Regenerative braking of electric vehicles

This paper discusses the problems met in applying regenerative control to electric railways. In the introductory section the purposes, advantages, requirements and disadvantages of regenerative control are pointed out, and then the author takes up the description of various systems. In doing this, special attention is paid to those systems which are well adapted to illustrate some fundamental principle, and to those which are of some practical importance. Other systems are, on account of space limitations, mentioned only briefly, or entirely omitted. The three-phase system is discussed under the following heads: regeneration near synchronous and above synchronous speeds; line regulation; practical results and safety of operation; influence upon power factor; regeneration at speeds below synchronism. The phase converter system is next taken up, with a consideration of the requirements of such a system, and practical results attained. Direct-current systems of regenerative control and their problems are exhaustively discussed, under the following heads: series, shunt, and separately excited generator; classification and description of separately excited systems with generators operated by line voltage; inherently constant excitation; excitation varying with the line voltage; excitation varying with the regenerated current; series-parallel control; capacity of exciter and switches; systems with variable armature voltage; miscellaneous direct-current systems; transmission system and substations. The next division of the paper deals with alternating-current commutator motor systems, including those with separately excited generators, armature self-excited generators, excitation varying with the regenerated current, and stator self (load)-excited generators, and the subject of commutation is discussed. The possibilities of regenerative control with a vapor converter system are then analyzed, and the paper ends with a statement of the general conclusions reached.