ECE 477 Design Review ECE 477 Design Review Team 12 Team 12 Spring 2006 Spring 2006

Eric Daniel Atandra Sriharsha Aasen da Silva Burman Vengapaty

OutlineOutline• Project overview Project overview • Project-specific success criteriaProject-specific success criteria• Block diagramBlock diagram• Component selection rationaleComponent selection rationale• Packaging designPackaging design• Schematic and theory of operationSchematic and theory of operation• PCB layoutPCB layout• Software design/development statusSoftware design/development status• Project completion timelineProject completion timeline• Questions / discussionQuestions / discussion

Project OverviewProject Overview

Maximum Power Point Tracker (MPPT) :Maximum Power Point Tracker (MPPT) :

• DC to DC converter that converts the input voltage from a solar cell DC to DC converter that converts the input voltage from a solar cell array to the output voltage of a battery pack.array to the output voltage of a battery pack.

• Optimum “power point” along Optimum “power point” along

current vs. voltage curve that current vs. voltage curve that

produces power for solar array.produces power for solar array.

• Our tracking algorithm will provideOur tracking algorithm will provide

control of the DC to DC converter control of the DC to DC converter

in order to achieve this power point. in order to achieve this power point.

• Relay data to the telemetry unit on the solar car via the CAN bus.Relay data to the telemetry unit on the solar car via the CAN bus.

Project-Specific Success CriteriaProject-Specific Success Criteria• An ability to measure pertinent voltages and currents within anAn ability to measure pertinent voltages and currents within an

accuracy of 2% over the range of possible values [0-8A and 0-accuracy of 2% over the range of possible values [0-8A and 0-70V]70V]

• An ability to send I-V and temperature data to other peripherals An ability to send I-V and temperature data to other peripherals via the CAN.via the CAN.

• An ability to switch to a "debug" mode (when an RS-232 cable An ability to switch to a "debug" mode (when an RS-232 cable

is connected) in which the I-V curve is continuously scanned.is connected) in which the I-V curve is continuously scanned. • An ability to maintain the maximum power point of the solar An ability to maintain the maximum power point of the solar

array under standardized artificial light conditions through a array under standardized artificial light conditions through a high powered halogen lamphigh powered halogen lamp

• An ability to disconnect the solar array in response to a CAN An ability to disconnect the solar array in response to a CAN command.command.

Block DiagramBlock Diagram

Micro

Controller

Power Block

Analog Block

CAN Transceiver

Serial Communication

(Debugging)

Programming Port

Clock

CAN Address

Outputs2

4

52

3

2

5

5

• Microcontroller - PIC18F2680(SOG.050/28/WB.420/L.700)

• Power Supply - MAX1684(SOG.025/WG.244/L.200)

• Op Amp - MCP6001/2/4(SOG.050/14/WB.224/L.350)

• CAN Transceiver - MCP2551(SOG.050/14/WB.244/L.200)

Component Selection RationaleComponent Selection Rationale

MicrocontrollerMicrocontroller Pin CountPin Count CANCAN RAM(bytes)RAM(bytes) Flash(bytes)Flash(bytes) CostCost

MC68HC08AZ60MC68HC08AZ60 6464 YesYes 2KB2KB n/an/a 16.0016.00

PIC18F2680PIC18F2680 2828 YesYes 15681568 32K32K 12.0012.00

AT90CAN32AT90CAN32 6464 Yes Yes 2K2K 32K32K 16.0016.00

Packaging DesignPackaging Design

• The packaging would have the following dimensions: The packaging would have the following dimensions:

Width = 5.210”, Length = 5.300”,Height = 2.750”Width = 5.210”, Length = 5.300”,Height = 2.750”

• Enclosed within a 0.125” thick Foam CoreEnclosed within a 0.125” thick Foam Core

Fiberglass packaging with nearlyFiberglass packaging with nearly

0.250” spacing0.250” spacing

on both sideson both sides

• Includes 80mm x 80mm x 10 mmIncludes 80mm x 80mm x 10 mm

ventilation enclosureventilation enclosure

Schematic/Theory of OperationSchematic/Theory of OperationMain Block:Main Block:• Microcontroller and oscillatorMicrocontroller and oscillator• Power SupplyPower Supply• Overvoltage ProtectionOvervoltage Protection• HeadersHeaders• CAN InterfaceCAN Interface• SPI Shift Register and diagnostic LEDsSPI Shift Register and diagnostic LEDs

Analog Block:Analog Block:• Voltage translators and filtersVoltage translators and filters• Current sensing insightCurrent sensing insight• Output current senseOutput current sense• Input current senseInput current sense

Main SchematicMain Schematic

Microcontroller and oscillatorMicrocontroller and oscillator

• Crystal runs at 10Mhz.Crystal runs at 10Mhz.• Microcontroller’s PLL can multiply that Microcontroller’s PLL can multiply that

frequency by 4 time – 40Mhz.frequency by 4 time – 40Mhz.• For power saving condition, For power saving condition,

microcontroller can run at 10Mhz.microcontroller can run at 10Mhz.

• Microcontroller is Microcontroller is interfaced with 5 interfaced with 5 analog inputs. analog inputs.

• It drives 3 Mosfets.It drives 3 Mosfets.• It uses several It uses several

communication communication ports.ports.

• It uses a shift It uses a shift register for register for additional I/Os. additional I/Os.

Power SupplyPower Supply

• 5V supply is used to supply microcontroller and peripherals. 5V supply is used to supply microcontroller and peripherals. • Expected to operate at 90% efficiency, between 30mA to 400mA.Expected to operate at 90% efficiency, between 30mA to 400mA.

• 4.096V supply is used as analog 4.096V supply is used as analog inputs reference voltage.inputs reference voltage.

• All amplifier also are supplied by All amplifier also are supplied by this voltage regulator. this voltage regulator.

Overvoltage ProtectionOvervoltage Protection• Disconnects solar array from power board if voltage at battery Disconnects solar array from power board if voltage at battery

exceeds 70V.exceeds 70V.

• Comparator’s OUT goes to 0V if Vbat ≥ Comparator’s OUT goes to 0V if Vbat ≥ 70V.70V.

• Mosfet’s source is connected to a Mosfet’s source is connected to a BJT’s base, which requires 5V to turn BJT’s base, which requires 5V to turn ON. ON.

• RELAY_CONTROL is disregarded in RELAY_CONTROL is disregarded in that case.that case.

HeadersHeaders• FAN_SUPPLY turns external fan on or off FAN_SUPPLY turns external fan on or off

through the FAN_SUPPLY signal.through the FAN_SUPPLY signal.

• Serial Connector is primarily used for Serial Connector is primarily used for debugging.debugging.

• Programming board is used primarily Programming board is used primarily for programming. for programming.

• Header pin 1 is pulled up. This is Header pin 1 is pulled up. This is because it’s connected to nMCLR, because it’s connected to nMCLR, which is a low-active external reset for which is a low-active external reset for the microcontroller.the microcontroller.

• CAN Transceiver translates voltage level for CAN Transceiver translates voltage level for the CAN line.the CAN line.

• RS value changes the slew-rate for the CAN RS value changes the slew-rate for the CAN line. RS=4.7KΩ is for rather fast slew-rate, line. RS=4.7KΩ is for rather fast slew-rate, which can be adjusted afterwards.which can be adjusted afterwards.

• CAN Connectors are connected in a CAN Connectors are connected in a parallel manner with the remaining 7 parallel manner with the remaining 7 MPPT boards in the solar car.MPPT boards in the solar car.

• CABLE_DETECT is connected to CABLE_DETECT is connected to microcontroller to alert it in case of microcontroller to alert it in case of connectors being unconnected.connectors being unconnected.

CAN InterfaceCAN Interface

• CAN Address Setup simply CAN Address Setup simply inputs CAN address to the inputs CAN address to the microcontroller. microcontroller.

SPI Shift Register and SPI Shift Register and Diagnostic LEDsDiagnostic LEDs

• SPI Shift Register SPI Shift Register accommodate extra I/Os accommodate extra I/Os that would otherwise that would otherwise require a larger require a larger microcontroller.microcontroller.

• Diagnostic LEDs provide a visual Diagnostic LEDs provide a visual insight to the MPPT operation. insight to the MPPT operation.

Analog InputsAnalog Inputs

INPUT_V_SENSEINPUT_V_SENSE• Summing amplifier to translate 70V to 4.096VSumming amplifier to translate 70V to 4.096V

• 22ndnd order Butterworth low-pass filter with cut- order Butterworth low-pass filter with cut-off frequency of 20 Hzoff frequency of 20 Hz

SolarArray

Solar Car

Batteries

GND

DC/DCConverter

Power board

current direction current direction

Input current sense Output current sense

Input voltage sense Output voltage sense

Current sense rationaleCurrent sense rationale

INPUT_I_SENSEINPUT_I_SENSE• Summing amplifier to translate -[0 to 8]A to Summing amplifier to translate -[0 to 8]A to

[0.1024 to (4.096 - 0.1024)] V[0.1024 to (4.096 - 0.1024)] V

OUTPUT_I_SENSEOUTPUT_I_SENSE

• Summing amplifier to translate [0 to 8]A into Summing amplifier to translate [0 to 8]A into [0.1024 to (4.096 - 0.1024)] V[0.1024 to (4.096 - 0.1024)] V

PCB LayoutPCB Layout

ConstraintsConstraints1.1. Size (no more that 1.8” tall by 3.0” wide)Size (no more that 1.8” tall by 3.0” wide)

2.2. Accurate analog conversionAccurate analog conversion

3.3. Need for high-speed signal integrityNeed for high-speed signal integrity

PCB LayoutPCB Layout

Placement PrioritiesPlacement Priorities1.1. PowerPower

2.2. DigitalDigital

3.3. AnalogAnalog

4.4. Everything ElseEverything Else

PCB LayoutPCB Layout

Routing PrioritiesRouting Priorities1.1. PowerPower

2.2. Clock Signals and CANClock Signals and CAN

3.3. AnalogAnalog

4.4. Digital (shift register, etc)Digital (shift register, etc)

5.5. Everything Else (LEDs, switches, etc.)Everything Else (LEDs, switches, etc.)

PCB LayoutPCB Layout

First Attempt - RatsnestFirst Attempt - Ratsnest

PCB LayoutPCB Layout

First Attempt - CombinedFirst Attempt - Combined

PCB LayoutPCB Layout

Second Attempt - RatsnestSecond Attempt - Ratsnest

PCB LayoutPCB Layout

Second Attempt - CombinedSecond Attempt - Combined

PCB LayoutPCB Layout

Second Attempt – Top LayerSecond Attempt – Top Layer

PCB LayoutPCB Layout

Second Attempt – Bottom LayerSecond Attempt – Bottom Layer

Software Design/Development StatusSoftware Design/Development Status• Researched CANOpen protocolResearched CANOpen protocol

• Researched PIC18F2680 programming related featuresResearched PIC18F2680 programming related features

• Consulted with the other two solar teams to decide upon how to Consulted with the other two solar teams to decide upon how to handle the object dictionaryhandle the object dictionary

Object Dictionary

CAN Open

Application

I/O

CAN

Software Design/Development StatusSoftware Design/Development Status

• MPPT Algorithm:MPPT Algorithm:– Find the initial MPP at startupFind the initial MPP at startup– Every 50 ms check the points to the left and the Every 50 ms check the points to the left and the

right of the MPP and adjust the MPP accordinglyright of the MPP and adjust the MPP accordingly– Re-sweep the IV curve every minute to acquire the Re-sweep the IV curve every minute to acquire the

proper MPP in case of a imperfect IV curveproper MPP in case of a imperfect IV curve

Project Completion TimelineProject Completion Timeline

TaskTask StartStart FinishFinish DurationDuration

Finalized Schematic and Finalized Schematic and PCBPCB

03/02/0603/02/06 03/10/0603/10/06 9 d9 d

Prototype Design on Prototype Design on Eval. BoardEval. Board

03/02/0603/02/06 03/22/0603/22/06 21 d21 d

Implementation of MPPT Implementation of MPPT algorithm and CANOpen algorithm and CANOpen

protocolprotocol

03/02/0603/02/06 03/24/0603/24/06 23 d23 d

Hardware and software Hardware and software integratedintegrated

03/24/0603/24/06 04/14/0604/14/06 22 d22 d

Debugging and Debugging and troubleshootingtroubleshooting

04/14/0604/14/06 04/21/0604/21/06 8 d8 d

Questions / DiscussionQuestions / Discussion