Page 1
For Training Purposes Only
The information, specifications, and
illustrations in this Student Workbook are for
Training Purposes Only.
Instructions, photos, and/or drawings in this
manual may not be reproduced, used for any
reason, and/or distributed without written
permission from:
Liebherr Mining Equipment Newport News Co.
Training Department
4100 Chestnut Avenue
Newport News, Virginia
23607-2420
Email: technicaltraininglme@liebherr.com
© Copyright 2014
All rights reserved.
2014-02-01
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Student Workbook Power Conversion and Inversion
Table of Contents
1 INTRODUCTION ............................................................................................ 7
1.1 LEARNING OBJECTIVES ....................................................................... 7
2 OVERVIEW .................................................................................................... 8
3 EXCITER FIELD REGULATOR ..................................................................... 8
3.1 Location ................................................................................................... 9
3.2 System Description .................................................................................. 9
3.3 Principle of Operation ............................................................................ 11
3.3.1 Exciter Field Regulator Principle of Operation (cont.)...................... 12
4 TRACTION ALTERNATOR .......................................................................... 13
4.1 Location ................................................................................................. 13
4.2 System Description ................................................................................ 14
4.3 Principle of Operations .......................................................................... 14
4.3.1 Traction Alternator Principle of Operation (cont) ............................. 16
5 MAIN RECTIFIER ........................................................................................ 18
5.1 Location ................................................................................................. 18
5.2 System Description ................................................................................ 18
5.3 Principle of Operation ............................................................................ 19
6 CONTROL CABINET - POWER COMPONENTS ................................ ........ 20
6.1 DC Link Capacitors ................................................................................ 21
6.1.1 Location ........................................................................................... 21
6.1.2 System Description ......................................................................... 21
6.1.3 Principle of Operation ...................................................................... 22
6.2 Power Stacks (IGBT Inverters) .............................................................. 23
6.2.1 Location ........................................................................................... 23
6.2.2 System Description ......................................................................... 23
6.2.3 Principle of Operation ...................................................................... 24
6.3 Chopper Module .................................................................................... 26
6.3.1 Location ........................................................................................... 26
6.3.2 System Description ......................................................................... 26
6.3.3 Principle of Operation ...................................................................... 26
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Power Conversion and Inversion Student Workbook
6.4 Dynamic Braking .................................................................................... 28
6.4.1 Acceleration Process ....................................................................... 28
6.4.2 Braking Process .............................................................................. 30
6.5 DC Braking ............................................................................................ 32
7 TRACTION MOTOR ..................................................................................... 34
7.1 Location ................................................................................................. 34
7.2 System Description ................................................................................ 34
7.3 Principles of Operation .......................................................................... 35
7.3.1 Stator Windings ............................................................................... 35
7.3.2 Rotor ............................................................................................... 36
7.3.3 Temperature Modules and Sensors ................................................ 37
7.3.4 Speed Sensor ................................................................................. 37
7.3.5 Speed Sensor Designation .............................................................. 38
8 AUXILIARY POWER CONVERSION ........................................................... 39
8.1 DC to DC Converter ............................................................................... 40
8.1.1 Location ........................................................................................... 40
8.1.2 System Description ......................................................................... 40
8.1.3 Principle of Operation ...................................................................... 41
8.2 Auxiliary Frequency Converters ............................................................. 43
8.2.1 Location ........................................................................................... 43
8.2.2 System Description ......................................................................... 43
8.2.3 Principle of Operation ...................................................................... 44
8.3 Main Blower Assembly .......................................................................... 45
8.3.1 Location ........................................................................................... 45
8.3.2 System Description ......................................................................... 45
8.3.3 Principle of Operation ...................................................................... 46
8.4 Grid Blower Assembly ........................................................................... 47
8.4.1 Location ........................................................................................... 47
8.4.2 System Description ......................................................................... 47
8.4.3 Principle of Operation ...................................................................... 48
8.5 Cooling Pump ........................................................................................ 49
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Student Workbook Power Conversion and Inversion
8.5.1 Location ........................................................................................... 49
8.5.2 System Description ......................................................................... 50
8.5.3 Principle of Operation ...................................................................... 51
9 FIGURE INDEX ............................................................................................ 53
10 TABLE INDEX .............................................................................................. 55
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Student Workbook Power Conversion and Inversion
1 INTRODUCTION
Power conversion is simply changing power from one form to another. The
power conversion system on the Litronic Plus haul trucks uses AC power
generated from the traction alternator and converts it into DC power to supply a
common DC Bus.
Figure 1 - Litronic Plus AC Drive Control Cabinet
1.1 LEARNING OBJECTIVES
Upon completion of this module the student will be able to:
•
Identify and list the functions of all main components of
the Power Conversion and Inversion sub-system(s)
•
Explain the theory of operation of each main component
•
Describe how all main components interact within the AC drive
system as a whole
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Legend:
Main Bus
1. Traction Alternator
2. Field Regulator
3. Main Rectifier
4. DC Link Capacitors
5. Chopper Module
6. Grid Blower Assembly
7. Power Stacks (IGBT Inverters)
8. Traction Motors
Auxiliary Bus
9. DC/DC Converter
9.1 Auxiliary Frequency Converter
9.1.1 Main Blower Motor
9.2 Auxiliary Frequency Converter
9.2.1 Grid Blower Motor
9.3 Auxiliary Frequency Converter
9.3.1 Cooling Pump Motor
Figure 2 - Power Conversion and Inversion Overview
2 OVERVIEW
3 EXCITER FIELD REGULATOR
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The exciter field regulator supplies a magnetizing current to the stationary exciter
field to control the output voltage of the main traction alternator.
Figure 3 - Exciter Field Regulator Location
3.1 Location
The Field Regulator is located in the upper compartment of the Control Cabinet
on the right side.
3.2 System Description
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The Field Regulator:
Controls Field Current
Controls AC power produced
by Alternator
24 VDC input
Output
0-10 A
0-90 VDC
Outputs current to alternator
based on signal received from
PLC
Field Regulator Terminal Connections
T1 & T2
Temperature
T3 & T4
Stationary exciter windings current feedback to PLC analog I/O
T5 & T6
Current set point from PLC analog I/O
T7 & T8
Enable signal from PLC digital output
T9 & T 10
24 VDC control power
The exciter field regulator supplies a magnetizing current to the stationary exciter
field in order to control the output voltage of the main traction alternator.
Figure 4 - Exciter Field Regulator
Table 1 - Field Regulator Terminal Connections
The regulated output current Iout (e.g. 0 - 10A) is proportional to the isolated setpoint value (e.g. 4 – 20mA) and constant over the whole input voltage range,
load range and temperature range. The output voltage is the result of Iout and
the field winding‘s reactance.
Furthermore the output current is isolated fed back with 0 – 4V as the actual
current value for the customer‘s control loop.
The output is activated with an integral ramp-up (t = 500ms) to the set-point given
output current by connecting a control voltage of 8 - 50V with an OK-Signal
control input.
An open OK-Signal control input deactivates the converter. The output UAout is
dynamically and statically overload protected, short circuit proof and no-load
stable.
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Figure 5 - Electricity Producing Elements
3.3 Principle of Operation
Producing a voltage with magnetism is accomplished through mutual induction
also known as transformer action. Three requirements need to be met. You
must have:
1. Magnetic Field
2. Current carrying conductor
3. Relative Motion between the two
The exciter field regulator produces a DC current into the Stationary Exciter Field
Windings. The current produces a magnetic flux in the windings. As the
Rotating Exciter Windings turn, the windings cut the magnetic flux which causes
a voltage to be induced into them. The voltage produced is AC.
The Main Rotor Windings require a DC current to produce a magnetic flux. It is
for this reason the Rotating Rectifier Assembly is used. The rectifier changes the
AC output of the rotating exciter windings to DC. The induced DC current
produces a magnetic flux in the Main Rotor Windings.
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Legend:
1. Field Regulator
2. Stationary Exciter Field Winding (Stator Mounted)
3. Rotating Exciter Field Winding
4. Rotating Rectifier
5. Rotating Main Windings
6. Main Stator Windings
Figure 6 - Field Regulator and Rotor Electrical Diagram
Figure 6 - Field Regulator and Rotor Electrical Diagram
3.3.1 Exciter Field Regulator Principle of Operation (cont.)
Figure 7 - Magnetic Field
The turning of the main rotor windings causes the magnetic flux to cut across the
Main Stator Windings which induces a voltage into the Main Stator Windings. This
induced voltage is the output of the alternator. The magnitude of the AC output is
directly proportional to the DC input from the exciter field regulator and of the
alternator rpm
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Figure 8 - 264 Traction Alternator
4 TRACTION ALTERNATOR
The Traction Alternator allows for production of electricity from mechanical
power. The alternator is an AC generator using the interaction of magnetic fields
to produce voltage when coupled to a rotating engine.
4.1 Location
The traction alternator is mechanically coupled to both the diesel engine and
driveshaft, via the hydraulic pump drive transmission.
Figure 9 - T282C and 284 Traction Alternator
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SPECIFICATION
264
T282C
284
Rated Voltage
1400 VAC
1872 VAC
1872 VAC
Normal Power
2043 kW
2147 kW
2725kW
Apparent Power
2150 kVA
2260 kVA
2260 kVA
Rated Current
825 Amps
697 Amps
697 Amps
Frequency
120 Hz
120 Hz
120 Hz
RPM
1800
1800
1800
Legend:
1. Exciter Rotor
2. Exciter Stator
3. Main Rotor
4. Main Stator
Figure 10 - Traction Alternator Internal Components
4.2 System Description
The Traction Alternator is a brushless 3 phase, 6 wire, 8 pole synchronous AC
generator. That provides the variable AC voltage source for the electric drive
system during diesel operations and is electrically connected to the main rectifier.
Table 2 - Traction Alternator Specifications
4.3 Principle of Operations
The brushless Traction Alternator is an electromechanical device that converts
mechanical energy from the diesel engine into AC electrical energy.
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Legend:
1. Exciter Stator Windings
2. Exciter Rotor
3. Rotating Rectifier Assembly
4. Main Rotor
5. Main Stator Windings
The alternator generates electricity when the rotating magnetic field established
in the rotor windings turns within the stationary set of conductors wound in coils,
called the stator.
The magnetic fields established in the (main) rotor windings cuts across the
conductors in the (main) stator windings, inducing an AC voltage in them as the
engine’s crankshaft causes the rotor to turn.
The output of the rotating exciter winding is controlled by a stationary winding
mounted on the stator called the stationary exciter field winding.
Figure 11 - Traction Alternator Internal Windings
The magnetic flux (field strength) of the stationary exciter field winding is directly
proportional to the current supplied by the exciter field regulator.
The stationary exciter field magnetic field interacts with the rotating exciter field
winding to produce an AC voltage output. This output is then rectified by the
rotating rectifier as a DC current source and induced to the main rotor windings.
The magnitude of AC voltage generated by the alternator is dependent upon the
rotor magnetic field strength and speed of the rotor.
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Legend:
1. Main Stator
2. Exciter Stator
Figure 13 - Traction Alternator Main Stator Assembly
4.3.1 Traction Alternator Principle of Operation (cont)
The magnitude of AC voltage generated by the alternator is dependent upon the
rotor magnetic field strength and speed of the rotor. The DC current to produce
the magnetic field in the rotor windings is supplied by the rotating rectifier located
on the rotor itself. The rotating rectifier coverts the AC voltage supplied by the
rotating exciter windings into DC current
Figure 12 - Rotating Rectifier Assembly
The Traction Alternator housing contains the Main Stator 3 phase wye connected
windings. It also contains the Exciter Stator winding that interacts with the
Exciter Rotor.
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Legend:
1. Main Rotor Windings
2. Exciter Rotor Windings
3. Rotating Rectifier Assembly
Calculating Output Frequency F= NP / 120
F=
Frequency (Hz)
N=
Rotor speed (rpm)
P=
Total number of poles
120=
Conversion from minutes to seconds and from poles to pole pairs
Traction Alternator Set Speeds
1.
750 RPM
Idle Set Point
2.
1350 RPM
Minimum Speed for Propel
3.
1800 RPM
Rated Speed
Figure 14 - Traction Alternator Rotor Assembly
The Traction Alternator Rotor is mechanically coupled to the engine crankshaft
and rotates at diesel engine RPM. The rotor contains the Main Rotor Windings,
the Exciter Rotor Windings and the Rotating Rectifier Assembly.
Output frequency is important in selecting an alternator. Damage can occur to
equipment if improper frequency is being applied. The frequency of the generated
AC voltage is dependent upon the number of field poles and the speed at which
the generator is operated, as indicated in the equation below.
Table 3 - Output Frequency Calculation
The main traction alternator has three set speeds
Table 4 - Traction Alternator Speed Set Points
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Figure 15 - Main Rectifier
5 MAIN RECTIFIER
The Main Rectifier is an electrical device that converts alternating current (AC),
from the Traction Alternator to direct current (DC), which is the power source for
the DC Bus
5.1 Location
The Main Rectifier is mounted in the Control Box behind the Auxiliary Frequency
Converters.
5.2 System Description
The unit is a non-controlled 6 pulse rectifier which provides 3 phase rectified DC
bus voltage. The rectifier assembly has six diodes. The DC Output is rated at
2000V @ 1250A. AC Input is rated at 1600 V @ 900A. The unit is liquid cooled
.
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Figure 16 - Main Rectifier 2
Figure 17 - Full Wave Rectification
5.3 Principle of Operation
The rectifier assembly works on the process of converting alternating current to
direct current, by permitting current flow in one direction and blocking the current
flow in the other direction.
The rectifier assembly works on the process of converting alternating current to
direct current, by permitting current flow in one direction and blocking the current
flow in the other direction.
Full bridge rectifier is made up of four diodes in a bridge arrangement to achieve
full-wave rectification. For both positive and negative alternations of the
transformer, there is a forward path through the diode bridge. Both conduction
paths cause current to flow in the same direction through the load resistor,
accomplishing full-wave rectification.
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Legend:
1. Main Rectifier
2. DC Link Capacitors
3. Chopper Module
4. Power Stacks
Figure 18 - Power Components
6 CONTROL CABINET - POWER COMPONENTS
The power components in the control cabinet that are used to, convert and invert
power. The power components makeup the backbone of the AC Drive system.
The power components that will be discussed in this section are:
DC Link Capacitors
Power Stacks (IGBT Inverter)
Chopper Module
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Legend:
1. DC Link Capacitor
2. Fuse
3. Power Module (Power Stack / Chopper
Figure 19 - DC Link Capacitor
6.1 DC Link Capacitors
The DC Link capacitors are used to minimize the ripple voltage, which improves
the operation of the IGBTs.
6.1.1 Location
The DC Link capacitors are connected directly to the power stacks and brake
choppers. As a unit they set at the back of the control cabinet
6.1.2 System Description
The system has up to five 4mF capacitors that are labeled C5, for the brake
chopper and C1 – C4 which correspond to the power stacks.
The Capacitors are equipped with fuses between the DC-Link and the Power
Modules that are designed to limit the damage during a major power component
failure.
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Legend:
1. AC Input
2. Main Rectifier
3. DC Link Capacitor
4. DC Output
RC Time Constant
Time = Resistance X Capacitance (t-RC)
Figure 20 - Capacitor Discharging
6.1.3 Principle of Operation
Capacitance is the property of a circuit which opposes a change in voltage by
storing energy in an electrostatic field.
In an AC sine wave, voltage goes from zero to peak positive to zero to peak
negative to zero. As the AC input alternates between positive and negative, the
DC output follows the sine wave amplitude going from zero to peak to zero. The
only difference is the output is always in the same direction. This type of output
is undesirable due to the inconsistent voltage on the load. Most electronic
components cannot function properly with this type of voltage.
From zero to peak, in either the positive or negative alternation, the applied
voltage is charging the capacitor. As the voltage goes from peak to zero, in
either the positive or negative alternation, the capacitor begins to discharge. The
time it will take the capacitor to discharge is dependent on two factors,
capacitance measured in farads and resistance measured in ohms. This is
known as RC time constant and can be expressed as:
Table 5 - RC Time Constant
The discharge time of the capacitor is slower than the applied voltage alternation
change. This has the effect of maintaining a near constant voltage on the load.
The resulting output is more constant. Capacitors store energy in the electrostatic
field. A charged capacitor has the potential to cause damage or injury if not
properly discharged. Even a haul truck that has not been energized for several
days can still hold a charge in the capacitors.
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Legend:
1. Power Stack
2. DC-Link Capacitor
Figure 21 - Power Stack
6.2 Power Stacks (IGBT Inverters)
The Power Stacks, often referred to as the Inverters, are electronic devices that
are used to convert direct current (DC) to alternating current (AC).
6.2.1 Location
The Power Stacks mount to the front of the DC-Link Capacitors in the bottom right
compartment of the Control Cabinet.
The Power Stacks are comprised of 6 Insulated Gate Bipolar Transistors (IGBT).
The IGBTs are used to provide 3-phase AC current for the traction motors located
on the rear wheels. The control cabinet can contain a maximum 4 power stacks
depending on truck type. Each module is liquid cooled.
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6.2.2 System Description
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Power Conversion and Inversion Student Workbook
Legend:
1. Insulated Gate Bipolar Transistor (IGBT)
2. Gate Driver
Figure 22 - Power Stack IGBT
6.2.3 Principle of Operation
The Power Stacks use Pulse Width Modulation (PWM) to convert the DC Link
voltage to a variable frequency AC current. As stated before, each power stack
contains six IGBTs. Two IGBTs will provide AC current to a single phase of the
traction motor. The IGBTs are designated T and B or top and bottom. Each pair,
designated U, V, and W provide the three phase AC current to the traction motor.
The IGBT’s are High power semiconductor switch (no mechanical switch). The
housing includes up to 3 single chip and 1 anti parallel diode
The Gate Driver Module provides four basic functions:
1. Control and monitors the IGBT
2. Defines the switching process vio the gate terminal
3. Protects the IGBT during the switch on process
4. Coded status- and error-message to the FC
Each traction motor is controlled by a Frequency Converter (FC) Controller. The
FC Controller monitors and controls the power stack output. It will control the
PWM on time and off time length to conduct the top IGBT and the bottom IGBT
alternately to create the AC current output, based on the Programmable Logic
Controller (PLC) torque request value.
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Figure 23 - Pulse Width Modulation
Figure 24 - Power Stack Configuration
Looking at the figure above we see two PWM inputs to each of the IGBTs. The
Top input gates the Top IGBT which allows current flow from the positive DC bus
to the traction motor. This will provide the positive alternation. After the positive
alternation is complete, the Bottom input begins to gate the Bottom IGBT allowing
current to flow from the negative bus to the traction motor.
The FC controller will control PWM on time and off time length to provide the proper
voltage, current, and frequency to control the traction motor torque and speed.
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Figure 25 - Chopper Module
6.3 Chopper Module
The Chopper Module is an electrical device that is used to chop DC link voltage
above a desired level to the grid resistors.
6.3.1 Location
The Chopper Module is installed to the left of the power stacks.
6.3.2 System Description
The Brake Chopper is comprised of four IGBTs and four diodes. This unit is
controlled and monitored by the chopper controller. Like the Power Stacks, the
Brake Chopper is liquid cooled.
6.3.3 Principle of Operation
The AC output from the main alternator is first converted into DC by a diode
rectifier bridge. The main rectifier only handles power in the “motoring” direction.
For an AC drive and motor in a regenerative condition, the AC power from the
motor flows backward through the inverter bridge diodes.
If the motor is regenerating, the DC bus voltage will increase. Some of the
energy may be consumed by the motor through mechanical losses and some
may be stored in the DC Link Capacitors, but continued regeneration and the
resultant energy will need to a place to go.
DC bus voltage sensing allows this energy to be released in the form of heat
through a transistor and resistor grid bank.
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Figure 26 - Chopper Module and Grid Resistor Box
Figure 27 - DC Bus Circuit
In the figure below we see a schematic representation of the Brake Chopper.
We see four IGBTs, two connected to the positive DC bus and two connected to
the negative DC bus. A diode is connected in series with each IGBT. This diode
acts as a self-induction recuperation diode during switch off of the IGBT. This is
used to avoid over voltages at the IGBT. Each IGBT is connected to a grid
resistor bank. Of the four grid resistor banks, two are connected to the positive
DC bus and two are connected to the negative DC bus.
If the motor is regenerating, the DC bus voltage will increase. Some of the
energy may be consumed by the motor through mechanical losses and some
may be stored in the DC Link Capacitors, but continued regeneration and the
resultant energy will need to a place to go.
DC bus voltage sensing allows this energy to be released in the form of heat
through a transistor and resistor grid bank.
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Figure 28 - Power Inversion
6.4 Dynamic Braking
Before the braking process is discussed it helps to understand how the truck is
propelled. After the acceleration process is defined, dynamic braking will be
defined.
6.4.1 Acceleration Process
When the operator depresses the throttle pedal the engine speeds up the main
alternator and ultimately produces a higher voltage at the rectifier and
subsequently on the DC link. The 3 phase drive frequency controllers switch the
DC link voltage to produce a variable frequency AC waveform at the motor
terminals and the motors develop torque and start to rotate. The truck will
continue to accelerate up to its controlled top speed.
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Figure 29 - Power Inversion 2
It can be stated that when the motor is accelerating the rotor speed is slightly
lagging the speed of the rotating magnetic field in the stator windings. This is
referred to as slip. Without slip (rotor and stator magnetic field would rotate at the
same speed) no torque is produced.
NO TORQUE NO GO!
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Figure 30 - Power Regeneration
6.4.2 Braking Process
The Braking Process is a bit more complicated than the acceleration process,
due to a buildup of energy that needs to be dissipated. Pay close attention to
what happens to the stator speed and the torque.
When the operator depresses the dynamic brake pedal the frequency controllers
produce an AC frequency that causes the rotating magnetic field in the stator to
rotate slower than the rotor speed. This situation causes a reverse torque in the
motor and a generator action that regenerates power back to the DC Link via the
diodes that are paralleled across the IGBT’s.
The regenerated power has the effect of raising the DC Link voltage to a level that
may damage the DC Link capacitors. Prior to that, the control system senses the
higher voltage and switches in the chopper module that regulates DC Link voltage
to a level that will not damage inverter components. The excess DC voltage is
dissipated in the form of heat via the grid resistors.
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Figure 31 - Power Regeneration 2
The reverse torque in the traction motor serves as an electric brake and slows
the traction motor (rotor) speed until it is again rotating at less than the rotating
magnetic field in the stator.
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Legend:
1. Activation of DC Brake
2. Service Brake Open
3. Service Brake Closed
4. De-Activation of DC Brake
Figure 32 - DC Brake Data Log File
6.5 DC Braking
Trucks on wet roads are hard to control to zero speed. The rear wheels often start
turning backwards before they stop, and the stop may also feel unsteady. DC
Braking is a software configuration that is used to achieve a smooth stopping of
the truck without any abrasion of the mechanical brakes (brake blending is no
longer needed).
DC power is applied to 2 of the windings in the motor stator. That creates a
stationary (non-rotating) magnetic field, into which the spinning rotor passes. That
magnetic field then creates a counter-rotating magnetic field in the rotor cage
which opposes the rotor rotation, bringing the load to a stop.
The FC Rack applies a DC current to the electrical motor at a low speed
(approximately 40 rpm) to force the motor to zero speed (same principle like in an
elevator).
The mechanical brake is activated at 0 rpm speed no friction = no abrasion
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Figure 33 - Variable Switching Frequency at the Main Drive
Each switching process of the variable switching frequency at the main drive
creates losses (heat) inside the semiconductor modules (IGBT or Chopper).
During slower vehicle speeds (wheel motor speed), the switching frequency will
be reduced. With the switching strategy employed with DC Braking the losses
will be reduced and the lifetime of the semi-conductors will be increased.
Typical Uphill Speed - 16km/h/10mph
Switching Frequency - Old configuration 765 Hz – New configuration 400 Hz
Switching Losses 48% in this driving situation
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Traction Motor Specifications
264
T282C
284
Rated Voltage
1300VAC
1310 VAC
1310 VAC
Maximum Voltage
1550 VAC
1650 VAC
1650 VAC
Rated Current
900 A
770 A
770 A
Maximum Current
1500 A
1900 A
1900 A
Rated Power
1100 kW
1500 kW
1500 kW
Rated Speed
988 rpm
1488.5 rpm
1488.5 rpm
Maximum Speed
3260 rpm
3460 rpm
3460 rpm
Rated Frequency
50 Hz
50 Hz
50 Hz
Gear Ratio
36.1:1
43.1:1
43.1:1
Figure 34 - Traction Motor
7 TRACTION MOTOR
Drive torque, for both motoring (propel) and braking (retarding), is provided by two
squirrel cage AC induction motors.
7.1 Location
The Traction Motors are mounted to their respective gear set.
7.2 System Description
The traction motor is a four-pole three-phase induction motor designed specifically
to power the drive wheels on AC Drive haul trucks. The motors are open air cooling
circuit and are forced ventilated. The motors are independently controlled by the
power stacks. The traction motor is intended for transverse mounting in the
vehicle.
Table 6 - Traction Motor Specifications
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Legend:
1. Traction Motor
2. Gear Set Assembly
Figure 35 - Traction Motor and Gear Set
7.3 Principles of Operation
7.3.1 Stator Windings
The stator core assembly, consisting of insulated steel laminations, is welded to
the thrust rings on both sides. The stator core assembly has axial cooling air
ducts. The winding ends of the coil, the stator coil connections, and the
connector bars are brazed to each other. The insulation meets the specifications
of thermal class C (200°C).
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Legend:
1. Stationary (Stator) Windings
2. Rotating (Rotor) Windings
7.3.2 Rotor
A core assembly, consisting of insulated electric sheet steel, is shrink-fitted on the
rotor shaft. The rotor has axial cooling air ducts. The copper rotor bars lie in slots
of the core assembly. These constitute the cage winding together with brazed
short circuiting rings.
The armature of the wheel motor assembly is coupled to the planetary gear box.
The wheel motor assembly transmits the propulsion force to the planetary gear
box. In dynamic retarding, the force on the wheel motors is reversed to stop the
haul truck.
Figure 36 - Traction Motor / Rotor and Stator
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Legend:
1. PT 100 Temperature Sensor
2. Speed Sensor
3. CAN Temperature Module
Figure 37 - Traction Motor Sensors
7.3.3 Temperature Modules and Sensors
There are various sensors that are used to provide protection to traction motor
assembly and its components. The CAN Temperature Module and Temperature
Sensors are discussed in more detail in the 24 VDC section)
7.3.4 Speed Sensor
The speed sensor monitors speed and direction and sends this information back
to the FC Controllers Sensor-In cards in the form of pulses. Gap setting for the
speed sensors range from 0.2mm to 1.0mm. Mounting to the traction motor is
fixed so gap settings are not adjustable.
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Figure 38 - Speed Sensor
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Power Conversion and Inversion Student Workbook
Speed Signal Designation
Signal Designation
Conductor Color
Pin Name
Signal 1
Yellow
B
Signal 1
Black
C
Signal 2
White
D
Signal 2
Brown
E
OV GND
Blue
F Red
A
Housing
Shield
Housing
U
B
Each speed sensor has two channels and two negated channels which allow for
the determination of direction. The channel that senses positive first identifies
which direction the motor is turning.
7.3.5 Speed Sensor Designation
Table 7 - Speed Sensor Signal Designation
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8 AUXILIARY POWER CONVERSION
The AC Drive system power components require cooling for proper
operations. The components, such as the traction alternator, traction
motors, and cooling pump frequency controller are cooled using forced
ventilated unfiltered air. While the power stacks (inverters) choppers
and Auxiliary Frequency Controllers for the Grid Blower, Main Blower are
liquid cooled.
Figure 39 - DC/DC Converter
The Auxiliary components that will be discussed in this section are:
DC/DC Converter
Auxiliary Frequency Converters(IGBT Inverter)
Main Blower Assembly
Grid Blower Assembly
Cooling Pump
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Power Conversion and Inversion Student Workbook
Legend:
1. Cooling Pump
2. Snubber Capacitors
3. Snubber Resistors
4. DC to DC Converter
5. Inductors
6. Fuse
Figure 40 - Control Cabinet Rear View
8.1 DC to DC Converter
The DC/DC Converter provides a steady DC voltage for the auxiliary frequency
converters.
8.1.1 Location
The DC/DC Converter is located in the back of the Control Cabinet.
8.1.2 System Description
The DC/DC Converter uses IGBTs and current mode controller to provide a
constant 650 volt DC supply to the auxiliary frequency converters. The Inductors
are placed in series with the output to provide filtering. The unit is liquid cooled. It
is important for the liquid cooling to be present prior to enabling the converter. Loss
of flow will result in catastrophic failure.
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Legend:
1. Snubber Capacitors
2. Cooling Fan
3. Frequency Controller
4. IGBT Circuit
Figure 41 - DC/DC Converter Components
TTAC0041
2
1
4
3
8.1.3 Principle of Operation
The DC/DC Converter has a 24 volt DC supply used to gate the IGBTs. The CAN
(Controller Area Network) Bus is the connection used for the PLC (Programmable
Logic Controller). As stated before, the converter uses current mode controller to
control the output voltage.
The converter regulates its output voltage by varying the peak inductor current on
a cycle-by-cycle basis to output a regulated voltage despite variations in loadcurrent and input-voltage.
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Power Conversion and Inversion Student Workbook
Legend:
1. 900-1800 VDC Input from DC Bus
2. Snubber Capacitors
3. 24 VDC Supply
4. Output Fuse Protection
5. 650 VDC Output to Auxiliary
Frequency Converters
6. 2.8 mH Inductors
7. CAN Connection
8. (IGBT) Frequency Converter
Figure 42 - DC/DC Converter External Components
The DC Link voltage varies with the speed and the excitation of the traction
alternator. The control of the DC/DC Converter varies the length of time of the on
pulses and the off pulses in order to maintain a constant output. Inductors are
connected in series with the output and are used to resist changes in current which
help further filter the voltage to the frequency converters.
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Student Workbook Power Conversion and Inversion
Legend:
1. Main Blower FC
2. Cooling Pump FC
3. Grid Blower FC
Figure 43 - Auxiliary Frequency Converters
8.2 Auxiliary Frequency Converters
The Auxiliary Frequency Converters are used to control auxiliary motors.
8.2.1 Location
The Auxiliary Frequency Converters are located in the far left compartment of the
Control Box.
8.2.2 System Description
There are 3 Auxiliary Frequency Converters on the Haul Truck. The Main
Blower, Grid Blower, Cooling Pump, are each controlled by an Auxiliary
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Power Conversion and Inversion Student Workbook
Legend:
1. In From DC/DC Converter
2. AC out to Motor
3. Temperature Sensor
4. Enable Signal
5. 24 VDC Supply
6. Main PLC Connection
7. Water Cooled
Figure 44 - Auxiliary Frequency Converter Terminal Connections
Frequency Converter. The Auxiliary Frequency Converter changes the DC input
from the DC/DC Converter to a variable frequency, three phase, AC output.
The unit is connected to the Main PLC which monitors and controls the output.
This provides controls of start-up, stopping, and speed control. The converter
can be programmed with a wide variety of parameters. It also contains a selfdiagnostic system which enables the technician to quickly diagnose faults. The
converters for the main blower and grid blower are liquid cooled. The converters
for the coolant pump and gear oil pump are air cooled.
8.2.3 Principle of Operation
The Auxiliary Frequency Converters use IGBTs to invert the DC voltage from the
DC/DC Converter to a variable frequency AC current. In the diagram above
terminals 16 is the enable signal from a digital output module. Terminals 21 and
22 are the 24 volt supply for the controller. The (Digital Operator) is the
connection to the Main PLC. The Main PLC monitors the auxiliary motors and
frequency converters. If the auxiliary motors need to speed up or slow down, the
Main PLC commands the set values. A pulse width modulation created by the
frequency converter will control output AC current.
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Figure 45 – Main Blower Motor Assembly
8.3 Main Blower Assembly
The Main Blower Assembly provides cooling for the traction alternator and wheel
motors.
8.3.1 Location
The main blower assembly mounts under the rear portion of the control cabinet
above the traction alternator.
8.3.2 System Description
The main blower motor is a TEAO (Totally Enclosed Air Over) 4-pole, 3 phase
induction motor. It is a NEMA class H insulation motor with a max speed of 4080
rpm.
The blower is controlled by an auxiliary frequency converter and runs at a
nominal speed of 3600 RPM at 460 volts and a variable frequency up to 137 Hz.
The blower speeds can be varied over its full operating range independent of the
engine speed or truck operating mode.
This provides the maximum flexibility for optimum cooling while allowing the engine
to run at idle during retard.
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Power Conversion and Inversion Student Workbook
Legend:
1. Axle Box
2. Air Flow
3. Traction Alternator
4. Main Blower Housing
5. Heat Exchanger
6. Control Cabinet
Figure 46 - Main Blower Cooling Flow
8.3.3 Principle of Operation
Air drawn into the main blower through the control cabinet also cools an air/waterheat exchanger. The 75 kW motor is connected to two fans in the main blower
assembly. The wheel motor airflow is 6000 CFM and the traction alternator airflow
is 6300 CFM. Total system airflow is approximately 12,300 CFM. This will vary
according to truck specifications and location of the truck.
Blower speed is controlled by the PLC depending on traction motor, alternator, and
cooling fluid temperatures.
The alternator and axle box fan sizes are slightly different from each other in order
to compensate for the different static pressure drop between the alternator and
traction motors while still moving the same volume of air. Traction motor fan blower
is wider than the fan blower used for the traction alternator. Should a ground fault
occur, the blower is automatically run at full speed to remove moisture out of the
system which could be the cause of the ground fault error.
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Student Workbook Power Conversion and Inversion
Figure 47 - Grid Box Assembly
8.4 Grid Blower Assembly
The Grid Box is used to house the resistor grids and blower motor. It dissipates
the energy generated by the traction motors during electrical braking
8.4.1 Location
The Grid Box is located on the main deck adjacent to the Control Cabinet.
8.4.2 System Description
The Grid Box is used to house the resistor grids and blower motor. It dissipates
the energy generated by the traction motors during electrical braking (Retarding).
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Power Conversion and Inversion Student Workbook
Figure 48 – Grid Resistor Location
TTAC0048
8.4.3 Principle of Operation
The resistor grid box is comprised of four banks of resistors which are forced
ventilated by a dual-wheel centrifugal blower system. The grid box blower motor is
controlled by an auxiliary frequency converter.
The four banks of are configured to allow dissipation of the load/heat generated
during electrical braking (retard). The resistors are capable of dissipating excess
power from 2.5 to 5 MW depending on truck specification.
The resistor grid is connected directly to the DC link bus. It is extremely important
that the DC link bus be discharged prior to opening the grid box. A potential shock
hazard exists even after the truck is shut down.
The Grid Blower Motor is a series-wound AC motor, powered by an auxiliary
frequency converter. The speed of the blower motor varies according to input set
points from the PLC. The 75 kW motor is connected to two dual centrifugal wheels
with dual air inlets. This configuration provides approximately 12,000 CFM of
airflow across the resistor grid per wheel.
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Figure 49 - Cooling Pump
Figure 50 - Cooling System
8.5 Cooling Pump
The cooling pump system is used to cool the
power components of the drive system.
8.5.1 Location
The coolant pump (1) and air/water-heat exchanger (2) are located in the back of
the control cabinet.
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Power Conversion and Inversion Student Workbook
Legend:
1. Cooling Pump
2. Heat Exchanger
3. Power Stack 1 Supply and Return
4. Power Stack 2 Supply and Return
5. Power Stack 3 Supply and Return
6. Power Stack 4 Supply and Return
7. Chopper Module Supply and
Return
8. Main Rectifier Supply and Return
9. DC/DC Converter Supply and
Return
10. Grid Blower Freq. Converter
Supply and Return
11. Main Blower Freq. Converter
Supply and Return
Figure 51 - Cooling System Manifold
8.5.2 System Description
The system consists of a pump with a 1.8 kW motor, an air/water-heat exchanger,
water distribution rack, and fluid expansion tank. The system capacity is 15.85
gallons (60 liters) of a 50% water and 50% glycol mixture.
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Student Workbook Power Conversion and Inversion
Figure 52 - Cooling System Line Diagram
8.5.3 Principle of Operation
The cooling system pump is run at a constant speed of 3600 RPM. Upon start-up
of the haul truck, the Cooling pump begins to run. All of the power components in
the diagram below begin to receive cooling liquid. The PLC monitors the flow rate
in the system to ensure proper flow to the power components. Without proper flow,
the PLC will not allow the drive system to come online.
In the event of cooling liquid loss during truck operations the PLC will allow
dynamic braking until the truck is safely stopped. The PLC will then inhibit propel.
Overheating of the power components will result in catastrophic failure.
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Student Workbook Power Conversion and Inversion
9 FIGURE INDEX
Figure 1 - Litronic Plus AC Drive Control Cabinet ................................................. 7
Figure 2 - Power Conversion and Inversion Overview .......................................... 8
Figure 3 - Exciter Field Regulator Location ........................................................... 9
Figure 4 - Exciter Field Regulator ....................................................................... 10
Figure 5 - Electricity Producing Elements ........................................................... 11
Figure 6 - Field Regulator and Rotor Electrical Diagram ..................................... 12
Figure 7 - Magnetic Field .................................................................................... 12
Figure 8 - T264 Traction Alternator ..................................................................... 13
Figure 9 - T282C and T284 Traction Alternator .................................................. 13
Figure 10 - Traction Alternator Internal Components .......................................... 14
Figure 11 - Traction Alternator Internal Windings ............................................... 15
Figure 12 - Rotating Rectifier Assembly .............................................................. 16
Figure 13 - Traction Alternator Main Stator Assembly ........................................ 16
Figure 14 - Traction Alternator Rotor Assembly .................................................. 17
Figure 15 - Main Rectifier .................................................................................... 18
Figure 16 - Main Rectifier 2 ................................................................................. 19
Figure 17 - Full Wave Rectification ..................................................................... 19
Figure 18 - Power Components .......................................................................... 20
Figure 19 - DC Link Capacitor ............................................................................ 21
Figure 20 - Capacitor Discharging ...................................................................... 22
Figure 21 - Power Stack ..................................................................................... 23
Figure 22 - Power Stack IGBT ............................................................................ 24
Figure 23 - Pulse Width Modulation .................................................................... 25
Figure 24 - Power Stack Configuration ............................................................... 25
Figure 25 - Chopper Module ............................................................................... 26
Figure 26 - Chopper Module and Grid Resistor Box ........................................... 27
Figure 27 - DC Bus Circuit .................................................................................. 27
Figure 28 - Power Inversion ................................................................................ 28
Figure 29 - Power Inversion 2 ............................................................................. 29
Figure 30 - Power Regeneration ......................................................................... 30
Figure 31 - Power Regeneration 2 ...................................................................... 31
Figure 32 - DC Brake Data Log File .................................................................... 32
Figure 33 - Variable Switching Frequency at the Main Drive .............................. 33
Figure 34 - Traction Motor .................................................................................. 34
Figure 35 - Traction Motor and Gear Set ............................................................ 35
Figure 36 - Traction Motor / Rotor and Stator ..................................................... 36
Figure 37 - Traction Motor Sensors .................................................................... 37
Figure 38 - Speed Sensor ................................................................................... 37
Figure 39 - DC/DC Converter ............................................................................. 39
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Power Conversion and Inversion Student Workbook
Figure 40 - Control Cabinet Rear View ............................................................... 40
Figure 41 - DC/DC Converter Components ........................................................ 41
Figure 42 - DC/DC Converter External Components .......................................... 42
Figure 43 - Auxiliary Frequency Converters ........................................................ 43
Figure 44 - Auxiliary Frequency Converter Terminal Connections ...................... 44
Figure 45 – Main Blower Motor Assembly .......................................................... 45
Figure 46 - Main Blower Cooling Flow ................................................................ 46
Figure 47 - Grid Box Assembly ........................................................................... 47
Figure 48 – Grid Resistor Location ..................................................................... 48
Figure 49 - Cooling Pump ................................................................................... 49
Figure 50 - Cooling System ................................................................................ 49
Figure 51 - Cooling System Manifold .................................................................. 50
Figure 52 - Cooling System Line Diagram .......................................................... 51
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Student Workbook Power Conversion and Inversion
10 TABLE INDEX
Table 1 - Field Regulator Terminal Connections ................................................. 10
Table 2 - Traction Alternator Specifications ........................................................ 14
Table 3 - Output Frequency Calculation ............................................................. 17
Table 4 - Traction Alternator Speed Set Points ................................................... 17
Table 5 - RC Time Constant ............................................................................... 22
Table 6 - Traction Motor Specifications ............................................................... 34
Table 7 - Speed Sensor Signal Designation ....................................................... 38
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Power Conversion and Inversion Student Workbook
Index
(IGBT) ................................ ................................................................................. 23
Auxiliary Frequency Converters ........................................................ 18, 39, 43, 44
Chopper Module ........................................................................... 8, 12, 20, 26, 27
cooling pump ................................................................................................ 39, 49
Cooling pump ...................................................................................................... 51
DC Bus ................................................................................................................. 7
DC Link Capacitors ............................................... 8, 12, 14, 17, 20, 21, 22, 26, 27
DC Link voltage....................................................................................... 24, 30, 42
dynamic brake..................................................................................................... 30
dynamic braking ............................................................................................ 28, 51
Dynamic Braking ................................................................................................. 28
exciter field regulator ..................................................................... 9, 10, 11, 12, 15
Full bridge rectifier .............................................................................................. 19
Grid Blower ................................................................................... 8, 39, 43, 47, 48
Grid Box .............................................................................................................. 47
grid resistor bank ................................................................................................ 27
IGBT ................................................................................. 8, 20, 23, 24, 25, 27, 39
Insulated Gate Bipolar Transistors ...................................................................... 23
magnetism .......................................................................................................... 11
Main Blower Assembly .................................................................................. 39, 45
Main Rectifier .............................................................. 8, 12, 14, 17, 18, 20, 21, 22
Main Rotor Windings ........................................................................................... 11
Power Stacks ................................................................................ 8, 20, 23, 24, 26
regenerating .................................................................................................. 26, 27
Rotating Rectifier .......................................................................................... 11, 15
speed sensor ................................................................................................ 37, 38
Stationary Exciter Field Windings ....................................................................... 11
Traction Alternator8, 12, 13, 14, 16, 17, 18, 20, 21, 22, 23, 24, 32, 34, 35, 36, 37,
40, 41, 42, 43, 44, 46, 50
Traction Motor ..................................................................................................... 34
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