Formula SAE Electric Drive Control

Design  Team  05    

Nick  Ga1a  Alex  Klein  

Alex  Spickard  Tyler  Zoner  

 Faculty  Advisor:  Dr.  Sozer  

 

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.

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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

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Hardware Diagram

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Final Hardware Design

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

Final Hardware Design

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

Final Hardware Design

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Wheel Sensors

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•  Inductive Sensors

•  Pepperl+Fuchs •  NBB8-18GM30-E2-V1

•  8mm sensing range •  Sense at 500 Hz max

•  Application at 135 Hz

Design Requirement: Capable of sensing holes of the wheels at 16 RPS

Driver Inputs

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•  Steering Potentiometer •  Capable of Traveling 305° •  180° Needed For Competition •  Powered by 3.3VDC in

application

Design Requirement: Steering sensor must be able to sense movement up to 180° Design Requirement: Throttle Sensors must create a redundancy

 

•  Two Pedal Potentiometers •  Software disables motors

if varied by >10% •  0-5k resistance •  Powered by 3.3VDC within

application  

3.3 Voltage Regulator

Output Signal

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Opto-Isolator

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•  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  

Design Requirement: High voltage system must be electrically isolated from low voltage system

PWM Input Signal

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Low Pass Filter

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•  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  =𝑅𝐶

•  Desired 𝞽 at 5ms •  R = 47kΩ •  C = .1µF

•  These values give time

constant of 4.7ms

Filtered Output Signal

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Printed Circuit Board

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Printed Circuit Board

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Printed Circuit Board

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Drive Control Box

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Design Requirement: Sensors must have detachable connectors

Software Diagram

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Software Diagram

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Software Flow

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Processor Expert

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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

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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

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Communication

•  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

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Design Requirement: Serial communication between battery management system and drive control system

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

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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 56.89

ticks per pulse; more than enough resolution

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Speed(m/s)=   27   Wheel  Circumference(m)  =   1.595928206  Timer  

frequency(Hz):   7700  

RPS   Pulses  Per  Second   Ticks  Per  Pulse  16.91805427   135.3444341   56.89188513  

Torque Vectoring

•  Height  H,  Track  T,  Weight  W,  Inward  acceleration  a↓r  •  𝐹↓𝑁𝑂 = 𝐹↓𝑁𝑂𝑆 + 𝐹↓𝑇 = 𝑊𝑇↓𝐼 /𝑇 + 𝑚𝑎↓𝑟 𝐻/𝑇  •  𝐹↓𝑁𝐼 = 𝐹↓𝑁𝐼𝑆 − 𝐹↓𝑇 = 𝑊𝑇↓𝑂 /𝑇 − 𝑚𝑎↓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

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Torque Vectoring

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•  Simulated  Torque  pro?iles  in  MATLAB

Torque Vectoring

•  Fully calculated in the microcontroller

•  Achieving ~15k calculations per second

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Non-applicable Design Requirements Design Requirement Reason Max power drawn from the battery must not exceed 85kW for 100ms continuously

Batteries cannot provide more than 54kw without blowing fuses or shutting down.

When an analog sensor is used, it must be considered to have failed when it achieves an open or short circuit condition

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.

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Conclusion

•  We have built an easily extensible system to serve as a foundation for the future of the UA FSAE Electric team.

•  Any questions?

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