초록 ▼

A propulsion system for an electrically driven traction vehicle includes a chopper, a d-c traction motor, and means effective when the system is operating in a motoring mode for connecting the chopper in series with the armature and the field windings of the motor to a d-c electric power source that

A propulsion system for an electrically driven traction vehicle includes a chopper, a d-c traction motor, and means effective when the system is operating in a motoring mode for connecting the chopper in series with the armature and the field windings of the motor to a d-c electric power source that includes a filter capacitor. Cyclically operative means provides periodic gating signals for alternately turning on and turning off the chopper, and it can be smoothly changed from a constant frequency, variable pulse width mode to a variable frequency, constant (minimum) off time mode so as to vary the “duty factor”of the chopper over a wide range extending up to 100 percent on time. Brake set up means is operative in response to a motoring-to-braking command for reconnecting the chopper in parallel with the motor and the filter capacitor and for reversing the polarity of the connection of the series field winding relative to the armature. In response to this operation of the brake set up means, current in the field of the motor is momentarily boosted, and an extended chopper turn on signal having a duration substantially longer than that of the aforesaid periodic gating signals is supplied to the chopper to ensure that it turns on and conducts armature current to begin the braking mode of operation even if the command happens to take place at low speeds when the electromotive force of the motor is correspondingly low.

대표청구항 ▼

Improved means for effecting electrical braking of a traction vehicle equipped with a propulsion system having motoring and braking modes of operation, said propulsion system comprising a d-c traction motor that behaves as a generator during said braking mode of operation, said motor having an armat

Improved means for effecting electrical braking of a traction vehicle equipped with a propulsion system having motoring and braking modes of operation, said propulsion system comprising a d-c traction motor that behaves as a generator during said braking mode of operation, said motor having an armature and a series field winding and said propulsion system further comprising a filter capacitor adapted to be coupled to a siource of d-c electric power, a chopper, means for connecting said chopper in series with said armature and field windings across said capacitor when the propulsion system is operating in its motoring mode, cyclically operative means for normally producing periodic gating signals of relatively short predetermined duration, means responsive to said gating signals for alternatively turning on and turning off said chopper, and free wheeling rectifier means connected in circuit with said armature and series field winding to conduct motor current during intervals when said chopper is turned off, wherein the improvement comprises: (a) command means having alternative motoring and braking states; (b) brake set up means operative in response to a motoring-to-braking state change of said command means for reconnecting the propulsion system to establish an armature current path comprising said field winding in series with first and second parallel branches, said first branch including said chopper and said second branch including said capacitor in series with said free wheeling rectifier means, and for reversing the polarity of the connection of said series field winding relative to said armature, said brake set up means being effective whenever said command means is in its braking state to maintain said armature current path and to maintain the reversed polarity connection of said field winding and armature; and (c) burst firing means effective in response to the reconnecting operation of said brake set up means and the start of a braking state of said command means for supplying to said gating signal responsive means an extended chopper turn-on signal having a duration substantially longer than said predetermined duration of the gating signals normally produced by said cyclically operative means, thereby ensuring that said chopper turns on and conducts armature current to begin the braking mode of operation of the propulsion system.