In principle, the parameters describing the resulting A.C voltage (frequency, amplitude, phase number, e.t.c.) can be arbitrarily chosen. In practice, single phase and three phase realization are most common. Frequency is limited by the dynamic behavior of the electric element chosen.
The pole changes required to turn out an A.C voltage is performed by means of suitably chosen electronic switching elements usually transistors or thyristors. Depending on the switching elements used, we have thus, a thyristor switching inverter and a transistor switching inverter.
Furthermore, due to elimination of mechanical contacts, transistor and /or thyristor inverters are not subject to wear, and there is no soot deposit. They are faster in term of switching speed, they are portable and are maintenance free.
Moreover, in designing inverter, the basic components; the simple diodes, transistors, the power MOSFETS, the thyristors, the transformers, and Battery are effectively utilized.
2.2 THE DIODE
A diode is a rectifying device, which permits current flow in one direction only, being able to withstand a potential difference without current flow in the opposite direction.
The active material from which the semi-conductor power diodes is formed is silicon, a semi-conducting material, that is, a material of which the conductivity is classified as being between insulating and conducting; its resistance decreases with temperature rise. The diode is a P-N junction device from which all other semiconductor components are made.
The N-type semiconductor has electrons (Negative charges) and P-type semiconductor has holes (Positive charges).
2.3 Operation of the P – N Diode
When the P-type is more positive with respect to the N-type by the application of voltage, the electrons in N-type are pulled to the side of P-type and hole is pulled to the side of N-type. In this way, the electric current flows through the semiconductors. And the diode is said to conduct. Conversely, when the N-type is made more positive with respect to the P-type, by the application of potential difference, electrons in N-type are pulled with positive voltage on the side of N-type and holes in the P-type are pulled with the negative voltage on the side of P-type. In this case, the electrons in the semiconductor do not move an so, the diode will not conduct and is said to be reverse biased.