6
Operating modes and limit values
Special application
Operating Instructions – EDR..71 – 315, EDRN63 – 315
118
Voltage drop at the line filter ΔU
NF
The line filter consists of current-compensated radio interference suppression chokes.
The current flows through the winding of the chokes and the resulting magnetic fields
compensate each other.
This is why the inverter current that flows through the line filter is only dampened by
the ohmic share of the inductance and by the leakage inductance. The leakage induct-
ance is very low compared to the main inductance. The voltage drop across the line
filter can therefore be neglected.
Typical connection pattern
L1
L2
L3
L1´
L2´
L3´
PE
PE
Equation for calculating the voltage drop
∆
V
I
f
L
R
LF
I
FI
Leak
LF
=
×
×
×
×
×
+
_
(
)
3
2
2
2
π
ΔU
NF
Voltage drop across line filter, in V
I
I_FI
Nominal input current of the inverter in A
L
leak
Leakage inductance in H
R
NF
Ohmic resistance in Ω
Determining the inverter input voltage Δ U
I_FI
The inverter input voltage is determined by doing the following:
•
Measuring the line voltage
•
Calculating the voltage according to the formula
V
V
V
V
FI
Line
LC
LF
I_
=
− ∆
− ∆
•
Reading-off the DC link voltage in the inverter
Determining the inverter output voltage ΔU
O_FI
The voltage drop at the inverter is determined by the following:
•
Voltages across the rectifier path
•
Voltages at the output stage transistors
•
The principle of converting supply voltage into DC link voltage and into the rotating
field voltage
•
Anti-overlap times resulting from the clocking of the output stage and the missing
voltage-time areas
•
Modulation process
•
Load state and energy dissipation of the DC link capacitors
INFORMATION
To simplify the calculation, use the value of 7.5% of the line input voltage. This value
is to be taken as the maximum possible voltage drop at the inverter. This allows for a
reliable project planning. U
O_FI
= 0.925 × U
I_FI
25896334/EN – 06/2019