Today, the industry often uses frequency converters for asynchronous motors. It is worth noting that such motors have three windings in their design, which are connected according to the “star” or “triangle” scheme. But they have one drawback - it is very difficult to regulate the speed of rotation of the rotor. But it was like that before. Now, when micro- and power electronics come to the rescue, this task is simplified. By turning the variable resistor, you can change the rotation speed in a wide range.
For what purpose do you need a frequency converter?
This device has a lot of functions, but most often a small amount is used. In fact, to control an asynchronous motor, you need to be able to adjust not only the rotation speed, but also the acceleration and deceleration time. In addition, any system requires protection. It is necessary thatthe frequency converter took into account the current consumed by the asynchronous motor.
Chastotniki are widely used in ventilation systems. Despite the apparent lightness of the fan impeller, the loads on the rotor are very large. And instant overclocking is impossible. There are also situations in which it is necessary to increase the rotation speed so that the air flow becomes more or less. But this is just an example, the frequency converter is often used in other systems. With the help of a frequency converter, you can synchronize the speed of a conveyor consisting of several tapes.
The working principle of frequency converter
It is based on microprocessor control and several circuits for converting AC and DC voltages. Several processes occur with the voltage that is applied to the power input of the device. The operation of the frequency converter is simple, it is enough to consider three stages. First, there is alignment. Second, filtering. Thirdly, inverting is the conversion of direct current into alternating current.
Only at the last stage it is possible to change the properties and parameters of the current. By changing the characteristics of the current, it is possible to control the speed of rotation of the rotor of an asynchronous motor. Powerful assemblies of transistors are used in the inverter stage. These elements have three outputs - two power, and one control. The current-voltage characteristic at the output of the frequency converter depends on the magnitude of the signal applied to the latter.
What can replace the inverter?
Frequency converters for asynchronous motors began to be used relatively recently. But science went to them gradually, at first the speed of rotation of the rotor was changed using gears or a variator. True, such control was very cumbersome, and the drive power was wasted due to unnecessary mechanisms. The belt drive helped to increase the rotation speed, but it turned out to be very difficult to accurately set the final parameter. For these reasons, it is much more profitable to use a frequency converter, as it avoids power losses. But most importantly, it makes it possible to change the drive parameters without making changes to the mechanics.
Which IF to choose for home use?
It is worth noting that the connection can be made to a single- and three-phase current network. It all depends on the specific inverter model, and more specifically, on which circuit of the frequency converter of the asynchronous motor was used in production. To understand the principle of operation, just look at the structure of the device. The very first node is a rectifier, which is assembled on semiconductor diodes. This is a bridge circuit for converting one or three phase AC to DC. For use at home, it is necessary to choose those models of chastotnikov, the input of which is connected to a single-phase alternating current network. The choice is connected with the fact that it is problematic and unprofitable to conduct a three-phase network in private houses, becausemore sophisticated electricity meters must be used.
Main inverter components
A little has been said about what the frequency converter circuit is. But for a detailed study, you need to consider it in more detail. At the first stage, transformation is carried out - rectification of alternating current. Regardless of how many phases are supplied to the input (three or one), at the output of the rectifier you get a constant unipolar (one plus and one minus) voltage of 220 volts. That is how much between phase and zero.
Followed by a filter block, which helps to get rid of all the variable components of the rectified current. And at the very last stage, inversion occurs - an alternating current is made from direct current using power transistors controlled by a microcontroller. As a rule, frequency converters for asynchronous motors have a monochrome LCD display, which displays the necessary parameters.
Can I make the device myself?
Manufacturing of this device involves many difficulties. You need to learn the basics of microcontroller programming in order to expand the capabilities of the device. It is important to take into account all the basic requirements. For example, the possibility of automatic emergency shutdown when the maximum permissible current consumed by the electric motor is exceeded. To do this, it is necessary to install current transformers at the output, which will carry out constant monitoring. There should also be an activepassive cooling of all power elements of the system - diodes and transistors, as well as turning off the device in case of excessive heating. Only then can frequency converters for asynchronous motors be operated safely.
