The gray secret of clean energy vehicles

Automakers are taking a variety of approaches to achieve "green cars", including all-electric vehicles, hybrid or microhybrid vehicles with different formulations. However, no matter which one, I am afraid it will not become a mainstream technology in a short period of time, mainly because in the foreseeable future, automotive batteries are still too large, too heavy, expensive and not powerful enough. In addition, there are many challenges to be overcome in the design of automotive power electronic components.

According to the forecast of Pike Research, a clean technology market research organization, the number of hybrid vehicles worldwide will increase from the current 870,000 to 1.5 million in 2017, a growth rate of only 1.6%. In contrast, the engine automatic stop-start (start-stop) vehicles, which are not very popular in the US market, have the opportunity to emerge.

Europeans will buy nearly 3 million of these stop-start vehicles, which are "mild hybrids" that don't have electric motors but use a more powerful starter/alternator/lead-acid battery combination to shut down the car when it's idle and restart it when the driver hits the accelerator, Pike estimates. In 2011, Europeans will buy nearly 3 million of them, and global sales will reach 37 million by 2020.

However, Pike also expects that all-gasoline powered vehicles will still account for 90% of the general passenger car market in 2017.

Philip Gott, managing director of IHS Automotive, another market research firm, said automakers have tried various approaches, but "plug-in hybrid technology looks like a good solution to meet the most stringent emissions standards and fuel economy requirements."

"I think we will continue to see a variety of hybrid solutions because there are so many different market demands and it's hard to predict what people will want," said Rich Scholer, an electronic systems engineer who is responsible for promoting hybrid and fuel cell vehicle standards at Ford Motor. Ford is based on regular internal combustion engines and offers different hybrid systems and plug-in hybrid solutions.

Scholer pointed out that unlike Ford's approach, hybrid models such as Chevy's Volt, Nissan's Leaf and Toyota's Prius were designed from scratch, "Those approaches are very expensive, and it would be more cost-effective to use an existing platform as a basis."

Volt's E-Flex system

Meanwhile, newcomers such as Coda and Tesla are preparing to release new models, including all-electric five-passenger sedans. Scholer believes: "It will take at least three to five years for the market to mature."

The most vexing problem of electric vehicles is the battery pack. John Gartner, a senior analyst at Pike, said that the current car battery adds at least $10,000 to the vehicle price, and the current best solution, lithium-ion batteries, cost up to $1,000 per kilowatt-hour.

The U.S. Department of Energy's goal is to reduce the cost of automotive batteries to $250 per kilowatt-hour. IHS's Gott believes that this goal may not be achieved until after 2020. According to his observation, there are at least four lithium-ion battery variants and dozens of other chemical formulas that hope to make a breakthrough. "It's too early to say who will win because the relevant technologies are changing very quickly. I won't rule out any technology first, even lead-acid batteries."

The role of chip manufacturers

In terms of car battery chargers, Ford's Scholer pointed out that the current onboard charger solutions are usually slow and low-power 3.3kW or 6.6kW devices, which take several hours to fully charge the car battery. The higher-power 15~20kW DC chargers are faster, but they are too bulky and there are risks in placing them in the car. They are suitable for use in the garage as external devices.

To prevent overheating and fire, the charging and discharging of each battery cell in a large lithium-ion battery pack must be carefully monitored. "We are developing such chips, but we don't have a product yet," said Cherif Assad, marketing manager for automotive powertrain and hybrid vehicle components at Freescale Semiconductor.

Freescale released a low-voltage battery control chip earlier this year that targets micro-hybrid vehicles or regenerative braking applications. The latter is to convert the power of the car when it stops into electricity to charge the car battery or supercapacitor. It is understood that so far, most of the chips used in plug-in hybrid battery chargers are off-the-shelf industrial-grade components modified for automotive applications.

In addition, hybrid vehicles require pre-driver and controller circuits to drive 30~120kW electric motors. To this end, Freescale and Fuji Electric have collaborated to design related components using slim inverters that can be integrated into mechanical modules and cooling systems. Assad pointed out that the newly developed components can increase power efficiency from the current 35% to more than 90%.

Smart fortwo mhd, a representative model of micro-hybrid system

Dan Viza, Freescale's director of corporate strategy and business development, said inverters have never received much attention in improving the performance, size and weight of chargers: "Initial solutions are all using off-the-shelf industrial parts, but soon we will see semiconductor components designed specifically for the inverter and the charger."

Transmission specialist ZF Friedrichshafen and carmaker BMW also announced a research project earlier this year to develop integrated solutions for hybrid vehicle components. The main goal is to combine control and power components to simplify hybrid production and service processes.

Semiconductor giant Infineon and passive component manufacturer Kemet also participated in the research and development project, which requires a new cooling technology concept to allow components to withstand the high temperatures in the gearbox. The design developed by the project will reduce the number of cables in the car and simplify the system interface.

Freescale's Assad also pointed out that the overall electronic architecture of hybrid or electric vehicles is completely different from that of existing vehicles, which leads to electromagnetic compatibility (EMC) issues for 650V signals and 400A switches. This means that new high-voltage interfaces need to be designed for components that monitor power signals, such as converters, inverters and controllers.

Standards—particularly for chargers—are also needed, and driving them is what Ford's Scholer is responsible for. "We started with electric vehicle standards 20 years ago, and now we are pushing for updated standards for plug-in hybrid vehicles and starting to develop fuel cell standards," he said. "We have been working on SAE standards for about three years, and some of them are now in the implementation stage."

However, Scholer also pointed out that it will take another 3 to 5 years for the standardization work to be completed. Currently, there are multiple standard working groups working on the research demonstration projects and field deployment. The related work includes the communication protocol and technical specifications for fast charging through direct current, and the Smart Energy Profile 2.0 standard for transmitting rate information to utilities through power lines.

One company, ECOtality, is said to be building up to 1,300 public charging stations in California, Oregon, Tennessee, Washington, and other places with the assistance of the U.S. Department of Energy, of which 350 will use fast charging technology. Scholar pointed out: "Automakers know how to control the charger on the circuit board, but there are still many issues to control through the off-board controller."

A draft standard for fast chargers is now awaiting its first round of voting, and engineers still have more to learn about their characteristics once the systems are deployed. "When we start deploying, there will be some changes," Scholer said.