BASIC OPERATION AND FEATURES
SX TRANSISTOR CONTROL
Page
5
Section 2.1.1.a Standard Operation
The oscillator section of the card has two adjustable
features, creep speed and minimum field current.
The creep speed can be adjusted by Function 2 of
the handset. The field control section allows the
adjustment of the field weakening level in order to set
the top speed of the motor. This top speed function
(Minimum Field Current) is enabled when the
armature current is less than the value set by
Function 24. Top Speed can be adjusted by Function
7 of the handset .
The % ON-time has a range of approximately 0 to
100 percent. The SX controllers operate at a constant
frequency and the % ON-time is controlled by the
pulse width of the voltage/current applied to the motor
circuits.
Section 2.1.1.b Control Acceleration
This feature allows for adjustment of the rate of time it
takes for the control to accelerate to 100% applied
battery voltage to the motor on hard acceleration.
Armature C/A is adjusted by Function 3 from 0.1 to 22
seconds.
Section 2.1.2 Current Limit
This circuit monitors motor current by utilizing sensors
in series with the armature and field windings. The
information detected by the sensor is fed back to the
card so that current may be limited to a preset value.
If heavy load currents are detected, this circuit
overrides the oscillator and limits the average current
to a value set by Function 4 and Function 8 of the
Handset. The C/L setting is based on the maximum
thermal rating of the control. Because of the flyback
current through 3REC, the motor current is usually
greater than battery current, except at 100% ON time.
Section 2.1.3 Regenerative Braking to Zero Speed
Slow down is accomplished when
releasing accelerator pedal or
depressing brake pedal by
providing a regulated amount of
retarding torque for deceleration.
If the vehicle is moving, and the
accelerator pedal is released, the
regen signal is initiated. Once the
regen signal has been initiated,
the field current is increased
(armature circuit shown in Figure
5). Armature current is regulated to the regen current
limit as set by Function 9. As the vehicle slows down,
the field current continues to increase, and transistor
Q2 begins to chop. The field current will increase
until it reaches a preset value set by Function 10, and
transistor Q2 on-time will increase until it reaches
100% on-time. Once both of the above conditions
have been met, and regen current limit can no longer
be maintained, the braking function is canceled. Part
of the energy produced by the motor during regen is
returned to the battery, and part is dumped in the
motor as heat.
Section 2.1.4 Auxiliary Speed Control
Section 2.1.4.a Field Weakening
This function allows the adjustment of the field
weakening level in order to set the top speed of the
motor. The function is enabled when the armature
current is less than the value set by Function 24 and
the accelerator input voltage is greater than 2.9 volts.
It is important to note that this function is used to
optimize motor and control performance, and this
setting will be determined by GE and OEM engineers
at the time of vehicle development.
This setting must
not be changed by field personnel without the
permission of the OEM.
Section 2.1.4.b Speed Limits
This feature provides a means to control speed by
limiting motor volts utilizing "adjustable speed limits",
initiated by individual limit switches. The NC switches
are connected between input points on the control
card and battery positive. The lower motor volt limit
always takes priority when more than one switch input
is open. This motor volt limit regulates top speed of
the transistor controller, but actual vehicle speed will
vary at any set point depending on the loading of the
vehicle.
Section 2.1.4.c Top Speed Regulation
This feature requires a system tachometer. The
standard GE system tach is built into the motor and
provides four pulses per armature revolution. Once
the control has been calibrated to the vehicle
parameters (gear ratio
and wheel rolling radius), using Function 1, speed can
be measured with a resolution of +/- 1 mph. When
traveling down an incline, if the vehicle speed
increases to the overspeed setting, the control
automatically transitions to the regen mode. The
maximum incline on which the control will be able to
maintain regulation is determined by the
characteristics of the motor, the maximum regen
armature current limit setting (Function 9), and the
maximum regen field current limit setting (Function
10).
When the vehicle reaches the bottom of the incline,
and the vehicle speed decreases below the
overspeed setting on the level surface, the control
ARM
Q1
Q2
Figure 5
Updated Sept 2019
