Adaptive Fractional-Order Impedance for Current Balancing Control

The parallel operation of multi-phase LLC resonant converters finds extensive application in scenarios with low voltage and high current, such as photovoltaic and electric vehicle charging systems. However, minor differences in resonant network parameters can lead to significant current imbalances. This paper, after analyzing the shortcomings of traditional virtual impedance parallel current-sharing methods, proposes an adaptive fractional-order impedance current-sharing control method based on the EDF method and small-signal modeling. Adaptive-order impedances are constructed for both system circulating and sharing currents, achieving balanced current output. In comparison to traditional methods, this approach not only accomplishes inter-system current sharing but also exhibits minimal voltage deviation and outstanding transient response. Finally, a prototype of a 960W two-phase parallel LLC resonant converter is constructed, and experimental results successfully validate the proposed method, reducing system current imbalance from nearly 100% to within 5% while maintaining constant voltage under half-load and above operating conditions.