Regenerative braking capability of converter-controlled induction machines

Induction machines are good candidates for traction applications, due to their rugged construction and to their use of low-cost readily available materials. Traction applications typically require that the converter-controlled induction machine be capable of providing both motoring torque and braking torque. It is important to distinguish between regenerative and non-regenerative braking torque modes; the converter-controlled induction machine is a source of electric power in the former mode, but it is a sink of electric power in the latter mode. Although the existing literature discusses regenerative braking operation of induction machines in general terms, no prior work has yet identified the location of the boundary that separates the regenerative and non-regenerative braking regions of converter-controlled induction machines in the torque-speed plane. This paper provides all the analysis required to identify this critical operational boundary, and in the process reveals a fundamental difference between the regenerative braking capability of induction machine drives and permanent-magnet synchronous machine drives in the low speed region. The results of this paper are relevant to the design of power management systems associated with electric and hybrid electric vehicles.