Racing Green Endurance, www.racinggreenendurance.com National Instruments Corp., www.ni.com |
The Racing Green Endurance project wants to prove the perceived limitations of electrically powered vehicles (EVs) — slow speeds and a limited range — don’t have to be the case. So they created a new class of race car with thoughts of making it the world’s most fun-to-drive, alternative-powered vehicle while pushing the boundaries of EV technology. They call their car the Radical SRZero.
The Radical SRZero is basically a Radical Sportscars SR8 chassis modified into a high-power electric car. Hub motors on the rear wheels reduce mechanical losses while opening space for more batteries. Two 140-kW (200-bhp) motors give the car 400 bhp total. Power for the two motors, as well as the rest of the vehicle, comes from a 54-kW-hr lithium iron-phosphate battery pack.
The electric supercar, as the RGE team has dubbed the SRZero, weighs 2,400 lb and has a top speed of 124 mph (200 kph). It can accelerate from 0 to 62 mph (100 kph) in 7 sec and travel over 248 miles (400 km) on a fully charged battery pack.
Direct-wheel drive removes the transmission, gearbox, and mechanical differential. However, a differential was still needed for handling and to reduce tire wear. The design team created an electrical differential by speeding up the outer wheel motor and slowing the inside wheel motor as the vehicle takes turns. The control system had to process analog signals from sensors throughout the car, such as the accelerator pedal and brake, as well as properly control the inverters, battery management system, and high-voltage systems to avoid damaging components.
From the team’s past experience building a single-seat Formula race car for a design contest, the Team picked the CompactRio from National Instruments (NI), Austin, Tex., as the control system. They knew CompactRio would reliably and deterministically run code written into its FPGA. This lets it run time and safety-critical tasks and have the real-time controller give the car the benefits of an operating system with file input/output.
CompactRio lets the car behave like a normal car. For example, when the driver turns the ignition key, the car starts normally and is ready to drive away. The driver is unaware of the complex start-and-drive process, which includes checking and verifying that all systems and sensors are operating normally.
CompactRio controls each component separately under normal driving conditions. For example, there are independent software segments on the FPGA to supervise battery management, inverter control, thermal management, vehicle stability, and charger control. Additionally, the general state of the car is recorded and logged, such as whether it is charging, being driven, or is in debug mode. NI LabView Real-Time logs all of the data for further research while a MathScript RT Module runs an advanced, nonlinear state-dependant Ricatti equation algorithm for vehicle stability control.
Other algorithms on CompactRio try to maximize operation availability. For example, a torque-reduction algorithm lowers the motor’s torque when it detects a component operating close to its limits, such as an overheated motor or low-voltage levels on a battery cell.
The FPGA was also used for safety functions. Detecting any anomaly typically shuts down the car to help avoid accidents and protect the mechanical and electrical systems.
The car now has more than 16,000 miles (26,000 km) on it, and has traveled the Pan-American highway from Fairbanks, Alaska, to Ushuaia, Argentina, the world’s southernmost city. CompactRio has been one of the most-reliable components in the car without a single failure.