ABB ACS880-04 drive modules, Application Manual

Page: 18 / 48

18 Planning – basics
Defining the DC link duty cycle and key variables

Defining the DC link duty cycle
1. Define the DC link duty cycle for each drive. See section DC link duty cycle diagram
on page 19 . Use the duty cycle diagram of the motor shaft power and:
•
Add the inverter and motor losses during the motoring mode of the motor.
•
Subtract the inverter and motor losses during the generating mode of the motor.
2. Sum the DC link duty cycle diagrams of the individual drives to one common DC link
duty cycle diagram for the common DC system. See section DC link duty cycle
diagram on page 19 .
3. On basis of the common DC link duty cycle diagram, define the key variables P
mot,ave
,
P
mot,max
, P
gen,ave
and P
gen,max
for the whole system. See section DC link key
variables on page 19 .
Inverter losses
Motor losses
P
m
P
mot
k
eff
Efficiency factor (1/efficiency) to include drive and motor losses.
If not known, value 1.25 can be used
n Motor shaft speed [rpm]
P
dc
DC link power
P
mot
Power that the motor takes from the DC link
P
gen
Power that the motor supplies to the DC link
P
m
Motor mechanical shaft power
T Torque [Nm] on motor shaft
P
mot
= k
eff
× P
m
P
gen
=
k
eff
P
m
P
m
[kW] =
9550
T × n