A Fault Protection Strategy Based on Z-Source Solid State Circuit Breaker for More Electric Aircraft

High-voltage direct-current (HVDC) rated at 270 Vdc is one of the main power supply technologies expected for future more electric aircraft (MEA); however, dc protection is still one major challenge preventing the wide deployment of HVDC. To overcome this, Z-source solid-state circuit breakers (Z-SSCBs) could be employed due to their simple structure and fast speed of response. Z-SSCBs alone, however, cannot effectively isolate a short-circuit fault when a large fault resistance and a small fault current ramp rate are present, which would greatly damage MEA. In this article, an auxiliary protection strategy based on Z-SSCBs is presented to address this problem. The strategy combines inverse-time overcurrent and voltage protection to force the opening of the Z-SSCB when its automatic triggering fails. The principle of operation of a Z-SSCB is discussed, and the design process of the protection strategy is presented in detail. Software simulations using Saber and experimental tests have been carried out to validate the protection strategy. Both sets of results match well, offering a good performance and meeting IEEE protection (Std C37.112-2018) and aircraft electrical standards (MIL-STD-704F). It is shown that with the auxiliary protection strategy, the Z-SSCB successfully isolates faults against overcurrent, overvoltage and undervoltage operating conditions.