BLDC Motor Controller for EV Scooter
Proposal
Members:
Logan Fegenbush
Karun Vijay
Yun-Hao (Eric) Hsieh
Ming Lin
Abstract
Design, build, and demonstrate a three-phase motor drive train for use in electric transportation.
The goal is to create an electric drive train powerful enough to power a scooter using brushless DC
motor and high capacity batteries.
Overview
Using a brushless DC (BLDC) motor, a passenger will control the motor speed on an EV
scooter through a handle bar “throttle.” A BLDC motor is a highly efficient three phase motor that uses
digital switching to simulate a conventional DC brushed motor. In order to implement this design, a
BLDC motor requires a pulse width modulated (PWM) signal divided into three separate phases, each
being 120 degrees out of phase with respect to the other two. Also, each phase will have an inverted
signal resulting in 6 total PWM signals. These PWM signals will be generated via a PIC I/O board.
The motor speed will be adjusted via variable frequency. In other words, the low frequency
carrier of the PWM signal will be adjusted from 0 Hz to ~200 Hz, depending on the electrical cycles
per RPM of the BLDC motor. At 0Hz, the PWM signal will be resting at a 50% duty cycle. The PWM
frequency will be at least 10 times that of the low frequency carrier.
The three signals are then used to drive insulated gate bipolar transistors built as an inverter
stage in order to deliver high amounts of power into the motor coils.
Finally, hall sensors on the motor return rotor position back to the PIC board in order to correct
for EM slip and report motor speed as well as rotor position.
Scooter Specifications
-100% battery powered
-BLDC motor between 1000W & 1500W ~(48V, 30A)
-Speed controlled through a potentiometer (variable frequency)
-Projected speed of at least 30 MPH
-20 minute runtime between charging at full speed
-At least 80% power efficiency from battery to motor
Projected Components
What follows is a basic block diagram of each component required for the motor control. Also,
a summary of the purpose of each component will be included.
Accelerator
Pot
Pic
Controller
D.C. Battery Array
Gate
Drivers
Inverter
Hall Sensor Feedback
BLDC
Motor
Battery:
The battery must be able to source at least 35 amps at 48V. Li-poly batteries are light and more
than capable of providing the specified current at 10Ah capacity. Cost effective li-poly packs have been
found for purchase rated at 48V and 15 Ah.
PIC Controller:
This stage generates 6 separate PWM signals of three phases, each a pair of inverted signals.
The PIC controller will also receive feedback from the hall sensors as voltage highs and lows. The
feedback is used to correct for electromagnetic slip and give rotor position and speed. The PIC receives
as input an analogue voltage directly from the “throttle” of the scooter. This will adjust the RPM of the
motor.
Gate Drivers:
This stage is a level shifter/amplifier for driving the IGBT gates. The output from the PIC
controller is expected to be logic 5 volts. In order to turn the IGBTs hard on and hard off, the voltage
will have to go from 0 volts to DC+ or DC- or as the specifications of the inverter stage require.
Inverter:
This is a high powered output stage that will deliver the power to the three different legs of the
electric motor. It will consist of 6 IGBTs of three pairs, each pair delivering DC+ or DC- to a single
coil. Only two transistors will be on at any given time except during transition periods. The IGBTs
must be able to handle power up to 1500 watts.*
BLDC Motor:
Brushless 3 phase motor over 1 horse power. Maximum RPM should be somewhere between
2500 and 4000.
Hall Sensor:
This is a small ring on the back of the BLDC motor which detects the position of the permanent
magnets on the rotor of the motor. The output of the sensor is 0V or Vhall (the dc voltage of the
sensor). This data is fed back into the PIC controller on three separate wires, each one being a hall
phase. The PIC controller can use this data to adjust the motor speed and rotor slip.
*MOSFETs may be used in place of IGBTs, if low voltage IGBTs cannot be found.
Timeline
Fall 2007
Website Construction
Component Selection
Approximate System Interconnection
Design and Testing of Gate Driver (Breadboard)
Software Simulation
Purchase Components
Detail System Layout
Design Sent Out For Fabrication
Winter 2007
PCB Assembly
Motor Testing
Begin Scooter Assembly
Integrate Components
Begin Microcontroller Programming
Spring 2008
Receive PCB
Microcontroller Programming
Testing and Debugging
Mount Components on Scooter
Compile Documents
Presentation Preparation
Completion Date
10/28/07 (0.5 weeks)
10/28/07 (0.5 weeks)
11/4/07 (1 week)
11/28/07 (3 weeks)*
11/28/07 (3 weeks)
12/1/07 (1 week)
12/9/07 (1 week)
1/20/08 (2 weeks)
2/3/08 (2 weeks)
2/17/08 (2 weeks)
2/17/08
4/13/08 (2 weeks)
5/4/08 (3 weeks)
5/11/08 (1 week)
5/18/08 (1 week)
5/25/08 (1 week)
*Gate drivers may need to be implemented using drive IC’s due to large L*dI/dt and relatively high
PWM frequencies.
Critical Tasks
The over all goal will be to complete a working EV scooter by the end of the year. The most
important step is to have the basic motor drive system working. This includes the motor, inverter,
driver, and pic controller to be working to all specifications. The first step to this goal is to select
components that will integrate well with each other. To this end the design team has already been at
work reading application notes on different PICs as well as motors and inverter drivers.
Once the components are confirmed, analysis of the system and simulations can be synthesized.
This will allow early debugging and show proof of concept that the system has a chance of success.
Once successful, the over all detailed system layout can be written. These are the primary goals for the
first quarter.
The next two quarters, the goals are more tentative. The microcontroller code must be written or
well underway by the end of the winter quarter. The code and having the PCB board assembled are the
primary concerns for the second quarter. Motor mounts and mechanical issues must be resolved on the
scooter as well.
Finally, in the spring quarter, the final overall build of the scooter will take place. At this point,
the electrical system should be near complete and operational to spec. Any final mechanical issues will
be resolved, and the scooter will be tested for basic functionality. All documented work will be
compiled into a presentation, including pictures and schematics, and presented at the end of the year.
Design Team
The members of the design team are all electrical engineers with experience in circuits, signal
processing, and electromagnetic theory. Each member has his own unique ability and background to
add to the project's success
Logan Fegenbush
Logan is experienced in circuit design, including music amplifiers. He also has an
educational background in electromagnetic field theory. He has worked on industrial VFD
motors as an electrician.
Ming Lin
Ming had taken basic analog circuit design and some digital design courses. His lab
experiences includes fiber optic links, basic amplifier and basic processor.
Yun-Hao (Eric) Hsieh
Eric has both analog and digital circuit design experience. He is also familiar with digital
system programming and architecture design.
Karun Vijay
Karun is an experienced circuit designer and researcher with a knack for signal
processing.