QUT Motorsport is an Australian Formula SAE team competing in the Formula SAE-A competition. Our Team is composed of students from a diverse field of degrees with a strong presence in engineering and business. Our project is to design, manufacture, manage, and market a single seater, electric race car for the FSAE-A competition. QEV-3 Electrical System UpgradeAfter taking QEV-3 to competition at the end of 2020, the team set about iterating on its electrical system in the pursuit of reliability and ease of maintenance. Our existing system had a complex harness running from a single point, where quite often wires would run from the front to the rear of the car due to the placement of a single board. With this in light, the team set about designing a series of smaller 'Vehicle Control Units' which distributed sensor reading and control around the vehicle, all tied together on a single 12V and CAN communication bus, significantly simplifying the harness and making spares easier. Vehicle Control Unit Rev CThe VCU is the brains of the car, with several PCBs distributed throughout sitting on the canbus. These boards are capable of driving fans, pumps and other 12V devices through a 2 channel PROFET, reading 5V sensors through an ADC, as well as reading NTC thermistors and driving LEDs through a 0-30mA current steering source. After building two revs, the board is now in a state where Rev C will be tested and go into production.Rev A VCURev C VCUSteering Wheel Rev BThe steering wheel PCB sits within the steering wheel, reading the state of 4 buttons and 3 potentiometers, allowing the driver to change inputs to the car. It also has a screen to display critical information to the driver including battery state of charge and temperatures of vehicle components. EBS ControllerThe EBS controller interfaces to a VCU, and to the driverless emergency brake system, allowing a VCU to control and test the status of the emergency brake system before autonomous driving can commence. It also interfaces with the output of the shutdown safety loop in the car to trip the emergency brake in a shutdown situation.Shutdown BoardOur shutdown board interfaces all shutdown segments of our vehicle back to one latching point, allowing any safety-critical system or e-stop to latch off the vehicle in a shutdown situation. This board then uses a DAC to convert the binary segment statuses into 4 analog pins that a vehicle control unit (VCU) can read to determine which segment has tripped the shutdown system.Battery Management Unit (BMU) Rev COur battery management unit, or BMU, interfaces with the cell monitoring units on an RS485 bus, receiving critical cell temperature and voltage information. In a state where any of these values are bad, it safely shuts the car down and trips the shutdown loop. The BMU also controls vehicle contactors, connecting the battery to the vehicle. The Rev B BMU is still in the design stages.Cell Monitoring Unit (CMU)The cell monitoring unit (previously BMS), measures the voltage and temperature of each battery cell to ensure they are within a safe range. It also balances the cells through the use of bleed resistors. Significant research was pursued into Kalman filtering to accurately estimate the state of charge SoC of our Lithium Iron Phosphate (LiFePO4) battery cells. We are now developing a new revision of these to improve reliability and simplify complexity. Motor Controller Isolation Interface (MCISO)The motor controllers used by the team in QEV-3 do not feature any galvanic isolation between the power stage and control stage. As a requirement of the competition, these systems must be galvanically isolated to ensure the safety of the driver. The MCISO was designed to isolate the vehicle CANbus into an isolated motor controller canbus to allow the VCUs to send motor commands. TSAL ControlThe TSAL control PCB uses a comparator to compare the tractive system voltage to a known reference voltage, and then isolates this signal back to some control logic and a 555 to enable a flashing red 'tractive system active light'. Future revisions of this PCB will integrate LED drivers and lower BOM cost in other areas.
