Switch Current-Based Closed-Loop Control for ZCS Bidirectional Current-Fed DC-DC Converters

A significant challenge of current-fed DC-DC converters is managing the primary-side switch voltage stress at turn-off. One way to manage this stress is to use advanced modulation techniques that ensure soft turn-off of the primary-side switches. These advanced modulation techniques work by predicting the switch currents at turn-off and, therefore, are partially open loop. Consequently, due to circuit tolerances and converter non-idealities, significant control margin must be added in practical settings to ensure soft-switching is achieved over the full operating range of the converter. This control margin leads to increased switch current at turn-off and, therefore, increased circulating currents within the converter, impacting the overall efficiency potential. In this paper, a novel switch current-based closed-loop control technique is proposed that incorporates actual switch current measurements within the modulation technique, enabling the minimization of the switch currents at turn-off and, therefore, the circulating currents. The paper presents the operation, implementation, simulation results, and hardware-in-the-loop results obtained using an RTDS NovaCor system and B-Box RCP from Imperix.