Electricity: single generator systems – Automatic control of generator or driving means – Voltage of generator or circuit supplied
Reexamination Certificate
2000-01-24
2001-06-26
Ponomarenko, Nicholas (Department: 2834)
Electricity: single generator systems
Automatic control of generator or driving means
Voltage of generator or circuit supplied
C322S020000, C322S025000, C363S145000
Reexamination Certificate
active
06252381
ABSTRACT:
The invention is based on a method for regulating a generator that can be driven by an internal combustion engine, in particular a three-phase generator in a motor vehicle, as generically defined by the preamble to the main claim.
PRIOR ART
Currently, claw-pole generators are usually used to produce the electrical energy required in a motor vehicle. These claw-pole generators are three-phase generators whose output current is rectified with the aid of a diode bridge and is used to supply the electrical consumers of the vehicle as well as for charging the battery. The essential components of a three-phase generator are shown in FIG.
1
. The excitation current or field current IF flows through the excitation coil
10
, which is also called a field coil. The voltage of the excitation coil
10
is the field voltage UF.
The current flowing through the excitation coil
10
induces a magnetic field in the stator coils
11
,
12
,
13
. The flux change produces an induced voltage in the stator coils which drives a voltage IS through the diodes
14
to
19
in the on-board network. This current is used to supply the consumers
20
and the battery
21
. The battery voltage is labeled UB. The current flow through the field winding
10
is usually regulated with the aid of a voltage regulator, not shown here, so that the desired voltage is present at the output of the generator. Usually the entire system with the excitation coil
10
and the stator coils
11
to
13
is referred to as a generator
34
.
With a generator and the associated rectifier circuit as shown in
FIG. 1
, a power output only begins after a certain speed has been achieved. This speed depends on the dimensioning of the generator, and in particular, on the embodiments of the stator coils. The speed at which the generator begins to output power or the speed at which a current flow begins is the so-called switch-on speed nE.
The relationship between the power Pe in kW output by the generator and the generator speed n in rpm is shown in
FIG. 3
for a conventional generator. The lower (solid) curve stands for an output voltage of 14 V; the upper (dashed) curve stands for an output voltage of 28 V. In addition, the so-called tangent line TG has been plotted on the graph. With a 14 V output voltage, the tangent point is disposed at a generator speed of n
1
=approx. 1500/min. The calculation of the power output as a function of the speed for the output voltages 14 V and 28 V, which are indicated in
FIG. 3
, was carried out with constant parameters. In particular, the following parameters were selected:
stator leakage inductance: 19 &mgr;H
stator shunt inductance: 47 &mgr;H
stator series inductance: 77 &mgr;H
stator resistance: 12 m&OHgr;
excitation current: 3.5 A
The diodes and switches were assumed to be n ideal components. All calculations were carried out in phasor diagrams.
As can be inferred from
FIG. 3
, at speeds below 1500 rpm, a conventional three-phase generator only produces a low output. At low speeds of this kind, the generator can only output a very low current. In order for a current flow to start, the instantaneous values of the rectified generator voltage must be greater than the on-board network voltage. Only when this prerequisite is met can the generator even produce a current (of any consequence) in the first place. As the speed increases so does the voltage that the excitation coil
10
induces in the stator windings
11
,
12
, and
13
, which is called the synchronous generated voltage. Accordingly, as the speed increases, so does the generator current. At a high speed, the terminal voltage present at the output of the stator coils is very low in relation to the synchronous generated voltage so that the generator is operated almost at a short circuit. For these reasons, the power output can only be increased insignificantly as the speed increases.
At the short circuit point, the power output of the generator can be increased considerably by virtue of the fact that the on-board network voltage is increased. With a doubled voltage, i.e. with a 28 V output voltage in the generator, the power output for high speeds is approximately twice as high as with a 14 V generator voltage. The doubling of the output power is produced because the short circuit current has been achieved once more. In lieu of a doubling of the generator voltage, a halving of the winding count also leads to a doubling of the output current and therefore to a doubling of the power. The two methods magnetically produce the same states in the generator. Therefore, the considerations stated below will be explained for only one method, namely for the voltage doubling with an unchanged winding count.
As explained above, a doubling of the generator voltage at high speeds leads to a considerable power increase. At low generator speeds, however, the voltage increase leads to a disadvantage. The switch-on speed nE at which the output of current begins is proportional to the battery voltage. With an increase in the battery voltage, the switch-on speed is consequently also increased and at low generator speeds, no power is output. Since conventional generators must be designed for speeds from approx. 1800 to 6000 rpm, problems can arise in the lower speed range. The tangent point is the contact point with the characteristic curve of the generator, which is understood to be the characteristic curve of the generator power over generator speed, with an origin line that is as steep as possible. As can be inferred from
FIG. 3
, with a simple battery voltage, the tangent point is disposed at approx. 1500 rpm. Since the tangent points for different battery voltages are disposed on a line, it turns out that with a doubled battery voltage, the tangent point is reached at twice as high a speed n
2
. At the speed n
1
, the power output of this generator is equal to zero at 28 V (see FIG.
3
).
Since sometimes speeds even lower than 1800 rpm need to be permitted as a generator operating speed, the battery voltage would have to be reduced in order to move the tangent point toward the lower speeds. Alternatively, the winding count could also be increased. In both instances, though, the maximal generator power decreases and therefore these generator changes are not possible. On the other hand, future generators will have to produce more power. With required outputs of over 5 kW, the generators would have to be enlarged. But since the claw geometry does not permit any elongation of the claws due to the speed rating and it is not possible to increase the stator bore diameter, the current proposal is to use double generators, but these are expensive and have the disadvantage of a relatively high moment of inertia.
Another known possibility for power increase is comprised in adapting the terminal voltage of the generator to the respective requirements. This path is also called generator operation with free voltage. The generator then functions on a capacitor and a d.c. voltage converter transforms the power into the on-board network and in this connection, stabilizes its voltage at 14 V, for example. Through the selection of a suitable voltage for the respective speed, the generator can function at the tangent point at every speed. For speeds that are greater than the speed at the tangent point n
1
with 14 V and n
2
with 28 V, the capacitor voltage should be selected as greater than the on-board network voltage. The d.c. voltage converter that converts the capacitor voltage into the on-board network voltage must therefore function as a reduction device and convert the voltage from higher to lower values. For speeds that are lower than the respective speed n
1
or n
2
, the d.c. voltage converter must function as an increase device. Therefore a d.c. voltage converter must be used which converts the low capacitor voltage into the higher on-board network voltage.
This known embodiment with the variable generator voltage combines the advantages of both battery voltages according to
FIG. 3
, since both tangent points can be approached. At a higher speed, the
Ponomarenko Nicholas
Robert & Bosch GmbH
Striker Michael J.
LandOfFree
Method for regulating a generator capable of being driven by... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for regulating a generator capable of being driven by..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for regulating a generator capable of being driven by... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2538190