What is an electric motor and what are its classifications?
An electric motor, also known as a motor (commonly known as a motor), is represented by the letter "M" (D in the old standard) in a circuit. Its main function is to produce driving torque, as the power source of electrical appliances or small machinery.
This article introduces the electric motor for household appliances or electronic products used in the small power motor, the so-called micro-motor.
(A) types of electric motors
There are many types of electric motors.
1. According to the working power source classification According to the different working power source of the motor, can be divided into DC motor and AC motor. Among them, AC motors are also divided into single-phase motors and three-phase motors.
2. According to the structure and working principle of classification motor according to the structure and working principle can be divided into asynchronous motor and synchronous motor.
Synchronous motor can also be divided into permanent magnet synchronous motor, reluctance synchronous motor and hysteresis motor.
Asynchronous motors can be divided into induction motors and AC commutator motors. Induction motor is divided into three-phase asynchronous motor, single-phase asynchronous motor and shaded pole asynchronous motor. AC commutator motor is also divided into single-phase series-excited motor, AC and DC dual-use motor and push repulsion motor.
Direct current motor according to the structure and working principle can be divided into brushless DC motor and brush DC motor. Brush DC motor can be divided into permanent magnet DC motor and electromagnetic DC motor. Electromagnetic DC motors are divided into series-excited DC motors, parallel-excited DC motors, other-excited DC motors and compound-excited DC motors. Permanent magnet DC motor is divided into rare earth permanent magnet DC motor, ferrite permanent magnet DC motor and alnico permanent magnet DC motor.
3. according to the starting and running mode classification motor according to the starting and running mode can be divided into capacitor starting motor, capacitor qa motor, capacitor starting and running motor and split-phase motor.
4. Classification according to the use of electric motors can be divided into drive motors and control motors.
Drive motor is divided into power tools (including drilling, polishing, grinding, grooving, cutting, reaming and other tools) with electric motors, home appliances (including washing machines, electric fans, refrigerators, air conditioners, tape recorders, VCRs, video recorders, video disk players, vacuum cleaners, cameras, hair dryers, electric shavers, etc.) with electric motors and other general-purpose small machinery and equipment (including a variety of small machine tools, small machines, medical equipment, electronic instruments, etc.) with motors and other general-purpose small mechanical equipment (including a variety of small machine tools, small machines, medical equipment, electronic instruments, etc.).
Motor for small general-purpose machinery and equipment (including a variety of small machine tools, small machinery, medical equipment, electronic instruments, etc.)
Control motors are divided into stepper motors and servo motors.
5. According to the structure of the rotor classification motor according to the structure of the rotor can be divided into cage induction motor (the old standard called squirrel cage asynchronous motor) and wire-wound rotor induction motor (the old standard called wire-wound asynchronous motor).
6. according to the operating speed classification motor according to the operating speed can be divided into high-speed motor, low-speed motor, constant speed motor, speed motor.
Low-speed motor is divided into gear motor, electromagnetic reduction motor, torque motor and claw pole synchronous motor.
Speed motors can be divided into step constant speed motors, stepless constant speed motors, step variable speed motors and infinitely variable speed motors, but also can be divided into electromagnetic speed motors, DC speed motors, PWM frequency conversion speed motors and switched reluctance speed motors.
(B) DC motor
Direct current motor is relying on direct current operating voltage operation of the motor, widely used in recorders, video recorders, video players, video players, electric shavers, hairdryers, electronic watches and toys.
1. electromagnetic DC motor electromagnetic DC motor by the stator pole, rotor (armature), commutator (commonly known as rectifier), brushes, casing, bearings, etc.
Electromagnetic DC motor stator pole (main pole) by the core and excitation winding. According to its excitation (the old standard called excitation) can be divided into series-excited dc motor, parallel-excited dc motor, his excitation dc motor and compound-excited dc motor. Due to the different excitation methods, the stator pole flux (generated by the stator pole of the excitation coil is energized) of the law is also different.
Series-excited DC motor excitation winding and rotor winding connected in series through the brush and commutator, the excitation current is proportional to the armature current, stator flux increases with the increase in the excitation current, torque is approximately proportional to the square of the armature current, the speed of rotation with the increase in torque or current and a rapid decline. Its starting torque can be more than 5 times the rated torque, short-time overload torque can be more than 4 times the rated torque, the rate of change of rotational speed is large, the no-load speed is very high (generally do not allow it to run under no load). Speed control can be realized by connecting the external resistor in series (or in parallel) with the series-excited winding, or by switching the series-excited winding in parallel.
Parallel excitation DC motor excitation winding and rotor winding in parallel, the excitation current is more constant, starting torque and armature current is proportional to the starting current is about 2.5 times the rated current. The rotational speed decreases slightly with the increase of current and torque, and the short-time overload torque is 1.5 times of the rated torque. The rate of change of rotational speed is small, 5%~15%. The speed can be regulated by dissipating the constant power of the magnetic field.
The excitation winding of he-excited DC motor receives independent excitation power supply, and its excitation current is also more constant, and the starting torque is proportional to the armature current. The speed change is also 5%~15%. The speed can be increased by dissipating the constant power of the magnetic field or reduced by lowering the voltage of the rotor winding.
The stator pole of a compound-excitation DC motor is equipped with a series-excitation winding in series with the rotor winding (which has fewer turns) in addition to the parallel-excitation winding. The direction of magnetic flux generated by the series winding is the same as that of the main winding, and 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 winding). The rotational speed can be adjusted by weakening the magnetic field strength.
The commutator's commutator piece uses alloys such as silver-copper and cadmium-copper, molded in high-strength plastic.
The brushes are in sliding contact with the commutator to provide armature current to the rotor windings. Electromagnetic DC motor brushes generally use metal graphite brushes or electrified graphite brushes.
The core of the rotor is made of silicon steel sheet stacked, generally 12 slots, embedded in 12 groups of armature windings, the windings are connected in series, and then connected to 12 pieces of commutator respectively.
2. permanent magnet DC motor
Permanent magnet DC motor also consists of stator pole, rotor, brushes, shell, etc.
Stator pole using permanent magnets (permanent magnets), ferrite, alnico, neodymium-iron-boron and other materials. According to its structural form can be divided into cylinder type and tile type and so on several kinds. Most of the electric machines used in video recorders are cylindrical magnets, while most of the electric motors used in power tools and automotive appliances use special block-type magnets. Figure 18-12 is a schematic diagram of the magnetic circuit of the two types of permanent magnets.
The rotor is generally made of laminated silicon steel sheets and has fewer slots than the rotor of an electromagnetic DC motor. Most of the low-power motors used in video recorders have 3 slots, and the higher-grade ones have 5 or 7 slots. Enameled wire is wound between the two slots of the rotor core (three slots means three windings), and its joints are welded to the metal sheets of the changer. Brushes are the conductive parts connecting the power supply with the rotor windings, with conductive and wear-resistant properties. Permanent magnet motor brushes use unisex metal sheet or metal graphite brush, electrified graphite brush.
Permanent magnet DC motors used in VCRs adopt electronic speed stabilizing circuits or centrifugal speed stabilizing devices.
3. Brushless DC motor Brushless DC motor is the use of semiconductor switching devices to realize electronic commutation, that is, electronic switching devices instead of the traditional contact commutator and brush. It has the advantages of high reliability, no commutation sparks, low mechanical noise, etc., widely used in high-grade audio recorders, video recorders, electronic instruments and automated office equipment.
The brushless DC motor consists of a permanent magnet rotor, a multi-pole winding stator, and a position sensor, as shown in Figure 18-13. Position sensing according to changes in rotor position, along a certain order of the stator winding current exchange (i.e., detection of the rotor pole relative to the position of the stator winding, and in the determined position of the position sensing signals generated by the signal conversion circuit to control the power switching circuit, according to a certain logical relationship between the winding current switching). The working voltage of the stator winding is provided by the electronic switching circuit controlled by the output of the position sensor.
There are three types of position sensors: magnetic, photoelectric and electromagnetic.
Brushless DC motors with magnetic position sensors have magnetic sensor devices (e.g., Hall elements, magnetic diodes, magnetic exemplary tubes, magnetic resistors, or special integrated circuits, etc.) mounted on the stator assembly, which are used to detect changes in the magnetic field generated by the permanent magnets and the rotor when it rotates.
The use of photoelectric position sensor brushless DC motor, in the stator assembly according to a certain position configured with photoelectric sensors, the rotor is equipped with a shading plate, the light source for the light-emitting diode or a small light bulb. Rotor rotation, due to the role of the visor, the stator on the photosensitive components will be a certain frequency intermittent pulse signal.
Brushless DC motor with electromagnetic position sensor is installed with electromagnetic sensor components (such as coupling transformer, proximity switch, LC resonant circuit, etc.) on the stator assembly, and when the rotor position of the permanent magnet changes, the electromagnetic effect will cause the electromagnetic sensor to generate a high-frequency modulation signal (the amplitude of which varies with the rotor position).
(C) AC asynchronous motor
AC asynchronous motor is the leading AC voltage operation of the motor, widely used in electric fans, refrigerators, washing machines, air conditioners, hairdryers, vacuum cleaners, hoods, dishwashers, electric sewing machines, food processing machines and other household appliances and a variety of power tools, small mechanical and electrical equipment.
AC asynchronous motor is divided into induction motor and AC commutator motor. Induction motor is also divided into single-phase asynchronous motor, AC and DC dual-use motor and push repulsion motor.
1. single-phase asynchronous motor single-phase asynchronous motor consists of stator, rotor, bearings, casing, end caps and so on.
The stator is composed of the seat and the core with windings. The core is made of silicon steel sheet punching groove stacking, groove embedded in two sets of space between 900 electrical angle of the main winding (also known as the operation of the winding) and auxiliary winding (also known as the starting winding into the secondary winding). The main winding is connected to the AC power supply, and the auxiliary winding is connected to the power supply after connecting the centrifugal switch S or the starting capacitor, running capacitor, etc. in series.
The rotor is a cage-type cast aluminum rotor, which is stacked with aluminum cast into the slot of the core, and cast together with the end ring, so that the rotor guide short-circuited into a rat-cage type.
Single-phase asynchronous motor is divided into single-phase resistance starting asynchronous motor, single-phase capacitor starting asynchronous motor, single-phase capacitor running asynchronous motor and single-phase double-value capacitor asynchronous motor, Figure 18-14 is a few single-phase asynchronous motor of the principle of electricity line.
2. three-phase asynchronous motor three-phase asynchronous motor structure and single-phase asynchronous motor is similar to the stator core groove embedded in three-phase windings (single-layer chain, single-layer concentric and single-layer cross type three structures). After the stator winding is connected to the three-phase AC power supply, the rotating magnetic field generated by the winding current produces an induced current in the rotor conductor, and the rotor produces an electromagnetic rotating cabinet (i.e., asynchronous rotating cabinet) under the interaction of the induced current and the rotating magnetic field of the air gap, which makes the motor rotate.
3. Shaded-pole motor Shaded-pole motor is the simplest type of unidirectional AC motor, usually using a cage-type slotted cast aluminum rotor. It is based on the stator shape and structure of the different, but also divided into convex-pole shaded-pole motor hidden-pole shaded-pole motor.
Convex shaded-pole motor stator core shape for the square, rectangular or circular magnetic field frame, magnetic poles protruding, each pole has one or more auxiliary role of the short-circuit copper ring, that is, the cover pole winding. Concentrated winding on the convex pole magnetic poles as the main winding.
Hidden-pole shaded-pole motor stator core and ordinary single-phase motor core is the same, the stator winding distribution winding, the main winding is distributed in the stator groove, shaded-pole winding does not use short-circuiting copper ring, but with a thicker enameled wire wound into a distribution winding (short-circuiting after series connection) embedded in the stator groove (about 1/3 of the total number of grooves), to play the role of auxiliary group. The main winding and shaded-pole winding are separated by a certain angle in space.
When the main winding of a shaded-pole motor is energized, the shaded-pole winding also generates an induced current that rotates the flux in the part of the stator pole that is shaded by the shaded-pole winding with the unshrouded portion rotating in the direction of the shaded portion.
34. Single-phase series-excited motor The stator of single-phase series-excited motor consists of convex pole core and excitation winding, and the rotor consists of hidden pole core, armature winding, commutator and rotor shaft. A series circuit is formed between the excitation winding and the armature winding through brushes and commutator. Figure 18-16 shows the structure of a unidirectional series-excited motor.
Single-phase series-excited motors are AC and DC motors, which can work with either AC or DC power.
(D) AC synchronous motor
AC synchronous motor is a kind of constant speed drive motor, its rotor speed and power supply frequency to maintain a constant proportionality, is widely used in electronic instruments, modern office equipment, textile machinery and so on.
1. permanent magnet synchronous motor permanent magnet synchronous motor belongs to the asynchronous start permanent magnet synchronous motor, its magnetic field system consists of one or more permanent magnets, usually in the cast aluminum or copper welded into the cage rotor, according to the required number of poles mounted with the magnetic poles of the permanent magnets. The stator structure is similar to that of an asynchronous motor.
When the stator winding is connected to the power supply, the motor is started by the principle of asynchronous motor, accelerated to the synchronous speed, the synchronous electromagnetic torque generated by the rotor permanent magnetic field and stator magnetic field (electromagnetic torque generated by the rotor permanent magnetic field and stator magnetic field generated by the reluctance of the torque synthesis) will be drawn into the synchronization of the rotor, the motor enters the synchronous operation.
Resistance Synchronous Motor The reluctance synchronous motor, also known as reactive synchronous motor, is a synchronous motor that generates reluctance torque by using unequal rotor cross-axis and straight-axis reluctance, and its stator is similar to that of an asynchronous motor, except that the rotor structure is different.
The reluctance synchronous motor is evolved with the cage asynchronous motor, in order to enable the motor to produce asynchronous starting torque, the rotor is also equipped with a cage cast aluminum winding resistance. The rotor is equipped with reaction slots corresponding to the number of stator poles (only the role of the convex part, no excitation windings and permanent magnets), which are used to generate the reluctance synchronous torque. According to the different structure of the reaction slot on the rotor, it can be divided into internal reaction rotor, external reaction rotor and internal and external reaction rotor, of which, the external reaction rotor reaction slot is open to the outer circle of the rotor, so that the straight axis and the direction of the intersection of the axes of the air gap is not equal. The inner reactive rotor has grooves on the inside, so that the magnetic flux in the direction of the intersection axis is blocked and the magnetic resistance is increased. The internal and external reactive rotor combines the structural characteristics of the above two rotors, and the difference between the straight and intersecting axes is large, so that the force energy of the motor is large. The reluctance synchronous motor is also divided into single-phase capacitor running type, single-phase capacitor starting type, single-phase double-value capacitor type and other types.
3. Hysteresis synchronous motor Hysteresis synchronous motor is the use of hysteresis material to produce hysteresis torque and work of synchronous motor. It is divided into internal rotor type hysteresis synchronous motor, external rotor type hysteresis synchronous motor and single-phase shaded pole type hysteresis synchronous motor.
The inner rotor hysteresis synchronous motor rotor structure for hidden pole type, the appearance of a smooth cylinder, no winding on the rotor, but the core of the outer circle of the ring made of hysteresis material effective layer.
After the stator winding is connected to the power supply, the rotating magnetic field generated makes the hysteresis rotor produce asynchronous torque and start to rotate, and then draw into synchronous operation by itself. In the asynchronous operation of the motor, the stator rotating magnetic field to the rotational frequency repeatedly magnetized rotor; in synchronous operation, the hysteresis material on the rotor is magnetized and the emergence of a permanent magnetic poles, thus generating synchronous torque.