Overview of Green Car Technology
All-electric vehicles are very different from conventional gasoline-powered vehicles. To illustrate the differences, let’s start by breaking them down to the individual parts of a BEV.
EV Batteries
The battery is physically the largest component in an all-electric car. The “traction battery pack” stores all the electrical energy needed to power the car. Most modern EV batteries are currently made from lithium because they can store high levels of energy while also remaining relatively lightweight. Assuming every EV has the same electrical efficiency, it would be fair to say that a bigger battery means more electric range. Because BEVs run exclusively on electricity, they tend to have the largest batteries, followed by PHEVs then HEVs.
Electric Motor
Using the electrical energy stored inside the battery pack, the electric traction motor converts that energy into mechanical energy. The electric transmission then moves the mechanical energy from the motor to drive the wheels. Depending on the number and placement of these motors, a BEV’s drivetrain can either be front-wheel drive (FWD), rear-wheel drive (RWD), or all-wheel drive (AWD).
The electric motor (or motors) inside a BEV are responsible for a useful energy recovery mechanism called “regenerative braking.” This occurs when the driver takes their foot off the accelerator pedal, causing the motor to act in reverse and convert the car’s forward motion ("coasting” in gasoline cars) into electrical energy. The energy is then stored in the battery and ready to power the motor again. In other words, this mechanism recovers energy that would otherwise be wasted, directing it into the battery.
Charge Port & Onboard Charger
In both BEVs and PHEVs, the battery pack is charged using an external power source. To recharge, a charging plug is inserted into the car’s charge port. Think of the charging plug as the EV equivalent to a fuel nozzle at a gas station. Similarly, the charge port is the EV equivalent to a gas cap – where a fuel nozzle is inserted during refueling.
Working in tandem with the charge port is the onboard charger. Think of this as the computer system responsible for converting the charging plug’s electrical current into an acceptable power level to charge the battery. Whether it’s AC (Alternating Current) – like the kind of power in our home wall outlets – or DC (Direct Current) – like the kind available at public fast charging stations – the onboard charger does the thinking and converting so the driver doesn’t have to. This ensures the battery is not harmed accidently by using the wrong type of charger.
Power Electronics & Auxiliary Systems
Let’s talk about another important component inside electric vehicles – the power electronics control system. The primary function of the power electronics controller is to manage the flow of electrical energy delivered by the traction battery to the electric motor. The controller accomplishes this by managing the speed at which the motor turns or by controlling the torque the motor produces.
The secondary function of the power electronics controller is to distribute electrical energy from the traction battery to the auxiliary vehicle systems, such as the lighting, heating, ventilation, and infotainment systems. Rather than the traction battery, a separate auxiliary battery – identical to the ones found in gasoline vehicles – is responsible for powering these systems. This 12-volt battery is kept charged by the DC/DC converter, which converts high-voltage DC power from the traction battery into the low-voltage DC power required to power the auxiliary systems. Therefore, the traction battery powers all the auxiliary systems, too.
When it comes to auxiliary systems, the vehicle thermal management system deserves to be mentioned. One of the biggest determining factors of a safe, long-lasting and functional PHEV battery is its ability to effectively maintain a uniform temperature distribution across its cells. Since traction batteries are designed to only operate between a certain temperature range, they will cease to work if there is no thermal system to monitor it.
The main function of the thermal management system is to keep the traction battery within this specific temperature range. When an EV accelerates, the battery’s electrical energy is discharged, and heat is generated inside the battery. Since acceleration is often the primary method of discharging the battery, without a proper cooling system the battery will quickly overheat and lead to deterioration.
Indirect Liquid Cooling
Most modern EVs are manufactured with indirect liquid cooling systems for several reasons:
1. They are highly efficient systems
2. They can store large amounts of heat energy
3. They are currently the most compact and lightweight solution
As the name implies, the liquid coolant in this type of system does not have direct contact with the vehicle battery. It is instead circulated through a series of metal pipes either surrounding the battery or embedded between the battery’s cells to transfer the heat away. This method allows the cooling system to consume a small amount of energy from the battery to keep it at an operable temperature. In other words, more of the battery’s energy can be devoted to powering the motor and maximizing the powertrain’s performance all the while being uninterrupted by the weight of the system.
Breakdown of Electric Car Motors
Before we can understand how a three-phase induction motor works, we have to break it down into its two main components: the stator, which is the stationary part of the motor, and the rotor, which is the moving part of the motor.
Stator
The stator consists of three parts: the stator core, conducting wire and frame. The stator core is built by stacking thin, laminated rings and forming them into a hollow cylinder. This cylinder has slots in the hollow interior that allows the conducting wire (typically made of copper) to wrap around and shape the coils. For a three-phase induction motor, a different wire type exists for each of the three phases that forms its own individual coil. The stator core and the coils are both found within the frame, which is simply the exterior of the entire motor.
Rotor
The rotor also consists of three parts: the rotor core, conducting rods and two, end rings. The rotor core is built by stacking thin, laminated discs and forming them into a solid cylinder that has what appears to be a rod running through the center of it. On the exterior of the rotor core, there are similarly shaped slots to the stator core, but these run diagonally across the cylinder instead of parallel to the rod in the center.
The alignment of this rotor’s exterior slots is known as a squirrel-cage rotor, which is a popular design choice among many industries. Along these diagonal lines of the rotor core, the conducting rods are inserted, and the end rings are placed on both sides of the core to lock the rods in place. The rotor then slides into the hollow stator core, and two end bells are placed on either side of the rotor core’s center rod. Now that we have a firm understanding of the components inside an induction motor, let’s see how it functions inside an EV.
Motor
As mentioned earlier, all of an electric car’s power is derived from the battery pack. The electrical energy from the battery is supplied to the motor via the stator. The three copper coils within the stator core are arranged 120 degrees apart from each other and act as magnets. Think of these coils arranged in a “Y” formation.
As electrical energy is supplied to the motor, the coils produce a rotating magnetic field that induces current through the connecting rods of the squirrel-cage rotor, thus causing the rotor to spin. This spinning rotor is what creates the mechanical energy needed to turn the wheels of the car. Now let’s pull everything together: when you press your foot on the acceleration pedal, the traction battery powers the motor with electrical energy, which produces the rotating magnetic field in the stator, which spins the rotor via induction, which produces the mechanical energy needed to rotate the tires.
To the end user (that’s you), all this happens instantly and effortlessly, to get you where you need to go.
