What does the converter do? Frequency converter for electric motor: diagram

25.10.2023

Voltage converters are widely used both in everyday life and in production. For production and industry, they are most often made to order, because they need a powerful converter and not always with a standard voltage. Standard values for output and input parameters are often used in everyday life. That is, a voltage converter is an electronic device that is designed to change the type of electricity, its magnitude or frequency.

According to their functionality they are divided into:

Downgrades;
Raising;
Transformerless;
Inverter;
Adjustable with adjustable frequency and output AC voltage;
Adjustable with adjustable constant output voltage.

Some of them can be made in a special sealed design; these types of devices are used for wet rooms, or, in general, for installation under water.

So, what is each type?

High voltage voltage converter

This is an electronic device that is designed to produce alternating or direct high voltage (up to several thousand volts). For example, such devices are used to generate high-voltage energy for television picture tubes, as well as for laboratory research and testing electrical equipment with voltages increased several times. Cables or power circuits of oil switches designed for a voltage of 6 kV are tested at a voltage of 30 kV and higher, however, this voltage value does not have high power, and in the event of a breakdown it is immediately switched off. These converters are quite compact because they have to be carried by personnel from one substation to another, most often manually. It should be noted that all laboratory power supplies and converters have almost standard, accurate voltage.

Simpler high-voltage converters are used to start fluorescent lamps. The impulse can be greatly increased to the desired level using the starter and throttle, which can have an electronic or electromechanical basis.

Industrial installations that convert lower voltage to high voltage have many protections and are performed using step-up transformers (STVs). Here is one of these circuits that gives an output from 8 to 16 thousand volts, while only about 50 V is needed for its operation.

Due to the fact that quite high voltage is generated and flows in the windings of transformers, high demands are placed on the insulation of these windings, as well as on its quality. In order to eliminate the possibility of corona discharges, the parts of the high-voltage rectifier must be soldered to the board carefully, without burrs and sharp corners, and then filled on both sides with epoxy resin or a layer of paraffin 2...3 mm thick, ensuring insulation from each other. Sometimes these electronic systems and devices are called step-up voltage converters.

The following circuit is a linear resonant voltage converter that operates in boost mode. It is based on the separation of functions for increasing U and its clear stabilization in completely different cascades.

At the same time, some inverter units can be made to work with minimal losses on power switches, as well as on a rectified bridge, where high-voltage voltage appears.

Home voltage converter

The average person comes across voltage converters for the home very often, because many devices have a power supply. Most often these are step-down converters that have galvanic isolation. For example, chargers for mobile phones and laptops, personal desktop computers, radios, stereo systems, various media players, and this list can be continued for a very long time, since their variety and applications in everyday life have recently been very wide.

Uninterruptible power supplies are equipped with energy storage devices in the form of batteries. Such devices are also used to maintain the operation of the heating system during an unexpected power outage. Sometimes home converters can be made according to an inverter circuit, that is, by connecting it to a direct current source (battery) powered by a chemical reaction, you can obtain a normal alternating voltage at the output, the value of which will be 220 Volts. A feature of these circuits is the ability to obtain a pure sinusoidal signal at the output.

One of the very important characteristics of converters used in everyday life is the stable signal value at the output of the device, regardless of how many volts are supplied to its input. This functional feature of power supplies is due to the fact that for stable and long-term operation of microcircuits and other semiconductor devices, a clearly standardized voltage is required, and even without ripple.

The main criteria for choosing a converter for a house or apartment are:

Power;
The magnitude of the input and output voltage;
Possibility of stabilization and its limits;
Load current value;
Minimizing heating, that is, it is better for the converter to operate in a mode with a power reserve;
Ventilation of the device can be natural or forced;
Good sound insulation;
Availability of protection against overloads and overheating.

Choosing a voltage converter is not a simple matter, because the operation of the powered device depends on the correctly selected converter.

Transformerless voltage converters

Recently, they have become very popular, since their production, and in particular the production of transformers, requires a lot of money, because their winding is made of non-ferrous metal, the price of which is constantly growing. The main advantage of such converters is, of course, the price. Among the negative aspects, there is one thing that significantly distinguishes it from transformer power supplies and converters. As a result of a breakdown of one or more semiconductor devices, all the output energy can reach the terminals of the consumer, and this will certainly damage it. Here is the simplest AC to DC voltage converter. The role of the regulating element is played by the thyristor.

The situation is simpler with converters that do not have transformers, but operate on the basis and in the mode of a voltage-increasing device. Here, even if one or several elements fail, dangerous destructive energy will not appear on the load.

DC-DC converters

The AC/DC converter is the most commonly used type of device of this type. In everyday life these are all kinds of power supplies, and in production and industry these are power supply devices:

All semiconductor circuits;
Excitation windings of synchronous motors and DC motors;
Oil switch solenoid coils;
Operating and tripping circuits where coils require constant current.

A thyristor voltage converter is the most commonly used device for these purposes. A feature of these devices is the complete, rather than partial, conversion of alternating voltage to direct voltage without any kind of ripple. A powerful voltage converter of this type must necessarily include radiators and fans for cooling, since all electronic parts can operate for a long time and trouble-free only at operating temperatures.

Adjustable voltage converter

These devices are designed to operate in both voltage increase and decrease modes. Most often, these are still devices that smoothly adjust the value of the output signal, which is lower than the input signal. That is, 220 Volts are supplied to the input, and at the output we get an adjustable constant value, say, from 2 to 30 volts. Such devices with very fine adjustment are used to test pointer and digital instruments in laboratories. It is very convenient when they are equipped with a digital indicator. It must be admitted that every radio amateur took this type as the basis for his first work, since the power supply for certain equipment can be different in size, but this power source turned out to be very universal. How to make a high-quality converter that works for a long time is the main problem of young radio amateurs.

Inverter voltage converter

This type of converter forms the basis for innovative compact welding devices. Receiving an alternating voltage of 220 volts for power supply, the device rectifies it, after which it again makes it alternating, but with a frequency of several tens of thousands of Hz. This makes it possible to significantly reduce the dimensions of the welding transformer installed at the output.

The inverter method is also used to power heating boilers from batteries in the event of an unexpected power outage. Due to this, the system continues to operate and receives 220 volts of alternating voltage from 12 volts of direct voltage. A powerful booster device for this purpose must be operated from a large-capacity battery; this determines how long it will supply the boiler with electricity. That is, capacity plays a key role.

High frequency voltage converter

Due to the use of boost converters, it becomes possible to reduce the size of all electronic and electromagnetic elements that make up the circuits, which means the cost of transformers, coils, capacitors, etc. is reduced. However, this can cause high-frequency radio interference, which affects the operation of other electronic devices. systems, and even ordinary radio receivers, so their housings need to be reliably shielded. The calculation of the converter and its interference must be carried out by highly qualified personnel.

What is a resistance to voltage converter?
This is a special type that is used only in the production and manufacture of measuring instruments, in particular ohmmeters. After all, the basis of an ohmmeter, that is, a device that measures resistance, is made in measuring the drop in U and converting it into pointer or digital indicators. Typically measurements are made relative to direct current. A measuring transducer is a technical device used to convert a measured value into another value or a measuring signal, convenient for processing, storage, further transformations, indication, and transmission. It is part of any measuring device.

Current to voltage converter

In most cases, all electronic circuits are needed to process signals represented in the form of voltage. However, sometimes you have to deal with a signal in the form of current. Such signals arise, for example, at the output of a photoresistor or photodiode. Then it is advisable to convert the current signal into voltage at the first opportunity. Voltage-to-current converters are used when the current in the load must be proportional to the input U and independent of the R load. In particular, with a constant input U, the current in the load will also be constant, therefore such converters are sometimes conventionally called current stabilizers.

Voltage converter repair

Repair of these devices to convert one type of voltage to another is best done in service centers, where the personnel are highly qualified and will subsequently provide guarantees for the work performed. Most often, any modern high-quality converters consist of several hundred electronic parts, and if there are no obvious burnt elements, then it will be very difficult to find a breakdown and fix it. Some Chinese inexpensive devices of this type, in general, are in principle deprived of the possibility of repairing them, which cannot be said about domestic manufacturers. Yes, they may be a little bulky and not compact, but they can be repaired, since many of their parts can be replaced with similar ones.

To convert direct current into alternating current, special electronic power devices called inverters are used. Most often, an inverter converts DC voltage of one value into AC voltage of another value.

Thus, an inverter is a generator of periodically varying voltage, and the voltage shape can be sinusoidal, close to sinusoidal or pulsed. Inverters are used both as independent devices and as part of uninterruptible power supply (UPS) systems.

As part of uninterruptible power supplies (UPS), inverters allow, for example, to obtain continuous power supply to computer systems, and if the network voltage suddenly disappears, the inverter will instantly begin to power the computer with energy received from the backup battery. At least the user will have time to shut down correctly and turn off the computer.

Larger uninterruptible power supply devices use more powerful inverters with batteries of significant capacity that can autonomously power consumers for hours, regardless of the network, and when the network returns to normal again, the UPS will automatically switch consumers directly to the network, and the batteries will begin to charge.

Technical side

In modern technologies for converting electricity, an inverter can only act as an intermediate link, where its function is to convert voltage by transforming at a high frequency (tens and hundreds of kilohertz). Fortunately, today this problem can be easily solved, because for the development and construction of inverters, both semiconductor switches are available that can withstand currents of hundreds of amperes, as well as magnetic circuits with the required parameters, and electronic microcontrollers specially designed for inverters (including resonant ones).

Requirements for inverters, as for other power devices, include: high efficiency, reliability, and the smallest possible dimensions and weight. It is also necessary that the inverter maintains the permissible level of higher harmonics in the input voltage, and does not create unacceptably strong impulse noise for consumers.

In systems with “green” electricity sources (solar panels, wind turbines), Grid-tie inverters are used to supply electricity directly to the general network - inverters that can operate synchronously with the industrial network.

During operation of the voltage inverter, a constant voltage source is periodically connected to the load circuit with alternating polarity, while the frequency of connections and their duration are formed by a control signal that comes from the controller.

The controller in the inverter usually performs several functions: adjusting the output voltage, synchronizing the operation of semiconductor switches, and protecting the circuit from overload. In principle, inverters are divided into: autonomous inverters (current inverters and voltage inverters) and dependent inverters (grid-driven, Grid-tie, etc.)

Inverter circuit design

The semiconductor switches of the inverter are controlled by a controller and have reverse shunt diodes. The voltage at the inverter output, depending on the current load power, is regulated by automatically changing the pulse width in the high-frequency converter unit, in the simplest case this is.

The half-waves of the output low-frequency voltage must be symmetrical so that the load circuits in no case receive a significant constant component (this is especially dangerous for transformers); for this, the pulse width of the low-frequency block (in the simplest case) is made constant.

In controlling the output switches of the inverter, an algorithm is used that ensures a sequential change in the power circuit structures: direct, short-circuited, inverse.

One way or another, the magnitude of the instantaneous load power at the inverter output has a pulsating character with double the frequency, so the primary source must allow such an operating mode when pulsating currents flow through it, and withstand the corresponding level of interference (at the inverter input).

If the first inverters were exclusively mechanical, today there are many options for semiconductor-based inverter circuits, and there are only three typical circuits: bridge without a transformer, push-pull with zero terminal of the transformer, bridge with a transformer.

A bridge circuit without a transformer is found in uninterruptible power supply devices with a power of 500 VA or more and in automotive inverters. A push-pull circuit with a zero transformer terminal is used in low-power UPSs (for computers) with a power of up to 500 VA, where the voltage on the backup battery is 12 or 24 volts. A bridge circuit with a transformer is used in powerful uninterruptible power supplies (for units and tens of kVA).

In voltage inverters with a rectangular output, a group of switches with freewheeling diodes is switched so as to obtain an alternating voltage across the load and provide a controlled circulation mode in the circuit.

The proportionality of the output voltage is determined by: the relative duration of control pulses or the phase shift between the control signals of groups of keys. In an uncontrolled reactive energy circulation mode, the consumer influences the shape and magnitude of the voltage at the inverter output.

In voltage inverters with a step output, the high-frequency pre-converter generates a unipolar step voltage curve, roughly approximating a sinusoid in shape, the period of which is equal to half the period of the output voltage. The LF bridge circuit then turns the unipolar step curve into two halves of a multipolar curve, roughly resembling a sine wave in shape.

In voltage inverters with a sinusoidal (or almost sinusoidal) output waveform, the high-frequency preliminary converter generates a constant voltage close in magnitude to the amplitude of the future sinusoidal output.

After this, the bridge circuit forms a low-frequency alternating voltage from a direct voltage, using multiple PWM, when each pair of transistors at each half-cycle of the output sinusoid is opened several times for a time varying according to a harmonic law. The low-pass filter then extracts a sine wave from the resulting waveform.

The simplest circuits for preliminary high-frequency conversion in inverters are self-generating. They are quite simple in terms of technical implementation and are quite effective at low powers (up to 10-20 W) for powering loads that are not critical to the energy supply process. The frequency of self-oscillators is no more than 10 kHz.

Positive feedback in such devices is obtained from saturation of the transformer magnetic circuit. But for powerful inverters such schemes are not acceptable, since losses in the switches increase, and the efficiency ends up being low. Moreover, any short circuit at the output disrupts self-oscillations.

Better circuits for preliminary high-frequency converters are flyback (up to 150 W), push-pull (up to 500 W), half-bridge and bridge (more than 500 W) on PWM controllers, where the conversion frequency reaches hundreds of kilohertz.

Types of inverters, operating modes

Single-phase voltage inverters are divided into two groups: with pure sine wave output and with modified sine wave. Most modern devices allow a simplified form of the network signal (modified sine wave).

A pure sine wave is important for devices that have an electric motor or transformer at the input, or if it is a special device that works only with a pure sine wave at the input.

Three-phase inverters are typically used to create three-phase current for electric motors, such as power supply. In this case, the motor windings are directly connected to the inverter output. In terms of power, the inverter is selected based on its peak value for the consumer.

In general, there are three operating modes of the inverter: starting, continuous and overload mode. In the starting mode (charging the capacity, starting the refrigerator), the power can for a split second exceed twice the inverter rating; this is acceptable for most models. Long-term mode - corresponding to the inverter rating. Overload mode - when the consumer's power is 1.3 times higher than the nominal - in this mode, the average inverter can operate for about half an hour.

Frequency converters are technical devices that convert input network parameters into output parameters at various frequencies. Modern AC inverters have a wide frequency range.

The asynchronous frequency converter is designed to convert mains 3- or 1-phase alternating current f 50 Hz into 3-phase or 1-phase f 1 - 800 Hz.

Manufacturers produce electro-induction frequency generators, which are of the following design:

asynchronous electric motor;
inverters.

Frequency generators are often used to smoothly regulate the rotation speed of an asynchronous motor (IM) by generating specified network parameters at the output of the frequency generator. In the simplest cases, adjustment of f and U is performed with the corresponding V/f relationship; in more sophisticated inverters it is implemented as vector control.

Classification of frequency converters

According to the type of supply voltage, frequency converters are divided into types:

single-phase;
three-phase;
high-voltage devices.

The main task of a frequency converter can be formulated as follows: transferring the working process to an economical mode by controlling the speed and torque of the motor, according to the specified technical parameters and the nature of the load.

In this case, the digital display of the device shows such system operating parameters as:

the value of I and U of the engine;
output values of frequency, speed, power and torque (f, v, P and M);
displaying the status of discrete inputs for regulating the speed of rotation of the IM shaft and remote control of the system;
duration of operation of the frequency converter itself.

According to the area of use, the types of inverters are:

industrial use with power up to 315 kW;
Inverter with vector control with power up to 500 kW;
for controlling mechanisms with pump-fan type load (P 15 - 315 kW);
and other lifting structures;
for use in explosive environments;
VFDs installed directly on the electric motor.

Frequency converter structure

The structure of a modern inverter is built on the principle of energy conversion and includes a power and control component. The first, as a rule, is performed on thyristors or transistors, which play the role of electric switches. The control unit is implemented on microprocessors. Using keys that open and close circuits, it allows you to quickly solve many diagnostic, protection, and control tasks.

According to the principle of operation, frequency converters are of two types:

with the presence of an intermediate DC link;
with direct connection.

All of them have a number of advantages and disadvantages that determine the scope of effective use of each of them.

Direct frequency converters

They belong to the earliest devices with a simplified power unit, which is a rectifier based on thyristors.

The control system turns on the group thyristors and connects the motor windings to the power supply. Direct - this is a reversible thyristor frequency generator. Its main advantage is that it connects directly to the network without additional devices.

In this way, it turns out that the U out frequency generator is formed from truncated segments of the U out sinusoids. The figure shows an example of a formed Uout for one of the load phases. 3-phase sinusoidal components Uа, Uв, Uс are supplied to the thyristor input. The voltage Uout is represented by a non-sinusoidal “sawtooth” shape, which in approximated form looks like a sinusoid (thick curve). The drawing shows that the frequency U out cannot be equal to or exceed the power supply frequency. Therefore, the control range of the electric motor rotation speed is small (less than 1: 10). Limiting limits do not make it possible to use such ones in sophisticated VFDs. The latter are designed for a wide range of indicator adjustments.

The use of thyristors increases the complexity of the control system, and therefore the cost of the frequency converter increases.

The output “truncated” sinusoid of the frequency generator is a source of high-frequency harmonics, causing additional losses in the electric motor, overheating of the electric machine, reduction of torque, and noise in the power supply network that interferes with operation. The use of compensating devices increases the price, weight, size, and reduces the efficiency of the entire system.

Nevertheless, the immediate ones delight users with their certain advantages. These include:

sufficiently high efficiency achieved by one conversion of electricity;
operation in various modes, including with energy recovery into the network;
reliability, relative cheapness, complete controllability and convenience;
availability of unlimited capacity expansion of the system;

Such circuits are used in electric drives produced in previous years. In new designs they are not developed in practice.

Frequency converters with DC link

These are devices made using a transistor or thyristor circuit. However, their main distinguishing feature is that the correct and safe operation of the frequency generator requires the presence of a constant voltage link. Therefore, to connect them to an industrial network, a rectifier is required. Typically, complete equipment is used, consisting of a frequency converter and rectifier, controlled by one control system.

The inverter of this group uses a two-stage conversion of electricity: sinusoidal U input with f = const is straightened in the rectifier (V), filtered by a filter (F), smoothed, and then re-converted by the inverter (I) into U ̴. Due to the two-stage conversion of electricity, the efficiency decreases and the weight and size indicators slightly deteriorate in comparison with direct connection.

To create a sinusoidal U ̴ self-governing. They use an advanced thyristor and transistor base as the key base.

The main advantage of thyristor converter equipment is the ability to operate with large network parameters, while withstanding continuous load and pulsed influences. The devices have higher efficiency.

Frequency converters based on thyristors today are superior to other high-voltage drives, the power of which amounts to tens of MW with U out from 3 to 10 kV and more. However, their price is correspondingly the highest.

Advantages:

highest efficiency;
possibility of use in powerful drives;
reasonable cost, despite the introduction of additional elements.

Operating principle of the frequency converter

The fundamental drive is determined by a double conversion inverter. The principle of operation is to:

input variable toxinusoidal type 380 or 220V is rectified by a block of diodes;
then filtered by capacitors to minimize voltage ripple;
then the voltage is supplied to microcircuits and transistor bridges, which create a 3-phase wave from it with set parameters;
At the output, rectangular pulses are converted into sinusoidal voltage.

How to connect and configure a frequency converter?

The general connection diagram for an asynchronous electric motor using a frequency converter is, in principle, not complicated, since all the main wiring is contained in the device housings. For a techie with practical knowledge, understanding it will not be difficult. In the circuit, a place is allocated for the converter immediately after the circuit breaker with a rated current equal to the rating of the electric motor. When installing the converter into a 3-phase network, it is necessary to use a three-pole circuit breaker that has a common lever. In case of overload, this will allow you to instantly disconnect all phases from the power supply network. The operating current must be equal to the current of one phase of the electric motor. For single-phase power supply, you should choose a circuit breaker with triple the current value of one phase.

In all cases, the inverter must be installed with circuit breakers connected to the neutral or ground wire.

In practice, setting up a frequency converter means connecting the cable cores to the visible contacts of the electric motor. The specific connection is determined by the nature of the voltage generated directly by the frequency converter. For 3-phase networks at industrial facilities, the electric motor is connected in a “star” - this diagram implies a parallel connection of the winding wires. For domestic use in single-phase networks, a “triangle” circuit is used (where U out does not exceed U nom by more than 50%).

The control panel must be located where it will be comfortable to use. The connection diagram for the remote control is usually shown in the user manual for the frequency converter. Before installation, before power is applied, the lever must be moved to the “off” position. After this, the corresponding indicator light should light up. By default, to start the device you need to press the “RUN” key. To smoothly increase the speed of the electric motor, you need to slowly turn the remote control handle. When rotating in reverse, you must reset the mode using the reverse button. Now you can move the handle to the working position and set the required rotation speed. It is worth noting that the control panels of individual inverters indicate not the mechanical speed, but the frequency of the supply voltage.

Why do you need a frequency converter?

The use of gate valves and control valves in production is gradually becoming a thing of the past. The asynchronous motors that replaced them are distinguished by their high performance and power, but they are also not without characteristic disadvantages. For example, control over the speed of rotation of the rotor requires additional elements. Starting currents exceed the rated currents up to seven times. Such shock overload affects the service life of the unit.

The highly economical operation of pumps is based on constant adjustment of technical indicators such as temperature, pressure and water flow. and fans require adjustment of temperature, air pressure and gas rarefaction. The economical use of machines is provided by adjusting the engine rotation speed. In the conveyor specificity of work, an important feature is productivity. Special frequency units are designed to solve such problems.

For companies and enterprises, private converters are necessary in terms of:

saving energy resources;
long service life of the mechanical and electrical parts of process equipment;
reducing cash costs for planned repair and maintenance procedures;
conducting operational management, fundamental control over technical parameters, etc.

It also increases the technical efficiency of production by freeing up some equipment.

Where are frequency converters used?

The equipment is widely used in industrial applications and devices where it is necessary to change the motor rotation speed, measures to combat amplitude starting currents or adjustments in control parts (combinations of elementary converters using feedback), etc. Let's consider their use as needed:

Pumps. Since power consumption is proportional, as is known, to the cube of the rotation speed, its use allows saving energy consumption by up to 60%, in comparison with the method of power regulation using dampers on the pipe. The annual use of the frequency converter pays for all the costs of its purchase. The devices also allow:

reduce heat and water losses by 5 - 10%,
reduce the number of pipeline accidents;
provide complete protection of the electric motor.

An additional advantage is the solution to the problem with water hammer: working inverters smooth out the start/stop of the pump. At modernized pumping stations, systems have been installed that make it possible without the need to install a controller.

Fans. Everything said above for pumps also applies to fans. As for the savings in electricity consumption, they are even more significant here, since in order to directly start large fans, more powerful motor units are often used. Improvement of technological installations leads to increased profitability of production. Efficiency is also achieved by reducing idle losses.

Transporters. Adaptation of the movement speed to the speed of the technological system, which is not a constant value. A smooth start significantly increases the service life of the mechanical part of the system, since shock loads damage technical equipment.

The scope of use of frequency converters is quite extensive. Among the controllable types of low power, we can also distinguish centrifugal pumps, compressors, centrifuges, blowers, etc.

The general industrial series of medium-power VFD-controlled frequency generators includes motors in fans, smoke exhausters, water supply systems, mixers, dispensers, and production lines.

It is difficult to imagine elevator and other lifting and transport equipment with significant overloads during start/stop without vector control using converters.

The use of an inverter with feedback makes it possible to ensure the accuracy of the rotation speed, which will be the key to improving the quality of the technological process and solving assigned problems. Well-known manufacturers have a number of models focused on operating mode in a closed system. The equipment is recommended for use in the woodworking industry, robotics, precision positioning systems, etc.

All of the listed equipment can be controlled using converters with analog-to-digital inputs/outputs for regulation, remote control and monitoring via a serial communication line.

Other advantages of frequency drivers:

smooth regulation of engine rotation speed makes it possible not to use gearboxes, variators, chokes and other control equipment, which makes the control structure simpler, cheaper and significantly more reliable;
Frequency generators combined with IM can be completely used to replace DC electric drives;
it is possible to create multifunctional drive control systems based on an inverter with a controller;
modernization of the technological structure can be carried out without interruption in work.

Conclusion

It is worth noting that in some cases, the use of modern production management using frequency converters leads to a reduction not only in energy resources, but also in losses of transported substances. In industrialized countries it is almost impossible to find an asynchronous electric motor without a frequency converter.

We roughly know how things stand for us today, but what awaits us in the future? Looking at the situation through the lens of the user, it is expected that frequency converters will be divided into two parts: the first will contain equipment aimed at the user amateur and having a minimum number of settings and a maximum of automatic ones, and the second will contain devices that have a maximum number of settings with greater capabilities and are designed for use specialists capable of using all these opportunities.

Voltage converters are special devices that, in the event of a lack of voltage in the network, convert direct current into alternating current. That is, from a DC battery you can get alternating current with a voltage of 220 volts and a frequency of 50 hertz.

Voltage converter is also called. For many electrical appliances, electric current parameters are of great importance. In case of deviations from the established parameters, damage to electrical appliances and devices may occur. And if surges in the network are permanent, then in addition to the inverter, it is used.

Advantages of voltage converters

If we compare a conventional generator and a converter, the latter has a number of advantages:

The device is highly environmentally friendly, since the electrical energy for conversion is stored in the battery. Unlike a generator, an inverter does not produce harmful emissions into the atmosphere;
The absolutely silent operation of the inverter allows it to be used not only in a private house, as an electric generator, but also in an apartment, almost anywhere;
Unlike an electric generator, a current converter does not require frequent maintenance, that is, it does not require additional material costs;
The operating time depends entirely on the amount of fuel and engine life. The converters are capable of independently maintaining the highest battery charge; if necessary, you can always install additional batteries;
The inverter, designed for 220 volts, switches automatically in the event of a power failure and does not require people to be present near it.

Using voltage converters

Who primarily needs current converters:

If it is necessary to maintain the heating system in working condition in the event that the electrical network is turned off. The same goes for refrigerators and computers. The converter will not only prevent failure of electrical equipment, but will also ensure its continuous operation;
The inverter can be used not only in a private house or apartment, but also in the field, where in the complete absence of electricity it can replace an electric generator;
A current converter can be indispensable in hospitals, especially during operations and in dental offices;
Inverters are indispensable in stores selling food products, as well as in food warehouses, where the failure of refrigerators can be very expensive.

From this article you will learn what it is, consider its circuit, operating principle, and also learn about the settings of industrial designs. The main emphasis will be on manufacturing. Of course, for this you will need to have at least a basic understanding of wiring technology. You need to start with the purposes for which frequency converters are used.

When does the need for an inverter arise?

Modern frequency converters are high-tech devices that consist of semiconductor-based elements. 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, using a frequency converter, you can change the rotation speed. The idea arises of purchasing 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 rotation speed using a gearbox built on the basis of a variator or a gear type. But such structures are very large, it is not always possible to use them. In addition, such mechanisms need to 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.

Main components of the frequency converter

Any frequency converter consists of four main modules:

Rectifier block.
DC voltage filtering devices.
Inverter unit.
Microprocessor control system.

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

It will be discussed in detail below and a diagram is provided. The frequency converter for an 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, the temperature of power semiconductor elements is monitored. In addition, there is a protection function against short circuit and overcurrent. The frequency converter must be connected to the power supply using protective devices. There is no need for it.

Frequency converter rectifier

This is the very first module through which current flows. With its help, alternating current is rectified - converted into direct current. This happens thanks to the use of elements such as semiconductor diodes. But now it’s worth mentioning a small feature. You know that most of the power comes from a three-phase AC network. But this is not available everywhere. Of course, large enterprises have it, but they rarely use it in everyday life, since it is easier to carry out a single-phase one. And taking into account electricity, things are simpler.

And frequency converters can be powered from both a three-phase network and a single-phase one. What's the difference? But 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 with 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, the result is AC rectification. The output will appear “plus” and “minus”.

DC voltage filtering

At the output of the rectifier you have a constant voltage, but it has large ripples, and the variable component still slips through. To smooth out all these “irregularities” in the current, you will need to use at least two elements - an inductor and an electrolytic capacitor. But everything is worth talking about in more detail.

The inductor has a large number of turns, it has some that allows you to slightly smooth out the ripples of the current flowing through it. The second element is a capacitor connected between 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 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 itself, as a result of which it simply disappears.

Inverter module

The inverter unit, to be precise, is 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 there are two semiconductor elements. It is worth noting that the inverter stage uses modern assemblies of IGBT transistors. Even a homemade one, even a Delta frequency converter, the most affordable and accessible today, consists of the same components. The possibilities are just different.

They have three inputs, the same number of outputs, as well as six connection points to the control device. It is worth noting that when making a frequency converter yourself, it is necessary to select the assembly according to power. Therefore, you must immediately decide 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 industrial designs have. The reason for this is not that the manufactured power transistor assemblies are inefficient. The fact is that making a control module at home turns out to be quite difficult. Of course, we are not talking about soldering elements, but about programming a microcontroller device. The simplest option is to make a control unit with which you can adjust the rotation speed, reverse, current and overheat protection.

To change it is necessary to use a variable resistor, 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 operates according to a specific algorithm, which is written before programming begins. The microprocessor system operates strictly according to it. Siemens control modules are very popular. The frequency converter from this manufacturer is highly reliable and 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 setup algorithm is almost the same for everyone. Of course, it will not be possible to configure the frequency converter without certain knowledge. You need to have two things - experience in adjustment and an instruction manual. The latter has an application that describes all the functions that can be programmed. Usually there are several buttons on the case of the frequency converter. At least four pieces must be present. Two are designed to switch between functions; the rest are used to select parameters or cancel entered data. To enter 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 an instruction manual. It is also worth noting that the functions are divided into several subgroups. And it won’t be difficult to get confused in them. Try not to change 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, setting up a frequency converter will seem very simple to you.

conclusions

When operating, servicing or manufacturing the frequency converter, all safety precautions must be observed. Remember that the device contains electrolytic capacitors that retain their charge even after being disconnected from the AC mains. Therefore, before disassembling, it is necessary to wait for the discharge. Please note that the design of frequency converters contains elements that are afraid of static electricity. This applies in particular to the microprocessor control system. Therefore, soldering should be carried out with all precautions.