All motors are composed of stator and rotor, in the DC motor, in order to make the rotor turn up, you need to constantly change the direction of the current, otherwise the rotor can only turn half a circle, which is like a bicycle pedal. So DC motors need commutators. The generalized DC motor includes brush motor and brushless motor. Brush motor is also known as DC motor or carbon brush motor, often said DC motor refers to the brush DC motor, it uses mechanical commutation, the external magnetic pole does not move the internal coil (armature) move, the commutator and the rotor coil rotate together, the brush and the magnet do not move, so the commutator and the brush friction friction, complete the current direction switch.
Disadvantages of brush motor
1. The spark generated by mechanical commutation causes the commutator and brush friction, electromagnetic interference, loud noise, short life.
2. Poor reliability, failure, need frequent maintenance.
3. Due to the existence of the commutator, the rotor inertia is limited, the maximum speed is limited, and the dynamic performance is affected. Since it has so many shortcomings, why is it still widely used, because it has high torque, simple structure and easy maintenance (that is, change the carbon brush) and cheap.
DC motor — brushless motor
Brushless motor is also called DC variable frequency motor (BLDC) in some fields, it uses electronic commutator (Hall sensor), coil (armature) does not move the magnetic pole, at this time the permanent magnet can be outside the coil can also be inside the coil, so there is an external rotor brushless motor and an internal rotor brushless motor.
Brushless motor construction is the same as permanent magnet synchronous motor. However, a single brushless motor is not a complete power system, brushless basically must be controlled by a brushless controller, that is, electrical regulation, in order to achieve continuous operation. What really determines its performance is the brushless electronic governor (that is, electrical regulation).
In general, the brushless motor drive current has two kinds, one is a square wave, the other is a sine wave. Sometimes the former is called DC brushless motor, and the latter is called AC servo motor, which is exactly a kind of AC servo motor. (video portal) The operation mode of brushless motors is different, and can be divided into internal rotor brushless motors and external rotor brushless motors. The inner rotor is three-phase, the price is more expensive. The external rotor is usually used in single-phase, affordable, mass production has been close to the carbon brush motor, so in recent years has been widely used. The price of the three phases of the outer rotor has approached the price of the inner rotor.
Well, you can guess that the disadvantages of brush motors are the advantages of brushless motors. It has the advantages of high efficiency, low energy consumption, low noise, long life, high reliability, servo control, stepless frequency conversion speed regulation (up to very high speed), it is relatively smaller than the brush DC motor, the control is simple than the asynchronous AC motor, the starting torque is large overload capacity, as for the disadvantages… Is more expensive than brush, difficult to maintain.
DC motor – speed regulation principle
DC motor speed regulation: the so-called speed regulation, that is, by adjusting the motor speed to obtain the required torque. DC (brush) motor by adjusting voltage, series resistance, change excitation can be adjusted, but the actual voltage adjustment is the most convenient and most commonly used, currently the main use of PWM speed regulation, PWM is actually through high-speed switch to achieve DC voltage regulation, a cycle, open time is long, the average voltage is high, close time is long, the average voltage is low, It is very convenient to adjust, as long as the switching speed is fast enough, the harmonics of the grid are less, and the current is more continuous.
However, the brush and commutator wear for a long time, while there is a huge current change when reversing, it is very easy to produce sparks, the commutator and the brush limit the capacity and speed of the DC motor, making the speed regulation of the DC motor encounter a bottleneck. For the brushless DC motor, only the input voltage is controlled on the surface of the speed regulation, but the automatic frequency conversion speed regulation system of the motor (the brushless DC motor itself comes with a rotor position detector and other rotor position signal acquisition device, and uses the rotor position signal of this device to control the commutation time of the variable voltage variable frequency speed regulation device) automatically controls the frequency according to the variable voltage.
It is almost the same as a DC (brushed) motor and is very convenient. Because the rotor adopts permanent magnet, no special excitation winding is required, in the case of the same capacity, the motor is smaller, lighter, more efficient, more compact, more reliable operation, and better dynamic performance, which has been widely used in the drive of electric vehicles.
