To improve the reliability of dc microgrids operation, an enhanced power line communication (PLC) strategy is proposed using switching frequency modulation (SFM) of a power converter. The proposed PLC strategy uses the voltage ripple on the dc bus voltage, which is inherently generated by converter's switching activities as an information signal. By using the SFM, all microgrid components sharing the dc bus as communication channel can obtain power flow information with fast Fourier transform analysis of dc bus line frequency. In addition, the operating performance of the dc bus voltage regulator is enhanced over a range of light load conditions. The proposed PLC strategy and design of modulated frequency range are verified through experimental results using a 3.3 kW prototype dual active bridge converter.

Isolated bi-direction DC-DC converters are widely used for energy storage systems (ESS) of DC microgrids. Particularly, a current-fed isolated bi-directional DC-DC converter (CF-IBDC) receives much attention due to its merits such as the naturally attenuated current ripple on the battery side. However, high efficiency cannot be obtained at the light and heavy load conditions under the conventional control methods. In this paper, a hybrid switching modulation is proposed to improve the power conversion efficiency of the CF-IBDC under light and heavy load conditions. The duty cycle of the secondary sides and the phase shift angle are independently controlled according to the amount of the transferred power. The control strategy is based on the optimization of zero-voltage switching (ZVS) conditions and the minimization of the circulating current in the power converter. Using the proposed control algorithm, the ZVS capability can be obtained under the entire load condition, and the circulating current can be minimized under the single phase-shift modulation (SPSM). Experimental results with a 1-kW laboratory prototype CF-IBDC validate the effectiveness of the proposed modulation algorithm.

Optics InfoBase is the Optical Society's online library for flagship journals, partnered and copublished journals, and recent proceedings from OSA conferences.

To improve the power conversion efficiency of a three-phase dual active bridge (3P-DAB) converter for LVDC distribution systems, a practical design methodology is proposed. Commonly, the 3P-DAB converter is designed by the only specification such as the rated power, input/output voltage, and frequency. However, using the conventional design method, the efficiency is low under heavy load conditions due to the high conduction loss. In this paper, based on the practical power loss analysis, the effective design methodology of the coupling inductance in the 3P-DAB converter is proposed, focusing on power conversion efficiency. It can mitigate the drawbacks of the common design by reducing the peak and RMS phase current and the IGBTs' turn-off current. Experimental results verify the validity of the proposed design methodology and controller using a 25-kW prototype 3P-DAB converter.

Due to dc based electric loads and renewable sources, the dc distribution system is an alternative future solution. Among the dc distribution systems, the bipolar dc type has higher performance and reliability than the unipolar one. To interlink two dc buses, an isolated bidirectional DC-DC converter is needed. A three-level dual-active-bridge DC-DC converter is proposed to interlink two bipolar dc buses. Between two dc buses, a galvanic isolation is provided by the high frequency transformer of the three-level dual-active-bridge. Besides, an asymmetrical switching modulation is proposed to compensate asymmetrical load condition of the bipolar dc bus system. Finally, a 1-kW prototype is built to verify the proposed converter.

An effective dead-time control strategy for the three-phase dual active bridge (3P-DAB) converter of a distribution system is studied to reduce the switching losses of power switches and improve the under-light-load power conversion efficiency. Because of the advantages of a dual-active bridge converter, such as an inherent zero-voltage switching (ZVS) capability without any additional resonant tank and a seamless bi-directional power transition, this is an attractive topology for bi-directional application. The 3P-DAB converter is apt for high-power applications such as aircraft due to an interleaved structure, which can reduce conduction losses. However, the design of the dead time depends on engineering experience and empirical methods. In order to overcome the conventional practicality of the dead-time design method, the effective control of dead time is proposed based on the theoretical analysis. In this paper, the overall explanation of the 3P-DAB converter is shown with operation principles. In addition, the dead-time effect of the 3P-DAB converter is examined and the practical variable dead-time control strategy is studied. Finally, experimental results validate the proposed variable dead-time control strategy using a 25 kW prototype 3P-DAB converter.