Most often, frequency converters are used for an induction motor, but they are also found in household appliances. Despite their prevalence, they have not only advantages, but also disadvantages, which have to be eliminated using additional devices. All converters perform important function, and it is impossible to imagine at least one production without a frequency converter for asynchronous motors.
Content
- Applications of the device
- The principle of operation of the chastotnik
- Application in asynchronous motors
- The main components of the device
Applications of the device
A frequency converter is a special device that is installed on powerful electric motors. Their main purpose is to change the frequency of the incoming current. As you know, the current that comes from the outlet has a frequency, it is equal to 50 Hz. In order to accelerate or, on the contrary, decelerate the motor, this frequency can be changed. The role played by the frequency player is the change in the frequency of the current.
The most striking example is washing machines, everyone has them in the house, to accelerate the speed of the drum the frequency converter of the electric motor increases the frequency of the current to reduce the number of revolutions, the opposite is done action. They are also used to smoothly start powerful motors: modern frequency converters can change the current fluctuation from 1-800 Hertz.
The principle of operation of the chastotnik
The operation of the frequency converter is based on a double conversion inverter. The converter works according to the following scheme:
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First, the alternating sinusoidal current (220-380 V) supplied to the inverter is rectified. A diode bridge is used for rectification. - After that, the current flows to a group of capacitors, where it is filtered and smoothed.
- Next, bridge keys of bipolar transistors (IGBT, IGBT) and control microcircuits take the filtered current and form from it three or single-phase pulse-width modulation with the required parameters.
- At the output, a sinusoidal current with already changed characteristics is obtained, sinusoidality is ensured by the inductance of the windings.
The whole process is shown in more detail in the following diagram:
Application in asynchronous motors
Induction motors are superior in power and performance to conventional electric motors, but they also have a number of disadvantages. The main one is the need to increase the rated power at startup by a factor of 5-7, as well as the fact that special devices must be used to regulate the rotor speed. An increase in power consumption at startup generates surges within the network and shock impulsesin turn, this negatively affects the life of any induction motor.
To solve all the problems, an asynchronous frequency converter was immediately developed. Their use is convenient due to the fact that the frequency converter operates in automatic mode, and therefore the currents are monitored constantly. This device reduces starting currents, thereby not creating overloads in the network and without harming the motor, it also allows you to adjust the rotor speed. There is no need to use a magnetic starter. The main advantages of the frequency player:
- energy savings;
- increased engine durability;
- the ability to regulate the operation of the engine;
- provides feedback to adjacent drives.
In fact, this is a real three-phase voltage generator with which you can achieve the desired magnitude and frequency.
The main components of the device
Any frequency converter includes four main modules:
- rectifier;
- voltage filtering unit;
- inverter unit;
- microprocessor-based control system.
All these modules are connected by a control unit, it controls the systems and is responsible for the operation of the output stage provided by the inverter. Modern devices of this type also have certain protective assemblies that protect it from overcurrent and short circuits. They are also equipped with temperature tracking sensors and other systems that allow you to track deviations from the norm during its operation.
Despite the fact that the frequency converter must rectify the current and keep its frequency constant, it cannot completely smooth out the ripple, this is due to the variable component and the inconstancy of the current in the network itself. In order to completely remove these vibrations, use inductors and capacitors. Their connection and adjustment takes place, as a rule, in the system of a frequency converter. The coil smoothes the current, due to its reactance, in turn, the capacitor, passing current through itself, produces not an alternating, but a constant voltage.
There are frequency converters for both single-phase and three-phase networks. They can also differ in the type of control, there are vector and scalar models. Vector are used in cases where it is necessary to tightly control the rotor speed, the second type frequency workers are used at facilities where there is no special need for strict regulation of the supplied frequency, they can meet in ventilation systems. The scalar type of control is used for single-phase systems, in turn, vector control for three-phase systems. The principle of frequency regulation in both cases remains the same.
