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ELECTRICAL PROPULSION SYSTEM COMPONENTS
The following information provides a brief description
of system operation and major components of the AC
propulsion system. Refer to the appropriate GE publi-
cation for detailed information and theory of operation.
A list of commonly used propulsion system component
abbreviations is listed in Table IV at the end of this
Section. Figures 2-3 through 2-8 illustrate the physical
location of these components where applicable.
GENERAL SYSTEM DESCRIPTION
The AC drive system consists of the following major
components:
• Alternator coupled to a diesel engine
• Auxiliary Blower System
• Gate Drive Power Converters
• Main Rectifier
• AC Power Inverters
• AC Induction Traction Motors
The Alternator supplies three phase power for the
Auxiliary Blower System, Gate Drive Power Convert-
ers and Main Rectifier. The Main Rectifier supplies DC
power to two AC Power Inverters. Each AC Power
Inverter inverts the rectified DC voltage, delivering
variable voltage, variable frequency power to each of
the AC Induction Traction Motors.
Refer to the diagram in Figure 2-1 for the following
description.
The two AC Induction Traction Motors, each with its
own Inverter, are connected in parallel across the
rectified output of the Alternator. The Inverters change
the rectified voltage back to AC by turning on and off
(chopping) the applied DC voltage.
The output AC voltage and frequency are controlled to
produce optimum slip and efficiency in the traction
motors. At low speeds, the rectified alternator output
(DC link, or DC bus) voltage is chopped with patterns
called pulse width modulation (PWM) inverter opera-
tion. At higher speeds, the DC link voltage is applied
to the motors using square wave inverter operation.
The voltage of the DC link is dependent upon the
Propulsion System Controller (PSC) and engine RPM
during propulsion. The link voltage will vary between
600 and 1400 volts during propulsion and 600 and
1500 volts during retarding.
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The alternator field is supplied from a tertiary winding
on the alternator and is controlled by a silicon control-
led rectifier (SCR) bridge. A starting boost circuit in-
itially energizes the alternator from the truck batteries
until the flux builds up enough to sustain excitation.
Cooling air for the Alternator only is supplied by an
internal fan assembly mounted on the rear. Cooling air
for the traction system is provided by an AC motor
driven auxiliary blower mounted behind the electrical
cabinet. The auxiliary blower motor is controlled by an
auxiliary inverter which receives 3-phase AC power
from the alternator. This blower provides cooling air to
the traction motors, propulsion inverters, dynamic re-
tarding choppers, and auxiliary inverter. Blower speed
is regulated by the PSC by monitoring component
temperatures to determine cooling needs.
A resistor grid package is used to dissipate power from
the traction motors (operating as generators) when in
dynamic retarding mode. The total retard power pro-
duced by the traction motors is controlled by the two
motor Inverters. The amount of retard power dissi-
pated by the grid package is controlled by a GTO
Chopper circuit and stage-controlled contactors.
The PSC, mounted in the main Electrical Control Cabi-
net, determines optimum engine operating speeds
based on what the operator requests, propulsion sys-
tem requirements, and efficient fuel usage. Interfaces
between the PSC and the truck brake system allow the
PSC to provide proper retarding, braking, and wheel
slide control.
The PSC interfaces with the Truck Control Interface
(TCI), mounted in the Electrical Interface Cabinet
mounted behind the cab at the side of the electrical
control cabinet. System status and control signals are
transmitted and received between these two compo-
nents. An RS422 serial link enables the TCI to access
real time data and event information stored in the PSC
for displaying on a Diagnostic Information Display
(DID), located in the cab behind the operator's seat.
Electrical Propulsion System Components
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