Lectte_4: Concept of energy and co-energy

Picked from a mixed channel: Power Electronics Lectures (title sample: The vast majority are structured power electronics lecture videos that clearly teach, but a handful of student capstone/project showcase videos (drone delivery, solar bicycle, IoT automation) are project demos rather than teaching and should be excluded.; 3 of 3 sampled transcripts read as real teaching); this title passed a strict title check.