Operating Principle with Resistive Load

The rectifier consists of a three-phase diode bridge, comprising the diodes D1 to D6. In the analysis, two main assumptions are made:

• the impedances of the power lines are low enough to be neglected

• the rectifier is supplied by a balanced undistorted three-phase voltage system, specified by the line-to-neutral voltages

Figure 14: Three-phase Diode Bridge Rectifier With Smoothing Capacitor

By defining:

• LaTeX Math Inline

  , as the RMS value of the phase (line-to-neutral) input voltages

• LaTeX Math Inline

  , is the output voltage

The three-phase voltage system can be represented as:

Where, the amplitude of the phase voltage  equals:

and

with

LaTeX Math Inline

the frequency having a value of 50 or 60 Hz.

The first conducting diode is forming the group of odd-indexed diodes {D1, D3, D5}, and it is connected by its anode to the highest of the phase voltages at the point considered.
The second conducting diode is formed by the group of even-indexed diodes {D2, D4, D6} and it is connected by its cathode to the lowest of the phase voltages.
Since one phase cannot be the highest and the lowest at the same time for the given set of phase voltages specified by (11), (12) and (13), two of the phases are connected to the load while one phase is unconnected at each point in time.
This results in an input current equal to zero in the time interval when the phase voltage is neither maximal nor minimal.

The minimum peak value of the output voltage is:

The maximum peak value of the output voltage is:

The average value of the output voltage is: