Patent Publication Number: US-2021184491-A1

Title: Power supply system

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of U.S. application Ser. No. 16/255,066 filed Jan. 23, 2019, which is based on and claims priority under 35 U.S.C. 119 from Japanese Patent Application No. 2018-026154 filed on Feb. 16, 2018. The contents of the above applications are incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     The disclosure relates to a power supply system. 
     2. Description of Related Art 
     Japanese Unexamined Patent Application Publication No. 2004-328988 (JP 2004-328988 A) discloses a power supply system for a vehicle in which a power supply is redundantly constituted using a main battery and a sub-battery. In such a power supply system, redundancy of a power supply is secured by connecting the main battery directly to a load mounted in the vehicle and connecting the sub-battery to a load mounted in the vehicle via a DC-DC converter or a relay switch. 
     SUMMARY 
     When a sub-battery is used as a backup power supply for an important load in automatic driving, a state of a sub-battery may be diagnosed to maintain the state of the sub-battery in a predetermined state which is required for a backup power supply. However, in the power supply system described in JP 2004-328988 A, since the sub-battery is normally connected to a load via one of a DC-DC converter and a relay switch, there may be a case in which it is not easy to diagnose a state of the sub-battery alone and to maintain a predetermined state. 
     The disclosure provides a power supply system that can easily diagnose a state of a predetermined battery alone and maintain a predetermined state. 
     An aspect of the disclosure provides a power supply system including: a first battery connected to a first load; a second battery; a DC-DC converter connecting the first battery and the second battery; and a connection switching unit including a first switch configured to connect the first battery to a second load and a second switch configured to connect the second battery to the second load. The connection switching unit is configured to switch selectively to a first mode in which the first switch is closed and the second switch is opened and a second mode in which the first switch is opened and the second switch is closed. 
     In the power supply system according to the aspect, when the first switch is closed to supply electric power directly from the first battery to the second load, the second switch is opened to disconnect the second battery from the second load (the first mode). Accordingly, by charging and discharging control using the DC-DC converter, it is possible to easily diagnose a state of the second battery alone and to easily maintain a predetermined state. In the first mode, since it is not necessary to supply electric power to the second load and only state diagnosis and state maintenance of the second battery have to be performed, the DC-DC converter can curb power consumption. On the other hand, when the first switch is opened to disconnect the first battery from the second load, the second switch is closed to connect the second battery to the second load (the second mode). Accordingly, even when the first battery malfunctions, it is possible to supply electric power from the second battery to the second load. 
     In the above aspect, the connection switching unit may be configured to switch states of the first switch and the second switch after controlling a voltage difference between a primary side and a secondary side of the DC-DC converter such that the voltage difference becomes equal to or less than a predetermined value. 
     Since the voltage difference between the primary side and the secondary side of the DC-DC converter can be decreased by this control, it is possible to curb fluctuation of a voltage when a mode is switched. It is possible to quickly switch a mode. 
     In the above aspect, the power supply system may be mounted in a vehicle, and the connection switching unit may be configured to switch to the first mode when the vehicle is in a manual driving mode and to switch to the second mode when the vehicle is in an automatic driving mode. 
     In the above aspect, the connection switching unit may be configured to perform a diagnosis of a state of charge of the second battery by causing the second battery to discharge electric power to a first battery side via the DC-DC converter. 
     In the above configuration, the connection switching unit may be configured to perform the diagnosis at predetermined time intervals in the first mode. 
     In the above configuration, the connection switching unit may be configured to charge the second battery via the DC-DC converter when it is determined as a result of the diagnosis that the state of charge of the second battery is less than a predetermined state of charge. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
         FIG. 1  is a diagram schematically illustrating a configuration of a power supply system according to an embodiment of the disclosure; 
         FIG. 2  is a diagram illustrating an example of a configuration of a DC-DC converter; 
         FIG. 3  is a flowchart illustrating mode switching control which is performed by a connection switching unit; 
         FIG. 4  is a diagram illustrating states of first and second switches in a manual driving mode; and 
         FIG. 5  is a diagram illustrating states of first and second switches in an automatic driving mode. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Outline 
     In a power supply system redundantly including a plurality of batteries according to the disclosure, a sub-battery is disconnected from a load in a normal state in which electric power is supplied from a main battery to the load. Accordingly, it is possible to easily diagnose a state of a sub-battery alone and to easily maintain a predetermined state. 
     Configuration of Power Supply System 
       FIG. 1  is a diagram schematically illustrating a configuration of a power supply system  1  according to an embodiment of the disclosure. The power supply system  1  illustrated in  FIG. 1  includes a first battery  11 , a second battery  12 , a first load  21 , a second load  22 , a connection switching unit  30 , and a power generator  40 . 
     The first battery  11 , the first load  21 , the connection switching unit  30 , and the power generator  40  are connected to a first electric wire  51 . The second battery  12  and the connection switching unit  30  are connected to a second electric wire  52 . The second load  22  and the connection switching unit  30  are connected to a third electric wire  53 . 
     The power supply system  1  according to this embodiment can be mounted in a facility requiring a redundant power supply configuration. In the following embodiment, it is assumed that the power supply system  1  is mounted in a vehicle which is switchable between a manual driving mode and an automatic driving mode. 
     The power generator  40  is a device that can output predetermined electric power such as an alternator or a DC-DC converter. Electric power output from the power generator  40  is supplied to the first battery  11 , the first load  21 , or the like. 
     The first battery  11  is a power storage element which is configured to be chargeable and dischargeable such as a lead storage battery or a lithium-ion battery. The first battery  11  stores electric power output from the power generator  40  or discharges electric power stored therein to the first load  21  and the connection switching unit  30 . The first battery  11  is provided as a main battery which is used for traveling of the vehicle. A capacitor may be used instead of the battery. 
     The second battery  12  is a power storage element which is configured to be chargeable and dischargeable such as a lead storage battery or a lithium-ion battery. The second battery  12  stores electric power output from the power generator  40  or electric power supplied from the first battery  11  via the connection switching unit  30  or discharges (supplies) electric power stored therein to the second load  22  or the like via the connection switching unit  30 . The second battery  12  is redundantly provided as a sub-battery for backing up the first battery  11 . 
     The first load  21  is an onboard device that consumes electric power. The first load  21  is configured to operate with electric power output from the power generator  40  and/or electric power stored in the first battery  11 . 
     The second load  22  is an onboard device that consumes electric power and can be set as a device associated with safe traveling of a vehicle. More specifically, the second load  22  is an important load that requires supply of electric power based on a predetermined current for a predetermined period from the second battery  12  even when supply of electric power using the first battery  11  malfunctions, and can be set as, for example, a load that takes charge of an important function of allowing the vehicle to safely run in a limp-home mode in an emergency in automatic driving. As will be described later, the second load  22  is configured to operate with electric power output from the power generator  40  and/or electric power stored in the first battery  11  at the time of manual driving and to operate with electric power stored in the first battery  11  and/or electric power stored in the second battery  12  at the time of automatic driving. 
     The connection switching unit  30  includes a first switch  31 , a second switch  32 , and a DC-DC converter  33 . These elements are controlled by a control unit such as a microcomputer which is not illustrated. 
     The first switch  31  is disposed between the first electric wire  51  and the third electric wire  53 , and is configured to be opened and closed based on a driving mode of a vehicle. The first switch  31  is closed to connect the first electric wire  51  and the third electric wire  53  when the vehicle is in a manual driving mode, and is opened to disconnect the third electric wire  53  from the first electric wire  51  when the vehicle is in an automatic driving mode. For example, a normally-ON type semiconductor relay or an excitation type mechanical relay can be used as the first switch  31 . 
     The second switch  32  is disposed between the second electric wire  52  and the third electric wire  53  and is configured to be opened and closed based on the driving mode of the vehicle. The second switch  32  is closed to connect the second electric wire  52  and the third electric wire  53  when the vehicle is in the automatic driving mode, and is opened to disconnect the third electric wire  53  from the second electric wire  52  when the vehicle is in the manual driving mode. For example, a normally-OFF type semiconductor relay or an excitation type mechanical relay can be used as the second switch  32 . 
     The DC-DC converter  33  is a voltage converter that converts an input voltage into a predetermined voltage and outputs the predetermined voltage. A primary side of the DC-DC converter  33  is connected to the first electric wire  51  and a secondary side thereof is connected to the second electric wire  52 . The DC-DC converter  33  can be, for example, a bidirectional step-up/down type DC-DC converter having a step-down function of stepping down a primary-side voltage and outputting the stepped-down voltage to the secondary side and a step-up function of stepping up a secondary-side voltage and outputting the stepped-up voltage to the primary side. 
     An example of the bidirectional step-up/down type DC-DC converter is illustrated in  FIG. 2 . In the DC-DC converter illustrated in  FIG. 2 , a switching element M 1 , an inductor L, and a switching element M 3  which are connected in series are interposed between a primary-side terminal and a secondary-side terminal. A node between the switching element M 1  and the inductor L is grounded via a switching element M 2 , and a node between the inductor L and the switching element M 3  is grounded via a switching element M 4 . Smoothing capacitors C 1  and C 2  which are grounded are connected to the primary-side terminal and the secondary-side terminal. For example, a metal oxide semiconductor field effect transistor (MOSFET) can be used as the switching elements M 1  to M 4 . Gate voltages of the switching elements M 1  to M 4  are controlled by a control unit which is not illustrated and the switching elements are turned on and off 
     Control Performed by Power Supply System 
     Control which is performed by the power supply system  1  according to this embodiment will be described below with reference to  FIGS. 3 to 5 .  FIG. 3  is a flowchart illustrating a process routine of mode switching control which is performed by the connection switching unit  30 .  FIG. 4  is a diagram illustrating the states of the first switch  31  and the second switch  32  in the manual driving mode.  FIG. 5  is a diagram illustrating the states of the first switch  31  and the second switch  32  in the automatic driving mode. 
     The control illustrated in  FIG. 3  is started when a power supply of the vehicle is turned on and is repeatedly performed until the power supply is turned off. It is assumed that the manual driving mode is set in an initial state of the vehicle immediately after the power supply is turned on. 
     Step S 301 : The connection switching unit  30  closes the first switch  31  and opens the second switch  32  to set the power supply system  1  to the “manual driving mode ( FIG. 4 ).” When the manual driving mode is set, the process routine transitions to Step S 302 . 
     In the manual driving mode, since electric power can be supplied from the first battery  11  to the second load  22  without passing through the DC-DC converter  33  (a solid arrow in  FIG. 4 ), power consumption in the DC-DC converter  33  can be curbed. Since the second battery  12  is disconnected from the second load  22  and a current does not flow from the second battery  12  to the second load  22 , discharging of the second battery  12  can be curbed. Since the second battery  12  is connected to the first battery  11  and the power generator  40  via the DC-DC converter  33 , the second battery  12  can be charged with electric power from the first battery  11  or electric power from the power generator  40 . Since the DC-DC converter  33  is of a bidirectional type, electric power can be discharged from the second battery  12  (the second electric wire  52  side) to the first battery  11  or the like (the first electric wire  51  side). 
     Step S 302 : The connection switching unit  30  diagnoses the state of the second battery  12 . This diagnosis is performed, for example, by determining whether the second battery  12  is in a predetermined state at predetermined time intervals. That is, the connection switching unit  30  may be configured to automatically determine whether the second battery  12  is in a predetermined state at predetermined time intervals. The predetermined state refers to, for example, a state in which the second battery  12  is storing electric power with which the second battery  12  can output a prescribed current value continuously for a prescribed time. Whether the second battery is in the predetermined state is determined based on a state of charge (SOC) or an internal resistance value of the second battery  12 . This diagnosis can be performed, for example, based on change in a voltage value and a current value when electric power is discharged from the second battery  12  to the first electric wire  51  via the DC-DC converter  33  (a dotted arrow in  FIG. 4 ). The process routine transitions to Step S 304  when the second battery  12  is in the predetermined state (OK in S 302 ), and the process routine transitions to Step S 303  when the second battery  12  is not in the predetermined state (NG in S 302 ). 
     Step S 303 : The connection switching unit  30  performs a predetermined recovery process such that the second battery  12  is brought into the predetermined state. Examples of the recovery process include a process of charging the second battery  12  with electric power from the first battery  11  or the like via the DC-DC converter  33  when the state of charge of the second battery  12  is less than a predetermined state of charge and a process of discharging electric power from the second battery  12  to the first electric wire  51  via the DC-DC converter  33  when the state of charge of the second battery  12  is greater than the predetermined state of charge (a dotted arrow in  FIG. 4 ). When the recovery process is performed, the process routine transitions to Step S 304 . 
     Step S 304 : The connection switching unit  30  determines whether the vehicle has been switched from manual driving to automatic driving. The process routine returns to Step S 302  when the vehicle has not been switched to automatic driving and is maintained in manual driving (NO in S 304 ), and the process routine transitions to Step S 305  when the vehicle has been switched from manual driving to automatic driving (YES in S 304 ). 
     The determination of Step S 304  may be performed in parallel to the processes of Steps S 302  and S 303 , and Step S 305  is preferably performed after recovery of the second battery  12  in Step S 303  has been completed. 
     Step S 305 : The connection switching unit  30  opens the first switch  31  and closes the second switch  32  to set the power supply system  1  to the “automatic driving mode ( FIG. 5 ).” When the automatic driving mode is set, the process routine transitions to Step S 306 . 
     In the automatic driving mode, electric power is supplied from the first battery  11  to the second load  22  via the DC-DC converter  33  and electric power is also supplied from the second battery  12  (a solid arrow in  FIG. 5 ). Accordingly, for example, in an emergency in which the first battery  11  malfunctions, the second battery  12  is not easily affected by the malfunction due to the operation of the DC-DC converter  33  and thus supply of electric power from the second battery  12  to the second load  22  can be backed up. 
     Reasons why the second battery  12  is not easily affected even when the first battery  11  malfunctions will be described below with reference to  FIG. 2 . When the primary-side voltage of the DC-DC converter  33  connected to the first battery  11  becomes lower than the secondary-side voltage connected to the second battery  12 , a step-up operation of allowing a current to flow from the primary side to the secondary side (charging of the inductor L with energy due to turning-on of the switching elements M 1  and M 4  and discharging of energy from the inductor L due to turning-off of the switching element M 4  and turning-on of the switching element M 3 ) is performed by a control unit which his not illustrated. Accordingly, a current is not discharged from the second battery  12  via the DC-DC converter  33 . When a voltage drop of the primary side of the DC-DC converter  33  progresses further, a control unit which is not illustrated stops operation of the DC-DC converter  33  (turns off all the switching elements M 1  to M 4 ) and thus a current is not discharged from the second battery  12  via the DC-DC converter  33 . In this way, electric power of the second battery  12  is maintained. 
     Step S 306 : The connection switching unit  30  determines whether the vehicle has been switched from automatic driving to manual driving. The determination of Step S 306  is continuously performed when the vehicle has not been switched to manual driving and is maintained in automatic driving (NO in S 306 ), and the process routine returns to Step S 301  when the vehicle has been switched from automatic driving to manual driving (YES in S 306 ). 
     When a driving mode is switched, it is preferable that one battery be charged or discharged such that a voltage difference between the primary side and the secondary side of the DC-DC converter  33  is less than a predetermined value as much as possible in order to curb an influence of a voltage change. Here, when a current is discharged from the secondary side to the primary side of the DC-DC converter  33 , there is concern that a source voltage of the first electric wire  51  will become higher than an output voltage of the power generator  40  and will exceed the rated voltage of the first load  21 . In order to prevent this likelihood, it is useful to decrease the output voltage of the power generator  40  in advance when a current is discharged from the secondary side to the primary side of the DC-DC converter  33 . 
     Operations and Advantages in Embodiment 
     With the power supply system  1  according to the embodiment of the disclosure, the connection switching unit  30  closes the first switch  31  to supply electric power from the first battery  11  to the second load  22  and opens the second switch  32  to disconnect the second battery  12  from the second load  22  in the manual driving mode (the first mode). 
     Accordingly, in the manual driving mode, it is possible to easily diagnose the state of the second battery  12  for backup in automatic driving by charging and discharging control using the DC-DC converter  33  alone and to easily maintain the state in which electric power can be supplied with a predetermined current for a predetermined period. In the manual driving mode, the DC-DC converter  33  does not need to supply electric power to the second load  22  and has only to perform state diagnosis and state maintenance of the second battery  12  and thus can reduce power consumption. 
     With the power supply system  1  according to the embodiment, when the connection switching unit  30  opens the first switch  31  to disconnect the first battery  11  from the second load  22  in the automatic driving mode (the second mode), the connection switching unit  30  closes the second switch  32  to connect the second battery  12  to the second load  22 . 
     Accordingly, in the automatic driving mode, it is possible to supply electric power from the second battery  12  to the second load  22  even when the first battery  11  malfunctions. 
     With the power supply system  1  according to the embodiment, the connection switching unit  30  switches the states of the first switch  31  and the second switch  32  after performing control such that the voltage difference between the primary side and the secondary side of the DC-DC converter  33  is equal to or less than a predetermined value. Accordingly, since the voltage difference between the primary side and the secondary side of the DC-DC converter  33  can be decreased, it is possible to curb occurrence of a voltage change when the driving mode is switched. It is possible to quickly switch the driving mode. 
     When the power supply of the vehicle is turned off, it is preferable that the manual driving mode in which the first switch  31  illustrated in  FIG. 4  is closed and the second switch  32  is open be set such that a standby current flowing in the second load  22  is supplied from the first battery  11 . 
     In the embodiment, the bidirectional step-up/down type DC-DC converter  33  is used, but a DC-DC converter not the “bidirectional” type may be used. 
     The power supply system according to the disclosure is applicable to a vehicle which redundantly includes a plurality of batteries.