Hybrid Modulation Strategy for Wide Load Range ZVS and Reactive Power Circulation Optimization in DAB Micro-Inverters Considering Excitation Current
Huang Wencong1, Jiang Xuanyan1, Rao Tianbiao1, Chang Yufang1, Yan Huaicheng2
1. Hubei Collaborative Innovation Centre for High-Efficiency Utilization of Solar Energy Hubei University of Technology Wuhan 430068 China; 2. College of Information Science and Engineering East China University of Science and Technology Shanghai 200237 China
Abstract：The dual-active-bridge (DAB) DC-AC converter technology, due to its efficient and flexible power conversion characteristics, has become a key technology for improving energy efficiency and system stability. However, because of the wide output voltage range and considerable output power variation, it is challenging for the DAB DC-AC converter to achieve zero-voltage switching (ZVS) for all switches over a wide output voltage and power range. Additionally, the ZVS condition of the primary lagging switch in the DAB DC-AC converter leads to reactive power during high-frequency power transmission, increasing the conduction loss of the switches. To reduce the impact of these issues on the transmission efficiency of the DAB DC-AC converter, this paper proposes a hybrid modulation control strategy based on mode switching. This strategy combines frequency control with extended phase-shift control to expand the ZVS zone of the DAB micro-inverter while optimizing the circulating power. Firstly, the ZVS characteristics and reactive power characteristics of two extended phase-shift modulation modes of the DAB micro-inverter are analyzed, and a phase-shift trajectory with minimum circulating power within the ZVS zone is proposed. Then, a frequency control law is designed, which increases the switching frequency under light load conditions to expand the ZVS zone and decreases the switching frequency under heavy load conditions to reduce the turn-off loss of the switches. At the same time, A control loop is constructed to achieve precise control of the current. Finally, a 400 W experimental platform is established, and the superiority of the proposed algorithm is verified through experiments. According to experimental results, the proposed control strategy can achieve ZVS for all switches under full load and 20% load conditions. Compared with other phase-shift strategies operating within the ZVS zone under light load conditions, the proposed algorithm reduces the transformer current stress by about 40% and increases efficiency by about 3%. The maximum efficiency of the experimental prototype is 95.69%. The following conclusions are drawn: (1) The proposed phase-shift angle trajectory considers the effects of excitation inductance and the output capacitance of switches. It minimizes reactive power while ensuring ZVS for all switches. (2) The proposed variable-frequency control law increases the switching frequency under light-load conditions, extending the ZVS zone to 20% of the rated power. Under heavy-load conditions, it reduces the switching frequency to minimize turn-off losses. (3) The proposed control loop balances the effects of the filter inductance and the half-bridge capacitance on the output current phase, thereby achieving precise output current control.
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2026, Vol. 41 
