Energy storage requirements of buffer in power conversion system significantly limit miniaturization of grid interface systems. Since the requirement of the buffer is proportional to the system average power and the line period, the size of the buffer cannot be reduced simply through increased switching frequency. Conventional power conversion systems typically utilize electrolytic capacitors to provide high-density energy storage for buffering. However, these capacitors also represent a significant source of system lifetime and reliability problems. Development of energy buffering circuits that eliminate electrolytic capacitors while maintaining high energy storage density and high efficiency is one important key for future grid interface systems that have both a small size and a high reliability.