Alexander Ferguson
Peter Hansen
The USF “Electro-Cycle” Project
Specifications Document
University of South Florida
Department of Electrical Engineering
EEL 4914 Senior Design Project
Spring 2014
April 25, 2013
Team Advisor: Dr. Paris Wiley
GENERAL
1.1 Scope
The general purpose of the Electro-Cycle is to produce an efficient, cost effective, and selfsustainable electric bicycle. The primary focus of our design is to facilitate traveling within a
20 mile distance, but the bike can also be used recreationally. In this specifications
document, we will outline the necessary components required to meet our electric bicycle
objective, as well as highlight some constraints that must be taken into consideration for safe
and proper operation.
1.2 Operating Conditions
One initial concern is that electric bicycle must be able to handle large I/O current and
voltage conditions of roughly 3-3.5 A and 24-28 V respectively. Given that the circuit
components must be tolerable of high current, we decided upon using short circuit rated
IGBT (Isolated Gate Bipolar Transistor) which will be able to handle well over the necessary
conditions (15A and 600V). We will also require power diodes to complement this threephase inverter network.
Commutation is a crucial part of this network due to alternating phases every 120°; therefore
certain transistors will turn on and off to allow proper current through each of the phases.
This commutation process will also need Hall Effect sensors in order to sense the position of
rotor (relative to the stator) and allow current to be supplied through the proper coil in
sequence for smooth/efficient rotation. To implement this type of controller, we will utilize
shunt resistors, as shown in figure 1, to relay ampere measurements to the microcontroller
(STM32) enabling Field Oriented Control (FOC). Fuses had been considered due to such
high readings; however, we had not decided the best location for these.
Alexander Ferguson
Peter Hansen
Figure 1.1: H-bridge circuit diagram
PRELIMARY CALCULATIONS AND SIMULATIONS
2.1 Physics Involved
Provided the bicycle is operated under ideal conditions, the following calculations can be
determined and must be taken into consideration for maximum efficiency.
The power consumed in overcoming hill resistance where 𝑀 is the mass of the rider (cargo
and bicycle in kilograms), 𝑣𝑔 is the ground speed (meters per second), and 𝐺 is the grade
(ratio of elevation change to distance traveled) can be modeled with the following equation:
𝑷𝒖 = 𝟗. 𝟖𝟏𝑴𝒗𝒈 𝑮 (𝑾)
An important variable in power consumption when dealing with electric bicycles is wind
drag 𝑅𝑤 expressed in Newtons:
𝑹𝒘 = (𝑪𝒅 𝝆𝑨𝒗𝒓 𝟐 ) (𝑵)
Using the above calculations and table below, we modeled our bicycle to serve under specified
constraints.
Alexander Ferguson
Peter Hansen
Table 2.1: Coefficient of Drag for Various Shapes
Table 2.2: Frontal Area of Certain Parts of the Human Body Riding on a 26-inch Mountain Bicycle
Rolling resistance
𝑪𝒓 = 𝑨 + 𝑩/𝑾
Table 2.3: Measured Values of Coefficient of Rolling Resistance for Various Road Surfaces
Alexander Ferguson
Peter Hansen
Table 2.4: Battery Life-Cycle Cost Comparisons
3.1
EXECUTION
To create the controller that will operate the 24V 3-phase BLDC motor, we will require a
controller, able to withstand at least 24V and 3A. Our H-bridge circuit will have to be developed
using IBJTs as mentioned above, with the correct power diodes and shunt resistors (for current
sensing capability). Our generating (charging) operation will also be performed using the same
circuit with all transistors off. The signals generated through pedaling will bypass the transistors
and feed directly into the power diodes, acting as a full wave bridge rectifier. Along with this
circuit, we will include some voltage regulation in order to keep the supply voltage for the
battery at a steady level for maximum charging.
3.2
PRODUCT
The following table lists the quantity and type of components necessary for the design
specifications for the circuit to be constructed. We plan on ordering extra in case of any
unexpected fried circuit components.
Short Circuit IGBT’s
STM32
Capacitor
Shunt Resistor (1kΩ)
555 Timer
Power diodes
QUANTITY
PRICE ($)
12
2.66
1
6.40
2
2.29
4
0.89
2
1.12
6
0.29
Table 3.1: Parts list with prices
COST ($ tax included)
33.86
6.85
4.90
3.56
2.40
1.86
Alexander Ferguson
Peter Hansen
3.3
BATTERY SELECTION
Because our underlying goal is to design the most cost-effective and efficient electric bicycle
given the time frame, we looked into different types of batteries and the different characteristics,
such as complete discharge cycle, ampere-hour rating, weight, efficiency, no load discharge, and
cost. With the selection of batteries on the market, we decided upon using two 12V lead acid
(non-AMG) connected in series. This decision was based upon the cost of the batteries as well as
the relative weight compared to other alternative batteries we researched.
4.1
CONCLUSION
Due to the complexity of the power electronics involved with properly operating the 3-phase
BLDC, we hope to create the necessary power controller to run the motor. We plan on
developing speed control when we test and verify that the motor is working. This speed control
will utilize feedback, via a PID controller to measure and adjust the speed with a thumb throttle.
We also hope to construct and test the generating circuit with successful results. This will call for
ordering the correct components so that all voltage and current signals will not overheat or
overdrive any circuitry with the motor control circuit.
5.1
REFERENCES
[1]
http://cache.freescale.com/files/32bit/doc/brochure/BB3PHCRMSRART.pdf
[2]
http://www.allaboutcircuits.com/vol_3/chpt_3/11.html
[3]
http://www.electronics-tutorials.ws/io/io_7.html