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The three-phase dual active bridge (3p-DAB) converter is widely considered in dc-grid applications. Because of the higher number of switches in the 3p-DAB, it can be argued that the reliability of the 3p-DAB is reduced when compared to other isolated-bidirectional dc–dc converter topologies. The previous work has shown that the 3p-DAB can be operated in a frozen leg fault-tolerant mode, i.e., with the two transistors of the same phase being opened by their gate driver internal protections. Because the free-wheeling diodes are left self-commutated, the analytical characterization of the converter for all voltage and loading conditions is not trivial. In this article, it is proposed to open the faulty phase such as it eliminates the interaction with the faulty-phase free-wheeling diodes. This allows the converter to fall in a characterizable operating mode for all voltage and loading conditions. The results further show that the open-phase operation provides advantages over the frozen leg operation in terms of current stress and power transfer capability. Experimental results on a small-scale closed-loop gallium nitride-based prototype as well as time-domain simulation results are provided to support the theoretical analyses. [ABSTRACT FROM AUTHOR]

The three-phase dual active bridge (3p-DAB) converter is widely addressed in emerging power systems applications such as solid-state transformer and dc microgrids. Its successful integration requires accurate modeling of its small-signal characteristics. Due to its dc–ac–dc structure, the DAB converter brings many challenges to small-signal modeling. The state-space averaging (SSA) has been the first proposed methodology to approximate the control-to-output and line-to-output transfer functions of the 3p-DAB. However, as shown in this paper, SSA is not precise for the stability analysis of 3p-DAB converters. A generalized state-space averaging (GSSA) model based on the dynamic phasor concept is developed in this paper for the Y-Δ 3p-DAB. A hybrid SSA and GSSA model representation is then proposed for the evaluation of all the converter transfer functions. The developed models are validated with detailed time-domain switch-level simulations in an electromagnetic transient-type (EMT-type) program. They are also used for the accelerated stability prediction in an EMT-type program. [ABSTRACT FROM PUBLISHER]

During the operation of dc rapid transit systems, the rail passenger vehicles are subjected to surge transient events that can damage the on-board equipment and cause service interruption. During the testing phase, vehicle manufacturers must demonstrate the performance of the vehicles under the specified transients. However, system testing is generally not available during design. Engineering analysis must be performed to ensure that the design will meet the transient requirements, and that the overvoltage and overcurrent protective devices are coordinated on a system level. In response to these design challenges, detailed time-domain simulation models of a switching surge transient generator and the vehicle equipment have been developed and validated experimentally. These models are used to evaluate vehicle system parameters sensitivity, as well as to provide design guidelines for increased vehicle power system safety, reliability, and availability. [ABSTRACT FROM AUTHOR]

This paper presents the development of detailed simulation models to study short-circuit protection of on-board dc auxiliary systems in a rapid transit train. As the investigation of protection solutions during the testing phases is costly, it is necessary to perform detailed protection analysis earlier in order to detect potential protection issues. This requires modeling the behavior of batteries, auxiliary converters, and the detection and arcing mechanisms of protection devices in detail, as shown in this paper. The protection device under consideration in this study is the molded-case circuit breakers (MCCBs) equipped with adjustable thermomagnetic trip unit which are widely used in the railway industry. To maintain battery system availability, they are selected, sized, and adjusted to avoid false tripping during emergency conditions. However, they must also be sensitive enough to detect the limited available fault current which is specific to rapid transit train dc auxiliary systems. Tolerances on the detection time of thermomagnetic units may be unacceptable as shown in this study. In order to overcome this problem, electronic trip unit assistance to conventional thermomagnetic-type MCCBs is proposed and the requirements for such a device are evaluated using the detailed simulation platform. [ABSTRACT FROM AUTHOR]