Creation and testing of a brushless motor. Three-phase brushless motor

Surely he wondered how such an engine differs from other engines, for example, from those that are in drilling machines. Motors installed in not very powerful machines usually do not spark, and they are not as noisy as the same drill, which has less power than the machine.

What's the matter? The fact is that brush motor is commutator motor, and the brushless motor is brushless. To solve different problems, your type of engine is suitable - somewhere better fit collector, and somewhere you can install only brushless.

Collector motor

The collector motor has, as a rule, only two power wires, it is easy to control, it is enough to adjust the DC or AC supply voltage and the speed will change accordingly. You can even control the collector motor with a simple dimmer. The main advantage of the collector engine is high revolutions (tens of thousands per minute) with high torque.

The principle of operation of the collector motor is very simple. In fact, its rotor is a set of copper frames in a magnetic circuit, which are switched in turn to the power source on the collector-brush assembly. The stator can be either from permanent magnets, and with a winding fed from the same source as the rotor, or from a separate source, and sometimes the stator and rotor are included in a single series circuit (such as the motors of automatic washing machines).

For each section of the rotor winding, through the collector-brush assembly, in turn, during the rotation of the rotor, electricity, as a result, the rotor is remagnetized, acquiring clearly defined north and south magnetic poles, due to which the rotor rotates inside the stator (the rotor poles are pushed out by the stator poles, then the rotor is further remagnetized and pushed out again). Since the rotor is switched to the power source each time by the next section, the rotation does not stop while the collector is energized.

The main disadvantage of the collector engine

The speed of the commutator motor is very convenient to regulate, but when they are high enough, the brushes make themselves felt. Since the brushes always fit snugly against the commutator, high revs they wear out quickly, become clogged in one way or another over time, and eventually begin to spark.

Wear of the brushes, and in general of the collector-brush assembly, leads to a decrease in the efficiency of the collector motor. So myself collector-brush assembly - this is main disadvantage commutator motors. Today, collector motors are being abandoned in favor of brushless stepper motors.

A brushless motor does not have a commutator or brushes. The simplest example brushless motor - asynchronous three-phase motor with a squirrel cage rotor. Another example of a brushless motor is a more modern one - stepper motor with magnetic rotor. The stator windings of a brushless motor are themselves remagnetized so that the rotor turns around all the time and rotates continuously in this way.

Most often, modern brushless motors are equipped with a rotor position sensor, according to the signals from which the motor speed controller operates. The signal from the rotor position sensor is transmitted to the processor more than 100 times per second, resulting in accurate rotor positioning and high torque. There are, of course, brushless motors without a rotor position sensor, a vivid example is the same asynchronous three-phase motor. Motors without encoder are cheaper than those with encoder.

Advantages of brushless motors

Since the life of the rotor bearings is extremely long, it can be said that in a brushless motor there are practically no parts that wear out over time, and it does not require maintenance at all during operation. Here, friction is minimized, there is no problem of collector overheating, in general, the reliability and efficiency of brushless motors are very high.

There are no sparking brushes, the rotor position sensor will help make the control accurate - there are practically no drawbacks, only advantages. Is that the price of quality stepper motors higher than the collector (plus driver), but this is nothing compared to regular replacement springs, brushes and collectors for collector motors.

Published on 11.04.2013

Shared device (Inrunner, Outrunner)

brushless motor direct current consists of a rotor with permanent magnets and a stator with windings. There are two types of engines: Inrunner, in which the rotor magnets are inside the stator with windings, and Outrunner, in which the magnets are located outside and rotate around a fixed stator with windings.

scheme Inrunner usually used for high speed engines with few poles. Outrunner if necessary, obtain a high-torque motor with relatively low speed. Structurally, Inrunners are simpler due to the fact that the fixed stator can serve as a housing. Mounting devices can be mounted to it. In the case of Outrunners, the entire outer part rotates. The engine is fastened by a fixed axle or stator parts. In the case of a motor-wheel, the fastening is carried out for the fixed axis of the stator, the wires are led to the stator through the hollow axis.

magnets and poles

The number of poles on the rotor is even. The shape of the magnets used is usually rectangular. Cylindrical magnets are used less frequently. They are installed with alternating poles.

The number of magnets does not always correspond to the number of poles. Several magnets can form one pole:

In this case, 8 magnets form 4 poles. The size of the magnets depends on the geometry of the motor and the characteristics of the motor. The stronger the magnets used, the higher the moment of force developed by the motor on the shaft.

The magnets on the rotor are fixed with a special adhesive. Less common are designs with a magnet holder. The rotor material can be magnetically conductive (steel), non-magnetically conductive (aluminum alloys, plastics, etc.), combined.

Windings and teeth

The winding of a three-phase brushless motor is carried out with a copper wire. The wire can be single-core or consist of several insulated cores. The stator is made of several sheets of magnetically conductive steel folded together.

The number of stator teeth must be divided by the number of phases. those. for a three-phase brushless motor, the number of stator teeth must be divisible by 3. The number of stator teeth can be either more or less than the number of poles on the rotor. For example, there are motors with schemes: 9 teeth / 12 magnets; 51 teeth / 46 magnets.

An engine with a 3-tooth stator is used extremely rarely. Since only two phases work at any time (when turned on by a star), the magnetic forces act on the rotor not evenly around the entire circumference (see Fig.).

The forces acting on the rotor try to warp it, which leads to an increase in vibrations. To eliminate this effect, the stator is made with a large number of teeth, and the winding is distributed over the teeth of the entire circumference of the stator as evenly as possible.

In this case, the magnetic forces acting on the rotor cancel each other out. There is no imbalance.

Options for the distribution of phase windings by stator teeth

Winding option for 9 teeth

Winding option for 12 teeth

In the above diagrams, the number of teeth is chosen in such a way that it divisible not only by 3. For example, when 36 teeth accounted for 12 teeth per phase. 12 teeth can be distributed as follows:

The most preferred scheme is 6 groups of 2 teeth.

Exists motor with 51 teeth on the stator! 17 teeth per phase. 17 is a prime number, it is only divisible by 1 and itself. How to distribute the winding over the teeth? Alas, I could not find examples and techniques in the literature that would help solve this problem. It turned out that the winding was distributed as follows:

Consider real scheme windings.

Please note that the winding has different winding directions on different teeth. Different winding directions are indicated by capital and capital letters. Details about the design of windings can be found in the literature offered at the end of the article.

Classical winding is performed with one wire for one phase. Those. all windings on the teeth of one phase are connected in series.

The windings of the teeth can also be connected in parallel.

There can also be combined inclusions

Parallel and combined connection allows to reduce the inductance of the winding, which leads to an increase in the stator current (hence the power) and the motor speed.

Turnovers electric and real

If the motor rotor has two poles, then with one full revolution magnetic field on the stator, the rotor makes one complete revolution. With 4 poles, it takes two turns of the magnetic field on the stator to turn the motor shaft one full turn. How more quantity rotor poles, the more electrical revolutions are required to rotate the motor shaft one revolution. For example, we have 42 magnets on the rotor. In order to turn the rotor one revolution, 42/2 = 21 electrical revolutions are required. This property can be used as a kind of reducer. Picking up required amount poles, you can get the motor with the desired speed characteristics. In addition, an understanding of this process will be necessary for us in the future, when choosing the parameters of the controller.

Position sensors

The design of engines without sensors differs from engines with sensors only in the absence of the latter. Other fundamental differences No. The most common position sensors based on the Hall effect. The sensors respond to a magnetic field, they are usually located on the stator in such a way that they are affected by the rotor magnets. The angle between the sensors must be 120 degrees.

Meaning "electric" degrees. Those. for a multi-pole motor, the physical arrangement of the sensors could be:

Sometimes sensors are located outside the engine. Here is one example of the location of the sensors. In fact, it was an engine without sensors. So in a simple way it was equipped with hall sensors.

On some engines, sensors are installed on special device, which allows you to move the sensors within certain limits. With the help of such a device, the timing is set. However, if the motor requires reverse (rotation in reverse side) will require a second set of sensors set to reverse. Since timing is not critical at the start and low revs, you can set the sensors to the zero point, and adjust the lead angle programmatically when the engine starts to rotate.

Main characteristics of the engine

Each engine is calculated for specific requirements and has the following main characteristics:

• Working mode for which the engine is designed: long-term or short-term. Long operating mode implies that the engine can run for hours. Such engines are calculated in such a way that the heat transfer to the environment is higher than the heat release of the engine itself. In this case, it will not warm up. Example: ventilation, escalator or conveyor drive. Short-term - implies that the engine will turn on for a short period, during which it will not have time to warm up to the maximum temperature, after which a long period time for the engine to cool down. Example: elevator drive, electric shavers, hair dryers.
• Motor winding resistance. Motor winding resistance affects Engine efficiency. The lower the resistance, the higher the efficiency. By measuring the resistance, you can find out the presence of an interturn circuit in the winding. Motor winding resistance is thousandths of an ohm. To measure it, a special device or a special measurement technique is required.
• Maximum operating voltage . The maximum voltage that the stator winding can withstand. The maximum voltage is related to the following parameter.
• Max RPM. Sometimes they indicate maximum speed, A kv- the number of revolutions of the motor per volt with no load on the shaft. Multiplying this figure by the maximum voltage, we get the maximum engine speed without a load on the shaft.
• Maximum current. The maximum allowable winding current. As a rule, the time during which the motor can withstand the specified current is also indicated. The maximum current limitation is associated with a possible overheating of the winding. Therefore, when low temperatures environment real time there will be more work with maximum current, and in the heat the engine will burn out earlier.
• Maximum engine power. Directly related to the previous parameter. This is the peak power that the engine can develop for a short period of time, usually a few seconds. At long work on maximum power inevitable overheating of the engine and its failure.
• Rated power. The power that the engine can develop during the entire turn-on time.
• Phase advance angle (timing). The stator winding has some inductance, which slows down the growth of current in the winding. The current will reach its maximum after a while. In order to compensate for this delay, the phase switching is performed with some advance. Similar to engine ignition internal combustion, where the ignition advance angle is set, taking into account the ignition time of the fuel.

You should also pay attention to the fact that at rated load you will not get the maximum speed on the motor shaft. kv indicated for an unloaded engine. When powering the engine from batteries, one should take into account the “sinking” of the supply voltage under load, which in turn will also reduce the maximum engine speed.

There are two types of motors in multi-rotor devices: collector and brushless. Their main difference is that for a collector motor, the windings are on the rotor (rotating part), and for a brushless motor, on the stator. Without going into details, we will say that a brushless motor is preferable to a collector motor, since it most satisfies the requirements set before it. Therefore, in this article we will focus on this type of motors. You can read more about the difference between brushless and brushed motors in.

Despite the fact that the use of BC motors began relatively recently, the very idea of ​​​​their device appeared quite a long time ago. However, the advent of transistor switches and powerful neodymium magnets made their commercial use possible.

Device BC - motors

The design of a brushless motor consists of a rotor on which magnets are fixed and a stator on which the windings are located. Just according to the relative position of these components, BC engines are divided into inrunner and outrunner.

In multi-rotor systems, the Outrunner scheme is more often used, since it allows you to get the highest torque.

Pros and cons of BC engines

Pros:

• Simplified design of the motor due to the exclusion of the collector from it.
• Higher efficiency.
• Good cooling
• BC engines can work in water! However, do not forget that because of the water on mechanical parts the engine can rust and break down after a while. To avoid similar situations it is recommended to treat the engines with a water-repellent lubricant.
• Least radio interference

Minuses:

Of the minuses, only the impossibility of using these engines without ESC (rotation speed controllers) can be noted. This somewhat complicates the design and makes BK motors more expensive than collector ones. However, if the complexity of the design is a priority parameter, then there are BC motors with built-in speed controllers.

How to choose motors for a copter?

When choosing brushless motors, first of all, you should pay attention to the following characteristics:

• Maximum current - this characteristic shows what maximum current can withstand the motor winding for a short period of time. If this time is exceeded, then engine failure is inevitable. This parameter also affects the choice of ESC.
• The maximum voltage - as well as the maximum current, shows how much voltage can be applied to the winding for a short period of time.
• KV is the number of engine revolutions per volt. Since this indicator directly depends on the load on the motor shaft, it is indicated for the case when there is no load.
• Resistance - the efficiency of the engine depends on the resistance. Therefore, the lower the resistance, the better.

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, such as an 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.

Characteristics of a DC motor. Like DC motors, brushless motors operate on direct current. VD can be considered as a DC motor, in which the brush-collector assembly is replaced by electronics, which is emphasized by the word “valve”, that is, “ controlled by power keys" (valves). The phase currents of a brushless motor have a sinusoidal shape. As a rule, an autonomous voltage inverter with pulse-width modulation (PWM) is used as a power amplifier.

The valve motor should be distinguished from the brushless DC motor (BDC), which has a trapezoidal distribution of the magnetic field in the gap and is characterized by a rectangular shape of the phase voltages. The BLDT structure is simpler than the VD structure (there is no coordinate converter, instead of PWM, 120- or 180-degree switching is used, the implementation of which is simpler than PWM).

In the Russian-language literature, a motor is called a valve motor if the back-EMF of the controlled synchronous machine is sinusoidal, and contactless motor DC if the back-EMF is trapezoidal.

In the English-language literature, such motors are usually not considered separately from the electric drive and are referred to under the abbreviations PMSM (Permanent Magnet Synchronous Motor) or BLDC (Brushless Direct Current Motor). It is worth noting that the abbreviation PMSM in English literature is more often used to refer to the synchronous machines themselves with permanent magnets and with a sinusoidal form of phase back-EMF, while the abbreviation BLDC is similar to the Russian abbreviation BDPT and refers to motors with a trapezoidal form of back-EMF (if other form is not specified).

Generally speaking, a brushless motor is not an electric machine in the traditional sense, since its problems affect a number of issues related to the theory of electric drives and automatic control systems: structural organization, the use of sensors and electronic components, as well as software.

BLDC motors, which combine the reliability of AC machines with the good controllability of DC machines, are an alternative to DC motors, which are characterized by a number of shortcomings associated with the control panel, such as sparking, noise, brush wear, poor armature heat dissipation, etc. The absence of the control panel allows use VD in those applications where the use of DPT is difficult or impossible.

Description and principle of operation[ | ]

Rice. 2. The structure of a two-phase brushless motor with a synchronous machine with permanent magnets on the rotor. PC - coordinate converter, PA - power amplifier,
SEMP - synchronous electromechanical converter (synchronous machine), DPR - rotor position sensor.

U α = − u q ⋅ sin ⁡ θ , (\displaystyle u_(\alpha )=-u_(q)\cdot \sin (\theta ),)

U β = (\displaystyle u_(\beta )=) u q ⋅ cos ⁡ θ , (\displaystyle u_(q)\cdot \cos (\theta ),)

where is the angle of rotation of the rotor (and the system of rotating coordinates) relative to the axis α (\displaystyle \alpha ) fixed coordinate system. To measure the instantaneous value of an angle θ (\displaystyle \theta ) a rotor position sensor (RPS) is installed on the HP shaft.

In fact, in this case, it is the assignment of the value of the amplitude of the phase voltages. A PC, carrying out position modulation of the signal u q (\displaystyle u_(q)), generates harmonic signals u α , u β (\displaystyle u_(\alpha ),u_(\beta )), which the power amplifier (PA) converts into phase voltages u A , u B (\displaystyle u_(A),u_(B)). Synchronous motor as part of a brushless motor, it is often called a synchronous electromechanical converter (SEMC).

As a rule, the electronic part of the HP switches the stator phases of the synchronous machine so that the stator magnetic flux vector is orthogonal to the rotor magnetic flux vector (the so-called vector control). If the orthogonality of the stator and rotor flows is observed, the maximum torque of the HP is maintained under conditions of a change in the rotational speed, which prevents the rotor from falling out of synchronism and ensures the operation of the synchronous machine with the highest possible efficiency for it. To determine the current position of the rotor flux, current sensors can be used instead of the rotor position sensor (indirect position measurement).

The electronic part of a modern VD contains a microcontroller and a transistor bridge, and the principle of pulse-width modulation (PWM) is used to form phase currents. The microcontroller monitors compliance with the specified control laws, and also performs system diagnostics and its software protection against emergency situations.

Sometimes there is no rotor position sensor, and the position is estimated by the control system from measurements of current sensors with the help of observers (the so-called "sensorless" control of the HP). In such cases, due to the removal of an expensive and often cumbersome position sensor, the price and weight and dimensions of an electric drive with HP are reduced, but control becomes more complicated, and the accuracy of position and speed determination decreases.

In applications of medium and high power electrical filters can be additionally included in the system to mitigate the negative effects of PWM: overvoltages on the windings, bearing currents and reduced efficiency. However, this is true for all types of engines.

Advantages and disadvantages[ | ]

Valve motors are designed to combine best qualities AC motors and DC motors. This determines their dignity.

Advantages:

Valve motors are also characterized by some disadvantages, the main of which is high cost. However, speaking of high cost, one should also take into account the fact that brushless motors are usually used in expensive systems with increased requirements for accuracy and reliability.

Flaws:

Design [ | ]

Structurally, modern valve drives consist of an electromechanical part (synchronous machine and rotor position sensor) and a control part (microcontroller and power bridge).

When referring to the design of the VD, it is useful to keep in mind a non-constructive element of the system - the control program (logic).

The synchronous machine used in the HP consists of a laminated (assembled from separate electrically insulated sheets of electrical steel - to reduce eddy currents) stator, in which a multi-phase (usually two- or three-phase) winding is located, and a rotor (usually on permanent magnets).

Hall sensors are used as rotor position sensors in BDPT, and rotating transformers and accumulating sensors are used in VD. In so-called. In "sensorless" systems, the position information is determined by the control system from the instantaneous values ​​of the phase currents.

Information about the position of the rotor is processed by the microprocessor, which, according to the control program, generates control PWM signals. The low-voltage PWM signals from the microcontroller are then converted by a power amplifier (usually a transistor bridge) into power voltages applied to the motor.

The combination of the rotor position sensor and the electronic assembly in the HP and BDPT can be compared with a certain degree of reliability with the brush-collector unit of the DT. However, remember that motors are rarely used outside the drive. Thus, electronic equipment is characteristic of VD almost to the same extent as for DPT.

stator [ | ]

The stator has a traditional design. It consists of a housing, a core made of electrical steel and a copper winding laid in grooves along the perimeter of the core. The winding is divided into phases, which are laid in grooves in such a way that they are spatially shifted relative to each other by an angle determined by the number of phases. It is known that two phases are sufficient for uniform rotation of the motor shaft of an AC machine. Usually synchronous machines, used in HP, are three-phase, however, there are also HP with four- and six-phase windings.

Rotor [ | ]

According to the location of the rotor, brushless motors are divided into intra-rotor (eng. inrunner) and external-rotor (eng. outrunner).

The rotor is made using permanent magnets and usually has two to sixteen pairs of poles with alternating north and south poles.