Rockwell Automation 2364E Non-Regenerative DC Bus Supply Unit (NRU) - Manual (Page 20)

Publication 2364E-5.01 April 2002
1-6 Overview
Power Conversion Operation
The diodes in the rectifier bridge will only permit current flow in one
direction, from anode to cathode. When an AC voltage is applied to a
diode, the output of that diode is a pulsating DC signal (positive half-
cycles only).
For any particular phase, the anode of the upper diode is positive
relative to its cathode during the positive half-cycle of the AC input.
This forward (voltage) biases the upper diode and it conducts.
Meanwhile, the anode of the lower diode is negative relative to its
cathode. This reverse biases the lower diode and it does not conduct.
Similarly, during the negative half-cycle of the AC input, the lower
diode conducts and the upper diode does not conduct.
During the operation of a 3-phase bridge rectifier, multiple upper and/
or lower diodes may simultaneously be biased correctly for
conduction.
A 3-phase bridge provides an average DC output voltage that is
approximately 1.35 times the rms line-to-line voltage. Refer to
Figure 1.2 for an illustration of the 3-phase AC input signal applied to
the bridge rectifier and the DC output.
Figure 1.2
3-Phase AC Line Voltage and DC Output Voltage and Current
Typical Output Voltage Waveform From Diode Bridge
Average DC Bus Voltage
Typical 3-Phase AC Input Waveform
0
Typical DC Choke Current
0