Control and power electronics technology in renewable energy

As the cut-in point of research on control and power electronics technology used in renewable energy, this paper does not aim to analyze particular theories or technologies in this field, but, instead, is to go back to the fountainhead of the issue to illustrate the essential concepts in this field, which are usually neglected and may become bottle-neck of the research. Research experiences have shown that confusion and trouble may be created if researchers do not understand these essential concepts well.