With the conventional secondary phase-shifted (PS) control, a semi-dual-active-bridge (S-DAB) DC-DC converter suffers from low efficiency at light load in buck mode due to hard-switching and high tank current. In order to avoid this phenomenon and extend soft-switching range, a hybrid control including the primary pulse-width modulation plus secondary phase-shifted (PWM+PS) is proposed in this paper. Under the proposed hybrid control, all steady-state operation modes with distinctive features are identified and analysed. Based on the operation range, power characteristics and switching behaviours in each mode, a minimum peak current control route is developed, which can enable the converter to work with low tank current and soft-switching over the whole load range. A labscale S-DAB converter is implemented to validate the theoretical analysis, and experimental results reveal that the higher efficiency can be achieved using the proposed control route.

An energy storage system (ESS) plays an important part in a renewable energy generation system for stable and efficient power harvesting. To realize the function of an ESS, a bidirectional DC/DC converter with high power density and high efficiency is highly desired. In this paper, a high-frequency (HF) isolated dual-bridge series resonant converter (DBSRC) with a piecewise control strategy is proposed for an application with a wide variation of voltage gain. The proposed control strategy is based on dual-phase-shift modulation for a balance between complexity and flexibility. With this proposed control strategy, zero-voltage switching is kept for all switches on the low-voltage side and half of switches on the high-voltage side. Besides, there is no circulation energy on the low-voltage high-current side for full load operation. A step-by-step design procedure is also included to calculate the converter components and control parameters. Verification of the analysis and design are performed successfully through simulation and n experimental test. Comparisons with some existing control methods are also made experimentally, which highlights that the proposed control strategy is able to achieve comparable performance as the reported optimal current control with simpler calculation and implementation.

One of the significant factors contributing to high energy consumption is the unutilized waste heat from flue gas in industrial boilers. Thermoelectric generator (TEG) technology can directly convert thermal energy into electrical energy, and has been gradually applied in the field of waste heat recovery due to its simple and reliable structure, environmental protection, and other advantages. In this paper, a thermoelectric generator simulation system of boiler flue gas waste heat is proposed. The experimental platform is designed by simulating the flue gas waste heat temperature condition of boiler, and the structure of cold end module and hot end module is optimized. During the experiment, the fixed temperature difference was set at 120 °C (hot end:150 °C~cold end: 30 °C). An analysis is conducted on the volt-ampere characteristics and output power of the TEG module. The output characteristics of the TEG system are analyzed under the conditions of variable load, constant load, different pump speed, different heat dissipation modes, and series and parallel connection method. The results show that the experimental platform can instantaneously and accurately test the output parameters of the TEG system, and ensure the intended design requirements. When the ratio of the load resistance to the internal resistance of the TEG module is approximately 1–1.15, the output power of the system reaches its maximum. In order to optimize the output power of the TEG system, a power prediction-based adaptive variable step size maximum power point tracking (MPPT) algorithm is introduced. Additionally, a corresponding mathematical model is formulated. Simulations demonstrate that the time of the improved algorithm to reach the stable maximum power point is 1.54 s faster than that of the traditional algorithm. The improved MPPT algorithm satisfies the criteria for speed and accuracy, diminishes superfluous energy waste, and enhances the overall system efficiency. The research results have certain guiding significance for the design and application of subsequent TEG system.