For the first time the world met with such a device as a three-phase asynchronous electric motor, at the end of the 19th century. And since that time, it began to be applied in every industrial enterprise, where it became an indispensable element. During operation of the electric motor, it is important to ensure its smooth start and stop. This can be done only with a special device - frequency converter.
First of all, it is advisable to equip large electric motors with a high power output with a converter. The advantage of having such a device is the ability to change the starting currents, setting the required value.
- 1 The principle of operation of the frequency converter
2 What to look for when choosing?
- 2.1 Materials
- 2.2 Self-assembly frequency converter
- 2.3 The procedure for assembling the inverter circuit
- 3 Connecting the frequency converter
- 4 Recommendations for equipment maintenance
- 5 Conclusion
The principle of operation of the frequency converter
Of course, you can adjust the starting current manually, but in this case a certain amount of energy will be spent. the amount of energy wasted that will adversely affect the operational resource electric motor. Observed in devices that do not have such a device, the current has a value greater than 5-7 times the rated voltage. In such conditions it is impossible to create normal conditions for equipment operation.
The operation of a device such as a frequency converter is based on the use of electronic mechanismwhich controls the operation of the engine. But its capabilities are not limited to a soft launch. With the help of a frequency converter, you can smoothly adjust the operation of the drive by choosing the optimal indicator between voltage and frequency, which is calculated strictly according to a given formula.
Among the advantages of such a device, the main thing to mention is that it helps to reduce the power consumption by an average of 50%. In addition, the frequency converter allows you to set a mode of operation that will take into account the needs of a specific production to the maximum extent.
The action of such a converter is based on the principle of double voltage conversion.
- At the initial stage, the network voltage is adjusted by rectifying and filtering it, which is achieved through the use of a capacitor system.
- Next comes the turn of the electronic control, due to which the current corresponding to the pre-selected mode is set for the current.
As a result, there are rectangular pulses that are corrected by the stator winding of the motor, which allows it to be brought to the level of a sinusoid.
What to look for when choosing?
If you pay attention to the models of converters available today, the determining factor is precisely the price of the choker. The fact is that only expensive models of frequency converters have the greatest functionality. However, in order for the selected converter to successfully cope with the necessary tasks, you need to proceed from specific conditions its use.
- The frequency converter can provide two types of control: vector and scalar. In the first case, you can set with high accuracy the required amount of current. A feature of scalar control is that the device operates only in one specified ratio between frequency and output voltage. Such devices can be used only for ordinary household devices, like a fan.
- Power characteristics largely affect the versatility of the frequency converter. This not only expands its capabilities, but also creates less maintenance problems.
- For the operation of the device should be provided with a network having the widest possible voltage range. In this case, the danger is reduced that the device will fail in case of sharp jumps. The greatest threat to equipment is an increase in voltage, which can lead to an explosion of line capacitors.
- An important parameter is the frequency, the value of which should be sufficient to meet the needs of production. By its lower limit, one can understand how wide opportunities there are for choosing the optimal drive speed. If there is a need for a device with a wider frequency range, then attention should be paid to vector-controlled models. In practice, the most common frequency with a range of 10-60 Hz, in rare cases, up to 100 Hz are used.
- Availability of various entrances and exitsused to manage. It is much more convenient to use a device that has a sufficiently large number of such connectors. However, this also leads to an increase in the cost of equipment, and also creates difficulties with proper configuration. Devices of this type can be provided with three types of connectors: discrete, digital, analog. The main purpose of the first is to enter control commands and output event messages. With the help of digital connectors input signals of digital sensors. Analog connectors are designed to solve the problem of inputting feedback signals.
- When choosing a converter model, you should pay attention to the control bus, the characteristics of which should match the capabilities of the frequency converter circuit, which is manifested in an appropriate amount connectors. The best option when there are enough of them in case of a possible upgrade.
- Overload capacity. It is recommended to give preference to the models of chastotnikov, the power reserve of which is 15% higher than the power of the engine used. In order to avoid mistakes, it will not hurt before making a decision to read the documentation. They usually give all the basic characteristics of the engine. If the task is to choose a chastotnik capable of withstanding peak loads, then it is recommended to give preference for equipment that will be able to maintain the current value at peak operation conditions by 10% more specified.
To make a do-it-yourself frequency converter for single phase electric motornecessary prepare the following:
- IR2135 (IR2133) - three-phase bridge driver;
- AT90SPWM3B - microcontroller (used as a PWM generator);
- programmer (for example, AVReAl);
- six pieces of transistors IRG4BC30W;
- LCD indicator;
- six buttons.
Self-assembly frequency converter
Do not give up the idea to make a converter on your own. This task can be solved by any owner, given that the network can be found a large number of instructions and diagrams on the assembly of such a device and its connection to asynchronous motor.
Considering this option, the most important thing to remember is that a model assembled by hand should differ not only affordable price, but also reliability, and also be able to successfully solve problems in household conditions. If there is a need for a device for industrial use, then, naturally, the best choice would be the converters offered by stores.
The procedure for assembling the inverter circuit
The following scheme is designed for wiring with a voltage of 220V and one phase. The device is intended for an engine whose power does not exceed 1 kW.
First, it is necessary to interconnect the motor windings, for which the “triangle” variant is used.
The basis of the design of the equipment form two boards. The first will give way to accommodate items such as power supply and driver. In addition to them, transistors and power terminals will be installed here. The second board is used for mounting the microcontroller and indicator. A flexible cable is used to connect the boards with each other.
For the manufacture of a pulsed power supply uses a conventional scheme that can be found on the network.
To control the operation of the engine, there is no need to influence the current with the help of external devices. However, it will not be superfluous to add an IC (IL300) to the design by introducing a linear junction.
Common radiator Used to accommodate not only transistors, but also a diode bridge.
It is obligatory to have OS2-4 optocouplers, the purpose of which is to duplicate the control buttons. OS-1 is entrusted with the task of performing user functions.
If the selected frequency converter has one phase, then it can work without a transformer. An alternative to it can serve as a current shunt, which is performed in the form of four turns of a manganin wire with a cross section of 0.5 km on a 3mm frame. Used shunt can be supplemented with an amplifier DA-1.
If a engine power is 400 wattsthen it can work without a thermal sensor. The task of measuring the voltage of the network can successfully cope and DA-1-2 (amplifier).
Care should be taken to protect the buttons by installing plastic pushers on them, while the control is carried out by means of opto-decoupling.
If long wires are present, then noise suppression rings should be added to them.
During operation of the motor rotor, you can choose any speed within the frequency range of 1: 40. In the low-frequency mode, the fixed-voltage mode should be enabled.
Connecting the frequency converter
If the wiring used has one phase and 220V voltage, then the delta option is used as the preferred wiring diagram. It is important to remember that the output current can be more than the nominal no more than 50%.
If it comes about three-phase wiring with a voltage of 380V, then for the connection to the motor of the frequency converter the “star” scheme is selected. For ease of implementation of this procedure, there are terminals on the converter, on the surface of which there are hints in the form of letters.
- R, S, T– to these contacts feed the network wires in any order;
- U, V, W - with the help of them the asynchronous motor is switched on (in those cases when the motor runs in reverse mode, to return to normal rotation, it is enough to swap any of the two wires for contacts).
Be sure to design has a terminal used for grounding.
Recommendations for equipment maintenance
In order for the self-assembled frequency converter to successfully perform its functions for a long time, the owner must follow these guidelines:
- To monitor the state of internal elements, avoiding the accumulation of dust on them. If necessary, use a small compressor, since the vacuum cleaner may not be able to remove the dust, which lies in a dense layer.
- Check the operation of the nodes and change them if necessary. A normal life for electrolytic capacitors is considered to be a life span of 5 years, for fuses - 10 years. Cooling fans should be changed after 2-3 years of operation. Domestic trains are allowed to use no more than 6 years.
- It is necessary to monitor the temperature of the internal mechanisms, as well as the voltage on the DC bus. If the temperature rises, there is a danger of drying the thermally conductive paste, which may result in the failure of capacitors. It is necessary to apply as a rule at least every three years a new layer of paste on the power components of the drive.
- It is necessary to strictly observe the operating conditions. The optimum temperature is the ambient temperature up to + 40 degrees. Extremely negative impact on the work of the elements have a high humidity and dust content of the air.
Frequency converter is the necessary equipment that improves efficiency induction motor operation. If necessary, it can be made on its own. To do this, it is enough to prepare the necessary materials and follow the assembly scheme exactly. In this case, special attention should be paid to the maintenance of the frequency converter, since in the absence of due attention to its condition, this equipment may soon fail, which will have a negative impact on work electric motor.