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Being an integral part of many high-power converters, it is imperative to estimate the natural resonance frequencies of a medium/high-frequency (MF/HF) transformer. Experiment/measurement based methods reported in literature determine the resonance frequencies based on the input impedance measurements. However, their applications are limited if these resonance frequencies are to be estimated prior to the transformer prototyping. To ameliorate the drawback, this article provides a comprehensive modeling procedure for the winding capacitances of a two-winding transformer and its resonance frequency estimation. By integrating the prior capacitance modeling techniques, this article establishes an electrostatic energy based transformation model, which directly translates the static winding capacitances into equivalent model based capacitances. These derived capacitances are further utilized to represent a reduced ${\pi }$ -model of a two-winding transformer, compute its frequency responses and estimate the resonance frequencies. The proposed model based approach is simple and easily executable, and helps avoiding any infeasible transformer design during the preprototyping stage. Experimental results derived from MF transformer prototypes, constructed of solid round, foil, and litz wires, are used to corroborate the theoretical analysis and feasibility of the proposed model based approach. [ABSTRACT FROM AUTHOR]

A split dc-link dual-active-bridge (SDLDAB)-based multiport converter (MPC) is proposed in this article. The intended application of the SDLDAB converter is to interface two solar photovoltaic (PV) modules and a battery bank with a dc microgrid. Depending upon the prevailing atmospheric condition, these two solar PV modules can be operated at their maximum power points. This is achieved by maintaining appropriate voltages at the input terminals of the two PV modules. A high-frequency transformer is employed to provide high voltage gain between the dc microgrid and PV as well as battery ports. A direct power flow path is established between the solar PV modules and the battery without involving the transformer. The transformer current is minimized by appropriately modulating the switching sequence of the SDLDAB. Detailed simulation studies are carried out to predict the performance of the system. A laboratory prototype of the SDLDAB having 1-kW power rating is fabricated. The performance of the MPC is validated by carrying out detailed experimental studies on the developed prototype. [ABSTRACT FROM AUTHOR]

An optimized configuration of bidirectional Z-source circuit breaker using a coupled inductor is introduced for the fault isolation in low-voltage dc microgrid. The proposed circuit breaker is designed to operate with a single coupled inductor for bidirectional power flow. Use of the single coupled inductor for the power flow in both the directions reduces the component count. In this article, the operating principle of the breaker is explained for a short-circuit fault condition and breaker design criteria are derived. The performance of the circuit breaker is evaluated by carrying out a MATLAB simulation study. The functional prototype is developed to validate the breaker capabilities. Experimental results show that the fault is cleared within few microseconds. Additionally, the breaker is tested under the step load change condition for a current five times the steady-state rated current of the breaker and results are satisfactory. [ABSTRACT FROM AUTHOR]