GE IC3645SR4W746HL1 Installation And Operation Manual page 6

BASIC OPERATION AND FEATURES
SX TRANSISTOR CONTROL
LINE POS
FUSE
CAP
Q2
vehicle, i.e. activate on key, seat 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 of
independent 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 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, armature rotation slows with the
increase of current in the field.
Regenerative braking (braking energy returned to the battery) may be accomplished completely with solid-state technology. The
main advantage of regenerative braking is increased motor life. Motor current is reduced by 50% or more during braking while
maintaining the same braking torque as electrical braking with a diode clamp around the armature. The lower current translates
into longer brush life and reduced motor heating. Solid state regenerative braking also eliminates a power diode, current sensor
and contactor from the circuit.
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.
Q3
A1 +
F1
ARM
A2 -
Q4
Q1
NEG
Figure 4
By energizing the transistors in pairs, current can be
made to flow in either direction in the field. The
armature control circuit typically operates at 12KHZ to
Q5
15KHZ, a frequency range normally above human
hearing. This high frequency coupled with the
F2
elimination of directional contactors, provides very
quiet vehicle operation. The field control circuits
typically operate at 2 KHZ.
Q6
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
Page 7
November 2002