How is the brushless motor

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 high coercive force and a sufficient level of magnetic saturation, it became possible to obtain a strong magnetic field and, as a consequence, valve constructions of a new type, in which there is no winding on the rotor elements or the starter. The extensive distribution of semiconductor type switches with high power and reasonable cost has accelerated the creation of such structures, facilitated the implementation and eliminated many switching complexities.

Principle of operation

Increase in reliability, reduction in price and simpler manufacturing is ensured by the absence of mechanical switching elements, rotor winding and permanent magnets. At the same time, the increase in efficiency is possible due to a reduction in frictional losses in the collector system. The brushless motor can operate on alternating or continuous current. The latter variant is distinguished by a marked similarity with the collector motors. 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.

Calculation of position

Generation of pulses occurs in the control system after a signal reflecting the position of the rotor. The degree of tension and feed depends directly on the speed of rotation of the motor. The sensor in the starter determines the position of the rotor and provides an electrical signal. Together with the magnetic poles passing near the sensor, the amplitude of the signal changes. There are also sensorless positioning techniques, including current passing points and transducers. PWM on the incoming terminals ensures the preservation of the AC voltage level and power control.

For a rotor with unchanged magnets, the current is not necessary, so there is no loss in the rotor winding. The brushless motor for screwdrivers is characterized by a low level of inertia, provided by the absence of windings and a mechanized collector. Thus, it became possible to use at high speeds without sparking and electromagnetic noise. High current values and simplification of 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 location of the magnets can be different according to the dimensions of the motor, for example, at the poles or along the entire rotor. Creation of high-quality magnets with higher power is possible due to the use of neodymium in combination with boron and iron. Despite the high performance, the brushless motor for screwdrivers With permanent magnets has some drawbacks, among them the loss of magnetic characteristics at high temperatures. But they are more efficient and have no losses compared to machines in the construction of which there are windings.

The pulses of the inverter determine the speed of rotation of the mechanism. With a constant supply frequency, the motor is operated at a constant speed in an open system. Accordingly, the rotational speed varies depending on the level of the supply frequency.

Characteristics

The valve motor operates in the specified modes and has a brush analog function, the speed of which depends on the applied voltage. The mechanism has many advantages:

• No change in magnetization and leakage current;
• Correspondence of speed of rotation and the most twisting moment;
• The speed is not limited by the centrifugal force affecting the collector and the rotor electro-winding;
• There is no need for a commutator and excitation winding;
• The magnets used are small in weight and compact in size;
• High moment of strength;
• Energy saturation and efficiency.

Using

Brushless DC motor with permanent magnets is found mainly in devices with a power within 5 kW. In more powerful equipment, their application is irrational. It is also worth noting that magnets in engines of this type are particularly sensitive to high temperatures and strong fields. Induction and brush variants are devoid of such drawbacks. Engines are actively used in electric motorcycles, automobile drives due to the absence of friction in the manifold. Among the features it is necessary to distinguish the uniformity of the torque and current, which ensures the reduction of acoustic noise.