PMS-Prototype

Power Management System that includes a MPPT solar input, USB-C PD input, BMS w/ active balancing, load output, power path control, and power monitoring.

Goals

• Solar input with MPPT
• USB-C PD input for charging
• BMS with active cell balancing
• Regulated load output
• "Power path" control (Select power source for load [battery, solar, USB], select battery charging/discharging/disconnected, and select source for battery charging)
• Power monitoring (Current, voltage, power input/output for each sink/source)
• Protections (Temperature, OVP, UVP, OCP, RVP, RCP, etc)
• Programmable control (eg. SPI, CAN Bus, RS232/TTL, etc)

V1.0 Scope

• One solar panel input (12v 100W - 24v Vos 6A Isc)
  • 6A limit (19v Vmp: 100W / 19v = 5.26A)
  • 24v limit
• One load output (12v @ 3A = 36W)
• 1S battery (no balancing)
• Solar (~18v-20v) -> MPPT Buck -> Battery (~13v-14.5v) -> Buck -> Load (12v)
• Battery current/voltage sensing and MOSFET disconnect switch
• Control battery charge current by subtracting load current from total current draw? (removes the need for battery current sensing)
  • Or, use battery current and total current to determine load current (better safety for battery)

Design 'Units'

• MCU / Control
• Solar Input / MPPT
• USB-C PD Input
• BMS / Battery
• Load Output / Regulation
• "Power Path" Switching

Planning / Parts

MCU / Control

Main contender is the STM32G4x4:

• Cortex-M4 (with FPU and DSP instructions) running at 170 MHz
• Rich advanced analog peripherals (comparator, op-amps, DAC)
• ADC with hardware oversampling (16-bit resolution)
• Dual-bank Flash memory with error-correcting code (ECC) (supports in-field firmware upgrades)
• High-resolution timer version 2 (HRTIM for digital power conversion)
• USB Type-C interface with Power Delivery including physical layer (PHY)

Solar Input / MPPT

• Synchronous Buck Topology
• 48v input (to support 2x series 12v 100W panels with an Voc of ~24v each)
• 15A input (to support 2x series 12v 100W panels with an Isc of ~6A each)
• (Idea) Output is programmable: Can be set to match load output or controlled to charge the battery (CV/CC)

Power Path

• Individual Enable/Disable for Solar/USB/Battery/Load

• Input priority control

• Output priority control

• Solar/USB/Battery/Load all in parallel

• Each sink/source either takes from or contributes to the pool of energy

• The battery has a disconnect, but can't regulate

• If the system voltage drops, you can either:

  • Increase the power input (switching battery from sink to source?)
  • Decrease load (Limit the battery charge current or send a signal to )

• The PMB should be able to identify when the maximum solar power available isn't being used

  • Increase battery charging speed
  • Signal to the main vessel controller to use more power (speed up, perform comms transmissions, etc)

• USB-C PD || Solar || Battery ||

• Only one power input (Solar or USB-C)

  • USB->Buck (USB supply must be at least load voltage)
  • Solar->MPPT->Sys

• Battery in parallel with load

• Sys->

Other Parts

• Hall effect current sensor:
  • ACS712 (popular but noisy!)
  • LEM HLSR50 (expensive - $16 - but 50A, shielded, internal voltage ref, can be used with differential ADC eliminating need for calibration)
• MOSFET Driver for synconous buck converter:
  • IR2101 and IR2110 (seperate PWM inputs for high and low side MOSFETS)
  • IR2104 (One PWM input drives both high and low side MOSFETS)
    • Be careful!!! Setting the PWM too low causes the high side to stay off and the low side to stay on, resulting in a short circuit if a battery is attached and potentially burning out the low-side MOSFET.
    • PWM Floor Duty Cycle = (Output Voltage / Input Voltage) * 100)
    • When PWM signal has a lower duty cycle than the computed PWM floor value, the current flows in reverse and causes the low-side MOSFET to conduct when it isn't supposed to be conducting.
• Isolated DC-DC Converter:
  • B1212S
• ADC:
  • ADS1115 (16bit 860sps) / ADS1015 (12bit 3300sps)
  • (the STM32G4x4's internal ADC might be good enough?)
• MOSFET:
  • CSD19505

Resources

Relion LiFePO3 Battery Specs

RB20-LT:

• Recommended Charge Voltage: 14.2 V - 14.6 V
• BMS Charge Voltage Cut-Off: 15.6 V (3.9 ±0.025 vpc) (1 ±0.3 s)
• Reconnect Voltage: 14.6 V (3.8 ±0.050 vpc)
• Balancing Voltage: 14.4 V (3.6 ±0.025 vpc)
• Recommended Low Voltage Disconnect: 11.0 V
• Discharge Under-Voltage Protection: 8.0 V (2.0 ±0.08 vpc) (20 ±8 ms)
• Reconnect Voltage: 9.04V (2.26 ±0.34 vpc)

Battery Charging

• https://en.wikipedia.org/wiki/Battery_balancing

MPPT Solar Charger

• https://www.instructables.com/DIY-1kW-MPPT-Solar-Charge-Controller/
  • https://drive.google.com/drive/folders/1Sd2jWAb-F8NAXlJ6PLdhcnPDQV0alD15
• https://www.instructables.com/ARDUINO-SOLAR-CHARGE-CONTROLLER-Version-30/
  • https://microcontrolere.wordpress.com/2016/12/16/mppt-solar-charger/
• https://www.opengreenenergy.com/
  • https://www.opengreenenergy.com/arduino-solar-charge-controller-v2-02/
• https://www.instructables.com/How-to-Design-and-Build-a-MPPT-Solar-Charger-Using/
• https://www.mathworks.com/discovery/mppt-algorithm.html
• In an MPPT buck converter, when the PV voltage is lower than the battery voltage, the high-side MOSFET body diode causes current leakage from the batteries into the solar panels.
  • Solution: Add reverse blocking MOSFET
  • Drive the MOSFET with and isolated DC-DC converter (B1212S)