Brushless AC motor. Brushless motors "educational program and design

The principle of operation of which is based on frequency regulation and self-synchronization is called the demon commutator motor. In this design, the vector magnetic field the stator is controlled relative to the position of the rotor. The brushless motor was designed to improve the performance of standard DC brushed motors.

He organically combined the most best qualities DC motors and non-contact electric motors.

Main differences from conventional engines

The brushless motor is often used in radio controlled models aircraft. Their outstanding performance and durability have gained wide popularity due to the absence of rubbing parts in the form of brushes that carry out current transmission.

In order to more fully represent the difference, you need to remember that in the standard collector electric motor the rotor rotates with windings inside the stator, which are based on permanent magnets. The windings are switched using a collector, depending on the position of the rotor. In the electric motor alternating current on the contrary, a rotor with a magnet rotates inside a stator with windings. Approximately the same design has an engine.

Unlike standard engines, in the brushless one, the stator acts as a moving part, in which permanent magnets are placed, and the role of the fixed part is played by a rotor with three-phase windings.

How a brushless motor works

The rotation of the motor is carried out by changing the direction of the magnetic field in the rotor windings in a certain sequence. In this case, the permanent magnets interact with the magnetic fields of the rotor and set the moving stator in motion. This movement is based on the main property of magnets, when like poles repel, and dissimilar - are attracted.

The magnetic fields in the rotor windings and their change are controlled by the controller. It is a fairly complex device capable of switching high currents with high speed. The controller must have in its circuit brushless motor which greatly increases the cost of its use.

Brushless motors do not have any rotating contacts and any contacts capable of switching. This is their main advantage over conventional electric motors, since all frictional losses are minimized.

Household and medical appliances, aeromodelling, pipe shut-off drives for gas and oil pipelines - this is far from complete list areas of application of brushless DC motors (BD). Let's look at the device and principle of operation of these electromechanical drives in order to better understand their advantages and disadvantages.

General information, device, scope

One of the reasons for the interest in the DB is the increased need for high-speed micromotors with precise positioning. The internal structure of such drives is shown in Figure 2.

Rice. 2. The device of the brushless motor

As you can see, the design is a rotor (armature) and a stator, the first has a permanent magnet (or several magnets arranged in a certain order), and the second is equipped with coils (B) to create a magnetic field.

It is noteworthy that these electromagnetic mechanisms can be either with an internal anchor (this type of construction can be seen in Figure 2) or external (see Figure 3).

Rice. 3. Design with an external anchor (outrunner)

Accordingly, each of the designs has a specific scope. Devices with an internal armature have high speed rotation, therefore they are used in cooling systems, as power plants drones, etc. Drives with external rotor are used where accurate positioning and resistance to torque overloads are required (robotics, medical equipment, CNC machines, etc.).

Principle of operation

Unlike other drives, for example, asynchronous machine alternating current, for the operation of the DB, a special controller is required, which turns on the windings in such a way that the vectors of the magnetic fields of the armature and the stator are orthogonal to each other. That is, in fact, the driver device regulates the torque acting on the DB armature. This process is clearly shown in Figure 4.

As you can see, for each movement of the armature, it is necessary to perform a certain commutation in the motor stator winding brushless type. This principle of operation does not allow smooth control of rotation, but makes it possible to quickly gain momentum.

Differences between brushed and brushless motors

The collector type drive differs from the DB as design features(see Fig. 5.), and the principle of operation.

Rice. 5. A - collector motor, B - brushless

Consider design differences. Figure 5 shows that the rotor (1 in Fig. 5) of a collector-type motor, unlike a brushless one, has coils in which simple circuit windings, and permanent magnets (usually two) are mounted on the stator (2 in Fig. 5). In addition, a collector is installed on the shaft, to which brushes are connected that supply voltage to the armature windings.

Briefly describe the principle of operation collector machines. When voltage is applied to one of the coils, it is excited and a magnetic field is formed. It interacts with permanent magnets, this causes the armature and the collector placed on it to rotate. As a result, power is supplied to the other winding and the cycle repeats.

The frequency of rotation of an armature of this design directly depends on the intensity of the magnetic field, which, in turn, is directly proportional to the voltage. That is, to increase or decrease the speed, it is enough to increase or decrease the power level. And to reverse it is necessary to switch the polarity. This control method does not require a special controller, since the travel controller can be made based on a variable resistor, and a conventional switch will work as an inverter.

We considered the design features of brushless motors in the previous section. As you remember, their connection requires a special controller, without which they simply will not work. For the same reason, these motors cannot be used as a generator.

It should also be noted that in some drives of this type for more efficient control, the rotor positions are monitored using Hall sensors. This significantly improves the characteristics of brushless motors, but leads to an increase in the cost of an already expensive design.

How to start a brushless motor?

To make this type of drive work, a special controller is required (see Figure 6). Without it, launch is impossible.

Rice. 6. Brushless Motor Controllers for Modeling

It makes no sense to assemble such a device yourself, it will be cheaper and more reliable to purchase a ready-made one. You can pick it up by the following characteristics, characteristic of PWM channel drivers:

• The maximum allowable current, this characteristic is given for the normal operation of the device. Quite often, manufacturers indicate this parameter in the model name (for example, Phoenix-18). In some cases, a value is given for peak mode, which the controller can maintain for several seconds.
• The maximum nominal voltage for continuous operation.
• The resistance of the internal circuits of the controller.
• Permissible number of revolutions, indicated in rpm. Above this value, the controller will not allow to increase the rotation (the restriction is implemented at the software level). Please note that the speed is always given for 2-pole drives. If there are more pole pairs, divide the value by their number. For example, the number 60000 rpm is indicated, therefore, for 6 magnetic motor the rotational speed will be 60000/3=20000 prm.
• The frequency of the generated pulses, for most controllers, this parameter lies in the range from 7 to 8 kHz, more expensive models allow you to reprogram the parameter, increasing it to 16 or 32 kHz.

Note that the first three characteristics determine the capacity of the database.

Brushless motor control

As mentioned above, the commutation of the drive windings is controlled electronically. To determine when to switch, the driver monitors the position of the armature using Hall sensors. If the drive is not equipped with such detectors, then the back EMF that occurs in the unconnected stator coils is taken into account. The controller, which, in fact, is a hardware-software complex, monitors these changes and sets the switching order.

Three-phase brushless DC motor

Most databases are performed in a three-phase design. To control such a drive, the controller has a converter constant voltage into a three-phase pulse (see Fig. 7).

Figure 7. DB voltage diagrams

To explain how such a brushless motor works, one should consider Figure 4 together with Figure 7, where all stages of the drive operation are shown in turn. Let's write them down:

1. A positive impulse is applied to coils "A", while a negative impulse is applied to "B", as a result, the armature will move. The sensors will record its movement and give a signal for the next commutation.
2. Coil "A" is turned off, and a positive pulse goes to "C" ("B" remains unchanged), then a signal is given to the next set of pulses.
3. On "C" - positive, "A" - negative.
4. A pair of "B" and "A" works, which receive positive and negative impulses.
5. A positive pulse is re-applied to "B", and a negative pulse to "C".
6. Coils "A" are turned on (+ is supplied) and a negative pulse is repeated on "C". Then the cycle repeats.

In the apparent simplicity of management there are a lot of difficulties. It is necessary not only to track the position of the armature in order to produce the next series of pulses, but also to control the rotational speed by adjusting the current in the coils. In addition, you should choose the most optimal parameters for acceleration and deceleration. It is also worth noting that the controller must be equipped with a block that allows you to control its operation. Appearance such a multifunctional device can be seen in Figure 8.

Rice. 8. Multi-function brushless motor controller

Advantages and disadvantages

An electric brushless motor has many advantages, namely:

• The service life is much longer than that of conventional collector counterparts.
• High efficiency.
• speed dial top speed rotation.
• It is more powerful than CD.
• The absence of sparks during operation allows the drive to be used in fire hazardous conditions.
• No additional cooling required.
• Simple operation.

Now let's look at the cons. Significant disadvantage, which limits the use of the database - their relatively high cost (taking into account the price of the driver). Among the inconveniences is the impossibility of using the database without a driver, even for short-term activation, for example, to check the performance. Problem repair, especially if rewinding is required.

Motors are used in many areas of technology. In order for the motor rotor to rotate, a rotating magnetic field is required. In conventional DC motors, this rotation is carried out mechanically using brushes sliding along the collector. This causes sparking, and, in addition, due to friction and wear of the brushes, such motors require constant maintenance.

Thanks to the development of technology, it became possible to generate a rotating magnetic field electronically, which was embodied in brushless DC motors (BLDC).

Device and principle of operation

The main elements of the BDPT are:

• rotor on which permanent magnets are fixed;
• stator on which the windings are installed;
• electronic controller.

By design, such an engine can be of two types:

with an internal arrangement of a rotor (inrunner)

with external rotor arrangement (outrunner)

In the first case, the rotor rotates inside the stator, and in the second case, the rotor rotates around the stator.

inrunner engine used when you need to get high speed rotation. This motor has a simpler standard design which allows the use of a fixed stator to mount the motor.

outrunner engine suitable for receiving big moment at low revs. In this case, the engine is mounted using a fixed axle.

inrunner engine high RPM, low torque. outrunner engine- low speed, high torque.

The number of poles in the BLDT can be different. By the number of poles, one can judge some of the characteristics of the motor. For example, a motor with a rotor having 2 poles has a higher number of revolutions and a small torque. Motors with an increased number of poles have greater moment, but fewer turns. By changing the number of rotor poles, you can change the number of revolutions of the engine. Thus, by changing the design of the engine, the manufacturer can choose required parameters engine torque and rpm.

Directorate of the BDPT

Speed ​​controller, appearance

Used to control a brushless motor special controller - motor shaft speed controller direct current. Its task is to generate and feed into right moment to the desired winding of the required voltage. In the controller for devices powered by a 220 V mains, an inverter circuit is most often used, in which the current is converted at a frequency of 50 Hz first into D.C., and then into pulse-width modulated (PWM) signals. To supply voltage to the stator windings, powerful electronic switches on bipolar transistors or other power elements are used.

Adjustment of the power and speed of the engine is carried out by changing the duty cycle of the pulses, and, consequently, the effective value of the voltage supplied to the stator windings of the engine.

Schematic diagram of the speed controller. K1-K6 - keys D1-D3 - rotor position sensors (Hall sensors)

An important issue is the timely connection electronic keys to each winding. To ensure this the controller must determine the position of the rotor and its speed. To obtain such information, optical or magnetic sensors can be used (for example, hall sensors), as well as reverse magnetic fields.

More common use hall sensors, which react to the presence of a magnetic field. The sensors are placed on the stator in such a way that they are affected by the magnetic field of the rotor. In some cases, sensors are installed in devices that allow you to change the position of the sensors and, accordingly, adjust the timing.

Rotor speed controllers are very sensitive to the amount of current passing through it. If you pick rechargeable battery with a higher output current, the regulator will burn out! Choose the right combination of characteristics!

Advantages and disadvantages

Compared with conventional engines BDPT have the following advantages:

• high efficiency;
• high performance;
• the possibility of changing the speed;
• no sparkling brushes;
• small noises, both in the audio and high-frequency ranges;
• reliability;
• ability to withstand torque overloads;
• excellent size to power ratio.

The brushless motor is highly efficient. It can reach 93-95%.

The high reliability of the mechanical part of the DB is explained by the fact that it uses ball bearings and there are no brushes. Demagnetization permanent magnets occurs quite slowly, especially if they are made using rare earth elements. When used in a current protection controller, the life of this node is quite high. Actually the service life of the BLDC can be determined by the service life of the ball bearings.

The disadvantages of the BDP are the complexity of the control system and the high cost.

Application

The scopes of BDTP are as follows:

• creating models;
• medicine;
• automotive;
• Oil and gas industry;
• Appliances;
• military equipment.

Usage DB for aircraft models gives a significant advantage in terms of power and dimensions. A comparison of a conventional Speed-400 brushed motor and a BDTP of the same class Astro Flight 020 shows that the first type motor has an efficiency of 40-60%. The efficiency of the second engine under the same conditions can reach 95%. Thus, the use of the DB makes it possible to almost double the power of the power part of the model or its flight time.

Due to the low noise and lack of heating during operation, BLDCs are widely used in medicine, especially in dentistry.

In automobiles, such engines are used in glass lifts, electric wipers, headlight washers and electric seat lift controls.

No commutator and brush sparks allows using the database as elements of locking devices in the oil and gas industry.

As an example of using a database in household appliances you can note washing machine with LG direct drum drive. This company uses an Outrunner-type BDTP. There are 12 magnets on the motor rotor, and 36 inductors on the stator, which are wound with a wire with a diameter of 1 mm on magnetically conductive steel cores. The coils are connected in series with 12 coils per phase. The resistance of each phase is 12 ohms. Hall sensor is used as rotor position sensor. The motor rotor is attached to the tub of the washing machine.

Everywhere this engine is used in hard drives for computers, which makes them compact, in CD and DVD drives and cooling systems for micro-electronic devices and not only.

Along with low and medium power DUs, large BLDCs are increasingly being used in the heavy duty, marine and military industries.

DB high power designed for the US Navy. For example, Powertec has developed a 220kW 2000rpm CBTP. The engine torque reaches 1080 Nm.

Except specified areas, DB are used in the design of machine tools, presses, plastic processing lines, as well as in wind energy and the use of tidal wave energy.

Characteristics

Main characteristics of the engine:

• rated power;
• maximum power;
• maximum current;
• maximum operating voltage ;
• maximum speed(or Kv factor);
• winding resistance;
• lead angle;
• working mode;
• overall weight characteristics engine.

The main indicator of the engine is its rated power, that is, the power generated by the engine for a long time of its operation.

Max power- this is the power that the engine can give for a short period of time without collapsing. For example, for the Astro Flight 020 brushless motor mentioned above, it is 250 watts.

Maximum current. For Astro Flight 020 it is 25 A.

Maximum operating voltage- the voltage that the motor windings can withstand. The Astro Flight 020 is set to operate at 6V to 12V.

Maximum engine speed. Sometimes the passport indicates the Kv coefficient - the number of engine revolutions per volt. For Astro Flight 020 Kv= 2567 rpm. In this case maximum number rpm can be determined by multiplying this factor by the maximum operating voltage.

Usually winding resistance for engines is tenths or thousandths of an ohm. For Astro Flight 020 R= 0.07 ohm. This resistance affects the efficiency of the BPDT.

lead angle represents the advance of switching voltages on the windings. It is associated with the inductive nature of the resistance of the windings.

The mode of operation can be long-term or short-term. In long-term operation, the engine can run for a long time. At the same time, the heat generated by it is completely dissipated and it does not overheat. In this mode, motors operate, for example, in fans, conveyors or escalators. Momentary mode is used for devices such as elevator, electric shaver. In these cases, the engine runs for a short time and then for a long time cools down.

In the passport for the engine, its dimensions and weight are given. In addition, for example, for engines intended for aircraft models, landing dimensions and shaft diameter are given. In particular, the following specifications are given for the Astro Flight 020 engine:

• length is 1.75”;
• diameter is 0.98”;
• shaft diameter is 1/8”;
• weight is 2.5 ounces.

Conclusions:

1. In modeling, in various technical products, in industry and in defense technology, BLDTs are used, in which a rotating magnetic field is generated by an electronic circuit.
2. According to their design, BLDCs can be with internal (inrunner) and external (outrunner) rotor arrangement.
3. Compared to other motors, BLDC motors have a number of advantages, the main of which are the absence of brushes and sparks, high efficiency and high reliability.

A bit of history:

The main problem of all engines is overheating. The rotor rotated inside some kind of stator, and therefore the heat from overheating did not go anywhere. People came up with a brilliant idea: to rotate not the rotor, but the stator, which would be cooled by air during rotation. When such an engine was created, it became widely used in aviation and shipbuilding, and therefore it was nicknamed the Brushless Motor.

Soon an electrical analogue was created brushless motor. They called it a brushless motor because it did not have collectors (brushes).

Brushless motor.

Brushless (brushless English) electric motors came to us relatively recently, in recent 10-15 years old. Unlike collector motors, they are powered by three-phase alternating current. Brushless motors operate efficiently over a wider RPM range and have more high efficiency . At the same time, the design of the engine is relatively simple, it does not have a brush assembly that constantly rubs against the rotor and creates sparks. We can say that brushless motors practically do not wear out. The cost of brushless motors is slightly higher than brushed motors. This is because all brushless motors have bearings and are generally of higher quality.

Tests have shown:
Rod with screw 8x6 = 754 grams,
RPM = 11550 rpm,
Power consumption = 9 watts(without screw) , 101 watts(with screw),

Power and efficiency

Power can be calculated like this:
1) Power in mechanics is calculated by the following formula: N=F*v, where F is force and v is speed. But since the screw is in a static state, there is no movement, except rotational. If this motor is installed on an aircraft model, then it would be possible to measure the speed (it is equal to 12 m / s) and calculate the useful power:
N useful \u003d 7.54 * 12 \u003d 90.48 watts
2) efficiency electric motor is found according to the following formula: Efficiency = N useful / N spent * 100%, Where N costs = 101 watts
Efficiency= 90.48/101 *100%= 90%
On average, the efficiency of brushless motors is real and fluctuates around 90% (the highest efficiency achieved by this type of motor is 99.68% )

Engine Specifications:

Voltage: 11.1 volts
Turnovers: 11550 rpm
Maximum current: 15A
Power: 200 watts
Thrust: 754 grams (screw 8x6)

Conclusion:

The price of any thing depends on the scale of its production. Manufacturers brushless motors multiply like mushrooms after rain. Therefore, I want to believe that in the near future the price of controllers and brushless engines will fall how it fell on the radio control equipment ... The possibilities of microelectronics are expanding every day, the size and weight of the controllers are gradually decreasing. It can be assumed that in the near future controllers will be built directly into the engines! Maybe we'll live to see this day...

Surely every beginner who first connected his life with radio-controlled electric models, after a thorough study of the filling, has a question. What is a collector and? Which one is better to put on your radio-controlled electric model?

The brushed motors so often used to power radio controlled electric models have only two outgoing power wires. One of them is "+" the other is "-". In turn, they are connected to the speed controller. Having disassembled the collector motor, you will always find there 2 curved magnets, a shaft together with an anchor, on which a copper thread (wire) is wound, where a gear is on one side of the shaft, and on the other side there is a collector assembled from plates, which include pure copper.

The principle of operation of the collector motor

Electric current (DC or direct current), flowing to the armature windings (depending on their number for each in turn) creates an electromagnetic field in them, which has a south pole on one side and a north pole on the other.

Many people know that if you take any two magnets and attach them poles of the same name to each other, then they will not come together for nothing, and if they are attached with opposite names, then they will stick so that it is not always possible to separate them.

So, this electromagnetic field that occurs in any of the armature windings, interacting with each of the poles of the stator magnets, drives (rotation) the armature itself. Further, the current passes through the collector and brushes to the next winding, and so sequentially, passing from one armature winding to another, the motor shaft rotates together with the armature, but only as long as voltage is applied to it.

In a standard collector motor, the armature has three poles (three windings) - this is done so that the engine does not “stick” in one position.

Cons of collector motors

By themselves, collector motors do a good job with their work, but this is only until the moment when it becomes necessary to get the highest possible speed from them at the output. It's all about the very brushes mentioned above. Since they are always in close contact with the collector, as a result high speed friction occurs at the point of their contact, which in the future will cause rapid wear of both and subsequently lead to a loss of effective electric power. engine. This is the most significant disadvantage of such motors, which nullifies all its positive qualities.

The principle of operation of a brushless motor

Here, the opposite is true, motors of the type do not have both brushes and a collector. The magnets in them are located strictly around the shaft and act as a rotor. Windings that already have several magnetic poles are placed around it. A so-called sensor (sensor) is installed on the rotor of brushless motors, which will control its position and transmit this information to the processor that works in conjunction with the rotation speed controller (data exchange on the position of the rotor occurs more than 100 times per second). As a result, we get a smoother operation of the motor itself with maximum efficiency.

Brushless motors can be with a sensor (sensor) and without it. The absence of a sensor slightly reduces the efficiency of the motor, so their absence is unlikely to upset a beginner, but on the other hand, the price tag will pleasantly surprise you. It is easy to distinguish them from each other. For motors with a sensor, in addition to 3 thick power wires, there is also an additional loop of thin ones that go to the speed controller. It is not worth chasing motors with a sensor for both a beginner and an amateur, because only the pros will appreciate their potential, and the rest will simply overpay, and significantly.

Advantages of brushless motors

Almost no wear parts. Why “almost”, because the rotor shaft is mounted on bearings, which in turn tend to wear out, but their resource is extremely large, and their interchangeability is very simple. These motors are very reliable and efficient. A rotor position sensor is installed. On collector motors, the operation of brushes is always accompanied by sparking, which subsequently causes interference in the operation of radio equipment. So, for collectorless, as you already understood, these problems are excluded. No friction, no overheating, which is also a significant advantage. Compared with collector motors do not require additional service during operation.

Cons of brushless motors

These motors have only one minus, this is the price. But if you look at it from the other side, and take into account the fact that operation frees the owner immediately from such troubles as replacing springs, anchors, brushes, collectors, then you can easily give preference to the latter.