Research on current sharing strategy of parallel LLC resonant converter

In recent years, LLC resonant converter has been widely used because of its superior performance. The structure of parallel LLC resonant converter is very suitable for use of low voltage and large current. But the difficulty lies in the current sharing between modules. The small difference in the parameters of the resonant network may cause the larger current imbalance of the module. In this paper, the virtual impedance is used to simulate the series impedance of the resonant network from the point of impedance. To improve the equivalent output impedance, the equivalent output impedance is adjusted by the series impedance. Taking the two parallel LLC module as an example, the control block diagram and the realization method based on the virtual impedance are given. Finally, by using DSP digital control, a prototype of a two way parallel LLC resonant converter with 400V input and 12V/80A output is built. The experimental results show that the proposed control method can reduce the output current imbalance to 5% within the full load range, and the effectiveness of the proposed method is verified.