Abstract:
An apparatus for correcting leakage current during a vehicle charging operation is provided. The apparatus comprises a balance circuit configured to receive a sensed current indicative of a vehicle leakage current in response to an external power source providing a charging current to a vehicle. The vehicle leakage current includes a first leakage component and a second leakage component. The balance circuit is further configured to generate a first voltage value that corresponds to a negative value of the first leakage component and to provide a second voltage value that generally corresponds to a positive value of the first leakage component. The balance circuit is further configured to apply the second voltage value to the first voltage value to substantially remove the first leakage component from the vehicle leakage current.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional Application No. 61/469,964 filed on Mar. 31, 2011, the disclosure of which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    Embodiments of the present disclosure generally relate to an apparatus for correcting a direct current (DC) bias for leakage current. 
       BACKGROUND 
       [0003]    It is known to detect leakage current for vehicle applications. One example for detecting leakage current in a charging cable for an electric vehicle is set forth below. 
         [0004]    International Publication No: WO 2010/049775 A2 to Mukai et al. discloses a charging cable for an electric vehicle, which includes a power plug adapted to be detachably connected to a power socket of a commercial power source. The charging cable includes a temperature detecting unit for detecting a temperature of the power plug and a cable connector adapted to be detachably connected to an electric vehicle for supplying a charging current to a battery of the electric vehicle. The charging cable further includes a switching unit for opening and closing a current path between the power plug and the cable connector. The charging cable further includes a leakage detecting unit for detecting an electric leakage based on a current flowing through the current path and a power cutoff unit for opening the switching unit when the detected temperature of the temperature detection means exceeds a threshold value or when the leakage detection means detects the electric leakage. 
       SUMMARY 
       [0005]    An apparatus for correcting leakage current during a vehicle charging operation is provided. The apparatus comprises a balance circuit configured to receive a sensed current indicative of a vehicle leakage current in response to an external power source providing a charging current to a vehicle. The vehicle leakage current includes a first leakage component and a second leakage component. The balance circuit is further configured to generate a first voltage value that corresponds to a negative value of the first leakage component and to provide a second voltage value that generally corresponds to a positive value of the first leakage component. The balance circuit is further configured to apply the second voltage value to the first voltage value to substantially remove the first leakage component from the vehicle leakage current. 
         [0006]    A method for correcting a leakage current during a vehicle charging operation is provided. The method comprises determining a vehicle leakage current in response to an external power source providing a charging current to a vehicle, the vehicle leakage current including a first leakage component and a second leakage component. The method further comprises generating a first voltage value that corresponds to a negative value of the first leakage current and providing a second voltage value that generally corresponds to a positive value of the first leakage component. The method further comprises applying the second voltage value to the first voltage value to substantially remove the first leakage component from the vehicle leakage current. 
         [0007]    An apparatus comprising a balance circuit is provided. The balance circuit is configured to receive a sensed current indicative of a vehicle leakage current in response to an external power source providing a charging current to a vehicle, the vehicle leakage current including a direct current (DC) leakage component. The balance circuit is further configured to generate a first voltage value that corresponds to a negative value of the DC leakage component and to provide a second voltage value that generally corresponds to a positive value of the DC leakage component. The balance circuit is further configured to apply the second voltage value to the first voltage value to substantially remove the DC leakage component from the vehicle leakage current. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The embodiments of the present disclosure are pointed out with particularity in the appended claims. However, other features of the various embodiments will become more apparent and will be best understood by referring to the following detailed description in conjunction with the accompany drawings in which: 
           [0009]      FIG. 1  depicts an apparatus for correcting a DC bias for leakage current in accordance to one embodiment of the present invention; 
           [0010]      FIG. 2  depicts a balance bias circuit in accordance to one embodiment of the present invention; and 
           [0011]      FIG. 3  depicts a method for correcting the DC bias for leakage current in accordance to one embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
         [0013]    Embodiments of the present disclosure as set forth herein and in  FIGS. 1-3  generally describe and/or illustrate a plurality of circuits or other electrical devices. All references to the circuits and other electrical devices and the functionality provided by each, are not intended to be limited to encompassing only what is illustrated and described herein. While particular labels may be assigned to the various circuits or other electrical devices disclosed, such labels are not intended to limit the scope of operation for the circuits and the other electrical devices. Such circuits and other electrical devices may be combined with each other and/or separated in any manner based on the particular type of electrical implementation that is desired. It is recognized that any circuit or other electrical device disclosed herein may include any number of microprocessors, integrated circuits, memory devices (e.g., FLASH, RAM, ROM, EPROM, EEPROM, or other suitable variants thereof) and software which co-act with one another to perform operation(s) disclosed herein. 
         [0014]      FIG. 1  depicts an apparatus  10  for correcting a DC bias for leakage current in accordance to one embodiment of the present disclosure. It is recognized that the apparatus  10  may correct an alternating current (AC) as well. The apparatus  10  includes a cord set  12 . A connection  13  is formed between the cord set  12  and a wall outlet  14 . The wall outlet  14  is generally positioned about a residence, commercial establishment, or charging station for providing AC energy to a vehicle  18  for charging the same. 
         [0015]    The cord set  12  enables the delivery of AC based energy from a power supply (not shown) operably coupled to the wall outlet  14  (that is equipped with a ground fault interrupt (GFI  15 )) to a power conversion device  16  (such as a battery charger or other suitable device) in the vehicle  18 . The cord set  12  may be a portable device that is capable of electrically coupling the vehicle  18  to the wall outlet  14 . The cord set  12  may include a number of switches  21  that enable electrical transfer between the wall outlet  14  and the vehicle  18 . Such switches  21  are generally closed to enable energy transfer to the vehicle  18 . In one example, the cord set  12  may also be a device that is positioned within the residence, commercial establishment, or charging station. In another example, the cord set  12  may be incorporated within an on-board computer/controller in the vehicle  18 . The power conversion device  16  converts the AC energy into DC energy for storage on one or more batteries (not shown) in the vehicle  18 . As depicted, the cord set  12  receives an input line (“L 1 ”), a neutral line (“N”), and ground (“GND”) from the connection  13 . 
         [0016]    The cord set  12  includes a balance circuit  22  to reduce vehicle AC leakage current (see vehicle leakage current  17  in  FIG. 1 ) to a value that is less than a tripping current of the GFI  15  at the wall outlet  14 . During a charging operation, vehicle AC leakage current may exceed the maximum amount of leakage current allowed at the GFI  15 . A current sensor  19  provides a current reading that is indicative of the vehicle leakage current  17  (or I sense ) to the balance circuit  22 . The current reading received at the balance circuit  22  and depicted as I sense  generally corresponds to the vehicle leakage current  17 . The vehicle leakage current  17  may be attributed to a differential resistance that causes input energy flowing from the wall outlet  14  to the vehicle  18  through L 1  to be different from the energy flowing from the vehicle  18  back to the wall outlet  14  through N. The vehicle leakage current  17  as shown in  FIG. 1  is provided for illustrative purposes. 
         [0017]    The balance circuit  22  may adjust the flow of AC current flowing from the vehicle  18  back to the wall outlet  14  (e.g., through N) to be generally similar to the flow of AC current flowing from the wall outlet  14  to the vehicle  18  (e.g., through L 1 ) to prevent undesired tripping at the GFI  15 . For example, the balance circuit  22  reduces the amount of vehicle AC leakage current to be less than the maximum amount of leakage current at the GFI  15  to prevent undesired/unwarranted tripping of the GFI  15 . The balance circuit  22  provides a compensated current (e.g., I comp ) that is indicative of an adjusted amount of AC current that is flowing from the vehicle  18  back to the wall outlet  14 . I comp  is generally equal to the amount of alternating current that flows from the wall outlet  14  to the vehicle  18  during the charging operation (e.g., between L 1  and N to and from the vehicle  18 ). Because L comp  is generally similar to the amount of current flowing to the vehicle  18 , such a condition may prevent the GFI  15  from an undesired tripping event. One example of the manner in which the balance circuit  22  reduces (or balances) the leakage current is set forth in co-pending U.S. Ser. No. 12/775,124; entitled “APPARATUS AND METHOD FOR BALANCING THE TRANSFER OF ELECTRICAL ENERGY FROM AN EXTERNAL POWER” filed on May 6, 2010 which is hereby incorporated by reference in its entirety. 
         [0018]    The switches  21  may be opened during a charging operation in the event the vehicle leakage current  17  is detected to exceed a predetermined current value for safety purposes. However, if the vehicle leakage current  17  is detected to be below the predetermined current value (i.e., a safe current level), it is still possible for the GFI  15  to experience an undesired tripping event. For example, the GFI  15  may be set to trip at 5 mA and the predetermined current value may be set to 20 mA. If the vehicle leakage current  17  exceeds 5 mA and yet, remains below 20 mA, then the GFI  15  may trip. Such an undesired tripping event could prevent vehicle charging. Thus, the balance circuit  22  may compensate (or balance) for the vehicle leakage current  17  so long as such a current is detected to be below the predetermined current level. In general, the switches  21  are configured to trip faster than the GFI  15  in the event the current exceeds the predetermined current value. 
         [0019]    In general, the balance circuit  22  includes any number of electrical devices (or electronics) for enabling the transfer of the AC energy to the vehicle and for balancing the vehicle AC leakage current. A byproduct of such electronics is the presence of a DC leakage current along with the AC leakage current that may be generated when the vehicle is undergoing a charging operation. In one example, the DC leakage current may be generated from various electronics such as amplifier input offset currents or input offset voltages. The DC leakage current may also cause the GFI  15  (in addition to the AC leakage current) to experience unwanted tripping events and may lead to an overall reduction in vehicle charging efficiency due to power loss attributed therefrom. As noted above, the balance circuit  22  may generate I comp  to offset the vehicle AC leakage current. The balance circuit  22  may also mitigate or reduce the DC leakage current as will be discussed in more detail below. 
         [0020]      FIG. 2  depicts a more detailed implementation of the balance bias circuit  22  in accordance to one embodiment of the present invention. The circuit  22  is generally configured to determine the amount of DC leakage current that is present along with the AC leakage current and to minimize or eliminate the DC leakage current to prevent unwarranted tripping events at the GFI  15  and/or to ensure a high vehicle charging efficiency. The vehicle leakage current  17  (or I sense  as received from the current sensor  19 ) as depicted in  FIG. 2  may include an AC leakage current component (“ACLCC”) and a DC leakage current component (“DCLCC”). The circuit  22  includes an adder circuit  50 , a current measure circuit  52 , a filter  54 , an inverter  56  and a DC measurement error circuit  58 . The adder circuit  50  receives I sense , which includes the ACLCC and the DCLCC. As noted above, the vehicle leakage current  17  in the apparatus  10  may be present during a vehicle charging operation. 
         [0021]    The current measure circuit  52  measures the amount of ACLCC and DCLCC that is present in the vehicle leakage current  17 . Such information may be stored in memory (not shown). The filter  54  may be implemented as a low pass filter (or other suitable device) to separate the ACLCC from the DCLCC on the vehicle leakage current  17 . The filter  54  outputs a voltage that corresponds to the amount of DCLCC that is part of the vehicle leakage current  17 . The inverter  56  inverts the voltage output of the filter  54 . The circuit  22  uses the ACLCC to output I comp . 
         [0022]    The DC measurement error circuit  58  is generally configured to generate a voltage output that corresponds to the DCLCC, which is attributed to various electronics within the apparatus  10 . For example, it is known that various electronics (such as, but not limited to, operational amplifiers, comparators, etc.) may be imperfect. The output of such electronics may drift over time and temperature, which can lead to the generation of the DCLCC in the apparatus  10 . The electronics and their respective imperfections associated in providing electromagnetic compatibility (EMC) filtering inside the vehicle in connection with performing the battery charging operation may also add to the DCLCC. The DC measurement error circuit  58  is configured to store a voltage that corresponds to the amount of DCLCC by taking into account the imperfections of the various electronics. The filter  54  separates the DCLCC from the ACLCC and passes the DCLCC therethrough. Generally, the circuit  58  may be comprised of, but not limited to, an amplifier and various resistors. The overall formation of the circuit  58  may be formed in a number or arrangements upon recognition of its intended function as is now disclosed herein. 
         [0023]    The DC measurement error circuit  58  may take into account various conditions of the electronics which cause the DCLCC such as temperature, offsets, and drifts that are generated therefrom and output an offset voltage that corresponds to the DCLCC. The offset value is stored within the cord set  12  may be a predefined voltage value that is based on the temperature, offsets, or drifts of various electronics used within the apparatus  10  (or various electronics generally used in enabling a vehicle charging operation). The DCLCC may be ascertained by performing circuit analysis of the various electronics in the apparatus  10  to understand the impact of the various temperatures, offset and drifts of the electronics in the apparatus  10 . 
         [0024]    The DC measurement error circuit  58  outputs a positive voltage value (or offset voltage) that is generally similar to the measured DCLCC. The positive offset voltage, provided from the DC measurement error circuit  58 , is summed to the negative value of the DCLCC from the output of the inverter  56 . By summing the DCLCC of opposite values at the output of the inverter  56  and at the output of the DC measurement error circuit  58 , the DCLCC present in the apparatus  10  may be substantially canceled out, minimized, or negated. The balance circuit  22  outputs I comp  which may be similar to ACLCC (e.g., does not include DCLCC which can increase the overall vehicle leakage current and cause undesired tripping events). 
         [0025]      FIG. 3  depicts a method  70  for correcting the DC bias for leakage current in accordance to one embodiment of the present disclosure. The particular order of the operations in the method  70  when performed can be in any order and are not to be limited to only being performed sequentially. The order of the operations may be modified and vary based on the desired criteria of a particular implementation. 
         [0026]    In operation  72 , the adder circuit  50  receives I sense  from the current sensor  19 . As noted above, the current sensor  19  measures current which is generally indicative of the vehicle leakage current  17 . The vehicle leakage current  17  is considered to be similar to I sense . 
         [0027]    In operation  74 , the current measure circuit  52  measures the ACLCC and the DCLCC that is present on I sense . The balance circuit  22  generates I comp  to balance the AC leakage current that is present vehicle leakage current  17  in response to measuring the ACLCC. 
         [0028]    In operation  76 , the filter  54  removes the ACLCC from the vehicle leakage current  17  and allows the DCLCC to pass therethrough. 
         [0029]    In operation  78 , the inverter  56  inverts the DCLCC to generate a negative value of DCLCC once received from the filter  54 . 
         [0030]    In operation  80 , the DC measurement error circuit  58  provides a stored positive offset value of DCLCC. The positive offset value of DCLCC may be a predefined value that is determined based on the various drifts that may occur overtime in connection with the electronics in the apparatus  10 . The positive offset of the DCLCC is applied to the negative DCLCCC to cancel out the negative DCLCC. 
         [0031]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.