Motor Technology – The ‘Centre’ of an Electric Vehicle Efficiency

In the energy starving world, demand of energy is continuously raising, of-course not parallel to its supply. This issue become more significant when traditional sources of energy are continuously depleting and people are rushing to resort the renewable energy sources. Electricity is one of the chief renewable energy sources. In the meanwhile, rising prices of the fuel has occurred as an opportunistic symbol for the electric vehicles to come into the picture.

World is witnessing the regular increase in the demand for electric vehicle since last few decades. So, the demand for new ideas and innovation is also intensifying in this field. Motors are the fundamentals to any vehicle. The basic functioning of the vehicle is largely governed by the power and efficiency of the motor and its supporting technology inside.

In an electric vehicle, usually direct current (DC) electricity is fed from a battery bank to AC/DC inverter. This inverter converts DC into alternating current(AC) electricity and then it is fed to 3 phase AC induction motor. For small range and slow speed application of electric vehicle, even brushless DC motor is also used. The electrical energy is converted into mechanical energy through motor and fed to wheels through transmission and differential. Normally, it is said that inverter is the brain and motor is heart of the electric vehicle.

In order to understand the potential of the electric motor, the following range of motors can be taken as example:

· 15 Kw Traction Motor: It provides almost unlimited maximum speed.

· 8 Kw Traction Motor: It is designed for small e-vehicles with speed limit of 45 Km/h. It can be used without a fan in normal operation and can be suitable for tight spaces.

· 4 Kw Traction Motor: It is the ideal motor for light weight e-vehicles for recreational uses, for off-road vehicles- for example, golf cars or ATVs (All Terrain Vehicles) and alternatively for transport vehicles that have limited space.

· 1.5 Kw Traction Motor: Typical uses for this electric motor are for scooter and go-carts.

The rotor in an induction motor is specially designed with internal magnet that creates almost sine distribution of the magnetic flux. Because no external magnetization is required, there are no losses in the rotor through magnetization currents. The efficiency of electric motor is judged through its function of torque and speed. However, the heating of the motors at high speed is an area which require further innovation and development.

The manufacturers have started using permanent magnet electric motor instead of the AC induction motor. The advantage is that unlike AC induction motor which uses electricity to generate the magnetic currents inside the motor, which causes rotor to spin, permanent magnet motors does not require that additional current since its magnets which are created from rare-earth materials are always on. But these motors are suitable only for smaller and lighter cars. The high performance cars require greater power which can only be produced by induction motors.

Efforts are also on to reduce the cost of electric motors by using different materials that can reduce the losses with improved performance. Another, effort manufacturers have put in to reduce the size of motor is by using square copper wires instead of round ones in its stator. The stator is a stationary part of an electric motor, which generates the alternating magnetic field to spin the rotor. This is because square wires nest more compactly and densely.

The motor designers have also used three smaller magnets in place of two larger ones for the motor which helps to improve torque. Some innovators have even used non-rare- earth materials like Daido Steel to make magnets to reduce their cost. One more example is Neodymium magnet that contains no rare-earth-material but it is still powerful enough for vehicle use. The aim is to develop motors with high RPM of 30,000. At present it ranges from 12,000 to 18,000 RPM.

There is no exaggeration in making a statement that a lot is required to be done in development of motors with higher efficiency and torque in case we wish to replace gasoline driven vehicles with all electric vehicles.