Transcript Poster - Senior Design

MOBILE POWER STATION
ABSTRACT
PROBLEM STATEMENT & SOLUTION
The Mobile Power Station (MPS) is a device that manages and stores solar energy
in a lithium ion (Li-ion) battery pack while tracking the maximum power point
(MPPT) of the connected solar array. The MPS utilizes a DC buck converter design
to control the impedance of the Li-ion battery pack and external load, allowing
maximum power transfer from source to load. Our client, PowerFilm Inc.,
expressed a need for the MPS in military and consumer markets.
Photovoltaic (PV) solar arrays can be used to power mobile devices; however, solar
array output power is non-constant and most mobile device chargers require a
constant voltage and current source.
MAIN PROJECT REQUIREMENTS
GUI
FR-01 Solar panel input – 1.2A @ 5.4V (20W) Amorphous Silicon Panel
FR-02 100W minimum Lithium-Ion battery capacity
FR-03 15V DC input (with AC-DC Adapter)
FR-04 12V DC output
FR-05 Operation in temperature range of -20°C and 60°C
FR-07 Charge Balancing Circuitry to keep Li-Ion Batteries balanced
FR-08 Achieve 80% or greater efficiency
NFR-01 MPS should have a weight of less than 5 pounds
NFR-02 MPS should be manufactured for a cost of under $500 per unit
NFR-03 MPS should easily fit inside a military backpack
A GUI was developed
to display and plot
critical data (via USB)
from the MPS
including voltage,
current, and duty
cycle.
PROJECT DESIGN
MPPT & LI-ION CHARGING CONCEPT
The basis of the MPS is a buck converter, which controls the voltage to the battery
pack, and thus the current flowing to pack. The buck convertor is controlled by
varying the duty cycle of a PWM signal generated and controlled by the MSP430.
Programmed in C code, the MSP430 follows a charging algorithm based on
feedback voltages and currents. UART communication to a PC provides
diagnostic information, and the charge controller balances the Li-ion battery pack.
Li-ion battery charging cycle includes thee phases: trickle, constant current, and
constant voltage. The charging cycle must be strictly followed to prevent battery
pack overcharge and fire.
Solar Panel
Source
Buck Converter
Voltage and
Current Sense
PWM
Control
Signal
Feedback
Voltage/Current
Sense
Li-ion Batteries
(3 series cells
x 8Ah)
Possible Loads
5VDC (USB)
12VDC
120VAC
Team dec1013 purposed building a MPS that would supply a constant voltage and
current to mobile devices, while tracking the maximum power point of a PV solar
array.
Measuring the output voltage and current of the buck converter, the MPS changes
the duty cycle of the buck converter to follow the Li-ion charging cycle. When the
MPS enters the constant current charging phase, it will also track the MPP,
providing maximum power transfer until the battery pack voltage reaches 12.6V.
The MPS will continue to hold the output voltage at 12.6V during the constant
voltage phase until the battery pack is fully charged.
Charge Control
(BQ20Z70)
Microprocessor
(MSP430)
Serial Communication
(UART) to PC
TESTING & FABRICATION
The MPS was rapidly developed and tested on a breadboard for functionality.
Next, a PCB was designed, populated, and tested with great improvements in
voltage and current sensing. The MPS was first tested with a constant power
supply, then a solar array.
SCHEDULE & BUDGET
Costs Per Unit (when ordered in units of 100)
11%
18%
21%
38%
12%
Research
Design
Implementation
Testing
Documentation
MPS components
Battery protection circuitry
Battery (3x 3.7V 8Ah Li-ion)
PCB
AC/DC input & output adapters
$
$
$
$
$
21.25
9.55
97.25
5.00
12.75
Total
$ 145.80
CONCLUSION
Team:
Brad Jensen (EE)
Will Klema (EE)
Nate Schares (EE)
Advisor:
Dr. Ayman Fayed
Client:
PowerFilm Inc.
Project ID:
dec1013
Our team designed and created the MPS, which effectively tracks the MPP of a
connected solar array while charging and balancing a Li-ion battery pack. The MPS
will provide an efficient, lightweight, and affordable source of energy for users in
remote locations, with the adaptability of charging from a non-solar source.