High power brushless motor. "brushless motors" educational program and design. Features of brushless machines

Published on 11.04.2014

Regulator circuit

The circuit is conditionally divided into two parts: the left one is a microcontroller with logic, the right one is the power part. The power section can be modified to work with motors of a different power or with a different supply voltage.

Controller - ATMEGA168. Gourmets may say that it would be enough and ATMEGA88, A AT90PWM3- it would be “more like Feng Shui”. I just made the first regulator “according to Feng Shui”. If you have the opportunity to apply AT90PWM3- this will be the most suitable choice. But for my ideas, 8 kilobytes of memory was definitely not enough. So I used a microcontroller ATMEGA168.

This scheme was conceived as a test bench. On which it was supposed to create a universal adjustable regulator for working with various “calibers” of brushless motors: both with sensors and without position sensors. In this article I will describe the scheme and principle of operation of the regulator firmware for controlling brushless motors with and without Hall sensors.

Nutrition

The power circuit is separate. Since the key drivers require a 10V to 20V power supply, a 12V power supply is used. The microcontroller is powered through a DC-DC converter assembled on a microcircuit. You can use a linear regulator with an output voltage of 5V. It is assumed that the voltage VD can be from 12V and higher and is limited by the capabilities of the key driver and the keys themselves.

PWM and key signals

At the exit OC0B(PD5) microcontroller U1 PWM signal is generated. It enters the switches JP2, JP3. With these switches, you can select the option of applying PWM to the keys (top, bottom or all keys). In the diagram, the switch JP2 is set to the position for supplying a PWM signal to the upper keys. Switch JP3 on the diagram is set to the position to disable the supply of PWM signal to the lower keys. It is not difficult to guess that if you turn off the PWM on the upper and lower keys, we will get a permanent “full speed ahead” at the output, which can break the engine or the regulator into the trash. Therefore, do not forget to turn on the head, switching them. If you do not need such experiments - and you know which keys you will apply PWM to and which ones not, just do not make switches. After the PWM switches, the signal is fed to the inputs of the logic elements “&” ( U2, U3). The same logic receives 6 signals from the microcontroller pins PB0..PB5, which are control signals for 6 keys. Thus, the logical elements ( U2, U3) impose a PWM signal on the control signals. If you are sure that you will apply PWM, say, only to the lower switches, then unnecessary elements ( U2) can be excluded from the circuit, and the corresponding signals from the microcontroller can be sent to the key drivers. Those. the signals to the drivers of the upper keys will go directly from the microcontroller, and to the lower ones - through the logic elements.

Feedback (motor phase voltage monitoring)

Motor phase voltage W,V,U through resistive dividers W - (R17, R25), V - (R18, R24), U - (R19, R23) arrive at the controller input ADC0(PC0), ADC1(PC1), ADC2(PC2). These pins are used as comparator inputs. (In the example described in AVR444.pdf from company Atmel not comparators are used, but voltage measurement using ADC (ADC). I abandoned this method as the ADC conversion time did not allow for high speed motors.) Resistive dividers are selected in such a way that the voltage applied to the input of the microcontroller does not exceed the allowable voltage. In this case, resistors 10K and 5K are divided by 3. Ie. When the engine is powered by 12V. to the microcontroller will be supplied 12V*5K/(10K+5K)=4V. Reference voltage for the comparator (input AIN1) is supplied from half the motor supply voltage through a divider ( R5, R6, R7, R8). Note that resistors ( R5, R6) at face value are the same as ( R17, R25), (R18, R24),(R19, ​​R23). Further, the voltage is halved by the divider R7, R8, after which it goes to the leg AIN1 internal comparator of the microcontroller. Switch JP1 allows you to switch the reference voltage to the “midpoint” voltage generated by the resistors ( R20, R21, R22). This was done for experiments and did not justify itself. If not in need, JP1, R20, R21, R22 can be excluded from the diagram.

Hall sensors

Since the regulator is universal, it must receive signals from Hall sensors if a motor with sensors is used. It is assumed that Hall sensors are discrete, type SS41. It is also possible to use other types of sensors with a discrete output. Signals from three sensors are received through resistors R11, R12, R13 on switches JP4, JP5, JP6. Resistors R16, R15, R14 act as pull-up resistors. C7, C8, C9- filter capacitors. switches JP4, JP5, JP6 motor feedback type is selected. In addition to changing the position of the switches in the program settings of the controller, you must specify the appropriate type of engine ( Sensorless or Sensored).

Analog signal measurements

At the entrance ADC5(PC5) through the divider R5, R6 supply voltage to the motor. This voltage is controlled by a microcontroller.

At the entrance ADC3(PC3) an analog signal is received from the current sensor. current sensor ACS756SA. This is a current sensor based on the Hall effect. The advantage of this sensor is that it does not use a shunt, which means that it has an internal resistance close to zero, so no heat is generated on it. In addition, the sensor output is analog within 5V, therefore, without any conversion, it is fed to the input of the ADC of the microcontroller, which simplifies the circuit. If you need a sensor with a large current measurement range, you simply replace the existing sensor with a new one, without changing the circuit at all.

If you want to use a shunt with a subsequent amplification scheme, matching - please.

Command signals

Engine speed signal from potentiometer RV1 enters the input ADC4(PC4). Pay attention to the resistor R9- it shunts the signal in the event of a wire break to the potentiometer.

In addition, there is an entrance RC signal, which is universally used in remote-controlled models. The selection of the control input and its calibration is performed in the software settings of the controller.

UART interface

Signals TX, RX are used to adjust the controller and issue information about the state of the controller - engine speed, current, supply voltage, etc. To configure the controller, it can be connected to the USB port of the computer using . Configuration is done through any terminal program. For example: Hyperterminal or Putty .

Other

There are also reverse contacts - microcontroller output PD3. If these contacts are closed before starting the motor, the motor will rotate in the reverse direction.

The LED signaling the state of the regulator is connected to the output PD4.

Power part

Key drivers used IR2101. This driver has one advantage - low price. Suitable for low-current systems, for powerful keys IR2101 will be weak. One driver drives two “N” channel MOSFET transistors (top and bottom). We need three such chips.

The keys must be selected depending on the maximum current and voltage of the motor supply (a separate article will be devoted to the choice of keys and drivers). The diagram shows IR540, in reality we used K3069. K3069 designed for voltage 60V and current 75A. This is a clear overkill, but I got them for free in large quantities (I wish you such happiness too).

Capacitor C19 connected in parallel with the supply battery. The larger its capacity, the better. This capacitor protects the battery from surges and the keys from significant voltage drops. In the absence of this capacitor, you are provided with at least problems with the keys. If you connect the battery directly to VD- a spark can jump. spark quenching resistor R32 used when connected to the battery. Connecting right away – ”batteries, then serve“ + ” to a contact Antispark. Current flows through the resistor and slowly charges the capacitor. C19. After a few seconds, connect the battery contact to VD. With a 12V supply, you can not do Antispark.

Firmware capabilities

• the ability to control motors with and without sensors;
• for a sensorless motor, there are three types of start: without determining the initial position; with the definition of the initial position; combined;
• setting the phase advance angle for a sensorless motor in 1 degree steps;
• the ability to use one of two reference inputs: 1-analog, 2-RC;
• calibration of input signals;
• engine reverse;
• adjusting the regulator via the UART port and receiving data from the regulator during operation (speed, current, battery voltage);
• PWM frequency 16, 32 KHz.
• setting the PWM signal level to start the engine;
• battery voltage control. Two thresholds: limit and cutoff. When the battery voltage drops to the limit threshold, the engine speed decreases. When falling below the cutoff threshold, a complete stop occurs;
• motor current control. Two thresholds: limit and cutoff;
• adjustable damper of the driving signal;
• setting Dead time for keys

Regulator operation

Inclusion

The supply voltage of the regulator and the motor is separate, so the question may arise: in what sequence to apply voltage. I recommend applying voltage to the regulator circuit. And then connect the power supply to the motor. Although the other sequence of problems did not arise. Accordingly, with the simultaneous supply of voltage, there were no problems either.

After turning on, the engine emits 1 short beep (if the sound is not turned off), turns on and the LED is constantly lit. The regulator is ready to work.

To start the engine, increase the value of the setting signal. If a setpoint potentiometer is used, the engine will start when the setpoint voltage reaches approximately 0.14V. If necessary, the input signal can be calibrated, which allows the use of earlier control voltage ranges. By default, the setpoint damper is set. With a sharp jump in the setting signal, the engine speed will increase smoothly. The damper has an asymmetrical characteristic. Resetting occurs without delay. If necessary, the damper can be adjusted or completely disabled.

launch

Starting a sensorless motor is performed with the starting voltage level set in the settings. At the moment of launch, the position of the throttle stick does not matter. If a start attempt fails, the start attempt is repeated until the engine starts to rotate normally. If the engine cannot start within 2-3 seconds, stop trying, remove the gas and proceed to adjust the regulator.

If the motor stalls or the rotor is mechanically jammed, the protection is activated and the regulator tries to restart the motor.

Starting an engine with Hall sensors is also performed using the settings for starting the engine. Those. if you give full throttle to start the engine with sensors, the regulator will supply the voltage specified in the start settings. And only after the motor starts to rotate, full voltage will be applied. This is somewhat unusual for a sensored motor, since such motors are mainly used as traction motors, and in this case it may be difficult to achieve maximum torque at the start. However, this regulator has a feature that protects the engine and regulator from failure if the engine is mechanically jammed.

During operation, the controller outputs data on engine speed, current, battery voltage through the UART port in the following format:

E: minimum battery voltage: maximum battery voltage: maximum current: engine speed (rpm) A: current battery voltage: current current: current engine speed (rpm)

Data is issued at intervals of approximately 1 second. Transfer rate on port 9600.

Regulator setting

To configure the controller, connect it to the computer using . Transfer rate on port 9600.

The transition of the regulator to the adjustment mode occurs when the regulator is turned on, when the setting signal of the potentiometer is greater than zero. Those. To switch the regulator to the setting mode, turn the knob of the setting potentiometer, and then turn on the regulator. The terminal will display a prompt in the form of the symbol “ > “. Then you can enter commands.

The controller accepts the following commands (in different firmware versions, the set of settings and commands may differ):

h- displaying a list of commands;
? - output settings;
c– calibration of the driving signal;
d– Resetting the settings to factory settings.

team " ? ” prints to the terminal a list of all available settings and their value. For example:

motor.type=0 motor.magnets=12 motor.angle=7 motor.start.type=0 motor.start.time=10 pwm=32 pwm.start=15 pwm.min=10 voltage.limit=128 voltage.cutoff =120 current.limit=200 current.cutoff=250 system.sound=1 system.input=0 system.damper=10 system.deadtime=1

You can change the desired setting with the following command:

<настройка>=<значение>

For example:

pwm.start=15

If the command was given correctly, the setting will be applied and saved. You can check the current settings after changing them with the command “ ? “.

Measurements of analog signals (voltage, current) are performed using the ADC of the microcontroller. The ADC operates in 8-bit mode. The measurement accuracy is deliberately underestimated to ensure an acceptable analog signal conversion rate. Accordingly, the controller outputs all analog values ​​in the form of an 8-bit number, i.e. from 0 to 255.

Purpose of settings:

List of settings, their description:

Parameter	Description	Meaning
motor type	motor type	0-Sensorless; 1-Sensored
motor magnets	Number of magnets in the motor rotor. It is used only to calculate the engine speed.	0..255, pcs.
motor angle	Phase advance angle. Used for Sensorless motors only.	0..30, degrees
motor.start.type	Start type. Used for Sensorless motors only.	0-without determining the position of the rotor; 1-with determining the position of the rotor; 2-combined;
motor.start.time	Start time.	0..255, ms
pwm	PWM frequency	16, 32, kHz
pwm.start	PWM value (%) to start the motor.	0..50 %
pwm.min	The value of the minimum PWM value (%) at which the motor rotates.	0..30 %
voltage limit	The battery voltage at which to limit the power supplied to the motor. Indicated in the ADC readings.	0..255*
voltage.cutoff	Battery voltage at which to turn off the engine. Indicated in the ADC readings.	0..255*
current limit	The current at which the power supplied to the motor should be limited. Indicated in the ADC readings.	0..255**
current cutoff	The current at which the motor should be switched off. Indicated in the ADC readings.	0..255**
system.sound	Enable / disable the sound signal emitted by the engine	0-disabled; 1-enabled;
system.input	Command signal	0-potentiometer; 1-RC signal;
system.damper	Input Damping	0..255, conventional units
system.deadtime	Dead Time value for keys in microseconds	0..2, µs

* – numerical value of 8-bit analog-to-digital converter.
Calculated according to the formula: ADC = (U*R6/(R5+R6))*255/5
Where: U- voltage in Volts; R5, R6 is the resistance of the divider resistors in ohms.

The principle of operation of a brushless DC motor (BCDM) has been known for a very long time, and brushless motors have always been an interesting alternative to traditional solutions. Despite this, such electric machines have found wide application in technology only in the 21st century. The decisive factor in the widespread implementation was the multiple reduction in the cost of the BDKP drive control electronics.

Collector Motor Problems

At a fundamental level, the job of any electric motor is to convert electrical energy into mechanical energy. There are two main physical phenomena underlying the design of electrical machines:

The engine is designed in such a way that the magnetic fields created on each of the magnets always interact with each other, giving the rotor rotation. A traditional DC motor consists of four main parts:

• stator (fixed element with a ring of magnets);
• anchor (rotating element with windings);
• carbon brushes;
• collector.

This design provides for the rotation of the armature and the commutator on the same shaft relative to the fixed brushes. The current passes from the source through brushes spring-loaded for good contact to the commutator, which distributes electricity between the armature windings. The magnetic field induced in the latter interacts with the stator magnets, which causes the stator to rotate.

The main disadvantage of the traditional motor is that mechanical contact on the brushes cannot be achieved without friction. As the speed increases, the problem becomes more pronounced. The collector assembly wears out over time and, in addition, is prone to sparking and is able to ionize the surrounding air. Thus, despite the simplicity and low cost of manufacture, such electric motors have some insurmountable disadvantages:

• brush wear;
• electrical interference as a result of sparking;
• restrictions on maximum speed;
• difficulties with cooling a rotating electromagnet.

The appearance of processor technology and power transistors allowed designers to abandon the mechanical switching unit and change the role of the rotor and stator in a DC electric motor.

The principle of operation of the BDKP

In a brushless electric motor, unlike its predecessor, the role of a mechanical switch is performed by an electronic converter. This makes it possible to implement an "inside-out" circuit of the BDKP - its windings are located on the stator, which eliminates the need for a collector.

In other words, the main fundamental difference between a classical motor and a BDCT is that instead of stationary magnets and rotating coils, the latter consists of stationary windings and rotating magnets. Despite the fact that the switching itself takes place in a similar way, its physical implementation in brushless drives is much more complex.

The main issue is the precise control of a brushless motor, which implies the correct sequence and frequency of switching of individual winding sections. This problem is constructively solvable only if it is possible to continuously determine the current position of the rotor.

The necessary data for processing by electronics is obtained in two ways:

• detection of the absolute position of the shaft;
• measuring the voltage induced in the stator windings.

To implement control in the first way, either optical pairs or Hall sensors fixed to the stator, which react to the magnetic flux of the rotor, are most often used. The main advantage of such systems for collecting information about the position of the shaft is their performance even at very low speeds and at rest.

Sensorless control to evaluate the voltage in the coils requires at least a minimum rotation of the rotor. Therefore, in such designs, a mode of starting the engine up to speed is provided, at which the voltage on the windings can be estimated, and the rest state is tested by analyzing the effect of the magnetic field on the test current pulses passing through the coils.

Despite all these design difficulties, brushless motors are gaining more and more popularity due to their performance and a set of characteristics inaccessible to collectors. A short list of the main advantages of BDKP over the classic ones looks like this:

• no mechanical energy loss due to brush friction;
• comparative noiselessness of work;
• ease of acceleration and deceleration of rotation due to the low inertia of the rotor;
• rotation control accuracy;
• the possibility of organizing cooling due to thermal conductivity;
• ability to work at high speeds;
• durability and reliability.

Modern application and prospects

There are many devices for which increasing uptime is critical. In such equipment, the use of BDCT is always justified, despite their relatively high cost. These can be water and fuel pumps, cooling turbines for air conditioners and engines, etc. Brushless motors are used in many models of electric vehicles. Currently, brushless motors have received serious attention from the automotive industry.

BDKP are ideal for small drives operating in difficult conditions or with high accuracy: feeders and belt conveyors, industrial robots, positioning systems. There are areas in which brushless motors dominate uncontested: hard drives, pumps, silent fans, small appliances, CD / DVD drives. The low weight and high power output have made the BDCT also the basis for the production of modern cordless hand tools.

It can be said that significant progress is now being made in the field of electric drives. The continued fall in the price of digital electronics has created a trend towards the widespread use of brushless motors to replace traditional ones.

Brushless motors are quite common today. These devices are most often used with electric drives. They can also be found on various refrigeration equipment. In the industrial sector, they are involved in heating systems.

Additionally, brushless modifications are installed in conventional fans for air conditioning. Nowadays, there are many models on the market with and without sensors. At the same time, according to the type of regulators, the modifications are quite different. However, in order to understand this issue in more detail, it is necessary to study the structure of a simple engine.

Brushless model device

If we consider a conventional three-phase brushless motor, then a copper-type inductor is installed in it. Stators are used both wide-width and pulse. Their teeth are of different sizes. As mentioned earlier, there are models with sensors, as well as without them.

Blocks are used to fix the stator. The induction process itself occurs due to the stator winding. Rotors are most often used of the bipolar type. They have steel cores. To fix the magnets on the models there are special grooves. The direct control of the brushless motor occurs with the help of regulators, which are located at the stator. To supply voltage to the external winding, insulating gates are installed in the devices.

Two digit models

Collectorless el. motors of this type are often used in freezing equipment. At the same time, a wide variety of compressors are suitable for them. On average, the power of the model can reach 3 kW. The circuit of a brushless coil motor most often includes a double type with a copper winding. Stators are installed only pulse. Depending on the manufacturer, the length of the teeth may vary. Sensors are used both electrical and inductive type. For heating systems, these modifications are bad.

It should also be borne in mind that the cores in brushless motors are mainly steel. At the same time, the grooves for the magnets are used quite wide, and they are located very close to each other. Due to this, the frequency of devices can be high. Regulators for such modifications are selected most often of a single-channel type.

Three-digit modifications

Three-bit brushless motor is great for ventilation systems. His sensors are usually of the electrical type. In this case, the coils are installed quite wide. Due to this, the induction process is carried out quickly. In this case, the frequency of the device depends on the stator. The winding is most often of the copper type.

Three-digit brushless motors can withstand the maximum voltage at a level of 20 V. Thyristor modifications are quite rare nowadays. It should also be noted that the magnets in such configurations can be mounted on both the outer and inner side of the rotor plate.

Do-it-yourself four-digit modifications

Making a four-bit brushless motor with your own hands is absolutely simple. To do this, you must first prepare a plate with grooves. The thickness of the metal in this case should be approximately 2.3 mm. The grooves in this situation must be at a distance of 1.2 cm. If we consider a simple model, then the coil should be selected with a diameter of 3.3 cm. At the same time, it must withstand the threshold voltage at 20 V.

Pads for the device are most often selected steel. In this case, much depends on the size of the rotor plate. The stator itself must be used with a double winding. In this case, it is important to prepare the core of a steel type. If we consider modifications without regulators, then you can complete the assembly of a brushless motor by installing an insulating gate. In this case, the contacts of the device must be brought to the outer side of the plate. For a conventional fan, such brushless models are ideal.

Devices with ABP2 regulator

A brushless motor with regulators of this type is very popular today. These systems are most suitable for air conditioning devices. They are also widely used in the industrial field for refrigeration equipment. They are able to work with electric drives of various frequencies. Their coils are most often installed of a double type. In this case, stators can only be found pulsed. In turn, latitudinal modifications are not very common.

Sensors in brushless motors with regulators of this series are used only inductive. In this case, the frequency of the device can be monitored by the display system. The pads, as a rule, are installed in a contact type, and they can be mounted directly on the stator plate. The controller of the brushless motor in this case allows you to change the frequency quite smoothly. This process occurs by changing the output voltage parameter. In general, these modifications are very compact.

Engines with AVR5 regulators

This series of brushless motor with governor is often used in the industrial field to control various electrical appliances. In household devices, it is installed quite rarely. A feature of such brushless modifications can be called an increased frequency. At the same time, it is easy to change the power parameter for them. Coils in these modifications are very diverse. It should also be noted that magnets are most often installed on the outside of the rotor box.

The closures are mainly used insulated type. They can be mounted both at the stator box and the core. In general, the adjustment of the device is quite fast. However, the disadvantages of such systems should also be taken into account. First of all, they are associated with power outages at low frequencies. It is also important to mention that models of this type have a rather high power consumption. At the same time, the devices are not suitable for controlling integrated electric drives.

Using ABT6 controls

This type of brushless motor speed controller is in great demand today. Its distinctive feature can be safely called versatility. Regulators are installed, as a rule, on brushless motors, the power of which does not exceed 2 kW. At the same time, these devices are ideal for controlling ventilation systems. Controllers in this case can be installed in a variety of ways.

The signal transmission rate in this case depends on the type of control system. If we consider thyristor modifications, then they have a fairly high conductivity. However, they rarely have problems with magnetic interference. It is quite difficult to assemble a model of this type on your own. In this situation, the shutters are most often selected non-insulated.

Models with Hall effect sensors

Hall sensor brushless motors are widely used in heating applications. At the same time, they are suitable for electric drives of various classes. Only single-channel regulators are used directly. Coils in the device are installed copper type. In this case, the size of the teeth of the model depends solely on the manufacturer. Directly pads for devices are selected contact type. To date, sensors are most often installed on the stator side. However, models with their lower location are also on the market. In this case, the dimensions of the brushless motor will be slightly large.

Low frequency modifications

The low-frequency brushless motor is actively used today in the industrial field. At the same time, it is ideal for freezers. On average, its efficiency parameter is at the level of 70%. The shutters of the models are most often used with insulators. At the same time, thyristor modifications are quite common in our time.

Control systems are used by the ABP series. In this case, the frequency of the model depends on the type of core and not only. It should also be borne in mind that there are models with double rotors. In this case, the magnets are located along the plate. Stators are most often used with copper windings. At the same time, low-frequency brushless motors with sensors are very rare.

High frequency motors

These modifications are considered the most popular for resonant electric drives. In industry, such models are quite common. Their sensors are installed both electronic and inductive type. In this case, the coils are most often located on the outer side of the plate. Rotors are mounted both in horizontal and vertical position.

Directly changing the frequency of such devices is carried out through controllers. They are installed, as a rule, with a complex contact system. Directly, starters are used only of a double type. In turn, control systems depend on the power of the brushless device.

A DC motor is an electric motor that is powered by direct current. 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 brought to the stator through a hollow axis of which is less than 0.5 mm.

An AC motor is called electric motor powered by alternating current. There are the following types of AC motors:

There is also a UKD (universal commutator motor) with the function of operating mode both on alternating and direct current.

Another type of engine is stepper motor with a finite number of rotor positions. A certain indicated position of the rotor is fixed by supplying power to the necessary corresponding windings. When the supply voltage is removed from one winding and transferred to others, a process of transition to another position occurs.

An AC motor when powered by a commercial network usually does not achieve speeds of more than three thousand revolutions per minute. For this reason, when it is necessary to obtain higher frequencies, a collector motor is used, the additional advantages of which are lightness and compactness while maintaining the required power.

Sometimes a special transmission mechanism called a multiplier is also used, which changes the kinematic parameters of the device to the required technical indicators. Collector assemblies sometimes occupy up to half the space of the entire motor, so AC motors are reduced in size and made lighter in weight through the use of a frequency converter, and sometimes due to the presence of a network with an increased frequency of up to 400 Hz.

The resource of any asynchronous AC motor is noticeably higher than the collector one. It is determined state of insulation of windings and bearings. A synchronous motor, when using an inverter and a rotor position sensor, is considered an electronic analogue of a classic collector motor that supports DC operation.

Brushless DC motor. General information and device device

A brushless DC motor is also called a three-phase brushless motor. It is a synchronous device, the principle of operation of which is based on self-synchronized frequency regulation, due to which the vector (starting from the position of the rotor) of the stator magnetic field is controlled.

These types of motor controllers are often powered by DC voltage, hence the name. In the English-language technical literature, the brushless motor is called PMSM or BLDC.

The brushless motor was created primarily to optimize the any DC motor generally. Very high demands were placed on the actuator of such a device (especially on a high-speed microdrive with precise positioning).

This, perhaps, led to the use of such specific DC devices, brushless three-phase motors, also called BLDTs. By their design, they are almost identical to AC synchronous motors, where the rotation of the magnetic rotor occurs in a conventional laminated stator in the presence of three-phase windings, and the number of revolutions depends on the voltage and loads of the stator. Based on certain coordinates of the rotor, different stator windings are switched.

Brushless DC motors can exist without any separate sensors, however, they are sometimes present on the rotor, such as a Hall sensor. If the device works without an additional sensor, then stator windings act as a fixing element. Then the current arises due to the rotation of the magnet, when the rotor induces an EMF in the stator winding.

If one of the windings is turned off, then the signal that was induced will be measured and further processed, however, such a principle of operation is impossible without a signal processing professor. But to reverse or brake such an electric motor, a bridge circuit is not needed - it will be enough to supply control pulses in the reverse sequence to the stator windings.

In the VD (switched motor), the inductor in the form of a permanent magnet is located on the rotor, and the armature winding is on the stator. Based on the position of the rotor, the supply voltage of all windings is formed electric motor. When used in such constructions of the collector, its function will be performed in the valve motor by a semiconductor switch.

The main difference between synchronous and brushless motors is the self-synchronization of the latter with the help of DPR, which determines the proportional frequency of rotation of the rotor and the field.

Most often, a brushless DC motor finds application in the following areas:

stator

This device has a classic design and resembles the same device of an asynchronous machine. The composition includes copper winding core(laid around the perimeter into the grooves), which determines the number of phases, and the housing. Usually, the sine and cosine phases are sufficient for rotation and self-starting, however, often the valve motor is made three-phase and even four-phase.

Electric motors with reverse electromotive force according to the type of coiling on the stator winding are divided into two types:

• sinusoidal form;
• trapezoidal shape.

In the corresponding types of motor, the electric phase current also changes according to the method of supply sinusoidally or trapezoidal.

Rotor

Usually the rotor is made of permanent magnets with two to eight pairs of poles, which, in turn, alternate from north to south or vice versa.

The most common and cheapest for the manufacture of the rotor are ferrite magnets, but their disadvantage is low level of magnetic induction, therefore, devices made from alloys of various rare earth elements are now replacing this material, since they can provide a high level of magnetic induction, which, in turn, allows to reduce the size of the rotor.

DPR

The rotor position sensor provides feedback. According to the principle of operation, the device is divided into the following subspecies:

• inductive;
• photoelectric;
• Hall effect sensor.

The latter type is the most popular due to its almost absolute inertialess properties and the ability to get rid of the delay in the feedback channels by the position of the rotor.

Control system

The control system consists of power switches, sometimes also of thyristors or power transistors, including an insulated gate, leading to the collection of a current inverter or a voltage inverter. The process of managing these keys is most often implemented by using a microcontroller, which requires a huge amount of computational operations to control the engine.

Principle of operation

The operation of the engine lies in the fact that the controller switches a certain number of stator windings in such a way that the vector of the magnetic fields of the rotor and stator are orthogonal. With PWM (Pulse Width Modulation) the controller controls the current flowing through the motor and regulates the torque exerted on the rotor. The direction of this acting moment is determined by the mark of the angle between the vectors. Electrical degrees are used in calculations.

Switching should be carried out in such a way that Ф0 (rotor excitation flux) is kept constant relative to the armature flux. When such excitation and the armature flow interact, a torque M is formed, which tends to turn the rotor and in parallel ensure the coincidence of the excitation and the armature flow. However, during the rotation of the rotor, the various windings are switched under the influence of the rotor position sensor, as a result of which the armature flux turns towards the next step.

In such a situation, the resulting vector shifts and becomes stationary with respect to the rotor flux, which, in turn, creates the necessary torque on the motor shaft.

Engine management

The controller of a brushless DC electric motor regulates the moment acting on the rotor by changing the value of the pulse-width modulation. Switching is controlled and carried out electronically, unlike a conventional brushed DC motor. Also common are control systems that implement pulse-width modulation and pulse-width regulation algorithms for the workflow.

Vector controlled motors provide the widest known range for self speed control. The regulation of this speed, as well as maintaining the flux linkage at the required level, is due to the frequency converter.

A feature of the regulation of the electric drive based on vector control is the presence of controlled coordinates. They are in a fixed system and converted to rotating, highlighting a constant value proportional to the controlled parameters of the vector, due to which a control action is formed, and then a reverse transition.

Despite all the advantages of such a system, it is also accompanied by a disadvantage in the form of the complexity of controlling the device for controlling the speed in a wide range.

Advantages and disadvantages

Nowadays, in many industries, this type of motor is in great demand, because the brushless DC motor combines almost all the best qualities of non-contact and other types of motors.

The undeniable advantages of the brushless motor are:

Despite significant positives, brushless DC motor also has a few disadvantages:

Based on the foregoing and the underdevelopment of modern electronics in the region, many still consider it appropriate to use a conventional asynchronous motor with a frequency converter.

Three-phase brushless DC motor

This type of motor has excellent performance, especially when performing control by means of position sensors. If the moment of resistance varies or is not known at all, and also if it is necessary to achieve higher starting torque sensor control is used. If the sensor is not used (usually in fans), the control eliminates the need for wired communication.

Features of controlling a three-phase brushless motor without a position sensor:

Control Features three-phase brushless motor with position encoder using the example of a Hall effect sensor:

Conclusion

A brushless DC motor has a lot of advantages and will be a worthy choice for use by both a specialist and a simple layman.

Household and medical appliances, aeromodelling, pipe shut-off drives for gas and oil pipelines - this is not a complete list of applications for 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 a high rotation speed, therefore they are used in cooling systems, as power plants for drones, etc. External rotor drives are used where precise positioning and torque tolerance are required (robotics, medical equipment, CNC machines, etc.).

Principle of operation

Unlike other drives, for example, an asynchronous AC machine, a special controller is required for the operation of the DB, 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 stator winding of a brushless motor. 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 DU both in design features (see Fig. 5.) and in the principle of operation.

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

Let's take a look at the design differences. Figure 5 shows that the rotor (1 in Fig. 5) of a collector-type motor, unlike a brushless one, has coils that have a simple winding scheme, and permanent magnets (usually two) are installed 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 of 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 is also worth noting that in some drives of this type, for more efficient control, the positions of the rotor 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 select it according to the following characteristics inherent in 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 a 6-magnet motor, the rotational speed will be 60000/3=20000 prm.
• The frequency of the generated pulses, for most controllers, this parameter ranges 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 DC to three-phase pulse converter (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. The appearance of 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.
• Quick set to maximum rotation speed.
• 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. A significant drawback that limits the use of databases is 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.