The excitation mode of a DC motor refers to the problem of how to supply power to the field winding and generate a field magnetomotive force to establish a main magnetic field. According to the different excitation modes, DC motors can be divided into the following types of compound-excited DC motors with two excitation windings, shunt and series excitation.
If the magnetomotive force generated by the series winding is the same as the direction of the magnetomotive force generated by the shunt winding, it is called product recombination. If the two magnetomotive forces are in opposite directions, DC motors called different excitation modes have different characteristics. In general, the main excitation methods of DC motors are shunt-type, series-excitation and compound-excitation. The main excitation modes of DC generators are the overexcitation, shunt-excitation and compound-excitation modes. The structure of the stator of the brushless DC motor is the same as that of an ordinary synchronous motor or induction motor. Embed multiphase windings in the core. Three-phase, four-phase, five-phase.
The windings can be connected in a star or a triangle and connected to the power tubes of the inverter for reasonable commutation. The rotor is made of high coercivity and high remanence density rare earth materials such as samarium cobalt or neodymium iron boron, due to the difference in the position of the magnetic material in the magnetic pole. Can be divided into surface magnetic poles, embedded magnetic poles and toroidal magnetic poles. Since the motor body is a permanent magnet motor, it is customary to call a brushless DC motor a permanent magnet brushless DC motor. Brushed DC motor: 2 brushes (copper brush or carbon brush) of brushed motor are fixed on the motor back cover through the insulating seat to directly introduce the positive and negative poles of the power supply to the commutator of the rotor, and the commutator is connected.
The coils on the rotor are alternately changed in polarity and the two magnets fixed on the outer casing form a force to rotate. Since the phase changer is fixed to the rotor and the brush is fixed to the outer casing stator, the friction between the brush and the phase changer continuously generates a large amount of resistance and heat when the motor rotates. Therefore, the efficiency of the brush motor is very low. But it also has the advantage of being simple to manufacture and low in cost.