Variable Frequency Control Strategy of Four-Switch Buck-Boost Converter Based on Interleaved Dual-Edge Modulation
Luo Lijiang1, Shi Jianan1, Ren Xiaoyong1, Lin Congzhi2
1. Jiangsu Key Laboratory of New Energy Generation and Power Conversion Nanjing University of Aeronautics and Astronautics Nanjing 210016 China; 2. Chengyi College Jimei University Xiamen 361021 China
Abstract The four-switch Buck-Boost converter (FSBB) has the advantages of a wide input voltage range, input and output polarity, and high control degree of freedom, which is suitable for charging photovoltaic cells in a DC microgrid. At present, research on FSBB mainly focuses on the smooth switching of multi-mode control and efficiency improvement. After discussing the influence of multi-mode control and modulation mode on FSBB efficiency, this paper proposes a variable frequency control strategy that considers efficiency improvement and smooth mode switching. Through the analysis of the inductor current under multi-mode control, it can be concluded that the inductor current ripple and average value of the two-mode control are the smallest when the input and output voltages are close, and its efficiency performance is optimal. Under the same gain, reducing d2 can reduce the average value of inductance current. In addition, under the same duty cycle d2, reducing or avoiding the simultaneous conduction of S1 and S4 can reduce the ripple of the inductor current. Both are beneficial in improving the efficiency of the converter. Then, this paper proposes an interleaved dual-edge modulation method, which avoids the simultaneous conduction of S1 and S4 while ensuring that d2 is a small value. Under the two-mode control, when the converter gain is close to 1, the inductor current ripple is close to 0. The multi-switch switch works, and the switching loss ratio increases. Because the current ripple is small at this time, reducing the switching loss is convenient. The average value of the inductor current formed by the interleaved dual-edge modulation is exactly the starting and ending position values of each switching cycle. Thus, the frequency can be modified to achieve a smooth transition of the converter operating mode. A variable frequency multi-mode control strategy is proposed. Then, the half-bridge on both sides of the inductor of FSBB is divided into high-frequency and low-frequency bridges. When the input and output voltages are close, the frequency of the two bridges is the lowest fbase. When the input voltage increases (decreases), ensuring the inductor current ripple does not exceed ΔIL_max, the Buck duty cycle is reduced, and the frequency of the Buck bridge is increased (the Boost duty cycle and the frequency of the Boost bridge are increased). A 600 W FSBB prototype is built to verify the proposed variable frequency control strategy. The experimental results show that the converter can achieve Buck-Boost conversion in different modes. When the input voltage changes, the strategy can automatically adjust the frequency to improve the conversion efficiency. When the switching frequency is adjusted, the inductor current ripple changes, and the converter can always maintain the stability of the output voltage during the mode-switching process. Compared with the fixed- frequency two-mode control, the proposed frequency conversion significantly reduces the switching loss due to the decrease of the switching frequency. Although the increase in the inductor current ripple increases the conduction loss, the overall loss is reduced, thereby improving the efficiency. Especially near the operating point when the input and output voltages are close, the converter’s efficiency is significantly improved.
Luo Lijiang,Shi Jianan,Ren Xiaoyong等. Variable Frequency Control Strategy of Four-Switch Buck-Boost Converter Based on Interleaved Dual-Edge Modulation[J]. Transactions of China Electrotechnical Society, 2025, 40(6): 1878-1887.
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