Brushless DC motor is a typical mechatronics product, which is composed of motor body and driver. Because the brushless DC motor is operated in automatic control mode, it will not add starting windings to the rotor as the synchronous motor started under frequency conversion speed regulation, and will not produce oscillation and out-of-step when the load changes. The permanent magnets of small and medium-sized brushless DC motors now mostly use rare earth Ndfeb (Nd-Fe-B) materials with high magnetic energy product. Therefore, the volume of the rare earth permanent magnet brushless motor is smaller than that of the three-phase asynchronous motor with the same capacity.
The stator winding of the motor is mostly made of three-phase symmetrical star connection, which is very similar to the three-phase asynchronous motor. A magnetized permanent magnet is attached to the rotor of the motor, and a position sensor is installed in the motor to detect the polarity of the rotor. The driver is composed of power electronic devices and integrated circuits, etc. Its function is: to accept the start, stop and brake signals of the motor to control the start, stop and brake of the motor; The position sensor signal and positive and negative turning signal are accepted to control the on-off of each power tube of the inverter bridge to generate continuous torque; Receive speed instructions and speed feedback signals to control and adjust the speed; Provide protection and display and more.
In the past 30 years, the research on variable frequency speed regulation of asynchronous motor is to find a way to control the torque of asynchronous motor in the final analysis. Rare earth permanent magnet brushless DC motor will show advantages in the field of speed regulation with its characteristics of wide speed regulation, small size, high efficiency and small steady-state speed error.
Because the brushless DC motor has the characteristics of DC brushed motor, it is also a frequency change device, so it is also known as DC frequency conversion, and the international common term is BLDC. The operation efficiency, low speed torque, speed accuracy and so on of brushless DC motor are better than any inverter control technology, so it is worth the attention of the industry. This product has been produced more than 55kW, can be designed to 400kW, can solve the industry's power saving and high-performance drive needs.
Background information on brushless motors
In recent years, brushless motors have become a rapidly developing power in the field of models. Due to the production and price reasons, in the past few years, the brushless motor is more used in the high-end aviation model, and now due to the rapid development of machining technology, the production cost of the brushless motor has dropped a lot, and it is now entering all levels of the model field, from electric remote control cars to electric remote control boats to electric model planes, everywhere.
There are misunderstandings about brushless motors
Many people have seen the model of the brushless motor, they use battery power, so many people in the knowledge has always had such a misunderstanding, that brushless motor is DC motor, in fact, brushless motor belongs to AC motor, is a three-phase AC permanent magnet motor, input model brushless motor 3 wires of the current is alternating current, But this alternating current is not a 50HZ mains sine wave, but a three-phase alternating rectangular wave modulated from the brushless motor controller (commonly known as brushless modulation), the frequency is much higher than 50HZ, and changes with the motor speed.
Brushless motor structure analysis
Structurally, the brushless motor and the brush motor have similarities, there are also rotor and stator, but the structure of the brush motor is opposite; The rotation of the brush motor is coil winding, and the power output shaft is connected, and the stator is permanent magnet magnetic steel; The rotor of the Brushless motor is a permanent magnet steel, which is connected with the output shaft together with the housing, and the stator is a winding coil. The commutator brush used by the brushless motor to alternately transform the electromagnetic field is removed, so it is called brushless motor. Then there is a problem: how to make the brushless motor rotate without the transformation of the electromagnetic field?
Brushless motor simple operation principle
Simply put, by changing the alternating frequency and waveform of the current wave input to the stator coil of the brushless motor, a magnetic field is formed around the winding coil around the geometric axis of the motor. This magnetic field drives the permanent magnet steel on the rotor to rotate, and the motor will turn. The performance of the motor is related to the number of magnetic steel, the magnetic flux strength of the magnetic steel, the input voltage of the motor and other factors. It has a great relationship with the control performance of the brushless motor, because the input is direct current, the current needs an electronic governor to turn it into 3-phase alternating current, and it also needs to receive a control signal from the remote control receiver to control the speed of the motor to meet the needs of the model. In general, the structure of the brushless motor is relatively simple, really determines its performance or the brushless electronic governor, a good electronic governor needs a single chip microcomputer control program design, circuit design, complex processing technology and other processes of the overall control, so the price is much higher than the brush motor.
Comparison of model brushless and brushless motor performance
The shortcomings of the brush motor model friends may feel strange, how to pick the fault of the brush; Oh, I put the following shortcomings out, we know that there is a brush motor is not small.
1, large friction, large loss
Old model friends have encountered this problem when playing brush motor in the past, that is, after using the motor for a period of time, you need to open the motor to clean the carbon brush of the motor, which is time-consuming and laborious, and the maintenance intensity is no less than a household cleaning.
2, heat, short life
Due to the structure of the brush motor, the contact resistance of the brush and the commutator is very large, resulting in the overall resistance of the motor is large, easy to heat, and the permanent magnet is a thermal element, if the temperature is too high, the magnetic steel will be demagnetized, so that the motor performance is reduced, affecting the life of the brush motor.
3, low efficiency, small output power
The heating problem of the brushed motor mentioned above is largely because the current does work on the internal resistance of the motor, so the electric energy is largely converted into heat energy, so the output power of the brushed motor is not large and the efficiency is not high.
Advantages of brushless motor
1, no brush, low interference
In addition to the brush, the most direct change is that there is no electrical spark generated when the brush motor is running, which greatly reduces the interference of electrical spark to remote control radio equipment.
2, low noise, smooth operation
The brushless motor has no brush, the friction during operation is greatly reduced, the operation is smooth, and the noise will be much lower, which is a great support for the stability of the model.
3, long life, low maintenance costs
Without the brush, the wear of the brushless motor is mainly on the bearing, from the mechanical point of view, the brushless motor is almost a maintenance free motor, when necessary, just do some dust removal maintenance. The next comparison, you know where the advantages of the brushless motor relative to the brushless motor, but everything is not absolute, the brushless motor low speed torque performance, torque and other performance characteristics are irreplaceable brushless motor, but on the brushless motor ease of use, with the cost of the brushless controller decline trend and the development of brushless technology at home and abroad and market competition, Brushless power system is in the stage of rapid development and popularization, which also greatly promoted the development of model movement.
The parameters of the model brushless motor, in addition to the dimensions (outside diameter, length, axle diameter, etc.), weight, voltage range, no-load current, maximum current and other parameters, there is also an important indicator -KV value, which is a unique performance parameter of the brushless motor, and an important data to judge the performance characteristics of the brushless motor.