Determination of the Optimal Number of Phases of a Multiphase Bidirectional Chopper Considering AC Loss in Inductor

This study focuses on the loss of inductors in a multiphase bidirectional chopper, which is a DC-DC conversion system. The current at the inductors in a multiphase bidirectional chopper consists of a DC current equivalent to the load current and an AC current called ripple current. The discussion regarding the effect of the increased number of phases should include the loss due to the ripple current, which is caused by semiconductor switching. Therefore, this study clarifies the loss due to the ripple current from an experiment with an increase in temperature. From the extraction of AC loss from the total loss, it is demonstrated that the loss due to the ripple current is equivalent to the no-load loss in the multiphase bidirectional chopper. When the number of phases increases, the load loss decreases whereas the no-load loss increases. This relationship indicates that an optimal number of phases exist according to the load current. This study deduces an analytical solution for the optimal number of phases and applies the methodology for determining the optimal number of phases to an actual onboard bidirectional chopper for an onboard energy storage system and traction system as an example. The optimal number of phases differs depending on the application.