ABB ACS800 Application Manual page 17

Example 3
The DC buses of three converters ACS800-0140-5, 110 kW, R6; ACS800-0140-5,
110 kW, R6, and ACS800-0070-5, 55 kW, R5 are connected together. Only one
110 kW converter is connected to the main supply. The duty cycle is shown in the
table below.
Phase
R6 (AC supplied)
0...t1
t1...t2
t2...t3
t3...t4
t4...t5
Allowed braking powers
R6 connected to main supply:
Condition 1: 70 kW < 110 kW
Condition 2:
70kW 70kW – + 30kW
-------------------------------------------------------- - 110kW
110kW
– ( ) – (
70kW 50kW +
------------------------------------------------------------------- - 110kW
110kW
P of the system is 110 kW.
out.tot
R6 not connected to main supply:
Condition 1: 30 kW < 110 kW
R5 not connected to main supply:
Condition 1: 30 kW < 55 kW
Need for a brake resistor
The total power of the common DC system is negative during phase interval t3...t4,
therefore a brake chopper and a brake resistor are needed.
Converter powers (kW)
110
60
-70
-50
0
⋅
+ 70kW
)kW
30
⋅
+ 50kW
R6 R5
-30 30
0 30
70 30
70 -30
-30 30
≤
= 100kW 110kW
≤
= 40kW 110kW
17
Common DC
duty cycle (kW)
110
90
30
-10
0
OK
OK
OK
Design