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How synchronous motors work
- Jan 12, 2019 -

How synchronous motors work

The synchronous motor is an AC motor. Its working principle is that the rotor speed is always equal to the rotational speed of the armature rotating magnetic field, that is, there is a strictly constant relationship between the rotor speed and the frequency of the armature current.

First, the working principle of synchronous motor

Basic structure of synchronous motor

The synchronous motor is structurally embedded with a three-phase symmetrical winding on the stator core, and a DC excitation winding is arranged on the rotor core.

Establishment of the main magnetic field

The field winding is connected with a DC excitation current to establish an excitation magnetic field between the polar phases, that is, the main magnetic field is established.

Current carrying conductor

The three-phase symmetrical armature winding acts as a power winding, and the gearbox becomes the carrier for the induced or induced current.


Cutting motion

The prime mover drags the rotor to rotate (injecting mechanical energy into the motor), and the exciting magnetic field between the polar phases rotates with the shaft and sequentially cuts the stator windings.

Generation of alternating potential

Due to the relative cutting motion between the armature winding and the main magnetic field, a three-phase symmetric alternating potential whose magnitude and direction change periodically will be induced in the armature winding. AC power is available through the lead wires.

Second, the main operating mode of synchronous motor

1. Generator: It is the most important operation mode of synchronous motor.

2. Electric motor: It is another important operation mode of synchronous motor. The power factor of the synchronous motor can be adjusted. In the case where the speed regulation is not required, the synchronous motor using the large bevel gear reducer can improve the operating efficiency. In recent years, small synchronous motors have begun to find more applications in variable frequency speed control systems.

3. Compensation machine: The synchronous motor is connected to the power grid as a synchronous compensation machine. At this time, the motor does not carry any mechanical load, and the excitation current in the rotor is adjusted to send the required inductive or capacitive reactive power to the grid to achieve the purpose of improving the power factor of the grid or adjusting the voltage of the grid.