Railway rolling stock – Locomotives – Generating electric
Reexamination Certificate
2001-12-26
2003-07-15
Le, Mark T. (Department: 3617)
Railway rolling stock
Locomotives
Generating electric
C105S050000, C105S061000, C180S065310
Reexamination Certificate
active
06591758
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to hybrid energy systems and methods for use in connection with large, off-highway vehicles such as locomotives. In particular, the invention relates to a system and method for selectively capturing, storing, and regenerating electrical energy, such as dynamic braking energy, produced by locomotives driven by electric traction motors.
BACKGROUND OF THE INVENTION
FIG. 1A
is a block diagram of an exemplary prior art locomotive
100
. In particular,
FIG. 1A
generally reflects a typical prior art diesel-electric locomotive such as, for example, the AC6000 or the AC4400, both or which are available from General Electric Transportation Systems. As illustrated in
FIG. 1A
, the locomotive
100
includes a diesel engine
102
driving an alternator/rectifier
104
. As is generally understood in the art, the alternator/rectifier
104
provides DC electric power to an inverter
106
which converts the AC electric power to a form suitable for use by a traction motor
108
mounted on a truck below the main engine housing. One common locomotive configuration includes one inverter/traction motor pair per axle. Such a configuration results in three inverters per truck, and six inverters and traction motors per locomotive.
FIG. 1A
illustrates a single inverter
106
for convenience.
Strictly speaking, an inverter converts DC power to AC power. A rectifier converts AC power to DC power. The term converter is also sometimes used to refer to inverters and rectifiers. The electrical power supplied in this manner may be referred to as prime mover power (or primary electric power) and the alternator/rectifier
104
may be referred to as a source of prime mover power. In a typical AC diesel-electric locomotive application, the AC electric power from the alternator is first rectified (converted to DC). The rectified AC is thereafter inverted (e.g., using power electronics such as IGBTs or thyristors operating as pulse width modulators) to provide a suitable form of AC power for the respective traction motor
108
.
As is understood in the art, traction motors
108
provide the tractive power to move locomotive
100
and any other vehicles, such as load vehicles, attached to locomotive
100
. Such traction motors
108
may be AC or DC electric motors. When using DC traction motors, the output of the alternator is typically rectified to provide appropriate DC power. When using AC traction motors, the alternator output is typically rectified to DC and thereafter inverted to three-phase AC before being supplied to traction motors
108
.
The traction motors
108
also provide a braking force for controlling speed or for slowing locomotive
100
. This is commonly referred to as dynamic braking, and is generally understood in the art. Simply stated, when a traction motor is not needed to provide motivating force, it can be reconfigured (via power switching devices) so that the motor operates as a generator. So configured, the traction motor generates electric energy which has the effect of slowing the locomotive. In prior art locomotives, such as the locomotive illustrated in
FIG. 1A
, the energy generated in the dynamic braking mode is typically transferred to resistance grids
110
mounted on the locomotive housing. Thus, the dynamic braking energy is converted to heat and dissipated from the system. In other words, electric energy generated in the dynamic braking mode is typically wasted.
It should be noted that, in a typical prior art DC locomotive, the dynamic braking grids are connected to the traction motors. In a typical prior art AC locomotive, however, the dynamic braking grids are connected to the DC traction bus because each traction motor is normally connected to the bus by way of an associated inverter (see FIG.
1
B).
FIG. 1A
generally illustrates an AC locomotive with a plurality of traction motors; a single inverter is depicted for convenience.
FIG. 1B
is an electrical schematic of a typical prior art AC locomotive. It is generally known in the art to employ at least two power supply systems in such locomotives. A first system comprises the prime mover power system that provides power to the traction motors. A second system provides power for so-called auxiliary electrical systems (or simply auxiliaries). In
FIG. 1B
, the diesel engine (see
FIG. 1A
) drives the prime mover power source
104
(e.g., an alternator and rectifier), as well as any auxiliary alternators (not illustrated) used to power various auxiliary electrical subsystems such as, for example, lighting, air conditioning/heating, blower drives, radiator fan drives, control battery chargers, field exciters, and the like. The auxiliary power system may also receive power from a separate axle driven generator. Auxiliary power may also be derived from the traction alternator of prime mover power source
104
.
The output of prime mover power source
104
is connected to a DC bus
122
which supplies DC power to the traction motor subsystems
124
A-
124
F. The DC bus
122
may also be referred to as a traction bus because it carries the power used by the traction motor subsystems. As explained above, a typical prior art diesel-electric locomotive includes four or six traction motors. In
FIG. 1B
, each traction motor subsystem comprises an inverter (e.g., inverter
106
A) and a corresponding traction motor (e.g., traction motor
108
A).
During braking, the power generated by the traction motors is dissipated through a dynamic braking grid subsystem
110
. As illustrated in
FIG. 1A
, a typical prior art dynamic braking grid includes a plurality of contactors (e.g., DB
1
-DB
5
) for switching a plurality of power resistive elements between the positive and negative rails of the DC bus
122
. Each vertical grouping of resistors may be referred to as a string. One or more power grid cooling blowers (e.g., BL
1
and BL
2
) are normally used to remove heat generated in a string due to dynamic braking.
As indicated above, prior art locomotives typically waste the energy generated from dynamic braking. Attempts to make productive use of such energy have been unsatisfactory. For example, systems that attempt to recover the heat energy for later use to drive steam turbines require the ability to heat and store large amounts of water. Such systems are not suited for recovering energy to propel the locomotive itself. Another system attempts to use energy generated by a traction motor in connection with an electrolysis cell to generate hydrogen gas for use as a supplemental fuel source. Among the disadvantages of such a system are the safe storage of the hydrogen gas and the need to carry water for the electrolysis process. Still other prior art systems fail to recapture the dynamic braking energy at all, but rather selectively engage a special generator that operates when the associated vehicle travels downhill. One of the reasons such a system is unsatisfactory is because it fails to recapture existing braking energy.
Therefore, there is a need for an improved system that captures and stores the electric energy, such as the energy generated in the dynamic braking mode, and that supplies the stored energy for later use.
SUMMARY OF THE INVENTION
In one aspect, the invention relates to a hybrid energy locomotive system for use in connection with a train. The hybrid energy locomotive system comprises a locomotive having a plurality of locomotive wheels. A locomotive traction motor is associated with one of the plurality of locomotive wheels. The locomotive traction motor has a first rotatable shaft mechanically coupled to the one of the plurality of locomotive wheels. An electric power source selectively supplies locomotive electric power to the locomotive traction motor. The locomotive traction motor is operable in response to the locomotive electric power to rotate the first rotatable shaft and to drive the one of the plurality of locomotive wheels. The locomotive traction motor further has a dynamic braking mode of operation in which the locomotive traction motor generates electric
General Electric Company
Le Mark T.
Rowald Carl
Senniger Powers Leavitt & Roedel
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