Transcript Design_Review - Purdue College of Engineering

ECE 477 Design Review
Team 12  Spring 2006
Eric
Aasen
Daniel
da Silva
Atandra
Burman
Sriharsha
Vengapaty
Outline
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Project overview
Project-specific success criteria
Block diagram
Component selection rationale
Packaging design
Schematic and theory of operation
PCB layout
Software design/development status
Project completion timeline
Questions / discussion
Project Overview
Maximum Power Point Tracker (MPPT) :
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DC to DC converter that converts the input voltage from a solar cell
array to the output voltage of a battery pack.
Optimum “power point” along
current vs. voltage curve that
produces power for solar array.
Our tracking algorithm will provide
control of the DC to DC converter
in order to achieve this power point.
Relay data to the telemetry unit on the solar car via the CAN bus.
Project-Specific Success Criteria
• An ability to measure pertinent voltages and currents within an
accuracy of 2% over the range of possible values [0-8A and 070V]
• An ability to send I-V and temperature data to other peripherals
via the CAN.
• An ability to switch to a "debug" mode (when an RS-232 cable
is connected) in which the I-V curve is continuously scanned.
• An ability to maintain the maximum power point of the solar
array under standardized artificial light conditions through a
high powered halogen lamp
• An ability to disconnect the solar array in response to a CAN
command.
Block Diagram
Analog
Block
Power
Block
2
5
2
Micro
5
4
Clock
2
Serial
Communication
(Debugging)
Controller
3
CAN
Address
CAN
Transceiver
5
Programming
Port
Outputs
Component Selection Rationale
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Microcontroller - PIC18F2680(SOG.050/28/WB.420/L.700)
Microcontroller
Pin Count
CAN
RAM(bytes)
Flash(bytes)
Cost
MC68HC08AZ60
64
Yes
2KB
n/a
16.00
PIC18F2680
28
Yes
1568
32K
12.00
AT90CAN32
64
Yes
2K
32K
16.00
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Power Supply - MAX1684(SOG.025/WG.244/L.200)
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Op Amp - MCP6001/2/4(SOG.050/14/WB.224/L.350)
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CAN Transceiver - MCP2551(SOG.050/14/WB.244/L.200)
Packaging Design
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The packaging would have the following dimensions:
Width = 5.210”, Length = 5.300”,Height = 2.750”
Enclosed within a 0.125” thick Foam Core
Fiberglass packaging with nearly
0.250” spacing
on both sides
Includes 80mm x 80mm x 10 mm
ventilation enclosure
Schematic/Theory of Operation
Main Block:
• Microcontroller and oscillator
• Power Supply
• Overvoltage Protection
• Headers
• CAN Interface
• SPI Shift Register and diagnostic LEDs
Analog Block:
• Voltage translators and filters
• Current sensing insight
• Output current sense
• Input current sense
Main Schematic
Microcontroller and oscillator
• Microcontroller is
interfaced with 5
analog inputs.
• It drives 3 Mosfets.
• It uses several
communication
ports.
• It uses a shift
register for
additional I/Os.
• Crystal runs at 10Mhz.
• Microcontroller’s PLL can multiply that
frequency by 4 time – 40Mhz.
• For power saving condition,
microcontroller can run at 10Mhz.
Power Supply
• 5V supply is used to supply microcontroller and peripherals.
• Expected to operate at 90% efficiency, between 30mA to 400mA.
• 4.096V supply is used as analog
inputs reference voltage.
• All amplifier also are supplied by
this voltage regulator.
Overvoltage Protection
• Disconnects solar array from power board if voltage at battery
exceeds 70V.
• Comparator’s OUT goes to 0V if Vbat ≥
70V.
• Mosfet’s source is connected to a
BJT’s base, which requires 5V to turn
ON.
• RELAY_CONTROL is disregarded in
that case.
Headers
• FAN_SUPPLY turns external fan on or off
through the FAN_SUPPLY signal.
• Programming board is used primarily
for programming.
• Header pin 1 is pulled up. This is
because it’s connected to nMCLR,
which is a low-active external reset
for the microcontroller.
• Serial Connector is primarily used for
debugging.
CAN Interface
• CAN Connectors are connected in a
parallel manner with the remaining 7
MPPT boards in the solar car.
• CABLE_DETECT is connected to
microcontroller to alert it in case of
connectors being unconnected.
• CAN Transceiver translates voltage level for
the CAN line.
• RS value changes the slew-rate for the CAN
line. RS=4.7KΩ is for rather fast slew-rate,
which can be adjusted afterwards.
• CAN Address Setup simply
inputs CAN address to the
microcontroller.
SPI Shift Register and
Diagnostic LEDs
• SPI Shift Register
accommodate extra I/Os
that would otherwise
require a larger
microcontroller.
• Diagnostic LEDs provide a visual
insight to the MPPT operation.
Analog Inputs
INPUT_V_SENSE
• Summing amplifier to translate 70V to 4.096V
• 2nd order Butterworth low-pass filter with cutoff frequency of 20 Hz
Current sense rationale
Input voltage sense
Output voltage sense
DC/DC
Converter
Solar
Array
Solar
Car
Batteries
Power board
current direction
Input current sense
current direction
GND
Output current sense
INPUT_I_SENSE
• Summing amplifier to translate -[0 to 8]A to
[0.1024 to (4.096 - 0.1024)] V
OUTPUT_I_SENSE
• Summing amplifier to translate [0 to 8]A into
[0.1024 to (4.096 - 0.1024)] V
PCB Layout
Constraints
1. Size (no more that 1.8” tall by 3.0” wide)
2. Accurate analog conversion
3. Need for high-speed signal integrity
PCB Layout
Placement Priorities
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Power
Digital
Analog
Everything Else
PCB Layout
Routing Priorities
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Power
Clock Signals and CAN
Analog
Digital (shift register, etc)
Everything Else (LEDs, switches, etc.)
PCB Layout
First Attempt - Ratsnest
PCB Layout
First Attempt - Combined
PCB Layout
Second Attempt - Ratsnest
PCB Layout
Second Attempt - Combined
PCB Layout
Second Attempt – Top Layer
PCB Layout
Second Attempt – Bottom Layer
Software Design/Development Status
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Researched CANOpen protocol
Researched PIC18F2680 programming related features
Consulted with the other two solar teams to decide upon how to
handle the object dictionary
I/O
Application
Object Dictionary
CAN Open
CAN
Software Design/Development Status
• MPPT Algorithm:
– Find the initial MPP at startup
– Every 50 ms check the points to the left and the
right of the MPP and adjust the MPP accordingly
– Re-sweep the IV curve every minute to acquire the
proper MPP in case of a imperfect IV curve
Project Completion Timeline
Task
Start
Finish
Duration
Finalized Schematic and
PCB
03/02/06
03/10/06
9d
Prototype Design on
Eval. Board
03/02/06
03/22/06
21 d
Implementation of MPPT
algorithm and CANOpen
protocol
03/02/06
03/24/06
23 d
Hardware and software
integrated
03/24/06
04/14/06
22 d
Debugging and
troubleshooting
04/14/06
04/21/06
8d
Questions / Discussion