Active Disturbance Rejection Control Strategy Based on Fuzzy Sliding Mode for LLC Resonant Converters

In order to enhance the anti-interference capability and dynamic performance of LLC resonant converters implementing traditional PID control, an active disturbance rejection control strategy based on fuzzy sliding mode is proposed. By establishing a mathematical model for LLC resonant converters, the initial design creates a second-order linear extended state observer (LESO). The LESO, which enables real-time estimation of disturbances due to systematic errors, is used to optimize the feedback control. Next, a fuzzy control approach is incorporated into the sliding mode structure, to develop fuzzy reasoning rules. These rules are utilized for fuzzy reasoning on error signals based on the operating state of the system. The tendency-rate parameter is adjusted depending on the distance between the system equilibrium point and sliding mode surface, allowing for real-time adjustments to the rate of convergence for the sliding mode. Finally, a 500 W LLC resonant converter prototype was built for experiments. The experimental results showed that the implementation of the proposed control strategy shortened the adjustment time of the output voltage by 4.3 ms and 3 ms respectively compared to PID when the converter is disturbed by sudden load increases and decreases, and reduced overshoot of the output voltage by 1.31 percentage points and 1.07 percentage points respectively, indicating good dynamic response performance and verifying the correctness and effectiveness of the proposed control strategy.