The principle of operation of a brushless DC motor (BKDP) 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 only in the 21st century have found widespread use in technology. The decisive factor in the widespread implementation was the multiple reduction in the cost of the drive control electronics of the BDKP.
Content
- Collector motor problems
- The principle of operation of the BDKP
- Modern application and perspectives
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 that underlie the design of electrical machines:
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Electric and magnetic fields are interconnected. That is, each moving charge creates a magnetic field and, accordingly, magnetic fields are capable of producing a potential difference. - The magnets interact with each other. The work of all electric motors is based on the interaction of magnets. Some of them are constant, others are a coil in which a magnetic field is induced by passing through the loops of an electric current.
The motor 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 has four main parts:
- stator (stationary element with a ring of magnets);
- armature (rotating element with windings);
- carbon brushes;
- collector.
This design provides for the rotation of the armature and the collector on the same shaft relative to the stationary brushes. The current flows from the source through the brushes spring-loaded for good contact to the commutator, which distributes the 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 manifests itself more strongly. The manifold assembly wears out over time and is also prone to arcing and can ionize the surrounding air. Thus, despite the simplicity and low cost to manufacture, such electric motors have some insurmountable disadvantages:
- wear of brushes;
- electrical interference due to arcing;
- maximum speed limits;
- difficulties with cooling a rotating electromagnet.
The advent 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, an electronic converter plays the role of a mechanical switch. This makes it possible to carry out the "turned inside out" scheme 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 the classic engine and the BDKP 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 in it occurs in a similar way, its physical implementation in brushless drives is much more complicated.
The main issue is the precise control of the brushless motor, assuming the correct sequence and frequency of switching individual sections of the windings. This problem is constructively solvable only if it is possible to continuously determine the current position of the rotor.
The data required for processing by the electronics is obtained in two ways.:
- detecting the absolute position of the shaft;
- by 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 rotor magnetic flux, 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 estimate the voltage in the coils requires at least a minimum rotor rotation. Therefore, in such designs, a mode is provided for starting the engine up to revolutions, at which the voltage on the windings can be evaluated and the resting state tested by analyzing the effect of the magnetic field on the test current pulses passing through coils.
Despite all the above design difficulties, brushless motors are conquering everything great popularity due to its performance and inaccessible manifold set characteristics. A short list of the main advantages of the 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 due to low rotor inertia;
- precise rotation control;
- the possibility of organizing cooling due to thermal conductivity;
- ability to work at high speeds;
- durability and reliability.
Modern application and perspectives
There are many devices for which increasing uptime is critical. In such equipment, the use of BDKP is always justified, despite their relatively high cost. These can be water and fuel pumps, turbines for cooling air conditioners and engines, etc. Brushless motors are used in many electric vehicle models. Nowadays, the automotive industry is seriously focusing on brushless motors.
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. Low weight and high power output have made the BDKP also the basis for the production of modern cordless hand tools.
We can say that there is significant progress in the field of electric drives. The continuing decline in the price of digital electronics has given rise to a trend towards widespread use of brushless motors to replace traditional ones.
