(1) Type of motor
There are many kinds of motors.
1. According to the classification of working power supply and the different working power supply of motor, it can be divided into DC motor and AC motor. Among them, AC motors are divided into single-phase motors and three-phase motors.
2. Classification of motors according to structure and working principle Motors can be divided into DC motors, asynchronous motors and synchronous motors according to structure and working principle.
Synchronous motors can also be divided into permanent magnet synchronous motors, reluctance synchronous motors and hysteresis synchronous motors.
Asynchronous motors can be divided into induction motors and AC commutator motors. Induction motors are divided into three-phase asynchronous motors, single-phase asynchronous motors and shielded pole asynchronous motors. AC commutator motor is divided into single-phase series motor, AC -DC dual-purpose motor and repulsion motor.
According to the structure and working principle, DC motors can be divided into brushless DC motors and brushed DC motors. Brushed DC motors can be divided into permanent magnet DC motors and electromagnetic DC motors. Electromagnetic DC motors are divided into series DC motors, parallel DC motors, separately excited DC motors and composite DC motors.
Excitation DC motor. Permanent magnet DC motors are divided into rare earth permanent magnet DC motors, ferrite permanent magnet DC motors and Al-Ni-Co permanent magnet DC motors.
3. Classification of motors according to starting and running modes Motors can be divided into capacitor-started single-phase asynchronous motors, capacitor-operated single-phase asynchronous motors, capacitor-started single-phase asynchronous motors and split-phase single-phase asynchronous motors according to starting and running modes.
4. Motors can be classified into drive motors and control motors according to their uses.
The driving motor is divided into electric tools (including drilling, grinding, polishing, slotting, cutting, reaming and other tools) and household appliances (including washing machines, electric fans, refrigerators, air conditioners, tape recorders, video recorders, DVD players, vacuum cleaners, cameras, hair dryers, electric shavers and so on). ) and other general small mechanical equipment (including all kinds of small machine tools, small machinery, medical instruments and electronic instruments).
Control motors are divided into stepper motors and servo motors.
5. According to the structure of the rotor, the motor can be divided into squirrel-cage induction motor (called squirrel-cage asynchronous motor in the old standard) and wound induction motor (called wound asynchronous motor in the old standard).
6. Classify motors according to running speed. According to running speed, motors can be divided into high-speed motors, low-speed motors, constant-speed motors and variable-speed motors.
Low-speed motors are divided into gear reduction motors, electromagnetic reduction motors, torque motors and claw-pole synchronous motors.
Speed regulating motors can be divided into step constant speed motors, stepless constant speed motors, step variable speed motors and stepless variable speed motors, as well as electromagnetic speed regulating motors, DC speed regulating motors, PWM frequency conversion motor and switched reluctance speed regulating motors.
(2) DC Motor Company
DC motor is a kind of motor that runs on DC working voltage. Widely used in tape recorders, video recorders, DVD players, electric razors, hair dryers, electronic watch toys and so on.
1. Electromagnetic DC Motor The electromagnetic DC motor consists of stator poles, rotor (armature), commutator (commonly known as commutator), brushes, casing, bearings, etc.
The stator pole (main pole) of electromagnetic DC motor consists of iron core and excitation winding. According to different excitation modes, it can be divided into series-excited DC motor, parallel-excited DC motor, separately-excited DC motor and compound-excited DC motor. Due to different excitation modes, the laws of stator flux (generated by energizing the excitation coils of stator poles) are also different.
The excitation winding and rotor winding of series-excited DC motor are connected in series through brushes and commutator. Excitation current is proportional to armature current, stator flux increases with the increase of excitation current, torque is approximately proportional to the square of armature current, and speed decreases rapidly with the increase of torque or current. Its starting torque can reach more than 5 times of rated torque, short-term overload torque can reach more than 4 times of rated torque, with large speed change and high no-load speed (generally no-load operation is allowed). Speed adjustment can be achieved by using an external resistor in series (or parallel) with the series winding or switching the series winding in parallel.
The excitation winding of shunt DC motor is connected in parallel with the rotor winding, and its excitation current is relatively constant. The starting torque is proportional to the armature current, which is about 2.5 times the rated current. The speed decreases slightly with the increase of current and torque, and the short-term overload torque is 1.5 times the rated torque. The speed change rate is small, ranging from 5% to 15%. The speed can be adjusted by weakening the constant power of the magnetic field.
The excitation winding of separately excited DC motor is powered by an independent excitation power supply, and its excitation current is relatively constant, and the starting torque is proportional to the armature current. The speed change is also 5%~ 15%. The rotating speed can be increased by weakening the constant power of the magnetic field, or decreased by reducing the voltage of the rotor winding.
In addition to the parallel winding, the stator pole of the compound DC motor is also equipped with a series winding with few turns in series with the rotor winding. The direction of the 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-term overload torque is about 3.5 times of the rated torque. The speed change rate is 25%~30% (related to string winding). The rotating speed can be adjusted by weakening the magnetic field strength.
The commutator segment of the commutator is made of alloy materials such as silver, copper, cadmium and copper, and molded with high-strength plastic.
The brush is in sliding contact with the commutator to provide armature current for the rotor winding. Generally, the brush of electromagnetic DC motor is used.
Use metal graphite brush or electrochemical graphite brush.
The iron core of the rotor is made of silicon steel sheet, which is generally 12 slot and embedded with 12 armature winding. After the windings are connected in series, they are respectively connected with 12 commutators.
2. Permanent magnet DC motor
Permanent magnet DC motor is also composed of stator pole, rotor, brush and shell.
The stator pole adopts permanent magnet (permanent magnet steel) and is made of ferrite, Al-Ni-Co, NdFeB and other materials. According to its structural form, it can be divided into cylinder type and tile type. Most of the electric motors used in tape recorders are cylindrical magnets, while most of the motors used in electric tools and automobile appliances are special block magnets. Fig. 18- 12 is a schematic diagram of the magnetic circuit of two permanent magnets.
The rotor is generally made of silicon steel sheets laminated, which has fewer slots than the rotor of electromagnetic DC motor. Most of the low-power motors used in tape recorders have three slots, and the high-end ones have five slots or seven slots. The enameled wire is wound between two slots of the rotor core (three slots have three windings), and its joints are welded on the metal plate of the transformer respectively. Brush is a conductive component connecting power supply and rotor winding, which has both conductive and wear-resistant properties. The brush of permanent magnet motor adopts neutral metal sheet or metal graphite brush and electrochemical graphite brush.
The permanent magnet DC motor used in the recorder adopts electronic speed stabilizing circuit or centrifugal speed stabilizing device.
3. Brushless DC motor Brushless DC motor uses semiconductor switching devices to realize electronic commutation, that is, electronic switching devices replace traditional contact commutation.
Equipment and brushes. It has the advantages of high reliability, no commutation spark and low mechanical noise, and is widely used in high-end recording studios, video recorders, electronic instruments and automatic office equipment.
Brushless DC motor is composed of permanent magnet rotor, multipole winding stator and position sensor, as shown in figure 18- 13. Position induction converts the current of the stator winding in a certain order according to the change of the rotor position (that is, detecting the position of the rotor pole relative to the stator winding, generating a position induction signal at a certain position, controlling the power switch circuit after being processed by the signal conversion circuit, and switching the winding current according to a certain logical relationship). The working voltage of the stator winding is provided by the electronic switch circuit controlled by the output of the position sensor.
There are three types of position sensors: magnetic sensitive, photoelectric and electromagnetic.
Brushless DC motor with magnetic sensitive position sensor, its magnetic sensitive sensing devices (such as Hall element, magnetic sensitive diode, magnetic sensitive diode, magnetic sensitive resistor or ASIC, etc.). ) is installed on the stator assembly to detect the change of magnetic field generated when the permanent magnet and rotor rotate.
Brushless DC motor with photoelectric position sensor is equipped with photoelectric sensing device at a certain position of stator assembly, with shading plate on rotor, and light source is light emitting diode or small bulb. When the rotor rotates, the photosensitive element on the stator will intermittently generate pulse signals with a certain frequency due to the action of the light shielding plate.
Brushless DC motor with electromagnetic position sensor is equipped with electromagnetic sensor elements (such as coupling transformer, proximity switch, LC resonant circuit, etc.). ) on the stator assembly. When the position of the permanent magnet rotor changes, the electromagnetic effect will make the electromagnetic sensor produce a high-frequency modulation signal (its amplitude changes with the position of the rotor).