There are two major factors influencing the future of vehicle transportation and semiconductor technology today. The industry is embracing exciting new ways to drive our cars with clean electricity, while redesigning the semiconductor materials that underpin electric vehicle (EV) subsystems to maximize power efficiency and, in turn, increase EV range .

By Timothé Rossignol, Marketing Manager, Analog Devices

There are two major factors influencing the future of vehicle transportation and semiconductor technology today. The industry is embracing exciting new ways to drive our cars with clean electricity, while redesigning the semiconductor materials that underpin electric vehicle (EV) subsystems to maximize power efficiency and, in turn, increase EV range .

Government regulators continue to require auto OEMs to reduce the overall carbon dioxide emissions of their vehicle lines, impose tough penalties for non-compliance, and begin adding electric vehicle charging infrastructure along roads and parking areas. But despite these advances, mainstream consumers still have doubts about the range of EVs, hindering EV adoption.

To complicate matters, a large EV battery can increase its driving range and ease consumers’ anxiety about driving range, but it will increase the price of EVs – the cost of the battery accounts for more than 25% of the total vehicle cost. %.

Fortunately, contemporaneous revolutions in semiconductor technology have spawned new wide-bandgap devices, such as silicon carbide (SiC) MOSFET power switches, placing consumers’ expectations for EV driving range and OEMs’ actual achievable range under cost architectures. gap has been narrowed.

Delivering the promise of EV range expansion with SiC technology motor inverters
Figure 1. Power conversion components in an electric vehicle.
The motor inverter converts the DC voltage of the high-voltage battery into an AC waveform to drive the motor and drive the car forward.

Making the most of SiC technology

Delivering the promise of EV range expansion with SiC technology motor inverters
Figure 2. Battery-to-motor signal chain. To increase driving range, each module should be designed to provide maximum energy efficiency.

It is well known that SiC-based power switches inherently have advantages in power density and efficiency, which are significant for both system heat dissipation and device size reduction. The use of SiC is expected to reduce the size of the inverter by a factor of three at 800 V/250 kW, and if used in conjunction with DC link film capacitors, further size and cost savings can be achieved. Compared to traditional silicon power switches, SiC power switches can help achieve better driving range and/or smaller battery size, making the switch cost more advantageous at both the device level and the system level.

When considering both range and cost, there is still a need for continuous innovation with a focus on motor inverters, aiming to further improve the efficiency and range of electric vehicles. As the most expensive and functionally important component of a motor inverter, SiC power switches require precise control to fully realize the value of the additional switching costs.

Virtually all of the inherent benefits of SiC switching are disrupted by common-mode noise, as well as extremely high and damaging voltage and current transients (dv/dt and di/dt) caused by ultrafast voltage and current transients (dv/dt and di/dt) in a poorly managed power switching environment. Voltage overshoot effects. Generally speaking, the underlying technology aside, the function of a SiC switch is relatively simple, it is just a 3-terminal device, but it must be carefully connected to the system.

Delivering the promise of EV range expansion with SiC technology motor inverters
Figure 3. Voltage and current waveforms at turn-on (left) and turn-off (right).
In a SiC environment, the dv/dt will exceed 10 V/ns, which means that switching 800 V DC will take no more than 80 ns.
Likewise, a di/dt of 10 A/ns means that the current is 800 A in 80 ns, from which the di/dt change can be observed.

About gate drivers

Delivering the promise of EV range expansion with SiC technology motor inverters
Figure 4. An isolated gate driver bridges the signal world (control unit) and the power world (SiC switch).
In addition to isolation and signal driving, the driver performs telemetry, protection, and diagnostic functions, making it a critical element of the signal chain.

The role of the isolated gate driver is related to the optimal switching point of the power switch, ensuring short and accurate propagation delays through the isolation barrier, while providing system and safety isolation, avoiding overheating of the power switch, detecting and preventing short circuits, and promoting in ASIL Insert submodule drive/switch function in D system.

However, high slew rate transients caused by SiC switching can disrupt data transfer across the isolation barrier, so measuring and understanding susceptibility to these transients is critical. ADI’s proprietary iCoupler®The technology has excellent Common Mode Transient Immunity (CMTI) with measurement performance up to 200 V/ns and above. In a safe operating environment, this can fully unlock the potential of SiC switching times.

Delivering the promise of EV range expansion with SiC technology motor inverters
Figure 5. For more than 20 years, ADI has been at the forefront of digital isolation technology development with the iCoupler® digital isolation IC.
The technology uses transformers with thick polyimide insulation.
The digital isolator uses a wafer CMOS process. The transformer uses a differential architecture for excellent common-mode transient immunity.

High-performance gate drivers have proven their worth in real-world testing with leading SiC MOSFET power switch providers such as Wolfspeed. For key parameter performance, such as short-circuit detection time and total fault clearing time, can be as low as 300 ns and 800 ns, respectively. In order to improve the safety and protection level, the test results show that the adjustable soft-off capability is crucial to the smooth operation of the system.

Likewise, switching energy and electromagnetic compatibility (EMC) can be maximized to maximize power performance and electric vehicle range. With higher drive capabilities, users can achieve faster edge rates, resulting in lower switching losses. Not only does this help improve efficiency, it saves board space and cost by eliminating the need to allocate external buffers for each gate driver. Conversely, under certain conditions, the system may need to reduce switching speed to achieve excellent efficiency, or even graded switching, which studies show can further improve efficiency. ADI offers adjustable slew rate to allow the user to do this, and the elimination of external buffers further reduces the hindrance.

System elements

It is important to note that the combined value and performance of a gate driver and SiC switching solution may be completely offset by compromises and/or inefficiencies of surrounding components. ADI’s experience in power control and sensing combined with our system-level approach to performance optimization can cover multiple design considerations.

From a holistic perspective, EVs reveal additional opportunities to optimize driveline power efficiency, which is critical to maximizing the available battery capacity while ensuring safe and reliable operation. The quality of the battery management system directly affects the number of miles an electric vehicle can travel per charge. A high-quality battery management system can maximize the overall life of the battery, thereby reducing the total cost of ownership (TCO).

In terms of power management, being able to overcome complex electromagnetic interference (EMI) issues without reducing BOM cost or PCB size will become critical. Whether it’s power supply circuits for isolated gate drivers or high voltage to low voltage DC-DC circuits, high power efficiency, thermal performance and packaging remain key considerations in the power domain. In all cases, the ability to eliminate EMI is extremely important to EV designers. Electromagnetic interference is a critical pain point when it comes to switching multiple power supplies, and good EMC performance can go a long way toward reducing test cycles and design complexity, resulting in faster time to market.

If you delve into the ecosystem of supporting components, advances in electromagnetic sensing technology have led to a new generation of contactless current sensors that offer high bandwidth, high accuracy, and no power loss, in addition to enabling sophisticated and Reliable position sensor for end-of-shaft and off-shaft arrangements. A typical plug-in hybrid electric vehicle deploys 15 to 30 current sensors and employs rotation and position sensors to monitor the traction motors. Accuracy and reliability under disturbing electromagnetic fields are important attributes for measuring and maintaining performance across electric vehicle power systems.

end-to-end efficiency

Looking at all elements of an electric vehicle drivetrain as a whole, from batteries to motor inverters to support components, ADI sees countless opportunities to improve electric vehicles, both to increase their overall energy efficiency and to increase electric vehicle range. As SiC power switching technology penetrates into electric vehicle motor inverters, digital isolation has become an important part of it.

Likewise, automotive OEMs can leverage a multidisciplinary approach to optimizing electric vehicles to ensure that all available power sensing and control devices work closely together to maximize performance and efficiency. At the same time, they could help remove the last hurdle for mainstream consumers to buy an EV, range and cost, while helping to create a greener future.

References
1 Richard Dixon. “MEMS Sensors for Future Cars.” 4th Annual Automotive Sensors and Electronics Summit, February 2019.

About the Author

Timothé Rossignol holds an MS and PhD in Electrical Engineering from the University of Toulouse. He has been working in the automotive industry for the past 10 years and has extensive experience in the entire supply chain. Timothé started his career in France, first with OEM and Tier 1 supplier companies, before moving to the UK as Head of Hardware Design. He joined ADI in Limerick, Ireland as a systems engineer in 2018 and has recently returned to France as marketing manager for e-mobility power conversion systems. Contact information:[email protected]

"There are two major factors influencing the future of vehicle transpo…