Series hybrid

A series hybrid uses an electric motor(s), which is powered by a single-speed internal combustion engine. While operating at its most efficient single speed, the combustion engine drives an electric generator instead of directly driving the wheels. This engine can do any combination of the following: charge a battery, charge a capacitor, directly power the electric motor. When large amounts of power and torque are required, the electric motor can draw electricity from a combination of batteries, capacitors, and the generator. A series hybrid does not require batteries in its design as a capacitor can act as a storage device.

There are three main options for series hybrid electric motors: Permanent Magnet, 3-Phase AC Induction, Multi-Phase AC Induction. Permament Magnet motors, like those found in the Prius, degrade in performance at higher temperatures and require a cooling system in the design. They allow for regenerative braking, and this comes with a safety trade off as any time there is motion by the magnets, they produce voltage. Permanent magnets also require rare earth which are expensive and difficult to source.

In contrast, 3-Phase AC Induction motors can be air cooled and therefore have better stamina, but have less power density which means that the weight saved from removing the cooling system is replaced with heavier and more complex gearing for the drivetrain. This more complex transmission gearing is also needed to compensate for the fact that a standard 3-Phase AC Induction motor can be either low-speed high-torque (like a standard vehicles starter) or a high-speed low-torque (like a standrd vehicles alternator) but not both.

A Multi-Phase AC Induction motor (called a Chorus Motor) co-opts the harmonics that limit motor performance, which means a that it can smoothly change from behaving like a high-torque low-speed motor to behaving like a low-torque high-speed motor, without the need for efficiency robbing physical gearing that would be required to compensate for a 3-Phase AC Induction motors lower power density. The January 2009 issue of Motor Trend magazine discusses this third choice and its use in planes and vehicles. Furthermore, by co-opting the harmonics that limit standard motor performance, greater torque can be generated by this motor; up to 10 times the torque of a standard motor. This extra torque can be generated for short 'burst' or 'startup' torque requirements, which means that the Chorus Motor used in a series hybrid can both be smaller and be sized for its 'average' torque requirements while still providing the acceleration torque needed for occasional circumstances like joining a highway from a dead stop. This motor is presently only being used in WheelTug and its use turns an airplane into a series hybrid with a turbine in the APU generating the electricity needed to power the Chorus Motor in the WheelTug

BYD Auto's F3DM sedan is the world's first mass-produced plug-in hybrid, which went on sale in China on December 15, 2008. It costs the equivalent of USD $16,062 and has an all-electric range of 68.4 miles. The F3DM is set to debut in North America and Europe in 2011. Meanwhile, GM hopes to introduce the Chevy Volt by 2011, aiming for an all-electric range of 40 miles and a price tag of around $40,000.

by wikipedia