13-06-2013, 04:45 PM
Recent Advances in Mining Haul Trucks
[attachment=55373]
Abstract
Electric mining haul trucks are one of the most challenging
applications of power electronics in automotive systems.
This paper presents some advances in very-high-power trucks
used in copper mines. The special operational and environmental
requirements for this application are highlighted. It is established
that the use of inverter-fed three-phase induction motors with
vector control is the preferred solution to reach the required
high starting torque and good dynamic performance required by
these vehicles. Packaging is a key issue and special attention is
dedicated to the forced-air cooling system, because the air has a
high dust level including conductive and corrosive materials. The
truck’s high-performance electric retarding system is described
along with a novel use of trolley lines in a diesel boost mode as
a way to increase the power and speed of the truck and reduce
fuel consumption. Advanced features like remote monitoring, the
use of global positioning systems and Internet diagnostics and
troubleshooting are also discussed. The paper clearly shows that
modern electric haul trucks are highly sophisticated systems that
make full use of advances in modern technologies to increase
safety and productivity levels.
INTRODUCTION
ONE OF THE MOST demanding areas for automotive
electronic systems is found on electric haul trucks
used in the mining industry. These vehicles are employed
for ore transportation under severe environmental conditions,
stringent safety issues, and production requirements, including
economies of scale that demand larger trucks.
Automotive systems are one of the most challenging fields
for electronic systems design and applications, with embedded
software for communication and control of sensors, actuators,
microprocessors and networks. Recent advances in electronics
systems state new system approaches for dealing with the
new challenges [1]–[7]. Low- and high-speed networks are
employed for noncritical and critical applications including
real-time functions [5].
POWER CIRCUIT OF THE DRIVE
Fig. 2 represents the simplified block diagram of the drive’s
electrical power system for haul trucks within the 240-360-tons
payload range.
Diesel Engine, Generator, and Rectifiers
The power of the diesel engine is 2540–3380 hp, depending
on the truck model and load to be transported [17]. AC power is
generated in the alternator and rectified to produce a dc voltage
of 2400 in the dc link. This voltage is filtered and supplied to
voltage-source inverters, each of which powers one motor and
a pair of tandem rear wheels. The rectifiers are nonregenerative
so the control system ensures that the dc-link voltage will not
reach an excessive value during the braking of the truck by operating
the choppers to dissipate the electric braking energy in
the resistor grid.
Main Power Inverters
Three-phase inverters deliver voltages with variable amplitude
and frequency to control the traction motors. Smaller trucks
(240 tons) use IGBTs as the main power switches. The use of
IGBT devices brings important operational advantages: simpler
and smaller gate driver circuits and more efficient overcurrent
protection (by eliminating the driving pulses until the overcurrent
disappears). In addition, IGBT driver circuits increase the
overall reliability of the drive system to meet the harsh operating
demands of the trucks.
Local and Remote Monitoring
It is desirable that advanced and expensive machines such as
haul trucks run 100% of the time. Of course, this is not possible
so the goal is to reduce the causes of failure and the required repair
time. This is of particular importance when the machinery,
like haul trucks, is a fundamental part of the production process.
Therefore the trucks are equipped with devices to monitor the
status and performance, such as the display system, which informs
the operator about the system status with text messages
in a color LCD display.
Remote access technology makes it possible for maintenance
experts to communicate with the truck control electronics
via radio, telephone and satellite links in a more rapid form,
reducing the time to detect and repair any fault, or to prescribe
preventive maintenance procedures before failures occur. An
application of this remote diagnostic capability is the use of the
Internet for diagnostics and troubleshooting. This new technology
has been successfully demonstrated in modern shovels
and haul trucks [25]. The remote access allows authorized
technicians all over the world to monitor, analyze, diagnose,
and suggest a corrective action. It is even possible to make
changes in the control software remotely.
TROLLEY ASSIST OPERATION
One of the advantages of using electric drives in haul trucks
compared to a conventional mechanical transmission, torque
converter and differential is the possibility to draw power
from dc overhead trolley lines and bypass or supplement the
diesel engine as the truck’s source of power [11]. Fig. 6 shows
a haul truck running under trolley lines. Overhead trolley
lines are most commonly installed in mines that have a single
road coming out of a deep pit or where fuel costs are much
higher than the cost of electricity. The principal characteristic
of trolley assist operation is that the power available for the
traction motors is greatly increased.
COMMENTS AND CONCLUSIONS
Drive technology in haul trucks has shown enormous developments
in recent years, yielding an important improvement in
performance with increasing payload capacity.
A diesel–electric motor–generator system with inverter-fed
ac induction motors is the only solution found in electric haulers
300 tons and larger. The use of IGBT transistors in place of
GTO thyristors can reduce the cost, and increase the reliability
of the power inverters, due to simpler and more compact driver
circuits. It is foreseeable that IGBTs with higher voltage and
current ratings will replace GTOs in larger trucks in the near
future.
The use of sealed modules for power semiconductors is a
key factor to increase the reliability of the drive, due to the
high amount of dust in mining applications. Maintenance-free
high-performance electric braking choppers have replaced mechanical
contactors to connect the braking resistors. Vector-controlled
induction motors provide very good control of speed including
high starting torque and smooth controlled braking, in
addition to very low maintenance requirements.
[attachment=55373]
Abstract
Electric mining haul trucks are one of the most challenging
applications of power electronics in automotive systems.
This paper presents some advances in very-high-power trucks
used in copper mines. The special operational and environmental
requirements for this application are highlighted. It is established
that the use of inverter-fed three-phase induction motors with
vector control is the preferred solution to reach the required
high starting torque and good dynamic performance required by
these vehicles. Packaging is a key issue and special attention is
dedicated to the forced-air cooling system, because the air has a
high dust level including conductive and corrosive materials. The
truck’s high-performance electric retarding system is described
along with a novel use of trolley lines in a diesel boost mode as
a way to increase the power and speed of the truck and reduce
fuel consumption. Advanced features like remote monitoring, the
use of global positioning systems and Internet diagnostics and
troubleshooting are also discussed. The paper clearly shows that
modern electric haul trucks are highly sophisticated systems that
make full use of advances in modern technologies to increase
safety and productivity levels.
INTRODUCTION
ONE OF THE MOST demanding areas for automotive
electronic systems is found on electric haul trucks
used in the mining industry. These vehicles are employed
for ore transportation under severe environmental conditions,
stringent safety issues, and production requirements, including
economies of scale that demand larger trucks.
Automotive systems are one of the most challenging fields
for electronic systems design and applications, with embedded
software for communication and control of sensors, actuators,
microprocessors and networks. Recent advances in electronics
systems state new system approaches for dealing with the
new challenges [1]–[7]. Low- and high-speed networks are
employed for noncritical and critical applications including
real-time functions [5].
POWER CIRCUIT OF THE DRIVE
Fig. 2 represents the simplified block diagram of the drive’s
electrical power system for haul trucks within the 240-360-tons
payload range.
Diesel Engine, Generator, and Rectifiers
The power of the diesel engine is 2540–3380 hp, depending
on the truck model and load to be transported [17]. AC power is
generated in the alternator and rectified to produce a dc voltage
of 2400 in the dc link. This voltage is filtered and supplied to
voltage-source inverters, each of which powers one motor and
a pair of tandem rear wheels. The rectifiers are nonregenerative
so the control system ensures that the dc-link voltage will not
reach an excessive value during the braking of the truck by operating
the choppers to dissipate the electric braking energy in
the resistor grid.
Main Power Inverters
Three-phase inverters deliver voltages with variable amplitude
and frequency to control the traction motors. Smaller trucks
(240 tons) use IGBTs as the main power switches. The use of
IGBT devices brings important operational advantages: simpler
and smaller gate driver circuits and more efficient overcurrent
protection (by eliminating the driving pulses until the overcurrent
disappears). In addition, IGBT driver circuits increase the
overall reliability of the drive system to meet the harsh operating
demands of the trucks.
Local and Remote Monitoring
It is desirable that advanced and expensive machines such as
haul trucks run 100% of the time. Of course, this is not possible
so the goal is to reduce the causes of failure and the required repair
time. This is of particular importance when the machinery,
like haul trucks, is a fundamental part of the production process.
Therefore the trucks are equipped with devices to monitor the
status and performance, such as the display system, which informs
the operator about the system status with text messages
in a color LCD display.
Remote access technology makes it possible for maintenance
experts to communicate with the truck control electronics
via radio, telephone and satellite links in a more rapid form,
reducing the time to detect and repair any fault, or to prescribe
preventive maintenance procedures before failures occur. An
application of this remote diagnostic capability is the use of the
Internet for diagnostics and troubleshooting. This new technology
has been successfully demonstrated in modern shovels
and haul trucks [25]. The remote access allows authorized
technicians all over the world to monitor, analyze, diagnose,
and suggest a corrective action. It is even possible to make
changes in the control software remotely.
TROLLEY ASSIST OPERATION
One of the advantages of using electric drives in haul trucks
compared to a conventional mechanical transmission, torque
converter and differential is the possibility to draw power
from dc overhead trolley lines and bypass or supplement the
diesel engine as the truck’s source of power [11]. Fig. 6 shows
a haul truck running under trolley lines. Overhead trolley
lines are most commonly installed in mines that have a single
road coming out of a deep pit or where fuel costs are much
higher than the cost of electricity. The principal characteristic
of trolley assist operation is that the power available for the
traction motors is greatly increased.
COMMENTS AND CONCLUSIONS
Drive technology in haul trucks has shown enormous developments
in recent years, yielding an important improvement in
performance with increasing payload capacity.
A diesel–electric motor–generator system with inverter-fed
ac induction motors is the only solution found in electric haulers
300 tons and larger. The use of IGBT transistors in place of
GTO thyristors can reduce the cost, and increase the reliability
of the power inverters, due to simpler and more compact driver
circuits. It is foreseeable that IGBTs with higher voltage and
current ratings will replace GTOs in larger trucks in the near
future.
The use of sealed modules for power semiconductors is a
key factor to increase the reliability of the drive, due to the
high amount of dust in mining applications. Maintenance-free
high-performance electric braking choppers have replaced mechanical
contactors to connect the braking resistors. Vector-controlled
induction motors provide very good control of speed including
high starting torque and smooth controlled braking, in
addition to very low maintenance requirements.