Electric vehicle (EV) and hybrid electric vehicle (HEV) technologies are on a roll. Major automotive manufacturers around the world have unveiled or are on the verge of unveiling many such cars for the market, as all of these companies are eager to adopt the technology.
That’s not surprising, given governmental regulations and incentives. There’s also the need to reduce pollutants as well as our dependence on oil. And, the mass market is ready for a car that fits into the average consumer’s already squeezed budget.
Most experts say that such an inexpensive EV or HEV won’t be easy to achieve in the short term, though. Plus, no one knows how the current electric grid infrastructure will handle a significant increase in automotive batteries that require daily recharging. And, today’s most advanced battery technologies are still quite costly.
Most projections for HEVs put their price tag around $40,000 to $50,000, which is too high for mass-market appeal. Some numbers bandied about for EV end-user prices are over $100,000. Much of this is due to high battery pack costs, which are projected to range anywhere from several thousand dollars to well over $10,000 each (see “Battery Challenges For Electric Vehicles”).
A study by Carnegie Mellon University published by Energy Policy points out that HEVs like the Chevy Volt from General Motors (GM) will not save enough on gas to cover the higher purchasing cost of the car. The study’s authors conclude that the only way the Volt will save car owners energy costs over the vehicle’s lifetime would be for both gasoline and electricity costs to drop substantially from present levels, which is unlikely to happen.
Still, GM is putting its muscle behind the Chevy Volt, a plug-in series HEV slated for market introduction this year. Its internal combustion engine (ICE) is engaged to generate power for its electric-drive motor and its battery pack, not to power the wheels. In a parallel hybrid vehicle, the electric motor is connected directly to the car’s ICE flywheel, allowing the clutchless powertrain to capture torque from both the electric motor and the ICE.
Besides GM, other major automakers are actively pursuing more energy-efficient HEV and EV technologies. One of the most notable HEVs is the Ford Fusion, which was introduced to the market last year. The Fusion can be driven at speeds up to 47 mph from solely its nickel-metal-hydride (NiMH) battery. After that, its gas-powered ICE kicks in. The popular Toyota Prius automatically starts its gas ICE at 25 mph.
A MILD HYBRID FORM
In a typical HEV system, a gasoline-powered high-efficiency ICE works with a rechargeable battery (Fig. 1) to power the car. The ICE’s output is also fed to a planetary gear power-split device, which in turn feeds an ac synchronous generator. The battery’s output is fed to a high-voltage dc-ac inverter. The inverter also accepts the generator’s output and feeds a permanent-magnet ac motor. A circuit controls the power.
To satisfy legislative efficiency and environmental requirements, automakers are grappling with many different forms of relatively inexpensive HEV technologies. One such form that may soon take off rapidly is the belt alternator starter (BAS) system. Many call it a “mild” hybrid technology, though pure hybrid enthusiasts may cringe at this naming convention. A BAS system is considered a relatively low-cost approach to HEV technology that can provide some meaningful benefits.
General Motors is an advocate of BAS systems, which offer additional fuel savings and fewer tailpipe emissions at a slightly higher cost. Fuel savings of 5% to 10% are possible, mostly for city driving. Currently, most BAS systems are limited to being used with engines of about 3 liters and six cylinders or less. However, such engines are expected to see rapid growth in the next few years, making the adoption of BAS systems easier.
In a BAS system (Fig. 2), an electric motor replaces the conventional belt-driven alternator and starter. When the engine is running, the electric motor acts as a generator and charges a separate 36-V battery. When the engine has to be started, the motor starts its torque via the accessory belt for cranking. The BAS system can perform engine stop/start, electromechanical launch assist, regenerative braking, high-power generation, and other functions without the need for large changes in a car’s design.
The actual implementation of the BAS system depends on the performance level sought in the car in terms of motor/generator efficiency and output-power capability. Some BAS systems, which might not include a starter motor, will have heavier loads while starting an engine, particularly in very cold weather. In general, BAS systems improve fuel economy by 10% to 15% (mostly in city driving) over conventional gas-powered ICE cars.
Although they provide only about half the benefit of a full HEV, BAS systems only cost automakers 15% to 20% more and don’t require significant engine-compartment and chassis modifications. Vehicles equipped with BAS systems don’t provide much of a benefit for highway driving, though. Nevertheless, their relative simplicity is causing a lot of optimism among automotive system designers.
“Within the next five to 10 years, every car will have a BAS system, because it will provide a lot of benefit for very little added cost and complexity,” says Ted Bohn, an electrical engineer at the Argonne National Laboratory’s Center for Transportation Research.
Regulations covering the use of the BAS concept in HEVs are under discussion in both the U.S. and Europe and will probably be finalized by 2015. Germany’s BMW has been adopting leading-edge implementations of the BAS concept in all of its HEVs.
THE ALL-ELECTRIC VEHICLE
All-electric vehicles have been in development for many years. EVs are generally propelled by electric motors powered by rechargeable NiMH and more recently by lithium-ion (Li-ion) batteries. Yet due to the battery technologies, EVs are expensive to produce commercially. Moreover, their driving range and speed are limited.
Two decades ago, General Motors demonstrated the EV1, one of the company’s Impact concept electric cars, as an example of how GM would meet future “clean air” government mandates. In 2007, Miles Electric Vehicles in the U.S. announced that it would bring the XS500, a highway-capable all-electric sedan, to the market by 2009. The car is not available yet. And despite the success of its high-end Roadster, Tesla Motors Inc. doesn’t expect its standard Model S sedan to hit the market—with a $49,900 base price—until 2012.
The success of EV technology has been more pronounced in overseas markets than the U.S. According to The Wall Street Journal, about 56,000 EVs are in use, most of which are limited to low-speed driving and have limited range. Nissan’s Leaf operates from a Li-ion battery with a top speed of 90 mph and a range of 100 miles. Tesla’s Roadster also operates from a Li-ion battery and has an electronically limited top speed of 125 mph.
Tesla says the Roadster set the world distance record of 311 miles (501 km) for a production electric car on a single charge on Oct. 27, 2009, during the Global Green Challenge in the outback of Australia. According to an independent analysis from the U.S. Environmental Protection Agency (EPA), the Roadster can travel 244 miles (393 km) on a single charge from its battery pack and can accelerate from 0 to 60 mph in 3.7 s. Tesla says the Roadster operates with an average efficiency of 92%.
The world’s most popular EV is the REVAi, also known as the G-Whiz, made by India’s REVA Electric Car Co. The car is used in 24 countries across Europe, Asia, and Central America. It was launched in the United Kingdom in 2001.
Another EV in the works, the Mini E from BMW, is being assembled in the United Kingdom. Its Li-ion battery pack provides enough power for a 150-mile range. It uses a transversely mounted 204-hp-torque electric motor mated to a single-stage helical gearbox. It can go from 0 to 60 mph in 8.4 s, and its top speed is 95 mph.
One aspect of plug-in EV (PEV) technology that makes for a new business model: selling a PEV’s stored energy back to the electric-grid utility during charging. Delaware is set to become the first U.S. state to allow electric-car owners to charge PEVs at night when electricity rates are low. They can then sell back excess stored electricity during the day at a profit.
To take advantage of this new business model, GE and Juice Technologies announced a joint development agreement to create intelligent PEV charging devices for U.S. and global markets. The chargers integrate GE’s smart meters with Juice Technologies’ Plug Smart engine to help customers charge their cars during low-demand and lower-cost time periods.
“Our smart charging system and advanced technology have been in development over the past two years,” says Rich Housh, CEO of Juice Technologies. “We’ve collaborated with utilities and Ohio State University’s Center for Automotive Research to develop the right solution for both utilities and consumers, and our collaboration with GE gives us the expertise we need to bring our solutions to market.”
The University of Delaware has already developed a vehicle-to-grid (V2G) technology (Fig. 3). The enabling technology has been licensed to AutoPort Inc., which has retrofitted a few test PEVs for the state government of Delaware and plans to have 100 more such vehicles on the road within the next 15 months. The converted vehicles will make use of an electric-drive system called the eBox, which is manufactured to the V2G specifications by AC Propulsion Co. Initially, the Toyota Scion EV will use such eBoxes.
For those PEV drivers concerned about the hassle of having to plug in their vehicle’s batteries for recharging, Evatran LLC’s “hands-free” technology simplifies matters. Its patented Plugless Power concept is a dual-component system based on inductive charging. Its vehicle adapter, which can be attached to any car, inductively links up with a basestation located at a Plugless Power station.
Evatran is launching the proximity charging system in field trials using pre-production units in and around the company’s location in Wytheville, Va. The trial involves three Whip EVs from Wheego Electric Cars Inc., a Current EV from Electric City Motors, and a ZENN EV from ZENN Motor Co. Evatran’s parent company is MTC Transformers.
THE ACTIVE WHEEL CONCEPT
A couple of years ago, Michelin Tire Co. suggested propelling cars by putting a motor in one or more of their tires, improving fuel efficiency and reducing carbon-dioxide (CO2) emissions. Michelin showcased the latest generation of this technology, known as the active wheel (Fig. 4), on the Volage electric roadster from Monaco’s Venturi at this year’s North American Auto Show.
The concept is basically a standard wheel that houses a pair of electric motors. One of these motors spins the wheel and transmits power to the ground. The other motor acts as an active suspension system to improve comfort, handling, and stability. The system can be used on electric cars powered by batteries or fuel cells. It also eliminates the need for any gearbox, clutch, transmission shaft, universal joint, or anti-roll bar.
The active wheel’s compact drive motor and integrated suspension system allow for standard disc brakes to be fitted between the motors. This means a single wheel can house all needed braking, drive, and suspension components.
Palmer Labs is trying to commercialize a retrofit kit that can transform existing cars into HEVs by placing an electric motor inside each of their four wheels. The Hybrid Retrofit Kit was developed by former IBM researcher Charles Perry, who has partnered with the Tennessee Technological University, which will build a working prototype.
“Our approach is different in that we don’t need to modify anything in existing vehicles to turn them into hybrids,” Perry says. The Retrofit Kit is installed in the space between the wheel’s brake mechanism and the hub.
CONTROL AND POWER OPPORTUNITIES
Given the many aspects and complexity of HEV, EV, and PEV designs and relevant safety and energy requirements, semiconductor IC manufacturers perceive many opportunities to supply necessary control and power IC components.
“There’s a need for ICs to handle high-voltage, battery, charging, and electric-motor management and control,” says Cherif Assad, power and hybrid segment manager for Freescale Semiconductor. “At each level, there will be a requirement for a microcontroller. I believe that this will lead to the use of multicore processing.”
An example of this is Freescale Semiconductor’s MPC564XL single-chip dual-core 32-bit microcontroller (Fig. 5), co-developed with STMicroelectronics (ST’s part number is SPC56EL) for safety-critical automotive systems. This complex device is designed to specifically address the safety requirements of the International Electrotechnical Commission’s 61508 standard and the International Standards Organization’s 26262 standard. It is based on Freescale Semiconductor’s Power Architecture.
Rechargeable Li-ion batteries in HEVs, EVs, and PEVs are bringing in the need for battery monitoring and management (see “Li-ion Suppliers Try To Find The Right Chemistry With Car Buyers”). This is necessary to ensure that all the cells in the battery are at the same voltage level prior to charging them, enabling accurate measurement data and cell balancing. The more information that is known about a battery’s power status, the more accurately one can predict mileage. Battery management involves sensors, an analog-to-digital converter (ADC), and a microcontroller.
“In a multicell environment like that of a Li-ion battery pack, each cell has its own impedance and discharge characteristics, requiring sophisticated battery management. This extends the battery’s lifetime and the application’s runtime,” explains Matthew Borne, marketing manager in Texas Instruments’ power management unit and a member of TI’s C2000 team.
The C2000 is a high-performance 32-bit microcontroller (Fig. 6). The C2000 team develops the algorithms for this type of battery management, as well as for power conversion and electric motor control. Many of the functions needed for precision battery management and control are available from TI (see “Texas Instruments controlSUITE Streamlines Motor Control Development”).