Download Power Electronics Design

University of Portland
School of Engineering
5000 N. Willamette Blvd.
Portland, OR 97203-5798
Phone 503 943 7314
Fax 503 943 7316
Theory of Operations
Project Umpqua: Electric Vehicle Drive
System
Contributors:
Team Members:
Steven O. Arlint, Team Lead
[email protected]
Abdullah Binsaeed
[email protected]
Dustin Buscho
[email protected]
Faculty Advisor:
Robert J. Albright, Ph. D, P.E.
[email protected]
Industry Representative:
Paul M. Menig
[email protected]
Version 0.9
Approvals
Name
Signature file
Date
Date
Dr. Lillevik
Dr. Albright
Mr. Menig
UNIVERSITY OF PORTLAND
2/8/06
Name
Date
Signature file
Date
Steven Arlint
1/27/06
Dustin Buscho
1/27/06
Abdullah Binsaeed
1/27/06
SCHOOL OF ENGINEERING
CONTACT: S ARLINT
.
.
.
.
.
Revision History
.
.
Rev.
Date.
0.9
10/27/05 .
THEORY OF OPERATIONS
PROJECT UMPQUA
UNIVERSITY OF PORTLAND
REV. 0.9
Author
S. Arlint, D. Buscho, A.
Binsaeed
SCHOOL OF ENGINEERING
PAGE II
Reason for Changes
Initial draft of document
CONTACT: S. ARLINT
.
.
.
.
.
Table of Contents
.
.
Summary.......................................................................................................................
1
.
.
Introduction ..................................................................................................................
2
THEORY OF OPERATIONS
PROJECT UMPQUA
REV. 0.9
PAGE III
Background .................................................................................................................. 3
Technologies ...........................................................................................................................................3
Architecture .................................................................................................................. 4
General Description ................................................................................................................................4
Embedded System Architecture.............................................................................................................5
Microcontroller and Firmware ..........................................................................................................5
Supporting Circuitry..........................................................................................................................5
Power Electronics....................................................................................................................................5
Sections ............................................................................................................................................5
Motor Drive .......................................................................................................................................5
Current and Voltage Sensing ..........................................................................................................6
RPM Sensing ...................................................................................................................................6
Throttle ..............................................................................................................................................6
Design Overview.......................................................................................................... 7
Embedded System Design .....................................................................................................................7
Power Supply (low voltage) .............................................................................................................7
Microcontroller ..................................................................................................................................7
User Input Throttle............................................................................................................................7
LCD Display......................................................................................................................................7
Current and Voltage Sensors ..........................................................................................................7
RPM Sensor .....................................................................................................................................8
Power Electronics Design .......................................................................................................................8
Forward Drive Mode ........................................................................................................................8
UNIVERSITY OF PORTLAND
SCHOOL OF ENGINEERING
CONTACT: S. ARLINT
.
.
.
.
Regenerative Braking Mode ............................................................................................................9
.
.
Power Electronics Attributes ...................................................................................................................9
.
.
Performance .....................................................................................................................................
9
.
THEORY OF OPERATIONS
PROJECT UMPQUA
REV. 0.9
PAGE IV
Losses...............................................................................................................................................9
Conclusions ...............................................................................................................11
Appendix A: Glossary ...............................................................................................12
UNIVERSITY OF PORTLAND
SCHOOL OF ENGINEERING
CONTACT: S. ARLINT
.
.
.
.
List of Figures.
.
.
.
.
Figure1:
Architecture
of Project Umpqua
THEORY OF OPERATIONS
PROJECT UMPQUA
REV. 0.9
Figure 2:
Speed vs. Voltage and Torque vs. Current
Figure 3:
PWM Operation
Figure 4:
Heat Dissipation Characteristics
UNIVERSITY OF PORTLAND
SCHOOL OF ENGINEERING
PAGE V
CONTACT: S. ARLINT
THEORY OF OPERATIONS
PROJECT UMPQUA
Chapter
1
.
.
.
.
.
.
.
.
.
REV. 0.9
PAGE 1
Summary
Umpqua’s Theory of Operations document provides a detailed technical summary of the
project, including all hardware, firmware, software, and the protocol that links them
together.
The bulk of this document is covered in two chapters. Chapter 4 discusses the project
architecture, chapter 5 discusses the design overview. The architecture chapter explains
how the project as a whole is pieced together. It is an in-depth analysis of our original
functional block diagram. The design overview chapter describes each module that is
used in the composition of the system architecture. The design overview gives a mix of
both the qualitative and quantitative aspects of these modules.
UNIVERSITY OF PORTLAND
SCHOOL OF ENGINEERING
CONTACT: S. ARLINT
THEORY OF OPERATIONS
PROJECT UMPQUA
Chapter
2
.
.
.
.
.
.
.
.
.
REV. 0.9
PAGE 2
Introduction
Umpqua’s theory of operations is intended to provide a detailed technical description of
Project Umpqua as documentation of our current design and reference for any future use
or modification thereof.
Project Umpqua is the drive system for a Light-Weight Electric Vehicle (LWEV) which will
hold a single driver meant to emulate single-person transportation in a real world
application (mainly work commuting). It will allow that one person to travel at a maximum
speed of 40 miles per hour with a range that is proportional to the rating of the battery
system that they choose. This speed limit is acceptable for most roads within a city. It will
not be meant for interstate travel.
In order to achieve this range and speed, power electronics that have a very high
efficiency will need to be used. The permanent magnet DC motor used has a voltage
rating of 130 volts with a coil resistance of 1.5 ohms. We will operate this motor at 120
volts. Given the coil resistance, this voltage will allow for a maximum motor current of 80
amperes. In order to keep at least 97% efficiency in the forward drive part of the motor
controller, the maximum forward on resistance should be no greater than 0.045 ohm.
The information contained herein is a technical description of our present product, limited
to a description of how Umpqua works with only a rough focus on a target market, so it
does not include marketing plans or projected modifications. It has been divided into four
major sections as follows:
-
The Background describes the uses and market for the finished product.
-
The Architecture section describes both the embedded system and the hardware
architecture with diagrams.
-
The Design Overview gives detailed technical descriptions of the manner in which
the architecture is composed.
-
The Conclusions section gives a short recap of the entire project and references
the other three sections in stating the conclusions drawn by Team Umpqua.
UNIVERSITY OF PORTLAND
SCHOOL OF ENGINEERING
CONTACT: S. ARLINT
THEORY OF OPERATIONS
PROJECT UMPQUA
Chapter
3
.
.
.
.
.
.
.
.
.
REV. 0.9
PAGE 3
Background
In today’s economic world, fuel has created many types of conflicts around the world that
has led many engineers to research and develop alternative energy sources. To improve
the situation, companies have developed higher fuel economy vehicles, hybrid cars, and
have done research in areas dealing with hydrogen power. While all of these sound like
great ideas, the first two still put a heavy dependence on the “insanely profitable” oil
industry. The problem with hydrogen is that at this time it has not proven practical in a
consumer vehicle application due to the present way hydrogen is produced. This leaves
the world with few alternatives to the gasoline engine. One of these alternatives is electricbased transportation.
Electric vehicles have existed since the start of the 20th century, but few are practical. The
reason for this is that it is not efficient for a two or three thousand pound vehicle to move a
single person, especially if powered by electricity. The main reason for this is because of
the relatively low performance of any of the batteries that currently exist. What is possible
and highly efficient is for something along the lines of a motor scooter or motor cycle to be
powered by an electric motor and batteries. In this case it would be about a 150 to 350 lb
vehicle that will transport a single driver.
The mechanics in electric-based transportation are simpler than their gasoline engine
counterparts. Electric motors themselves have only two parts, a stator (static) and a rotor
(moving). Generally, in smaller applications a direct-drive or single-speed transmission
can be used. This makes the mechanics easier and directs the focus of electric vehicle
development into the three most important parts: batteries, motor, and control electronics.
The members of project Umpqua decided to pursue this project for several reasons. The
first was the benefits of the project. This project is a physical and tangible device that can
make a direct impact on peoples’ lives. In this case, that impact will be in transportation.
The second reason is that the project falls within the skill areas of all three of the members
of project Umpqua. The Microprocessor interfacing, power electronics, and the energy
conversion classes - all of which are vital to the development of the project - have been
completed by at least one member of the team.
Technologies
Microchip’s MPLAB software and the ICD2 in-circuit debugger has been used to perform
all of the assembling, debugging, and programming necessary to design and construct the
embedded design system. Microchip was chosen for its excellent online resources.
.
UNIVERSITY OF PORTLAND
SCHOOL OF ENGINEERING
CONTACT: S. ARLINT
THEORY OF OPERATIONS
PROJECT UMPQUA
Chapter
4
.
.
.
.
.
.
.
.
.
REV. 0.9
PAGE 4
Architecture
General Description
Figure 1 illustrates the general architecture of the project:
User Input
Regeneration
Control
MOSFET
70A 500V x1
High Voltage
(DC)
Embedded
System
Free
Wheeling
Diode
DC
Permanent
Magnet
Motor
Tachometer
Speed Control
MOSFET
70A 500V x1
Ground
Sensor Logic
LCD
Display
Current
Sensor
Figure 2: Architecture of Project Umpqua
The architecture of Project Umpqua is divided into an embedded system and a hardwarebased power electronics module. The embedded system consists of a microcontroller
and its firmware, and the various supporting circuitry and IC’s.
The hardware power electronics module consists of STMicroelectronics Isotop power
modules and one Gordos 50A SCR-based power module. Supporting circuitry is used for
all of the sensing functions.
UNIVERSITY OF PORTLAND
SCHOOL OF ENGINEERING
CONTACT: S. ARLINT
.
.
.
.
.
Embedded System Architecture
.
.
Microcontroller and Firmware
.
.
THEORY OF OPERATIONS
PROJECT UMPQUA
REV. 0.9
PAGE 5
The microcontroller and its firmware will control all functionality of the embedded system
(ES). There is one mode of operation in which three actions can take place, described as
follows:
1. Forward Drive – This occurs when the throttle is depressed. The amount of
power is proportional to the amount by which the throttle is depressed. Forward
drive will continue until the throttle is released. If a specified value of current is
exceeded the power is reduced and limited to that specified value.
2. Braking (regeneration) – This occurs when the brake is applied. Energy from the
forward inertia is recovered and this action slows the vehicle. The rate of braking
is proportional to the vehicle speed and the amount that the brake is depressed.
The electrical brake is applied before the mechanical brake. The mechanical
brake is used to stop more urgently and is used in conjunction with the electrical
brake.
3. Display Driving Data – This occurs as long as the vehicle is operating. Six values
are displayed for the user. These values are speed, distance traveled, voltage,
current, instantaneous power, and power consumed in watt-hours.
Supporting Circuitry
The supporting circuitry includes all of the IC’s and electronics components required to get
data into and out of the microcontroller. This includes reading the sensors and controlling
the power components. Chapter 5 discusses this in detail.
Power Electronics
Sections
The power electronics consists of 4 fundamental sections. The first controls the forward
drive and regenerative braking actions of the vehicle. The second senses current and
voltage. The third senses motor speed in RPM. The last is the throttle which interfaces to
the user and allows for speed control.
Motor Drive
The motor drive circuitry concept that is applied is simple yet robust. It is capable of
proportional forward drive and regenerative braking. This section has four high power
wires and three low power wires. This keeps circuit connectivity simple and thus reduces
manufacturing and servicing costs. The motor drive circuitry was designed to be
independent of the motor parameters. It was still necessary to establish our motor
parameters so that we knew the “safe area of operation” with the motor being used. All of
this was calculated from the motor’s armature resistance, inductance, and speed per volt
UNIVERSITY OF PORTLAND
SCHOOL OF ENGINEERING
CONTACT: S. ARLINT
.
.
.
.
constant. All of these measurements are measurable with typical lab equipment. (Figure
.
2: Speed vs. Voltage and Torque vs. Current)
.
.
.
RPM vs. Voltage
Torque vs. Current
.
REV. 0.9
PAGE 6
5000
14.00
4500
4000
12.00
Shaft Torque (ft-lbs)
motor rotation (RPM)
THEORY OF OPERATIONS
PROJECT UMPQUA
3500
3000
2500
2000
1500
1000
500
0
10.00
8.00
6.00
4.00
2.00
0.00
0
50
100
150
0
Voltage applied
20
40
60
80
100
Current (Am peres)
Figure 2: Speed vs. Voltage and Torque vs. Current
Current and Voltage Sensing
Feedback is necessary in all power systems in order to keep the device stable and ensure
long service-life. The current sensing allows for precise values to be sensed by the shunt
resistor that is connected to the between the negative terminal and ground of the motor
drive. This value is sent to the microcontroller to reduce power transferred to the motor in
order to protect the motor, batteries, and user. The voltage value is only used to calculate
instantaneous and cumulative power.
Speed Sensing
A small DC generator is coupled to the motor shaft. The voltage produced by this
generator is proportional to the speed of the motor and the speed of the vehicle. This
value is used for displaying vehicle speed and total distance traveled in miles.
Throttle
Our throttle is a BWM throttle-by-wire system. It uses a hall-effect sensor instead of a
potentiometer for reliability. The throttle interfaces directly to the analog to digital converter
on the microcontroller. The 0.7 volt to 3.7 volt DC range on the throttle in converted to a 0100% output in the microcontroller.
UNIVERSITY OF PORTLAND
SCHOOL OF ENGINEERING
CONTACT: S. ARLINT
THEORY OF OPERATIONS
PROJECT UMPQUA
Chapter
5
.
.
.
.
.
.
.
.
.
REV. 0.9
PAGE 7
Design Overview
Embedded System Design
Power Supply (low voltage)
The power supply is the combination of a 12 Volt auxiliary battery with an output of 12
Volts and a 5 Volt voltage regulator IC. All system logic level components are run off of this
regulated 5 Volt DC source. The fan and gate drive chip are run off of the 12 Volt auxiliary
battery directly. The 12 Volt DC battery is charged at the same time of the vehicle battery.
This battery always stays in the range of 12 to 13.2 Volts which is within the tolerances for
the fan and the gate driver chip.
Microcontroller
The microcontroller (µC) is a PIC18F452 in the 40-pin DIP package. Our system runs the
chip at 8 MHz yielding 2 MIPS. The µC clock is an oscillator external to the chip. The
firmware controlling the embedded system is loaded into the µC flash program memory.
User Input Throttle
The throttle consists of a BMW throttle-by-wire system. It is a Hall Effect sensor type of
throttle. The open circuit values for this sensor are 0.7 Volts for 0% throttle and 3.7 Volts
for 100% throttle. This is the output when the input voltage is the specified 5 Volts DC. A
1k Ω series resistor is added to limit the current that flows from this device to the analogto-digital converter (ADC) on the µC. A pull-down 10 k Ω resistor is added between the
µC ADC input and ground to account for a disconnected or broken throttle; this helps
prevent a runaway vehicle condition.
LCD Display
The LCD display is an industry standard display that uses the HD44780 LCD driver chip.
A 20 Character by 4 line display is used. This device interfaces directly between the µC
and PORTB of the µC. This is an 8-bit port which can allow for communication to and
from the LCD display and the µC. Project Umpqua will communicate from the µC to the
LCD display only.
Current and Voltage Sensors
The wires from the current sensing resistor interface directly to the µC ADC and ground.
The value of the shunt is 5 milli-Ohms. In the case of 100 Amperes of current passing
through the circuit, the voltage drop across the shunt is 0.5 Volts. With a reference voltage
of 5 Volts on the µC, the resolution of the ADC is 4 milli-Volts. There will be 125 equally
spaced intervals for current value between 0 and 100 Amperes. The current resolution will
be at intervals of 0.8 Amperes.
UNIVERSITY OF PORTLAND
SCHOOL OF ENGINEERING
CONTACT: S. ARLINT
.
.
.
.
Speed Sensor
.
.
A Maxon 25 .mm moving coil DC motor is being used as the speed sensor. It is directly
coupled to the
. motor tail shaft to allow for accurate operation. The coupling is done by
using flexible tubing to avoid the vibration problems with a welded coupler or a press fit
.
coupler. The shafts on the Maxon motors are prone to shearing off. The speed sensor
THEORY OF OPERATIONS
PROJECT UMPQUA
REV. 0.9
PAGE 8
was chosen to match the specifications of the driving motor. When the driving reaches it’s
full no-load speed (4500 RPM @ 120 Volts DC), the speed sensor outputs 6.8 Volts DC.
This voltage is then scaled down to 5 Volts DC in order to interface to the ADC of the µC.
The resolution of the speed sensor as seen by the µC is 900 RPM per Volt or 18/5 RPM
per 4 milli-Volts.
Power Electronics Design
Forward Drive Mode
The forward drive mode is a standard low-side n-channel MOSFET topology. The nchannel MOSFET has a built in reverse body diode and there is a freewheeling diode in
parallel with the motor to prevent inductive “kickbacks”. A Texas Instruments SN754410
quad-half H-Bridge chip is used to drive the gate of this MOSFET as well as the
regenerative braking MOSFET and SCR. This mode is controlled by a Pulse-WidthModulation (PWM) signal from the µC. The signal is demodulated in the low-pass filter
created by the inductance of the motor.
% Power of Applied
PWM operation
100
80
Linear Throttle
Curve
60
40
20
0
0
20
40
60
80 100
PWM % (same as throttle position
percentgage)
Figure 3: PWM Operation
UNIVERSITY OF PORTLAND
SCHOOL OF ENGINEERING
CONTACT: S. ARLINT
.
.
.
. Mode
Regenerative Braking
.
. braking mode takes the standard topology of the forward drive stage and
The regenerative
.
adds an SCR.that is used as a switch to turn off the battery at the point of the forward drive
stage and route the power from the motor through a series inductor and the braking
.
MOSFET back to ground. This “shorts” the motor terminals together, but the current takes
THEORY OF OPERATIONS
PROJECT UMPQUA
REV. 0.9
PAGE 9
time to build up due to the 60 µH series inductor. Once current has built up for a
predefined (adjustable) amount of time the regenerative braking MOSFET turns off and
the current flows from that series inductor to a reverse-biased diode. The energy from the
inductor has to be dissipated so the voltage builds up until current can pass through the
diode and to the positive terminal of the battery. From a broad perspective this can be
viewed as a “boost” converter. Combined with the simple forward drive stage, this design
allows for a low parts count product, which in turn reduces cost.
Power Electronics Attributes
Performance
This product is designed to be a high-voltage medium-current device. The voltage limit for
the main battery is 240 Volts DC. The continuous current rating is 50 Amperes. The 30
second peak is 150 Amps. This configuration with a higher voltage than current rating
becomes useful in designs where space is an issue. The recommended application is for
dual permanent-magnet motors is series configuration. This allows for smaller motors to
be used, as well as smaller wire and is a design best suited for using large series strings of
NiCad, NIMH, or Li-Ion batteries.
Losses
The main energy losses in the project come from the power electronic components and
the shunt resistor. The wire used is high-quality, low resistance rated to 50 Amperes
continuous. The wire size can be changed to suit applications where larger wire is
necessary. The voltage loss in the forward drive stage (the only stage where power is
drawn from the battery) is 0.75 Volt due to the SCR plus 0.045*I Volts due to the Forward
drive MOSFET. At 120 Volts DC and 50 Amperes, the loss is 3.0 Volts. This
corresponding power is lost in the form of heat (Figure 4: Heat Dissipation
Characteristics). This results in an efficiency of 97.5% in the controller. This value is
independent of which motor is used.
UNIVERSITY OF PORTLAND
SCHOOL OF ENGINEERING
CONTACT: S. ARLINT
.
.
.
.
.
Heat .Dissipation Characteristics
.
.
.
Heat dissipation (Watts)
THEORY OF OPERATIONS
PROJECT UMPQUA
500
450
400
350
300
250
200
150
100
50
0
0
REV. 0.9
20
40
60
80
Current (Amperes)
PAGE 10
1 MOSFET
2 MOSFETs
1 Diode
2 Diodes
100
120
Figure 4: Heat Dissipation Characteristics
UNIVERSITY OF PORTLAND
SCHOOL OF ENGINEERING
CONTACT: S. ARLINT
THEORY OF OPERATIONS
PROJECT UMPQUA
Chapter
6
.
.
.
.
.
.
.
.
.
REV. 0.9
PAGE 11
Conclusions
At the end of the project, the user of this light electric vehicle will be presented with a
vehicle that will be easy to control, highly efficient, and have ample power. Along with
these characteristics, there will be the benefits of reducing the dependency on oil and
having zero emissions. The user will also incur less vehicle maintenance since electric
motors need very little service when compared to gasoline engines.
Eventually, given the trend of the gasoline market, the light electric vehicle will have great
importance in the commuter environment. While battery technology right now might be
mediocre at best, part of engineering involves making the best of what devices are
available at the present time. Over time, as battery technology improves, these highlyefficient electric vehicle power plants will find an even more prominent place in the
transportation market.
UNIVERSITY OF PORTLAND
SCHOOL OF ENGINEERING
CONTACT: S. ARLINT
THEORY OF OPERATIONS
PROJECT UMPQUA
.
.
.
.
.
.
.
.
.
REV. 0.9
PAGE 12
Appendix A
DC
-direct current
HP
-horsepower = 746 watts or 550 ft-lbs/sec
LCD
-liquid crystal display
LWEV
-light-weight electric vehicle
MOSFET
-metal-oxide semiconductor field-effect transistor
PWM
-pulse width modulation
SCR
-silicon controlled rectifier
UNIVERSITY OF PORTLAND
SCHOOL OF ENGINEERING
CONTACT: S. ARLINT