BLDC Motors
(1)Electric motors, including the increasingly popular BLDC motors, also known as brushless motors or synchronous DC motors, are devices used to convert energy electricity to mechanical energy, most often in the form of rotational motion. BLDC motors, thanks to their undoubted advantages, are used in an increasing number of devices, ranging from computer components such as optical drives and cooling fans, through hand-held power tools, toys, and remotely controlled vehicles, e.g., drones, household appliances, to machines and devices for transport and movement, including scooters, bicycles, and electric cars.
BLDC motor structure
Brushless motors have a different structure compared to commutator motors. The biggest difference between the two types of motors is the lack of a commutator, a rotary switch that supplies power to the rotor windings, in BLDC motors. Instead, they are electronically commutated - a special controller adapted for use with BLDC motors switches current through the stator windings producing magnetic fields which smoothly rotate in space and which the permanent magnet (usually a powerful neodymium magnet) rotor follows. The switching of current through successive windings is carried out by means of semiconductor elements such as transistors. If the electromagnetic fields produced by the stator windings and rotor magnets are misaligned, a torque develops that sets the rotor in motion.
Three-phase motors can be connected in a delta configuration, where the end of each winding is connected to the beginning of the next, and power is supplied to each of the three points created in this way. The windings can also be star-connected, where their ends are connected at a central point while power is supplied to the remaining end of each winding. The delta connection system provides less torque at low speeds but achieves a higher maximum speed than star connection. In practice, star connection is the most common in the case of BLDC motors, as it is more efficient in typical applications.
Brushless DC electric motors come in three varieties: the stator is surrounded by the rotor (outrunners), the rotor is surrounded by the stator (inrunners), or the rotor and stator are flat and parallel (axial). In any case, it is the permanent magnet rotor that moves with respect to the stationary winding part. Typically, BLDC motors where the stator is surrounded by the rotor (outrunners) have higher torque values at low speeds. As the stator is stationary and integral with the housing, cooling can be done primarily through conduction, and no additional forced air circulation is required to cool the motor. The maximum power of a brushless motor is in practice limited only by heat, excess of which can damage the insulation of the windings and eventually destroy it.
Brushless DC electric motors control
BLDC motors commonly use feedback control system. An electronic sensor, usually a Hall sensor, checks the position of the rotor, which provides the controller with information on how to switch windings to achieve the smoothest and most stable rotation of the shaft. By adjusting the phase (the switching of the stator windings) and the amplitude of the DC pulses, the controller can control the rotational speed and the torque of the shaft. There are also solutions without rotor angular position sensors. The "Back EMF" (Back Electromotive Force) signal is then used, which is generated by rotating magnets (magnetic field) attached to the rotor. The voltage induced on each coil is compared to the centre voltage, which occurs at the point where all three windings are connected (when they are star connected). These signals are amplified and sent to the rotor position detection system, and their waveforms are shifted in relation to each other by 120 °. The problem when using such a solution is the start, i.e., motor start-up, as these signals are not yet generated and the rotor position is not known.
It is worth knowing that BLDC motors come in different phase configurations. There are single-phase, 2-phase and. 3-phase BLDC motors. The higher the number of phases, the higher the power and efficiency of the motor, and the quieter it runs because of the smoother switching of the windings, which causes less vibration in the structure.
Advantages of BLDC motors
Electronic commutation in BLDC motors, the so-called ECM (Electronically Commutative Motors), and therefore the lack of a commutator and carbon brushes, brings many advantages. This is primarily the absence of sparks, which is a common problem with commutator motors, making them suitable for use in explosive atmospheres. There is also no loss of energy as there is no friction between the brushes and the commutator, which can in addition lead to improper operation of nearby microelectronics due to the resulting electronic noise. The working life of a BLDC motor is only limited by the lifetime of its bearings. The absence of brushes and commutator also means that BLDC motors are lighter, more efficient (compared to traditional DC electric motors) and quieter. They can also achieve high speeds, but it is easy to set limits on this parameter and control them at low speeds.
When choosing a BLDC motor, pay attention to the supply voltage. This will usually be based on the parameters of the power supply that will be used with the controller to operate that particular motor. The shaft diameter and rotor configuration can also be considered.
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