LLC Resonant Converter Of AVP Control

With the rapid development of distributed generation, LLC resonant converter among the resonant converter has not only many advantages in common, such as high efficiency, small switching loss, high switching frequency, but also the characteristics of zero voltage turn-on of primary-side switch, while zero current shutdown of secondary rectifier diode i n the whole load range. Besides, wide input voltage range is referred as its unique advantage. So much attention has been obtained due to the above advantages. It is being required more and better dynamic performance.This dissertation analyzes the working principle of LLC resonant converter. Furthermore, an equivalent steady-state model is established using First Harmonic Approximation, then the DC gain characteristics is gotten. Through analysis and research on its steady-state characteristic, after calculation of its resonance parameters, the individual parameter values of LLC resonant converter can be obtained finally. In order to improve the dynamic response of the system, this dissertation studies the Adaptive Droop Resistance(ADR) techniques for Adaptive Voltage Positioning(AVP) control mode in LLC resonant converter. In this mode, LLC resonant converter can achieve constant outpu t impedance and make the output voltage stable. Small-signal model of LLC resonant converter needs to be modeled to establish AVP control loop. In a variety of modeling methods, the extended describing function method is adopted for the reason that only with steady-state operation information in the non-modulation, then simple small-signal model of continuous time in any work cycle can be obtained, which reduces the complexity of the simulation work and is more generality. The small-signal model of LLC resonant converter with this method, and the control loop is designed by using this model.The control block diagram of AVP control loop is designed by studying the AVP control principle combined with LLC resonant converter features. By simulating the open-loop, closed-loop and AVP control loop of LLC resonant converter, the design in theory is verified feasible. The hardware platform is built to test AVP Control LLC resonant converter design correctly with practical experiment.