bound final report

Hybrid-Electric Drive for the SAE Mini-Baja Car

Hybrid-Electric Drive for the SAE Mini Baja Car

FINAL REPORT

Project Number: May05-13

Client: Iowa State University, Society of Automotive Engineers

Faculty Advisor: Dr. Venkataramana Ajjarapu

Team Members:

Chris ZachME

Godwin ItteeraEE

Douglas MilewskyCprE

Nicholas OlsonEE

Rajdeep Wadhwa (Team leader)EE

DISCLAIMER: This document was developed as a part of the requirements of an electrical and computer engineering course at Iowa State University, Ames, Iowa. This document does not constitute a professional engineering design or a professional land-surveying document. Although the information is intended to be accurate, the associated students, faculty, and Iowa State University make no claims, promises, or guarantees about the accuracy, completeness, quality, or adequacy of the information. The user of this document shall ensure that any such use does not violate any laws with regard to professional licensing and certification requirements. This use includes any work resulting from this student-prepared document that is required to be under the responsible charge of a licensed engineer or surveyor. This document is copyrighted by the students who produced this document and the associated faculty advisors. No part may be reproduced without the written permission of the senior design course coordinator.

Date: April 1, 2005

Table of ContentsPage Number

List of Figuresii

List of Tablesiii

List of Definitionsiv

Introductory Material

Executive Summary01

Acknowledgement02

Problem Statement03

Operating Environment03

Intended Users and Intended Uses03

Assumptions and Limitations04

Expected End Product and Other Deliverables04

Proposed Approach and Statement of Work

Proposed Approach05

Detailed Design08

Estimated Resources and Schedules

Estimated Resource Requirement23

Schedules30

Closure Material

Project Team Information38

Closing Summery39

References40

List of FiguresPage Number

Figure 1: Diagram of series set-up hybrid-electric driveiv

Figure 2: Diagram of detailed electric drive8

Figure 3: Model of a gas engine in Simulink9

Figure 4: Model of a dc motor in SimPower9

Figure 5: DC-DC Buck Chopper10

Figure 6: A diagram of a dc-dc buck chopper13

Figure 7: Model for dc-dc buck chopper in SimPower 15

Figure 8: Output plot of dc-dc buck chopper given in Figure 7 15

Figure 9: Model of DC motor with variable load in SimPower16

Figure 10: Simulation Result for motor with different loads17

Figure 11: Buck chopper and motor together running off

18

generator idealized as a voltage source

Figure 12: Simulation of Figure 11 with no load19

Figure 13: Simulation of Figure 11 with varying duty ratio20

on buck chopper

Figure 14: Simulation of Figure 11 with varying load21

Figure 15: Original Gantt Chart30

Figure 16: Revised Gantt Chart31

Figure 17: Final Gantt Chart32

List of TablesPage Number

Table 1: Original Group Schedule25

Table 2: Revised Group Schedule25

Table 3: Final Group Schedule26

Table 4: Original Other Resources27

Table 5: Revised Other Resources27

Table 6: Final Other Resources27

Table 7: Original Financial Costs28

Table 8: Revised Financial Costs29

Table 9: Final Financial Costs29

Table 10: Evaluation process33

Table 11: Milestone success scoring34

Table 12: Anticipated risks37

Table 13: Unanticipated risks37

List of Definitions

Buck chopper

DC to DC converter that lowers the voltage. Part of the motor controller.

SAE

Society of Automotive Engineers

Simulink

Control systems toolbox within the MATLAB software

SimPower

Simulink library for power electronics analysis

Series hybridHybrid power train architecture with all components arranged in a series (see Figure 1). An engine rotates a generator that converts mechanical energy to electrical energy. This energy can be stored, if desired, before being sent through a controller and on to a traction motor(s), through the transmission, and finally to the vehicles wheels.

Figure 1: Series hybrid architecture (AC type)

Introduction

Executive Summary

The Society of Automotive Engineers (SAE) Mini Baja team at Iowa State University (ISU) is seeking to integrate innovative design components in their competitive, off-road racecar. The team participates in an annual Mini Baja competition with more than a hundred other universities present. Points are awarded based on design, cost, presentation, and performance. ISUs SAE team feels that a new car design featuring a hybrid-electric drive would gain their team a distinct competitive advantage.

The May05-13 senior design team was assigned the task of developing such a drive for future ISU Baja cars. This is a two-phase project split into two year-long segments. The May05-13 conducted the first years work, creating a concept and simulating the solution with computer software. The projects second phase will be conducted by a new design team who will install and test the hybrid-electric drive in a Mini Baja car.

Between project start and November 12, 2004, the May05-13 team successfully completed a preliminary design of the hybrid-electric drive for the car. The drive is powered by a Briggs and Stratton engine, the standard power plant provided by SAE, which spins a DC generator and generates electrical power. This power is then fed to a DC-DC converter, or buck chopper, which regulates the power sent to a DC traction motor for propulsion. The cars driver controls the power sent from the controller to the motor through a foot pedal. The pedal varies a potentiometer which adjusts the duty ratio of the buck chopper, and hence the power sent to the motor.

The team conducted extensive research to locate the best components for this project design. Factors considered included cost, weight, performance, durability, and availability. Etek motors, by Briggs and Stratton, were used for both the motor and generator. An Alltrax DC motor controller was chosen to regulate current and voltage flows.After creating the concept, the team began work on a computer simulation to analyze the performance of the concept system. The parts needed to build the electric drive design are expensive, so it was advantageous to virtually prove their performance before purchasing. The SimPower software, which integrates with MATLAB and Simulink, was chosen to simulate the electric drive concept design.

The design team recently succeeded in creating a working simulation of the hybrid drive. The next challenge in evaluating this simulation is to obtain the remainder of the missing component parameters and to create a motor load vs. motor speed equation to assess the systems performance on a typical track.

Two main options exist for future work on this project. The Baja team could decide to close the project and discontinue any future plans, particularly if their budget does not allow for the development of an electric drivetrain. However, if the funds are available, the design team is confident in the success of this project and recommends that work on this project continues in full-force. The next task required is the construction of a full-scale prototype for performance and endurance testing. After the competitiveness and durability of the system is proven, it will be ready to take to competition and to victory.

Acknowledgement

The ISU SAE Mini Baja team, through its general fund and hybrid drive-specific sponsorships, provided for all project costs outside of those associated with the EE/CprE 491/492 class requirements (poster, report binding, printing, etc.).

Ethan Slattery, the lead client, provided assistance in the form of technical advice and access to SAE materials and workshop facilities.

Problem Statement

The Iowa State Universitys Society of Automotive Engineers Mini Baja team requested the assistance of a senior design group to engineer a hybrid-electric drive for their off-road racecar. Design and implementation of the project will occur over a two-year period. Phase I, the design stage, was conducted during the 2004-2005 academic year. Phase II, the implementation and testing stage, is planned for the 2005-2006 academic year.

A series hybrid drivetrain concept was chosen as the best solution to Phase 1 of this project. In this layout, the gas engine spins a DC generator whose output current is routed through a controller and on to the DC traction motor. This system has been researched, its components selected, and its performance both predicted through calculations and through simulations. The design team is now prepared to fully document the system in preparation for its construction into a prototype next year.

Operating Environment

The hybrid-electric drive system was integrated into the space behind the drivers seat of the Baja car. Being near the engine of a car on a jump-filled dirt track, the system is subjected to many extreme conditions, including dust, dirt, mud, water, high temperatures (>200F), grease and oil, shocks, vibrations, and a potential collision with another car or the track itself. All components of the system must be designed to withstand these torturous conditions. Critical components such as gears and electronics must be sealed from all potential contaminants. Adequate air cooling must be supplied to the motor, generator, and controller at all times. Mechanical components must be designed for high cycle life. Electrical equipment must be protected from current or voltage over the rated values. At all times, the car must present no danger of electrical shock, fire, or mechanical failure to the driver or nearby race personnel.

Intended Users

The hybrid drives sole user is the Iowa State Mini Baja team. Before handing over the final design, the project team will prepare extensive documentation and training for the Baja team on the systems proper usage. This ensures each individual working on the team understands the hybrid functionality and its hazards and is aware of useful troubleshooting methods.

Intended Use

The hybrid drive system was designed specifically for use in a Mini Baja car driven on a closed-course dirt track. Like any Baja car, the hybrid car is not intended for use on public roadways. Doing so places the cars driver and other vehicles occupants at risk of injury or death, because the Baja car was not designed to comply with governmental automobile safety regulations.

Assumptions

Simplifications adopted to aid design and analysis included:

Constant electrical output from generator

Gasoline engine delivers constant power at its governed speed of 3800 rpm

All power for brake light, speedometer, and other instrumentation will be available from separate 12V battery

Simulink models, when properly designed, will accurately predict the performance of real-world components

Limitations

Rules and constraints that affected the design included:

Design must adhere to all rules defined by SAE Mini Baja Collegiate Design Series

Car may possess no potential energy (including electrical) at the start of race

Car must use unmodified 10 hp Briggs and Stratton engine

All electrical and mechanical components must withstand wet and muddy conditions

Power is routed through chain drive from motor to rear axle

Design is intended to meet performance of original car (i.e. comparable efficiency)

The hybrid power train must fit within a space envelope similar in size to that of the current mechanical drive train. This space is approximately 8 cubic feet.

The hybrid power train shall not add considerably to the cars overall weight. The addition of 60 pounds is considered the maximum feasible weight increase.Expected End Product and Other Deliverables

End Product System Design (Delivery date: 5/5/2005)The end product, soon to be delivered to the Baja team, is a design for a hybrid powertrain to propel a Mini Baja car via electric motor. The design includes component specifications needed to construct the entire hybrid system and computer simulation results predicting its performance.

Other Final Project Report (Delivery date: 5/5/2005)This report, once revised at the end of the project term, will also be delivered to the Baja team as documentation of the entire project process.

Product Approach and Results

This section includes the functional requirements, design constraints, approaches considered and use, and detailed system design.

Functional Requirements

This section defines required characteristics of the end design.

Control

Vehicle acceleration shall be controlled by driver with a foot pedal.

Durability

Hybrid drive system must be able to withstand adverse conditions, including vibrations, shocks, and moisture.

Performance

Hybrid Baja car must be capable of acceleration and top speed figures competitive with opponents vehicles.

100 ft drag race:5.74 sec

Top speed:

11.72 m/s

Regulations

System design must comply with all SAE rules.

Safety

Driver shall be safe from any electrical hazards.

Power delivery

Wheels shall be powered by an electrical motor.

Design Constraints

This section lists restrictions imposed on the final design.

System voltageThe system should operate safely at a peak voltage of 55 volts.

Power

The hybrid power train must be able to endure a 10 hp input power over the course of a 4-hour race.

SizeDesign the system for a space of six cubic feet.

Weight

Net weight gain of less than forty pounds.

Approaches Considered and Used

This section summarizes the technologies and technical approaches considered for this design.

Technologies

Various technologies were considered for each component, as discussed below.

Motor and Generator

Permanent magnet, axial flux Etek DC motors from Briggs and Stratton

Advantages:

The lightest (21 lbs) and most efficient (~91%) motor in the teams price and power range. Relatively inexpensive at $400. DC motor controllers are much less expensive than those for AC motors. Using a DC generator and motor requires no inverter to convert AC electricity.

Disadvantages:

Available in only one size and power rating.

Controller (DC-DC Converter)

Alltrax 7245 motor controller, 24-72 VDC, 450 A

Advantages:

Common (used in golf carts) and inexpensive ($500). High voltage and current ratings will help resist overheating. Maximum current protection. Programmable and waterproof.

Disadvantages:

Originally designed for use with battery packs.

Battery pack

No energy storage integrated in system because SAE rules prohibit stored energy at race start.

Theoretical advantages:

Excess electrical power could be stored when it is not demanded by the driver and then used later to effectively increase the vehicles power.

Disadvantages:

Not within competition rules.

Rectifier

Not necessary for converting AC current because DC motor and generator were used.

Technical approach Simulation

Computerized testing was accomplished without the purchase of any expensive components. Presumed to be an easy way to approximate the total design, but turned out to be more difficult than initially predicted. SimPower and Simulink software were used.

Advantages:

Ensure compatibility of components. Test whether design will operate near desired performance levels.

Disadvantages:

Some component parameters were not published and instead had to be estimated. Some real world factors might not have been included in the simulation.

CAD Model

Not used. These models would have helped to visualize the physical components and how they fit together in space. However, the Baja team instructed that it could create the models once the system was designed.

Advantages:

Ensure design will fit properly in vehicle.

Disadvantages:

Time and resources needed to produce the models.

Electrical schematics

The schematics proved to be a good way to organize the design of the electrical system. They also helped to keep records for future work. The schematics were created in the simulation software mentioned above.

Advantages:

Provided clear diagrams of the drives functionality. Should assist with future repairs or troubleshooting of electrical system.

Disadvantages:

Schematics must be updated regularly or will soon become out-of-date.

Detailed Design

General Overview

Figure 2 shows a detailed system layout, the basis of which was the series hybrid architecture shown earlier in Figure 1. That initial design was modified to meet the specific requirements of this project. For simplicity, the generator was changed from an AC source to a DC generator, removing the need for the rectifier. The use of a DC generator also increases the efficiency of the system as rectifier losses are eliminated. The controls box from Figure 1 became the buck chopper block and its controls, which together form the motor controller. Test points were added to Figure 2, allowing for instrumentation and system safety features. Lastly, the transmission of Figure 1 was removed, and the final design will only require a simple chain reduction to the drive axle. Overall, the design remains a basic series setup, but with some necessary changes in response to the projects specific requirement.

Figure 2: Detailed electric drive design

This diagram shows the flow of power from the 10 hp engine through the system to the wheels and how this power is controlled by the user. First, the mechanical energy from the engine is converted to electrical power by a generator. Before reaching the motor, it travels through a controller that lowers the voltage proportional to the depression of the drivers accelerator pedal. If the pedal is fully depressed, no voltage reduction will occur. The electrical energy sent to the DC motor is converted back into mechanical energy where it drives the wheels. Auxiliary features of the system include some testing points to ensure proper operation.

Engine and Motor

For the simulation, a model for the gas engine and the electric motor were found in the block libraries. After the appropriate parameters are entered, the model will simulate the expected outputs. Figure 3 shows the engine model while Figure 4 shows the motor model.

Figure 3: Model of a gas engine in Simulink

Figure 4: Model of a dc motor in SimPowerBuck Chopper

The buck chopper was more difficult to model because no pre-constructed block was available. Instead, one was built from individual electrical components. The general design was taken from Introduction to Power Electronics, by Hart. The design is shown in the figure below.

Figure 5: DC-DC Buck Chopper

(a) Diagram of DC-DC Buck Chopper

(b) Equivalent for switch closed

(c) Equivalent for switch open

The potentiometer would be connected with the buck chopper in order to control the duty ratio

During simulation, it was found that the values for the capacitor, inductor, and load are crucial and will affect the output greatly. The book gave some equations that were used to set general values for this model. These are only the basic DC equations; the differential equations were not necessary for determining L, C, and R.

Parameters:

R:

load resistor

L:

inductor

C:

capacitor

D:

duty ratio

f:

switching frequency

Vripple:

output voltage ripple in relation to input voltage

Vo:

output voltage

Vs:

input voltage

Using these equations, the following values were calculated. The team wrote a small program in C to calculate the values below.

L = 400 uH

C = 100 uF

R = 20 ohms

Component Specification

Engine

The engine used in the Baja car, as stipulated in the SAE rulebook, is an unmodified, 10 hp (nominal), single cylinder, air-cooled, four-stroke Briggs and Stratton model. The rules also specify a maximum governed engine speed of 3800 rpm. As shown in Figure 2, the engine rotates the generator to deliver a voltage and current output. This engine is provided by the Baja team and no cost will be assigned to the design team for its use.

Generator

The second stage in the system is the generator. The design team has chosen to use an Etek motor as the systems generator, because it has been demonstrated in the past to provide good regeneration abilities. The generator will supply a continuous output power of 6.62 kW at 53 V to the controller, an efficiency of approximately 91%. A switch was included the open circuits the generator, removing any load from the engine at times when the car must be idled for long periods of time.

Motor

The motor is also an Etek model obtained from Briggs and Stratton. As mentioned earlier, it is of a brushed, permanent magnet, axial flux design. While standard motors use stacks of steel laminations around which copper wire is inserted or wound, the Etek motor uses copper bus bars as the basic building block of the armature. These copper bus bars are stamped, bent, coated and assembled into a thin rotary disk. Unlike conventional motors, the commutator of this motor is produced by simply machining the edges of the copper bars, eliminating the need for an additional assembly. Neodymium magnets provide three times the magnetic force of an equivalent ferrite magnet in this permanent magnet motor.

Once integrated into the hybrid system, this motor will output a power of 6.00 kW and a torque of 16.15 N*m, also at an efficiency of 91%.

Accelerator Pedal

Required by SAE rules to be foot-operated, this is the drivers control of the speed of the vehicle. The pedal will be attached to a potentiometer, which in turn modifies the buck choppers output.

Voltage and Current Meters

These meters are used for troubleshooting and monitoring. For high-current applications such as this, these devices will cost in the range of $300 to $400.

Speedometer

A digital speedometer is desired to record actual wheel speed, which can then be compared to monitored electrical values to develop and improve the systems performance. This can also be used to compare actual results to estimated results. A speedometer costs approximately $100.

DC-DC converter

A DC-DC converter, or DC motor controller when it is used to drive a motor specifically, accepts a DC input voltage and produces a DC output voltage at a different voltage level. The design team used a buck chopper, which is a step down DC-DC converter. The buck chopper allows the design team to control the voltage being provided to the dc motor, and thus by altering the duty ratio of the buck chopper, the speed of the motor can be controlled. The buck chopper has an input voltage of 53 Vdc and an output voltage range of 0 to 53 Vdc. The step down dc-dc converter used in this system costs approximately $500.

Figure 6: Basic PWM IC DC motor controller schematic

Implementation Process Description

This design team did not do any actual implementation of the power drive system that was designed. However, as previously mentioned a simulation was made of the power drive system to make sure that the parts and design were compatible and could meet the requirements.

As mentioned under the technical approach section the project was implemented using Simulink in MATLAB as a basis for the simulations. The team made extensive use of the SimPower library, which was purchased for this purpose. The model for the gas engine and the dc machine, which were used, were found as built in models. Values for this specific project are needed as parameters of those devices for the simulation. A model for the buck chopper was not available and therefore was built by the team. The specifics of this model are described in the detailed design section.

Throughout the simulation, several problems were encountered. The first problem that was encountered was the acquisition of the SimPower software. The software took longer to obtain and install than initially planned. This prompted the design team with a time problem by shortening the time the design team had to do the simulation. This problem was taken care of by splitting up sections of the simulation among the team members in order to get the simulation done more quickly. A second problem was in the use and functionality of SimPower, which was not quite what the design team had in mind when it was purchased. The software contained built in power drive system models with controls and all, but they were not used due to the fact that the team could not modify the existing models enough to properly simulate this design teams power drive system. This problem was overcome by researching SimPower and building some of its own models, as mentioned above. Another problem was the lack of help for Simulink and SimPower. Whenever the design team ran into a small problem or was unsure how to do something related to the simulation there was no outside help. The team could not find another individual within the University that was well enough acquainted with these software libraries to guide them through the problem/question. This was probably the most difficult problem faced by the design team and was overcome by many hours of online research and going through online tutorials.

The process may have been improved in several ways. The first would to be to speak with other people that have done work in this area or had experience with different simulation software. This would help to ensure adequate resources or expertise when working on the project. The second major way that would help implementation would be to start the process of getting the simulation software sooner. Valuable time was lost waiting for the software and trying to get it installed onto a computer that the whole team could use. Research was placed in other simulation software, namely Simplorer and Advisor. These software simulators are often used in the industry for simulation of hybrid vehicles. Unfortunately, the design team was unable to obtain either of these due to cost restrictions. For example, a license for Advisor costs 5000.

End-Product Testing Description

The theoretical performance of the hybrid drive was compared to that of past Baja cars through efficiency and acceleration calculations. It was predicted that the overall engine driveshaft to motor output shaft efficiency is 82.6% with an output torque of 16.15 N*m and an output power of 6.00 kW. The fastest-accelerating Baja cars from last years competition only put an average of 4.32 kW of power to the ground during their top-scoring runs. This suggests several observations worth noting:

1. Mechanical drive trains are not ideally efficient with their belt-driven CVT transmissions and duel chain reductions.

2. The hybrid-electric car has a strong chance of performing as well as a mechanically powered car; especially near zero wheel RPM where a motor displays high torque, but an engine possesses no torque.

The end product was also tested using Simulink and SimPower in MATLAB. Values for parameters that correspond to real life available components were entered and used in the simulation runs.

The team first simulated a dc-dc generator (step down) or a buck chopper. The design team used an Insulated Gate Bipolar Transistor (IGBT) switch along with a pulse generator. These two work as a switch, which opens and closes at given rate. A diode, capacitor, inductor and resistor were used from the SimPower library. SimPower does not have independent registers or capacitors. It only has series and parallel RLC circuits. Thus, the team had to set certain values at zero and infinity to obtain independent L, C and R parts.

Figure 7 shows the simulation diagram for a buck chopper. When the simulation is run with a duty ratio of 0.5, an output as shown in Figure 8 is attained. Make notice of the very little ripple in the output voltage.

The maximum and minimum values accepted by the buck chopper as duty ratios are .99 and .1.In the practical sense a 0 duty ratio would mean no voltage and a 1 duty ratio would correspond to the maximum voltage

The parameters that were used in the above simulation are as follows:

L= 400 uH

C= 100 uF

R= 20 ohm

Figure 7: Model for dc-dc buck chopper in SimPower

Figure 8: Output plot of dc-dc buck chopper given in Figure 7 The above figure shows the Vout when the duty ratio is set at 0.5. Thus, an input voltage of 50V is reduced to an output Voltage of 25 V. The successful simulation of the buck-chopper made it possible for the design team to go ahead with the simulation of the entire system, including the dc motor, since the buck chopper would now function as a controller for the motor.

The team then designed a subsystem, which consisted of a dc motor connected to an external reference load torque. The simulation of this subsystem enabled the design team to study the change of motor speed with respect to change in the load torque.

Figure 9: Model of DC motor with variable load in SimPowerDuring the simulation of this system, the team varied the torque at different intervals and obtained the results in the following graph.

Figure 10: Simulation Result for motor with different loads

The graph clearly shows the change in speed with change in torque. The team set the initial torque at 10 Nm, then changed it to 5 Nm and then finally changed it to 40 Nm. The speed increases when the torque changes from 10 Nm to 5 Nm and then decreases when the torque suddenly increases to 40 Nm as seen in the top graph.

The next test was to run the complete system together with the controllers and the motor to test if the model was accurate. Dr. Ajjarapu asked the team to simulate the system with a given set of values to obtain a speed of 12.7 radians per second. This test was basically to determine the correctness of the system. The simulation model attained a speed of 12.709 radians per second, which was very close to the theoretical values.

Figure 11: Buck chopper and motor together running off generator idealized as a voltage source

Figure 12: Simulation of Figure 11 with no load

The above graph shows that at the end of 0.5 seconds the system attains a speed of 12.709 radians per second.

The next test performed by the design team was done to check the controls used to control the speed of the motor. The objective was to vary the duty ratio of the buck chopper, which in turn varied the voltage going into the motor. This change in the input voltage of the motor in turn varied the speed of the motor. The simulation diagram is the same setup as in Figure 11.

The team started the simulation with a duty ratio of 0.99. The duty ratio was then changed to 0.2 and finally 0.7. The results are as follows:

Figure 13: Simulation of Figure 11 with varying duty ratio on buck chopper

The graphs show that as the duty ratio in the buck chopper changes from 0.99 to 0.2 the motor gradually stops increasing in speed and gradually starts to decelerate. However, the change is only for 0.05 seconds. The duty ratio is again changed to 0.7 and the speed starts to stabilize in accordance with the corresponding voltage from the buck chopper. One may note that there is not much change in the speed after 0.2 seconds. This is because when the duty ratio is brought down to 0.2, the voltage suddenly changes and the system starts to loose speed, but soon thereafter the duty ratio is increased to 0.7. The speed still falls, as it has not reached the minimum point corresponding to the duty ratio of 0.2. It appears to fall a little bit, as there is not much difference between the output voltages produced at duty ratios of 0.99 and 0.7.

The next test was to check if the system responded to the change in load. The same simulation diagram was used. The only difference was that torque was varied. The results are shown in Figure 14.

Figure 14: Simulation of Figure 11 with varying loadThe diagram clearly indicates that as the load torque increases the speed of the motor decreases. During this test the torque was changed three times from 20 Nm to 2 Nm and finally to 40 Nm. In the above graph, the speed suddenly increases when the torque reduces from 20 Nm to 2 Nm, but as soon as the torque is changed to 40 Nm the system starts to decelerate.

The above test clearly indicates that our model is able to simulate an electric drive .The design team has the option of changing the parameters of any component it wants depending upon the specification of the component.

Project End Results

The first phase of the Baja hybridization project is almost completed.

The design stage of this phase is finished. The block diagram design, shown in Figure 2, will successfully meet the requirements set by the client. The SimPower modeling is done, with models for the buck chopper and motor simulated and tested. The generator, as previously mentioned in the Assumptions section, is being modeled as an ideal voltage source for the time being.

Work continues on producing additional simulations with more accurate, real-world component parameters. Components that should work in this design have been found, but some specific parameters about these components are not yet known. Specifically, this is true for several parameters for the DC motor required by SimPower, which were not listed on the motors datasheet.

Because the DC-DC buck chopper model created for simulation is a simplification of the actual commercial controller design, parameter values are approximate. However, the end result should prove accurate, with the primary difference being the internal complexity of the two devices, as seen in Figures 5 and 6 above.

With simulations boding well for the future performance of the hybrid system, the team will now begin to work on extensive product documentation to ease the construction process for the Baja team.

Resources and Schedules

The project proceeded while keeping the following requirements in mind:

Personnel effort requirements

As shown in Table 3, group members Daniel Robinson and Jeremy Boon worked 87 and 85 hours respectively. These hours are about half as much as the other members because they only worked with the project for one semester instead of a full year. Group members Godwin Itteera, Doug Milewsky, Nicholas Olson, and Rajdeep Wadhwa worked 158, 161, 164 and 170 hours for the academic year. Chris Zach joined for the second semester and worked 92 hours. Like Robinson and Boon, Zach is only working on this project for one semester.

Other resource requirements

The team had access to the SAE shop, free of charge, as needed. The team used SimPower to simulate the hybrid drive system.

Financial requirements

As shown in Table 9, the estimated total cost of the project, including student labor, is $11628.50.

Personnel effort requirements

The project is divided into 8 different tasks:

Task 1 Project Plan

Plan Project9/6/2004-9/17/200412 days

Revise Project9/20/2004-10/5/200411 days

Task 2 Paper Work

Weekly ReportsUnbound Design Report10/18/2004- 11/9/200418 days

Status Report10/18/2004-11/9/200418 days

Revised Design Report11/15/2004 -12/15/200422 days

Final Design Report 3/11/2005 4/1/200516 days

Task 3 Component selection

Research9/6/2004-10/4/200420 days

Set specification9/27/2004-10/8/200410 days

Select Components10/25/2004-3/18/200593 days

Task 4 Map power and efficiency thru drive

Block diagram9/27/2004-10/8/200410 days

Mathematical Diagram10/4/2004-10/15/200410 days

Task 5 Circuit diagram

Research9/6/2004-10/4/200420 days

Define system9/27/2004-10/8/200410 days

Design10/25/2004-3/4/200585 days

Error check and Compatibility1/24/2005-4/1/200555 days

Task 6 Control System

Research9/6/2004-10/4/200420 days

Design Control system9/27/2004-10/22/200420 days

Task 7 Simulation

Develop model10/18/2004-3/25/200490 days

Test specifications1/24/2005-4/1/200544 days

Task 8 Design poster

Design poster11/15/2004-12/15/200418 days

Table 1: Original Group Schedule. Breakdown of hours by team-member by task

Group memberTask 1Task 2Task 3Task 4Task 5Task 6Task

7Task

8Task 9Total

Godwin Itteera102040040200520155

Doug Milewsky10202000010450159

NickOlson11200010000520156

Jeremy Boon92002500052584

Daniel Robinson202002000052085

Rajdeep Wadhwa14110040068520158

Total Hrs6611160451802017230105797

Table 2: Revised Group Schedule. Breakdown of hours by team-member by task


7Task

8Total



NickOlson11202404232305164




Total Hrs74121155458213419230833

Table 3: Final Group Schedule. Breakdown of hours by team-member by task


7Task

8Total



NickOlson112624036282910164




Chris

Zach03326010023092

Total Hrs74154181459013221630922

As shown in Tables 1, 2, and 3, there are several tasks designated throughout the year. The hours specific to each task and team member can easily be seen in the right most and bottom most column and row respectively. The total number of hours is in the lower right corner.

Other resource requirements

Upon completion of the design phase, the design team has been focusing on the simulation/testing of the electric drive. The power lab, which is a part of the electrical engineering department, is where the simulation software has been installed and all the simulation hours as indicated in Table 6 have been spent. The Baja team is also willing to let the senior design team use their shop facilities.

Table 4: Original Other Resources. This table shows other resources that will be utilized

ItemTeam hoursOther hoursCost

Poster120$50

Power lab4000

Baja Shop3500

Totals870$50

Table 5 Revised other Resources. This table shows other resources that will be utilized


Poster120$50

Power lab13000

Baja Shop3500

Totals1770$50

Table 6 Final other Resources. This table shows other resources that were utilized


Poster120$50

Power lab20000

Baja Shop3500

Totals2470$50

Financial Requirements

The financial budget is presented in Tables 7, 8 and 9. The SAE Mini Baja team funded a major part of the project. The costs for the poster were covered by the student design team. The design teams advisor, Dr. Ajjarapu provided some reference materials.

Table 7. Initial cost estimates

ItemW/o laborWith labor

Parts and Materials

Poster$50$50

Motors ( two)$418$418

Briggs and Stratton engineDonatedDonated

Rectifier unit$40$40

Alternator$25$25

Subtotal$533$533

Labor at & 10.50/hr

Godwin Itteera $1627.50

Doug Milewsky $1669.50

Nick Olson$1638.00

Jeremy Boon $882.00

Daniel Robinson $808.00

RajdeepWadhwa$1659.00

Subtotal$8284.00

Totals$533$8817.00

Table 8. Revised cost estimates


Parts and Materials

Poster$50$50

Generator$10000$10000

Motor$8000$8000


DC-DC Buck Chopper$3500$3500

Testing Equipment$500$500

Misc.$250$250

Subtotal$22300$22300

Labor at & 10.50/hr



Nick Olson$1722.00

Jeremy Boon $892.50



Subtotal$8746.50

Totals$22300$31046.50

Table 9. Final cost estimates


Parts and Materials

Poster$50$50

Generator$400$400

Motor$400$400


DC-DC Buck Chopper$500$500

Testing Equipment$400$400

Misc.$250$250

Subtotal$2000$2000

Labor at & 10.50/hr



Nick Olson$1722.00

Jeremy Boon $892.50



Chris Zach$966.00

Subtotal$9628.50

Totals$2000$11628.50

Schedules

These schedules show the transition of how progress was made on different tasks. All the lines represent one of the eight tasks listed above. Except for the removable of battery task, the schedule has stayed close to the original. This means that not much change was needed to the schedule was needed and the original timetables were adhered to closely. The table showing the deliverable schedule is listed after the charts. It shows that the deliverables will be on time.

Figure 15: Original Gantt Chart. The chart above shows the necessary order of operation graphically

Figure 16: Revised Gantt Chart. The chart above shows the necessary order of operation graphically

Figure 17: Final Gantt Chart. The chart above shows the necessary order of operation graphically

Table 10. Deliverable ScheduleDeliverablesDate DueDate Delivered

Bound final report due5/3/20055/3/2005

Simulation for client5/5/2005*5/5/2005

Report for client5/5/2005*5/5/2005

*Will be delivered on that date

Closure Material

Project Evaluation

In order to evaluate the success of the project as a whole, measurable milestones were first identified and briefly described. These milestones were assigned a relative importance of high, medium, or low. This importance rating was converted into a percentage of the total project's success, as shown in Table 10.

Table 10. Evaluation process

NumberMilestoneDescriptionImportanceImportance %RatingScoreProduct

1Problem definitionDefine project goals, scope, description, structure, and deliverablesHigh17.00%Met100%17.00%

2ResearchInvestigate current state-of-the art regarding technologies employedHigh17.00%Exceeded100%17.00%

3Technology selectionChoose the best technologies and components to employ in the designMedium11.00%Met100%11.00%

4Design SimulationSimulate the system architectureMedium11.00%Met100%11.00%

5Performance comparisonCompare theoretical performance of hybrid Baja car to past mechanical versionsLow6.00%Partially met80%4.80%

6End-product designOverall result of the project in meeting the goals of the definitionHigh17.00%Almost met90%15.30%

7End-product documentationCreate a comprehensive report with all specifications necessary for client to construct systemMedium11.00%Partially met80%8.80%

8Project reportingCommunicate weekly the progress of the project with the advisor and clientMedium10.00%Met100%10.00%

Total100%94.90%

The research milestone was rated as exceeded because of the number of hours spent thoroughly investigating all options for component technologies and simulation software. The performance comparison milestone was ranked partially met because, although complete calculations were made, no physical hybrid car was tested to verify these predictions. The end-product design milestone was rated almost met, with the one shortcoming being that no CAD drawings were created to assist the team in building. The end-product documentation milestone was ranked partially met for a similar reason: no engineering drawings were created to document the system layout at a highly detailed level.

Next, the milestones were evaluated non-numerically to determine to what degree they were completed, and these values were then converted to percentages (see). The first scoring method, with no ratings over 100%, was used for this project. The weighted rating for each milestone was calculated by multiplying the importance and score percentages.

Table 11. Milestone success scoring

RatingScore IScore II

Greatly exceeded100%120%

Exceeded100%110%

Met100%100%

Almost met90%90%

Partially met80%80%

Did not meet40%40%

Did not attempt0%0%

The total project evaluation resulted in a score of 94.9%, so the project was considered a success.

Commercialization

Commercialization is not a logical future path for the hybrid drive system, at least in its current form. The product was designed specifically to comply with SAE rules for the Mini Baja competition. If a similar product were developed for the commercial market, many changes would need to be made to increase its competitive advantage. In fact, a hybrid drive system provides a negligible advantage, in any form, in the commercial recreational vehicle market. Unlike the automotive market, the sale of motorcycles and ATVs is rarely driven by fuel consumption figures. Hybrid drive adds to the sale price of a machine, and there are no government tax breaks to subsidize its purchase as with a hybrid automobile. For reference, the hybrid system in the Baja car would add approximately $2000 to the purchase price of the vehicle. With the original target price of a Baja car being only $3000, this is a price increase of 67%, enough to remove the purchase from the reach of most buyers.

Additional Work

Three general paths exist for the future of this project. First, if another design team or the client desires to continue pursuing a hybrid drive system for use in competition, a prototype car can be built for testing. Second, some of the same technologies utilized in the hybrid system could be employed in a unique manner to create a different vehicle propulsion method. Alternatively, the project could be closed and no further activity be conducted.

A full-scale prototype is the next milestone in this project for a team wishing to continue along the current path. Before a prototype can be a built, however, the decision must be made whether to integrate an ultra capacitor pack into the car. If this is desired, then the system design should be modified and an ultra capacitor-based energy storage system inserted between the generator and motor controller. Additionally, protection circuits, such as maximum and minimum voltage levels and maximum current draw, would need to be engineered to protect the ultra capacitor pack from damage.

The most efficient and cost-effective way to build a prototype hybrid Baja car would require converting a previous year's car rather than constructing a new one specifically for this purpose. In addition to saving money and time, this approach would allow for a direct comparison of performance figures between the original configuration and the new hybrid configuration. If a new car was built, it would undoubtedly differ in many aspects from any previous car, since the car is completely redesigned for each competition season. Once the Etek motors and Alltrax controller were obtained, conversion of the car could begin.

After completion of prototype construction, extensive testing would be necessary before the car would be used in any competitions. This testing would be divided between performance- and endurance-type. The former involves acceleration and top speed runs and lap timing around a motocross track. The latter is composed of tests with longer duration, the minimum test length being four hours, or the length of the endurance race during competition. During this endurance test, temperature-based data acquisition would be desired from the motor, generator, controller, and ultra capacitor pack (if present). A post-test teardown would also be recommended to investigate for any problematic wear issues.

Other unique drive train possibilities exist for the team if they wish to create a car for a purpose other than competitive use. The most obvious of these is to employ a battery-based energy storage system and create a hybrid more similar to urban bus-types. Another possibility is an all-electric, plug-in Baja car which provide smooth and quiet propulsion in areas where gas engines are not approved.

The alternative to the additional work suggestions above is to suspend any further engineering and close the project, either temporarily or permanently. Several arguments could be made for this approach. First, the integration of such a hybrid system in the Baja car, while innovative, would be nearly impossible in accordance with the cost outlines included in the SAE rules. The intention of the team, according to the rulebook, is to produce a car that could be mass-produced at a cost under $3000, as mentioned earlier. Even in a mass-production environment, achieving this low of a product cost is highly unlikely. The addition of an ultra capacitor pack, because of their especially high cost, would make this goal impossible. Since the energy storage ability of the ultra capacitors is necessary to give the hybrid design any performance advantage over traditional cars, the only reason to implement the storage-less design would be for engineering points at competition.

Lessons Learned

Like any challenging project, the teams success in its work varied up and down, but many important lessons were learned, both technical and non-technical.

The design of the drive system concept progressed very smoothly and successfully for the team. After some research, the design team discovered there were two primary options for how the drive system could be built, series or parallel. The design team decided to employ a series setup because a parallel hybrid would be useless without energy storage capabilities. The design team selected all the pertinent parts and laid out a fairly straightforward design for the power drive system. Since the first design there have only been a couple changes made, most of which were minimal and only for protection purposes, like the overload circuit.

As mentioned in the Implementation Process Description, the first and primary problem was the acquisition of the MATLAB software library of SimPower. Acquiring this software did not proceed smoothly because it took much longer to obtain the software than the design team had anticipated. Then, once the software was obtained, new problems emerged with getting the software installed.

Technical knowledge gained while completing this project included the latest in hybrid technology and a working knowledge of power electronics simulation software. Some specific parts, such as the buck chopper and DC motor, were most challenging and provided the most valuable experiences. The design team learned how buck choppers functioned, how they are used, and how they are controlled. The design team learned how to derive values from the motor equations and how to evaluate DC motor efficiency, cost, performance, and loads. The team also gained in-depth knowledge of the Simulink and SimPower software libraries and their limitations.

Along side all the technical knowledge that was gained was also some non-technical knowledge. This knowledge was in the form of learning about the format of good reports and a little bit on how to deal with real world clients. For writing reports, the design team learned what a project plan, design document, and final document were, what goes into each of them and what importance they play. As far as dealing with clients goes the design team has talked to a member of the Mini Baja team several times in order to make sure we had the correct requirements for the project.

If this project were repeated, the design team would desire clearer initial design requirements and would begin acquisition work sooner. Early in this project, the problem statement was very muddled and the first few weeks were spent trying to meet with the Mini Baja team to clarify their goals in this project. Acquiring materials sooner would help prevent a lack of work available later in the project, as team members sit and wait for necessary tools to arrive.

Risks and Management

The risks encountered in this project can be divided into two groups for analysis: those that were anticipated and managed in advance, and those that were unanticipated and were dealt with upon occurrence. These categories are shown below in Tables 12 and 13, respectively, along with the management outcome from each risk.

Table 12. Anticipated risks

Anticipated RisksPlanned ManagementOutcome

Full-scale prototype is too costly to manufactureConsider scale model to allow for hardware development at a reasonable costScale model also proved too expensive to develop

Real world reliability of the system is unknown because no prototype is testedSelect components that have been widely used by others with demonstrated reliabilityComponents chosen have been used in many electric vehicles

Software for virtual development is not present and expensive to purchase Have ISU acquire SimPower softwareDr. Ajjarapu acquired SimPower early in second semester

The cost of the system exceeds the budget of the customerKeep costs as low as possible to increase affordability for customerRelatively inexpensive components were eventually identified after high estimates initially found

The customer is unable to support and troubleshoot the system independentlyLeave client detailed design/schematic/documentationSystem documentation is currently in progress

The hybrid system fails to outperform the Baja car's current drive systemInform team thoroughly prior to any expenditures of realistic expected system performanceUnlikely that team will proceed to build full-scale prototype

Replacement of team members results in lost knowledge and a duplication of effort Share information with all team members, no one member works on any major task aloneSmooth transition between team members achieved

Table 13. Unanticipated risks

Unanticipated RisksAdopted ManagementOutcome

SimPower took longer to acquire than expectedRelied initially on hand calculationsand some use of SimulinkAble to progress on design despite lacking desired software tools

SimPower capabilities more limited than anticipatedSome blocks were created manually rather than pulled from existing libraryAble to use a combination of existing and custom blocks to model system

Lack of expertise in SimPower availableSpoke with experienced graduate student and referred to Internet for supportEventually became fluent with software after education and practice

Project Team InformationActing client:

Ethan Slattery

Project Manager 2004-2005

ISU SAE Mini Baja

1306 Iowa Cir

Ames, IA 50014

Cell: (641) 821-0202

[email protected]

Faculty advisor:

Dr. Venkataramana Ajjarapu

Office: 1122 Coover

Ames, IA 50011

Home: 2704 Valley View Rd

Ames, IA 50014

Office: (515) 294-7687

Home: (515) 292-3887

Fax: (515) 294-4263

[email protected]

Team members:

Chris Zach

Mechanical Engineering

119 Stanton Ave. #605

Ames, IA 50013

Home: (515) 708-1135

[email protected]

Godwin Itteera

Electrical Engineering

4290 Birch Lange

Ames, IA 50013

Home: (515) 572-3559

[email protected]

Douglas Milewsky

Computer Engineering

3218 Lincoln Way

Ames, IA 50014

Home: (515) 268-1569

[email protected]

Nicholas Olson

Electrical Engineering

4138 Fredericksen Ct

Ames, IA 50010

Home: (515) 572-7880

[email protected]

Rajdeep Wadhwa (Team leader)Electrical Engineering

4112 Lincoln Swing #216

Ames, IA 50014

Home: (515) 441-0284

[email protected]

Closing Summary

Two semesters ago, the ISU SAE Mini Baja team desired a modern, innovative drive system for one of its future cars. For this task, they turned to a senior design team composed of electrical, computer, and mechanical engineering students. The team was posed the challenge of integrating a hybrid-electric drivetrain into an off-road racecar typically powered by an automatic belt-driven transmission and chain reductions.

A series hybrid drivetrain concept was chosen as the best solution to this project. In this layout, the gas engine spins a DC generator whose output current is routed through a controller and on to the DC traction motor. This system has been researched, its components selected, and its performance both predicted through calculations and through simulations. Next, the design team will hand over full documentation of the system to the client, the Baja team, so that they can examine the project results and decide whether to pursue a prototype in the next year.

The design team believes that a hybrid-electric drivetrain integrated into a Mini Baja car, if built as engineered in this project, would provide a valuable distinction amongst a sea of similar vehicles at competition. The Iowa State car would possess unique powertrain architecture and could profess itself as one of a kind. However, the cars engineering design is not the only feature that would win it points. Its performance on the track would be point deserving, also, impressing spectators and sending other teams running for their textbooks as they rushed to catch up with the innovations at Iowa State.

References

Hart, Daniel. Introduction to Power Electronics. New Jersey: Prentice Hall, 1997

http://students.sae.org/competitions/minibaja/

http://www.4qdtec.com/pwm-01.html#simple

http://www.briggsandstratton.com

http://www.maxwell.com/ultracapacitors/index.html

http://www.public.iastate.edu/~isusae/Baja/

http://www.thunderstruck-ev.com/

Pearman. Electrical Machinery & Transformer Technology. Orlando: Saunders College Publishing, 1994.

DC generator

Buck chopper (DC-DC converter)

DC motor

Gas pedal

Potentiometer (controls duty ratio of chopper)

Throttle lever

Voltage and/or current meters

Overload circuit for safety

Speedometer

10 hp engine provided

Wheels

Driver

Output for testing/ operation

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bound final report

Documents

simulation of figure

simpower16 figure

simpower9 figure

simulink9 figure

load19 figure

buck chopper figure

dcdc buck chopper13

dcdc buck chopper10