Electricity: battery or capacitor charging or discharging – One cell or battery charges another – Vehicle battery charging
Reexamination Certificate
1999-05-11
2001-04-10
Berhane, Adolf Deneke (Department: 2838)
Electricity: battery or capacitor charging or discharging
One cell or battery charges another
Vehicle battery charging
C322S058000
Reexamination Certificate
active
06215271
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to vehicle charging systems, and more particularly to a charging system having a half-wave or a full-wave controlled rectifier bridge and a single voltage sensor.
2. Background
A typical prior art charging circuit
10
is depicted in FIG.
1
. The charging system provides electrical energy while the engine is running to recharge the battery and to power electrical devices. As shown in
FIG. 1
, a battery
12
is connected between a ground
14
and a positive or “hot” lead
16
, which leads to the electrical systems (not shown) of the vehicle and to the alternator
18
. This lead
16
is a path for current out of the battery
12
during undercharging or discharging, and a path for current into the battery
12
during charging. The alternator
18
is typically driven by a pulley
20
, which is driven by a belt (not shown) from the prime mover or engine (not shown). The electrical systems of the vehicle are powered through lead
22
. An ignition switch
24
is also connected to the hot lead
16
. Typically, an indicator lamp
26
is present to indicate a discharge state. A voltage regulator input lead
28
connects to the voltage regulator
30
, which determines the output of the alternator
18
by controlling the excitation voltage provided to the field winding of the alternator via line
32
, as will be discussed in greater detail below.
The basic layout of a vehicle alternator is well known. An alternator is typically a three-phase AC generator that typically comprises a rotor, which is essentially a spinning magnetic field which is turned by the vehicle's engine, and a stator, which is a stationary output winding. The operation is based on Faraday's law of electromagnetic induction. As the rotor is moved creating a varying magnetic field, electromotive force, or EMF, is induced in the windings resulting in current output. In order to produce a magnetic field in the rotor, field windings in the rotor are connected to a source of excitation current. The output from each of the three phases is AC, which is then rectified into DC through a rectifier bridge.
A prior art rectifier bridge is depicted in FIG.
2
. Prior art rectifier bridges for vehicular alternators have typically used an arrangement of diodes D
1
-D
6
, which serve as electrical check valves. Each of the three phases V
1
-V
3
is connected to two diodes, such that the negative and positive AC output of each phase are each rectified into DC voltage.
FIG. 3
depicts the output that results from the prior art diode bridge, as is well known to those skilled in the art.
The prior art rectifier bridge is very dependable and has been used successfully in claw pole, synchronous (Lundell) alternators in vehicles for decades. However, the modern era has placed increasing power demands on vehicle electrical systems through the constant addition of new electrical and electronic accessories, control systems, etc. to the vehicle. It has also become increasingly less desirable to solve these power requirement problems through increasing the size of the alternator, as available space under the hood of the modern vehicle is densely packed. Further, the additional engine power required to turn a larger alternator decreases overall efficiency of the vehicle, as does the additional weight. Finally, overall cost is an extremely important criterion in evaluating vehicular design solutions, rendering a larger more costly alternator less desirable.
A result of the increasing demands placed on the alternator is that often when the engine is at an idle, when alternator speed and hence power output efficiency are quite low, a deficit in the charging system results. In such situations, the battery supplies the required energy in a discharging state. Repetitive charging and discharging of batteries used in vehicles, typically lead-acid storage batteries, leads to shorter longevity, which is undesirable both from the point of view of the consumer and the environment.
One limitation of the diode is that it is not controllable in the sense that its switching points are inherent in its design. The prior art contains other arrangements, which replace the diodes of a conventional rectifier or inverter bridge with controllable elements, such as transistors or thyristors, but satisfactory control regimens for these controllable elements have been difficult to achieve and have not been successfully implemented.
U.S. Pat. No. 4,489,323 discloses a three-phase alternator whose output is rectified by a full wave thyristor, or semiconductor-controlled rectifier (SCR), bridge. One phase output is measured to generate a square wave in order to determine the speed of the alternator, so that the full-wave rectification can be switched to half-wave rectification when the speed of the alternator becomes too fast for the SCRs to fire reliably for proper rectification. The disadvantage with SCRs is that they naturally commutate with zero crossings of fundamental voltage waveform, rendering them less amenable to control. This apparatus disadvantageously does not address the problems associated with underspeed operation, only those associated with overspeed operation and SCR switching reliability.
U.S. Pat. No. 5,648,705 discloses a system for improving the power output of a vehicular alternator at low speeds through the use of a controllable rectifier bridge. A current detector and a voltage detector measure the state of one phase of the three-phase stator winding, and this information on the state of the single phase is passed to a controller. The controller uses the information provided by the detectors to control a full-wave controlled rectifier bridge in order to optimize the phase shift between the back EMF in the stator winding and phase voltages at the three output connections of the stator winding. The functioning of the device defined in this patent in its basic phases can be understood starting with reference to
FIG. 5
of the patent, which describes a prior art alternator device comprising a conventional diode rectifier. For a Lundell alternator such is commonly used in vehicles, the power angle &bgr; represents the angle between the back EMF and the phase voltage (V). As can be seen on the bottom vector of
FIG. 5
, a conventional diode bridge has an angle of zero between the current (I) and voltage (V). The resulting angle &bgr; is therefore less than 90 degrees, which results in a lower power output jIX
s
. It is accordingly desirable to increase the power angle &bgr;. To avoid the use of rotation sensors, and because the EMF cannot be directly measured during loading of the alternator because it cannot be electromagnetically separated from the armature current (reaction), the '705 device and methodology measure the current and the voltage of a single phase of the stator winding. By these measures, the synchronous frequency of the alternator can be determined, which reveals certain information about the back EMF. This information can then be used to maintain a phase shift a between the phase current and its associated phase voltage to maximize output, as seen in FIG.
4
. The phase shift can be induced by controlling the switching of the rectifier bridge. The control strategy employed uses a phase current detector and a phase voltage detector to estimate the position of the back EMF from the determined phase current and voltage. This estimated position provides an existing delay angle between the phase current and voltage, which is compared to a desired delay angle read from experimentally determined optimum values in a look-up table. The controllable bridge switching is then manipulated to match the estimated delay angle to the optimum angle. Disadvantageously, this control regimen requires the measuring of current and voltage, which requires two sensors and the electronics to gather and process the two data.
U.S. Pat. No. 5,793,167 discloses a system for increasing output power from an alternator, wherein a conventional full-wave diode bri
Donegan Kevin J.
Heyman Albert M.
LeRow Kevin E.
Berhane Adolf Deneke
Dike Bronstein, Roberts & Cushman LLP
Neuner George W.
SatCon Technology Corporation
Tibbits Pia
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