Vfd Scalability; Vfd Output Ratings - Siemens 6SR41 series Product User Manual

Overview
2.3 Perfect Harmony Features
2.3.2

VFD Scalability

The Perfect Harmony Power cells provide truly scalable technology that is provided by the
wide range of output power configurations offered by the power cells, and the ability to
connect up to 8 cells in series for each output phase. When connected in series, the current
rating for each phase is simply equal to the output current rating of the cells; the output
voltage rating is simply the sum of the output voltage ratings of the cells.
Note
Cells of different power ratings should not be intermixed.
The Control system for the Harmony is identical regardless of the output ratings of the VFD,
where the only configuration differences are the feedback sensor configurations and the
number of cell communication channels required. The Control is based on a per unit
implementation, where the user simply enters the nameplate ratings for the Motor and VFD.
The controller automatically scales itself, based on these ratings. This results in a common
control implementation and "touch and feel" for all drives, regardless of the power ratings.
2.3.3

VFD Output Ratings

Using the cell output voltage rating, the output capability of the VFD can be calculated based
on the number of power cells connected in series in each of the 3 output phases, which
establishes the Available System Output Capability, also known as "VAVAILABLE." This is
also the maximum voltage that can be supported on the output terminals of the drive when
energized.
The rated output voltage of the drive is then calculated as follows:
VAVAILABLE (Volts) = 1.78 * #Cells * CellV * Vin / Vrated * TransformerTapSetting
Where:
#Cells =
Vin =
Vrated =
TransformerTap Setting: use
0.95
1.00
1.05
Note
Overmodulation (O-M) is used for GenIV and WCIII product families to achieve output
voltages that are 5% higher than VAVAILABLE.
The VFD Rating is then calculated using VAVAILABLE and the rated cell current.
24
Number series power cells per phase
Measured Line Input voltage (rms)
Rated VFD Input Voltage (rms)
when +5% tap on input transformer is used
when 0% tap is used
when -5% tap is used
Operating Instructions, Version AE 12/2009, A5E01454341C
Product User Manual