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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