Frequency converter for the motor: circuit

From this article you will learn what a frequency converter is for an electric motor, consider its scheme, the principle of operation, and also learn about the settings of industrial designs. The main emphasis will be placed on manufacturing the frequency converter with our 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 there is a need for an IF

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, by means of a frequency converter, the speed of rotation of the electric motor can be varied . There is an idea 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 about 5-7 thousand rubles.

It is worth noting that you can change the speed of rotation using a reducer built on the basis of a variator, or gear type. But such constructions are very large, they can not always be used. In addition, such mechanisms must be serviced in a timely manner, and their reliability is extremely low. The use of a frequency converter reduces the costs of servicing the electric drive, and also increases its capabilities.

Main components of the frequency converter

Any frequency converter consists of four main modules:

1. Rectifier block.
2. Devices of a filtration of a constant pressure.
3. Inverter node.
4. Microprocessor control system.

All of them are interconnected, and the control unit controls the operation of the output stage - the inverter. It is with its help that the output characteristics of the alternating current are changed.

About it will be described in detail below, the scheme is given. The frequency converter for the electric motor has several more features. It should be noted that the device includes several degrees of protection, which are also controlled by a microcontroller device. In particular, the temperature of the power semiconductor elements is monitored. In addition, there is a short circuit and overcurrent protection function. The frequency converter must be connected to the mains by means of protective devices. The need for a magnetic starter is eliminated.

Rectifier of frequency converter

This is the very first module through which current flows. With its help, rectification of alternating current is carried out - conversion into a constant one. 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 asynchronous motors are powered by a three-phase alternating current network. But not everywhere such is available. Of course, it is in large enterprises, but it is rarely used in everyday life, since it is easier to conduct single-phase operation. And taking into account the electricity, things are simpler.

And frequency converters can be fed either from a three-phase network or from a single-phase network. What is the difference? And it is insignificant, different 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 switched on in 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 arm, as a result, you will receive AC rectification. The output will be "plus" and "minus".

DC Filtration

At the output of the rectifier, you have a constant voltage, but it has large pulsations, the variable component still jumps. To smooth out all these "unevenness" currents, you 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 a little to smooth the ripple of the current flowing through it. The second element is a capacitor connected between two poles. It has really interesting properties. When a direct current flows, according to Kirchhoff's law, it must be replaced by a cliff, that is, there is nothing between the plus and minus. But when the alternating current flows through a conductor, a piece of wire without resistance. As mentioned above, a direct current flows, but there is a small fraction of the variable current. And she is locked, as a result of which she simply disappears.

Inverter module

The inverter node, to be precise, is the most important in the whole design. With its help, the output current parameters are changed. In particular, its frequency, voltage, etc. There is an inverter of six controlled transistors. For each phase there are two semiconductor elements. It should be noted that in the inverter cascade modern assemblies of IGBT-transistors are used. Though the homemade, although the frequency converter Delta, the most budgetary and available today, consist of the same nodes. The possibilities are just different.

They have three inputs, as many outputs, and six points of connection to the control device. It is worth noting that when self-manufacturing frequency inverter it is necessary to select the assembly for power. Therefore, you must immediately determine which type of motor will be connected to the frequency converter.

Microprocessor control system

When self-made, it is unlikely to achieve the same parameters as those available for industrial designs. The reason for this lies not in the fact that the produced assemblies of power transistors are inefficient. The fact is that it's quite difficult to make a control module at home. Of course, this is not about soldering the elements, but about programming the microcontroller device. The simplest option is to manufacture a control unit, through which it is possible to carry out speed adjustment, reversal, current protection and overheating.

To change the speed of rotation, you must use the variable resistance, which is connected to the input port of the microcontroller. This is the master that signals the chip. The latter analyzes the level of voltage change compared to the reference voltage, which is 5 V. The control system operates according to a certain algorithm, which is written before the programming begins. Strictly, the microprocessor system operates. Very popular are Siemens control modules. The frequency converter of this manufacturer has high reliability, it can be used in any type of electric drive.

How to set up the frequency converter

To date, there are many manufacturers of this device. But the adjustment algorithm for all is almost the same. Of course, it's impossible to adjust the frequency converter without certain knowledge. You need to have two things - experience in the adjustment and operation manual. In the latter, there is an application that describes all the functions that can be programmed. Usually on the case of the frequency converter there are several buttons. At least four pieces must be present. Two are intended for switching between functions, with the help of the others, parameters are selected or data entered is canceled. To enter the programming mode, you must press a certain button.

For each model of the frequency converter 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 it will not be difficult to get lost in them. Try not to change those settings that the manufacturer does not recommend to touch. These parameters need to be changed only in exceptional cases. When the programming function is selected, you will see its alphanumeric designation on the display. As you gain experience, adjusting the frequency converter will seem like a very simple task for you.

conclusions

When operating, servicing or manufacturing a frequency converter, all precautions must be followed. Remember that in the design of the device there are electrolytic capacitors, which retain the charge even after disconnecting from the AC mains. Therefore, before disassembling, it is necessary to wait for the discharge. Pay attention to the fact that in the design of frequency converters there are elements that are afraid of static electricity. In particular, this applies to the microprocessor control system. Therefore, soldering should be followed with all precautions.