Onboard chargers today are typically limited to relatively slow and small 3.3or 6.6kW devices that take hours to charge a car battery. Larger, 15to 20kW dc chargers are fast but are still too bulky and risky to put in the car itself and are instead being built into external units for use in the garage at home, said Ford’s Scholer.
To prevent overheating and fires, the charging and discharging of each cell in a large lithium-ion battery pack needs to be carefully supervised. "We are looking into chips for that, but there's nothing in production today," said Cherif Assad, a marketing manager for power train and hybrid vehicle components at Freescale Semiconductor.
The company earlier this year announced low-voltage battery controllers targeted at the microhybrids or for use in regenerative braking, wherein the power generated from stopping is used to help charge a battery or ultracapacitor. Thus far, however, most of the circuits used for chargers in plug-in vehicles are off-thes-helf industrial parts that are modified for automotive use.
Separately, hybrids require pre-driver and controller circuits to drive 30to 120kW electric motors. Freescale and Fuji Electric struck a partnership to design parts using slim inverters that can be integrated with mechanical modules and their cooling systems. The new components must drive up efficiency from about 35 percent for today's parts to more than 90 percent, Assad said.
"Inverters have never been the subject of much attention for how you improve performance, size and weight," said Dan Viza, director of corporate strategy and business development at Freescale. "Initial implementations are using available industrial components, but we will soon see the first purpose-built semiconductors for inverters and charging units."
Transmission specialist ZF Friedrichshafen and BMW launched a research project earlier this year to create an integrated solution for hybrid-vehicle components, aiming to integrate control and power electronics to simplify production and servicing of hybrids. Infineon and passive component maker Kemet are taking part in the project. The integration will require work on new cooling concepts so components can tolerate the high temperatures inside the transmission. The resulting design promises to reduce cabling and simplify system interfaces.
The overall electrical architecture of a hybrid or electric car is "totally different" from what has existed before, posing problems of EMC compliance with 650V signals and 400amp switches, said Assad of Freescale. That implies new kinds of high-voltage interfaces for converters, inverters and controllers that monitor the power signals, he said.
Standards, especially for chargers, are also needed, and pursuing them has become a full-time job for Scholer of Ford. "We started with EV standards 20 years ago, and now we’re updating them for plug-in hybrids and starting work on fuel cell standards," Scholer said. "We have been working on SAE standards for about three years and are in the implementation phase with some of them, but we are going to be working on the standards for another three to five years until we get everything done." Multiple standards groups are working in parallel with research demonstration projects and live deployments, he said.
The efforts include protocols such as supporting fast charging over dc. Smart Energy Profile 2.0, for communicating rate information over power lines to utilities, as well as specifications supporting fast charging over dc.
One proponent of the latter, ECOtality, is said to be gearing up with help from the U.S. Department of Energy to install as many as 1,300 public charging stations in California, Oregon, Tennessee, Washington and other states. The plan includes about 350 fast-charging stations.
"Carmakers know how to control an onboard charger, but there are more things to control with offboard controllers," said Scholer.
Initial draft standards for fast chargers are now up for an initial ballot, but once systems are deployed engineers will learn more about their behavior.
"We will have changes as we start implementing," Scholer said.
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