Hybrid Control Strategy for DAB-LLC Sigma Converter

DAB-LLC sigma converter has been an attractive topology, which combines the high efficiency of LLC and the high controllability of DAB. However, traditional PI controller manages output voltage/power by adjusting the phase shift angle of DAB and allows LLC to operate in an open loop mode, which leads to poor transient response. In this paper, an improved simplified optimal trajectory controller (SOTC) suitable for LLC in sigma converter is investigated. And then a new hybrid control strategy is proposed, which can not only control DAB by PI controller, but also control LLC by improved SOTC at transient. The hybrid control strategy compensates the load current and enhances the intrinsic voltage feedback of the sigma converter. Furthermore, it reduces current overshoot and improves transient response without reducing the efficiency. Finally, a prototype rated at 1 kW is built and tested, and experimental results verified the effectiveness of proposed strategy.