Note: Descriptions are shown in the official language in which they were submitted.
37
ELECTRICAL BRAKE SYSTEM
FOR ELECTRIC ROLLING STOCK
BACKGROUND OF THE INVENTION
_
~ield of the Invention
The present invention relates to an electrical brake
system for an electric rolling stock and, more particularly,
to a control system wherein a filter condenser and a control
unit are connected in parallel to the DC power supply so
that the control unit operates on the driving motor to
perform regenerative control and generation control for
the vehicle driving motor.
Description of the Prior Art
In the conventional regenerative brake control for
the electric rolling stock, if the regenerative load on
the trolly varies abruptly or the pantagraph comes off
the trolly momentarily due to the vibration of the vehicle
during a regenerative braking operation, the voltage across
the filter condenser rises excessively. On this account,
when a voltage rise is detected, the regenerative brake
circuit is opened immediately so as to protect the control
uni.t and driving motor. However, when this method is used
for vehicles running on lines with large variation of
regenerative load or for street cars whose pantagraph come
off the trolly frequently, the regenerative braking
operation is interrupted frequently, resulting in a poor
regenerat.ive duty cycle. In addition, an abrupt release
037
of the regenerative braking force and a switching to the
additional mechanical braking force with a time lag
following the first event create a shock, thereby causing
uncomfortableness for the passengers.
SU~IARY OF THE INVE2~TION
_
A primary object of the present invention is to provide
an electric brake system for an electric rolling stock
which is rid of the foregoing prior art deficiencies.
Another object of the present invention is to provide
a control system which detects immediately a rising voltage
across the filter condenser entering into the excessive
range caused by an abrupt variation of the regenerative load
on the trolly or a momentary separation of the pantagraph
from the trolly, and operates a resistor chopper connected
15 in parallel to the filter condenser so as to suppress the
excessive voltage
Still another object of the present invention is to
provide a control system which reduces the current in the
resistor chopper automatically in accordance with a pre-
determined timing pattern, and retains the regenerativecontrol so that the regenerative braking current is not
cut off completely, thereby allowing a ~uick rise of the
regenerative current after the regenerative load on the
trolly is restored or the pantagraph goes back to the
trolly.
These and other objects and advantages of the invention
will become more apparent from the following detailed
~36t)3~7
description of the embodiments taken in conjunction with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a systematic diagram showing one embodiment
of the inventive electrical brake system;
Figure 2 is a block diagram explaining the control
circuit shown in Fig. l;
Figure 3 is a block diagram explaining the modified
control circuit' and
Figure 4 is a systematic diagram showing another
embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In Figs. 1 and 2, refe~ence number 1 denotes a trolly
connected to a DC power source, 2 is a pantagraph, 3 is a
filter reactor, 4 is a filter condenser, and 5 is a series
circuit of a resistor 6 and resistor-chopper 7 connected
in parallel to the filter condenser 4. Reference number 8
is a regenerative chopper made up of a chopping section 9,
a blocking diode 10 and a smoothing reactor 11. Reference
number 12 is a DC motor having an excitation winding 13 and
an armature 14. Reference number 15 is a DC potential
transformer (DCPT), 16 is a serial resistor, 17 is a DC
current transformer (DCCTl) for sensing the current in the
DC motor 12, and 18 is a DC current transformer (DCCT2)
for sensing the current in the series circuit 5. Reference
number 19 is a main motor current pattern (Ip) generator,
and 20 ls a regenerative current limiter which operates
~86(~37
on the regenerative chopper ~ to reduce the motor current
when the detected voltage Vc across the filter condenser 4
exceeds the first preset voltage level Vl, and provides
the maximum limiter output to minimize the motor current
when the detected voltage Vc has reached the second preset
voltage level V2 (V2 > Vl) thereby to suppress the regene-
rative current indirectly. The regenerative current
limiter 20 is designed to have a control stability and
proper response constant so that the electrical braking
force and mechanical braking force are switched smoothly.
Reference number 21 is a filter condenser voltage
comparator which issues a start command to operate the
resistor-chopper 5 immediately when the voltage Vc has
reached a predetermined level V3 (V3 _ V2). The voltage
comparator 21 is designed to have proper hysteresis
characteristics and timer characteristics so that it is
deactivated when the voltage Vc goes down below V0
(VO < Vl) or a predetermined To has elapsed.
Reference number 22 is a current detector for
measuring the regenerative current IL and, in this embodi-
ment, the detector performs the arithmetic operation
IL = IM x (1 - y) based on the current conducting duty
cycle y of the regenerative chopper 8 and the detected
motor current IM~ As an alternative arrangement, the
current iL flowing in the filter reactor 3 may ~e detected
using a DC current transformer (not shown) instead of using
the regenerative current detector 22.
~i36C~37
Reference number 23 is a current pattern generator for
creating a pattern IRp of the current iR conducted through
-the resistor-chopper 7. The current pattern generator 23
provides a current pattern IRp so that current iR is
substantially equal to current IL at the initial state
when the voltage comparator 21 has issued a command to the
resistor-chopper 5, and upon expiration of time To~ the
circuit 23 reduces the IRp smoothly so that the iR becomes
substantially zero. The resistor-chopper 5 receives the
detected value IR of iR from the DC current transformer
(DCCT2) 18 so as to perform the current control in accor-
dance with the current pattern I~p.
In such an arrangement, if an abrupt varia-tion of the
trolly load or the like has occurred, the regenerative
current iL is transferred immediately to the current iR
through the resistor chopper 7 so as to preven-t the
electrical braking force from varying sharply. When the
filter condenser voltage Vc rises gradually due to the
reduction of the resistor chopper current iR based on the
timer pattern IRp, on the other hand the regenerative current
limiter 20 operates to reduce the motor current smoothly.
If the resistor chopper current finally becomes minimal or
is cut off completely, the current control is performed for
a small trolly load condition or no-load condition, ~here
the power .system is loaded only with auxiliary devices
within the vehicle, solely by the regenerative chopper 8
including the current limiter 20. In consequence, when the
()37
-trolly load is restored and the power voltage falls,
causing the Vc to go back below V1, the current limiter 20
is deactivated so that the regenexative chopper 8 increases
the motor current automaticallv and promptly up to Ip, and
the normal regenerative control is restored.
The arrangement of the control circuit shown in Fig. 3
is basically identical to that of Fig. 2, and performs a
slightly simplfied control for the resistor-chopper 7.
Specifically, the feedback of IR is eliminated and the
resistor chopper current is controlled on an open loop ,basis
following the current conduction duty cycle pat-tern YRp
provided by the current pattern generator 23. In this case,
the value ~L of the timer pattern ~RP at starting is set
automatically basing on the arithmetic operation ~L = R/V2 x
IL (where R is the resistance of the resistor 6, V2 is the
second preset voltage level and IL is the regenerative
current value), and it becomes zero or minimal upon exp.ira-
tion of the time To~
Figure 4 shows another embodiment of the present
invention wherein the control unit employs a VVVF inverter
24 so that the same effect of control is achieved for an
induction motor 25 which serves as the driving motor for
the electric rolling stock, whereas in the previous
embodiment the regenerative chopper is used as the control
unit.
Furthermore, the control unit may be of the conventional
cam-contacts system.
-- 6 --
1~l8~;~37
According to the present invention, as described above,
the voltage across the filter condenser is measured and
compared with several preset values, and the control mode
for the regenerative current is determined depending on the
threshold exceeded by the filter condenser voltage.
Accordingl~, even after an abrupt variation in the trolly
load or a coming off of the pantagraph from the trolly has
occurred, the braking force is controlled stably while
suppressing an excessive voltage across the filter con-
denser, and the regenerative braking is restored promptly.
In Figure 4, the VVVF inverter is an abbreviation ofa variable voltage variable frequency inverter.
