Danfoss VLT Series Design Manual page 33

VLT ® HVAC Drive Design Guide
2.7. VLT HVAC Controls
2.7.1. Control Principle
An adjustable frequency drive rectifies AC voltage from line into DC voltage, after which DC voltage
is converted into an AC current with a variable amplitude and frequency.
The motor is supplied with variable voltage / current and frequency, which enables infinitely var-
iable speed control of three-phased, standard AC motors.
2.7.2. Control Structure
Control structure in open-loop and closed-loop configurations:
In the configuration shown in the illustration above, par. 1-00 is set to
reference from the reference handling system is received and fed through the ramp limitation and
speed limitation before being sent to the motor control. The output of the motor control is then
limited by the maximum frequency limit.
Select
level or pressure in the controlled application. The PID parameters are located in par. group 20-
**.
2.7.3. Local (Hand On) and Remote (Auto On) Control
The adjustable frequency drive can be operated manually via the local control panel (LCP) or
remotely via analog and digital inputs and serial bus.
If allowed in par. 0-40, 0-41, 0-42, and 0-43, it is possible to start and stop the adjustable fre-
quency drive via the LCP using the [Hand ON] and [Off] keys. Alarms can be reset via the [RESET]
key. After pressing the [Hand On] key, the adjustable frequency drive goes into hand mode and
follows (as default) the local reference set by using the LCP arrow keys.
Closed-loop
[3] in par. 1-00 to use the PID controller for closed-loop control of, e.g., flow,
MG.11.B4.22 - VLT ® is a registered Danfoss trademark.
2. Introduction to the VLT HVAC Drive
Open-loop
[0]. The resulting
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