Komatsu 830E-AC Shop Manual page 387

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
publication for detailed information and theory of
operation.
A list of commonly used propulsion system
component abbreviations is listed in Table V at the
end of this Section. Figures 2-3 through 2-11
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)
• In-line Cooling Blower
• Gate Drive Power Converters
• Rectifier Diode Modules
• AC Power Inverters
• AC Induction Traction Motors
The alternator supplies three phase AC power for the
gate driver power converters and rectifier diode
modules. The rectifier diode modules convert the AC
power to DC power, then supply that DC power to
two AC power inverters via the DC link. Each AC
power inverter inverts the rectified DC voltage,
delivering variable voltage, variable frequency power
to each of the AC induction traction motors.
NOTE: Refer to 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
operation. At higher speeds, the DC link voltage is
applied to the traction 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 DC
link voltage will vary between 600 and 1600 volts.
E02020 10/06
The alternator field is supplied from a tertiary winding
on the alternator and is controlled by a silicon
controlled rectifier (SCR) bridge. A starting boost
circuit initially energizes the alternator from the truck
batteries until the flux builds up enough to sustain
excitation.
Cooling air for the alternator, control cabinet and
traction motors is supplied by a dual in-line fan
assembly mounted on the rear of the alternator. This
blower provides cooling air to the traction motors,
propulsion inverters, dynamic retarding choppers,
and control system.
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 produced by the traction motors is controlled
by the two motor inverters. The amount of retard
power dissipated by the grid package is controlled by
an IGBT chopper circuit and stage-controlled
contactors.
The PSC, which is mounted in the main control
cabinet, determines the optimum engine operating
speeds based on what the operator requests,
propulsion system 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), which is mounted in the same card rack as the
PSC. System status and control signals are
transmitted
components to access real time data and event
information that is stored in the PSC. This data is
displayed on the Diagnostic Information Display
(DID) panel located in the cab behind the operator's
seat.
Electrical Propulsion System Components
and received between these two
E2-3