Patent Document

TECHNICAL FIELD 
     This disclosure relates to isolation detection circuitry for battery packs used in automotive vehicles. 
     BACKGROUND 
     High voltage may be required to increase the output of a power supply for driving an electric or hybrid-electric vehicle: output is proportional to the product of voltage and current. The output voltage of a power supply for driving an electric or hybrid-electric vehicle, for example, may be 200 V or more. These power supplies may not be grounded. Hence, leakage currents associated with these power supplies may be undesirable. A leakage current may exist when a resistance between a power supply and chassis is present. 
     SUMMARY 
     A vehicle may include first and second battery packs spaced away from each other within the vehicle, and a leakage detection circuit. The leakage detection circuit may include a first precision resistor disposed within the first battery pack and electrically connected with chassis ground, and a switching element and first series limiting resistor disposed within the second battery pack and electrically connected in series with the first precision resistor. The leakage detection circuit responds to leakage currents within the second battery pack. 
     A vehicle may include a plurality of battery packs positioned at different locations within the vehicle. One of the packs may include a plurality of resistors each being electrically connected with chassis ground and a different one of the packs, and sense circuitry configured to detect voltage across each of the resistors. The vehicle may further include at least one controller configured to determine presence of leakage currents associated with other of the packs based on the detected voltages. 
     A power system for a vehicle may include a first battery pack including a plurality of battery cells and a switching element electrically connected with the battery cells. The power system may also include a second battery pack spaced away from the first battery pack and including a resistor electrically connected in series with the switching element, and sense circuitry configured to detect voltage across the resistor indicative of leakage current associated with the first battery pack. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a battery pack and associated isolation detection circuitry for an automotive vehicle. 
         FIG. 2  is a block diagram of an alternatively powered vehicle having a distributed set of battery packs. 
         FIG. 3  is a schematic diagram of the distributed set of battery packs of  FIG. 2  and associated isolation detection circuitry. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     Referring to  FIG. 1 , a battery pack  10  for an automotive vehicle (not shown) may include a plurality of battery cells  12   a - 12   n  (electrically connected in series), switches  14 ,  16  (e.g., contactors, etc.), isolation detection circuitry  18 , and sense circuitry  19  disposed within a housing  20 . The switches  14 ,  16  may be closed to electrically connect the battery cells  12   a - 12   n  to terminals  22 ,  24  associated with a high voltage bus. As known in the art, an electric machine configured to generate motive power for the vehicle may be electrically connected with such a high voltage bus. Hence, the battery cells  12   a - 12   n  may provide electrical current for consumption by the electric machine. 
     The isolation detection circuitry  18  includes a switch  26 , a (series limiting) resistor  28 , and a (precision) resistor  30  electrically connected in series between chassis ground and a node defined by the electrical connection between the battery cell  12   a  and the switch  14  (referred to herein as node A). The isolation detection circuitry  18  also includes a switch  32 , a (series limiting) resistor  34 , and a (precision) resistor  36  electrically connected in series between chassis ground and a node defined by the electrical connection between the battery cell  12   n  and the switch  16  (referred to herein as node B). The voltage across each of the resistors  30 ,  36  is proportional to the current flowing through them. 
     A current leak at node A may be detected by opening the switch  26 , closing the switches  14 ,  16 ,  32 , and measuring the voltage across the resistor  36 . (That is, an Ohmic leak is intentionally created between node B and the chassis, and the resulting voltage across the resistor  36  is measured via the sense circuitry  19 . Ohm&#39;s law may then be used to determine the current flowing through the resistor  36 , which is equal to the leakage current associate with node A.) Similarly, a current leak at node B may be detected by opening the switch  32 , closing the switches  14 ,  15 ,  26  and measuring the voltage across the resistor  30 . Other techniques and architectures may also be used to detect current leaks in a single battery pack. 
     Referring to  FIG. 2 , an alternatively powered vehicle  38  (e.g., a battery electric vehicle, a hybrid-electric vehicle, a plug-in hybrid-electric vehicle, etc.) may include an electric machine  40  (e.g., motor, motor/generator, etc.), a transmission  42  (e.g., power-split, mechanical, etc.), and wheels  44 . The electric machine  40  is arranged to mechanically drive the transmission  42  (as indicated by thick line), and the transmission  42  is arranged to mechanically drive the wheels  44  (as indicated by thick line). If the vehicle  38  is a hybrid-type vehicle, it may of course include an engine (not shown) arranged to also selectively mechanically drive the transmission  42 . Other arrangements are also possible. 
     The vehicle  38  may also include battery packs  46 ,  48  (or more battery packs in certain arrangements) and controllers  50 ,  51  disposed within the battery packs  46 ,  48  respectively. The battery packs  46 ,  48  are electrically connected together (as indicated by thin line) in series, and the battery pack  46  is electrically connected with the electric machine  40  (as indicated by thin line). Hence, the battery packs  46 ,  48  may provide electrical current for consumption by the electric machine  40 . In the example of  FIG. 2 , the battery packs  46 ,  48  are distributed throughout the vehicle  38 . That is, the battery pack  46  is positioned in a certain location within the vehicle  38  (e.g., inside the vehicle&#39;s cabin) and the battery pack  48  is positioned in a different location within the vehicle  38  (e.g., underneath the vehicle&#39;s cabin). Such battery pack arrangements may be used to better package battery cells within the vehicle  38 . In other examples, the controllers  50 ,  51  may be separate from the battery packs  46 ,  48 ; the battery packs  46 ,  48  may be electrically connected together in parallel; and/or the battery packs  46 ,  48  may each be electrically connected with the electric machine  40 . Other arrangements are also contemplated. 
     The battery pack  46  is in communication with/under the control of the controller  50 . The battery pack  48  is in communication with/under the control of the controller  51 . The controllers  50 ,  51  are in communication with each other (as indicated dashed line). 
     Current leaks may occur within either or both of the battery packs  46 ,  48 . Hence, it may be desirable to detect the presence of such leaks. Merely providing isolation detection circuitry similar to that described with respect to  FIG. 1  in each of the battery packs  46 ,  48 , however, may not be practical. It may be cost prohibitive, for example, to provide sense circuitry similar to that described with respect to  FIG. 1  in each of the battery packs  46 ,  48 . Moreover, it may be difficult to coordinate isolation checks of battery packs so arranged. As discussed in more detail below, the battery packs  46 ,  48  may include isolation detection circuitry that enables the detection of current leaks with centrally located sense circuitry. 
     Referring to  FIG. 3 , the battery pack  46  may include the controller  50 , a plurality of battery cells  52   a - 52   n  (electrically connected in series), switch  54  (e.g., a contactor, etc.), isolation detection circuitry  56 , and sense circuitry  58  disposed within a housing  60 . The switch  54  may be closed to electrically connect the battery cells to a terminal  61 , which is electrically connected with a high voltage bus (not shown). The electric machine  40  ( FIG. 2 ) is also electrically connected with this high voltage bus. 
     The isolation detection circuitry  56  may include a switch  62 , a (series limiting) resistor  64 , and a (precision) resistor  66  electrically connected in series between chassis ground and a node defined by the electrical connection between the battery cell  52   a  and the switch  54  (referred to herein as node X). The isolation detection circuitry  56  may also include a switch  68 , a (series limiting) resistor  70 , and a (precision) resistor  72  electrically connected in series between chassis ground and a node defined by the electrical connection between the battery cell  52   n  and a battery cell  74   a  (referred to herein as node Y). The voltage across each of the resistors  66 ,  72  is proportional to the current flowing through them. 
     The battery pack  48  may include the controller  51 , a plurality of battery cells  74   a - 74   n  (electrically connected in series) and switch  76  disposed within a housing  78 . The switch  76  may be closed to electrically connect the battery cells to a terminal  80 , which is electrically connected with the high voltage bus described above and the electric machine  40  ( FIG. 2 ). 
     Isolation detection circuitry  82  is distributed between the battery packs  46 ,  48 . That is in the example of  FIG. 3 , the isolation detection circuitry  82  may include a switch  84  and a (series limiting) resistor  86  disposed within the housing  78 , and a (series limiting) resistor  88  and a (precision) resistor  90  disposed within the housing  60 . Hence, the centrally located sense circuitry  58 , which in this example happens to be associated with the battery pack  46 , may be used to detect the voltage across any of the resistors  66 ,  72 ,  90  by way of an analog to digital converter whose reference node is connected with chassis ground. A multiplexer circuit as commonly found in such converters may then be used to select among the voltages associated with the resistors  66 ,  72 ,  90 . 
     The switch  84  and resistor  86  are electrically connected in series between the resistor  88  and a node defined by the electrical connection between the battery cell  74   n  and the switch  76  (referred to herein as node Z). The resistors  88 ,  90  are electrically connected in series between chassis ground and the resistor  86 . The resistors  86 ,  88  prevent excessive current from flowing through them when their associated wires are shorted. Either of the resistors  86 ,  88 , in other examples, may be omitted. Such omission, however, may result in thermal or other issues. 
     The controller  50  may include, inter alia, the isolation detection circuitry  56 , the sense circuitry  58 , and the resistors  88 ,  90 . The controller  51  may include, inter alia, the switch  84  and the resistor  86 . Other configurations are also contemplated. 
     This architecture may be used with any number of battery packs. That is, a central battery pack may include centrally located sense circuitry and (precision) resistors electrically connected with chassis ground for each of a set of satellite battery packs. Each of the (precision) resistors may then be electrically connected with a switch located within a corresponding satellite battery pack via one or more (series limiting) resistors located within the satellite battery pack and/or the central battery pack similar to that described with reference to  FIG. 3 . Other arrangements are also possible. 
     The controllers  50 ,  51  may operate to determine whether the isolation detection circuits  56 ,  82  and sense circuitry  58  are in proper working order: (a) the switch  68  may be opened, the switches  62 ,  84  may be closed, and the voltages across the resistors  66 ,  90  and the voltage from node X to node Z may be measured. This information may then be evaluated according to (1) and (2):
 
 V pack-est=(( V 66/ R 66)*( R 66+ R 64))+(( V 90/ R 90)*( R 90+( R 88+ R 86)))  (1)
 
| V pack-est− VXZ|≦α   (2)
 
where VXZ is the voltage difference between the nodes X and Z, V 66  is the voltage across the resistor  66 , V 90  is the voltage across the resistor  90 , R 64 , R 66 , R 86  and R 88  are the resistances of the resistors  64 ,  66 ,  86  and  88  respectively, and α is a predetermined value; (b) the switch  84  may be opened, the switches  62 ,  68  may be closed, and the voltages across the resistors  66 ,  72  and the voltage from node X to node Y may be measured. This information may then be evaluated according to (3) and (4):
 
 V 2pack-est=(( V 66/ R 66)*( R 66+ R 64))+(( V 72/ R 72)*( R 72+ R 70))  (3)
 
| V 2pack-est− VXY|≦β   (4)
 
where VXY is the voltage difference between the nodes X and Y, V 66  is the voltage across the resistor  66 , V 72  is the voltage across the resistor  72 , R 64 , R 66 , R 70  and R 72  are the resistances of the resistors  64 ,  66 ,  70  and  72  respectively, and β is a predetermined value; and (c) the switch  62  may be opened, the switches  68 ,  84  may be closed, and the voltages across the resistors  72 ,  90  and the voltage from node Y to node Z may be measured. This information may then be evaluated according to (5) and (6):
 
 V 3pack-est=(( V 90/ R 90)*( R 90+ R 88))+(( V 72/ R 72)*( R 72+ R 70))  (5)
 
| V 3pack-est− VYZ|≦γ   (6)
 
where VYZ is the voltage difference between the nodes Y and Z, V 90  is the voltage across the resistor  90 , V 72  is the voltage across the resistor  72 , R 70 , R 72 , R 88  and R 90  are the resistances of the resistors  70 ,  72 ,  88  and  90  respectively, and γ is a predetermined value.
 
     If (2), (4) and (6) are true, the isolation detection circuits  56 ,  82  and sense circuitry  58  are in proper working order. If any of (2), (4) and (6) is not true, the isolation detection circuits  56 ,  82  or sense circuitry  58  may not be in proper working order. 
     The controllers  50 ,  51  may perform a leakage check from node X to chassis: the switch  84  may be closed, the switches  62 ,  68  may be opened, and the voltage across the resistor  90 , V 90 , and the voltage from node X to node Z, VXZ, may be measured. The system leakage resistance, Rleakx, may then be expressed as a function of VXZ and V 90 :
 
 VXZ *( R 90/( R 90+ R 88+ R 86+ R leak x ))= V 90  (7)
 
where R 86 , R 88  and R 90  are the known resistances of the resistors  86 ,  88 ,  90  respectively. (7) may be rearranged to solve for Rleakx using known techniques.
 
     The controllers  50 ,  51  may perform a leakage check from node Z to chassis: the switch  62  may be closed, the switches  68 ,  84  may be opened, and the voltage across the resistor  66 , V 66 , and the voltage from node X to node Z, VXZ, may be measured. The system leakage resistance, Rleakz, may then be expressed as a function of VXZ and V 66 :
 
 VXZ*[R 66/( R 66+ R 64+ R leak z )]= V 66  (8)
 
where R 64  and R 66  are the known resistances of the resistors  64 ,  66  respectively. (8) may be rearranged to solve for Rleakz using known techniques.
 
     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.

Technology Category: 4