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| Optimal Control Strategy for Triple Active Bridge Current RMS Based on Circuit Decomposition Model |
| Lan Zheng1, Wang Xueli1, Yu Xueping1, Zou Bin1, Liu Bei2 |
1. College of Electrical and Information Engineering Hunan University of Technology Zhuzhou 412007 China;
2. National Electric Power Conversion and Control Engineering Technology Research Center Hunan University Changsha 410082 China |
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Abstract As an effective solution for renewable energy, electric vehicles, and energy storage flexible access to the DC grid, the triple active bridge DC-DC converter (TAB) has widespread adoption in the DC grid. The main research of TAB involves topology improvement, decoupling control strategy, modeling methodology, and soft-switching characteristics. However, the rms value of the inductor current, as an important indicator affecting the efficiency of TAB, has few optimization studies. Therefore, this paper focuses on the rms value optimization for inductor current in TAB.
As the most basic control strategy of TAB, the SPS control strategy is simple and easy to implement. However, it has many shortcomings, such as few control degrees of freedom, low flexibility, increased loss, and reduced operating efficiency of the TAB. PS-PWM control strategy is usually used to optimize these objectives, but the mathematical model under PS-PWM control is complex. This paper proposes a TAB inductor current rms optimization control strategy based on the circuit decomposition model. Firstly, the operating principle of TAB under PS-PWM is analyzed, and the circuit decomposition model under PS-PWM is established. Then, the unified expressions for the power and the rms value of the inductor current at each port under different operating modes are derived. The optimized mathematical model for summing the rms value squares of the inductor current at each port of the TAB is constructed, and a genetic algorithm is applied to reduce the inductor current rms value by the optimal shift ratio. Simulation and experimental results show that the proposed analysis method and control strategy can reduce the complexity and computational difficulty of the model. The rms value of inductance current at each port is effectively reduced, and the system efficiency is improved.
The following conclusions can be drawn. (1) The on-state loss of the TAB is proportional to the square of the rms value of the inductor current. The sum of rms value squares of the inductor currents is primarily related to the voltage matching ratios k21 and k31, the phase shift angle between the ports, and the duty ratio of the switching tubes. These factors provide the theoretical basis for constructing the decomposition model of the TAB circuit. (2) The circuit decomposition model based on PS-PWM control can simplify the TAB circuit analysis. The complexity and computational difficulty of optimizing the mathematical model can be reduced by introducing a genetic algorithm. (3) When the voltage matching ratio k21>1, the sum of rms value squares of the TAB inductor current can be effectively reduced, and the power transfer efficiency of the TAB can be improved by the proposed GAOS control strategy.
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Received: 14 September 2023
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2024, Vol. 39 
