1. Classification of DC motors
1. Brushless DC motor:
The brushless DC motor is to exchange the stator and rotor of the ordinary DC motor. Its rotor is a permanent magnet to generate air-gap flux: the stator is an armature and consists of multi-phase windings. In structure, it is similar to permanent magnet synchronous motor. The structure of the brushless DC motor stator is the same as that of an ordinary synchronous motor or an induction motor. Multi-phase windings (three-phase, four-phase, five-phase, etc.) are embedded in the iron core. The windings can be connected in star or delta, and connected with The power tubes of the inverter are connected for reasonable commutation. The rotor mostly uses rare earth materials with high coercive force and high remanence density such as samarium cobalt or neodymium iron boron. Due to the different positions of the magnetic materials in the magnetic poles, it 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 also called the permanent magnet brushless DC motor.
Brushless DC motors are developed in recent years with the development of microprocessor technology and the application of new power electronic devices with high switching frequency and low power consumption, as well as the optimization of control methods and the emergence of low-cost, high-level permanent magnet materials. A new type of DC motor developed.
Brushless DC motors not only maintain the good speed regulation performance of traditional DC motors, but also have the advantages of no sliding contact and commutation sparks, high reliability, long service life and low noise, so they are widely used in aerospace, CNC machine tools, robots, electric vehicles, etc. , computer peripherals and household appliances have been widely used.
According to different power supply methods, brushless DC motors can be divided into two categories: square wave brushless DC motors, whose back EMF waveform and supply current waveform are both rectangular waves, also known as rectangular wave permanent magnet synchronous motors; Brushed DC motor, its back EMF waveform and supply current waveform are both sine waves.
2. Brushed DC motor
(1) Permanent magnet DC motor
Permanent magnet DC motor division: rare earth permanent magnet DC motor, ferrite permanent magnet DC motor and alnico permanent magnet DC motor.
① Rare earth permanent magnet DC motor: Small in size and better in performance, but expensive, mainly used in aerospace, computers, downhole instruments, etc.
② Ferrite permanent magnet DC motor: The magnetic pole body made of ferrite material is cheap and has good performance, and is widely used in household appliances, automobiles, toys, electric tools and other fields.
③ Alnico permanent magnet DC motor: It needs to consume a lot of precious metals, and the price is high, but it has good adaptability to high temperature. It is used in occasions where the ambient temperature is high or the temperature stability of the motor is required.
(2) Electromagnetic DC motor.
Electromagnetic DC motor division: series excited DC motor, shunt excited DC motor, separately excited DC motor and compound excited DC motor.
① Series excited DC motor: The current is connected in series, shunted, and the field winding is connected in series with the armature, so the magnetic field in this motor changes significantly with the change of the 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, so the DC series excitation motor is usually wound with a thicker wire, and its number of turns is less.
② Shunt excited DC motor: The field winding of the shunt excited DC motor is connected in parallel with the armature winding. As a shunt generator, the terminal voltage from the motor itself supplies power to the field winding; as a shunt motor, the field winding Sharing the same power supply with the armature , it is the same as the separately excited DC motor in terms of performance.
③ Separately excited DC motor: The field winding has no electrical connection with the armature, and the field circuit is supplied by another DC power supply. The field current is therefore not affected by the armature terminal voltage or the armature current.
④ Compound-excited DC motor: The compound-excited DC motor has two excitation windings, shunt excitation and series excitation. If the magnetomotive force generated by the series excitation winding is in the same direction as the magnetomotive force generated by the shunt excitation winding, it is called product compound excitation. If the directions of the two magnetomotive forces are opposite, it is called differential compound excitation.
2. Working principle of DC motor
There is a ring-shaped permanent magnet fixed inside the DC motor, and the current passes through the coil on the rotor to generate an ampere force. When the coil on the rotor is parallel to the magnetic field, the direction of the magnetic field will change when it continues to rotate, so the brush at the end of the rotor will switch The plates are alternately in contact, so that the direction of the current on the coil also changes, and the direction of the Lorentz force generated remains unchanged, so the motor can keep rotating in one direction
The working principle of the DC generator is to convert the AC electromotive force induced in the armature coil into a DC electromotive force when it is drawn out from the brush end by the commutator and the commutation effect of the brush.
The direction of the induced electromotive force is determined according to the right-hand rule (the magnetic field line points to the palm of the hand, the thumb points to the movement direction of the conductor, and the direction of the other four fingers is the direction of the induced electromotive force in the conductor).
The direction of the force acting on the conductor is determined by the left-hand rule. This pair of electromagnetic forces forms a torque acting on the armature. This torque is called electromagnetic torque in the rotating electrical machine. The direction of the torque is counterclockwise, trying 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.
Post time: Mar-18-2023