Solid-State Reversing; Flexible System Application; More Features With Fewer Components; Performance - GE H4V262Y1 Installation And Operation Manual

BASIC OPERATION AND FEATURES
SX TRANSISTOR CONTROL
following description provides a brief introduction to some
of these features.
Section 1. 2 Solid-State Reversing
The direction of armature rotation on a shunt motor is
determined by the direction in which current flows through
the field windings. Because of the shunt motor field,
typically only requires about 10% of the armature current at
full torque, it is normally cost effective to replace the
double-pole, double-throw reversing contactor with a low
power transistor H-Bridge circuit (Figure 4).
By energizing the transistors in pairs, current can be made
to flow in either direction in the field. The field and
armature control circuits typically operate at 15KHZ, a
frequency range normally above human hearing. This high
frequency, coupled with the elimination of directional
contactors, provides for very quiet vehicle operation.
The line contactor is normally the only contactor required
for the shunt motor traction circuit. This contactor is used
for both pre-charge of the line capacitors and for
emergency shut down of the motor circuit, in case of
problems that would cause a full motor torque condition.
The line can be energized and de-energized by the various
logic combinations of the vehicle, i.e. activate on key or
start switch closure, and de-energize on time out of idle
vehicle. Again, these options add to the quiet operation of
the vehicle.
Section 1. 3 Flexible System Application
Because the shunt motor controller has the ability to
control both the armature and field circuits independently,
the system can normally be adjusted for maximum system
efficiencies at certain operating parameters. Generally
speaking, with the ability to independently control the field
and armature, the motor performance curve can be
maximized through proper control application.
Section 1. 4 More Features with Fewer Components
Field weakening with a series wound motor is
accomplished by placing a resistor in parallel with the field
winding of the motor. Bypassing some of the current
flowing in the field into the resistor causes the field current
to be less, or weakened. With the field weakened, the motor
speed will increase, giving the effect of "overdrive". To
change the "overdrive speed", it is necessary to change
the resistor value. In a separately excited motor,
independent control of the field current provides for
infinite adjustments of "overdrive" levels, between the
motor base speed and maximum weak field. The
desirability of this feature is enhanced by the elimination
of the contactor and resistor required for field
weakening with a series motor.
With a separately excited motor, overhauling speed
limit, or downhill speed, will also be more constant. By
its nature, the shunt motor will try to maintain a
constant speed downhill. This characteristic can be
enhanced by increasing the field strength with the
control. Overhauling load control works in just the
opposite way of field weakening, as armature rotation
slows with the increase of current in the field. An
extension of this feature is a zero-speed detect feature
which prevents the vehicle from free-wheeling down an
incline, should the operator neglect to set the brake.
For GE, the future is now, as we make available a new
generation of electric traction motor systems for electric
vehicles having separately excited DC shunt motors and
controls. Features that were once thought to be only
available on future AC or brushless DC technology vehicles
systems are now achievable and affordable.
Section 2. FEATURES OF SX FAMILY OF TRANSISTOR
MOTOR CONTROLLERS
Section 2.1 Performance
Section 2.1.1 Oscillator Card Features
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
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June 2002