Komatsu 830E-AC, Shop Manual

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E02020 10/06 Electrical Propulsion System Components E2-31
Self-Load
During self-load, the alternator provides power to the
resistor grids. The rectifying diodes will be forward
biased, and DC link voltage will be controlled by the
alternator. The alternator field control will be based
on the following:
• The DC link voltage will not be allowed to drop
below 600 volts.
• One mode of self-load will require the alternator
output to be controlled to maintain a set desired
horsepower dissipation in the resistor grids.
• Another mode of self-load will require the
alternator output to be controlled to maintain a
set desired link voltage between 600 and 1500
volts.
Propel Torque Control
This software function commands the appropriate
motor torque to the inverters during propel. The
torque command is primarily a function of the accel
pedal position and is limited by the physical
constraints of the system.
Each wheel torque is computed independently
because the wheels may be operating at different
speeds. Each torque command is adjusted to
account for the following constraints:
• Speed Override
The propulsion system will attempt to limit truck
speed to the design envelope of the wheel
motors. The torque command will be modulated
as the truck speed approaches the motor
overspeed limit so that this limit is not exceeded
if possible. Note, however, that steady state
operation is kept as close to the overspeed limit
as possible without exceeding it.
• Motor Torque Limits
The torque command will be constrained to the
operating envelope of the inverters and the
traction motors. The maximum torque that can
be commanded is dependent on motor speed
and DC link voltage.
• Gear Stress
The torque commanded will not exceed that
which will produce excess gear stress.
• Horsepower Available
The horsepower available will be estimated
from the engine speed. Parasitic loads are
taken into account. The torque will be limited so
that the engine does not overload.
• Jerk Limit
The torque command will be slew-rate limited to
prevent jerking motion.
• Wheel Spin
In the event that the inverters detect a wheel
spin condition and reduce torque in the slipping
wheel, the motor torque in the other wheel may
be increased within the above constraints such
that as much of the total desired torque as
possible is maintained.
Retard Torque Control
The retard system converts braking torque from the
wheel motors to energy dissipated in the resistor
grid. The requested retard torque is based on the
following three sources:
• Retard Foot Pedal or Lever
The maximum short time retard torque (at any
speed, hence the constant torque level) will be
scaled (linearly) by the retard foot pedal input
(RPINHI) to produce the foot pedal retard
torque call.
• Overspeed
While overspeed is active, the full available
retard torque will be requested.
• Retard Speed Control
While RSC is active, the RSC retard torque call
will be adjusted to control truck speed to the
RSC set point. Retard speed control will not
request any retard torque if RSC is not active.
The maximum torque call from the above three
sources will be selected as the retard torque call.
Retard torque limits are as follows:
• The retard torque call will be limited to the
maximum torque level based on speed.
• The retard torque call will be limited to the
maximum torque level available within the
thermal constraints of the motors.
• The retard torque call will be limited as needed to
prevent overvoltage on the DC link.
• While in retard, the minimum retard torque call
will provide enough power to support at least one
grid with 600 volts on the DC link. Retard will be
dropped if the torque call falls below this value.
• At low speed, the available retard torque will be
ramped to zero.