In order to solve the problems of controlling modern precision systems, the brushless motor is increasingly being used. This is characterized by the great advantage of such devices, as well as the active formation of the computational capabilities of microelectronics. As you know, they can provide high long torque density and energy efficiency compared to other kinds of motors.
Schematic of the brushless motor
The engine consists of the following parts:
1. Back of case.
2. Stator.
3. Bearing.
4. Magnetic disk (rotor).
5. Bearing.
6. Coiled stator.7. Front of case.
A brushless motor has a relationship between the polyphase winding of the stator and rotor. They have permanent magnets and a built-in position sensor. The switching of the device is implemented using a valve converter, as a result of which it received such a name.
The circuit of a brushless motor consists of a rear cover and a printed circuit board of sensors, a bearing sleeve, a shaft and thebearing, rotor magnets, insulating ring, winding, Belleville spring, spacer, Hall sensor, insulation, housing and wires.
In the case of connecting the windings with a "star", the device has large constant moments, so this assembly is used to control the axes. In the case of fastening the windings with a "triangle", they can be used to work at high speeds. Most often, the number of pole pairs is calculated by the number of rotor magnets, which help determine the ratio of electrical and mechanical revolutions.
The stator can be made with iron-free or iron core. Using such designs with the first option, it is possible to ensure that the rotor magnets are not attracted, but at the same instant, the efficiency of the engine is reduced by 20% due to a decrease in the value of the constant torque.
From the diagram it can be seen that in the stator current is generated in the windings, and in the rotor it is created with the help of high-energy permanent magnets.
Symbols:
- VT1-VT7 - transistor communicators; - A, B, C – winding phases;
- M – motor torque;
- DR – rotor position sensor;
- U – motor supply voltage regulator;
- S (south), N (north) – magnet direction;
- UZ – frequency converter;
- BR – speed sensor;
- VD – zener diode;
- L is an inductor.
The motor diagram shows that one of the main advantages of a rotor in which permanent magnets are installed is a reduction in its diameterand, consequently, a reduction in the moment of inertia. Such devices can be built into the device itself or located on its surface. A decrease in this indicator very often leads to small values of the balance of the moment of inertia of the motor itself and the load brought to its shaft, which complicates the operation of the drive. For this reason, manufacturers can offer standard and 2-4 times higher moment of inertia.
Working principles
Today, the brushless motor is becoming very popular, the principle of operation of which is based on the fact that the device controller begins to switch the stator windings. Due to this, the magnetic field vector always remains shifted by an angle approaching 900 (-900) relative to the rotor. The controller is designed to control the current that moves through the motor windings, including the magnitude of the stator magnetic field. Therefore, it is possible to adjust the moment that acts on the device. An exponent of the angle between vectors can determine the direction of rotation that is acting on it.
It should be taken into account that we are talking about electrical degrees (they are much smaller than geometric ones). For example, let's take a calculation of a brushless motor with a rotor, which has 3 pairs of poles. Then its optimal angle will be 900/3=300. These pairs provide for 6 phases of the switching windings, then it turns out that the stator vector can move in jumps of 600. From this it can be seen that the real angle between the vectors will necessarily vary from 600 to1200 starting from rotor rotation.
The valve motor, the principle of operation of which is based on the rotation of the switching phases, due to which the excitation flow is maintained by a relatively constant movement of the armature, after their interaction begins to form a rotating moment. He rushes to turn the rotor in such a way that all the excitation and armature flows coincide together. But during its turn, the sensor starts to switch the windings, and the flow moves to the next step. At this point, the resulting vector will move, but remain completely stationary relative to the rotor flux, which will eventually create a shaft torque.
Benefits
Using a brushless motor in work, we can note its advantages:
- possibility of using a wide range to modify the speed;
- high dynamics and performance;
- maximum positioning accuracy;
- low maintenance costs;
- the device can be attributed to explosion-proof objects;
- has the ability to endure large overloads at the moment of rotation;
- high efficiency, which is more than 90%;
- there are sliding electronic contacts, which significantly increase the working life and service life;
- no overheating of the electric motor during long-term operation.
Flaws
Despite the huge number of advantages, the brushless motor also has disadvantages in operation:
- rather complicated motor control;- relativelythe high price of the device due to the use of a rotor in its design, which has expensive permanent magnets.
Reluctance motor
The valve-reluctance motor is a device in which a switching magnetic resistance is provided. In it, energy conversion occurs due to a change in the inductance of the windings, which are located on the pronounced stator teeth when the toothed magnetic rotor moves. The device receives power from an electric converter, which alternately switches the motor windings in strictness according to the movement of the rotor.
The switched reluctance motor is a complex complex system in which components of various physical nature work together. Successful design of such devices requires in-depth knowledge of machine and mechanical design, as well as electronics, electromechanics and microprocessor technology.
Modern device acts as an electric motor, acting in conjunction with an electronic converter, which is manufactured by integrated technology using a microprocessor. It allows you to perform high-quality engine control with the best performance in energy processing.
Engine properties
Such devices have high dynamics, high overload capacity and precise positioning. Since there are no moving parts,their use is possible in an explosive aggressive environment. Such motors are also called brushless motors, their main advantage, compared to collector motors, is the speed, which depends on the supply voltage of the loading torque. Also, another important property is the absence of abradable and rubbing elements that switch contacts, which increases the resource of using the device.
BLDC motors
All DC motors can be called brushless. They operate on direct current. The brush assembly is provided for electrically combining the rotor and stator circuits. Such a part is the most vulnerable and rather difficult to maintain and repair.
The BLDC motor operates on the same principle as all synchronous devices of this type. It is a closed system including a power semiconductor converter, a rotor position sensor and a coordinator.
AC AC Motors
These devices get their power from AC mains. The speed of rotation of the rotor and the movement of the first harmonic of the magnetic force of the stator completely coincide. This subtype of engines can be used at high powers. This group includes step and reactive valve devices. A distinctive feature of stepping devices is the discrete angular displacement of the rotor during its operation. The power supply of the windings is formed using semiconductor components. The valve motor is controlled bysequential displacement of the rotor, which creates the switching of its power from one winding to another. This device can be divided into single-, three- and multi-phase, the first of which may contain a starting winding or a phase-shifting circuit, as well as be started manually.
The principle of operation of a synchronous motor
The valve synchronous motor works on the basis of the interaction of the magnetic fields of the rotor and stator. Schematically, the magnetic field during rotation can be represented by the pluses of the same magnets, which move at the speed of the stator magnetic field. The rotor field can also be depicted as a permanent magnet that rotates synchronously with the stator field. In the absence of an external torque that is applied to the shaft of the apparatus, the axes completely coincide. The acting forces of attraction pass along the entire axis of the poles and can compensate each other. The angle between them is set to zero.
If the braking torque is applied to the machine shaft, the rotor moves to the side with a delay. Due to this, the attractive forces are divided into components that are directed along the axis of positive indicators and perpendicular to the axis of the poles. If an external moment is applied, which creates acceleration, that is, it begins to act in the direction of rotation of the shaft, the picture of the interaction of fields will completely change to the opposite. The direction of the angular displacement begins to transform to the opposite, and in connection with this, the direction of the tangential forces changes andelectromagnetic moment. In this situation, the engine becomes a brake, and the device works as a generator, which converts the mechanical energy supplied to the shaft into electrical energy. Then it is redirected to the network that feeds the stator.
When there is no external, salient-pole moment will begin to take a position in which the axis of the poles of the stator magnetic field will coincide with the longitudinal one. This placement will correspond to the minimum flow resistance in the stator.
If the braking torque is applied to the machine shaft, the rotor will deviate, while the stator magnetic field will be deformed, as the flow tends to close at the least resistance. To determine it, lines of force are needed, the direction of which at each of the points will correspond to the movement of the force, so a change in the field will lead to the appearance of a tangential interaction.
Having considered all these processes in synchronous motors, we can identify the demonstrative principle of the reversibility of various machines, that is, the ability of any electrical apparatus to change the direction of the converted energy to the opposite.
Permanent magnet brushless motors
The permanent magnet motor is used for serious defense and industrial applications, as such a device has a large power reserve and efficiency.
These devices are most often used in industries where relatively low power consumption andsmall dimensions. They can have a variety of dimensions, without technological restrictions. At the same time, large devices are not completely new, they are most often produced by companies that are trying to overcome the economic difficulties that limit the range of these devices. They have their own advantages, among which are high efficiency due to rotor losses and high power density. To control brushless motors, you need a variable frequency drive.
A cost-benefit analysis shows that permanent magnet devices are much more preferable than other alternative technologies. Most often they are used for industries with a rather heavy schedule for the operation of marine engines, in the military and defense industries and other units, the number of which is constantly increasing.
Jet engine
The switched reluctance motor operates using two-phase windings that are installed around diametrically opposite stator poles. The power supply moves towards the rotor according to the poles. Thus, his opposition is completely reduced to a minimum.
Handmade DC motor provides high efficient drive speed with optimized magnetism for reversing operation. Information about the location of the rotor is used to control the phases of the voltage supply, as this is optimal to achieve continuous and smooth torque.torque and high efficiency.
The signals produced by the jet engine are superimposed on the angular unsaturated phase of the inductance. The minimum pole resistance fully corresponds to the maximum inductance of the device.
A positive moment can only be obtained at angles when the indicators are positive. At low speeds, the phase current must necessarily be limited in order to protect the electronics from high volt-seconds. The conversion mechanism can be illustrated by a reactive energy line. The power sphere characterizes the power that is converted into mechanical energy. In the event of an abrupt shutdown, excess or residual force returns to the stator. The minimum indicators of the influence of the magnetic field on the performance of the device are its main difference from similar devices.
