Patent Publication Number: US-11656265-B2

Title: Apparatus for measuring insulation resistance

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Korean Patent Application No. 10-2020-0044425 filed Apr. 13, 2020, the disclosure of which is hereby incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an apparatus capable of measuring an insulation resistance of a battery. 
     Description of Related Art 
     Recently, an electric vehicle (EV) using an electric battery capable of charging and discharging as a power source has been commercialized as an eco-friendly vehicle. The electric vehicle includes a battery pack used as a power source that provides a high voltage (HV) to a driving electric motor, an inverter, a converter, and the like that require the high voltage for the operation of vehicle, and a lead acid battery used as a power source providing a low voltage (LV) to electronics of vehicle. 
     At this time, the insulation resistance of the battery pack may decrease or the insulation thereof may be destroyed due to a deterioration. In this case, it is very dangerous because a person touching a chassis may be electrocuted by the high voltage of the battery pack, and thus it needs to continuously measure and monitor the insulation resistance of the battery pack so that the insulation resistance is not reduced less than a certain level. 
     Meanwhile, an insulation resistance measurement circuit of the related art has been measured with respect to a low voltage (LV) side ground (for example, a negative terminal of a lead acid battery, a chassis). 
     RELATED ART DOCUMENT 
     Patent Document 
     
         
         KR 2010-16109211B1 
       
    
     SUMMARY OF THE INVENTION 
     Technical Problem 
     An object of the present invention is to provide an apparatus for measuring an insulation resistance capable of reducing cost by minimizing the number of measuring devices requiring a high precision. 
     Another object of the present invention is to provide an apparatus for measuring an insulation resistance capable of better securing an insulation performance between a high voltage (HV) side of a sensing substrate and a low voltage (LV) side of the sensing substrate. 
     Technical Solution 
     In one general aspect, an apparatus for measuring an insulation resistance of a battery includes: a resistance unit including a voltage measurement resistor configured to divide and measure a voltage of the battery; a switching unit coupled to the resistance unit and including a first switch for forming a different electrical path; and a control unit measuring a voltage applied to the voltage measurement resistor and monitoring the insulation resistance of the battery, and the control unit may measure the voltage applied to the voltage measurement resistor based on a potential of a negative terminal of the battery. 
     The control unit further comprising a voltage measurement unit configured to measure the voltage applied to the voltage measurement resistor, the voltage measurement resistor may be coupled to the negative terminal of the battery, and the voltage measurement unit may be coupled to the voltage measurement resistance and the negative terminal of the battery. 
     The apparatus may further include: a first sensing substrate coupled to the battery; and a second sensing substrate coupled to a lead-acid battery having a lower voltage than the battery, and isolated from the first sensing substrate, and the resistance unit and the switching unit may be mounted on the first sensing substrate, and the control unit may be mounted on the second sensing substrate. 
     The apparatus may further include: a first sensing substrate coupled to the battery; and a second sensing substrate coupled to a lead-acid battery having a lower voltage than the battery, and isolated from the first sensing substrate, and the resistance unit, the switching unit, the voltage measurement unit and the control unit may be mounted on the first sensing substrate. 
     The resistance unit may further include: a first resistor coupled to a positive terminal of the battery, and a second resistor coupled between the first resistance and the voltage measurement resistor, and the first switch may be coupled between the first resistor and a ground, and the second switch may be coupled between the second resistor and the ground. 
     The control unit may receive the voltage applied to the voltage measurement resistor while operating the first switch in an off state and the second switch in an on state, and receive the the voltage applied to the voltage measurement resistor while operating both the first switch and the second switch in the on state. 
     The control unit may calculate a positive insulation resistance and a negative insulation resistance by combining Equation 1 and Equation 2 below. 
     
       
         
           
             
               
                 
                   
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     (where V Rmes_SW2  denotes a voltage applied to the voltage measurement resistor when the first switch operates in the off state and the second switch operates in the on state, V Rmes_SW1_SW2  denotes a voltage applied to the voltage measurement resistor when both the first switch and the second switch operate in the on state, Pack V denotes a voltage of the battery, R mes  denotes a value of the voltage measurement resistor, R 1  denotes a value of the first resistor, R 2  denotes a value of the second resistor, R Leak + denotes a value of the positive insulation resistance, and R Leak − denotes a value of the negative insulation resistance) 
     The resistance unit may further include a third resistor coupled between the switching unit and the ground. 
     The control unit may receive the voltage applied to the voltage measurement resistor while operating the first switch in an off state and the second switch in an on state, and receive the voltage applied to the voltage measurement resistor while operating both the first switch and the second switch in the on state. 
     The control unit may calculate a positive insulation resistance and a negative insulation resistance by combining Equation 3 and Equation 4 below. 
     
       
         
           
             
               
                 
                   
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     V Rmes_SW2  denotes a voltage applied to the voltage measurement resistor when the first switch operates in the off state and the second switch operates in the on state, V Rmes_SW1_SW2  denotes a voltage applied to the voltage measurement resistor when both the first switch and the second switch operate in the on state, Pack V denotes a voltage of the battery, R mes  denotes a value of the voltage measurement resistor, R 1  denotes a value of the first resistor, R 2  denotes a value of the second resistor, R 3  is a value of a third resistor, R Leak + denotes a value of the positive insulation resistance, and R Leak − denotes a value of the negative insulation resistance.) 
     Advantageous Effects 
     According to an apparatus for measuring an insulation resistance of the present invention, a voltage measurement unit may measure a voltage with respect to a potential of a negative terminal of a battery rather than the ground, and thus parameters requiring a high precision may be measured using one device, thereby reducing cost. 
     In addition, according to the apparatus for measuring the insulation resistance of the present invention, because a first sensing substrate and a second sensing substrate are separated, different potentials may be used as the ground, thereby securing a better insulation performance between the first sensing substrate that is a HV side and the second sensing substrate that is an LV side. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram schematically showing an apparatus for measuring an insulation resistance of the present invention. 
         FIG.  2    is a circuit diagram of a first circuit formed in the apparatus for measuring the insulation resistance of the present invention. 
         FIG.  3    is a circuit diagram of a second circuit formed in the apparatus for measuring the insulation resistance of the present invention. 
         FIG.  4    is a view showing in more detail a connection structure of the apparatus for measuring the insulation resistance of the present invention. 
         FIG.  5    is a block diagram showing a case in which a position of a control unit is changed as another embodiment of the apparatus for measuring the insulation resistance of the present invention. 
         FIG.  6    is a circuit diagram showing a case in which a resistance device is added as another embodiment of the apparatus for measuring the insulation resistance of the present invention. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. Detailed descriptions of known functions and configurations that may unnecessarily obscure the subject matter of the present invention will be omitted. In addition, the terms such as ‘ . . . unit’ and ‘module’ mean a unit that processes at least one function or operation, which may be implemented by hardware or software, or a combination of hardware and software. 
       FIG.  1    is a block diagram schematically showing an apparatus for measuring an insulation resistance of the present invention,  FIGS.  2  and  3    are circuit diagrams of a first circuit and a second circuit formed in the apparatus for measuring the insulation resistance of the present invention, respectively, and  FIG.  4    is a view showing in more detail a connection structure of the apparatus for measuring the insulation resistance of the present invention. 
     Referring to  FIGS.  1  to  3   , the apparatus for measuring the insulation resistance of the present invention includes a resistance unit  100 , a switching unit  200 , a voltage measurement unit  300 , and a control unit  400 . Here, the control unit  400  may include the voltage measurement unit  300 . 
     The resistance unit  100  may include a plurality of resistors to distribute a voltage of a battery  10 . At this time, the plurality of resistors include a voltage measurement resistor  110 , a first resistor  120  and a second resistor  130 , the first resistor  120  is connected(coupled) to a positive terminal  11  of the battery  10 , and the second resistor  130  is connected between the first resistor  120  and the voltage measurement resistor  110 . Here, the battery  10  may be formed by connecting a plurality of battery cells in series or in parallel. 
     The switching unit  200  is connected to the resistance unit  100  and includes a first switch  210  and a second switch  220 , and may form circuits having different paths according to on-off operations of the first switch  210  and the second switch  220 . That is, the switching unit  200  coupled to the resistance unit  100  and including the first switch  210  and the second switch  220  for forming a different electrical path. 
     Next, the voltage measurement unit  300  is a configuration that measures an voltage applied to the voltage measurement resistor  110 , and may include an analog-to-digital converter (ADC) that receives an analog voltage signal and converts the analog voltage signal into digital data. In this case, an operation power of the voltage measurement unit  300  may be supplied from a pack of the battery  10  or may be supplied from a lead acid battery  20  through an insulation type DC-DC converter. 
     Meanwhile, in the apparatus for measuring the insulation resistance of the present invention, the voltage measurement unit  300  measures an voltage applied to the voltage measurement resistor  110  with respect to a potential of a negative terminal  12  of the battery  10 . 
     Next, the control unit  400  measuring a voltage applied to the voltage measurement resistor  110  and monitoring the insulation resistance of the battery. The control unit  400  is a configuration that controls the switching unit  200  and simultaneously receives the voltage applied to the voltage measurement resistor  110  measured by the voltage measurement unit  300  to calculate a positive insulation resistance and a negative insulation resistance. 
     More specifically, the control unit  400  may receive the voltage applied to the voltage measurement resistor  110  measured by the voltage measurement unit  300  while the first switch  210  operates in an off state and the second switch  220  operates in an on state, and may receive the voltage applied to the voltage measurement resistor  110  measured by the voltage measurement unit  300  while both the first switch  210  and the second switch  220  operate in an on state. Here, the control unit  400  may be a microcontrol unit (MCU). 
     In this regard, the positive insulation resistance means a resistance between the positive terminal  11  of the battery  10  and the ground, and the negative insulation resistance means a resistance between the negative terminal  12  of the battery  10  and the ground. The ground is a low voltage (LV) ground, and is generally a chassis of a vehicle. 
     Hereinafter, a specific connection structure of the apparatus for measuring the insulation resistance of the present invention will be described. 
     Referring to  FIGS.  2  and  3   , one end of the first resistor  120  is connected to the positive terminal  11  of the battery  10  and the other end is connected to one end of the first switch  210 . One end of the second resistor  130  is connected to the voltage measurement resistor  110  and the other end is connected to one end of the second switch  220 . The other ends of the first switch  210  and the second switch  220  are connected to the ground. 
     At this time, the voltage measurement resistor  110  has one end connected to the negative terminal  12  of the battery  10  and the other end connected to the second resistor  130 . In addition, the voltage measurement unit  300  is connected to each of the negative terminal  12  of the battery  10  and the voltage measurement resistor  110 , thereby measuring the voltage applied to the voltage measurement resistor  110  with respect to the potential of the negative terminal  12  of the battery  10 . 
     Meanwhile, a voltage and current of a battery, and an inverter voltage (hereinafter referred to as high voltage (HV) measurement parameters), etc. are measured with respect to a potential of a negative terminal of the battery. The HV measurement parameters are parameters for diagnosing the battery and are related to a safe operation of the vehicle, and thus need to be measured with a high precision, which is the same as a measurement of the insulation resistance. 
     However, as described above, the insulation resistance measurement circuit of the related art is measured with respect to the ground. To explain this more specifically, one end of a voltage measurement resistor is connected to the ground, and accordingly, a voltage measurement unit is configured to measure a voltage applied to the voltage measurement resistor with respect to a ground potential. 
     Therefore, in the related art, because HV measurement parameters and insulation resistance are measured using different potentials as a reference point, a device for measuring the insulation resistance needs to use a different device independent from the measurement device of the above-described HV measurement parameters. 
     In the present invention, the voltage measurement unit  300  is connected to the negative terminal  12  of the battery  10 , other than the ground, so that the potential of the negative terminal  12  of the battery  10  is used as a reference potential when measuring the voltage applied to the voltage measurement resistor  110 . Accordingly, the voltage measurement unit  300  may be configured by adding a voltage measurement function to a device (e.g., an ADC) used when measuring HV measurement parameters. That is, by implementing the measurement of parameters related to a safe driving of an electric vehicle with one device, the number of devices that require a measurement of a high precision may be reduced. Meanwhile, because the high precision is a factor that increases the cost, a cost reduction effect increases as the number of devices that require the high precision decreases. 
     As a result, by connecting the voltage measurement unit  300  to the negative terminal  12  of the battery  10  other than the ground, there is an effect of reducing the manufacturing cost in configuring a battery system. 
     Referring to  FIG.  4   , this may be more easily understood. As a reference input of the voltage measurement unit  300  of the apparatus of measuring the insulation resistance of the present invention, the potential of the negative terminal  12  of the battery  10  is connected. Therefore, a voltage measurement circuit of the battery  10 , a current measurement circuit of the battery  10 , and the voltage measurement resistor  110  of the apparatus of measuring the insulation resistance may all be connected to one voltage measurement unit  300 , and thus other measurement unit except for the measurement device included in the voltage measurement unit  300  does not need to have a high precision. 
     Hereinafter, a method of measuring the insulation resistance using the apparatus of measuring the insulation resistance of the present invention will be described in detail. 
     First, the control unit  400  may form a first circuit by operating the first switch  210  in the off state and the second switch  220  in the on state as shown in  FIG.  2   . Here, operating a switch in the on state means that the switch is electrically conducted, and operating a switch in the off state means that the switch is not electrically conducted but is cut off. 
     The first circuit includes a closed circuit connecting the battery  10 , the positive insulation resistance, the second resistor  130 , and the voltage measurement resistor  110 , and a closed circuit connecting the second resistor  130 , the voltage measurement resistor  110 , and the negative insulation resistance. 
     While the first circuit is formed, the voltage measurement unit  300  measures the voltage applied to the voltage measurement resistor  110  and transmits the voltage to the control unit  400 . Meanwhile, when applying a voltage distribution principle to the first circuit, the following Equation 1 is calculated. 
     
       
         
           
             
               
                 
                   
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                           m 
                           ⁢ 
                           e 
                           ⁢ 
                           s 
                         
                       
                       
                         ( 
                         
                           
                             R 
                             
                               m 
                               ⁢ 
                               e 
                               ⁢ 
                               s 
                             
                           
                           + 
                           
                             R 
                             2 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     Here, V Rmes_SW2  denotes a voltage applied to a voltage measurement resistor R mes  when the first switch  210  operates in the off state and the second switch  220  operates in the on state, Pack V denotes a voltage of the battery  10 , R mes  denotes a value of the voltage measurement resistor  110 , R 1  denotes a value of the first resistor  120 , R 2  denotes a value of the second resistor  130 , R Leak + denotes a value of the positive insulation resistance, and R Leak − denotes a value of the negative insulation resistance. 
     Next, as shown in  FIG.  3   , the control unit  400  may form a second circuit by operating both the first switch  210  and the second switch  220  in the on state. 
     The second circuit includes a closed circuit connecting the battery  10 , the first resistor  120 , the second resistor  130 , and the voltage measurement resistor  110 , a closed circuit connecting the positive insulation resistance and the first resistor  120 , and a closed circuit connecting the second resistor  130 , the voltage measurement resistor  110 , and the negative insulation resistance. 
     While the second circuit is formed, the voltage measurement unit  300  measures the voltage applied to the voltage measurement resistor  110  and transmits the voltage to the control unit  400 . Meanwhile, when applying the voltage distribution principle to the second circuit, the following Equation 2 is calculated. 
     
       
         
           
             
               
                 
                   
                     V 
                     
                       
                         Rmes_SW 
                         ⁢ 
                         1 
                       
                       ⁢ 
                       
                         _SW 
                         ⁢ 
                         2 
                       
                     
                   
                   = 
                   
                     Pack 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     V 
                     × 
                     
                       
                         
                           R 
                           
                             
                               L 
                               ⁢ 
                               e 
                               ⁢ 
                               a 
                               ⁢ 
                               k 
                             
                             - 
                           
                         
                         ⁢ 
                         
                            
                           
                             ( 
                             
                               
                                 R 
                                 
                                   m 
                                   ⁢ 
                                   e 
                                   ⁢ 
                                   s 
                                 
                               
                               + 
                               
                                 R 
                                 2 
                               
                             
                             ) 
                           
                         
                       
                       
                         
                           ( 
                           
                             
                               
                                 R 
                                 1 
                               
                               ⁢ 
                               
                                  
                                 
                                   R 
                                   
                                     
                                       L 
                                       ⁢ 
                                       e 
                                       ⁢ 
                                       a 
                                       ⁢ 
                                       k 
                                     
                                     + 
                                   
                                 
                                 ) 
                               
                             
                             + 
                             
                               R 
                               
                                 
                                   L 
                                   ⁢ 
                                   e 
                                   ⁢ 
                                   a 
                                   ⁢ 
                                   k 
                                 
                                 - 
                               
                             
                           
                            
                         
                         ⁢ 
                         
                           ( 
                           
                             
                               R 
                               
                                 m 
                                 ⁢ 
                                 e 
                                 ⁢ 
                                 s 
                               
                             
                             + 
                             
                               R 
                               2 
                             
                           
                           ) 
                         
                       
                     
                     × 
                     
                       
                         R 
                         
                           m 
                           ⁢ 
                           e 
                           ⁢ 
                           s 
                         
                       
                       
                         ( 
                         
                           
                             R 
                             
                               m 
                               ⁢ 
                               e 
                               ⁢ 
                               s 
                             
                           
                           + 
                           
                             R 
                             2 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ] 
                 
               
             
           
         
       
     
     Here, V Rmes_SW1_SW2  denotes a voltage applied to the voltage measurement resistor R mes  when both the first switch  210  and the second switch  220  operate in the on state, Pack V denotes the voltage of the battery  10 , R mes  denotes the value of the voltage measurement resistor  110 , R 1  denotes the value of the first resistor  120 , R 2  denotes the value of the second resistor  130 , R Leak + denotes the value of the positive insulation resistance, and R Leak − denotes the value of the negative insulation resistance. 
     In this regard, in Equations 1 and 2, ∥ denotes a symbol indicating a parallel connection of resistances. In addition, V Rmes_SW2  and V Rmes_SW1_SW2  are values measured by the voltage measurement unit  300 , and the value R mes  of the voltage measurement resistor  110 , the value R 1  the first resistor  120  and the value R 2  of the second resistor  130  are known resistance values and may be stored in the control unit  400 . Accordingly, because there are two unknowns R Leak + and R Leak −, and Equations 1 and 2 including the unknowns are calculated, the positive insulation resistance and the negative insulation resistance may be calculated by a simultaneous equation. 
     That is, the control unit  400  may calculate the value R Leak + of the positive insulation resistance and the value R Leak − of the negative insulation resistance by combining Equation 1 and Equation 2 calculated from the first circuit and the second circuit. 
     In addition, the control unit  400  may determine whether the battery  10  has an insulation breakdown based on the value R Leak + of the positive insulation resistance and the value R Leak − of the negative insulation resistance calculated as described above. In this regard, the control unit  400  may store a threshold value of the insulation resistance which is a reference for determining whether the battery  10  has the insulation breakdown. In addition, the control unit  400  may generate a warning signal or generate a signal to cut off power to a main relay of the battery  10  as a follow-up measure when it is determined that the battery  10  has the insulation breakdown. 
     Meanwhile, the apparatus for measuring the insulation resistance of the present invention may further include a first sensing substrate  500  and a second sensing substrate  600 . 
     Here, the first sensing substrate  500  is a substrate connected to the battery  10  having a high voltage to sense the voltage and current of the battery  10 , and the second sensing substrate  600  is a substrate provided with an MCU and communication components and connected to the lead acid battery  20  having a relatively low voltage compared to the battery  10 . The sensing substrate may be a printed circuit board (PCB). 
     In the apparatus for measuring the insulation resistance of the present invention, the first sensing substrate  500  may be a substrate separated (isolated) from the second sensing substrate  600 . Here, separating means not only that the first sensing substrate  500  and the second sensing substrate  600  are insulated through an insulating device (for example, a DC-DC converter including a transformer, an isolated(insulated) communication line, etc.) but also that the first sensing substrate  500  and the second sensing substrate  600  are spatially separated different substrates. 
     At this time, as shown in  FIG.  1   , the resistance unit  100 , the switching unit  200 , and the voltage measurement unit  300  may be mounted on the first sensing substrate  500 , and the control unit  400  may be mounted on the second sensing substrate  600 . In this case, the control unit  400  may send an on/off control signal to the switching unit  200  through an isolated communication line, and receive the voltage applied to the voltage measurement resistor  110  measured by the voltage measurement unit  300  through the isolated communication line. 
     Alternatively, in the apparatus for measuring the insulation resistance of the present invention, all of the resistance unit  100 , the switching unit  200 , the voltage measurement unit  300 , and the control unit  400  may be mounted on the first sensing substrate  500  as shown in  FIG.  5   . In this case, the control unit  400  may be an MCU additionally provided on the first sensing substrate  500 . As described above, when the control unit  400  is provided on the first sensing substrate  500  with other configurations, the control unit  400  may control other measurement circuits in addition to the apparatus for measuring the insulation resistance. For example, in addition to the control of the switching unit  200 , the control unit  400  may control a battery voltage measurement circuit switch signal or a battery current measurement circuit switch signal. Therefore, the second sensing substrate  600  which is an LV side does not need to insulate the above-described signals and transmit the above-described signals to the first sensing substrate  500  which is the HV side, and components are configured to exchange only a communication signal between the HV side and the LV side, and thus the cost may be reduced. 
     Referring again to  FIG.  4   , a voltage measurement circuit of the battery  10 , a current measurement circuit of the battery  10 , and the voltage measurement unit  300  for measuring the insulation resistance are mounted on the first sensing substrate  500 , and the voltage measurement unit  300  measures the voltage using the negative terminal  12  of the battery  10  as a reference potential, and thus the negative terminal  12  of the battery  10  may be used as the ground (HV ground) of the first sensing substrate  500 . 
     In addition, the second sensing substrate  600  on which a device (an MCU, a communication component, etc.) using a negative terminal of the lead acid battery  20  as the ground are mounted may use a negative terminal of the lead acid battery  20  as the ground (LV ground) of the second sensing substrate  600 . 
     That is, because the first sensing substrate  500  and the second sensing substrate  600  are separated into different substrates, different potentials (the HV ground and the LV ground) may be used as grounds, and because the voltage measurement unit  300  is mounted on the first sensing substrate  500 , the voltage of the battery  10  having the high voltage is not applied to the second sensing substrate  600 , thereby securing a better insulation performance between the sensing substrate  500  which is the HV side and the second sensing substrate  600  which is the LV side. 
     In addition, as described above, a device requiring a relatively high measurement accuracy is mounted on the first sensing substrate  500 , and the first sensing substrate  500  is spatially separated from the second sensing substrate  600 , and thus means (for example, a cover for impact protection) protecting the first sensing substrate  500  may be manufactured in a more robust material. 
       FIG.  6    is a circuit diagram showing an embodiment in which a resistance device is added to the apparatus for measuring the insulation resistance of the present invention. 
     Referring to  FIG.  6   , the resistance unit  100  may further include a third resistor  140  connected to the other end of the first switch  210  and the other end of the second switch  220 . 
     In this regard, the control unit  400  may form a third circuit by operating the first switch  210  in an off state and the second switch  220  in an on state and form a fourth circuit by operating both the first switch  210  and the second switch  220  in the on state. 
     Here, the third circuit includes a closed circuit to which the battery  10 , a positive insulation resistance, the third resistor  140 , the second resistor  130 , and the voltage measurement resistor  110  are connected and a closed circuit to which the third resistor  140 , the second resistor  130 , the voltage measurement resistor  110 , and a negative electrode insulation resistance are connected. 
     In addition, the fourth circuit includes a closed circuit to which the battery  10 , the first resistor  120 , the third resistor  140 , the second resistor  130 , and the voltage measurement resistor  110  are connected, a closed circuit to which the first resistor  120 , the positive insulation resistance, and the third resistor  140  are connected, and a closed circuit to which the third resistor  140 , the second resistor  130 , the voltage measurement resistor  110 , and the negative insulation resistance are connected. 
     While the third circuit is formed, the voltage measurement unit  300  measures the voltage applied to the voltage measurement resistor  110  and transmits the voltage to the control unit  400 . When a voltage distribution principle is applied to the third circuit, Equation 3 below is calculated. 
     
       
         
           
             
               
                 
                   
                     V 
                     
                       Rmes_SW 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       2 
                     
                   
                   = 
                   
                     Pack 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     V 
                     × 
                     
                       
                         
                           R 
                           
                             
                               L 
                               ⁢ 
                               e 
                               ⁢ 
                               a 
                               ⁢ 
                               k 
                             
                             - 
                           
                         
                         ⁢ 
                         
                            
                           
                             ( 
                             
                               
                                 R 
                                 
                                   m 
                                   ⁢ 
                                   e 
                                   ⁢ 
                                   s 
                                 
                               
                               + 
                               
                                 R 
                                 2 
                               
                               + 
                               
                                 R 
                                 3 
                               
                             
                             ) 
                           
                         
                       
                       
                         
                           R 
                           
                             
                               L 
                               ⁢ 
                               e 
                               ⁢ 
                               a 
                               ⁢ 
                               k 
                             
                             + 
                           
                         
                         + 
                         
                           
                             R 
                             
                               
                                 L 
                                 ⁢ 
                                 e 
                                 ⁢ 
                                 a 
                                 ⁢ 
                                 k 
                               
                               - 
                             
                           
                           ⁢ 
                           
                              
                             
                               ( 
                               
                                 
                                   R 
                                   
                                     m 
                                     ⁢ 
                                     e 
                                     ⁢ 
                                     s 
                                   
                                 
                                 + 
                                 
                                   R 
                                   2 
                                 
                                 + 
                                 
                                   R 
                                   3 
                                 
                               
                               ) 
                             
                           
                         
                       
                     
                     × 
                     
                       
                         R 
                         
                           m 
                           ⁢ 
                           e 
                           ⁢ 
                           s 
                         
                       
                       
                         ( 
                         
                           
                             R 
                             
                               m 
                               ⁢ 
                               e 
                               ⁢ 
                               s 
                             
                           
                           + 
                           
                             R 
                             2 
                           
                           + 
                           
                             R 
                             3 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     3 
                   
                   ] 
                 
               
             
           
         
       
     
     Thereafter, while the fourth circuit is formed, the voltage measurement unit  300  measures the voltage applied to the voltage measurement resistor  110  and transmits the voltage to the control unit  400 . Equation 4 below is calculated through the fourth circuit. 
     
       
         
           
             
               
                 
                   
                     V 
                     
                       
                         Rmes_SW 
                         ⁢ 
                         1 
                       
                       ⁢ 
                       
                         _SW 
                         ⁢ 
                         2 
                       
                     
                   
                   = 
                   
                     
                       Pack 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       V 
                       × 
                       
                         1 
                         
                           R 
                           c 
                         
                       
                     
                     - 
                     
                       
                         
                           ( 
                           
                             
                               R 
                               a 
                             
                             ⁢ 
                             
                                
                               
                                 ( 
                                 
                                   R 
                                   
                                     
                                       L 
                                       ⁢ 
                                       e 
                                       ⁢ 
                                       a 
                                       ⁢ 
                                       k 
                                     
                                     - 
                                   
                                 
                                 ) 
                               
                             
                           
                         
                         
                           ( 
                           
                             
                               
                                 R 
                                 b 
                               
                               ⁢ 
                               
                                  
                                 
                                   R 
                                   
                                     
                                       L 
                                       ⁢ 
                                       e 
                                       ⁢ 
                                       a 
                                       ⁢ 
                                       k 
                                     
                                     + 
                                   
                                 
                                 ) 
                               
                             
                             + 
                             
                               
                                 ( 
                                 
                                   R 
                                   a 
                                 
                                  
                               
                               ⁢ 
                               
                                 R 
                                 
                                   
                                     L 
                                     ⁢ 
                                     e 
                                     ⁢ 
                                     a 
                                     ⁢ 
                                     k 
                                   
                                   - 
                                 
                               
                             
                           
                           ) 
                         
                       
                       × 
                       
                         1 
                         
                           R 
                           a 
                         
                       
                       × 
                       
                         R 
                         
                           m 
                           ⁢ 
                           e 
                           ⁢ 
                           s 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     4 
                   
                   ] 
                 
               
             
           
         
       
     
     Here, Equation 4 satisfies 
     
       
         
           
             
               
                 R 
                 a 
               
               = 
               
                 
                   
                     ( 
                     
                       
                         R 
                         1 
                       
                       × 
                       
                         R 
                         3 
                       
                     
                     ) 
                   
                   + 
                   
                     ( 
                     
                       
                         R 
                         1 
                       
                       × 
                       
                         ( 
                         
                           
                             R 
                             2 
                           
                           + 
                           
                             R 
                             
                               m 
                               ⁢ 
                               e 
                               ⁢ 
                               s 
                             
                           
                         
                         ) 
                       
                     
                     ) 
                   
                   + 
                   
                     ( 
                     
                       
                         R 
                         3 
                       
                       × 
                       
                         ( 
                         
                           
                             R 
                             2 
                           
                           + 
                           
                             R 
                             
                               m 
                               ⁢ 
                               e 
                               ⁢ 
                               s 
                             
                           
                         
                         ) 
                       
                     
                     ) 
                   
                 
                 
                   R 
                   1 
                 
               
             
             ⁢ 
             
               
 
             
             ⁢ 
             
               
                 R 
                 b 
               
               = 
               
                 
                   
                     ( 
                     
                       
                         R 
                         1 
                       
                       × 
                       
                         R 
                         3 
                       
                     
                     ) 
                   
                   + 
                   
                     ( 
                     
                       
                         R 
                         1 
                       
                       × 
                       
                         ( 
                         
                           
                             R 
                             2 
                           
                           + 
                           
                             R 
                             
                               m 
                               ⁢ 
                               e 
                               ⁢ 
                               s 
                             
                           
                         
                         ) 
                       
                     
                     ) 
                   
                   + 
                   
                     ( 
                     
                       
                         R 
                         3 
                       
                       × 
                       
                         ( 
                         
                           
                             R 
                             2 
                           
                           + 
                           
                             R 
                             
                               m 
                               ⁢ 
                               e 
                               ⁢ 
                               s 
                             
                           
                         
                         ) 
                       
                     
                     ) 
                   
                 
                 
                   ( 
                   
                     
                       R 
                       2 
                     
                     + 
                     
                       R 
                       
                         m 
                         ⁢ 
                         e 
                         ⁢ 
                         s 
                       
                     
                   
                   ) 
                 
               
             
             ⁢ 
             
               
 
             
             ⁢ 
             
               
                 R 
                 c 
               
               = 
               
                 
                   
                     ( 
                     
                       
                         R 
                         1 
                       
                       × 
                       
                         R 
                         3 
                       
                     
                     ) 
                   
                   + 
                   
                     ( 
                     
                       
                         R 
                         1 
                       
                       × 
                       
                         ( 
                         
                           
                             R 
                             2 
                           
                           + 
                           
                             R 
                             
                               m 
                               ⁢ 
                               e 
                               ⁢ 
                               s 
                             
                           
                         
                         ) 
                       
                     
                     ) 
                   
                   + 
                   
                     ( 
                     
                       
                         R 
                         3 
                       
                       × 
                       
                         ( 
                         
                           
                             R 
                             2 
                           
                           + 
                           
                             R 
                             
                               m 
                               ⁢ 
                               e 
                               ⁢ 
                               s 
                             
                           
                         
                         ) 
                       
                     
                     ) 
                   
                 
                 
                   R 
                   3 
                 
               
             
           
         
       
     
     V Rmes_SW2  denotes a voltage applied to the voltage measurement resistor R mes  when the first switch  210  operates in the off state and the second switch  220  operates in the on state, V Rmes_SW1_SW2  denotes a voltage applied to the voltage measurement resistor R mes  when both the first switch  210  and the second switch  220  operate in the on state, Pack V denotes the voltage of the battery  10 , R mes  denotes the value of the voltage measurement resistor  110 , R 1  denotes the value of the first resistor  120 , R 2  denotes the value of the second resistor  130 , R 3  is a value of the third resistor  140 , R Leak + denotes the value of the positive insulation resistance, and R Leak − denotes the value of the negative insulation resistance. 
     That is, the insulation resistance is calculated based on the same principle as the embodiment of  FIGS.  2  and  3    except that the third resistor  140  is added. 
     As described above, according to the apparatus for measuring the insulation resistance of the present invention, a voltage measurement unit may measure a voltage with respect to a potential of a negative terminal of a battery rather than the ground, and thus parameters requiring a high precision may be measured using one device, thereby reducing cost. 
     In addition, because a first sensing substrate and a second sensing substrate are separated, different potentials may be used as the ground, thereby securing a better insulation performance between the first sensing substrate that is an HV side and the second sensing substrate that is an LV side. 
     Meanwhile, the embodiment of  FIGS.  2  and  3    in which Equations 1 and 2 are calculated and the embodiment of  FIG.  6    in which Equations 3 and 4 are calculated are exemplary. Although the present invention is described by the above-described embodiments and drawings, the present invention is not limited to the above embodiments, and various modifications and variations are possible from these descriptions by those of ordinary skill in the art to which the present invention pertains. Therefore, the technical idea of the present invention should be understood only by the claims, and all equal or equivalent modifications thereof belong to the scope of the technical idea of the present invention. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           10 : battery 
           11 : battery positive terminal 
           12 : battery negative terminal 
           20 : lead acid battery 
           100 : resistance unit 
           110 : voltage measurement resistor 
           120 : first resistor 
           130 : second resistor 
           140 : third resistor 
           200 : switching unit 
           210 : first switch 
           220 : second switch 
           300 : voltage measurement unit 
           400 : control unit 
           500 : first sensing substrate 
           600 : second sensing substrate