Optimized Control for ISOP LLC-DAB Converter to Achieve Full-Power-Range Zero-Voltage Switching and Fast Dynamic Response

In recent years, the input-series-output-parallel (ISOP) LLC-DAB converter has been applied to DC microgrids and energy routers. However, the existing control methods still have some limitations, such as a limited range of soft switching, large current stress, and slow dynamic response speed, which restrict the efficiency and dynamic performance of the converter. This paper optimizes the Triple-Phase-Shift (TPS) modulation scheme to achieve full-range soft-switching operation across varying input voltages, while simultaneously optimizing current stress characteristics and improving the converter's efficiency. Meanwhile, a more concise closed-loop control strategy is developed. Then, a direct power control (DPC) strategy based on inductor current stress optimization is presented. This strategy calculates the phase-shift ratio parameters according to the converter's required power transmission. The calculation ensures the transmitted power quickly matches the load power. The approach improves the converter's dynamic performance during input voltage and load variations. The improvement is achieved while maintaining optimized current stress conditions. Finally, the effectiveness of the proposed control strategy is verified by experimental results of a 2.5kW prototype.