In order to realize power flow control among photovoltaic (PV) panel port, battery port, and load port in the distributed photovoltaic power generation system, integrated three-port DC/DC converters (TPCs) are widely adopted. The objective of this paper is to provide a comprehensive, comparative, and insightful analysis and overview of these TPCs. Firstly, based on the power transmission and control requirements of the system, five topological structures of a three-port DC/DC conversion system (TPCS) composed of two or three two-port DC/DC converters are presented. And the five structures are comparatively analyzed. Secondly, based on these topological structures, and combing with the basic two-port DC/DC converters, three groups of typical TPCs with different galvanic isolation requirements are derived respectively by sharing switches, combining branches, etc. And comprehensive analysis, comparisons, and reviews of these TPCs with different structures of each isolation type are presented with tables and figures. Finally, the comparison results of the three isolation groups are summarized, which leads to a guidance for the selection of TPCs in different applications, and then some suggestions for the future research on TPCs are given.

A five-degree-of-freedom (5-DOF) modulation scheme is proposed in this paper for dual active bridge (DAB) converter to improve its efficiency in a wide operation range. Firstly, the possible operation modes of the converter under the 5-DOF modulation scheme is analyzed. As a result, eleven effective modes are obtained and their steady-state characteristics are analyzed, including the inductor root-mean-square (RMS) current, inductor peak-to-peak current, and transmission power, etc. It is worth mentioning that the inductor peak-to-peak current expression is simple and it can be regarded as an indicator for RMS current. Thus, the peak-to-peak current is treated as the objective to obtain the optimal solutions of each mode, and the global minimum peak-to-peak (GMPP) modulation scheme is obtained. However, there are only two switches that can realize soft-switching operation in the low power range under GMPP modulation scheme, which results in significant switching loss. Therefore, to further expand the soft-switching operation range in the low power range, the soft-switching conditions are also taken into consideration, and an optimized five-degree-of-freedom (O5-DOF) modulation scheme is proposed. With the proposed O5-DOF modulation scheme, almost all switches can realize soft-switching operation during the whole load range, and the inductor RMS current is minimized simultaneously.

This article performs a comprehensive steady-state performance optimization for the isolated triple active bridge (TAB) dc–dc converter adopting the five-variable modulation (FVM) technique. First of all, a universal analytical model suitable for all the hardware conditions of the TAB converter is established using frequency-domain analysis method. Second, considering the influence of port voltages and the energy stored in parasitic capacitances, a simplified and accurate zero-voltage switching (ZVS) constraint is derived without complicated condition judgments. Based on this, aiming at reducing the overall system losses, a comprehensive efficiency optimization modulation scheme with FVM is proposed in this article. Distinct from the previous optimization methods, the proposed scheme is not only a multiobjective optimization with minimized circulating current level and full-ZVS operation. It is also a generic optimization scheme covering all the five operation modes, and there is no individual optimization for each mode, which greatly simplifies difficulty of implementation. Afterward, to overcome the cumbersome optimization process, an advanced particle swarm optimization algorithm is used to seek the global optimal operating point in the entire power flowing range. Extensive simulation is carried out using MATLAB/Simulink. And the steady-state characteristics of the proposed scheme are fully compared with the traditional phase shift modulation method. Finally, a 1.2 kW laboratory platform is built. A significant efficiency improvement under light-load condition up to 21% is achieved, which substantiates the feasibility of the proposed optimization scheme.

Asymmetric duty modulation (ADM), as a recently proposed modulation scheme, provides new chance to improve the performance of dual active bridge (DAB) converter. On this basis, an optimal asymmetric duty modulation (OADM) scheme is proposed in this paper to minimize the inductor peak-to-peak current over the whole voltage and power range. Firstly, the DAB converter adopting ADM scheme is analyzed in frequency-domain and time-domain, and four operating modes are established. Then, the minimum peak-to-peak inductor current for each operating mode is obtained under Karush—Kuhn—Tucker (KKT) condition, and the corresponding optimal closed-loop control with low calculation complexity is derived. Then, the key values and features of the OADM scheme are compared with recent state-of-the-art, mainly including the inductor root mean square (RMS) current and soft-switching performance. Finally, an experimental prototype was built to validate the efficiency enhancement of the converter by adopting the proposed OADM scheme.

In order to further improve the efficiency of dual-active-bridge (DAB) converter, a hybrid five-variable modulation scheme with minimal root mean square (rms) current is proposed in this article, which combines the traditional phase-shift and pulsewidth modulation schemes. By adopting the proposed optimal scheme, a wider zero-voltage switching (ZVS) operation range and lower rms current level are achieved simultaneously when compared with other modulation schemes, which significantly improves the efficiency of the DAB converter. Moreover, for the complexity of the proposed modulation scheme with five variables, the Fourier decomposition based analytical expressions are derived for the converter and a generalized performance analysis results are presented. Besides, in order to avoid the analysis error, especially at light-load condition, the optimization strategy takes the rms current as the optimal objective, which includes the eight harmonic component of the inductor current rather than just considers the fundamental component. And an offline particle swarm optimization algorithm is introduced to acquire the optimal operating points for the whole power range. To substantiate the effectiveness of the proposed modulation scheme, a comprehensive comparison among related works in terms of the rms value and ZVS range were carried out under various operation condition. Finally, a 1.2 kW experimental platform was built and the highest experimental efficiency under the proposed modulation scheme reaches 96.8%.

Due to the contradiction between