PWM Strategy for Start up Process of LLC Resonant Converter Based on Event Trigger Control Method

For reduce the high inrush current caused by the low impedance of the resonant tank of LLC resonant converter during the start-up process, this paper proposes a PWM strategy based on the event triggered control (ETC) method. In order to select the trigger event, the segmented state space modeling is used to analyze the relationship between the system state variables and the driving signals. Then, it selects the current and the capacitor voltage in the resonant tank to establish the ETC function to obtain the PWM strategy for the start-up process. When the output voltage is gradually established, the amplitude of the resonant current will be less than the pre-set threshold. Then the resonant capacitor voltage can be used to trigger the event. Finally, by comparing with the experimental results using the traditional soft start-up strategy, the proposed PWM strategy can limit the current and the capacitor voltage in the resonant tank during the start-up process to below the pre-set threshold, while greatly reducing the settling time of output voltage. In addition, the ETC method can achieve smooth switching from the start-up process to the steady state.