Abstract:
A method and device for determining an insulation variable of a network. The method may comprise measuring a first voltage at the network, connecting the auxiliary system to the network, measuring a second voltage at the network, disconnecting the auxiliary system from the network, measuring a third voltage at the network, and determining the insulation variable based on the first voltage, the second voltage, and the third voltage.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of prior German Patent Application No. 10 2015 101 074.7, filed on Jan. 26, 2015, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a method and device for determining an insulation variable of a network, such as an insulation resistance of a battery, which may operate in the high-voltage range. 
     BACKGROUND OF THE DISCLOSURE 
     For safety reasons, it is important to determine insulation resistances with respect to high-voltage devices. 
     WIPO Patent Application No. 2011/160881 A1 describes a method for determining the insulation resistance of an ungrounded electrical network, in which a measuring voltage may be fed into the network via a voltage divider. A measuring current flowing after applying the measuring voltage is measured during at least three different time intervals during a transient period of the network. The insulation resistance may be determined based on the measurement results. However, the method requires a high component complexity and includes a variety of drawbacks. For example, it is only possible to determine the overall insulation resistance, and partial insulation resistances cannot be determined. 
     German Patent Application No. 196 18 897 B4 describes a circuit for determining the insulation resistance of a battery (such as a rechargeable battery) in stand-alone operation. The circuit may determine the insulation resistance by measuring an open-circuit voltage and a load voltage, wherein a series connection of two capacitors may be connected to the battery terminals for storing the voltage values during the measurement, and the shared point of the capacitors may connect to a bleeder resistor. However, this requires long measuring times for large insulation capacitances. 
     SUMMARY 
     Embodiments of the present disclosure provide a method and device for efficiently determining an insulation resistance of a battery in the high-voltage range. 
     According to embodiments of the present disclosure, a method for determining an insulation variable of a network is disclosed, wherein a measuring system, also referred to herein as an auxiliary system, may be temporarily connected to the network and a reference point, the method comprising: measuring a first voltage at the network when the measuring system is not connected to the network; connecting the measuring system to the network; measuring a second voltage at the network; disconnecting the measuring system from the network; measuring a third voltage at the network; and determining an insulation variable based on the first voltage, the second voltage, and the third voltage. 
     Embodiments of the present disclosure may enable determining the insulation measurement at reduced cost and material expenditure. Furthermore, the duration of the insulation measurement may be reduced. 
     In some embodiments, the second voltage and third voltage may be measured as voltages that drop at the measuring system. The first voltage may be determined between the network and the reference point. The measuring system may be an auxiliary circuit or an auxiliary system. 
     According to embodiments of the present disclosure, a processing unit may carry out the voltage measurements. For example, the processing unit may control the measuring system to temporarily connect to the network. The measuring system may disconnect from the network, for example, by intermittently interrupting a connection between the network and the measuring system. 
     In some embodiments, the reference point may be ground. Ground may correspond to a connection to a car body or to another reference potential in a vehicle. 
     In some embodiments, the insulation variable is an insulation capacitance or an insulation resistance. 
     In some embodiments, the network is an electrical supply network. For example, the network may be an electrical supply network of a motor vehicle. The network may comprise at least one DC voltage source, such as a battery. 
     In some embodiments, the measuring system may temporarily connect to the network, between a supply terminal of the network and the reference point (such as ground), using a switch. The switch may be an electronic or a mechanical switch. 
     In some embodiments, the measuring system may comprise a capacitor, a first resistor, and a switch connected in series, and a second resistor connected in parallel to the capacitor. 
     In some embodiments, a predefined settling time is allowed to pass after the measuring system is connected to the network, and before the second voltage is measured. This settling time may be determined by a time constant τ (RC circuit) from the first resistor and the capacitor of the measuring system, which are connected in series. The time during which the measuring system is connected to the network may be shorter than the time constant τ. 
     In some embodiments, a predefined duration is allowed to pass after the measuring system is disconnected from the network, and before the third voltage is measured. 
     In some embodiments, a parallel insulation resistance RP, equal to the values of insulation resistances R 1  and R 2  connected in parallel, is measured as the insulation variable in accordance with 
     
       
         
           
             RP 
             = 
             
               
                 
                   - 
                   t 
                 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 1 
               
               
                 CP 
                 · 
                 
                   ln 
                   ⁡ 
                   
                     ( 
                     
                       1 
                       - 
                       
                         
                           
                             U 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                             ⁢ 
                             
                               ( 
                               
                                 t 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                               
                               ) 
                             
                           
                           - 
                           
                             U 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             12 
                           
                         
                         
                           
                             U 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             11 
                           
                           - 
                           
                             U 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             12 
                           
                         
                       
                     
                     ) 
                   
                 
               
             
           
         
       
     
     wherein CP is a parallel insulation capacitance equal to the values of insulation capacitors C 1  and C 2  connected in parallel, and measured in accordance with 
     
       
         
           
             CP 
             = 
             
               Cm 
               * 
               
                 
                   U 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   12 
                 
                 
                   
                     U 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     11 
                   
                   - 
                   
                     U 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     12 
                   
                 
               
             
           
         
       
     
     wherein
         RP is the parallel insulation resistance,   CP is the parallel insulation capacitance,   U 11  is the first voltage,   U 12  is the second voltage,   U 1 ( t   1 ) is the third voltage,   t 1  is the predefined duration before the third voltage is measured, and   Cm is the capacitor in the measuring system.       

     According to embodiments of the present disclosure, a fourth voltage may be measured before the measuring system is connected to the network. The fourth voltage is measured between the reference point and a supply terminal of the network that is not used for measuring the second voltage. Insulation resistances R 1  and R 2  of the network are determined in accordance with 
     
       
         
           
             
               R 
               ⁢ 
               
                   
               
               ⁢ 
               1 
             
             = 
             
               RP 
               · 
               
                 ( 
                 
                   1 
                   - 
                   
                     
                       U 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       11 
                     
                     
                       U 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       21 
                     
                   
                 
                 ) 
               
             
           
         
       
       
         
           and 
         
       
       
         
           
             
               R 
               ⁢ 
               
                   
               
               ⁢ 
               2 
             
             = 
             
               
                 
                   - 
                   R 
                 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   1 
                   · 
                   U 
                 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 11 
               
               
                 U 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 21 
               
             
           
         
       
     
     wherein
         R 1  is an insulation resistance in parallel to the measuring system,   R 2  is an insulation resistance at which the fourth voltage drops, and   U 21  is the fourth voltage.       

     In some embodiments, the duration t 1  depends on a resolution of an analog-to-digital converter connected to the measuring system. 
     In some embodiments, a device for determining an insulation variable of a network is disclosed. The device may comprise a measuring system and a processing unit, wherein the measuring system may be temporarily connected to the network and a reference point, and wherein the processing unit is configured to perform the following operations: measuring a first voltage at the network when the measuring system is not connected to the network; connecting the measuring system to the network; measuring a second voltage at the network; disconnecting the measuring system from the network; measuring a third voltage at the network; and determining an insulation variable based on at least one element of the measuring system, the first voltage, the second voltage, and the third voltage. 
     In some embodiments, the measuring system and processing unit may be implemented in a shared component or unit. For example, the measuring system may comprise a corresponding processing unit, or the processing unit may comprise at least one of the measuring systems disclosed in the present disclosure. 
     In some embodiments, the device may be a circuit. The device may comprise hardware and/or software. 
     In some embodiments, a motor vehicle is disclosed, the motor vehicle comprising at least one device as described in the present disclosure. 
     Embodiments of the present disclosure may be used to determine an insulation measurement in a high-voltage system. Such a high-voltage system may comprise a battery, for example, which supplies a voltage of more than 50 V, or more than 100 V. 
     Descriptions in the present disclosure relating to a particular claim category, such as a method, apply correspondingly to all other claim categories disclosed herein. 
     The properties, features and advantages as described in the present disclosure, and the manner in which these are achieved, will become more apparent and understandable in connection with the following detailed description. The foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of embodiments consistent with the present disclosure. Further, the accompanying drawings illustrate embodiments of the present disclosure, and together with the description, serve to explain principles of the present disclosure. For clarity and illustrative purposes, identical or like-acting elements may be denoted by the same reference numerals. 
    
    
     
       BRIEF DESCRIPTION OF FIGURES 
         FIG. 1  shows an exemplary device for determining an insulation resistance of a battery according to the present disclosure. 
         FIG. 2  shows an exemplary method for measuring an insulation resistance according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     According to embodiments of the present disclosure, an insulation resistance may be determined for a network or on a network. The network may comprise an energy source, such as a battery, which may be connected via electrical lines (such as multicore cables) to at least one consumer device. The battery may be a rechargeable battery. The network may be part of an autonomous system, such as an energy supply network in a vehicle. 
     According to embodiments of the present disclosure, a voltage is measured in at least one point of the network. A measuring system may be temporarily connected to the network. For example, the measuring system may be temporarily connected to the network for a predefined duration. The measuring system may include a circuit comprising at least one resistor and at least one capacitor. The measuring system may measure a change in voltage, and an insulation capacitance of the network may be determined based on the measured change in voltage. The measuring system may then be disconnected from the network, and an insulation resistance may be determined from a change in voltage that varies over time. 
       FIG. 1  shows an exemplary measuring system comprising a circuit  110  for determining at least one insulation resistance of a battery  101 . The circuit  110  may be arranged between the battery  101  and ground  111 . The battery  101  comprises two terminals  103  and  104 , which are also referred to as poles of the battery, and to which at least one consumer device may be connected. The battery  101  may be designed as a high-voltage battery to supply a voltage of 100 V or more, for example. 
     As shown in  FIG. 1 , an exemplary circuit  102  comprises the battery  101 , including terminals  103  and  104 , two insulation resistors R 1  and R 2 , and two insulation capacitors C 1  and C 2 . The insulation resistors R 1  and R 2  may be connected in series to each other, and this series connection may be arranged in parallel to the battery  101 . The insulation capacitor C 1  may be arranged in parallel to the insulation resistance R 1 , and the insulation capacitor C 2  may be arranged in parallel to the insulation resistance R 2 . The center tap of the series connection composed of the insulation resistances R 1 , R 2  (and the insulation capacitors C 1 , C 2 ) may be denoted as a node  109 . Node  109  may be connected to ground  111  by way of, for example, the body of a motor vehicle, as the reference potential. 
     The circuit  110  may at least be temporarily connected to the battery  101  by being connected via terminal  116  to terminal  103 , and via terminal  117  to ground  111 . The circuit  110  may comprise a capacitor Cm, a resistor Rm 1 , a resistor Rm 2 , and a switch S 1 . The terminal  116  may be connected to terminal  117  via a series connection comprising the capacitor Cm, the resistor Rm 1 , and the switch S 1 . The resistor Rm 2  may be connected in parallel to the capacitor Cm. Switch S 1  may comprise an electronic switch, such as a transistor, or a mechanical switch or push-button. Switch S 1  may be actuated by a control and/or calculation unit configured to record the measured values and calculate the insulation resistance. 
     As shown in  FIG. 1 , voltage U 1  drops between terminal  103  and node  109 , and a voltage U 2  drops between node  109  and terminal  104 . 
       FIG. 2  shows an exemplary method for measuring the insulation resistances R 1  and R 2 . The following designations are used in describing the exemplary method shown in  FIG. 2 .
         U 11  denotes the voltage U 1  at the time before switch S 1  is closed.   U 21  denotes the voltage U 2  at the time before switch S 1  is closed.   U 1 ( t ) denotes the voltage U 1  at the time after switch S 1  has been closed and then re-opened.   U 12  denotes the voltage U 1  just before switch S 1  is re-opened. The voltage U 12  equals the voltage U 1 ( t =0) immediately after the switch S 1  is re-opened.       

     In step  201 , the measurement starts. This may take place prior to starting the vehicle, for example, to determine whether insulation resistances satisfy predetermined criteria before the vehicle starts. 
     In step  202 , voltage U 11  is measured. Optionally, voltage U 21  may also be measured. However, if only the parallel circuit of the insulation resistances R 1  and R 2  is to be determined, the measurement of voltage U 21  may not be required. 
     In step  203 , switch S 1  is closed. 
     In step  204 , a predefined settling time is allowed to lapse. This settling time may be influenced by the time constant:
 
τ= Rm 1· Cm.  
 
     The time during which switch S 1  is closed, however, may be shorter than time constant τ. For example, time constant τ may be greater than the duration during which switch S 1  is dosed by at least a factor of 2 or at least a factor of 10. 
     In step  205 , voltage U 12 =U 1 ( t =0) is measured at time t=0. 
     In step  206 , switch S 1  is opened at time t 0 =0. 
     In step  207 , a predefined settling time is allowed to lapse. The waiting period may correspond to the resolution of an analog to digital converter that is connected to the measuring system and takes the analog measured value of voltage U 1 , at three different times, and converts it to a digital value. For example, the higher the resolution of the converter, the shorter the waiting period may be, because a digital value may be determined for voltage U 1  a short time after t 0 =0. 
     In step  208 , voltage U 1 ( t ) is measured. 
     In step  209 , at least one insulation variable may be determined based on at least one of the calculations as described in the present disclosure. 
     A parallel insulation capacitance CP, equal to the values of insulation capacitors C 1  and C 2  connected in parallel, may be determined as follows: 
     
       
         
           
             CP 
             = 
             
               Cm 
               * 
               
                 
                   U 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   12 
                 
                 
                   
                     U 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     11 
                   
                   - 
                   
                     U 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     12 
                   
                 
               
             
           
         
       
     
     A parallel insulation resistance RP, equal to the values of insulation resistances R 1  and R 2  connected in parallel, may then be calculated using the following formula: 
     
       
         
           
             RP 
             = 
             
               
                 
                   - 
                   t 
                 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 1 
               
               
                 CP 
                 · 
                 
                   ln 
                   ⁡ 
                   
                     ( 
                     
                       1 
                       - 
                       
                         
                           
                             U 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                             ⁢ 
                             
                               ( 
                               
                                 t 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                               
                               ) 
                             
                           
                           - 
                           
                             U 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             12 
                           
                         
                         
                           
                             U 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             11 
                           
                           - 
                           
                             U 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             12 
                           
                         
                       
                     
                     ) 
                   
                 
               
             
           
         
       
     
     wherein time t 1  corresponds to the time at which voltage U 1 ( t ) is measured in step  208 . 
     The individual insulation resistances may then be determined according to the following calculations: 
     
       
         
           
             
               R 
               ⁢ 
               
                   
               
               ⁢ 
               1 
             
             = 
             
               RP 
               · 
               
                 ( 
                 
                   1 
                   - 
                   
                     
                       U 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       11 
                     
                     
                       U 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       21 
                     
                   
                 
                 ) 
               
             
           
         
       
       
         
           
             
               R 
               ⁢ 
               
                   
               
               ⁢ 
               2 
             
             = 
             
               
                 
                   - 
                   R 
                 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   1 
                   · 
                   U 
                 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 11 
               
               
                 U 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 21 
               
             
           
         
       
     
     For illustrative purposes, an example for calculating an insulation variable is provided below. 
     Provided with illustrative the measured values 
     Cm=1 μF 
     U 11 =200V, 
     U 12 =134V, 
     t 1 =0.1 s, and 
     U 1 ( t   1 )=140V, 
     CP may be calculated in accordance with: 
     
       
         
           
             
               
                 
                   
                     C 
                     P 
                   
                   = 
                     
                   ⁢ 
                   
                     
                       C 
                       m 
                     
                     * 
                     
                       
                         U 
                         12 
                       
                       
                         
                           U 
                           11 
                         
                         - 
                         
                           U 
                           12 
                         
                       
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                   ⁢ 
                   
                     1 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     µ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       F 
                       · 
                       
                         
                           134 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           V 
                         
                         
                           
                             200 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             V 
                           
                           - 
                           
                             134 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             V 
                           
                         
                       
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                   ⁢ 
                   
                     2 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     µ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     F 
                   
                 
               
             
           
         
       
     
     RP may then be calculated in accordance with: 
     
       
         
           
             
               
                 
                   
                     R 
                     P 
                   
                   = 
                     
                   ⁢ 
                   
                     
                       - 
                       
                         t 
                         1 
                       
                     
                     
                       
                         C 
                         P 
                       
                       ⁢ 
                       
                         ln 
                         ⁡ 
                         
                           ( 
                           
                             1 
                             - 
                             
                               
                                 
                                   
                                     U 
                                     1 
                                   
                                   ⁡ 
                                   
                                     ( 
                                     
                                       t 
                                       1 
                                     
                                     ) 
                                   
                                 
                                 - 
                                 
                                   U 
                                   12 
                                 
                               
                               
                                 
                                   U 
                                   11 
                                 
                                 - 
                                 
                                   U 
                                   12 
                                 
                               
                             
                           
                           ) 
                         
                       
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                   ⁢ 
                   
                     
                       
                         - 
                         0.1 
                       
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       s 
                     
                     
                       
                         2 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         µ 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         F 
                         * 
                         
                           ln 
                           ⁡ 
                           
                             ( 
                             
                               1 
                               - 
                               
                                 
                                   
                                     140 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     V 
                                   
                                   - 
                                   
                                     134 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     V 
                                   
                                 
                                 
                                   
                                     200 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     V 
                                   
                                   - 
                                   
                                     134 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     V 
                                   
                                 
                               
                             
                             ) 
                           
                         
                       
                       ⁢ 
                       
                           
                       
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                   ⁢ 
                   
                     500 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     k 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Ω 
                   
                 
               
             
           
         
       
     
     The individual insulation resistances R 1  and R 2  may then be determined according to the following calculations: 
     
       
         
           
             
               
                 
                   
                     R 
                     1 
                   
                   = 
                     
                   ⁢ 
                   
                     
                       R 
                       P 
                     
                     * 
                     
                       ( 
                       
                         1 
                         - 
                         
                           
                             U 
                             11 
                           
                           
                             U 
                             21 
                           
                         
                       
                       ) 
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                   ⁢ 
                   
                     500 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     k 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Ω 
                     * 
                     
                       ( 
                       
                         1 
                         - 
                         
                           
                             200 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             V 
                           
                           
                             - 
                             200 
                           
                         
                       
                       ) 
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                   ⁢ 
                   
                     1 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     M 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Ω 
                   
                 
               
             
           
         
       
       
         
           and 
         
       
       
         
           
             
               
                 
                   
                     R 
                     2 
                   
                   = 
                     
                   ⁢ 
                   
                     
                       
                         - 
                         
                           R 
                           1 
                         
                       
                       ⁢ 
                       
                         U 
                         11 
                       
                     
                     
                       U 
                       21 
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                   ⁢ 
                   
                     
                       
                         - 
                         1 
                       
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       M 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       Ω 
                       * 
                       200 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       V 
                     
                     
                       
                         - 
                         200 
                       
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       V 
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                   ⁢ 
                   
                     1 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     M 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Ω 
                   
                 
               
             
           
         
       
     
     While the present disclosure is illustrated and described in detail according to the above embodiments, the present disclosure is not limited to these embodiments and additional embodiments may be implemented. Further, other embodiments and various modifications will be apparent to those skilled in the art from consideration of the specification and practice of one or more embodiments disclosed herein, without departing from the scope of the present disclosure. 
     LIST OF REFERENCE NUMERALS 
     
         
         
           
               101  battery (for example, a high-voltage battery) 
               102  circuit of battery  101   
               103  terminal of battery  101   
               104  terminal of battery  101   
               109  node 
               110  circuit for measuring the insulation resistance of battery  101   
               111  ground 
               116  terminal of circuit  110   
               117  terminal of circuit  110   
               201  to  208  method steps 
             C 1 , C 2  insulation capacitor 
             Cm capacitor 
             R 1 , R 2  insulation resistance 
             Rm 1  resistor 
             Rm 2  resistor 
             t time