In this example the effect that the distortion in the input current of the rectifier has on the AC system voltage is examined. In any real power system the AC voltage source is not ideal. There is always some impedance between the generating voltage source and the load. This impedance is caused by the transmission lines and the power transformers. Generally this impedance is almost made up entirely of inductance terms since the resistance terms are very small. Therefore the AC power system is represented as an ideal AC voltage source with a series inductance. 

When the bridge rectifier is connected on to the power network, which has other loads already connected (in this case a load with a series inductance), a voltage divider effect occurs at the point of common coupling (PCC) between the loads and AC source. The voltage at this point of coupling is now dependent on the level of distortion in the current waveforms of each load, and the relatively size of the load inductors and the supply impedance. 

In this case, the current drawn by the rectifier has a very sharp and discontinuous profile (it contains significant harmonic currents). This current now causes the input voltage to the bridge rectifier to be distorted (as in the previous example). This voltage distortion now appears at the PCC, with the magnitude of the voltage distortion dependent on the inductor value of the bridge rectifier circuit. The smaller the inductor value the greater the voltage distortion that appears on the mains voltage. It is therefore important to size the inductor value correctly to reduce the disturbance that your design is causing on the mains voltage. However there is a trade-off between making the inductor value too large and the level of ripple in the output voltage.

• Adjust the size of the bridge rectifier input inductor. Notice how this has an impact on the level of mains voltage distortion and output voltage ripple.
• Examine the effect that the level of output current has on the level of distortion. Does an increase in the load current cause an increase or decrease in the main voltage distortion?