Patent Publication Number: US-2006012338-A1

Title: Charging device for charging a battery and method for the operation thereof

Description:
PRIOR ART  
      The invention relates to a method for operating a line-voltage-fed charger for a battery, to a computer program, and to a charger for performing this method, as well as to a data medium having the computer program.  
      Such methods and chargers are fundamentally known in the prior art, for instance in the form of the battery charger LW 20/30 E made by Robert Bosch GmbH. The known charger is connected to the line voltage and serves to charge a battery, in particular a car battery. It includes a charge transformer for transforming the line voltage on the primary side into a secondary voltage, and a rectifier, downstream of the charge transformer on its secondary side, for furnishing a charging voltage for the battery. The key element in the known charger is a control unit for triggering the rectifier via a control signal in response to the charging voltage. The control unit is embodied not only for charging the battery when it is empty but also for keeping in its charged state and in this way counteracting its own self-discharging. This is done in a so-called charge-receiving mode. This charge-receiving mode includes a cyclical succession of a resting phase and a charging phase. In the resting phase, the battery discharges, particularly because of its self-discharging, from a predetermined upper threshold voltage to a lower threshold voltage that is lower than the upper threshold voltage, but preferably greater than the rated voltage of the battery. Once this lower threshold voltage is reached, the resting phase is ended within the charge-receiving mode, and the control unit is embodied to alternate from the resting phase to a refreshing phase. Within the refreshing phase, the battery is charged again via the charge transformer of the charger from the lower to the upper threshold voltage. The refreshing phase is substantially shorter chronologically than the resting phase.  
      This known charger has the disadvantage that even during the charge holding phase and particularly during the long-lasting resting phase, it has high current consumption and thus a high power loss. This high power loss is explained by the fact that even during the resting phase, that is, when no charging current is flowing, the charge transformer in particular nevertheless exhibits high current consumption for achieving remagnetizations.  
      With this prior art as the point of departure, it is therefore the object of the invention to embody a charger for charging a battery, a method for its operation, a computer program for performing this method, and a data medium having this computer program, in such a way that the power loss of the charger while it is in a charge-receiving mode is minimized.  
      This object is attained by the method claimed in claim  1 . For the method described at the outset, that is, the described cyclical alternation between a resting phase and a refreshing phase within a charge-receiving mode, the object is attained by providing that at least individual components and in particular the charge transformer of the charger are switched off from the line voltage during the resting phase.  
     ADVANTAGES OF THE INVENTION  
      Proceeding in this way offers the advantage that during the resting phases, that is, when the battery is fully charged and no refreshing charging operations take place, particularly the charge transformer does not draw current to furnish a charging current. Moreover, the claimed shutoff also assures that the charge transformer does not draw current for other purposes, particularly for remagnetization purposes, during the resting phase. In this way, the power loss of the charge transformer during the resting phase is lowered to a value of 0 W. The shutoff of the charge transformer and the supply transformer from the line voltage furthermore offers the advantage that simultaneously all the other components of the charger that are supplied from the secondary side of the supply transformer are also simultaneously switched off from the line voltage and thus made loss-free.  
      The aforementioned object of the invention is furthermore attained by a computer program and a charger for performing the claimed method and by a data medium having the computer program. The advantages of these embodiments are essentially equivalent to those named above with reference to the claimed method. Furthermore, additional advantages can be attained by various versions of the charger in the form of various exemplary embodiments. Various exemplary embodiments of the method and of the charger are the subject of the dependent claims. 
    
    
     DRAWINGS  
      A total of three drawings are appended to the description, and in them  
       FIG. 1  shows a first exemplary embodiment for the charger of the invention;  
       FIG. 2   a  shows the course of the battery voltage during a charging mode and a charge-receiving mode;  
       FIG. 2   b  shows one example for the course of a charging current during the modes of  FIG. 2   a;    
       FIG. 2   c  shows the activation and deactivation behavior of a switching device in the charger of the invention; and  
       FIG. 3  shows a second exemplary embodiment for the charger of the invention. 
    
    
     DESCRIPTION OF THE EXEMPLARY EMBODIMENTS  
      The invention will be described in detail below in the form of exemplary embodiments, with reference to  FIGS. 1 through 3 .  
       FIG. 1  shows a first exemplary embodiment for the charger  100  of the invention. It is connected to a line voltage U N  and serves to charge a battery  200 . It includes a switching device  110 , controlled by a switching signal S 2 , for applying the line voltage U N  to a charge transformer  120  and a supply transformer  140  connected parallel on the primary side to the charge transformer  120 . Downstream of the charge transformer  120 , which serves essentially to furnish the requisite charging current for charging the battery  200 , is a rectifier  130  for furnishing a charging voltage U B  for the battery  200 . The supply transformer  140  serves to furnish a supply voltage for a control unit  150  and a first comparator  160 . The control unit  150  controls the rectifier  130 , via a control signal S 1 . Via a status signal Z, the control unit  150  informs the first comparator  160  of the operating mode, such as the charge-receiving mode, in which the charger is currently being operated. The first comparator  160  compares the charging voltage U B,  which when the battery is connected is equivalent to the battery voltage, with a predetermined upper threshold voltage and generates a first comparison signal V 1 , if the battery voltage has reached or exceeded this upper threshold voltage U OG .  
      Besides the first comparator  160 , the charger  100  also includes a second comparator  170 . This second comparator, in the first exemplary embodiment, unlike the first comparator  160  is supplied not by the supply transformer  140  but rather from the battery voltage U B . The battery voltage U B  simultaneously serves as an input variable. The second comparator  170  compares the battery voltage with a predetermined lower threshold voltage U UG  and generates a second comparison signal V 2 , if the battery voltage has reached or undershot the lower threshold voltage U UG . For forming the aforementioned switching signal S 2  for triggering the switching device  110 , the first and second comparison signals V 1 , V 2  are OR-linked with one another in an OR logic module  180 .  
      With the aid of  FIGS. 2   a,    2   b  and  2   c,  the mode of operation of the charger shown in  FIG. 1  will now be explained. The charger  100  serves first to charge the battery  200 . To that end, the control unit  150  puts the charger  100  in a so-called charging mode AL. This charging mode comprises two successive phases. The first phase can be seen in  FIG. 2   b  from the fact that during this first phase the battery is charged with a constant current. Because of this charging with a constant current, the battery voltage initially increases only slowly, but over the course of time increasingly rapidly up to the level of the upper threshold voltage U OG . Once this upper threshold voltage U OG  is reached, the first phase ends, and the second phase of the charging mode AL is initiated. During this second phase, the battery is supplied with a constant charging voltage, which is equivalent to the upper threshold voltage; see  FIG. 2   a.  This second phase of the charging mode AL ends whenever the charging current has dropped to a predefined threshold current which is substantially less than the constant current during phase  1 . During the entire charging mode AL, that is, during both its first and its second phase, the switching device  110  is switched on.  
      When both these criteria are present, that is, U B =U OG  and the charging current is less than or equal to the threshold current, the control unit  150  directs the charger from the charging mode AL to a so-called charge-receiving mode. This mode is characterized by a sawtooth course of the battery voltage, as shown in  FIG. 2   a.  It can be broken down into two cyclically successive phases, that is, a resting phase R and a refreshing phase A. After the charging mode, the charger first changes over, within the charge-receiving mode, to the resting phase R. During this resting phase, the battery is no longer supplied with a charging current IL, as shown in  FIG. 2   b;  its voltage drops from the upper threshold voltage U OG  to the lower threshold voltage U UG . It must be remembered that the battery, after the conclusion of the charging mode or in other words during the charge-receiving mode, is fully charged. The lower threshold voltage U UG , while considerably below the upper threshold voltage U OG , is still preferably above the rated voltage of the battery  200 . The values given in  FIG. 2   a  for the battery voltage U B  pertain to a battery  200  with a rated voltage of 12 V. According to the invention, the switching device  110  is switched off during the resting phase R by the switching signal S 2 , or more precisely by the comparison signal V 1 , or in other words is opened; see  FIG. 2   c.  Thus in the first exemplary embodiment of the charger shown in  FIG. 1 , the charge transformer  120  and the supply transformer  140  are likewise decoupled from the line voltage on their primary side. Their current consumption and hence their power loss are in this way made to be zero during the resting phase R. This is true particularly because in this way they are also prevented from drawing a current for remagnetization purposes.  
      As soon as the second comparator  170  has ascertained that the battery voltage U B,  particularly from self-discharging of the battery, has dropped to a value of the predetermined lower threshold voltage U UG , it generates the second comparison signal V 2  and thus, regardless of the state of the first comparison signal V 1 , switches the switching device  110  back on again via the OR logic module  180 . On being switched on, that is, upon the application of the line voltage to the charge transformer and to the supply transformer, the charger is again put in a position to perform a charging operation. However, in this situation during the charge-receiving mode, since the battery  200  is still charged, but its battery voltage has merely dropped to the lower threshold voltage U UG , a brief refreshing of the battery  200  suffices to raise its battery voltage U B  back to the upper threshold value U OG . To that end, the charger briefly changes over to a refreshing phase A, during which, as noted, the line voltage is again applied to the charger, and the battery is charged via a slight charging current, which is substantially less than the constant charging current during the first phase of the charging mode. The end of this refreshing phase A is recognized and initiated by the first comparator  160  when the comparator detects that the battery voltage has again reached the upper threshold voltage U OG  after previously, during the preceding resting phase, having dropped to the lower threshold voltage U UG . To make this finding, the first comparator  160  assesses not only the battery voltage U B  but also a status signal Z, which is delivered to it by the control unit  150  and contains information about the current operating mode of the charger, and in particular about the presence of a current refreshing phase.  
      After the end of a refreshing phase A, the charger changes back again to a succeeding resting phase. According to the invention, the line voltage is switched off again via the switching device  110 , in order as noted to minimize the ohmic losses during this time. However, so that the first comparison signal, via the OR logic module  180  and the switching signal S 2 , can be at all capable of switching off the switching device  110 , it is necessary that the second comparison signal V 2  also be put in a suitable state. According to the invention, this is attained by synchronizing the two comparison signals with one another in this situation, that is, at the transition from a refreshing phase to a resting phase.  
      In the first exemplary embodiment shown in  FIG. 1 , the charge transformer  120 , the rectifier  130 , the supply transformer  140 , the control unit  150 , and the first comparator  160  are connected to the line voltage and are supplied by it. This has the advantage that upon shutoff of the line voltage, for instance during a resting phase, they do not generate any power loss. However, this is not true for the second comparator  170 , because in the first exemplary embodiment it is supplied via the battery voltage. This is disadvantageous in the sense that the second comparator  170  puts a load on the charged battery, even during the charge-receiving mode in particular, and thus unfavorably contributes to discharging the battery that is supposed to be getting charged at the time.  
      This disadvantage is circumvented with the second exemplary embodiment of the charger, shown in  FIG. 3 . Unlike the first exemplary embodiment shown in  FIG. 1 , in the second exemplary embodiment the control unit  150 , the first and second comparators  160 ,  170 , and the OR logic module  180  are supplied with a voltage via a supply transformer  140 ′; the supply transformer  140 ′, unlike the supply transformer  140 , cannot be shut off, or in other words is connected permanently to the line voltage U N . Thus not only is there not the disadvantage that the battery is loaded by the second comparator and in particular even during the charge-receiving mode, but there is only an improved capability, via the control unit, of triggering displays or light-emitting diodes, since in the second exemplary embodiment a continuous voltage supply is assured. The second exemplary embodiment shown in  FIG. 3  does offer the advantage over the first exemplary embodiment shown in  FIG. 1  that none of the components of the charger load the battery, but it also has the disadvantage that the control unit  150 , the first and second comparators  160 ,  270 , and the OR logic module  180  are supplied continuously with a supply voltage, that is, particularly even during the charge-receiving mode and particularly during the resting phase, via the supply transformer and therefore generate a power loss. The power loss of these components of the charger, which are included inside the outline shown in dashed lines in  FIG. 3 , is considerably less, however, than the power loss generated during an identical unit of time by the charge transformer  120 . In this respect, this second exemplary embodiment of the charger  100  is entirely advantageously usable in practice.  
      For exemplary embodiments, the following is true: The switching device  110  is embodied preferably as an opto-triac. Individual components of the charger  100 , and in particular the components outlined by dashed lines in  FIGS. 1 and 3 , are preferably embodied as an integrated circuit, for instance in the form of a microcontroller, with a suitable computer program. However, the comparators  160  and  170  in particular may also be embodied in hardware form as analog circuits.