The operation of the brushless electric motor is based on electric drives that create a magnetic rotating field. Currently, there are several types of devices with different characteristics. With the development of technologies and the use of new materials, characterized by a high coercive force and a sufficient level of magnetic saturation, it became possible to obtain a strong magnetic field and, as a result, valve structures of a new type, in which there is no winding on the rotor elements or the starter. The widespread use of semiconductor-type switches with high power and reasonable cost has accelerated the creation of such designs, facilitated execution and eliminated many switching difficulties.
Working principle
Increase in reliability, decrease in price and easier production is ensured by the absence of mechanical switching elements, rotor winding and permanent magnets. At the same time, an increase in efficiency is possible due to a decrease infriction losses in the collector system. The brushless motor can operate on AC or continuous current. The latter option has a noticeable resemblance to collector engines. Its characteristic feature is the formation of a magnetic rotating field and the application of a pulsed current. It is based on an electronic switch, which increases the complexity of the design.
Position calculation
Generation of pulses occurs in the control system after a signal that reflects the position of the rotor. The degree of voltage and supply directly depends on the speed of rotation of the motor. A sensor in the starter detects the position of the rotor and provides an electrical signal. Along with the magnetic poles passing near the sensor, the amplitude of the signal changes. Sensorless positioning techniques also exist, including current passing points and transducers. PWM on the input terminals provides variable voltage retention and power control.
For a rotor with permanent magnets, current supply is not necessary, so there is no loss in the rotor winding. The brushless screwdriver motor features low inertia due to the absence of windings and a mechanized commutator. Thus, it became possible to use at high speeds without sparking and electromagnetic noise. High currents and easier heat dissipation are achieved by placing heating circuits on the stator. It is also worth noting the presence of an electronic built-in unit on some models.
Magnetic elements
The position of the magnets can vary according to the size of the motor, for example, on the poles or around the entire rotor. Creating high-quality magnets with greater power is possible through the use of neodymium in combination with boron and iron. Despite the high performance, the brushless permanent magnet screwdriver motor has some disadvantages, including the loss of magnetic characteristics at high temperatures. But they are more efficient and have no losses compared to machines that have windings in their design.
Inverter pulses determine the rotation speed of the mechanism. With a constant supply frequency, the motor runs at a constant speed in an open loop. Accordingly, the rotation speed varies depending on the power frequency level.
Features
The valve motor operates in the set modes and has the functionality of a brush analogue, the speed of which depends on the applied voltage. The mechanism has many advantages:
- no change in magnetization and current leakage;
- correspondence of the speed of rotation and the torque itself;
- speed is not limited by centrifugal force affecting the collector and rotary winding;
- no need for commutator and field winding;
- The magnets used are lightweight andcompact size;
- high torque;
- energy saturation and efficiency.
Use
Permanent magnet DC brushless motor is mainly found in devices with power within 5KW. In more powerful equipment, their use is irrational. It is also worth noting that the magnets in this type of motors are particularly sensitive to high temperatures and strong fields. Induction and brush options are devoid of such disadvantages. Motors are widely used in electric motorcycles, car drives due to the absence of friction in the manifold. Among the features, it is necessary to highlight the uniformity of torque and current, which ensures the reduction of acoustic noise.
