Inversor de frequencia danfoss

Drives 101 Lesson 3

This lesson covers the basic parts and operation of an Adjustable Frequency Drive (AFD). These parts are divided into 4 sections: Rectifier, Intermediate circuit (DC Link), Inverter and Control & Regulation.

1.

AFD in a Larger System

This section covers the parts and operation of the Adjustable Frequency Drive (AFD). It is important to keep in mind that the Drive is just one part of a system. In the diagram above, notice the disconnect switch, fuses, bypass switch, thermal overloads, PLC etc. all play an important part in making an application work correctly. Inside the AFD there are 4 major sections: rectifier, intermediate circuit (DC Link), inverter and control/regulation. This fourth section, control and regulation, interfaces with the other 3 sections. In very general terms the operation of the drive is as follows. Power first goes into the rectifier, where the 3-phase AC is converted into a rippling DC voltage. The intermediate circuits then smoothes and holds the DC Voltage at a constant level or energy source for the inverter. The last section, the inverter, uses the DC voltage to pulse the motor with varying levels of voltage and current depending upon the control circuit. The pattern of the pulses going to the motor makes it appear similar to AC sinusoidal waveform voltage. Each one of these sections is reviewed in some detail in the pages that follow.

To understand the parts of an AFD better, an example of a 400kW (500Hp) drive is used.

Fuses Disconnect

In the picture above notice the fuses and disconnect switch.

As each part is explained pictures of these parts on a 400kW (500Hp) drive are displayed. This large drive is used in this lesson for the size of the parts are easy to identify. One of the options for these large drives 225 – 400kW (300 – 500Hp) is to have fuses and a disconnect switch mounted inside the drive. With smaller size drives fuses and a disconnect are separate but are still part of the