Electric racing control system design

"CompactRIO allows electric cars to run like ordinary cars."

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– Robert Repas, Racing Green Endurance

The Challenge:

Author(s):

Robert Repas - Racing Green Endurance

It is generally believed that electric vehicles are traveling at a lower speed and cannot travel far distances. The Racing Green Endurance team wants to overthrow this view. So they created the latest car Radical SRZero. They hope that while driving the development of electric vehicle technology, this car can become the world's most fun and alternative energy vehicle.

Radical SRZero is a high-power electric vehicle based on the Radical Sportscars SR8 chassis. Its hub motor on the rear wheel makes room for more batteries and reduces mechanical losses. Two 140-kilowatt (200 brake horsepower) motors provide a total of 400 brake horsepower for the car. The lithium iron phosphate battery pack, powered by 54-kilowatt hours, powers the two motors and the rest of the car.

The RGE team called the electric supercar SRZero, which weighs 2,400 pounds and has a top speed of 124 mph (200 km/h). It can accelerate from 0 mph to 62 mph (100 km/h) in 7 seconds and can drive 248 miles (400 km) when the battery is fully charged.

Straight drive does not require a drive train, gearbox and mechanical differential. However, mechanical differentials still need to be used for racing operations and to reduce tire wear. The design team created an electrical differential system by speeding up the speed of the outer wheel motor and reducing the speed of the inner wheel motor while the car was turning. The control system must handle the analog signals from sensors mounted on the entire race car (such as the accelerator pedal and brakes) and properly control the inverter, battery management system and high voltage system to avoid damage to the components.

Based on past experience in manufacturing a single-seat formula car to participate in the design competition, the team selected the CompactRIO produced by National Instruments (NI) as the control system. They know that CompactRIO will run the code of a pre-written FPGA absolutely reliably. This allows it to run critical tasks in a timely and safe manner and provides file input/output to the operating system of the car through a real-time controller.

CompactRIO allows electric cars to run like ordinary cars. For example, when the driver turns the ignition key, the car will start normally and be ready to drive. The driver does not feel the complexity of the start-up process (including checking and verifying that all systems and sensors are functioning properly).

CompactRIO controls each component separately under normal driving conditions. For example, a separate software program segment on the FPGA can monitor battery management, inverter control, thermal management, vehicle stability, and charger management. In addition, you can record the general status of the car, such as whether it is charging, driving or in a debugging state. While the MathScript RT Module runs an advanced, non-linear state-dependent Ricatti equation algorithm for vehicle stability control, NI LabVIEW Real-Time records all data for further study.

Other algorithms on CompactRIO try to maximize operational availability. For example, the torque reduction algorithm reduces the torque of the motor when it detects that the running component is approaching a limit (eg, the motor is overheated or the battery pack voltage is too low).

FPGAs are also used for security functions. When any abnormality is detected, it generally stops the car from running to avoid accidents and protect the electromechanical system.