In this applet the operation of the full-wave rectifier from either a 2-phase, 3-phase or 4-phase voltage supply is compared. For the 2-phase supply the phase voltages are 180deg apart, for the 3-phase case they are 120deg apart, and for the 4-phase case they are 90deg apart. To simplify the analysis it is assumed that the output load is drawing a constant current no matter what the output voltage is doing. 

Two-phase case: The output voltage has a rectified sinusoidal shape, where the peak voltage is twice the peak phase voltage. Every 180deg the output voltage drops to zero. From the harmonic composition of the output voltage it can be seen that it has a major frequency of twice the supply frequency. It also contains smaller levels of other even harmonics. The input phase current is a square wave with a zero offset. From the harmonic spectrum of the current it can be seen that it has a larger fundamental magnitude than the output current. It also contains significant level of the other odd harmonics. Therefore if there are even harmonics in the DC output voltage, there are odd harmonics in the AC input current. 

Three-phase case: The output voltage in this case is much more continuous and does not reduce to zero at any stage. In one fundamental period there are 6 voltage ripples on the output voltage. The dominant frequency in the DC output voltage is the 6th harmonic, with smaller contributions from the 12th, 18th, ... harmonics. The AC supply current has a quasi square-wave shape, where current flows for 120deg in the positive half cycle and 120deg in the negative half cycle. From the harmonic spectrum it can be seen that there are much lower levels of harmonics than in the two phase case. There are also now no triplen harmonic components. So on the DC side there are harmonic voltages with frequencies of 6n, where n=1,2,3..., and in the AC phase currents the harmonic components are 6n+/-1. 

Four-phase case: In this case the output voltage ripple is much greater and the harmonics of the order 4n. The phase current flows for a shorter time and compared to the 3-phase case there is a much longer time where the current is zero. The AC source current also contains all odd harmonic frequencies compared to the 3-phase case where the triplen harmonics are zero. 

Overall it can be seen that the use of 3-phases produces a more continuous output voltage compared to the 2-phase and 4-phase cases and has a reduced complexity (1 less voltage source and 2 less diodes) than the 4-phase case.

• Use the red check boxes to change between the rectifier operating from either a 2-phase, 3-phase or 4-phase voltage supply. When you change between the various supplies notice how the output voltage waveform shape changes, assuming a
• By adjusting the time line you can see the path the current flows around in the rectifier.