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1. If the truck is in neutral, the commanded engine
speed at full scale accel pedal will be the engine's
high idle. If the truck is not in neutral, the maxi-
mum commanded engine speed will be the en-
gine's rated horsepower rpm. This allows faster
hoisting of the truck bed, if desired. These maxi-
mum speeds apply to the MTU engine.
2. During retard state the engine speed command
will not be increased to support the DC link when
retard is being ramped out at low truck speeds.
However, engine speed may be increased if
needed to support the DC link during normal
retard when wheel slides are occurring.
The following constraints are applied to generating the
engine speed command during all operating states:
• The engine speed command will always be
greater or equal to minimum idle signal. The
TCI can request the engine speed command
be increased by setting minimum idle.
• The engine speed command will be increased
if more alternator cooling is needed.
Alternator Field Control
The alternator is controlled by controlling the Alternator
field reference sent to the AFSE.
The desired alternator output voltage is dependent on
system state. The PSC will command an alternator
field reference such that the desired DC link voltage or
three-phase voltage is maintained.
Desired Three-Phase Voltage
During all powered states, the three-phase line-to-line
voltage will not be allowed to drop below 444 volts.
This is the minimum voltage needed to supply the gate
drive power converters and the auxiliary blower in-
verter.
During all powered states except retard, the DC link
voltage will represent the rectified three-phase volt-
age. In this case, as long as the DC link voltage is
above 600 volts, the three-phase voltage will be ade-
quate.
During retard, the DC link voltage is not necessarily
related to the three-phase voltage since the motors will
be powering the DC link and reverse biasing the
rectification diodes. In this case, the control ensures
that the minimum three-phase voltage is maintained.
E2-34
Desired DC Link Voltage
The desired link voltage is controlled by the alternator
during all powered states except retard. The desired
voltage is based on:
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:
Electrical Propulsion System Components
1. During propel, the desired DC link voltage will be
adjusted based on motor speed and horsepower
commanded to the inverters.
2. During retard, the DC link voltage may rise above
the rectified three-phase voltage. When this oc-
curs, the DC link voltage is controlled by the retard
torque command, grid resistor command and
chopper start. If conditions occur which prevent
the motors from producing power to support the
resistor grids, the alternator may be required to
supply some power. In this case, the alternator
field control will maintain at least 600 volts on the
DC link.
3. During all powered states, the DC link voltage will
not be allowed to drop below 600 volts.
4. While the DC link is being powered up, the voltage
will be controlled to the levels necessary to sup-
port the inverter self-tests.
1. The DC link voltage will not be allowed to drop
below 600 volts.
2. One mode of self-load will require the alternator
output to be controlled to maintain a set desired
horsepower dissipation in the resistor grids.
3. Another mode of self-load will require the alterna-
tor output to be controlled to maintain a set de-
sired link voltage between 600 volts and 1500
volts.
E02014 3/01
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Table of Contents
Troubleshooting
