Enabling High Efficiency in Low-Voltage Soft-Switching Current Source Converters

Abstract

While conventional reverse blocking (RB) switch structures consisting of an active switch (MOSFET or IGBT) and a series diode can enable high efficiency operation in high-voltage (>600 VAC and >1000 VDC), high-power (25-50 kVA) current source converters (CSCs), the high conduction losses associated with conventional RB structures have prevented widescale adoption of CSCs in low-voltage applications. This work presents the design and experimental validation of the patent-pending Synchronous Reverse Blocking Switch, a method of integrating a bidirectional dual-active-switch structure into the Soft-Switching Solid-State Transformer (S4T) topology to unlock high efficiency operation in low-voltage, high-current applications. By leveraging the operating principles of the S4T, whose control eliminates the possibility of shoot-through and provides zero-voltage switching (ZVS) conditions for all power devices across the entire load range, the Synchronous Reverse Blocking Switch has been demonstrated to offer significant conduction loss reductions while also mitigating the reverse recovery of the PN-junction MOSFET body diode which replaces the series diode of the conventional RB switch. Key contributions of this work include device-level validation of the reverse recovery mitigation mechanism of the Synchronous RB Switch, and system level validation through the design and performance measurement of a 48 VDC S4T bridge, which achieved 97.8% efficiency at a power delivery level of 750W and evidenced the strategy’s benign reverse recovery properties.