What are the current modes of permanent magnet synchronous motors?

We have learned about the development and armature reaction of permanent magnet synchronous motors before. We can understand from this that when the permanent magnet synchronous motor is no-load, there is only one permanent magnet magnetic field rotating at synchronous speed in the air gap, which occurs in the armature winding. Three-phase symmetrical induced electromotive force. And the magnetic field in the air gap of this motor is generated by the simultaneous action of the armature magnetomotive force and the permanent magnet magnetomotive force.

When changing the excitation current of a permanent magnet synchronous motor, it is generally not done directly in its rotor circuit because the current in this circuit is very large and it is not convenient to directly adjust it. Therefore, the method we usually use is to change the excitation current of the exciter to achieve the purpose of adjusting the rotor current of the permanent magnet synchronous motor. So what are the current modes of permanent magnet synchronous motors? Let’s find out together below!

Current mode of permanent magnet synchronous motor:

Commonly used methods include changing the resistance of the excitation circuit of the exciter, changing the additional excitation current of the exciter, changing the conduction angle of the thyristor, etc.

What we are mainly talking about today is: the method of changing the conduction angle of the silicon-controlled rectifier. It is based on the change of the voltage, current or power factor of the permanent magnet synchronous motor, and accordingly changes the conduction angle of the silicon-controlled rectifier, so the generator The excitation current changes accordingly.

This device is generally composed of transistors and thyristor electronic components. It has the advantages of sensitivity, speed, no failure zone, high output power, small size and light weight. In the event of an accident, it can effectively suppress the overvoltage of the permanent magnet synchronous motor and achieve rapid demagnetization.

Automatically adjusting excitation devices are usually composed of a measurement unit, a synchronization unit, an amplification unit, an adjustment unit, a stabilization unit, a limiting unit and some auxiliary units. The measured signal (such as voltage, current, etc.) is compared with the given value after being transformed by the measuring unit, and then the comparison result (deviation) is amplified by the preamplifier unit and power amplification unit, and used to control the conduction of the thyristor angle to achieve the purpose of adjusting the excitation current of the permanent magnet synchronous motor.

The function of the synchronization unit is to synchronize the trigger pulse output by the phase-shifting part with the AC excitation power of the silicon-controlled rectifier to ensure the correct triggering of the silicon-controlled rectifier. The function of the differential control unit is to enable the generators running in parallel to distribute the reactive load stably and reasonably. The stabilization unit is a unit introduced to improve the stability of the power system.

The excitation system stabilization unit is mainly used to improve the stability of the excitation system. The limiting unit is designed to prevent the generator from operating under over- or under-excitation conditions. It must be pointed out that not every automatic regulating excitation device has the above-mentioned various units. The units of a regulator device are related to the specific tasks it undertakes.