With the help of DC motors, variable electric drives with high operational and dynamic performance are created.
DC motors are subdivided into subtypes:

Collector. In these electrical appliances there is a brush-collector unit that provides electrical connection of the stationary and rotating parts of the engine. Devices are self-excited and independently excited from permanent magnets and electromagnets.

The following types of self-excitation of motors are distinguished:

• parallel;
• consistent;
• mixed.

Collector devices have several disadvantages:

• low reliability of devices;
• the brush-collector unit is a rather difficult component of the magnetoelectric motor to maintain.

Collectorless (valve). These are closed-loop motors that operate on a similar principle to synchronous devices. Equipped with a rotor position sensor, a coordinate converter, and an inverter, a power semiconductor converter.

These machines come in a variety of sizes, from the smallest low voltage to huge sizes (mostly up to megawatts).

In AC motors, the electric current is described according to a sinusoidal harmonic law, which periodically changes its sign (direction).

Electric motors, according to the principle of operation, are synchronous and asynchronous. Their main difference is that the speed of the stator magnetomotive force in synchronous devices is equal to the rotor speed, and in asynchronous motors these speeds do not coincide, usually the rotor rotates slower than the field.

Synchronous electric motor

Due to the same (synchronous) rotation of the rotor with a magnetic field, the devices are called synchronous electric motors.

They are subdivided into subspecies:

• Reactive.
• Stepper.
• Reactive-hysteresis.
• With permanent magnets.
• With field windings.
• Reactive valve.
• Hybrid reluctance synchronous motor.

Asynchronous motor

By design features, there are two types of asynchronous motors:

• With a phase rotor.
• With squirrel cage rotor.

Otherwise, the design of the electric motors is identical, the stator is absolutely the same

Squirrel cage induction motor:

The rotor can be all-metal (latest models) or consist of a squirrel cage with aluminum-filled gaps between the cage rods. The rotor is inserted into the stator, a minimum gap is left between them, no more than a couple of millimeters, even for the most powerful ones. A voltage is applied to the stator, which forms a rotating magnetic field. The rotor enters the zone of action of the magnetic field, currents are induced in it. The resulting field has a certain direction, so that the rotor starts rotating.

The field arises by induction, there is no electrical contact between the rotor and the stator, there is no collector and brushes. The shaft is only fixed in the stator covers on bearings. This motor belongs to the brushless (brushless) group.

An asynchronous motor with a wound rotor has a collector unit. A magnetic core made of stacked plates with cells for three phase windings is put on the shaft. Power is supplied to the windings through the collector assembly, a magnetic field is alternately generated in them, which is put in with the stator magnetic field. This creates rotation.

Servomotors are not a separate class of electric motors. AC and DC motors with a rotor position sensor can be used as a servomotor. A servo motor is used as part of a servo mechanism to precisely control the angular position, speed and acceleration of the actuator. A servo motor requires a relatively complex control system to operate, which is usually designed specifically for a servo drive.