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 focus will be on making a frequency converter with your own hands. Of course, for this you will need to have at least a general idea of \u200b\u200bconductor technology. It is necessary to start with the purpose for which frequency converters are used.
When the need arises for the 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, with the help of a frequency converter, it is possible to change the rotation speed of the electric motor. There is an idea to purchase a frequency converter forelectric 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 rotation speed using a gearbox built on the basis of a variator, or a 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 allows you to 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 filtering devices.
- Inverter assembly.
- 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.
It will be described in detail below, a diagram 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 control of power semiconductor elements is carried out. In addition, there is a function of protection against short circuit and overcurrent. FrequencyThe converter must be connected to the supply network by means of protective devices. There is no need for a magnetic starter.
Frequency converter rectifier
This is the very first module that current flows through. With its help, alternating current is rectified - converted to direct current. This happens due to the use of elements such as semiconductor diodes. But now it is worth mentioning a small feature. You know that most induction motors are powered by a three-phase AC mains. But this is not available everywhere. Of course, large enterprises have it, but it is rarely used in everyday life, since it is easier to conduct a single-phase one. Yes, and taking into account electricity, things are easier.
And frequency converters can be powered both from a three-phase network and from a single-phase one. 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 use a circuit on four semiconductor diodes connected in 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 arm, as a result you will get AC rectification. The output will show plus and minus.
DC voltage filtering
On the way outrectifier, you have a constant voltage, but it has large ripples, the variable component still slips. To smooth out all these "roughnesses" 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 two poles. It has some really interesting properties. When a direct current flows, according to Kirchhoff's law, it should be replaced by a break, that is, there is, as it were, nothing between plus and minus. But when an alternating current flows, it is a conductor, a piece of wire without resistance. As mentioned above, direct current flows, but there is a small proportion of alternating current in it. And it closes, as a result of which it simply disappears.
Inverter module
The inverter assembly is, to be precise, the most important in the entire design. It is used to change the parameters of the output current. In particular, its frequency, voltage, etc. The inverter consists of six controlled transistors. For each phase, two semiconductor elements. It is worth noting that modern assemblies of IGBT transistors are used in the inverter stage. Even home-made, even the Delta frequency converter, the most budgetary and affordable today, consist of the same nodes. The possibilities are just different.
They have three inputs, the same number of outputs, as well as six points of connection to the control device. It should be noted that in the independent manufacture of a frequency converter, it is necessary to select an assembly according to power. Therefore, you must immediately decide what type of motor will be connected to the frequency converter.
Microprocessor control system
With self-production, it is unlikely that it will be possible to achieve the same parameters that industrial designs have. The reason for this lies not at all in the fact that the manufactured assemblies of power transistors are inefficient. The fact is that at home it is quite difficult to make a control module. Of course, this is not about soldering elements, but about programming a microcontroller device. The easiest option is to make a control unit with which you can adjust the rotation speed, reverse, current and overheat protection.
To change the rotation speed, you must use a variable resistance, which is connected to the input port of the microcontroller. This is a master device that sends a signal to the microcircuit. 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. Strictly according to it, the work of the microprocessor system takes place. Very popular company control modulesSiemens. The frequency converter of this manufacturer has high reliability, can be used in any type of electric drive.
How to set up the frequency converter
Today, there are many manufacturers of this device. But the tuning algorithm is almost the same for everyone. Of course, it will not work to tune the frequency converter without certain knowledge. You need to have two things - experience in adjustment and an operating manual. The latter has an appendix that describes all the functions that can be programmed. There are usually several buttons on the case of the frequency converter. At least four pieces must be present. Two are intended for switching between functions, with the help of the rest, parameters are selected or the entered data is canceled. To switch to the programming mode, you must press a specific button.
Each frequency converter model has its own algorithm for entering the programming mode. Therefore, it is impossible to do without the instruction manual. It is also worth noting that the functions are divided into several subgroups. And it's easy to get lost in them. Try not to change those settings that the manufacturer does not recommend touching. These settings should only be changed 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 very simple to you.
Conclusions
Whenoperation, maintenance or manufacture of the frequency converter, all safety precautions must be observed. Remember that the design of the device contains electrolytic capacitors that retain their charge even after disconnecting from the AC mains. Therefore, before disassembling, it is necessary to wait for the discharge. Please note that there are elements in the design of frequency converters that are afraid of static electricity. In particular, this applies to the microprocessor control system. Therefore, soldering should be done with all precautions.
