America cannot produce all the power it drinks. It has to get help from its neighboring countries like Mexico to satisfy her. So power transfer between two grids must take place.

Circuits employing semi conductor devices were used for this purpose. But there is a problem. The power flowing in grid is in the form of AC-alternating current. This AC cannot be controlled using semiconductors. For that purpose we convert the AC to DC-Direct Current. Using the circuits we can alter any parameters of the power such as amplitude, frequency, phase etc. After that, DC is converted back to AC, ie we synthesize AC. But this AC is not as good as natural AC. The problem is harmonic distortions. As we change DC to AC a spike appears at each pulse, which is a noise and is undesired, but hard to eliminate