This book proposes several new utility interface converters to reduce cost, harmonic contents in line currents and to increase the reliability in interconnecting renewable energy sources such as wind, solar (photovoltaic), and fuel cells to electric utility. A new third harmonic current injection technique has been presented to reduce harmonic contents in the line current of controlled converters. A low cost, high efficiency, four-switch, three-phase PWM converter has been presented to interface small wind turbine with electric utility. A modular wind energy system along with modular utility interface converter concept is presented for higher power wind energy systems with increased reliability and power quality of the power electronics converter. A combined low cost, high efficient inverter and peak power tracker has been presented for photovoltaic energy systems. A combined low cost, high efficient inverter and peak power tracker has been presented for photovoltaic energy systems. A combined low cost, high efficiency inverter and peak power tracker has been proposed. This converter operates close to the maximum power point of the photovoltaic array and forms a DC to AC inverter.