Increasingly, designers are switching to SiC and GaN power devices to leverage faster switching frequencies, as well as higher voltage and thermal operation ranges in EVs.
Climate concerns and evolving consumer preferences are driving technology innovations for electric vehicles (EVs) as a means towards a greener transportation future.
Innovations for this expanding e-mobility market range from smart inverters that can help integrate solar energy and other distributed energy resources into the electric grid, to ultra-fast charging EV supply equipment (EVSE), and increasingly potent battery cells. These technologies help to provide range assurance and drive the adoption of EVs.
EV sales surged by 160% in the first half of 2021 from a year earlier, to 2.6 million units globally, despite the global pandemic. Technological innovations, including better design and test methods across the electronic microcosms of power devices, converters, batteries, and chargers, are just some of the developments helping to fuel the overall growth of the e-mobility ecosystem. Let’s explore some recent automotive innovations and test methods that are enabling the rolling chassis.
Double Pulse Test for SiC and GaN Power Devices
Within the EV power ecosystem are power semiconductors – these tiny chips help to convert power among the different systems – such as the power steering and braking, infotainment system, lighting, air-conditioning, and of course, the electric powertrain. Increasingly, designers are switching to new wide bandgap (WBG) SiC and GaN power devices to leverage faster switching frequencies, as well as higher voltage and thermal operation ranges (Figure 1).
Figure 1 SiC and GaN applications in the modern EV (Image copyright and source: Keysight Automotive Power Electronics Test)
While WBGs improve functional efficiency and help reduce both design size and cost, they also suffer from higher switching losses due to the extremely fast oscillations, resulting in reduced efficiency of the power converter.
Power converter designers are turning to a relatively new method called the double pulse test (DPT) technique to make repeatable and reliable measurements for determining these switching losses.
Double pulse tests can help designers ensure their end products conform to industry standards, such as those set by the JEDEC, a global leader in developing open standards and publications for the microelectronics industry.
Testing, and Saving with Regenerative Power
Power conversion occurs throughout the EV (Figure 2).
Figure 2 Simplified block diagram of power conversion in an EV (Image source: Keysight E-Mobility Design and Test Technologies)
Power levels in the electrified vehicle range from ~50 kW up to and over 180 kW. Most of the components in the EV support bidirectional power flow. Besides the humble 12 V battery that powers the vehicle windows and lights, today’s EVs sport batteries from 280 V to 800 V.
Testing at high-power is not a simple extension of low power testing carried out for conventional combustion engine cars. Working with hundreds of volts, the automaker must prioritize the safety of both human and devices under test. High-power testing also generates tremendous amounts of heat, which add to air-conditioning operation costs.
Power management applications in the booming electric vehicle (EV) sector and consumer electronics devices, such as chargers or adapters, are fueling demand for silicon carbide (SiC) and gallium nitride (GaN) components. This month, we look into the latest developments in the wide-bandgap (WBG) materials and the way forward for the industry.
An increasingly popular cost-down solution is to use commercially available regenerative power systems which provide bi-directional, regenerative DC or AC power. The regenerative capabilities of these power supplies allow the energy consumed to be put back onto the grid cleanly, instead of being dissipated as heat, hence saving costs from energy consumption and cooling.
Understanding Cell Self-Discharge to Make Longer-Lasting Batteries
EV batteries have improved vastly since the early 2010s, where they supplied only 50-60 miles per full charge. These days, the average EV battery offers 250 miles per full charge, enough to assuage the range anxiety of most drivers.
Creating better batteries starts from understanding cell chemistry. A pet peeve of cell designers is the phenomenon of abnormally fast self-discharge in Lithium ion cells. Cell self-discharge is the reduction of the stored charge of the battery even when it is not connected to any device. Self-discharge decreases the shelf life of Li-ion cells, and causes them to initially have less than a full charge when used.
To detect abnormal self-discharge in Li-ion cells, developers and manufacturers have traditionally relied on measuring the drop of a cell’s open-circuit voltage (OCV) over a period of several weeks or even months to get good validation results. Having to wait this long during development results in lost opportunities by being late to the market with new designs. This is further compounded if self-discharge testing must be repeated. In manufacturing, storing large quantities of cells for a long time to screen them for self-discharge presents major expense, logistics, and safety problems.
To address these challenges, Keysight created a revolutionary ‘potentiostatic’ self-discharge measurement technique (Figure 3) that slashes the time required to measure cell self-discharge currents. For smaller cells like cylindrical 18650 or 21700 cells, developers can now measure stable self-discharge current in as little as 30-minutes to 2-hours, depending on the cell characteristics. For larger capacity pouch cells (e.g., 10-60 Ah), this takes as little as 1 to 4 hours. This shaves off a huge amount of test time and cost of the product development cycle, contributing to cheaper EV batteries.
Figure 3 Results from 4-hour test of 18650 cells using a high-performance potentiostatic analyzer
(Image souce: Keysight Li-Ion Self-Discharge Measurement Solutions)
EV & EVSE – Ensuring Interoperability
The EV is connected to the grid via an increasingly sophisticated network of EVSE. According to a Reuters report, there are more than 300 EV charging companies globally. Combine that with over 500 EV models, different charging modes and charging standards around the globe, we can see why charging EVs at different charging stations is not as simple as filling up the gas tank.
To address this interoperability challenge and accelerate time-to-market, many EV and EVSE manufacturers are investing in simulation solutions that can save them time and money.
These design verifications use machines that can simulate both electric vehicles or charging stations, solving the challenges of uniquely testing a new product under different EV or EVSE models.
Creating a Sustainable Energy Ecosystem
The automotive industry will face evolving consumer demands, such as whether the product meets environment, social, and governance goals. New test technology will need to evolve in tandem to help develop better electronic microcosms such as power devices, converters, cells, batteries, and drivetrains. At the macrocosm level, we will see smarter grids harnessing renewable energy to power the growing fleets of EVs, and meet our ESG goals as a civilization.
About the Author
Hwee Yng Yeo is the Industry Solutions Manager for Automotive and Energy at Keysight Technologies.