Understand the classification and application of motor

Motor: also known as motor (commonly known as motor), refers to an electromagnetic device that realizes the conversion or transmission of electric energy according to the law of electromagnetic induction. Its main role is to produce driving torque, as a power source for electrical appliances or various machinery. The impetus for the widespread use of electric motors comes from the advent of the direct current motor, which was invented by Belgian engineer Gram in 1870 and produced in large quantities, and then continued to improve the efficiency of the motor. Siemens of Germany, another research unit in electric motors, is also working hard. At about the same time as Gram's success, Siemens introduced the electric locomotive, which does not burn oil, to much acclaim at the Berlin Industrial exhibition. The invention of the AC motor is completed by the American inventor Tesla, the earliest AC motor is designed according to the principle of electromagnetic induction, the structure is simpler than the DC motor, and it is more widely used than the DC motor that can only be used in the trolley, and its invention makes the motor really enter the field of home appliances. After the advent of AC motors, synchronous motors, series motors, and AC commutator motors have gradually been invented and put into actual production to provide more convenience for people's lives. The invention and application of electric motor is of great significance to human beings, and it can be said that it has brought earth-shaking changes to human life.

Classification of motors

1.1 Classification of motors

Motor according to the type of working power supply: can be divided into DC motor and AC motor. Dc motors can be divided into brushless DC motors and brushless DC motors 

according to their structure and working principle. Brush DC motor can be divided into: permanent magnet DC motor and electromagnetic DC motor. Electromagnetic DC motor division: 

series excited DC motor, shunt excited DC motor, separately excited DC motor and compound DC motor. Permanent magnet DC motor division: rare earth permanent magnet DC motor, 

ferrite permanent magnet DC motor and aluminum nickel cobalt permanent magnet DC motor. The AC motor can also be divided into: synchronous motor and asynchronous motor. 

Synchronous motor can be divided into: permanent magnet synchronous motor, reluctance synchronous motor and hysteresis synchronous motor. Induction motor can be divided into 

induction motor and AC commutator motor. Induction motors can be divided into: three-phase asynchronous motors, single-phase asynchronous motors and cowl pole asynchronous 

motors. Ac commutator motor can be divided into: single-phase series motor, AC-DC motor and repulsion motor.

Classification of motor characteristics and applications

2.1 DC motor DC motor is a motor that relies on DC operating voltage, widely used in radio recorders, video recorders, DVD players, electric shavers, hair dryers, electronic watches, toys 

and so on.

2.1.1 Brushless DC motor

The brushless DC motor uses semiconductor switching devices to achieve electronic commutation, that is, electronic switching devices instead of the traditional contact commutator and 

brush. It has the advantages of high reliability, no commutation spark, low mechanical noise, and is widely used in high-grade recording stand, video recorder, electronic instrument and 

automatic office equipment.

The brushless DC motor is composed of permanent magnet rotor, multipole winding stator, position sensor and so on. The position sensor converts the current of the stator winding in a 

certain order according to the change of the rotor position (that is, the position of the rotor magnetic pole relative to the stator winding is detected, and the position sensing signal is 

generated at the determined position, and the power switching circuit is controlled after the signal conversion circuit is processed, and the winding current is switched according to a 

certain logical relationship). The operating voltage of the stator winding is provided by the electronic switching circuit controlled by the position sensor output.

There are three types of position sensors: magnetic, photoelectric and electromagnetic.

A brushless DC motor with a magnetically sensitive position sensor has a magnetically sensitive sensor (such as a Hall element, a magnetically sensitive diode, a magnetically sensitive 

electrode, a magnetically sensitive resistor or an ASIC, etc.) mounted on a stator assembly to detect changes in the magnetic field generated when a permanent magnet or rotor rotates.

A brushless DC motor with photoelectric position sensor is provided with a photoelectric sensor in a certain position on the stator assembly, a light shield is arranged on the rotor, and the 

light source is a light-emitting diode or a small bulb. When the rotor rotates, due to the action of the light shield, the photosensitive components on the stator will generate pulse signals 

intermittently according to a certain frequency.

The brushless DC motor with electromagnetic position sensor is equipped with electromagnetic sensor components (such as coupling transformers, proximity switches, LC resonant circuits,

 etc.) on the stator assembly. When the rotor position of the permanent magnet changes, the electromagnetic effect will cause the electromagnetic sensor to produce a high-frequency 

modulated signal (its amplitude changes with the rotor position).

2.1.2 Permanent magnet DC motor

Permanent magnet DC motor is also composed of stator pole, rotor, brush, shell, etc. The stator pole is made of permanent magnet (permanent magnetic steel), with ferrite, aluminum 

nickel cobalt, NdFeb and other materials. According to its structural form, it can be divided into cylinder type and tile type. Most of the electricity used in the video recorder is a cylinder 

magnet, while most of the motors used in power tools and automotive appliances use special block magnets.

The rotor is generally made of silicon steel sheet superimposed, which has fewer slots than the rotor of electromagnetic DC motor. Most of the low-power motors used in the video 

recorder are 3 slots, and the higher-grade ones are 5 slots or 7 slots. The enameled wire is wound between two slots of the rotor core (three slots are three windings), and its joints are 

welded to the metal sheet of the commutator. The brush is a conductive part connecting the power supply and the rotor winding, which has two properties of conduction and wear 

resistance. The brush of a permanent magnet motor uses a single metal sheet or a metal graphite brush or an electrochemical graphite brush.

The permanent magnet DC motor used in the video recorder adopts electronic speed stabilizing circuit or centrifugal speed stabilizing device.

2.1.3 Electromagnetic DC motor

Electromagnetic DC motor is composed of stator magnetic pole, rotor (armature), commutator (commonly known as commutator), brush, housing, bearing, etc.

The stator magnetic pole (main magnetic pole) of an electromagnetic DC motor is composed of an iron core and an exciting winding. According to its excitation (the old standard is called

 excitation) mode can be divided into series excited DC motor, shunt excited DC motor, separately excited DC motor and compound DC motor. Because of the different excitation mode, 

the law of stator magnetic flux (generated by the excitation coil of the stator magnetic pole) is also different.

The excitation windings and rotor windings are connected in series by brushes and commutators, and the excitation current is proportional to the armature current, the stator's magnetic 

flux increases with the increase of the excitation current, the torque is approximately proportional to the square of the armature current, and the speed decreases rapidly with the increase 

of torque or current. Its starting torque can reach more than 5 times the rated torque, short-term overload torque can reach more than 4 times the rated torque, the speed change rate is 

large, and the no-load speed is very high (generally not allowed to run under no-load). Speed regulation can be realized by using external resistors in series (or parallel) with the series 

winding, or by connecting the series winding in parallel.

The excitation winding of shunt DC motor is in parallel with the rotor winding, the excitation current is relatively constant, the starting torque is proportional to the armature current, and 

the starting current is about 2.5 times of the rated current. The speed decreases slightly with the increase of current and torque, and the short-term overload torque is 1.5 times of the rated

 torque. The speed change rate is small, 5%~15%. Speed can be adjusted by the constant power of weakening the magnetic field.

The excitation winding of separately excited DC motor is connected to an independent excitation power supply, and its excitation current is also relatively constant, and the starting torque 

is proportional to the armature current. The speed change is also 5% to 15%. The speed can be increased by weakening the constant power of the magnetic field or reduced by reducing 

the voltage of the rotor winding.

In addition to shunt winding, series winding (with fewer turns) is also installed on the stator magnetic pole of the compound DC motor. The direction of magnetic flux generated by the 

series winding is the same as that of the main winding, the starting torque is about 4 times of the rated torque, and the short-time overload torque is about 3.5 times of the rated torque. 

The speed change rate is 25%~30% (related to series windings). The speed can be adjusted by weakening the magnetic field strength.

2.2 AC Motor

2.2.1 AC synchronous motor

Ac synchronous motor is a kind of constant speed drive motor, its rotor speed and power frequency to maintain a constant proportional relationship, is widely used in electronic 

instruments, modern office equipment, textile machinery and so on.

2.2.1.1. Permanent magnet synchronous motor Permanent magnet synchronous motor is an asynchronous start permanent magnet synchronous motor, its magnetic field system is 

composed of one or more permanent magnets, usually in the cage rotor welded with cast aluminum or copper bars, according to the required number of poles mounted with permanent 

magnet poles. The stator structure is similar to that of asynchronous motors.

When the stator winding is connected to the power supply, the motor starts with the principle of asynchronous motor, accelerates to the synchronous speed, and the rotor permanent 

magnetic field and the stator magnetic field are used