Motor Types Used in Electric Vehicles

In recent years, vehicles using internal combustion engines have started to be replaced by Electric Vehicles (EV), which are driven by electric motors. It is certain that the use of electric vehicles will increase rapidly in the near future.

In this context, we will examine the engine types used in electric vehicles in terms of their advantages and disadvantages.

Brushed DC Motors (DCM)

The high starting torque capacity of the DC Series makes it a suitable choice for traction application. The advantages of this motor are that it is easy to control speed and withstands sudden load changes.

The torque produced is directly proportional to the square of the current.  All these features make it an ideal traction motor. These motors are frequently used in railways as high power.

The disadvantage of the DC motor, which limits its use in electric vehicle applications, is that the failure rates are high due to the wear and tear of the mechanical brushes.

Asynchronous Motors (ACIM)

The asynchronous induction motor is based on the principle of electromagnetic induction, where conductors in a changing magnetic field induce an EMF along the conductor.

The motor rotates by the interaction of rotor and stator flux. Squirrel cage asynchronous motors are widely used. The advantages of the asynchronous motor are structural simplicity, low cost and low maintenance. There are no sparking brushes. Therefore, it can be operated in explosive areas, water and dusty polluted environments.

The disadvantage is that speed control is difficult. The motor operates at low power factor. Therefore, some power factor correction devices are required. High copper losses lead to a decrease in efficiency. Excessive air gap may cause efficiency decrease and sometimes mechanical friction.

Permanent Magnet Synchronous Motors (PMSM)

The field excitation of Permanent Magnet Synchronous Motors is provided by permanent magnets. These motors are basically an AC synchronous motor with a sinusoidal opposite EMC waveform. PMSM is structurally a combination of a brushless DC motor and an induction motor. Like a brushless DC motor, it has windings in the stator and a permanent magnet rotor.

At the same time, the machine has a stator structure with windings made to produce a sinusoidal flux density in the air gap. This structure is similar to induction motors. The absence of rotor copper losses gives PM motors an advantage in terms of cooling.

The disadvantage is that high temperature and load conditions cause loss of magnetisation properties.

Brushless DC Motors (PMBLDC)

A permanent magnet DC motor is a synchronous motor in which the rotor rotates at the same speed as the stator. It differs from a conventional DC motor in that the field winding of the rotor is replaced by a permanent magnet. Permanent magnet synchronous motor is also called BLDC.

Thanks to its small dimensions, power density is high. Since there are no field windings (copper, heat, etc.), losses are less and efficiency is high. By using permanent magnets, the energy requirement of motors to produce magnetic poles is eliminated. Thus, higher efficiency can be obtained from DC motors, induction motors and SRMs.

The disadvantage is that the motor is more costly than DC series and AC induction motors. The high cost of the magnet makes it difficult for the mechanical power of the magnet to generate a large torque in the motor. There is no brush to limit the speed in PMBLDC motors, but problems with the fixing density of the magnet remain because it limits the maximum speed in internal rotor type motors.

Switched Reluctance Motors (SRM)

Switched reluctance motors have a simple structure. Both the stator and rotor have dislocated poles. Therefore, the motors are also called double dislocation reluctance motors.

The rotor is brushless and can operate at high speed. High power and moment can be obtained. It is easy to cool as there is only winding in the stator. The phases are independent of each other and thus the motor continues to operate even if one phase fails. Its efficiency is quite high.

The disadvantages of the SRM motor can be listed as the size of the stator inductance, high voltage generation at the ends of the winding inductance during switching, the need to place a sensor on the motor shaft to determine the phase excitation sequence, and high noise due to the decreasing moment when there is a delay in switching from one phase to another.