Introduction to AC and DC Motors

In a variety of electrical and electronic products that require power, from personal care products to large industrial equipment, motors are required to drive them. Motors can be simply divided into DC motors and AC motors.

Here is the list

• Synchronous and asynchronous motors

• Difference between synchronous motor and asynchronous motor

• Permanent magnet, electromagnetic, magnetic induction stator/rotor

• Brushed DC Motors and Brushless DC Motors

Synchronous and asynchronous motors

1. The rotational speed of the rotor and the rotational magnetic field of the stator are the same as those of the synchronous motor; 2. The rotational speed of the rotor is the same as the rotational speed of the rotational magnetic field of the stator, which is an asynchronous motor. Note: Only AC motors have the concept of synchronous and asynchronous.

Synchronous motor

1. Principle: The magnetic poles of the rotor and the rotating magnetic field of the stator correspond one-to-one through the magnetic field along the shortest direction of the magnetic circuit, so the rotational speed of the rotor is the same as that of the rotating magnetic field;

   
   

2. Features: Whether a synchronous motor is used as a motor or a generator, the rotational speed and frequency of the alternating current are strictly unchanged, and the rotational speed of the motor is constant and is not affected by load changes.

Induction motor

1. Principle: The motor moves by induction. The rotating magnetic field of the stator cuts the squirrel cage to generate an induced current, and the rotor rotates after the current is stressed. Note that there must be a speed difference between the motor speed and the stator rotating magnetic field speed, forming a magnetic field to cut the squirrel cage and generate an induced current;

   
   

2. Features: The rotor winding of the motor does not need to be connected to other power sources, and the stator current is directly taken from the AC power system. The motor has a simple structure, is easy to manufacture, use and maintain, and has high operational reliability, light weight and low cost.

Difference between synchronous motor and asynchronous motor

1. A synchronous motor can both emit reactive power and absorb it; an asynchronous motor can only absorb reactive power.

   
   

2. The rotational speed of the synchronous motor is synchronized with the AC power frequency 50Hz current; the rotational speed of the asynchronous motor lags

   
   

3. The current of the synchronous motor leads the voltage in the same phase, that is, the synchronous motor is a capacitive load.

   
   

4. When the synchronous motor is energized, the rotor excitation winding of the motor is static, and the synchronous motor cannot be started directly.

Permanent magnet, electromagnetic, magnetic induction stator/rotor

1. Permanent magnet DC motor: using permanent magnet as material;

   
   

2. Electromagnetic: energized coil;

   
   

3. Magnetic induction: closed winding without electricity, squirrel cage type.

In most cases, permanent magnets and electromagnets are interchangeable. Electromagnets and permanent magnets are usually used in the rotor of a three-phase synchronous motor, while induction magnets are used where a rotating magnetic field is required.

Brushed DC Motors and Brushless DC Motors

The difference between brushed and brushless DC motors is very large. We classify motors into two categories: DC motors and AC motors, that is, DC motors are driven by DC motors; AC motors are driven by AC motors.

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