People have been using different types of motors for ages. Primarily, motors can be broadly classified into AC and DC types, depending on the power source they require to operate. However, the basics of operation remain the same for all types of motors. Current running through a wire generates magnetic fields around it, and if there is another magnetic field present such as from an external magnet, the two interact to generate a mechanical force on the wire capable of moving the wire. This is the basic principle on which all motors operate.
AC and DC Motors
AC induction motors have a number of coils controlled and powered by the AC input voltage. This input voltage also creates the stator field, which then induces the rotor field. Another type of AC motor, a synchronous motor, can operate with precision supply frequency.
An AC motor operates at a specific point on its performance curve, which coincides with the peak efficiency of the motor. If forced to operate beyond this point, the motor runs with a significant reduction in efficiency. As the magnetic field in an AC motor is created by inducing a current in the rotor, AC motors consume extra energy from the input. This makes the AC motors less efficient than DC motors are.
DC motors generate their secondary magnetic field using permanent magnets rather than windings. They rely on commutation rings and carbon brushes to switch the direction of the current and the polarity of the magnetic field in the rotating armature. The interaction between the magnetic field from the fixed permanent magnets and the magnetic field from the internal rotor induces rotation in the rotor.
Although DC motors run at high efficiency, they suffer from specific losses. The initial resistance in the rotor, brush friction, eddy current losses cause the motor to lose efficiency.
To achieve higher energy efficiency and control the energy output, engineers have designed the EC or electronically commuted motors. They combine the best of both AC and DC motors by removing the brush and slip ring system of commutation, and replacing them with solid-state devices. This electronic control allows them to operate with a higher efficiency.
EC motors are also called brushless DC motors, and they are controlled by external electronics, which may be an electronic circuit board or a variable frequency drive. Permanent magnets are on the rotor, while the fixed windings are on the stator.
The circuit board keeps the motor running by switching the phases in the fixed windings as necessary. This supplies the armature with the right amount of current at the right time, resulting in the motor achieving higher accuracy and efficiency.
EC motors offer several benefits. Absence of brushes eliminates sparking and increases the life of the motor. As electronics controls the power to the motor, there is less wastage with better performance and controllability. This allows even small EC motors to equal the performance of larger AC or DC motors. Heat generation in EC motors is also lower than that generated in AC or DC motors.