In this article, a quasi-two-stage buck-DAB (QBDAB) converter is proposed for improving the performance of the conventional dual active bridge (DAB) solution under a wide voltage range. For the proposed QBDAB converter, the DAB can always work under voltage matching conditions for wide voltage range applications, and the gain is adjusted through the added front-end circuit. The front-end circuit is similar to a buck converter, while only part of the transmission power flows through the circuit, which could also reduce the burden of achieving ZVS of the front-end circuit. Therefore, compared with the traditional two-stage buck-DAB converter solution, the related loss for the buck circuit can be reduced. The working principle, power transfer characteristics, and full load range ZVS design are analyzed deeply in this article. A detailed comparison of the QBDAB and other related combined buck+DAB topologies is also presented. Finally, the effectiveness of the proposed QBDAB is verified through experimental results from a 1kW prototype.

Input-series output-parallel (ISOP) connected Dual Active Bridge (DAB) converters allow the use for occasions requiring high input voltage and galvanic isolation with bidirectional power capability. However, when DAB converters are ISOP connected, the traditional analysis without consideration of the dead-time cannot effectively explain the reason why the ISOP converter system is stable under common phase shift control when parameters are mismatched. In this paper, it is firstly revealed that the stability of the ISOP DAB converter under common phase ratio control can be ensured by consideration of the dead-time. Based on the analysis of the DAB power transmission characteristics with consideration of dead time, a new model is derived for the ISOP DAB converter, which can reveal the reason why the converter can operate stably under common phase shift control when the design parameters of the individual module are mismatched. Then based on the derived model, the stability analysis and the parameters design are further performed. Finally, the effectiveness of the working principle and analysis are verified through results from a two-module ISOP experimental prototype.

In this letter, a switch-multiplexed quasi-two-stage buck-dual-active-bridge (DAB) (SMBDAB) and its modulation strategy are proposed. Under the quasi-two-stage buck-DAB architecture, one bridge of the primary side of the proposed converter is multiplexed as both the bridge of the buck circuit and the DAB circuit to reduce the power switches. In addition, with the voltage-matching modulation, multiplexing still ensures that the voltages on both sides of the leakage inductor of the DAB circuit are always matched when the voltage gain of the converter changes, and thus, the zero-voltage switching (ZVS) of all the switches can be achieved. Furthermore, the partial power transfer characteristics of the buck circuit still maintains, which could reduce the power rating of the inductor for the buck circuit. The working principle, power transfer characteristics, and full range ZVS design are analyzed. Finally, the effectiveness of the SMBDAB converter is verified through experimental results from a 1kW prototype.

DC-link voltage pulsation is a technical challenge for grid-connected three-phase voltage source rectifiersunder unbalanced grids. To suppress dc-link voltage ripples arising from unbalanced grids, a frequency-divided resistance-emulating control strategy is proposed in this letter. According to the frequency-divided idea, the dc-link voltage control loop consists of two parts: one dedicated to regulating the average voltage and the other focused on suppressing pulsating voltage. The inner loop is synchronized based on the resistance-emulating approach. The frequency-divided resistance-emulating control offers the following advantages: grid voltage sensors are eliminated, detailed information about circuit parameters is not required, and easy to implement because only one proportional–integral controller, one quasi-proportional–resonantcontroller, and two bandpass filters are used. To sum up, the proposed method is simple, cost effective, and robust. Experiments confirm the effectiveness and performance of the proposed method.

An integrated Buck-LC converter for a wide voltage range is proposed in this paper based on a quasi-two-stage structure. In the integrated quasi-two-stage Buck-LC (IQBLC) converter, the LC resonant stage is under DCX mode and the Buck stage can achieve voltage regulation. The buck stage is integrated into the DCX stage, which can reduce the number of switches. The inductor of the buck stage only transfers a part of the output power which benefits the efficiency improvement and ZVS achievement. Different working modes and modulation strategies are presented for the IQBLC converter to further extend the voltage gain. The soft switching of all switches can be realized under different modes and loads. Besides, a duty cycle control trajectory is proposed to realize continuous voltage gain adjustment under multimode operation. The voltage gain characteristics, partial power characteristics, ZVS conditions, and discontinuous mode constraints of the LC stage are analyzed in detail in the paper. Experimental results are obtained from a 1kW prototype to validate the effectiveness of the proposed converter.

This article presents a single-stage matrix-type solid-state transformer, which integrates a shared filter capacitor between the line frequency (LF) rectifier and the high frequency half bridge on the primary side, a modified push–pull dual active bridge to eliminate the leakage inductor effect on the secondary side, and a full-bridge LF inverter on the load side. Due to its electrolytic capacitorless nature, the proposed structure ensures identical instantaneous powers, thereby eliminating ripple power with double grid frequency, and unit power factor is inherently performed without a current control loop. Moreover, the operating characteristics of the converter under resistive and inductive–resistive loads are analyzed respectively, examining the conditions for zero voltage switching with time-varying dc-link voltage and the factors affecting total harmonic distortion. In addition, optimization strategies to reduce operating losses are considered in the parametric design. Finally, a 1 kW prototype is constructed and tested to validate the correctness and feasibility of the proposed method.