Influence of inverse coupled inductors on fault-tolerant operation of two-phase DC-DC converters

Multiphase DC-DC converters with coupled inductors are applied to increase the power density and efficiency. But coupling also creates an interference between still active and failed phases as well as influences the inductance characteristic. This paper investigates the fault-tolerance of multiphase DC-DC converters with focus on the behaviour of the total as well as phase current ripples and the inductor saturation depending on duty cycle and coupling coefficient. Compared to non-coupled inductors, the total current ripple can be kept similar after loss of a converter phase if no saturation occurs. Moreover, the influence of the induced voltage due to coupling on the deactivated phase is analysed. Design hints for fault-tolerant strategies with coupled inductors are presented. Measurement results with various coupled inductors prove the theoretical considerations.