At this moment, the book I most admire on the Wind Power field, it is this one written by Ackermann. He can transmit dept concepts of power systems by using a clear vocabulary and illustrative examples. In this book, for example, there is an appendix in the chapter three, that explains in a very easy way how the Power System works by using a long bike as an equivalent.
Imagine a long bike with much cyclists running on a flat and straight road. We are the manager of this team and we want to keep the bike at a constant speed (the same frequency) and in an upright position (the nominal voltage equals to 1). How can we achieve this?