How do electric cars work: Motor, Controller and Battery

Electric car hood
We all know the working of IC engines. Most of us know them from our textbooks and if you are a car enthusiast you might have worked on them. Now the technologies have changed, it’s the time of electric vehicles and most of us don’t know how an electric car works. It is not just a motor connected to the battery with a speed regulator.

What kind of motor does an electric car have?

There are different types of motors used for different applications. There are DC motors, AC motors, Brushless DC motors (BLDC), AC induction motors and permanent magnet synchronous motors (PMSM) . An electric vehicle needs more torque and should be more reliable. Most widely used are BLDC and AC induction motors but the AC motor is now being replaced by PMSM motors due to efficiency.

How do electric cars work: Brushless DC motors

As the name suggests it is a DC motor without brushes. A normal DC motor stator (non moving part) is made of magnets and a rotor (rotating parts) is made of coils.  A DC motor has carbon brushes which gives electrical connectivity to the rotor. In a BLDC motor the stator is made of coils and the rotating part is made of permanent magnets. Since the rotating part is a magnet, it needs no power hence no need of brushes. This will reduce wear and tear in the motor, it will also have less friction and more efficiency.

Permanent magnet synchronous motor

PMSM motor working
The PMS motor is very similar to the BLDC motor in terms of construction. The working is also similar to BLDC but you can call it a BLAC motor. The PMS motor uses Alternating current to energize the coils.

How do these motors work?

BLDC circuit
1.There are three phases in a brushless motor: A,B and C. These three phases represent three coils
2.There are hall effect sensors inside the motor that send the position of the rotor as a feedback to the controller.
3.Since the rotor is a permanent magnet it has two poles north and south. The three phases can be energized to become north or south poles depending on the current direction.
4. In the above Image you can see that phase C (red) and phase A (Blue) are energized. 
5. Phase A(blue) turns into a south pole and will attract the north pole of the rotor and repel the south pole.
6. Phase C(red) turns into a north pole which will repel the north pole of the rotor and attract the south pole. 
7. The permanent magnet rotor will make a 1/3 rotation
8. Once this step is completed the next coil which is phase A should become north pole and Phase B will become south pole.
9. Another 1/3 a rotation will complete and the steps will repeat.

How do electric cars work: Controller

These motors are blind motors, which means if you connect them to a battery they don’t know how to rotate. This is where the controller comes in. Power to the motor has to be supplied in the above motor working format. In order to provide the power in the above steps mentioned, a controller must be able to convert single phase battery power into 3 phase, know the rotor position by hall effect sensors and regulate the motor speed.

How does the motor controller work?

Electric car controller work
The motor controllers are made by a transistor bridge called H-bridge. There are 6 MOSFET (high power transistors) 2 for each phase. This part is a bit difficult to understand but let’s see the working step by step. 
1. Imagine the transistors are switches 
2. To make Phase A into the south pole and Phase C into the north pole.
3. The TA+ transistor and TC- has to be ON which will charge the phase A positively and Phase C negatively.
4. For the next step TB+ and TA- is ON now this will make phase B south pole and Phase A as north pole. 
5. Now in the Final step TC+ and TB- is ON which will complete the rotation.

What other things do the controllers do?

Motor controller
Other than rotating the motor the controller does a lot of other things. It has a current monitoring system that will detect overcurrent, regenerative braking systems, process information to be displayed on the instrument cluster. By changing the frequency of the transistors switching sound of the motors can also be altered. This sound alteration is made for pedestrian safety at slow speeds (since EVs will not make any sound and put pedestrians in danger).

How do electric cars work: Transmission

BLDC hub motor
The motors used in Electric cars and 3 wheelers will have a single speed transmission. This is because an electric motor has enough torque at zero RPM to move the vehicle. There are motors used in two wheelers called hub motors. The motors are built into the rims or hubs. These have a gear system within the wheels called planetary gear system and the gears are made up of nylons to reduce noise. 

How do electric cars work: Battery

Lucid battery
Most of you might know how an EV battery is made. EV batteries are made of cells which are arranged in series and parallel to increase voltage and current.

Image Credits:
All about circuits
Electrical baba

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