Current stress minimization is one of the most important challenges for the steady-state studies of dual-active-bridge (DAB) dc–dc converter. Triple-phase-shift (TPS) control can minimize the current stress to the utmost extent, and a segmented analytical method-based TPS (SA-TPS) control has been proposed in this paper to minimize the current stress of DAB within the whole operating range. The full model of DAB with TPS control was classified into 12 operating modes by a complete operating mode classification method. On the basis of the analytical expressions of transmission power and current stress in different modes, the current stress minimization issue was transferred to inequality constraints’ problems in different operating modes. The mathematical derivation process of the SA-TPS control method is described in detail, and the analytical expressions of current stress minimization results as a function of voltage conversion ratio and transmission power have been derived by solving the forward and reverse power transmission processes, respectively. The operating mode selection principle and the regularities of minimization results varying with transmission power and voltage conversion ratio have been explored. Experiments under different conditions have been implemented on a laboratory prototype to validate the correctness and effectiveness of the proposed SA-TPS control method.

A comprehensive time-domain model of CLLC class isolated bidirectional DC-DC converter (IBDC) is proposed in this article. Based on the circuit analysis and the solution of the state equations, analytical expressions of the state variables are provided. The model is a piecewise time-domain analytical model and can accurately describe the transformer currents and capacitor voltages under almost all basic types of control strategies, e.g. phase-shift control and frequency modulation control. With the model, the steady-state analysis of IBDC can speed up evidently (up to 330 times faster compared to MATLAB/Simulink and more than 10 times compared to SIMPLIS and PLECS), which gives great support to parameter sweep and case comparison in design procedure. By assigning specific parameters, the presented model can also be applied to the analysis of LLC resonant IBDC or typical DAB IBDC since LLC converter and DAB converter are similar to CLLC converter in circuit topology. The transformation of the model from CLLC to LLC/DAB is provided and several application examples are given. Finally, the simulation and experimental results are presented, verifying the effectiveness of the model.

For the bidirectional wireless power transfer (BWPT) technology, the phase synchronization between the transmitting and receiving converters is very essential and difficult to achieve by wireless communication between two sides because the delay and data transfer interval of wireless communication severely influence the control performance. This paper proposes a novel control strategy for BWPT, which can achieve the phase synchronization and maximum efficiency point tracking (MEPT) independent of the real-time wireless communication. To solve the overshoot and oscillation problem incurred by the proposed control strategy and the nature of the system itself, the dynamics of a series-series (SS) compensated BWPT system is then analyzed and a small-signal model of this system is derived based on the generalized state space averaging (GSSA) and extended describing function (EDF) methods. Using the small-signal model, a BWPT control system based on the proposed control strategy is designed and optimized. The validity of the proposed strategy and the performance of the control system are verified experimentally using a 3.3-kW prototype system.

This letter proposes a deadbeat current controller for isolated bidirectional dual-active-bridge dc-dc converter (IBDC). The controller uses an enhanced single phase shift (ESPS) modulation method by exploiting pulse width as an extra control variable besides phase shift ratio the only control variable of the conventional single phase shift (CSPS) modulation. The current reference can be tracked within one switching cycle during the bidirectional power transmission and transition of the two directions. Deadtime effect is studied and the compensation method for the controller is presented. Parameter robustness is analyzed by mathematical derivation and the online auto-tuning method for the inductance is presented. The proposed deadbeat current controller is simple and easy for implementation. Moreover, it shows superior dynamic performance, which is verified by experimental results during the transient processes of the converter. The effectiveness of the auto-tuning method is also validated by the prototype experiment.

With high penetration of various distributed energy resources and DC loads in modern power system, AC/DC hybrid distributed grid attracts a lot of attention due to its compatibility. Aiming for interface of the AC/DC hybrid distributed grid, a four-port megawatt-level power electronic transformer (PET) is focused on in this paper. A novel high-frequency-bus based multi-port PET topology is proposed, which is found to have superiorities such as mutual isolation, mutual independence among different ports and fewer power stages, compared with the conventional DC-bus based solution. Design and implementation of the four-port PET prototype is presented in this paper. Modular structure is adopted, and similar power cell is used for all the four ports for easy manufacture. The parameter design principle based on the port-equality is proposed to guarantee the suitable operating range of all the ports. The functions of this four-port high-frequency-bus based PET are tested and verified from the cell-level, port-level to the system level with maximum efficiency over 96%, which confirms the practicability of this industrial prototype.

With the increasing popularity of renewable energy and electric terminal equipment, the large-scale application of isolated bidirectional DC-DC converters (IBDCs) are growing. Among these converters, the dual active bridge (DAB) converter, as the core topology of IBDCs, has garnered significant attention due to its bidirectional power transmission capability, simple modularity and wide soft-switching range. To enhance the efficiency of DAB, various multi-degree-of-freedom (M-DOF) modulation techniques and related solutions have been proposed. However, there is currently a lack of in-depth understanding and thorough comparison of different M-DOF modulation techniques, making it difficult to obtain the optimal solution for different application scenarios. Therefore, based on the latest research and contributions, this paper provides an overview of M-DOF, including models, objectives, and algorithms. Furthermore, existing typical M-DOF modulation techniques are compared through experiments, exploring the differences and advantages among these technologies. Through these analyses, this paper offers robust support for the advancement and application of M-DOF modulation techniques in DAB converters.