Moeller DF51 - Features of the Frequency Inverters; Selection Criteria

About the DF51 series
10/05 AWB8230-1541GB
12
Features of the frequency inverters
The DF51 frequency inverters convert the voltage and frequency of
an existing three-phase supply to a DC voltage and use this
voltage to generate a three-phase supply with adjustable voltage
and frequency. This variable three-phase supply allows stepless
variability of three-phase asynchronous motors.
a Mains input
Mains voltage U
e
(EU rated voltage):
DF51-320 3 AC 230 V, 50/60 Hz
DF51
-322 1/3 AC 230 V, 50/60 Hz
DF51
-340 3 AC 400 V, 50/60 Hz
b The bridge rectifier converts the AC voltage of the electrical supply to
a DC voltage.
c The DC link contains a charging resistor, smoothing capacitor and
switched-mode power supply unit. It enables coupling of the DC bus
voltage and the DC current supply (U
ZK
) = W2 x mains voltage (U
e
)
d IGBT power inverter:
The power inverter converts the DC voltage of the internal DC link to
a variable three-phase alternating voltage with variable frequency.
e Output voltage (U
2
), motor connection:
three-phase, variable alternating voltage, 0 to 100 % of input voltage
(U
e
)
Output frequency (f
2
): variable from 0 to 400 Hz
Rated output current (I
2N
):
1.4 to 32 A (230 V series), 1.5 to 16 A (400 V series) with about 1.5
times starting current for 60 s, at an operating frequency of 5 kHz and
an ambient temperature of 40 °C. Starting torque: 100 % at 6 Hz.
Motor connection, assigned shaft power (P
2
):
0.25 to 7.5 kW at 230 V
0.37 to 7.5 kW at 400 V
f LCD keypad with interface (RJ 45, Modbus).
Selection criteria
Select a suitable frequency inverter according to the rated motor
current. The frequency inverter’s rated output current must be
greater than or equal to the motor’s rated current.
The following drive data is assumed to be known:
• Type of motor (three-phase asynchronous motor),
• Mains voltage = supply voltage of the motor (for
example 3 ~ 400 V),
• Rated motor current (guide value, dependent on the circuit type
and the supply voltage)
• Load torque (square-law, constant, with 1.5 times the starting
torque)
• Ambient temperature (rated value 40 °C).
Figure 7: Function diagram of the frequency inverter
M
3
˜
bc
f
d
a
e
+
h
If several motors are connected in parallel to the output of
a frequency inverter, the motor currents are geometrically
added, i.e. separately by active and reactive current
components. Select a frequency inverter with a sufficient
rating to allow it to supply the total required current.