Evolutions in Electric Vehicle Technologies

Recent high-profile demonstrations by an estimated 1.5 million students in over 100 countries echo growing levels of public concern over climate change. With the transport sector accounting for around 24% of CO2 emissions globally, car manufacturers are rising to the challenge, setting ambitious targets for carbon emissions reductions.

Global sales of electric vehicles exceeded 2 million in 2018, up from just a few thousand in 2010 and industry analysts are forecasting an acceleration of this growth, (figure 1), with electric vehicles expected to account for 57% of all passenger vehicle sales by 2040 at which time 30% of the global passenger vehicle fleet will be electric vehicles (EV).

Figure 1: EV market growth forecast
(Source: https://about.bnef.com/electric-vehicle-outlook/#toc-download)

2018 was a pivotal year for the EV with global sales of 2.1 million. China currently leads the market for the fifth successive year, with 55.5% share with the Asia Pacific region comprising 60.3% of the market and Europe in second place with 22.0%. This trend is set to continue in 2019 with sales of 2.8 million electric vehicles forecast, (68% will be BEVs and 32% PHEVs), giving the EV market a 3% share of the total passenger car market.

The 20-year timeframe of the above forecasts may not at first glance seem ambitious but transforming the basic powertrain of the automobile requires carmakers to implement huge changes to their operations – and many are making this in a single product generation. This article examines how market demands for increased power and efficiency are driving innovations in these electric vehicle technologies and how these developments pose new challenges for testing and integration during manufacture.

Manufacturers Get Serious About the Electric Car

In the face of ever-tighter global emissions regulations, car manufacturers are making transformational changes to their operations and many have made aggressive commitments to reduce carbon emissions by increasing their ranges of electric vehicles.

Tesla is the current market leader with the Chinese automaker, BYD, close behind and many other manufacturers gearing up to launch products in this increasingly competitive market.

The Volkswagen Group, for example, whose brands include Audi, Porsche, and Bentley, plans to increase global production levels and product options of its electric vehicles, aiming to launch 70 full-electric models over the next 10 years, with expected sales of 22 million vehicles. In doing so the group plans to reduce 2030 emission levels from its vehicles by 40% when compared to 2015 levels. VW Group CEO, Herbert Diess has been quoted as committing the car manufacturer to become fully carbon-neutral across all its operations by 2050.

Vehicle Technologies – What’s Under the Hood?

There are effectively two types of Electric Vehicle, all-electric vehicles (AEVs) and plug-in hybrid electric vehicles (PHEVs). AEVs can be further classified as battery electric vehicles (BEVs) or fuel cell electric vehicles (FCEVs), both of which must be charged from the electrical grid and are also usually capable of generating electricity through regenerative braking. Figures 2 and 3 show simplified block diagrams for a BEV and a PHEV.

Figure 2: BEV Block diagram
(Source: https://toshiba.semicon-storage.com/ap-en/application/automotive/ecology/hev-ev.html)

A BEV is propelled entirely by electric motors powered by on-board batteries, does not use an internal combustion engine hence does not rely on fossil fuel. During braking, the electric motor can function as a generator, recharging the battery by converting the vehicle kinetic energy into electric energy.

Figure 3: PHEV Block diagram
(Source: https://toshiba.semicon-storage.com/ap-en/application/automotive/ecology/hev-ev.html)

In a PHEV, the internal combustion engine remains the main energy source, with the battery and electric motor used to improve overall efficiency; the PHEV is propelled by the electric motor when the ICE is less efficient and otherwise runs on the ICE. Again, during braking, the electric motor works as a generator, recharging the battery. Since they rely less heavily on the electric motor, PHEVs can use smaller battery packs than BEVs.

In both the BEV and PHEV, a large battery provides current to high voltage components within the system, which supply the electric powertrain of the vehicle. The Inverter and the DC-DC Converter are key high-voltage sub-components within both types of vehicle; the inverter converts the DC current from the battery to the three-phase ac current required by the electric motor. The DC-DC Converter converts the high voltage generated by the vehicle motor, (during braking, for example), to the typical battery voltage, usually either 12V or 20V.

The inverter, the DC-DC Converter, and the battery system are all key parts of the EV drivetrain, each presenting unique design challenges and requiring specific testing approaches during manufacture.

The Inverter

The power transistors used within an inverter must seamlessly convert, switch and regulate large amounts of high voltage currents in a high-temperature, hostile environment. Traditionally the domain of Insulated Gate Bipolar Transistor devices, (IGBT), new Wide Bandgap, (WGB), Silicon Carbide, (SiC), and Gallium Nitride, (GaN) based technologies are increasingly being adopted by manufacturers seeking improvements in power and efficiency levels. Transistors based on these technologies offer several advantages, including high temperature and high voltage operation and improved efficiency. At the same time, however, they bring new challenges to the designer in ensuring stable and safe designs. With the very fast switching speeds of GaN power transistors, great care must be taken to avoid the high levels of EMI emissions or transistor breakage that can be caused by parasitic inductance.

While well-designed circuits and board layouts can address these issues, iterative design cycles can be time-consuming and expensive. Leading-edge power circuit simulator software are now available that offer valuable performance verification during the design phase, greatly speeding time to market.

The DC-DC Converter

DC-DC Converters also bring design challenges; traditional solutions, based on silicon devices required expensive water-cooling systems. The new WBG devices can reduce the need, and hence the cost, for water cooling but introduce potential safety issues as they enable multiple converter applications to be integrated into a single module, raising the operating voltages above the 60V safety limit. Testing of converters can, therefore, be a hazardous process and suitable test equipment, conforming to the recommendations of standards such as NFPA 79, must be used to protect designers, technicians, and operators.

Today, innovative systems for this purpose are being developed, which are equipped with safety features designed to protect both the people doing the testing and the equipment under test. These systems have been designed with regenerative capabilities, which transfer the energy used during testing back to the grid, thereby enabling savings from energy consumption and cooling costs.

The Battery

The battery is the third of the key onboard components, its characteristics determining how far the EV can travel between charges. EV battery technology has evolved rapidly over the years, with current, averagely priced models enabling a car to travel for over 100 miles. The 2018 Nissan Leaf, for example, has a 40-kWh battery pack, with 192 Lithium-Ion cells, giving it a range of 151 miles. At the high end of the market, the battery in the Tesla Model S has 7,104 Li-Ion cells, enabling it to travel 315 miles between charges. The market for EV batteries is buoyant and analysts forecast continued high growth as manufacturers look to develop faster-charging batteries which enable more miles per charge.

For battery manufacturers, effective testing of each individual cell is key to the overall performance of the battery pack. A phenomenon known as cell self-discharge can decrease the shelf life of the battery and reduce its initial charge level. Traditional testing techniques involved monitoring a cell’s open-circuit voltage over a period of many weeks which is not ideal, given the increasing need to get to market quickly.

Equipment providers are nowadays able to address this problem, by developing self-discharge measuring solutions that reduce test time from weeks to hours, enabling manufacturers to significantly reduce test cycle time and hence speed up time-to-market.

Fred Weiller, Senior Director of Solutions Marketing, Keysight Technologies

The Roadside Ecosystem

Outside of the car itself, charging stations are a vital enabler of the growth in the market for EVs and understanding charging patterns and behaviours of drivers is key to the ability of power companies to plan for peak loading on the grid. Modern charging networks, such as Inonity, (BMW, Mercedes, Ford and Volkswagen) and Ultra-E, (Allego, Audi, BMW, Magna, Renault, Hubject and others) are about more than providing charge to the EV. As effective points of sale, these stations can capture and generate vast amounts of data that can be used to model demand and help provides balance loads on the grid. Applications are beginning to appear from companies like Bosch and Chargepoint, which offer convenience and visibility of charging options to drivers. As this big-data ecosystem develops, developers will need an array of tools to give visibility of these emerging networks.

Conclusion

With the market for EV cars set for significant growth, a broad and diverse ecosystem, encompassing on-board and roadside technologies is expanding. As the demand for newer, more powerful and more efficient electric drivetrains continues, further innovations in power devices, cells and batteries will emerge. This wide range of devices and applications will need a correspondingly wide range of powerful test solutions to verify designs and ensure compliance with relevant standards.