ELECTRIC The Electric Motor/Generator The term electric motor/generator is

ELECTRIC CARS

HOW THEY RUN

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MECHANISM USED IN DRIVING SYSTEMS

CHARGING AND STORAGE SYSTEMS

 

The Main Components of an Electric Vehicle

The electric vehicle drive system
includes:

• High-voltage battery with control
unit for battery regulation and charger

• Electric motor/generator with
electronic control (power electronics) and cooling system

• Transmission including the
differential

• Brake system

 

The Electric Motor/Generator

The term electric motor/generator
is used instead of alternator, electric motor and starter. In principle, any
electric motor can also be used as an alternator. When the electric
motor/generator is driven mechanically, it supplies electrical energy as an
alternator. When the electric motor/generator is supplied with an electrical
current, it works as a drive. Electric motors/generators used for propulsion
are water-cooled. Air cooling would also be possible but complex due to space
and the smount of heat generated. In full hybrid vehicles (HEV), the electric
motor/generator also functions as the starter for the combustion engine.
Three-phase synchronous motors are often used as the electric motor/generator.
A three-phase motor is powered by a three-phase alternating current. It works
with three coils that are arranged in a circle around the rotor to form the
stator and are each electrically connected to one of the three phases. Several
pairs of permanent magnets are located on the rotor in this synchronous motor.
Since the three coils are supplied sequentially with a current, together they
generate a rotating electrical field that causes the rotor to rotate when the
electric motor/ generator is used to drive the vehicle. When used as an
alternator, the movement of the rotor induces a three-phase alternating voltage
in the coils that is transformed into a direct voltage for the high-voltage
battery in the power electronics. Normally so-called “synchronous motors” are
used in vehicles. In this context, the term “synchronous” means “running in
synchronism” and refers to the ratio of the rotation speed of the energised
field in the stator coils to the rotation speed of the rotor with its permanent
magnets. The advantage of synchronous motors compared with asynchronous motors
is the more precise control of the motor in automobile applications.

 

 

 

Strengths of the Electric Motor/Generator

 The electric motor/generator is very
environmentally compatible thanks to the lack of noise and harmful emissions.
The electric motor/generator responds quickly, has good acceleration figures
and a high level of efficiency. In contrast to combustion engines, electric
motors supply their nominal power steplessly over a broad rpm range. The
maximum torque is available even at low rpm (i.e. when pulling away) and only
drops once the motor reaches very high speeds. As a result, neither a manually
operated transmission, an automatic transmission nor a clutch are required. The
direction of rotation of an electric drive motor is freely selectable. It can
turn clockwise to move the vehicle forwards and counter-clockwise to reverse
it. Electric motors start automatically. A separate starter motor is not
required. Electric motors have a simpler design and have considerably fewer
moving parts than internal-combustion engines. Only the rotor with its
permanent magnets rotates inside the electric motor/generator. There are no
vibrating masses as in internal combustion engines. Oil changes are not
necessary as lubricating oil is not required. Consequently, electrically
powered vehicles are low-maintenance in terms of their drive unit.

 

Transmission

Pure electric vehicles (BEV) do not
require the traditional transmission with several speeds. The polarity of the
electric motor is simply reversed when you want to reverse the vehicle. This
means that the direction of rotation of the electric motor changes. This is
done with a gear selector lever, which simply has the positions “Neutral”,
“Forward” and “Reverse”. The speed can be regulated infinitely with the accelerator
pedal. Full hybrid vehicles (HEV) and plug-in hybrid vehicles (PHEV) still have
a conventional transmission. As a rule, these are not manual transmissions, but
automatic or dual clutch transmissions.

 

 

 Brake System

 An electric vehicle has two independent brake
systems. One system is the traditional mechanical/ hydraulic brake system. The
second brake system is formed by the electric drive motor as an “engine brake”.
The advantage of this “engine brake” compared with the combustion engine is
that the energy released by the electric motor/generator during braking and
deceleration is recovered and fed into the high-voltage battery. This
regenerative braking contributes to the high efficiency of the electric
vehicles in particular in city traffic. In addition, the wear of the vehicle
brakes is reduced by the regenerative braking system.

The High-Voltage Battery

The battery is the heart of
electric vehicles. The high voltage battery supplies its direct voltage to the
power electronics. The power electronics convert the direct voltage into an
alternating voltage and supply the electric motor/ generator with three
electrical phases via the three wires (U, V and W).

 

Energy Density

This figure indicates the
performance of a battery related to its weight. The higher the energy density,
the more energy can be stored and then released again. The unit of energy
density is watt hours per kilogram Wh/kg and is calculated from the
electrical work Wh and the weight kg of the battery. The range of an
electric vehicle can be determined from the energy density.

 Life cycle

stability of a high-voltage battery
is set at a total of 3,000 cycles over a period of 10 years, i.e. 300
cycles/year. On the basis of this property, so-called “automotive batteries”,
i.e. batteries for use in a high-voltage vehicle, cannot be compared with the
“consumer batteries” used in laptops or mobile telephones.

Efficiency

The efficiency indicates how much
of the energy that is invested into charging can be made useful again when the
battery is discharged. A battery can never have 100% efficiency since a small
part of the charging energy is released in the form of heat (charge loss).

 

 

 

 

 

 

Types of Rechargeable Battery

The different types of rechargeable
batteries are distinguished by the materials used for the electrodes
andelectrolytes. The most common rechargeable batteries are lead-acid,
nickel-cadmium, nickel-metal hydride andlithium-ion batteries.

Lead-Acid Battery

The traditional 12 V vehicle
electrical system battery has plates made from lead and lead/lead oxide and are
usedas electrodes. Sulfuric acid is the electrolyte.

• Requires maintenance (distilled
water needs to be added to ensure the required electrolyte liquid level)

• Not well suited for powering
electric vehicles because they are very heavy and large, reducing the load

capacity

• Can lose a large part of its
capacity after just six years

• If damaged, electrolyte (acid)
can leak

Nickel-Cadmium Battery

Cadmium (Cd) and a nickel compound
are used for the electrodes in these batteries. Potassium hydroxide is used as
the electrolyte.

• Also called an alkaline battery

• Has a higher energy density than
lead acid batteries

• Less prone to damage and
electrolyte leaks

• Subject to a memory effect. This
type of battery can tolerate deep-discharging or overcharging only to a certain

extent without becoming less
efficient

• Cadmium and cadmium compounds are
poisonous

Nickel-Metal Hydride Battery

These batteries use a nickel
compound and a compound of another metal for the electrodes. Potassium
hydroxide is the electrolyte. They have a higher energy density than Ni-Cd
batteries and are relatively resistant to damage. Even if a memory effect does
not occur to the extent of the Ni-Cd batteries, these batteries also lose
efficiency over the course of their life. To a certain extent, this loss in
efficiency is reversible. Nickel metal hydride batteries do not contain any
poisonous heavy metals like lead or cadmium. The electrolyte is stored in the
battery in solid form. If the housing is broken, only a few droplets will
escape.

Lithium-Ion Battery

This battery uses lithium metal
oxides and graphite for electrodes. Different solvents for lithium salts form
the electrolyte. Lithium ion batteries contain only a small amount of water and
do not have a memory effect. Compared with the nickel cadmium batteries, they
have more than twice as much energy density. This means that this battery type
requires less space in an electric vehicle leaving more room for the occupants
and the luggage compartment.