Can I assemble frequency converters myself? Principle of operation and connection diagram of frequency converters

It is rather difficult to manufacture frequency converters by oneself, since it is necessary to understand very well the power electronics and semiconductor technology. But before thinking about designing this device, you need to find out for what purpose they are used. You will also need to know what are the main components of these electronic systems.

What is a frequency converter?

Everyone knows that there is an alternating current in the network, and it has a certain frequency. In Russia, the standard is 50 Hertz. In some Western countries, a slightly different standard is 60 Hertz. The operation of many devices depends on the frequency of the current. Converters are used to supply asynchronous motors. There are many reasons for using electronic means. For example, in the industry, the inverter is widely used, as their use makes it possible to get rid of huge mechanisms.

If in more detail, then change the speed of rotation of the belt on the conveyor can be by using a gearbox, which is based on some kind of box of speeds of the car. And it can be both mechanical (using several gears) and variator. But much more effective is the change in the parameters of the current, which feeds the motor. Turn the variable resistor to change the speed of rotation of the conveyor. And the frequency can be changed in a wide range.

What are the properties of frequency converters?

In addition, the inverter settings allow to achieve that the electric motor will gradually gain momentum within a few seconds. The time is set by the user by programming the functions of the frequency converter. Similarly, you can do with the stopping time of the motor armature. This allows you to reduce the load on the drive, which directly affects its resource.

In addition, for small businesses that do not have the ability to provide themselves with a three-phase network, but the need for it is available, the use of frequency converters is a true panacea. There are many models of such devices that are connected to a single-phase alternating current network, and three are produced at the output. Therefore, it is possible to turn on the electric motor in the usual socket. And in this case, he will not lose power, his work will be correct.

Power components of converters

In all frequency converters, powerful IGBTs or MOSFETs are used. They are ideal for this type of work. They are mounted in separate modules. Such an installation method can improve the performance of an electronic device. These transistors work in key mode, the control is performed using a microprocessor system. The fact is that all control is low-current, high-voltage switching is not required. Therefore, it can be provided with the help of the simplest microprocessor.

Most often used special assemblies series IR2132 and IR2130. They consist of six drivers that control the keys. Three are used for the lower one, and three for the upper one. Such an assembly makes it possible to realize a simple cascade of a frequency converter. In addition, it has several degrees of protection. For example, from short circuit and overload. More detailed characteristics of all elements can be found in the manuals. But all power cells have a huge drawback - high cost of products.

Block diagram of the converter

Any frequency converter for the engine has in its composition three main units - rectifier, filters, inverter. It turns out that the alternating voltage is first converted to a constant voltage, then filtered. After all this, it is inverted to the variable. But there is a third unit - microprocessor control of the inverter. And to be more precise, powerful IGBT-transistors. If you happen to deal with the frequency band, then you know that on the front panel they have several buttons for programming.

The instruction of the frequency converter will tell you how to carry out the settings of all the functions. This is a very complex matter, since there are quite a few settings even in the simplest device. In addition, that the electronic device allows you to change the engine's rotation speed, adjust the acceleration and deceleration time, there are several degrees of protection. For example, on exceeding the current. If such a device is used, there is no need to install circuit breakers.

Rectifier block

Depending on the purpose of the frequency converter, different rectifier stages are used. A power supply variant can be either from a three-phase network, or from a single-phase network. But at the output of the inverter in any case is a three-phase alternating voltage. But in order to conduct current control, it is necessary to straighten it first. The thing is that it is quite difficult to manage variables - you need to use large rheostats, which is not very convenient. Moreover, now the time of microelectronics and automation, to apply obsolete technologies is not just unreasonable, but also very unprofitable.

To rectify an alternating three-phase current , an electronic device consisting of six semiconductor diodes is used. They are included in the bridge circuit, it turns out that each pair of diodes serves to straighten one phase. At the output of the rectifier unit, there is a constant voltage, its value is equal to that which flows to the input. At this stage, all the transformations are completed, no control of this block is made. In the event that power is supplied from a single-phase network, a rectifier cascade is sufficient, even from one diode. But it is more efficient to use a bridge circuit of four.

Filter unit

This module is used to filter the DC voltage. The simplest version of the unit is the inductor, included in the break of the plus arm. Between the poles, an electrolytic capacitor is turned on. It has one function - to get rid of the variable component. The thing is that the rectifier can not completely get rid of pulsations. There remains a small component of the alternating current, which can give considerable interference during operation.

In order to consider the principle of the filter block, it is necessary to perform an analysis by replacing the elements. When operating under DC conditions, the inductance is replaced by a resistance, the capacitor is replaced by a break in the circuit. But when AC power is applied, the capacitance is replaced by resistance. Consequently, the entire variable component disappears, since a short circuit occurs in this case. It is difficult to understand this, it is necessary to understand the theoretical foundations of electrical engineering. But the frequency converter of the 3 phase can not be done without this.

Inverter cascade

And here begins the most interesting - the use of powerful IGBT-transistors. They are controlled by a microprocessor system, the performance of the entire frequency converter depends on the quality of their functioning. Such a voltage converter circuit is widely used. In fact, with the help of power transistors, you can invert any voltage. In total, six elements are used in the simplest scheme - two for each phase. The frequency converter 220 volts produces in each phase with respect to zero.

To get rid of the occurrence of reverse voltage, it is necessary to use semiconductor diodes. They are switched between the collector and the emitter of power transistors. The control is performed at the input of the base. As stated earlier, frequency converters, manufactured by themselves, have two transistors per phase in the inverter cascade. Include their pn-junctions in series. The middle phase of each shoulder is removed. On sale there are ready-made modules, they have terminals for supplying a constant voltage, and also three contacts for the removal of a three-phase alternating current. In addition, there is a connector for connecting the microcontroller control system.

Microprocessor control

Used to change the motor shaft speed converter, the voltage whose default frequency is 50 hertz, can be changed in amplitude over a wide range. And more specifically, from zero to the frequency that the microprocessor can provide. The last requirement is the main one - it is possible to connect several devices. When you design a converter, the voltage whose frequency varies with the variable resistance must be controlled by the processor. It is chosen carefully, it must have a sufficient number of input-output ports.

It is possible to complicate the system a little by connecting an LCD display to the microcontroller. It does not require a high color rendering, enough monochrome, as in simple calculators. The buttons for programming are also connected to the I / O ports. That's how you can make a simple frequency converter. The price of all elements will be no more than two thousand rubles. But the cost of an inverter with a power of 200-750 watts varies in the range from 6500 to 12000 rubles. It depends on the manufacturer and the capabilities of the device.

Housing for the device

Frequency converters, manufactured by themselves, must have a reliable housing. It depends not only on ease of use, but also on efficiency. The base is made of aluminum. The reason for using this material is the need for high-quality cooling. In operation, the IGBT-module becomes very hot, and the temperature also increases for semiconductor diodes. And it does not really matter if the frequency converter is 380 or you have 220 volts.

The rest of the body is made of plastic. It is necessary that all power elements are hidden by it, so that there is no accidental contact of high-voltage terminals during operation. In the front part, it is necessary to provide a hole for the LCD display and buttons. Separately, in a convenient place, a variable resistor is installed. When programming the microcontroller, it is necessary to take into account that this resistance changes the frequency of the output current.

Heat exchange elements of the system

Particular attention should be paid to heat removal. The more powerful the device being developed, the more reliable the cooling system should be. As mentioned above, the substrate must be made of aluminum. The circuit of the voltage converter must provide protection against overheating. For this purpose, it is required to drill a hole in the housing, a temperature sensor is mounted in it. With it, the signal is fed through the matching device to the microcontroller. If the maximum temperature is exceeded, the load must be disconnected. Consequently, the power transistor module is turned off.

To improve heat transfer, fans must be used. Their location should be chosen so that the airflow cools the fins of the body heat sink. To increase the efficiency of the cooling system, it is necessary to use thermal paste. It is more reasonable to switch on the fans when the device is started. But it is also possible to program the controller using a signal from the temperature sensor. When the temperature is reached equal to half of the one at which the device switches off accidentally, the fans are turned on.

Circuit board

As a circuit board it is best to use ready-made options. On sale there are boards of different sizes with holes around which there are small tinned contacts. In common speech they are called "fish". The only thing that should be taken into account is the possibility of replacing the processor and chips. For this purpose, you need to use connectors that are soldered to the board. Frequency converters with their own hands to produce the best with the calculation of a rapid replacement of elements. A chip or controller is simply installed into this connector, like a plug into an outlet.

conclusions

You can also manufacture the frequency converter yourself. The price of analogs, as we found out, is much higher. Although, of course, they have more opportunities. But in practice, if you look closely, it turns out that only five functions are actually used. When the drive is running, it is necessary to change the speed of rotation, and also to adjust the acceleration and deceleration time. A little bit less is used the function of reversing and changing the maximum permissible current.