The rotor of any electric motor is driven by forces caused by a rotating electromagnetic field inside the stator winding. The speed of its revolutions is usually determined by the industrial frequency electrical network.
Its standard value of 50 hertz implies the completion of fifty periods of oscillation within one second. In one minute, their number increases 60 times and is 50x60 = 3000 revolutions. The rotor rotates the same number of times under the influence of the applied electromagnetic field.
If you change the value of the mains frequency applied to the stator, then you can adjust the speed of rotation of the rotor and the drive connected to it. This principle is the basis of electric motor control.
Types of frequency converters
By design, frequency converters are:
1. induction type;
2. electronic.
Asynchronous electric motors, made and launched into the generator mode, are representatives of the first type. They have low efficiency during operation and are noted for low efficiency. That's why they didn't find wide application in production and are rarely used.
The method of electronic frequency conversion allows you to smoothly adjust the speed of both asynchronous and synchronous machines. In this case, one of two control principles can be implemented:
1. according to a predetermined characteristic of the dependence of the speed of rotation on the frequency (V / f);
2. vector control method.
The first method is the simplest and less perfect, and the second is used to precisely control the rotation speeds of critical industrial equipment.
Features of vector control of frequency conversion
The difference of this method is the interaction, the influence of the control device of the converter on the "spatial vector" of the magnetic flux, rotating with the frequency of the rotor field.
Algorithms for the operation of converters according to this principle are created in two ways:
1. sensorless control;
2. flow control.
The first method is based on the assignment of a certain dependence of the inverter sequence interleaving for pre-prepared algorithms. In this case, the amplitude and frequency of the voltage at the output of the converter are regulated by slip and load current, but without the use of feedback on the speed of rotation of the rotor.
This method is used when controlling several electric motors connected in parallel to the frequency converter. Flux regulation implies control of operating currents inside the motor with their decomposition into active and reactive components and making adjustments to the operation of the converter to set the amplitude, frequency and angle for the output voltage vectors.
This allows you to improve the accuracy of the engine and increase the boundaries of its regulation. The use of flow control enhances the capabilities of drives operating at low speeds with high dynamic loads, such as crane lifting devices or winding industrial machines.
The use of vector technology makes it possible to apply dynamic torque control to .
equivalent circuit
Basic simplified electrical circuit induction motor can be imagined next view.
A voltage u1 is applied to the stator windings, which have active R1 and inductive X1 resistances. It, overcoming the resistance of the air gap Xv, is transformed into the rotor winding, causing a current in it that overcomes its resistance.
Equivalent Circuit Vector Diagram
Its construction helps to understand the ongoing processes inside the induction motor.
The stator current energy is divided into two parts:
iµ - flow-forming share;
iw - moment-forming component.
In this case, the rotor has an active resistance R2/s, which depends on the slip.
For sensorless control, the following are measured:
voltage u1;
current i1.
Their values are calculated:
iµ - flux-forming current component;
iw - moment-generating quantity.
The calculation algorithm has already included an electronic equivalent circuit asynchronous motor with current controllers, which takes into account the conditions of saturation of the electromagnetic field and the loss of magnetic energy in steel.
Both of these components of the current vectors, which differ in angle and amplitude, rotate together with the rotor coordinate system and are recalculated into stationary system stator orientation.
According to this principle, the parameters of the frequency converter are adjusted to the load of the asynchronous motor.
The principle of operation of the frequency converter
This device, which is also called an inverter, is based on a double change in the waveform of the power supply network.
First, industrial voltage is applied to a power rectifier unit with powerful diodes that remove sinusoidal harmonics, but leave signal ripples. To eliminate them, a capacitor bank with an inductance (LC filter) is provided, which provides a stable, smoothed shape to the rectified voltage.
Then the signal is fed to the input of the frequency converter, which is a three-phase bridge circuit of six IGBT or MOSFET series with reverse polarity breakdown protection diodes. The thyristors previously used for these purposes do not have sufficient speed and operate with great noise.
To enable the "braking" mode of the engine, a controlled transistor with a powerful resistor that dissipates energy can be installed in the circuit. This technique allows you to remove the voltage generated by the motor to protect the filter capacitors from overcharging and failure.
The method of vector frequency control of the converter allows you to create circuits that automatically control the signal by ATS systems. For this, the control system is used:
1. amplitude;
2. PWM (Width Pulse Simulation).
The method of amplitude regulation is based on a change in the input voltage, and PWM is based on the switching algorithm of power transistors with a constant input voltage.
With PWM regulation, a signal modulation period is created when the stator winding is connected in strict order to the positive and negative terminals of the rectifier.
Since the generator clock frequency is quite high, then in the winding of the electric motor, which has inductive reactance, they are smoothed to a sinusoid normal view.
PWM control methods make it possible to eliminate energy losses as much as possible and provide high conversion efficiency due to the simultaneous control of frequency and amplitude. They have become available due to the development of technologies for driving power gate-off thyristors of the GTO series or bipolar brands of IGBT transistors with an insulated gate.
The principles of their inclusion to control a three-phase motor are shown in the picture.
Each of the six IGBTs is connected in an anti-parallel circuit to its own reverse current diode. In this case, through the power circuit of each transistor passes active current asynchronous motor, and its reactive component is sent through diodes.
To eliminate the influence of external electrical interference on the operation of the inverter and the motor, the design of the frequency converter circuit can include , eliminating:
radio interference;
electrical discharges induced by operating equipment.
Their occurrence is signaled by the controller, and to reduce the impact, shielded wiring is used between the motor and the output terminals of the inverter.
In order to improve the accuracy of asynchronous motors, the control circuit of frequency converters includes:
input communication with advanced interface options;
built-in controller;
memory card;
software;
information LED-display showing the main output parameters;
brake chopper and built-in EMC filter;
cooling system of the circuit, based on blowing by fans of increased resource;
engine warm-up function direct current and some other possibilities.
Operating wiring diagrams
Frequency converters are designed to work with single-phase or three-phase networks. However, if there are industrial DC sources with a voltage of 220 volts, then inverters can also be powered from them.
Three-phase models are calculated for a mains voltage of 380 volts and give it to the electric motor. Single-phase inverters are powered by 220 volts and produce three phases separated in time at the output.
The connection diagram of the frequency converter to the motor can be made according to the schemes:
stars;
triangle.
The motor windings are assembled into a "star" for a converter powered from a three-phase 380 volt network.
According to the "triangle" scheme, the motor windings are assembled when the converter supplying it is connected to a single-phase 220 volt network.
When choosing a method of connecting an electric motor to a frequency converter, one must pay attention to the ratio of powers that a running motor can create in all modes, including slow, loaded start, with the capabilities of an inverter.
You can not constantly overload the frequency converter, and a small margin of its output power will ensure its long and trouble-free operation.
Add tagFrequency converter
Hello everybody. So I decided to write an article about an asynchronous drive and a frequency converter that I made. My friend had to turn the sawmill, and turn it well. And I myself was engaged in impulse electronics and immediately offered him a frequency converter. Yes, it was possible to buy a branded converter, and I had to deal with them, parameterize them, but I wanted my own, HOME-MADE! Yes, and the circular drive is not critical to the quality of speed control, but it must be ready for shock loads and overload operation. Also, the most-simple control with a couple of buttons and no parameters there.
The main advantages of a variable frequency drive (maybe I repeat for someone):
We form from one phase 220V full-fledged 3 phases 220V with a shift of 120 degrees, and we have a full torque and power on the shaft.
Increased starting torque and soft start without high starting current
There is no magnetization and unnecessary heating of the motor, as when using capacitors.
Ability to easily adjust speed and direction if needed.
Here's the schematic I came up with:
A 3-phase IGBT bridge with freewheeling diodes (used the existing G4PH50UD) is controlled via an HCPL 3120 optodriver (bootstrap power supply) by a PIC16F628A microcontroller. At the input, a quenching capacitor for a smooth charge of electrolytes of the DC link. Then it is shunted by a relay and the microcontroller simultaneously receives logic level readiness. There is also an overcurrent protection trigger. and severe engine overload. The control is carried out by 2 buttons and a toggle switch for changing the direction of rotation.
The power part was assembled by me by hinged mounting. The controller board is ironed out in this form:
Parallel resistors of 270k each on feed-through gate capacitors (I forgot to draw places for them) soldered on the back of the board, then I wanted to replace it with smd, but left it like that.
There is appearance this board, when already soldered:
On the other side
To power the control, a typical pulsed flyback (FLAYBACK) power supply was assembled.
His schema:
You can use any 24V power supply, but stabilized and with a delay in the loss of output voltage from the moment the mains power is lost for a couple of seconds. This is necessary so that the drive has time to trip on a DC error. Achieved by installing electrolyte C1 of a larger capacity.
Now about the most important thing ... about the microcontroller program. Programming simple blinkers was not difficult for me, but here it was necessary to strain the brains. Poryskav in nete, I did not find at that time suitable information. I was also offered to supply specialized controllers, for example, the MOTOROLA MC3PHAC controller. But I would like, I repeat, my own. I began to deal in detail with PWM modulation, how and when to open which transistor ... Some patterns were discovered and a template came out of the simplest program for working out delays, with which you can issue a satisfactorily sinus PWM and regulate the voltage. Of course, the controller did not have time to count anything, the interrupts did not give what was needed, and therefore I immediately discarded the idea of a steep PWM calculation on the PIC16F628A. As a result, a matrix of constants was obtained, which was processed by the controller. They set both frequency and voltage. Fumbled honestly for a long time. The sawmill was already sawing capacitors to the fullest when the first version of the firmware was released. I checked the whole circuit first on a 180 watt fan engine. Here's what the "experimental setup" looked like:
The first experiments showed that this project definitely has a future.
The program was being finalized and, as a result, after the promotion of the 4kW engine, it could be assembled and sent to the sawmill.
The comrade was pleasantly surprised, although he was skeptical from the very beginning. I was also surprised, because short circuit protection checked (accidentally happened in boro engine). Everything is alive. The 1.5kW 1440rpm engine easily gnawed the timber with a 300mm disc. Pulleys one to one. With blows and knots, the light dimmed slightly, but the engine did not stop. I also had to tighten the belt a lot, because. slipped under heavy load. Then they put in a double gear.
Now I’m still finalizing the program, it will become even better, the PWM algorithm is a little more complicated, there are more modes, the ability to spin up above the face value ... and here below is the simplest version that has been working on the saw for about a year.
Its characteristics:
Output Frequency: 2.5-50Hz, step 1.25Hz; The PWM frequency is synchronous, variable. Range approximately 1700-3300Hz.; V/F scalar control mode, motor power up to 4kW.
The minimum operating frequency after a single press of the RUN button is 10Hz.
When the RUN button is held down, acceleration occurs, when the frequency is released, the frequency remains the one to which it managed to accelerate. Maximum 50Hz - signaled by LED. Acceleration time about 2s.
The "ready" LED indicates that the drive is ready to start.
The reverse is interrogated in the ready state.
There are no braking and frequency control modes down, but they are not needed in this case.
Pressing Stop or RESET causes a coast to stop.
That's all for now. Thanks for reading to the end.
|
How do you like this article? |
In the modern energy market, electricians had to use a large starting or phase-shifting capacitor to connect an asynchronous motor.
The engine was running, but significantly lost power. Also, the use of capacitors greatly heated the motor windings, which greatly reduced its service life, and the motors often had to be “rewound”. Given that the windings of an induction motor are made of copper wire, such repairs brought great damage.
Since the asynchronous motor is integral part almost everyone modern drive, then the issue of creating frequency regulation rose to a special level. And now, chastotniki are already widely used to connect an electric motor to the network and control it.
In fact, a frequency inverter is a device that changes the frequency of the voltage applied to the windings with PWM control. Thanks to the chastotnik, it turned out to connect an asynchronous motor to the network without damaging its resource, without overheating, and also give a lot of opportunities to control the speed of rotation of the shaft.
Also, using various interfaces for transmitting data and commands, the use of chastotnikov made it possible to combine all the drives of a large enterprise into one dispatcher control and parameter control system.
In the world of modern process automation, this is a weighty argument.
A modern frequency inverter consists of two fundamental blocks. The first block completely smoothes the voltage and produces a constant output. DC voltage is applied to the frequency generation power unit. After conversion, at the output of the second block, the voltage frequency will already be the same as set by the setting.
The microprocessor, which is built into the frequency converter, is responsible for the ability to change the voltage frequency. Using given program, the processor monitors the output frequency of the voltage, as well as the parameters of the electric motor.
In fact, frequency converters for asynchronous motors, the principle of operation of which is to simply generate the desired frequency of alternating current, these are modulators of the desired voltage nature, which is necessary for this or that equipment. This is what reduced Negative influence on the operation of the electric motor, which took place when using condensates.
The electric motor receives exactly the voltage that it is supposed to have for normal and full operation.
We consider it necessary to note that even in the presence of a three-phase voltage line, it is not always rational to connect an electric motor to the network simply through a switch. In this case, the engine will work, but it will not be possible to regulate its operation. It will not work and monitor the condition of the windings.
In industrial performance, two main types can be found:
- Special.
- Universal.
A special frequency converter for an asynchronous motor, the circuit of which is somewhat different from the universal one, is made for specific equipment according to specific needs. As a rule, these are very stripped-down versions that are not capable of working with any equipment.
Universal frequency inverters can work both in special equipment and in all other applications. That's why they are universal, that they can be customized and programmed for any needs.
Therefore, the choice for an asynchronous motor should be dictated not so much by the specific needs of the production, but also by the possibility of upgrading the equipment.
Almost all chastotniki today implemented the ability to set and control the operating mode of the electric motor from the control panel. The first control interface is built into the chassis itself. There is also a knob for regulating the speed of rotation of the engine.
But you can also use remote control panels. Which can be located both in the control room and directly on the machine, which is driven by an electric motor.
This is more common in situations where the machine with the engine is located in a room where installation is not recommended. frequency inverter. And it is installed away from the equipment.
Most frequency inverters allow you to program the operation of the equipment. But, setting the program simply from the control panel will not work. For this, a data transfer and settings interface is used, which, using a computer, allows you to set desired program work.
Control Signal Type Difference
When designing a workshop, it is very important to take into account that the communication of frequency converters with the control panel will occur using electrical impulses via communication wires. In this case, do not forget that different communication standards affect each other in different ways. Therefore, data transmission in one way can significantly reduce the quality of data transmission in another way.
Therefore, the calculation of the frequency converter for an asynchronous motor should be carried out not only according to its electrical performance, but also in terms of compatibility with the network.
The question of the power of the chastotnik, most likely, is in the foreground when calculating the drive for any machine or unit. The fact is that most frequency inverters are able to withstand large overloads up to 200 - 300%. But, this does not mean at all that to power an electric motor, you can safely buy a frequency converter with a segment lower than what is required by planning.
The choice is made with a mandatory margin of 20 - 30%. Ignoring this rule may result in the failure of the frequency converter and equipment downtime.
It is also important to take into account the peak loads that the frequency converter can withstand. The fact is that when starting an electric motor, its starting currents can greatly exceed the nominal ones. In some cases, the starting current exceeds the rated current by six times! The frequency must be designed for such changes.
Each electric motor is equipped with a cooling fan. These are blades that are installed at the rear of the engine and as the shaft rotates, they drive air through the motor housing.
If the electric motor is running at low speed, there may not be enough air flow to cool it.
In this case, you need to choose a frequency converter with engine temperature sensors. Or organize additional cooling.
Electromagnetic compatibility of frequency converters
When calculating both the network and the electric motor, it should be remembered that it is very susceptible to interference. Also, the frequency converter itself can become a source of interference to other equipment. That is why all connections to and from the chastotnik are made with shielded cables and maintaining a distance of 10 cm from each other.
At its core, the use of a private converter to power an asynchronous electric motor made it possible to significantly extend the life of the electric motor, made it possible to regulate the operation of the motor and save well on the consumption of electrical energy.
A simple frequency converter for an asynchronous motor.
The first was a restaurant - in winter, cold air should be strictly dosed on heated visitors, and in summer, on the contrary, those frozen from cold ice cream should be smoothly warmed with hot air from the street. You can't do without an inverter.
The second wants to shear shaggy sheep, but the trouble is the three-phase machine. And in the field there is only one and that is not 220v. Again you need an inverter.
The third general emery stone, drilling machine and winder - wanted to attach to the engine.
In the end, looking around, I saw - everything ... everything is made by Japanese, French, German inverters .... , but I don't have my own screwdriver sharpener yet. And besides, all decent companies have already written how to do it.
So since the asynchronous motor is so common and the three-phase voltage system created by M. O. Dolivo-Dobrovolsky is so convenient. And modern element base so good. To make a frequency converter is only a matter of personal desire and some financial possibilities. Perhaps someone will say “Well, why do I need an inverter, I will put a phase-shifting capacitor and everything is decided”. But at the same time, you can’t turn the speed and lose power, and then it’s not interesting.
Let's take it as a basis - in everyday life there is single-phase network 220v, popular motor size up to 1kw. So we connect the motor windings with a triangle. Further, it’s easier, you need a three-phase bridge driver IR2135 (IR2133), we choose this one because it is used in industrial technology, it has an SD output and a convenient pin layout. IR2132 is also suitable, but it has more dead time and no SD output. As a PWM generator, we will choose the AT90SPWM3B microcontroller - it is accessible, understandable to everyone, has a lot of features and is inexpensive, there is a simple programmer -https://real.kiev.ua/avreal/. We will choose power transistors of 6 pieces IRG4BC30W with some current margin - starting currents of AD can exceed the nominal ones by 5-6 times. And while we do not put a "brake" key and a resistor, we will brake and magnetize the rotor with direct current before starting, but more on that later .... The entire process of work is displayed on a 2-line LCD indicator. 6 buttons are sufficient for control (frequency +, frequency -, start, stop, reverse, menu).
It turned out here is such a scheme.
I do not pretend to be a complete design at all and I propose to take this design as a kind of basis for home electric drive enthusiasts. The boards shown here were made under the parts at my disposal.
Structurally, the inverter is made on two boards - the power part (power supply, driver and bridge transistors, power terminals) and the digital part (microcontroller + indicator). The boards are electrically connected by a flexible cable. This design has been chosen for transition to the TMS320 or STM32 or STM8 controller in the future.
The power supply is assembled according to the classical scheme and does not need comments. Chip IL300 linear opto isolation for current control 4-20mA. OS2-4 optocouplers simply duplicate the "start, stop, reverse" buttons for galvanically isolated control. Optocoupler output OS-1 "user function" (alarm, etc.)
Power transistors and a diode bridge are fixed to a common radiator. Shunt 4 turns of manganin wire with a diameter of 0.5 mm on a mandrel of 3 mm.
Immediately, I note some nodes and elements are not required at all. In order to simply turn the engine, it is not necessary external control current 4-20 Ma. There is no need for a current transformer, a current shunt is also suitable for evaluation measurement. No external alarm required. With an engine power of 400 W and a radiator area of 100 cm 2, there is no need for a temperature sensor.
IMPORTANT! - the control buttons available on the board are isolated from the power supply only by plastic pushers. Optocoupler must be used for safe control.
Possible changes in the circuit depending on the firmware.
The DA-1 amplifier can be connected to a current transformer or to a shunt. The DA-1-2 amplifier can be used to measure the mains voltage or to measure the thermistor resistance if the PD-1 temperature sensor is not used.
In the case of long connecting wires, at least an interference suppression ring must be put on each wire. There are interferences. For example, until I did this, my “mouse” hung.
I also consider it important to note the verification of the reliability of the insulation of blood pressure - because. when switching power transistors, voltage surges on the windings can reach values of 1.3 Upit.
General form. 
A little about management.
After reading books with long formulas, basically describing how to make a sine wave using PWM. And how to stabilize the speed of rotation of the motor shaft using a tachometer and a PID controller. I came to the conclusion - BP has a fairly rigid characteristic in the entire range of permissible loads on the shaft.
Therefore, for personal needs, the management described by law is quite suitable. Kostenko M.P. or as it is also called scalar. Sufficient for most practical cases of using a frequency-controlled electric drive with an engine speed control range of up to 1:40. Those. roughly speaking, in the simplest case, we make an ordinary 3-phase socket with a variable frequency and voltage that changes in direct proportion. With small “buts” in the initial sections of the characteristic, it is necessary to perform IR compensation, i.e. at low frequencies, a fixed voltage is needed. The second "but" to mix the 3rd harmonic into the voltage supplying the engine. Everything else will be done for us. physical principles HELL. You can read more about this in the document AVR494.PDF
Based on my personal observations and modest experience, these methods are most often used without any frills in drives up to 15 kW.
Further I will not delve into the theory and description of math models of blood pressure. Even without me, this was stated quite well by professors back in the 60s.
But in no case should you underestimate the complexity of managing blood pressure. All my simplifications are justified only by the non-commercial use of the inverter.
Power element board. 
V-1.0 program for AT90SPWM3B implements
1- Frequency control of AD. The voltage form is a sinusoid with 3 harmonics.
2- Reference frequency 5Hz-50Hz in 1Hz steps. PWM frequency 4 kHz.
3- Fixed acceleration-deceleration time
4- Reverse (only through the STOP button)
5- Acceleration to the set frequency in steps of 1 Hz
6 - Indication of the readings of the ADC channel 6 (bit depth 8 bits, window filter aperture 4 bits)
I use this channel to measure shunt current.
7 - Indication of the operating mode START, STOP, RUN, RAMP, and Frequency in Hz.
8- Alarm processing from ms IR2135
Why do you need to make a converter for a 3-phase electric motor yourself, and how to make it yourself? In order to protect the environment, regulations are being created everywhere that recommend that manufacturers of electrical devices make products that will save electrical energy. Often this can be achieved by proper control of the motor speed. The frequency converter easily solves this problem.
They are called differently: inverter, frequency current changer, frequency-controlled drive mechanism. Today, such devices are made by different factories, but many craftsmen make their own hands no worse.
How I made a frequency converter myself
I also made an asynchronous drive for my friend. He needed a drive for a sawmill, powerful and good. Since I liked to do electronics, I immediately offered him the following scheme:
Three-phase bridge on transistors with diodes feedback I used what was available. The control was carried out through the HCPL 3120 optodriver by the PIC16F628A microcontroller. At the entrance, I soldered a quenching container so that the electrolytes are charged smoothly. Then I soldered the shunt relay. I also installed a current protection trigger against short circuit and overload. For control, I installed two buttons and a switch for reverse rotation.
I assembled the power part on a hinged installation.
Resistors, connected in parallel by 270 kOhm using gate pass-through capacitors, soldered them behind the board. My board is shown in appearance:
View of this my board from the other side:
To connect the supply voltage, I assembled a power supply that works on impulses, flyback. Here is a diagram of this power supply:
How do I program the microcontroller? Simple blinkers didn't pose any problem for me. We got constants in the form of a matrix, on which my controller worked. The frequency and voltage were given by these values. I checked the entire scheme of operation on a low-power fan motor, 200 watts. My design looked like this:
Initial experiments gave good results. Then I modified the program. I spun the engine by 4 kW, and went to assemble the sawmill control.
During installation, my friend and I accidentally had a short circuit and the protection worked, we checked its operation. A 2 kW 1500 rpm motor sawed boards with ease. Now the program is still being finalized to promote the engine above par. Characteristics: frequency from 2 to 50 hertz in steps of 1.5 hertz, synchronous frequency, constantly changing, run-up from 1500 to 3500 hertz, U / F scalar type control, motor power up to 5 kW.
Hold the RUN button and accelerate the engine. We release, the frequency is kept at the level. When the LED lights up, the drive is ready to start.
How to make an inverter yourself with your own hands?
Along with the production of factory inverters, amateurs make them themselves, with their own hands. There is nothing complicated here. Such a frequency converter converts one phase, makes three phases out of it. An electric motor with a similar frequency converter is used at home, its power will not be lost.
The rectifier block in the circuit is located at the beginning. Next come, which cut off the current variables. To make these inverters, IGBT transistors are used.
Thyristors are the future, although they have been used in the present for a long time. A purchased chastotnik on bipolar transistors is expensive and is used in few places (servo drives, metal-cutting). These drives, like conveyors and conveyors, carousel machines, water pumping stations, climate control systems - this is a large part of the entire application of factory devices, where it is better to use frequency converters to control electric motors with short-circuited armatures and you can control the engine speed if you apply a potential by changing the frequency up to 50 hertz.
Let's bring simple examples frequency converters that pulled powerful electric motors of diesel locomotives and electric trains, which included many wagons of commodity platforms, large stations with 600-volt pumps that provide urban areas with drinking water. Obviously, these strong motors will not work on bipolar transistors. Therefore, apply active thyristors type GTO, GCT, IGCT and SGCT. They convert from direct current to a three-phase current network with good power. However, there are simple circuits on thyristors of a simple type, closed by the reverse cathode current. Such thyristors will not operate in PWM mode, they are well used in the direct regulation of electric motors, without a constant current. Frequency converters on thyristors in stagnant times were used for DC motors. Siemens has invented that has transformed the industry beyond recognition.
The cost of all parts of a homemade inverter is significantly lower than the price of a factory device.
Such homemade devices well suited for electric motors up to 0.75 kW.
What is the purpose of the inverter - its principle of operation
The inverter acts on the rotational speed of asynchronous motors. Motors convert electricity into mechanical motion. The rotational movement is converted into mechanical movements. This creates great convenience. Asynchronous motors are very popular in many aspects of people's lives.
The speed of the electric motor can be changed by other devices. But, they have many disadvantages. They are difficult to use, expensive, work with poor quality, the adjustment range is small.
For a motor with three phases, this problem is easily solved. Everyone knows that the use of frequency converters to change the speed is the best and correct method. Such an apparatus gives a soft start and braking, and also controls many processes occurring in the motor. In this case, emergencies are reduced to nothing.
To smoothly and quickly regulate the operation of the engine, experts have developed a special electrical circuit. The use of a chastotnik in the work makes it possible to work the engine without interruption, economically. Its efficiency reaches 98%. This is done by increasing the switching frequency. Mechanical devices cannot perform such functions.
How to control the speed of the inverter?
How can a chastotnik change an electric motor? First, he changes the mains voltage. Further, from it the desired amplitude and frequency of the voltage is obtained, it goes to the electric motor.
The run-up of the speed control interval by the converter is large. You can change the rotation of the motor in the other direction. So that the engine does not fail, you need to take into account the data from its characteristics, permissible revolutions, power.
What is the control drive made of?
Frequency diagram.
It has three units:
- a rectifier that gives a direct current potential when turned on to the power supply of the electrical network. The network may or may not be managed;
- a filter element that smoothes the output voltage (capacitance is used);
- an inverter that produces the desired frequency of the potential, the extreme link near the electric motor.
Frequency control mode
They are divided into types of engine speed control:
- (no connection to reverse side);
- vector control mode (there is or is no communication from the reverse side).
In the first case, the stator with its magnetic field is controlled. The vector control takes into account the action of the fields of the rotor magnet and the stator, the torque improves when different speeds rotation. This is the main difference between their control modes.
The vector method is more accurate and efficient. Servicing is more expensive. It is more suitable for professionals with good professional skills and knowledge. The scalar type control method is the easiest to work with. It is used with output parameters that do not require special precision adjustment.
How to connect an inverter in delta and star?
When we bought an inverter at an inexpensive price, then the need arises: connecting it to the electric motor ourselves without specialists. First you need to install a circuit breaker for de-energizing for safety. If a short circuit occurs in the phases, the entire system will shut down.
To the motor can be a star or a triangle.
When the control drive is with one phase, then the contacts of the electric motor are connected in a triangle. Then the power will not be lost. The power of this frequency converter will be no more than 3 kW.
Three-phase inverters are technically the most modern. They are powered by factory three-phase networks, connected by a star.
To limit the starting current and reduce the starting torque when starting the electric motor over 5 kW, you can use the triangle and star switching method.
When the stator is turned on, the star circuit is applied, and if the engine speed is normal, then they switch to the triangle version. But this is used when there is a possibility of connecting according to two schemes.
We note that in the star-delta version, there will always be large current drops. When switching to the second scheme, the engine speed will drop significantly. To restore the rotation speed, it is necessary to increase the current strength.
Chastotniki for motors up to 8 kW are of great applicability.
Application of new generation inverters
Modern ones are made using devices such as microcontrollers. This significantly increases the functions of inverters in control and monitoring algorithms from the point of view of work safety.
Frequency converters are successfully used in the following areas of production:
- in water supply, heat supply when changing the feed rate of the cold and hot water supply pump;
- in factory conditions of mechanical engineering;
- in light and textile industry;
- in energy and fuel production;
- for sewage pumps and wells;
- v technological processes for automatic control.
In order to manage and control the frequency converters, the device manufacturer offers a created program that will always communicate with the controller via the port, will show the status on the monitor and allow control. Data is documented by an exchange protocol and used by users who create control programs for electronics and controllers.
Data is exchanged in three stages:
- Identification.
- Initialization.
- Management and control.
The cost of uninterruptible voltage power supplies depends on whether it has a frequency converter. Such devices are the future. The sectors of the economy and energy will develop faster thanks to new modern devices.
