The power system of an electric vehicle consists of just two components: the Motor that provides the power and the Controller that controls the application of this power. In comparison, the power system of gasoline-powered vehicles consists of a number of components, such as the engine, carburetor, oil pump, water pump, cooling system, starter, exhaust system etc.
Thus, it acts as the decisive factor of vehicle dynamic performance. It obtains the electric energy from the power battery package, and through the modulation of its own inverter, it gets the current and voltage to control the motor, making the motor speed and torque meet the requirements of the whole vehicle.
As the control center of the whole braking system, the motor controller is composed of two parts, the inverter and the controller. The inverter receives the direct current power from the battery and converts it into three phase alternating current to provide power for the motor. The controller receives the signal of the motor speed and other signals to the instrument.
When the braking or acceleration behavior occurs, the controller controls the frequency rise and fall of the frequency converter so as to achieve the purpose of acceleration or deceleration.
Types of Motors used in EVs:-
There are various types of motors that are used in electric vehicles nowadays:
1. DC Series Motor
It was a widely used motor back in the 1990s. They are also known as Brushed DC Motors. These motors are still in use by the Indian railways.
- High initial torque
- Easy speed control
- Sudden load increase bearing capacity
- The major drawback is high maintenance due to brushes and commutators
2. Brushless DC Motor (BLDC)
These motors are the technically advanced versions of DC series motors. Instead of brushes and commutators, permanent magnets are used. BLDCs are widely used these days either as the hub motor or belt-driven.
- PM brushless DC (PMBDC) motors possess the highest power density as compared with other AC drives
- High starting torque,
- High efficiency and
- Low maintenance as they don’t use brushes and commutators.
With the advent of better and less expensive electronics which can controllably convert battery
DC power into AC, a large number of today’s electric vehicles are using AC motor/controller
systems because of their improved motor efficiency and lighter weight.
3. Permanent Magnet Synchronous Motor (PMSM)
It is very similar in construction to the BLDCs. But the major difference is in the back emf. PMSM has a sinusoidal back emf whereas BLDC has a trapezoidal one. They are used in high-performance applications such as sports cars, buses, etc. For eg. Nissan Leaf uses a PMSM for propulsion.
- High torque-to-current ratio
- High power-to-weight ratio
- High efficiency and robustness
- High power rating and therefore can be used in high-performance applications
4. Three Phase Induction Motor
Induction motors are considered the most cost-effective and reliable ones among the industry. The control of these motors is quite simple to implement. It operates based on Vector Control Technology. Tesla Model S uses this type of motor.
Even Tata and TVS are planning to use induction motors in their electric vehicles. Indian Railways have also started using induction motors over DC motors.
- Unlike the DC motors, Induction Motors doesn’t have a high starting torque.
- High efficiency & good Speed Regulation
- Low maintenance due to simple design
- Can easily withstand rugged environmental conditions.
5. Switched Reluctance Motors
Switched reluctance motor produces torque by a variable reluctance method. Rotor tends to move to a position of least reluctance thus causing torque.
The rotor of the Switched Reluctance Motor is a piece of laminated steel with no windings or permanent magnets on it. This makes the inertia of the rotor less which helps in high acceleration. It is also suitable for high speed applications.
- High starting torque
- Wide speed range
- Good inherent fault-tolerance capability
- Drawback of SRM is the complexity in control & increase in the switching circuit