In this 3-phase rectifier circuit there are both AC and DC side inductors used. From the previous 3-phase rectifier circuits it has been shown how both AC and DC inductors can be used to reduce the level of current distortion. However to decide on the optimal combination of the AC and DC inductor values must take into account the level of distortion and the physical size/cost of the inductors. 

In this applet there is another kind of graph that is presented; this is a space vector diagram. In this diagram the 3-phase currents are represented as a 2-phase quantity that is plotted as a vector on the real and imaginary axes. Balanced, fundamental sinusoidal currents would appear as a circle on the vector plot for one fundamental cycle. As time progresses the dot on the vector plot tracks around. However in this example fundamental sinusoidal currents are not flowing, so the vector diagram does not track a circle. The more distortion in the current then the more star-like the vector shape becomes. By adjusting the inductor values it is possible to make the input currents more sinusoidal or circular like on the vector diagram. The level of distortion can also be seen in the harmonic spectrum.

• Adjust the AC and DC inductor values to see the influence they have on the levels of current distortion. What combinations do you need to make the vector diagram look like a pointy star or more like a circle?
• By moving the time point line, you will track across the current time waveforms and the instantaneous point on the vector diagram.