EV Reality: Advanced Electric Vehicle Battery Charger

1. EV Reality: Advanced Electric Vehicle Battery Charger Robert Steinmetz Craig Steinhauser Julio Mayen ECE 445 TA: Wayne Weaver

2. Quick Overview: • Introduction and objectives • Original design • Final design • Power circuit • Controls circuit • Testing procedures • Efficiency and overall testing results • Successes, challenges and recommendations • Conclusion

3. Introduction • Part of RSO Electric Vehicle Reality • Multiple teams working together, including ME students, to convert a donated Mazda Miata into an electric vehicle • Electric Vehicle benefits: • Fossil Fuel concerns • Emission control • Foreign oil dependency eliminated • $$$!!!

4. Team Objectives • Charge one (1) 60Ah Lithium-Ion Battery and, time permitting, alter design to accommodate ninety (90) Li-I batteries • Implement safety features to protect users, circuit, and battery • Integrate user friendly feedback system that provides critical feedback • Charge effectively, in a timely manner, without damaging the battery or compromising battery life

5. Original Design • Use a full bridge rectifier circuit • Coupled with a PIC to for controls • Convert circuit to accommodate the charging of ninety (90) batteries • Give as much charging feedback as possible, including: • Battery temperature • Current and voltage readings • Charge time remaining/elapsed

6. Final Design: Block Diagram

7. Final Design: Overall Schematic

8. Power Circuit • Its main purpose is to provide the high, steady current necessary to charge the battery in a timely manner • Essentially a buck converter designed to charge to 4.25V, at a current up to 10A (given the selected components)

9. Controls Circuit • Uses the bq2954 IC • MOD signal is sent out from bq2954 which helps regulate current via the duty cycle • Outputs to three LED’s which indicate battery status

10. Sub-circuits within controls: • Max Time Out Circuit Time out circuit measurements: Time Out Circuit Calculation:

11. Sub-circuits within controls: • Temperature Sensing Circuit Low side measurements: High side measurements: Putting them together: Low Side Measurements: High Side Measurements: Time out circuit measurements: Putting them together: Putting them together:

12. Sub-circuits within controls: • LED’s Circuit Low side measurements: High side measurements: Putting them together: • GREEN LED – signifies the transformer has been plugged in and power is to the circuit, this is the bit sent to the control group to shut down the car’s driving ability • RED LED – signifies the battery is charging, uses the “mod” signal • YELLOW LED – signifies a battery is present and hooked up Putting them together:

13. Battery Charger States • “Qualification” state • Battery temperature and voltage are checked to ensure within range and safe to charge • “Conditioning” state • After passing qualification • Battery is charged at a lower current in order to bring the voltage up at a slower rate • “Current regulation” state • After conditioning complete • Battery is charged at maximum current via the largest duty cycle from the MOD output (approximately 80%)

14. Battery Charger States, cont. • “Done” state • Battery fully charged • Remains here unless the voltage falls below the limit or if any sort of fault occurs • If at any point there is a fault (such as a time out, a fault, the battery is removed, etc.) the circuit will return to the qualification state

15. Testing and debugging: power circuit • Used a function generator and MOSFET driver (MIC4420) to simulate the MOD signal (from the bq2954) • Combined the function generator and driver to power a single FET and verify functionality Channel 1 is the driver’s output Channel 2 is the voltage at the drain of the FET

16. Testing and debugging: power circuit • Completed building of the power circuit • Tested again with the power circuit alone using the function generator and driver

17. Power Circuit Tests • 5 kHz generated MOD signal, Vin = 12V • Channel 1 - current into the battery - approximately 5A max • Channel 2 - collector of NPN transistor Q3 (part of isolated gate drive) • Channel 3 - gate of PNP FET Q5 (high current FET)

18. Power Circuit Tests, cont. • Same signals at a frequency of 50 kHz • Less current ripple with increased frequency

19. Power Circuit Tests, cont. • Same signals at 50kHz MOD signal • Using 20% and 80% duty cycles

20. Controls Circuit testing: • Built and tested the controls circuit with bq2954 on a separate board • Allowed to simulate various voltages at different pins in order to learn more about chip operation and proper functionality

21. Testing and debugging: components • Voltage regulator testing: • Input various voltages (because the circuit calls for 8-24VDC input) and read voltage regulator output 12V input test: 24V input test:

22. Testing and debugging: components • Voltage Compensator test: • Vcomp tries to stabilize the regulated voltage at the battery • Input various voltages via a power supply, simulating the battery voltage & read Vcomp output Simulating 2.46V battery: Simulating 4.20V battery:

23. Testing and debugging: components • Voltage Compensator test, cont. Simulating 2.05V battery: Switching from a 2.25V to 3.20V battery:

24. Testing and debugging: components BTST output (on bq2954): • Designed to be driven high in the absence of a battery in order to put a voltage (4.25V) at the battery terminals • BTST driven high when the simulated battery (using a power supply) voltage drops below about 1.75V-2.0V • Agrees with data sheet - chip recognizes at battery with voltage 2.05V or greater

25. Complete Circuit Functional Test • Channel 1: • Current into the battery, approximately 3A (higher with a greater input voltage, this test was at approximately 10VDC) • Nearly a DC signal, frequency of the signal switching the PNP MOSFET is around 50 kHz and 80% duty cycle • Channel 3: • MOD signal output from the BQ2954 control chip • Frequency is controlled by circuit design, we designed for 50 kHz (screen shot shows 53 kHz) • The duty cycle is typically around 80% when fast charging, approximately 68% during this test

26. Efficiency Tests

27. Vbatt vs Time Data Done Current Regulation Conditioning Qualification

28. Ibatt vs Time

29. Successes and Challenges Successes -Fully functional charging system! -Correct design for various control inputs and outputs -Ability to regulate current via duty cycle -LED’s indicate status -Temperature sensing and circuit shut down -Time out and circuit shut down -Knowledge absorbed from the class is far greater than any other class to date Challenges -Learning various components and correct operation -Functionality of control and power circuits when put together -Proper circuit layout and component placement -Additional design modifications -Ability to incorporate other add-ons such as digital voltage, current, and time readouts -Modifying design to charge ninety (90) batteries

30. Recommendations • Needs a housing with appropriate “plug-ins” to eliminate user/circuit/battery damage • Use PCB to eradicate any connection problems • Incorporate a “low temperature sensing” circuit in order to protect against extreme lows • Finish digital readouts to give user more feedback about status

31. Conclusion • Circuit worked as expected: • Fully charge one (1) 60Ah Li-I battery in approximately 6 hours • Circuit automatically shut off when battery voltage reached the nominal 4.25V • Maximum time out worked perfectly and can be designed for longer or shorter periods, depending on transformer and charge current

32. Conclusion, cont. -Temperature Sensing functioned properly: circuit shuts down when battery gets hot, and would then proceed to start up when temperature returns within range -LED’s indicated status to user -Fuse in circuit successfully protected the circuit and battery from a surge

33. Thank you • Dr. Wayne Weaver • Professor Krein • ECE shop employees • Texas Instruments

34. Questions?