motive power based on electric power received from the plurality of battery units by the power receiving apparatus. 
     That is, the power receiving apparatus described above can be applied to a known electric power unit. 
     A tenth aspect relates to a work machine (for example,  1 ). The work machine includes: the electric power unit (for example, PU); and a work mechanism (for example,  11 ) capable of executing work based on the motive power of the electric motor. 
     That is, the above-described electric power unit can be applied to a known work machine. 
     A 11th aspect relates to a battery unit (for example,  13   a ). The battery unit is configured to be electrically connectable to any of a plurality of connection portions (for example,  144   a ,  144   b ) included in a power receiving apparatus (for example,  14 ). The plurality of connection portions are configured such that voltages supplied to a plurality of battery units have different values when the plurality of battery units are electrically connected to the connection portions. The battery unit includes a processor (for example,  131   a ) capable of controlling a power feeding function based on a voltage supplied by a connection portion to which the battery unit is electrically connected. 
     According to such a configuration, in each battery unit, the processor can detect which of the plurality of connection portions the battery unit is electrically connected to, and can appropriately control a power feeding function according to the connection portion. 
     In a 12th aspect, each of the plurality of connection portions includes a resistance element (for example, R 3   a , R 3   b ) configured to be capable of receiving a DC voltage (for example,  48  [V]) from a corresponding battery unit and causing a current corresponding to the DC voltage to flow. Resistance values of the resistance elements are different from each other among the plurality of connection portions. The battery unit is configured to be capable of outputting the DC voltage. 
     Such a configuration can relatively easily achieve the first aspect. 
     In a 13th aspect, the battery unit further includes a communication unit (for example,  132   a ) configured to communicate with the power receiving apparatus via the connection portion. 
     Such a configuration makes it possible to individually control the power feeding function of each battery unit. 
     In a 14th aspect, the communication unit is further configured to be communicable with another battery unit (for example,  13   b ), to allow the processor to control another processor (for example,  131   b ) included in the other battery unit. 
     Such a configuration also makes it possible to cause a certain battery unit to control the power feeding function of the other battery unit. 
     In a 15th aspect, the communication unit allows the processor to control the other processor based on the voltage supplied by the connection portion. 
     Such a configuration makes it possible to appropriately achieve the 14th aspect. 
     In a 16th aspect, the battery unit and the other battery unit are connected in series when each of the battery unit and the other battery unit is electrically connected to the corresponding connection portion. 
     Such a configuration makes it possible to supply a relatively large voltage to the power receiving apparatus. 
     A 17th aspect relates to an electric power unit (for example, PU). The electric power unit includes: the battery unit (for example,  13   a ); the power receiving apparatus; and an electric motor (for example, 12) that generates motive power based on electric power received from the battery unit. 
     That is, the above-described battery unit can be applied to a known electric power unit. 
     A 18th aspect relates to a work machine. The work machine includes: the electric power unit (for example, PU); and a work mechanism (for example, 11) capable of executing work based on the motive power of the electric motor. 
     That is, the above-described electric power unit can be applied to a known work machine. 
     The invention is not limited to the foregoing embodiments, and various variations/changes are possible within the spirit of the invention.