Power electronics is one of our daily engagements. Cell phones, tablets, notebooks and ... chargers are common usage of power solid state devices (a combination of Rectifiers, Ac to DC Converters and Choppers or DC to Dc converters. Many power system dynamic stability problems can be solved by Flexible AC Transmission systems (FACTS) which are mainly based of Power Electronics. Even Transient Stability margin indirectly increase by FACTS controllers. Steel Making Plants and other plants that have Electric Arc Furnaces (EAFs) cannot produce any kind of melting materials without SVCs o STATCOMS which avoid flickers using Power Electronics. Control of speed and torque of any kind of electrical motors, which are basis of fully automated high efficiency factories, cannot be accomplished without inverter (DC to AC converters) based drives. In homes and offices, power supply of computers, Televisions, new lightings (LEDs) are main sources of Harmonics, which cause overvoltages, overcurrents, extra need to protections and specially damages electric motors and transformers in industries. Most of the new high level harmonics cannot be eliminated using conventional filter and they need Active Power Filters, which are mainly based on Power Electronics. Now a days, Global Warming is one of main concerns of modern societies, which causes many costly defects in environment. The only solution is renewable energies. Power Electronics makes renewable energies such as wind energy or solar cells usable. In green production of vehicles, hybrid or fully electrical engines are based of Power Electronic circuits. The only way to control electrical trains is Power Electronics. Even conventional fossil fuel engine trains have a great generator that convert mechanical energy to electrical and the only way to use and control of their electrical motors is also Power Electronics. In recent decades Power electronics has become one of majors of Electrical Engineers to study in universities and colleges. Most of concentrations were to calculate circuit parameters; it is necessary but having a vision to the end of theoretical concepts and make a brief sense to the applications and what happens in practical is also important. In this book has been tried to make complicated concepts, simple and easy to learn specially for beginners and non-electrical engineers and show them the end and help them to decide whether they want to continue researching Power Electronics or not. Meanwhile for the others, this book can help them have better view of their daily activities and knowing cause of some unknowing problems in their facilities and equipments.