Abstract:
The present invention is an in-vehicle charger for detecting ground faults originating in sections in which alternating current is flowing. This device is an in-vehicle charger ( 100 ) for charging a vehicle-mounted battery, wherein the device is provided with: a bridge rectifier ( 14 ) for converting alternating current supplied from a power source to direct current; a ground fault detecting circuit ( 21 ) for outputting a test voltage when a test current flows in a circuit in the in-vehicle charger ( 100 ) and, based on changes in the test current in response to the presence or absence of a ground fault resistor, for detecting a ground fault in the circuit of the in-vehicle charger ( 100 ); and a controller ( 23 ) for controlling the ground fault sensing circuit ( 21 ) so as to output a test voltage exceeding the forward voltage of a diode provided by the bridge rectifier ( 14 ).

Description:
TECHNICAL FIELD 
     The present invention relates to an in-vehicle charging apparatus which charges a battery mounted on a vehicle, using a predetermined power supply. 
     BACKGROUND ART 
     Since a high-voltage battery is mounted on a vehicle such as an electric automobile or a hybrid automobile, there is a need to provide a ground fault detector in order to ensure the safety of a passenger. 
     As an example of the ground fault detector, for example, PTL 1 discloses a vehicle ground fault detecting apparatus which highly precisely detects a ground fault of a DC power supply (battery). The vehicle ground fault detecting apparatus applies a rectangular wave pulse signal to one end (a measurement point A) of a coupling capacitor, obtains a measurement voltage when the rectangular wave pulse signal is an H level and a measurement voltage when the rectangular wave pulse signal is an L level, and detects an occurrence of a ground fault based on a difference between the measurement voltages. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1 
         Japanese Patent Application Laid-Open No. 2003-250201 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, the vehicle ground fault detecting apparatus of PTL 1 has the following problem. 
     In the vehicle ground fault detecting apparatus of PTL 1, when the DC power supply is charged through a charger including a bridge rectifier from a commercial power supply, a direct current which is converted from an alternating current by the bridge rectifier is supplied to the DC power supply. In such case, even when a rectangular wave pulse signal for detecting a ground fault is outputted, a test current does not flow through an interval where the alternating current flows if a test voltage for detecting the ground fault is smaller than a forward voltage (Vf) of a diode constituting the bridge rectifier. For this reason, the ground fault occurring in the interval where the alternating current flows cannot be detected. 
     Due to the above-described circumstance, there arises a problem in that although the vehicle ground fault detecting apparatus of PTL 1 can detect a ground fault occurring in the interval where a direct current flows, but cannot detect a ground fault occurring in the interval where an alternating current flows. 
     An object of the invention is to provide an in-vehicle charging apparatus capable of detecting a ground fault occurring in the interval where an alternating current flows. 
     Solution to Problem 
     An in-vehicle charging apparatus according to an aspect of the present invention is an apparatus that charges a battery mounted on a vehicle, the apparatus including: a bridge rectifier that converts an alternating current supplied from a power supply into a direct current; a ground fault detecting circuit that is provided at a side of the bridge rectifier where the direct current obtained by the conversion of the bridge rectifier flows, that outputs a test voltage, and that detects a ground fault occurring in the in-vehicle charging apparatus, based on a test current which changes in response to the presence or absence of a ground fault resistance; and a control section that controls the ground fault detecting circuit so that the ground fault detecting circuit outputs the test voltage of a value larger than a forward voltage of a diode included in the bridge rectifier. 
     Advantageous Effects of Invention 
     According to the invention, it is possible to detect a ground fault occurring in the interval where an alternating current flows. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating the configuration of an in-vehicle charging apparatus according to an embodiment of the present invention; 
         FIG. 2  is a diagram illustrating a case where a test voltage in the in-vehicle charging apparatus according to the embodiment of the present invention is smaller than Vf; 
         FIG. 3  is a diagram illustrating a case where the test voltage in the in-vehicle charging apparatus according to the embodiment of the present invention is larger than Vf; 
         FIG. 4  is a diagram illustrating a case where the test voltage in the in-vehicle charging apparatus according to the embodiment of the present invention is larger than Vf and is an AC voltage; 
         FIG. 5  is a flowchart illustrating an example of a ground fault detection operation of the in-vehicle charging apparatus according to the embodiment of the present invention; and 
         FIG. 6  is a flowchart illustrating an example of a test voltage conversion operation of the in-vehicle charging apparatus according to the embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of the invention will be described in detail with reference to the accompanying drawings. 
     (Embodiment) 
       FIG. 1  is a diagram illustrating the configuration of in-vehicle charging apparatus  100  according to the embodiment of the present invention. 
     In-vehicle charging apparatus  100  includes a charger and a battery apparatus. The charger includes power supply circuit  10 , primary inverter  11 , primary transformer  12 , secondary transformer  13 , bridge rectifier  14 , choke coil  16 , and capacitor  17 . Further, the battery apparatus includes P-side relay  18 , N-side relay  19 , vehicle-side GND (ground)  20 , ground fault detecting circuit  21 , battery  22 , and control section  23 . 
     In the charger, an alternating current which is supplied from the primary side (power supply circuit  10 , primary inverter  11 , and primary transformer  12 ) is inputted to secondary transformer  13 . 
     Secondary transformer  13  steps up or down the alternating current inputted from primary transformer  12  and inputs the result to bridge rectifier  14 . 
     Bridge rectifier  14  converts the alternating current inputted from secondary transformer  13  into a direct current after the rectification thereof, and inputs the direct current to choke coil  16 . Bridge rectifier  14  includes diodes  15   a ,  15   b ,  15   c , and  15   d.    
     Furthermore, in the description below, the interval on the left side of bridge rectifier  14  as a boundary in the drawing, for example, the interval between bridge rectifier  14  and secondary transformer  13  (on the side of bridge rectifier  14  which is opposite to ground fault detecting circuit  21 ) is referred to as an “AC interval” in that an alternating current flows through the interval. Meanwhile, the interval on the right side of bridge rectifier  14  as a boundary in the drawing, for example, the interval between bridge rectifier  14  and battery  22  (on the side of bridge rectifier  14  where ground fault detecting circuit  21  exists) is referred to as a “DC interval” in that a direct current flows through the interval. 
     Choke coil  16  is configured with a predetermined impedance and constitutes a low-pass filter along with capacitor  17 . Then, when P-side relay  18  is connected (becomes an ON state) by the control of control section  23 , choke coil  16  smoothes the direct current inputted from bridge rectifier  14  in cooperation with capacitor  17 . 
     The smoothed direct current is inputted to battery  22  as a secondary battery. Accordingly, battery  22  is charged. 
     Control section  23  controls ON (connection)/OFF (disconnection) states of P-side relay  18  and N-side relay  19 . Further, control section  23  controls an operation involving the ground fault detection of ground fault detecting circuit  21 . The arrows indicated by the dashed lines illustrated in  FIG. 1  indicate a control signal (an instruction and a command) from control section  23 . 
     Further, control section  23  includes, for example, a central processing unit (CPU), a read only memory (ROM), and a random access memory (RAM). Control section  23  performs the above-described control and other controls involving in-vehicle charging apparatus  100  in a manner such that a CPU executes a program stored in a ROM, using a RAM. 
     Upon reception of an instruction for performing a ground fault detection and an instruction for a value of a test voltage to be outputted (applied) from control section  23 , ground fault detecting circuit  21  outputs a test voltage of the instructed value in order to detect a ground fault occurring in in-vehicle charging apparatus  100 . The test voltage may be outputted as a DC voltage or an AC voltage. At this time, P-side relay  18  and N-side relay  19  become an ON (connection) state by the control of control section  23 . 
     When the test voltage is outputted from ground fault detecting circuit  21 , a test current changes in in-vehicle charging apparatus  100  in response to the occurrence of the ground fault. Ground fault detecting circuit  21  detects the occurrence of the ground fault based on a change in the test current. 
     That is, a test current larger than a predetermined value flows when the ground fault occurs in the case where the test voltage is outputted, but only a test current of a value smaller than the predetermined value flows when no ground fault occurs in the same case. 
     Accordingly, ground fault detecting circuit  21  detects the occurrence of the ground fault if a state where the test current becomes larger than the predetermined value is detected when the test voltage is outputted, and detects that no ground fault occurs if a state where the test current becomes larger than the predetermined value is not detected. The predetermined value is set in advance for the test voltage in the state where no ground fault occurs, so that the predetermined value becomes larger than the test current obtained when the ground fault caused by the impedance among the DC interval, the AC interval, and the vehicle body does not occur. 
     Furthermore, a route through which the test current flows when the ground fault occurs becomes a route having the lowest impedance. Further, the arrow of the one-dotted chain line illustrated in  FIG. 1  indicates a detection result signal (which will be described in detail later) to control section  23 . Further, the method of the ground fault detection which is performed by ground fault detecting circuit  21  may be, for example, a method disclosed in PTL 1. That is, a method which is generally used in the related art may be employed. 
     Hereinafter, a description will be given of examples of the ground fault detection which is performed by in-vehicle charging apparatus  100  with reference to  FIGS. 2 to 4 . 
       FIG. 2  illustrates a case where value V 1  of a test voltage instructed from control section  23  to ground fault detecting circuit  21  is smaller than a forward voltage Vf of diode  15   a ,  15   b , or the like included in bridge rectifier  14 . When the ground fault occurs when the test voltage V 1  is outputted from ground fault detecting circuit  21 , a test current larger than the predetermined value flows, and the test current is smaller than the predetermined value when the ground fault does not occur. Furthermore, the forward voltage Vf is, for example 0.5 V to 2 V. 
     In the case of  FIG. 2 , since test voltage V 1  is smaller than forward voltage Vf, the test current may not flow through, for example, diode  15   b . Accordingly, the test current does not flow through the AC interval and flows only through the DC interval. The arrow indicated by the bold line illustrated in  FIG. 2  indicates the test current which flows in the event of ground fault resistance R 1 . 
     Accordingly, in the case of  FIG. 2 , ground fault detecting circuit  21  cannot detect the ground fault occurring in the AC interval (for example, a ground fault resistance R 2 ), but can detect the ground fault occurring only in the DC interval (for example, the ground fault resistance R 1 ). 
       FIG. 3  illustrates a case where value V 2  of a test voltage instructed from control section  23  to ground fault detecting circuit  21  is larger than forward voltage Vf of diode  15   a ,  15   b , or the like included in bridge rectifier  14 . Ground fault detecting circuit  21  can output an AC voltage as a test voltage. The “state where value V 2  of the test voltage is larger than forward voltage Vf of diode  15   a ,  15   b , or the like” means that control section  23  performs a control so that the amplitude of the AC voltage outputted from ground fault detecting circuit  21  is larger than forward voltage Vf. In a case where the test voltage V 2  is outputted from ground fault detecting circuit  21 , When the ground fault occurs in the case where the test voltage V 2  is outputted from ground fault detecting circuit  21 , the test current becomes larger than the predetermined value if the ground fault occurs, and the test current becomes smaller than the predetermined value if no ground fault occurs in this case. 
     In the case of  FIG. 3 , since test voltage V 2  is larger than forward voltage Vf, the test current may flow through diode  15   b , for example. Accordingly, the test current flows through the AC interval. The arrow of the bold line illustrated in  FIG. 3  indicates the test current which flows in the event of ground fault resistance R 2 . 
     Accordingly, in the case of  FIG. 3 , ground fault detecting circuit  21  can detect the ground fault occurring in the AC interval (for example, the ground fault resistance R 2 ). 
       FIG. 4  illustrates a case where value V 2  of the test voltage instructed from control section  23  to ground fault detecting circuit  21  is larger than forward voltage Vf of diode  15   a ,  15   b , or the like included in bridge rectifier  14  and test voltage V 2  is an AC voltage. The configuration illustrated in  FIG. 4  is different from the configurations illustrated in  FIGS. 1 to 3  in that resonance capacitors  24  and  25  are provided between bridge rectifier  14  and secondary transformer  13 . 
     When the AC interval is provided with resonance capacitors  24  and  25 , test voltage V 2  needs to be larger than forward voltage Vf and needs to be an AC voltage in order that the test voltage V 2  flows through the AC interval so as to detect the ground fault between secondary transformer  13  and resonance capacitors  24  and  25 . Therefore, in the case of the configuration illustrated in  FIG. 4 , a voltage which is outputted from ground fault detecting circuit  21  is set as an AC voltage in advance. 
     In the case of  FIG. 4 , since test voltage V 2  is larger than forward voltage Vf and is an AC voltage, the test current can flow through the AC interval provided with resonance capacitors  24  and  25 . The arrow of the bold line illustrated in  FIG. 4  indicates the test current flowing in the event of ground fault resistance R 2 . 
     Accordingly, in the case of  FIG. 4 , ground fault detecting circuit  21  can detect the ground fault occurring in the AC interval (for example, the ground fault resistance R 2 ). 
     As described above, in in-vehicle charging apparatus  100  of the embodiment, the test voltage which is outputted from ground fault detecting circuit  21  is variable. Accordingly, the ground fault occurring in the DC interval can be detected by setting the test voltage to be outputted to a value smaller than the forward voltage of the diode, and the ground fault occurring in the AC interval can be detected by setting the test voltage to be outputted to a value larger than the forward voltage of the diode. Further, since the test voltage to be outputted is set to a value larger than the forward voltage of the diode and is set to an AC voltage, it is possible to detect the ground fault occurring in the AC interval provided with the resonance capacitor. 
     Next, an operation example according to the ground fault detection of in-vehicle charging apparatus  100  will be described with reference to  FIGS. 5 and 6 . 
     OPERATION EXAMPLE 1 
       FIG. 5  is a flowchart illustrating operation example 1 of in-vehicle charging apparatus  100 . The operation illustrated in  FIG. 5  is performed before charging, for example. 
     First, ground fault detection for battery  22  alone is performed (step S 100 ). That is, control section  23  performs a control so that P-side relay  18  and N-side relay  19  become an OFF state and instructs ground fault detecting circuit  21  to perform the ground fault detection and instructs ground fault detecting circuit  21  to use a value of the test voltage to be outputted. This value is, for example, value V 1  smaller than that of forward voltage Vf. Ground fault detecting circuit  21  which receives the instruction from control section  23  outputs a test voltage of the instructed value and performs ground fault detection based on a magnitude relation between the test current and the predetermined value. 
     When ground fault detecting circuit  21  detects a test current larger than the predetermined value (YES in step S 101 ), a signal indicating the detection result (a detection result signal) is outputted to control section  23 . 
     Upon reception of a detection result signal indicating that the test current larger than the predetermined value has been detected from ground fault detecting circuit  21  as input, control section  23  determines that a ground fault exists (a ground fault occurs) (step S 102 ). This determination result may be output from an indicator (not illustrated), for example. 
     Meanwhile, when not detecting a test current larger than the predetermined value (NO in step S 101 ), ground fault detecting circuit  21  outputs a detection result signal indicating the detection result to control section  23 . 
     Upon reception of a detection result signal indicating that a test current larger than the predetermined value has not been detected from ground fault detecting circuit  21  as input, control section  23  turns on P-side relay  18  and N-side relay  19  (step S  103 ). 
     Here, ground fault detection is performed on the AC interval of in-vehicle charging apparatus  100  (step S 104 ). That is, control section  23  instructs ground fault detecting circuit  21  to perform the ground fault detection and instructs ground fault detecting circuit  21  to use a value of the test voltage to be outputted. This value is, for example, value V 2  larger than forward voltage Vf. Then, upon reception of the instruction from control section  23 , ground fault detecting circuit  21  outputs a test voltage of the instructed value and performs ground fault detection based on the magnitude relation between the test current and the predetermined value. 
     When detecting a test current larger than the predetermined value (YES in step S 105 ), ground fault detecting circuit  21  outputs a detection result signal indicating the detection result to control section  23 . Subsequently, the operation proceeds to step S 102  described above. 
     Meanwhile, when not detecting a test current larger than the predetermined value (NO in step S 105 ), ground fault detecting circuit  21  outputs a detection result signal indicating the detection result to control section  23 . 
     Upon reception of a detection result signal indicating that a test current larger than the predetermined value has not been detected from ground fault detecting circuit  21  as input, control section  23  determines that there is no ground fault (ground fault does not occur) (step S 106 ). The determination result may be outputted using an indicator (not illustrated), for example. After step S 106 , the charging operation for battery apparatus  2  starts. 
     The description of operation example 1 has been given thus far. 
     Furthermore, in operation example 1, the target of the ground fault detection in step S 104  can be a DC interval. Further, in operation example 1, the test voltage can be an AC voltage. 
     OPERATION EXAMPLE 2 
       FIG. 6  is a flowchart illustrating operation example 2 of in-vehicle charging apparatus  100 . The operation illustrated in  FIG. 6  may be replaced by step S 104  and step S 105  of operation example 1. 
     First, a ground fault detection using test voltage V 1  is performed (step S 201 ). That is, control section  23  instructs ground fault detecting circuit  21  to perform the ground fault detection and instructs ground fault detecting circuit  21  to use value V 1  of the test voltage to be outputted. This value V 1  is smaller than that of forward voltage Vf. Upon reception of the instruction from control section  23 , ground fault detecting circuit  21  outputs a test voltage of the instructed value V 1  and performs ground fault detection on the DC interval based on the magnitude relation between the test current and the predetermined value. 
     When detecting a test current larger than the predetermined value (YES in step S 202 ), ground fault detecting circuit  21  outputs a detection result signal indicating the detection result to control section  23 . 
     Upon reception of a detection result signal indicating that a test current larger than the predetermined value has been detected from ground fault detecting circuit  21  as input, control section  23  determines that there is a ground fault (ground fault occurs) in the DC interval (step S 203 ). The determination result may be outputted using an indicator (not illustrated), for example. 
     Meanwhile, when not detecting a test current larger than the predetermined value (NO in step S 202 ), ground fault detecting circuit  21  outputs a detection result signal indicating the detection result to control section  23 . 
     Upon reception of a detection result signal indicating that a test current larger than the predetermined value is not detected from ground fault detecting circuit  21  as input, control section  23  determines that there is a ground fault (ground fault occurs) in the AC interval (step S 203 ). 
     Next, ground fault detection using test voltage V 2  is performed (step S 204 ). That is, control section  23  instructs ground fault detecting circuit  21  to perform the ground fault detection and instructs ground fault detecting circuit  21  to use value V 2  of the test voltage to be outputted. This value V 2  is larger than that of forward voltage Vf. Upon reception of the instruction from control section  23 , ground fault detecting circuit  21  outputs a test voltage of the instructed value V 2  and performs ground fault detection on the AC interval in addition to the DC interval based on the magnitude relation between the test current and the predetermined value. 
     When detecting a test current larger than the predetermined value (YES in step S 205 ), ground fault detecting circuit  21  outputs a detection result signal indicating the detection result to control section  23 . Subsequently, the procedure proceeds to step S 203  described above. 
     Meanwhile, when not detecting a test current larger than the predetermined value (NO in step S 205 ), ground fault detecting circuit  21  outputs a detection result signal indicating the detection result to control section  23 . 
     Upon reception of a detection result signal indicating that a test current larger than the predetermined value has not been detected from ground fault detecting circuit  21  as input, control section  23  determines that there is no ground fault (ground fault does not occur) in the AC interval in addition to the DC interval (step S 206 ). This determination result may be outputted using an indicator (not illustrated), for example. 
     The description of operation example 2 has been given thus far. When it is determined that there is a ground fault in step S 202 , it can be estimated that a ground fault occurs at the side of bridge rectifier  14  where ground fault detecting circuit  21  exists (the DC interval). When it is determined that there is a ground fault in step S 205  after it is determined that a ground fault does not exist in step S 202 , it can be estimated that a ground fault occurs at the side (the AC interval) of bridge rectifier  14  which is opposite to ground fault detecting circuit  21 . 
     In step S 202 , since value V 1  of the test voltage is smaller than that of forward voltage Vf, the ground fault detection of the DC interval may be performed. Meanwhile, when it is determined that there is a ground fault in step S 205 , value V 2  of the test voltage is larger than that of forward voltage Vf, and hence the ground fault detection of at least one of the DC interval and the AC interval can be performed. 
     By combining step S 202  and step S 205 , it is possible to identify in which one of the DC interval and the AC interval the ground fault occurs. 
     In this way, it is possible to estimate where the ground fault occurs by performing the ground fault detection in two stages as in this operation example. Further, it is possible to detect the ground fault by automatically changing the detection interval (range). Furthermore, in the operation example, the detection interval is changed in two stages, but may be changed in two stages or more. 
     Further, in operation example 2, the test voltage may be an AC voltage. 
     Further, a predetermined value used to determine the ground fault may be a different value according to the test interval and the test voltage to be applied. 
     Further, operation example 2 may be performed alone without the replacement of step S 104  to step S 105  of operation example 1. 
     Further, in operation examples 1 and 2, the AC voltage serving as the test voltage is not limited to a sine wave, and may be a rectangular wave or a triangular wave. 
     According to the embodiment, it is possible to detect the ground default occurring in the AC interval by performing a control so that a test voltage larger than the forward voltage of the diode included in the bridge rectifier is outputted. 
     Further, according to the embodiment, it is possible to estimate where the ground fault occurs by performing a control on the test voltage to be outputted so that a voltage of a value larger or smaller than the forward voltage of the diode included in the bridge rectifier is selectively outputted. 
     Further, according to the embodiment, it is possible to detect the ground fault occurring in the AC interval even when the resonance capacitor is provided in the AC interval, by outputting an AC voltage as the test voltage. 
     While the embodiment has been described, the present invention is not limited to the description above, and various modifications may be made within a scope without departing from the gist of the present invention. 
     The disclosure of Japanese Patent Application No. 2012-043048 filed on Feb. 29, 2012 including the specification, drawings, and abstract is incorporated herein by reference in its entirety. 
     INDUSTRIAL APPLICABILITY 
     An in-vehicle charging apparatus according to the present invention is suitable for ground fault detection when a battery mounted on a vehicle is charged using a predetermined power supply. 
     REFERENCE SIGNS LIST 
     
         
           10  Power supply circuit 
           11  Primary inverter 
           12  Primary transformer 
           13  Secondary transformer 
           14  Bridge rectifier 
           15   a ,  15   b ,  15   c ,  15   d  Diode 
           16  Choke coil 
           17  Capacitor 
           18  P-side relay 
           19  N-side relay 
           20  Vehicle-side GND 
           21  Ground fault detecting circuit 
           22  Battery 
           23  Control section 
           24 ,  25  Resonance capacitor 
           100  In-vehicle charging apparatus