Abstract:
In the present invention, the connection between an external power supply and a unit for detecting welding of a relay is disestablished at least when a short circuit is detected, thereby preventing the short circuit from being falsely detected in the event that the short circuit and the welding of the relay can both be detected. A device for detecting welding of a relay detects welding of a relay provided to a path via which a cell is charged by an external power supply. Welding of a power-supply-side relay or a ground-side relay is detected on the basis of a current flowing disproportionately more toward the external power supply than the power-supply-side relay or ground-side relay when a control unit has deactivated the power-supply-side relay or ground-side relay during an interrupting in charging. A disconnecting switch establishes or disestablishes the connection between the external power supply and a weld-detection switch.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a relay welding detection apparatus that detects welding of a relay provided to a charging path extending from an external power supply to a storage battery. 
       BACKGROUND ART 
       [0002]    In a charging circuit of an electric vehicle, a relay circuit for connecting and disconnecting a quick charger to and from a junction circuit for connecting a storage battery during charging has been used heretofore. Such a relay circuit includes mechanical relay contacts (hereinafter, referred to as “relay”) used therein, and such a relay is sometimes welded due to an on-off operation during application of a high voltage and high current. Relay welding detection circuits for detecting this kind of welding of a relay are known (e.g., see Patent Literature (hereinafter, referred to as “PTL”) 1). 
         [0003]    In PTL 1, a dead front relay (DFR) is provided between a charging inlet and a neutral point of a motor, and in addition, a voltage sensor is provided between the charging inlet and DFR. In PTL 1, one DFR is turned on while the other DFR is turned off, and when the voltage sensor detects a voltage, it is determined that the DFR that has been turned off is welded. 
         [0004]    Moreover, detection of electrical leakage on a vehicle side using a charger has been known, heretofore (PTL 2). 
       CITATION LIST 
     Patent Literature 
     PTL 1 
     Japanese Patent Application Laid-Open No. 2009-100568 
     PTL 2 
     Japanese Patent Application Laid-Open No. 2010-239845 
     SUMMARY OF INVENTION 
     Technical Problem 
       [0005]    PTL 1, however has a problem in that although the welding of a relay is detectable, electrical leakage is not detectable. PTL 2 has a problem in that although electrical leakage is detectable, the welding of a relay is not detectable. In a case where a charger outside of a vehicle is configured to detect, as illustrated in PTL 2, electrical leakage in the welding detection apparatus of PTL 1, the current flows through the voltage sensor for detecting the welding of a relay during detection of electrical leakage. This case involves a problem in that wrong detection of electrical leakage may occur even when no electrical leakage occurs. 
         [0006]    An object of the present invention is to provide a relay welding detection apparatus capable of preventing wrong detection of electrical leakage by interrupting the connection between a detection section for welding of a relay, and an external power supply at least during detection of electrical leakage in a case where the welding of a relay and electrical leakage are both detectable. 
       Solution to Problem 
       [0007]    A relay welding detection apparatus according to the present invention is an apparatus that detects welding of a relay provided to a charging path extending from an external power supply to a storage battery, the apparatus including: a detection section that detects welding of the relay based on a current flowing through a region of the charging path that extends from the relay toward the external power supply, when the relay is turned off during stop of charging; and a switch that opens and closes connection between the external power supply and the detection section. 
       Advantageous Effects of Invention 
       [0008]    According to the present invention, it is possible to prevent wrong detection of electrical leakage by interrupting the connection between a detection section for welding of a relay, and an external power supply at least during detection of electrical leakage in a case where the welding of a relay and electrical leakage are both detectable. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]      FIG. 1  is a block diagram illustrating a configuration of a charging system in Embodiment 1 of the present invention; 
           [0010]      FIG. 2  is a flowchart illustrating an operation during detection of electrical leakage by a relay welding detection apparatus according to Embodiment 1 of the present invention; 
           [0011]      FIG. 3  is a flowchart illustrating an operation during detection of welding of relays by the relay welding detection apparatus according to Embodiment 1 of the present invention; 
           [0012]      FIG. 4  is a flowchart illustrating an operation during detection of electrical leakage by a relay welding detection apparatus according to Embodiment 2 of the present invention; and 
           [0013]      FIG. 5  is a flowchart illustrating an operation during detection of welding of relays by the relay welding detection apparatus according to Embodiment 2 of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0014]    Hereinafter, a detailed description will be given of embodiments of the present invention with reference to the accompanying drawings. 
       Embodiment 1 
     Configuration of Charging System 
       [0015]    A description will be given of a configuration of charging system  10  according to Embodiment 1 of the present invention with reference to  FIG. 1 . 
         [0016]    Charging system  10  mainly includes vehicle  150 , external power supply apparatus  160 , cable  170 , and charging plug  180 . 
         [0017]    Vehicle  150  runs on storage battery  152  as a power source. Vehicle  150  is an automobile that runs on the power of storage battery  152  such as a hybrid electric vehicle (HEV), plug-in electric vehicle (PEV), or electric vehicle (EV). 
         [0018]    External power supply apparatus  160  supplies power to storage battery  152  via cable  170  and charging plug  180 , thereby charging storage battery  152 . External power supply apparatus  160  is a quick charger or the like provided to a commercial power supply or a downtown plug-in station. External power supply apparatus  160  detects electrical leakage on vehicle  150 . External power supply apparatus  160  does not perform charging on vehicle  150  when detecting electrical leakage. 
         [0019]    Cable  170  connects between external power supply apparatus  160  and charging plug  180 . 
         [0020]    Charging plug  180  is connectable to power supply connection section  151 . Charging plug  180  supplies storage battery  152 , via relay welding detection apparatus  100 , with power supplied from external power supply apparatus  160  via cable  170 . 
         [0021]    &lt;Configuration of Vehicle&gt; 
         [0022]    A description will be given of a configuration of vehicle  150  according to Embodiment 1 of the present invention with reference to  FIG. 1 . 
         [0023]    Vehicle  150  includes relay welding detection apparatus  100 , power supply connection section  151 , and storage battery  152 . 
         [0024]    Relay welding detection apparatus  100  detects welding of power-supply-side relay  101  and welding of ground-side relay  102 . The detection result of welding of relays detected by relay welding detection apparatus  100  is displayed on a display section (not illustrated) provided to vehicle  150 , for example. Note that, the configuration of relay welding detection apparatus  100  will be described in detail, hereinafter. 
         [0025]    Power supply connection section  151  is connected to relay welding detection apparatus  100 . Power supply connection section  151  is connected to charging plug  180 , thereby connecting between charging plug  180  and relay welding detection apparatus  100 . Power supply connection section  151  is provided so as to be exposed from the body surface of vehicle  150 , for example. Power supply connection section  151  includes power-supply-side terminal  151   a  and ground-side terminal  151   b . A positive (+) terminal of storage battery  152  is connected to power-supply-side terminal  151   a  via power-supply-side relay  101 . A negative (−) terminal of storage battery  152  is connected to ground-side terminal  151   b  via ground-side relay  102 . 
         [0026]    Storage battery  152  stores the power supplied from external power supply apparatus  160  via cable  170 , charging plug  180 , power supply connection section  151 , and relay welding detection apparatus  100 . Storage battery  152  is mounted on vehicle  150 . 
         [0027]    &lt;Configuration of Relay Welding Detection Apparatus&gt; 
         [0028]    In Embodiment 1, the connection between welding detection switch  103  and external power supply apparatus  160  is disconnected by turning off connection interrupting switch  104  during a period other than a period of detecting welding of relays. In Embodiment 1, no current thus flows through electrical leakage detection section  163  via welding detection switch  103  when power-supply-side relay  101  and ground-side relay  102  are turned off. 
         [0029]    A description will be given of a configuration of relay welding detection apparatus  100  according to Embodiment 1 of the present invention with reference to  FIG. 1 . 
         [0030]    Relay welding detection apparatus  100  mainly includes power-supply-side relay  101 , ground-side relay  102 , welding detection switch  103 , connection interrupting switch  104 , resistor  105 , and control section  106 . Welding detection switch  103  and control section  106  constitute the detection section configured to detect welding of relays. 
         [0031]    Power-supply-side relay  101  is provided to the charging path extending from external power supply apparatus  160  to storage battery  152 . More specifically, power-supply-side relay  101  is placed in series in the power line connecting external power supply apparatus  160  and storage battery  152 . The term “charging path” herein refers to a path extending from external power supply apparatus  160  to storage battery  152  when storage battery  152  is charged using external power supply apparatus  160 . 
         [0032]    Power-supply-side relay  101  is turned on (ON) by the control of control section  106  to connect between external power supply apparatus  160  and storage battery  152 . In addition, power-supply-side relay  101  is turned off (OFF) by the control of control section  106  to disconnect external power supply apparatus  160  and storage battery  152  from each other. 
         [0033]    Ground-side relay  102  is provided to the charging path extending from external power supply apparatus  160  to storage battery  152 . More specifically, ground-side relay  102  is placed in series in the power line connecting external power supply apparatus  160  and storage battery  152 . 
         [0034]    Ground-side relay  102  is turned on by the control of control section  106  to connect between external power supply apparatus  160  and storage battery  152 . In addition, ground-side relay  102  is turned off by the control of control section  106  to disconnect external power supply apparatus  160  and storage battery  152  from each other. 
         [0035]    Welding detection switch  103  is connected in parallel with the charging path. Welding detection switch  103  is a photocoupler having light-emitting diode  103 A and phototransistor  103 B (second photocoupler). A collector terminal of phototransistor  103 B is connected to voltage detection terminal Vde of control section  106 . An emitter terminal of phototransistor  103 B is connected to the body ground of vehicle  150 . An anode terminal of light-emitting diode  103 A is connected to the external power supply side of power-supply-side relay  101 . A cathode terminal of light-emitting diode  103 A is connected to connection interrupting switch  104 . 
         [0036]    Light-emitting diode  103 A lights up when a current of at least a predetermined value flows between power-supply-side relay  101  and power-supply-side terminal  151   a  or between ground-side relay  102  and ground-side terminal  151   b.    
         [0037]    Phototransistor  103 B conducts (is turned on) upon receiving the light emitted when light-emitting diode  103 A lights up. Welding detection switch  103  connects between voltage detection terminal Vde of control section  106  and the body ground of vehicle  150  when turned on. 
         [0038]    In addition, phototransistor  103 B does not conduct (is turned off) unless light-emitting diode  103 A lights up. Welding detection switch  103  disconnects the connection between voltage detection terminal Vde of control section  106  and the body ground of vehicle  150  when turned off. 
         [0039]    Thus, a different voltage value is detected from voltage detection terminal Vde of control section  106  of control section  106  between the cases where welding detection switch  103  is turned on and turned off. 
         [0040]    Connection interrupting switch  104  is connected in parallel with the charging path and placed in series between welding detection switch  103  and power supply connection section  151 . Connection interrupting switch  104  opens and closes the connection between external power supply apparatus  160  (or power supply connection section  151  when charging plug  180  is not connected to power supply connection section  151 ) and welding detection switch  103 . Connection interrupting switch  104  is a photocoupler having light-emitting diode  104 A and phototransistor  104 B (first photocoupler). An anode terminal of light-emitting diode  104 A is connected to control terminal Vc 2  of control section  106 . A cathode terminal of light-emitting diode  104 A is connected to the body ground of vehicle  150 . A collector terminal of phototransistor  104 B is connected to a cathode terminal of light-emitting diode  103 A. An emitter terminal of the phototransistor  104 B is connected to the external power supply side of ground-side relay  102 . 
         [0041]    Light-emitting diode  104 A lights up when receiving a predetermined level control signal from control terminal Vc 2  of control section  106 . 
         [0042]    Phototransistor  104 B conducts (is turned on) upon receiving the light emitted when light-emitting diode  104 A lights up. Connection interrupting switch  104  connects between welding detection switch  103  and external power supply apparatus  160  when turned on. 
         [0043]    In addition, phototransistor  104 B does not conduct (is turned off) unless light-emitting diode  104 A lights up. In other words, connection interrupting switch  104  disconnects the connection between welding detection switch  103  and external power supply apparatus  160  when turned off. 
         [0044]    Resistor  105  is placed in series between the external power supply side of power-supply-side relay  101  and light-emitting diode  103 A. 
         [0045]    Control section  106  outputs control signal Vryp to make ON/OFF control of power-supply-side relay  101  to power-supply-side relay  101 . Control section  106  outputs control signal Vryn to make ON/OFF control of ground-side relay  102  to ground-side relay  102 . Control section  106  turns off power-supply-side relay  101  or ground-side relay  102  and detects welding of power-supply-side relay  101  or welding of ground-side relay  102  while charging stops. During this detection, control section  106  detects welding of power-supply-side relay  101  or welding of ground-side relay  102  based on a current flowing through a region of the charging path that extends from power-supply-side relay  101  to external power supply apparatus  160  or a current flowing through a region of the charging path that extends from ground-side relay  102  to external power supply apparatus  160 . 
         [0046]    More specifically, control section  106  detects welding of power-supply-side relay  101  or welding of ground-side relay  102  based on a voltage detected from voltage detection terminal Vde to which the collector terminal of phototransistor  103 B is connected. During this detection, control section  106  determines that welding of power-supply-side relay  101  or ground-side relay  102  has occurred, when the voltage detected from voltage detection terminal Vde drops by at least a predetermined value because a current of at least the predetermined value flows through phototransistor  103 B and turns on welding detection switch  103 . In other words, control section  106  detects welding of power-supply-side relay  101  or welding of ground-side relay  102  based on a detection result of a voltage that varies between the cases where welding detection switch  103  is turned on and off. 
         [0047]    For example, control section  106  determines that welding of power-supply-side relay  101  or ground-side relay  102  has occurred, when the voltage detected from voltage detection terminal Vde changes from an “H” level to “L” level. Note that, a description of the relay welding detection method will be given, hereinafter. 
         [0048]    The region of the charging path that extends from power-supply-side relay  101  to external power supply apparatus  160  is path “k 1 ” between power-supply-side relay  101  and power-supply-side terminal  151   a . In addition, the region of the charging path that extends from ground-side relay  102  to external power supply apparatus  160  is path “k 2 ” between ground-side relay  102  and ground-side terminal  151   b.    
         [0049]    Control section  106  outputs a control signal from control terminal Vc 2  to light-emitting diode  104 A to turn on connection interrupting switch  104 . In addition, control section  106  outputs a control signal from control terminal Vc 2  to light-emitting diode  104 A to turn off connection interrupting switch  104 . Control section  106 , for example, outputs an “H” level control signal to light-emitting diode  104 A to cause light-emitting diode  104 A to light up, thereby turning on connection interrupting switch  104 . In addition, control section  106  outputs an “L” level control signal to light-emitting diode  104 A not to cause light-emitting diode  104 A to light up, thereby turning off connection interrupting switch  104 . 
         [0050]    Control section  106  turns off connection interrupting switch  104  during a period other than a period of detecting welding of power-supply-side relay  101  and welding of ground-side relay  102 . 
         [0051]    Control section  106  is electrically insulated from the high voltage side (the direction of external power supply apparatus  160 ) by welding detection switch  103  and connection interrupting switch  104 . Note that, a method of detecting electrical leakage will be described, hereinafter. 
         [0052]    &lt;Configuration of External Power Supply Apparatus&gt; 
         [0053]    A description will be given of a configuration of external power supply apparatus  160  according to Embodiment 1 of the present invention with reference to  FIG. 1 . 
         [0054]    External power supply apparatus  160  mainly includes power generating section  161 , input and output section  162 , and electrical leakage detection section  163 . 
         [0055]    Power generating section  161  supplies power to input and output section  162 . 
         [0056]    Input and output section  162  is connected to cable  170  and supplies the power supplied from power generating section  161  to cable  170 . 
         [0057]    Electrical leakage detection section  163  detects electrical leakage on vehicle  150  side. When power-supply-side relay  101  and ground-side relay  102  are turned off and power is supplied from power generating section  161 , electrical leakage detection section  163  detects electrical leakage by detecting a predetermined level voltage. In other words, electrical leakage detection section  163  detects the flow of a voltage which is not supposed to flow because power-supply-side relay  101  and ground-side relay  102  are turned off. Electrical leakage detection section  163  detects the flow of the voltage which is not supposed to flow as a change in voltage. Note that, the power supplied from power generating section  161  during detection of electrical leakage is smaller than the power supplied from power generating section  161  during charging. 
         [0058]    &lt;Operation During Detection of Electrical Leakage of Relay Welding Detection Apparatus&gt; 
         [0059]    A description will be given of an operation during detection of electrical leakage of relay welding detection apparatus  100  according to Embodiment 1 of the present invention with reference to  FIG. 2 . 
         [0060]    In Embodiment 1, control section  106  turns off connection interrupting switch  104  even before detection of electrical leakage is performed (before operation of step ST 201 ). Accordingly, control section  106  does not control opening and closing of connection interrupting switch  104  when detection of electrical leakage is performed. 
         [0061]    First, control section  106  outputs control signal Vryp to power-supply-side relay  101  to turn off power-supply-side relay  101  (step ST 201 ). 
         [0062]    Next, control section  106  outputs control signal Vryn to ground-side relay  102  to turn off ground-side relay  102  (step ST 202 ). Note that the order of the operations of steps ST 201  and ST 202  can be reversed. 
         [0063]    Next, power generating section  161  starts supplying power for detecting electrical leakage, and electrical leakage detection section  163  starts detection of electrical leakage (step ST 203 ). 
         [0064]    Next, electrical leakage detection section  163  determines whether or not it has detected a voltage (step ST 204 ). 
         [0065]    When electrical leakage detection section  163  determines that it has detected no voltage (step ST 204 : NO), electrical leakage detection section  163  determines that no electrical leakage occurs (step ST 205 ). 
         [0066]    Power generating section  161  stops supplying power for detecting electrical leakage, and electrical leakage detection section  163  ends detection of electrical leakage (step ST 206 ). 
         [0067]    Meanwhile, when detecting that it has detected a voltage (step ST 204 : YES), electrical leakage detection section  163  determines that electrical leakage occurs (step ST 207 ). 
         [0068]    Power generating section  161  then stops supplying power for detecting electrical leakage, and electrical leakage detection section  163  ends detection of electrical leakage (step ST 206 ). Note that when electrical leakage is detected, the user performs an operation to identify where electrical leakage occurs and to fix the electrical leakage, for example. 
         [0069]    Note that, when connection interrupting switch  104  is turned on during detection of electrical leakage, the current flows in the following order: power generating section  161 , input and output section  162 , cable  170 , charging plug  180 , power supply connection section  151 , resistor  105 , welding detection switch  103 , connection interrupting switch  104 , power supply connection section  151 , charging plug  180 , cable  170 , input and output section  162 , and electrical leakage detection section  163 . As a result, electrical leakage detection section  163  detects a voltage generated during this flow of the current and wrongly detects that electrical leakage occurs even when no electrical leakage occurs. Accordingly, in Embodiment 1, connection interrupting switch  104  is turned off during a period other than a period of detection of welding of relays, thereby, preventing wrong detection of electrical leakage. 
         [0070]    &lt;Operation During Detection of Welding of Relays by Relay Welding Detection Apparatus&gt; 
         [0071]    A description will be given of an operation during detection of welding of relays by relay welding detection apparatus  100  according to Embodiment 1 of the present invention with reference to  FIG. 3 . 
         [0072]    Relay welding detection apparatus  100  stops charging when detection of welding of relays is performed. 
         [0073]    First, control section  106  outputs control signal Vryp to power-supply-side relay  101  to turn off power-supply-side relay  101  (step ST 301 ). 
         [0074]    Next, control section  106  outputs control signal Vryn to ground-side relay  102  to turn off ground-side relay  102  (step ST 302 ). Note that, the order of the operations of steps ST 301  and ST 302  can be reversed. 
         [0075]    Next, control section  106  outputs a control signal from control terminal Vc 2  connected to light-emitting diode  104 A to turn on connection interrupting switch  104  (step ST 303 ). Thus, relay welding detection apparatus  100  can detect welding of relays. 
         [0076]    Control section  106  determines whether or not the voltage detected from voltage detection terminal Vde connected to welding detection switch  103  has dropped by at least a predetermined value (step ST 304 ). Control section  106 , for example, determines whether or not the voltage detected from voltage detection terminal Vde has changed from the “H” level to “L” level. 
         [0077]    When determining that the voltage detected from voltage detection terminal Vde has dropped by at least the predetermined value (step ST 304 : YES), control section  106  determines that welding of power-supply-side relay  101  and welding of ground-side relay  102  occur (step ST 305 ) and skips processing until step ST 314  to be described, hereinafter. 
         [0078]    Meanwhile, when determining that the voltage detected from voltage detection terminal Vde has not dropped by at least the predetermined value (step ST 304 : NO), control section  106  outputs control signal Vryp to power-supply-side-relay  101  to turn on power-supply-side-relay  101  (step ST 306 ). 
         [0079]    Next, control section  106  determines whether or not the voltage detected from voltage detection terminal Vde has dropped by at least a predetermined value (step ST 307 ). 
         [0080]    When determining that the voltage detected from voltage detection terminal Vde has dropped by at least the predetermined value (step ST 307 : YES), control section  106  determines that only welding of ground-side relay  102  occurs (step ST 308 ), and thus skips processing until step ST 314  to be described, hereinafter. 
         [0081]    Meanwhile, when determining that the voltage detected from voltage detection terminal Vde has not dropped by at least the predetermined value (step ST 307 : NO), control section  106  outputs control signal Vryp to power-supply-side relay  101  to turn off power-supply-side relay  101  (step ST 309 ). 
         [0082]    Next, control section  106  outputs control signal Vryn to ground-side relay  102  to turn on ground-side relay  102  (step ST 310 ). 
         [0083]    Next, control section  106  determines whether or not the voltage detected from voltage detection terminal Vde has dropped by at least a predetermined value (step ST 311 ). 
         [0084]    When determining that the voltage detected from voltage detection terminal Vde has dropped by at least the predetermined value (step ST 311 : YES), control section  106  determines that only welding of power-supply-side relay  101  occurs (step ST 312 ), and thus skips processing until step ST 314  to be described, hereinafter. 
         [0085]    Meanwhile, when determining that the voltage detected from voltage detection terminal Vde has not dropped by at least the predetermined value (step ST 311 : NO), control section  106  determines that nothing unusual occurs (step ST 313 ). 
         [0086]    Next, control section  106  outputs control signal Vryp to power-supply-side relay  101  to turn off power-supply-side relay  101  and also outputs control signal Vryn to ground-side relay  102  to turn off ground-side relay  102  (step ST 314 ). 
         [0087]    Next, control section  106  outputs a control signal from control terminal Vc 2  to turn off connection interrupting switch  104  (step ST 315 ). Thus, electrical leakage detection section  163  can prevent wrong detection during detection of electrical leakage. 
         [0088]    &lt;Effects of Embodiment 1&gt; 
         [0089]    In Embodiment 1, connection interrupting switch  104  is turned off to disconnect the connection between welding detection switch  103  and an external power supply during a period other than a period of detection of welding of relays. Accordingly, wrong detection of electrical leakage can be prevented in a case where both electrical leakage and welding of power-supply-side relay  101  or ground-side relay  102  are detectable. 
         [0090]    Moreover, according to Embodiment 1, it is possible to prevent a situation where charging becomes unavailable due to wrong detection of electrical leakage even when charging can be performed safely because there is no electrical leakage in a system configured to stop charging when detecting electrical leakage. 
         [0091]    In addition, according to Embodiment 1, a photocoupler is adopted as the welding detection switch, so that the control section on the low voltage side can be electrically insulated from the external power supply on the high voltage side. As a result, in Embodiment 1, when a quick charger configured to perform charging with a charging voltage of 400V is used as external power supply apparatus  160 , control section  106  can be operated at 12V which is the same voltage as the conventional case. 
       Embodiment 2 
       [0092]    The configuration of a charging system in Embodiment 2 of the present invention is the same as the configuration illustrated in  FIG. 1 , so that the description of the configuration is omitted. Note that, a description will be given in Embodiment 2 using the reference numerals of relay welding detection apparatus  100  illustrated in Embodiment 1. 
         [0093]    In Embodiment 2, connection interrupting switch  104  is turned off to disconnect the connection between welding detection switch  103  and external power supply apparatus  160 . Thus, in Embodiment 2, no current flows into electrical leakage detection section  163  via welding detection switch  103  while power-supply-side relay  101  and ground-side relay  102  are turned off. 
         [0094]    &lt;Operation During Detection of Electrical Leakage by Relay Welding Detection Apparatus&gt; 
         [0095]    A description will be given of an operation during detection of electrical leakage by relay welding detection apparatus  100  according to Embodiment 2 of the present invention with reference to  FIG. 4 . 
         [0096]    First, control section  106  outputs a control signal from control terminal Vc 2  connected to light-emitting diode  104 A to turn off connection interrupting switch  104  (step ST 401 ). Thus, electrical leakage detection section  163  can prevent wrong detection when detection of electrical leakage is performed. 
         [0097]    Control section  106  turns off power-supply-side relay  101  (step ST 402 ). 
         [0098]    Next, control section  106  turns off ground-side relay  102  (step ST 403 ). Note that, the order of operations of step ST 402  and step ST 403  can be reversed. 
         [0099]    Power generating section  161  starts supplying power for detecting electrical leakage, and electrical leakage detection section  163  starts detection of electrical leakage (step ST 404 ). 
         [0100]    Next, electrical leakage detection section  163  determines whether or not it has detected a voltage (step ST 405 ). 
         [0101]    When determining that it has detected no voltage (step ST 405 : NO), electrical leakage detection section  163  determines that there is no electrical leakage (step ST 406 ). 
         [0102]    Power generating section  161  stops supplying power for detecting electrical leakage, and electrical leakage detection section  163  ends detection of electrical leakage (step ST 408 ). 
         [0103]    Meanwhile, when determining that it has detected a voltage (step ST 405 : YES), electrical leakage detection section  163  determines that electrical leakage occurs (step ST 407 ). 
         [0104]    Power generating section  161  stops supplying power for detecting electrical leakage, and electrical leakage detection section  163  ends detection of electrical leakage (step ST 408 ). Note that, when electrical leakage is detected, the user performs an operation to identify where the electrical leakage occurs and to fix the electrical leakage, for example. 
         [0105]    Lastly, control section  106  outputs a control signal from control terminal Vc 2  to turn on connection interrupting switch  104  (step ST 409 ). Thus, relay welding detection apparatus  100  can detect welding of relays. 
         [0106]    Note that, the reason why wrong detection of electrical leakage occurs when connection interrupting switch  104  is turned on during detection of electrical leakage is the same as that of Embodiment 1, so that the description of the reason will be omitted. In Embodiment 2, wrong detection of electrical leakage is prevented by turning off connection interrupting switch  104  when detection of electrical leakage is performed. 
         [0107]    &lt;Operation During Detection of Welding of Relays by Relay Welding Detection Apparatus&gt; 
         [0108]    A description will be given of an operation during detection of welding of relays by relay welding detection apparatus  100  according to Embodiment 2 of the present invention with reference to  FIG. 5 . 
         [0109]    In Embodiment 2, control section  106  turns off connection interrupting switch  104  during detection of electrical leakage or during charging and turns on connection interrupting switch  104  during a period other than a period of detection of electrical leakage or a period of charging. Accordingly, control section  106  does not control opening and closing of connection interrupting switch  104  when detection of welding of relays is performed. In addition, relay welding detection apparatus  100  stops charging when detection of welding of relays is performed. Note that, the reason for turning off connection interrupting switch  104  during charging is to prevent a charging loss and not to prevent wrong detection of electrical leakage. 
         [0110]    First, control section  106  turns off power-supply-side relay  101  (step ST 501 ). 
         [0111]    Next, control section  106  turns off ground-side relay  102  (step ST 502 ). Note that the order of the operations of steps ST 501  and ST 502  can be reversed. 
         [0112]    Next, control section  106  determines whether or not the voltage detected from voltage detection terminal Vde connected to welding detection switch  103  has dropped by at least a predetermined value (step ST 503 ). 
         [0113]    When determining that the voltage detected from voltage detection terminal Vde has dropped by at least the predetermined value (step ST 503 : YES), control section  106  determines that welding of power-supply-side relay  101  and welding of ground-side relay  102  occur (step ST 504 ), and thus skips the processing until step ST 513  to be described, hereinafter. 
         [0114]    Meanwhile, when determining that the voltage detected from voltage detection terminal Vde has not dropped by at least the predetermined value (step ST 503 : NO), control section  106  turns on power-supply-side relay  101  (step ST 505 ). 
         [0115]    Next, control section  106  determines whether or not the voltage detected from voltage detection terminal Vde has dropped by at least a predetermined value (step ST 506 ). 
         [0116]    When determining that the voltage that has been detected from voltage detection terminal Vde has dropped by at least the predetermined value (step ST 506 : YES), control section  106  determines that only welding of ground-side relay  102  occurs (step ST 507 ), and thus skips the processing until step ST 513  to be described, hereinafter. 
         [0117]    Meanwhile, when determining that the voltage detected from voltage detection terminal Vde has not dropped by at least the predetermined value (step ST 506 : NO), control section  106  turns off power-supply-side relay  101  (step ST 508 ). 
         [0118]    Next, control section  106  turns on ground-side relay  102  (step ST 509 ). 
         [0119]    Next, control section  106  determines whether or not the voltage detected from voltage detection terminal Vde has dropped by at least a predetermined value (step ST 510 ). 
         [0120]    When determining that the voltage detected from voltage detection terminal Vde has dropped by at least the predetermined value (step ST 510 : YES), control section  106  determines that only welding of power-supply-side-relay  101  (step ST 511 ) occurs, and thus skips the processing until step ST 513  to be described, hereinafter. 
         [0121]    Meanwhile, when determining that the voltage detected from voltage detection terminal Vde has not dropped by at least the predetermined value (step ST 510 : NO), control section  106  determines that nothing unusual occurs (step ST 512 ). 
         [0122]    Next, control section  106  turns off power-supply-side relay  101  and ground-side relay  102  (step ST 513 ). 
         [0123]    &lt;Effects of Embodiment 2&gt; 
         [0124]    In Embodiment 2, connection interrupting switch  104  is turned off to disconnect the connection between welding detection switch  103  and external power supply when detection of electrical leakage is performed. Accordingly, wrong detection of electrical leakage can be prevented in a case where both welding of power-supply-side relay  101  or ground-side relay  102  and electrical leakage are detectable. 
         [0125]    Moreover, according to Embodiment 2, it is possible to prevent a situation where charging becomes unavailable due to wrong detection of electrical leakage even when charging can be performed safely because there is no electrical leakage in a system configured to stop charging when detecting electrical leakage. 
         [0126]    In addition, according to Embodiment 2, a photocoupler is adopted as the welding detection switch, so that the control section on the low voltage side can be electrically insulated from the external power supply on the high voltage side. As a result, in Embodiment 2, when a quick charger configured to perform charging with a charging voltage of 400V is used as external power supply apparatus  160 , control section  106  can be operated at 12V which is the same voltage as the conventional case. 
         [0127]    &lt;Variations Common to all Embodiments&gt; 
         [0128]    In Embodiments 1 and 2, although photocouplers are used as a welding detection switch and a connection interrupting switch, a switch other than a photocoupler may be used. 
         [0129]    In Embodiments 1 and 2, a relay welding detection apparatus is mounted on a vehicle, but the relay welding detection apparatus may be mounted on not only a vehicle but also an apparatus including a storage battery. 
         [0130]    In Embodiments 1 and 2, connection interrupting switch  104  is turned off by the control of control section  106 , but connection interrupting switch  104  may be manually turned off, and as long as connection interrupting switch  104  can be turned off at least when detection of electrical leakage is performed, any method may be used to turn off connection interrupting switch  104 . 
         [0131]    The disclosure of Japanese Patent Application No. 2012-201415, filed on Sep. 13, 2012, including the specification, drawings and abstract, is incorporated herein by reference in its entirety. 
       INDUSTRIAL APPLICABILITY 
       [0132]    The relay welding detection apparatus according to the present invention is suitable for detecting welding of a relay provided to a charging path extending from an external power supply to a storage battery. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           10  Charging system 
           100  Relay welding detection apparatus 
           101  Power-supply-side relay 
           102  Ground-side relay 
           103  Welding detection switch 
           103 A,  104 A Light-emitting diode 
           103 B,  104 B Phototransistor 
           104  Connection interrupting switch 
           105  Resistor 
           106  Control section 
           150  Vehicle 
           151  Power supply connection section 
           151   a  Power-supply-side terminal 
           151   b  Ground-side terminal 
           152  Storage battery 
           160  External power supply apparatus 
           161  Power generating section 
           162  Input and output section 
           163  Electrical leakage detection section 
           170  Cable 
           180  Charging plug 
         Vc 2  Control terminal 
         Vde Voltage detection terminal