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 technology 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 kind, in which there is no winding on rotor elements or starter. The widespread adoption of semiconductor type switches with high power and affordable cost has accelerated the creation of such designs, facilitated execution, and eliminated many switching difficulties.
Principle of operation
An increase in reliability, a decrease in prices and simpler manufacturing are ensured by the absence of mechanical switching elements, rotor windings and permanent magnets. In this case, an increase in efficiency is possible due to a decrease in friction losses in the collector system. The brushless motor can operate on alternating or continuous current. The latter option is notable for its similarity to collector motors. Its characteristic feature is the formation of a magnetic rotating field and the use of a pulsed current. It is based on an electronic switch, which increases the complexity of the design.
Position calculation
Pulse generation occurs in the control system after a signal reflecting the position of the rotor. The degree of voltage and supply directly depends on the speed of rotation of the motor. The sensor in the starter detects the position of the rotor and gives an electrical signal. Together with the magnetic poles passing near the sensor, the signal amplitude changes. There are also sensorless positioning techniques, including current passage points and transducers. PWM at the input terminals maintains a variable voltage level 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 motor for a screwdriver is characterized by a low level of inertia, which is ensured 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 simplified heat dissipation are achieved by placing heating circuits on the stator. It is also worth noting the presence of an electronic integrated unit on some models.
Magnetic elements
The location of the magnets can be different in accordance with the size of the motor, for example, at the poles or around the rotor. The creation of high-quality magnets with greater power is possible due to the use of neodymium in combination with boron and iron. Despite high performance, brushless motor for screwdriver with permanent magnets has some disadvantages, including the loss of magnetic characteristics at high temperatures. But they are distinguished by greater efficiency and the absence of losses compared to machines in the design of which there are windings.
The pulses of the inverter determine the speed of rotation of the mechanism. With a constant supply frequency, the engine operates at a constant speed in an open system. Accordingly, the rotation speed varies depending on the level of the supply frequency.
Specifications
The valve electric motor operates in the established modes and has the functionality of a brush analog, the speed of which depends on the applied voltage. The mechanism has many advantages:
- lack of changes during magnetization and current leakage;
- correspondence of rotation speed and torque itself;
- speed is not limited by centrifugal force affecting the collector and rotor electric winding;
- no need for a switch and field winding;
- used magnets are lightweight and compact in size;
- high moment of force;
- energy saturation and efficiency.
Using
The brushless DC motor with permanent magnets is found mainly in devices with power within 5 kW. In more powerful equipment, their use 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 options are free from 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 highlight the uniformity of torque and current, which ensures a reduction in acoustic noise.