Formula SAE Electric Drive Control

Transcription

1 Formula SAE Electric Drive Control Design Team 05 Nick Ga1a Alex Klein Alex Spickard Tyler Zoner Faculty Advisor: Dr. Sozer

2 Need This Drive Control System must enable a driver to be competitive on the racetrack in both speed and efficiency. Adherence to these rules ensures that the vehicle is safe, and is required to foster fair competition. 2

3 Objective Design an intelligent Drive Control System Implement torque vectoring Implement traction control Deliver as much power as possible from batteries Follow all guidelines provided by Society of Automotive Engineers (SAE) Create a safe and successful vehicle 3

4 Hardware Diagram 4

5 Final Hardware Design Design Requirement: System must receive input from throttle, steering, brake and wheels 5

6 Final Hardware Design Design Requirement: System must receive input from throttle, steering, brake and wheels 6

7 Final Hardware Design 7

8 Wheel Sensors Design Requirement: Capable of sensing holes of the wheels at 16 RPS Inductive Sensors Pepperl+Fuchs NBB8-18GM30-E2-V1 8mm sensing range Sense at 500 Hz max Application at 135 Hz 8

9 Driver Inputs Design Requirement: Steering Throttle Sensors sensor must be create able to a redundancy sense movement up to 180 Steering Potentiometer Capable of Traveling Needed For Competition Powered by 3.3VDC in application Two Pedal Potentiometers Software disables motors if varied by >10% 0-5k resistance Powered by 3.3VDC within application 9

10 3.3 Voltage Regulator

11 Output Signal 11

12 Opto-Isolator Design Requirement: High voltage system must be electrically isolated from low voltage system Isolates low voltage system Receives power (5VDC) from motor controller at collector pin Receives input pulse width modulated signal from microcontroller torque and brake outputs 12

13 PWM Input Signal 13

14 Low Pass Filter Output needs to be converted to analog signal Output filtered through low pass RC circuit After filtering a smooth analog output is achieved τ =RC Desired τ at 5ms R = 47kΩ C =.1µF These values give time constant of 4.7ms 14

15 Filtered Output Signal 15

16 Printed Circuit Board 16

17 Printed Circuit Board 17

18 Printed Circuit Board 18

19 Drive Control Box Design Requirement: Sensors must have detachable connectors 19

20 Software Diagram 20

21 Software Diagram 21

22 Software Flow 22

23 Processor Expert 23

24 Efficient Control Design Requirement: System must use limited power available efficiently. Motors are ~90% efficient, controllers are 99% efficient Traction Control and Torque Vectoring prevent unnecessary wheel spin and keep power evenly distributed to each motor Torque output maximum is lowered as battery charge decreases 24

25 Regeneration Design Requirement: Regenerating energy is not allowed at or below 5 km/h. Wheel speed sensors are used to measure overall vehicle speed Software puts regenerative outputs at 0 when speed is less than 3 m/s (10.8km/h) to be safe 25

26 Communication Design Requirement: Serial communication between battery management system and drive control system One UART is used to communicate to the Windows PC running the diagnostics interface Second UART used to listen for messages from BMS Message struct allows for easy extendibility to more functions 26

27 User Display Design Requirements: System must process inputs and provide information to user display Dash display for car is currently unfinished Current code outputs all of the required information to a UART that is currently connected to a Windows diagnostics application 27

28 Traction Control Wheel speed sensors pulse 8 times per rotation of the wheel We need to be able to detect differences as small as 10% between wheel speeds Top speed is around 60mph in normal use To detect 10% differences, we need at least 10 ticks per pulse Selected a 7700Hz timer and achieved ticks per pulse; more than enough resolution Speed(m/s)= 27 Wheel Circumference(m) = Timer frequency(hz): 7700 RPS Pulses Per Second Ticks Per Pulse

29 Torque Vectoring Height H, Track T, Weight W, Inward acceleration a r F NO = F NOS + F T = W T I /T + m a r H/T F NI = F NIS F T = W T O /T m a r H/T R= F NO / F NI Radius of curve approximated from the steering angle Velocity is average of the front two wheel speeds Mass, Track, Height are predefined 29

30 Torque Vectoring Simulated Torque pro?iles in MATLAB 30

31 Torque Vectoring Fully calculated in the microcontroller Achieving ~15k calculations per second 31

32 Non-applicable Design Requirements Design Requirement Max power drawn from the battery must not exceed 85kW for 100ms continuously When an analog sensor is used, it must be considered to have failed when it achieves an open or short circuit condition Reason Batteries cannot provide more than 54kw without blowing fuses or shutting down. Throttle failure is cared for by the throttle redundancy and mismatch shutdown. It was decided to continue operation if the steering or brake sensors fail. All parts of the vehicle which may become electrically conductive which are within 100mm of any tractive system or GLV component, must have a resistance below 5 Ohm to GLV system ground. Vehicle is not yet finished so was not able to be demonstrated. 32

33 Conclusion We have built an easily extensible system to serve as a foundation for the future of the UA FSAE Electric team. Any questions? 33