Patent Abstract:
A method for monitoring a temperature change of a power distribution circuit having a power line and return line includes measuring an output current and output voltage of the power distribution circuit at an input to a load electrically connected to the power distribution circuit, and determining a change in temperature of at least one of the power line and return line based on a change in at least one of the output current and output voltage.

Full Description:
BACKGROUND 
       [0001]    A power cable is an assembly of two or more electrical conductors, usually held together with a sheath. The assembly may be used for transmission of electrical power. Power cables may be installed, for example, as permanent wiring within buildings, buried in the ground, run overhead or exposed. Flexible power cables may be used for portable devices, mobile tools and machinery. 
         [0002]    Cables may include three major components: conductors, insulation and protective jacketing. The makeup of individual cables may vary according to application. The construction and material may be determined by the working voltage, current-carrying capacity and environmental conditions. 
         [0003]    Power cables may use stranded copper or aluminum conductors. Small power cables may use solid conductors. The cable may include un-insulated conductors for circuit neutral or ground (earth) connection. 
         [0004]    The overall assembly may be round or flat. Non-conducting filler strands may be added to the assembly to maintain its shape. Special purpose power cables for overhead or vertical use may have additional elements such as steel or Kevlar structural supports. 
         [0005]    Common types of general-purpose cables are regulated by national and/or international codes. These codes define the various wire alloys that may make up a cable, its insulation type and characteristics, including its resistance to chemicals and sunlight. 
         [0006]    Commonly-used power cables may contain an un-insulated bare wire for connection to earth ground. Three prong power outlets and plug-cords require a grounding wire. Extension cables often have an insulated grounding wire. 
         [0007]    ROMEX is a cable made of solid copper wires with a nonmetallic plastic jacket containing a waxed paper wrapped inner group of at least a pair of 600 volt THWN plastic insulated service wires and a bare ground wire. A common ROMEX cable may thus have three wires: a neutral wire (colored white), a wire providing power to the load (colored black) and a bare grounding wire. 
         [0008]    Another common ROMEX variant has a neutral, identified by white coloring, two phase wires: a first conductor (black) and a second conductor (usually red), and an un-insulated copper grounding wire. This type may be generally used for multiple switching locations of a common or shared lighting arrangement, such as for switches located at either end of a hallway, or on both upper and lower floors for stairway lighting. 
       SUMMARY 
       [0009]    A method for monitoring a temperature change of a power distribution circuit having a power line and return line includes measuring an output current and output voltage of the power distribution circuit at an input to a load electrically connected to the power distribution circuit, and determining a change in temperature of at least one of the power line and return line based on a change in at least one of the output current and output voltage. 
         [0010]    An automotive vehicle having a power storage unit capable of receiving power from a power distribution circuit having a power line and return line includes a monitoring circuit capable of being electrically connected between the power distribution circuit and the power storage unit. The monitoring circuit is configured to measure an output current and output voltage of the power distribution circuit, and determine a change in temperature of at least one of the power line and return line based on a change in at least one of the output current and output voltage. 
         [0011]    A battery charger capable of receiving power from a power distribution circuit having a power line and return line, and capable of transferring the power to a battery includes a monitoring circuit. The monitoring circuit is configured to measure an output current and output voltage of the power distribution circuit at the battery charger, and to determine a change in temperature of at least one of the power line and return line based on a change in at least one of the output current and output voltage. 
         [0012]    A method for monitoring a temperature change of a power distribution circuit having a power line and return line includes measuring an output current or output voltage of the power distribution circuit at an input to a load electrically connected to the power distribution circuit, measuring an input current and input voltage to the load, and determining a change in temperature of at least one of the power line and return line based on a change in at least one of the output current, output voltage, input current and input voltage. 
         [0013]    While example embodiments in accordance with the invention are illustrated and disclosed, such disclosure should not be construed to limit the invention. It is anticipated that various modifications and alternative designs may be made without departing from the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a schematic diagram of an automotive vehicle according to an embodiment of the invention. 
           [0015]      FIG. 2  is a schematic diagram of a battery charger according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Referring now to  FIG. 1 , an embodiment of an automotive vehicle  10 , e.g., hybrid electric, electric, etc., includes a traction battery  12 , electric machine  13 , battery charger  14  and chassis  15 . As apparent to those of ordinary skill, the traction battery  12  may provide motive power for the vehicle  10  via the electric machine  13 . 
         [0017]    The battery charger  14  may include a pair of coils  16 ,  18 , a bridge rectifier  20 , transistor  22 , diode  24  and inductor  26 . As apparent to those of ordinary skill, the transistor  22 , diode  24  and inductor  26  form a buck regulator  27  and may be used to regulate the current from the bridge rectifier  20  to the traction battery  12 . 
         [0018]    The coil  18  includes a power terminal  28  and a return terminal  30 . The coil  18  may be electrically connected with an electrical outlet  32  via a power cable  34 . The electrical outlet  32  of  FIG. 1  is a 120 V wall outlet. In other embodiments, the electrical outlet  32  may be a 240 V wall outlet, a multiphase wall outlet, etc. As known in the art, the turn ratio of the coils  16 ,  18  may depend on the voltages associated with the battery  12  and outlet  32 . 
         [0019]    The coil  16  may be electrically connected with the traction battery  12  through the bridge rectifier  20 , transistor  22  and inductor  26 . As known in the art, the bridge rectifier  20  (or diode bridge) may be an arrangement of four diodes in a bridge configuration. This arrangement may provide the same polarity of output voltage for any polarity of input voltage. In this embodiment, the bridge rectifier  20  converts alternating current input into direct current output. 
         [0020]    The power cable  34  includes a power line  36 , return line  38  and ground line  40 . The power line  36  is electrically connected with the power terminal  28 . The return line  38  is electrically connected with the return terminal  30 . The ground line  40  is electrically connected with the chassis  15 . In the embodiment of  FIG. 1 , the power line  36  delivers current from the outlet  32  to the coil  18  and the return line  38  delivers current from the coil  18  to the outlet  32 . 
         [0021]    The battery charger  14  may also include a microprocessor  42 , current sensors  44 ,  45  and voltage sensors  46 ,  47 . The microprocessor receives current and voltage information from the current sensors  44 ,  45  and voltage sensors  46 ,  47 . In the embodiment of  FIG. 1 , the current sensor  44  senses current through the coil  18  and return terminal  30  and the voltage sensor  46  senses voltage between the return terminal  30  and ground line  40 . The current sensor  45  senses current to the traction battery  12  and the voltage sensor  47  senses voltage across the traction battery  12 . Other arrangements, however, are also possible. As an example, the voltage sensor  46  may be positioned to sense voltage between the power terminal  28  and return terminal  30 . As another example, the current sensor  44  and/or voltage sensor  46  may be positioned to sense current and/or voltage between the bridge rectifier  20  and transistor  22 . Other configurations are also contemplated. 
         [0022]    The microprocessor  42  may determine a change in temperature of the power and/or return lines  36 ,  38  based on, for example, the current and voltage measured by the current and voltage sensors  44 ,  46 . The instantaneous resistance, R, of a wire having a temperature coefficient of resistance, α, may be related to a change in temperature, ΔT, of the power and/or return lines  36 ,  38  by the following relation: 
         [0000]    
       
         
           
             
               
                 
                   
                     R 
                     = 
                     
                       
                         R 
                         i 
                       
                        
                       
                         ( 
                         
                           1 
                           + 
                           
                             αΔ 
                              
                             
                                 
                             
                              
                             T 
                           
                         
                         ) 
                       
                     
                   
                   , 
                   
                     
 
                   
                    
                   or 
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
             
               
                 
                   
                     Δ 
                      
                     
                         
                     
                      
                     T 
                   
                   = 
                   
                     
                       Δ 
                        
                       
                           
                       
                        
                       R 
                     
                     
                       α 
                        
                       
                           
                       
                        
                       
                         R 
                         i 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where R i  is the initial resistance of the wire. In terms of voltages and currents, equation (2) may be rewritten as 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       Δ 
                        
                       
                           
                       
                        
                       T 
                     
                     = 
                     
                       
                         ( 
                         
                           
                             V 
                             I 
                           
                           - 
                           
                             
                               V 
                               i 
                             
                             
                               I 
                               i 
                             
                           
                         
                         ) 
                       
                        
                       
                         ( 
                         
                           
                             I 
                             i 
                           
                           
                             V 
                             i 
                           
                         
                         ) 
                       
                        
                       
                         ( 
                         
                           1 
                           α 
                         
                         ) 
                       
                     
                   
                   , 
                   
                     
 
                   
                    
                   or 
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
             
               
                 
                   
                     Δ 
                      
                     
                         
                     
                      
                     T 
                   
                   = 
                   
                     
                       ( 
                       
                         
                           
                             VI 
                             i 
                           
                           
                             
                               V 
                               i 
                             
                              
                             I 
                           
                         
                         - 
                         1 
                       
                       ) 
                     
                      
                     
                       ( 
                       
                         1 
                         α 
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where I and V are the instantaneous current and voltage measured respectively by the sensors  44 ,  46 , and I i  and V i  are the initial current and voltage measured respectively by the sensors  44 ,  46 . Based on equation (4), the microprocessor  42  may determine a change in temperature of the power and/or return lines  36 ,  38  based on the current and voltage measured by the current and voltage sensors  44 ,  46 . In other embodiments, the battery charger  14  may control the current flow through it to keep it generally constant, in a known fashion, and thus the microprocessor  42  may determine a change in temperature of the power and/or return lines  36 ,  38  based only on the voltage measured by the voltage sensor  46 . In still other embodiments, the microprocessor  42  may determine a change in temperature of the power and/or return lines  36 ,  38  based on the voltage measured between the power terminal  28  and return terminal  30 . As apparent to those of ordinary skill (using the notation described above), 
         [0000]    
       
         
           
             
               
                 
                   
                     R 
                     i 
                   
                   = 
                   
                     
                       
                         V 
                         LN 
                         - 
                       
                       - 
                       
                         V 
                         
                           LN 
                           i 
                         
                         + 
                       
                     
                     
                       2 
                        
                       I 
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
             
               
                 
                   R 
                   = 
                   
                     
                       
                         V 
                         LN 
                         - 
                       
                       - 
                       
                         V 
                         LN 
                         + 
                       
                     
                     
                       2 
                        
                       I 
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where V LN   −  is the instantaneous voltage between the power terminal  28  and return terminal  30  just before current begins passing through the battery charger  14 , V LNi   +  is the instantaneous voltage between the power terminal  28  and return terminal  30  just after current begins passing through the battery charger  14 , and V LN   +  is the instantaneous voltage between the power terminal  28  and return terminal  30  at any time after current begins passing through the battery charger  14 . Substituting equations (5) and (6) into equation (2) (and simplifying) yields 
         [0000]    
       
         
           
             
               
                 
                   
                     Δ 
                      
                     
                         
                     
                      
                     T 
                   
                   = 
                   
                     
                       ( 
                       
                         
                           
                             
                               V 
                               LN 
                               - 
                             
                             - 
                             
                               V 
                               LN 
                               + 
                             
                           
                           
                             
                               V 
                               LN 
                               - 
                             
                             - 
                             
                               V 
                               LNi 
                               + 
                             
                           
                         
                         - 
                         1 
                       
                       ) 
                     
                      
                     
                       ( 
                       
                         1 
                         α 
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
         [0000]    Based on equation (7), the microprocessor  42  may thus determine a change in temperature of the power and/or return lines  36 ,  38  based on the voltage measured between the power terminal  28  and return terminal  30 . 
         [0023]    Alternatively, a temperature or change in temperature of the power and/or return lines  36 ,  38  may be determined in any suitable fashion. For example, temperature sensors (not shown), e.g., Wheatstone bridge, diode junction, etc., in communication with the microprocessor  42  and connected with the power and/or return lines  36 ,  38  may detect and communicate the temperature of the power and/or return lines  36 ,  38  to the microprocessor  42 . 
         [0024]    The microprocessor  42  may turn on and turn off the transistor  22  to control the flow of current to the traction battery  12 . The microprocessor  42  may thus control the flow of current through the power and/or return lines  28 ,  30  via the transistor  22 . 
         [0025]    The power, P in , into the coil  18  is equal to the power, P out , out of the coil  16  (assuming negligible losses): 
         [0000]      P i =P out    (8) 
         [0000]    In terms of currents and voltages, equation (8) may be rewritten as 
         [0000]      ( I   rms   ·V   rms )cos θ= I   BAT   ·V   BAT    (9) 
         [0000]    where I rms  and V rms  are the root mean square current into and root mean square voltage across the coil  18  respectively, I BAT  and V BAT  are the current into and voltage across the traction battery  12  (the current and voltage measured by sensors  45 ,  47  respectively), and Cos θ is the phase angle between I rms  and V rms . (As apparent to those of ordinary skill, Cos θ is typically equal to 1 in systems with unity power factor correction.) Assuming V rms  and V BAT  are generally constant and according to equation (9), changes in I BAT  will result in changes to I rms . That is, decreasing the duty cycle of the transistor  22  to reduce I BAT  will reduce I rms . (The microprocessor  42  may thus also determine a change in temperature of the power and/or return lines  36 ,  38  based on the current and voltage measured by the current sensor  44 ,  45  and voltage sensor  47 . For example, equation (9) may be rearranged to solve for V rms  and substituted into (7)). 
         [0026]    To maintain the temperature of the power and/or return lines  28 ,  30  within a desired range, the microprocessor  42  may begin to cycle the transistor  22 , in a known manner, as the temperature and/or change in temperature of the power and/or return lines  28 ,  30  begins to approach an upper end of the range. For example, the microprocessor  42  may begin to cycle the transistor  42  to reduce the current flow if the change in temperature of the power and/or return lines  28 ,  30  exceeds 35 degrees C. Alternatively, the microprocessor  42  may begin to cycle the transistor  42  to reduce the current flow if the temperature of the power and/or return lines  28 ,  30  is within 7 degrees C. of the upper end of the range. Any suitable control scheme, however, may be used. 
         [0027]    As illustrated, the charger  14  is integrated with the vehicle  10 . In other embodiments, however, the charger  14  may be remote from the vehicle  10 . For example, the charger  14  may be a stand alone unit that may be plugged into the electrical outlet  32  and vehicle  10 . Other arrangements are also possible. 
         [0028]    Referring now to  FIG. 2 , numbered elements that differ by 100 relative to numbered elements of  FIG. 1  have descriptions that are similar, although not necessarily identical, to the numbered elements of  FIG. 1 . 
         [0029]    An embodiment of a battery charger  114  includes a bridge rectifier  120 , boost regulator  121 , buck regulator  127  and microprocessor  142 . The bridge rectifier  120  is electrically connected with the boost regulator  121 . The boost regulator  121  is electrically connected with the buck regulator  127 . The microprocessor  142  may control the boost and buck regulators  121 ,  127 . The circuitry of the bridge rectifier  120 , boost regulator  121  and buck regulator  127  may take any suitable form. 
         [0030]    The bridge rectifier  120  may be electrically connected with an electrical power outlet (not shown) and convert alternating current input into direct current output. As apparent to those of ordinary skill, the microprocessor  142  may control the boost regulator  121 , in a known fashion, to regulate the direct current output by the bridge rectifier  120  for power factor correction. Based on current and/or voltage measurements by the sensors  144 ,  146 , the microprocessor  142  may control the buck regulator  127 , using techniques similar to those described above, for power distribution temperature management. Of course, other arrangements and/or configurations are also possible. 
         [0031]    While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. 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.

Technology Classification (CPC): 8