DC motor: device and principle of operation, design and control, application of dpt

A device that converts electrical energy into mechanical energy can be used as a motor or generator, since the design and principle of operation of the DC motor (DC motor) is similar to the design generator. A feature of the DCT is a mechanical inverter (switch). This commutator has sliding contacts in the form of brushes, which are positioned so that they change the polarity of the armature windings (coils) during rotation.

Features and device DPT

DPT is a rotating electric machine powered by direct current. Depending on the direction of power flow, a distinction is made between the motor (electric motor with electric and mechanical power) and a generator (an electrical generator to which mechanical power is supplied, and electricity). DPTs can be started under load, their speed is easy to change. In generator mode DCT converts AC voltagesupplied by the rotor into a pulsating constant voltage.

History of invention

Building on the development of the first electrochemical cells in the first half of the 19th century, DC machines were the first electromechanical energy converters. The original form of the electric motor was developed in 1829, and in 1832 the Frenchman Hippolyte Piksii built the first generator. Antonio Pacinotti built in 1860 a DC electric motor with a multicomponent commutator. Friedrich von Hefner-Alteneck developed the drum armature in 1872, which opened up the possibility of industrial use in the field of large-scale mechanical engineering.

In the following decades, such machines lost their importance in large-scale mechanical engineering due to the development of three-phase alternating current. Synchronous machines and low maintenance induction motor systems have replaced them in many devices.

Engine design

To understand the principle of operation of the DPT, you must first study its design features, one of which is that a rotating conductive is installed in the magnetic field of a permanent magnet circuit.

Simplifying this structure, we can say that the engine consists of two main components:

1. The main magnet (permanent magnet) that is attached to the stator. The magnetic field can also be electrically generated. The stator contains the so-called exciting windings (coils).
2. Conductive loop (reinforcement) on the armature core, usually composed of laminated metal sheets.

Both designs are called externally excited DC motors. The electrodynamic law indicates that the conductive loop of a conductor in a magnetic field is a force [F], which depends on the current [I] and the strength of the magnetic field [B]. A conductive conductor is surrounded by a circular magnetic field. If you combine the magnetic field of the magnetic field with the magnetic field of the conductive loop, you can find the superposition of the two fields, as well as the resulting force effect.

The armature winding consists of two coil halves. If you apply a DC voltage to the two ends of the armature winding, you can imagine that moving charge carriers enter the bottom half of the coil from the top half of the coil.

Each conductive coil develops its own magnetic field, and the magnetic field of the permanent magnet is superimposed on the magnetic field of the lower half of the coil and the field of the upper half of the coil. The field lines of a constant magnetic field are always in the same direction, they always show from the north to the south pole. In contrast, the fields of the two halves of the coil have opposite directions.

On the left side of the coil half field, the field lines of the exciter field and the coil field are in the same direction. This force effect creates a torque in the opposite direction at the lower and upper ends of the armature, which causes the armature to rotate.

The anchor is a so-called I-beam anchor. This design gets its name from its shape, which resembles two T-pieces. The armature coils are connected to the commutator (collector) boards. The current in the armature winding is usually supplied through carbon brushes, which provide sliding contact with the rotating commutator and supply the coils with electricity. Brushes are made of self-lubricating graphite, partially mixed with copper powder for small motors.

Principle of operation and use

This device is an electrical machine that converts electrical energy into mechanical energy. The principle of operation of a DC motor is that whenever a conductor carried by a current is placed in a magnetic field, it experiences a mechanical force.

A permanent magnet converts electrical energy into mechanical energy through the interaction of two magnetic fields. One field is created by an assembly with permanent magnets, the other is created by an electric current flowing in the motor windings. These two fields result in a torque that tends to rotate the rotor. As the rotor spins, the current in the windings is switched, providing a continuous torque output.

The switch consists of conductive copper segments (rods), which are the termination of individual coils of wire distributed around the reinforcement. The second half of the mechanical switch is equipped with brushes. These brushes usually remain stationary with the motor housing.

As electrical energy passes through the brushes and armature, a torsional force is created in the form of a reaction between the motor field and the armature, causing the motor armature to rotate. When the armature turns, the brushes switch to adjacent strips on the commutator. This action transfers electrical energy to the adjacent winding and armature.

The movement of the magnetic field is achieved by switching the current between the coils inside the motor. This action is called switching. Many motors have built-in commutation. This means that when the motor rotates, the mechanical brushes automatically commute the coils on the rotor.

Speed ​​setting

DPT can be easily adjusted. The speed can be changed using the following variables:

1. Armature voltage U_A (voltage control).
2. Main field flux (field control), magnetic field strength.
3. Anchoring resistance.

The simplest method to control the speed of rotation is to control the drive voltage. The higher the voltage, the higher the speed that the motor is trying to reach. In many applications, simple voltage regulation can lead to large power losses in the control circuit, therefore pulse width modulation is widely used.

In the basic PWM method, the operating power is turned on and off to modulate the current. The ratio of the on time to the off time determines the motor speed.

An externally excited motor is easy to control because the currents through the armature and stator windings can be controlled separately. Therefore, such motors had a certain value, especially in the field of highly dynamic drive systems, for example, for driving machines with precise control of speed and torque.

Modern application

DPT are used in various fields.

It is an essential element in various products:

1. toys;
2. servo-mechanical devices;
3. valve drives;
4. robots;
5. automotive electronics.

High quality everyday items (kitchen appliances) use a servo motor known as a universal motor. These universal motors are typical DC motors in which the stationary and rotating coils are serial wires.