CHAPTER 5.0 Functional Overview
5-3
CDS7324 (FORMERLY LSF-0819)
Rev. A
INSTALLATION & USER’S MANUAL
5.3.2 High Voltage Rectification and Filtering
The a.c. mains input is rectified by a three phase diode bridge and filtered by a bank of electrolytic capacitors to
generate the internal DC Bus. This high power d.c. supply is unregulated and will vary in direct proportion with the
a.c. mains input voltage magnitude. The dc bus voltage is monitored continuously and is available for user
display, parameter
bus_voltage_actual
(Field Number 1232). Once the softstart relay has closed, the nominal DC
bus voltage is set in software, parameter
bus_voltage_nominal
(Field Number 1229), which will limit the maximum
speed at which a motor can rotate.
The software will generate a fault on both undervoltage (F12) and overvoltage (F2) level being detected. The
undervoltage level, parameter
bus_under_voltage_limit
(Field Number 1234) is set, by default, to 75% of the
nominal bus voltage. This undervoltage percentage level, parameter
bus_under_voltage_limit_percentage
(Field
1235) can be changed to different levels to suit application requirements..
The overvoltage level parameter
bus_over_voltage_limit
(Field Number 1233) is typically set by the motor
configuration and will generally be either 400V or 800V. Bus voltage level is based on equation: A.C. Mains x
1.414 = D.C. Bus.
A.C. Mains Type
D.C. Bus Voltage Level
230V Three Phase Mains
325Vd.c.
480V Three Phase Mains
679Vd.c.
Table 5.1 Magnitude of the D.C. Bus
5.3.3 Soft
Start
Soft start is used to limit the inrush current to the d.c. bus capacitor bank on application of a.c. mains power. This
is intended to prevent nuisance tripping of circuit breakers or blowing of line fuses on power-up.
The soft start relay will close when the monitoring circuit and associated control software determines that the
high-voltage d.c. bus has charged up and the DC bus is at steady state. Softstart will only occur if the DC bus
voltage level is above 70V.
