An electric motor, also known as a motor or an electric motor, is an electrical device that converts electrical energy into mechanical energy, and can then use the mechanical energy to generate kinetic energy to drive other devices. There are many types of motors, but they can be roughly divided into AC motors and DC motors for different occasions. Electric motors are so common in our lives that you may have overlooked them. Let's take a look at how does an electric motor work.
This passage is going to talk about the followings of electric motor:
(1)Introduction to electric motor
(2)The working principle of electric motor
(3)Where is electric motor used?
The advantage of a DC motor is that it is relatively simple in speed control. It only needs to control the voltage to control the speed. However, this type of motor is not suitable for operation in high temperature, flammable and other environments, and because the motor needs to use carbon brushes as a commutator component (brush motors), so it is necessary to regularly clean up the dirt generated by carbon brush friction. A brushless motor is called a brushless motor. Compared with a brush, a brushless motor is less power-saving and quieter because of the less friction between the carbon brush and the shaft. The production is more difficult and the price is higher. AC motors can operate in high temperature, flammable and other environments, and do not need to clean carbon brush dirt regularly, but it is more difficult to control the speed, because controlling the speed of the AC motor requires controlling the frequency of the AC (or using induction For the motor, the internal resistance is increased to reduce the motor speed at the same AC frequency), and controlling the voltage will only affect the torque of the motor. Generally, the voltage of civil motors is 110V and 220V. In industrial applications, there are also 380V or 440V.
The principle of rotation of an electric motor is based on John Ambrose Fleming’s left-hand rule.
When a wire is placed in a magnetic field, if the wire is energized, the wire will cut the magnetic field line and move the wire. The electric current enters the coil to generate a magnetic field, and the magnetic effect of the electric current is used to continuously rotate the electromagnet in a fixed magnet, which can convert electrical energy into mechanical energy. It interacts with a permanent magnet or a magnetic field generated by another set of coils to generate power.
The principle of a DC motor is that the stator does not move, and the rotor moves in the direction of the force generated by the interaction. The AC motor is the stator winding coil is energized with alternating current to generate a rotating magnetic field. The rotating magnetic field attracts the rotor to rotate together. The basic structure of a DC motor includes "armature", "field magnet", "snubber ring", and "brush".
The soft iron core of which the armature can rotate around the axis is wound with multiple coils. A field magnet is a powerful permanent magnet or electromagnet that generates a magnetic field. The collector ring is a collector ring with two semi-circular coils connected to about two ends of the coil, which can be used to change the direction of current as the coil rotates. Every half turn (180 degrees), the direction of current on the coil changes. The brush is usually made of carbon, and the collector ring contacts the brush in a fixed position to connect to the power source.
Anything you can think of, as long as it is converted into electrical energy by mechanical energy, can be driven by an electric motor. Electric motors have many uses, ranging from heavy industries to small toys. The conveyor belts of factories and hypermarkets, the electric automatic doors and electric rolls on common cars are also driven by electric motors.
How to power and control the brushless DC motor? This article will introduce some professional knowledge of brushless motors.
This passage is going to talk about the followings of brushless motor:
(1) Basic knowledge of brushless motor
(2) BLDC motor control features
(3) Control schemes for electronic commutation of brushless motor
All motors, whether mechanical or electronic, follow the same basic method of converting electrical energy into mechanical energy. The current passing through the winding generates a magnetic field, which in the presence of a second magnetic field (usually caused by a permanent magnet) will generate a force on the winding. When its conductor is at 90° to the second field, the force reaches Maximum value. The increase in the number of coils will increase the output of the motor and smooth the power output.
Brushless DC motors overcome the need for mechanical commutators by reversing the motor setting. The winding becomes the stator and the permanent magnet becomes part of the rotor. The stator is usually composed of steel laminations that are axially slotted to accommodate an even number of windings along their inner circumference. The rotor consists of a shaft and a hub with permanent magnets arranged to form two to eight pole pairs alternating between "N" and "S". Figure 1 shows an example of a common magnet arrangement. In this case, two pairs of magnets are directly bonded to the rotor hub.
In BLDC motors, permanent magnets are fixed on the rotor. A typical configuration consists of two pairs and eight pairs, alternating between "N" and "S" poles.
Because the windings are fixed, a permanent connection can be established to excite them. In order for the fixed winding to move the permanent magnet, the winding needs to be energized (or commutated) in a controlled sequence to generate a rotating magnetic field.
Since the rotating magnetic field generated by the stator causes the rotor to rotate at the same frequency, the BLDC motor is called a "synchronous" type. BLDC motors can be one-phase, two-phase or three-phase. The three-phase BLDC motor is the most common motor.
So far, the most common configuration used to sequentially apply current to a three-phase BLDC motor is to use three pairs of power Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) arranged in a bridge structure. Each pair of switches controls one phase of the motor. In a typical configuration, the high-side MOSFET is controlled by pulse width modulation (PWM), which converts the input DC voltage into a modulated drive voltage. Using PWM can limit the starting current and provide precise control of speed and torque. The PWM frequency is a compromise between the switching loss that occurs at high frequencies and the ripple current that occurs at low frequencies, which can damage the motor in extreme cases. Generally, the PWM frequency used by designers is at least an order of magnitude higher than the maximum motor speed.
There are three control schemes for electronic commutation: trapezoidal, sinusoidal and field-oriented control. The trapezoidal technique (described in the example below) is the simplest. In each step, both windings are energized (one winding is "high" and one winding is "low") while the other winding is floating. The disadvantage of the trapezoidal method is that this "stepped" commutation causes torque "fluctuation", especially at low speeds.
Sinusoidal control is more complicated, but it can reduce torque ripple. In this control mode, all three coils are kept energized, and the drive current in each coil changes sinusoidally with each other, at 120° to each other. Compared with trapezoidal technology, the result is smoother power transfer.
The field-oriented control relies on measuring and adjusting the stator current, so the angle between the rotor and stator flux is always 90°. Compared with all other technologies, this technology is more effective than the sinusoidal method at high speeds and has better performance during dynamic load changes. There is almost no torque fluctuation, and smoother and more accurate motor control can be achieved at low speed and high speed.
