Abstract:
A three-phase generator that has a plurality of stator windings, a rectifier system connected with the stator windings, an exciter winding, a generator controller, and an additional circuit that effects an increase in voltage. This additional circuit is a passively operated booster circuit that is integrated into the generator and that has no controlled components.

Description:
BACKGROUND INFORMATION 
   In known claw-pole generators, the energy for the excitation is taken from the electrical system of the respective motor vehicle. This takes place using a generator controller that has a switched semiconductor as a switching element. The generator controller sets the excitation voltage between 0 V and the electrical system voltage. This is shown in  FIG. 1 , which depicts a diagram illustrating the positioning of generator controller R between electrical system BN and excitation winding WE of the generator. 
     FIG. 2  shows a known generator circuit having a generator controller R, an excitation winding WE, a rectifier system G and three stator windings WS. The stator windings form a star connection, and are offset by 120° from one another with respect to the rotor (not shown). The beginnings of the windings, which are connected to the rectifier system, are designated with the letters U, V, W. When the rotor is turned, an alternating voltage is produced in each of these stator windings. The three alternating voltages produced are offset from one another by 120°. 
   From German Published Patent Application No. 196 34 096, a voltage supply system is known that has an increased output power, produced when an increased power requirement is signaled by an external control signal. The known system has a three-phase generator whose windings supply the voltage for a vehicle electrical system via rectifiers. In addition, the generator contains an exciter winding through which the excitation voltage, which can be influenced by a voltage controller, flows. The exciter winding can be operated with a voltage that is higher than the supply voltage during times that can be predetermined. This increased voltage is produced through the activation of additional windings having rectifiers in the generator, or by a direct-current converter allocated to the generator. In this way, the controlling of the generator takes place through the voltage controller, which has controlled transistors, in such a way that the output voltage of the generator remains at the level of the electrical system. 
   SUMMARY OF THE INVENTION 
   In contrast, the present invention achieves an increased output power of the generator by using, as an improved magnetic utilization of the generator, the ripple at the exciter winding ends in order to achieve a capacitive voltage increase. This takes place economically through the use of a passive additional circuit that has no transistors. In comparison with circuit topologies that, for example, use direct-current converters for voltage multiplication, this results in advantages with respect to the electromagnetic compatibility. 
   In comparison to all actively controlled additional circuits, advantages result the fact that no actively controlled components are required. Conventional diodes and capacitors can be used. In addition, no saturation effects occur. The additional circuit according to the present invention is secure against short-circuiting and against open-circuit operation. 
   An additional voltage increase can advantageously be achieved through the use of a cascade connection. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows an arrangement including a generator controller. 
       FIG. 2  shows a generator circuit provided with a generator controller. 
       FIG. 3  shows a drawing illustrating the arrangement of the additional circuit according to a first exemplary embodiment of the present invention. 
       FIG. 4  shows a drawing illustrating the arrangement of the additional circuit according to a second exemplary embodiment of the present invention. 
       FIG. 5  shows an exemplary embodiment of an additional circuit according to the present invention. 
       FIG. 6  shows a first exemplary embodiment of a generator circuit according to the present invention. 
       FIG. 7  shows a second exemplary embodiment of a generator circuit according to the present invention. 
       FIG. 8  shows a diagram illustrating the voltage curves at the winding taps of the stator windings. 
   

   DETAILED DESCRIPTION 
   According to the present invention, an additional circuit that uses only passive components is inserted into a three-phase generator, preferably a claw-pole generator, and through the use of said circuit an increase is achieved in the excitation voltage drop at the excitation winding of the generator. In this way, the excitation current flowing through the excitation winding, and thus the output power provided by the generator, are also increased. 
   With an additional circuit according to the present invention, the output voltage of the generator can for example be doubled or tripled. A further increase of the output voltage of the generator is possible through the additional use of a cascade connection. 
     FIG. 3  shows a drawing illustrating the arrangement of an additional circuit according to a first exemplary embodiment of the present invention. In this first exemplary embodiment, one terminal of additional circuit ZS 1  is connected with the 14V electrical system, and a second terminal is connected, via generator controller R, to the terminal away from ground of excitation winding WE. The other terminal of excitation winding WE is connected directly to ground GND. In addition, additional circuit ZS 1  has terminals U, V, W, that are connected to the stator windings. 
     FIG. 4  shows a drawing illustrating the arrangement of an additional circuit according to a second exemplary embodiment of the present invention. In the second exemplary embodiment, a terminal of additional circuit ZS 2  is connected to the 14V electrical system, and a second terminal is connected, via generator controller R, to the terminal away from ground of excitation winding WE. In addition, additional circuit ZS 2  also extends to the connection between the terminal adjacent to ground of excitation winding WE and ground GND. In addition, additional circuit ZS 2  has terminals U, V, W that are connected to the stator windings. 
     FIG. 5  shows an exemplary embodiment of an additional circuit ZS 1  that can be used in combination with  FIG. 3 . This additional circuit is a passively operated booster circuit situated between the 14V terminal and generator controller R according to  FIG. 3 . This booster circuit has a parallel circuit of three signal branches, each signal branch containing two diodes connected in series. The connection point between the two diodes of the first signal branch can be connected with terminal U via a capacitor. The connection point between the two diodes of the second signal branch can be connected with terminal V via a capacitor. The connection point between the two diodes of the third signal branch can be connected with terminal W via a capacitor. 
   In alternative exemplary embodiments, not shown in the drawing, the additional circuit has only one parallel circuit having two signal branches, or simply has only one signal branch, each of these signal branches being constructed in the same way as one of the signal branches shown in  FIG. 5 . 
   If a booster circuit according to  FIG. 5  is used in a claw-pole generator, there results the device shown in  FIG. 6 , which shows a first exemplary embodiment of a generator circuit according to the present invention. 
   In addition, if such a booster circuit is additionally placed into the connection branch between the terminal adjacent to ground of excitation winding WE and ground, there results the device shown in  FIG. 7 , which shows a second exemplary embodiment of a generator circuit according to the present invention. This exemplary embodiment is based on the schematic design according to  FIG. 4 . 
   The curve of the winding voltages at taps U, V, W is shown in  FIG. 8  for one of these winding phases. In this Figure, time is plotted on the abscissa and voltage is plotted on the ordinate. It can be seen that the winding voltages run in approximately rectangular fashion. 
   In the following, the functioning of the voltage increase circuit in the exemplary embodiment according to  FIG. 6  is explained in more detail on the basis of one phase of the three-phase generator. First, a voltage of −0.7 V is present at tap U. This is because this tap U is connected with ground GND via a diode, this diode having a forward voltage of 0.7 V. 
   A voltage of 14V is present at the capacitor situated in the U phase, said capacitor being connected to the electrical system via a diode of the additional circuit. A flow of current takes place from the electrical system to the capacitor via the diode. In this way, the potential at tap U increases to a value that corresponds to the sum of the electrical system voltage and the forward voltage of the diode, i.e., to a value (U BN ÷0.7 V). This corresponds to an increase in the charge of the capacitor. 
   Subsequently, charge flows from the capacitor into the exciter circuit via the second diode of the additional circuit. In this way, the potential at tap U sinks again to −0.7 V. This process, which is constantly repeated, takes place in each of phases U, V, W, with a time offset of 120°. 
   For example, let exciter current I err =8 A and let exciter voltage U err =24V. The energy output of the capacitor is then calculated as 
   
     
       
         
           E 
           = 
           
             
               1 
               2 
             
             ⁢ 
             
               C 
               ⁡ 
               
                 [ 
                 
                   
                     
                       ( 
                       
                         2 
                         · 
                         
                           U 
                           14 
                         
                       
                       ) 
                     
                     2 
                   
                   - 
                   
                     
                       ( 
                       
                         
                           U 
                           err 
                         
                         - 
                         
                           U 
                           14 
                         
                       
                       ) 
                     
                     2 
                   
                 
                 ] 
               
             
           
         
       
     
   
   For the power of the booster circuit, the following holds: 
   
     
       
         
           P 
           = 
           
             
               f 
               e1 
             
             · 
             
               3 
               2 
             
             · 
             
               C 
               ⁡ 
               
                 [ 
                 
                   
                     
                       ( 
                       
                         2 
                         · 
                         
                           U 
                           14 
                         
                       
                       ) 
                     
                     2 
                   
                   - 
                   
                     
                       ( 
                       
                         
                           U 
                           err 
                         
                         - 
                         
                           U 
                           14 
                         
                       
                       ) 
                     
                     2 
                   
                 
                 ] 
               
             
           
         
       
     
   
   In this way, the following is obtained:
 
C≈1500 μF, if f=180 Hz.
 
   If the boundary conditions change, different values will result.