Internal Adjustable Frequency Drive Operation; General; Description Of Operation - Danfoss VLT FC 100 Service Manual

Internal Adjustable Frequen... Service Manual

3 Internal Adjustable Frequency Drive Operation

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3.1 General

This section is intended to provide an operational overview of the main assemblies and circuitry. Tis information gives the
repair technician a better understanding of the frequency converter and aid in the troubleshooting process.

3.2 Description of Operation

An adjustable frequency drive is an electronic controller that supplies a regulated amount of AC power to a three-phase
induction motor to control the speed of the motor. By supplying variable frequency and voltage to the motor, the
adjustable frequency drive controls the motor speed, or maintains a constant speed as the load on the motor changes. The
adjustable frequency drive can also stop and start a motor without the mechanical stress associated with a line start.
In its basic form, the adjustable frequency drive can be divided into four main sections: rectifier, intermediate circuit (DC
bus), inverter, and control (see Figure 3.1).
Power Section
Logic to Power Interface
Control Logic
Figure 3.1 Basic Block Diagram
To provide an overview, the main adjustable frequency drive components are grouped into three categories: The control
logic section, logic to power interface, and power section. The sequence of operation description describes these sections in
greater detail while explaining how power and control signals move throughout the adjustable frequency drive.
MG94A222 Danfoss A/S © Rev. 2014-02-10 All rights reserved. 33