Understand the frequency converter and its structure

The function of the frequency converter explained in a simplified way

• Perhaps you already know - but for all those who do not know, let me tell you first that a frequency converter converts current. This means that it turns alternating voltage into a convertible voltage that can be sent directly to electrical devices.
• By and large, the frequency converter changes, as the name suggests, the frequency, but also the amplitude of a given AC voltage. The values ​​that the output voltage should have depends on which machines are ultimately to be supplied with the converted current.
• Most frequency converters make it easy for you, the operator, to find the right output voltage because they have special inputs for sensors that record the properties of the machine to be supplied can. This includes, for example, the speed.
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• If you are now wondering to what extent the frequency converter differs from the converter, let me tell you that the converter is the same as the frequency converter in terms of its structure, however, the converter works with a constant frequency and amplitude of a constant voltage and is not intended to control machines, but rather several machines from the same source supply.

Frequency converter - for the functional structure of the device

Frequency converters are most commonly used for three-phase motors. They are supposed to convert the sinusoidal form of an output alternating voltage into a voltage with variable frequency and amplitude.

• Since frequency converters are supposed to convert the voltage intermediate circuit in this way, they initially build on one Bridge circuit which converts the corresponding AC voltage at the input of the device into DC voltage switches.
• The voltage finally reaches the memory of the frequency converter, which contains a special capacitor that is supposed to smooth the incoming voltage. The voltage can only be passed on to the inverter circuit after smoothing.
• It is the inverter circuit within the structure of frequency converters that converts the already smoothed voltage into three-phase voltage. GTOs and IGBTs are located in the inverter circuit for this purpose. Depending on the desired output of the target voltage, a control pattern is used to control a GTO or IGTB valve.
• The sinusoidal output voltage has already lost its sinusoidal shape. The motor that is ultimately to be supplied is connected to the output of the frequency converter. The voltage converted by the converter now flows through it. High-frequency pulse regulators ensure that the peaks of the current output remain as low as possible.
• The drive voltage is now generated within the motor windings based on self-induction, so that the current direction remains the same. Free-wheeling diodes are used so that the voltage within the motor winding inductances does not rise so much that the transistors are damaged built in, which are the only current path available to the current of the motor after the transistors are blocked at the beginning of the inductance Experienced.

Are you in physics and not too knowledgeable about electrics, the explanation above may find you a little difficult. In this case, it is advisable to inquire about directional circuits and inductance before you deal with how the frequency converter works. Unfortunately, the basic principles of inductance and corresponding circuits cannot be explained at this point for reasons of space.