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Analysis of power-side reflow power and load-side reflow power present in isolated bidirectional DC converters
Researchers from the State Key Laboratory of New Energy Power Systems at North China Electric Power University, including Yu De, Fu Chao, Wang Yi, Wang Yanxu, and Yang Yuming, published a study in the 24th issue of the *Journal of Electrical Engineering* in 2017. Their work highlighted the reduction of isolation type and the use of return power from bidirectional DC converters to enhance conversion efficiency. This approach is crucial for the practical application of extended isolated bidirectional DC converters in DC distribution networks.
The paper first explains the working principle of double-phase shift control and the mechanism of inverter return power generation. It then establishes a mathematical model for both the power supply side and load side return power. The analysis shows that reducing return power helps lower current stress and improve overall system efficiency.
Next, the authors introduce a minimum return power phase shift control method. Compared to traditional double-phase shift control, this method achieves the lowest return power under the same power transmission conditions, optimizing performance.
Experimental validation on a 2 kW test platform confirmed that the proposed control strategy effectively reduces return power across various operating conditions. This leads to lower current stress, reduced power loss, and improved efficiency.
DC distribution networks are considered an ideal solution for integrating distributed power sources and energy storage systems. They minimize power conversion stages and filtering components, making them a popular research area. Isolated bidirectional DC-DC converters (IBDCs) serve as key interface circuits in these networks, using series connection to boost voltage and parallel operation to increase power levels while ensuring electrical isolation.
Currently, IBDCs commonly use phase shift control methods such as Single-Phase-Shift (SPS), Extended-Phase-Shift (EPS), Dual-Phase-Shift (DPS), and Triple-Phase-Shift (TPS). While SPS is widely used due to its simplicity, it has limitations in adjusting return power and current stress. EPS improves ZVS range and efficiency, while DPS offers better dynamic performance.
Traditional phase shift methods often result in high peak currents and switching stress, largely due to excessive return power. This increases losses and lowers efficiency. To address these issues, previous studies have explored ways to manage return power, but the behavior of return power under dual-phase shift control remains less understood.
This paper investigates the return power phenomenon in IBDCs under dual-phase shift control, develops a mathematical model for both sides, and proposes a minimum return power phase shift control method. Experimental results validate the effectiveness of the approach.
Figures 1 and 9 illustrate the converter structure and experimental setup, respectively. The conclusion summarizes the findings, showing that increasing the outer phase shift angle affects current stress and return power differently depending on the operating point. Reducing return power significantly lowers current stress, though not always to the minimum. The proposed method outperforms traditional approaches by minimizing return power, peak current, and overall losses, thereby improving efficiency.