Brushless DC motor: principle of operation, device, types

the main problem collector motors - this is just the presence of a collector unit. The brushes are erased, and the lamellas wear out, short circuits occur from the layer of graphite dust between them, sparking occurs. These problems do not exist in asynchronous machines, but they cannot operate on direct current. The brushless DC motor is devoid of the above disadvantages. About, what it is, how it works and where it is used we will talk about BDPT engines in this article.

Content:

Definition
Device and operating principle
Types of BDPT
How to connect a brushless motor
Where brushless motors are used
Advantages and disadvantages

Definition

A DC motor is called a brushless motor, the current in the windings of which switches a special switching device - it is called "driver" or "inverter" and these windings are always located on stator. The switch consists of 6 transistors, and they supply current to one or another winding, depending on the position of the rotor.

In the domestic literature, such motors are called "valve" (because semiconductor switches are called "valves"), and there is a division of such electric machines into two types according to the form of counter-EMF. In foreign literature, such a difference remains, one of them is called similarly to the Russian "BLDC" (brushless direct current drive or motor), which literally sounds like a "brushless DC motor" in their windings, a trapezoidal EMF. Valve electric motors with sinusoidal EMF are called PMSM (Permanent magnet synchronous machine), which translates as "synchronous electric motor with permanent magnet excitation."

Device and operating principle

The collector in the KDPT serves as a node for switching the current in the armature windings. In a brushless DC motor (BDCT), this role is played not by brushes with lamellas, but by a switch, it is a semiconductor switch - transistors. Transistors switch the stator windings, creating a rotating magnetic field that interacts with the field of the rotor magnets. And when current flows through a conductor that is in a magnetic field, it acts on ampere force, due to the action of this force, a torque is generated on the shaft of electrical machines. This is what is based on principle of operation any electric motor.

Now let's figure it out how it works brushless motor. There are usually 3 windings on the BDPT stator, by analogy with AC motors, they are often called three-phase. This is partly true: brushless motors operate from a direct current source (often from batteries), but the controller turns on the current in the windings one by one. However, it is not entirely true to say that alternating current flows through the windings. The final form of the supply voltage winding is formed by rectangular transistor control pulses.

The three-phase brushless motor can be three-wire or four-wire, where the fourth wire is a tap from the midpoint (if the windings are connected along star pattern).

Winding or, speaking in simple words, the coils of copper wire fit into the teeth of the stator core. Depending on the design and purpose of the drive, there may be a different number of teeth on the stator. There are different variants of the distribution of the phase windings along the rotor teeth, which is illustrated in the following figure.

The windings of each of the teeth within one phase can be connected in series or in parallel, depending on the supplied the designer of tasks for the power and torque of the projected drive, and the phase windings themselves are interconnected according to a star or triangle like asynchronous or synchronous three-phase AC motors.

Rotor position sensors can be installed in the stator. Hall sensors are often used, they give a signal to the controller when they are affected by the magnetic field of the rotor magnets. This is necessary in order for the controller to "know" in which position the rotor is and to supply power to the corresponding windings. This is necessary to increase the efficiency and stability of work, and if briefly, - to squeeze all possible power out of the engine. There are usually 3 sensors installed. But the presence of sensors complicates the design of a brushless electric motor, additional wires for power and data lines need to be connected to them.

In the BDPT, permanent magnets mounted on the rotor are used for excitation, and the stator is an armature. Recall that in collector machines, the opposite is true (the rotor is an armature), and for excitation in the CD, both permanent magnets and electromagnets (windings) are used.

The magnets are installed with alternating poles, and accordingly their number determines the number of pole pairs. But this does not mean that as many magnets, there are as many pairs of poles. Several magnets can form one pole. The number of poles, as in the case of an asynchronous motor (and others), depends on the number of revolutions per minute. That is, brushless motors with a different number of pole pairs will rotate at different speeds from the same controller at the same settings.

Types of BDPT

Now let's figure it out what are brushless motors permanent magnets. They are classified by the form of back-EMF, design, and also by the presence of rotor position sensors. So, the two main type characterized by the form of back-EMF, which is induced in the windings when the rotor rotates:

BLDC - trapezoidal counter-EMF in them;
PMSM - sinusoidal back EMF.

Ideally, they require different power supplies (controllers), but in practice they are interchangeable. But if you use a controller with a square or trapezoidal output voltage with a PMSM motor, you will hear characteristic sounds similar to knocking during rotation.

And by design, brushless DC motors are:

With internal rotor. This is a more familiar representation of an electric motor, when the stator is a housing, and the shaft located in it rotates. They are often called the English word "Inrunner". This option is usually used for high-speed electric motors.
With external rotor. Here the outer part of the engine rotates with a shaft fixed on it, in English-speaking sources it is called "outrunner". This device scheme is used when a high torque is needed.

Choose construction whichever what is it needed for a brushless motor in a specific application.

Modern industry produces brushless motors with or without rotor position sensors. The fact is that there are many ways to control the BDPT, for some of them position sensors are needed, others determine the positions by EMF in windings, the third ones simply supply power to the required phases and the electric motor independently synchronizes with such a power supply and enters the working mode.

The main specifications brushless DC motors:

Operating mode - long or short-term.
Maximum operating voltage.
Maximum operating current.
Maximum power.
Maximum revolutions, often indicate not revolutions, but KV - rev / v, that is, the number of revolutions per 1 volt of applied voltage (no load on the shaft). To get the maximum speed, multiply this number by the maximum voltage.
The resistance of the winding (the less it is, the higher the efficiency), is usually hundredths and thousandths of Ohm.
The phase advance angle (timing) is the time after which the current in the winding reaches its maximum, this is due to its inductance and the laws of commutation (the current in the inductance cannot change instantly.

How to connect a brushless motor

As mentioned above, a special controller is needed to operate a brushless motor. On aliexpress, you can find both sets of the engine and controller, and separately. The controller is also called ESC Motor or Electric Speed Controller. They are selected according to the strength of the current supplied to the load.

Usually, connecting the electric motor to the controller is straightforward and even understandable for Dummies. The main thing you need to know is that to change the direction of rotation, you need to change the connection of any two phases, in fact, just like in three-phase asynchronous or synchronous motors.

The network also has a number of technical solutions and schemes, both complex and for teapotswhich you can see below.

In this video, the author tells how to make friends between the BC motor and the "Arduina".

And in this video you will learn about the different ways of connecting to different regulators and how you can do it yourself. The author demonstrates this with an example of a motor from an HDD, and a couple of powerful copies - inrunner and outrunner.

By the way, we also attach the diagram from the video for repetition:

Where brushless motors are used

The scope of application of such electric motors is wide ahead of schedule. They are used both to drive small mechanisms: in CD drives, DVD drives, hard disks, and in powerful devices: a battery and a mains power tool (with power supply of the order 12V), radio-controlled models (for example, quadcopters), CNC machines for driving the working body (usually motors with a rated voltage 24V or 48V).

BDPTs are widely used in electric vehicles, almost all modern motor-wheels of electric scooters, bicycles, motorcycles and cars are brushless motors. By the way, the nominal voltage of electric motors for transport lies in a wide range, for example, a motor-wheel for a bicycle often operates from 36V or from 48V, with rare exceptions, and more, and in cars, for example, on the Toyota Prius, about 120V, and on the Nissan Leaf - it reaches 400, while it is charged from the mains 220V (this is implemented with a built-in converter).

Actually application area brushless electric motors are very extensive, the absence of a manifold unit allows it to be used in hazardous places, as well as in places with high humidity, without fear of short circuits, sparks or fire due to defects in the brush node. Due to their high efficiency and good weight and dimensions, they have found application in the space industry.

Advantages and disadvantages

Brushless DC motors, like other types of electric machines, have certain advantages and disadvantages.

Advantages the BDPT are as follows:

Due to excitation by powerful permanent magnets (neodymium, for example), they surpass in torque and power and have smaller dimensions than induction motors. What most electric vehicle manufacturers use, from scooters to cars.
No sparkling brush-collector assembly that requires regular maintenance.
When using a high-quality controller, in contrast to the same CD, they do not give out interference to the supply network, which especially important in radio-controlled devices and vehicles with advanced electronic equipment in the onboard networks.
Efficiency more than 80, more often 90%.
High rotation speed, in some cases up to 100,000 rpm.

But there is also a significant disadvantage: a brushless motor without a controller is just a piece of iron with a copper winding. He won't be able to work in any way. Controllers are not cheap and most often they have to be ordered from online stores or from aliexpress. Because of this, it is not always possible to use BC motors in home-made models and devices.

Now you know what a brushless DC motor is, how it works and where it is applied. We hope our article helped you sort out all the issues!

Related materials: