From this article you will learn what a frequency converter for an electric motor is, consider its circuit, the principle of operation, and also learn about the settings of industrial designs. The main emphasis will be placed on the manufacture of a frequency converter with your own hands. Of course, for this you need to have at least a general idea of the conductor technique. It is necessary to start with the purpose for which frequency converters are used.
When the need arises for inverters
Modern frequency converters are high-tech devices that consist of elements based on semiconductors. In addition, there is an electronic control system built on a microcontroller. With its help, all the most important parameters of the electric motor are controlled. In particular, with the help of a frequency converter, the rotation speed of an electric motor can be changed . The idea arises of acquiring a frequency converter for an electric motor. The price of such a device for motors with a power of 0.75 kW will be approximately 5-7 thousand rubles.
It is worth noting that you can change the speed of rotation using a gearbox, built on the basis of a variator, or gear type. But such designs are very large, it is not always possible to use them. In addition, such mechanisms must be serviced in a timely manner, and their reliability is extremely low. The use of a frequency converter can reduce the cost of servicing an electric drive, as well as increase its capabilities.
The main components of the frequency converter
Any frequency converter consists of four main modules:
- Rectifier unit.
- DC voltage filtering devices.
- Inverter unit.
- Microprocessor control system.
All of them are interconnected, and the control unit controls the operation of the output stage - inverter. It is with its help that the output characteristics of the alternating current are changed.
About it will be described in detail below, a diagram. The frequency converter for the electric motor has several more features. It is worth noting that the device includes several degrees of protection, which are also controlled by a microcontroller device. In particular, temperature control of power semiconductor elements is performed. In addition, there is a function of protection against short circuit and over current. The frequency converter must be connected to the mains by means of protective devices. There is no need for a magnetic starter .
Frequency converter rectifier
This is the very first module through which current flows. With its help, rectification of alternating current is carried out - conversion to constant. This is due to the use of elements such as semiconductor diodes. But now it’s worth mentioning a small feature. You know that most of the induction motors are powered by a three-phase AC network. But not everywhere there is one. Of course, it is at large enterprises, but it is rarely used in everyday life, since it is easier to conduct a single-phase one. And considering electricity, things are simpler.
And frequency converters can be powered by either a three-phase network or a single-phase. What is the difference? And it is insignificant, various types of rectifiers are used in the design. If we are talking about a single-phase frequency converter for an electric motor, then it is necessary to apply a circuit on four semiconductor diodes connected by a bridge type. But if there is a need for power from a three-phase network, you should choose a different circuit consisting of six semiconductor diodes. Two elements in each shoulder, as a result you get AC rectification. The output will show “plus” and “minus”.
DC voltage filtering
At the output of the rectifier you have a constant voltage, but it has large ripples, the alternating component still skips. To smooth out all these "irregularities" of the current, you will need to use at least two elements - an inductor and an electrolytic capacitor. But everything should be told in more detail.
The inductor has a large number of turns, it has some reactance, which allows you to slightly smooth out the ripple of the current flowing through it. The second element is a capacitor connected between the two poles. It has truly interesting properties. When direct current flows, according to Kirchhoff’s law, it must be replaced by a break, that is, there is nothing between the plus and minus. But when the variable flows - a conductor, a piece of wire without resistance. As mentioned above, direct current flows, but a small fraction of the variable is present in it. And it closes, as a result of which it simply disappears.
Inverter module
The inverter assembly, to be precise, is the most important in the entire design. With its help, the output current parameters are changed. In particular, its frequency, voltage, etc. The inverter consists of six controlled transistors. For each phase, two semiconductor elements. It is worth noting that the inverter cascade uses modern assemblies from IGBT transistors. Although the home-made, even the Delta frequency converter, the most budgetary and affordable today, consists of the same nodes. The possibilities are only different.
They have three inputs, the same number of outputs, as well as six points of connection to the control device. It is worth noting that with the independent manufacture of a frequency converter, it is necessary to select the assembly for power. Therefore, you should immediately determine what type of electric motor will be connected to the frequency converter.
Microprocessor control system
With independent production, it is unlikely that it will be possible to achieve the same parameters that are available for industrial designs. The reason for this is not at all that the manufactured power transistor assemblies are inefficient. The fact is that at home it is rather difficult to make a control module. Of course, this is not about soldering the elements, but about programming a microcontroller device. The simplest option is to make a control unit, with which you can adjust the speed of rotation, reverse, current protection and overheating.
To change the rotation speed it is necessary to use a variable resistance, which is connected to the input port of the microcontroller. This is a master device that sends a signal to a chip. The latter analyzes the level of voltage change compared to the reference, which is 5 V. The control system works according to a certain algorithm, which is written before programming begins. Strictly on it, the microprocessor system works. Siemens control modules are very popular. The frequency converter of this manufacturer has high reliability, can be used in any type of electric drive.
How to set up a frequency converter
Today, there are many manufacturers of this device. But the tuning algorithm is almost the same for everyone. Of course, tuning the frequency converter without certain knowledge will fail. You need to have two things - experience in adjusting and operating manual. The latter has an application that describes all the functions that can be programmed. Typically, there are several buttons on the inverter housing. At least four pieces must be present. Two are designed to switch between functions, using the rest you can select parameters or cancel the entered data. To enter the programming mode, you must press a specific button.
Each model of the frequency converter has its own algorithm for entering the programming mode. Therefore, it is impossible to do without a manual. It is also worth noting that the functions are divided into several subgroups. And getting confused in them is not difficult. Try not to change the settings that the manufacturer does not recommend touching. These parameters need to be changed only in exceptional cases. When you select a programming function, you will see its alphanumeric designation on the display. As you gain experience, tuning the frequency converter will seem to you a very simple matter.
findings
When operating, maintaining or manufacturing a frequency converter, all safety precautions must be observed. Remember that the design of the device has electrolytic capacitors that retain charge even after disconnecting from AC power. Therefore, before disassembling, it is necessary to wait for the discharge. Please note that in the design of frequency converters there are elements that are afraid of static electricity. In particular, this relates to a microprocessor control system. Therefore, soldering should be carried out with all precautions.