Electric Cars: What’s Inside an Electric Car?

PAVOL BAUER: Ladies and
gentlemen, in this lecture, we’ll talk about the key parts of an
electric vehicle and their function. We will then look into
how they operate together to create one of the most
advanced vehicles on the planet. In this figure, you can see the
key parts of an electric car. First, we have a charging port
with the connector and cable. We have the high voltage
structured battery and the low voltage auxiliary battery. We have an electric
motor and transmission system, which are used for propulsion. And finally, there are several
power electronic converters that are used for battery
charging for driving the motors and for generative braking. The schematic shows how the
different components are connected to each other in the electric car. To explain what is
inside an electric car, let us follow the power flow direction
and take a look at an electric car by identifying the key components. The first part we look
at is the charging port with charging connector and cable. The charging port together
with the connector and cable, allows the electric car to connect
to an external power supply in order to charge the
traction battery pack. The charging port is often
referred to as a vehicle inlet. If the car is charged with power from
the conventional electricity grid, it requires an onboard charger– which is a power electronic converter. The power electronic converter is made
of high-powered semiconductor devices, which act as high speed switches. Different switching states after
the input voltage and current through the use of capacitive
and inductive elements. The result is an output
voltage and current which has a different magnitude and
wave form compared to the input. The onboard charger converts
the incoming alternating current, or AC power,
supplied with the charge port to direct current, or DC power,
for charging the traction battery. The onboard charger is
like a phone charger, but can handle much higher
voltages and powers. Next is high voltage
traction battery, which is the heart of any electric vehicle. Generally, the battery is
located at the bottom of the car, but this can vary depending
on the manufacturer. The role of the battery
is to store energy for the proportion of the vehicle. The battery has a battery management
system that monitors and regulates the battery charging characteristics,
such as voltage, current, temperature, and state of charge. The energy content of a battery is
normally expressed in kilowatt hours. Nowadays, electric
cars have battery sizes in the range of 10 to
100 kilowatt hours. Let us now look at the
battery technologies that have been applied to electric cars. First is the lead acid battery. The prospects for the use of the lead
acid batteries in the electric vehicles are limited due to the low energy
densities, sensitivity to temperature, and the lifecycle. Next is nickel metal hybrid batteries. They have been extensively
used for traction purposes. And are optimized for
high energy content. Finally, and the most popular,
are lithium-based batteries. Lithium batteries are classified
by the type of active material into lithium ion liquid electrolytes
and lithium ion polymer electrolyte batteries. The lithium ion batteries
is generally preferred for electric vehicle
applications, mainly driven by its high energy density. The table shows how a 20 kilowatt
hours lithium ion battery has a much lower weight
than its competitors. When we drive the
electric car, the power flows from the battery to the motor
and to the vehicle accessories, like light and audio system. To regulate the power
between these devices, it is necessary to use a
power electronic converter. In an electric car, a DC
to DC converter steps up the DC voltage of the
traction battery pack to a higher DC voltage
needed to run the motor. A secondary DC to DC converter– not shown in the diagram– is used to step down the voltage
of the traction battery pack to charge the lower
voltage axillary battery. The next component is the motor drive. The motor drive controls
the speed, torque, and rotational direction of the motor. Depending on the motor, the motor drive
is a DC to AC inverter or a DC to DC converter that is used
to control the power flow between the battery and the motor. Unlike the power converters
we have seen earlier, the motor drive is a
bi-directional converter capable of delivering power
to the motor for propulsion. But to remove it out of the
motor for regenerative braking. We will now look at the electric motor,
which together with the batteries, are the two vital parts
of an electric vehicle. The electric motor is responsible
for converting electrical energy to mechanical energy for driving
the wheels, the other transmission. Normally, a single-geared
transmission– the differential is used as opposed to variable
gears found in the combustion engine vehicles. This is why electric cars are
automatic-geared cars by default. This is due to the unique
nature of electric motor to deliver close to full
torque at all speeds. Further, the same electric motor
can be used both as a motor and as a generator during driving and
regenerative braking, respectively. Four types of electric
machines have been used in both plug-in hybrid electric
vehicles and battery electric vehicles to date, namely brushed DC motor,
induction motor, permanent magnet motor, and switched reluctance motor. It can generally be concluded that
induction motors and permanent magnet motors are the most
popular when considering various parameters such as control,
efficiency, power density, reliability, and cost. Finally, the last two key
parts of an electric car are the auxiliary battery and
power electronic controller. The auxiliary battery
provides electricity to start the car before the
traction battery’s engaged and also it powers the vehicle accessories. The auxiliary battery is usually
12 volts for current vehicles but may be increased to 48
volts for future vehicles. On the other hand, the
power electronic controller directly controls the different power
converters and hence, indirectly, the operation of the battery,
motors, and the vehicle. It uses the driver, accelerator, and
brake pedals to control the power flow and select the operating mode between
the driving and regenerative braking. It controls the onboard
charger and the battery charging, together with the
battery management system. Now that we know the different
parts of electric vehicle, let’s have a look at how does that
vehicle, based on electrical power flow. This figure shows the
typical electrical layout of the components in an
electric car as seen earlier. Let us analyze it step by step. The power is delivered
from the AC grid to charge the battery via the onboard AC-to-DC
electrifier and DC-to-DC battery converter. When the car is in driving mode,
the power provided by the battery goes through the battery of DC/DC
converter to the high-voltage DC bus. Then the DC-to-AC inverter of the motor
drive sends the power to the motor. The motor then converts the
electrical energy to mechanical energy and it is sent to the
wheels via the transmission. Further, a DC-to-DC
unidirectional converter steps down the voltage from
the high-voltage DC bus to charge the auxiliary battery, which,
in turn powers the electric vehicle accessories. To wrap up, the traction
battery, the electric motor, and the power electronics
play a key role in the operation of an electric vehicle. Since power is exchanged between these
components electrically using cables, it provides great flexibility
in the design of the car. This flexibility is not possible with
cars with a mechanical drivetrain due to large size and weight
of the mechanical components.