Formula E Racers Help Advance EV Design

Formula E auto racing is not just a favorite spectator sport among auto hobbyists, but as a performance innovation hub, the sport continually contributes to the advancement of battery electric vehicles (BEVs)—or EVs, for short. The electronic systems in EV racers are complex in several ways. Today’s high-end racers contain over 60 embedded semiconductor processors, and when fully instrumented, they also include many sensors, telemetry, and data acquisition components that communicate environmental data. This complex system of components operates in extreme environmental conditions, such as temperature, vibration, pressure, and radiation, which means the system of electronics must have protection while operating at top performance in small spaces.

This article explores the four key types of extreme conditions that EV race car’s experience and how electronic measurement sensors play a role in monitoring and communicating vital data about these conditions. This article will also share design techniques and insights on how to protect these valuable electronic sensors and ultimately improve an EV racer’s overall design, safety, and performance.

Harsh Conditions in EVs

EV racing systems require electronic components that can withstand wide temperature ranges, vibration, and pressure as well as simultaneously reduce EMI, voltage spikes, and ground currents. From a design perspective, this is easier said than done, given the different types of harsh conditions (four of which we will look at below) and how those conditions affect the vehicle:

• Extreme temperature (cold and heat): In addition to causing physical damage, extreme temperatures can affect both the operation of electronics and the driving range of EVs. While cold temperatures are more stressful on battery performance, warmer conditions still reduce the overall range.
• Extreme vibration: Without the strong vibrations of an internal combustion engine (ICE), the primary sources of vibration in an EV are low-profile tires, stiff suspension, motors, and differential gears (if so equipped).
• Extreme pressure: Pressure levels are directly affected by temperature (and vice versa) in both ICE-powered vehicles and EVs. In the former, engine oil, fuel, and even water pressure must be at optimal levels for peak performance. However, in EV racers, the major pressure concerns are the tires and the suspension system.
• Extreme radiation: Any electrical current racing through a conducting cable creates electromagnetic radiation that can interfere with nearby electronics, sensors, and data flow. High DC- and AC-powered EV racers amplify the potential EMI problem. Also, requirements for increasingly lightweight, small components mean electronics are closely crammed together, creating the possibility of more EMI.

Powertrains Make a Difference

To appreciate the harsh conditions that EV race cars experience, it helps to understand how an EV operates in contrast to traditional, internal combustion engine or gas-powered vehicles.

In general, an automotive powertrain embodies components that generate power-feeds to a set of wheels. In a gas-powered vehicle, the powertrain includes the engine, transmission, drive shafts, differentials, and the drive wheels. Of course, the powertrain minus the engine is the drivetrain or driveline.

Compared to a gas-powered-vehicle powertrain, the EV powertrain is functionally less complex, as a simple electric motor replaces the more complex, gas-powered engine, as shown in Figure 1. However, EV powertrains do contain additional electronics that include power converters, ferrite cores, shielded cables, and electromagnetic compatibility (EMC) filters to reduce the extra energy leakage and electromagnetic interference (EMI) caused by an all-electric power system.

Figure 1: This diagram highlights the differences between EV and gas-powered powertrains.

According to Formula E racing rules, set by the Fédération Internationale de l'Automobile (FIA), the powertrain is the primary area where manufacturers can add innovation to differentiate their race vehicles. This flexibility has led to significant technological improvements since the inception of the race. For example, during Season 2 race preparations, regulations allowed each racing team to deviate from their former season one powertrain design (including the motor, gearbox, differentials, and casings).

This freedom in design allowed Renault Sport, the Season 2 champions, to position their electric motor transversely within the car with a two-speed gearbox drive to the differentials. The advantage of this design was the motor’s in-line position with the transmission, which reduced friction in the gearbox. This arrangement also resulted in a shorter drivetrain distance between the motor and differentials, thus allowing the inverter to be placed inside the gearbox—saving space and lowering the overall center of gravity for better handling. The inverter transformed the DC-powered battery into AC power, which was required to run the electric motor.

Further weight reductions and better materials were also used to improve the powertrain performance in Season 3. Together, these improvements increased the overall efficiency of the powertrain, which resulted in faster speeds, less charging, and a longer traveling range.

Monitoring and Communicating Conditions

Monitoring and communicating environmental data are two top priorities that optimize race car performance. But what specific measurements do EV racers monitor and communicate during a typical Formula E race that differs from gas-powered racers? Table 1 shows the type of measurements that occur in gas- versus electric-powered vehicles.

Table 1: This table shows the measurement differences between gas- and electric-powered vehicles.

Noise sources, for both mechanical vibration and EMI, are distinctly different among electric- and gas-powered vehicles. For EVs, the primary sources of mechanical vibration are the electric motor and transmission (if present) that send power feeds to the wheels. Contrary to a gas-powered vehicle, an EV can be at greater risk of EMI because of its high currents and voltages. That’s why radio-frequency (RF) probe sensors that detect EMI radiation leaks are more frequently present in EVs—at least during the test phase of an EV racer’s design.

EV racers have an additional requirement that ICE-powered racers don’t. Per the FIA standards, to qualify for Formula E racing, EV race cars need to carry a ruggedized current sensor to measure and monitor battery-power levels to ensure that the levels don’t exceed 200kW. This requirement means that a battery-management system is necessary to control maximum temperature and current-flow rates during the race. Interestingly, these temperature variables are controllable using a software system that manages the motor’s torque.

Once the data collected from the sensors is complete, it can assist to monitor, control, and optimize car performance. Anything that compromises the accuracy and function of the sensors—such as harsh racing conditions of excessive temperatures, vibration, pressure, and EMI—will negatively affect a vehicle’s performance.

Design Techniques

While it can be very effective, the design practice of ruggedizing measurement sensors to withstand high temperatures, excessive vibration, pressure (from the tire and shock systems), and EMI can come at a price. For example, sometimes additional cooling technology is essential to keep the temperature sensors from rising and causing in incorrect measurements. Pressure sensors can also be negatively affected by high surrounding temperatures, so engineers should appropriately consider cooling techniques.

Similarly, protecting sensors from excessive vibration often means adding dampening structures, which add weight and consume more space in the race car, but without this protection, vibration could destroy the sensors or lead to less accurate readings.

In addition to maintaining the integrity of a sensor, the exact sensor placement is critical in EV racing. The motor temperature in a racer is very high, and the temperature differences between the hottest spots on the motor and its surroundings can be great. Placing a sensor even 1mm off can result in misleading measurements that could make the driver push the motor harder than is safe.

Another design challenge in EV racers is controlling energy leakage and EMI in the powertrain, which consists of a variety of different electric components—as mentioned earlier. Due to functional considerations, these electronics are often placed together in small spaces with exposure to extreme temperature, vibration, pressure, and EMI spikes. Finally, each component needs to be as energy efficient as possible to extend the life of the battery systems.

One way to optimize the performance of the individual components is to integrate them carefully into a single system. Performance optimization is what Mouser Electronics, Infineon Technologies, and TDK® have done with their integrated filter and power converter EV powertrain solution.

A materials change can also help to reduce harsh EMI. Consider the ongoing development of power-device technology based on silicon carbide (SiC) materials, which have several advantages over conventional silicon in harsh environments. For example, SiC can withstand much higher electric fields, which helps SiC devices work with higher voltages and currents. This advantage leads to increases in power density and reductions in switching power losses under high temperatures. One example of SiC usage is in embedded Schottky diodes within EV power converters and inverters used in changing battery-pack DC power into AC power for motor operation.

Conclusion

As Formula E competitions continue to challenge EV race cars with harsh racing conditions, they are providing designers with ongoing opportunities to present innovative ways, particularly using ruggedized, measurement sensors, to overcome these obstacles—especially the four key types of conditions. While FIA has set strict standards on how to design Formula E-level performance racers, the organization is continuing to grant more and more leeway as an open gate for new advancements into the future. Now, it seems that Formula E race cars are not just spectacles for the leisurely entertainment of automotive-sports enthusiasts, but we could be watching the beginnings of a transformation in the performance, operation, and safety of all EVs—even those in the consumer realm. Maybe we can bounce this around as our next topic for discussion.

For information about how Mouser Electronics is helping to advance electronic vehicle technology, visit our Formula-e website.