Today in industry very often used frequency converters for induction 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 rotor speed. But that was before. Now, when micro and power electronics come to the rescue, this task is simplified. By turning a variable resistor, you can change the rotation speed in a wide range.
For what purpose is a frequency converter necessary?
This device has many functions, but most often a small amount is used. In fact, to control an induction motor you need to be able to adjust not only the speed of rotation, but also the time of acceleration, braking. In addition, any system requires security. It is necessary that the frequency converter takes into account the current consumed by the induction motor.
Chastotniks 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 an increase in the rotation speed is necessary so that the air flow becomes larger or smaller. But this is just an example, a frequency converter is often used in other systems. Using the chastotnik, you can synchronize the speed of the conveyor, consisting of several tapes.
The principle of operation of the frequency converter
It is based on microprocessor control and several circuits for converting AC and DC voltages. Several processes occur with a voltage that is supplied to the power input of the device. The operation of the frequency converter is simple, it is enough to consider three stages. First, straightening occurs. Secondly, filtering. Thirdly, inversion is the conversion of direct current to alternating current.
Only at the last stage is it possible to change the properties and parameters of the current. By changing the characteristics of the current, you can adjust the rotational speed of the rotor of an induction motor. In the inverter cascade, powerful assemblies of transistors are used. These elements have three conclusions - two power, and one control. From the magnitude of the signal supplied to the latter depends on the current-voltage characteristic at the output of the chastotnik.
How can I replace the inverter?
Frequency converters for induction motors began to be used relatively recently. But science went towards them gradually, at first the rotor speed was changed using gears or a variator. True, this control was very cumbersome, and the drive power was wasted due to unnecessary mechanisms. Belt transmission helped to increase the speed of rotation, but it was very difficult to precisely set the final parameter. For these reasons, using a frequency converter is much more profitable, since it avoids power loss. But most importantly, it makes it possible to change the parameters of the drive without making changes to the mechanics.
Which inverter to choose for use at home?
It is worth noting that the connection can be made to a network of single and three-phase current. It all depends on the specific inverter model, and more specifically, on the type of frequency converter of the induction motor used in the 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 single or three phase AC to DC. To use the house, it is necessary to choose those models of chastotniks whose input is connected to a single-phase alternating current network. The choice is connected with the fact that in private houses a three-phase network is problematic, and unprofitable, because it is necessary to use more sophisticated electricity meters.
The main components of the inverter
Little has been said about what constitutes a frequency converter circuit. But for a detailed study, you need to consider it in more detail. At the first stage, conversion is performed - 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 so much between phase and zero.
This is 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 takes place - an alternating current is made from direct current using power transistors controlled by a microcontroller. As a rule, frequency converters for induction motors have a monochrome LCD display, which displays the necessary parameters.
Can I make a device myself?
The manufacture of this device is associated with many difficulties. You need to learn the basics of programming microcontrollers to expand the capabilities of the device. It is important to consider all the basic requirements. For example, the possibility of automatic emergency shutdown when exceeding the maximum permissible current that is consumed by the electric motor. To do this, it is necessary to install current transformers at the output, which will conduct constant monitoring. It should also include active and passive cooling of all power elements of the system - diodes and transistors, as well as turning off the device during excessive heating. Only in this case, the frequency converters for induction motors can be safely operated.