Precision systems require a lot of control. To perform control functions in such systems, it is customary to use a valve motor (VD), which makes it possible to increase the computing capabilities of microelectronic equipment. It also improves the properties of DC motors, providing a high density of long-term torque.
Content
- Design features
- Operating principle
- Advantages and disadvantages
- Number of phases
Design features
This type of electric motor has a standard design. It consists of a rotor, which is played by a magnetic disk, stators and bearings. All parts are enclosed in a robust case. The HP stator is similar to that used in asynchronous devices. Its main element is a steel core, along the perimeter of which a copper winding is located. It depends on the number of windings to which type the valve motor will belong (single-phase, two-phase, three-phase).
Depending on how the winding turns are located in the stator, the form of its electromotive force can be:
- Keystone (BLDC).
- Sinusoidal (PMSM).
The shape of the winding has a direct influence on the way the motors are supplied. The change in electric current can also occur sinusoidally or trapezoidally.
The rotor consists of several permanent-field magnets. Previously, ferrite magnets were used for its production. But the level of their magnetic induction is small enough, so they were replaced by alloy products. rare earth elements, allowing to achieve the required level of induction and at the same time to make the rotor more compact.
An integral part of any brushless motor is the rotor position sensor. Its work can be based on:
- photoelectric principle;
- inductive principle;
- Hall effect and other phenomena.
The photoelectric position sensor consists of three stationary photodetectors, which are closed in turn by a rotating shutter. Its movement is synchronous with the movement of the rotor. Thanks to the binary code from the sensor, the rotor can be locked in six different positions. Converting into a combination of control voltages, the signals regulate the power switches according to a special scheme. Each phase of the electric motor uses two keys, and two of the three windings are connected to the network.
The position sensor of the photoelectric type belongs to the category of the most common, since it is practically inertialess. It also allows you to eliminate the delay in the feedback channel.
Operating principle
Depending on the design features and technical characteristics, an asynchronous, synchronous and inductive brushless motor is distinguished. The principle of operation of each of them is based on the induction of variable magnetic poles on the rotor. When voltage is applied, it begins to rotate in accordance with the stator poles, as a result of which the magnetic field resistance is minimized.
The rotor status information is used as a tool to control the voltage phase. The signals are superimposed on the angular unsaturated phase of the inductance in such a way that its maximum value coincides with the minimum pole resistance.
So that high volt-seconds do not have a negative effect on working electronics, phase current limitation should be provided at low motor speeds. The role of limiters in this case is performed by sensors. At high speeds, there is no need for current limiting.
The equalized angle of the single pulse control voltage optimizes equipment performance. The process of its transformation is clearly demonstrated in the form of a trajectory of reactive energy. The power converted into mechanical energy is responsible for the power area. A power outage leads to the fact that excess or residual energy is transferred to the stator. The influence of the magnetic field on a working brushless electric motor is minimal. This distinguishes the VD from other similar devices.
Advantages and disadvantages
Electric motors of this type are widely used in the manufacturing and industrial fields. This is due to the following advantages of VD:
- a wide interval for modifying the rotational speed;
-
the most accurate positioning; - high-speed performance and high dynamics;
- cost-effective maintenance;
- sufficient protection against explosions;
- resistance to heavy loads during rotation;
- soft gear shifting;
- good efficiency in excess of 90%;
- great work resource and service life.
During long-term operation of the valve motor, dangerous overheating of the main elements does not occur, which makes the process of its operation more efficient and safe.
This type of electric motor has certain disadvantages. They are expressed in a complex control system and a high level of noise during operation. Also, the obvious disadvantages include the high price due to the use of expensive permanent magnets used in the manufacture of the rotor.
Number of phases
The valve motor, like other types of devices, can operate on direct and alternating current. There are motors designed for a different number of phases.
Single phase belongs to the category of the simplest, having the minimum number of connections with electronics. It is characterized by pulsation, high torque. A single-phase device cannot start at all angular positions, it is used in installations where high speed is important.
Two-phase motor activates the air gap, and with additional tuning, asymmetry is created in the rotor poles. Has a high torque, which can provoke negative consequences during operation.
Three-phase device shows efficiency in starting and torque generation without involving a large number of phases. With an even number of poles, it is optimal for technology in which high power plays an important role at low operating speeds (for example, for pumps). During operation, high torque and high noise levels are generated.
Four-phase motor is devoid of disadvantages due to excessive torque and the presence of pulsations. However, its characteristic high power and cost does not allow widespread use of such a motor in various equipment.
