The Electric Vehicle (EV) is the mobility option of the future. In the last 5 years alone, the presence of full-electric vehicles on the U.S. roads surged to 1.7 million, increasing by around 250% compared to the previous last 5 years.
As EVs become more and more popular, you will need to eventually start learning about how these vehicles work internally and what are their main components. This is especially useful if you want to purchase a Battery Electric Vehicle (BEV) since it will give you a deeper understanding of this technology and its potential for mobility.
What is the Working Principle of an EV?
An EV operates by creating perfect synchrony between its electrical and mechanical parts. Most BEVs feature a high-voltage and large-capacity battery that uses a DC-to-DC voltage converter to deliver the right voltage to electronic and electromechanical components. This includes the onboard electronics, auxiliary systems, the engine, and any other component operating with electricity.
In an EV, power is sent from the battery to the engine, and that power is converted into mechanical power (usually measured in HPs) for the wheels. After an EV battery is low on capacity or depleted, it has to be charged, which is done by using the on-board EV charger for AC charging or by using the Battery Management System (BMS) to charge in DC. These last two components limit the current going to the battery within safe values.
When learning about the inner operation of an EV, it is important to divide this between the electrical parts and the mechanical parts, making it easy to understand. Let us see first the electrical section of the vehicle.
Electric Parts of an EV
How Does the Electric Power Go From the Charger to the Battery?
The first and most important part of an EV is the battery. Most EVs feature two batteries: A high voltage Traction Battery Pack featuring a voltage going up to 800V and a 12V Auxiliary battery that supplies power to auxiliary systems and accessories like headlights, lighting systems, radio, and others.
In order to start charging the battery, we must first use the EV charging connector. This is a special plug designed for EV charging. There are several types of EV charging plugs and sockets, including the SAE standard, IEC standard, GB/T standard, CHAdeMO standard, and the Tesla standard.
After the EV plug or EV charging connector is inserted into the EV socket, the communication protocol pins start the whole charging process.
Now, there are two charging methods used to recharge the battery of electric vehicles: AC charging and DC charging.
For AC charging, the current is delivered from the grid to the EV charger, finally going to the On-Board Charger (OBC), the device responsible for converting AC to DC power and for limiting the maximum AC power that the vehicle can handle. This device converts the single-phase 240V AC or three-phase 208V AC coming from the power supply, into DC power at 450V DC – 850V DC (required to charge the battery).
Meanwhile, for DC charging, the current is converted externally from AC power coming from the grid to DC power, and is then delivered to the battery, the maximum power rate for this type of charging is limited by the Battery Management System (BMS).
The charging curves from both AC and DC charging are illustrated in Figure 2. In both cases, the battery of the electric car goes through the same bulking, absorption, and float stages that all Lithium-ion batteries go through when charging.
How Does the Electric Power Get Distributed in an EV?
EVs do not generate power on the run like gas vehicles do when burning gasoline, instead they use stored energy at the Battery Traction Pack to power all components in the vehicle. The main inconvenient with EVs is that most components do not work at the same high voltage as the battery does, which is why they need a DC to DC converter.
The DC to DC converter takes the voltage from up to 800V to a lower voltage used by most components. For instance, EV motors operate at a voltage range of 100V – 200V for some engines or up to more than 300V for engines like the ones used in Tesla EVs. The DC to DC converter also recharges the Auxiliary Battery in the battery electric vehicle.
Electric Drivetrain System: Mechanical Parts of an EV
The Electric Drivetrain System in a battery electric automobile is in charge of transferring the energy from the battery to the wheels, in other words, the mechanical parts of the vehicle. In this section, we explain how the three main mechanical components in the Electric Drivetrain System work.
How Does the Electric Traction Motor Work?
EVs can operate with an AC or DC Electric Traction Motor. Unlike the motor of an Internal Combustion Engine (ICE) vehicle, these do not require pressurizing and igniting gasoline. The working principle slightly varies depending on the type of motor.
An EV Electric Traction Motor uses AC power to be energized, working under the physical principle of electromagnetic induction. This type of motors shifts the polarity of alternating current by powering electromagnetic coils (AC powered electromagnets), inducing a current in the rotor to create its own magnetic field opposing that of the magnets, resulting in the magnetic force that puts the rotor in motion.
Most Electric Traction Motors installed in a battery-powered electric vehicle are either brushed or brushless DC motors. These motors work similarly to AC motors, but use permanent DC magnets instead of electromagnets. Motion created in the rotor of these motors is achieved by using a physical or electronic commutation system, turning on and off windings that create magnetic fields, attracting and repelling the rotor. DC motors are slightly less powerful than AC motors, but they are much more efficient and precise, making them ideal for the battery electric propulsion system.
How Does the Drive Shaft Connect the Electric Traction Motor and the Wheels?
One of the most common ways to transfer torque and force created by the rotor of the EV Electric Traction Motor is using a Drive Shaft. This is a simple mechanical gear system that moves the wheels of the vehicle as the rotor of the battery-electric vehicle engine rotates, however, this is rapidly changing in some new cutting-edge EV models being released to the market.
The most innovating EVs are implementing an in-wheel motor system. This is a more sophisticated system that generates fewer energy losses and improves efficiency for the vehicle. An in-wheel motor system consists on installing DC motors directly at the wheels of the vehicle, eliminating the need for a Drive Shaft and reducing losses created by this mechanical motion transfer system.
What Is the Importance of the Electric Transmission?
ICE vehicles feature extremely inefficient engines that lose from 75% up to 84% of the energy generated by the combustion process. This is why ICE vehicles require between five and six gears with different ratios for power output. This allows increasing and optimizing energy transfer from the engine to the wheels.
An electric battery vehicle instead features a highly efficient engine with a single gear that only loses around 23% of the energy stored in the Traction Battery Pack. This high efficiency engine rapidly varies speeds and increases acceleration, without requiring implementing any additional gears. The single gear of a pure-electric vehicle is in charge of precisely controlling the speed and direction of the wheels.
How Is Temperature Regulated in the Electrical and Mechanical Components of the EV?
The operating temperature on an EV can impact performance and reliability in an all-electric vehicle, especially high temperatures that rapidly affect performance and range for the vehicle. To avoid battery degradation and to optimize performance for an EV, temperature is regulated in the engine, power electronics, and the traction battery pack by using the thermal management or cooling system of the EV.
Thermal management system for EVs does not only cool down the internal components of the vehicle like the cooling system for ICE vehicles does. Instead, the EV thermal management uses external and internal temperatures by heating or cooling the Traction Battery Pack and other components, this is performed to control the temperature of electrical and mechanical components for them to work in optimal conditions.
Final Words: Understanding EVs to Make Better Use of Them
There are some similarities between how ICE vehicles and EVs work, but there are a large number of differences considering the mechanical and electrical components. EVs work more efficiently, make better use of energy, and produce fewer power losses, but they require a more controlled temperature.
Now with all of this information, you will be able to understand how your electric vehicle works and will give you an insight to some important functioning differences between electric cars and combustion engine vehicles.