The electromechanical systems employed in different branches of industry are utilized most often as drives of working machines which must be fed with electric energy in a continuous, periodic or even discrete way. Some of these machines operate at constant speed, others require wide and varying energy control. In many designs the synchronous cooperation of several electric drives is required in addition to the desired dynamic properties. For these reasons the control of the cooperation and dynamics of electromechanical systems requires the use of computers. This book adopts an unusual approach to the subject in that it treats the electric drive system on the one hand as an element of a control system and on the other as an element of a complex automatic system. These two trends in the development of the automatic control of electric drives have resulted in a volume that provides a thorough overview on the variety of different approaches to the design of control systems.