Chastotnik for the electric motor with their own hands: circuit, instruction and connection

In this article, we will look at the chastotnik for the electric motor, the principle of its operation and the main components. The main emphasis will be placed on the theory, so that you understand the principle of the frequency converter and could later carry out the design and manufacture with your own hands. But first you need a small introductory course, which will tell you what a chastotnik is and for what purpose it is needed.

Functions of the frequency converter

The lion's share is occupied in the industry by asynchronous motors. And they were always difficult to control, because they have a constant rotor speed, and changing the input voltage is very difficult, and sometimes even impossible. But the chastotnik reverses the picture completely. And if earlier to change the speed of the conveyor, for example, used a variety of reducers, then today it is enough to apply one electronic device.

In addition, the frequency band allows you to get not only the possibility of changing the drive parameters, but also several additional degrees of protection. There is no need for electromagnetic starters, and sometimes even do not need a three-phase network to ensure the normal operation of the induction motor. All these duties, connected with switching and switching on the electric drive, pass to the frequency converter. It allows you to change the phases at the output, the frequency of the current (and therefore the rotor speed varies), carry out the start and brake adjustment, and many other functions can be realized. It all depends on the microcontroller used in the control circuit.

Operating principle

Make a chastotnik for the electric motor with their own hands, the scheme of which is given in the article, is quite simple. It allows you to convert one phase into three. Consequently, it becomes possible to use an asynchronous motor in everyday life . At the same time, its efficiency and power are not lost. After all, you know that when you turn on the motor in a network with a single phase, the reduction of these parameters almost doubles. And it's all about several transformations of the voltage coming to the input of the device.

The first is the rectifier block. More details about it will be described below. After the rectified voltage is filtered. And a pure direct current flows to the input of the inverter. It carries out the conversion of a direct current into an alternating current with the required number of phases. This cascade can be subjected to adjustments. It consists of semiconductors, to which a microcontroller control circuit is connected. But now about all the nodes in more detail.

Rectifier block

It can be of two types - single- and three-phase. The first type of rectifier can be used in any network. If you have three-phase, then it is enough to connect to one. Scheme chastotnika for the electric motor is not complete without a rectifying unit. Since there is a difference in the number of phases, it means that it is necessary to use a certain number of semiconductor diodes. If we are talking about frequency converters, which are fed from one phase, then a rectifier of four diodes is required. They are switched on by bridge circuit.

It allows you to reduce the difference between the value of the voltage at the input and output. Of course, one half-wave circuit can be used, but it is inefficient, a large number of oscillations arise. But if it is a question of a three-phase connection, then it is necessary to use six semiconductors in the circuit. Exactly the same scheme in the rectifier of the car generator, there are no differences. The only thing that can be added here is three additional diodes designed to protect against reverse voltage.

Filter elements

After the rectifier there is a filter. Its main purpose is to cut off the entire variable component of the rectified current. For a clearer picture, a substitution pattern must be drawn up. So, plus passes through the coil. And then an electrolytic capacitor is added between the plus and minus. Here it is and is interesting in the scheme of substitution. If the coil is replaced by a reactance, the capacitor can be either a conductor or a break in the presence of a different current.

As it was said, there is a direct current in the rectifier. And when it is fed to the electrolytic capacitor, nothing happens, since the latter is a break in the circuit. But there is a small variable in the current. And if an alternating current flows, then in the replacement circuit, the capacitor becomes a conductor. Consequently, the plus sign is closed to minus. These findings are made according to the laws of Kirchhoff, which are basic in electrical engineering.

Power inverter inverter

But now we have reached the main node - a cascade of transistors. They made an inverter - a DC-to-AC converter. If you manufacture a chastotnik for the electric motor with your own hands, then it is recommended to use IGBT-transistor assemblies, you can find them in any store of radio components. And the cost of all the components for making a chastotnik will be ten times less than the price of the finished product, even of Chinese production.

Two transistors are used for each phase. They are included between the plus and minus, as depicted in the diagram given in the article. But each transistor has a feature - a control output. Depending on what signal is applied to it, the properties of the semiconductor element change. Moreover, this can be done both by manual switching (for example, by applying several microswitches to apply voltage to the necessary control terminals) or automatic. Here's the last and will go further.

Control scheme

And if the connection of the frequency converter to the electric motor is simple, it is only necessary to connect the corresponding terminals, then everything is much more complicated with the control circuit. The thing is that there is a need to program the device in order to achieve the maximum possible adjustments from it. At the core is a microcontroller, it connects the readers and the executive. So, it is necessary to have current transformers that will constantly monitor the power consumed by the electric drive. And in case of exceeding, the chronograph must be switched off.

Connecting the control circuit

In addition, protection against overheating is provided. At the output of the microcontroller, using the matching device (Darlington assembly), the control terminals of the IGBT transistors are connected. In addition, you need to visually monitor the parameters, so you need to include a LED display in the circuit. From the readers, you need to add buttons that allow you to switch between programming modes, as well as variable resistance, by rotating it changes the rotor speed of the motor.

Conclusion

I want to note that it is possible to produce a freewheel for the electric motor, the price of the finished product starts from 5000 rubles. And this is for electric motors whose power does not exceed 0.75 kW. If you want to control more powerful drive, you need a freewheel expensive. For use in everyday life, the following scheme is sufficient. The reason is that there is no need for a large number of functions and settings, the most important is the possibility of changing the rotor speed.