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Motors are widely used in many kinds. We generally distinguish the application of motors in transactions according to the classification of motors. Motors are classified as follows:
1. according to the type of working power supply: it can be divided into DC motor and AC motor.
DC motor can be divided into brushless DC motor and brush DC motor according to its 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, separately 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 aluminum nickel cobalt permanent magnet DC motor.
AC motor can also be divided into single-phase motor and three-phase motor. The
2. according to the structure and working principle, it can be divided into DC motor, asynchronous motor and synchronous motor.
Synchronous motor can be divided into permanent magnet synchronous motor, reluctance 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.
AC commutator motor can be divided into single-phase series excitation motor, AC / DC dual-purpose motor and repulsion motor.
3. according to the starting and operation modes: capacitor starting single-phase asynchronous motor, capacitor running single-phase asynchronous motor, capacitor starting single-phase asynchronous motor and split phase single-phase asynchronous motor.
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According to different excitation modes, DC motors can be divided into the following types:
1. separately excited DC motor
The excitation winding is not connected with the armature winding, but the DC motor supplied by other DC power supplies to the excitation winding is called separately excited DC motor, and the wiring is shown in figure (a). In the figure, M represents the motor, and if it is a generator, G represents it. Permanent magnet DC motor can also be regarded as separately excited DC motor.
2. Shunt DC motor
The excitation winding and armature winding of Shunt DC motor are connected in parallel, and the wiring is shown in figure (b). As a shunt excitation generator, the terminal voltage from the motor itself supplies power to the excitation winding; As a shunt motor, the excitation winding and armature share the same power supply, which is the same as that of the separately excited DC motor in terms of performance.
3. series excited DC motor
The excitation winding of the series excited DC motor is connected in series with the armature winding, and then connected to the DC power supply. The wiring is shown in figure (c). The excitation current of this DC motor is the armature current.
4. compound DC motor
The compound excitation DC motor has two excitation windings, parallel excitation and series excitation, and the wiring is shown in figure (d). If the magnetic flux generated by the series excitation winding and the parallel excitation winding have the same direction, it is called cumulative compound excitation. If two magnetic fluxes have opposite directions, it is called differential compound excitation.
DC motors with different excitation modes have different characteristics. Generally, the main excitation modes of DC motor are parallel excitation, series excitation and compound excitation. The main excitation modes of DC generator are separate excitation, parallel excitation and compound excitation.
Classification:
1. brushless DC motor: brushless DC motor interchanges the stator and rotor of ordinary DC motor. The rotor is a permanent magnet to generate air gap magnetic flux; the stator is an armature, which is composed of polyphase windings. In structure, it is similar to permanent magnet synchronous motor.
Excitation mode:
The performance of DC motor is closely related to its excitation mode. Generally, there are four excitation modes of DC motor: DC separately excited motor, DC parallel excited motor, DC series excited motor and DC compound excited motor. Master the characteristics of the four methods:
1. DC separately excited motor: the excitation winding has no electrical connection with the armature, and the excitation circuit is supplied by another DC power supply. Therefore, the excitation current is not affected by the armature terminal voltage or armature current.
2. DC shunt motor: the circuit is connected in parallel and divided. The voltage at both ends of the shunt winding is the voltage at both ends of the armature. However, the excitation winding is wound with thin wires and has a large number of turns. Therefore, it has a large resistance, making the excitation current passing through it small.
3. DC series excited motor: the current is connected in series and shunted. The excitation winding is connected in series with the armature, so the magnetic field in this motor changes significantly with the change of armature current. In order not to cause large loss and voltage drop in the excitation winding, the smaller the resistance of the excitation winding, the better. Therefore, DC series excited motors are usually wound with thicker wires, with fewer turns.
4. DC compound excitation motor: the magnetic flux of the motor is generated by the excitation current in the two windings.
DC motor can be divided according to structure and working principle:
1. the structure of Brushless DC motor stator is the same as that of ordinary synchronous motor or induction motor. Polyphase winding (three-phase, four-phase and five phase) is embedded in the iron core. The winding can be connected into star or triangle and connected with each power tube of the inverter respectively for reasonable phase change. Rare earth materials with high coercivity and high remanence density, such as samarium cobalt or neodymium iron boron, are mostly used for rotors. Due to different positions of magnetic materials in magnetic poles, they can be divided into surface magnetic poles, embedded magnetic poles and ring magnetic poles. Since the motor body is a permanent magnet motor, it is customary to call the brushless DC motor a permanent magnet brushless DC motor.
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2. brush DC motor: the two brushes (copper brush or carbon brush) of the brush motor are fixed on the rear cover of the motor through the insulating base, and the positive and negative poles of the power supply are directly introduced to the phase converter of the rotor, and the phase converter is connected with the coil on the rotor. The polarity of the three coils is continuously changed alternately to form a force with the two magnets fixed on the shell and rotate. Since the inverter is fixed with the rotor, and the brush is fixed with the housing (stator), the brush and the inverter constantly rub when the motor rotates, resulting in a lot of resistance and heat. Therefore, the brush motor has low efficiency and large loss. However, it also has the advantages of simple manufacture and low cost!
Control structure: the control structure of the brushless DC motor. The brushless DC motor is a kind of synchronous motor, that is, the speed of the motor rotor is affected by the speed of the rotating magnetic field of the motor stator and the number of rotor poles (P), n=120.f/p. When the number of rotor poles is fixed, the rotor speed can be changed by changing the frequency of the stator rotating magnetic field. Brushless DC motor is a synchronous motor plus electronic control (driver),
Control the frequency of the rotating magnetic field of the stator and feedback the speed of the motor rotor to the control center for repeated correction, so as to achieve a way close to the characteristics of the DC motor. In other words, the brushless DC motor can control the motor rotor to maintain a certain speed when the load changes within the rated load range.
The DC brushless driver includes a power supply unit and a control unit: the power supply unit provides three-phase power to the motor, and the control unit converts the input power frequency as required. The power supply unit can directly input DC (usually 24V) or AC (110v/220 V). If the input is AC, it must first be converted to DC through the converter. Whether DC input or AC input is to be transferred to the motor coil, the DC voltage must be converted from inverter to 3-phase voltage to drive the motor. The inverter is generally composed of 6 power transistors (Q1 ~ Q6), which are divided into upper arm (Q1, Q3, Q5) / lower arm (Q2, Q4, Q6) and connected to the motor as a switch to control the flow through the motor coil. The control unit provides PWM (pulse width modulation) to determine the switching frequency of the power transistor and the timing of inverter commutation. The brushless DC motor generally wants to use the speed control that can stabilize the speed at the set value without too much change when the load changes, so the motor is equipped with a Hall sensor that can induce the magnetic field as the closed-loop control of speed and the basis of phase sequence control. But this is only used for speed control, not for positioning control.
Control principle: the control principle of the brushless DC motor. To make the motor rotate, the control unit must first determine the sequence of opening (or closing) the power transistors in the inverter according to the current position of the motor rotor sensed by the hall sensor, and then according to the stator winding. Ah, BH, CH (these are called upper arm power transistors) and Al, BL, Cl (these are called lower arm power transistors) in the inverter, Make the current flow through the motor coil in sequence to generate a forward (or reverse) rotating magnetic field, and interact with the magnet of the rotor, so that the motor can rotate clockwise / counterclockwise. When the motor rotor rotates to the position where the hall sensor senses another group of signals, the control unit turns on the next group of power transistors, so that the circulating motor can continue to rotate in the same direction until the control unit decides to stop the motor rotor, then turn off the power transistor (or only turn on the lower arm power transistor); If the motor rotor is reversed, the power transistor opening sequence is reversed.
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Basically, the opening method of power transistors can be exemplified as follows: ah, BL group → ah, CL group → BH, CL group → BH, Al group → ch, Al group → ch, BL group, but never ah, Al or BH, BL or CH, CL. In addition, because the electronic parts always have the response time of the switch, the response time of the parts should be taken into account in the interleaving time between the off and on of the power transistor. Otherwise, when the upper arm (or lower arm) has not been completely closed, the lower arm (or upper arm) has been opened, resulting in a short circuit between the upper and lower arms and burning out the power transistor.
When the motor rotates, the control unit will compare the command composed of the speed set by the driver and the acceleration / deceleration rate with the speed at which the hall sensor signal changes (or calculate by software), and then decide whether the next group of switches (ah, BL or ah, CL or BH, Cl or...) will be turned on and the length of time. If the speed is not enough, it will be longer, and if the speed is too high, it will be shorter. This part of the work is completed by PWM. PWM is the way to determine whether the motor speed is fast or slow. How to generate such PWM is the core to achieve more accurate speed control.
For high-speed speed speed control, it is necessary to consider whether the clock resolution of the system is sufficient to master the time for processing software instructions. In addition, the data access mode for Hall sensor signal changes also affects the processor performance and judgment accuracy
Real time. As for the speed control of low-speed, especially the low-speed starting, because the returned Hall sensor signal changes more slowly, how to capture the signal mode, processing time and properly configure the control parameter values according to the motor characteristics are very important. Or the change of speed return takes the change of encoder as the reference, so as to increase the signal resolution for better control. The motor can run smoothly and respond well, and the appropriateness of P.I.D. control cannot be ignored. As mentioned earlier, the brushless DC motor is under closed-loop control, so the feedback signal is equivalent to telling the control department how much the motor speed is different from the target speed, which is called error. If you know the error, it will be compensated naturally. There are traditional engineering controls such as P.I.D. control. However, the control state and environment are actually complex and changeable. If the control is robust, the factors to be considered may not be fully mastered by the traditional engineering control. Therefore, fuzzy control, expert system and neural network will also be incorporated into the important theory of intelligent P.I.D. control
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4. classification by use: drive motor and control motor.
Motor for driving: motor for electric tools (including drilling, polishing, polishing, slotting, cutting, reaming and other tools) Motors for household appliances (including washing machines, electric fans, refrigerators, air conditioners, tape recorders, video recorders, DVD players, vacuum cleaners, cameras, hair dryers, electric shavers, etc.) and motors for other general small mechanical equipment (including various small machine tools, small machinery, medical appliances, electronic instruments, etc.).
Control motor is divided into stepping motor and servo motor.
5. according to the structure of rotor: cage induction motor (called squirrel cage asynchronous motor in the old standard) and wound rotor induction motor (called wound rotor asynchronous motor in the old standard).
6. divided by operation speed: high-speed motor, low-speed motor, constant speed motor and speed regulating motor. Low speed motors are divided into gear reduction motors, electromagnetic reduction motors, torque motors and claw pole synchronous motors.
In addition to the stepwise constant speed motor, stepless constant speed motor, stepwise variable speed motor and stepless variable speed motor, the variable speed motor can also be divided into electromagnetic variable speed motor, DC variable speed motor, PWM Variable frequency variable speed motor and switched reluctance variable speed motor.
The rotor speed of asynchronous motor is always slightly lower than the synchronous speed of rotating magnetic field.
The rotor speed of a synchronous motor is always kept at the synchronous speed regardless of the load.
DC motor is a motor that converts DC electric energy into mechanical energy. The excitation mode of DC motor refers to the problem of how to supply power to the excitation winding and generate excitation magnetic flux to establish the main magnetic field.
