Basic Operating Principles; General; Description Of Operation; Sequence Of Operation - Danfoss VLT AutomationDrive FC 301 Series Design Manual

Basic Operating Principles

3 Basic Operating Principles

3.1 General

This chapter provides an overview of the adjustable
frequency drive's primary assemblies and circuitry. It is
intended to describe the internal electrical and signal
processing functions. A description of the internal control
structure is also included.
Also described are automated and optional adjustable
frequency drive functions available for designing robust
operating systems with sophisticated control and status
reporting performance.

3.2 Description of Operation

The adjustable frequency drive supplies a regulated
amount of AC line power to a standard 3-phase induction
motor to control the motor speed. The adjustable
frequency drive supplies variable frequency and voltage to
the motor.
The adjustable frequency drive is divided into four main
modules.
•
Rectifier
•
Intermediate circuit
•
Inverter
•
Control and regulation
In chapter 3.3 Sequence of Operation, these modules are
covered in greater detail and describe how power and
control signals move within the adjustable frequency drive.
MG33BF22
Design Guide
Figure 3.1 Internal Control Logic

3.3 Sequence of Operation

3.3.1 Rectifier Section

When power is first applied to the adjustable frequency
drive, it enters through the input terminals (L1, L2, and L3)
and on to the disconnect and/or RFI filter option,
depending on the unit's configuration.

3.3.2 Intermediate Section

Following the rectifier section, voltage passes to the
intermediate section. This rectified voltage is smoothed by
an sine-wave filter circuit consisting of the DC bus inductor
and the DC bus capacitor bank.
The DC bus inductor provides series impedance to
changing current. This aids the filtering process while
reducing harmonic distortion to the input AC current
waveform normally inherent in rectifier circuits.

3.3.3 Inverter Section

In the inverter section, once a run command and speed
reference are present, the IGBTs begin switching to create
the output waveform. This waveform, as generated by the
Danfoss VVC
provides optimal performance and minimal losses in the
motor.
Rev. 2014-04-04 All rights reserved.
plus
PWM principle at the control card,
3 3
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