Chipping in to Get More From Battery Packs

Power semiconductors help extend range, keeping their cool while improving efficiency at higher voltages.

August 1, 2015

Terry Costlow

Infineon’s high-voltage HybridPACK devices for full hybrid electrical vehicles are based on IGBT trench-field-stop technology that offers low conduction and switching losses.

Electrified vehicle designers are pushing semiconductor technologies to help them extend ranges and reduce the weight of battery packs. Power semiconductor improvements are helping powertrain designers move to higher voltages and reduce losses while managing a battery pack’s nemesis, heat.

Falling oil prices curtailed electrified vehicle sales during 2014. Hybrid volumes dropped, with market share of just 2.8%, according to a survey by HybridCars.com and Baum & Associates. In the U.S., plug-in vehicle sales soared by 23% in 2014, yet still barely cracked 120,000, according to InsideEVs.

Handling higher voltages succumbing to the effects of heat are among the goals for Magna’s power semiconductor designers.

The ardor of early buyers also seems to be cooling. Only 45% of last year’s hybrid and EV trade-ins went toward buying another alternative fuel vehicle, down from around 60% in 2012, according to Edmunds.com.

Power rangers

Power semiconductor advances are helping developers improve efficiency and increase range with fewer batteries. Improvements are making it more cost effective to use higher voltage systems while still meeting lifetime requirements.

“Semiconductors for higher voltage levels can transfer more power at less losses, [and] power semiconductors for higher voltage levels (1200 V) will help to increase mileage,” said Markus Schermann, Director New Product Area Electrification at Magna Powertrain. “Those that can bear more amps are able to provide more power. Semiconductors that can withstand higher temperatures allow higher continuous power output.”

Many of the changes occur in insulated gate bipolar transistors (IGBTs) and field effect transistors (FETs), central players in electrified powertrain components. Infineon recently introduced a line of automotive IGBTs with a breakdown voltage of 750 V, up from 650 V for the preceding generation. That simplifies designs for powertrain developers who opt to increase battery-pack voltages while providing other benefits.

“We have faster switching, which everyone wants because they get lower losses,” said Carl Bonfiglio, Senior Segment Marketing Manager, Powertrain and Electric Vehicle, at Infineon Technologies North America. “In the past, people often had to slow down so they would not surpass the breakdown voltage.”

Keep your cool

Inverter modules from Magna convert stored electric energy to meet powertrain demands.

As voltages rise, cooling challenges follow suit. Chipmakers are trimming resistance factors such as RDS(on), which helps determine both maximum current ratings and loss.

“Lower RDS(on) and reduced switching losses are reducing thermal losses in the FET or IGBT,” said Antonio Leone, Product Marketing Manager at Freescale Automotive Battery Management. “This leads to reduced requirements regarding cooling as well as increased efficiency of the drivetrain.”

Silicon carbide MOSFETs from STMicro provide higher switching frequencies than silicon-based IGBTs.

Metal oxide semiconductor FETs and IGBTs are competing in many instances, creating competition that drives innovation. Early this year, STMicroelectronics rolled out a silicon-carbide power MOSFET with RDS(on) better than 290 mΩ at the 200°C (392°F) maximum operating junction temperature. That facilitates switching frequencies up to three times higher than similar-rated silicon IGBTs offer, letting designers employ smaller external components to trim size and simplify cooling-system design.

On the other hand, Fairchild trimmed energy loss by 30% in its latest IGBTs. An advanced high-density-pitch self-balancing cell uses a self-aligned contact technology for extremely high current densities and improved dynamic switching features.

Packaging is a major factor in all power devices. Component housings and heat sinks can help system designers improve efficiency while meeting temperature goals.

“The IGBT chip is soldered to a ceramic substrate that’s soldered to copper fins that are immersed in liquid,” Bonfiglio said. “That increases the power cycling capability of the package, letting you run more current through, around 20% more.”

While power semiconductors play a central role in electrified powertrains, other digital devices can’t be overlooked. The electronic control units that oversee powertrains constantly make adjustments to maximize overall efficiency.

“A big role is going to be played by a central ECU, which controls the ICE, the transmission, and the electric propulsion,” Schermann said. “This ECU can choose the optimum setup of the entire powertrain for every operating condition. Ideally also the vehicle dynamics are controlled by this central ECU.”

Look everywhere

Texas Instruments and other suppliers are reducing power consumption on automotive parts to help reduce the drain on batteries.

While there’s a major focus on semiconductors in the powertrain, chipmakers are looking at all aspects of vehicle power requirements. Power saved in the instrument cluster can drive the powertrain.

For example, Texas Instruments trimmed the quiescent current of its low drop-out regulators to 10 μA in standby mode, cutting power consumption in infotainment systems, clusters, and other applications. Other vendors are focusing on sleep modes and networking.

“Amps equal ‘miles per gallon,’ especially in hybrids,” said Paul Kanan, Senior Manager, Automotive Controls Solutions Marketing at Renesas Electronics America’s Automotive Marketing Unit. “Instead of having door or sun roof modules alive during operations, they go to sleep and wake up only when needed. That’s done using partial networking.”

The focus on communications extends into the battery pack. A lot of data is moved when controllers and chargers interact to power vehicle components and recharge batteries. Simplifying data links can trim costs without sacrificing efficiency.

“Significant advancements are made in the battery internal communication between the individual cell monitoring ICs and the battery-management system,” Leone said. “Cheaper daisy chain and bus communication systems are available, eliminating costly isolated CAN communication.”

Magna technology helps OEMs combine internal combustion engines with electric traction drives, reducing complexity.

Electronics can also help vehicle owners improve mileage. Clusters and infotainment systems display mileage and find energy-saving routes. Navigation software is being tweaked to find routes that conserve power requirements by minimizing hills, among other tricks.

“There is also a big impact caused by the driver; the driver determines the route and the dynamics,” Schermann said. “Thus, control units can assist the driver. Navigation units can select the route with the minimum energy consumption; the vehicle controller can determine the optimum acceleration and cruise speed.”