Electronics & Software – Tips & Guide


What is a synchronous motor?

What is a synchronous motor?

A synchronous motor is an essential type of AC motor that operates at the same speed as the mains frequency, resulting in no slip between its armature and field fluxes. Let’s explore the features and functions of synchronous motors in detail.

Synchronous Motor Characteristics

A synchronous motor is a type of AC motor that runs at a constant speed, precisely synchronized with the frequency of the power supply. This synchronization ensures that the rotation period of the motor’s shaft is exactly equal to an integer number of cycles of the alternating current.

Constant Speed and Variable Torque

As a constant speed, variable torque motor, the synchronous motor maintains a consistent rotational speed regardless of the load it experiences. This characteristic makes synchronous motors suitable for applications requiring precise and stable speed control.

Double Excitation Design

Synchronous motors are doubly excited machines. They feature two types of excitations:

  1. Induction Excitation: Synchronous motors utilize an induction method for creating a rotating magnetic field (RMF) in the stator. This RMF is crucial for the motor’s operation.
  2. DC Excitation: The second excitation involves supplying direct current (DC) to the rotor’s winding, which is mounted on a rotating part. This DC excitation imparts an additional rotational speed, allowing the motor to run at synchronous speed.

Working Principle

In a synchronous motor, the stator functions similarly to an induction motor, generating the rotating magnetic field. The rotor, equipped with either permanent magnets or coils excited by a continuous DC supply, interacts with the stator’s rotating magnetic field.

As the stator’s RMF and the magnetic field of the rotor have different polarities, they lock together, causing the rotor to rotate at synchronous speed. Due to this precise synchronization, the motor operates at a constant speed, hence its name “synchronous motor.”

Self-Excited Motor

Synchronous motors are known as self-excited motors because their field winding is excited by a separate DC source. This arrangement allows for the consistent rotational speed even under varying load conditions.

Synchronous Motors in Practical Applications

Synchronous motors find applications in various industries and systems requiring constant-speed operation. They are widely used in power generation, industrial processes, and equipment where accurate and stable speed control is critical.


In summary, a synchronous motor is an AC motor operating at a constant speed, synchronized with the frequency of the power supply. Its constant rotation speed, regardless of the load, makes it suitable for applications that demand precise and stable speed control. The double excitation design, using both induction and DC excitation, enables synchronous motors to maintain their synchronous speed. These motors are essential components in numerous industries, providing reliable and consistent performance in a wide range of applications.

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