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Design for Prius C Plug-In Conversion

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Presentation on theme: "Design for Prius C Plug-In Conversion"— Presentation transcript:

1 Design for Prius C Plug-In Conversion

2 Objective Add an additional battery and charger to compliment the Prius C’s existing hybrid drive system to improve overall efficiency

3 Outline Will roughly follow what is known as the “contactor method” already proven in full-sized Prius conversions LiFePO4 pack as extra battery with higher voltage than hybrid battery to avoid using a DC-DC converter Connected to Hybrid Drive system in parallel with original hybrid battery Battery connection controlled by an electrically controlled contactor Contactor controlled by an Arduino microcontroller Arduino monitors state of charge, current, voltage and cell under/over voltage and sets state of the contactor

4 Build Steps Get Arduino to read the CANbus, specifically the State of Charge (SOC) of the Prius’ battery Build the hybrid battery pack, including Battery Monitoring System Build the interface board between Arduino and the battery as well as instrumentation and control to include LiFePO4 battery current Relay for charge control Main contactor control Display system for hybrid pack information Display hybrid pack SOC Warning for system faults Incorporate LiFePO4 pack battery charger Develop Arduino code for system control

5 Arduino and CANBus CANBus Shield gives Arduino the ability to read and log CANBus data Reading of CANBus is necessary to find the Hybrid Battery’s SOC to know when to open and close the contactor between it and the LiFePO4 battery to prevent over/under charging

6 Arduino and CANBus I have already developed and Arduino sketch (program) to read and log CANBus data

7 Arduino and CANBus No publicly available data identifies PID codes for Prius C’s unique attributes Reverse engineering was necessary to find the Hybrid Battery’s SOC on the CANBus

8 Battery LiFePO4 chemistry chosen due to proven use in full-EV conversions Long cycle life Flat discharge curve High power/weight Hybrid battery is 144V nominal LiFePO4 nominal voltage will be 154V to allow for low-rate charge of Hybrid battery when connected in parallel 48 Cell, 20AH GBS Batteries, 3KWH pack

9 Battery Management System
To provide LiFePO4 cell under/overvoltage (UCV/OCV) protection and alarm as well as inter-cell balancing, a Battery Management System(BMS) is necessary Ready made systems for full-EV conversions are expensive (~$1000 for my application) and redundant to capabilities inherent to Arduino

10 Battery Management System
Maxim MAX11068 IC chosen for my application Provides UCV/OCV alarms Total pack voltage Inter-cell balancing Pack temperature Two wire interface (I2C) to Arduino to provide alerts MAX11068 Evaluation Kit (~$250) will be used to reduce time and cost in producing PCB

11 Interface Board A small PCB will be necessary to support several interface features Provide 12V Battery power to Arduino and interface systems Transistor interface to activate contactor Allegro MicroSystems ACS758 IC chosen to measure bidirectional current for LiFePO4 pack Relay for controlling LiFePO4 battery charger Relay for sensing if AC is still plugged in

12 Display System A small LCD will be mounted in view of the driver to provide information about the system LiFePO4 pack voltage, current, SOC State of contactor Warning for system faults

13 Battery Charger Elcon PFC 1500 chosen
Mounted onboard to allow for charging away from home Will recharge a fully discharged pack within three hours via 120VAC

14 Safety Features Numerous software and hardware features
Software trip of contactor OCV/UCV Abnormally high charge/discharge current Over-temperature Hardware Fuses for main cabling Barrel switch near driver to allow for manual disconnection of LiFePO4 pack Inertial switch to trip contactor in event of a crash

15 Pseudo-Code Initialization
Determine SOC of Hybrid battery Verify system health If Hybrid SOC <80% and LiFePO4 pack healthy (>20% SOC, no OCV/UCV or over-temp) Shut main contactor If Hybrid SOC >90% or any fault detected Open main contactor SOC for shutting and opening contactor will be modified after initial testing to optimize use of stored energy in LiFePO4 pack

16 Performance Estimates
Stock Prius C advertises ½ mile on EV only mode 0.9KWH NIMH pack, max DOD 45% With addition of 3KWH LiFePO4 pack, max 80% DOD, up to 6 additional miles in EV only mode In blended mode, full sized Prius conversions have resulted in >80MPG during normal commuting Due to smaller vehicle size and larger proportional pack size, expect as good or better than 80MPG

17 Follow my progress at:
Conclusion Follow my progress at:

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