Photon 3

Description

The Photon 3 MPPT is a boost mode Solar Array Maximum Point Power Tracker (MPPT) designed primarily for solar powered car racing, specifically for cars entering the World Solar Challenge and the American Solar Challenge. It has been optimized for the new generation of lower voltage, higher current silicon solar arrays and it has been specifically optimized to convert series strings of unmodified SunPower™ solar cells.

Features

• Dual Channel
  • The MPPT features two independently tracked channels in a single unit.
• Automatic Precharge/Isolation Relay
  • The unit isolates itself from the battery output using a dual pole relay when power is off or a fault is detected.
  • The unit automatically pre-charges itself through a separate relay and 1kohm resistor until it detects that it's appropriate to close the main relay.
• Robust Design
  • High temperature rated and automotive grade components used wherever possible
  • High mass components glued to assembly with high temperature rated epoxy for vibration toughness
  • High impact automotive grade plastic enclosure
  • IP67 automotive connector
  • IP65 enclosure design
  • Machined aluminum baseplate / heat-spreader
• High Efficiency
  • MPPT designed for the highest possible efficiency across the entire operating range while weighing only 460 grams per channel including enclosure and baseplate.
• Closed loop
  • MPPT will track any array that it's connected to without additional configuration. It's closed loop tracking algorithm will find and hold the maximum power point in varying conditions.
  • FPGA based high bandwidth current control for precise tracking down to low input current levels.
• Wide Input Range - Design Flexibility
  • Designed for lower voltage, high efficiency silicon arrays. Architecture allows a 22 to 1 ratio between the array voltage and the battery voltage, allowing designs that use very small subarrays.
• Optimized for Modern Solar Cars
  • Maximum efficiency point chosen for ~6A cells, matching common configurations
  • Hardware overvoltage protection aligned with common motor controller specifications to reduce risk of damage and to maximize total system reliability.
  • Powered by 12V or 24V vehicle power, the MPPT turns on and shuts off with the rest of your electrical system
• Telemetry
  • Telemetry allows remote monitoring of array performance
  • Tested with 125kbit and 500kbit CAN busses
  • Easily parsed CAN messages, the MPPT does the math for you in converting to useful units.
  • Configurable as automatically reporting at a programmed frequency.

Specifications

Mechanical CAD

Efficiency Data

CAN Data Format

• The default configuration for the device is to output CAN messages at a constant rate, consuming a constant fraction of the bus bandwidth.
• At 125kbps, the unit will send updates for each channel at 12.5hz, at 250kbps, the unit will send at 25hz and and 500kbps, 50hz.
• Each unit comes programmed to send data based on a pair of fixed addresses, each representing one of the two channels.
• Photon MPPT uses a very simple CAN structure, this is an 8 byte packet with array voltage, array current, battery voltage and MPPT temperature info encoded.
• Scaling is simplified and standardized.
  • Array voltage is scaled by 100, or 1 count = 10mV
    • Value 12345 = 123.45V
  • Array current is scaled by 1000, or 1 count = 1mA
    • Value 12345 = 12.345A
  • Battery voltage is scaled by 100 or 1 count = 10mV
    • Value 12345 = 123.45V
  • MPPT Temperature is scaled by 100 or 1 count = 10mC
    • Value 12345 = 123.45C

Example Configuration

Array in four segments, each 64 cells in series, two units are required.

Battery is 30 cells in series lithium ion.

Note - do not connect array or battery return leads together. Photon 3 measures the array current on the low side returns, if they are connected together, the MPPT will not properly track the max power point.

Updating Firmware / Configuration

1. Download CAN Logger Software
2. Set up a small CAN bus with only these things on the bus - Don't trust your car's fully operating CAN bus to not interfere with the programming cycle
   • Tritium CAN-Ethernet Bridge
   • Bus termination (should measure 60 ohms from CANH to CANL)
   • Unit you would like to program
   • Power connection
   • It’s essential that you have a quality connection here, as loss of power/data during programming can cause undefined behavior and may require opening the case and re-flashing the bootloader with a Microchip ICD
3. Open the can logging and programming tool (can_logger.exe)
4. Start the CAN Interface (Interface toolbar drop-down)
   • Select your bitrate (likely 125k, 250k or 500k depending on your bus)
   • Click ‘Init Can Eth’ - this initializes your adapter - you should start seeing packets from your unit in the logging window
5. Change to the Photon 3 Programming tab
6. Click the Select Hexfile button, and then click fw.hex from the firmware directory
7. Click the Select Bitstream button, and then click fpga.bit from the firmware directory
8. Click the Detect Trackers button, this will detect all of the units on your bus, reset them and read off their parameters. After Detect Trackers has completed, click the dropdown next to it, and you should be able to select your unit - it should say something like ‘MPPT 0x600 - Serial 013’
9. Click Save MPPT's Parameters to File to save out the present parameters on the device. The default will save to a plaintext protobuf format file, and will default the name based on the serial number of your device.
10. Click Select Parameters and select the parameters file that matches the serial number for your unit from the params folder. For example, Serial 13 would be params/parameters_013.txt
11. Once you’ve done these things, the Program and Force Program buttons should be enabled and you should be allowed to program the unit.
    • The program checks the crc of the firmware on the unit and will not reprogram if a crc match is detected, and will not program if the parameters file does not match the expected unit serial number.
    • If you click Force Program, it ignores the CRCs and the unit’s serial number and programs anyways USE WITH CAUTION.
12. Update Rate (the rate at which each of the two channels spews CAN packets) and the Constant Voltage Charge limit can be set from this screen as well. To update either of these parameters, click the relevant Get parameter button, edit the parameter to your desired value and then click the relevant Set parameter button to set it in the MPPT's FRAM. Before modifying these values, ensure you have programmed the most recent firmware on the device.
13. If you have trouble, please email with the text from the black command window that opens up