What is an Electric Motor?
An electric motor is an electrical machine that converts electrical energy into mechanical energy. Electric motors can be powered by direct current (DC) sources, such as from batteries, or rectifiers, or by alternating current (AC) sources, such as a power grid, inverters or electrical generators. An electric generator is mechanically identical to an electric motor, but operates with a reversed flow of power, converting mechanical energy into electrical energy.
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Types of Electric motors in Electrical Vehicles.
- DC Series Motors.
- Brushless DC Motors.
- Permanent magnets Synchronous Motor (PMSM).
- Three Phase AC Induction Motors.
- Switched Reluctance Motors (SRM).
1. DC Series Motors
It is the most widely used motor for traction application in the early 1900s. The advantages of this motor are easy speed control and it can also withstand a sudden increase in load. All these characteristics make it an ideal traction motor. The main drawback of DC series motors is high maintenance due to brushes and commutators. These motors are used in Indian railways.
2. Brushless DC Motors (BLDC).
It is similar to DC motors with Permanent Magnets. It is called brushless because it does not have the commutator and brush arrangement. The commutation is done electronically in this motor because BLDC motors are maintenance free. BLDC motors have traction characteristics like high starting torque, high efficiency around 95-98%.
BLDC Motors have two types.
A. Out-runner type BLDC Motor:
As the name indicates the rotor of the motor is present outside & the stator is present inside. This motor is widely preferred by electric cycle manufacturers, light speed bicycles, etc. It is also used by two-wheeler manufacturers.
B. In-runner type BLDC Motor:
In this type, the rotor of the motor is present inside and the stator is outside like conventional motors. These motors require an external transmission system to transfer the power to the wheels, because of this the out-runner configuration is a little bulky when compared to the in-runner configuration. Many three- wheeler manufacturers use BLDC motors. Low and medium performance scooter manufacturers also use BLDC motors for propulsion
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3. Permanent Magnet Synchronous Motor (PMSM).
This motor is also similar to the BLDC motor which has permanent magnets on the rotor. Similar to BLDC motors these motors also have traction characteristics like high power density and high efficiency. The difference is that PMSM has sinusoidal back EMF (electromotive force) whereas BLDC has trapezoidal back EMF. PMSM is the best choice for high performance applications like cars, buses. PMSM is also costlier than BLDC motors. Most of the automotive manufacturers use PMSM motors for their hybrid and electric vehicles.
4. Three Phase AC Induction Motors
A 3-phase induction motor is an electromechanical energy conversion device which converts 3-phase input electrical power into output mechanical power. The stator carries a 3-phase stator winding while the rotor carries a short-circuited winding called rotor winding. The stator winding is supplied from a 3-phase supply.
5. Switched Reluctance Motors (SRM)
Switched reluctance motors operate by switching currents in the stator windings in response to changes in the magnetic circuit formed by the rotor and stator. The stator of a switched reluctance motor contains windings, similar to a brushless DC motor, but the rotor is simply made of steel that is shaped into salient poles, with no windings or magnets.
How do the manufacturers select the best Electric motors for EV depending on the Applications?
For selecting the appropriate electric vehicle motors, one has to first list down the requirements of the performance that the vehicle has to meet, the operating conditions and the cost associated with it. For example, go-kart vehicle and two-wheeler applications which require less performance (mostly less than 3 kW) at a low cost, it is good to go with BLDC Hub motors. For three-wheelers and two-wheelers, it is also good to choose BLDC motors with or without an external gear system. For high power applications like performance two-wheelers, cars, buses, trucks the ideal motor choice would be PMSM or Induction motors.