Electric machine and electric machine theory concept

(electric machine and electric machine theory concept)

Definition of electric machine: It is an electromagnetic device that converts or transmits electrical energy according to the law of electromagnetic induction.

An electric motor is also called an electric machine (commonly known as a motor) and is represented by the letter "M" (old standard "D") in the circuit. Its main function is to produce driving torque, as a power source for appliances or various machines.

Types of electric motors

1. According to the working power supply, there are different types of DC motors and AC motors. Among them, AC motor is also divided into single-phase motor and three-phase motor.

2. According to the structure and working principle, the motor can be divided into DC motor, asynchronous motor and synchronous motor according to the structure and working principle.

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

Asynchronous motor can be divided into induction motor and AC commutator motor. Induction motor can be divided into three-phase asynchronous motor, single-phase asynchronous motor and shaded-pole asynchronous motor, etc. AC commutator motor is divided into single-phase series-excited motor, AC-DC dual-use motor and push-repulsion motor.

DC motor can be divided into brushless DC motor and brushed DC motor according to the structure and working principle. Brush DC motor can be divided into permanent magnet DC motor and electromagnetic DC motor. Electromagnetic DC motor is divided into series-excited DC motor, parallel-excited DC motor, other-excited DC motor and compound-excited DC motor. Permanent magnet DC motor is divided into rare earth permanent magnet DC motor, ferrite permanent magnet DC motor and alnico permanent magnet DC motor.

According to the different starting and running methods, the motor can be divided into capacitor-started single-phase asynchronous motor, capacitor-running single-phase asynchronous motor, capacitor-started running single-phase asynchronous motor and split-phase single-phase asynchronous motor.

4. According to the classification of use, it can be divided into motor for driving and motor for control.

The driving motor is divided into electric tools (including drilling, polishing, grinding, slotting, cutting, reaming, etc.), home appliances (including washing machine, electric fan, refrigerator, air conditioner, tape recorder, video recorder, video player, vacuum cleaner, camera, hair dryer, electric razor, etc.) and other general small mechanical equipment (including various small machine tools, small machinery, medical equipment, electronic instruments, etc.). The motors for control are divided into stepper motors and stepper motors.

The motors for control are divided into stepper motors and servo motors, etc.

According to the structure of rotor, the motor can be divided into cage induction motor (old standard called squirrel cage induction motor) and wound rotor induction motor (old standard called wound asynchronous motor).

6. According to the speed of operation, the motor can be divided into high speed motor, low speed motor, constant speed motor and speed control motor.

Low speed motor is divided into gear motor, electromagnetic motor, torque motor and claw pole synchronous motor, etc.

In addition to stepped constant speed motor, stepless constant speed motor, stepped variable speed motor and stepless variable speed motor, speed control motor can also be divided into electromagnetic speed control motor, DC speed control motor, PWM frequency control motor and switched reluctance speed control motor.

The rotor speed of asynchronous motor is always slightly lower than the synchronous speed of rotating magnetic field.

The rotor speed of synchronous motor is always synchronous speed regardless of the load size.

I. DC Motor

DC motor is an electric motor running on DC working voltage, which is widely used in recorder, video recorder, video disc player, electric shaver, hair dryer, electronic watch, toys, etc.

1.Electromagnetic DC motor Electromagnetic DC motor consists of stator pole, rotor (armature), commutator (commonly known as rectifier), brush, case, bearing, etc.

The stator pole (main pole) of an electromagnetic DC motor consists of an iron core and an excitation winding. According to its excitation (old standard called excitation) can be divided into series-excited DC motor, parallel-excited DC motor, other-excited DC motor and compound-excited DC motor. Due to the different excitation methods, the law of stator pole flux (generated by the excitation coil of stator pole after energizing) is also different.

The excitation winding of series-excited DC motor is connected in series with the rotor winding through brushes and commutator, the excitation current is proportional to the armature current, the stator flux increases with the increase of excitation current, the torque is approximately proportional to the square of armature current, and the speed decreases rapidly with the increase of torque or current. The starting torque can be more than 5 times of the rated torque, and the short time overload torque can be more than 4 times of the rated torque, the speed change rate is large, and the no-load speed is very high (generally it is not allowed to run under no-load). The speed can be adjusted by connecting an external resistor in series (or in parallel) with the series-excited winding, or by connecting the series-excited winding in parallel.

The excitation winding of parallel-excited DC motor is connected in parallel with the rotor winding, and the excitation current is more constant. The 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 speed variation rate is small, 5%-15%. The speed can be regulated by weakening the constant power of the magnetic field.

The excitation winding of the other-excited DC motor is connected to an independent excitation power supply, and its excitation current is also more constant, and the starting torque is proportional to the armature current. The speed variation is also 5% to 15%. The speed can be increased by weakening the constant power of the magnetic field or reduced by decreasing the voltage of the rotor winding.

Compound-excited DC motors have a series-excited winding (which has fewer turns) in series with the rotor winding in addition to a parallel-excited winding on the stator pole. The direction of magnetic flux produced 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 variation rate is 25%~30% (related to the series winding). The rotational speed can be adjusted by weakening the magnetic field strength.

The commutator of commutator uses silver copper, cadmium copper and other alloy materials, molded with high strength plastic. The brushes are in sliding contact with the commutator to provide armature current to the rotor winding. The brushes of electromagnetic DC motors generally use metal graphite brushes or electrified graphite brushes. The core of the rotor is made of laminated silicon steel sheet, generally 12 slots, embedded with 12 sets of armature windings, each winding is connected in series, and then connected with 12 pieces of commutator respectively.

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 magnet), ferrite, Alnico, NdFeB and other materials. According to its structural form can be divided into cylindrical and tile type and other types. Most of the electricity used in the recorder is cylindrical magnets, while most of the electric motors used in power tools and automotive appliances use special block type magnets.

The rotor is generally made of silicon steel laminated, and the number of slots in the rotor is less than that of electromagnetic DC motors. Most of the small power motors used in VCRs have 3 slots, while the higher grade ones have 5 or 7 slots. The enameled wire is wound between the two slots of the rotor core (three slots, i.e., three windings), and the joints are welded to the metal pieces of the changer. The brush is the conductive part connecting the power supply and the rotor winding, with both conductive and wear-resistant properties. The brushes of permanent magnet motors use single metal sheet or metal graphite brushes or electroplated graphite brushes.

The permanent magnet DC motor used in the recorder uses electronic speed stabilization circuit or centrifugal speed stabilization device.

3. Brushless DC motor

Brushless DC motor uses semiconductor switching device to realize electronic commutation, i.e., electronic switching device instead of traditional contact commutator and brush. It has the advantages of high reliability, no commutation sparks, low mechanical noise, etc. It is widely used in high-grade recording docks, video recorders, electronic instruments and automatic office equipment.

Brushless DC motor consists of permanent magnet rotor, multi-pole winding stator, position sensor, etc., as shown in Figure 18-13. The position sensing changes the rotor position and switches the current of the stator winding along a certain sequence (i.e., it detects the position of the rotor pole relative to the stator winding and generates a position sensing signal at the determined position, which is processed by the signal conversion circuit to control the power switching circuit and switch the winding current according to a certain logical relationship). The operating 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: magneto-sensitive, photoelectric and electromagnetic.

Brushless DC motors with magnet-sensitive position sensors have magnet-sensitive sensor devices (such as Hall elements, magnet-sensitive diodes, magnet-sensitive exodes, magnet-sensitive resistors or special integrated circuits, etc.) mounted on the stator assembly to detect changes in the magnetic field generated by the permanent magnet and rotor rotation.

The brushless DC motor with photoelectric position sensor is equipped with a photoelectric sensor in a certain position on the stator assembly, and the rotor is equipped with a light shield, and the light source is a light-emitting diode or a small light bulb. When the rotor rotates, the photosensitive components on the stator will intermittently generate pulse signals at a certain frequency due to the role of the light shield.

Brushless DC motors with electromagnetic position sensors are equipped with electromagnetic sensor components (e.g., coupling transformers, proximity switches, LC resonant circuits, 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 modulated signal (whose amplitude varies with the rotor position).

II. AC asynchronous motor

AC asynchronous motor is the leading AC voltage running motor, widely used in electric fan, refrigerator, washing machine, air conditioner, hair dryer, vacuum cleaner, hood, dishwasher, electric sewing machine, food processing machine and other household appliances and various power tools, small electromechanical equipment.

AC asynchronous motor is divided into induction motor and AC commutator motor. Induction motor is further divided into single-phase asynchronous motor, AC-DC dual-use motor and push-repulsion motor.

The speed of the motor (stator speed) is less than the speed of the rotating magnetic field, thus it is called asynchronous motor. It is basically the same as induction motor. s=(ns-n)/ns. s is the slew rate and

ns is the magnetic field speed, and n is the rotor speed.

Basic principle: (1) When a three-phase asynchronous motor is connected to a three-phase AC power supply, the three-phase stator winding flows through the three-phase magnetic potential (stator rotating magnetic potential) generated by the three-phase symmetrical current and produces a rotating magnetic field.

(2) The rotating magnetic field has relative cutting motion with the rotor conductor, and according to the principle of electromagnetic induction, the rotor conductor generates the induced electric potential and the induced current.

(3) According to the law of electromagnetic force, the current-carrying rotor conductor is subjected to electromagnetic force in the magnetic field, which forms electromagnetic torque and drives the rotor to rotate, and when the motor shaft is loaded with mechanical load, it outputs mechanical energy outward.

Asynchronous motor is a kind of AC motor, the ratio of its speed at load and the frequency of the connected grid is not a constant relationship. It also varies with the size of the load. The higher the load torque, the lower the rotor speed. Asynchronous motors include induction motors, double-fed asynchronous motors and AC commutator motors. Induction motors are the most widely used and can generally be referred to as induction motors without causing misunderstanding or confusion.

The stator winding of an ordinary asynchronous motor is connected to the AC grid, and the rotor winding does not need to be connected to other power sources. Therefore, it has the advantages of simple structure, easy manufacturing, use and maintenance, reliable operation as well as smaller mass and lower cost. Asynchronous motor has high operating efficiency and good working characteristics, from no-load to full-load range close to constant speed operation, can meet the majority of industrial and agricultural production machinery transmission requirements. Asynchronous motor is also easy to generate a variety of protection types to adapt to the needs of different environmental conditions. Asynchronous motor operation, must draw reactive excitation power from the grid, so that the power factor of the grid becomes bad. Therefore, for driving ball mills, compressors and other high-power, low-speed mechanical equipment, often using synchronous motors. As the speed of asynchronous motor has a certain rotation difference relationship with its rotating magnetic field speed, its speed regulation performance is poor (except for AC commutator motor). For transportation machinery, rolling mills, large machine tools, printing, dyeing and paper making machinery, etc., which require a wide and smooth speed range, DC motors are more economical and convenient. However, with the development of high-power electronic devices and AC speed control system, the speed control performance and economy of asynchronous motors suitable for wide speed control are comparable to those of DC motors.

1. Single-phase asynchronous motor

Single-phase asynchronous motor consists of stator, rotor, bearings, housing, end caps, etc.

The stator is composed of the seat and the core with winding. The core is made of silicon steel sheet punching slot laminated, and the slot is embedded with two sets of main winding (also called running winding) and auxiliary winding (also called starting winding into a secondary winding) that are separated by 900 electrical angles in space. The main winding is connected to the AC power supply, and the auxiliary winding is connected to the power supply after the series connection of centrifugal switch S or starting capacitor and running capacitor.

The rotor is cage-type cast aluminum rotor, it is the core laminated with aluminum cast into the groove of the core, and cast together with the end ring, so that the rotor guide bar short-circuit into a squirrel cage type.

Single-phase asynchronous motor is also 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.

2. Three-phase asynchronous motor

The structure of three-phase asynchronous motor is similar to that of single-phase asynchronous motor, with three-phase windings embedded in the stator core slot (single-layer chain type, single-layer concentric type 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 generates induction current in the rotor conductor, and the rotor generates electromagnetic rotating cabinet (i.e. asynchronous rotating cabinet) under the interaction of induction current and air gap rotating magnetic field, which makes the motor rotate.

3. Shaded-pole motor

The shaded-pole motor is the simplest type of one-way AC motor, which usually adopts cage-type slant slotted cast aluminum rotor. It is divided into convex shaded-pole motor and hidden-pole shaded-pole motor according to the different stator shape structure.

Convex shaded-pole motor has a square, rectangular or circular stator core with protruding poles and one or more short-circuiting copper rings on each pole, i.e. shaded-pole winding. The concentrated winding on the convex pole is used as the main winding.

The stator core of the hidden pole shaded pole motor is the same as the core of ordinary single-phase motor, and its stator winding adopts distribution winding, the main winding is distributed in the stator slot, and the shaded pole winding does not use short-circuiting copper ring, but uses thicker enameled wire wound into distribution winding (short-circuiting itself after series connection) embedded in the stator slot (about 1/3 of the total number of slots), playing the role of auxiliary group. The main winding and shaded pole winding are at a certain angle apart in space.

When the main winding of shaded-pole motor is energized, the shaded-pole winding also generates induction current, which makes the magnetic flux of the stator pole covered by the shaded-pole winding rotate in the direction of the covered part with the uncovered part.

4. Single-phase series-excited motor

The stator of single-phase series-excited motor consists of convex pole core and excitation winding, while the rotor consists of hidden pole core, armature winding, commutator and rotor shaft, etc. The stator of single-phase series-excited motor consists of convex pole core and excitation winding. The excitation winding and armature winding form a series circuit through brushes and commutator. Figure 18-16 shows the structure of one-way series-excited motor.

Single-phase series-excited motor belongs to AC and DC dual-use motor, it can work with both AC power and DC power.

III. AC synchronous motor

AC synchronous motor is a kind of constant speed driving motor, whose rotor speed keeps a constant proportional relationship with the power supply frequency, and is widely used in electronic instruments and meters, present **** public equipment, textile machinery, etc.

1.Permanent magnet synchronous motor

The permanent magnet synchronous motor is an asynchronous start permanent magnet synchronous motor, whose magnetic field system consists of one or more permanent magnets, usually inside the cage-type rotor welded with cast aluminum or copper bars, with magnetic poles of permanent magnets mounted according to the required number of poles. The stator structure is similar to that of an asynchronous motor.

When the stator winding is connected to the power supply, the motor starts to rotate on the principle of asynchronous motor and accelerates to the synchronous speed, the synchronous electromagnetic torque generated by the permanent magnetic field of the rotor and the magnetic field of the stator (synthesized by the electromagnetic torque generated by the permanent magnetic field of the rotor and the reluctance torque generated by the magnetic field of the stator) draws the rotor into synchronization and the motor enters into synchronous operation.

Magneto-resistive synchronous motor is also called reactive synchronous motor, it is a synchronous motor that uses rotor cross-axis and straight-axis magneto-resistance to generate magneto-resistive torque unequally, its stator is similar to the stator structure of asynchronous motor, only the rotor structure is different.

2. Magneto-resistive synchronous motor

In order to produce asynchronous starting torque, the rotor is equipped with cage-type cast aluminum winding resistance. The rotor is equipped with reaction slots corresponding to the number of stator poles (only the convex part, no excitation winding and permanent magnet) to generate reluctance synchronous torque. According to the 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, where the external reaction rotor reaction slot is opened to the outer circle of the rotor, so that its straight axis and cross-axis direction air gap is not equal. The inner reaction rotor has grooves inside so that the magnetic flux in the cross-axis direction is blocked and the magnetic resistance is increased. The internal and external reactive rotor combines the structural characteristics of the above two types of rotors, and the difference between the straight axis and the cross-axis is large, so that the force energy of the motor is larger. The reluctance synchronous motor is also divided into various types such as single-phase capacitor running type, single-phase capacitor starting type and single-phase double-value capacitor type.

3.Hysteresis synchronous motor

Hysteresis synchronous motor is a synchronous motor that uses hysteresis material to produce hysteresis torque. It is divided into inner rotor type hysteresis synchronous motor, outer rotor type hysteresis synchronous motor and single phase shaded pole type hysteresis synchronous motor.

The rotor structure of inner-rotor hysteresis synchronous motor is hidden-pole type, with a smooth cylindrical appearance and no winding on the rotor, but there is a ring-shaped effective layer made of hysteresis material on the outer circle of the core.

When the stator winding is connected to the power supply, the rotating magnetic field generates the asynchronous torque of the hysteresis rotor and then leads the rotor into synchronous operation by itself. During asynchronous operation, the stator rotating magnetic field repeatedly magnetizes the rotor at a differential frequency; during synchronous operation, the hysteresis material on the rotor is magnetized and the permanent magnetic poles appear, thus generating synchronous torque.

The soft starter uses a three-phase parallel thyristor as a regulator, which is connected between the power supply and the motor stator. This circuit is like a three-phase fully controlled bridge rectifier circuit. When using the soft starter to start the motor, the output voltage of the thyristor gradually increases, the motor gradually accelerates until the thyristor is fully conducting, the motor works on the mechanical characteristics of the rated voltage, realizing smooth starting, reducing the starting current and avoiding overcurrent tripping. When the motor reaches rated rpm, the starting process ends and the soft starter automatically replaces the completed thyristor with a bypass contactor to provide rated voltage for normal motor operation to reduce the thermal loss of the thyristor, extend the service life of the soft starter, improve its efficiency and avoid harmonic pollution of the power grid. The soft starter also provides soft stop function. Soft stop is the opposite of soft start process, the voltage gradually decreases and the rpm gradually drops to zero, avoiding the torque shock caused by free stop.

Motor classification

I. DC motor

1、DC motor

a、Permanent magnet DC motor

b、Electromagnetic DC motor

c、DC torque motor

2、Permanent magnet linear DC motor

a、?κ Street Bi-kow Velocity?

b, oscillating linear motor

3、Brushless DC motor

a、Brushless DC motor with slotted armature

b, brushless DC motor with slotless armature

c、Wound disk armature brushless DC motor

d、Sheet armature brushless DC motor

e、Brushless DC torque motor

4、AC/DC dual-use motor

5、Motor enlarger

6、Variable current machine

Second, AC motor

1、Asynchronous motor

a、Three-phase asynchronous motor

b、Single-phase asynchronous motor

2、AC servo motor

a、Squirrel cage rotor servo motor

b、Non-magnetic hollow cup rotor servo motor

3、AC torque motor

4、Synchronous motor

a、Permanent magnet synchronous motor

b、Hysteresis synchronous motor

c、Resistive synchronous motor

d、Electromagnetic reduction type synchronous motor

5、AC linear motor

a、Synchronous linear motor

b、Asynchronous linear motor

6、AC generator

a、Synchronous generator

b、Asynchronous generator

Stepping motor

1、Resistive stepping motor

a, step-by-step stepping motor

b, multi-stage stepping motor

2、Permanent magnet stepping motor

a, hidden pole stepping motor

b, single-phase permanent magnet stepping motor

3、Hybrid stepping motor

4、Linear and planar stepping motor

a, reluctance linear and planar stepping motor

b, hybrid linear and planar stepping motor

5, spiral stepping motor

Four, sensing motor

1、Self-adjusting angle machine

2、Rotary transformer

3, speed generator

4、Multi-pole self-adjusting angle and resolver