What is the motor for?

Motor, commonly known as "motor", refers to an electromagnetic device that realizes electric energy conversion or transmission according to the law of electromagnetic induction. Motor is also called (commonly known as motor), which is represented by the letter "M" (the old standard is "D") in the circuit. Its main function is to generate driving torque. As the power source of electrical appliances or various machinery, the generator is represented by the letter "G" in the circuit. Motor refers to an electromagnetic device that realizes electric energy conversion or transmission according to the law of electromagnetic induction. Motor is also called (commonly known as motor), which is represented by the letter "M" (the old standard is "D") in the circuit. Its main function is to generate driving torque as the power source of electrical appliances or various machinery. The generator is represented by the letter "G" in the circuit. Its main function is to convert mechanical energy into electrical energy. At present, the most commonly used is to use heat energy and water energy to drive the generator rotor to generate electricity. With the maturity of wind power generation technology, wind power generation has gradually entered our lives. In some books, transformers are called static motors. From the definition of motor, it makes sense to say so. 1. According to the type of working power supply, it can be divided into DC motor and AC motor. 1. 1 DC motor can be divided into brushless DC motor and brushed DC motor according to its structure and working principle. 1. 1. 1 Brushed DC motors can be divided into permanent magnet DC motors and electromagnetic DC motors. 1. 1. 1 Electromagnetic DC motors are divided into series DC motors, parallel DC motors, separately excited DC motors and composite DC motors. 1. 1. 1.2 permanent magnet DC motors are divided into rare earth permanent magnet DC motors, ferrite permanent magnet DC motors and alnico permanent magnet DC motors. 1.2 Among them, AC motors can be divided into single-phase motors and three-phase motors. 2. According to the structure and working principle, it can be divided into DC motor, asynchronous motor and synchronous motor. 2. 1 Synchronous motors can be divided into permanent magnet synchronous motors, reluctance synchronous motors and hysteresis synchronous motors. 2.2 Asynchronous motors can be divided into induction motors and AC commutator motors. 2.2. 1 induction motors can be divided into three-phase asynchronous motors, single-phase asynchronous motors and shielded pole asynchronous motors. 2.2.2 AC commutator motor can be divided into single-phase series motor, AC /DC dual-purpose motor and repulsion motor. 3. According to the starting and running modes, it can be divided into three types: capacitor-started single-phase asynchronous motor, capacitor-started single-phase asynchronous motor, capacitor-started single-phase asynchronous motor and split-phase single-phase asynchronous motor. 4. According to the purpose: drive motor and control motor. 4. 1 Division of driving motors: motors for electric tools (including drilling, polishing, slotting, cutting, reaming and other tools) and motors for household appliances (including washing machines, electric fans, refrigerators, air conditioners, tape recorders, video recorders, DVD players, vacuum cleaners, cameras, hair dryers, electric razors, etc.). ) and other general small mechanical equipment (including all kinds of small machine tools, etc. ) 4.2 Control motors are divided into stepper motors and servo motors. 5. According to the structure of rotor, it is divided into cage induction motor (old standard called squirrel cage asynchronous motor) and wound rotor induction motor (old standard called wound asynchronous motor). 6. According to running speed: high-speed motor, low-speed motor, constant-speed motor and variable-speed motor. 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. The rotor speed of asynchronous motor is always slightly lower than the synchronous speed of rotating magnetic field. Regardless of the load, the rotor speed of the synchronous motor is always kept at the synchronous speed. Working principle of DC motor 1. The working principle of DC generator is that the AC electromotive force induced in armature coil is converted into DC electromotive force when it is led out from the end of brush through commutator with brush commutation function. The direction of induced electromotive force is determined according to the right-hand rule (the magnetic induction line points to the palm, the thumb points to the direction of conductor movement, and the other four fingers point to the direction of induced electromotive force in the conductor. ) At the instant shown in figure 1. 1, the induced electromotive force directions of conductors a b and c d point from B to A and from D to C respectively. At this time, brush A is positive polarity and brush B is negative polarity. Figure 1. 1 DC generator principle model When the coil rotates counterclockwise180, the conductor c d is below the N pole and the conductor a b is below the S pole, and the electromotive force in each conductor changes direction respectively. Figure 1.2 DC generator principle model As can be seen from the figure, the conductor in contact with the brush A is always under the N pole, and similarly, the conductor in contact with the brush B is always under the S pole. Therefore, the brush A always has a positive polarity and the brush B always has a negative polarity, so the pulse electromotive force with constant direction but variable size can be drawn from the end of the brush. If the number of coils on the armature is increased and connected according to a certain rule, the degree of pulse vibration can be reduced, and the DC electromotive force can be obtained. This is the working principle of DC generator. Second, the working principle of DC motor The direction of conductor stress is determined by the left-handed rule. This pair of electromagnetic forces forms a torque acting on the armature, which is called electromagnetic torque in rotating electric machine. The direction of the torque is counterclockwise, in an attempt to make the armature rotate counterclockwise. If this electromagnetic torque can overcome the resistance torque on the armature (such as the resistance torque caused by friction and other load torques), the armature can rotate counterclockwise. Figure 1.3 DC motor principle model When the armature rotates180, the conductor cd turns to the N pole and the conductor ab turns to the S pole. Because the direction of the current supplied by the DC power supply remains unchanged, it still flows in from the brush A and flows out from the brush B after passing through the conductors cd and ab. At this time, the stress direction of conductor cd changes from right to left, and the stress direction of conductor ab changes from left to right, and the direction of electromagnetic torque generated is still counterclockwise. Figure 1.4 DC motor principle model Therefore, once the armature rotates, due to the commutation between the commutator and the brush, DC current alternately flows in from the conductors ab and cd, so that the coil side is under the N pole, in which the direction of passing current always flows in from the brush A and always flows out from the brush B under the S pole. This ensures that the current on the side of each pole coil is always in one direction, thus forming a torque in the same direction, so that the motor can rotate continuously. This is how DC cars work. Principle and structure of DC motor 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 watches, 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. The brushes of electromagnetic DC motors generally adopt metal graphite brushes or electrochemical graphite brushes. 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. 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. 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 sheet of the commutator 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. [Edit this paragraph] 2. Brushless DC motor Brushless DC motor uses semiconductor switching devices to realize electronic commutation, that is, electronic switching devices replace the traditional contact commutator and brush. 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. 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). 2. Advantages of1DC brushless motor DC motor has fast response speed and large starting torque, and can provide rated torque from zero speed to rated speed. But the advantage of DC motor is also its disadvantage, because the armature magnetic field and rotor magnetic field must be kept at 90 degrees to produce constant torque performance under rated load, which depends on carbon brush and commutator. When the motor rotates, the carbon brush and commutator will produce sparks and toner, which will not only damage components, but also limit the use occasions. AC motor has no carbon brush and commutator, so it is maintenance-free, durable and widely used. However, if the performance of AC motor is equivalent to that of DC motor, it must be realized by complex control technology. Nowadays, with the rapid development of semiconductors, the switching frequency of power devices is much faster, which improves the performance of driving motors. The speed of microprocessor is getting faster and faster, and it can control the AC motor in a rotating two-axis orthogonal coordinate system, and properly control the current components of the AC motor in two axes, so as to achieve control similar to that of DC motor, with the same performance as DC motor. In addition, many microprocessors put the necessary functions of controlling the motor in the chip, and the volume is getting smaller and smaller; Like analog-to-digital converter (adc), pulse width modulator (PWM) and so on. Brushless DC motor is an application of electronically controlling the commutation of AC motor to obtain similar characteristics to DC motor without lack of DC motor mechanism. 2.2 control structure of brushless motor DC brushless motor is a synchronous motor, that is, the speed of motor rotor is affected by the speed of rotating magnetic field of motor stator and the number of rotor poles (P): n = 120. F/P. When the number of rotor poles is fixed, the speed of rotor can be changed by changing the frequency of stator rotating magnetic field. Brushless DC motor is a kind of synchronous motor with electronic control (driver). By controlling the frequency of stator rotating magnetic field, the rotating speed of motor rotor is fed back to the control center for repeated correction, so as to achieve a way close to the characteristics of DC motor. That is to say, when the load changes within the rated load range, DC brushless motor can still control the motor rotor to maintain a certain speed. The DC brushless driver includes a power supply part and a control part, as shown in the figure (1). The power supply part provides three-phase power to the motor, and the control part converts the input power frequency as required. The power supply unit can directly input DC (generally 24v) or AC (1 10v/220 v). If the input is AC, it must be converted to DC by a converter. Before DC input or AC input is transmitted to the motor coil, DC voltage must be converted from inverter to three-phase voltage to drive the motor. Inverter is generally divided into six power transistors (q 1 ~ q6) into upper arms (q 1, q3, q5)/ lower arms (q2, q4, q6) which are connected to the motor as switches to control the current passing through the motor coil. The control part provides pwm (pulse width modulation) to determine the switching frequency of the power transistor and the timing of inverter commutation. Generally, DC brushless motors want to use speed control. When the load changes, the speed can be stabilized at the set value without changing too much. Therefore, Hall sensor which can induce magnetic field is installed in the motor as the basis of speed closed-loop control and phase sequence control. But this is only used as speed control, not as positioning control.