Electricity: single generator systems – Generator control – With excitation winding and/or circuit control
Reexamination Certificate
1999-08-05
2001-02-20
Ponomarenko, Nicholas (Department: 2834)
Electricity: single generator systems
Generator control
With excitation winding and/or circuit control
C322S068000, C322S069000, C323S282000
Reexamination Certificate
active
06191562
ABSTRACT:
BACKGROUND INFORMATION
During the operation of motor vehicle generators, for instance claw pole generators, sudden surge voltages occur in response to a load dump because the magnetomotive force or the stored magnetic energy of the field winding of the generator can only be degraded at a finite rate. Traditionally, the resultant voltage increase in the vehicle electrical system can only be prevented by using additional, expensive components, such as power zener diodes.
Various circuits for quenching or degrading the stored magnetic energy of a field winding are known from the related art.
We will first describe one known quenching circuit with reference to
FIG. 3. A
generator G is furnished with a field winding
10
that is characterized by its inductor L and its ohmic resistor R. The storage or quenching of energy of field winding
10
is controlled by a power transistor T, which in normal operation is operated by timed pulses from a clock control
20
. Field coil
10
and power transistor T are connected in series to a battery voltage Ubatt.
As mentioned above, in normal operation, power transistor T is operated by timed pulses, for instance by the process of pulse width modulation. During the conductive state of power transistor T, energy is stored in field coil
10
. A diode D makes a free-running circuit of field coil
10
. During the non-conducting state of power transistor T, i.e. the free-running phase of field coil
10
, the magnetic energy stored in the field coil is degraded via the free-running circuit. The counter-voltage required for the energy degradation corresponds to the conducting-state voltage of diode D of the free-running circuit, which is typically about 0.7 V. The degradation of energy proceeds relatively slowly, corresponding to this low counter-voltage. While this behavior is desirable in normal operation, in the event of a load dump, the energy degradation in the field coil proceeds too slowly, despite immediate intervention by the regulator, because the low counter-voltage does not permit rapid degradation of energy. This leads to surge voltages in the vehicle electrical system which must be suppressed, as for example by the use of expensive power zener diodes.
FIG. 4
shows a so-called H-bridge circuit for degradation of the energy of a field coil, which is known from the related art. The components illustrated here have the same reference numbers as those in FIG.
3
. The circuit has two power switches S
1
, S
2
that can take the form, for example, of transistors. In normal operation, both power switches S
1
, S
2
are closed for storage of energy in field winding
10
. In this case, current flows via power switch S
1
, inductor L, resistor R and power switch S
2
. During the free-running, one of the power switches is closed, which facilitates a degradation of the magnetic energy of field winding
10
according to the design approach described above with reference to FIG.
3
.
For rapid degradation or quenching of the magnetic energy of field winding
10
, both power switches S
1
, S
2
are opened simultaneously. The current now flows via diode D
2
, inductor L, resistor R and diode D
1
. In this case, diodes D
1
, D
2
are traversed by the flow in the direction of conductance. Hence the current flows against the battery voltage (for example, 14 V) and the conducting-state voltages of the two diodes D
1
, D
2
. The counter-voltage required for this is built up by the self-inductance of field coil
10
.
SUMMARY OF THE INVENTION
An object of the present invention is to create an inexpensive circuit configuration to ensure a rapid and reliable degradation of the stored magnetic energy in a field coil of a generator, especially for compensation of a sudden load dump.
With the present invention, it becomes possible to degrade the stored energy or the inductance of a field winding of a generator much more quickly than is possible with the related art. This is particularly important in the event of a load dump, that is, the disconnection or sudden outage of a load. The duration of the surge voltage at the output side of a generator is substantially reduced by the present invention. The amount of quenching energy to be absorbed by protective elements, for instance power zener diodes, at the output side of the generator is likewise substantially smaller. This leads to cost savings, since it becomes possible to use protective elements of lesser capacity. Further benefits result from a smaller requisite installation space and less thermal energy to dissipate. It should be noted that the power switch for the timed control of the field winding is not necessarily the same power switch whose control input can be triggered via the zener diode. However, it is preferable to furnish just one power switch to carry out the aforementioned functions.
It is efficacious to furnish the circuit configuration of the present invention with a free-running circuit that is in operative connection with the field winding and which includes at least one diode and at least one power switch. This arrangement provides for traditional diode quenching, as for example was explained above with reference to
FIG. 3
, when the circuit configuration is operating normally. The normal operation of the exciting current regulator of the generator, especially a motor vehicle generator, is not affected by the inventive quenching of the energy of the field winding by a zener diode. In addition, the inventive principle of quenching via a zener diode can also be utilized during normal operation as an expanded corrective intervention for generator regulation. This permits an increase in the control dynamic response, since the corrective intervention on the excitation side is improved. In a preferred embodiment of the circuit configuration according to the present invention, a diode is situated between the field coil and the zener diode.
In a preferred form of the circuit configuration of the present invention, the power switch for control of the storage and degradation of energy of the field winding and/or the power switch of the free-running circuit are MOS field effect transistors. These transistors are reliably and inexpensively available. However, other controllable switches may also be used, for instance a bipolar transistor or an IGBT. This power switch can be triggered by way of the known high-side drives; however, use of a smart-power MOS field effect transistor in which the high-side drive is integrated is also conceivable, among other possibilities.
The generator can be a synchronous generator, for example a claw pole generator. A generator such as this is relatively light and is inexpensive to manufacture. In combination with the circuit configuration of the present invention which, as mentioned above, requires little installation space, one can obtain very compact generator units.
One distinguishing feature of the process of the present invention is that, in case of an event such as a sudden load dump, a change-over takes place from a first mode of operation, in which the power switch that controls the field winding of the generator is operated with timed pulses, to a second operating state in which the discharging current of the field winding, which is induced by the voltage applied to the field winding, at first can flow only via the zener diode (switched in the non-conducting direction relative to this voltage). The voltage applied to the field winding or the voltage that drops off at the zener diode in this mode of operation is essentially the total of the battery voltage and the voltage caused by self-induction of the field winding. The control input of the power switch or transistor is triggered only when the breakdown (avalanche) voltage of the zener diode is exceeded such that the power switch or transistor is at least partially force-tripped and can dissipate a discharging current from the field winding.
In the second operating state, it is efficacious to have the power switch of the free-running circuit open. This provides a simple manner for decoupling the free-running circu
Frey David
Luz Oliver
Mueller Wolfgang
Schoettle Richard
Kenyon & Kenyon
Ponomarenko Nicholas
Robert & Bosch GmbH
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