Performance improvement of alternators with switched-mode rectifiers

The use of a switched-mode rectifier (SMR) allows automotive alternators to operate at a load-matched condition at all operating speeds, overcoming the limitation of optimum performance at just one speed [D.J.Perreault and V.Caliskan, (2000)]. While use of an SMR and load matching control enables large improvements in output power at cruising speed, no extra power is obtained at idle. This document introduces a new SMR modulation strategy capable of improving alternator output power at idle speed without violating thermal or current limits of the alternator. The new modulation scheme may be implemented with simple control hardware, and without the use of expensive current or position sensors. After introducing the new modulation method, we develop approximate analytical models that establish the underlying basis for the approach. Implementation considerations are addressed, and both simulation and experimental results are provided that demonstrate the advantages of the proposed control method.