Abstract:
A method for charging a vehicle battery which stores electrical power for an electrical drive motor of a vehicle, wherein the vehicle battery is electrically connectable to a charging socket via a switch arrangement. The method includes: measuring a first electrical variable on the switch arrangement side facing the charging socket, by a first measuring device, measuring a second electrical variable on the switch arrangement side facing the vehicle battery, by a second measuring device, comparing the first and second electrical variables and closing the switch arrangement, if the first and second electrical variables substantially correspond, measuring the first and second electrical variables while the switch arrangement is closed, and adjusting the first measuring device and the second measuring device on the basis of a first measurement difference between measurement results of the first and second electrical variables while the switch arrangement is closed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to German Patent Application No. 102016109074.3, filed May 18, 2016, the content of such application being incorporated by reference herein in its entirety. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to a method for charging a vehicle battery, in particular a high-voltage vehicle battery, which stores electrical power for an electrical drive motor of a vehicle, wherein the vehicle battery is electrically connectable to a charging socket via a switch arrangement, comprising the steps of measuring a first electrical variable on that side of the switch arrangement which faces the charging socket, by means of a first measuring device, measuring a second electrical variable on that side of the switch arrangement which faces the vehicle battery, by means of a second measuring device, comparing the first electrical variable and the second electrical variable and closing the switch arrangement, if the first electrical variable and the second electrical variable substantially correspond. 
         [0003]    Furthermore, the present invention relates to a charging arrangement for a motor vehicle, comprising an electrical charging socket connectable to a stationary electrical charging station, comprising a vehicle battery terminal, to which a vehicle battery is connectable, comprising a switch arrangement, by means of which the charging socket and the vehicle battery terminal are electrically connectable, comprising a first measuring device configured to measure a first electrical variable in the region of the charging socket, comprising a second electrical measuring device configured to measure a second electrical variable on that side of the switch arrangement which faces the vehicle battery, and comprising a control device. 
       BACKGROUND OF THE INVENTION 
       [0004]    Electrically operated motor vehicles or electric vehicles have an electrically chargeable energy store. The latter may be configured as a high-voltage battery, the rated voltage of which may be 800 volts, for example. Such an energy store is typically charged by establishing an electrical connection between an external charging column (charging station) and a charging socket fitted to the vehicle. A switchable electrical connection is provided between the charging socket and the vehicle battery, specifically by means of the switch arrangement, which may also be referred to as a disconnector and may be embodied as a contactor, for example. The switch arrangement is initially open at the beginning of a charging process, in order to bring the voltages of the vehicle battery and of the charging socket to almost the same value. Afterward, the switch arrangement is closed and the vehicle battery is charged. 
         [0005]    In order to measure the first and second electrical variables, for example in the form of a voltage measurement, a high measurement accuracy is required. This is because the voltage difference is permitted to be only very small for technical reasons, for legal reasons and for reasons relevant to safety. 
         [0006]    In this case, the accuracy of the voltage measurements is also not permitted to decrease over the entire operational time of the components. 
         [0007]    DE 10 2013 221 970 A1, which is incorporated by reference herein, describes a charging system for a plug-in vehicle which can be connected to a charging column via a windable charging cable and can be charged. In this case, the current and the voltage are measured during a charging process and the resistance of the charging cable is thus calculated. 
         [0008]    DE 10 2014 208 696 A1, which is incorporated by reference herein, discloses a charging apparatus for an electrically operated vehicle, wherein the charging apparatus has an interface with a contact part, a power converter, a control unit and a circuit-breaker and is configured to detect a voltage between the contact part and the circuit-breaker. 
         [0009]    Furthermore, US 2009/0128158 A1, which is incorporated by reference herein, discloses providing an apparatus for the voltage measurement of a plurality of battery modules interconnected in series. A difference voltage is determined during the discharging process of two capacitors in the charged state and in the uncharged state. A measurement error is calculated therefrom. 
         [0010]    US 2012/0313562 A1, which is incorporated by reference herein, discloses a battery control unit for an electric vehicle that can determine the present voltage of each individual battery cell during a charging process and adapt the charging voltage. 
         [0011]    Finally, WO 2012/139778 A2, which is incorporated by reference herein, discloses a method for charging an electric vehicle, wherein the charging current is adapted to the temperature of the electrical connection between the charging apparatus and the vehicle in order to prevent the electrical connection from overheating. 
       SUMMARY OF THE INVENTION 
       [0012]    Against this background described herein is an improved method for charging a vehicle battery and an improved charging arrangement in a motor vehicle or for a motor vehicle. 
         [0013]    The method according to aspects of the invention advantageously makes it possible to carry out an adjustment of voltage measurements or measurements of other electrical variables during a vehicle battery charging process. 
         [0014]    If the switch arrangement is closed, the first and second electrical variables should be exactly identical on account of the spatial proximity. However, if the measuring devices yield different measurement results, then it can be assumed that one of measuring devices needs to be adjusted to match the other. 
         [0015]    Preferably, in one embodiment, the first measuring device is adjusted, that is to say that measuring device which is arranged on that side of the switch arrangement which faces the charging socket. 
         [0016]    If a measurement difference arises, a correction factor for the measuring devices can be calculated and integrated or incorporated into software of the measuring devices. 
         [0017]    Preferably, such an adjustment is carried out during each charging process. It is thereby possible to keep the accuracy of the measurement of the electrical variables high over the entire operational time. 
         [0018]    For a case in which the voltage of the charging station used and that of the battery differ, a converter unit, for example in the form of a DC/DC converter, may also be provided between the charging socket and the vehicle battery. In this case, it is advantageous if a third measuring device is provided, which is arranged between the switch arrangement and the converter unit. Furthermore, the switch unit for this case generally does not comprise two switches, as in one basic embodiment, but rather three individual switches. 
         [0019]    In this case, either a measuring device between the switch arrangement and the charging socket may be adjusted, and/or a measuring device between the switch arrangement and the converter unit may be adjusted. 
         [0020]    It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the combination respectively indicated, but also in other combinations or by themselves, without departing from the scope of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Exemplary embodiments of the invention are illustrated in the drawing and are explained in greater detail in the following description. In the figures: 
           [0022]      FIG. 1  shows a schematic illustration of a vehicle with a charging arrangement at a charging station; 
           [0023]      FIG. 2  shows a timing diagram of electrical measurement variables and of switch positions of a switch arrangement; 
           [0024]      FIG. 3  shows a temporal sequence of successive adjusting processes with respective measurement differences; 
           [0025]      FIG. 4  shows an illustration, comparable to  FIG. 1 , of a further embodiment of a charging arrangement; and 
           [0026]      FIG. 5  shows a schematic illustration of a flow diagram of a charging method according to aspects of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]      FIG. 1  schematically illustrates a motor vehicle  10  arranged at a charging station  12 . The charging station  12  has a charging terminal  14 , which can provide for example a charging voltage with a magnitude of 400 volts or a charging voltage with a magnitude of 800 volts. The charging terminal  14  is connected, generally via a cable, to a charging plug  16  at which the charging voltage is provided. 
         [0028]    A vehicle battery  20  is arranged on the vehicle  10 , said vehicle battery serving for storing electrical power for an electrical drive motor of the vehicle  10 , that is to say generally having a capacity of more than one kilowatt-hour, in particular of more than 10 kilowatt-hours. 
         [0029]    Furthermore, a charging socket  22  is arranged on the vehicle  10 , into which charging socket the charging plug  16  can be plugged. The charging socket  22  is preferably provided on the exterior of a vehicle bodywork. 
         [0030]    A switch arrangement  24  is provided between the charging socket  22  and the vehicle battery  20 , said switch arrangement having a first switch S 2  and a second switch S 3  in the present case. The switches may be configured as disconnectors for high-voltage applications, for example as contactors. 
         [0031]    The first switch S 2  is arranged in a first line  26  between the charging socket  22  and the vehicle battery  20 . The second switch S 3  is arranged in a second line  28  between the charging socket  22  and the vehicle battery  20 . 
         [0032]    The vehicle battery  20  is connected to the first line  26  and the second line  28  in the region of a vehicle battery terminal  29 . 
         [0033]    The charging socket  22  and the vehicle battery  20  are furthermore coupled to one another via communication lines  30   a ,  30   b  and a control unit. Said communication lines are generally bidirectional. 
         [0034]    The illustration does not show that the charger can also be in communication, preferably likewise bidirectionally, with the charging station  12  via the charging socket  22  and the charging plug  16 . 
         [0035]    A first measuring device for measuring a first electrical variable, an electrical voltage U 1  in the present case, is provided between the switch arrangement  24  and the charging socket  22 . A second measuring device  34  for measuring a second electrical variable, preferably the electrical voltage U 3 , is provided between the switch arrangement  24  and the vehicle battery  20  or the vehicle battery terminal  29 . 
         [0036]    The first measuring device  32  supplies a first measurement result U 1meas  to a control device. Correspondingly, the second measuring device  34  supplies a measurement result U 3meas  to the control device  40 . 
         [0037]    Overall,  FIG. 1  illustrates a charging arrangement  50  for a motor vehicle  10 . 
         [0038]      FIG. 2  shows a timing diagram of a charging process. 
         [0039]    At a point in time t 0 , the charging plug  16  is connected to the charging socket  22 . At this point in time, the switches S 2 , S 3  of the switch arrangement are open. At a point in time t 1 , firstly a so-called “precharge” process begins, in which the charging voltage U 1  is adapted or set to a setpoint value corresponding to the voltage U 3 . If the charging voltage has attained the setpoint value at t 2 , the switches S 2 , S 3  can be closed at t 3  and an adjustment of the charging voltage U 1  and the voltage U 3  can be carried out. 
         [0040]    The charging process ends at the point in time t 4 , such that no electrical current is exchanged between the charging socket  22  and the battery  20 . Since the switches S 2 , S 3  are closed at this point in time, it is possible to adjust the voltages U 1  and U 3  in the heated state of the switches S 1 , S 2 , S 3 . At the point in time t 5  after adjustment has been carried out, the switches S 2 , S 3  are opened again. 
         [0041]    The adjustment is carried out because, for the case where the switch arrangement  24  is closed, the measurement results U 1meas  and U 3meas  should actually be identical, in particular on account of the spatial proximity within the vehicle. 
         [0042]    Therefore, upon the occurrence of a measurement difference ΔU 1 , it is assumed that the first measuring device  32  supplies a certain incorrect measurement that needs to be corrected, namely by the adjustment according to aspects of the invention. 
         [0043]      FIG. 3  illustrates that respective adjusting processes are carried out at different points in time T 1 , T 2 . Measurement differences can respectively occur here, which are respectively shown schematically by ΔU a , ΔU b , etc. 
         [0044]    If a measurement difference ΔU occurs, then it must not be greater than a first predefined difference threshold value ΔU MAX1 . Otherwise, an error message is output since it can be assumed that the measuring device is defective. 
         [0045]    On the other hand, it is possible to sum the measurement differences ΔU over the successive adjusting processes. Consequently, a summation value of measurement differences always results. In this case, the measurement differences can assume positive or negative values. By way of example, the measurement difference ΔU c  is negative such that the sum of the measurement differences after T 3  is smaller again than before T 3 . 
         [0046]    At the point in time T 5 , the sum of the measurement differences exceeds a second difference threshold value ΔU MAX2 . This means that it is assumed that the affected measuring device is defective, such that an error signal F is output at the point in time T 5 . 
         [0047]    ΔU MAX2  is preferably greater than ΔU MAX1 . 
         [0048]      FIG. 4  shows a further embodiment of a charging arrangement  50 ′, which corresponds generally to the charging arrangement  50  in  FIG. 1  with regard to construction and functioning. Identical elements are therefore identified by identical reference signs. Substantially the differences are explained below. 
         [0049]    In the case of the charging arrangement  50 ′, a converter unit  60  is provided between the switch arrangement  24 ′ and the vehicle battery  20 , which converter unit may be configured for example as a DC/DC converter, in particular as a DC/DC booster. 
         [0050]    Furthermore, a third line  62  with a third switch S 1  is provided between the first measuring device  32  and the second measuring device  34 . 
         [0051]    In addition thereto, a further measuring device  34 ′ for measuring the electrical voltage U 2  is provided between the switch arrangement  24 ′ and the converter unit  60 . 
         [0052]    If the charging socket  22  is connected to a charging station  14  that provides for example a first charging voltage, such as 800 volts, for example, the switches S 1 , S 3  are closed for the purpose of charging. If the charging station connected to the charging socket  22  supplies a second, lower charging voltage, of 400 volts, for example, the switches S 2 , S 3  are closed for the purpose of charging such that the charging process is carried out via the converter unit  60 , which boosts the low charging voltage provided at the charging socket  22  to a higher voltage for the high-voltage battery, for example 800 volts. 
         [0053]    During a charging process at a charging station in which the low charging voltage is provided and the converter unit  60  is used, the measuring device  34 ′ can be adjusted with the measuring device  32  specifically in the same way as described above for the adjustment of the measuring device  32  to match the measuring device  34 . 
         [0054]      FIG. 5  shows a method for charging a vehicle battery. In a step L 1 , a charging arrangement is in a quiescent state. 
         [0055]    A step L 2  involves adjusting the second measuring device  34  to the battery voltage, that is to say adjusting U 3  to U BATT . 
         [0056]    A step L 3  involves deciding whether a charging process is carried out at a high-voltage charging station with 800 volts or at a normal charging station with 400 volts. 
         [0057]    If a charging process is carried out at a high-voltage charging station with 800 volts, step L 4  involves initiating the charging process at such a charging station. 
         [0058]    Step L 5  involves adjusting U 1  to U 3 . 
         [0059]    The charging process is ended in step L 6 . 
         [0060]    If, on the other hand, in step L 3  it is decided that the charging process is carried out at a charging station with 400 volts, the charging process begins at such a charging station in step L 7 . 
         [0061]    Step L 8  involves adjusting U 2  to U 1 . 
         [0062]    Overall, in accordance with DIN 61851-23 it is provided that a vehicle must be disconnectable from the charging socket by means of a switch arrangement or a disconnector (contactors). If a charging cable with a charging plug is plugged in, a charging process is started. In this case, the switch arrangement  24 ;  24 ′ is initially open. Afterward, a preparation takes place prior to charging “precharge”, in which the voltage at the charging socket (voltage U 1 ), that is provided by the charging station is adjusted to the voltage of the vehicle battery  20  (voltage measurement U 3 ). If the measurement difference between U 1  and U 3  is less than a limit value, the switch arrangement  24  or.  24 ′ is permitted to be closed. 
         [0063]    According to DIN 61851-22, a limit value for the voltage difference between U 1  and U 3  is exactly 20 volts. This limit value is preferably even smaller, for example 10 volts. Assuming that the maximum voltage is 800 volts, said 10 volts correspond to exactly 1.25% of 800 volts. A measurement accuracy of at least 1.25% is thus necessary for U 1  and U 3  in order to be able to assess the voltage difference. Including safety factors the requirement thus arises that the accuracy of the voltage measurement must be smaller than 1%. Preferably over the envisaged 15-year operational time of the component and all temperature ranges, this requirement can generally be fulfilled only with difficulty, which results in an expensive and complex measuring circuit in the prior art. 
         [0064]    According to aspects of the invention, the switch arrangement  24  or  24 ′ is closed after a successful preparation process (voltage adaptation). As a result of the spatial proximity of the measuring devices U 1  and U 3 , it can be assumed that U 1actual =U 3actual . This phase of the charging process can be utilized in order to adjust the measuring devices to match one another or with respect to one another (this preferably involves generating a correction factor that is stored in software for one of the two measuring devices). As a result of heating of the component it is possible to determine a plurality of correction factors for different temperatures. 
         [0065]    Since such an adjustment can be carried out during each charging process, it is possible for the two measuring devices for U 1  and U 3  not to drift apart over their lifetime. It is thus possible to use simpler measuring circuits which by themselves could not fulfil the measuring accuracy requirements over the lifetime. 
         [0066]    The principle according to aspects of the invention can be applied to voltage measurements, but to current measurements if operating states arise in which the assumption that the currents of different sensors have the same value is legitimate. 
         [0067]    The correction factor of a sensor or of a measuring device can be monitored to a maximum possible value (for example ΔU MAX2 ). The limitation can be implemented both absolutely and temporally. If such a value is attained, it can be assumed that a defect of the measuring device is present.