The most comprehensive brushless motor information, an article to help you understand its control principle

What technologies are there in the brushless motors we commonly use? How to explain those professional terms? What are the differences and connections between various parameters and devices?

Basic Concepts of Brushless Motors

According to the structure and working principle of the motor, we can divide the motor into brushed motor, inner rotor brushless motor and outer rotor brushless motor.

Brushed motor: We also call it DC motor or carbon brush motor. It is the oldest type of motor and the most common type of motor at present. When the motor is working, the coil and commutator rotate, while the magnet and carbon brush do not rotate. The alternating change of the direction of the coil current is completed by the commutator and brushes that rotate with the motor. This type of motor has the advantages of relatively low cost, high torque, simple structure, and easy maintenance. However, due to structural limitations, the disadvantages are also obvious:1. Sparks generated by mechanical commutation cause friction between the commutator and brushes, electromagnetic interference, high noise, and short life.；2. Complex structure, poor reliability, frequent failures, and frequent maintenance required；3. Due to the existence of the commutator, the further decrease of the rotor inertia is limited, affecting the dynamic performance. Therefore, in the model industry, it is mainly used in car models and ship models with slow speeds and insensitive to vibrations, and brushless motors are rarely used in aircraft models.

Brushless motor: This is the most commonly used motor in the model industry besides the brushed motor. The brushless DC motor does not use a mechanical brush device, but uses a square wave self-controlled permanent magnet synchronous motor, replaces the carbon brush commutator with a Hall sensor, and uses neodymium iron boron as the permanent magnet material of the rotor. It has great performance advantages over conventional DC motors. It has the advantages of high efficiency, low energy consumption, low noise, ultra-long life, high reliability, servo control, and stepless frequency conversion speed regulation. As for the disadvantages,...It is more expensive and difficult to maintain than brushed ones. It is widely used in model airplanes, high-speed car models and ship models.

However, a single brushless motor is not a complete power system. A brushless motor must be controlled by a brushless controller, or an electronic controller, to achieve continuous operation. Ordinary carbon brush motors rotate windings, while brushless motors, whether they are outer rotor structures or inner rotor structures, rotate magnets. Therefore, any motor is composed of a stator and a rotor.

The stator of a brushless motor is the part that generates a rotating magnetic field and supports the rotor to rotate. It is mainly composed of silicon steel sheets, enameled wires, bearings, and supports. The rotor is the part that adheres the NdFeB magnets and rotates under the action of the stator's rotating magnetic field. It is mainly composed of a shaft, magnets, and supports. In addition, the number of magnetic poles formed by the stator and rotor also affects the speed and torque of the motor.

The structure of brushless motor

The front cover, middle shell and rear cover of the brushless motor are mainly integral structural parts, which play the role of constructing the overall structure of the motor. However, the outer shell of the outer rotor brushless motor is also the magnetic path of the magnet, so the outer shell must be made of magnetically conductive materials. The outer shell of the inner rotor is only a structural part, so there is no material limit. However, the inner rotor motor has one more rotor core than the outer rotor motor, and the role of this rotor core is also to serve as a magnetic path.

Magnet: It is installed on the rotor and is an important component of the brushless motor. Most of the performance parameters of the brushless motor are related to the magnet, including power, speed, torque, etc.

Silicon steel sheet: It is an important component of slotted brushless motor. Of course, slotless brushless motor does not have silicon steel sheet, but most brushless motors have slots. Its role in the whole system is mainly to reduce magnetic resistance and participate in magnetic circuit operation.

Shaft: It is the direct force-bearing part of the motor rotor. The hardness of the shaft must be able to meet the requirements of high-speed rotation of the rotor.

Bearings: They are the guarantee for the smooth operation of the motor. Bearings can be divided into sliding bearings and rolling bearings. Rolling bearings can be further divided into ten categories: deep groove ball bearings, needle roller bearings and angular contact bearings. Currently, most brushless motors use deep groove ball bearings.

Working Principle of Brushless DC Motor

The brushless DC motor power system consists of three parts: rotor, stator and position sensor. The position sensor commutates the current of the stator winding in a certain order according to the change of the rotor position.(That is, the position of the rotor pole relative to the stator winding is detected, and a position sensing signal is generated at a certain position. After being processed by the signal conversion circuit, the power switch circuit is controlled to switch the winding current according to a certain logical relationship.) The working voltage of the stator winding is provided by the electronic switch circuit controlled by the position sensor output.

There are three types of position sensors: magnetic, photoelectric and electromagnetic.

A DC brushless motor using a magnetic position sensor, the magnetic sensor device(For example, Hall element, magnetic sensitive diode, magnetic sensitive diode, magnetic sensitive resistor or special integrated circuit, etc.) is installed on the stator assembly to detect the changes in the magnetic field generated when the permanent magnet and rotor rotate.

The DC brushless motor using photoelectric position sensor has photoelectric sensor components configured at certain positions on the stator assembly, a shading plate installed on the rotor, and a light-emitting diode or a small bulb as the light source. When the rotor rotates, due to the effect of the shading plate, the photosensitive components on the stator will generate pulse signals at a certain frequency.

The brushless DC motor using electromagnetic position sensor is an electromagnetic sensor component installed on the stator assembly.(such as coupling transformer, proximity switch, LC resonant circuit, etc.). When the permanent magnet rotor position changes, the electromagnetic effect will cause the electromagnetic sensor to generate a high-frequency modulated signal (whose amplitude changes with the rotor position).

In simple terms, a brushless DC motor relies on changing the alternating frequency and waveform of the current wave input to the stator coil of the brushless motor to form a magnetic field around the winding coil that rotates around the geometric axis of the motor. This magnetic field drives the permanent magnets on the rotor to rotate, and the motor rotates. The performance of the motor is related to factors such as the number of magnets, the magnetic flux intensity of the magnets, and the size of the motor input voltage. It is also closely related to the control performance of the brushless motor, because the input is direct current, and the current needs to be converted by an electronic speed regulator.Three-phase AC power is also needed to receive control signals from the remote control receiver to control the speed of the motor to meet the needs of model use.

In general, the structure of a brushless motor is relatively simple, and what really determines its performance is the brushless electronic speed regulator (also known as the ESC). A good ESC requires overall control of processes such as microcontroller control program design, circuit design, and complex processing technology, so generally speaking, its price is much higher than that of a brushless motor.

First, let me review a few basic rules: the left-hand rule, the right-hand rule, and the right-hand spiral rule. Don't be confused, I'll explain them to you below.

The left-hand rule is the basis for analyzing the forces acting on motor rotation. Simply put, a current-carrying conductor in a magnetic field will be affected by a force.

Let the magnetic lines of force pass through the front of the palm, with the direction of the fingers being the direction of the current, and the direction of the thumb being the direction of the magnetic force. I believe that people who like to play with models have a certain basic knowledge of physics, haha.

The right-hand rule is the basis for generating induced electromotive force. It is the opposite of the left-hand rule. The conductor in the magnetic field generates electromotive force by cutting the magnetic lines of force due to the traction.

Let the magnetic flux lines pass through the palm of your hand, with the direction of the thumb as the direction of movement and the direction of the fingers as the direction of the generated electromotive force. Why do we need to talk about induced electromotive force? I wonder if you have had similar experiences. When you put the three-phase wires of a motor together and turn the motor by hand, you will find that the resistance is very large. This is because the induced electromotive force is generated in the process of turning the motor, which generates current. The current in the magnetic field flows through the conductor and generates a force opposite to the direction of rotation, so you will feel a lot of resistance to rotation. If you don't believe it, you can try it.

The three-phase wires are separated, and the motor can rotate easily

The three-phase line is combined, and the motor rotation resistance is very large

Right-hand screw rule: Hold the energized solenoid with your right hand and bend your four fingers in the same direction as the current. Then the end pointed by your thumb is the end of the energized solenoid.N pole.

This rule is the basis for determining the polarity of an energized coil. The direction of the red arrow is the direction of the current.

After reading the three major laws, let's take a look at the basic principles of motor rotation.

Part 1: DC Motor Model

We found a model of a DC motor that we learned in high school physics and performed a simple analysis using the magnetic circuit analysis method.

state1

When current is passed through the coils at both ends, according to the right-hand screw rule, an external magnetic induction intensity pointing to the right is generated.B (as shown in the direction of the thick arrow), and the middle rotor will try to keep the direction of its internal magnetic flux lines consistent with the direction of the external magnetic flux lines to form a shortest closed magnetic flux line loop, so that the inner rotor will rotate in a clockwise direction.

When the direction of the rotor magnetic field is perpendicular to the direction of the external magnetic field, the rotor is subjected to the maximum torque.The "torque" is the largest, not the "force". It is true that when the rotor magnetic field is in the same direction as the external magnetic field, the magnetic force on the rotor is the largest, but at this time the rotor is horizontal and the lever arm is 0, so of course it will not rotate. In addition, the torque is the product of the force and the lever arm. If one of them is zero, the product is zero.

When the rotor turns to the horizontal position, although it is no longer affected by the torque, it will continue to rotate clockwise due to inertia. At this time, if the current direction of the two solenoids is changed, as shown in the figure below, the rotor will continue to rotate forward clockwise.。

state2

By constantly changing the direction of the current in the two solenoids, the inner rotor will keep turning. This action of changing the direction of the current is called commutation. One more thing to add: when commutation occurs is only related to the position of the rotor, and has no direct relationship with any other quantity.

Part 2: Three-phase two-pole inner rotor motor

Generally speaking, the three-phase winding of the stator has star connection and delta connection.The "two-two conduction method of three-phase star connection" is the most commonly used, and this model is used here to make a simple analysis.

The figure above shows the connection of the stator winding (the rotor is not drawn and is assumed to be a two-pole magnet). The three windings are connected through the central connection point.The motor is connected in a "Y" shape. The three wires A, B, and C are connected together. When they are powered on in pairs, there are 6 situations, namely AB, AC, BC, BA, CA, and CB. Note that there is a sequence.

I'll look at it belowPhase 1:AB phase is energized

whenWhen the AB phase is energized, the direction of the magnetic flux generated by the A-pole coil is shown by the red arrow, and the direction of the magnetic flux generated by the B-pole coil is shown by the blue arrow. The direction of the resultant force is shown by the green arrow. If there is a two-pole magnet, then according to "the rotor in the middle will try to keep the direction of its internal magnetic flux lines consistent with the direction of the external magnetic flux lines", the direction of the N-pole will coincide with the direction shown by the green arrow. As for C, it has nothing to do with it for now.

Phase 2:AC phase energization

Phase 3:BC phase is energized

Phase 3:BA phase is powered

To save space, we will not describe them one by one.The CA\CB model can be deduced by yourself. The following is the state diagram of the middle magnet (rotor):

Each process rotor rotates60 degrees

Six processes complete a complete rotation, among which6 commutations.

Part 3: Three-phase multi-winding multi-pole inner rotor motor

Let's look at a more complicated one.(a) is a three-phase nine-winding six-pole (three-pole pair) inner rotor motor, and its winding connection method is shown in Figure (b). As can be seen from Figure (b), its three-phase windings are also connected together at the midpoint, which is also a star connection method. Generally speaking, the number of windings in a motor is inconsistent with the number of permanent magnet poles (for example, 9 windings and 6 poles are used instead of 6 windings and 6 poles). This is to prevent the stator teeth from attracting and aligning with the rotor magnets.

The principle of its movement is: the rotorThe N pole tends to align with the S pole of the energized winding, and the S pole of the rotor tends to align with the N pole of the energized winding.

That isS and N attract each other. Note that there are certain differences from the previous analysis method.

Okay, let me analyze it for you again.。

Phase 1:AB phase is energized

Phase 2:AC phase energization

Phase 3:BC phase is energized

Phase 4:BA powered on

Phase 5:CA Power On

Phase 6:CB powered

The above are six different power-on states, which go through five rotation processes. Each process is20 degrees.

Part 4: Outer rotor brushless DC motor

After looking at the structure of the inner rotor brushless DC motor, let's look at the outer rotor. The difference is that the outer rotor motor makes the magnetic steel originally in the center into pieces and sticks them to the outer shell. When the motor is running, it is the entire outer shell that rotates, while the coil stator in the middle does not move. The outer rotor brushless DC motor has a much larger moment of inertia than the inner rotor (because the main mass of the rotor is concentrated on the outer shell), so the speed is slower than the inner rotor motor, usuallyThe KV value is between several hundred and several thousand. It is also the brushless motor mainly used in model airplanes.。

Brushless motorThe KV value is defined as: speed/V, which means that the speed value of the brushless motor's idling speed increases for every 1 volt increase in input voltage. For example, for an outer rotor brushless motor with a nominal value of 1000KV, under the voltage condition of 11 volts, the maximum no-load speed is: 11000rpm (rpm means: revolutions per minute).

Brushless motors of the same series and dimensions will show different performances depending on the number of winding turns.KV characteristics. The more turns the winding has, the lower the KV value, the lower the maximum output current, and the higher the torque; the fewer turns the winding has, the higher the KV value, the higher the maximum output current, and the lower the torque. I have previously tested the current limit of the 2204 motor of the drone, and a single motor can reach 25A, while the 2212 series motors cannot even reach 15A.

The structure of the outer rotor brushless DC motor:

The analysis method is similar to that of the inner rotor motor. You can analyze it yourself and judge the coil according to the right-hand screw theorem.N/S pole, the N pole of the rotor permanent magnet and the S pole of the stator winding tend to align (attract), and the S pole of the rotor permanent magnet and the N pole of the stator winding tend to align (attract), thereby driving the motor to rotate.

Classic brushless motor22121000kv motor structure analysis.

PicturedDJI2312S motor and XXD2212 motor (anatomy diagram)

Its structure is as follows: the stator winding is fixed on the base, the rotating shaft and the housing are fixed together to form the rotor, and the bearing is inserted in the middle of the stator.

Picturedxxd2212 coil disassembly diagram

Pictured12 windings and 14 poles (i.e. 7 pairs of poles), motor winding diagram.

Draw it laterFrom the six two-phase power-on situations, it can be seen that although the number of windings and magnetic poles can vary in many ways, from the perspective of electronic control, the power-on sequence is actually the same, that is, whether it is an outer rotor or inner rotor motor, the power-on and phase change are carried out in the order of AB->AC->BC->BA->CA->CB.

Of course, if you want the motor to reverse, the electronic method is to power it in reverse order; the physical method is to simply swap any two wires.If A and B are swapped, the order will be BA->BC->AC->AB->CB->CA. Have you noticed that the order is completely reversed here?

AB phase is energized

AC phase energization

BC phase is energized

BA Communication

CA communication

CB phase is energized

It should be noted that since each lead wire is connected to two windings at the same time, the current flows in two ways. To simplify the problem as much as possible, the following figures only show the current direction of the main way, and the other way is not shown. The specific situation of the other way will be analyzed later, which involves the circuit detection of the commutation position.

Professional terms in brushless motors

Rated voltage: This is the working voltage suitable for brushless motors. In fact, the working voltage suitable for brushless motors is very wide. The rated voltage is obtained by specifying the load conditions. For example,The 2212-850KV motor specifies the load of 1045 propellers, and its rated working voltage is 11V. If the load is reduced, such as with 7040 propellers, then this motor can work at 22V voltage. However, this working voltage is not infinitely increased, mainly subject to the maximum frequency supported by the electronic controller. Therefore, the rated working voltage is determined by the working environment.

KV value: The rated speed of brushed DC motors is marked according to the rated working voltage. The concept of KV value is introduced for brushless motors, which allows users to intuitively know the specific speed of brushless motors under specific working voltages. Actual speed = KV value * working voltage. This is the actual meaning of KV, which is the speed per minute under 1V working voltage. The speed of brushless DC motors is directly proportional to the voltage, and the speed of the motor will increase linearly as the voltage increases. For example, the speed of a 2212-850KV motor at 10V voltage is: 850*10=8500RPM (RPM, speed per minute).

Torque:(Torque, torque) The driving torque generated by the rotor in the motor can be used to drive the mechanical load. We can understand the power of the motor.

Speed: The speed of the motor per minute, generally usedRPM indicates.

Maximum current: The maximum current that the motor can withstand and work safely

Maximum power: The maximum power that the motor can withstand and work safelypower= voltage * current

Brushless Motor Power and Efficiency

We can simply understand it as the motor output power= speed * torque. Under the same power, torque and speed are in a trade-off relationship. That is, the higher the speed of the same motor, the lower its torque, and vice versa. It is impossible to require a motor with a higher speed and a higher torque. This rule applies to all motors. For example: a 2212-850KV motor can drive a 1045 propeller at 11V. If the voltage is doubled, its speed is also doubled. If the load is still 1045 propellers, the motor will soon burn out due to the sharp increase in current and temperature.

Each motor has its own upper limit, and the maximum power is this upper limit. If the working condition exceeds this maximum power, the motor will burn out due to high temperature. Of course, this maximum power is also obtained under the specified working voltage. If it is under a higher working voltage, the reasonable maximum power will also increase. This is because:Q=I2R, the heat generated by the conductor is proportional to the square of the current. At a higher voltage, if the power is the same, the current will decrease, resulting in less heat and an increase in the maximum power. This also explains why professional aerial photography aircraft use a large number of 22.2V or even 30V batteries to drive multi-axis aircraft. The brushless motor under high voltage has a small current, less heat and higher efficiency.

People often ask:What is the difference between 2208 1000KV and 2216 1000KV? They are both 1000KV, aren't they the same? Haha, there is a big difference.

In motor diameter,Under the same KV value, the higher the motor, the greater the power. The greater the power, the greater the load. For example, a man weighs 100 jin and a man weighs 160 jin. You ask them to carry a bag of 50 jin rice. The 100-jin man can carry it even though it is a little bit difficult, while the 160-jin man thinks it is a piece of cake. But, what if you ask them to carry two bags of rice? The 160-jin man can carry it with gritted teeth, but the 100-jin man may not even be able to straighten his back. This is their difference. For motors, the easier the work, the higher the efficiency. Using the previous theory, the iron loss is low and the copper loss is low.

Remember this formula: Torque is proportional to the square of the current

As the motor works harder and harder, its efficiency will decrease rapidly. Therefore, when choosing a multi-axis motor, you must choose a motor with the right power and a propeller to match it so that the motor can work in a relatively relaxed state. Generally speaking, the working power is the maximum power when hovering.30-45% is better. You can't use a small ox to pull a big cart, nor can you use a big ox to pull a small cart.

Relationship between brushless motor voltage and efficiency

Here are two formulas:
1. Power = voltage * current
2. Heat generation = current square * resistance

Two conclusions can be drawn from the formula: Under the same power, the higher the voltage, the smaller the current, and it can be deduced that under the same power, the higher the voltage, the smaller the heat generated. It can be concluded that for the same aircraft, the higher the voltage used, the smaller the current and the less heat generated, the higher the efficiency.

Now I know why high voltage wires are installedIt’s a high voltage of 100KV or even 220KV or 550KV (KV stands for kilovolts).

Of course, aircraft need batteries to drive them, to be more precise, lithium batteries. The number of lithium batteries depends on the size of the battery. The larger the battery, the higher the voltage. So in terms of voltage, there is not much we can do, because many batteries on the market are serialized, for exampleFor a model like 450, you can look for 6S batteries for 450 helicopters, but the price is very high, and the required ESC is also more expensive. So what we should do in terms of voltage is: try to avoid using low-voltage batteries for large models, which will cause the working current to be relatively high, resulting in greater copper consumption. At the same time, we should also avoid using high-voltage batteries for small aircraft, as the battery weight is too large.

About the number of magnetic pole pairs of brushless motor

The rotation speed of the magnetic field is also called the synchronous speed, which is related to the frequency of the three-phase current and the number of magnetic poles.p. If the stator winding has only one pair of magnetic poles (pole pair number p=1) at any time, that is, only two magnetic poles, for a rotating magnetic field with only one pair of magnetic poles, the three-phase current changes one cycle, and the synthetic magnetic field also rotates one cycle. If it is 50hz alternating current, the synchronous speed of the rotating magnetic field is 50 rpm or 3000 rpm. In engineering technology, revolutions per minute (r/min) are often used to represent the speed. If the magnetic field composed of the stator winding has two pairs of magnetic poles (pole pair number p=2), that is, there are four magnetic poles, it can be proved that when the current changes for one cycle, the synthetic magnetic field rotates 180 degrees in space. From this, it can be generalized that the synchronous speed of the rotating magnetic field with p pairs of magnetic poles per minute is n=60f/p.

When the number of magnetic pole pairs is constant, if the frequency of the alternating current is changed, the synchronous speed of the rotating magnetic field can be changed. This is the basic principle of variable frequency speed regulation. Since the magnetic poles of the motor appear in pairs, the number of pole pairs is often used to represent it.

About Brushless Motor Magnets

The brushless motor in the mold industry is almost100% of the "King of Magnets" is neodymium iron boron magnets. It is well-deserved to describe neodymium iron boron magnets as the king of magnets. Neodymium iron boron magnets are three times more magnetic than the common black ferrite magnets in our lives! Of course, the price is more than 10 times that of ferrite magnets. Brushless motors are permanent magnet motors after all, and the power, characteristics and other characteristics of permanent magnet motors are completely determined by the magnets. Basically, it can be said that the volume and brand of the magnets determine the maximum power of the motor.

There are also differences in magnet shapes. If you disassemble some cheap motors, you will find that most of the magnets are in the shape of square pieces. Square magnets are easy to process and relatively cheap, so they are naturally the choice for cost-conscious motors. Many brands of motors choose arc-shaped magnets. The arc shape can ensure that the air gap between the magnet and the silicon steel sheet remains consistent, which seems to be better than square magnets in terms of power and efficiency. However, when disassembling some motors, so-called bread-shaped magnets were found. They can fit perfectly with the iron shell, but the distance from the silicon steel sheet is the same as that of square magnets, which are not consistent. Regarding this type of magnet, I consulted some industry insiders, and they are convinced that this type of magnet is even better than the arc-shaped magnet, so I will not draw a conclusion here.

However, there is another situation where square magnets can actually be used. In brushless motors with multiple slots and multiple poles (for example36-slot 42-pole motors) basically use square magnets. This is because the diameter of the iron shell is large, the square magnets can also bond well with the iron shell, and the air gap with the silicon steel sheet is also very uniform.

About Silicon Steel Sheets for Brushless Motors

In fact, when I was studying electromagnetism in junior high school, the question I often thought about was why motors need silicon steel sheets??Don't we say that a conductor with electricity can work in a magnetic field? Then why do we need silicon steel sheets? Later, I thought about it for a long time and finally came to a conclusion, that is, the people who do design are not stupider than you!

Air is weakly magnetic, but iron is magnetic. The function of silicon steel sheet is to guide the magnetic circuit of magnet and form a loop, which requires motor magnetic resistance.(You can think of it as resistance) It is relatively small. But everyone has seen why the stator is made up of pieces?

Do you know the principle of induction cooker?Why does an iron pan heat up when placed on an induction cooker? Actually, this is because - materials similar to iron placed in a rapidly changing electromagnetic field (think of alternating current, which flies back and forth in an instant, unlike direct current which always goes from positive to negative) will generate eddy current loss and heat, and the higher the frequency, the greater the heat generated. Silicon steel sheets are in the rotating magnetic field of the motor, which is the same problem as the iron pan placed on the induction cooker. The solution is to add silicon to the steel and make it into thin sheets. In theory, the thinner the silicon steel sheet, the less eddy current loss it generates.

So do you understand that most ordinary fixed-wing motors are relatively thick?Why is it that helicopter and ducted motors mostly use 0.2MM silicon steel sheets? The faster the motor speed, the faster the magnetic field changes, and the greater the eddy current loss. Now most multi-axis motors use 0.2MM single-piece silicon steel sheets, so the iron loss of the motor will be lower.

Related knowledge: Why is it highWill the KV motor get very hot when idling at full throttle?

The answer is: it is not the copper wire that generates heat, because the current passing through it is very small. It is the eddy current loss and hysteresis loss that generate heat, because the motor is completely unloaded at this time, the speed is relatively high, the eddy current loss is large, and all the losses are converted into heat.

About the use and maintenance of brushless motors

The brushless DC motor consists of a motor body and a driver. It is a typical mechatronic product and is widely used in many fields. There are some issues that users need to pay attention to when using a brushless DC motor. So what should you pay attention to when using a brushless DC motor??

(1) Before disassembly, use compressed air to blow away dust on the motor surface and wipe off the surface dirt.
(2) Select the work site for motor dismantling and clean up the on-site environment.
(3) Be familiar with the structural characteristics and maintenance technical requirements of motors.
(4) Prepare the tools (including special tools) and equipment required for dismantling.
(5) In order to further understand the defects in the operation of the motor, if conditions permit, an inspection test can be performed before disassembly. To this end, the motor should be tested with load, and the temperature, sound, vibration, etc. of each part of the motor should be checked in detail, and the voltage, current, speed, etc. should be tested. Then the load should be disconnected and a no-load inspection test should be performed separately to measure the no-load current and no-load loss, and keep records.
(6) Cut off the power supply, remove the external wiring of the motor, and keep records.
(7) Use a megohmmeter with a suitable voltage to test the motor insulation resistance. In order to compare with the insulation resistance value measured during the last maintenance to determine the insulation change trend and insulation status of the motor, the insulation resistance values ​​measured at different temperatures should be converted to the same temperature, generally to 75°C.
(8) Test the absorption ratio K. When the absorption ratio is greater than 1.33, it indicates that the motor insulation has not been affected by moisture or the degree of moisture is not serious. In order to compare with previous data, the absorption ratio measured at any temperature should also be converted to the same temperature.

source:

blog.sina "The most comprehensive sharing of brushless motor working and control principles so far" Author: Shaoshuai-Z

5imx "The veteran driver will give you a comprehensive understanding of brushless motors"

《EMAX Yinyan: One article will give you a comprehensive understanding of brushless motors》

Motor DriverPCB Layout Guidelines

Design goals of DC motor drive circuits

In the design of DC motor drive circuit, the following points are mainly considered:

Function: Whether the motor rotates in one direction or two directions?Does it need speed regulation? For unidirectional motor drive, just use a high-power transistor or field effect tube or relay to directly drive the motor. When the motor needs to rotate in both directions, you can use an H-bridge circuit composed of 4 power components or a double-pole double-throw relay. If speed regulation is not required, just use a relay; but if speed regulation is required, you can use transistors, field effect tubes and other switching elements to achieve PWM (pulse width modulation) speed regulation.

Performance: ForThe PWM speed-controlled motor drive circuit has the following performance indicators:

- Output current and voltage range, which determines how powerful the circuit can drive the motor.

- Efficiency. High efficiency not only means saving power, but also reduces the heat of the drive circuit. To improve the efficiency of the circuit, we can start from ensuring the switching working state of the power device and preventing common conduction (a problem that may occur in H-bridge or push-pull circuits, that is, two power devices are turned on at the same time to short-circuit the power supply).

- Impact on the control input terminal. The power circuit should have good signal isolation on its input terminal to prevent high voltage and high current from entering the main control circuit. This can be achieved by using high input impedance or optocoupler.

- Impact on power supply. Common-mode conduction can cause a momentary drop in power supply voltage, resulting in high-frequency power supply pollution; large currents may cause ground potential to float.

- Reliability. The motor drive circuit should be as safe as possible regardless of the control signal or passive load.

1. Input and level conversion part:

The input signal line isDATA is introduced, pin 1 is the ground wire, and the rest are signal wires. Note that a 2K ohm resistor is connected to the ground on pin 1. When the driver board and the MCU are powered separately, this resistor can provide a path for the signal current to flow back. When the driver board and the MCU share a set of power supplies, this resistor can prevent large currents from flowing into the ground wire of the MCU motherboard along the connection line and causing interference. In other words, it is equivalent to separating the ground wire of the driver board from the ground wire of the MCU to achieve "one-point grounding".

High-speed op ampThe function of KF347 (TL084 can also be used) is a comparator, which compares the input logic signal with the 2.7V reference voltage from the indicator light and a diode, and converts it into a square wave signal close to the power supply voltage amplitude. The input voltage range of KF347 cannot be close to the negative power supply voltage, otherwise an error will occur. Therefore, a diode is added to the input of the op amp to prevent the voltage range from overflowing. The two resistors at the input end are used to limit the current and pull the input end to a low level when the input is floating.

The ____ does not workLM339 or any other open-circuit output comparator replaces the op amp, because the high-level output impedance of the open-circuit output is above 1 kilo-ohm, the voltage drop is large, and the transistor of the next stage will not be able to cut off

2. Gate drive part:

The circuit composed of transistors, resistors, and voltage regulators further amplifies the signal, drives the gate of the field effect tube, and uses the gate capacitance of the field effect tube itself.(about 1000pF) is used for delay to prevent the field effect transistors of the upper and lower arms of the H-bridge from being turned on at the same time ("common conduction") and causing a power short circuit.

When the output of the op amp is lowWhen the output of the op amp is at a high level (about VCC-(1V to 2V), which cannot reach VCC completely), the lower transistor is turned on and the field effect tube is turned on. The upper transistor is turned on, the field effect tube is turned off, and the output is a high level. When the output of the op amp is at a high level (about VCC-(1V to 2V), which cannot reach VCC completely), the lower transistor is turned on and the field effect tube is turned off. The upper transistor is turned off, the field effect tube is turned on, and the output is a low level.

The above analysis is static. The following discusses the dynamic process of switch conversion: the on-resistance of the transistor is much smaller than2 kilo-ohms, so when the transistor switches from cut-off to on, the charge on the gate capacitance of the field effect tube can be quickly released, and the field effect tube is quickly cut off. However, when the transistor switches from on to off, it takes a certain amount of time for the field effect tube gate to charge through the 2 kilo-ohm resistor. Accordingly, the speed of the field effect tube switching from on to off is faster than the speed of switching from off to on. If the switching actions of the two transistors occur at the same time, this circuit can make the field effect tubes of the upper and lower arms cut off first and then turn on, eliminating the common-state conduction phenomenon.

In fact, it takes a certain amount of time for the op amp output voltage to change. During this period of time, the op amp output voltage is at the middle value between the positive and negative power supply voltages. At this time, the two transistors are turned on at the same time, and the field effect tubes are turned off at the same time. Therefore, the actual circuit is safer than this ideal situation.

The gate of the field effect tubeThe 12V Zener diode is used to prevent the gate of the field effect tube from breaking down due to overvoltage. The gate voltage of a general field effect tube is 18V or 20V, and it will break down if a 24V voltage is directly applied. Therefore, this Zener diode cannot be replaced by an ordinary diode, but it can be replaced by a 2 kilo-ohm resistor, which can also obtain a 12V voltage divider.

3. Field effect tube output part:

A diode is connected in reverse parallel between the source and drain of a high-power field effect tube.When the H-bridge is used, it is equivalent to connecting four diodes in parallel at the output end to eliminate voltage spikes, so there is no external diode here. Connecting a small capacitor in parallel at the output end (between out1 and out2) has certain benefits in reducing the peak voltage generated by the motor, but it has the side effect of generating peak current when using PWM, so the capacity should not be too large. This capacitor can be omitted when using a low-power motor. If this capacitor is added, it must be high-voltage-resistant, and ordinary ceramic capacitors may cause breakdown and short circuit failure.

The output end is connected in parallel by a resistor and a light emitting diode, the circuit composed of capacitors indicates the direction of rotation of the motor.

4. Performance indicators:

Supply voltage15~30 V, maximum continuous output current 5A/each motor, short-term (10 seconds) can reach 10A, PWM frequency can be up to 30KHz (usually 1 to 10KHz). The circuit board contains 4 logically independent power amplifier units with output ends connected in pairs to form an H bridge, which can be directly controlled by a single-chip microcomputer. Realize bidirectional rotation and speed regulation of the motor.

5.PCB layout and wiring:

High current lines should be as short and thick as possible, and try to avoid passing through vias. If they must pass through vias, make the vias larger.(>1mm) and make a circle of small vias on the pad, fill them with solder during welding, otherwise they may burn out. In addition, if a voltage regulator is used, the wires from the source of the field effect tube to the power supply and ground should be as short and thick as possible, otherwise, when the current is large, the voltage drop on this wire may pass through the forward-biased voltage regulator and the conducting transistor and burn it out. In the initial design, a 0.15 ohm resistor was connected between the source of the NMOS tube and the ground to detect the current. This resistor became the culprit for the continuous burning of the board. Of course, if the voltage regulator is replaced with a resistor, this problem will not exist.

Motor drive circuitPCBs require special cooling techniques to address power dissipation. Printed circuit board (PCB) substrates, such as FR-4 epoxy glass, are poor thermal conductors. In contrast, copper is an excellent thermal conductor. Therefore, increasing the copper area in the PCB is a desirable solution from a thermal management perspective. Thick copper foils, such as 2 oz (68 micron thick), conduct heat better than thinner copper foils. However, using thick copper foils is costly and difficult to achieve with fine geometries.

Therefore, use1 oz (34 micron) copper foil became common. ½ oz to 1 oz copper foil is common on outer layers. Solid copper planes used on the inner layers of multilayer boards are good for heat dissipation. However, since these planes are usually placed in the center of the board stackup, heat is concentrated inside the board. Increasing the copper area on the outer layers of the PCB and connecting or "stitching" them to the inner layers with many vias helps transfer heat outside the inner layers.

Due to the presence of traces and components, double layerIt can be more difficult to dissipate heat from the PCB. Therefore, it is essential to provide as much solid copper plane as possible and achieve a good thermal connection to the motor driver IC. Adding copper pours on both outer layers and connecting them with many vias can help dissipate heat between areas separated by traces and components.

a. Trace width: the wider the better

Since the motor driverICs can draw high currents in and out (over 10 A in some cases), so the width of the PCB traces going in and out of the device should be carefully considered. The wider the trace, the lower the resistance. The trace must be sized so that the resistance of the trace does not dissipate too much power and cause the trace to heat up. A trace that is too small can actually act as an electrical fuse and burn out easily!

Designers usually useThe IPC-2221 standard is used to determine the appropriate trace width. This specification provides corresponding graphs showing the copper cross-sectional area for various current levels and the allowed temperature rise, which can be converted to trace width for a given copper layer thickness. For example, a trace carrying 10 A in a 1-ounce copper layer needs to be slightly wider than 7 mm to achieve a 10°C temperature rise. For a 1-A current, the trace width only needs to be 0.3 mm.

In view of this,It seems impossible for 10 A to flow through a tiny IC board.

It is important to understand thatThe trace widths recommended in IPC-2221 apply to PCB traces of equal width and length. It is possible to pass much higher currents with shorter PCB traces without any adverse effects. This is because the short, narrow PCB trace has less resistance, and any heat generated will be absorbed into the wider copper area, which acts as a heat sink.

WidenPCB 走线，

To makeThe IC board is better able to handle continuous current.

See the example in the figure. Although the deviceIC pads are only 0.4 mm wide, but they must carry continuous currents of up to 3 A. So we need to make the traces as wide as possible and as close to the device as possible.

Any heat generated in the narrow portion of the trace is conducted to the wider copper area so that the temperature rise of the narrow trace is negligible.

Embedded inTraces on the inner layers of a PCB cannot dissipate heat as well as traces on the outer layers because the insulating substrate does not conduct heat well. For this reason, inner traces should be designed to be approximately twice as wide as outer traces.

As a rough guideline, the following table shows the maximum value for longer traces (more than approximately2 cm) is the recommended trace width.

If space permits, routing using wider traces or copper pours can minimize temperature rise and voltage drop.

b. Thermal vias: Use as many as possible

Through holes are small plated holes that are usually used to pass a trace from one layer to another. Thermal vias are made in the same way but are used to transfer heat from one layer to another. Proper use of thermal vias is important forHeat dissipation from the PCB is critical, but several process issues must be considered.

Vias have thermal resistance, which means that when heat flows through a via, there is some temperature drop across the via, measured inTo minimize this thermal resistance and increase the efficiency of the via in transferring heat, large vias should be used with as much copper area as possible within the hole.

Large vias should be used (the picture shows a cross section of a via) and should contain as much copper area as possible to minimize thermal resistance.

DespiteLarge vias can be used in open areas of the PCB, but vias are often placed in the IC pad area to transfer heat directly from the IC package. In this case, large vias cannot be used. This is because large plated through holes may cause "tin seepage", that is, the solder used to connect the IC to the PCB flows down into the via, resulting in a poor solder joint quality.

There are several ways to reduce solder penetration. One is to use very small vias to reduce the amount of solder that penetrates into the hole. However, small vias have a higher thermal resistance, so more vias are needed to achieve the same thermal performance.

Another technique is to create through holes on the back of the board."Pitch a tent." This involves removing the gaps in the solder mask on the back side of the board so that the solder mask material covers the via. If the via is small, the solder mask will plug the via; therefore, the solder cannot penetrate the PCB.

However, this can create another problem: flux accumulation. After the vias are plugged, flux (a component of solder paste) can accumulate in the vias. Some flux formulations can be corrosive and cause reliability issues over time if not removed. However, most modern no-clean flux processes are not corrosive and will not cause problems.

Please note that thermal vias must not use thermal pads, they must connect directly to the copper area.

Thermal vias should be directly connectedCopper areas on a PCB.

suggestionPCB designers review the PCB assembly with surface mount technology (SMT) process engineers to select via sizes and structures appropriate for the assembly process, especially when thermal vias are placed within the IC board area.

c. Capacitor placement

Motor DriverComponent placement guidelines for ICs are similar to other types of power ICs. Bypass capacitors should be placed as close as possible to the device power pins, with bulk capacitors placed next to them. Many motor driver ICs use boot and/or charge pump capacitors, which should also be placed close to the IC.

Most signals are routed directly on the top layer. Power is routed from the bulk capacitors to the bypass and charge pump capacitors on the bottom layer, using multiple vias at the layer transitions.

The TSSOP and QFN packaged devices have a large exposed IC pad on the bottom side. This IC pad is connected to the back side of the die and is used to remove heat from the device. This IC pad must be adequately soldered to the PCB to dissipate power.

To deposit theThe stencil openings used to deposit solder paste on an IC board are not always detailed in the IC datasheet. Typically, SMT process engineers have their own rules for how much solder should be deposited on the stencil and what pattern the stencil should use.

If you use something likeIf a single opening the size of an IC board is used, a large amount of solder paste will be deposited. This can cause the device to lift due to surface tension when the solder melts. Another problem is solder voiding (cavities or gaps within the solder area). Solder voiding occurs when the volatile components of the flux evaporate or boil during the reflow process. This can cause the solder to be pushed out of the solder joint.

To address these issues, for areas larger than aboutFor a 2 mm2 IC board, solder paste is usually deposited in several small square or circular areas. Dividing the solder paste into smaller areas allows the volatile components of the flux to escape from the solder paste more easily without causing the solder to shift.

This solder stencil for the QFN package has four small openings for depositing solder paste on the center IC pad.

SOT-23 and SOIC packages

Standard leaded packages (such asSOIC and SOT-23 packages) are commonly used in low-power motor drives.

In order to fully improve the power dissipation capability of the lead package, the"Flip chip lead frame" construction. Copper bumps and solder are used to attach the chip to metal leads without using bond wires, allowing heat to be conducted from the chip to the PCB through the leads.

The flip chip leadframe structure helps to fully improve the power dissipation capability of the leaded package.

Thermal performance can be optimized by connecting larger copper areas to leads that carry higher currents.On an IC, typically the power, ground, and output pins are connected to copper areas.

As shown in the figure belowTypical PCB layout for a "flip chip lead frame" SOIC package. Pin 2 is the device power pin. Note that a copper area is placed near the device on the top layer, with several thermal vias connecting this area to the copper layer on the back side of the PCB. Pin 4 is the ground pin and is connected to the ground copper pour on the top layer. Pin 3 (device output) is also routed to a larger copper area.

Flip ChipSOIC PCB Layout

Please note,There are no thermal pads on SMT boards; they are firmly connected to the copper area. This is critical to achieve good thermal performance.


QFN and TSSOP packages

The TSSOP package is rectangular and uses two rows of pins. TSSOP packages for motor driver ICs usually have a large exposed pad on the bottom of the package to remove heat from the device.

TSSOP packages typically have a large exposed pad on the bottom to remove heat.

The QFN package is a leadless package with pads around the outside edge of the device and a larger pad in the center of the bottom of the device. This larger pad is used to absorb heat from the die.

To remove heat from these packages, the exposed pad must be well soldered. The exposed pad is usually at ground potential so that it can be connected toPCB ground plane.

Ideally, thermal vias are located directly in the board area.In the example of a TSSOP package, an 18-via array is used with a drill diameter of 0.38 mm. The calculated thermal resistance of this via array is approximately 7.7°C/W.

Adopted a18 TSSOP Package PCB Layout with Thermal Via Array

Typically, these thermal vias are usedDrill hole diameters of 0.4 mm and smaller are recommended to prevent tin seepage. If the SMT process requires a smaller hole diameter, the number of holes should be increased to keep the overall thermal resistance as low as possible.

In addition to the through holes located in the board area,Thermal vias are also provided in areas outside the IC body. In the TSSOP package, the copper area can extend beyond the ends of the package, providing another path for heat from the device to pass through the top copper layer.

Avoid using copper layers on the top side to absorb heat around the edges of the QFN device package. Thermal vias must be used to dissipate the heat to inner layers or the bottom layer of the PCB.

useQFN package PCB layout with 9 thermal vias

In the pictureThe PCB layout shows a small QFN (4 × 4 mm) device. Only nine thermal vias are accommodated in the exposed pad area. Therefore, the thermal performance of this PCB is not as good as that of a TSSOP package.

Flip ChipQFN Package

Flip ChipThe FQFN (FCQFN) package is similar to the regular QFN package, but the die is flipped and attached directly to a pad on the bottom of the device, rather than using bond wires to attach to the package pad. These pads can be placed on the opposite side of the heat-generating power devices on the die, so they are usually arranged in long strips rather than small pads.

These packages use rows of copper bumps on the surface of the chip bonded to a lead frame.

The FCQFN package uses multiple rows of copper bumps on the surface of the chip bonded to the lead frame.

Small vias can be placed in the board area similar to conventionalQFN package. On multilayer boards with power and ground planes, vias can connect these boards directly to the layers. In other cases, copper areas must be connected directly to the board to draw heat from the IC into the larger copper area.

The device shown below has long power and ground planes, and three outputs. Note that this package is only4 × 4 mm size.

PCB layout for FCQFN packaged ICs

The copper area on the left side of the device is the power input. This large copper area connects directly to the two power pads of the device.

The three output pads connect to the copper area on the right side of the device. Note that the copper area extends as far as possible after exiting the pad. This allows for adequate heat transfer from the pad to the ambient air.

Also, note the rows of small vias in the two pads on the right side of the device. These pads are connected to ground andA solid ground plane is placed on the back side of the PCB. The vias have a diameter of 0.46 mm and a drill diameter of 0.25 mm. The vias are small enough to fit within the board area.

In summary, in order to use the motor driverTo successfully implement PCB design for IC, the PCB must be carefully laid out.

Source: Internet

DIY Adjustable Speed ​​DC Motor Fan

1. Project Introduction

I have participated in the breadboard organization before.I learned a lot of new knowledge from the ST development board and uFun development board activities. Later, I wanted to make some of the small experiments I had done before into a small board. The main hardware function is to use the STM32 to collect encoders or receive infrared data to adjust the speed of the DC motor, monitor the corresponding relationship between the speed and current in real time, and output the print message to the PC display through the USB to serial port chip.

2. Hardware Design

2.1. Schematic design

2.2.PCB Design

3. Back-to-board welding and debugging

When debugging the hardware, the output pin of the infrared receiver is abnormal, and there is an abnormal waveform output. After checking, it is becauseThe series resistor R7 was initially 10K, which was too large. The data sheet recommends 100~200R, so after changing it to 150R, the infrared reception became normal. In addition, R8 is an optional solder component.

4.STM32CubeMX settings

In useAfter STM32CubeMX automatically generates the Keil project of MDK 5 version, I open the project directly and configure the debugging tool to J-LINK, SWD mode. No matter how I operate, the STM32 chip cannot be recognized. I check the schematic diagram and soldering and find no problems. Just when I was about to crash, I manually created a KEIL project and configured it step by step. It can actually correctly recognize the chip and download it. I have never encountered this problem before. I wonder if any netizens have had such experience and know what is going on...

A large wave chart allows you to truly understand the motor

A motor is an electromagnetic mechanical device that converts electrical energy into mechanical energy. There are two general applications of motors: the first is to convert mechanical energy into electrical energy, which is called a generator.;The second type converts electrical energy into mechanical energy, which is called an electric motor.

The operating principle of the motor is based on the law of electromagnetic induction and the law of electromagnetic force. When the motor performs energy conversion, it should have two parts that can move relative to each other: the part that establishes the excitation magnetic field, and the induced part that induces electromotive force and flows the working current. Of these two parts, the stationary one is called the stator, and the rotating one is called the rotor. There is an air gap between the stator and the rotor to allow the rotor to rotate.

Electromagnetic torque is generated by the interaction between the excitation magnetic field in the air gap and the magnetic field established by the current in the induced component. Through the action of electromagnetic torque, the generator absorbs mechanical power from the mechanical system and the motor outputs mechanical power to the mechanical system. Different ways of establishing the above two magnetic fields form different types of motors.

1. Classification by working power type

2. Classification by structure and working principle

3. Classification by startup and operation mode

4. Classification by rotor structure