Patent Application
20160176296
This disclosure relates generally to traction motor drive systems and, more specifically, to systems and methods for regenerative dynamic braking of a locomotive.
During dynamic braking, traction motors may function as generators to slow the movement of the locomotive by converting the kinetic energy of the locomotive into electrical energy. In rheostatic dynamic braking, grid resistors can be incorporated to dissipate the generated electrical energy as heat. As dynamic braking operations are performed, the temperature of the grid resistors may increase and may be cooled using a grid blower. Not only is this a waste of the power generated by the traction motors, but it also requires expending power to operate the grid blower used to prevent the grid resistors from overheating. For fuel efficiency and environmental purposes, rather than waste the energy generated by the traction motors, it may be advantageous to use the electrical energy to at least partially power the locomotive and its subsystems.
One solution for using the electrical energy generated by the traction motors is described in U.S. Pat. No. 8,179,084 (“the '084 patent”). The '084 patent is directed to a drive system for a grid blower used to cool the grid resistors. According to the '084 patent, the blower is powered by a motor that is coupled to taps across the grid of resistive elements. As such, the blower operates whenever there is electrical power on the grid of resistive elements, or grid resistors, such as during a dynamic braking operation. Since the blower is directly powered by electrical power from the grid resistors, additional electrical power need not be generated specifically to power the blower.
The '084 patent provides only a limited solution in which the grid blowers are powered with the electricity generated by the traction motors. The '084 patent only provides a solution for the grid blower to be powered directly from the resistive elements. However, as grid resistors can generate more electricity than is used to operate the grid blower, a solution is needed to enable other systems to use the electricity generated by the traction motors.
The presently disclosed systems and methods are directed to overcoming one or more of the problems set forth above and/or other problems in the art.
According to one aspect, this disclosure is directed to a regenerative braking system. The system may include a converter having a converter output and a converter input. The converter input may be electrically connected to a traction motor. The system may also include a resistive grid electrically connected to the converter output. The resistive grid may include at least one grid resistor. The system may also include a tap electrically coupled in parallel between the at least one grid resistor and a direct-current power bus.
In accordance with another aspect, this disclosure is directed to a locomotive. The locomotive may include an axle and a pair of wheels connected to the axle. The locomotive may also include a traction motor rotatably coupled to the axle. The locomotive may also include a regenerative braking system. The system may include a converter having a converter output and a converter input. The converter input may be electrically connected to the traction motor. The system may also include a resistive grid electrically connected to the converter output. The resistive grid may include at least one grid resistor. The system may also include a tap electrically coupled in parallel between the at least one grid resistor and a direct-current power bus of the locomotive.
According to another aspect, this disclosure is directed to a method. The method may include dynamically braking a traction motor, thereby resulting in an alternating current. The method may include converting the alternating current into a direct current and supplying the direct current to a resistive grid to dissipate a first portion of the direct current. The method may also include tapping into the resistor grid to draw a second portion of the direct current and supplying the second portion of the direct current to an electrical output.
When traction motor 130 is operating in a dynamic braking mode, traction motor 130 may operate as a generator. For example, as shown in
For example, system 200 may include a converter 240 having a converter input 245 and a converter output 250. Traction motor 130 may be electrically connected to converter input 245. Converter 240 may be configured to convert the alternating current of traction motor 130 into a direct current, which may flow at converter output 250.
System 200 may also include a resistive grid 260 electrically connected to converter output 250. Resistive grid 260 may be configured to dissipate at least a portion of the direct current across converter output 250. Resistive grid 260 may include at least one grid resistor 270. As grid resistor 270 of resistive grid 260 draws direct current from converter output 250, resistor 270 may overheat. To prevent or decrease the likelihood of overheating, system 200 may include a grid blower 280a, 280b to cool grid resistor 270. Grid blower 280a may be electrically connected directly to resistive grid 260, such that grid blower 280a may draw current from converter output 250. Additionally or alternatively, grid blower 280b may be electrically connected to direct-current power bus 220, such that grid blower 280b may draw current from direct-current power bus 220.
Grid blower 280a, 280b may be configured in different ways to cool resistive grid 260. For example, grid blower 280a, 280b may be configured to operate when traction motor 130 is operating in a dynamic braking mode. Additionally or alternatively, grid blower 280a, 280b may be configured to operate at different power modes. According to some embodiments, grid blower 280a, 280b may be configured to operate as a function of the temperature of resistive grid 260. For example, grid blower 280a, 280b may operate at a lower mode when the resistive grid temperature is below a threshold temperature and at a higher mode when resistive grid temperature is above a threshold temperature.
A tap 290 may be electrically connected to resistive grid 260 to draw the direct current outputted by converter output 250. According to some embodiments, tap 290 may be electrically connected in parallel to grid resistor 270 of resistive grid 260. In this manner, tap 290 may draw current from converter output 250, consistent with principles of electricity like Kirchoff's current law and Kirchoff's voltage law. Tap 290 may be configured to draw less than all of the current output by converter output 250. The output of tap 290 may be electrically connected to direct-current power bus 220. Tap may be electrically coupled in parallel between grid resistor 270 and direct current power bus 220. In this manner, direct-current power bus 220 may draw current from tap 290 such that the direct-current power bus 220 may include the sum of the current from engine 140 and tap 290.
At step 320, method 300 may include converting the generated alternating current into direct current. For example, step 320 may include operating converter 240 to convert the three-phase alternating current produced by traction motor 130 during step 310 into a direct current.
At step 330, the direct current from converter 240 may be supplied to resistive grid 260. Resistive grid 260 may dissipate a first portion of the direct current as it travels through resistive grid 260. For example, resistive grid 260 may be electrically connected to converter output 250 of converter 240 to draw direct current from converter 240.
At step 340, method 300 may include tapping into resistive grid 260 to draw a second portion of the direct current. For example, tap 290 may be electrically connected in parallel to resistive grid 260. At step 350, method 300 may include supplying the second portion of the direct current from tap 290 to an electrical output. For example, tap 290 may be electrically connected to direct-current power bus 220.
The disclosed system and methods provide a robust solution for using the power generated by traction motors during braking of the locomotive. The presently disclosed regenerative braking systems and methods may have several advantages. While other systems provide a solution for powering only the grid blower, the disclosed systems provides a solution by which the generated electricity feeds directly into the DC bus for powering accessory loads.
It will be apparent to those skilled in the art that various modifications and variations can be made to the systems for regenerative dynamic braking and associated methods for operating the same. Other embodiments of the present disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the present disclosure. It is intended that the specification and examples be considered as exemplary only, with a true scope of the present disclosure being indicated by the following claims and their equivalents.
