Basic Operating Principles Of A Drive; Description Of Operation; Drive Controls - Danfoss VLT HVAC Drive FC 102 Design Manual

Basic Operating Principles ...

11 Basic Operating Principles of a Drive

This chapter provides an overview of the primary
assemblies and circuitry of a Danfoss drive. It describes the
internal electrical and signal processing functions. A
description of the internal control structure is also
included.

11.1 Description of Operation

A drive is an electronic controller that supplies a regulated
amount of AC power to a 3-phase inductive motor. By
supplying variable frequency and voltage to the motor, the
drive varies the motor speed or maintains a constant
speed as the load on the motor changes. Also, the drive
can stop and start a motor without the mechanical stress
associated with a line start.
In its basic form, the drive can be divided into the
following 4 main areas:
Rectifier
The rectifier consists of SCRs or diodes that convert 3-
phase AC voltage to pulsating DC voltage.
DC link (DC bus)
The DC link consists of inductors and capacitor banks that
stabilize the pulsating DC voltage.
Inverter
11 11
The inverter uses IGBTs to convert the DC voltage to
variable voltage and variable frequency AC.
Control
The control area consists of software that runs the
hardware to produce the variable voltage that controls and
regulates the AC motor.
L1
L2
L3
1 Rectifier (SCR/diodes)
2 DC link (DC bus)
3 Inverter (IGBTs)
Illustration 11.1 Internal Processing
200
VLT
1 2 3
Danfoss A/S © 11/2017 All rights reserved.
®
HVAC Drive FC 102

11.2 Drive Controls

The following processes are used to control and regulate
the motor:
•
User input/reference.
•
Feedback handling.
•
User-defined control structure.
•
Control algorithms (VVC
with motor feedback, and internal current control
VVC
11.2.1 User Inputs/References
The drive uses an input source (also called reference) to
control and regulate the motor. The drive receives this
input either
•
Manually via the LCP. This method is referred to
as local (Hand On).
•
Remotely via analog/digital inputs and various
serial interfaces (RS485, USB, or an optional
fieldbus). This method is referred to as remote
(Auto On) and is the default input setting.
Active reference
The term active reference refers to the active input source.
The active reference is configured in
parameter 3-13 Reference Site. See Illustration 11.2 and
Table 11.1.
For more information, see the programming guide.
Remote
T1
reference
T2
T3
Local
reference
Illustration 11.2 Selecting Active Reference
- Open loop/closed-loop mode.
- Motor control (speed, torque, or
process).
+
, flux sensorless, flux
+
).
Remote
(Auto On)
Linked to hand/auto
(Hand On)
Local
LCP keys:
P 3-13 Reference Site
(Hand On), (O ),
and (Auto On)
Reference
MG16C302