This applet investigates the rectification of 3-phase voltage sources with thyristors. The topology is similar to the 6-pulse diode rectifier. If the thyristors are always triggered at their natural ignition point, the rectifier behaves exactly like a diode rectifier (trigger angle is zero). Via delay of the trigger pulse (with reference to the natural ignition point) a controller can control the average DC output voltage without losses. For a smaller DC voltage it is necessary to increase the delay of the trigger pulse. The trigger angle causes a phase shift of the input currents which reduces the power factor of the converter. 

With a resistive-inductive load (as in this animation) a trigger angle of 90 degrees results in an average DC voltage of zero. In the case of an electric machine at the DC side, which is a main application of this converter, it is possible to invert the output voltage and feed energy back into the mains (trigger angle between 90 and 180 degrees). The current can only flow from AC to DC and always only two of the six thyristors are conducting.

• Change the resistance or inductance values of the load. This will influence the AC current shape.
• Set a different trigger angle by changing the signal 'ref'. If 'ref' crosses the triangular signal 'sig', the firing pulse triggers the thyristor into the on-state. This will change the average output voltage. It will also phase shift the current and change the power factor accordingly.
• Drag the time slider from left to right. After passing the trigger point, the trigger pulse is animated. After triggering, the thyristor is in the on-state and the load current keeps flowing.
• If the trigger angle is larger than 90 degrees, the DC voltage is zero.