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This paper proposes a double Y-configuration multi active bridge converter (DYAB) capable of single stage bidirectional AC-DC isolated power conversion with a simple sinusoidal phase shift modulation. Compared to other dual active bridge (DAB) based AC-DC converters, the DYAB achieves power factor correction (PFC) with a simpler control method while maintaining nearly full-range zero-voltage switching (ZVS) and relatively low circulating current, resulting in high efficiency. The paper details the equivalent model and modulation method. A steady-state analysis tool based on the fast fourier transform (FFT) is developed to calculate the ZVS range, PFC performance, and loss breakdown. A 2.66kW hardware test demonstrating an efficiency of 97.14% is implemented to verify the proposed circuit and the steady state model.

The increasing adoption of power electronic devices may lead to large disturbance and destabilization of future power systems. However, stability criteria are still an unsolved puzzle, since traditional small-signal stability analysis is not applicable to power electronics-enabled power systems when a large disturbance occurs, such as a fault, a pulse power load, or load switching. To address this issue, this paper presents for the first time the rigorous derivation of the sufficient criteria for large-signal stability in DC microgrids with distributed-controlled DC-DC power converters. A novel type of closed-loop converter controllers is designed and considered. Moreover, this paper is the first to prove that the well-known and frequently cited Brayton-Moser mixed potential theory (published in 1964) is incomplete. Case studies are carried out to illustrate the defects of Brayton-Moser mixed potential theory and verify the effectiveness of the proposed novel stability criteria.

This letter proposes a new design of frequency-locked loop (FLL) which is based on synchronous (dq) reference frame instead of stationary ({\alpha}\b{eta}) reference frame. First, a synchronous reference frame FLL (briefly called SRF-FLL0) equivalent to the conventional FLL is proposed. Then the SRF-FLL0 is improved by utilizing the phase error to acquire a better performance. The small-signal modeling and parameter tuning of the improved synchronous reference frame FLL (SRF-FLL) are presented. Finally, the theoretical analysis and experiment results verify the superiority and effectiveness of proposed SRF-FLL., Comment: 4 pages, 6 figures